Science.gov

Sample records for ceramic pebble beds

  1. Ceramic pebble bed development for fusion blankets

    SciTech Connect

    Gierszewski, P.; Kawamura, H.; Donne, M.D.

    1994-12-31

    Research on lithium ceramic breeders has been intensive since the late 1970`s. The bulk material properties of several candidate lithium ceramics are generally available, although there is still much work to be done on properties under irradiation and on overall behavior in blanket modules. Based on these results, lithium ceramic breeders have been selected in many fusion design studies. These lithium ceramics are incorporated into blankets typically as monolithic pellets of packed pebble beds. There is substantial industrial experience with pebble beds made from other ceramics, notably in chemical processes as catalyst supports and grinding media, and in advanced fission reactor fuels. In fusion blankets, the pebble bed form offers several attractive features, including simpler assembly into complex geometry, uniform pore network, and low sensitivity to cracking or irradiation damage. Ceramic breeder pebbles have been a focus for several research groups. In general, the database is similar to that of monolithic pellets for the materials studied: basic production and material property data are available, but the irradiation and engineering database remains sparse.

  2. Effective Thermal Conductivity of Lithium Ceramic Pebble Beds for Fusion Blankets: A Review

    SciTech Connect

    Abou-Sena, A.; Ying, A.; Abdou, M.

    2005-05-15

    The use of lithium ceramic pebble beds has been considered in many blanket designs for the fusion reactors. Lithium ceramics have received a significant interest as tritium breeders for the fusion blankets during the last three decades. The thermal performance of the lithium ceramic pebble beds plays a key role for the fusion blankets. In order to study the heat transfer in the blanket, the effective thermal conductivity of the lithium ceramics pebble beds has to be well measured and characterized. The data of effective thermal conductivity of lithium ceramic pebble beds is important for the blanket design. Several studies have been dedicated to investigate the effective conductivity of the lithium ceramics pebble beds. The objective of this work is to review and compare the available data, presented by various studies, of effective conductivity of lithium ceramic pebble beds in order to address the current status of these data.

  3. Crush probability analysis of ceramic breeder pebble beds under mechanical stresses

    NASA Astrophysics Data System (ADS)

    Gan, Yixiang; Kamlah, Marc; Riesch-Oppermann, Heinz; Rolli, Rolf; Liu, Ping

    2011-10-01

    A framework for analyzing crush events of individual ceramic pebbles in solid breeder blankets is developed by means of probabilistic methods. As a brittle material, ceramic breeder pebbles show considerable scatter in crush strengthen for single pebbles. The combination of the discrete element method and experimental data of crush loads provides the possibility of obtaining the overall crush probability of a pebble bed under compression. Furthermore, micro-macro relations are used to correlate the crush probability of pebbles with the overall stress level of the bed. Analysis of uniaxial compression of a mono-sized lithium-orthosilicate pebble bed is presented to demonstrate the application of this tool.

  4. Characterization of the thermal conductivity for ceramic pebble beds

    NASA Astrophysics Data System (ADS)

    Lo Frano, R.; Aquaro, D.; Scaletti, L.; Olivi, N.

    2015-11-01

    The evaluation of the thermal conductivity of breeder materials is one of the main goals to find the best candidate material for the fusion reactor technology. The aim of this paper is to evaluate experimentally the thermal conductivity of a ceramic material by applying the hot wire method at different temperatures, ranging from 50 to about 800°C. The updated experimental facility, available at the Department of Civil and Industrial Engineering (DICI) of the University of Pisa, used to determine the thermal conductivity of a ceramic material (alumina), will be described along with the measurement acquisition system. Moreover it will be also provided an overview of the current state of art of the ceramic pebble bed breeder thermos-mechanics R&D (e.g. Lithium Orthosilicate (Li4SiO4) and Lithium Metatitanate (Li2TiO3)) focusing on the up-to-date analysis. The methodological approach adopted is articulated in two phase: the first one aimed at the experimental evaluation of thermal conductivity of a ceramic material by means of hot wire method, to be subsequently used in the second phase that is based on the test rig method, through which is measured the thermal conductivity of pebble bed material. In this framework, the experimental procedure and the measured results obtained varying the temperature, are presented and discussed.

  5. Numerical and experimental studies on thermal deformation of ceramic breeder pebble bed systems

    NASA Astrophysics Data System (ADS)

    An, Zhiyong

    The goal of this work is to develop modeling capabilities for understanding and predicting thermo-mechanical behavior of ceramic breeder pebble bed systems at elevated temperatures (600-800°C). The thermo-mechanical behavior of solid breeder pebble beds is a critical issue for the solid breeder blanket designs and is different from the behaviors of solid materials. The issue includes potential breakage of pebble materials and change in heat transfer characteristics across the breeder materials and cladding interface. Furthermore, at elevated temperatures, thermal creep deformation plays an uncertain role related to the contact stresses in the pebble beds. To understand these effects, the following efforts have been undertaken: First, experiments of a typical breeder blanket design have been conducted to study the thermal creep behaviors of the pebble bed system. Other than providing data for benchmarking numerical simulation, the experimental results show that the thermal deformation behaviors of typical pebble materials, such as Li2O and Li4SiO4 lithium ceramics, are nonlinear with respect to time and temperature. Under fixed temperatures (higher than 600°C), stresses generated from differential thermal expansion begin to decrease as a result of creep deformation. Second, a new numerical program, based on discrete element method (DEM), has been developed to simulate the fundamental mechanical behaviors of the packed pebble bed system. Considering the effects in a high temperature situation, inelastic contact models have been derived to predict thermal creep deformation. Our DEM program is mainly used to derive the effective mechanical constitutive equations for a pebble bed system. Besides that, it can provide the stress distribution inside the pebble bed and the force evolution related to the changes of boundary loadings. Last, a numerical program based on the finite element analysis (FEA) has been utilized to simulate the stress magnitude and deformation

  6. Experimental and Numerical Study of Ceramic Breeder Pebble Bed Thermal Deformation Behavior

    SciTech Connect

    An Zhiyong; Ying, Alice; Abdou, Mohamed

    2005-05-15

    Experiments on thermomechanics interactions between clad and pebble beds have been performed with overstoichiometric lithium orthosilicate pebbles (pebble diameters between 0.25 and 0.63 mm) at temperatures of 700-800 deg. C. The experimental results show that the thermal deformation of our pebble bed system is nonlinear and when the operating temperature is higher than 600 deg. C, thermal creep deformation is generated. In this paper, constitutive equations of the elastic and creep deformation are derived from the experimental results. Incorporating the effective constitutive equations in finite element method (FEM), numerical investigations presenting the elastic and plastic deformation characteristics of pebble bed system are comparable to the experimental behaviors. In addition, discrete element method (DEM) is underdevelopment to derive constitutive equations for different pebble beds. The preliminary results of DEM show the stress distribution inside the pebble beds at steady or transient states, which helps us to identify the destructive region in a pebble bed system.

  7. Pebble-bed pebble motion: Simulation and Applications

    SciTech Connect

    Joshua J. Cogliati; Abderrafi M. Ougouag

    2011-11-01

    Pebble bed reactors (PBR) have moving graphite fuel pebbles. This unique feature provides advantages, but also means that simulation of the reactor requires understanding the typical motion and location of the granular flow of pebbles. This report presents a method for simulation of motion of the pebbles in a PBR. A new mechanical motion simulator, PEBBLES, efficiently simulates the key elements of motion of the pebbles in a PBR. This model simulates gravitational force and contact forces including kinetic and true static friction. It's used for a variety of tasks including simulation of the effect of earthquakes on a PBR, calculation of packing fractions, Dancoff factors, pebble wear and the pebble force on the walls. The simulator includes a new differential static friction model for the varied geometries of PBRs. A new static friction benchmark was devised via analytically solving the mechanics equations to determine the minimum pebble-to-pebble friction and pebble-to-surface friction for a five pebble pyramid. This pyramid check as well as a comparison to the Janssen formula was used to test the new static friction equations. Because larger pebble bed simulations involve hundreds of thousands of pebbles and long periods of time, the PEBBLES code has been parallelized. PEBBLES runs on shared memory architectures and distributed memory architectures. For the shared memory architecture, the code uses a new O(n) lock-less parallel collision detection algorithm to determine which pebbles are likely to be in contact. The new collision detection algorithm improves on the traditional non-parallel O(n log(n)) collision detection algorithm. These features combine to form a fast parallel pebble motion simulation. The PEBBLES code provides new capabilities for understanding and optimizing PBRs. The PEBBLES code has provided the pebble motion data required to calculate the motion of pebbles during a simulated earthquake. The PEBBLES code provides the ability to determine

  8. Preparation of Li2TiO3-Li4SiO4 core-shell ceramic pebbles with enhanced crush load by graphite bed process

    NASA Astrophysics Data System (ADS)

    Xiang, Maoqiao; Zhang, Yingchun; Zhang, Yun; Liu, Shuya; Liu, Hui; Wang, Chaofu; Gu, Cheng

    2015-11-01

    Li4SiO4 and Li2TiO3 have been regarded as the most favored ceramic breeders of the test blanket modules (TBMs). The lithium density of Li4SiO4 is higher than that of Li2TiO3; however, the thermo-mechanical stability of Li2TiO3 is better than that of Li4SiO4. Hence, the biphasic yLi2TiO3-(1-y)Li4SiO4 (y = 25%, 50%, 75%, molar ratio) pebbles were fabricated by a graphite bed process for the next generation of advanced tritium breeder materials. The pebbles with interesting core-shell structure (core: Li2TiO3 and Li4SiO4, shell: Li2TiO3) were fabricated for the first time. The thickness of Li2TiO3 shell can be controlled by sintering time. Crystal structure, microstructure, and mechanical properties of the biphasic pebbles were investigated. The experimental results showed that the core-shell structure improved the crush load dramatically. The average crush load of 50%Li2TiO3-50%Li4SiO4 pebbles sintered at 1100 °C for 5 h was up to104.79 N.

  9. PEBBLES: A COMPUTER CODE FOR MODELING PACKING, FLOW AND RECIRCULATIONOF PEBBLES IN A PEBBLE BED REACTOR

    SciTech Connect

    Joshua J. Cogliati; Abderrafi M. Ougouag

    2006-10-01

    A comprehensive, high fidelity model for pebble flow has been developed and embodied in the PEBBLES computer code. In this paper, a description of the physical artifacts included in the model is presented and some results from using the computer code for predicting the features of pebble flow and packing in a realistic pebble bed reactor design are shown. The sensitivity of models to various physical parameters is also discussed.

  10. Pebble Bed Reactor Dust Production Model

    SciTech Connect

    Abderrafi M. Ougouag; Joshua J. Cogliati

    2008-09-01

    The operation of pebble bed reactors, including fuel circulation, can generate graphite dust, which in turn could be a concern for internal components; and to the near field in the remote event of a break in the coolant circuits. The design of the reactor system must, therefore, take the dust into account and the operation must include contingencies for dust removal and for mitigation of potential releases. Such planning requires a proper assessment of the dust inventory. This paper presents a predictive model of dust generation in an operating pebble bed with recirculating fuel. In this preliminary work the production model is based on the use of the assumption of proportionality between the dust production and the normal force and distance traveled. The model developed in this work uses the slip distances and the inter-pebble forces computed by the authors’ PEBBLES. The code, based on the discrete element method, simulates the relevant static and kinetic friction interactions between the pebbles as well as the recirculation of the pebbles through the reactor vessel. The interaction between pebbles and walls of the reactor vat is treated using the same approach. The amount of dust produced is proportional to the wear coefficient for adhesive wear (taken from literature) and to the slip volume, the product of the contact area and the slip distance. The paper will compare the predicted volume with the measured production rates. The simulation tallies the dust production based on the location of creation. Two peak production zones from intra pebble forces are predicted within the bed. The first zone is located near the pebble inlet chute due to the speed of the dropping pebbles. The second peak zone occurs lower in the reactor with increased pebble contact force due to the weight of supported pebbles. This paper presents the first use of a Discrete Element Method simulation of pebble bed dust production.

  11. South Africa slashes pebble-bed cash

    NASA Astrophysics Data System (ADS)

    Cartlidge, Edwin

    2010-04-01

    A novel modular technology that promised to make nuclear power cheaper and safer has suffered a serious blow following withdrawal of support from the South African government. It decided not to renew funding for the pebble-bed modular reactor beyond 31 March this year following a lack of interest from other investors and no customers for its product. The company developing the reactor concept - Pebble Bed Modular Reactor Ltd (PBMR) - is to axe three-quarters of its roughly 800 staff and its chief executive has resigned.

  12. Multiscale Analysis of Pebble Bed Reactors

    SciTech Connect

    Hans Gougar; Woo Yoon; Abderrafi Ougouag

    2010-10-01

    – The PEBBED code was developed at the Idaho National Laboratory for design and analysis of pebble-bed high temperature reactors. The diffusion-depletion-pebble-mixing algorithm of the original PEBBED code was enhanced through coupling with the THERMIX-KONVEK code for thermal fluid analysis and by the COMBINE code for online cross section generation. The COMBINE code solves the B-1 or B-3 approximations to the transport equation for neutron slowing down and resonance interactions in a homogeneous medium with simple corrections for shadowing and thermal self-shielding. The number densities of materials within specified regions of the core are averaged and transferred to COMBINE from PEBBED for updating during the burnup iteration. The simple treatment of self-shielding in previous versions of COMBINE led to inaccurate results for cross sections and unsatisfactory core performance calculations. A new version of COMBINE has been developed that treats all levels of heterogeneity using the 1D transport code ANISN. In a 3-stage calculation, slowing down is performed in 167 groups for each homogeneous subregion (kernel, particle layers, graphite shell, control rod absorber annulus, etc.) Particles in a local average pebble are homogenized using ANISN then passed to the next (pebble) stage. A 1D transport solution is again performed over the pebble geometry and the homogenized pebble cross sections are passed to a 1-d radial model of a wedge of the pebble bed core. This wedge may also include homogeneous reflector regions and a control rod region composed of annuli of different absorbing regions. Radial leakage effects are therefore captured with discrete ordinates transport while axial and azimuthal effects are captured with a transverse buckling term. In this paper, results of various PBR models will be compared with comparable models from literature. Performance of the code will be assessed.

  13. Survey of Dust Production in Pebble Bed Reactors Cores

    SciTech Connect

    Joshua J. Cogliati; Abderafi M. Ougouag; Javier Ortensi

    2011-06-01

    Graphite dust produced via mechanical wear from the pebbles in a pebble bed reactor is an area of concern for licensing. Both the German pebble bed reactors produced graphite dust that contained activated elements. These activation products constitute an additional source term of radiation and must be taken under consideration during the conduct of accident analysis of the design. This paper discusses the available literature on graphite dust production and measurements in pebble bed reactors. Limited data is available on the graphite dust produced from the AVR and THTR-300 pebble bed reactors. Experiments that have been performed on wear of graphite in pebble-bed-like conditions are reviewed. The calculation of contact forces, which are a key driving mechanism for dust in the reactor, are also included. In addition, prior graphite dust predictions are examined, and future areas of research are identified.

  14. Contact detection acceleration in pebble flow simulation for pebble bed reactor systems

    SciTech Connect

    Li, Y.; Ji, W.

    2013-07-01

    Pebble flow simulation plays an important role in the steady state and transient analysis of thermal-hydraulics and neutronics for Pebble Bed Reactors (PBR). The Discrete Element Method (DEM) and the modified Molecular Dynamics (MD) method are widely used to simulate the pebble motion to obtain the distribution of pebble concentration, velocity, and maximum contact stress. Although DEM and MD present high accuracy in the pebble flow simulation, they are quite computationally expensive due to the large quantity of pebbles to be simulated in a typical PBR and the ubiquitous contacts and collisions between neighboring pebbles that need to be detected frequently in the simulation, which greatly restricted their applicability for large scale PBR designs such as PBMR400. Since the contact detection accounts for more than 60% of the overall CPU time in the pebble flow simulation, the acceleration of the contact detection can greatly enhance the overall efficiency. In the present work, based on the design features of PBRs, two contact detection algorithms, the basic cell search algorithm and the bounding box search algorithm are investigated and applied to pebble contact detection. The influence from the PBR system size, core geometry and the searching cell size on the contact detection efficiency is presented. Our results suggest that for present PBR applications, the bounding box algorithm is less sensitive to the aforementioned effects and has superior performance in pebble contact detection compared with basic cell search algorithm. (authors)

  15. Granular flow in pebble bed reactors: Dust generation and scaling

    SciTech Connect

    Rycroft, C. H.; Lind, T.; Guentay, S.; Dehbi, A.

    2012-07-01

    In experimental prototypes of pebble bed reactors, significant quantities of graphite dust have been observed due to rubbing between pebbles as they flow through the core. At the high temperatures and pressures in these reactors, little data is available to understand the frictional properties of the pebble surfaces, and as a result, the Paul Scherrer Institut (Switzerland) proposes a conceptual design of a scaled-down version of a pebble bed reactor to investigate this issue in detail. In this paper, simulations of granular flow in pebble bed reactors using the discrete-element method are presented. Simulations in the full geometry (using 440,000 pebbles) are compared to those in geometries scaled down by 3:1 and 6:1. The simulations show complex behavior due to discrete pebble packing effects, meaning that pebble flow and dust generation in a scaled-down facility may be significantly different. The differences between velocity profiles, packing geometry, and pebble wear at the different scales are discussed. The results can aid in the design of the prototypical facility to more accurately reproduce the flow in a full-size reactor. (authors)

  16. Effective Thermal Conductivity of a Li{sub 2}TiO{sub 3} Pebble Bed for a DEMO Blanket

    SciTech Connect

    Hatano, T.; Enoeda, M.; Suzuki, S.; Kosaku, Y.; Akiba, M.

    2003-07-15

    In development of the ceramic breeder blanket, the effective thermal conductivity of pebble beds is an important design parameter. For thermo-mechanical design of blanket, pebble beds were investigated used for Li{sub 2}TiO{sub 3} that was a candidate for tritium breeder. Li{sub 2}TiO{sub 3} pebble beds, whose size was 0.28-1.91 mm diameter, were measured on load under no neutron irradiation. The effective thermal conductivity was increased with load increasing was obtained.

  17. The effects of temperatures on the pebble flow in a pebble bed high temperature reactor

    SciTech Connect

    Sen, R. S.; Cogliati, J. J.; Gougar, H. D.

    2012-07-01

    The core of a pebble bed high temperature reactor (PBHTR) moves during operation, a feature which leads to better fuel economy (online refueling with no burnable poisons) and lower fuel stress. The pebbles are loaded at the top and trickle to the bottom of the core after which the burnup of each is measured. The pebbles that are not fully burned are recirculated through the core until the target burnup is achieved. The flow pattern of the pebbles through the core is of importance for core simulations because it couples the burnup distribution to the core temperature and power profiles, especially in cores with two or more radial burnup 'zones '. The pebble velocity profile is a strong function of the core geometry and the friction between the pebbles and the surrounding structures (other pebbles or graphite reflector blocks). The friction coefficient for graphite in a helium environment is inversely related to the temperature. The Thorium High Temperature Reactor (THTR) operated in Germany between 1983 and 1989. It featured a two-zone core, an inner core (IC) and outer core (OC), with different fuel mixtures loaded in each zone. The rate at which the IC was refueled relative to the OC in THTR was designed to be 0.56. During its operation, however, this ratio was measured to be 0.76, suggesting the pebbles in the inner core traveled faster than expected. It has been postulated that the positive feedback effect between inner core temperature, burnup, and pebble flow was underestimated in THTR. Because of the power shape, the center of the core in a typical cylindrical PBHTR operates at a higher temperature than the region next to the side reflector. The friction between pebbles in the IC is lower than that in the OC, perhaps causing a higher relative flow rate and lower average burnup, which in turn yield a higher local power density. Furthermore, the pebbles in the center region have higher velocities than the pebbles next to the side reflector due to the

  18. Calculation of the Dancoff Factor for Pebble Bed Reactors

    SciTech Connect

    Valko, J.; Tsvetkov, P.V.; Hoogenboom, J.E.

    2000-07-15

    The double heterogeneity of the core of pebble bed-type high-temperature reactors (HTRs) requires special attention when lattice codes are applied to a unit cell of such systems. As the self-shielding of the resonance absorption takes place in the small fuel grains in the pebbles, the grain-lattice calculation should apply a Dancoff factor for the grain lattice yet take into account the finiteness of the grain lattice in a pebble and the possibility of a neutron reaching another pebble. In a study of HTR lattices, the Dancoff factor was calculated using the DANCOFF-MC program. For a finite lattice of fuel grains in the fuel region of a pebble, the space-dependent Dancoff factor was calculated, and it was averaged over the volume of the fuel in one pebble. This single-pebble Dancoff factor was further corrected to include the effect of other pebbles. The sensitivity of the Dancoff factor to core composition and the sensitivity of core calculations to the Dancoff factor are discussed, and a numerical example is given.

  19. The challenges on uncertainty analysis for pebble bed HTGR

    SciTech Connect

    Hao, C.; Li, F.; Zhang, H.

    2012-07-01

    The uncertainty analysis is very popular and important, and many works have been done for Light Water Reactor (LWR), although the experience for the uncertainty analysis in High Temperature Gas cooled Reactor (HTGR) modeling is still in the primary stage. IAEA will launch a Coordination Research Project (CRP) on this topic soon. This paper addresses some challenges for the uncertainty analysis in HTGR modeling, based on the experience of OECD LWR Uncertainty Analysis in Modeling (UAM) activities, and taking into account the peculiarities of pebble bed HTGR designs. The main challenges for HTGR UAM are: the lack of experience, the totally different code packages, the coupling of power distribution, temperature distribution and burnup distribution through the temperature feedback and pebble flow. The most serious challenge is how to deal with the uncertainty in pebble flow, the uncertainty in pebble bed flow modeling, and their contribution to the uncertainty of maximum fuel temperature, which is the most interested parameter for the modular HTGR. (authors)

  20. Experimental Results of Pebble Beds Thermal Hydraulic Characteristics

    SciTech Connect

    Rimkevicius, S.; Uspuras, E.

    2006-07-01

    The purpose of this paper is to present the results of the experimental investigation of the thermal hydraulic characteristics for two types of test sections - thin annular pebble beds (i.e. spheres dumped in thin annular slots) and pebble beds placed between cylinders. The experimental results of heat transfer from the spheres and from a cylinder, as well as hydraulic drag for both types of test sections are presented in this paper. The results of performed experiments in the case of thin annular pebble beds demonstrated that maximum heat transfer and hydraulic drag is at the relative width of the annular slot K equal to 1.07 and 1.75 of spheres diameter. The heat transfer in internal layers at these values of K is equal to the heat transfer in the internal layers of large (unlimited) rhombic packing. The results of the experimental investigation of pebble beds between cylinders demonstrated that the randomly arranged pebble bed is preferable to the regular rhombic structure from the point of view of design simplicity, heat transfer from the cylinder and drag coefficient. (authors)

  1. PEBBLE: a two-dimensional steady-state pebble bed reactor thermal hydraulics code

    SciTech Connect

    Vondy, D.R.

    1981-09-01

    This report documents the local implementation of the PEBBLE code to treat the two-dimensional steady-state pebble bed reactor thermal hydraulics problem. This code is implemented as a module of a computation system used for reactor core history calculations. Given power density data, the geometric description in (RZ), and basic heat removal conditions and thermal properties, the coolant properties, flow conditions, and temperature distributions in the pebble fuel elements are predicted. The calculation is oriented to the continuous fueling, steady state condition with consideration of the effect of the high energy neutron flux exposure and temperature history on the thermal conductivity. The coolant flow conditions are calculated for the same geometry as used in the neutronics calculation, power density and fluence data being used directly, and temperature results are made available for subsequent use.

  2. PEBBED ANALYSIS OF HOT SPOTS IN PEBBLE-BED REACTORS

    SciTech Connect

    Abderrafi M. Ougouag; Hans D. Gougar; William K. Terry; Frederik Reitsma; Wessel Joubert

    2005-09-01

    The Idaho National Laboratory’s PEBBED code and simple probability considerations are used to estimate the likelihood and consequences of the accumulation of highly reactive pebbles in the region of peak power in a pebble-bed reactor. The PEBBED code is briefly described, and the logic of the probability calculations is presented in detail. The results of the calculations appear to show that hot-spot formation produces only moderate increases in peak accident temperatures, and no increases at all in normal operating temperatures.

  3. Automated Design and Optimization of Pebble-bed Reactor Cores

    SciTech Connect

    Hans D. Gougar; Abderrafi M. Ougouag; William K. Terry

    2010-07-01

    We present a conceptual design approach for high-temperature gas-cooled reactors using recirculating pebble-bed cores. The design approach employs PEBBED, a reactor physics code specifically designed to solve for and analyze the asymptotic burnup state of pebble-bed reactors, in conjunction with a genetic algorithm to obtain a core that maximizes a fitness value that is a function of user-specified parameters. The uniqueness of the asymptotic core state and the small number of independent parameters that define it suggest that core geometry and fuel cycle can be efficiently optimized toward a specified objective. PEBBED exploits a novel representation of the distribution of pebbles that enables efficient coupling of the burnup and neutron diffusion solvers. With this method, even complex pebble recirculation schemes can be expressed in terms of a few parameters that are amenable to modern optimization techniques. With PEBBED, the user chooses the type and range of core physics parameters that represent the design space. A set of traits, each with acceptable and preferred values expressed by a simple fitness function, is used to evaluate the candidate reactor cores. The stochastic search algorithm automatically drives the generation of core parameters toward the optimal core as defined by the user. The optimized design can then be modeled and analyzed in greater detail using higher resolution and more computationally demanding tools to confirm the desired characteristics. For this study, the design of pebble-bed high temperature reactor concepts subjected to demanding physical constraints demonstrated the efficacy of the PEBBED algorithm.

  4. PEBBLES

    SciTech Connect

    Cogliati, Joshua J.

    2010-09-01

    The PEBBLES code is a computer program designed to simulate the motion, packing and vibration of spheres that undergo various mechanical forces including gravitation, Hooke's law force and various friction forces. The frictional forces include true static friction that allows non-zero angles of repose. Each pebble is individually simulated using the distinct element method. The program outputs various tallies as textual numbers. These tallies include pebble position, pebble angular and linear velocity, force on the wall and between pebbles, probabilities of pebbles moving between different locations, accumulated amount of linear motion between pebbles, and average velocity in different regions of the container.

  5. Nuclear Safeguards Considerations For The Pebble Bed Modular Reactor (PBMR)

    SciTech Connect

    Phillip Casey Durst; David Beddingfield; Brian Boyer; Robert Bean; Michael Collins; Michael Ehinger; David Hanks; David L. Moses; Lee Refalo

    2009-10-01

    High temperature reactors (HTRs) have been considered since the 1940s, and have been constructed and demonstrated in the United Kingdom (Dragon), United States (Peach Bottom and Fort Saint Vrain), Japan (HTTR), Germany (AVR and THTR-300), and have been the subject of conceptual studies in Russia (VGM). The attraction to these reactors is that they can use a variety of reactor fuels, including abundant thorium, which upon reprocessing of the spent fuel can produce fissile U-233. Hence, they could extend the stocks of available uranium, provided the fuel is reprocessed. Another attractive attribute is that HTRs typically operate at a much higher temperature than conventional light water reactors (LWRs), because of the use of pyrolytic carbon and silicon carbide coated (TRISO) fuel particles embedded in ceramic graphite. Rather than simply discharge most of the unused heat from the working fluid in the power plant to the environment, engineers have been designing reactors for 40 years to recover this heat and make it available for district heating or chemical conversion plants. Demonstrating high-temperature nuclear energy conversion was the purpose behind Fort Saint Vrain in the United States, THTR-300 in Germany, HTTR in Japan, and HTR-10 and HTR-PM, being built in China. This resulted in nuclear reactors at least 30% or more thermodynamically efficient than conventional LWRs, especially if the waste heat can be effectively utilized in chemical processing plants. A modern variant of high temperature reactors is the Pebble Bed Modular Reactor (PBMR). Originally developed in the United States and Germany, it is now being redesigned and marketed by the Republic of South Africa and China. The team examined historical high temperature and high temperature gas reactors (HTR and HTGR) and reviewed safeguards considerations for this reactor. The following is a preliminary report on this topic prepared under the ASA-100 Advanced Safeguards Project in support of the NNSA Next

  6. Core Optimization of a Deep-Burn Pebble Bed Reactor

    SciTech Connect

    Brian Boer; Abderrafi M. Ougouag

    2010-06-01

    Achieving a high fuel burnup in the Deep-Burn (DB) pebble bed reactor design, while remaining within the limits for fuel temperature, power peaking and temperature reactivity feedback, is challenging. The high content of Pu and Minor Actinides in the Deep-Burn fuel significantly impacts the thermal neutron energy spectrum as compared to a ’standard’ UO2 fueled core. This can result in power and temperature peaking in the pebble bed core in locally thermalized regions near the graphite reflectors. Furthermore, the interplay of the Pu resonances of the neutron absorption cross sections at low-lying energies can lead to a positive temperature reactivity coefficient for the graphite moderator at certain operating conditions. The DB concept focuses on the destruction of spent fuel transuranics in TRISO coated particle fueled gas-cooled reactors with the aim of a fractional fuel burnup of 60-70% in fissions per initial metal atom (FIMA), using a single-pass, multi in-core fuel (re)cycling scheme. In principle, the DB pebble bed concept employs the same reactor designs as the present low enriched uranium core designs, i.e. the 400 MWth Pebble Bed Modular Reactor (PBMR-400). A Pu and Minor Actinide fueled PBMR-400 design serves as the starting point for a core optimization study. The fuel temperature, power peak, temperature reactivity coefficients, and burnup capabilities of the modified designs are analyzed with the PEBBED code. A code-to-code coupling with the PASTA code allows for the analysis of the TRISO fuel performance for both normal and Loss Of Forced Cooling conditions. An improved core design is sought, maximizing the fuel discharge burnup, while retaining negative temperature reactivity feedback coefficients for the entire temperature range and avoiding high fuel temperatures (fuel failure probabilities).

  7. Computational fluid dynamics analysis of aerosol deposition in pebble beds

    NASA Astrophysics Data System (ADS)

    Mkhosi, Margaret Msongi

    2007-12-01

    The Pebble Bed Modular Reactor is a high temperature gas cooled reactor which uses helium gas as a coolant. The reactor uses spherical graphite pebbles as fuel. The fuel design is inherently resistant to the release of the radioactive material up to high temperatures; therefore, the plant can withstand a broad spectrum of accidents with limited release of radionuclides to the environment. Despite safety features of the concepts, these reactors still contain large inventories of radioactive materials. The transport of most of the radioactive materials in an accident occurs in the form of aerosol particles. In this dissertation, the limits of applicability of existing computational fluid dynamics code FLUENT to the prediction of aerosol transport have been explored. The code was run using the Reynolds Averaged Navier-Stokes turbulence models to determine the effects of different turbulence models on the prediction of aerosol particle deposition. Analyses were performed for up to three unit cells in the orthorhombic configuration. For low flow conditions representing natural circulation driven flow, the laminar flow model was used and the results were compared with existing experimental data for packed beds. The results compares well with experimental data in the low flow regime. For conditions corresponding to normal operating of the reactor, analyses were performed using the standard k-ɛ turbulence model. From the inertial deposition results, a correlation that can be used to estimate the deposition of aerosol particles within pebble beds given inlet flow conditions has been developed. These results were converted into a dimensionless form as a function of a modified Stokes number. Based on results obtained in the laminar regime and for individual pebbles, the correlation developed for the inertial impaction component of deposition is believed to be credible. The form of the correlation developed also allows these results to be applied to pebble beds of different

  8. Packing microstructure and local density variations of experimental and computational pebble beds

    SciTech Connect

    Auwerda, G. J.; Kloosterman, J. L.; Lathouwers, D.; Van Der Hagen, T. H. J. J.

    2012-07-01

    In pebble bed type nuclear reactors the fuel is contained in graphite pebbles, which form a randomly stacked bed with a non-uniform packing density. These variations can influence local coolant flow and power density and are a possible cause of hotspots. To analyse local density variations computational methods are needed that can generate randomly stacked pebble beds with a realistic packing structure on a pebble-to-pebble level. We first compare various properties of the local packing structure of a computed bed with those of an image made using computer aided X-ray tomography, looking at properties in the bulk of the bed and near the wall separately. Especially for the bulk of the bed, properties of the computed bed show good comparison with the scanned bed and with literature, giving confidence our method generates beds with realistic packing microstructure. Results also show the packing structure is different near the wall than in the bulk of the bed, with pebbles near the wall forming ordered layers similar to hexagonal close packing. Next, variations in the local packing density are investigated by comparing probability density functions of the packing fraction of small clusters of pebbles throughout the bed. Especially near the wall large variations in local packing fractions exists, with a higher probability for both clusters of pebbles with low (<0.6) and high (>0.65) packing fraction, which could significantly affect flow rates and, together with higher power densities, could result in hotspots. (authors)

  9. Benchmark Evaluation of HTR-PROTEUS Pebble Bed Experimental Program

    SciTech Connect

    Bess, John D.; Montierth, Leland; Köberl, Oliver; Snoj, Luka

    2014-10-09

    Benchmark models were developed to evaluate 11 critical core configurations of the HTR-PROTEUS pebble bed experimental program. Various additional reactor physics measurements were performed as part of this program; currently only a total of 37 absorber rod worth measurements have been evaluated as acceptable benchmark experiments for Cores 4, 9, and 10. Dominant uncertainties in the experimental keff for all core configurations come from uncertainties in the ²³⁵U enrichment of the fuel, impurities in the moderator pebbles, and the density and impurity content of the radial reflector. Calculations of keff with MCNP5 and ENDF/B-VII.0 neutron nuclear data are greater than the benchmark values but within 1% and also within the 3σ uncertainty, except for Core 4, which is the only randomly packed pebble configuration. Repeated calculations of keff with MCNP6.1 and ENDF/B-VII.1 are lower than the benchmark values and within 1% (~3σ) except for Cores 5 and 9, which calculate lower than the benchmark eigenvalues within 4σ. The primary difference between the two nuclear data libraries is the adjustment of the absorption cross section of graphite. Simulations of the absorber rod worth measurements are within 3σ of the benchmark experiment values. The complete benchmark evaluation details are available in the 2014 edition of the International Handbook of Evaluated Reactor Physics Benchmark Experiments.

  10. Benchmark Evaluation of HTR-PROTEUS Pebble Bed Experimental Program

    DOE PAGES

    Bess, John D.; Montierth, Leland; Köberl, Oliver; ...

    2014-10-09

    Benchmark models were developed to evaluate 11 critical core configurations of the HTR-PROTEUS pebble bed experimental program. Various additional reactor physics measurements were performed as part of this program; currently only a total of 37 absorber rod worth measurements have been evaluated as acceptable benchmark experiments for Cores 4, 9, and 10. Dominant uncertainties in the experimental keff for all core configurations come from uncertainties in the ²³⁵U enrichment of the fuel, impurities in the moderator pebbles, and the density and impurity content of the radial reflector. Calculations of keff with MCNP5 and ENDF/B-VII.0 neutron nuclear data are greatermore » than the benchmark values but within 1% and also within the 3σ uncertainty, except for Core 4, which is the only randomly packed pebble configuration. Repeated calculations of keff with MCNP6.1 and ENDF/B-VII.1 are lower than the benchmark values and within 1% (~3σ) except for Cores 5 and 9, which calculate lower than the benchmark eigenvalues within 4σ. The primary difference between the two nuclear data libraries is the adjustment of the absorption cross section of graphite. Simulations of the absorber rod worth measurements are within 3σ of the benchmark experiment values. The complete benchmark evaluation details are available in the 2014 edition of the International Handbook of Evaluated Reactor Physics Benchmark Experiments.« less

  11. Delineating Glacial Till Bed Kinematics using AMS and Pebble Fabrics

    NASA Astrophysics Data System (ADS)

    Gentoso, M. J.; Evenson, E.; Kodama, K. P.

    2010-12-01

    Anisotropy of magnetic susceptibility (AMS) and pebble fabric analysis was used to explore glacial till bed kinematics in streamlined glacial landforms of the Weedsport Drumlin field of north central New York State. Five wave-truncated drumlins were sampled at two locations each along the shore of Lake Ontario. A total of 500 pebble orientations and 250 AMS samples were collected from 10 sampling sites in the drumlins. Six flutes were also sampled at 10 sampling sites for a total of 500 pebble orientations and 200 AMS measurements. All AMS measurements were conducted on a KLY-3s Kappabridge. The average orientation of the maximum principal susceptibility axes for the drumlins (N2°E) was parallel, within 95% confidence limits, to the average pebble long-axis orientations (N5°W) and parallel to the N-S trend of the drumlins. Both AMS and pebble average orientations plunge toward the north in the “up glacier” direction indicating an imbrication due to ice flow. The clustering of the AMS principal axis directions indicates that the strength of the AMS drumlin fabric is highly variable, at 3 of the 10 sites it is as strong as fabrics developed in a ring shear device (Iverson et al., 2008) at intermediate shear strains. AMS fabrics in the flutes are stronger and more unidirectional than for the drumlins with the average pebble direction (N4°E) parallel to the average AMS maximum susceptibility direction (N12°E), but not at the 95% confidence level. Northward plunge of these average orientations indicates an imbrication. The flutes trend N10°W, so the fabric orientations are not as closely parallel to the glacial landforms for the flutes as they are for the drumlins. Thermal demagnetization of three orthogonal components of an isothermal remanent magnetization indicates that the AMS is carried primarily by maghemite. The stronger AMS fabric in the flutes compared to the drumlins suggests that the till of the flutes has been subjected to higher strains and perhaps

  12. Tritium localisation and release from the ceramic pebbles of breeder

    NASA Astrophysics Data System (ADS)

    Kizane, G.; Tiliks, J.; Vitinš, A.; Rudzitis, J.

    2004-08-01

    Magnetic field (MF) effects on the radiolysis and tritium release from Li 4SiO 4 (FZK) and Li 2TiO 3 (CEA) ceramic pebbles were investigated. The tritium chemical forms in Li 4SiO 4 were estimated by means of lyomethods. In the case of the neutron fluence Fn⩽10 18 n m -2, the tritium is mostly in the T + form, but in the case of Fn≈10 25 n m -2, the T + form accounts for 86-95% of the tritium. A high subsurface concentration of tritium is characteristic of a separate pebble and correlates with the distribution of radiation-induced defects. The MF increases the radiolysis of Li 4SiO 4 by 20-25%. Irradiation with electrons to 1000 MGy at 1200 K increases the grain size by 5-10%, decreasing the parameters of tritium release. The increased grain size was observed for the Li 4SiO 4 pebbles irradiated in EXOTIC-8. A considerable tritium detention (up to 40%) was observed after annealing to 1120 K in the MF of 2.4 T.

  13. From CANDLE reactor to pebble-bed reactor

    SciTech Connect

    Chen, X. N.; Maschek, W.

    2006-07-01

    This paper attempts to reveal theoretically, by studying a diffusion-burn-up coupled neutronic model, that a so-called CANDLE reactor and a pebble-bed type reactor have a common burn-up feature. As already known, a solitary burn-up wave that can develop in the common U-Pu and Th-U conversion processes is the basic mechanism of the CANDLE reactor. In this paper it is demonstrated that a family of burn-up wave solution exists in the boundary value problem characterizing a pebble bed reactor, in which the fuel is loaded from above into the core and unloaded from bottom. Among this solution family there is a particular case, namely, a partial solitary wave solution, which begins from the fuel entrance side and extends into infinity on the exit side, and has a maximal bum-up rate in this family. An example dealing with the {sup 232}Th-{sup 233}U conversion chain is studied and the solutions are presented in order to show the mechanism of the burn-up wave. (authors)

  14. Experimental study of fluid dynamics in the pebble bed in a radial coolant flow

    NASA Astrophysics Data System (ADS)

    Smorchkova, Y. V.; Varava, A. N.; Dedov, A. V.; Komov, A. T.

    2016-10-01

    The results of experimental studies of pebble bed hydrodynamics are presented. For the first time experimental data on the pressure loss in a radial flow of fluid through the pebble bed was obtained. Experiments were carried out in the liquid flow rate ranging from 0.09 to 0.4 kg / s, fluid temperature is 20°C.

  15. Deleterious Thermal Effects Due To Randomized Flow Paths in Pebble Bed, and Particle Bed Style Reactors

    NASA Technical Reports Server (NTRS)

    Moran, Robert P.

    2013-01-01

    A review of literature associated with Pebble Bed and Particle Bed reactor core research has revealed a systemic problem inherent to reactor core concepts which utilize randomized rather than structured coolant channel flow paths. For both the Pebble Bed and Particle Bed Reactor designs; case studies reveal that for indeterminate reasons, regions within the core would suffer from excessive heating leading to thermal runaway and localized fuel melting. A thermal Computational Fluid Dynamics model was utilized to verify that In both the Pebble Bed and Particle Bed Reactor concepts randomized coolant channel pathways combined with localized high temperature regions would work together to resist the flow of coolant diverting it away from where it is needed the most to cooler less resistive pathways where it is needed the least. In other words given the choice via randomized coolant pathways the reactor coolant will take the path of least resistance, and hot zones offer the highest resistance. Having identified the relationship between randomized coolant channel pathways and localized fuel melting it is now safe to assume that other reactor concepts that utilize randomized coolant pathways such as the foam core reactor are also susceptible to this phenomenon.

  16. Calculational approach and results of the safe shutdown earthquake event for the pebble bed modular reactor

    SciTech Connect

    Van Heerden, G.; Sen, S.; Reitsma, F.

    2006-07-01

    The Pebble Bed Modular Reactor (PBMR) concept can be described as a high-temperature helium-cooled, graphite-moderated pebble-bed reactor with a multi-pass fuelling scheme. The fuel is contained in 6 cm diameter graphite spheres containing carbon-based coated UO{sub 2} kernels. An online fuel reload scheme is applied with the fuel spheres being circulated through the reactor. The pebble-bed reactor core thus consists of fuel pebbles packed in the core cavity in a random way. The packing densities and pebble flow is well known through analysis and tests done in the German experimental and development program. The pebble-bed typically has a packing fraction of 0.61. In the event of an earthquake this packing fraction may increase with the effect that the core geometry and core reactivity will change. The Safe Shutdown Earthquake (SSE) analysis performed for the PBMR 400 MW design is described in this paper, and it specifically covers SSE-induced pebble-bed packing fractions of 0.62 and 0.64. The main effects governing the addition of reactivity in the SSE event are the changes in core neutronic leakage due to the decreased core size and the decreased effectiveness of the control rods as the pebble-bed height decreases. This paper describes the models, methods and tools used to analyse the event, the results obtained for the different approaches and the consequences and safety implications of such an event. (authors)

  17. Tightly Coupled Multiphysics Algorithm for Pebble Bed Reactors

    SciTech Connect

    HyeongKae Park; Dana Knoll; Derek Gaston; Richard Martineau

    2010-10-01

    We have developed a tightly coupled multiphysics simulation tool for the pebble-bed reactor (PBR) concept, a type of Very High-Temperature gas-cooled Reactor (VHTR). The simulation tool, PRONGHORN, takes advantages of the Multiphysics Object-Oriented Simulation Environment library, and is capable of solving multidimensional thermal-fluid and neutronics problems implicitly with a Newton-based approach. Expensive Jacobian matrix formation is alleviated via the Jacobian-free Newton-Krylov method, and physics-based preconditioning is applied to minimize Krylov iterations. Motivation for the work is provided via analysis and numerical experiments on simpler multiphysics reactor models. We then provide detail of the physical models and numerical methods in PRONGHORN. Finally, PRONGHORN's algorithmic capability is demonstrated on a number of PBR test cases.

  18. Proliferation resistant fuel for pebble bed modular reactors

    SciTech Connect

    Ronen, Y.; Aboudy, M.; Regev, D.; Gilad, E.

    2012-07-01

    We show that it is possible to denature the Plutonium produced in Pebble Bed Modular Reactors (PBMR) by doping the nuclear fuel with either 3050 ppm of {sup 237}Np or 2100 ppm of Am vector. A correct choice of these isotopes concentration yields denatured Plutonium with isotopic ratio {sup 238}Pu/Pu {>=} 6%, for the entire fuel burnup cycle. The penalty for introducing these isotopes into the nuclear fuel is a subsequent shortening of the fuel burnup cycle, with respect to a non-doped reference fuel, by 41.2 Full Power Days (FPDs) and 19.9 FPDs, respectively, which correspond to 4070 MWd/ton and 1965 MWd/ton reduction in fuel discharge burnup. (authors)

  19. Spectral zone selection methodology for pebble bed reactors

    SciTech Connect

    Ramatsemela Mphahlele; Abderrafi M. Ougouag; Kostadin N. Ivanov; Hans D. Gougar

    2011-01-01

    A methodology is developed for determining boundaries of spectral zones for pebble bed reactors. A spectral zone is defined as a region made up of a number of nodes whose characteristics are collectively similar and that are assigned the same few-group diffusion constants. The spectral zones are selected in such a manner that the difference (error) between the reference transport solution and the diffusion code solution takes a minimum value. This is achieved by choosing spectral zones through optimally minimizing this error. The objective function for the optimization algorithm is the total reaction rate error, which is defined as the sum of the leakage, absorption and fission reaction rates errors in each zone. The selection of these spectral zones is such that the core calculation results based on diffusion theory are within an acceptable tolerance as compared to a proper transport reference solution. Through this work, a consistent approach for identifying spectral zones that yield more accurate diffusion results is introduced.

  20. EVALUATION OF THE INITIAL CRITICAL CONFIGURATION OF THE HTR-10 PEBBLE-BED REACTOR

    SciTech Connect

    William K. Terry

    2005-11-01

    This report describes the evaluation of data from the initial criticality measurement of the HTR-10 pebble-bed reactor at the Institute of Nuclear Energy Technology in China to determine whether the data are of sufficient quality to use as benchmarks for reactor physics computer codes intended for pebble-bed reactor analysis. The evaluation applied the INL pebble-bed reactor physics code PEBBED to perform an uncertainty analysis on the core critical height. The overall uncertainty in k-effective was slightly over 0.5%, which is considered adequate for an experimental benchmark.

  1. Heat transfer and technological investigations on mixed beds of beryllium and Li 4SiO 4 pebbles

    NASA Astrophysics Data System (ADS)

    Dalle Donne, M.; Goraieb, A.; Huber, R.; Schmitt, B.; Schumacher, G.; Sordon, G.; Weisenburger, A.

    1994-09-01

    For the European BOT DEMO solid breeder blanket design the use of mixtures of 2 mm beryllium and 0.1-0.2 mm Li 4SiO 4 pebbles with and without 0.1-0.2 mm beryllium pebbles has been proposed. A series of heat transfer and technological investigations are being performed for these pebbles. Namely: (a) Measurements of the thermal conductivity and of the wall heat transfer coefficient of a 2 mm Be pebble bed, of a bed with 2 mm Be plus 0.1-0.2 mm Li 4SiO 4 pebbles and of a bed with 2 mm Be pebbles plus 0.1-0.2 mm Li 4SiO 4 and Be pebbles. (b) Thermal cycle tests of mixed beds of Li 4SiO 4 and beryllium pebbles; during these tests the pressure drop across the bed of the helium purging flow is measured. (c) Annealing tests at 650°C of the Li 4SiO 4 pebbles with and without the beryllium pebbles. (d) Measurement of the failure loads of the Li 4SiO 4 pebbles before and after annealing. Tests (a) and (b) have been performed for bigger Li 4SiO 4 pebbles (0.3-0.6 mm) as well. The results of the experiments are reported in the paper.

  2. Experimental investigation of the pebble bed structure by using gamma ray tomography

    NASA Astrophysics Data System (ADS)

    Ahmed, Fadha Shakir

    Pebble Bed Reactors offer a future for new nuclear energy plants. They are small, inherently safe, and can be competitive with fossil fuels. The fuel forms a randomly stacked pebble with non-uniform fuel densities. The thermal-mechanical behavior of pebble bed reactor core is depends strongly on the spatial variation of packing fraction in the bed and in particular on the number of contacts between pebbles, and between the pebbles and the blanket walls. To investigate these effects, experimental data to characterize bed structure are needed along with other numerical simulation and computational tools for validation. In this study, a powerful technique of high-energy gamma-ray computed tomography (CT scanner system) is employed for the first time for the quantification of the structure of pebble bed in term of the cross-sectional time-averaged void and distributions, it radial profiles and the statistical analysis. The alternative minimization (AM) iteration algorithm is used for image reconstruction. The spatial resolution of the CT scan is about 2 mm with 100 x 100 pixel used to reconstruct the cross-sectional image. Results of tomography with this advanced technique on three different pebble sizes at different axial levels are presented. The bed consisted of a glass spheres (Marbles) with a diameter d1= 1.27 cm, d2= 2.54 cm and d3= 5 cm in a Plexiglas cylinder with diameter D = 30.48 cm (D/d1 = 24, D/d2 = 12 and D/d3 = 6), and had an average void fraction epsilon1= 0.389, epsilon2 = 0.40 and epsilon 3 =0.43, respectively. The radial void fraction profile showed large oscillations with the bigger pebble diameters and the void fraction is higher on the wall with a minimum void fraction of 0.33 at 0.68 pebble diameter away from the wall. It was found that the void distribution in random packed bed depends strongly on the pebble diameter with respect to the bed diameter (D/d p) and the packing mode. The oscillation is quiet large with the smaller aspect ratio (D

  3. A COMPARISON OF PEBBLE MIXING AND DEPLETION ALGORITHMS USED IN PEBBLE-BED REACTOR EQUILIBRIUM CYCLE SIMULATION

    SciTech Connect

    Hans D. Gougar; Frederik Reitsma; Wessel Joubert

    2009-05-01

    Recirculating pebble-bed reactors are distinguished from all other reactor types by the downward movement through and reinsertion of fuel into the core during operation. Core simulators must account for this movement and mixing in order to capture the physics of the equilibrium cycle core. VSOP and PEBBED are two codes used to perform such simulations, but they do so using different methods. In this study, a simplified pebble-bed core with a specified flux profile and cross sections is used as the model for conducting analyses of two types of burnup schemes. The differences between the codes are described and related to the differences observed in the nuclide densities in pebbles discharged from the core. Differences in the methods for computing fission product buildup and average number densities lead to significant differences in the computed core power and eigenvalue. These test models provide a key component of an overall equilibrium cycle benchmark involving neutron transport, cross section generation, and fuel circulation.

  4. METHODS FOR MODELING THE PACKING OF FUEL ELEMENTS IN PEBBLE BED REACTORS

    SciTech Connect

    Abderrafi M. Ougouag; Joshua J. Cogliati; Jan-Leen Kloosterman

    2005-09-01

    Two methods for the modeling of the packing of pebbles in the pebble bed reactors are presented and compared. The first method is based on random generation of potential centers for the pebbles, followed by rejection of points that are not compatible with the geometric constraint of no (or limited) pebbles overlap. The second method models the actual physical packing process, accounting for the dynamic of pebbles as they are dropped onto the pebble bed and as they settle therein. A simplification in the latter model is the assumption of a starting point with very dilute packing followed by settling. The results from the two models are compared and the properties of the second model and the dependence of its results on many of the modeling parameters are presented. The first model (with no overlap allowed) has been implemented into a code to compute Dancoff factors. The second model will soon be implemented into that same code and will also be used to model flow of pebbles in a reactor and core densification in the simulation of earthquakes. Both methods reproduce experimental values well, with the latter displaying a high level of fidelity.

  5. INVESTIGATION OF BOUNDS ON PARTICLE PACKING IN PEBBLE-BED HIGH TEMPERATURE REACTORS

    SciTech Connect

    Nuclear Engineering and Design; Jan Leen Kloosterman; Wilfred F.G. van Rooijen; Hans D. Gougar; William K. Terry

    2006-03-01

    Models and methods are presented for determining practical limits of the packing density of TRISO particles in fuel pebbles for a pebble-bed reactor (PBR). These models are devised for designing and interpreting fuel testing experiments. Two processes for particle failure are accounted for: failure of touching particles at the pressing stage in the pebble manufacturing process, and failure due to inner pressure buildup during irradiation. The second process gains importance with increasing fuel temperature, which limits the particle packing density and the corresponding fuel enrichment. Suggestions for improvements to the models are presented.

  6. Computational and experimental prediction of dust production in pebble bed reactors, Part II

    SciTech Connect

    Mie Hiruta; Gannon Johnson; Maziar Rostamian; Gabriel P. Potirniche; Abderrafi M. Ougouag; Massimo Bertino; Louis Franzel; Akira Tokuhiro

    2013-10-01

    This paper is the continuation of Part I, which describes the high temperature and high pressure helium environment wear tests of graphite–graphite in frictional contact. In the present work, it has been attempted to simulate a Pebble Bed Reactor core environment as compared to Part I. The experimental apparatus, which is a custom-designed tribometer, is capable of performing wear tests at PBR relevant higher temperatures and pressures under a helium environment. This environment facilitates prediction of wear mass loss of graphite as dust particulates from the pebble bed. The experimental results of high temperature helium environment are used to anticipate the amount of wear mass produced in a pebble bed nuclear reactor.

  7. Pebble Bed Reactors Design Optimization Methods and their Application to the Pebble Bed Fluoride Salt Cooled High Temperature Reactor (PB-FHR)

    NASA Astrophysics Data System (ADS)

    Cisneros, Anselmo Tomas, Jr.

    The Fluoride salt cooled High temperature Reactor (FHR) is a class of advanced nuclear reactors that combine the robust coated particle fuel form from high temperature gas cooled reactors, direct reactor auxillary cooling system (DRACS) passive decay removal of liquid metal fast reactors, and the transparent, high volumetric heat capacitance liquid fluoride salt working fluids---flibe (33%7Li2F-67%BeF)---from molten salt reactors. This combination of fuel and coolant enables FHRs to operate in a high-temperature low-pressure design space that has beneficial safety and economic implications. In 2012, UC Berkeley was charged with developing a pre-conceptual design of a commercial prototype FHR---the Pebble Bed- Fluoride Salt Cooled High Temperature Reactor (PB-FHR)---as part of the Nuclear Energy University Programs' (NEUP) integrated research project. The Mark 1 design of the PB-FHR (Mk1 PB-FHR) is 236 MWt flibe cooled pebble bed nuclear heat source that drives an open-air Brayton combine-cycle power conversion system. The PB-FHR's pebble bed consists of a 19.8% enriched uranium fuel core surrounded by an inert graphite pebble reflector that shields the outer solid graphite reflector, core barrel and reactor vessel. The fuel reaches an average burnup of 178000 MWt-d/MT. The Mk1 PB-FHR exhibits strong negative temperature reactivity feedback from the fuel, graphite moderator and the flibe coolant but a small positive temperature reactivity feedback of the inner reflector and from the outer graphite pebble reflector. A novel neutronics and depletion methodology---the multiple burnup state methodology was developed for an accurate and efficient search for the equilibrium composition of an arbitrary continuously refueled pebble bed reactor core. The Burnup Equilibrium Analysis Utility (BEAU) computer program was developed to implement this methodology. BEAU was successfully benchmarked against published results generated with existing equilibrium depletion codes VSOP

  8. The importance of the AVR pebble-bed reactor for the future of nuclear power

    SciTech Connect

    Pohl, P.

    2006-07-01

    The AVR pebble-bed high temperature gas-cooled reactor (HTGR) at Juelich (Germany)) operated from 1967 to 1988 and was certainly the most important HTGR project of the past. The reactor was the mass test bed for all development steps of HTGR pebble fuel. Some early fuel charges failed under high temperature conditions and contaminated the reactor. An accurate pebble measurement (Cs 137) allowed to clean the core from unwanted pebbles after 1981. The coolant activity went down and remained very low for the remaining reactor operation. A melt-wire experiment in 1986 revealed max. coolant temperatures of >1280 deg. C and fuel temperatures of >1350 deg. C, explained by under-estimated bypasses. The fuel still in the core achieved high burn-ups and showed under the extreme temperature conditions excellent fission product retention. Thus, the AVR operation qualified the HTGR fuel, and an average discharge burn-up of 112% fifa revealed an excellent fuel economy of the pebble-bed reactor. Furthermore, the AVR operation offers many meaningful data for code-to-experiment comparisons. (authors)

  9. CORE ANALYSIS, DESIGN AND OPTIMIZATION OF A DEEP-BURN PEBBLE BED REACTOR

    SciTech Connect

    B. Boer; A. M. Ougouag

    2010-05-01

    Achieving a high burnup in the Deep-Burn pebble bed reactor design, while remaining within the limits for fuel temperature, power peaking and temperature reactivity feedback, is challenging. The high content of Pu and Minor Actinides in the Deep-Burn fuel significantly impacts the thermal neutron energy spectrum. This can result in power and temperature peaking in the pebble bed core in locally thermalized regions near the graphite reflectors. Furthermore, the interplay of the Pu resonances of the neutron absorption cross sections at low-lying energies can lead to a positive temperature reactivity coefficient for the graphite moderator at certain operating conditions. To investigate the aforementioned effects a code system using existing codes has been developed for neutronic, thermal-hydraulic and fuel depletion analysis of Deep-Burn pebble bed reactors. A core analysis of a Deep-Burn Pebble Bed Modular Reactor (400 MWth) design has been performed for two Deep-Burn fuel types and possible improvements of the design with regard to power peaking and temperature reactivity feedback are identified.

  10. Stress Analysis of Coated Particle Fuel in the Deep-Burn Pebble Bed Reactor Design

    SciTech Connect

    B. Boer; A. M. Ougouag

    2010-05-01

    High fuel temperatures and resulting fuel particle coating stresses can be expected in a Pu and minor actinide fueled Pebble Bed Modular Reactor (400 MWth) design as compared to the ’standard’ UO2 fueled core. The high discharge burnup aimed for in this Deep-Burn design results in increased power and temperature peaking in the pebble bed near the inner and outer reflector. Furthermore, the pebble power in a multi-pass in-core pebble recycling scheme is relatively high for pebbles that make their first core pass. This might result in an increase of the mechanical failure of the coatings, which serve as the containment of radioactive fission products in the PBMR design. To investigate the integrity of the particle fuel coatings as a function of the irradiation time (i.e. burnup), core position and during a Loss Of Forced Cooling (LOFC) incident the PArticle STress Analysis code (PASTA) has been coupled to the PEBBED code for neutronics, thermal-hydraulics and depletion analysis of the core. Two deep burn fuel types (Pu with or without initial MA fuel content) have been investigated with the new code system for normal and transient conditions including the effect of the statistical variation of thickness of the coating layers.

  11. Fabrication and characterization of LiH ceramic pebbles by wet process

    NASA Astrophysics Data System (ADS)

    Xiang, Maoqiao; Zhang, Yingchun; Hong, Ming; Liu, Zhiang; Leng, Jiaxun; Zhang, Yun; Zhang, Jialiang; Wang, Wenchang

    2014-09-01

    Lithium hydride (LiH) ceramic pebbles, a new potential tritium breeding material in fusion-fission or fusion reactor blanket, were prepared by wet process for the first time. XRD results showed that LiOH, LiOH·H2O, Li2CO3 and Li2O were found in the surface of LiH pebbles. However, the pure phase of LiH pebbles without cracks could be obtained by paraffin wax coating technique. The average value (a.v.) of the sphericity and the diameter were 1.01 and 0.98 mm, respectively. The LiH pebbles sintered at 450 °C for 3 h under 80 ml/min flowing argon, reached ∼92.3% of the theoretical density, with the grain size of 5.59 μm (a.v.). And the crush load was measured to be 15 N on average. The described wet process exhibited multiple advantages for fabricating LiH pebbles.

  12. Stability analysis of the high temperature thermal pebble bed nuclear reactor concept

    SciTech Connect

    Vondy, D.R.

    1981-02-01

    A study was made of the stability of the high temperature gas-cooled pebble bed core against xenon-driven oscillation. This generic study indicated that a core as large as 3000 MW(t) could be stable. Several aspects present a challenge to analysis including the void space above the pebble bed, the effects of possible control rod configurations, and the temperature feedback contribution. Special methods of analysis were developed in this effort. Of considerable utility was the scheme of including an azimuthal buckling loss term in the neturon balance equations admitting direct solution of the first azimuthal harmonic for a core having azimuthal symmetry. This technique allows the linear stability analysis to be done solving two-dimensional (RZ) problems instead of three-dimensional problems. A scheme for removing the fundamental source contribution was also implemented to allow direct iteration toward the dominant harmonic solution, treating up to three dimensions with diffusion theory.

  13. Conceptual Design of a Very High Temperature Pebble-Bed Reactor

    SciTech Connect

    Hans D. Gougar; A. M. Ougouag; Richard M. Moore; W. K. Terry

    2003-11-01

    Efficient electricity and hydrogen production distinguish the Very High Temperature Reactor as the leading Generation IV advanced concept. This graphite-moderated, helium-cooled reactor achieves a requisite high outlet temperature while retaining the passive safety and proliferation resistance required of Generation IV designs. Furthermore, a recirculating pebble-bed VHTR can operate with minimal excess reactivity to yield improved fuel economy and superior resistance to ingress events. Using the PEBBED code developed at the INEEL, conceptual designs of 300 megawatt and 600 megawatt (thermal) Very High Temperature Pebble-Bed Reactors have been developed. The fuel requirements of these compare favorably to the South African PBMR. Passive safety is confirmed with the MELCOR accident analysis code.

  14. Modular Pebble-Bed Reactor Project: Laboratory-Directed Research and Development Program FY 2002 Annual Report

    SciTech Connect

    Petti, David Andrew; Dolan, Thomas James; Miller, Gregory Kent; Moore, Richard Leroy; Terry, William Knox; Ougouag, Abderrafi Mohammed-El-Ami; Oh, Chang H; Gougar, Hans D

    2002-11-01

    This report documents the results of our research in FY-02 on pebble-bed reactor technology under our Laboratory Directed Research and Development (LDRD) project entitled the Modular Pebble-Bed Reactor. The MPBR is an advanced reactor concept that can meet the energy and environmental needs of future generations under DOE’s Generation IV initiative. Our work is focused in three areas: neutronics, core design and fuel cycle; reactor safety and thermal hydraulics; and fuel performance.

  15. HTR-PROTEUS Pebble Bed Experimental Program Cores 1, 1A, 2, and 3: Hexagonal Close Packing with a 1:2 Moderator-to-Fuel Pebble Ratio

    SciTech Connect

    John D. Bess; Barbara H. Dolphin; James W. Sterbentz; Luka Snoj; Igor Lengar; Oliver Köberl

    2012-03-01

    In its deployment as a pebble bed reactor (PBR) critical facility from 1992 to 1996, the PROTEUS facility was designated as HTR-PROTEUS. This experimental program was performed as part of an International Atomic Energy Agency (IAEA) Coordinated Research Project (CRP) on the Validation of Safety Related Physics Calculations for Low Enriched HTGRs. Within this project, critical experiments were conducted for graphite moderated LEU systems to determine core reactivity, flux and power profiles, reaction-rate ratios, the worth of control rods, both in-core and reflector based, the worth of burnable poisons, kinetic parameters, and the effects of moisture ingress on these parameters. Four benchmark experiments were evaluated in this report: Cores 1, 1A, 2, and 3. These core configurations represent the hexagonal close packing (HCP) configurations of the HTR-PROTEUS experiment with a moderator-to-fuel pebble ratio of 1:2. Core 1 represents the only configuration utilizing ZEBRA control rods. Cores 1A, 2, and 3 use withdrawable, hollow, stainless steel control rods. Cores 1 and 1A are similar except for the use of different control rods; Core 1A also has one less layer of pebbles (21 layers instead of 22). Core 2 retains the first 16 layers of pebbles from Cores 1 and 1A and has 16 layers of moderator pebbles stacked above the fueled layers. Core 3 retains the first 17 layers of pebbles but has polyethylene rods inserted between pebbles to simulate water ingress. The additional partial pebble layer (layer 18) for Core 3 was not included as it was used for core operations and not the reported critical configuration. Cores 1, 1A, 2, and 3 were determined to be acceptable benchmark experiments.

  16. HTR-PROTEUS Pebble Bed Experimental Program Cores 1, 1A, 2, and 3: Hexagonal Close Packing with a 1:2 Moderator-to-Fuel Pebble Ratio

    SciTech Connect

    John D. Bess; Barbara H. Dolphin; James W. Sterbentz; Luka Snoj; Igor Lengar; Oliver Köberl

    2013-03-01

    In its deployment as a pebble bed reactor (PBR) critical facility from 1992 to 1996, the PROTEUS facility was designated as HTR-PROTEUS. This experimental program was performed as part of an International Atomic Energy Agency (IAEA) Coordinated Research Project (CRP) on the Validation of Safety Related Physics Calculations for Low Enriched HTGRs. Within this project, critical experiments were conducted for graphite moderated LEU systems to determine core reactivity, flux and power profiles, reaction-rate ratios, the worth of control rods, both in-core and reflector based, the worth of burnable poisons, kinetic parameters, and the effects of moisture ingress on these parameters. Four benchmark experiments were evaluated in this report: Cores 1, 1A, 2, and 3. These core configurations represent the hexagonal close packing (HCP) configurations of the HTR-PROTEUS experiment with a moderator-to-fuel pebble ratio of 1:2. Core 1 represents the only configuration utilizing ZEBRA control rods. Cores 1A, 2, and 3 use withdrawable, hollow, stainless steel control rods. Cores 1 and 1A are similar except for the use of different control rods; Core 1A also has one less layer of pebbles (21 layers instead of 22). Core 2 retains the first 16 layers of pebbles from Cores 1 and 1A and has 16 layers of moderator pebbles stacked above the fueled layers. Core 3 retains the first 17 layers of pebbles but has polyethylene rods inserted between pebbles to simulate water ingress. The additional partial pebble layer (layer 18) for Core 3 was not included as it was used for core operations and not the reported critical configuration. Cores 1, 1A, 2, and 3 were determined to be acceptable benchmark experiments.

  17. Advanced Core Design And Fuel Management For Pebble-Bed Reactors

    SciTech Connect

    Hans D. Gougar; Abderrafi M. Ougouag; William K. Terry

    2004-10-01

    A method for designing and optimizing recirculating pebble-bed reactor cores is presented. At the heart of the method is a new reactor physics computer code, PEBBED, which accurately and efficiently computes the neutronic and material properties of the asymptotic (equilibrium) fuel cycle. This core state is shown to be unique for a given core geometry, power level, discharge burnup, and fuel circulation policy. Fuel circulation in the pebble-bed can be described in terms of a few well?defined parameters and expressed as a recirculation matrix. The implementation of a few heat?transfer relations suitable for high-temperature gas-cooled reactors allows for the rapid estimation of thermal properties critical for safe operation. Thus, modeling and design optimization of a given pebble-bed core can be performed quickly and efficiently via the manipulation of a limited number key parameters. Automation of the optimization process is achieved by manipulation of these parameters using a genetic algorithm. The end result is an economical, passively safe, proliferation-resistant nuclear power plant.

  18. Pebble-bed core design option for VHTRs - Core configuration flexibility and potential applications

    SciTech Connect

    Pritchard, M. L.; Tsvetkov, P. V.

    2006-07-01

    Gas-cooled nuclear reactors have been receiving specific attention for Generation IV possibilities due to desired characteristics such as relatively low cost, short construction period, and inherent safety. Attractive inherent characteristics include an inert, single phase helium coolant, refractory coated fuel with high temperature capability and low fission product release, and graphite moderator with high temperature stability and long response times. The passively safe design has a relatively low power density, annular core, large negative temperature coefficient, and passive decay heat removal system. The objective of the U.S. DOE NERI Project is to assess the possibility, advantages and limitations of VHTRs with fuel loadings containing minor actinides. This paper presents the analysis of pebble-bed core configurations. Whole-core 3D models for pebble-bed design with multi-heterogeneity treatments in SCALE 5.0 are developed to compare computational results with experiments. Obtained results are in agreement with the available HTR-10 data. Actinide fueled VHTR configurations reveal promising performance. With an optimized pebble-bed model, the spectrum shifting abilities become more apparent. Effects of altered moderator to fuel ratio, Dancoff factor, and core and reflector configurations are investigated. This effort is anticipated to contribute to a facilitated development of new fuel cycles in support of future operation of Generation IV nuclear energy systems. (authors)

  19. Neutronic design of a Liquid Salt-cooled Pebble Bed Reactor (LSPBR)

    SciTech Connect

    De Zwaan, S. J.; Boer, B.; Lathouwers, D.; Kloosterman, J. L.

    2006-07-01

    A renewed interest has been raised for liquid salt cooled nuclear reactors. The excellent heat transfer properties of liquid salt coolants provide several benefits, like lower fuel temperatures, higher coolant outlet temperatures, increased core power density and better decay heat removal. In order to benefit from the online refueling capability of a pebble bed reactor, the Liquid Salt Pebble Bed Reactor (LSPBR) is proposed. This is a high temperature pebble-bed reactor with a fuel design similar to existing HTRs, but using a liquid salt as a coolant. In this paper, the selection criteria for the liquid salt coolant are described. Based on its neutronic properties, LiF-BeF{sub 2} (FLIBE) was selected for the LSPBR. Two designs of the LSPBR were considered: a cylindrical core and an annular core with a graphite inner reflector. Coupled neutronic-thermal hydraulic calculations were performed to obtain the steady state power distribution and the corresponding fuel temperatures. Finally, calculations were performed to investigate the decay heat removal capability in a protected loss-of-forced cooling accident. The maximum allowable power that can be produced with the LSPBR is hereby determined. (authors)

  20. Analysis of granular flow in a pebble-bed nuclear reactor.

    PubMed

    Rycroft, Chris H; Grest, Gary S; Landry, James W; Bazant, Martin Z

    2006-08-01

    Pebble-bed nuclear reactor technology, which is currently being revived around the world, raises fundamental questions about dense granular flow in silos. A typical reactor core is composed of graphite fuel pebbles, which drain very slowly in a continuous refueling process. Pebble flow is poorly understood and not easily accessible to experiments, and yet it has a major impact on reactor physics. To address this problem, we perform full-scale, discrete-element simulations in realistic geometries, with up to 440,000 frictional, viscoelastic 6-cm-diam spheres draining in a cylindrical vessel of diameter 3.5m and height 10 m with bottom funnels angled at 30 degrees or 60 degrees. We also simulate a bidisperse core with a dynamic central column of smaller graphite moderator pebbles and show that little mixing occurs down to a 1:2 diameter ratio. We analyze the mean velocity, diffusion and mixing, local ordering and porosity (from Voronoi volumes), the residence-time distribution, and the effects of wall friction and discuss implications for reactor design and the basic physics of granular flow.

  1. Analysis of granular flow in a pebble-bed nuclear reactor

    SciTech Connect

    Rycroft, C H; Grest, Gary S; Landry, James W; Bazant, Martin Z

    2006-04-17

    Pebble-bed nuclear reactor technology, which is currently being revived around the world, raises fundamental questions about dense granular flow in silos. A typical reactor core is composed of graphite fuel pebbles, which drain very slowly in a continuous refueling process. Pebble flow is poorly understood and not easily accessible to experiments, and yet it has a ma jor impact on reactor physics. To address this problem, we perform full-scale, discrete-element simulations in realistic geometries, with up to 440,000 frictional, viscoelastic 6cm-diameter spheres draining in a cylindrical vessel of diameter 3.5m and height 10m with bottom funnels angled at 30° or 60° . We also simulate a bidisperse core with a dynamic central column of smaller graphite moderator pebbles and show that little mixing occurs down to a 1:2 diameter ratio. We analyze the mean velocity, diffusion and mixing, local ordering and porosity (from Voronoi volumes), the residence-time distribution, and the effects of wall friction and discuss implications for reactor design and the basic physics of granular flow.

  2. A simplified DEM-CFD approach for pebble bed reactor simulations

    SciTech Connect

    Li, Y.; Ji, W.

    2012-07-01

    In pebble bed reactors (PBR's), the pebble flow and the coolant flow are coupled with each other through coolant-pebble interactions. Approaches with different fidelities have been proposed to simulate similar phenomena. Coupled Discrete Element Method-Computational Fluid Dynamics (DEM-CFD) approaches are widely studied and applied in these problems due to its good balance between efficiency and accuracy. In this work, based on the symmetry of the PBR geometry, a simplified 3D-DEM/2D-CFD approach is proposed to speed up the DEM-CFD simulation without significant loss of accuracy. Pebble flow is simulated by a full 3-D DEM, while the coolant flow field is calculated with a 2-D CFD simulation by averaging variables along the annular direction in the cylindrical geometry. Results show that this simplification can greatly enhance the efficiency for cylindrical core, which enables further inclusion of other physics such as thermal and neutronic effect in the multi-physics simulations for PBR's. (authors)

  3. Computational and experimental prediction of dust production in pebble bed reactors -- Part I

    SciTech Connect

    Maziar Rostamian; Gannon Johnson; Mie Hiruta; Gabriel P. Potirniche; Abderrafi M. Ougouag; Joshua J. Cogliati; Akira Tokuhiro

    2013-10-01

    This paper describes the computational modeling and simulation, and experimental testing of graphite moderators in frictional contacts as anticipated in a pebble bed reactor. The potential of carbonaceous particulate generation due to frictional contact at the surface of pebbles and the ensuing entrainment and transport into the gas coolant are safety concerns at elevated temperatures under accident scenarios such as air ingress in the high temperature gas-cooled reactor. The safety concerns are due to the documented ability of carbonaceous particulates to adsorb fission products and transport them in the primary circuit of the pebble bed reactor, thus potentially giving rise to a relevant source term under accident scenarios. Here, a finite element approach is implemented to develop a nonlinear wear model in air environment. In this model, material wear coefficient is related to the changes in asperity height during wear. The present work reports a comparison between the finite element simulations and the experimental results obtained using a custom-designed tribometer. The experimental and computational results are used to estimate the quantity of nuclear grade graphite dust produced from a typical anticipated configuration. In Part II, results from a helium environment at higher temperatures and pressures are experimentally studied.

  4. Computational prediction of dust production in graphite moderated pebble bed reactors

    NASA Astrophysics Data System (ADS)

    Rostamian, Maziar

    The scope of the work reported here, which is the computational study of graphite wear behavior, supports the Nuclear Engineering University Programs project "Experimental Study and Computational Simulations of Key Pebble Bed Thermomechanics Issues for Design and Safety" funded by the US Department of Energy. In this work, modeling and simulating the contact mechanics, as anticipated in a PBR configuration, is carried out for the purpose of assessing the amount of dust generated during a full power operation year of a PBR. A methodology that encompasses finite element analysis (FEA) and micromechanics of wear is developed to address the issue of dust production and its quantification. Particularly, the phenomenon of wear and change of its rate with sliding length is the main focus of this dissertation. This work studies the wear properties of graphite by simulating pebble motion and interactions of a specific type of nuclear grade graphite, IG-11. This study consists of two perspectives: macroscale stress analysis and microscale analysis of wear mechanisms. The first is a set of FEA simulations considering pebble-pebble frictional contact. In these simulations, the mass of generated graphite particulates due to frictional contact is calculated by incorporating FEA results into Archard's equation, which is a linear correlation between wear mass and wear length. However, the experimental data by Johnson, University of Idaho, revealed that the wear rate of graphite decreases with sliding length. This is because the surfaces of the graphite pebbles become smoother over time, which results in a gradual decrease in wear rate. In order to address the change in wear rate, a more detailed analysis of wear mechanisms at room temperature is presented. In this microscale study, the wear behavior of graphite at the asperity level is studied by simulating the contact between asperities of facing surfaces. By introducing the effect of asperity removal on wear rate, a nonlinear

  5. Development of a Pebble-Bed Liquid-Nitrogen Evaporator and Superheater for the Scaled Large Blast/Thermal Simulator Facility

    DTIC Science & Technology

    1991-04-01

    following materials in the respective application . Pebble Bed Pressure Vessel and Misc Piping: SA-105 Forgings , Carbon Steel , for Piping Components SA...High Temperature Service SA-312 Seamless and Welded Austenitic Stainless Steel Pipe for High Temperature and General Corrosive Service SA-403 Wrought... Austenitic Stainless Steel Fittings 6.1 Pebble-bed Heater System Components There are 6 main components of the pebble bed heater assembly. These are

  6. HTR-PROTEUS PEBBLE BED EXPERIMENTAL PROGRAM CORE 4: RANDOM PACKING WITH A 1:1 MODERATOR-TO-FUEL PEBBLE RATIO

    SciTech Connect

    John D. Bess; Leland M. Montierth

    2013-03-01

    In its deployment as a pebble bed reactor (PBR) critical facility from 1992 to 1996, the PROTEUS facility was designated as HTR-PROTEUS. This experimental program was performed as part of an International Atomic Energy Agency (IAEA) Coordinated Research Project (CRP) on the Validation of Safety Related Physics Calculations for Low Enriched HTGRs. Within this project, critical experiments were conducted for graphite moderated LEU systems to determine core reactivity, flux and power profiles, reaction-rate ratios, the worth of control rods, both in-core and reflector based, the worth of burnable poisons, kinetic parameters, and the effects of moisture ingress on these parameters. One benchmark experiment was evaluated in this report: Core 4. Core 4 represents the only configuration with random pebble packing in the HTR-PROTEUS series of experiments, and has a moderator-to-fuel pebble ratio of 1:1. Three random configurations were performed. The initial configuration, Core 4.1, was rejected because the method for pebble loading, separate delivery tubes for the moderator and fuel pebbles, may not have been completely random; this core loading was rejected by the experimenters. Cores 4.2 and 4.3 were loaded using a single delivery tube, eliminating the possibility for systematic ordering effects. The second and third cores differed slightly in the quantity of pebbles loaded (40 each of moderator and fuel pebbles), stacked height of the pebbles in the core cavity (0.02 m), withdrawn distance of the stainless steel control rods (20 mm), and withdrawn distance of the autorod (30 mm). The 34 coolant channels in the upper axial reflector and the 33 coolant channels in the lower axial reflector were open. Additionally, the axial graphite fillers used in all other HTR-PROTEUS configurations to create a 12-sided core cavity were not used in the randomly packed cores. Instead, graphite fillers were placed on the cavity floor, creating a funnel-like base, to discourage ordering

  7. HTR-PROTEUS PEBBLE BED EXPERIMENTAL PROGRAM CORE 4: RANDOM PACKING WITH A 1:1 MODERATOR-TO-FUEL PEBBLE RATIO

    SciTech Connect

    John D. Bess; Leland M. Montierth

    2014-03-01

    In its deployment as a pebble bed reactor (PBR) critical facility from 1992 to 1996, the PROTEUS facility was designated as HTR-PROTEUS. This experimental program was performed as part of an International Atomic Energy Agency (IAEA) Coordinated Research Project (CRP) on the Validation of Safety Related Physics Calculations for Low Enriched HTGRs. Within this project, critical experiments were conducted for graphite moderated LEU systems to determine core reactivity, flux and power profiles, reaction-rate ratios, the worth of control rods, both in-core and reflector based, the worth of burnable poisons, kinetic parameters, and the effects of moisture ingress on these parameters. One benchmark experiment was evaluated in this report: Core 4. Core 4 represents the only configuration with random pebble packing in the HTR-PROTEUS series of experiments, and has a moderator-to-fuel pebble ratio of 1:1. Three random configurations were performed. The initial configuration, Core 4.1, was rejected because the method for pebble loading, separate delivery tubes for the moderator and fuel pebbles, may not have been completely random; this core loading was rejected by the experimenters. Cores 4.2 and 4.3 were loaded using a single delivery tube, eliminating the possibility for systematic ordering effects. The second and third cores differed slightly in the quantity of pebbles loaded (40 each of moderator and fuel pebbles), stacked height of the pebbles in the core cavity (0.02 m), withdrawn distance of the stainless steel control rods (20 mm), and withdrawn distance of the autorod (30 mm). The 34 coolant channels in the upper axial reflector and the 33 coolant channels in the lower axial reflector were open. Additionally, the axial graphite fillers used in all other HTR-PROTEUS configurations to create a 12-sided core cavity were not used in the randomly packed cores. Instead, graphite fillers were placed on the cavity floor, creating a funnel-like base, to discourage ordering

  8. The preliminary analysis on the steady-state and kinetic features of the molten salt pebble-bed reactor

    SciTech Connect

    Xia, B.; Lu, Y.

    2012-07-01

    A novel design concept of molten salt pebble-bed reactor with an ultra-simplified integral primary circuit called 'Nuclear Hot Spring' has been proposed, featured by horizontal coolant flow in a deep pool pebble-bed reactor, providing 'natural safety' features with natural circulation under full power operation and less expensive primary circuit arrangement. In this work, the steady-state physical properties of the equilibrium state of the molten salt pebble-bed reactor are calculated by using the VSOP code, and the steady-state thermo-hydraulic analysis is carried out based on the approximation of absolutely horizontal flow of the coolant through the core. A new concept of 2-dimensional, both axial and radial, multi-pass on-line fuelling scheme is presented. The result reveals that the radial multi-pass scheme provides more flattened power distribution and safer temperature distribution than the one-pass scheme. A parametric analysis is made corresponding to different pebble diameters, the key parameter of the core resistance and the temperature at the pebble center. It is verified that within a wide range of pebble diameters, the maximum pebble center temperatures are far below the safety limit of the fuel, and the core resistance is considerably less than the buoyant force, indicating that the natural circulation under full power operation is achievable and the ultra-simplified integral primary circuit without any pump is possible. For the kinetic properties, it is verified that the negative temperature coefficient is achieved in sufficient under-moderated condition through the preliminary analysis on the temperature coefficients of fuel, coolant and moderator. The requirement of reactivity compensation at the shutdown stages of the operation period is calculated for the further studies on the reactivity control. The molten salt pebble-bed reactor with horizontal coolant flow can provide enhanced safety and economical features. (authors)

  9. AN EXPERIMENT TO STUDY PEBBLE BED LIQUID-FLUORIDE-SALT HEAT TRANSFER

    SciTech Connect

    Yoder Jr, Graydon L; Aaron, Adam M; Heatherly, Dennis Wayne; Holcomb, David Eugene; Kisner, Roger A; McCarthy, Mike; Peretz, Fred J; Wilgen, John B; Wilson, Dane F

    2011-01-01

    A forced-convection liquid-fluoride-salt loop is being constructed at Oak Ridge National Laboratory (ORNL). This loop was designed as a versatile experimental facility capable of supporting general thermal/fluid/corrosion testing of liquid fluoride salts. The initial test configuration is designed to support the Pebble Bed Advanced High-Temperature Reactor and incorporates a test section designed to examine the heat transfer behavior of FLiNaK salt in a heated pebble bed. The loop is constructed of Inconel 600 and is capable of operating at up to 700oC. It contains a total of 72 kg of FLiNaK salt and uses an overhung impeller centrifugal sump pump that can provide FLiNaK flow at 4.5 kg/s with a head of 0.125 MPa. The test section is made of silicon carbide (SiC) and contains approximately 600 graphite spheres, 3 cm in diameter. The pebble bed is heated using a unique inductive technique. A forced induction air cooler removes the heat added to the pebble bed. The salt level within the loop is maintained by controlling an argon cover gas pressure. Salt purification is performed in batch mode by transferring the salt from the loop into a specially made nickel crucible system designed to remove oxygen, moisture and other salt impurities. Materials selection for the loop and test section material was informed by 3 months of Inconel 600 and SiC corrosion testing as well as tests examining subcomponent performance in the salt. Several SiC-to-Inconel 600 mechanical joint designs were considered before final salt and gas seals were chosen. Structural calculations of the SiC test section were performed to arrive at a satisfactory test section configuration. Several pump vendors provided potential loop pump designs; however, because of cost, the pump was designed and fabricated in-house. The pump includes a commercial rotating dry gas shaft seal to maintain loop cover gas inventory. The primary instrumentation on the loop includes temperature, pressure, and loop flow rate

  10. Effects of Spatial Variations in Packing Fraction on Reactor Physics Parameters in Pebble-Bed Reactors

    SciTech Connect

    William K. Terry; A. M. Ougouag; Farzad Rahnema; Michael Scott McKinley

    2003-04-01

    The well-known spatial variation of packing fraction near the outer boundary of a pebble-bed reactor core is cited. The ramifications of this variation are explored with the MCNP computer code. It is found that the variation has negligible effects on the global reactor physics parameters extracted from the MCNP calculations for use in analysis by diffusion-theory codes, but for local reaction rates the effects of the variation are naturally important. Included is some preliminary work in using first-order perturbation theory for estimating the effect of the spatial variation of packing fraction on the core eigenvalue and the fision density distribution.

  11. Effects of Spatial Variations in Packing Fraction of Reactor Physics Parameters in Pebble-Bed Reactors

    SciTech Connect

    Terry, W K; Ougouag, A M; Rahnema, F; Mckinley, M S

    2003-06-11

    The well-known spatial variation of packing fraction near the outer boundary of a pebble-bed reactor core is cited. The ramifications of this variation are explored with the MCNP computer code. It is found that the variation has negligible effects on the global reactor physics parameters extracted from the MCNP calculations for use in analysis by diffusion-theory codes, but for local reaction rates the effects of the variation are naturally important. Included is some preliminary work in using first-order perturbation theory for estimating the effect of the spatial variation of packing fraction on the core eigenvalue and the fission density distribution.

  12. Very High Temperature Reactor (VHTR) Deep Burn Core and Fuel Analysis -- Complete Design Selection for the Pebble Bed Reactor

    SciTech Connect

    B. Boer; A. M. Ougouag

    2010-09-01

    The Deep-Burn (DB) concept focuses on the destruction of transuranic nuclides from used light water reactor fuel. These transuranic nuclides are incorporated into TRISO coated fuel particles and used in gas-cooled reactors with the aim of a fractional fuel burnup of 60 to 70% in fissions per initial metal atom (FIMA). This high performance is expected through the use of multiple recirculation passes of the fuel in pebble form without any physical or chemical changes between passes. In particular, the concept does not call for reprocessing of the fuel between passes. In principle, the DB pebble bed concept employs the same reactor designs as the presently envisioned low-enriched uranium core designs, such as the 400 MWth Pebble Bed Modular Reactor (PBMR-400). Although it has been shown in the previous Fiscal Year (2009) that a PuO2 fueled pebble bed reactor concept is viable, achieving a high fuel burnup, while remaining within safety-imposed prescribed operational limits for fuel temperature, power peaking and temperature reactivity feedback coefficients for the entire temperature range, is challenging. The presence of the isotopes 239-Pu, 240-Pu and 241-Pu that have resonances in the thermal energy range significantly modifies the neutron thermal energy spectrum as compared to a ”standard,” UO2-fueled core. Therefore, the DB pebble bed core exhibits a relatively hard neutron energy spectrum. However, regions within the pebble bed that are near the graphite reflectors experience a locally softer spectrum. This can lead to power and temperature peaking in these regions. Furthermore, a shift of the thermal energy spectrum with increasing temperature can lead to increased absorption in the resonances of the fissile Pu isotopes. This can lead to a positive temperature reactivity coefficient for the graphite moderator under certain operating conditions. The effort of this task in FY 2010 has focused on the optimization of the core to maximize the pebble discharge

  13. Estimating anisotropic diffusion of neutrons near the boundary of a pebble bed random system

    SciTech Connect

    Vasques, R.

    2013-07-01

    Due to the arrangement of the pebbles in a Pebble Bed Reactor (PBR) core, if a neutron is located close to a boundary wall, its path length probability distribution function in directions of flight parallel to the wall is significantly different than in other directions. Hence, anisotropic diffusion of neutrons near the boundaries arises. We describe an analysis of neutron transport in a simplified 3-D pebble bed random system, in which we investigate the anisotropic diffusion of neutrons born near one of the system's boundary walls. While this simplified system does not model the actual physical process that takes place near the boundaries of a PBR core, the present work paves the road to a formulation that may enable more accurate diffusion simulations of such problems to be performed in the future. Monte Carlo codes have been developed for (i) deriving realizations of the 3-D random system, and (ii) performing 3-D neutron transport inside the heterogeneous model; numerical results are presented for three different choices of parameters. These numerical results are used to assess the accuracy of estimates for the mean-squared displacement of neutrons obtained with the diffusion approximations of the Atomic Mix Model and of the recently introduced [1] Non-Classical Theory with angular-dependent path length distribution. The Non-Classical Theory makes use of a Generalized Linear Boltzmann Equation in which the locations of the scattering centers in the system are correlated and the distance to collision is not exponentially distributed. We show that the results predicted using the Non-Classical Theory successfully model the anisotropic behavior of the neutrons in the random system, and more closely agree with experiment than the results predicted by the Atomic Mix Model. (authors)

  14. Modular pebble-bed reactor reforming plant design for process heat

    SciTech Connect

    Lutz, D.E.; Cowan, C.L.; Davis, C.R.; El Sheikh, K.A.; Hui, M.M.; Lipps, A.J.; Wu, T.

    1982-09-01

    This report describes a preliminary design study of a Modular Pebble-Bed Reactor System Reforming (MPB-R) Plant. The system uses one pressure vessel for the reactor and a second pressure vessel for the components, i.e., reformer, steam generator and coolant circulator. The two vessels are connected by coaxial pipes in an arrangement known as the side-by-side (SBS). The goal of the study is to gain an understanding of this particular system and to identify any technical issues that must be resolved for its application to a modular reformer plant. The basic conditions for the MPB-R were selected in common with those of the current study of the MRS-R in-line prismatic fuel concept, specifically, the module core power of 250 MWt, average core power density of 4.1 w/cc, low enriched uranium (LEU) fuel with a /sup 235/U content of 20% homogeneously mixed with thorium, and a target burnup of 80,000 MWD/MT. Study results include the pebble-bed core neutronics and thermal-hydraulic calculations. Core characteristics for both the once-through-then-out (OTTO) and recirculation of fuel sphere refueling schemes were developed. The plant heat balance was calculated with 55% of core power allotted to the reformer.

  15. Supplemental Report on Nuclear Safeguards Considerations for the Pebble Bed Modular Reactor (PBMR)

    SciTech Connect

    Moses, David Lewis; Ehinger, Michael H

    2010-05-01

    Recent reports by Department of Energy National Laboratories have discussed safeguards considerations for the low enriched uranium (LEU) fueled Pebble Bed Modular Reactor (PBMR) and the need for bulk accountancy of the plutonium in used fuel. These reports fail to account effectively for the degree of plutonium dilution in the graphitized-carbon pebbles that is sufficient to meet the International Atomic Energy Agency's (IAEA's) 'provisional' guidelines for termination of safeguards on 'measured discards.' The thrust of this finding is not to terminate safeguards but to limit the need for specific accountancy of plutonium in stored used fuel. While the residual uranium in the used fuel may not be judged sufficiently diluted to meet the IAEA provisional guidelines for termination of safeguards, the estimated quantities of {sup 232}U and {sup 236}U in the used fuel at the target burn-up of {approx}91 GWD/MT exceed specification limits for reprocessed uranium (ASTM C787) and will require extensive blending with either natural uranium or uranium enrichment tails to dilute the {sup 236}U content to fall within specification thus making the PBMR used fuel less desirable for commercial reprocessing and reuse than that from light water reactors. Also the PBMR specific activity of reprocessed uranium isotopic mixture and its A{sub 2} values for effective dose limit if released in a dispersible form during a transportation accident are more limiting than the equivalent values for light water reactor spent fuel at 55 GWD/MT without accounting for the presence of the principal carry-over fission product ({sup 99}Tc) and any possible plutonium contamination that may be present from attempted covert reprocessing. Thus, the potentially recoverable uranium from PBMR used fuel carries reactivity penalties and radiological penalties likely greater than those for reprocessed uranium from light water reactors. These factors impact the economics of reprocessing, but a more significant

  16. On the evaluation of pebble bed reactor critical experiments using the PEBBED code

    SciTech Connect

    Hans D. Gougar; R. Sonat Sen

    2001-10-01

    The PEBBED pebble bed reactor fuel management code under development at the Idaho National Laboratory is designed for rapid design and analysis of pebble bed high temperature reactors (PBRs). Embedded within the code are the THERMIX-KONVEK thermal fluid solver and the COMBINE-7 spectrum generation code for inline cross section homogenization. Because 1D symmetry can be found at each stage of core heterogeneity; spherical at TRISO and pebble levels, and cylindrical at the control rod and core levels, the 1-D transport capability of ANISN is assumed to be sufficient in most cases for generating flux solutions for cross section homogenization. Furthermore, it is fast enough to be executed during the analysis or the equilibrium core. Multi-group diffusion-based design codes such as PEBBED and VSOP are not expected to yield the accuracy and resolution of continuous energy Monte Carlo codes for evaluation of critical experiments. Nonetheless, if the preparation of multigroup cross sections can adequately capture the physics of the mixing of PBR fuel elements and leakage from the core, reasonable results may be obtained. In this paper, results of the application of PEBBED to two critical experiments (HTR Proteus and HTR-10) and associated computational models are presented. The embedded 1-D transport solver is shown to capture the double heterogeneity of the pebble fuel in unit cell calculations. Eigenvalue calculations of a whole core are more challenging, particularly if the boron concentration is uncertain. The sensitivity of major safety parameters to variations in modeling assumptions, however, is shown to be minimal. The embedded transport solver can also be used to obtain control rod worths but only with adjustment of the local spectrum. Results are compared to those of other codes as well as Core 4 of the HTR-Proteus experiment which contains partially inserted rods. They indicate the need for a reference solution to adjust the radius of the graphite in the

  17. Plutonium and minor actinide utilisation in a pebble-bed high temperature reactor

    SciTech Connect

    Petrov, B. Y.; Kuijper, J. C.; Oppe, J.; De Haas, J. B. M.

    2012-07-01

    This paper contains results of the analysis of the pebble-bed high temperature gas-cooled PUMA reactor loaded with plutonium and minor actinide (Pu/MA) fuel. Starting from knowledge and experience gained in the Euratom FP5 projects HTR-N and HTR-N1, this study aims at demonstrating the potential of high temperature reactors to utilize or transmute Pu/MA fuel. The work has been performed within the Euratom FP6 project PUMA. A number of different fuel types and fuel configurations have been analyzed and compared with respect to incineration performance and safety-related reactor parameters. The results show the excellent plutonium and minor actinide burning capabilities of the high temperature reactor. The largest degree of incineration is attained in the case of an HTR fuelled by pure plutonium fuel as it remains critical at very deep burnup of the discharged pebbles. Addition of minor actinides to the fuel leads to decrease of the achievable discharge burnup and therefore smaller fraction of actinides incinerated during reactor operation. The inert-matrix fuel design improves the transmutation performance of the reactor, while the 'wallpaper' fuel does not have advantage over the standard fuel design in this respect. After 100 years of decay following the fuel discharge, the total amount of actinides remains almost unchanged for all of the fuel types considered. Among the plutonium isotopes, only the amount of Pu-241 is reduced significantly due to its relatively short half-life. (authors)

  18. Pebble bed modular reactor safeguards: developing new approaches and implementing safeguards by design

    SciTech Connect

    Beyer, Brian David; Beddingfield, David H; Durst, Philip; Bean, Robert

    2010-01-01

    The design of the Pebble Bed Modular Reactor (PBMR) does not fit or seem appropriate to the IAEA safeguards approach under the categories of light water reactor (LWR), on-load refueled reactor (OLR, i.e. CANDU), or Other (prismatic HTGR) because the fuel is in a bulk form, rather than discrete items. Because the nuclear fuel is a collection of nuclear material inserted in tennis-ball sized spheres containing structural and moderating material and a PBMR core will contain a bulk load on the order of 500,000 spheres, it could be classified as a 'Bulk-Fuel Reactor.' Hence, the IAEA should develop unique safeguards criteria. In a multi-lab DOE study, it was found that an optimized blend of: (i) developing techniques to verify the plutonium content in spent fuel pebbles, (ii) improving burn-up computer codes for PBMR spent fuel to provide better understanding of the core and spent fuel makeup, and (iii) utilizing bulk verification techniques for PBMR spent fuel storage bins should be combined with the historic IAEA and South African approaches of containment and surveillance to verify and maintain continuity of knowledge of PBMR fuel. For all of these techniques to work the design of the reactor will need to accommodate safeguards and material accountancy measures to a far greater extent than has thus far been the case. The implementation of Safeguards-by-Design as the PBMR design progresses provides an approach to meets these safeguards and accountancy needs.

  19. Safeguards Challenges for Pebble-Bed Reactors (PBRs):Peoples Republic of China (PRC)

    SciTech Connect

    Forsberg, Charles W.; Moses, David Lewis

    2009-11-01

    The Peoples Republic of China (PRC) is operating the HTR-10 pebble-bed reactor (PBR) and is in the process of building a prototype PBR plant with two modular reactors (250-MW(t) per reactor) feeding steam to a single turbine-generator. It is likely to be the first modular hightemperature reactor to be ready for commercial deployment in the world because it is a highpriority project for the PRC. The plant design features multiple modular reactors feeding steam to a single turbine generator where the number of modules determines the plant output. The design and commercialization strategy are based on PRC strengths: (1) a rapidly growing electric market that will support low-cost mass production of modular reactor units and (2) a balance of plant system based on economics of scale that uses the same mass-produced turbine-generator systems used in PRC coal plants. If successful, in addition to supplying the PRC market, this strategy could enable China to be the leading exporter of nuclear reactors to developing countries. The modular characteristics of the reactor match much of the need elsewhere in the world. PBRs have major safety advantages and a radically different fuel. The fuel, not the plant systems, is the primary safety system to prevent and mitigate the release of radionuclides under accident conditions. The fuel consists of small (6-cm) pebbles (spheres) containing coatedparticle fuel in a graphitized carbon matrix. The fuel loading per pebble is small (~9 grams of low-enriched uranium) and hundreds of thousands of pebbles are required to fuel a nuclear plant. The uranium concentration in the fuel is an order of magnitude less than in traditional nuclear fuels. These characteristics make the fuel significantly less attractive for illicit use (weapons production or dirty bomb); but, its unusual physical form may require changes in the tools used for safeguards. This report describes PBRs, what is different, and the safeguards challenges. A series of

  20. Reactor Pressure Vessel Temperature Analysis for Prismatic and Pebble-Bed VHTR Designs

    SciTech Connect

    H. D. Gougar; C. B. Davis

    2006-04-01

    Analyses were performed to determine maximum temperatures in the reactor pressure vessel for two potential Very-High Temperature Reactor (VHTR) designs during normal operation and during a depressurized conduction cooldown accident. The purpose of the analyses was to aid in the determination of appropriate reactor vessel materials for the VHTR. The designs evaluated utilized both prismatic and pebble-bed cores that generated 600 MW of thermal power. Calculations were performed for fluid outlet temperatures of 900 and 950 °C, corresponding to the expected range for the VHTR. The analyses were performed using the RELAP5-3D and PEBBED-THERMIX computer codes. Results of the calculations were compared with preliminary temperature limits derived from the ASME pressure vessel code.

  1. Comparative evaluation of pebble-bed and prismatic fueled high-temperature gas-cooled reactors

    SciTech Connect

    Kasten, P.R.; Bartine, D.E.

    1981-01-01

    A comparative evaluation has been performed of the HTGR and the Federal Republic of Germany's Pebble Bed Reactor (PBR) for potential commercial applications in the US. The evaluation considered two reactor sizes (1000 and 3000 MW(t)) and three process applications (steam cycle, direct cycle, and process heat, with outlet coolant temperatures of 750, 850, and 950/sup 0/C, respectively). The primary criterion for the comparison was the levelized (15-year) cost of producing electricity or process heat. Emphasis was placed on the cost impact of differences between the prismatic-type HTGR core, which requires periodic refuelings during reactor shutdowns, and the pebble bed PBR core, which is refueled continuously during reactor operations. Detailed studies of key technical issues using reference HTGR and PBR designs revealed that two cost components contributing to the levelized power costs are higher for the PBR: capital costs and operation and maintenance costs. A third cost component, associated with nonavailability penalties, tended to be higher for the PBR except for the process heat application, for which there is a large uncertainty in the HTGR nonavailability penalty at the 950/sup 0/C outlet coolant temperature. A fourth cost component, fuel cycle costs, is lower for the PBR, but not sufficiently lower to offset the capital cost component. Thus the HTGR appears to be slightly superior to the PBR in economic performance. Because of the advanced development of the HTGR concept, large HTGRs could also be commercialized in the US with lower R and D costs and shorter lead times than could large PBRs. It is recommended that the US gas-cooled thermal reactor program continue giving primary support to the HTGR, while also maintaining its cooperative PBR program with FRG.

  2. Heat-Transfer Coefficients for a Full-Scale Pebble-Bed Heater

    NASA Technical Reports Server (NTRS)

    Lancashire, R. B.; Lezberg, E. A.; Morris, J. F.

    1960-01-01

    Large quantities of high-temperature air are needed for work with hypersonic flight problems. At temperatures above 2500 degrees Reamur, where conventional heat exchangers have exceeded their material limits, regenerative pebble-bed exchangers may be used with high-temperature refractories. The design of such a heat exchanger requires the use of reliable heat-transfer coefficients for a packed bed. Considerable data are available on the subject, but they spread over two orders of magnitude at any one Reynolds number value. The facility from which the present data were obtained is used at the Lewis Research Center (NASA) for testing air-breathing engine components. The purpose of this work was to obtain heat-transfer data during the initial operation of the bed as a guide to the design of similar equipment. The facility was designed with a conservative estimate of the heat-transfer coefficient, and is shown schematically. Temperatures throughout the packing were measured continuously so that point values of the coefficient might be obtained.

  3. Final Report on Utilization of TRU TRISO Fuel as Applied to HTR Systems Part I: Pebble Bed Reactors

    SciTech Connect

    Brian Boer; Abderrafi M. Ougouag

    2011-03-01

    The Deep-Burn (DB) concept [ ] focuses on the destruction of transuranic nuclides from used light water reactor (LWR) fuel. These transuranic nuclides are incorporated into tri-isotopic (TRISO) coated fuel particles and used in gas-cooled reactors with the aim of a fractional fuel burnup of 60 to 70% in fissions per initial metal atom (FIMA). This high performance is expected through the use of multiple recirculation passes of the fuel in pebble form without any physical or chemical changes between passes. In particular, the concept does not call for reprocessing of the fuel between passes. In principle, the DB pebble bed concept employs the same reactor designs as the presently envisioned low-enriched uranium core designs, such as the 400 MWth Pebble Bed Modular Reactor (PBMR-400) [ ]. Although it has been shown in the previous Fiscal Year (FY) (2009) that a PuO2 fueled pebble bed reactor concept is viable, achieving a high fuel burnup while remaining within safety-imposed prescribed operational limits for fuel temperature, power peaking, and temperature reactivity feedback coefficients for the entire temperature range, is challenging. The presence of the isotopes 239Pu, 240Pu, and 241Pu that have resonances in the thermal energy range significantly modifies the neutron thermal energy spectrum as compared to a standard, UO2-fueled core. Therefore, the DB pebble bed core exhibits a relatively hard neutron energy spectrum. However, regions within the pebble bed that are near the graphite reflectors experience a locally softer spectrum. This can lead to power and temperature peaking in these regions. Furthermore, a shift of the thermal energy spectrum with increasing temperature can lead to increased absorption in the resonances of the fissile Pu isotopes. This can lead to a positive temperature reactivity coefficient for the graphite moderator under certain operating conditions. Regarding the coated particle performance, the FY 2009 investigations showed that no

  4. Thermo-mechanical Modelling of Pebble Beds in Fusion Blankets and its Implementation by a Return-Mapping Algorithm

    SciTech Connect

    Gan, Yixiang; Kamlah, Marc

    2008-07-01

    In this investigation, a thermo-mechanical model of pebble beds is adopted and developed based on experiments by Dr. Reimann at Forschungszentrum Karlsruhe (FZK). The framework of the present material model is composed of a non-linear elastic law, the Drucker-Prager-Cap theory, and a modified creep law. Furthermore, the volumetric inelastic strain dependent thermal conductivity of beryllium pebble beds is taken into account and full thermo-mechanical coupling is considered. Investigation showed that the Drucker-Prager-Cap model implemented in ABAQUS can not fulfill the requirements of both the prediction of large creep strains and the hardening behaviour caused by creep, which are of importance with respect to the application of pebble beds in fusion blankets. Therefore, UMAT (user defined material's mechanical behaviour) and UMATHT (user defined material's thermal behaviour) routines are used to re-implement the present thermo-mechanical model in ABAQUS. An elastic predictor radial return mapping algorithm is used to solve the non-associated plasticity iteratively, and a proper tangent stiffness matrix is obtained for cost-efficiency in the calculation. An explicit creep mechanism is adopted for the prediction of time-dependent behaviour in order to represent large creep strains in high temperature. Finally, the thermo-mechanical interactions are implemented in a UMATHT routine for the coupled analysis. The oedometric compression tests and creep tests of pebble beds at different temperatures are simulated with the help of the present UMAT and UMATHT routines, and the comparison between the simulation and the experiments is made. (authors)

  5. Deterministic Casualty Analysis of the Pebble Bed Modular Reactor for use with Risk-Based Safety Regulation

    DTIC Science & Technology

    2002-09-01

    regulatory process by analyzing a portion of a new reactor concept. A reactor similar to the Pebble Bed Modular Reactor ( PBMR ) is the design chosen...for the analyses. The designers of the PBMR assert that the reactor’s inherently safe design justifies the use of a non-standard containment system...incorporated into the PRA for the PBMR . The contributions to the event and fault trees of the PBMR are determined for two casualties that affect the

  6. Performance of a Li 2TiO 3 pebble-bed in the CRITIC-III irradiation

    NASA Astrophysics Data System (ADS)

    Verrall, R. A.; Miller, J. M.; Gierszewski, P.

    2000-09-01

    Lithium metatitanate (Li 2TiO 3) is a candidate material for tritium breeding in fusion reactor pebble-bed blankets. 173 g of Li 2TiO 3 pebbles were irradiated for 334 full power days (FPD) to a burnup of 0.9% 6Li in the CRITIC-III experiment in AECL's NRU reactor. A key objective was to determine tritium release over a wide temperature band from 200°C to 900°C. On-line release and temperature measurements are reported in this paper. New analytical methods led to calculated inventories ranging from 15 wppm average at the lowest temperature of operation (200°C outer surface to 700°C inner surface) to less than 1.2 wppm average at 375°C outer-surface temperature and 875°C inner-surface temperature. The thermocouples indicated that the bed remained stable during the irradiation, which included thermal shocks from 90 reactor shutdowns. From this swept-capsule irradiation, Li 2TiO 3 appears to be a good candidate for fusion blanket pebble-beds.

  7. Preliminary Study of Burnup Characteristics for a Simplified Small Pebble Bed Reactor

    SciTech Connect

    Irwanto, Dwi; Kato, Yukikata; Obara, Toru; Yamanaka, Ichiro

    2010-06-22

    Simplification of the pebble bed reactor by removing the unloading device from the system was peformed. For this reactor design, a suitable fuel-loading scheme is the Peu a Peu (little by little) fueling scheme. In the Peu a Peu modus, there is no unloading device; as such, the fuels are never discharged and remain at the bottom of the core during reactor operation. This means that the burnup cycle and reactivity is controlled by the addition of fuel. The objectives of the the present study were to find a means of carrying out the exact calculations needed to analyze the Peu a Peu fuel-loading scheme and to optimize the fuel composition, and fuel-loading scheme to achieve better burnup characteristics. The Monte Carlo method is used to perform calculations with high accuracy. Before the calculation of the whole core, the analysis for the infinite geometry was performed. The power generated per mass consumed for each combination of the uranium enrichment and packing fraction was analyzed from the parametric survey. By using the optimal value obtained, a whole-core calculation for the small 20 MWth reactor was performed and the criticality and burnup of this design was analyzed.

  8. Uncertainty and Sensitivity Analyses of a Pebble Bed HTGR Loss of Cooling Event

    DOE PAGES

    Strydom, Gerhard

    2013-01-01

    The Very High Temperature Reactor Methods Development group at the Idaho National Laboratory identified the need for a defensible and systematic uncertainty and sensitivity approach in 2009. This paper summarizes the results of an uncertainty and sensitivity quantification investigation performed with the SUSA code, utilizing the International Atomic Energy Agency CRP 5 Pebble Bed Modular Reactor benchmark and the INL code suite PEBBED-THERMIX. Eight model input parameters were selected for inclusion in this study, and after the input parameters variations and probability density functions were specified, a total of 800 steady state and depressurized loss of forced cooling (DLOFC) transientmore » PEBBED-THERMIX calculations were performed. The six data sets were statistically analyzed to determine the 5% and 95% DLOFC peak fuel temperature tolerance intervals with 95% confidence levels. It was found that the uncertainties in the decay heat and graphite thermal conductivities were the most significant contributors to the propagated DLOFC peak fuel temperature uncertainty. No significant differences were observed between the results of Simple Random Sampling (SRS) or Latin Hypercube Sampling (LHS) data sets, and use of uniform or normal input parameter distributions also did not lead to any significant differences between these data sets.« less

  9. PEBBLES Mechanics Simulation Speedup

    SciTech Connect

    Joshua J. Cogliati; Abderrafi M. Ougouag

    2010-05-01

    Pebble bed reactors contain large numbers of spherical fuel elements arranged randomly. Determining the motion and location of these fuel elements is required for calculating certain parameters of pebble bed reactor operation. These simulations involve hundreds of thousands of pebbles and involve determining the entire core motion as pebbles are recirculated. Single processor algorithms for this are insufficient since they would take decades to centuries of wall-clock time. This paper describes the process of parallelizing and speeding up the PEBBLES pebble mechanics simulation code. Both shared memory programming with the Open Multi-Processing API and distributed memory programming with the Message Passing Interface API are used in simultaneously in this process. A new shared memory lock-less linear time collision detection algorithm is described. This method allows faster detection of pebbles in contact than generic methods. These combine to make full recirculations on AVR sized reactors possible in months of wall clock time.

  10. Automated spectral zones selection methodology for diffusion theory data preparation for pebble bed reactor analysis

    NASA Astrophysics Data System (ADS)

    Mphahlele, Ramatsemela

    A methodology is developed for the determination of the optimum spectral zones in Pebble Bed Reactors (PBR). In this work a spectral zone is defined as a zone made up of a number of nodes whose characteristics are collectively similar and that are assigned the same few-group diffusion constants. In other words the spectral zones are the regions over which the few-group diffusion parameters are generated. The identification of spectral boundaries is treated as an optimization problem. It is solved by systematically and simultaneously repositioning all zone boundaries to achieve the global minimum error between the reference transport solution (MCNP) and the diffusion code solution (NEM). The objective function for the optimization algorithm is the total reaction rate error, which is defined as the sum of the leakage, absorption and fission reaction rates error in each zone. An iterative determination of group-dependent bucklings is incorporated into the methodology to properly account for spectral effects of neighboring zones. A preferred energy group structure has also been chosen. This optimization approach with the reference transport solution has proved to be accurate and consistent, however the computational effort required to complete the optimization process is significant. Thus a more practical methodology is also developed for the determination of the spectral zones in PBRs. The reactor physics characteristics of the spectral zones have been studied to understand the nature of the spectral zone boundaries. The practical tool involves the use of spectral indices based on few-group diffusion theory whole core calculations. With this methodology, there is no need to first have a reference transport solution. It is shown that the diffusion-theory coarse group fluxes and the effective multiplication factor computed using zones based on the practical index agrees within a narrow tolerance with those of the reference approach. Therefore the "practical" index

  11. An earthquake transient method for pebble-bed reactors and a fuel temperature model for TRISO fueled reactors

    NASA Astrophysics Data System (ADS)

    Ortensi, Javier

    This investigation is divided into two general topics: (1) a new method for analyzing the safe shutdown earthquake event in a pebble bed reactor core, and (2) the development of an explicit tristructural-isotropic fuel model for high temperature reactors. The safe shutdown earthquake event is one of the design basis accidents for the pebble bed reactor. The new method captures the dynamic geometric compaction of the pebble bed core. The neutronic and thermal-fluids grids are dynamically re-meshed to simulate the re-arrangement of the pebbles in the reactor during the earthquake. Results are shown for the PBMR-400 assuming it is subjected to the Idaho National Laboratory's design basis earthquake. The study concludes that the PBMR-400 can safely withstand the reactivity insertions induced by the slumping of the core and the resulting relative withdrawal of the control rods. This characteristic stems from the large negative Doppler feedback of the fuel. This Doppler feedback mechanism is a major contributor to the passive safety of gas-cooled, graphite-moderated, high-temperature reactors that use fuel based on TRISO particles. The correct prediction of the magnitude and time-dependence of this feedback effect is essential to the conduct of safety analyses for these reactors. An explicit TRISO fuel temperature model named THETRIS has been developed in this work and incorporated in the CYNOD-THERMIX-KONVEK suite of coupled codes. The new model yields similar results to those obtained with more complex methods, requiring multi-TRISO calculations within one control volume. The performance of the code during fast and moderately-slow transients is verified. These analyses show how explicit TRISO models improve the predictions of the fuel temperature, and consequently, of the power escalation. In addition, a brief study of the potential effects on the transient behavior of high-temperature reactors due to the presence of a gap inside the TRISO particles is included

  12. Design of Complex Systems to Achieve Passive Safety: Natural Circulation Cooling of Liquid Salt Pebble Bed Reactors

    NASA Astrophysics Data System (ADS)

    Scarlat, Raluca Olga

    This dissertation treats system design, modeling of transient system response, and characterization of individual phenomena and demonstrates a framework for integration of these three activities early in the design process of a complex engineered system. A system analysis framework for prioritization of experiments, modeling, and development of detailed design is proposed. Two fundamental topics in thermal-hydraulics are discussed, which illustrate the integration of modeling and experimentation with nuclear reactor design and safety analysis: thermal-hydraulic modeling of heat generating pebble bed cores, and scaled experiments for natural circulation heat removal with Boussinesq liquids. The case studies used in this dissertation are derived from the design and safety analysis of a pebble bed fluoride salt cooled high temperature nuclear reactor (PB-FHR), currently under development in the United States at the university and national laboratories level. In the context of the phenomena identification and ranking table (PIRT) methodology, new tools and approaches are proposed and demonstrated here, which are specifically relevant to technology in the early stages of development, and to analysis of passive safety features. A system decomposition approach is proposed. Definition of system functional requirements complements identification and compilation of the current knowledge base for the behavior of the system. Two new graphical tools are developed for ranking of phenomena importance: a phenomena ranking map, and a phenomena identification and ranking matrix (PIRM). The functional requirements established through this methodology were used for the design and optimization of the reactor core, and for the transient analysis and design of the passive natural circulation driven decay heat removal system for the PB-FHR. A numerical modeling approach for heat-generating porous media, with multi-dimensional fluid flow is presented. The application of this modeling

  13. Optimization of coupled multiphysics methodology for safety analysis of pebble bed modular reactor

    NASA Astrophysics Data System (ADS)

    Mkhabela, Peter Tshepo

    The research conducted within the framework of this PhD thesis is devoted to the high-fidelity multi-physics (based on neutronics/thermal-hydraulics coupling) analysis of Pebble Bed Modular Reactor (PBMR), which is a High Temperature Reactor (HTR). The Next Generation Nuclear Plant (NGNP) will be a HTR design. The core design and safety analysis methods are considerably less developed and mature for HTR analysis than those currently used for Light Water Reactors (LWRs). Compared to LWRs, the HTR transient analysis is more demanding since it requires proper treatment of both slower and much longer transients (of time scale in hours and days) and fast and short transients (of time scale in minutes and seconds). There is limited operation and experimental data available for HTRs for validation of coupled multi-physics methodologies. This PhD work developed and verified reliable high fidelity coupled multi-physics models subsequently implemented in robust, efficient, and accurate computational tools to analyse the neutronics and thermal-hydraulic behaviour for design optimization and safety evaluation of PBMR concept The study provided a contribution to a greater accuracy of neutronics calculations by including the feedback from thermal hydraulics driven temperature calculation and various multi-physics effects that can influence it. Consideration of the feedback due to the influence of leakage was taken into account by development and implementation of improved buckling feedback models. Modifications were made in the calculation procedure to ensure that the xenon depletion models were accurate for proper interpolation from cross section tables. To achieve this, the NEM/THERMIX coupled code system was developed to create the system that is efficient and stable over the duration of transient calculations that last over several tens of hours. Another achievement of the PhD thesis was development and demonstration of full-physics, three-dimensional safety analysis

  14. Cynod: A Neutronics Code for Pebble Bed Modular Reactor Coupled Transient Analysis

    SciTech Connect

    Hikaru Hiruta; Abderrafi M. Ougouag; Hans D. Gougar; Javier Ortensi

    2008-09-01

    The Pebble Bed Reactor (PBR) is one of the two concepts currently considered for development into the Next Generation Nuclear Plant (NGNP). This interest is due, in particular, to the concept’s inherent safety characteristics. In order to verify and confirm the design safety characteristics of the PBR computational tools must be developed that treat the range of phenomena that are expected to be important for this type of reactors. This paper presents a recently developed 2D R-Z cylindrical nodal kinetics code and shows some of its capabilities by applying it to a set of known and relevant benchmarks. The new code has been coupled to the thermal hydraulics code THERMIX/KONVEK[1] for application to the simulation of very fast transients in PBRs. The new code, CYNOD, has been written starting with a fixed source solver extracted from the nodal cylindrical geometry solver contained within the PEBBED code. The fixed source solver was then incorporated into a kinetic solver.. The new code inherits the spatial solver characteristics of the nodal solver within PEBBED. Thus, the time-dependent neutron diffusion equation expressed analytically in each node of the R-Z cylindrical geometry sub-domain (or node) is transformed into one-dimensional equations by means of the usual transverse integration procedure. The one-dimensional diffusion equations in each of the directions are then solved using the analytic Green’s function method. The resulting equations for the entire domain are then re-cast in the form of the Direct Coarse Mesh Finite Difference (D-CMFD) for convenience of solution. The implicit Euler method is used for the time variable discretization. In order to correctly treat the cusping effect for nodes that contain a partially inserted control rod a method is used that takes advantage of the Green’s function solution available in the intrinsic method. In this corrected treatment, the nodes are re-homogenized using axial flux shapes reconstructed based on the

  15. HTR-PROTEUS PEBBLE BED EXPERIMENTAL PROGRAM CORES 9 & 10: COLUMNAR HEXAGONAL POINT-ON-POINT PACKING WITH A 1:1 MODERATOR-TO-FUEL PEBBLE RATIO

    SciTech Connect

    John D. Bess

    2014-03-01

    PROTEUS is a zero-power research reactor based on a cylindrical graphite annulus with a central cylindrical cavity. The graphite annulus remains basically the same for all experimental programs, but the contents of the central cavity are changed according to the type of reactor being investigated. Through most of its service history, PROTEUS has represented light-water reactors, but from 1992 to 1996 PROTEUS was configured as a pebble-bed reactor (PBR) critical facility and designated as HTR-PROTEUS. The nomenclature was used to indicate that this series consisted of High Temperature Reactor experiments performed in the PROTEUS assembly. During this period, seventeen critical configurations were assembled and various reactor physics experiments were conducted. These experiments included measurements of criticality, differential and integral control rod and safety rod worths, kinetics, reaction rates, water ingress effects, and small sample reactivity effects (Ref. 3). HTR-PROTEUS was constructed, and the experimental program was conducted, for the purpose of providing experimental benchmark data for assessment of reactor physics computer codes. Considerable effort was devoted to benchmark calculations as a part of the HTR-PROTEUS program. References 1 and 2 provide detailed data for use in constructing models for codes to be assessed. Reference 3 is a comprehensive summary of the HTR-PROTEUS experiments and the associated benchmark program. This document draws freely from these references. Only Cores 9 and 10 are evaluated in this benchmark report due to similarities in their construction. The other core configurations of the HTR-PROTEUS program are evaluated in their respective reports as outlined in Section 1.0. Cores 9 and 10 were evaluated and determined to be acceptable benchmark experiments.

  16. HTR-PROTEUS PEBBLE BED EXPERIMENTAL PROGRAM CORES 9 & 10: COLUMNAR HEXAGONAL POINT-ON-POINT PACKING WITH A 1:1 MODERATOR-TO-FUEL PEBBLE RATIO

    SciTech Connect

    John D. Bess

    2013-03-01

    PROTEUS is a zero-power research reactor based on a cylindrical graphite annulus with a central cylindrical cavity. The graphite annulus remains basically the same for all experimental programs, but the contents of the central cavity are changed according to the type of reactor being investigated. Through most of its service history, PROTEUS has represented light-water reactors, but from 1992 to 1996 PROTEUS was configured as a pebble-bed reactor (PBR) critical facility and designated as HTR-PROTEUS. The nomenclature was used to indicate that this series consisted of High Temperature Reactor experiments performed in the PROTEUS assembly. During this period, seventeen critical configurations were assembled and various reactor physics experiments were conducted. These experiments included measurements of criticality, differential and integral control rod and safety rod worths, kinetics, reaction rates, water ingress effects, and small sample reactivity effects (Ref. 3). HTR-PROTEUS was constructed, and the experimental program was conducted, for the purpose of providing experimental benchmark data for assessment of reactor physics computer codes. Considerable effort was devoted to benchmark calculations as a part of the HTR-PROTEUS program. References 1 and 2 provide detailed data for use in constructing models for codes to be assessed. Reference 3 is a comprehensive summary of the HTR-PROTEUS experiments and the associated benchmark program. This document draws freely from these references. Only Cores 9 and 10 are evaluated in this benchmark report due to similarities in their construction. The other core configurations of the HTR-PROTEUS program are evaluated in their respective reports as outlined in Section 1.0. Cores 9 and 10 were evaluated and determined to be acceptable benchmark experiments.

  17. One-dimensional modeling of radial heat removal during depressurized heatup transients in modular pebble-bed and prismatic high temperature gas-cooled reactors

    SciTech Connect

    Savage, M.G.

    1984-07-01

    A one-dimensional computational model was developed to evaluate the heat removal capabilities of both prismatic-core and pebble-bed modular HTGRs during depressurized heatup transients. A correlation was incorporated to calculate the temperature- and neutron-fluence-dependent thermal conductivity of graphite. The modified Zehner-Schluender model was used to determine the effective thermal conductivity of a pebble bed, accounting for both conduction and radiation. Studies were performed for prismatic-core and pebble-bed modular HTGRs, and the results were compared to analyses performed by GA and GR, respectively. For the particular modular reactor design studied, the prismatic HTGR peak temperature was 2152.2/sup 0/C at 38 hours following the transient initiation, and the pebble-bed peak temperature was 1647.8/sup 0/C at 26 hours. These results compared favorably with those of GA and GE, with only slight differences caused by neglecting axial heat transfer in a one-dimensional radial model. This study found that the magnitude of the initial power density had a greater effect on the temperature excursion than did the initial temperature.

  18. KUGEL: a thermal, hydraulic, fuel performance, and gaseous fission product release code for pebble bed reactor core analysis

    SciTech Connect

    Shamasundar, B.I.; Fehrenbach, M.E.

    1981-05-01

    The KUGEL computer code is designed to perform thermal/hydraulic analysis and coated-fuel particle performance calculations for axisymmetric pebble bed reactor (PBR) cores. This computer code was developed as part of a Department of Energy (DOE)-funded study designed to verify the published core performance data on PBRs. The KUGEL code is designed to interface directly with the 2DB code, a two-dimensional neutron diffusion code, to obtain distributions of thermal power, fission rate, fuel burnup, and fast neutron fluence, which are needed for thermal/hydraulic and fuel performance calculations. The code is variably dimensioned so that problem size can be easily varied. An interpolation routine allows variable mesh size to be used between the 2DB output and the two-dimensional thermal/hydraulic calculations.

  19. A uranium bed with ceramic body for tritium storage

    SciTech Connect

    Khapov, A.S.; Grishechkin, S.K.; Kiselev, V.G.

    2015-03-15

    It is widely recognized that ceramic coatings provide an attractive solution to lower tritium permeation in structural materials. Alumina based ceramic coatings have the highest permeation reduction factor for hydrogen. For this reason an attempt was made to apply crack-free low porous ceramics as a structural material of a bed body for tritium storage in a setup used for hydrogenating neutron tube targets at VNIIA. The present article introduces the design of the bed. This bed possesses essentially a lower hydrogen permeation factor than traditionally beds with stainless steel body. Bed heating in order to recover hydrogen from the bed is suggested to be implemented by high frequency induction means. Inductive heating allows decreasing the time necessary for tritium release from the bed as well as power consumption. Both of these factors mean less thermal power release into glove box where a setup for tritium handling is installed and thus causes fewer problems with pressure regulations inside the glove box. Inductive heating allows raising tritium sorbent material temperature up to melting point. The latter allows achieving nearly full tritium recovery.

  20. Experimental Study and Computational Simulations of Key Pebble Bed Thermo-mechanics Issues for Design and Safety

    SciTech Connect

    Tokuhiro, Akira; Potirniche, Gabriel; Cogliati, Joshua; Ougouag, Abderrafi

    2014-07-08

    An experimental and computational study, consisting of modeling and simulation (M&S), of key thermal-mechanical issues affecting the design and safety of pebble-bed (PB) reactors was conducted. The objective was to broaden understanding and experimentally validate thermal-mechanic phenomena of nuclear grade graphite, specifically, spheres in frictional contact as anticipated in the bed under reactor relevant pressures and temperatures. The contact generates graphite dust particulates that can subsequently be transported into the flowing gaseous coolent. Under postulated depressurization transients and with the potential for leaked fission products to be adsorbed onto graphite 'dust', there is the potential for fission products to escape from the primary volume. This is a design safety concern. Furthermore, earlier safety assessment identified the distinct possibility for the dispersed dust to combust in contact with air if sufficient conditions are met. Both of these phenomena were noted as important to design review and containing uncertainty to warrant study. The team designed and conducted two separate effects tests to study and benchmark the potential dust-generation rate, as well as study the conditions under which a dust explosion may occure in a standardized, instrumented explosion chamber.

  1. The Pebble Recirculation Experiment (PREX) for the AHTR

    SciTech Connect

    Bardet, P.; An, J.Y.; Franklin, J.T.; Huang, D.; Lee, K.; Mai, A.; Toulouse, M.; Peterson, P.F.

    2007-07-01

    Conceptual design studies for the liquid-salt cooled Advanced High Temperature Reactor (AHTR) have identified three candidate TRISO fuel geometries: prismatic, pebble, and stringer fuels. This paper presents experimental results from the integral Pebble Recirculation Experiment (PREX) that verifies the viability of pebble recirculation in a Pebble Bed AHTR (PB-AHTR). The experiments conducted include injection and extraction of buoyant pebbles, measurements of packing density and pressure losses, and observations of pebble landing dynamics and bed formation. (authors)

  2. Aerobic degradation of a mixture of azo dyes in a packed bed reactor having bacteria-coated laterite pebbles.

    PubMed

    Senan, Resmi C; Shaffiqu, T S; Roy, J Jegan; Abraham, T Emilia

    2003-01-01

    A microbial consortium capable of aerobic degradation of a mixture of azo dyes consisting of two isolated strains (RRL,TVM) and one known strain of Pseudomonas putida (MTCC 1194) was immobilized on laterite stones. The amount of bacterial biomass attached to the laterite stones was 8.64 g per 100 g of the stone on a dry weight basis. The packed bed reactor was filled with these stones and had a total capacity of 850 mL and a void volume of 210 mL. The feed consisted of an equal mixture of seven azo dyes both in water as well as in a simulated textile effluent, at a pH of 9.0 and a salinity of 900 mg/L. The dye concentrations of influent were 25, 50, and 100 microg/mL. The residence time was varied between 0.78 and 6.23 h. It was found that at the lowest residence time 23.55, 45.73, and 79.95 microg of dye was degraded per hour at an initial dye concentration of 25, 50, and 100 microg, respectively. The pH was reduced from 9.0 to 7.0. Simulated textile effluent containing 50 microg/mL dye was degraded by 61.7%. Analysis of degradation products by TLC and HPLC showed that the dye mixture was degraded to nontoxic smaller molecules. The bacteria-coated pebbles were stable, there was no washout even after 2 months, and the reactor was found to be suitable for the aerobic degradation of azo dyes.

  3. PEBBLES Simulation of Static Friction and New Static Friction Benchmark

    SciTech Connect

    Joshua J. Cogliati; Abderrafi M. Ougouag

    2010-05-01

    Pebble bed reactors contain large numbers of spherical fuel elements arranged randomly. Determining the motion and location of these fuel elements is required for calculating certain parameters of pebble bed reactor operation. This paper documents the PEBBLES static friction model. This model uses a three dimensional differential static friction approximation extended from the two dimensional Cundall and Strack model. The derivation of determining the rotational transformation of pebble to pebble static friction force is provided. A new implementation for a differential rotation method for pebble to container static friction force has been created. Previous published methods are insufficient for pebble bed reactor geometries. A new analytical static friction benchmark is documented that can be used to verify key static friction simulation parameters. This benchmark is based on determining the exact pebble to pebble and pebble to container static friction coefficients required to maintain a stable five sphere pyramid.

  4. Modeling of the Fluid Flow and Heat Transfer an a Pebble Bed Modular Reactor Core With a Computational Fluid Dynamics Code

    SciTech Connect

    Taylor, J. Bryce; Yavuzkurt, Savas; Baratta, Anthony J.

    2002-07-01

    The Pebble Bed Modular Reactor (PBMR), a promising Generation IV nuclear reactor design, raises many novel technological issues for which new experience and techniques must be developed. This brief study explores a few of these issues, utilizes a computational fluid dynamics code to model some simple phenomena, and points out deficiencies in current knowledge that should be addressed by future research and experimentation. A highly simplified representation of the PBMR core is analyzed with FLUENT, a commercial computational fluid dynamics code. The applied models examine laminar and turbulent flow in the vicinity of a single spherical fuel pebble near the center of the core, accounting for the effects of the immediately adjacent fuel pebbles. Several important fluid flow and heat transfer parameters are examined, including heat transfer coefficient, Nusselt number, and pressure drop, as well as the temperature, pressure, and velocity profiles near the fuel pebble. The results of these 'unit cell' calculations are also compared to empirical correlations available in the literature. As FLUENT is especially sensitive to geometry during the generation of a computational mesh, the sensitivity of code results to pebble spacing is also examined. The results of this study show that while a PBMR presents a novel and complex geometry, a code such as FLUENT is suitable for calculation of both local and global flow characteristics, and can be a valuable tool for the thermal-hydraulic study of this new reactor design. FLUENT results for pressure drop deviate from the Darcy correlation by several orders of magnitude in all cases. When determining the heat transfer coefficient, FLUENT is again much lower than Robinson's correlation. Results for Nusselt number show better agreement, with FLUENT predicting results that are 10 or 20 times as large as those from the Robinson and Lancashire correlations. These differences may arise because the empirical correlations concern mainly

  5. Design and construction of a prototype advanced on-line fuel burn-up monitoring system for the modular pebble bed reactor

    SciTech Connect

    Su, Bingjing; Hawari, Ayman, I.

    2004-03-30

    Modular Pebble Bed Reactor (MPBR) is a high temperature gas-cooled nuclear power reactor currently under study as a next generation reactor system. In addition to its inherently safe design, a unique feature of this reactor is its multi-pass fuel circulation in which the fuel pebbles are randomly loaded and continuously cycled through the core until they reach their prescribed End-of-Life burn-up limit. Unlike the situation with a conventional light water reactor, depending solely on computational methods to perform in-core fuel management for MPBR will be highly inaccurate. An on-line measurement system is needed to accurately assess whether a given pebble has reached its End-of-Life burn-up limit and thereby provide an on-line, automated go/no-go decision on fuel disposition on a pebble-by-pebble basis. This project investigated approaches to analyzing fuel pebbles in real time using gamma spectroscopy and possibly using passive neutron counting of spontaneous fission neutrons to provide the speed, accuracy, and burn-up range required for burnup determination of MPBR. It involved all phases necessary to develop and construct a burn-up monitor, including a review of the design requirements of the system, identification of detection methodologies, modeling and development of potential designs, and finally, the construction and testing of an operational detector system. Based upon the research work performed in this project, the following conclusions are made. In terms of using gamma spectrometry, two possible approaches were identified for burnup assay. The first approach is based on the measurement of the absolute activity of Cs-137. However, due to spectral interference and the need for absolute calibration of the spectrometer, the uncertainty in burnup determination using this approach was found to range from {approx} {+-}40% at beginning of life to {approx} {+-}10% at the discharge burnup. An alternative approach is to use a relative burnup indicator. In this

  6. The Transient 3-D Transport Coupled Code TORT-TD/ATTICA3D for High-Fidelity Pebble-Bed HTGR Analyses

    NASA Astrophysics Data System (ADS)

    Seubert, Armin; Sureda, Antonio; Lapins, Janis; Bader, Johannes; Laurien, Eckart

    2012-01-01

    This article describes the 3D discrete ordinates-based coupled code system TORT-TD/ATTICA3D that aims at steady state and transient analyses of pebble-bed high-temperature gas cooled reactors. In view of increasing computing power, the application of time-dependent neutron transport methods becomes feasible for best estimate evaluations of safety margins. The calculation capabilities of TORT-TD/ATTICA3D are presented along with the coupling approach, with focus on the time-dependent neutron transport features of TORT-TD. Results obtained for the OECD/NEA/NSC PBMR-400 benchmark demonstrate the transient capabilities of TORT-TD/ATTICA3D.

  7. Fabrication of Li2TiO3 pebbles using PVA-boric acid reaction for solid breeding materials

    NASA Astrophysics Data System (ADS)

    Park, Yi-Hyun; Cho, Seungyon; Ahn, Mu-Young

    2014-12-01

    Lithium metatitanate (Li2TiO3) is a candidate breeding material of the Helium Cooled Ceramic Reflector (HCCR) Test Blanket Module (TBM). The breeding material is used in pebble-bed form to reduce the uncertainty of the interface thermal conductance. In this study, Li2TiO3 pebbles were successfully fabricated by the slurry droplet wetting method using the cross-linking reaction between polyvinyl alcohol (PVA) and boric acid. The effects of fabrication parameters on the shaping of Li2TiO3 green body were investigated. In addition, the basic characteristics of the sintered pebble were also evaluated. The shape of Li2TiO3 green bodies was affected by slurry viscosity, PVA content and boric acid content. The grain size and average crush load of sintered Li2TiO3 pebble were controlled by the sintering time. The boron was completely removed during the final sintering process.

  8. MHD oxidant intermediate temperature ceramic heater study

    NASA Technical Reports Server (NTRS)

    Carlson, A. W.; Chait, I. L.; Saari, D. P.; Marksberry, C. L.

    1981-01-01

    The use of three types of directly fired ceramic heaters for preheating oxygen enriched air to an intermediate temperature of 1144K was investigated. The three types of ceramic heaters are: (1) a fixed bed, periodic flow ceramic brick regenerative heater; (2) a ceramic pebble regenerative heater. The heater design, performance and operating characteristics under conditions in which the particulate matter is not solidified are evaluated. A comparison and overall evaluation of the three types of ceramic heaters and temperature range determination at which the particulate matter in the MHD exhaust gas is estimated to be a dry powder are presented.

  9. HTR-PROTEUS PEBBLE BED EXPERIMENTAL PROGRAM CORES 5, 6, 7, & 8: COLUMNAR HEXAGONAL POINT-ON-POINT PACKING WITH A 1:2 MODERATOR-TO-FUEL PEBBLE RATIO

    SciTech Connect

    John D. Bess

    2013-03-01

    PROTEUS is a zero-power research reactor based on a cylindrical graphite annulus with a central cylindrical cavity. The graphite annulus remains basically the same for all experimental programs, but the contents of the central cavity are changed according to the type of reactor being investigated. Through most of its service history, PROTEUS has represented light-water reactors, but from 1992 to 1996 PROTEUS was configured as a pebble-bed reactor (PBR) critical facility and designated as HTR-PROTEUS. The nomenclature was used to indicate that this series consisted of High Temperature Reactor experiments performed in the PROTEUS assembly. During this period, seventeen critical configurations were assembled and various reactor physics experiments were conducted. These experiments included measurements of criticality, differential and integral control rod and safety rod worths, kinetics, reaction rates, water ingress effects, and small sample reactivity effects (Ref. 3). HTR-PROTEUS was constructed, and the experimental program was conducted, for the purpose of providing experimental benchmark data for assessment of reactor physics computer codes. Considerable effort was devoted to benchmark calculations as a part of the HTR-PROTEUS program. References 1 and 2 provide detailed data for use in constructing models for codes to be assessed. Reference 3 is a comprehensive summary of the HTR-PROTEUS experiments and the associated benchmark program. This document draws freely from these references. Only Cores 9 and 10 are evaluated in this benchmark report due to similarities in their construction. The other core configurations of the HTR-PROTEUS program are evaluated in their respective reports as outlined in Section 1.0. Cores 9 and 10 were evaluated and determined to be acceptable benchmark experiments.

  10. HTR-Proteus Pebble Bed Experimental Program Cores 5,6,7,&8: Columnar Hexagonal Point-on-Point Packing with a 1:2 Moderator-to-Fuel Pebble Ratio

    SciTech Connect

    Bess, John D.; Sterbentz, James W.; Snoj, Luka; Lengar, Igor; Koberl, Oliver

    2015-03-01

    PROTEUS is a zero-power research reactor based on a cylindrical graphite annulus with a central cylindrical cavity. The graphite annulus remains basically the same for all experimental programs, but the contents of the central cavity are changed according to the type of reactor being investigated. Through most of its service history, PROTEUS has represented light-water reactors, but from 1992 to 1996 PROTEUS was configured as a pebble-bed reactor (PBR) critical facility and designated as HTR-PROTEUS. The nomenclature was used to indicate that this series consisted of High Temperature Reactor experiments performed in the PROTEUS assembly. During this period, seventeen critical configurations were assembled and various reactor physics experiments were conducted. These experiments included measurements of criticality, differential and integral control rod and safety rod worths, kinetics, reaction rates, water ingress effects, and small sample reactivity effects (Ref. 3). HTR-PROTEUS was constructed, and the experimental program was conducted, for the purpose of providing experimental benchmark data for assessment of reactor physics computer codes. Considerable effort was devoted to benchmark calculations as a part of the HTR-PROTEUS program. References 1 and 2 provide detailed data for use in constructing models for codes to be assessed. Reference 3 is a comprehensive summary of the HTR-PROTEUS experiments and the associated benchmark program. This document draws freely from these references. Only Cores 9 and 10 are evaluated in this benchmark report due to similarities in their construction. The other core configurations of the HTR-PROTEUS program are evaluated in their respective reports as outlined in Section 1.0. Cores 9 and 10 were evaluated and determined to be acceptable benchmark experiments.

  11. Tiny Pebbles

    NASA Technical Reports Server (NTRS)

    2004-01-01

    This image taken by the microscopic imager instrument located on the Mars Exploration Rover Opportunity's instrument deployment device, or 'arm,' shows the crater floor at Meridiani Planum, Mars, before the rover dug a trench on sol 23 (February 16, 2004). Grains of soil on the floor appear sand-sized with millimeter-sized pebbles on top. The area in this image measures approximately 3 centimeters (1.2 inches) across.

  12. Development Status of the PEBBLES Code for Pebble Mechanics: Improved Physical Models and Speed-up

    SciTech Connect

    Joshua J. Cogliati; Abderrafi M. Ougouag

    2009-09-01

    PEBBLES is a code for simulating the motion of all the pebbles in a pebble bed reactor. Since pebble bed reactors are packed randomly and not precisely placed, the location of the fuel elements in the reactor is not deterministically known. Instead, when determining operating parameters the motion of the pebbles can be simulated and stochastic locations can be found. The PEBBLES code can output information relevant for other simulations of the pebble bed reactors such as the positions of the pebbles in the reactor, packing fraction change in an earthquake, and velocity profiles created by recirculation. The goal for this level three milestone was to speedup the PEBBLES code through implementation on massively parallel computer. Work on this goal has resulted in speeding up both the single processor version and creation of a new parallel version of PEBBLES. Both the single processor version and the parallel running capability of the PEBBLES code have improved since the fiscal year start. The hybrid MPI/OpenMP PEBBLES version was created this year to run on the increasingly common cluster hardware profile that combines nodes with multiple processors that share memory and a cluster of nodes that are networked together. The OpenMP portions use the Open Multi-Processing shared memory parallel processing model to split the task across processors in a single node that shares memory. The Message Passing Interface (MPI) portion uses messages to communicate between different nodes over a network. The following are wall clock speed up for simulating an NGNP-600 sized reactor. The single processor version runs 1.5 times faster compared to the single processor version at the beginning of the fiscal year. This speedup is primarily due to the improved static friction model described in the report. When running on 64 processors, the new MPI/OpenMP hybrid version has a wall clock speed up of 22 times compared to the current single processor version. When using 88 processors, a

  13. Development Status of the PEBBLES Code for Pebble Mechanics: Improved Physical Models and Speed-up

    SciTech Connect

    Joshua J. Cogliati; Abderrafi M. Ougouag

    2009-12-01

    PEBBLES is a code for simulating the motion of all the pebbles in a pebble bed reactor. Since pebble bed reactors are packed randomly and not precisely placed, the location of the fuel elements in the reactor is not deterministically known. Instead, when determining operating parameters the motion of the pebbles can be simulated and stochastic locations can be found. The PEBBLES code can output information relevant for other simulations of the pebble bed reactors such as the positions of the pebbles in the reactor, packing fraction change in an earthquake, and velocity profiles created by recirculation. The goal for this level three milestone was to speedup the PEBBLES code through implementation on massively parallel computer. Work on this goal has resulted in speeding up both the single processor version and creation of a new parallel version of PEBBLES. Both the single processor version and the parallel running capability of the PEBBLES code have improved since the fiscal year start. The hybrid MPI/OpenMP PEBBLES version was created this year to run on the increasingly common cluster hardware profile that combines nodes with multiple processors that share memory and a cluster of nodes that are networked together. The OpenMP portions use the Open Multi-Processing shared memory parallel processing model to split the task across processors in a single node that shares memory. The Message Passing Interface (MPI) portion uses messages to communicate between different nodes over a network. The following are wall clock speed up for simulating an NGNP-600 sized reactor. The single processor version runs 1.5 times faster compared to the single processor version at the beginning of the fiscal year. This speedup is primarily due to the improved static friction model described in the report. When running on 64 processors, the new MPI/OpenMP hybrid version has a wall clock speed up of 22 times compared to the current single processor version. When using 88 processors, a

  14. Image reconstruction of single photon emission computed tomography (SPECT) on a pebble bed reactor (PBR) using expectation maximization and exact inversion algorithms: Comparison study by means of numerical phantom

    NASA Astrophysics Data System (ADS)

    Razali, Azhani Mohd; Abdullah, Jaafar

    2015-04-01

    Single Photon Emission Computed Tomography (SPECT) is a well-known imaging technique used in medical application, and it is part of medical imaging modalities that made the diagnosis and treatment of disease possible. However, SPECT technique is not only limited to the medical sector. Many works are carried out to adapt the same concept by using high-energy photon emission to diagnose process malfunctions in critical industrial systems such as in chemical reaction engineering research laboratories, as well as in oil and gas, petrochemical and petrochemical refining industries. Motivated by vast applications of SPECT technique, this work attempts to study the application of SPECT on a Pebble Bed Reactor (PBR) using numerical phantom of pebbles inside the PBR core. From the cross-sectional images obtained from SPECT, the behavior of pebbles inside the core can be analyzed for further improvement of the PBR design. As the quality of the reconstructed image is largely dependent on the algorithm used, this work aims to compare two image reconstruction algorithms for SPECT, namely the Expectation Maximization Algorithm and the Exact Inversion Formula. The results obtained from the Exact Inversion Formula showed better image contrast and sharpness, and shorter computational time compared to the Expectation Maximization Algorithm.

  15. Image reconstruction of single photon emission computed tomography (SPECT) on a pebble bed reactor (PBR) using expectation maximization and exact inversion algorithms: Comparison study by means of numerical phantom

    SciTech Connect

    Razali, Azhani Mohd Abdullah, Jaafar

    2015-04-29

    Single Photon Emission Computed Tomography (SPECT) is a well-known imaging technique used in medical application, and it is part of medical imaging modalities that made the diagnosis and treatment of disease possible. However, SPECT technique is not only limited to the medical sector. Many works are carried out to adapt the same concept by using high-energy photon emission to diagnose process malfunctions in critical industrial systems such as in chemical reaction engineering research laboratories, as well as in oil and gas, petrochemical and petrochemical refining industries. Motivated by vast applications of SPECT technique, this work attempts to study the application of SPECT on a Pebble Bed Reactor (PBR) using numerical phantom of pebbles inside the PBR core. From the cross-sectional images obtained from SPECT, the behavior of pebbles inside the core can be analyzed for further improvement of the PBR design. As the quality of the reconstructed image is largely dependent on the algorithm used, this work aims to compare two image reconstruction algorithms for SPECT, namely the Expectation Maximization Algorithm and the Exact Inversion Formula. The results obtained from the Exact Inversion Formula showed better image contrast and sharpness, and shorter computational time compared to the Expectation Maximization Algorithm.

  16. Formation and accumulation of radiation-induced defects and radiolysis products in modified lithium orthosilicate pebbles with additions of titanium dioxide

    NASA Astrophysics Data System (ADS)

    Zarins, Arturs; Valtenbergs, Oskars; Kizane, Gunta; Supe, Arnis; Knitter, Regina; Kolb, Matthias H. H.; Leys, Oliver; Baumane, Larisa; Conka, Davis

    2016-03-01

    Lithium orthosilicate (Li4SiO4) pebbles with 2.5 wt.% excess of silicon dioxide (SiO2) are the European Union's designated reference tritium breeding ceramics for the Helium Cooled Pebble Bed (HCPB) Test Blanket Module (TBM). However, the latest irradiation experiments showed that the reference Li4SiO4 pebbles may crack and form fragments under operation conditions as expected in the HCPB TBM. Therefore, it has been suggested to change the chemical composition of the reference Li4SiO4 pebbles and to add titanium dioxide (TiO2), to obtain lithium metatitanate (Li2TiO3) as a second phase. The aim of this research was to investigate the formation and accumulation of radiation-induced defects (RD) and radiolysis products (RP) in the modified Li4SiO4 pebbles with different contents of TiO2 for the first time, in order to estimate and compare radiation stability. The reference and the modified Li4SiO4 pebbles were irradiated with accelerated electrons (E = 5 MeV) up to 5000 MGy absorbed dose at 300-990 K in a dry argon atmosphere. By using electron spin resonance (ESR) spectroscopy it was determined that in the modified Li4SiO4 pebbles, several paramagnetic RD and RP are formed and accumulated, like, E' centres (SiO33-/TiO33-), HC2 centres (SiO43-/TiO3-) etc. On the basis of the obtained results, it is concluded that the modified Li4SiO4 pebbles with TiO2 additions have comparable radiation stability with the reference pebbles.

  17. Granular-bed and ceramic candle filters in commercial plants: A comparison

    SciTech Connect

    Wilson, K.B.; Haas, J.C.; Eshelman, M.B.

    1993-04-01

    Advanced coal fired power cycles require the removal of coal ash at high temperature and pressure. Granular-bed and ceramic candle filters can be used for this service. Conceptual designs for commercial size applications are made for each type of filter. The filters are incorporated in the design of a Foster Wheeler 450 MWe second generation pressurized fluidized bed combustion plant which contains a pressurized fluidized combustor and carbonizer. In a second application, the inters are incorporated in the design of a 100 MWe KRW (air) gasifier based power plant. The candle filter design is state of the art as determined from the open literature with an effort to minimize the cost. The granular-bed filter design is based on test work performed at high temperature and low pressure, tests at New York University performed at high pressure and temperate, and new analysis used to simplify the scale up of the filter and reduce overall cost. The incorporation of chemically reactive granites in the granular-bed filter for the removal of additional coal derived contaminants such as alkali or sulfur is considered. The conceptual designs of the granular-bed inter and the ceramic candle filter are compared in terms of the cost of electricity, capital cost, and operating and maintenance costs for each application.

  18. Integrated low emissions cleanup system for direct coal fueled turbines (moving bed, fluid bed contactor/ceramic filter)

    SciTech Connect

    Newby, R.A.; Alvin, M.A.; Bachovchin, D.M.; Yang, W.C.; Smeltzer, E.E.; Lippert, T.E.

    1992-10-20

    The United States Department of Energy, Morgantown Energy Research Center (DOE/METC), is sponsoring the development of direct coal-fired turbine power plants as part of their Heat Engines program. A major technical challenge remaining for the development of the direct coal-fired turbine is high-temperature combustion gas cleaning to meet environmental standards for sulfur oxides and particulate emissions, as well as to provide acceptable turbine life. The Westinghouse Electric Corporation, Science Technology Center, is evaluating two Integrated Low Emissions Cleanup (ILEC) concepts that have been configured to meat this technical challenge: a baseline ceramic barrier filter ILEC concept, and a fluidized bed ILEC concept. These ILEC concepts simultaneously control sulfur, particulate, and alkali contaminants in the high-pressure combustion gases at turbine inlet temperatures up to 2300[degree]F. This document reports the status of a program in the nineteenth quarter to develop this ILEC technology for direct coal-fired turbine power plants.

  19. Fabrication development of Li 2O pebbles by wet process

    NASA Astrophysics Data System (ADS)

    Tsuchiya, Kunihiko; Fuchinoue, Katsuhiro; Saito, Shigeru; Watarumi, Kazutoshi; Furuya, Takemi; Kawamura, Hiroshi

    1998-03-01

    Lithium oxide (Li 2O) is one of the best tritium breeding materials. A small sphere of Li 2O is proposed in some designs of fusion blankets. Recently, reprocessing technology on irradiated ceramic tritium breeders was developed from the viewpoint of effective use of resources and reduction of radioactive wastes. The wet process is advantageous for fabricating small Li 2O pebbles from the reprocessed lithium-bearing solutions. Preliminary fabrication tests of Li 2O pebbles by the wet process were carried out. However, the density of the pebbles obtained was only 55%. Therefore, process improvement tests were performed in order to increase the density of Li 2O pebbles fabricated by this method. The improved process yielded Li 2O pebbles in the target range of 80-85% T.D.

  20. Mechanisms of flow through compressible porous beds in sedimentation, centrifugation, deliquoring, and ceramic processing

    SciTech Connect

    1996-01-25

    The major topics covered in the investigation include: centrifugation; cake filtration; sedimentation and thickening; capillary suction operations; ceramics, slip casting; optimization studies; and wastewater. The research program was aimed at the specific areas of solid/liquid separation including sedimentation, thickening, cake filtration, centrifugation, expression, washing, deep-bed filtration, screening, and membrane separation. Unification of the theoretical approaches to the various solid/liquid separation operations was the principle objective of the research. Exploring new aspects of basic separation mechanisms, verification of theory with experiment, development of laboratory procedures for obtaining data for design, optimizing operational methods, and transferring the results to industry were part of the program.

  1. "Smart pebble" designs for sediment transport monitoring

    NASA Astrophysics Data System (ADS)

    Valyrakis, Manousos; Alexakis, Athanasios; Pavlovskis, Edgars

    2015-04-01

    Sediment transport, due to primarily the action of water, wind and ice, is one of the most significant geomorphic processes responsible for shaping Earth's surface. It involves entrainment of sediment grains in rivers and estuaries due to the violently fluctuating hydrodynamic forces near the bed. Here an instrumented particle, namely a "smart pebble", is developed to investigate the exact flow conditions under which individual grains may be entrained from the surface of a gravel bed. This could lead in developing a better understanding of the processes involved, focusing on the response of the particle during a variety of flow entrainment events. The "smart pebble" is a particle instrumented with MEMS sensors appropriate for capturing the hydrodynamic forces a coarse particle might experience during its entrainment from the river bed. A 3-axial gyroscope and accelerometer registers data to a memory card via a microcontroller, embedded in a 3D-printed waterproof hollow spherical particle. The instrumented board is appropriately fit and centred into the shell of the pebble, so as to achieve a nearly uniform distribution of the mass which could otherwise bias its motion. The "smart pebble" is powered by an independent power to ensure autonomy and sufficiently long periods of operation appropriate for deployment in the field. Post-processing and analysis of the acquired data is currently performed offline, using scientific programming software. The performance of the instrumented particle is validated, conducting a series of calibration experiments under well-controlled laboratory conditions.

  2. Two-Player Graph Pebbling

    NASA Astrophysics Data System (ADS)

    Prudente, Matthew James

    Given a graph G with pebbles on the vertices, we define a pebbling move as removing two pebbles from a vertex u, placing one pebble on a neighbor v, and discarding the other pebble, like a toll. The pebbling number pi( G) is the least number of pebbles needed so that every arrangement of pi(G) pebbles can place a pebble on any vertex through a sequence of pebbling moves. We introduce a new variation on graph pebbling called two-player pebbling. In this, players called the mover and the defender alternate moves, with the stipulation that the defender cannot reverse the previous move. The mover wins only if they can place a pebble on a specified vertex and the defender wins if the mover cannot. We define η(G), analogously, as the minimum number of pebbles such that given every configuration of the η( G) pebbles and every specified vertex r, the mover has a winning strategy. First, we will investigate upper bounds for η( G) on various classes of graphs and find a certain structure for which the defender has a winning strategy, no matter how many pebbles are in a configuration. Then, we characterize winning configurations for both players on a special class of diameter 2 graphs. Finally, we show winning configurations for the mover on paths using a recursive argument.

  3. "Smart pebble" design for environmental monitoring applications

    NASA Astrophysics Data System (ADS)

    Valyrakis, Manousos; Pavlovskis, Edgars

    2014-05-01

    Sediment transport, due to primarily the action of water, wind and ice, is one of the most significant geomorphic processes responsible for shaping Earth's surface. It involves entrainment of sediment grains in rivers and estuaries due to the violently fluctuating hydrodynamic forces near the bed. Here an instrumented particle, namely a "smart pebble", is developed to investigate the exact flow conditions under which individual grains may be entrained from the surface of a gravel bed. This could lead in developing a better understanding of the processes involved, while focusing on the response of the particle during a variety of flow entrainment events. The "smart pebble" is a particle instrumented with MEMS sensors appropriate for capturing the hydrodynamic forces a coarse particle might experience during its entrainment from the river bed. A 3-axial gyroscope and accelerometer registers data to a memory card via a microcontroller, embedded in a 3D-printed waterproof hollow spherical particle. The instrumented board is appropriately fit and centred into the shell of the pebble, so as to achieve a nearly uniform distribution of the mass which could otherwise bias its motion. The "smart pebble" is powered by an independent power to ensure autonomy and sufficiently long periods of operation appropriate for deployment in the field. Post-processing and analysis of the acquired data is currently performed offline, using scientific programming software. The performance of the instrumented particle is validated, conducting a series of calibration experiments under well-controlled laboratory conditions. "Smart pebble" allows for a wider range of environmental sensors (e.g. for environmental/pollutant monitoring) to be incorporated so as to extend the range of its application, enabling accurate environmental monitoring which is required to ensure infrastructure resilience and preservation of ecological health.

  4. Low energy single-staged anaerobic fluidized bed ceramic membrane bioreactor (AFCMBR) for wastewater treatment.

    PubMed

    Aslam, Muhammad; McCarty, Perry L; Shin, Chungheon; Bae, Jaeho; Kim, Jeonghwan

    2017-03-06

    An aluminum dioxide (Al2O3) ceramic membrane was used in a single-stage anaerobic fluidized bed ceramic membrane bioreactor (AFCMBR) for low-strength wastewater treatment. The AFCMBR was operated continuously for 395days at 25°C using a synthetic wastewater having a chemical oxygen demand (COD) averaging 260mg/L. A membrane net flux as high as 14.5-17L/m(2)h was achieved with only periodic maintenance cleaning, obtained by adding 25mg/L of sodium hypochlorite solution. No adverse effect of the maintenance cleaning on organic removal was observed. An average SCOD in the membrane permeate of 23mg/L was achieved with a 1h hydraulic retention time (HRT). Biosolids production averaged 0.014±0.007gVSS/gCOD removed. The estimated electrical energy required to operate the AFCMBR system was 0.039kWh/m(3), which is only about 17% of the electrical energy that could be generated with the methane produced.

  5. Sockets and Pebbles

    NASA Technical Reports Server (NTRS)

    1997-01-01

    This close-up Sojourner rover image of a small rock shows that weathering has etched-out pebbles to produce sockets. In the image, sunlight is coming from the upper left. Sockets (with shadows on top) are visible at the lower left and pebbles (with bright tops and shadowed bases) are seen at the lower center and lower right. Two pebbles (about 0.5 cm across) are visible at the lower center.

    Mars Pathfinder is the second in NASA's Discovery program of low-cost spacecraft with highly focused science goals. The Jet Propulsion Laboratory, Pasadena, CA, developed and manages the Mars Pathfinder mission for NASA's Office of Space Science, Washington, D.C. JPL is a division of the California Institute of Technology (Caltech).

  6. PEBBLES Operation and Theory Manual

    SciTech Connect

    Joshua J. Cogliati

    2011-02-01

    The PEBBLES manual describes the PEBBLES code. The PEBBLES code is a computer program designed to simulation the motion, packing and vibration of spheres that undergo various mechanical forces including gravitation, Hooke’s law force and various friction forces. The frictional forces include true static friction that allows non-zero angles of repose. Each pebble is individually simulated using the distinct element method.

  7. PEBBLES Operation and Theory Manual

    SciTech Connect

    Joshua J. Cogliati

    2010-09-01

    The PEBBLES manual describes the PEBBLES code. The PEBBLES code is a computer program designed to simulation the motion, packing and vibration of spheres that undergo various mechanical forces including gravitation, Hooke’s law force and various friction forces. The frictional forces include true static friction that allows non-zero angles of repose. Each pebble is individually simulated using the distinct element method.

  8. Pebble Puzzle Solved

    NASA Technical Reports Server (NTRS)

    2004-01-01

    [figure removed for brevity, see original site] Figure 1 In the quest to determine if a pebble was jamming the rock abrasion tool on NASA's Mars Exploration Rover Opportunity, scientists and engineers examined this up-close, approximate true-color image of the tool. The picture was taken by the rover's panoramic camera, using filters centered at 601, 535, and 482 nanometers, at 12:47 local solar time on sol 200 (August 16, 2004).

    Colored spots have been drawn on this image corresponding to regions where panoramic camera reflectance spectra were acquired (see chart in Figure 1). Those regions are: the grinding wheel heads (yellow); the rock abrasion tool magnets (green); the supposed pebble (red); a sunlit portion of the aluminum rock abrasion tool housing (purple); and a shadowed portion of the rock abrasion tool housing (brown). These spectra demonstrated that the composition of the supposed pebble was clearly different from that of the sunlit and shadowed portions of the rock abrasion tool, while similar to that of the dust-coated rock abrasion tool magnets and grinding heads. This led the team to conclude that the object disabling the rock abrasion tool was indeed a martian pebble.

  9. OPERATION PEBBLE. SUMMARY REPORT.

    ERIC Educational Resources Information Center

    NORRED, ROBERT B.

    A COMPREHENSIVE EVALUATION OF OPERATION PEBBLE'S 3 YEAR SUMMER PROGRAM FOR ECONOMICALLY AND EDUCATIONALLY DEPRIVED CHILDREN OF THE UPPER CUMBERLAND REGION OF TENNESSEE IS PRESENTED. THE INTENT OF THE PROJECT WAS TO INVOLVE THE CHILDREN IN EXPERIENCES THAT MIGHT EXPAND THE HORIZONS OF THEIR STAGNANT, HIGHLY STRUCTURED CULTURAL ENVIRONMENT, WITHOUT…

  10. Matrix Formulation of Pebble Circulation in the PEBBED Code

    SciTech Connect

    Gougar, Hans D; Terry, William Knox; Ougouag, Abderrafi Mohammed-El-Ami

    2002-04-01

    The PEBBED technique provides a foundation for equilibrium fuel-cycle analysis and optimization in pebble-bed cores in which the fuel elements are continuously flowing and, if desired, recirculating. In addition to the modern analysis techniques used in, or being developed for, the code, PEBBED incorporates a novel nuclide-mixing algorithm that allows for sophisticated recirculation patterns using a matrix generated from basic core parameters. Derived from a simple partitioning of the pebble flow, the elements of the recirculation matrix are used to compute the spatially averaged density of each nuclide at the entry plane from the nuclide densities of pebbles emerging from the discharge conus. The order of the recirculation matrix is a function of the flexibility and sophistication of the fuel handling mechanism. This formulation for coupling pebble flow and neutronics enables core design and fuel cycle optimization to be performed by manipulating a few key core parameters. The formulation is amenable to modern optimization techniques.

  11. Mechanisms of flow through compressible porous beds in sedimentation, filtration, centrifugation, deliquoring, and ceramic processing

    SciTech Connect

    Tiller, F.M.

    1992-06-01

    The University of Houston research program is aimed at the specific area of solid/liquid separation including sedimentation, thickening, cake filtration, centrifugation, expression, washing, deep-bed filtration, screening, and membrane separation. Unification of the theoretical approaches to the various solid/liquid separation operations is the principle objective of the research. Exploring new aspects of basic separation mechanisms, verification of theory with experiment, development of laboratory procedures for obtaining data for design, optimizing operational methods, and transferring the results to industry are a part of the Houston program. New methodology developed in our program now permits an engineer or scientist to handle thickening, cake filtration, centrigual filtration, and expression in a unified manner. The same fundamental equations are simply adapted to the differing parameters and conditions related to the various modes of separation. As the system is flexible and adaptable to computational software, new developments can continually be added. Discussions of the various research projects in this report have been kept to a minimum and are principally qualitative. The length of the report would be excessive if each topic were covered in depth. Although the number of research topics may appear larger than one would expect, many are closely interconnected and reflect our philosophy of working in apparently diverse fields such as ceramics, mining, wastewater, food, chemical processing, and oil well operations.

  12. From 'smart rocks' come 'brilliant pebbles'

    SciTech Connect

    Wood, L. )

    1990-04-01

    The development of the brilliant pebbles concept as part of the SDI kinetic kill vehicle mechanism is reviewed. The way in which the pebbles collide with a ballistic missile or reentry vehicle is outlined. Consideration is given to the computing capacity of the pebbles, the ground-based control of the pebbles, and the way in which the pebbles maneuver during flight. The pebble autonomy at the system level and at the individual level is described. Plans for the first suborbital pebble test flights and issues concerning the performance of the brilliant pebbles as a ballistic missile defense system are examined.

  13. ASATs vs Brilliant Pebbles

    SciTech Connect

    Speed, R.D.

    1990-03-01

    This paper examines the cost exchange ratio of Brilliant Pebbles satellites when attacked by small, ground-based, non-nuclear ASATs. If the satellites have no defenses, the exchange ratio is likely to be at least 40:1 in favor of the attacker in a general war or 4:1 in his favor in a war of attrition. The use of maneuver, decoys, and space-based defensive rockets to defeat that ASAT threat were examined, but non of these approaches appears to be clearly economically advantageous. 3 figs., 4 tabs.

  14. Pebbles, Cobbles, and Sockets

    NASA Technical Reports Server (NTRS)

    1997-01-01

    This Rover image of 'Shark' (upper left center), 'Half Dome' (upper right), and a small rock (right foreground) reveal textures and structures not visible in lander camera images. These rocks are interpreted as conglomerates because their surfaces have rounded protrusions up to several centimeters in size. It is suggested that the protrusions are pebbles and granules.

    Mars Pathfinder is the second in NASA's Discovery program of low-cost spacecraft with highly focused science goals. The Jet Propulsion Laboratory, Pasadena, CA, developed and manages the Mars Pathfinder mission for NASA's Office of Space Science, Washington, D.C. JPL is a division of the California Institute of Technology (Caltech).

  15. Integrated low emissions cleanup system for direct coal fueled turbines (moving bed, fluid bed contactor/ceramic filter). Twentieth quarterly status report, July--September 1992

    SciTech Connect

    Newby, R.A.; Alvin, M.A.; Bachovchin, D.M.; Yang, W.C.; Smeltzer, E.E.; Lippert, T.E.

    1992-10-20

    The United States Department of Energy, Morgantown Energy Research Center (DOE/METC), is sponsoring the development of direct coal-fired turbine power plants as part of their Heat Engines program. A major technical challenge remaining for the development of the direct coal-fired turbine is high-temperature combustion gas cleaning to meet environmental standards for sulfur oxides and particulate emissions, as well as to provide acceptable turbine life. The Westinghouse Electric Corporation, Science & Technology Center, is evaluating two Integrated Low Emissions Cleanup (ILEC) concepts that have been configured to meat this technical challenge: a baseline ceramic barrier filter ILEC concept, and a fluidized bed ILEC concept. These ILEC concepts simultaneously control sulfur, particulate, and alkali contaminants in the high-pressure combustion gases at turbine inlet temperatures up to 2300{degree}F. This document reports the status of a program in the nineteenth quarter to develop this ILEC technology for direct coal-fired turbine power plants.

  16. Reconstructing the transport history of pebbles on Mars

    PubMed Central

    Szabó, Tímea; Domokos, Gábor; Grotzinger, John P.; Jerolmack, Douglas J.

    2015-01-01

    The discovery of remarkably rounded pebbles by the rover Curiosity, within an exhumed alluvial fan complex in Gale Crater, presents some of the most compelling evidence yet for sustained fluvial activity on Mars. While rounding is known to result from abrasion by inter-particle collisions, geologic interpretations of sediment shape have been qualitative. Here we show how quantitative information on the transport distance of river pebbles can be extracted from their shape alone, using a combination of theory, laboratory experiments and terrestrial field data. We determine that the Martian basalt pebbles have been carried tens of kilometres from their source, by bed-load transport on an alluvial fan. In contrast, angular clasts strewn about the surface of the Curiosity traverse are indicative of later emplacement by rock fragmentation processes. The proposed method for decoding transport history from particle shape provides a new tool for terrestrial and planetary sedimentology. PMID:26460507

  17. Reconstructing the transport history of pebbles on Mars.

    PubMed

    Szabó, Tímea; Domokos, Gábor; Grotzinger, John P; Jerolmack, Douglas J

    2015-10-13

    The discovery of remarkably rounded pebbles by the rover Curiosity, within an exhumed alluvial fan complex in Gale Crater, presents some of the most compelling evidence yet for sustained fluvial activity on Mars. While rounding is known to result from abrasion by inter-particle collisions, geologic interpretations of sediment shape have been qualitative. Here we show how quantitative information on the transport distance of river pebbles can be extracted from their shape alone, using a combination of theory, laboratory experiments and terrestrial field data. We determine that the Martian basalt pebbles have been carried tens of kilometres from their source, by bed-load transport on an alluvial fan. In contrast, angular clasts strewn about the surface of the Curiosity traverse are indicative of later emplacement by rock fragmentation processes. The proposed method for decoding transport history from particle shape provides a new tool for terrestrial and planetary sedimentology.

  18. Reconstructing the transport history of pebbles on Mars

    NASA Astrophysics Data System (ADS)

    Szabó, Tímea; Domokos, Gábor; Grotzinger, John P.; Jerolmack, Douglas J.

    2015-10-01

    The discovery of remarkably rounded pebbles by the rover Curiosity, within an exhumed alluvial fan complex in Gale Crater, presents some of the most compelling evidence yet for sustained fluvial activity on Mars. While rounding is known to result from abrasion by inter-particle collisions, geologic interpretations of sediment shape have been qualitative. Here we show how quantitative information on the transport distance of river pebbles can be extracted from their shape alone, using a combination of theory, laboratory experiments and terrestrial field data. We determine that the Martian basalt pebbles have been carried tens of kilometres from their source, by bed-load transport on an alluvial fan. In contrast, angular clasts strewn about the surface of the Curiosity traverse are indicative of later emplacement by rock fragmentation processes. The proposed method for decoding transport history from particle shape provides a new tool for terrestrial and planetary sedimentology.

  19. High temperature gas-cooled reactor (HTGR) graphite pebble fuel: Review of technologies for reprocessing

    SciTech Connect

    Mcwilliams, A. J.

    2015-09-08

    This report reviews literature on reprocessing high temperature gas-cooled reactor graphite fuel components. A basic review of the various fuel components used in the pebble bed type reactors is provided along with a survey of synthesis methods for the fabrication of the fuel components. Several disposal options are considered for the graphite pebble fuel elements including the storage of intact pebbles, volume reduction by separating the graphite from fuel kernels, and complete processing of the pebbles for waste storage. Existing methods for graphite removal are presented and generally consist of mechanical separation techniques such as crushing and grinding chemical techniques through the use of acid digestion and oxidation. Potential methods for reprocessing the graphite pebbles include improvements to existing methods and novel technologies that have not previously been investigated for nuclear graphite waste applications. The best overall method will be dependent on the desired final waste form and needs to factor in the technical efficiency, political concerns, cost, and implementation.

  20. TEM study of impurity segregations in beryllium pebbles

    NASA Astrophysics Data System (ADS)

    Klimenkov, M.; Chakin, V.; Moeslang, A.; Rolli, R.

    2014-12-01

    Beryllium is planned to be used as a neutron multiplier in the Helium-cooled Pebble Bed European concept of a breeding blanket of demonstration power reactor DEMO. In order to evaluate the irradiation performance, individual pebbles and constrained pebble beds were neutron-irradiated at temperatures typical of fusion blankets. Beryllium pebbles 1 mm in diameter produced by the rotating electrode method were subjected to a TEM study before and after irradiation at High Flux Reactor, Petten, Netherlands at 861 K. The grain size varied in a wide range from sub-micron size up to several tens of micrometers, which indicated formation bimodal grain size distribution. Based on the application of combined electron energy loss spectroscopy and energy dispersive X-ray spectroscopy methods, we suggest that impurity precipitates play an important role in controlling the mechanical properties of beryllium. The impurity elements were present in beryllium at a sub-percent concentration form beryllide particles of a complex (Fe/Al/Mn/Cr)B composition. These particles are often ordered along dislocations lines, forming several micron-long chains. It can be suggested that fracture surfaces often extended along these chains in irradiated material.

  1. Pebble Fuel Handling and Reactivity Control for Salt-Cooled High Temperature Reactors

    SciTech Connect

    Peterson, Per; Greenspan, Ehud

    2015-02-09

    This report documents the work completed on the X-PREX facility under NEUP Project 11- 3172. This project seeks to demonstrate the viability of pebble fuel handling and reactivity control for fluoride salt-cooled high-temperature reactors (FHRs). The research results also improve the understanding of pebble motion in helium-cooled reactors, as well as the general, fundamental understanding of low-velocity granular flows. Successful use of pebble fuels in with salt coolants would bring major benefits for high-temperature reactor technology. Pebble fuels enable on-line refueling and operation with low excess reactivity, and thus simpler reactivity control and improved fuel utilization. If fixed fuel designs are used, the power density of salt- cooled reactors is limited to 10 MW/m3 to obtain adequate duration between refueling, but pebble fuels allow power densities in the range of 20 to 30 MW/m3. This can be compared to the typical modular helium reactor power density of 5 MW/m3. Pebble fuels also permit radial zoning in annular cores and use of thorium or graphite pebble blankets to reduce neutron fluences to outer radial reflectors and increase total power production. Combined with high power conversion efficiency, compact low-pressure primary and containment systems, and unique safety characteristics including very large thermal margins (>500°C) to fuel damage during transients and accidents, salt-cooled pebble fuel cores offer the potential to meet the major goals of the Advanced Reactor Concepts Development program to provide electricity at lower cost than light water reactors with improved safety and system performance.This report presents the facility description, experimental results, and supporting simulation methods of the new X-Ray Pebble Recirculation Experiment (X-PREX), which is now operational and being used to collect data on the behavior of slow dense granular flows relevant to pebble bed reactor core designs. The X

  2. Pebbles on Mars

    NASA Astrophysics Data System (ADS)

    Jerolmack, Douglas J.

    2013-05-01

    Mars is a cold, dry place. Yet there is abundant evidence that fluvial (river) processes have carved the planet's surface; witness deep canyons, streamlined islands, and drainage networks. Most of these features formed more than 3 billion years ago, and a long line of research has led to the "warm and wet early Mars" hypothesis. The idea is that early Mars had a thicker atmosphere with an enhanced greenhouse effect that allowed stable liquid water and a hydrologic cycle to exist. The search for life on Mars, or at least conditions suitable for life, is predicated on this idea. Until now, no observations have unambiguously identified and characterized river-lain sediments, although the Mars Exploration Rovers turned up some evidence of a watery past. As the first major finding from the Mars Science Laboratory mission and its car-sized rover, Curiosity, Williams et al. report on page 1068 of this issue the discovery of conglomerates on Mars - pebbles mixed with sand and turned to rock - resulting from ancient river deposits. The finding provides the clearest view yet on the nature of early martian rivers and should provide momentum for Curiosity's mission moving forward.

  3. Comet Formation in Collapsing Pebble Clouds: Pebble Formation

    NASA Astrophysics Data System (ADS)

    Lorek, Sebastian; Lacerda, Pedro; Blum, Jürgen

    2016-10-01

    The formation of comets by gradual growth from (sub-)micron sized ice and dust monomers to km-sized bodies suffers from growth barriers (bouncing, fragmentation, drift). Growth stalls at sizes between mm and m, rendering it considerably difficult to form km-sized objects. However, the streaming instability and subsequent gravitational collapse of clouds of pebbles (particle agglomerates) provide an alternative. The pebbles require Stokes numbers between 0.01 and 3, which corresponds to sizes between mm and dm, unless the pebbles are very porous. Furthermore, the local solid/gas density ratio must be near unity and the local total mass in solids must be >2-3x higher than the minimum mass solar nebula value (1% of gas mass). The gravitational collapse of the pebble clouds then bypasses the growth barriers, forming km-sized bodies directly. The observed bulk properties of comets, e.g. porosity near 80%, are consistent with this scenario. Okuzumi et al. (2012) showed that including porosity comets can form directly via coagulation from sub-micron monomers. However, this relies on using 0.1 micron monomers and pure sticking collisions. Krijt et al. (2015) included erosion and found that highly porous pebbles around 109 g in mass can form and might trigger the streaming instability. Drazkowska & Dullemond (2014) showed that compact coagulation can lead to triggering the streaming instability. All those studies include only ice and a simplified collision model. However, a large fraction of a comet's mass is dust. Here, we develop a pebble formation model that includes sticking, bouncing, mass transfer/erosion, and fragmentation, as well as porosity. To take dust and ice into account, we extended the collision model for the treatment of mixed pebbles by linearly interpolating the threshold velocities and compression curves between the cases of pure dust and pure ice based on the fractional abundance of dust monomers. Our simulations show that pebble formation with the full

  4. Integrated Low Emissions Cleanup system for direct coal fueled turbines (moving bed, fluid bed contactor/ceramic filter). Twenty-fifth quarterly report, October--December 1993

    SciTech Connect

    Newby, R.A.; Alvin, M.A.; Bachovchin, D.M.; Yang, W.C.; Smeltzer, E.E.; Lippert, T.E.

    1993-12-31

    The United States Department of Energy, Morgantown Energy Research Center (DOE/METC), is sponsoring the development of direct coal-fired turbine power plants as part of their Heat Engines program. A major technical challenge remaining for the development of the direct coal-fired turbine is high-temperature combustion gas cleaning to meet environmental standards for sulfur oxides and particulate emissions, as well as to provide acceptable turbine life. The Westinghouse Electric Corporation, Science & Technology Center, is evaluating two Integrated Low Emissions Cleanup (ILEC) concepts that have been reconfigured to meet this technical challenge: a baseline ceramic barrier filter ILEC concept, and a fluidized bed ILEC concept. These ILEC concepts simultaneously control sulfur, particulate, and alkali contaminants in the high-pressure combustion gases at turbine inlet temperatures up to 2300{degree}F. This document reports the status of a program in the twenty-fifth quarter to develop this ILEC technology for direct coal-fired turbine power plants.

  5. Formation of pebble-pile planetesimals

    NASA Astrophysics Data System (ADS)

    Wahlberg Jansson, Karl; Johansen, Anders

    2014-10-01

    Asteroids and Kuiper belt objects are remnant planetesimals from the epoch of planet formation. The first stage of planet formation is the accumulation of dust and ice grains into mm- and cm-sized pebbles. These pebbles can clump together through the streaming instability and form gravitationally bound pebble clouds. Pebbles inside such a cloud will undergo mutual collisions, dissipating energy into heat. As the cloud loses energy, it gradually contracts towards solid density. We model this process and investigate two important properties of the collapse: (i) the collapse timescale and (ii) the temporal evolution of the pebble size distribution. Our numerical model of the pebble cloud is zero-dimensional and treats collisions with a statistical method. We find that planetesimals with radii larger than ~100 km collapse on the free-fall timescale of ~25 years. Lower-mass clouds have longer pebble collision timescales and collapse much more slowly, with collapse times of a few hundred years for 10 km scale planetesimals and a few thousand years for 1 km scale planetesimals. The mass of the pebble cloud also determines the interior structure of the resulting planetesimal. The pebble collision speeds in low-mass clouds are below the threshold for fragmentation, forming pebble-pile planetesimals consisting of the primordial pebbles from the protoplanetary disk. Planetesimals above 100 km in radius, on the other hand, consist of mixtures of dust (pebble fragments) and pebbles which have undergone substantial collisions with dust and other pebbles. The Rosetta mission to the comet 67P/Churyumov-Gerasimenko and the New Horizons mission to Pluto will provide valuable information about the structure of planetesimals in the solar system. Our model predicts that 67P is a pebble-pile planetesimal consisting of primordial pebbles from the solar nebula, while the pebbles in the cloud which contracted to form Pluto must have been ground down substantially during the collapse.

  6. What is in a pebble shape?

    PubMed

    Durian, D J; Bideaud, H; Duringer, P; Schröder, A; Thalmann, F; Marques, C M

    2006-07-14

    We propose to characterize the shapes of flat pebbles in terms of the statistical distribution of curvatures measured along the pebble contour. This is demonstrated for the erosion of clay pebbles in a controlled laboratory apparatus. Photographs at various stages of erosion are analyzed, and compared with two models. We find that the curvature distribution complements the usual measurement of aspect ratio, and connects naturally to erosion processes that are typically faster at protruding regions of high curvature.

  7. Pebble ingestion: an unusual form of geophagia.

    PubMed

    Robertson, W D; Crabtree, J B

    1977-07-01

    Reported is a case representing an unusual form of geophagia, in which ingestion of pebbles by a 27-year-old mentally retarded woman resulted in impaction and complete filling of the colon with pebbles. Conservative therapy was successful in clearing the stones by the sixth day of treatment; however, a follow-up visit approximately six weeks later revealed that the patient was again ingesting pebbles.

  8. The geology of the Florida land-pebble phosphate deposits

    USGS Publications Warehouse

    Cathcart, J.B.; Blade, L.V.; Davidson, D.F.; Ketner, K.B.

    1952-01-01

    The land-pebble phosphate district is on the Gulf Coastal Plain of Florida. The phosphate deposits are in the Bone Valley formation, dated Pliocene by most writers. These strata overlie the Miocene Hawthorn formation and are overlain by consolidated sands 3 to 20 feet thick. The minable phosphate deposits, called “matrix” in the district, range from a featheredge to about 50 feet in thickness and consist of phosphatic pellets and nodules, quartz sand, and montmorillonitic clay in about equal proportions. Locally the matrix displays cross-bedding and horizontal laminations, but elsewhere it is structureless. The phosphorite particles, composed largely of carbonate-fluorapatite, range in diameter from less than 0.1 mm to about 60 cm and in P2O5 content from 30 to 36 percent. Coarse-pebble deposits, containing 30 to 34 percent P2O5 are found mainly on basement highs; and fine-pebble deposits, containing 32 to 36 percent P2O5 are, are found in basement lows. Deposits in the northern part of the field contain more phosphate particles and their P2O5 content is higher than those in the southern part. The upper part of the phosphatic strata is leached to an advanced degree and consists of quartz sand and clay-sized particules of pseudowavellite and wavellite. The leached zone ranges in thickness from a featheredge to 60 feet. The origin of the land-pebble deposits is incompletely known. Possible modes of origin are a residuum of Miocene age, or a reworked residuum of Pliocene or Quaternary age.

  9. Postirradiation examination of beryllium pebbles

    SciTech Connect

    Gelles, D.S.

    1998-03-01

    Postirradiation examinations of COBRA-1A beryllium pebbles irradiated in the EBR-II fast reactor at neutron fluences which generated 2700--3700 appm helium have been performed. Measurements included density change, optical microscopy, scanning electron microscopy, and transmission electron microscopy. The major change in microstructure is development of unusually shaped helium bubbles forming as highly non-equiaxed thin platelet-like cavities on the basal plane. Measurement of the swelling due to cavity formation was in good agreement with density change measurements.

  10. Molecular dynamics simulation for PBR pebble tracking simulation via a random walk approach using Monte Carlo simulation.

    PubMed

    Lee, Kyoung O; Holmes, Thomas W; Calderon, Adan F; Gardner, Robin P

    2012-05-01

    Using a Monte Carlo (MC) simulation, random walks were used for pebble tracking in a two-dimensional geometry in the presence of a biased gravity field. We investigated the effect of viscosity damping in the presence of random Gaussian fluctuations. The particle tracks were generated by Molecular Dynamics (MD) simulation for a Pebble Bed Reactor. The MD simulations were conducted in the interaction of noncohesive Hertz-Mindlin theory where the random walk MC simulation has a correlation with the MD simulation. This treatment can easily be extended to include the generation of transient gamma-ray spectra from a single pebble that contains a radioactive tracer. Then the inverse analysis thereof could be made to determine the uncertainty of the realistic measurement of transient positions of that pebble by any given radiation detection system designed for that purpose.

  11. Planetary growth by the accretion of pebbles

    NASA Astrophysics Data System (ADS)

    Lambrechts, Michiel; Johansen, Anders; Bitsch, Bertram; Morbidelli, Alessandro

    2015-11-01

    Pebbles, approximately cm-sized solids that drift through a protoplanetary disc, provide a reservoir of material that can be efficiently accreted by planetary embryos due to the dissipating effect of gas drag (Lambrechts & Johansen, 2012).Here, we will highlight the robust implications of pebble accretion on the formation of planets throughout the protoplanetary disc.In the outer disc, icy pebbles form by coagulation and consequently start drifting inwards. Nevertheless, we find that the pebble surface densities are sufficiently high to form giant planets on wide orbits, before the gas disc disperses after a few Myr (Lambrechts & Johansen, 2014). Growth is only halted when cores reach sizes of around 10 Earth masses, when their gravity creates pressure bumps trapping the inwards drifting pebbles.This accretion cutoff triggers the attraction of a massive gaseous envelope. Additionally, the fast growth of giant planets prevents the loss of the cores by type-I migration (Lambrechts et al 2014, Bitsch et al 2015).Closer to the star, interior to the ice line, pebble accretion takes on a different form. There, chondrule-sized particles lead to the formation of much smaller, Mars-sized embryos, before the pebble flux is terminated by the growth of the gas giants (Morbidelli et al, 2015). We will also discuss ongoing work on the conditions under which much larger Super-Earths can form.

  12. Stability and convergence analysis of the quasi-dynamics method for the initial pebble packing

    SciTech Connect

    Li, Y.; Ji, W.

    2012-07-01

    The simulation for the pebble flow recirculation within Pebble Bed Reactors (PBRs) requires an efficient algorithm to generate an initial overlap-free pebble configuration within the reactor core. In the previous work, a dynamics-based approach, the Quasi-Dynamics Method (QDM), has been proposed to generate densely distributed pebbles in PBRs with cylindrical and annular core geometries. However, the stability and the efficiency of the QDM were not fully addressed. In this work, the algorithm is reformulated with two control parameters and the impact of these parameters on the algorithm performance is investigated. Firstly, the theoretical analysis for a 1-D packing system is conducted and the range of the parameter in which the algorithm is convergent is estimated. Then, this estimation is verified numerically for a 3-D packing system. Finally, the algorithm is applied to modeling the PBR fuel loading configuration and the convergence performance at different packing fractions is presented. Results show that the QDM is efficient in packing pebbles within the realistic range of the packing fraction in PBRs, and it is capable in handling cylindrical geometry with packing fractions up to 63.5%. (authors)

  13. Pebbly mudstones in the Cretaceous Pigeon Point Formation, western California: a study in the transitional stages from submarine slumps to cohesive debris flows

    NASA Astrophysics Data System (ADS)

    López-Gamundí, Oscar R.

    1993-04-01

    The pebbly mudstones in the Late Cretaceous Pigeon Point Formation originated by slumping and related debris-flow processes in a submarine canyon/slope depositional system. The sedimentary characteristics of the pebbly mudstones (PM) enable the distinction of two main varieties: (a) heterogeneous or "patchy" pebbly mudstones (PPM) exhibiting irregular bed geometries and diffuse to irregular bed contacts, with maximum clast sizes in intraformational boulder-sized population, including abundant rip-up mudstone and sandstone clasts with common soft sediment deformations; (b) homogeneous pebbly mudstones (HPM) with tabular bed geometries, non-erosive and almost flat bed contacts, maximum clast sizes in extraformational pebble-sized fraction and scarce to absent soft-sediment deformations. The two varieties of pebbly mudstone represent the mechanical transition from slumps to cohesive debris flows. The presence of abundant intraformational clasts and disrupted, yet preserved slump-fold features in the PPM suggest that this facies represents a stage closer to the slump end-member. As the shear-strain progressed and a fully remolded cohesive debris flow developed, an almost complete disaggregation of the poorly consolidated sand and mud clasts and the incorporation into the remolded "matrix" phase took place.

  14. Giant planet formation with pebble accretion

    NASA Astrophysics Data System (ADS)

    Chambers, J. E.

    2014-05-01

    In the core accretion model for giant planet formation, a solid core forms by coagulation of dust grains in a protoplanetary disk and then accretes gas from the disk when the core reaches a critical mass. Both stages must be completed in a few million years before the disk gas disperses. The slowest stage of this process may be oligarchic growth in which a giant-planet core grows by sweeping up smaller, asteroid-size planetesimals. Here, we describe new numerical simulations of oligarchic growth using a particle-in-a-box model. The simulations include several processes that can effect oligarchic growth: (i) planetesimal fragmentation due to mutual collisions, (ii) the modified capture rate of planetesimals due to a core’s atmosphere, (iii) drag with the disk gas during encounters with the core (so-called “pebble accretion”), (iv) modification of particle velocities by turbulence and drift caused by gas drag, (v) the presence of a population of mm-to-m size “pebbles” that represent the transition point between disruptive collisions between larger particles, and mergers between dust grains, and (vi) radial drift of small objects due to gas drag. Collisions between planetesimals rapidly generate a population of pebbles. The rate at which a core sweeps up pebbles is controlled by pebble accretion dynamics. Metre-size pebbles lose energy during an encounter with a core due to drag, and settle towards the core, greatly increasing the capture probability during a single encounter. Millimetre-size pebbles are tightly coupled to the gas and most are swept past the core during an encounter rather than being captured. Accretion efficiency per encounter increases with pebble size in this size range. However, radial drift rates also increase with size, so metre-size objects encounter a core on many fewer occasions than mm-size pebbles before they drift out of a region. The net result is that core growth rates vary weakly with pebble size, with the optimal diameter

  15. Problems and Promises of Pebble Accretion

    NASA Astrophysics Data System (ADS)

    Kretke, Katherine A.; Levison, H. F.

    2013-05-01

    Abstract (2,250 Maximum Characters): Despite the large number of exoplanets indicating that planets are a common outcome of the star formation process, theoretical models still struggle to explain how ~10 Earth mass rocky/icy embryos can form within the lifetimes of gaseous circumstellar disks. Recently, aerodynamic-aided accretion of ``pebbles,'' particles ranging from millimeters to decimeters in size, has been suggested as a potential solution to this long-standing problem. Local simulations, simulations which look at the detailed behavior of these pebbles in the vicinity of a planetary embryo, have shown that the potential planetary growth rates can be surprisingly fast. If one assumes that most of the mass in a protoplanetary disk resides in these pebble-sized particles, a Mars mass core could grow to 10 Earth masses in only a few thousand years. However, these local studies cannot investigate how this accretion process behaves in the more complicated, multi-planet environment. We have incorporated a prescription of this pebble accretion into LIPAD, a Lagrangian code which can follow the collisional/accretional/dynamical evolution of a planetary system, to investigate the how this pebble accretion will manifest itself in the larger planet formation picture. We discuss how these more comprehensive models present challenges for using pebble accretion to form observed planetary systems.

  16. Promises and Problems of Pebble Accretion

    NASA Astrophysics Data System (ADS)

    Kretke, Katherine A.; Levison, H. F.

    2013-10-01

    Despite the large number of exoplanets indicating that giant planets are a common outcome of the star formation process, theoretical models still struggle to explain how ~10 Earth mass rocky/icy embryos can form within the lifetimes of gaseous circumstellar disks. In recent years, aerodynamic-aided accretion of ``pebbles,'' particles ranging from millimeters to decimeters in size, has been suggested as a potential solution to this long-standing problem. Local simulations, simulations which look at the detailed behavior of these pebbles in the vicinity of a planetary embryo, have shown that the potential planetary growth rates can be surprisingly fast. If one assumes that most of the mass in a protoplanetary disk resides in these pebble-sized particles, a Mars mass core could grow to 10 Earth masses in only a few thousand years. However, these local studies cannot investigate how this accretion process behaves in the more complicated, multi-planet environment. We have incorporated the local accretion physics into LIPAD, a Lagrangian code which can follow the collisional / accretional / dynamical evolution of a planetary system, to investigate the how this pebble accretion will manifest itself in the larger planet formation picture. We present how these more comprehensive models raise challenges to using pebble accretion to form observed planetary systems.

  17. Nanoparticle PEBBLE sensors in live cells.

    PubMed

    Lee, Yong-Eun Koo; Kopelman, Raoul

    2012-01-01

    Live cell studies are of fundamental importance to the life sciences and their medical applications. Nanoparticle (NP)-based sensor platforms have many advantages as sensors for intracellular measurements, due to their flexible engineerability, noninvasive nature (due to their nano-size and nontoxic matrix), and, for some of the NPs, intrinsic optical properties. NP-based fluorescent sensors for intracellular measurements, so called PEBBLE sensors, have been developed for many important intracellular analytes and functions, including ions, small molecules, reactive oxygen species, physical properties, and enzyme activities, which are involved in many chemical, biochemical, and physical processes taking place inside the cell. PEBBLE sensors can be used with a standard microscope for simultaneous optical imaging of cellular structures and sensing of composition and function, just like investigations performed with molecular probes. However, PEBBLE sensors of any design and matrix can be delivered into cells by several standard methods, unlike dye molecules that need to be cell permeable. Furthermore, new sensing possibilities are enabled by PEBBLE nanosensors, which are not possible with molecular probes. This review summarizes a variety of designs of the PEBBLE sensors, their characteristics, and their applications to cells.

  18. Pebble bed reactor fiscal year 1980: review summary report

    SciTech Connect

    Not Available

    1980-07-01

    Information on high-temperature reactor development is presented concerning reactor operating experience; core performance assessment; core control and shutdown; reflector and core support; maintenance and availability; safety aspects of PBR and prismatic comparison; PCRV dimensions; and fuel reprocessing cost estimate.

  19. A Pebble-Bed Breed-and-Burn Reactor

    SciTech Connect

    Greenspan, Ehud

    2016-03-31

    The primary objective of this project is to use three-dimensional fuel shuffling in order to reduce the minimum peak radiation damage of ~550 dpa present Breed-and-Burn (B&B) fast nuclear reactor cores designs (they feature 2-D fuel shuffling) call for to as close as possible to the presently accepted value of 200 dpa thereby enabling earlier commercialization of B&B reactors which could make substantial contribution to energy sustainability and economic stability without need for fuel recycling. Another objective is increasing the average discharge burnup for the same peak discharge burnup thereby (1) increasing the fuel utilization of 2-D shuffled B&B reactors and (2) reducing the reprocessing capacity required to support a given capacity of FRs that are to recycle fuel.

  20. Pebble Jammed in Rock Abrasion Tool

    NASA Technical Reports Server (NTRS)

    2004-01-01

    After the rock abrasion tool on NASA's Mars Exploration Rover Opportunity stopped working on sol 199 (Aug. 15, 2004), rover operators used the panoramic camera to take this image the next day for help in diagnosing the problem. The tool was closer than the camera could focus on sharply, but the image does show a dark spot just left of center, which engineers have determined is likely to be a pebble jammed between the cutting-blade rotor and the wire-brush rotor. If that diagnosis is confirmed by further analysis, the tool will likely be commanded to turn the rotors in reverse to release the pebble.

  1. Controls on pebbles size and shape in streams of the Swiss Alps

    NASA Astrophysics Data System (ADS)

    Litty, Camille; Schlunegger, Fritz

    2016-04-01

    Rivers in the Swiss Alps have been analyzed to determine the relationships between fluvial processes and grain size and shape to emphasize the factors controlling the grain characteristics. 18 bars of gravel-bed rivers have been sampled. At each site the long axis and the intermediate axis of about 500 pebbles have been measured. In addition the morphometric properties of each river basin have been studied. Looking for correlation between grain size and shape and other fluvial properties the study shows that grain size and shape are mainly controlled by the lithology on which the rivers are mainly flowing and by the supply of material through mass failure processes. Deposits of rivers flowing on sedimentary lithology are better sorted and the pebbles are more rounds and have smoother surface than the deposits of rivers flowing on metamorphic lithology. The percentage of hillslopes angles ranging between 20 and 30° correlate with the coarser fraction of the pebbles in all the studied streams. These hillslopes angles ranging between 20 and 30° reflect threshold conditions for failure and so it appeared that mass failure processes along the streams impact the grain size population through the supply of coarse grained material. However, no correlations have been found between grain size and shape and erosion rate, hydrological conditions or basins metric properties. The lack of correlation between grain size and shape and the water discharge is mainly explained by the fact that the streams of the Swiss Alps are in a supply limited state. Remarkably for all these different pebbles size and river/basin properties, the ratio of the intermediate axis and the long axis only ranges between 0.63 and 0.72 without any relationships with the lithology. This ratio named the elongation E is not impacted by any of the analyzed river processes in the studied rivers. Pebbles' size and shape reflect the sediment dynamics and can be used to explore the controls of river processes on

  2. Ceramic fiber ceramic matrix filter development

    SciTech Connect

    Judkins, R.R.; Stinton, D.P.; Smith, R.G.; Fischer, E.M.

    1994-09-01

    The objectives of this project were to develop a novel type of candle filter based on a ceramic fiber-ceramic matrix composite material, and to extend the development to full-size, 60-mm OD by 1-meter-long candle filters. The goal is to develop a ceramic filter suitable for use in a variety of fossil energy system environments such as integrated coal gasification combined cycles (IGCC), pressurized fluidized-bed combustion (PFBC), and other advanced coal combustion environments. Further, the ceramic fiber ceramic matrix composite filter, hereinafter referred to as the ceramic composite filter, was to be inherently crack resistant, a property not found in conventional monolithic ceramic candle filters, such as those fabricated from clay-bonded silicon carbide. Finally, the adequacy of the filters in the fossil energy system environments is to be proven through simulated and in-plant tests.

  3. Pebble Accretion and the Diversity of Planetary Systems

    NASA Astrophysics Data System (ADS)

    Chambers, J. E.

    2016-07-01

    This paper examines the standard model of planet formation, including pebble accretion, using numerical simulations. Planetary embryos that are large enough to become giant planets do not form beyond the ice line within a typical disk lifetime unless icy pebbles stick at higher speeds than in experiments using rocky pebbles. Systems like the solar system (small inner planets and giant outer planets) can form if icy pebbles are stickier than rocky pebbles, and if the planetesimal formation efficiency increases with pebble size, which prevents the formation of massive terrestrial planets. Growth beyond the ice line is dominated by pebble accretion. Most growth occurs early, when the surface density of the pebbles is high due to inward drift of the pebbles from the outer disk. Growth is much slower after the outer disk is depleted. The outcome is sensitive to the disk radius and turbulence level, which control the lifetime and maximum size of pebbles. The outcome is sensitive to the size of the largest planetesimals because there is a threshold mass for the onset of pebble accretion. The planetesimal formation rate is unimportant, provided that some large planetesimals form while the pebbles remain abundant. Two outcomes are seen, depending on whether pebble accretion begins while the pebbles are still abundant. Either multiple gas-giant planets form beyond the ice line, small planets form close to the star, and a Kuiper-belt-like disk of bodies is scattered outward by the giant planets; or no giants form and the bodies remain an Earth-mass or smaller.

  4. Mechanisms of flow through compressible porous beds in sedimentation, filtration, centrifugation, deliquoring, and ceramic processing. [Annual report], February 1, 1991--January 31, 1992

    SciTech Connect

    Tiller, F.M.

    1992-06-01

    The University of Houston research program is aimed at the specific area of solid/liquid separation including sedimentation, thickening, cake filtration, centrifugation, expression, washing, deep-bed filtration, screening, and membrane separation. Unification of the theoretical approaches to the various solid/liquid separation operations is the principle objective of the research. Exploring new aspects of basic separation mechanisms, verification of theory with experiment, development of laboratory procedures for obtaining data for design, optimizing operational methods, and transferring the results to industry are a part of the Houston program. New methodology developed in our program now permits an engineer or scientist to handle thickening, cake filtration, centrigual filtration, and expression in a unified manner. The same fundamental equations are simply adapted to the differing parameters and conditions related to the various modes of separation. As the system is flexible and adaptable to computational software, new developments can continually be added. Discussions of the various research projects in this report have been kept to a minimum and are principally qualitative. The length of the report would be excessive if each topic were covered in depth. Although the number of research topics may appear larger than one would expect, many are closely interconnected and reflect our philosophy of working in apparently diverse fields such as ceramics, mining, wastewater, food, chemical processing, and oil well operations.

  5. Pebbles and Cobbles at MPF Site

    NASA Technical Reports Server (NTRS)

    1997-01-01

    Pebbles are seen in lander images, along with cobbles. For example, in this picture, we see the same pebbles that were visible in the Sojourner rover image of the 'Cabbage Patch' (PIA00984). In addition, a cobble within the rock 'Lamb' (upper left) is apparent. This indicates that Lamb may be a conglomerate (Lamb is 0.32 m x 0.15 m).

    Mars Pathfinder is the second in NASA's Discovery program of low-cost spacecraft with highly focused science goals. The Jet Propulsion Laboratory, Pasadena, CA, developed and manages the Mars Pathfinder mission for NASA's Office of Space Science, Washington, D.C. JPL is a division of the California Institute of Technology (Caltech). The Imager for Mars Pathfinder (IMP) was developed by the University of Arizona Lunar and Planetary Laboratory under contract to JPL. Peter Smith is the Principal Investigator.

  6. Sojourner Rover View of Sockets and Pebbles

    NASA Technical Reports Server (NTRS)

    1997-01-01

    Well-rounded objects, like the ones in this image, were not seen at the Viking sites. These are thought to be pebbles liberated from sedimentary rocks composed of cemented silts, sands and rounded fragments; such rocks are called conglomerates. The 'sockets' could be the former sites of such pebbles.

    NOTE: original caption as published in Science Magazine

    Mars Pathfinder is the second in NASA's Discovery program of low-cost spacecraft with highly focused science goals. The Jet Propulsion Laboratory, Pasadena, CA, developed and manages the Mars Pathfinder mission for NASA's Office of Space Science, Washington, D.C. JPL is a division of the California Institute of Technology (Caltech).

  7. Tritium analyses of COBRA-1A2 beryllium pebbles

    SciTech Connect

    Baldwin, D.L.

    1998-03-01

    Selected tritium measurements have been completed for the COBRA-1A2 experiment C03 and D03 beryllium pebbles. The completed results, shown in Tables 1, 2, and 3, include the tritium assay results for the 1-mm and 3-mm C03 pebbles, and the 1-mm D03 pebbles, stepped anneal test results for both types of 1-mm pebbles, and the residual analyses for the stepped-anneal specimens. All results have been reported with date-of-count and are not corrected for decay. Stepped-anneal tritium release response is provided in addenda.

  8. Pebble fuel design for the PB-FHR

    SciTech Connect

    Cisneros, A. T.; Scarlat, R. O.; Laufer, M. R.; Greenspan, E.; Peterson, P. F.

    2012-07-01

    This paper presents the results of parametric studies of pebble fuel that can guide the design of future PB-FHR cores. The pebble fuel designs are assessed using the following performance characteristics: burnup, reactivity feedback, transient response, timescale to reach equilibrium cycle, and protection of structural components. The performance of a thorium pebble blanket is assessed by comparing against a seed-only system and system that utilizes a graphite pebble reflector instead of a thorium blanket. This paper presents the functional requirements and a methodology to assess these fuel pebble designs. This paper identifies a feasible design space for low enriched uranium pebbles and selected a baseline pebble design for safe, economic energy generation. Furthermore, this study finds a thorium blanket does not increase the performance of the system significantly with respect to a graphite pebble reflector. Therefore, a graphite pebble reflector is recommended in the baseline full-core design to extend the lifetime of the outer solid graphite reflector to the life of plant. (authors)

  9. Giant planet formation via pebble accretion

    NASA Astrophysics Data System (ADS)

    Guilera, O. M.

    2016-08-01

    In the standard model of core accretion, the formation of giant planets occurs by two main processes: first, a massive core is formed by the accretion of solid material; then, when this core exceeds a critical value (typically greater than ) a gaseous runaway growth is triggered and the planet accretes big quantities of gas in a short period of time until the planet achieves its final mass. Thus, the formation of a massive core has to occur when the nebular gas is still available in the disk. This phenomenon imposes a strong time-scale constraint in the giant planet formation due to the fact that the lifetimes of the observed protoplanetary disks are in general lower than 10 Myr. The formation of massive cores before 10 Myr by accretion of big planetesimals (with radii 10 km) in the oligarchic growth regime is only possible in massive disks. However, planetesimal accretion rates significantly increase for small bodies, especially for pebbles, particles of sizes between mm and cm, which are strongly coupled with the gas. In this work, we study the formation of giant planets incorporating pebble accretion rates in our global model of planet formation.

  10. Tissue distribution of PEBBLE RNA and pebble protein during Drosophila embryonic development.

    PubMed

    Prokopenko, S N; Saint, R; Bellen, H J

    2000-02-01

    pebble (pbl) is required for cytokinesis during postblastoderm mitoses (Hime, G., Saint, R., 1992. Zygotic expression of the pebble locus is required for cytokinesis during the postblastoderm mitoses of Drosophila. Development 114, 165-171; Lehner, C.F., 1992. The pebble gene is required for cytokinesis in Drosophila. J. Cell Sci. 103, 1021-1030) and encodes a putative guanine nucleotide exchange factor (RhoGEF) for Rho1 GTPase (Prokopenko, S.N., Brumby, A., O'Keefe, L., Prior, L., He, Y., Saint, R., Bellen, H.J., 1999. A putative exchange factor for Rho1 GTPase is required for initiation of cytokinesis in Drosophila. Genes Dev. 13, 2301-2314). Mutations in pbl result in the absence of a contractile ring leading to a failure of cytokinesis and formation of polyploid multinucleate cells. Analysis of the subcellular distribution of PBL demonstrated that during mitosis, PBL accumulates at the cleavage furrow at the anaphase to telophase transition when assembly of a contractile ring is initiated (Prokopenko, S.N., Brumby, A., O'Keefe, L., Prior, L., He, Y., Saint, R., Bellen, H.J., 1999. A putative exchange factor for Rho1 GTPase is required for initiation of cytokinesis in Drosophila. Genes Dev. 13, 2301-2314). In addition, levels of PBL protein cycle during each round of cell division with the highest levels of PBL found in telophase and interphase nuclei. Here, we report the expression pattern of pbl during embryonic development. We show that PEBBLE RNA and PBL protein have a similar tissue distribution and are expressed in a highly dynamic pattern throughout embryogenesis. We show that PBL is strongly enriched in dividing nuclei in syncytial embryos and in pole cells as well as in nuclei of dividing cells in postblastoderm embryos. Our expression data correlate well with the phenotypes observed in pole cells and, particularly, with the absence of cytokinesis after cellular blastoderm formation in pbl mutants.

  11. Deleterious Thermal Effects due to Randomized Flow Paths in Pebble Bed, and Particle Bed Style Reactors

    NASA Technical Reports Server (NTRS)

    Moran, Robert P.

    2013-01-01

    Reactor fuel rod surface area that is perpendicular to coolant flow direction (+S) i.e. perpendicular to the P creates areas of coolant stagnation leading to increased coolant temperatures resulting in localized changes in fluid properties. Changes in coolant fluid properties caused by minor increases in temperature lead to localized reductions in coolant mass flow rates leading to localized thermal instabilities. Reductions in coolant mass flow rates result in further increases in local temperatures exacerbating changes to coolant fluid properties leading to localized thermal runaway. Unchecked localized thermal runaway leads to localized fuel melting. Reactor designs with randomized flow paths are vulnerable to localized thermal instabilities, localized thermal runaway, and localized fuel melting.

  12. Provenance of the Subinal Formation, Central Guatemala, Based on Point-Counting of Pebbles in Conglomerates

    NASA Astrophysics Data System (ADS)

    Gutierrez, A.; Martens, U.

    2007-05-01

    milky quartz. Pebbles were probably derived from the underlying Padre Miguel volcanics that occur within the Chortis block, not from rock units in the Motagua suture zone. Pebbles contained in red beds in the Motagua valley were derived from rock units of the Motagua suture and the southern margin of the Maya block, but provenance from rock of the Chortis block is not clear. These findings suggest that red-bed-bearing basins in the Motagua valley and in the southeast of Guatemala were not connected, and may have formed at disparate times.

  13. Diverse eucritic pebbles in the Vaca Muerta mesosiderite

    NASA Astrophysics Data System (ADS)

    Rubin, A. E.; Jerde, E. A.

    1987-06-01

    Seven 5-cm basaltic pebbles from the Vaca Muerta mesosiderite were studied by neutron activation and electron microprobe analysis, and three additional pebbles were studied petrographically. The cumulate pebbles had low REE concentrations and high Eu/Sm ratios, indicating the absence of intercumulus liquid. Siderophile interelement ratios were similar to those found in Vaca Muerta metal except for anomalously low Ir concentrations. The presence of 20 percent impact-melt breccias among the pebbles and 35-40 percent melt breccias among the mesosiderite whole-rocks suggests that the mesosiderites were more extensively impact melted than the howardites. Three alternative models to explain this greater proportion of impact-melted material among the mesosiderites are proposed.

  14. 19. LOOKING NORTH ALONG ROAD BISECTING SITE; PEBBLE LIME SILO ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    19. LOOKING NORTH ALONG ROAD BISECTING SITE; PEBBLE LIME SILO ON THE RIGHT, MAIN SUPPLY BUILDING AND MACHINE SHOP ON THE LEFT. - Standard Lime & Stone Quarry, County Route 27, Millville, Jefferson County, WV

  15. Diverse eucritic pebbles in the Vaca Muerta mesosiderite

    NASA Technical Reports Server (NTRS)

    Rubin, Alan E.; Jerde, Eric A.

    1987-01-01

    Seven 5-cm basaltic pebbles from the Vaca Muerta mesosiderite were studied by neutron activation and electron microprobe analysis, and three additional pebbles were studied petrographically. The cumulate pebbles had low REE concentrations and high Eu/Sm ratios, indicating the absence of intercumulus liquid. Siderophile interelement ratios were similar to those found in Vaca Muerta metal except for anomalously low Ir concentrations. The presence of 20 percent impact-melt breccias among the pebbles and 35-40 percent melt breccias among the mesosiderite whole-rocks suggests that the mesosiderites were more extensively impact melted than the howardites. Three alternative models to explain this greater proportion of impact-melted material among the mesosiderites are proposed.

  16. The delivery of PEBBLE nanosensors to measure the intracellular environment.

    PubMed

    Webster, A; Coupland, P; Houghton, F D; Leese, H J; Aylott, J W

    2007-06-01

    Cellular introduction of PEBBLEs (photonic explorers for bioanalysis with biologically localized embedding) has been investigated by a wide variety of methods in a range of cell types. These methods include surface functionalization with CPPs (cell-penetrating peptides), pinocytosis, commercial lipid transfection agents, cytochalasin D, picoinjection, and Gene gun bombardment. This paper will overview several of the most popular methods used for the introduction of PEBBLE nanosensors to the cellular environment and discuss the efficacy of the techniques.

  17. Recovery and recycling of lithium value from spent lithium titanate (Li2TiO3) pebbles

    NASA Astrophysics Data System (ADS)

    Mandal, D.

    2013-09-01

    In the first generation fusion reactors the fusion of deuterium (D) and tritium (T) is considered to produce energy to meet the future energy demand. Deuterium is available in nature whereas, tritium is not. Lithium-6 (Li6) isotope has the ability to produce tritium in the n, α nuclear reaction with neutrons. Thus lithium-based ceramics enriched by Li6 isotope are considered for the tritium generation for its use in future fusion reactors. Lithium titanate is one such Li-based ceramic material being considered for its some attractive properties viz., high thermal and chemical stability, high thermal conductivity, and low tritium solubility. It is reported in the literature, that the burn up of these pebbles in the fusion reactor will be limited to only 15-17 atomic percentage. At the end of life, the pebbles will contain more than 45% unused Li6 isotope. Due to the high cost of enriched Li6 and the waste disposal considerations, it is necessary to recover the unused Li from the spent lithium titanate pebbles. Till date, only the feasibilities of different processes are reported, but no process details are available. Experiments were carried out for the recovery of Li from simulated Li2TiO3 pebbles and to reuse of lithium in lithium titanate pebble fabrication. The details of the experiments and results are discussed in this paper. Simulated lithium titanate (Li2TiO3) pebbles. The objective of the study is to develop a process which can be used to recover lithium value form the spent Li2TiO3 pebbles from future fusion reactor. The Li2TiO3 pebbles used in the study were synthesized and fabricated by the solid state reaction process developed by Mandal et al. described in details somewhere else [1,2]. Spherical Li2TiO3 pebbles of size 1.0 mm were used and the properties of the Li2TiO3 pebbles used in the study are shown in Table 1. Hydrochloric acid (HCl), of 99.8% purity, purchased from Merck and Loba Chemicals, Mumbai, India. To leach lithium from Li2TiO3

  18. A method for estimating maximum static rainfall retention in pebble mulches used for soil moisture conservation

    NASA Astrophysics Data System (ADS)

    Peng, Hongtao; Lei, Tingwu; Jiang, Zhiyun; Horton, Robert

    2016-06-01

    Mulching of agricultural fields and gardens with pebbles has long been practiced to conserve soil moisture in some semi-arid regions with low precipitation. Rainfall interception by the pebble mulch itself is an important part of the computation of the water balance for the pebble mulched fields and gardens. The mean equivalent diameter (MED) was used to characterize the pebble size. The maximum static rainfall retention in pebble mulch is based on the water penetrating into the pores of pebbles, the water adhering to the outside surfaces of pebbles and the water held between pebbles of the mulch. Equations describing the water penetrating into the pores of pebbles and the water adhering to the outside surface of pebbles are constructed based on the physical properties of water and the pebble characteristics. The model for the water between pebbles of the mulch is based on the basic equation to calculate the water bridge volume and the basic coordination number model. A method to calculate the maximum static rainfall retention in the pebble mulch is presented. Laboratory rain simulation experiments were performed to test the model with measured data. Paired sample t-tests showed no significant differences between the values calculated with the method and the measured data. The model is ready for testing on field mulches.

  19. The pebble gene is required for cytokinesis in Drosophila.

    PubMed

    Lehner, C F

    1992-12-01

    Cytokinesis is developmentally controlled during Drosophila embryogenesis. It is omitted during the initial nuclear division cycles. The nuclei of the resulting syncytium are then cellularized at a defined stage, and cytokinesis starts in somatic cells with mitosis 14. However, cytokinesis never occurs in somatic cells of embryos homozygous or transheterozygous for mutations in the pebble gene. Interestingly, the process of cellularization, which involves steps mechanistically similar to cytokinesis, is not affected. Moreover, all the nuclear aspects of mitosis (nuclear envelope breakdown, chromosome condensation, spindle assembly and function) proceed normally in pebble mutant embryos, indicating that pebble is specifically required for the coordination of mitotic spindle and contractile ring functions. The pebble phenotype is also observed, but only with very low penetrance, during the early divisions of the germ line progenitors (the pole cells). alpha-Amanitin injection experiments indicate that these early pole cell divisions, the first cell divisions during embryogenesis, do not require zygotic gene expression. These divisions might therefore rely on maternally contributed pebble function. The maternal contribution from heterozygous mothers might be insufficient in rare cases for all the pole cell divisions.

  20. Bacillus endolithicus sp. nov., isolated from pebbles.

    PubMed

    Parag, B; Sasikala, Ch; Ramana, Ch V

    2015-12-01

    Strain JC267T was isolated from pebbles collected from Pingleshwar beach, Gujarat, India. Cells are Gram-stain-positive, facultatively anaerobic, non-motile rods forming sub-terminal endospores in swollen ellipsoidal to oval sporangia. Strain JC267T contains anteiso-C15 : 0, iso-C15 : 0, iso-C14 : 0, iso-C16 : 0, C16 : 0 and anteiso-C17 : 0 as major (>5 %) cellular fatty acids. Polar lipids include phosphatidylglycerol, phospholipids (PL1-3), glycolipids (GL1-2) and an unidentified lipid. Cell-wall amino acids are composed of diagnostic meso-diaminopimelic acid, dl-alanine and a small amount of d-glutamic acid. The genomic DNA G+C content of strain JC267T is 45.5 mol%. The 16S rRNA gene sequence of strain JC267T showed highest sequence similarities of < 98.41 % with all species of the genus Bacillus when subjected to EzTaxon-e blast analysis. The reassociation values based on DNA-DNA hybridization of strain JC267T with Bacillus halosaccharovorans IBRC-M 10095T and Bacillus niabensis JCM 16399T were 26 ± 1 % and 34 ± 3 %, respectively. Based on taxonomic data obtained using a polyphasic approach, strain JC267T represents a novel species of the genus Bacillus, for which the name Bacillus endolithicus sp. nov. is proposed. The type strain is JC267T ( = IBRC-M 10914T = KCTC 33579T).

  1. Particle fuel bed tests

    SciTech Connect

    Horn, F.L.; Powell, J.R.; Savino, J.M.

    1985-01-01

    Gas-cooled reactors, using packed beds of small diameter coated fuel particles have been proposed for compact, high-power systems. The particulate fuel used in the tests was 800 microns in diameter, consisting of a thoria kernel coated with 200 microns of pyrocarbon. Typically, the bed of fuel particles was contained in a ceramic cylinder with porous metallic frits at each end. A dc voltage was applied to the metallic frits and the resulting electric current heated the bed. Heat was removed by passing coolant (helium or hydrogen) through the bed. Candidate frit materials, rhenium, nickel, zirconium carbide, and zirconium oxide were unaffected, while tungsten and tungsten-rhenium lost weight and strength. Zirconium-carbide particles were tested at 2000 K in H/sub 2/ for 12 hours with no visible reaction or weight loss.

  2. Letters initiating Clean Water Act 404(c) review of mining at Pebble deposit

    EPA Pesticide Factsheets

    Correspondence between EPA and the Pebble Limited Partnership and the State of Alaska initiating review under section 404(c) of the Clean Water Act of potential adverse environmental effects associated with mining the Pebble deposit in southwest Alaska.

  3. Pebble Accretion and the Diversity of Planetary Systems

    NASA Astrophysics Data System (ADS)

    Chambers, John E.

    2015-11-01

    Understanding how planetary systems form and why they exhibit great diversity are key questions in planetary science. Recently, several studies of planet formation have focussed on a mechanism called ``pebble accretion''. Here, mm-to-m size particles in a protoplanetary disk are strongly affected by both gas drag and gravity during an encounter with a growing planet. This can substantially increase the capture probability, speeding up planetary growth, and providing a possible solution to the long-standing problem of how gas-giant planets form within the short lifetimes of protoplanetary disks (Lambrechts and Johansen 2012 Astron Astrophys 544, A32). It has also been suggested that pebble accretion can explain the profound difference between the rocky inner planets and the gas-rich outer planets of the Solar System (Morbidelli et al. 2015 Icarus 258, 418). Here I will present new simulations of planet formation in an evolving protoplanetary disk, spanning both the regions in which rocky and gaseous planets are likely to form. The simulations cover the runaway, oligarchic and gas-accretion phases of planetary growth, and include approximate models for pebble growth and the formation of asteroid sized planetesimals from pebbles. Planetary growth rates in these models are sensitive to the poorly-constrained properties of pebbles in a protoplanetary disk, and also the properties of the gaseous disk itself, especially the strength of turbulence. Different disk and pebble properties lead to a wide range of outcomes, including some cases resembling the Solar System, and may explain the observed diversity of extrasolar planetary systems.

  4. Ceramic fiber filter technology

    SciTech Connect

    Holmes, B.L.; Janney, M.A.

    1996-06-01

    Fibrous filters have been used for centuries to protect individuals from dust, disease, smoke, and other gases or particulates. In the 1970s and 1980s ceramic filters were developed for filtration of hot exhaust gases from diesel engines. Tubular, or candle, filters have been made to remove particles from gases in pressurized fluidized-bed combustion and gasification-combined-cycle power plants. Very efficient filtration is necessary in power plants to protect the turbine blades. The limited lifespan of ceramic candle filters has been a major obstacle in their development. The present work is focused on forming fibrous ceramic filters using a papermaking technique. These filters are highly porous and therefore very lightweight. The papermaking process consists of filtering a slurry of ceramic fibers through a steel screen to form paper. Papermaking and the selection of materials will be discussed, as well as preliminary results describing the geometry of papers and relative strengths.

  5. Portfolio: Ceramics.

    ERIC Educational Resources Information Center

    Hardy, Jane; And Others

    1982-01-01

    Describes eight art activities using ceramics. Elementary students created ceramic tiles to depict ancient Egyptian and medieval European art, made ceramic cookie stamps, traced bisque plates on sketch paper, constructed clay room-tableaus, and designed clay relief masks. Secondary students pit-fired ceramic pots and designed ceramic Victorian…

  6. Mechanisms of flow through compressible porous beds in sedimentation, filtration, centrifugation, deliquoring, and ceramic processing. Progress report, January 1993--November 1993

    SciTech Connect

    Tiller, F.M.

    1993-11-01

    The research program is involved with the area of solid/liquid separation including sedimentation, thickening, cake filtration, centrifugation, expression, washing, deep-bed filtration, screening, and membrane separation. Objective is the unification of theoretical approaches to solid/liquid separations. The research is divided according to: Centrifugation, cake filtration, sedimentation/thickening, and optimization studies (tubular arrangements in candle filters; maximizing filtration rates with filter aids).

  7. Pebbles and PebbleJuggler: software for accurate, unbiased, and fast measurement and analysis of nanoparticle morphology from transmission electron microscopy (TEM) micrographs

    NASA Astrophysics Data System (ADS)

    Mondini, S.; Ferretti, A. M.; Puglisi, A.; Ponti, A.

    2012-08-01

    Pebbles is a user-friendly software program which implements an accurate, unbiased, and fast method to measure the morphology of a population of nanoparticles (NPs) from TEM micrographs. The morphological parameters of the projected NP shape are obtained by fitting intensity models to the TEM micrograph. Pebbles can be used either in automatic mode, where both fitting and validation are reliably carried out with minimal human intervention, and in manual mode, where the user has full control on the fitting and validation steps. Accuracy in diameter measurement has been shown to be <~1%. When operated in automatic mode, Pebbles can be very fast. The effective speed of 1 NP s-1 has been achieved in favorable cases (packed monolayer of NPs). Since Pebbles is based on a local modeling procedure, it successfully treats cases such as low contrast NPs, NPs with significant diffraction scattering, and inhomogeneous background which often make conventional thresholding procedures fail. Pebbles is accompanied by PebbleJuggler, a software program for the statistical analysis of the sets of best-fit NP models created by Pebbles. Effort has been devoted to make Pebbles and PebbleJuggler the most user-friendly and the least user-tedious we could. Pebbles and PebbleJuggler are available at http://pebbles.istm.cnr.it.Pebbles is a user-friendly software program which implements an accurate, unbiased, and fast method to measure the morphology of a population of nanoparticles (NPs) from TEM micrographs. The morphological parameters of the projected NP shape are obtained by fitting intensity models to the TEM micrograph. Pebbles can be used either in automatic mode, where both fitting and validation are reliably carried out with minimal human intervention, and in manual mode, where the user has full control on the fitting and validation steps. Accuracy in diameter measurement has been shown to be <~1%. When operated in automatic mode, Pebbles can be very fast. The effective speed of 1

  8. Bed Bugs

    EPA Pesticide Factsheets

    Prevent, identify, and treat bed bug infestations using EPA’s step-by-step guides, based on IPM principles. Find pesticides approved for bed bug control, check out the information clearinghouse, and dispel bed bug myths.

  9. Using PEBBLE for the evolutionary analysis of serially sampled molecular sequences.

    PubMed

    Goode, Matthew; Rodrigo, Allen G

    2004-05-01

    The PEBBLE (Phylogenetics, Evolutionary Biology, and Bioinformatics in a moduLar Environment) application is a relative newcomer to the field of phylogenetic applications. Although designed as a customizable generalist application, PEBBLE was initially developed to implement procedures for the analysis of sequences associated with different sampling times, e.g., rapidly evolving viral genes sampled over the course of infection, or ancient DNA sequences. The basic protocol describes the use of PEBBLE to infer a phylogenetic tree using the sUPGMA algorithm, and the inference of substitution rate parameters using maximum likelihood. The alternate and support protocols describe the simulation capabilities of PEBBLE, and general use of the PEBBLE application, respectively.

  10. Bed bugs.

    PubMed

    Foulke, Galen T; Anderson, Bryan E

    2014-09-01

    The term bed bug is applied to 2 species of genus Cimex: lectularius describes the common or temperate bed bug, and hemipterus its tropical cousin. Cimex lectularius is aptly named; its genus and species derive from the Latin words for bug and bed, respectively. Though the tiny pest is receiving increased public attention and scrutiny, the bed bug is hardly a new problem.

  11. Structural ceramics

    SciTech Connect

    Wachtman, J.B. Jr.

    1989-01-01

    The present work discusses opportunities for application of structural ceramics in heat engines, industrial-wear parts, prosthetics and bearings; conceptual and detailed design principles for structural ceramics; the processing, consolidation, and properties of members of the SiC family of structural ceramics; and the silicon nitride and sialon families of hot-pressed, sintered, and reaction-bonded, structural ceramics. Also discussed are partially-stabilized zirconia and zirconia-toughened ceramics for structural applications, the processing methods and mechanisms of fiber-reinforcement in ceramic-matrix fiber-reinforced composites, and the tribological properties of structural ceramics.

  12. Uranium assessment for the Precambrian pebble conglomerates in southeastern Wyoming

    SciTech Connect

    Borgman, L.E.; Sever, C.; Quimby, W.F.; Andrew, M.E.; Karlstrom, K.E.; Houston, R.S.

    1981-03-01

    This volume is a geostatistical resource estimate of uranium and thorium in quartz-pebble conglomerates, and is a companion to Volume 1: The Geology and Uranium Potential to Precambrian Conglomerates in the Medicine Bow Mountains and Sierra Madre of Southeastern Wyoming; and to Volume 2: Drill-Hole Data, Drill-Site Geology, and Geochemical Data from the Study of Precambrian Uraniferous Conglomerates of the Medicine Bow Mountains and the Sierra Madre of Southeastern Wyoming.

  13. Fluorescent nano-PEBBLE sensors designed for intracellular glucose imaging.

    PubMed

    Xu, Hao; Aylott, Jonathan W; Kopelman, Raoul

    2002-11-01

    Polyacrylamide-based, ratiometric, spherical, optical nanosensors, or polyacrylamide PEBBLEs (Probes Encapsulated By Biologically Localized Embedding), have been fabricated, aimed at real-time glucose imaging in intact biological systems, i.e. living cells. These nanosensors are prepared using a microemulsion polymerization process, and their average size is about 45 nm in diameter. The sensors incorporate glucose oxidase (GOx), an oxygen sensitive fluorescent indicator (Ru[dpp(SO3Na)2]3)Cl2, and an oxygen insensitive fluorescent dye, Oregon Green 488-dextran or Texas Red-dextran, as a reference for the purpose of ratiometric intensity measurements. The enzymatic oxidation of glucose to gluconic acid results in the local depletion of oxygen, which is measured by the oxygen sensitive ruthenium dye. The small size and inert matrix of these sensors allows them to be inserted into living cells with minimal physical and chemical perturbations to their biological functions. The PEBBLE matrix protects the enzyme and fluorescent dyes from interference by proteins in cells, enabling reliable in vivo chemical analysis. Conversely, the matrix also significantly reduces the toxicity of the indicator and reference dyes to the cells, so that a larger variety of dyes can be used in optimal fashion. Furthermore, the PEBBLE matrix enables the synergistic approach in which there is a steady state of local oxygen consumption, and this cannot be achieved by separately introducing free enzyme and dyes into a cell. The work presented here describes the production and characterization of glucose sensitive PEBBLEs, and their potential for intracellular glucose measurements. The sensor response is determined in terms of the linear range, ratiometric operation, response time, sensor stability, reversibility and immunity to interferences.

  14. On Ceramics.

    ERIC Educational Resources Information Center

    School Arts, 1982

    1982-01-01

    Presents four ceramics activities for secondary-level art classes. Included are directions for primitive kiln construction and glaze making. Two ceramics design activities are described in which students make bizarrely-shaped lidded jars, feet, and footwear. (AM)

  15. Evaluation of the Accumulation of Trace Metals (as, U, CR, CU, PB, Zn) on Iron-Manganese Coatings on in Situ Stream Pebbles and Emplaced Substrates

    NASA Astrophysics Data System (ADS)

    Turpin, M. M.; Blake, J.; Crossey, L. J.; Ali, A.; Hansson, L.

    2015-12-01

    Exposure to trace metals (As, U, Cr, Cu, Pb, Zn) has potential negative health effects on human populations and wildlife. Geothermal waters often have elevated concentrations of trace elements and understanding the geochemical cycling of these elements can be challenging. Previous studies have utilized in situ stream pebbles and glass or ceramic substrates with iron-manganese oxide coatings to understand contamination and or chemical cycling. This project's main focus is to develop an ideal tracing method using adsorption onto substrate surfaces and to define key parameters that are necessary for the phenomenon of adsorption between trace metals and these surface coatings to occur. Sampling locations include the Jemez River and Rio San Antonio in the Jemez mountains, northern New Mexico. Both streams have significant geothermal inputs. Pebbles and cobbles were gathered from the active stream channel and 6mm glass beads and 2 X1 in. ceramic plates were placed in streams for three weeks to allow for coating accumulation. Factors such as leachate type, water pH, substrate type, coating accumulation period and leach time were all considered in this experiment. It was found that of the three leachates (aqua regia, 10% aqua regia and hydroxylamine), hydroxylamine was the most effective at leaching coatings without dissolving substrates. Samples leached with aqua regia and 10% aqua regia were found to lose weight and mass over the following 5, 7, and 10 day measurements. Glass beads were determined to be more effective than in stream pebbles as an accumulation substrate: coatings were more easily controlled and monitored. Samples leached with hydroxylamine for 5 hours and 72 hours showed little difference in their leachate concentrations, suggesting that leach time has little impact on the concentration of leachate samples. This research aims to find the best method for trace metal accumulation in streams to aid in understanding geochemical cycling.

  16. Ceramic Material.

    DTIC Science & Technology

    1990-05-02

    A ceramic material which is (1) ceramics based on monoclinic BaO.Al2O3.2SiO2; (2) ceramics based on monoclinic SrO.Al2O3.2SiO2; or (3) ceramics based on monoclinic solid solution of BaO.Al2O3.2SiO2 and SrO.Al2O3.2SiO2.

  17. Structural Ceramics

    NASA Technical Reports Server (NTRS)

    1986-01-01

    This publication is a compilation of abstracts and slides of papers presented at the NASA Lewis Structural Ceramics Workshop. Collectively, these papers depict the scope of NASA Lewis' structural ceramics program. The technical areas include monolithic SiC and Si3N4 development, ceramic matrix composites, tribology, design methodology, nondestructive evaluation (NDE), fracture mechanics, and corrosion.

  18. Fluidized bed regenerators for Brayton cycles

    NASA Technical Reports Server (NTRS)

    Nichols, L. D.

    1975-01-01

    A recuperator consisting of two fluidized bed regenerators with circulating solid particles is considered for use in a Brayton cycle. These fluidized beds offer the possibility of high temperature operation if ceramic particles are used. Calculations of the efficiency and size of fluidized bed regenerators for typical values of operating parameters were made and compared to a shell and tube recuperator. The calculations indicate that the fluidized beds will be more compact than the shell and tube as well as offering a high temperature operating capability.

  19. PUCs move to halt Pebble Springs, Limerick nukes

    SciTech Connect

    Not Available

    1982-06-01

    Public utility commission (PUC) opposition to nuclear-power-plant construction in Oregon and Pennsylvania indicates a new trend for PUCs to take the initiative against nuclear projects. By not allowing utilities to finance new plants with construction work in progress (CWIP) costs added to the rate base, the Pennsylvania PUC essentially cancelled the Limerick units in accordance with the sentiment of the state legislature. The Oregon PUC ordered Pacific Power and Light Co. to write off investments in two Pebble Springs units and retire the financial liability. Both issues will be settled in the courts. (DCK)

  20. Signalling through the RhoGEF Pebble in Drosophila.

    PubMed

    Gregory, Stephen L; Lorensuhewa, Nirmal; Saint, Robert

    2010-04-01

    Small GTPase pathways of the Ras superfamily are implicated in a wide range of signalling processes in animal cells. Small GTPases control pathways by acting as molecular switches. They are converted from an inactive GDP-bound form to an active GTP-bound form by GTP exchange factors (GEFs). The spatial and temporal regulation of GEFs is a major component of the regulation of small GTPases. Here we review the role of the Drosophila RhoGEF, Pebble (the Drosophila ortholog of mammalian ECT2). We discuss its roles in cytokinesis and cell migration, highlighting the diversity with which Rho family signalling pathways operate in biological systems.

  1. Stepped-anneal helium release in 1-mm beryllium pebbles from COBRA-1A2

    SciTech Connect

    Oliver, B.M.

    1998-03-01

    Stepped-anneal helium release measurements on two sets of fifteen beryllium pebbles irradiated in the Experimental Breeder Reactor-II (EBR-II) at Argonne National Laboratory-West (ANL-w), are reported. The purpose of the measurements was to determine the helium release characteristics of the beryllium using larger sample sizes and longer anneal times relative to earlier measurements. Sequential helium analyses were conducted over a narrower temperature range from approximately 800 C to 1100 C in 100 C increments, but with longer anneal time periods. To allow for overnight and unattended operation, a temperature controller and associated circuitry were added to the experimental setup. Observed helium release was nonlinear with time at each temperature interval, with each step being generally characterized by an initial release rate followed by a slowing of the rate over time. Sample Be-C03 showed a leveling off in the helium release after approximately 3 hours at a temperature of 890 C. Sample Be-D03, on the other hand, showed a leveling off only after {approximately}12 to 24 hours at a temperature of 1100 C. This trend is consistent with that observed in earlier measurements on single microspheres from the same two beryllium lots. None of the lower temperature steps showed any leveling off of the helium release. Relative to the total helium concentrations measured earlier, the total helium releases observed here represent approximately 80% and 92% of the estimated total helium in the C03 and D03 samples, respectively.

  2. Modularity of the MIT Pebble Bed Reactor for Use by the Commercial Power Industry

    DTIC Science & Technology

    2008-06-01

    separate components that are designed to fit into a standardized frame which can then be put together in a more simplistic “plug and play” fashion ...modular-versus traditional- fashion . 27 2 Modularity 2.1 Modularity- Overview From oil rigs to nuclear powered...modularity there are some crucial requirements. First, the system must be designed to be built in a modular fashion . In order to do this, a system

  3. Advanced multi-dimensional deterministic transport computational capability for safety analysis of pebble-bed reactors

    NASA Astrophysics Data System (ADS)

    Tyobeka, Bismark Mzubanzi

    A coupled neutron transport thermal-hydraulics code system with both diffusion and transport theory capabilities is presented. At the heart of the coupled code is a powerful neutronics solver, based on a neutron transport theory approach, powered by the time-dependent extension of the well known DORT code, DORT-TD. DORT-TD uses a fully implicit time integration scheme and is coupled via a general interface to the thermal-hydraulics code THERMIX-DIREKT, an HTR-specific two dimensional core thermal-hydraulics code. Feedback is accounted for by interpolating multigroup cross sections from pre-generated libraries which are structured for user specified discrete sets of thermal-hydraulic parameters e.g. fuel and moderator temperatures. The coupled code system is applied to two HTGR designs, the PBMR 400MW and the PBMR 268MW. Steady-state and several design basis transients are modeled in an effort to discern with the adequacy of using neutron diffusion theory as against the more accurate but yet computationally expensive neutron transport theory. It turns out that there are small but significant differences in the results from using either of the two theories. It is concluded that diffusion theory can be used with a higher degree of confidence in the PBMR as long as more than two energy groups are used and that the result must be checked against lower order transport solution, especially for safety analysis purposes. The end product of this thesis is a high fidelity, state-of-the-art computer code system, with multiple capabilities to analyze all PBMR safety related transients in an accurate and efficient manner.

  4. 3-D transient analysis of pebble-bed HTGR by TORT-TD/ATTICA3D

    SciTech Connect

    Seubert, A.; Sureda, A.; Lapins, J.; Buck, M.; Bader, J.; Laurien, E.

    2012-07-01

    As most of the acceptance criteria are local core parameters, application of transient 3-D fine mesh neutron transport and thermal hydraulics coupled codes is mandatory for best estimate evaluations of safety margins. This also applies to high-temperature gas cooled reactors (HTGR). Application of 3-D fine-mesh transient transport codes using few energy groups coupled with 3-D thermal hydraulics codes becomes feasible in view of increasing computing power. This paper describes the discrete ordinates based coupled code system TORT-TD/ATTICA3D that has recently been extended by a fine-mesh diffusion solver. Based on transient analyses for the PBMR-400 design, the transport/diffusion capabilities are demonstrated and 3-D local flux and power redistribution effects during a partial control rod withdrawal are shown. (authors)

  5. A fluorescent PEBBLE nanosensor for intracellular free zinc.

    PubMed

    Sumner, James P; Aylott, Jonathan W; Monson, Eric; Kopelman, Raoul

    2002-01-01

    The development and characterisation of a fluorescent optical PEBBLE (Probe Encapsulated By Biologically Localised Embedding) nanosensor for the detection of zinc is detailed. A ratiometric sensor has been fabricated that incorporates two fluorescent dyes; one is sensitive to zinc and the other acts as a reference. The sensing components are entrapped within a polymer matrix by a microemulsion polymerisation process that produces spherical sensors that are in the size region of 20 to 200 nm. Cellular measurements are made possible by the small sensor size and the biocompatibility of the matrix. The effects of reversibility, photobleaching and leaching have been examined, as well as the selectivity towards zinc over other cellular ions such as Na+, Ca2+, K+, and Mg2+. The dynamic range of these sensors was found to be 4 to 50 microM Zn2+ with a linear range from 15 to 40 microM. The response time for the PEBBLE is less than 4 s and the sensor is reversible. In addition, the nanosensors are photostable and leaching from the matrix, determined using a novel method, is minimal. These sensors are capable of real-time inter- and intra-cellular imaging and are insensitive to interference from proteins.

  6. Ceramic joining

    SciTech Connect

    Loehman, R.E.

    1996-04-01

    This paper describes the relation between reactions at ceramic-metal interfaces and the development of strong interfacial bonds in ceramic joining. Studies on a number of systems are described, including silicon nitrides, aluminium nitrides, mullite, and aluminium oxides. Joints can be weakened by stresses such as thermal expansion mismatch. Ceramic joining is used in a variety of applications such as solid oxide fuel cells.

  7. Ceramic Processing

    SciTech Connect

    EWSUK,KEVIN G.

    1999-11-24

    Ceramics represent a unique class of materials that are distinguished from common metals and plastics by their: (1) high hardness, stiffness, and good wear properties (i.e., abrasion resistance); (2) ability to withstand high temperatures (i.e., refractoriness); (3) chemical durability; and (4) electrical properties that allow them to be electrical insulators, semiconductors, or ionic conductors. Ceramics can be broken down into two general categories, traditional and advanced ceramics. Traditional ceramics include common household products such as clay pots, tiles, pipe, and bricks, porcelain china, sinks, and electrical insulators, and thermally insulating refractory bricks for ovens and fireplaces. Advanced ceramics, also referred to as ''high-tech'' ceramics, include products such as spark plug bodies, piston rings, catalyst supports, and water pump seals for automobiles, thermally insulating tiles for the space shuttle, sodium vapor lamp tubes in streetlights, and the capacitors, resistors, transducers, and varistors in the solid-state electronics we use daily. The major differences between traditional and advanced ceramics are in the processing tolerances and cost. Traditional ceramics are manufactured with inexpensive raw materials, are relatively tolerant of minor process deviations, and are relatively inexpensive. Advanced ceramics are typically made with more refined raw materials and processing to optimize a given property or combination of properties (e.g., mechanical, electrical, dielectric, optical, thermal, physical, and/or magnetic) for a given application. Advanced ceramics generally have improved performance and reliability over traditional ceramics, but are typically more expensive. Additionally, advanced ceramics are typically more sensitive to the chemical and physical defects present in the starting raw materials, or those that are introduced during manufacturing.

  8. Ceramic filters

    SciTech Connect

    Holmes, B.L.; Janney, M.A.

    1995-12-31

    Filters were formed from ceramic fibers, organic fibers, and a ceramic bond phase using a papermaking technique. The distribution of particulate ceramic bond phase was determined using a model silicon carbide system. As the ceramic fiber increased in length and diameter the distance between particles decreased. The calculated number of particles per area showed good agreement with the observed value. After firing, the papers were characterized using a biaxial load test. The strength of papers was proportional to the amount of bond phase included in the paper. All samples exhibited strain-tolerant behavior.

  9. The pebble GTP exchange factor and the control of cytokinesis.

    PubMed

    O'Keefe, L; Somers, W G; Harley, A; Saint, R

    2001-12-01

    Several G proteins of the Rho family have been shown to be required for cytokinesis. The activity of these proteins is regulated by GTP exchange factors (GEFs), which stimulate GDP/GTP exchange, and by GTPase activating proteins (GAPs), which suppress activity by stimulating the intrinsic GTPase activity. The role of Rho family members during cytokinesis is likely to be determined by their spatial and temporal interactions with these factors. Here we focus on the role of the pebble (pbl) gene of Drosophila melanogaster, a RhoGEF that is required for cytokinesis. We summarise the evidence that the primary target of PBL is Rho1 and describe genetic approaches to elucidating the function of PBL and identifying other components of the PBL-activated Rho signalling pathway.

  10. Nanoparticle PEBBLE sensors in live cells and in vivo.

    PubMed

    Lee, Yong-Eun Koo; Smith, Ron; Kopelman, Raoul

    2009-01-01

    Nanoparticle sensors have been developed for real-time imaging and dynamic monitoring, both in live cells and in vivo, of molecular and ionic components, constructs, forces, and dynamics observed during biological, chemical, and physical processes. With their biocompatible small size and inert matrix, nanoparticle sensors have been successfully applied to noninvasive real-time measurements of analytes and fields in cells and in rodents, with spatial, temporal, physical, and chemical resolution. This review describes the diverse designs of nanoparticle sensors for ions and small molecules, physical fields, and biological features, as well as the characterization, properties, and applications of these nanosensors to in vitro and in vivo measurements. Their floating as well as localization abilities in biological media are captured by the acronym PEBBLE: photonic explorer for bioanalysis with biologically localized embedding.

  11. Functional constraints on nest characteristics of pebble mounds of breeding male hornyhead chub Nocomis biguttatus.

    PubMed

    Wisenden, B D; Unruh, A; Morantes, A; Bury, S; Curry, B; Driscoll, R; Hussein, M; Markegard, S

    2009-11-01

    Breeding male hornyhead chub Nocomis biguttatus constructed nests in areas with relatively high but less than maximum flow rate and greater than average water depth. Nests comprised c. 3000 pebbles for a total mass of 11 kg. Males selected pebbles of smaller diameter but higher density than pebbles in the immediate vicinity. Thus, nests balanced the risk of mound erosion and energetic cost of nest construction with the benefits of protection from egg predators and a stable internal flow rate for oxygenation. These data help establish environmental management goals for the conservation of N. biguttatus and the lotic ecosystems dependent upon them.

  12. Zygotic expression of the pebble locus is required for cytokinesis during the postblastoderm mitoses of Drosophila.

    PubMed

    Hime, G; Saint, R

    1992-01-01

    Mutations at the pebble locus of Drosophila melanogaster result in embryonic lethality. Examination of homozygous mutant embryos at the end of embryogenesis revealed the presence of fewer and larger cells which contained enlarged nuclei. Characterization of the embryonic cell cycles using DAPI, propidium iodide, anti-tubulin and anti-spectrin staining showed that the first thirteen rapid syncytial nuclear divisions proceeded normally in pebble mutant embryos. Following cellularization, the postblastoderm nuclear divisions occurred (mitoses 14, 15 and 16), but cytokinesis was never observed. Multinucleate cells and duplicate mitotic figures were seen within single cells at the time of the cycle 15 mitoses. We conclude that zygotic expression of the pebble gene is required for cytokinesis following cellularization during Drosophila embryogenesis. We postulate that developmental regulation of zygotic transcription of the pebble gene is a consequence of the transition from syncytial to cellular mitoses during cycle 14 of embryogenesis.

  13. Tectonic strain of a deformed conglomerate determined from a single pebble

    NASA Astrophysics Data System (ADS)

    Borradaile, Graham John

    1984-04-01

    Individual rounded pebbles of schist or foliated gneiss included in a conglomerate can each be used as strain markers when the conglomerate has been deformed subsequently. The shape, orientation and the attitude of the earlier schistosity within a single pebble allow one to determine the strain ratio assuming passive behaviour during deformation. The method may also be applicable to certain individual lava pillows containing paleo-horizontal "lava-level" markers.

  14. HTGR Unit Fuel Pebble k-infinity Results Using Chord Length Sampling

    SciTech Connect

    T.J. Donovan; Y. Danon

    2003-06-16

    There is considerable interest in transport models that will permit the simulation of neutral particle transport through stochastic mixtures. Chord length sampling techniques that simulate particle transport through binary stochastic mixtures consisting of spheres randomly arranged in a matrix have been implemented in several Monte Carlo Codes [1-3]. Though the use of these methods is growing, the accuracy and efficiency of these methods has not yet been thoroughly demonstrated for an application of particular interest--a high temperature gas reactor fuel pebble element. This paper presents comparison results of k-infinity calculations performed on a LEUPRO-1 pebble cell. Results are generated using a chord length sampling method implemented in a test version of MCNP [3]. This Limited Chord Length Sampling (LCLS) method eliminates the need to model the details of the micro-heterogeneity of the pebble. Results are also computed for an explicit pebble model where the TRISO fuel particles within the pebble are randomly distributed. Finally, the heterogeneous matrix region of the pebble cell is homogenized based simply on volume fractions. These three results are compared to results reported by Johnson et al [4], and duplicated here, using a cubic lattice representation of the TRISO fuel particles. Figures of Merit for the four k-infinity calculations are compared to judge relative efficiencies.

  15. Separating gas-giant and ice-giant planets by halting pebble accretion

    NASA Astrophysics Data System (ADS)

    Lambrechts, M.; Johansen, A.; Morbidelli, A.

    2014-12-01

    In the solar system giant planets come in two flavours: gas giants (Jupiter and Saturn) with massive gas envelopes, and ice giants (Uranus and Neptune) with much thinner envelopes around their cores. It is poorly understood how these two classes of planets formed. High solid accretion rates, necessary to form the cores of giant planets within the life-time of protoplanetary discs, heat the envelope and prevent rapid gas contraction onto the core, unless accretion is halted. We find that, in fact, accretion of pebbles (~cm sized particles) is self-limiting: when a core becomes massive enough it carves a gap in the pebble disc. This halt in pebble accretion subsequently triggers the rapid collapse of the super-critical gas envelope. Unlike gas giants, ice giants do not reach this threshold mass and can only bind low-mass envelopes that are highly enriched by water vapour from sublimated icy pebbles. This offers an explanation for the compositional difference between gas giants and ice giants in the solar system. Furthermore, unlike planetesimal-driven accretion scenarios, our model allows core formation and envelope attraction within disc life-times, provided that solids in protoplanetary discs are predominantly made up of pebbles. Our results imply that the outer regions of planetary systems, where the mass required to halt pebble accretion is large, are dominated by ice giants and that gas-giant exoplanets in wide orbits are enriched by more than 50 Earth masses of solids.

  16. Solar heated fluidized bed gasification system

    NASA Technical Reports Server (NTRS)

    Qader, S. A. (Inventor)

    1981-01-01

    A solar-powered fluidized bed gasification system for gasifying carbonaceous material is presented. The system includes a solar gasifier which is heated by fluidizing gas and steam. Energy to heat the gas and steam is supplied by a high heat capacity refractory honeycomb which surrounds the fluid bed reactor zone. The high heat capacity refractory honeycomb is heated by solar energy focused on the honeycomb by solar concentrator through solar window. The fluid bed reaction zone is also heated directly and uniformly by thermal contact of the high heat capacity ceramic honeycomb with the walls of the fluidized bed reactor. Provisions are also made for recovering and recycling catalysts used in the gasification process. Back-up furnace is provided for start-up procedures and for supplying heat to the fluid bed reaction zone when adequate supplies of solar energy are not available.

  17. Structural ceramics

    NASA Technical Reports Server (NTRS)

    Craig, Douglas F.

    1992-01-01

    This presentation gives a brief history of the field of materials sciences and goes on to expound the advantages of the fastest growing area in that field, namely ceramics. Since ceramics are moving to fill the demand for lighter, stronger, more corrosion resistant materials, advancements will rely more on processing and modeling from the atomic scale up which is made possible by advanced analytical, computer, and processing techniques. All information is presented in viewgraph format.

  18. Structural Ceramics Database

    National Institute of Standards and Technology Data Gateway

    SRD 30 NIST Structural Ceramics Database (Web, free access)   The NIST Structural Ceramics Database (WebSCD) provides evaluated materials property data for a wide range of advanced ceramics known variously as structural ceramics, engineering ceramics, and fine ceramics.

  19. The radial dependence of pebble accretion rates: A source of diversity in planetary systems. I. Analytical formulation

    NASA Astrophysics Data System (ADS)

    Ida, S.; Guillot, T.; Morbidelli, A.

    2016-06-01

    Context. The classical planetesimal accretion scenario for the formation of planets has recently evolved with the idea that pebbles, centimeter- to meter-sized icy grains migrating in protoplanetary disks, can control planetesimal and/or planetary growth. Aims: We investigate how pebble accretion depends on disk properties and affects the formation of planetary systems. Methods: We construct analytical models of pebble accretion onto planetary embryos that consistently account for the mass and orbital evolution of the pebble flow and reflect disk structure. Results: We derive simple formulas for pebble accretion rates in the so-called settling regime for planetary embryos that are more than 100 km in size. For relatively smaller embryos or in outer disk regions, the accretion mode is three-dimensional (3D), meaning that the thickness of the pebble flow must be taken into account, and resulting in an accretion rate that is independent of the embryo mass. For larger embryos or in inner regions, the accretion is in a two-dimensional (2D) mode, i.e., the pebble disk may be considered infinitely thin. We show that the radial dependence of the pebble accretion rate is different (even the sign of the power-law exponent changes) for different disk conditions such as the disk heating source (viscous heating or stellar irradiation), drag law (Stokes or Epstein, and weak or strong coupling), and in the 2D or 3D accretion modes. We also discuss the effect of the sublimation and destruction of icy pebbles inside the snow line. Conclusions: Pebble accretion easily produces a large diversity of planetary systems. In other words, to infer the results of planet formation through pebble accretion correctly, detailed prescriptions of disk evolution and pebble growth, sublimation, destruction and migration are required.

  20. Support services for ceramic fiber-ceramic matrix composites. Annual technical progress report

    SciTech Connect

    Hurley, J.P.; Nowok, J.W.

    1996-12-27

    Ceramic and advanced alloy corrosion in fossil energy systems is being investigated. During 1995-6, ash was collected for testing corrosion resistance of materials in air-blown fluidized-bed gasification systems. Descriptions of the activities are presented in this report, which is an extension of a technical paper on testing corrosion rates of ceramics in coal gasification systems. A section of this report covers factors affecting the composition of ash deposits.

  1. The colloidal chemistry of ceramic clays

    NASA Technical Reports Server (NTRS)

    Phelps, G. W.

    1984-01-01

    The colloidal chemistry and mineralogy of two argil minerals were studied. Deposits of kaolin and of ceramic clays in the United States and England are discussed for the probable mechanism of formation. The structural modifications of the bed, original material associated with the clays and the proper use of flocculants are discussed.

  2. Penn State geoPebble system: Design,Implementation, and Initial Results

    NASA Astrophysics Data System (ADS)

    Urbina, J. V.; Anandakrishnan, S.; Bilen, S. G.; Fleishman, A.; Burkett, P.

    2014-12-01

    The Penn State geoPebble system is a new network of wirelessly interconnected seismic and GPS sensor nodes with flexible architecture. This network will be used for studies of ice sheets in Antarctica and Greenland, as well as to investigate mountain glaciers. The network will consist of ˜150 geoPebbles that can be deployed in a user-defined spatial geometry. We present our design methodology, which has enabled us to develop these state-of- the art sensors using commercial-off-the-shelf hardware combined with custom-designed hardware and software. Each geoPebble is a self- contained, wirelessly connected sensor for collecting seismic measurements and position information. Key elements of each node encompasses a three-component seismic recorder, which includes an amplifier, filter, and 24- bit analog-to-digital converter that can sample up to 10 kHz. Each unit also includes a microphone channel to record the ground-coupled airwave. The timing for each node is available from GPS measurements and a local precision oscillator that is conditioned by the GPS timing pulses. In addition, we record the carrier-phase measurement of the L1 GPS signal in order to determine location at sub-decimeter accuracy (relative to other geoPebbles within a few kilometers radius). Each geoPebble includes 16 GB of solid-state storage, wireless communications capability to a central supervisory unit, and auxiliary measurements capability (including tilt from accelerometers, absolute orientation from magnetometers and temperature). A novel aspect of the geoPebble is a wireless charging system for the internal battery (using inductive coupling techniques). The geoPebbles include all the sensors (geophones, GPS, microphone), communications (WiFi), and power (battery and charging) internally, so the geoPebble system can operate without any cabling connections (though we do provide an external connector so that different geophones can be used). We report initial field-deployment results and

  3. The Role of Pebble Fragmentation in Planetesimal Formation. II. Numerical Simulations

    NASA Astrophysics Data System (ADS)

    Wahlberg Jansson, Karl; Johansen, Anders; Bukhari Syed, Mohtashim; Blum, Jürgen

    2017-01-01

    Some scenarios for planetesimal formation go through a phase of collapse of gravitationally bound clouds of millimeter- to centimeter-size pebbles. Such clouds can form, for example, through the streaming instability in protoplanetary disks. We model the collapse process with a statistical model to obtain the internal structure of planetesimals with solid radii between 10 and 1000 km. During the collapse, pebbles collide, and depending on their relative speeds, collisions have different outcomes. A mixture of particle sizes inside a planetesimal leads to better packing capabilities and higher densities. In this paper we apply results from new laboratory experiments of dust aggregate collisions (presented in a companion paper) to model collision outcomes. We find that the internal structure of a planetesimal is strongly dependent on both its mass and the applied fragmentation model. Low-mass planetesimals have no/few fragmenting pebble collisions in the collapse phase and end up as porous pebble piles. The number of fragmenting collisions increases with increasing cloud mass, resulting in wider particle size distributions and higher density. The collapse is nevertheless “cold” in the sense that collision speeds are damped by the high collision frequency. This ensures that a significant fraction of large pebbles survive the collapse in all but the most massive clouds. Our results are in broad agreement with the observed increase in density of Kuiper Belt objects with increasing size, as exemplified by the recent characterization of the highly porous comet 67P/Churyumov–Gerasimenko.

  4. Enhanced photoacoustic neuroimaging with gold nanorods and PEBBLEs

    NASA Astrophysics Data System (ADS)

    Witte, Russell S.; Kim, K.; Agarwal, A.; Fan, W.; Kopelman, R.; Kotov, N.; Kipke, D.; O'Donnell, M.

    2008-02-01

    Photoacoustic (PA) imaging provides excellent optical contrast with decent penetration and high spatial resolution, making it attractive for a variety of neural applications. We evaluated optical contrast agents with high absorption in the near infrared (NIR) as potential enhancers for PA neuroimaging: optical dyes, gold nanorods (GNRs) and PEBBLEs loaded with indocyanine green. Two PA systems were developed to test these agents in excised neural tissue and in vivo mouse brain. Lobster nerves were stained with the agents for 30 minutes and placed in a hybrid nerve chamber capable of electrical stimulation and recording, optical spectroscopy and PA imaging. Contrast agents boosted the PA signal by at least 30 dB using NIR illumination from a tunable pulsed laser. Photobleaching may be a limiting factor for optical dyes-the PA signal decreased steadily with laser illumination. The second setup enabled in vivo transcranial imaging of the mouse brain. A custom clinical ultrasound scanner and a 10-MHz linear array provided near real-time images during and after an injection of 2 nM gold nanorods into the tail vein. The peak PA signal from the brain vasculature was enhanced by up to 2 dB at 710 nm. Temporal dynamics of the PA signal were also consistent with mixing of the GNRs in the blood. These studies provide a baseline for enhanced PA imaging in neural tissue. The smart contrast agents employed in this study can be further engineered for molecular targeting and controlled drug delivery with potential treatment for a myriad of neural disorders.

  5. A panoptic model for planetesimal formation and pebble delivery

    NASA Astrophysics Data System (ADS)

    Krijt, S.; Ormel, C. W.; Dominik, C.; Tielens, A. G. G. M.

    2016-02-01

    Context. The journey from dust particle to planetesimal involves physical processes acting on scales ranging from micrometers (the sticking and restructuring of aggregates) to hundreds of astronomical units (the size of the turbulent protoplanetary nebula). Considering these processes simultaneously is essential when studying planetesimal formation. Aims: The goal of this work is to quantify where and when planetesimal formation can occur as the result of porous coagulation of icy grains and to understand how the process is influenced by the properties of the protoplanetary disk. Methods: We develop a novel, global, semi-analytical model for the evolution of the mass-dominating dust particles in a turbulent protoplanetary disk that takes into account the evolution of the dust surface density while preserving the essential characteristics of the porous coagulation process. This panoptic model is used to study the growth from sub-micron to planetesimal sizes in disks around Sun-like stars. Results: For highly porous ices, unaffected by collisional fragmentation and erosion, rapid growth to planetesimal sizes is possible in a zone stretching out to ~10 AU for massive disks. When porous coagulation is limited by erosive collisions, the formation of planetesimals through direct coagulation is not possible, but the creation of a large population of aggregates with Stokes numbers close to unity might trigger the streaming instability (SI). However, we find that reaching conditions necessary for SI is difficult and limited to dust-rich disks, (very) cold disks, or disks with weak turbulence. Conclusions: Behind the snow-line, porosity-driven aggregation of icy grains results in rapid (~104 yr) formation of planetesimals. If erosive collisions prevent this, SI might be triggered for specific disk conditions. The numerical approach introduced in this work is ideally suited for studying planetesimal formation and pebble delivery simultaneously and will help build a coherent

  6. Ceramic Seal.

    SciTech Connect

    Smartt, Heidi A.; Romero, Juan A.; Custer, Joyce Olsen; Hymel, Ross W.; Krementz, Dan; Gobin, Derek; Harpring, Larry; Martinez-Rodriguez, Michael; Varble, Don; DiMaio, Jeff; Hudson, Stephen

    2016-11-01

    Containment/Surveillance (C/S) measures are critical to any verification regime in order to maintain Continuity of Knowledge (CoK). The Ceramic Seal project is research into the next generation technologies to advance C/S, in particular improving security and efficiency. The Ceramic Seal is a small form factor loop seal with improved tamper-indication including a frangible seal body, tamper planes, external coatings, and electronic monitoring of the seal body integrity. It improves efficiency through a self-securing wire and in-situ verification with a handheld reader. Sandia National Laboratories (SNL) and Savannah River National Laboratory (SRNL), under sponsorship from the U.S. National Nuclear Security Administration (NNSA) Office of Defense Nuclear Nonproliferation Research and Development (DNN R&D), have previously designed and have now fabricated and tested Ceramic Seals. Tests have occurred at both SNL and SRNL, with different types of tests occurring at each facility. This interim report will describe the Ceramic Seal prototype, the design and development of a handheld standalone reader and an interface to a data acquisition system, fabrication of the seals, and results of initial testing.

  7. The giant Pebble Cu-Au-Mo deposit and surrounding region, southwest Alaska: introduction

    USGS Publications Warehouse

    Kelley, Karen D.; Lang, James R.; Eppinger, Robert G.

    2013-01-01

    The Pebble deposit is located about 320 km southwest of and 27 km northwest of the village of Iliamna in Alaska (Fig. 1A). It is one of the largest porphyry deposits in terms of contained Cu (Fig. 2A) and it has the largest Au endowment of any porphyry deposit in the world (Fig. 2B). The deposit comprises the Pebble West and Pebble East zones that represent two coeval hydrothermal centers within a single system (Lang et al., 2013). Together the measured and indicated resources total 5,942 million metric tons (Mt) at 0.42% Cu, 0.35 g/t Au, and 250 ppm Mo with an inferred resource of 4,835 Mt at 0.24% Cu, 0.26 g/t Au, and 215 ppm Mo. In addition, the deposit contains significant concentrations of Ag, Pd, and Re (Northern Dynasty Minerals, 2011).

  8. Smart Pebble: wireless sensors for structural health monitoring of bridge decks

    NASA Astrophysics Data System (ADS)

    Watters, David G.; Jayaweera, Palitha; Bahr, Alfred J.; Huestis, David L.; Priyantha, Namal; Meline, Robert; Reis, Robert; Parks, Douglas

    2003-08-01

    SRI International is developing a wireless sensor for monitoring the level of chloride ingress into concrete bridge decks. We call this device a Smart Pebble since it has roughly the size and weight of a typical piece of the rock aggregate that is used in such structures. It is "smart" in that it contains a chloride sensor and a radio-frequency identification (RFID) chip that can be queried remotely both to identify it and to indicate chloride concentration levels. The Smart Pebble is also powered remotely, thus precluding the need for any lifetime-limiting batteries. It is designed to be inserted in the bridge deck either during the initial construction (or during refurbishment) or in a back-filled core hole. This paper will discuss the Smart Pebble design, operation, and status.

  9. Formation of dust-rich planetesimals from sublimated pebbles inside of the snow line

    NASA Astrophysics Data System (ADS)

    Ida, S.; Guillot, T.

    2016-11-01

    Context. For up to a few millions of years, pebbles must provide a quasi-steady inflow of solids from the outer parts of protoplanetary disks to their inner regions. Aims: We wish to understand how a significant fraction of the pebbles grows into planetesimals instead of being lost to the host star. Methods: We examined analytically how the inward flow of pebbles is affected by the snow line and under which conditions dust-rich (rocky) planetesimals form. When calculating the inward drift of solids that is due to gas drag, we included the back-reaction of the gas to the motion of the solids. Results: We show that in low-viscosity protoplanetary disks (with a monotonous surface density similar to that of the minimum-mass solar nebula), the flow of pebbles does not usually reach the required surface density to form planetesimals by streaming instability. We show, however, that if the pebble-to-gas-mass flux exceeds a critical value, no steady solution can be found for the solid-to-gas ratio. This is particularly important for low-viscosity disks (α< 10-3) where we show that inside of the snow line, silicate-dust grains ejected from sublimating pebbles can accumulate, eventually leading to the formation of dust-rich planetesimals directly by gravitational instability. Conclusions: This formation of dust-rich planetesimals may occur for extended periods of time, while the snow line sweeps from several au to inside of 1 au. The rock-to-ice ratio may thus be globally significantly higher in planetesimals and planets than in the central star.

  10. Challenges in forming the solar system's giant planet cores via pebble accretion

    SciTech Connect

    Kretke, K. A.; Levison, H. F.

    2014-12-01

    Though ∼10 M {sub ⊕} mass rocky/icy cores are commonly held as a prerequisite for the formation of gas giants, theoretical models still struggle to explain how these embryos can form within the lifetimes of gaseous circumstellar disks. In recent years, aerodynamic-aided accretion of 'pebbles', objects ranging from centimeters to meters in size, has been suggested as a potential solution to this long-standing problem. While pebble accretion has been demonstrated to be extremely effective in local simulations that look at the detailed behavior of these pebbles in the vicinity of a single planetary embryo, to date there have been no global simulations demonstrating the effectiveness of pebble accretion in a more complicated, multi-planet environment. Therefore, we have incorporated the aerodynamic-aided accretion physics into LIPAD, a Lagrangian code that can follow the collisional/accretional/dynamical evolution of a protoplanetary system, to investigate how pebble accretion manifests itself in the larger planet formation picture. We find that under generic circumstances, pebble accretion naturally leads to an 'oligarchic' type of growth in which a large number of planetesimals grow to similar-sized planets. In particular, our simulations tend to form hundreds of Mars- and Earth-mass objects between 4 and 10 AU. While merging of some oligarchs may grow massive enough to form giant planet cores, leftover oligarchs lead to planetary systems that cannot be consistent with our own solar system. We investigate various ideas presented in the literature (including evaporation fronts and planet traps) and find that none easily overcome this tendency toward oligarchic growth.

  11. Challenges in Forming the Solar System's Giant Planet Cores via Pebble Accretion

    NASA Astrophysics Data System (ADS)

    Kretke, K. A.; Levison, H. F.

    2014-12-01

    Though ~10 M ⊕ mass rocky/icy cores are commonly held as a prerequisite for the formation of gas giants, theoretical models still struggle to explain how these embryos can form within the lifetimes of gaseous circumstellar disks. In recent years, aerodynamic-aided accretion of "pebbles," objects ranging from centimeters to meters in size, has been suggested as a potential solution to this long-standing problem. While pebble accretion has been demonstrated to be extremely effective in local simulations that look at the detailed behavior of these pebbles in the vicinity of a single planetary embryo, to date there have been no global simulations demonstrating the effectiveness of pebble accretion in a more complicated, multi-planet environment. Therefore, we have incorporated the aerodynamic-aided accretion physics into LIPAD, a Lagrangian code that can follow the collisional/accretional/dynamical evolution of a protoplanetary system, to investigate how pebble accretion manifests itself in the larger planet formation picture. We find that under generic circumstances, pebble accretion naturally leads to an "oligarchic" type of growth in which a large number of planetesimals grow to similar-sized planets. In particular, our simulations tend to form hundreds of Mars- and Earth-mass objects between 4 and 10 AU. While merging of some oligarchs may grow massive enough to form giant planet cores, leftover oligarchs lead to planetary systems that cannot be consistent with our own solar system. We investigate various ideas presented in the literature (including evaporation fronts and planet traps) and find that none easily overcome this tendency toward oligarchic growth.

  12. ATTAP/AGT101 - Year 2 progress in ceramic technology development

    NASA Technical Reports Server (NTRS)

    Kidwell, J. R.; Lindberg, L. J.; Morey, R. E.

    1990-01-01

    The progress made by the Advanced Turbine Technology Applications Project (ATTAP) is summarized, with emphasis on the following areas: ceramic materials assessment and characterization, ceramic impact damage assessment, ceramic combustor evaluation, turbine inlet particle separator development, impact-tolerant turbine designs, and net-shape ceramic component fabrications. In the evolutionary ceramics development in the Automotive Gas Turbine (AGT101) and ATTAP programs initial designs were conceived to reduce stresses by using well-established criteria: bodies of revolution were preferred over nonaxisymmetric geometries, sharp corners were avoided, the contact area between components was kept as large as possible, and small parts were preferred over large when feasible. Projects discussed include: initial ceramic component fabrication by ceramic suppliers in 1990, engine test to 1371 C in 1991, 100-hr test bed engine durability test in 1991, and 300-hr test bed engine durability in 1992.

  13. geoPebble: Combined Seismic, Acoustic, and GPS Sensor with Wireless Communications for Glaciological Applications

    NASA Astrophysics Data System (ADS)

    Anandakrishnan, S.; Burkett, P. G.; Long, B.

    2009-12-01

    Glaciologist and geophysicists study many dynamic processes in glaciated environments such as sliding, crevasse formation, and water flow. These processes generate signals that can be interpreted for fundamental parameters needed for numerical models of glacier and ice sheet flow. These signals include microearthquakes beneath glaciers and ice streams during stick-slip processes; seismically identifiable harmonic tremors associated with subglacial water flow; supraglacial lake drainage which can produce rapid uplift of the 1 m/hr. In addition, researchers use active seismic experiments to determine bed properties such as roughness and lubrication. Currently, each process requires different instrumentation and/or different field equipment to collect the data such as a GPS receiver for displacement, a passive seismic instrument for microearthquakes, and a multichannel seismic recorder for active seismic experiments. We report on the development of an instrument specifically designed for observing dynamic glaciated environments in a single platform, reducing the need for multiple field systems and reducing the cost considerably. The geoPebble wireless seismic acquisition system, designed and built at the Pennsylvania State University, comprises 4 channels of 24-bit seismic and acoustic digitizing, an L1 GPS engine, onboard data storage and an 802.15 ZigBee radio. Three of the four ADC channels are intended to be used with a 3 component seismic sensor. The fourth channel is a dedicated to an audio frequency microphone. The 1 Hz L1 GPS system is capable of horizontal position accuracy to better than 10 cm when post-processed against L1/L2 stations within 10 km. Onboard storage is achieved with a Secure Digital card where volumes now exceed 32 GB. The ZigBee radio is capable of forming a mesh network which reduces transmit and receive power requirements while maintaing communication throughout the array and provides state-of-health information as well as sufficient data

  14. Moving granular-bed filter development program. Topical report

    SciTech Connect

    Newby, R.A.; Yang, W.C.; Smeltzer, E.E.; Lippert, T.E.

    1994-04-01

    Advanced, coal-based, power plants, such as IGCC and Advanced-PFBC, are currently nearing commercial demonstration. These power plant technologies require hot gas filtration as part of their gas cleaning trains. Ceramic barrier filters are the major filter candidates being developed for these hot gas cleaning applications. While ceramic barrier filters achieve high levels of particle removal, concerns exist for their reliability and operability in these applications. An alternative hot gas filtration technology is the moving granular bed filter. An advanced, moving granular bed filter has been conceived, and early development activities performed by the Westinghouse Electric Corporation, Science and Technology Center. This document reports on the Base Contract tasks performed to resolve the barrier technical issues for this technology. The concept, the Standleg Moving Granular Bed Filter (SMGBF) has a concurrent downward, gas and bed media flow configuration that results in simplified features and improved scaleup feasibility compared to alternative designs. Two modes of bed media operation were assessed in the program: once-through using pelletized power plant waste as bed media, and recycle of bed media via standleg and pneumatic transport techniques. Cold Model testing; high-temperature, high-pressure testing; and pelletization testing using advanced power plant wastes, have been conducted in the program. A commercial, economic assessment of the SMGBF technology was performed for IGCC and Advanced-PFBC applications. The evaluation shows that the barrier technical issues can be resolved, and that the technology is potentially competitive with ceramic barrier filters.

  15. Experimental Investigation and Analysis of the Effective Thermal Properties of Beryllium Packed Beds

    SciTech Connect

    Abou-Sena, A.; Ying, A.; Abdou, M.

    2003-07-15

    Beryllium, in its pebble form, has been proposed in various blanket concepts to serve different purposes. Thermal property data for such a heterogeneous packed bed is needed, particularly data on the impact of compression forces on its magnitude and consequent temperature profile. The objectives of this work are to obtain and quantify experimental data on the effective thermal conductivity of a Be-He packed bed, on the interface heat conductance between Be and SiC, and on the effects of externally applied pressure on these effective thermal properties. The effective thermal conductivity of a Be-He pebble bed increases as the bed mean temperature increases. The values of effective thermal conductivity vary from 2.15 to 3.00 W/m.K for bed mean temperature ranges from 90 to 420 deg C. Similar temperature effects are seen in the Be/SiC interface heat conductance, as the values of interface heat conductance range from 1140 to 2200 W/m{sup 2}.K. In addition, effective thermal conductivity increases remarkably with the increase of applied pressure (by a factor of 2.53 at 2 MPa), while it remains higher than the initial value by {approx}0.3 W/m.K when external pressure is released (hysteresis effect)

  16. Microwave processing of ceramics

    SciTech Connect

    Katz, J.D.

    1989-01-01

    This paper discusses the following topics on microwave processing of ceramics: Microwave-material interactions; anticipated advantage of microwave sintering; ceramic sintering; and ceramic joining. 24 refs., 4 figs. (LSP)

  17. Catalyst functionalized buffer sorbent pebbles for rapid separation of carbon dioxide from gas mixtures

    DOEpatents

    Aines, Roger D.

    2013-03-12

    A method for separating CO.sub.2 from gas mixtures uses a slurried media impregnated with buffer compounds and coating the solid media with a catalyst or enzyme that promotes the transformation of CO.sub.2 to carbonic acid. Buffer sorbent pebbles with a catalyst or enzyme coating are provided for rapid separation of CO.sub.2 from gas mixtures.

  18. Growing Pebbles and Conceptual Prisms - Understanding the Source of Student Misconceptions about Rock Formation.

    ERIC Educational Resources Information Center

    Kusnick, Judi

    2002-01-01

    Analyzes narrative essays--stories of rock formation--written by pre-service elementary school teachers. Reports startling misconceptions among preservice teachers on pebbles that grow, human involvement in rock formation, and sedimentary rocks forming as puddles as dry up, even though these students had completed a college level course on Earth…

  19. Thermal ramp tritium release in COBRA-1A2 C03 beryllium pebbles

    SciTech Connect

    Baldwin, D.L.

    1998-03-01

    Tritium release kinetics, using the method of thermal ramp heating at three linear ramp rates, were measured on the COBRA-1A2 C03 1-mm beryllium pebbles. This report includes a brief discussion of the test, and the test data in graph format.

  20. The impact of ellipsoidal particle shape on pebble breakage in gravel

    PubMed Central

    Tuitz, Christoph; Exner, Ulrike; Frehner, Marcel; Grasemann, Bernhard

    2012-01-01

    We have studied the influence of particle shape and consequently loading configuration on the breakage load of fluvial pebbles. Unfortunately, physical strength tests on pebbles, i.e., point-load tests, can only be conducted under one specific stable loading configuration. Therefore, the physical uniaxial strength tests performed in this study were extended by a two-dimensional finite-element stress analysis, which is capable of investigating those scenarios that are not possible in physical tests. Breakage load, equivalent to that measured in unidirectional physical tests, was determined from the results of the stress analysis by a maximum tensile stress-based failure criterion. Using this assumption, allows the determination of breakage load for a range of different kind of synthetic loading configurations and its comparison with the natural breakage load distribution of the physical strength tests. The results of numerical modelling indicated that the configuration that required the least breakage load corresponded with the minor principal axis of the ellipsoidal pebbles. In addition, most of the simulated gravel-hosted loading configurations exceeded the natural breakage load distribution of fluvial pebbles obtained from the physical strength tests. PMID:26321870

  1. The impact of ellipsoidal particle shape on pebble breakage in gravel.

    PubMed

    Tuitz, Christoph; Exner, Ulrike; Frehner, Marcel; Grasemann, Bernhard

    2012-09-01

    We have studied the influence of particle shape and consequently loading configuration on the breakage load of fluvial pebbles. Unfortunately, physical strength tests on pebbles, i.e., point-load tests, can only be conducted under one specific stable loading configuration. Therefore, the physical uniaxial strength tests performed in this study were extended by a two-dimensional finite-element stress analysis, which is capable of investigating those scenarios that are not possible in physical tests. Breakage load, equivalent to that measured in unidirectional physical tests, was determined from the results of the stress analysis by a maximum tensile stress-based failure criterion. Using this assumption, allows the determination of breakage load for a range of different kind of synthetic loading configurations and its comparison with the natural breakage load distribution of the physical strength tests. The results of numerical modelling indicated that the configuration that required the least breakage load corresponded with the minor principal axis of the ellipsoidal pebbles. In addition, most of the simulated gravel-hosted loading configurations exceeded the natural breakage load distribution of fluvial pebbles obtained from the physical strength tests.

  2. Catalyst functionalized buffer sorbent pebbles for rapid separation of carbon dioxide from gas mixtures

    DOEpatents

    Aines, Roger D

    2015-03-31

    A method for separating CO.sub.2 from gas mixtures uses a slurried media impregnated with buffer compounds and coating the solid media with a catalyst or enzyme that promotes the transformation of CO.sub.2 to carbonic acid. Buffer sorbent pebbles with a catalyst or enzyme coating are provided for rapid separation of CO.sub.2 from gas mixtures.

  3. Nanoparticle PEBBLE sensors for quantitative nanomolar imaging of intracellular free calcium ions.

    PubMed

    Si, Di; Epstein, Tamir; Lee, Yong-Eun Koo; Kopelman, Raoul

    2012-01-17

    Ca(2+) is a universal second messenger and plays a major role in intracellular signaling, metabolism, and a wide range of cellular processes. To date, one of the most successful approaches for intracellular Ca(2+) measurement involves the introduction of optically sensitive Ca(2+) indicators into living cells, combined with digital imaging microscopy. However, the use of free Ca(2+) indicators for intracellular sensing and imaging has several limitations, such as nonratiometric measurement for the most-sensitive indicators, cytotoxicity of the indicators, interference from nonspecific binding caused by cellular biomacromolecules, challenging calibration, and unwanted sequestration of the indicator molecules. These problems are minimized when the Ca(2+) indicators are encapsulated inside porous and inert polyacrylamide nanoparticles. We present PEBBLE nanosensors encapsulated with rhodamine-based Ca(2+) fluorescence indicators. The rhod-2-containing PEBBLEs presented here show a stable sensing range at near-neutral pH (pH 6-9). Because of the protection of the PEBBLE matrix, the interference of protein-nonspecific binding to the indicator is minimal. The rhod-2 PEBBLEs give a nanomolar dynamic sensing range for both in-solution (K(d) = 478 nM) and intracellular (K(d) = 293 nM) measurements. These nanosensors are useful quantitative tools for the measurement and imaging of the cytosolic nanomolar free Ca(2+) levels.

  4. Two-photon nano-PEBBLE sensors: subcellular pH measurements.

    PubMed

    Ray, Aniruddha; Koo Lee, Yong-Eun; Epstein, Tamir; Kim, Gwangseong; Kopelman, Raoul

    2011-09-21

    Intracellular pH mapping is of great importance as it plays a critical role in many cellular events. Also, in tissue, pH mapping can be an indicator for the onset of cancer. Here we describe a biocompatible, targeted, ratiometric, fluorescent, pH sensing nano-PEBBLE (Photonic Explorer for Biomedical use with Biologically Localized Embedding) that is based on two-photon excitation. Two-photon excitation minimizes the photobleaching and cell autofluorescence drastically, leading to an increase in the signal-to-noise ratio. PEBBLE nanosensors provide a novel approach for introducing membrane impermeant dyes, like HPTS, into cells. We use both non-targeted and F3 peptide targeted PEBBLE nanosensors for intracellular pH measurement of 9L cells. The intracellular measurements suggest that the non-targeted nanosensors are mostly trapped in endosomes, whereas the F3 peptide targeting enables them to escape/avoid these acidic compartments. Combining the advantages of pH sensitive PEBBLE nanoparticles, including their specific targeting, with the advantages of two-photon microscopy provides an attractive and promising prospect for non-invasive real-time monitoring of pH inside cancer cells and tissues.

  5. Packed Bed Reactor Experiment

    NASA Video Gallery

    The purpose of the Packed Bed Reactor Experiment in low gravity is to determine how a mixture of gas and liquid flows through a packed bed in reduced gravity. A packed bed consists of a metal pipe ...

  6. Implications of pebble accretion on the composition of hot and cold Jupiters

    NASA Astrophysics Data System (ADS)

    Bitsch, Bertram; Johansen, Anders; Madhusudhan, Nikku

    2016-10-01

    The formation of the planetary cores of gas giants via the accretion of planetesimals takes very long and is not compatible with the lifetime of protoplanetary discs (Levison et al. 2010). This time-scale problem can be solved through the accretion of pebbles onto a planetary seed. Contrary to planetesimals, pebbles feel the headwind from the gas which robs them of angular momentum allowing an efficient growth from the entire Hill sphere, which reduces the growth time-scale by several orders of magnitude (Lambrechts & Johansen, 2012; 2014). However, pebble accretion self-terminates when the planets start to open a partial gap in the disc, which accelerates the gas outside of the planets orbit to super-Keplerian speeds and thus stops the flow of pebbles onto the planetary core (Lambrechts et al. 2014). Typically this mass is of the order of 10-20 Earth masses, depending on the local disc properties. The planet can then start to accrete a gaseous envelope without a pollution of pebbles. During its growth, the planet migrates through the disc, which evolves in time (Bitsch et al. 2015a,b).Different volatile species like CO2 or H2O have different condensation temperatures and are thus present in either solid or gaseous form at different locations in the disc. A pebble accreting planet can thus only accrete volatiles that are in solid form, while a gas accreting planet will only accrete volatiles which are in gaseous form. Therefore the final chemical composition of the planetary atmosphere of a giant planet is strongly influenced by the formation location of the initial planetary seed and its subsequent migration path through the disc. Additionally, the envelope can be enriched through the erosion of the planetary core.I will discuss the implications of the formation of planets via pebble accretion and their subsequent migration through the disc on the composition of gas giants. In particular I will focus on the carbon to oxygen ratio of hot Jupiters around other stars

  7. On the water delivery to terrestrial embryos by ice pebble accretion

    NASA Astrophysics Data System (ADS)

    Sato, Takao; Okuzumi, Satoshi; Ida, Shigeru

    2016-05-01

    Standard accretion disk models suggest that the snow line in the solar nebula migrated interior to the Earth's orbit in a late stage of nebula evolution. In this late stage, a significant amount of ice could have been delivered to 1 AU from outer regions in the form of mm to dm-sized pebbles. This raises the question why the present Earth is so depleted of water (with the ocean mass being as small as 0.023% of the Earth mass). Here we quantify the amount of icy pebbles accreted by terrestrial embryos after the migration of the snow line assuming that no mechanism halts the pebble flow in outer disk regions. We use a simplified version of the coagulation equation to calculate the formation and radial inward drift of icy pebbles in a protoplanetary disk. The pebble accretion cross section of an embryo is calculated using analytic expressions presented by recent studies. We find that the final mass and water content of terrestrial embryos strongly depends on the radial extent of the gas disk, the strength of disk turbulence, and the time at which the snow lines arrives at 1 AU. The disk's radial extent sets the lifetime of the pebble flow, while turbulence determines the density of pebbles at the midplane where the embryos reside. We find that the final water content of the embryos falls below 0.023 wt% only if the disk is compact (<100 AU), turbulence is strong at 1 AU, and the snow line arrives at 1 AU later than 2-4 Myr after disk formation. If the solar nebula extended to 300 AU, initially rocky embryos would have evolved into icy planets of 1-10 Earth masses unless the snow-line migration was slow. If the proto-Earth contained water of ~1 wt% as might be suggested by the density deficit of the Earth's outer core, the formation of the proto-Earth was possible with weaker turbulence and with earlier (>0.5-2 Myr) snow-line migration.

  8. Growing the gas-giant planets by the gradual accumulation of pebbles.

    PubMed

    Levison, Harold F; Kretke, Katherine A; Duncan, Martin J

    2015-08-20

    It is widely held that the first step in forming gas-giant planets, such as Jupiter and Saturn, was the production of solid 'cores' each with a mass roughly ten times that of the Earth. Getting the cores to form before the solar nebula dissipates (in about one to ten million years; ref. 3) has been a major challenge for planet formation models. Recently models have emerged in which 'pebbles' (centimetre-to-metre-sized objects) are first concentrated by aerodynamic drag and then gravitationally collapse to form objects 100 to 1,000 kilometres in size. These 'planetesimals' can then efficiently accrete left-over pebbles and directly form the cores of giant planets. This model is known as 'pebble accretion'; theoretically, it can produce cores of ten Earth masses in only a few thousand years. Unfortunately, full simulations of this process show that, rather than creating a few such cores, it produces a population of hundreds of Earth-mass objects that are inconsistent with the structure of the Solar System. Here we report that this difficulty can be overcome if pebbles form slowly enough to allow the planetesimals to gravitationally interact with one another. In this situation, the largest planetesimals have time to scatter their smaller siblings out of the disk of pebbles, thereby stifling their growth. Our models show that, for a large and physically reasonable region of parameter space, this typically leads to the formation of one to four gas giants between 5 and 15 astronomical units from the Sun, in agreement with the observed structure of the Solar System.

  9. Spatial Distribution of Bed Particles in Natural Boulder-Bed Streams

    NASA Astrophysics Data System (ADS)

    Clancy, K. F.; Prestegaard, K. L.

    2001-12-01

    The Wolman pebble count is used to obtain the size distribution of bed particles in natural streams. Statistics such as median particle size (D50) are used in resistance calculations. Additional information such as bed particle heterogeneity may also be obtained from the particle distribution, which is used to predict sediment transport rates (Hey, 1979), (Ferguson, Prestegaard, Ashworth, 1989). Boulder-bed streams have an extreme range of particles in the particle size distribution ranging from sand size particles to particles larger than 0.5-m. A study of a natural boulder-bed reach demonstrated that the spatial distribution of the particles is a significant factor in predicting sediment transport and stream bed and bank stability. Further experiments were performed to test the limits of the spatial distribution's effect on sediment transport. Three stream reaches 40-m in length were selected with similar hydrologic characteristics and spatial distributions but varying average size particles. We used a grid 0.5 by 0.5-m and measured four particles within each grid cell. Digital photographs of the streambed were taken in each grid cell. The photographs were examined using image analysis software to obtain particle size and position of the largest particles (D84) within the reach's particle distribution. Cross section, topography and stream depth were surveyed. Velocity and velocity profiles were measured and recorded. With these data and additional surveys of bankfull floods, we tested the significance of the spatial distributions as average particle size decreases. The spatial distribution of streambed particles may provide information about stream valley formation, bank stability, sediment transport, and the growth rate of riparian vegetation.

  10. Uncovering East Antarctic Bedrock using detrital zircon geochronology and pebble lithologies from Mount Howe, Scott Glacier

    NASA Astrophysics Data System (ADS)

    Dits, T.; Licht, K.; Bader, N.; Kaplan, M. R.; Schaefer, J. M.; Winckler, G.

    2012-12-01

    Till from the flanks of Mount Howe, the southernmost outcrop in the world at the head of the Scott Glacier, Antarctica, offers an exclusive view of East Antarctic bedrock through analysis of detrital zircon geochronology and pebble lithology. With no outcrops upstream of the Mount Howe nunatak, detrital zircons and pebbles incorporated in the supraglacial till place direct new age and lithologic constraints on unmapped, ice covered bedrock in the Scott Glacier catchment. Nine moraine crests were sampled along a 2 km transect from the modern ice edge toward exposed Beacon Supergroup bedrock, where rock weathering increases away from the ice margin. Preliminary cosmogenic ages on boulders on the same crests as the provenance study indicate most of the moraine complex formed over the last 100 ka, but some ridges close to the headwall may be much older. Pebble lithologies across the transect show minimal statistical variation, averaging 60% mafic igneous, 30% metamorphic, and 10% sedimentary lithologies dominantly from the Ferrar and Beacon Supergroups. Observations of faceting and striations on pebble surfaces reveal that up to 40-50% of the pebble fraction of the till was subglacially transported, and a minimum of 15% are exotic lithologies. Nearly 80% of cobbles collected from a non-random survey reveal the presence of several exotic rock types, including vesicular olivine basalt, quartzite, and four different compositions of granite. Guided by backscatter electron imagery of detrital zircons, 385 ages from U-Pb isotopes of detrital zircons from 8 sequential moraine crests were determined by laser ablation-inductively coupled plasma mass spectroscopy (LA-ICPMS). Distinct age populations were identified at 185-190 Ma, 255-270 Ma, 355-365 Ma, 550-580 Ma, and 2740 Ma. Four samples in the middle of the transect all display a similar 1010-1040 Ma peak that is statistically different from the remaining samples. The 185 Ma population differs from the typical East Antarctic

  11. Proposed Determination Pursuant to Section 404c of the Clean Water Act for Pebble Deposit Area, Southwest Alaska

    EPA Pesticide Factsheets

    EPA Region 10's proposed determination to restrict the use of certain waters in the Bristol Bay watershed for disposal of dredged or fill material associated with mining the Pebble deposit, a large ore body in southwest Alaska.

  12. polycrystalline ceramics

    NASA Astrophysics Data System (ADS)

    Cai, Yunqi; Ma, Ji; Cui, Qi; Wang, Wenzhang; Zhang, Hui; Chen, Qingming

    2014-12-01

    La2/3Ca1/3MnO3 polycrystalline ceramics were synthesized by sol-gel method. Sharp temperature coefficient of resistance (TCR) variation (with peak value up to 22 %) has been observed near the metal-insulator transition temperature T MI (273 K) for the sample sintered at 1,450 °C. This TCR value is much higher than the previously reported values for the undoped and Ag-doped La0.67Ca0.33MnO3 samples and is comparable to the optimized thin films. It was concluded that the improved physical properties of the La0.67Ca0.33MnO3 material are due to its improved microstructure and homogeneity.

  13. Bed disturbance patterns in two mediterranean impounded rivers

    NASA Astrophysics Data System (ADS)

    Lobera, Gemma; López-Tarazón, José A.; Vericat, Damià; Batalla, Ramon J.; Andrés-Doménech, Ignacio; Millán-Romero, Pedro; Vallés, Francisco

    2015-04-01

    ) characterisation of grain size distribution by means of pebble counts and bulk samples; 4) bed mobility by tracers (i.e. painted bed areas and tagged particles using radiofrequency techniques).

  14. Thermo-mechanical and neutron lifetime modeling and design of Be pebbles in the neutron multiplier for the LIFE engine

    SciTech Connect

    DeMange, P; Marian, J; de Caro, M S; Caro, A

    2009-03-16

    Concept designs for the laser-initiated fusion/fission engine (LIFE) include a neutron multiplication blanket containing Be pebbles flowing in a molten salt coolant. These pebbles must be designed to withstand the extreme irradiation and temperature conditions in the blanket to enable a safe and cost-effective operation of LIFE. In this work, we develop design criteria for spherical Be pebbles on the basis of their thermomechanical behavior under continued neutron exposure. We consider the effects of high fluence/fast flux on the elastic, thermal and mechanical properties of nuclear-grade Be. Our results suggest a maximum pebble diameter of 30 mm to avoid tensile failure, coated with an anti-corrosive, high-strength metallic shell to avoid failure by pebble contact. Moreover, we find that the operation temperature must always be kept above 450 C to enable creep to relax the stresses induced by swelling, which we estimate to be at least 16 months if uncoated and up to six years when coated. We identify the sources of uncertainty on the properties used and discuss the advantages of new intermetallic beryllides and their use in LIFE's neutron multiplier. To establish Be-pebble lifetimes with improved confidence, reliable experiments to measure irradiation creep must be performed.

  15. BRILLIANT PEBBLES: A METHOD FOR DETECTION OF VERY LARGE INTERSTELLAR GRAINS

    SciTech Connect

    Socrates, Aristotle; Draine, Bruce T. E-mail: draine@astro.princeton.edu

    2009-09-01

    A photon of wavelength {lambda} {approx} 1 {mu}m interacting with a dust grain of radius a{sub p} {approx} 1 mm (a 'pebble') undergoes scattering in the forward direction, largely within a small characteristic diffraction angle {theta}{sub s} {approx} {lambda}/a{sub p} {approx} 100''. Though millimeter-size dust grains contribute negligibly to the interstellar medium's visual extinction, the signal they produce in scattered light may be detectable, especially for variable sources. Observations of light scattered at small angles allow for the direct measurement of the large grain population; variable sources can also yield tomographic information of the interstellar medium's mass distribution. The ability to detect brilliant pebble halos requires a careful understanding of the instrument point-spread function.

  16. The dynamical evolution of the asteroid belt in the pebble accretion scenario

    NASA Astrophysics Data System (ADS)

    Pirani, Simona; Mustill, Alexander; Turrini, Diego; Johansen, Anders

    2016-10-01

    The high excitation of the asteroid belt could be the trace of a past cohexistence of asteroids and planetary embryos. After the formation of Jupiter and Saturn, the asteroid belt lost about 99% of its mass, depleted by gravitational interactions with these giant planets and it was left with only Ceres as a relic of the planetary embryo population. Our aim is to construct a main belt (based on new estimates for the birth distribution of asteroids and planetary embryos that grow by pebble accretion) and test its evolution with different parameters and configurations of the giant planets. We test new pebble accretion growth tracks for the giant planets and compare the evolution of the asteroid belt to the classical in-situ growth.

  17. EBSD characterization of pre-Cambrian deformations in conglomerate pebbles (Sierra de la Demanda, Northern Spain)

    NASA Astrophysics Data System (ADS)

    Puelles, Pablo; Ábalos, Benito; Fernández-Armas, Sergio

    2010-05-01

    Pre-Cambrian and unconformable earliest Cambrian rocks from the Sierra de la Demanda (N Spain) exhibit field and microstructural relationships that attest to orogenic events recorded by concealed basement rocks. Neoproterozoic foliated slates ("Anguiano Schists") crop out under up to 300 m thick, unfoliated quartz-rich conglomerates ("Anguiano Conglomerates") and quartzites which are stratigraphically ca. 600 m below the oldest, paleontologically dated, pre-trilobitic Cambrian layers (likely older than 520 Ma). The Anguiano Conglomerates contain mm to cm grainsized well-rounded pebbles of various types including monocrystalline quartz, detrital zircon and tourmaline-bearing sandstones, black cherts and metamorphic poly-crystalline quartz aggregates. The undeformed matrix is made of much smaller (diagenetically overgrown) monocrystaline quartz grains and minor amounts of accesory zircon, tourmaline and mica. Black chert pebbles exhibit microstructural evidence of brittle deformation (microfaults and thin veins of syntaxial fibrous quartz). These and the fine-grained sandstone pebbles can also exhibit ductile deformations (microfolds with thickened hinges and axial planar continuous foliations), too. Polycrystalline quartz pebbles exhibit a variety of microstructures that resulted from syn-metamorphic ductile deformations. These are recognisable under the petrographic microscope and include continuous foliations, quartz shape fabrics, various types of subgrain or recrystallized new grain microtextures, and lattice preferred orientations (LPOs). Conventional characterization of quartz fabrics (after oriented structural sections) is challenged in conglomerate pebble thin sections by the difficulty of unraveling in them the complete structural reference framework provided by foliation (whose trace can be unraveled) and lineation orientation (which cannot be directly identified). Quartz in various metamorphic polycrystalline pebbles was studied with the Electron Back

  18. Studies on crude oil removal from pebbles by the application of biodiesel.

    PubMed

    Xia, Wen-xiang; Xia, Yan; Li, Jin-cheng; Zhang, Dan-feng; Zhou, Qing; Wang, Xin-ping

    2015-02-15

    Oil residues along shorelines are hard to remove after an oil spill. The effect of biodiesel to eliminate crude oil from pebbles alone and in combination with petroleum degrading bacteria was investigated in simulated systems. Adding biodiesel made oil detach from pebbles and formed oil-biodiesel mixtures, most of which remained on top of seawater. The total petroleum hydrocarbon (TPH) removal efficiency increased with biodiesel quantities but the magnitude of augment decreased gradually. When used with petroleum degrading bacteria, the addition of biodiesel (BD), nutrients (NUT) and BD+NUT increased the dehydrogenase activity and decreased the biodegradation half lives. When BD and NUT were replenished at the same time, the TPH removal efficiency was 7.4% higher compared to the total improvement of efficiency when BD and NUT was added separately, indicating an additive effect of biodiesel and nutrients on oil biodegradation.

  19. Sojourner Rover View of Well-Rounded Pebbles in Cabbage Patch

    NASA Technical Reports Server (NTRS)

    1997-01-01

    Sojourner Rover image of rounded 4-cm-wide pebble (lower center) and excavation of cloddy deposit of Cabbage Patch at lower left. Note the bright wind tails of drift material extending from small rocks and the wheel track from upper right to lower left.

    Well-rounded objects, like the one in this image, were not seen at the Viking sites. These are thought to be pebbles liberated from sedimentary rocks composed of cemented silts, sands and rounded fragments; such rocks are called conglomerates.

    NOTE: original caption as published in Science Magazine

    Mars Pathfinder is the second in NASA's Discovery program of low-cost spacecraft with highly focused science goals. The Jet Propulsion Laboratory, Pasadena, CA, developed and manages the Mars Pathfinder mission for NASA's Office of Space Science, Washington, D.C. JPL is a division of the California Institute of Technology (Caltech).

  20. Thermal decomposition of expanded polystyrene in a pebble bed reactor to get higher liquid fraction yield at low temperatures

    SciTech Connect

    Chauhan, R.S. Gopinath, S.; Razdan, P.; Delattre, C.; Nirmala, G.S.; Natarajan, R.

    2008-11-15

    Expanded polystyrene is one of the polymers produced in large quantities due to its versatile application in different fields. This polymer is one of the most intractable components in municipal solid waste. Disposal of polymeric material by pyrolysis or catalytic cracking yields valuable hydrocarbon fuels or monomers. Literature reports different types of reactors and arrangements that have uniform temperatures during pyrolysis and catalytic cracking. The present study focuses on reducing the temperature to maximize the quantity of styrene monomer in the liquid product. A bench scale reactor has been developed to recover the styrene monomer and other valuable chemicals. Experiments were carried under partial oxidation and vacuum conditions in the temperature range of 300-500 deg. C. In the pyrolysis optimization studies, the best atmospheric condition was determined to be vacuum, the pyrolysis temperature should be 500 deg. C, yield of liquid product obtained was 91.7% and yield of styrene obtained was 85.5%. In the characterization studies, distillation and IR spectroscopy experiments were carried out. The remaining of the liquid product comprises of benzene, ethyl benzene, and styrene dimers and trimers.

  1. Thermal decomposition of expanded polystyrene in a pebble bed reactor to get higher liquid fraction yield at low temperatures.

    PubMed

    Chauhan, R S; Gopinath, S; Razdan, P; Delattre, C; Nirmala, G S; Natarajan, R

    2008-11-01

    Expanded polystyrene is one of the polymers produced in large quantities due to its versatile application in different fields. This polymer is one of the most intractable components in municipal solid waste. Disposal of polymeric material by pyrolysis or catalytic cracking yields valuable hydrocarbon fuels or monomers. Literature reports different types of reactors and arrangements that have uniform temperatures during pyrolysis and catalytic cracking. The present study focuses on reducing the temperature to maximize the quantity of styrene monomer in the liquid product. A bench scale reactor has been developed to recover the styrene monomer and other valuable chemicals. Experiments were carried under partial oxidation and vacuum conditions in the temperature range of 300-500 degrees C. In the pyrolysis optimization studies, the best atmospheric condition was determined to be vacuum, the pyrolysis temperature should be 500 degrees C, yield of liquid product obtained was 91.7% and yield of styrene obtained was 85.5%. In the characterization studies, distillation and IR spectroscopy experiments were carried out. The remaining of the liquid product comprises of benzene, ethyl benzene, and styrene dimers and trimers.

  2. 7 CFR 2902.15 - Bedding, bed linens, and towels.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 7 Agriculture 15 2011-01-01 2011-01-01 false Bedding, bed linens, and towels. 2902.15 Section 2902... PROCUREMENT Designated Items § 2902.15 Bedding, bed linens, and towels. (a) Definition. (1) Bedding is that..., bedspreads, comforters, and quilts. (2) Bed linens are woven cloth sheets and pillowcases used in bedding....

  3. 7 CFR 3201.15 - Bedding, bed linens, and towels.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... 7 Agriculture 15 2013-01-01 2013-01-01 false Bedding, bed linens, and towels. 3201.15 Section 3201... PROCUREMENT Designated Items § 3201.15 Bedding, bed linens, and towels. (a) Definition. (1) Bedding is that..., bedspreads, comforters, and quilts. (2) Bed linens are woven cloth sheets and pillowcases used in bedding....

  4. 7 CFR 3201.15 - Bedding, bed linens, and towels.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... 7 Agriculture 15 2012-01-01 2012-01-01 false Bedding, bed linens, and towels. 3201.15 Section 3201... PROCUREMENT Designated Items § 3201.15 Bedding, bed linens, and towels. (a) Definition. (1) Bedding is that..., bedspreads, comforters, and quilts. (2) Bed linens are woven cloth sheets and pillowcases used in bedding....

  5. 7 CFR 2902.15 - Bedding, bed linens, and towels.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 7 Agriculture 15 2010-01-01 2010-01-01 false Bedding, bed linens, and towels. 2902.15 Section 2902... PROCUREMENT Designated Items § 2902.15 Bedding, bed linens, and towels. (a) Definition. (1) Bedding is that..., bedspreads, comforters, and quilts. (2) Bed linens are woven cloth sheets and pillowcases used in bedding....

  6. 7 CFR 3201.15 - Bedding, bed linens, and towels.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... 7 Agriculture 15 2014-01-01 2014-01-01 false Bedding, bed linens, and towels. 3201.15 Section 3201... PROCUREMENT Designated Items § 3201.15 Bedding, bed linens, and towels. (a) Definition. (1) Bedding is that..., bedspreads, comforters, and quilts. (2) Bed linens are woven cloth sheets and pillowcases used in bedding....

  7. Alexa Fluor 488 as an iron sensing molecule and its application in PEBBLE nanosensors.

    PubMed

    Sumner, James P; Kopelman, Raoul

    2005-04-01

    Molecular Probes' Alexa Fluor dyes are generally used for biological labeling because of their ideal fluorescent properties, but here we detail Alexa Fluor 488's nanomolar sensitivity to free iron. Furthermore, the dye has been encapsulated into a polymer nanosphere by a microemulsion method, producing <100 nm particles. These nanosensors, PEBBLEs (Probe Encapsulated By Biologically Localized Embedding) have micromolar sensitivity and are non-responsive to other metal ions of biological interest.

  8. Ceramic inspection system

    DOEpatents

    Werve, Michael E.

    2006-05-16

    A system for inspecting a ceramic component. The ceramic component is positioned on a first rotary table. The first rotary table rotates the ceramic component. Light is directed toward the first rotary table and the rotating ceramic component. A detector is located on a second rotary table. The second rotary table is operably connected to the first rotary table and the rotating ceramic component. The second rotary table is used to move the detector at an angle to the first rotary table and the rotating ceramic component.

  9. Dental ceramics: An update

    PubMed Central

    Shenoy, Arvind; Shenoy, Nina

    2010-01-01

    In the last few decades, there have been tremendous advances in the mechanical properties and methods of fabrication of ceramic materials. While porcelain-based materials are still a major component of the market, there have been moves to replace metal ceramics systems with all ceramic systems. Advances in bonding techniques have increased the range and scope for use of ceramics in dentistry. In this brief review, we will discuss advances in ceramic materials and fabrication techniques. Examples of the microstructure property relationships for these ceramic materials will also be addressed. PMID:21217946

  10. Evaluation of phosphate pebble as a precipitant for acid mine drainage treatment

    SciTech Connect

    Choi, J.C.; West, T.R.

    1995-12-01

    Laboratory testing was performed to evaluate the effectiveness of phosphate pebbles from Florida in the treatment of acid mine drainage under aerobic conditions. Using different flow rates, results show that phosphate pebbles effectively removed ferric iron up to 1,200 mg/l, aluminum up to 800 mg/l and sulfate up to 8,600 mg/l in three weeks. In addition, the pH increased to values as high as 3.2 in the effluent water from a pH of the influent water ranging from 2.1 to 2.2. Removal of ferric iron, aluminum, and sulfate as well as pH increases were inversely proportional to flow rates, ranging from 1.17 {times} 10{sup {minus}4} to 1.05 {times} 10{sup {minus}3} liters per minute per kg of phosphate pebble. Apparently this method can be applied to reduce acid mine drainage from old coal refuse piles, even those containing high concentration of ferric iron and aluminum ions.

  11. Ratiometric optical PEBBLE nanosensors for real-time magnesium ion concentrations inside viable cells.

    PubMed

    Park, Edwin J; Brasuel, Murphy; Behrend, Caleb; Philbert, Martin A; Kopelman, Raoul

    2003-08-01

    This paper presents the development and characterization of a highly selective magnesium fluorescent optical nanosensor, made possible by PEBBLE (probe encapsulated by biologically localized embedding) technology. A ratiometric sensor has been developed by co-immobilizing a dye that is sensitive to and highly selective for magnesium, with a reference dye in a matrix. The sensors are prepared via a microemulsion polymerization process, which entraps the sensing components inside a polymer matrix. The resultant spherical sensors are approximately 40 nm in diameter. The Coumarin 343 (C343) dye, which by itself does not enter the cell, when immobilized in a PEBBLE is used as the magnesium-selective agent that provides the high and necessary selectivity over other intracellular ions, such as Ca2+, Na+, and K+. The dynamic range of these sensors was 1-30 mM, with a linear range from 1 to 10 mM, with a response time of <4 s. In contrast to free dye, these nano-optodes are not perturbed by proteins. They are fully reversible and exhibit minimal leaching and photobleaching over extended periods of time. In vitro intracellular changes in Mg2+ concentration were monitored in C6 glioma cells, which remained viable after PEBBLE delivery via gene gun injection. The selectivity for Mg2+ along with the biocompatibility of the matrix provides a new and reliable tool for intracellular magnesium measurements.

  12. Hybrid fluidized bed combuster

    DOEpatents

    Kantesaria, Prabhudas P.; Matthews, Francis T.

    1982-01-01

    A first atmospheric bubbling fluidized bed furnace is combined with a second turbulent, circulating fluidized bed furnace to produce heat efficiently from crushed solid fuel. The bed of the second furnace receives the smaller sizes of crushed solid fuel, unreacted limestone from the first bed, and elutriated solids extracted from the flu gases of the first bed. The two-stage combustion of crushed solid fuel provides a system with an efficiency greater than available with use of a single furnace of a fluidized bed.

  13. Bed material agglomeration during fluidized bed combustion

    SciTech Connect

    Brown, R.C.; Dawson, M.R.; Noble, S.

    1993-02-01

    The purpose of this project is to determine the physical and chemical reactions which led to the undesired agglomeration of bed material during fluidized bed combustion and to relate these reactions to specific causes. Survey of industrial-scale fluidized bed combustors is being conducted to determine the occurrence of bed agglomeration and the circumstances under which agglomeration took place. This task should be finished by the end of February. Samples of bed material, agglomerate material, and boiler deposits are being requested from boiler operators as part of the survey. Once received, these sample will be analyzed to determine chemical and mineralogic composition. The bulk chemical determination will be performed using x-ray fluorescence and inductively coupled plasma-optical emission (ICP). Mineralogy will be detected by x-ray diffraction (XRD). Chemical and mineral reactions will be determined by scanning electron microscopy, optical microscopy, and electron microprobe.

  14. Bed Bugs and Schools

    EPA Pesticide Factsheets

    Bed bugs have long been a pest – feeding on blood, causing itchy bites and generally irritating their human hosts. They are successful hitchhikers, and can move from an infested site to furniture, bedding, baggage, boxes, and clothing.

  15. Bed rest during pregnancy

    MedlinePlus

    ... on the inferior vena cava. How Can I Deal with Discomfort from Bed Rest? Bed rest can ... Group Health Cooperative, Bellevue, WA. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the ...

  16. Ceramic electrolyte coating methods

    DOEpatents

    Seabaugh, Matthew M.; Swartz, Scott L.; Dawson, William J.; McCormick, Buddy E.

    2004-10-12

    Processes for preparing aqueous suspensions of a nanoscale ceramic electrolyte material such as yttrium-stabilized zirconia. The invention also includes a process for preparing an aqueous coating slurry of a nanoscale ceramic electrolyte material. The invention further includes a process for depositing an aqueous spray coating slurry including a ceramic electrolyte material on pre-sintered, partially sintered, and unsintered ceramic substrates and products made by this process.

  17. Validation of In-Situ Iron-Manganese Oxide Coated Stream Pebbles as Sensors for Arsenic Source Monitoring

    NASA Astrophysics Data System (ADS)

    Blake, J.; Peters, S. C.; Casteel, A.

    2013-12-01

    Locating nonpoint source contaminant fluxes can be challenging due to the inherent heterogeneity of source and of the subsurface. Contaminants such as arsenic are a concern for drinking water quality and ecosystem health. Arsenic contamination can be the result of several natural and anthropogenic sources, and therefore it can be difficult to trace and identify major areas of arsenic in natural systems. Identifying a useful source indicator for arsenic is a crucial step for environmental remediation efforts. Previous studies have found iron-manganese oxide coated streambed pebbles as useful source indicators due to their high attraction for heavy metals in water. In this study, pebbles, surface water at baseflow and nearby rocks were sampled from the Pennypack Creek and its tributaries, in southwestern Pennsylvania, to test the ability of coated streambed pebbles as environmental source indicators for arsenic. Quartz pebbles, 5-7 cm in diameter, were sampled to minimize elemental contamination from rock chemistry. In addition, quartz provides an excellent substrate for iron and manganese coatings to form. These coatings were leached from pebbles using 4M nitric acid with 0.1% concentrated hydrochloric acid. Following sample processing, analyses were performed using an ICP-MS and the resulting data were spatially organized using ArcGIS software. Arsenic, iron and manganese concentrations in the leachate are normalized to pebble surface area and each location is reported as a ratio of arsenic to iron and manganese. Results suggest that iron-manganese coated stream pebbles are useful indicators of arsenic location within a watershed.

  18. Introduction to Bed Bugs

    EPA Pesticide Factsheets

    The common bed bug (Cimex lectularius) is a pest – feeding on blood, causing itchy bites and generally irritating their human hosts. EPA and other agencies all consider bed bugs a public health pest, but bed bugs are not known to transmit disease.

  19. Making a Bed

    ERIC Educational Resources Information Center

    Wexler, Anthony; Stein, Sherman

    2005-01-01

    The origins of this paper lay in making beds by putting pieces of plywood on a frame: If beds need to be 4 feet 6 inches by 6 feet 3 inches, and plywood comes in 4-foot by 8-foot sheets, how should one cut the plywood to minimize waste (and have stable beds)? The problem is of course generalized.

  20. Advanced Ceramic Armor Materials

    DTIC Science & Technology

    1990-05-11

    materials, toughened alumina, fiber -reinforced glass matrix composites, and multilayer-gradient materials for ballistic testing. Fabrication and...material systems: Multilayer advanced armor materials consisting of a hard ceramic faceplate bonded to a graphite fiber -reinforced glass matrix...toughened alumina, and fiber - applied studies of advanced reinforced ceramic matrix glass and glass -ceramic composites for ballistic testing. technologies

  1. Brittleness of ceramics

    NASA Technical Reports Server (NTRS)

    Kroupa, F.

    1984-01-01

    The main characteristics of mechanical properties of ceramics are summarized and the causes of their brittleness, especially the limited mobility of dislocations, are discussed. The possibility of improving the fracture toughness of ceramics and the basic research needs relating to technology, structure and mechanical properties of ceramics are stressed in connection with their possible applications in engineering at high temperature.

  2. Ceramic to metal seal

    DOEpatents

    Snow, Gary S.; Wilcox, Paul D.

    1976-01-01

    Providing a high strength, hermetic ceramic to metal seal by essentially heating a wire-like metal gasket and a ceramic member, which have been chemically cleaned, while simultaneously deforming from about 50 to 95 percent the metal gasket against the ceramic member at a temperature of about 30 to 75 percent of the melting temperature of the metal gasket.

  3. Collaborative Strategy on Bed Bugs

    EPA Pesticide Factsheets

    The Collaborative Strategy on Bed Bugs was developed by the Federal Bed Bug Workgroup to clarify the federal role in bed bug control and highlight ways that government, community, academia and private industry can work together on bed bug issues.

  4. Ceramic gas turbine shroud

    SciTech Connect

    Shi, Jun; Green, Kevin E.

    2014-07-22

    An example gas turbine engine shroud includes a first annular ceramic wall having an inner side for resisting high temperature turbine engine gasses and an outer side with a plurality of radial slots. A second annular metallic wall is positioned radially outwardly of and enclosing the first annular ceramic wall and has a plurality of tabs in communication with the slot of the first annular ceramic wall. The tabs of the second annular metallic wall and slots of the first annular ceramic wall are in communication such that the first annular ceramic wall and second annular metallic wall are affixed.

  5. Thin film ceramic thermocouples

    NASA Technical Reports Server (NTRS)

    Gregory, Otto (Inventor); Fralick, Gustave (Inventor); Wrbanek, John (Inventor); You, Tao (Inventor)

    2011-01-01

    A thin film ceramic thermocouple (10) having two ceramic thermocouple (12, 14) that are in contact with each other in at least on point to form a junction, and wherein each element was prepared in a different oxygen/nitrogen/argon plasma. Since each element is prepared under different plasma conditions, they have different electrical conductivity and different charge carrier concentration. The thin film thermocouple (10) can be transparent. A versatile ceramic sensor system having an RTD heat flux sensor can be combined with a thermocouple and a strain sensor to yield a multifunctional ceramic sensor array. The transparent ceramic temperature sensor that could ultimately be used for calibration of optical sensors.

  6. Out-of-pile tritium release study on Li 4SiO 4 pebbles from TRINPC-I experiments

    NASA Astrophysics Data System (ADS)

    Kang, Chunmei; Wang, Xiaolin; Xiao, Chengjian; Gao, Xiaoling; Gu, Mei; Liu, Jun; Wang, Heyi; Peng, Shuming; Chen, Xiaojun

    2011-05-01

    Out-of-pile tritium release examinations of irradiated Li 4SiO 4 pebbles were performed in TRINPC-I experiments for evaluating material performance and verifying the system design. To generate tritium the specimens were irradiated with neutrons. Li 4SiO 4 pebbles were made by a freeze-drying method. In the experiments, concentrations of tritium in the form of tritium gas (HT + T 2) and tritiated water (HTO + T 2O) in the outlet streams of a reactor tube were measured separately with an ionization chamber and a liquid scintillation radiometer. The results show that the percentage of tritium gas (HT + T 2) and tritiated water trapped by the breeder pebbles were about 72% and 19% of totally released tritium, respectively. Thus, more tritium was released in the form of tritium gas in this work. In addition to tritium trapped by the breeder pebbles, the amount of free tritium was also measured by breaking on-line a quartz capsule containing Li 4SiO 4 pebbles, the percentage of which was 9% of totally released tritium. The temperature peaks of tritium gas mainly appeared at about 477 °C and 654 °C, while the temperature peak of tritiated water appeared at about 402 °C, under which most of tritiated water released.

  7. All-ceramic crowns.

    PubMed

    Lehner, C R; Schärer, P

    1992-06-01

    Despite the good appearance and biocompatibility of dental porcelains, failures are still of considerable concern because of some limited properties common to all-ceramic crown systems. As in the years before, pertinent scientific articles published between November 1990 and December 1991 focused on strengthening mechanisms and compared fracture toughness for different ceramic systems by using various test methods. Some evaluated the clinical implications thereon for seating and loading crowns and measured wear against different ceramic surface conditions. Recently introduced with pleasing aesthetic qualities, IPS-Empress (Ivoclar, Schaan, Liechtenstein), a new European leucite-reinforced glass-ceramic, has finally drawn attention in some journals and has been reviewed with promising in vitro test results. Using a simple press-molding technique, well-fitting crowns, inlays, and veneers can be fabricated without an additional ceramming procedure. Again, only long-term clinical trials will validate achievements compared with other all-ceramic systems and with well-established metal ceramics.

  8. Jumping the gap: the formation conditions and mass function of `pebble-pile' planetesimals

    NASA Astrophysics Data System (ADS)

    Hopkins, Philip F.

    2016-03-01

    In a turbulent proto-planetary disc, dust grains undergo large-density fluctuations and under the right circumstances, grain overdensities can collapse under self-gravity (forming a `pebble-pile' planetesimal). Using a simple model for fluctuations predicted in simulations, we estimate the rate of formation and mass function of self-gravitating planetesimal-mass bodies formed by this mechanism. This depends sensitively on the grain size, disc surface density, and turbulent Mach numbers. However, when it occurs, the resulting planetesimal mass function is broad and quasi-universal, with a slope dN/dM ∝ M-(1-2), spanning size/mass range ˜10-104 km (˜10-9-5 M⊕). Collapse to planetesimal through super-Earth masses is possible. The key condition is that grain density fluctuations reach large amplitudes on large scales, where gravitational instability proceeds most easily (collapse of small grains is suppressed by turbulence). This leads to a new criterion for `pebble-pile' formation: τs ≳ 0.05 ln (Q1/2/Zd)/ln (1 + 10 α1/4) ˜ 0.3 ψ(Q, Z, α) where τs = ts Ω is the dimensionless particle stopping time. In a minimum-mass solar nebula, this requires grains larger than a = (50, 1, 0.1) cm at r=(1, 30, 100) au}. This may easily occur beyond the ice line, but at small radii would depend on the existence of large boulders. Because density fluctuations depend strongly on τs (inversely proportional to disc surface density), lower density discs are more unstable. Conditions for pebble-pile formation also become more favourable around lower mass, cooler stars.

  9. Accretion of Cometary Nuclei in the Solar Nebula: Boulders, Not Pebbles

    NASA Astrophysics Data System (ADS)

    Weissman, Paul R.; A'Hearn, Michael

    2015-11-01

    Comets are the most primitive bodies in the solar system. They retain a largely unprocessed record of conditions in the primordial solar nebula 4.56 Gyr ago, including the initial accretion of dust and ice particles into macroscopic bodies. Current accretion theory suggests that ice and dust aggregates grew to pebble (cm) sizes before streaming instabilities and gravitational collapse brought these pebble swarms together as km-sized (or larger) bodies. Recent imaging of the nucleus of comet 67P/Churyumov-Gerasimenko by the Rosetta OSIRIS camera team has revealed the existence of “goose bump” terrain on the nucleus surface and lining the interior walls of large, ~200 m diameter and 180 m deep cylindrical pits. These pits are believed to be sinkholes, formed when near-surface materials collapse into voids within the nucleus, revealing the fresh comet interior on the walls of the pits. The goose bump terrain consists of 3-4 m diameter “boulders” randomly stacked one on top of another. We propose that these boulders, likely with an icy-conglomerate composition, are the basic building blocks of cometary nuclei. This is the first observational confirmation of current accretion theories, with the caveat that rather than pebbles, the preferred size range is 3-4 m boulders for objects formed in the giant planets region of the solar system. The presence of icy grains beyond the solar nebula snow-line and the large heliocentric range of the giant planets region likely contribute to the formation of these larger boulders, before they are incorporated into cometary nuclei. This work was supported by NASA through the U.S. Rosetta Project.

  10. The Role of Pebble Fragmentation in Planetesimal Formation. I. Experimental Study

    NASA Astrophysics Data System (ADS)

    Bukhari Syed, M.; Blum, J.; Wahlberg Jansson, K.; Johansen, A.

    2017-01-01

    Previous work on protoplanetary dust growth shows a halt at centimeter sizes owing to the occurrence of bouncing at velocities of ≳0.1 m s‑1 and fragmentation at velocities ≳1 m s‑1. To overcome these barriers, spatial concentration of centimeter-sized dust pebbles and subsequent gravitational collapse have been proposed. However, numerical investigations have shown that dust aggregates may undergo fragmentation during the gravitational collapse phase. This fragmentation in turn changes the size distribution of the solids and thus must be taken into account in order to understand the properties of the planetesimals that form. To explore the fate of dust pebbles undergoing fragmenting collisions, we conducted laboratory experiments on dust-aggregate collisions with a focus on establishing a collision model for this stage of planetesimal formation. In our experiments, we analyzed collisions of dust aggregates with masses between 0.7 and 91 g mass ratios between target and projectile from 1 to 126 at a fixed porosity of 65%, within the velocity range of 1.5–8.7 m s‑1, at low atmospheric pressure of ∼10‑3 mbar, and in free-fall conditions. We derived the mass of the largest fragment, the fragment size/mass distribution, and the efficiency of mass transfer as a function of collision velocity and projectile/target aggregate size. Moreover, we give recipes for an easy-to-use fragmentation and mass-transfer model for further use in modeling work. In a companion paper, we use the experimental findings and the derived dust-aggregate collision model to investigate the fate of dust pebbles during gravitational collapse.

  11. Making Planet Nine: Pebble Accretion at 250-750 AU in a Gravitationally Unstable Ring

    NASA Astrophysics Data System (ADS)

    Kenyon, Scott J.; Bromley, Benjamin C.

    2016-07-01

    We investigate the formation of icy super-Earth mass planets within a gravitationally unstable ring of solids orbiting at 250-750 AU around a 1 {M}⊙ star. Coagulation calculations demonstrate that a system of a few large oligarchs and a swarm of pebbles generates a super-Earth within 100-200 Myr at 250 AU and within 1-2 Gyr at 750 AU. Systems with more than ten oligarchs fail to yield super-Earths over the age of the solar system. As these systems evolve, destructive collisions produce detectable debris disks with luminosities of {10}-5{--}{10}-3 relative to the central star.

  12. Optical nanosensors for chemical analysis inside single living cells. 1. Fabrication, characterization, and methods for intracellular delivery of PEBBLE sensors.

    PubMed

    Clark, H A; Hoyer, M; Philbert, M A; Kopelman, R

    1999-11-01

    Spherical optical nanosensors, or PEBBLEs (probes encapsulated by biologically localized embedding), have been produced in sizes including 20 and 200 nm in diameter. These sensors are fabricated in a microemulsion and consist of fluorescent indicators entrapped in a polyacrylamide matrix. A generalized polymerization method has been developed that permits production of sensors containing any hydrophilic dye or combination of dyes in the matrix. The PEBBLE matrix protects the fluorescent dye from interference by proteins, allowing reliable in vivo calibrations of dyes. Sensor response times are less than 1 ms. Cell viability assays indicate that the PEBBLEs are biocompatible, with negligible biological effects compared to control conditions. Several sensor delivery methods have been studied, including liposomal delivery, gene gun bombardment, and picoinjection into single living cells.

  13. The friction and wear of ceramic/ceramic and ceramic/metal combinations in sliding contact

    NASA Technical Reports Server (NTRS)

    Sliney, Harold E.; Dellacorte, Christopher

    1994-01-01

    The tribological characteristics of ceramics sliding on ceramics are compared to those of ceramics sliding on a nickel-based turbine alloy. The friction and wear of oxide ceramics and silicon-based ceramics in air at temperatures from room ambient to 900 C (in a few cases to 1200 C) were measured for a hemispherically-tipped pin on a flat sliding contact geometry. In general, especially at high temperature, friction and wear were lower for ceramic/metal combinations than for ceramic/ceramic combinations. The better tribological performance for ceramic/metal combinations is attributed primarily to the lubricious nature of the oxidized surface of the metal.

  14. The friction and wear of ceramic/ceramic and ceramic/metal combinations in sliding contact

    NASA Technical Reports Server (NTRS)

    Sliney, Harold E.; Dellacorte, Christopher

    1993-01-01

    The tribological characteristics of ceramics sliding on ceramics are compared to those of ceramics sliding on a nickel based turbine alloy. The friction and wear of oxide ceramics and silicon-based ceramics in air at temperatures from room ambient to 900 C (in a few cases to 1200 C) were measured for a hemispherically-tipped pin on a flat sliding contact geometry. In general, especially at high temperature, friction and wear were lower for ceramic/metal combinations than for ceramic/ceramic combinations. The better tribological performance for ceramic/metal combinations is attributed primarily to the lubricious nature of the oxidized surface of the metal.

  15. Fluidized bed combustor modeling

    NASA Technical Reports Server (NTRS)

    Horio, M.; Rengarajan, P.; Krishnan, R.; Wen, C. Y.

    1977-01-01

    A general mathematical model for the prediction of performance of a fluidized bed coal combustor (FBC) is developed. The basic elements of the model consist of: (1) hydrodynamics of gas and solids in the combustor; (2) description of gas and solids contacting pattern; (3) kinetics of combustion; and (4) absorption of SO2 by limestone in the bed. The model is capable of calculating the combustion efficiency, axial bed temperature profile, carbon hold-up in the bed, oxygen and SO2 concentrations in the bubble and emulsion phases, sulfur retention efficiency and particulate carry over by elutriation. The effects of bed geometry, excess air, location of heat transfer coils in the bed, calcium to sulfur ratio in the feeds, etc. are examined. The calculated results are compared with experimental data. Agreement between the calculated results and the observed data are satisfactory in most cases. Recommendations to enhance the accuracy of prediction of the model are suggested.

  16. Transport of marked pebbles in short periods of time on a coarse clastic beach (Marina di Pisa, Italy)

    NASA Astrophysics Data System (ADS)

    Bertoni, D.; Ciavola, P.; Grottoli, E.; Sarti, G.

    2012-04-01

    Transport of coarse sediments on coarse clastic beaches still presents aspects that are not fully understood. For instance, there is a generally perceived notion that during fair-weather periods coarse grains hardly move, if not at all. The aim of this experiment is to prove that sediments such as pebbles are subject to significant shift in very short lapses of time and under low energy waves. An artificial coarse clastic beach at Marina di Pisa (Tuscany, Italy) was chosen as study site: Barbarossa beach is 110 m long and is bounded by two groynes. The mean grain size is about 40-to-50 mm. About 80 pebbles were marked by means of the RFID technology, which enables to univocally identify the tracers. The marked pebbles were released along cross-shore transects (one pebble each on the fair-weather berm, on the beachface and on the step crest) on the morning of September 15th, and two recovery campaigns were carried out after 6 and 24 hours from the injection. No particular wave activity was recorded during the time frame of the experiment. After the first recovery campaign, which was performed 6 hours later than the injection, about 94% of the pebbles were detected. After the second recovery campaign, 24 hours later, the recovery rate decreased to 89%. Considering that the technique provides for detection of tracers within 50 cm, the resulting loss of pebbles after so brief spans of time is remarkable. The lack of detection of few tracers implies that the transport rate that they experienced is not negligible. The highest rate of losses was recorded on the beachface, the zone that is subjected the most to waves even under calm conditions. Pebble movement is also confirmed by the fact that tracers detected after the first recovery campaign were not detected once again after the second recovery campaign, and vice versa. The results of the experiment are useful to better define the transport of coarse sediments, verifying that pebbles have to be expected be moving even

  17. Geochemical And Petrological Investigations Of The Representative Cretaceous Bentonite Beds, Wyoming : Tectonic Implications

    NASA Astrophysics Data System (ADS)

    Khandaker, N. I.

    2004-12-01

    Representative bentonite samples were collected from the exposed Cretaceous siliciclastics in Bighorn Basin, north-central Wyoming. Bentonite beds constitute a significant stratigraphic importance with respect to local and regional correlation tool and are associated with the Thermopolis Shale (Lower Cretaceous), Mowry Shale (Lower Cretaceous), and Frontier Formation (Upper Cretaceous). These beds range in thickness from few inches to ten feet and are interbedded with thick cross-bedded sandstone, pebbly sandstone, polymictic conglomerate, siliceous-rippled shale, and lignitic shale. Preliminary petrological and geochemical investigations were carried out to establish a distinctive geochemical signature for each bed. Emphasis was given on the overall distribution of the immobile traces, high refractory elements, and ultrastable heavy mineral components among the selective bentonite beds. The outcome of petrological, bulk, and trace element studies involving multiple bentonite beds indicated a subtle difference in terms of abundance of trace-element and detrital components among the studied samples and can be attributed to the source region characteristics, distinctive diagenetic pathways, and depositional setting. Furthermore, geochemical analyses involving multi-element plots suggest to an evolving source terrain located in close proximity to the bentonite depositional basin.

  18. Ceramic tamper-revealing seals

    DOEpatents

    Kupperman, David S.; Raptis, Apostolos C.; Sheen, Shuh-Haw

    1992-01-01

    A flexible metal or ceramic cable with composite ceramic ends, or a u-shaped ceramic connecting element attached to a binding element plate or block cast from alumina or zirconium, and connected to the connecting element by shrink fitting.

  19. Analyses of fine paste ceramics

    SciTech Connect

    Sabloff, J A

    1980-01-01

    Four chapters are included: history of Brookhaven fine paste ceramics project, chemical and mathematical procedures employed in Mayan fine paste ceramics project, and compositional and archaeological perspectives on the Mayan fine paste ceramics. (DLC)

  20. Ceramic laser materials

    NASA Astrophysics Data System (ADS)

    Ikesue, Akio; Aung, Yan Lin

    2008-12-01

    The word 'ceramics' is derived from the Greek keramos, meaning pottery and porcelain. The opaque and translucent cement and clay often used in tableware are not appropriate for optical applications because of the high content of optical scattering sources, that is, defects. Recently, scientists have shown that by eliminating the defects, a new, refined ceramic material - polycrystalline ceramic - can be produced. This advanced ceramic material offers practical laser generation and is anticipated to be a highly attractive alternative to conventional glass and single-crystal laser technologies in the future. Here we review the history of the development of ceramic lasers, the principle of laser generation based on this material, some typical results achieved with ceramic lasers so far, and discuss the potential future outlook for the field.

  1. NDE of ceramics and ceramic composites

    NASA Technical Reports Server (NTRS)

    Vary, Alex; Klima, Stanley J.

    1991-01-01

    Although nondestructive evaluation (NDE) techniques for ceramics are fairly well developed, they are difficult to apply in many cases for high probability detection of the minute flaws that can cause failure in monolithic ceramics. Conventional NDE techniques are available for monolithic and fiber reinforced ceramic matrix composites, but more exact quantitative techniques needed are still being investigated and developed. Needs range from flaw detection to below 100 micron levels in monolithic ceramics to global imaging of fiber architecture and matrix densification anomalies in ceramic composites. NDE techniques that will ultimately be applicable to production and quality control of ceramic structures are still emerging from the lab. Needs are different depending on the processing stage, fabrication method, and nature of the finished product. NDE techniques are being developed in concert with materials processing research where they can provide feedback information to processing development and quality improvement. NDE techniques also serve as research tools for materials characterization and for understanding failure processes, e.g., during thermomechanical testing.

  2. Ect2, an ortholog of Drosophila Pebble, regulates formation of growth cones in primary cortical neurons

    PubMed Central

    Tsuji, Takahiro; Higashida, Chiharu; Aoki, Yoshihiko; Islam, Mohammad Saharul; Dohmoto, Mitsuko; Higashida, Haruhiro

    2016-01-01

    In collaboration with Marshall Nirenberg, we performed in vivo RNA interference (RNAi) genome-wide screening in Drosophila embryos. Pebble has been shown to be involved in Drosophila neuronal development. We have also reported that depletion of Ect2, a mammalian ortholog of Pebble, induces differentiation in NG108-15 neuronal cells. However, the precise role of Ect2 in neuronal development has yet to be studied. Here, we confirmed in PC12 pheochromocytoma cells that inhibition of Ect2 expression by RNAi stimulated neurite outgrowth, and in the mouse embryonic cortex that Ect2 was accumulated throughout the ventricular and subventricular zones with neuronal progenitor cells. Next, the effects of Ect2 depletion were studied in primary cultures of mouse embryonic cortical neurons: Loss of Ect2 did not affect the differentiation stages of neuritogenesis, the number of neurites, or axon length, while the numbers of growth cones and growth cone-like structures were increased. Taken together, our results suggest that Ect2 contributes to neuronal morphological differentiation through regulation of growth cone dynamics. PMID:22366651

  3. Building the giant planet cores by convergent migration of pebble-accreting embryos

    NASA Astrophysics Data System (ADS)

    Chrenko, Ondrej; Broz, Miroslav

    2016-10-01

    An explanation of the accretion buildup of giant planet cores on rather short (~Myr) time scales remains a long-standing challenge for scenarios of planetary system formation. One of the recently proposed processes that can take part during this evolutionary stage is the convergent Type I migration of Earth-sized embryos towards the zero-torque radius, occurring at an opacity transition within the dusty-gaseous protoplanetary disk (e.g. Pierens et al. 2013). Inconveniently, simulations show that such groups of embryos do not merge easily because they often get locked in mutual mean-motion resonances and consequently form an inward-migrating convoy.We revise this possibility of merging embryos while taking into account their ongoing growth by pebble accretion. Our aim is to check whether the rapid changes of masses combined with the migration of embryos through the feeding zone can break the resonant chain and allow for the giant planet core formation.The environment of the protoplanetary disk is modeled with the 2D FARGO code (Masset 2000), which we modified in order to perform non-isothermal hydrodynamic simulations, assuming flux-limited radiative diffusion (Levermore & Pomraning 1981). The embedded massive bodies are evolved simultaneously in 3D using the hybrid Wisdom-Holman/Gauss-Radau integrator from the Rebound package (Rein & Spiegel 2015). A semi-analytic method is used to evolve the masses of embryos by pebble accretion (e.g. Levison et al. 2015).

  4. A preliminary study on removal of AMD precipitate coatings on pebbles

    NASA Astrophysics Data System (ADS)

    Lee, W.; Min, K.; Lee, H.

    2011-12-01

    AMD(acid mine drainage) having a low pH and elevated concentrations of heavy metals affects environments as a major pollutant. In addition to AMD's water contamination, reddish brown precipitates from AMD spoil the watercourse scenery without suitable removal treatments. To examine the removal potentiality of ultrasonic cleaner, the pebble samples coated by reddish brown precipitates were collected at abandoned mine stream and scraped precipitate coatings were analyzed for their chemical compositions and mineralogy. Their average contents of Fe2O3, SO3, and Al2O3 were 84.3%, 6.13%, and 3.69%, respectively and goethite was the major constituent mineral. Laboratorial tests to remove precipitate coatings were performed in an ultrasonic cleaner with the frequency of 40kHz at 20 to 70oC for 10 to 60 minutes. Water and hydrochloric acid of 0.1M to 1M were used as a cleaning solvent and the ratio of solvent to precipitate coated pebbles was 5 in weight. In result, an ultrasonic cleaning treatment is expected to be applied successively in field and removal efficiency was increased as reaction time, temperature, and concentration of solvent rises.

  5. Ect2, an ortholog of Drosophila Pebble, regulates formation of growth cones in primary cortical neurons.

    PubMed

    Tsuji, Takahiro; Higashida, Chiharu; Aoki, Yoshihiko; Islam, Mohammad Saharul; Dohmoto, Mitsuko; Higashida, Haruhiro

    2012-11-01

    In collaboration with Marshall Nirenberg, we performed in vivo RNA interference (RNAi) genome-wide screening in Drosophila embryos. Pebble has been shown to be involved in Drosophila neuronal development. We have also reported that depletion of Ect2, a mammalian ortholog of Pebble, induces differentiation in NG108-15 neuronal cells. However, the precise role of Ect2 in neuronal development has yet to be studied. Here, we confirmed in PC12 pheochromocytoma cells that inhibition of Ect2 expression by RNAi stimulated neurite outgrowth, and in the mouse embryonic cortex that Ect2 was accumulated throughout the ventricular and subventricular zones with neuronal progenitor cells. Next, the effects of Ect2 depletion were studied in primary cultures of mouse embryonic cortical neurons: Loss of Ect2 did not affect the differentiation stages of neuritogenesis, the number of neurites, or axon length, while the numbers of growth cones and growth cone-like structures were increased. Taken together, our results suggest that Ect2 contributes to neuronal morphological differentiation through regulation of growth cone dynamics.

  6. Continuous Fiber Ceramic Composites

    SciTech Connect

    2002-09-01

    Fiber-reinforced ceramic composites demonstrate the high-temperature stability of ceramics--with an increased fracture toughness resulting from the fiber reinforcement of the composite. The material optimization performed under the continuous fiber ceramic composites (CFCC) included a series of systematic optimizations. The overall goals were to define the processing window, to increase the robustinous of the process, to increase process yield while reducing costs, and to define the complexity of parts that could be fabricated.

  7. Displacive Transformation in Ceramics

    DTIC Science & Technology

    1994-02-28

    oxidizing atmosphere. In the fiber pullout mechanism of toughening which is thought to be the most powerful to date in ceramics, in non-graphite coated ...induced transformation of the ceramic coating promotes not only fiber pullout mechanisms, but also dissipates crack energy as well as causing frictional...1-11, (1971). 15 G. W. Taylor, "Electrical Properties of Niobium -Doped Ferroelectric Pb(Zr,SnTi)0 3 Ceramics," J. Appl. Phys., 38 [12], 4696-4706

  8. Alumina-based ceramic composite

    DOEpatents

    Alexander, Kathleen B.; Tiegs, Terry N.; Becher, Paul F.; Waters, Shirley B.

    1996-01-01

    An improved ceramic composite comprising oxide ceramic particulates, nonoxide ceramic particulates selected from the group consisting of carbides, borides, nitrides of silicon and transition metals and mixtures thereof, and a ductile binder selected from the group consisting of metallic, intermetallic alloys and mixtures thereof is described. The ceramic composite is made by blending powders of the ceramic particulates and the ductile to form a mixture and consolidating the mixture of under conditions of temperature and pressure sufficient to produce a densified ceramic composite.

  9. Measuring Fracture Times Of Ceramics

    NASA Technical Reports Server (NTRS)

    Shlichta, Paul J.; Bister, Leo; Bickler, Donald G.

    1989-01-01

    Electrical measurements complement or replace fast cinematography. Electronic system measures microsecond time intervals between impacts of projectiles on ceramic tiles and fracture tiles. Used in research on ceramics and ceramic-based composite materials such as armor. Hardness and low density of ceramics enable them to disintegrate projectiles more efficiently than metals. Projectile approaches ceramic tile specimen. Penetrating foil squares of triggering device activate display and recording instruments. As ceramic and resistive film break oscilloscope plots increase in electrical resistance of film.

  10. Method of sintering ceramic materials

    DOEpatents

    Holcombe, Cressie E.; Dykes, Norman L.

    1992-01-01

    A method for sintering ceramic materials is described. A ceramic article is coated with layers of protective coatings such as boron nitride, graphite foil, and niobium. The coated ceramic article is embedded in a container containing refractory metal oxide granules and placed within a microwave oven. The ceramic article is heated by microwave energy to a temperature sufficient to sinter the ceramic article to form a densified ceramic article having a density equal to or greater than 90% of theoretical density.

  11. Method of sintering ceramic materials

    DOEpatents

    Holcombe, C.E.; Dykes, N.L.

    1992-11-17

    A method for sintering ceramic materials is described. A ceramic article is coated with layers of protective coatings such as boron nitride, graphite foil, and niobium. The coated ceramic article is embedded in a container containing refractory metal oxide granules and placed within a microwave oven. The ceramic article is heated by microwave energy to a temperature sufficient to sinter the ceramic article to form a densified ceramic article having a density equal to or greater than 90% of theoretical density. 2 figs.

  12. Corrosion of Ceramic Materials

    NASA Technical Reports Server (NTRS)

    Opila, Elizabeth J.; Jacobson, Nathan S.

    1999-01-01

    Non-oxide ceramics are promising materials for a range of high temperature applications. Selected current and future applications are listed. In all such applications, the ceramics are exposed to high temperature gases. Therefore it is critical to understand the response of these materials to their environment. The variables to be considered here include both the type of ceramic and the environment to which it is exposed. Non-oxide ceramics include borides, nitrides, and carbides. Most high temperature corrosion environments contain oxygen and hence the emphasis of this chapter will be on oxidation processes.

  13. Defect production in ceramics

    SciTech Connect

    Zinkle, S.J.; Kinoshita, C.

    1997-08-01

    A review is given of several important defect production and accumulation parameters for irradiated ceramics. Materials covered in this review include alumina, magnesia, spinel silicon carbide, silicon nitride, aluminum nitride and diamond. Whereas threshold displacement energies for many ceramics are known within a reasonable level of uncertainty (with notable exceptions being AIN and Si{sub 3}N{sub 4}), relatively little information exists on the equally important parameters of surviving defect fraction (defect production efficiency) and point defect migration energies for most ceramics. Very little fundamental displacement damage information is available for nitride ceramics. The role of subthreshold irradiation on defect migration and microstructural evolution is also briefly discussed.

  14. Thermoplastic Extrusion for Ceramic Bodies

    NASA Astrophysics Data System (ADS)

    Clemens, Frank

    Originally for the extrusion of ceramic bricks and tiles, clay and water were used to endow ceramic particle mixtures with sufficient plastic behaviour to permit practical shaping of the ceramic bodies. High-performance ceramics, however, often require the elimination of clay from extrusion formulations because the chemistry of the clay is incompatible with that of the desired ceramic materials. Therefore organic materials are frequently used in ceramic extrusion to provide plastic flow. Not only plastic behaviour is important for the extrusion of ceramic bodies. There are many other characteristics that can be tailored by the suitable addition of organics in a ceramic extrusion paste, or feedstock.

  15. Fluidized-bed boilers

    SciTech Connect

    Makansi, J.; Schwieger, B.

    1982-08-01

    This report reviews the current state of atmospheric fluidized-bed combustion. The fundamentals of fluidized-bed combustion and design considerations are first discussed. Tables provide details of manufacturers, worldwide, and of the boilers now installed. Eight plants in various countries and burning a variety of fuels, are described more fully.

  16. Fluidized bed calciner apparatus

    DOEpatents

    Owen, Thomas J.; Klem, Jr., Michael J.; Cash, Robert J.

    1988-01-01

    An apparatus for remotely calcining a slurry or solution feed stream of toxic or hazardous material, such as ammonium diurante slurry or uranyl nitrate solution, is disclosed. The calcining apparatus includes a vertical substantially cylindrical inner shell disposed in a vertical substantially cylindrical outer shell, in which inner shell is disposed a fluidized bed comprising the feed stream material to be calcined and spherical beads to aid in heat transfer. Extending through the outer and inner shells is a feed nozzle for delivering feed material or a cleaning chemical to the beads. Disposed in and extending across the lower portion of the inner shell and upstream of the fluidized bed is a support member for supporting the fluidized bed, the support member having uniform slots for directing uniform gas flow to the fluidized bed from a fluidizing gas orifice disposed upstream of the support member. Disposed in the lower portion of the inner shell are a plurality of internal electric resistance heaters for heating the fluidized bed. Disposed circumferentially about the outside length of the inner shell are a plurality of external heaters for heating the inner shell thereby heating the fluidized bed. Further, connected to the internal and external heaters is a means for maintaining the fluidized bed temperature to within plus or minus approximately 25.degree. C. of a predetermined bed temperature. Disposed about the external heaters is the outer shell for providing radiative heat reflection back to the inner shell.

  17. Bed Bugs FAQs

    MedlinePlus

    ... allow them to fit into the smallest of spaces and stay there for long periods of time, even without a blood meal. Bed bugs are usually transported from place to place as people travel. The bed bugs travel in the seams and ...

  18. Thermal/chemical degradation of ceramic cross-flow filter materials

    SciTech Connect

    Alvin, M.A.; Lane, J.E.; Lippert, T.E.

    1989-11-01

    This report summarizes the 14-month, Phase 1 effort conducted by Westinghouse on the Thermal/Chemical Degradation of Ceramic Cross-Flow Filter Materials program. In Phase 1 expected filter process conditions were identified for a fixed-bed, fluid-bed, and entrained-bed gasification, direct coal fired turbine, and pressurized fluidized-bed combustion system. Ceramic cross-flow filter materials were also selected, procured, and subjected to chemical and physical characterization. The stability of each of the ceramic cross-flow materials was assessed in terms of potential reactions or phase change as a result of process temperature, and effluent gas compositions containing alkali and fines. In addition chemical and physical characterization was conducted on cross-flow filters that were exposed to the METC fluid-bed gasifier and the New York University pressurized fluidized-bed combustor. Long-term high temperature degradation mechanisms were proposed for each ceramic cross-flow material at process operating conditions. An experimental bench-scale test program is recommended to be conducted in Phase 2, generating data that support the proposed cross-flow filter material thermal/chemical degradation mechanisms. Papers on the individual subtasks have been processed separately for inclusion on the data base.

  19. Ceramic Technology Project

    SciTech Connect

    Not Available

    1992-03-01

    The Ceramic Technology Project was developed by the USDOE Office of Transportation Systems (OTS) in Conservation and Renewable Energy. This project, part of the OTS's Materials Development Program, was developed to meet the ceramic technology requirements of the OTS's automotive technology programs. Significant accomplishments in fabricating ceramic components for the USDOE and NASA advanced heat engine programs have provided evidence that the operation of ceramic parts in high-temperature engine environments is feasible. These programs have also demonstrated that additional research is needed in materials and processing development, design methodology, and data base and life prediction before industry will have a sufficient technology base from which to produce reliable cost-effective ceramic engine components commercially. A five-year project plan was developed with extensive input from private industry. In July 1990 the original plan was updated through the estimated completion of development in 1993. The objective is to develop the industrial technology base required for reliable ceramics for application in advanced automotive heat engines. The project approach includes determining the mechanisms controlling reliability, improving processes for fabricating existing ceramics, developing new materials with increased reliability, and testing these materials in simulated engine environments to confirm reliability. Although this is a generic materials project, the focus is on the structural ceramics for advanced gas turbine and diesel engines, ceramic bearings and attachments, and ceramic coatings for thermal barrier and wear applications in these engines. To facilitate the rapid transfer of this technology to US industry, the major portion of the work is being done in the ceramic industry, with technological support from government laboratories, other industrial laboratories, and universities.

  20. Detrital zircon U-Pb geochronology and provenance of the Carboniferous-Permian glaciomarine pebbly slates in the Tibetan Plateau

    NASA Astrophysics Data System (ADS)

    Wang, Q.; Zhu, D.; Zhao, Z.; Chung, S.; Li, C.; Sui, Q.; Fu, X.; Mo, X.

    2011-12-01

    Glaciomarine diamictites (including pebbly slate, pebbly siltstone, and pebbly sandstone) in the Tibetan Plateau are widely interpreted to have been associated with the deglaciation of the Indian continent. Guiding by zircon cathodoluminescence images, we determined U-Pb ages for detrital zircons from five typical Carboniferous-Permian pebbly slate samples from the Qiangtang, Lhasa, and Tethyan Himalaya of the Tibetan Plateau. The age distributions of detrital zircons from two samples (180 analyses) from Qiwu and Gangma Tso of the Qiangtang Terrane are similar, with two main age peaks ca. 579 and ca. 816 Ma and one minor age peak ca. 2490 Ma. Two samples (177 analyses) from Jiangrang and Damxung of the Lhasa Terrane define similar age distributions with two main age peaks ca. 539 and ca. 1175 Ma. Ages of detrital zircons from one sample (110 analyses) from Kangmar of the Tethyan Himalaya display main age peaks ca. 535, ca. 949, and ca. 2490 Ma. The ca. 816-Ma detrital zircons from the Qiangtang Terrane were most likely derived from the Lesser Himalaya, and the ca. 950-Ma detrital zircons from the Tethyan Himalaya might have been sourced from the High Himalaya, Eastern Ghats Province of the Indian plate and the Rayner Province of East Antarctica. The distinctive ca. 1175-Ma age population characteristic of zircons in the pebbly slates from the Lhasa Terrane is identical to the detrital zircons from the late Paleozoic sandstones (Zhu et al., 2011a) and the inherited zircons from the Mesozoic peraluminous granites (Zhu et al., 2011b) in this terrane, but significantly absent in the pebbly slates from both the Qiangtang and the Tethyan Himalayan terranes. The ca. 1175-Ma detrital zircons in the Lhasa Terrane were most likely sourced from the Albany-Fraser-Wilkes in southwestern Australia and East Antarctica. These new data obtained in this study reveal a distinct difference of detrital zircon provenance for the coeval Carboniferous-Permian glaciomarine pebbly slates

  1. Using pebble lithology and roundness to interpret gravel provenance in piedmont fluvial systems of the Rocky Mountains, USA

    USGS Publications Warehouse

    Lindsey, D.A.; Langer, W.H.; Van Gosen, B. S.

    2007-01-01

    Clast populations in piedmont fluvial systems are products of complex histories that complicate provenance interpretation. Although pebble counts of lithology are widely used, the information provided by a pebble count has been filtered by a potentially large number of processes and circumstances. Counts of pebble lithology and roundness together offer more power than lithology alone for the interpretation of provenance. In this study we analyze pebble counts of lithology and roundness in two contrasting fluvial systems of Pleistocene age to see how provenance varies with drainage size. The two systems are 1) a group of small high-gradient incised streams that formed alluvial fans and terraces and 2) a piedmont river that formed terraces in response to climate-driven cycles of aggradation and incision. We first analyze the data from these systems within their geographic and geologic context. After this is done, we employ contingency table analysis to complete the interpretation of pebble provenance. Small tributary streams that drain rugged mountains on both sides of the Santa Cruz River, southeast Arizona, deposited gravel in fan and terrace deposits of Pleistocene age. Volcanic, plutonic and, to a lesser extent, sedimentary rocks are the predominant pebble lithologies. Large contrasts in gravel lithology are evident among adjacent fans. Subangular to subrounded pebbles predominate. Contingency table analysis shows that hard volcanic rocks tend to remain angular and, even though transport distances have been short, soft tuff and sedimentary rocks tend to become rounded. The Wind River, a major piedmont stream in Wyoming, drains rugged mountains surrounding the northwest part of the Wind River basin. Under the influence of climate change and glaciation during the Pleistocene, the river deposited an extensive series of terrace gravels. In contrast to Santa Cruz tributary gravel, most of the Wind River gravel is relatively homogenous in lithology and is rounded to

  2. Robocasting of Ceramics and Composites Using Fine Particle Suspensions

    SciTech Connect

    CESARANO III,JOSEPH

    1999-10-28

    Solid freeform fabrication is the near-net-shape manufacturing of components by sequentially stacking thin layers of material until complicated three dimensional shapes are produced. The operation is computer controlled and requires no molds. This exciting new field of technology provides engineers with the ability to rapidly produce prototype parts directly from CAD drawings and oftentimes little or no machining is necessary after fabrication. Techniques for freeform fabrication with several types of plastics and metals are already quite advanced and maybe reviewed in references 1 and 2. Very complicated plastic models can be fabricated by stereolithography, selective laser sintering, fused deposition modeling, or three-dimensional ink jet printing. Metals may be freeformed by the LENS{trademark} technique and porous ceramic bodies by three dimensional printing into a porous powder bed. However, methods for freeform fabrication that utilize particulate slurries to build dense ceramics and composites are not as well developed. The techniques that are being developed for the freeform fabrication of dense structural ceramics primarily revolve around the sequential layering of ceramic loaded polymers or waxes. Laminated Object Manufacturing and CAM-LEM processing use controlled stacking and laser cutting of ceramic tapes [2,3]. Similar to fused deposition modeling, ceramic loaded polymer/wax filaments are being used for the fused deposition of ceramics [2,4]. Extrusion freeform fabrication uses high pressure extrusion to deposit layers of ceramic loaded polymer/wax systems[1]. Modified stereolithographic techniques are also being developed using ceramic loaded ultraviolet curable resins [2]. Pre-sintered parts made with any of these techniques typically have 40-55 vol.% polymeric binder. In this regard, these techniques are analogous to powder injection molding of ceramics. Very long and complicated burnout heat treatments are necessary to produce a dense ceramic

  3. Irradiation behavior of LiAlO 2 and Li 2ZrO 3 ceramics in the ALICE 3 experiment

    NASA Astrophysics Data System (ADS)

    Rasneur, B.; Thevenot, G.; Bouilloux, Y.

    1992-09-01

    Within the framework of the investigation of ceramic breeders for the DEMO relevant solid blankets developed in Europe, the ALICE 3 experiment was foreseen to study the irradiation behavior of the ceramics. The irradiation was performed in the core of the OSIRIS reactor for 46 FPD (full power days) at 400°C and 600°C. The three ceramics in the configuration contemplated in the BIT and BOT concepts were tested, i.e. LiAlO 2 and Li 2ZrO 3 pellets, Li 4SiO 4 and Li 2ZrO 3 pebbles, respectively. In this paper are reported the results of the post-irradiation examination carried out at CEA on CEA Li 2ZrO 3 and LiAlO 2 specimens: dimensions, X-ray diffraction, ultimate bending strength, diametral compressive strength and residual tritium.

  4. Turning patients over in bed

    MedlinePlus

    Roll patients in bed ... following steps should be followed: Explain to the patient what you are planning to do so the ... Stand on the side of the bed the patient will be turning towards and lower the bed ...

  5. Method of making a modified ceramic-ceramic composite

    DOEpatents

    Weaver, Billy L.; McLaughlin, Jerry C.; Stinton, David P.

    1995-01-01

    The present invention provides a method of making a shaped ceramic-ceramic composite articles, such as gas-fired radiant heat burner tubes, heat exchangers, flame dispersers, and other furnace elements, having a formed-on ceramic-ceramic composite thereon.

  6. OXYGEN TRANSPORT CERAMIC MEMBRANES

    SciTech Connect

    Dr. Sukumar Bandopadhyay; Dr. Nagendra Nagabhushana

    2001-02-01

    This is the fifth quarterly report on a new study to develop a ceramic membrane/metal joint. Results of wetting experiments on commercially available Nickel based brazing alloys on perovskite surfaces are described. Additionally, experimental and numerical investigations on the strength of concentric ceramic/metal joints are presented.

  7. Industrial Ceramics: Secondary Schools.

    ERIC Educational Resources Information Center

    New York City Board of Education, Brooklyn, NY. Bureau of Curriculum Development.

    The expanding use of ceramic products in today's world can be seen in the areas of communications, construction, aerospace, textiles, metallurgy, atomic energy, and electronics. The demands of science have brought ceramics from an art to an industry using mass production and automated processes which requires the services of great numbers as the…

  8. Paleodischarge of the Mojave River, southwestern U.S.A, investigated with single-pebble measurements of 10Be

    USGS Publications Warehouse

    Cyr, Andrew J.; Miller, David; Mahan, Shannon

    2015-01-01

    The paleohydrology of ephemeral stream systems is an important constraint on paleoclimatic conditions in arid environments, but remains difficult to constrain quantitatively. For example, sedimentary records of the size and extent of pluvial lakes in the Mojave Desert have been used as a proxy for Quaternary climate variability. Although the delivery mechanisms of this additional water are still being debated, it is generally agreed that the discharge of the Mojave River, which supplied water for several Pleistocene pluvial lakes along its course, must have been significantly greater during lake high stands. We used the 10Be concentrations of 10 individual quartzite pebbles sourced from the San Bernardino Mountains and collected from a ~25 ka strath terrace of the Mojave River near Barstow, Calif., to test whether pebble ages record the timing of large paleodischarge of the Mojave River. Our exposure ages indicate that periods of discharge large enough to transport pebble-sized sediment occurred at least four times over the past ~240 ky; individual pebble ages cluster into four groups with exposure ages of 24.82 ± 2.52 ka (n=3), 55.79 ± 2.59 ka (n=2), 99.14 ± 6.04 ka (n=4) and 239.9 ± 52.16 ka (n=1). These inferred large discharge events occurred during both glacial and interglacial conditions. We demonstrate that bedload materials provide information about the frequency and duration of transport events in river systems. This approach could be further improved with the addition of additional measurements of one or more cosmogenic nuclides coupled with models of river discharge and pebble transport.

  9. Mounting for ceramic scroll

    DOEpatents

    Petty, Jack D.

    1993-01-01

    A mounting for a ceramic scroll on a metal engine block of a gas turbine engine includes a first ceramic ring and a pair of cross key connections between the first ceramic ring, the ceramic scroll, and the engine block. The cross key connections support the scroll on the engine block independent of relative radial thermal growth and for bodily movement toward an annular mounting shoulder on the engine. The scroll has an uninterrupted annular shoulder facing the mounting shoulder on the engine block. A second ceramic ring is captured between mounting shoulder and the uninterrupted shoulder on the scroll when the latter is bodily shifted toward the mouting shoulder to define a gas seal between the scroll and the engine block.

  10. Strain isolated ceramic coatings

    NASA Technical Reports Server (NTRS)

    Tolokan, R. P.; Brady, J. B.; Jarrabet, G. P.

    1985-01-01

    Plasma sprayed ceramic coatings are used in gas turbine engines to improve component temperature capability and cooling air efficiency. A compliant metal fiber strain isolator between a plasma sprayed ceramic coating and a metal substrate improves ceramic durability while allowing thicker coatings for better insulation. Development of strain isolated coatings has concentrated on design and fabrication of coatings and coating evaluation via thermal shock testing. In thermal shock testing, five types of failure are possible: buckling failure im compression on heat up, bimetal type failure, isothermal expansion mismatch failure, mudflat cracking during cool down, and long term fatigue. A primary failure mode for thermally cycled coatings is designated bimetal type failure. Bimetal failure is tensile failure in the ceramic near the ceramic-metal interface. One of the significant benefits of the strain isolator is an insulating layer protecting the metal substrate from heat deformation and thereby preventing bimetal type failure.

  11. Ceramic heat exchanger

    DOEpatents

    LaHaye, P.G.; Rahman, F.H.; Lebeau, T.P.; Severin, B.K.

    1998-06-16

    A tube containment system is disclosed. The tube containment system does not significantly reduce heat transfer through the tube wall. The contained tube is internally pressurized, and is formed from a ceramic material having high strength, high thermal conductivity, and good thermal shock resistance. The tube containment system includes at least one ceramic fiber braid material disposed about the internally pressurized tube. The material is disposed about the tube in a predetermined axial spacing arrangement. The ceramic fiber braid is present in an amount sufficient to contain the tube if the tube becomes fractured. The tube containment system can also include a plurality of ceramic ring-shaped structures, in contact with the outer surface of the tube, and positioned between the tube and the ceramic fiber braid material, and/or at least one transducer positioned within tube for reducing the internal volume and, therefore, the energy of any shrapnel resulting from a tube fracture. 6 figs.

  12. Ceramic heat exchanger

    DOEpatents

    LaHaye, Paul G.; Rahman, Faress H.; Lebeau, Thomas P. E.; Severin, Barbara K.

    1998-01-01

    A tube containment system. The tube containment system does not significantly reduce heat transfer through the tube wall. The contained tube is internally pressurized, and is formed from a ceramic material having high strength, high thermal conductivity, and good thermal shock resistance. The tube containment system includes at least one ceramic fiber braid material disposed about the internally pressurized tube. The material is disposed about the tube in a predetermined axial spacing arrangement. The ceramic fiber braid is present in an amount sufficient to contain the tube if the tube becomes fractured. The tube containment system can also include a plurality of ceramic ring-shaped structures, in contact with the outer surface of the tube, and positioned between the tube and the ceramic fiber braid material, and/or at least one transducer positioned within tube for reducing the internal volume and, therefore, the energy of any shrapnel resulting from a tube fracture.

  13. Status of the fluidized bed unit

    SciTech Connect

    Williams, P.M.; Wade, J.F.

    1994-06-01

    Rocky Flats has a serious mixed waste problem. No technology or company has a license and available facilities to remedy this dilemma. One solution under study is to use a catalytic fluidized bed unit to destroy the combustible portion of the mixed waste. The fluidized bed thermal treatment program at Rocky Flats is building on knowledge gained over twenty years of successful development activity. The FBU has numerous technical advantages over other thermal technologies to treat Rocky Flats` mixed waste, the largest being the lower temperature (700{degrees}C versus 1000{degrees}C) which reduces acid corrosion and mechanical failures and obviates the need for ceramic lining. Successful demonstrations have taken place on bench, pilot, and full-scale tests using radioactive mixed wastes. The program is approaching implementation and licensing of a production-scale fluidized bed system for the safe treatment of mixed waste. The measure for success on this project is the ability to work closely with the community to jointly solve problems and respond to concerns of mixed waste treatment at Rocky Flats.

  14. Air gasification of rice husk in bubbling fluidized bed reactor with bed heating by conventional charcoal.

    PubMed

    Makwana, J P; Joshi, Asim Kumar; Athawale, Gaurav; Singh, Dharminder; Mohanty, Pravakar

    2015-02-01

    An experimental study of air gasification of rice husk was conducted in a bench-scale fluidized bed gasifier (FBG) having 210 mm diameter and 1600 mm height. Heating of sand bed material was performed using conventional charcoal fuel. Different operating conditions like bed temperature, feeding rate and equivalence ratio (ER) varied in the range of 750-850 °C, 25-31.3 kg/h, and 0.3-0.38, respectively. Flow rate of air was kept constant (37 m(3)/h) during FBG experiments. The carbon conversion efficiencies (CCE), cold gas efficiency, and thermal efficiency were evaluated, where maximum CCE was found as 91%. By increasing ER, the carbon conversion efficiency was decreased. Drastic reduction in electric consumption for initial heating of gasifier bed with charcoal compared to ceramic heater was ∼45%. Hence rice husk is found as a potential candidate to use directly (without any processing) in FBG as an alternative renewable energy source from agricultural field.

  15. An orientation soil survey at the Pebble Cu-Au-Mo porphyry deposit, Alaska

    USGS Publications Warehouse

    Smith, Steven M.; Eppinger, Robert G.; Fey, David L.; Kelley, Karen D.; Giles, S.A.

    2009-01-01

    Soil samples were collected in 2007 and 2008 along three traverses across the giant Pebble Cu-Au-Mo porphyry deposit. Within each soil pit, four subsamples were collected following recommended protocols for each of ten commonly-used and proprietary leach/digestion techniques. The significance of geochemical patterns generated by these techniques was classified by visual inspection of plots showing individual element concentration by each analytical method along the 2007 traverse. A simple matrix by element versus method, populated with a value based on the significance classification, provides a method for ranking the utility of methods and elements at this deposit. The interpretation of a complex multi-element dataset derived from multiple analytical techniques is challenging. An example of vanadium results from a single leach technique is used to illustrate the several possible interpretations of the data.

  16. 3.3 CM JVLA Observations of Transitional Disks: Searching for Centimeter Pebbles

    NASA Astrophysics Data System (ADS)

    Zapata, Luis A.; Rodríguez, Luis F.; Palau, Aina

    2017-01-01

    We present sensitive (rms-noises ∼4–25 μJy) and high angular resolution (∼1″–2″) 8.9 GHz (3.3 cm) Karl G. Jansky Very Large Array radio continuum observations of 10 presumed transitional disks associated with young low-mass stars. We report the detection of radio continuum emission in 5 out of the 10 objects (RXJ1615, UX Tau A, LkCa15, RXJ1633, and SR 24s). In the case of LkCa15, the centimeter emission is extended, and has a similar morphology to that of the transitional disk observed at millimeter wavelengths with an inner depression. For these five detections, we construct the spectral energy distributions from the centimeter to submillimeter wavelengths, and find that they can be well fitted with a single (RXJ1633 and UX Tau A) or a two-component power law (LkCa15, RXJ1615, and SR 24s). For the cases where a single power law fits the data well, the centimeter emission is likely produced by optically thin dust with large grains (i.e., centimeter-size pebbles) present in the transitional disks. For the cases where a double power law fits the data, the centimeter emission might be produced by the combination of photoevaporation and a free–free jet. We conclude that RXJ1633 and UX Tau A are excellent examples of transitional disks where the structure of the emission from centimeter/millimeter pebbles can be studied. In the other cases, some other physical emitting mechanisms are also important in the centimeter regime.

  17. Bed Bug Information Clearinghouse

    EPA Pesticide Factsheets

    Its purpose is to help states, communities, and consumers in efforts to prevent and control bed bug infestations. Currently includes only reviewed material from federal/state/local government agencies, extension services, and universities.

  18. Bed Bug Tips

    EPA Pesticide Factsheets

    How to deal with bed bugs in one printable page. Ten tips include ensuring correct insect identification, reducing clutter, understand integrated pest management, using mattress and box spring encasements, and heat treatment.

  19. Tapered bed bioreactor

    DOEpatents

    Scott, Charles D.; Hancher, Charles W.

    1977-01-01

    A vertically oriented conically shaped column is used as a fluidized bed bioreactor wherein biologically catalyzed reactions are conducted in a continuous manner. The column utilizes a packing material a support having attached thereto a biologically active catalytic material.

  20. Moving-bed sorbents

    SciTech Connect

    Ayala, R.E.; Gupta, R.P.; Chuck, T.

    1995-12-01

    The objective of this program is to develop mixed-metal oxide sorbent formulations that are suitable for moving-bed, high-temperature, desulfurization of coal gas. Work continues on zinc titanates formulations and Z-sorb III sorbent.

  1. Additive Manufacturing of SiC Based Ceramics and Ceramic Matrix Composites

    NASA Technical Reports Server (NTRS)

    Halbig, Michael Charles; Singh, Mrityunjay

    2015-01-01

    Silicon carbide (SiC) ceramics and SiC fiber reinforcedSiC ceramic matrix composites (SiCSiC CMCs) offer high payoff as replacements for metals in turbine engine applications due to their lighter weight, higher temperature capability, and lower cooling requirements. Additive manufacturing approaches can offer game changing technologies for the quick and low cost fabrication of parts with much greater design freedom and geometric complexity. Four approaches for developing these materials are presented. The first two utilize low cost 3D printers. The first uses pre-ceramic pastes developed as feed materials which are converted to SiC after firing. The second uses wood containing filament to print a carbonaceous preform which is infiltrated with a pre-ceramic polymer and converted to SiC. The other two approaches pursue the AM of CMCs. The first is binder jet SiC powder processing in collaboration with rp+m (Rapid Prototyping+Manufacturing). Processing optimization was pursued through SiC powder blending, infiltration with and without SiC nano powder loading, and integration of nanofibers into the powder bed. The second approach was laminated object manufacturing (LOM) in which fiber prepregs and laminates are cut to shape by a laser and stacked to form the desired part. Scanning electron microscopy was conducted on materials from all approaches with select approaches also characterized with XRD, TGA, and bend testing.

  2. Test Bed For Telerobots

    NASA Technical Reports Server (NTRS)

    Matijevic, Jacob R.; Zimmerman, Wayne F.; Dolinsky, Shlomo

    1990-01-01

    Assembly of electromechanical and electronic equipment (including computers) constitutes test bed for development of advanced robotic systems for remote manipulation. Combines features not found in commercial systems. Its architecture allows easy growth in complexity and level of automation. System national resource for validation of new telerobotic technology. Intended primarily for robots used in outer space, test bed adapted to development of advanced terrestrial telerobotic systems for handling radioactive materials, dangerous chemicals, and explosives.

  3. Bed exit alarms.

    PubMed

    2004-09-01

    Bed-exit alarms alert caregivers that a patient who should not get out of bed unassisted is doing so. These alarms can help reduce the likelihood of falls and can promote speedy assistance to patients who have already fallen. But as we described in our May 2004 Guidance Article on bed-exit alarms, they don't themselves prevent falls. They are only effective if used as part of an overall fall-prevention program and with a clear understanding of their limitations. This Evaluation examines the effectiveness of 16 bed-exit alarms from seven suppliers. Our ratings focus primarily on each product's reliability in detecting bed-exit events and alerting caregivers, its ability to minimize nuisance alarms (alarms that sound even though the patient isn't leaving the bed or that sound while a caregiver is helping the patient to leave the bed), and its resistance to deliberate or inadvertent tampering. Twelve of the products use pressure-sensor-activated alarms (mainly sensor pads placed on or under the mattress); three use a cord that can attach to the patient's garment, alarming if the cord is pulled loose from the control unit; and one is a position-sensitive alarm attached to a leg cuff. All the products reliably detect attempted or successful bed exits. But they vary greatly in how effectively they alert staff, minimize nuisance alarms, and resist tampering. Ease of use and battery performance also vary for many units. Of the pressure-sensor units, three are rated Preferred. Those units meet most of our criteria and have no significant disadvantages. Five of the other pressure-sensor products are Acceptable, and the remaining four are Not Recommended. All three cord-activated alarms are rated Acceptable, as is the patient-worn alarm.

  4. Bed rest and immunity

    NASA Astrophysics Data System (ADS)

    Sonnenfeld, Gerald; Aviles, Hernan; Butel, Janet S.; Shearer, William T.; Niesel, David; Pandya, Utpal; Allen, Christopher; Ochs, Hans D.; Blancher, Antoine; Abbal, Michel

    2007-02-01

    Space flight has been shown to result in altered immune responses. The current study was designed to investigate this possibility by using the bed rest model of some space flight conditions. A large number of women are included as subjects in the study. The hypothesis being tested is: 60 days head-down tilt bed rest of humans will affect the immune system and resistance to infection. Blood, urine and saliva samples will be obtained from bed rest subjects prior to, at intervals during, and after completion of 60 days of head-down tilt bed rest. Leukocyte blastogenesis, cytokine production and virus reactivation will be assessed. The ability of the subjects to respond appropriately to immunization with the neoantigen bacteriophage φX-174 will also be determined. Bed rest is being carried out at MEDES, Toulouse France, and the University of Texas Medical Branch, Galveston, TX. The studies to be carried out in France will also allow assessment of the effects of muscle/bone exercise and nutritional countermeasures on the immune system in addition to the effects of bed rest.

  5. Ceramic-silicide composites

    SciTech Connect

    Petrovic, J.J.

    1998-12-01

    The area of ceramic-silicide composites represents a merging of structural ceramics and structural silicides. Such ceramic-silicide composites can possess the desirable characteristics of both classes of compounds. Important structural ceramics are materials such as Si{sub 3}N{sub 4}, SiC, Al{sub 2}O{sub 3}, and ZrO{sub 2}, which possess covalent, ionic, or mixed covalent-ionic atomic bonding. An important structural silicide is MoSi{sub 2}, which possesses mixed covalent-metallic bonding. The arena of ceramic-silicide composites encompasses both composites where the structural silicide is the matrix and the structural ceramic is the reinforcement, and composites where the structural ceramic is the matrix and the structural silicide is the reinforcement. In the former area, MoSi{sub 2}-SiC, MoSi{sub 2}-ZrO{sub 2}, and MoSi{sub 2}-Al{sub 2}O{sub 3} composites are discussed. In the latter area, Si{sub 3}N{sub 4}-MoSi{sub 2} composites are described.

  6. High pressure ceramic joint

    DOEpatents

    Ward, Michael E.; Harkins, Bruce D.

    1993-01-01

    Many recuperators have components which react to corrosive gases and are used in applications where the donor fluid includes highly corrosive gases. These recuperators have suffered reduced life, increased service or maintenance, and resulted in increased cost. The present joint when used with recuperators increases the use of ceramic components which do not react to highly corrosive gases. Thus, the present joint used with the present recuperator increases the life, reduces the service and maintenance, and reduces the increased cost associated with corrosive action of components used to manufacture recuperators. The present joint is comprised of a first ceramic member, a second ceramic member, a mechanical locking device having a groove defined in one of the first ceramic member and the second ceramic member. The joint and the mechanical locking device is further comprised of a refractory material disposed in the groove and contacting the first ceramic member and the second ceramic member. The present joint mechanically provides a high strength load bearing joint having good thermal cycling characteristics, good resistance to a corrosive environment and good steady state strength at elevated temperatures.

  7. High pressure ceramic joint

    DOEpatents

    Ward, M.E.; Harkins, B.D.

    1993-11-30

    Many recuperators have components which react to corrosive gases and are used in applications where the donor fluid includes highly corrosive gases. These recuperators have suffered reduced life, increased service or maintenance, and resulted in increased cost. The present joint when used with recuperators increases the use of ceramic components which do not react to highly corrosive gases. Thus, the present joint used with the present recuperator increases the life, reduces the service and maintenance, and reduces the increased cost associated with corrosive action of components used to manufacture recuperators. The present joint is comprised of a first ceramic member, a second ceramic member, a mechanical locking device having a groove defined in one of the first ceramic member and the second ceramic member. The joint and the mechanical locking device is further comprised of a refractory material disposed in the groove and contacting the first ceramic member and the second ceramic member. The present joint mechanically provides a high strength load bearing joint having good thermal cycling characteristics, good resistance to a corrosive environment and good steady state strength at elevated temperatures. 4 figures.

  8. The APS ceramic chambers

    SciTech Connect

    Milton, S.; Warner, D.

    1994-07-01

    Ceramics chambers are used in the Advanced Photon Source (APS) machines at the locations of the pulsed kicker and bumper magnets. The ceramic will be coated internally with a resistive paste. The resistance is chosen to allow the low frequency pulsed magnet field to penetrate but not the high frequency components of the circulating beam. Another design goal was to keep the power density experienced by the resistive coating to a minimum. These ceramics, their associated hardware, the coating process, and our recent experiences with them are described.

  9. Spacecraft ceramic protective shield

    NASA Technical Reports Server (NTRS)

    Larriva, Rene F. (Inventor); Nelson, Anne (M.); Czechanski, James G. (Inventor); Poff, Ray E. (Inventor)

    1995-01-01

    A low areal density protective shield apparatus, and method for making same, for protecting spacecraft structures from impact with hypervelocity objects, including a bumper member comprising a bumper ceramic layer, a bumper shock attenuator layer, and a bumper confining layer. The bumper ceramic layer can be SiC or B.sub.4 C; the bumper shock attenuator layer can be zirconia felt; and the bumper confining layer can be aluminum. A base armor member can be spaced from the bumper member and a ceramic fiber-based curtain can be positioned between the bumper and base armor members.

  10. Control of bed height in a fluidized bed gasification system

    DOEpatents

    Mehta, Gautam I.; Rogers, Lynn M.

    1983-12-20

    In a fluidized bed apparatus a method for controlling the height of the fdized bed, taking into account variations in the density of the bed. The method comprises taking simultaneous differential pressure measurements at different vertical elevations within the vessel, averaging the differential pressures, determining an average fluidized bed density, then periodically calculating a weighting factor. The weighting factor is used in the determination of the actual bed height which is used in controlling the fluidizing means.

  11. Striated and pitted pebbles as paleostress markers: an example from the central transect of the Betic Cordillera (SE Spain)

    NASA Astrophysics Data System (ADS)

    Ruano, Patricia; Galindo-Zaldívar, Jesús

    2004-02-01

    Striated and pitted pebbles provide scarce structures that preserve information on the stresses that their host rocks have undergone. This information can be obtained by the measurement of a large number of microfaults with striae and solution marks within a small rock volume. For non-rotational deformation, the statistical procedures for microfault analysis provide a valid tool for determining the overprinting of successive stress ellipsoids, including their axial ratios and the orientations of the main axes. The trends of compressions obtained from striae can be compared with the determinations from the pole of pebble solution pits. However, in complex tectonics settings, the solution pits of several deformation phases are mixed and only striae analysis allows overprinted paleostresses to be accurately distinguished. The analysis of several pebbles from the same outcrop, including five from moderately complex settings, allows determination of the homogeneity of the paleostresses at outcrop scale, the detection of redeposited pebbles, and supports the results of microtectonic analysis for large areas. Solution mark distributions on pebbles depend on the burial and tectonic stresses. Conglomerates from shallow levels, such as those from Quaternary fluvial terraces, only record horizontal compressional solution marks because the minimum vertical stress needed to develop these structures are not reached by burial. In the central Betic Cordillera, striated and pitted pebbles are composed of carbonate surrounded by a matrix containing siliciclastic elements. The study of several outcrops located across a transect of the Cordillera shows a change in the recent stress field. While conglomerates near the Internal-External zone boundary show extensional stresses that may be related to the uplift of the Cordillera since Tortonian times, the outcrops located in the External Zone and up to the mountain front indicate the existence of horizontal NW-SE and NE-SW compressions

  12. Tracing bed load sediment using PIT tags in a steep headwater channel.

    NASA Astrophysics Data System (ADS)

    Kubo, Y.; Hiraoka, M.; Gomi, T.; Nidaira, K.; Uchiyama, Y.

    2015-12-01

    Bed load transport in steep headwater channels is complex because of the particle size distribution, topography, channel roughness, and sediment supply from adjacent hillslope. We monitored movement bed load sediment using PIT tags in a steep headwater channel segments. Study area is located in 7.0ha Oobora-sawa observatory from 50km west of Tokyo metropolitan. Annual precipitation is 3000mm and mean temperature is 10°. Annual bed load sediment yields in the study catchment was from 6.5 to 7.6 t/ha/yr. Mean channel gradient is 24° with 0.5m low flow width. The channel is consisted by 0.2 to 1.6m interval of step-pool sequences. Based on pebble count method, D10, D50 and D90 of channel substrate were 8, 28 and 206mm respectively. We deployed 134 bed load tracers with five classes of diameter ranges (Class1:17.7, Class2:24.8, Class3:35.8, Class4:54.1 and Class5:83.8mm). Selected tracers represented from D20 to D77 of channel bed substrates. PIT tags (diameter 2mm, length 9mm and weight 0.1g) were placed into the particles by drilling and refilled with non-corrosive epoxy. We investigated the movement of bed load tracers every major storm event since February 2015. Channel morphology was measured using photographic survey and topographic model was developed using software of Surface from motion (PhotoScan). Mean bed load movement in the 5 storm event with 438 mm total and 33 mm maximum intensity was 168 mm. Then 51 mm of bed load movement occurred in 43 mm total and 16 mm intensity of rainfall. Recurrence interval of the two storm event was 1 and 4 year respectively. Receivable rates of bed load tracers was 70 and 74 % in the two events. Mobilized bed load (7 to 18%) deposited at cascade, pool and riffle, and among step clusters. Mobilized bed load tracers is rather random and we do not find any patterns for particle size for the movement and distance. Our field monitoring showed that bed load tracers were not mobilized for storm events with 10.5mm/h intensity of

  13. Effects of grain size and porosity on strength of Li2TiO3 tritium breeding pebbles and its grain growth behavior

    NASA Astrophysics Data System (ADS)

    Xiang, Maoqiao; Zhang, Yingchun; Zhang, Yun; Wang, Chaofu; Liu, Wei; Yu, Yonghong

    2016-12-01

    Tons of Li2TiO3 tritium breeding pebbles will be filled in the blanket for obtaining tritium fuel. In this work, isothermal sintering was carried out to study the grain growth behavior of the Li2TiO3 pebbles fabricated by agarose method. The grain growth exponent (n) and the activation energy (Q) calculated by the phenomenological kinetic equation were 2 and 435.65 kJ/mol, respectively. The grain growth was controlled by vapor transport (p = 2S/r). In addition, effects of porosity and grain-size on the strength of Li2TiO3 pebbles were investigated. The strength was affected by the grain size and the porosity of Li2TiO3 pebbles, and high strength (about 72 MPa) depended partly on achieving the optimum balance between the porosity (about 10%) and grain size (about 2 μm).

  14. EPA-Registered Bed Bug Products

    MedlinePlus

    ... Pest Bed Bugs EPA Registered Bed Bug Products EPA-Registered Bed Bug Products Resources Bed Bug Main ... Bugs Tips Joint Statement on Bed Bug Control EPA has developed a search tool that can help ...

  15. Corrosion resistant ceramic materials

    DOEpatents

    Kaun, T.D.

    1996-07-23

    Ceramic materials are disclosed which exhibit stability in severely-corrosive environments having high alkali-metal activity, high sulfur/sulfide activity and/or molten halides at temperatures of 200--550 C or organic salt (including SO{sub 2} and SO{sub 2}Cl{sub 2}) at temperatures of 25--200 C. These sulfide ceramics form stoichiometric (single-phase) compounds with sulfides of Ca, Li, Na, K, Al, Mg, Si, Y, La, Ce, Ga, Ba, Zr and Sr and show melting-points that are sufficiently low and have excellent wettability with many metals (Fe, Ni, Mo) to easily form metal/ceramic seals. Ceramic compositions are also formulated to adequately match thermal expansion coefficient of adjacent metal components. 1 fig.

  16. Corrosion resistant ceramic materials

    DOEpatents

    Kaun, Thomas D.

    1996-01-01

    Ceramic materials which exhibit stability in severely-corrosive environments having high alkali-metal activity, high sulfur/sulfide activity and/or molten halides at temperatures of 200.degree.-550.degree. C. or organic salt (including SO.sub.2 and SO.sub.2 Cl.sub.2) at temperatures of 25.degree.-200.degree. C. These sulfide ceramics form stoichiometric (single-phase) compounds with sulfides of Ca, Li, Na, K, Al, Mg, Si, Y, La, Ce, Ga, Ba, Zr and Sr and show melting-points that are sufficiently low and have excellent wettability with many metals (Fe, Ni, Mo) to easily form metal/ceramic seals. Ceramic compositions are also formulated to adequately match thermal expansion coefficient of adjacent metal components.

  17. Corrosion resistant ceramic materials

    DOEpatents

    Kaun, Thomas D.

    1995-01-01

    Ceramic materials which exhibit stability in severely-corrosive environments having high alkali-metal activity, high sulfur/sulfide activity and/or molten halides at temperatures of 200.degree.-550.degree. C. or organic salt (including SO.sub.2 and SO.sub.2 Cl.sub.2) at temperatures of 25.degree.-200.degree. C. These sulfide ceramics form stoichiometric (single-phase) compounds with sulfides of Ca, Li, Na, K, Al, Mg, Si, Y, La, Ce, Ga, Ba, Zr and Sr and show melting-points that are sufficiently low and have excellent wettability with many metals (Fe, Ni, Mo) to easily form metal/ceramic seals. Ceramic compositions are also formulated to adequately match thermal expansion coefficient of adjacent metal components.

  18. Fibrous ceramic insulation

    SciTech Connect

    Goldstein, H.E.

    1982-11-01

    Some of the reusable heat shielding materials used to protect the Space Shuttles, their manufacturing processes, properties, and applications are discussed. Emphasis is upon ceramic materials. Space Shuttle Orbiter tiles are discussed.

  19. Light emitting ceramic device

    DOEpatents

    Valentine, Paul; Edwards, Doreen D.; Walker, Jr., William John; Slack, Lyle H.; Brown, Wayne Douglas; Osborne, Cathy; Norton, Michael; Begley, Richard

    2010-05-18

    A light-emitting ceramic based panel, hereafter termed "electroceramescent" panel, is herein claimed. The electroceramescent panel is formed on a substrate providing mechanical support as well as serving as the base electrode for the device. One or more semiconductive ceramic layers directly overlay the substrate, and electrical conductivity and ionic diffusion are controlled. Light emitting regions overlay the semiconductive ceramic layers, and said regions consist sequentially of a layer of a ceramic insulation layer and an electroluminescent layer, comprised of doped phosphors or the equivalent. One or more conductive top electrode layers having optically transmissive areas overlay the light emitting regions, and a multi-layered top barrier cover comprising one or more optically transmissive non-combustible insulation layers overlay said top electrode regions.

  20. Making Ceramic Cameras

    ERIC Educational Resources Information Center

    Squibb, Matt

    2009-01-01

    This article describes how to make a clay camera. This idea of creating functional cameras from clay allows students to experience ceramics, photography, and painting all in one unit. (Contains 1 resource and 3 online resources.)

  1. Advanced Ceramics Property Measurements

    NASA Technical Reports Server (NTRS)

    Salem, Jonathan; Helfinstine, John; Quinn, George; Gonczy, Stephen

    2013-01-01

    Mechanical and physical properties of ceramic bodies can be difficult to measure correctly unless the proper techniques are used. The Advanced Ceramics Committee of ASTM, C-28, has developed dozens of consensus test standards and practices to measure various properties of a ceramic monolith, composite, or coating. The standards give the "what, how, how not, and why" for measurement of many mechanical, physical, thermal, and performance properties. Using these standards will provide accurate, reliable, and complete data for rigorous comparisons with other test results from your test lab, or another. The C-28 Committee has involved academics, producers, and users of ceramics to write and continually update more than 45 standards since the committee's inception in 1986. Included in this poster is a pictogram of the C-28 standards and information on how to obtain individual copies with full details or the complete collection of standards in one volume.

  2. Super Thin Ceramic Coatings

    NASA Video Gallery

    New technology being developed at NASA's Glenn Research Center creates super thin ceramic coatings on engine components. The Plasma Spray – Physical Vapor Deposition (PS-PVD) rig uses a powerful ...

  3. Cross hospital bed management system.

    PubMed

    Abedian, S; Kazemi, H; Riazi, H; Bitaraf, E

    2014-01-01

    The lack of adequate numbers of hospital beds to accommodate the injured is a main problem in public hospitals. For control of occupancy of bed, we design a dynamic system that announces status of bed when it change with admission or discharge of a patient. This system provide a wide network in country for bed management, especially for ICU and CCU beds that help us to distribute injured patient in the hospitals.

  4. OXYGEN TRANSPORT CERAMIC MEMBRANES

    SciTech Connect

    Dr. Sukumar Bandopadhyay; Dr. Nagendra Nagabhushana

    2000-07-01

    This is the fourth quarterly report on a new study to develop a ceramic membrane/metal joint. The first experiments using the La-Sr-Fe-O ceramic are reported. Some of the analysis performed on the samples obtained are commented upon. A set of experiments to characterize the mechanical strength and thermal fatigue properties of the joints has been designed and begun. Finite element models of joints used to model residual stresses are described.

  5. Battery utilizing ceramic membranes

    DOEpatents

    Yahnke, Mark S.; Shlomo, Golan; Anderson, Marc A.

    1994-01-01

    A thin film battery is disclosed based on the use of ceramic membrane technology. The battery includes a pair of conductive collectors on which the materials for the anode and the cathode may be spin coated. The separator is formed of a porous metal oxide ceramic membrane impregnated with electrolyte so that electrical separation is maintained while ion mobility is also maintained. The entire battery can be made less than 10 microns thick while generating a potential in the 1 volt range.

  6. USGS exploration geochemistry studies at the Pebble porphyry Cu-Au-Mo deposit, Alaska-pdf of presentation

    USGS Publications Warehouse

    Eppinger, Robert G.; Kelley, Karen D.; Fey, David L.; Giles, Stuart A.; Minsley, Burke J.; Smith, Steven M.

    2010-01-01

    From 2007 through 2010, scientists in the U.S. Geological Survey (USGS) have been conducting exploration-oriented geochemical and geophysical studies in the region surrounding the giant Pebble porphyry Cu-Au-Mo deposit in southwestern Alaska. The Cretaceous Pebble deposit is concealed under tundra, glacial till, and Tertiary cover rocks, and is undisturbed except for numerous exploration drill holes. These USGS studies are part of a nation-wide research project on evaluating and detecting concealed mineral resources. This report focuses on exploration geochemistry and comprises illustrations and associated notes that were presented as a case study in a workshop on this topic. The workshop, organized by L.G. Closs and R. Glanzman, is called 'Geochemistry in Mineral Exploration and Development,' presented by the Society of Economic Geologists at a technical conference entitled 'The Challenge of Finding New Mineral Resources: Global Metallogeny, Integrative Exploration and New Discoveries,' held at Keystone, Colorado, October 2-5, 2010.

  7. Granulometry of pebble beach ridges in Fort Williams Point, Greenwich Island, Antarctic Peninsula; a possible result from Holocene climate fluctuations

    USGS Publications Warehouse

    Santana, E.; Dumont, J.F.

    2007-01-01

    We present a granulometric study of emerged pebble beach ridges in the Fort Williams Point, Greenwich Island, Antarctic Peninsula. We studied 8 beach ridges from the shore up to 13.5 m above current sea level. The beach ridges are made of volcanic material from the surrounding relief, but also include glacially transported gneiss and granodiorite pebble and cobble. Based on granulometric distribution analysis of 2100 samples from 39 locations we identified evidence of 4 sequences of 1 to 3 ridges. Most of the material seems to be reworked from a till. Pavement formation by iceberg between the sequences of beach ridges suggests periods of lower temperature. The interpretation suggests that sequences of beach ridge construction formed during warmer periods of the late Holocene. This occurs in the framework of an isostatic postglacial uplift allowing the progressive mobilization of periglaciar material.

  8. Additives affecting properties of β-Li2TiO3 pebbles in a modified indirect wet chemistry process

    NASA Astrophysics Data System (ADS)

    Yu, Cheng-Long; Liu, Wei; Yang, Long-Tao; Wang, Dao-Yi; Wu, Kang; Zhang, Zeng-Ping; Wang, Xiu-Feng; Yanagisawa, Kazumichi

    2016-11-01

    Lithium metatitanate (β-Li2TiO3) pebbles were fabricated via the modified indirect wet chemistry method. Effect of varied additives, as polyvinyl alcohol, glycerol, and agar on the properties evolution was investigated. The highest density is obtained by adding 2 wt% (weight percent) polyvinyl alcohol, 3 wt% glycerol, and 3 wt% agar, respectively. β-Li2TiO3 pebbles with relative sintered density of 92.4%T.D. (Theoretical Density), the ratio of the intensity of diffraction peak (002) to that of (-133) of about 2.93, about 1.58 mm in diameter, a better sphericity of 1.02, the particle size of 5-6 μm, and the well-developed surface layered structure are successfully fabricated with 3 wt% glycerol. Glycerol is beneficial to improving the properties by other fabrication method as well.

  9. Geochemical Data for Samples Collected in 2007 Near the Concealed Pebble Porphyry Cu-Au-Mo Deposit, Southwest Alaska

    USGS Publications Warehouse

    Fey, David L.; Granitto, Matthew; Giles, Stuart A.; Smith, Steven M.; Eppinger, Robert G.; Kelley, Karen D.

    2008-01-01

    In the summer of 2007, the U.S. Geological Survey (USGS) began an exploration geochemical research study over the Pebble porphyry copper-gold-molydenum (Cu-Au-Mo) deposit in southwest Alaska. The Pebble deposit is extremely large and is almost entirely concealed by tundra, glacial deposits, and post-Cretaceous volcanic and volcaniclastic rocks. The deposit is presently being explored by Northern Dynasty Minerals, Ltd., and Anglo-American LLC. The USGS undertakes unbiased, broad-scale mineral resource assessments of government lands to provide Congress and citizens with information on national mineral endowment. Research on known deposits is also done to refine and better constrain methods and deposit models for the mineral resource assessments. The Pebble deposit was chosen for this study because it is concealed by surficial cover rocks, it is relatively undisturbed (except for exploration company drill holes), it is a large mineral system, and it is fairly well constrained at depth by the drill hole geology and geochemistry. The goals of the USGS study are (1) to determine whether the concealed deposit can be detected with surface samples, (2) to better understand the processes of metal migration from the deposit to the surface, and (3) to test and develop methods for assessing mineral resources in similar concealed terrains. This report presents analytical results for geochemical samples collected in 2007 from the Pebble deposit and surrounding environs. The analytical data are presented digitally both as an integrated Microsoft 2003 Access? database and as Microsoft 2003 Excel? files. The Pebble deposit is located in southwestern Alaska on state lands about 30 km (18 mi) northwest of the village of Illiamna and 320 km (200 mi) southwest of Anchorage (fig. 1). Elevations in the Pebble area range from 287 m (940 ft) at Frying Pan Lake just south of the deposit to 1146 m (3760 ft) on Kaskanak Mountain about 5 km (5 mi) to the west. The deposit is in an area of

  10. Pebble and bedrock abrasion during fluvial transport in active orogenic setting : experimental study and application to natural hydrographic networks.

    NASA Astrophysics Data System (ADS)

    Attal, M.; Lavé, J.

    2003-04-01

    At mountain range scale, rivers play an important role in shaping the landscape : in response to active uplift, they incise into bedrock and ensure base level lowering for hillslopes erosion. At the same time, they ensure evacuation of erosion products out of the range as suspended- or bedload. Incision rates are commonly equated with a stream power law, assuming that river incision depends only on hydrodynamic variables. However, this simplification is not mechanically satisfying : in many settings, river bedload fluxes exert an important control on incision rates, by limiting bedrock exposure or by providing an efficient tool for river mechanical abrasion. It is therefore important to better quantify the abrasion processes during bedload transport both to deduce pebble size reduction that controls carrying capacity and bedrock exposure, and to derive bedrock incision laws. Such characterization can be constrained through experimental studies or field measurements. Experimental studies on pebble and bedrock abrasion have been conducted for a long time [e.g. Daubree, 1879]. They generally provide incision rates around two orders of magnitude below natural downstream fining rates. Previous authors have suggested that this discrepancy could be explained by the fact that experimental device doesn’t reproduce really the abrasion phenomena effective in natural rivers, like saltation and following impacts. In this way, we have built an experimental device in order to reproduce these abrasion phenomena. It consists of a circular flume of 30 cm width and of 60 cm curvature radius. Water is injected tangentially on four points ; it generates a flow that produce sediment motion. Velocity vertical profile is roughly similar to what could be observed in natural rivers. The bottom and the sides of the device are interchangeable, in order to measure distinctly pebble abrasion or the interactions between sediment load and substratum. The aim of this experimental study is to

  11. Treatment bed microbiological control

    NASA Technical Reports Server (NTRS)

    Janauer, Gilbert E.; Fitzpatrick, Timothy W.; Kril, Michael B.; Wilber, Georgia A.; Sauer, Richard L.

    1987-01-01

    The effects of microbial fouling on treatment bed (TB) performance are being studied. Fouling of activated carbon (AC) and ion exchange resins (IEX) by live and devitalized bacteria can cause decreased capacity for selected sorbates with AC and IEX TB. More data are needed on organic species removal in the trace region of solute sorption isotherms. TB colonization was prevented by nonclassical chemical disinfectant compositions (quaternary ammonium resins) applied in suitable configurations. Recently, the protection of carbon beds via direct disinfectant impregnation has shown promise. Effects (of impregnation) upon bed sorption/removal characteristics are to be studied with representative contaminants. The potential need to remove solutes added or produced during water disinfection and/or TB microbiological control must be investigated.

  12. Alumina-based ceramic composite

    DOEpatents

    Alexander, K.B.; Tiegs, T.N.; Becher, P.F.; Waters, S.B.

    1996-07-23

    An improved ceramic composite comprising oxide ceramic particulates, nonoxide ceramic particulates selected from the group consisting of carbides, borides, nitrides of silicon and transition metals and mixtures thereof, and a ductile binder selected from the group consisting of metallic, intermetallic alloys and mixtures thereof is described. The ceramic composite is made by blending powders of the ceramic particulates and the ductile to form a mixture and consolidating the mixture of under conditions of temperature and pressure sufficient to produce a densified ceramic composite. 5 figs.

  13. Clinical application of bio ceramics

    NASA Astrophysics Data System (ADS)

    Anu, Sharma; Gayatri, Sharma

    2016-05-01

    Ceramics are the inorganic crystalline material. These are used in various field such as biomedical, electrical, electronics, aerospace, automotive and optical etc. Bio ceramics are the one of the most active areas of research. Bio ceramics are the ceramics which are biocompatible. The unique properties of bio ceramics make them an attractive option for medical applications and offer some potential advantages over other materials. During the past three decades, a number of major advances have been made in the field of bio ceramics. This review focuses on the use of these materials in variety of clinical scenarios.

  14. Ceramic electrolyte coating and methods

    DOEpatents

    Seabaugh, Matthew M.; Swartz, Scott L.; Dawson, William J.; McCormick, Buddy E.

    2007-08-28

    Aqueous coating slurries useful in depositing a dense coating of a ceramic electrolyte material (e.g., yttrium-stabilized zirconia) onto a porous substrate of a ceramic electrode material (e.g., lanthanum strontium manganite or nickel/zirconia) and processes for preparing an aqueous suspension of a ceramic electrolyte material and an aqueous spray coating slurry including a ceramic electrolyte material. The invention also includes processes for depositing an aqueous spray coating slurry including a ceramic electrolyte material onto pre-sintered, partially sintered, and unsintered ceramic substrates and products made by this process.

  15. Fluidized bed coal desulfurization

    NASA Technical Reports Server (NTRS)

    Ravindram, M.

    1983-01-01

    Laboratory scale experiments were conducted on two high volatile bituminous coals in a bench scale batch fluidized bed reactor. Chemical pretreatment and posttreatment of coals were tried as a means of enhancing desulfurization. Sequential chlorination and dechlorination cum hydrodesulfurization under modest conditions relative to the water slurry process were found to result in substantial sulfur reductions of about 80%. Sulfur forms as well as proximate and ultimate analyses of the processed coals are included. These studies indicate that a fluidized bed reactor process has considerable potential for being developed into a simple and economic process for coal desulfurization.

  16. Staged fluidized bed

    DOEpatents

    Mallon, R.G.

    1983-05-13

    The invention relates to oil shale retorting and more particularly to staged fluidized bed oil shale retorting. Method and apparatus are disclosed for narrowing the distribution of residence times of any size particle and equalizing the residence times of large and small particles in fluidized beds. Particles are moved up one fluidized column and down a second fluidized column with the relative heights selected to equalize residence times of large and small particles. Additional pairs of columns are staged to narrow the distribution of residence times and provide complete processing of the material.

  17. Geochemical Data for Samples Collected in 2008 Near the Concealed Pebble Porphyry Cu-Au-Mo Deposit, Southwest Alaska

    USGS Publications Warehouse

    Fey, David L.; Granitto, Matthew; Giles, Stuart A.; Smith, Steven M.; Eppinger, Robert G.; Kelley, Karen D.

    2009-01-01

    In the summer of 2007, the U.S. Geological Survey (USGS) began an exploration geochemical research study over the Pebble porphyry copper-gold-molybdenum deposit. This report presents the analytical data collected in 2008. The Pebble deposit is world class in size, and is almost entirely concealed by tundra, glacial deposits, and post-Cretaceous volcanic rocks. The Pebble deposit was chosen for this study because it is concealed by surficial cover rocks, is relatively undisturbed (except for exploration company drill holes), is a large mineral system, and is fairly well-constrained at depth by the drill hole geology and geochemistry. The goals of this study are to 1) determine whether the concealed deposit can be detected with surface samples, 2) better understand the processes of metal migration from the deposit to the surface, and 3) test and develop methods for assessing mineral resources in similar concealed terrains. The analytical data are presented as an integrated Microsoft Access 2003 database and as separate Excel files.

  18. Acoustic bed velocity and bed load dynamics in a large sand bed river

    USGS Publications Warehouse

    Gaeuman, D.; Jacobson, R.B.

    2006-01-01

    Development of a practical technology for rapid quantification of bed load transport in large rivers would represent a revolutionary advance for sediment monitoring and the investigation of fluvial dynamics. Measurement of bed load motion with acoustic Doppler current profiles (ADCPs) has emerged as a promising approach for evaluating bed load transport. However, a better understanding of how ADCP data relate to conditions near the stream bed is necessary to make the method practical for quantitative applications. In this paper, we discuss the response of ADCP bed velocity measurements, defined as the near-bed sediment velocity detected by the instrument's bottom-tracking feature, to changing sediment-transporting conditions in the lower Missouri River. Bed velocity represents a weighted average of backscatter from moving bed load particles and spectral reflections from the immobile bed. The ratio of bed velocity to mean bed load particle velocity depends on the concentration of the particles moving in the bed load layer, the bed load layer thickness, and the backscatter strength from a unit area of moving particles relative to the echo strength from a unit area of unobstructed bed. A model based on existing bed load transport theory predicted measured bed velocities from hydraulic and grain size measurements with reasonable success. Bed velocities become more variable and increase more rapidly with shear stress when the transport stage, defined as the ratio of skin friction to the critical shear stress for particle entrainment, exceeds a threshold of about 17. This transition in bed velocity response appears to be associated with the appearance of longer, flatter bed forms at high transport stages.

  19. Distributor for multistage fluidized beds

    SciTech Connect

    Wormser, A.

    1992-06-16

    This patent describes a multibed fluidized bed system. It comprises a fluidized bed vessel having a casing surrounding a first distributor and a second distributor downstream from the first distributor; a first bed material placed on the first distributor and a second bed material placed on the second distributor; each of the bed materials having an angle of repose; and wherein the angle formed by the substantially straight elongated tubular passages and the upper surface is less than the angle of repose of the second bed material.

  20. Fluid bed material transfer method

    DOEpatents

    Pinske, Jr., Edward E.

    1994-01-01

    A fluidized bed apparatus comprising a pair of separated fluid bed enclosures, each enclosing a fluid bed carried on an air distributor plate supplied with fluidizing air from below the plate. At least one equalizing duct extending through sidewalls of both fluid bed enclosures and flexibly engaged therewith to communicate the fluid beds with each other. The equalizing duct being surrounded by insulation which is in turn encased by an outer duct having expansion means and being fixed between the sidewalls of the fluid bed enclosures.

  1. Apparatus for controlling fluidized beds

    DOEpatents

    Rehmat, A.G.; Patel, J.G.

    1987-05-12

    An apparatus and process are disclosed for control and maintenance of fluidized beds under non-steady state conditions. An ash removal conduit is provided for removing solid particulates from a fluidized bed separate from an ash discharge conduit in the lower portion of the grate supporting such a bed. The apparatus and process of this invention is particularly suitable for use in ash agglomerating fluidized beds and provides control of the fluidized bed before ash agglomeration is initiated and during upset conditions resulting in stable, sinter-free fluidized bed maintenance. 2 figs.

  2. Apparatus for controlling fluidized beds

    DOEpatents

    Rehmat, Amirali G.; Patel, Jitendra G.

    1987-05-12

    An apparatus and process for control and maintenance of fluidized beds under non-steady state conditions. An ash removal conduit is provided for removing solid particulates from a fluidized bed separate from an ash discharge conduit in the lower portion of the grate supporting such a bed. The apparatus and process of this invention is particularly suitable for use in ash agglomerating fluidized beds and provides control of the fluidized bed before ash agglomeration is initiated and during upset conditions resulting in stable, sinter-free fluidized bed maintenance.

  3. Virtual Test Bed

    DTIC Science & Technology

    2016-06-07

    project is to develop a benchmark system for evaluating models for predicting the characteristics of ocean wind waves. SCIENTIFIC OBJECTIVES A...to be assembled within the virtual test bed. Wind fields for running these tests will be obtained from Oceanweather, Inc. from a separate ONR

  4. Bed Bug Myths

    EPA Pesticide Factsheets

    Learn the truth about bed bugs, such as how easy they are to see with the naked eye, their preferred habitat, whether they transmit diseases, their public health effects, and whether pesticides are the best way to deal with an infestation.

  5. MULTISTAGE FLUIDIZED BED REACTOR

    DOEpatents

    Jonke, A.A.; Graae, J.E.A.; Levitz, N.M.

    1959-11-01

    A multistage fluidized bed reactor is described in which each of a number of stages is arranged with respect to an associated baffle so that a fluidizing gas flows upward and a granular solid downward through the stages and baffles, whereas the granular solid stopsflowing downward when the flow of fluidizing gas is shut off.

  6. Fundamental tribological properties of ceramics

    NASA Technical Reports Server (NTRS)

    Buckley, D. H.; Miyoshi, K.

    1985-01-01

    When a ceramic is brought into contact with itself, another ceramic, or a metal, strong bond forces can develop between the materials. Adhesion between a ceramic and itself or another solid are discussed from a theoretical consideration of the nature of the surfaces and experimentally by relating bond forces to the interface resulting from solid state contact. Elastic, plastic, and fracture behavior of ceramics in solid-state contact are discussed as they relate to friction and wear. The contact load necessary to initiate fracture in ceramics is shown to be appreciably reduced with tangential motion. Both friction and wear of ceramics are anisotropic and relate to crystal structure as with metals. Both free energy of oxide formation and the d valence bond character of metals are related to the friction and wear characteristics for metals in contact with ceramics. Lubrication is found to increase the critical load necessary to initiate fracture of ceramics with sliding or rubbing contact.

  7. Piezoelectric Ceramics and Their Applications

    ERIC Educational Resources Information Center

    Flinn, I.

    1975-01-01

    Describes the piezoelectric effect in ceramics and presents a quantitative representation of this effect. Explains the processes involved in the manufacture of piezoelectric ceramics, the materials used, and the situations in which they are applied. (GS)

  8. Microstructure and properties of ceramics

    NASA Technical Reports Server (NTRS)

    Hamano, K.

    1984-01-01

    The history of research into the microstructure and properties of ceramic ware is discussed; methods of producing ceramics with particular characteristics are investigated. Bubbles, sintering, cracks, and electron microscopy are discussed.

  9. Automatic computation of pebble roundness using digital imagery and discrete geometry

    NASA Astrophysics Data System (ADS)

    Roussillon, Tristan; Piégay, Hervé; Sivignon, Isabelle; Tougne, Laure; Lavigne, Franck

    2009-10-01

    The shape of sedimentary particles is an important property, from which geographical hypotheses related to abrasion, distance of transport, river behavior, etc. can be formulated. In this paper, we use digital image analysis, especially discrete geometry, to automatically compute some shape parameters such as roundness, i.e. a measure of how much the corners and edges of a particle have been worn away. In contrast to previous work in which traditional digital images analysis techniques, such as Fourier transform, are used, we opted for a discrete geometry approach that allowed us to implement Wadell's original index, which is known to be more accurate, but more time consuming to implement in the field. Our implementation of Wadell's original index is highly correlated (92%) with the roundness classes of Krumbein's chart, used as a ground-truth. In addition, we show that other geometrical parameters, which are easier to compute, can be used to provide good approximations of roundness. We also used our shape parameters to study a set of pebbles digital images taken from the Progo basin river network (Indonesia). The results we obtained are in agreement with previous work and open new possibilities for geomorphologists thanks to automatic computation.

  10. A positive feedback loop between Dumbfounded and Rolling pebbles leads to myotube enlargement in Drosophila

    PubMed Central

    Menon, Sree Devi; Osman, Zalina; Chenchill, Kho; Chia, William

    2005-01-01

    In Drosophila, myoblasts are subdivided into founders and fusion-competent myoblasts (fcm) with myotubes forming through fusion of one founder and several fcm. Duf and rolling pebbles 7 (Rols7; also known as antisocial) are expressed in founders, whereas sticks and stones (SNS) is present in fcm. Duf attracts fcm toward founders and also causes translocation of Rols7 from the cytoplasm to the fusion site. We show that Duf is a type 1 transmembrane protein that induces Rols7 translocation specifically when present intact and engaged in homophilic or Duf–SNS adhesion. Although its membrane-anchored extracellular domain functions as an attractant and is sufficient for the initial round of fusion, subsequent fusions require replenishment of Duf through cotranslocation with Rols7 tetratricopeptide repeat/coiled-coil domain-containing vesicles to the founder/myotube surface, causing both Duf and Rols7 to be at fusion sites between founders/myotubes and fcm. This implicates the Duf–Rols7 positive feedback loop to the occurrence of fusion at specific sites along the membrane and provides a mechanism by which the rate of fusion is controlled. PMID:15955848

  11. Close-in planetesimal formation by pile-up of drifting pebbles

    NASA Astrophysics Data System (ADS)

    Drążkowska, J.; Alibert, Y.; Moore, B.

    2016-10-01

    Context. The consistency of planet formation models suffers from the disconnection between the regime of small and large bodies. This is primarily caused by so-called growth barriers: the direct growth of larger bodies is halted at centimetre-sized objects and particular conditions are required for the formation of larger, gravitationally bound planetesimals. Aims: We aim to connect models of dust evolution and planetesimal formation to identify regions of protoplanetary discs that are favourable for the formation of kilometre-sized bodies and the first planetary embryos. Methods: We combine semi-analytical models of viscous protoplanetary disc evolution, dust growth and drift including backreaction of the dust particles on the gas, and planetesimal formation via the streaming instability into one numerical code. We investigate how planetesimal formation is affected by the mass of the protoplanetary disc, its initial dust content, and the stickiness of dust aggregates. Results: We find that the dust growth and drift leads to a global redistribution of solids. The pile-up of pebbles in the inner disc provides local conditions where the streaming instability is effective. Planetesimals form in an annulus with its inner edge lying between 0.3 AU and 1 AU and its width ranging from 0.3 AU to 3 AU. The resulting surface density of planetesimals follows a radial profile that is much steeper than the initial disc profile. These results support formation of terrestrial planets in the solar system from a narrow annulus of planetesimals, which reproduces their peculiar mass ratios.

  12. EVIDENCE OF FAST PEBBLE GROWTH NEAR CONDENSATION FRONTS IN THE HL TAU PROTOPLANETARY DISK

    SciTech Connect

    Zhang, Ke; Blake, Geoffrey A.; Bergin, Edwin A.

    2015-06-10

    Water and simple organic molecular ices dominate the mass of solid materials available for planetesimal and planet formation beyond the water snow line. Here we analyze ALMA long baseline 2.9, 1.3 and 0.87 mm continuum images of the young star HL Tau, and suggest that the emission dips observed are due to rapid pebble growth around the condensation fronts of abundant volatile species. Specifically, we show that the prominent innermost dip at 13 AU is spatially resolved in the 0.87 mm image, and its center radius is coincident with the expected mid-plane condensation front of water ice. In addition, two other prominent dips, at distances of 32 and 63 AU, cover the mid-plane condensation fronts of pure ammonia or ammonia hydrates and clathrate hydrates (especially with CO and N{sub 2}) formed from amorphous water ice. The spectral index map of HL Tau between 1.3 and 0.87 mm shows that the flux ratios inside the dips are statistically larger than those of nearby regions in the disk. This variation can be explained by a model with two dust populations, where most of the solid mass resides in a component that has grown to decimeter size scales inside the dips. Such growth is in accord with recent numerical simulations of volatile condensation, dust coagulation, and settling.

  13. Spin Dynamics of Kelvin's Pebbles, Jellett's Eggs, and Shiva's Lingam Stones

    NASA Astrophysics Data System (ADS)

    Brecher, Kenneth

    2015-04-01

    Study of the problem of the rise of the center of mass (COM) of spinning objects is said to have begun in the late nineteenth century. These early mathematical treatments aimed to explain the motion of the newly invented and patented ``tippe top.'' This semi-spheroidal top will invert when spun on a smooth surface while raising its COM. Because of the importance of friction in their dynamics, such non-holonomic systems are not readily amenable to analytic treatment, or of intuitive understanding. In notes written in 1844 - before the invention of the tippe top - Lord Kelvin (William Thomson) discussed the problem of the rising COM of spinning objects. He experimented with both oblate and prolate ellipsoidal pebbles, but did not publish a complete theoretical treatment of the problem. J. H. Jellett, in his 1872 book ``Theory of Friction,'' provided a partial account of the related problem of the rise of the COM for an egg-shaped (ovoid) object, making use of a new (adiabatic) invariant of the motion that he devised. Naturally occurring prolate ellipsoidal ``Lingam stones'' from the Narmada River in India exhibit similar counter-intuitive dynamical behavior. When spun around its minor axis in a horizontal plane, a Lingam stone will stand erect and spin around its major axis in a vertical position. This presentation will explore the history and some of the experimental facts and theoretical ideas about the rotational dynamics of such physical objects.

  14. Applying Pebble-Rotating Game to enhance the robustness of DHTs.

    PubMed

    Ren, Liyong; Nie, Xiaowen; Dong, Yuchi

    2013-01-01

    Distributed hash tables (DHTs) are usually used in the open networking environment, where they are vulnerable to Sybil attacks. Pebble-Rotating Game (PRG) mixes the nodes of the honest and the adversarial randomly, and can resist the Sybil attack efficiently. However, the adversary may have some tricks to corrupt the rule of PRG. This paper proposes a set of mechanisms to make the rule of PRG be obliged to obey. A new joining node must ask the Certificate Authority (CA) for its signature and certificate, which records the complete process on how a node joins the network and obtains the legitimacy of the node. Then, to prevent the adversary from accumulating identifiers, any node can make use of the latest certificate to judge whether one identifier is expired with the help of the replacement property of RPG. This paper analyzes in details the number of expired certificates which are needed to store in every node, and gives asymptotic solution of this problem. The analysis and simulations show that the mean number of the certificates stored in each node are [Formula: see text], where n is the size of the network.

  15. Poly(decyl methacrylate)-based fluorescent PEBBLE swarm nanosensors for measuring dissolved oxygen in biosamples.

    PubMed

    Cao, Youfu; Lee Koo, Yong-Eun; Kopelman, Raoul

    2004-08-01

    150-250 nm Poly(decyl methacrylate)(PDMA) fluorescent ratiometric nanosensors for dissolved oxygen have been developed. Platinum octaethylporphine ketone (PtOEPK), the oxygen-sensitive dye, and octaethylporphyrin (OEP), the oxygen-insensitive dye, have been incorporated into PDMA nanoparticles to make the sensors ratiometric. Based on the corresponding Stern-Volmer plot, these nanosensors exhibit almost complete linearity over the whole range of dissolved molecular oxygen from 0 to 42.5 ppm (deoxygenated to pure oxygen-bubbled water). The overall quenching response is up to 97.5%, the best so far for all dissolved oxygen optical sensors. These PEBBLE nanosensors also show very good reversibility and stability to leaching and photobleaching, as well as very short response times and no perturbation by proteins. In human plasma they demonstrate a robust oxygen sensing capability, little affected by light scattering and autofluorescence. Potential applications include intracellular oxygen imaging and microresolved pressure profiles in biological and other heterogenous environments.

  16. Pebble/ECT2 RhoGEF negatively regulates the Wingless/Wnt signaling pathway.

    PubMed

    Greer, Elisabeth R; Chao, Anna T; Bejsovec, Amy

    2013-12-01

    Wingless (Wg)/Wnt signaling is essential for patterning invertebrate and vertebrate embryos, and inappropriate Wnt activity is associated with a variety of human cancers. Despite intensive study, Wnt pathway mechanisms are not fully understood. We have discovered a new mechanism for regulating the Wnt pathway: activity of a Rho guanine nucleotide exchange factor (GEF) encoded by pebble (pbl) in Drosophila and ECT2 in humans. This RhoGEF has an essential role in cytokinesis, but also plays an unexpected, conserved role in inhibiting Wg/Wnt activity. Loss and gain of pbl function in Drosophila embryos cause pattern defects that indicate altered Wg activity. Both Pbl and ECT2 repress Wg/Wnt target gene expression in cultured Drosophila and human cells. The GEF activity is required for Wnt regulation, whereas other protein domains important for cytokinesis are not. Unlike most negative regulators of Wnt activity, Pbl/ECT2 functions downstream of Armadillo (Arm)/beta-catenin stabilization. Our results indicate GTPase regulation at a novel point in Wg/Wnt signal transduction, and provide new insight into the categorization of ECT2 as a human proto-oncogene.

  17. Pebble treatment and use at Cleveland-Cliffs` autogenous milling operations

    SciTech Connect

    Greenwood, B.R.; McIvor, R.E.

    1996-12-31

    Subsidiaries of Cleveland-Cliffs Inc. operate seven iron mining operations worldwide. Of these seven operations, four North American facilities employ autogenous milling. Two of these autogenous milling circuits are in northern Michigan, the Tilden and Empire Mines, one is in northern Minnesota, Hibbing Taconite, and the fourth is the Wabush Mine in Labrador. The original autogenous milling circuit developed by Cleveland-Cliffs was at the Empire Mine. Extensive laboratory, pilot plant and full-scale testing was conducted prior to commissioning this first iron ore autogenous circuit in 1963. Since the original circuits were installed at the four mines, modifications have been made based on pilot plant and full-scale plant tests that have resulted in significant improvements in primary mill throughputs. The following is a discussion of the autogenous milling circuits at Empire, Tilden and Hibtac and the changes to the circuits related to pebble treatment and use that have been and are scheduled to be made to increase feed rates and/or improve efficiency.

  18. Using Kinect to analyze pebble to block-sized clasts in sedimentology

    NASA Astrophysics Data System (ADS)

    Moreno Chávez, G.; Sarocchi, D.; Arce Santana, E.; Borselli, L.; Rodríguez-Sedano, L. A.

    2014-11-01

    In this paper, we propose a new system for automatically measuring grain sizes in a range from pebbles to blocks. The system is based on use of the Microsoft Kinect device and a novel software developed by the authors which enables a tridimensional digital model of a selected area of an outcrop to be captured. With the tridimensional model, clasts are stacked using new segmentation algorithms based on level sets and Fourier analysis. The resulting binary image (clasts and matrix) is analyzed by means of the Rosiwal stereological method. The granulometric Cumulative Distribution Function (CDF), obtained automatically by this new methodology, was compared to the granulometric CDF, obtained manually by the Rosiwal technique, by means of a Kolmogorov-Smirnov test. The comparison showed good agreement between the methods and demonstrated that this inexpensive system (already used in several scientific fields) with great potential can also be used to obtain fast, automatic and accurate grain size distributions of sedimentary deposits. The software tools used to control the Kinect device, which provide the three-dimensional elevation models of the outcrops and allows its analysis, are freely available from the author.

  19. Ceramic automotive Stirling engine program

    NASA Technical Reports Server (NTRS)

    1986-01-01

    The Ceramic Automotive Stirling Engine Program evaluated the application of advanced ceramic materials to an automotive Stirling engine. The objective of the program was to evaluate the technical feasibility of utilizing advanced ceramics to increase peak engine operating temperature, and to evaluate the performance benefits of such an increase. Manufacturing cost estimates were also developed for various ceramic engine components and compared with conventional metallic engine component costs.

  20. Ceramic Automotive Stirling Engine Program

    SciTech Connect

    Not Available

    1986-08-01

    The Ceramic Automotive Stirling Engine Program evaluated the application of advanced ceramic materials to an automotive Stirling engine. The objective of the program was to evaluate the technical feasibility of utilizing advanced ceramics to increase peak engine operating temperature, and to evaluate the performance benefits of such an increase. Manufacturing cost estimates were also developed for various ceramic engine components and compared with conventional metallic engine component costs.

  1. Ceramic microstructure and adhesion

    NASA Technical Reports Server (NTRS)

    Buckley, D. H.

    1984-01-01

    When a ceramic is brought into contact with a ceramic, a polymer, or a metal, strong bond forces can develop between the materials. The bonding forces will depend upon the state of the surfaces, cleanliness and the fundamental properties of the two solids, both surface and bulk. Adhesion between a ceramic and another solid are discussed from a theoretical consideration of the nature of the surfaces and experimentally by relating bond forces to interface resulting from solid state contact. Surface properties of ceramics correlated with adhesion include, orientation, reconstruction and diffusion as well as the chemistry of the surface specie. Where a ceramic is in contact with a metal their interactive chemistry and bond strength is considered. Bulk properties examined include elastic and plastic behavior in the surficial regions, cohesive binding energies, crystal structures and crystallographic orientation. Materials examined with respect to interfacial adhesive interactions include silicon carbide, nickel zinc ferrite, manganese zinc ferrite, and aluminum oxide. The surfaces of the contacting solids are studied both in the atomic or molecularly clean state and in the presence of selected surface contaminants.

  2. Ceramic combustor mounting

    DOEpatents

    Hoffman, Melvin G.; Janneck, Frank W.

    1982-01-01

    A combustor for a gas turbine engine includes a metal engine block including a wall portion defining a housing for a combustor having ceramic liner components. A ceramic outlet duct is supported by a compliant seal on the metal block and a reaction chamber liner is stacked thereon and partly closed at one end by a ceramic bypass swirl plate which is spring loaded by a plurality of circumferentially spaced, spring loaded guide rods and wherein each of the guide rods has one end thereof directed exteriorly of a metal cover plate on the engine block to react against externally located biasing springs cooled by ambient air and wherein the rod spring support arrangement maintains the stacked ceramic components together so that a normal force is maintained on the seal between the outlet duct and the engine block under all operating conditions. The support arrangement also is operative to accommodate a substantial difference in thermal expansion between the ceramic liner components of the combustor and the metal material of the engine block.

  3. FATIGUE OF DENTAL CERAMICS

    PubMed Central

    Zhang, Yu; Sailer, Irena; Lawn, Brian R

    2013-01-01

    Objectives Clinical data on survival rates reveal that all-ceramic dental prostheses are susceptible to fracture from repetitive occlusal loading. The objective of this review is to examine the underlying mechanisms of fatigue in current and future dental ceramics. Data/sources The nature of various fatigue modes is elucidated using fracture test data on ceramic layer specimens from the dental and biomechanics literature. Conclusions Failure modes can change over a lifetime, depending on restoration geometry, loading conditions and material properties. Modes that operate in single-cycle loading may be dominated by alternative modes in multi-cycle loading. While post-mortem examination of failed prostheses can determine the sources of certain fractures, the evolution of these fractures en route to failure remains poorly understood. Whereas it is commonly held that loss of load-bearing capacity of dental ceramics in repetitive loading is attributable to chemically-assisted 'slow crack growth' in the presence of water, we demonstrate the existence of more deleterious fatigue mechanisms, mechanical rather than chemical in nature. Neglecting to account for mechanical fatigue can lead to gross overestimates in predicted survival rates. Clinical significance Strategies for prolonging the clinical lifetimes of ceramic restorations are proposed based on a crack-containment philosophy. PMID:24135295

  4. Ceramic impregnated superabrasives

    DOEpatents

    Radtke, Robert P.; Sherman, Andrew

    2009-02-10

    A superabrasive fracture resistant compact is formed by depositing successive layers of ceramic throughout the network of open pores in a thermally stable self-bonded polycrystalline diamond or cubic boron nitride preform. The void volume in the preform is from approximately 2 to 10 percent of the volume of the preform, and the average pore size is below approximately 3000 nanometers. The preform is evacuated and infiltrated under at least about 1500 pounds per square inch pressure with a liquid pre-ceramic polymerizable precursor. The precursor is infiltrated into the preform at or below the boiling point of the precursor. The precursor is polymerized into a solid phase material. The excess is removed from the outside of the preform, and the polymer is pyrolized to form a ceramic. The process is repeated at least once more so as to achieve upwards of 90 percent filling of the original void volume. When the remaining void volume drops below about 1 percent the physical properties of the compact, such as fracture resistance, improve substantially. Multiple infiltration cycles result in the deposition of sufficient ceramic to reduce the void volume to below 0.5 percent. The fracture resistance of the compacts in which the pores are lined with formed in situ ceramic is generally at least one and one-half times that of the starting preforms.

  5. Ceramics with Different Additives

    NASA Astrophysics Data System (ADS)

    Wang, Juanjuan; Feng, Lajun; Lei, Ali; Zhao, Kang; Yan, Aijun

    2014-09-01

    Li2CO3, MgCO3, BaCO3, and Bi2O3 dopants were introduced into CaCu3Ti4O12 (CCTO) ceramics in order to improve the dielectric properties. The CCTO ceramics were prepared by conventional solid-state reaction method. The phase structure, microstructure, and dielectric behavior were carefully investigated. The pure structure without any impurity phases can be confirmed by the x-ray diffraction patterns. Scanning Electron Microscopy (SEM) analysis illuminated that the grains of Ca0.90Li0.20Cu3Ti4O12 ceramics were greater than that of pure CCTO. It was important for the properties of the CCTO ceramics to study the additives in complex impedance spectroscopy. It was found that the Ca0.90Li0.20Cu3Ti4O12 ceramics had the higher permittivity (>45000), the lower dielectric loss (<0.025) than those of CCTO at 1 kHz at room temperature and good temperature stability from -30 to 75 °C.

  6. Ceramic coatings on smooth surfaces

    NASA Technical Reports Server (NTRS)

    Miller, R. A. (Inventor); Brindley, W. J. (Inventor); Rouge, C. J. (Inventor)

    1991-01-01

    A metallic coating is plasma sprayed onto a smooth surface of a metal alloy substitute or on a bond coating. An initial thin ceramic layer is low pressure sprayed onto the smooth surface of the substrate or bond coating. Another ceramic layer is atmospheric plasma sprayed onto the initial ceramic layer.

  7. Assessment of ceramic membrane filters

    SciTech Connect

    Ahluwalia, R.K.; Geyer, H.K.; Im, K.H.

    1995-08-01

    The objectives of this project include the development of analytical models for evaluating the fluid mechanics of membrane coated, dead-end ceramic filters, and to determine the effects of thermal and thermo-chemical aging on the material properties of emerging ceramic hot gas filters. A honeycomb cordierite monolith with a thin ceramic coating and a rigid candle filter were evaluated.

  8. Ceramic composites: Enabling aerospace materials

    NASA Technical Reports Server (NTRS)

    Levine, S. R.

    1992-01-01

    Ceramics and ceramic matrix composites (CMC) have the potential for significant impact on the performance of aerospace propulsion and power systems. In this paper, the potential benefits are discussed in broad qualitative terms and are illustrated by some specific application case studies. The key issues in need of resolution for the potential of ceramics to be realized are discussed.

  9. Ceramic tamper-revealing seals

    DOEpatents

    Kupperman, D.S.; Raptis, A.C.; Sheen, S.H.

    1992-12-08

    A flexible metal or ceramic cable is described with composite ceramic ends, or a U-shaped ceramic connecting element attached to a binding element plate or block cast from alumina or zirconium, and connected to the connecting element by shrink fitting. 7 figs.

  10. Ceramic technology for automotive turbines

    NASA Technical Reports Server (NTRS)

    Mclean, A. F.

    1982-01-01

    The paper presents an update on ceramic technology for automotive turbines. Progress in research and development of improved ceramics is reviewed, including approaches for assessing time-dependent strength characteristics. Processes for making shapes are discussed, and the design and testing of selected ceramic turbine components are reviewed.

  11. Artificial Voids In Ceramic Materials

    NASA Technical Reports Server (NTRS)

    Roth, Don J.; Generazio, Edward R.; Baaklini, George Y.

    1988-01-01

    Method for creating voids in ceramic specimens developed. Silicon carbide and silicon nitride are high-temperature structural ceramic materials considered for applications in advanced gas-turbine engines. Ability to detect and characterize voids (by sizes, shapes, and locations) in structural ceramics vital for increasing strengths and reliabilities of materials. Small holes made deliberately to help quantify techniques of nondestructive evaluation.

  12. Bed Bug Clearinghouse by Topic

    EPA Pesticide Factsheets

    This information is intended to help states, communities, and consumers prevent and control bed bug infestations. Topics include bed bug biology and behavior, detection and monitoring, non-chemical techniques such as heat treatment, and pesticides.

  13. Moving Granular Bed Filter Development Program

    SciTech Connect

    Wilson, K.B.; Haas, J.C.; Gupta, R.P.; Turk, B.S.

    1996-12-31

    For coal-fired power plants utilizing a gas turbine, the removal of ash particles is necessary to protect the turbine and to meet emission standards. Advantages are also evident for a filter system that can remove other coal-derived contaminants such as alkali, halogens, and ammonia. With most particulates and other contaminants removed, erosion and corrosion of turbine materials, as well as deposition of particles within the turbine, are reduced to acceptable levels. The granular bed filter is suitable for this task in a pressurized gasification or combustion environment. The objective of the base contract was to develop conceptual designs of moving granular bed filter (GBF) and ceramic candle filter technologies for control of particles from integrated gasification combined cycle (IGCC), pressurized fluidized-bed combustion (PFBC), and direct coal-fueled turbine (DCFT) systems. The results of this study showed that the GBF design compared favorably with the candle filter. Three program options followed the base contract. The objective of Option I, Component Testing, was to identify and resolve technical issues regarding GBF development for IGCC and PFBC environments. This program was recently completed. The objective of Option II, Filter Proof Tests, is to test and evaluate the moving GBF system at a government-furnished hot-gas cleanup test facility. This facility is located at Southern Company Services (SCS), Inc., Wilsonville, Alabama. The objective of Option III, Multicontaminant Control Using a GBF, is to develop a chemically reactive filter material that will remove particulates plus one or more of the following coal-derived contaminants: alkali, halogens, and ammonia.

  14. Ceramic regenerator program

    NASA Technical Reports Server (NTRS)

    Franklin, Jerrold E.

    1991-01-01

    The feasibility of fabricating an Air Turbo Ramjet (ATR) regenerator containing intricate hydraulic passages from a ceramic material in order to allow operation with high temperature combustion gas and to reduce weight as compared with metallic materials was demonstrated. Platelet technology, ceramic tape casting, and multilayer ceramic packaging techniques were used in this fabrication of subscale silicon nitride components. Proof-of-concept demonstrations were performed to simulate a methane cooled regenerator for an ATR engine. The regenerator vane was designed to operate at realistic service conditions, i.e., 600 psi in a 3500 R (3040 F), 500 fps combustion gas environment. A total of six regenerators were fabricated and tested. The regenerators were shown to be able to withstand internal pressurization to 1575 psi. They were subjected to testing in 500 fps, 3560 R (3100 F) air/propane combustion products and were operated satisfactorily for an excess of 100 hr and 40 thermal cycles which exceeded 2460 R (2000 F).

  15. Ceramic vane drive joint

    DOEpatents

    Smale, Charles H.

    1981-01-01

    A variable geometry gas turbine has an array of ceramic composition vanes positioned by an actuating ring coupled through a plurality of circumferentially spaced turbine vane levers to the outer end of a metallic vane drive shaft at each of the ceramic vanes. Each of the ceramic vanes has an end slot of bow tie configuration including flared end segments and a center slot therebetween. Each of the vane drive shafts has a cross head with ends thereof spaced with respect to the sides of the end slot to define clearance for free expansion of the cross head with respect to the vane and the cross head being configured to uniformly distribute drive loads across bearing surfaces of the vane slot.

  16. Microwave sintering of ceramics

    SciTech Connect

    Snyder, W.B.

    1989-01-01

    Successful adaptation of microwave heating to the densification of ceramic materials require a marriage of microwave and materials technologies. Using an interdisciplinary team of microwave and materials engineers, we have successfully demonstrated the ability to density ceramic materials over a wide range of temperatures. Microstructural evolution during microwave sintering has been found to be significantly different from that observed in conventional sintering. Our results and those of others indicate that microwave sintering has the potential to fabricate components to near net shape with mechanical properties equivalent to hot pressed or hot isostatically pressed material. 6 refs., 11 figs.

  17. Ceramic component for electrodes

    DOEpatents

    Marchant, David D.

    1979-01-01

    A ceramic component suitable for preparing MHD generator electrodes consists of HfO.sub.2 and sufficient Tb.sub.4 O.sub.7 to stabilize at least 60 volume percent of the HfO.sub.2 into the cubic structure. The ceramic component may also contain a small amount of PrO.sub.2, Yb.sub.2 O.sub.3 or a mixture of both to improve stability and electronic conductivity of the electrode. The component is highly resistant to corrosion by molten potassium seed and molten coal slag in the MHD fluid and exhibits both ionic and electronic conductivity.

  18. Ceramic breeder materials

    SciTech Connect

    Johnson, C.E.; Kummerer, K.R.; Roth, E.

    1987-01-01

    Ceramic materials are under investigation as potential breeder material in fusion reactors. This paper will review candidate materials with respect to fabrication routes and characterization, properties in as-fabricated and irradiated condition, and experimental results from laboratory and inpile investigations on tritium transport and release. Also discussed are the resources of beryllium, which is being considered as a neutron multiplier. The comparison of ceramic properties that is attempted here aims at the identification of the most-promising material for use in a tritium breeding blanket. 82 refs., 12 figs., 5 tabs.

  19. Environment Conscious Ceramics (Ecoceramics)

    NASA Technical Reports Server (NTRS)

    Singh, Mrityunjay; Levine, Stanley R. (Technical Monitor)

    2000-01-01

    Environment conscious ceramics (Ecoceramics) are a new class of materials, which can be produced with renewable natural resources (wood) or wood wastes (wood sawdust). Silicon carbide-based ecoceramics have been fabricated by reactive infiltration of carbonaceous preforms by molten silicon or silicon-refractory metal alloys. These carbonaceous preforms have been fabricated by pyrolysis of solid wood bodies at 1000 C. The fabrication approach, microstructure, and mechanical properties of SiC-based ecoceramics are presented. Ecoceramics have tailorable properties and behave like ceramic materials manufactured by conventional approaches.

  20. Performance of Dental Ceramics

    PubMed Central

    Rekow, E.D.; Silva, N.R.F.A.; Coelho, P.G.; Zhang, Y.; Guess, P.; Thompson, V.P.

    2011-01-01

    The clinical success of modern dental ceramics depends on an array of factors, ranging from initial physical properties of the material itself, to the fabrication and clinical procedures that inevitably damage these brittle materials, and the oral environment. Understanding the influence of these factors on clinical performance has engaged the dental, ceramics, and engineering communities alike. The objective of this review is to first summarize clinical, experimental, and analytic results reported in the recent literature. Additionally, it seeks to address how this new information adds insight into predictive test procedures and reveals challenges for future improvements. PMID:21224408

  1. Why ceramic engines?

    NASA Technical Reports Server (NTRS)

    Stadler, H. L.

    1984-01-01

    Oil is still a problem for the U.S. and its allies. Transportation uses 61 percent of U.S. oil and its share is increasing, so more efficient technology should be concentrated there. Trucks' share of oil use is increasing because they are already much more efficient than autos. The primary truck opportunities are streamlining, more efficient engines, and shifting freight to railroads. More efficient engines are possible using ceramics to allow elimination of cooling systems and better use of waste exhaust heat. A 60 percent improvement seems possible if ceramics can be made tough enough and durable enough.

  2. Battery utilizing ceramic membranes

    DOEpatents

    Yahnke, M.S.; Shlomo, G.; Anderson, M.A.

    1994-08-30

    A thin film battery is disclosed based on the use of ceramic membrane technology. The battery includes a pair of conductive collectors on which the materials for the anode and the cathode may be spin coated. The separator is formed of a porous metal oxide ceramic membrane impregnated with electrolyte so that electrical separation is maintained while ion mobility is also maintained. The entire battery can be made less than 10 microns thick while generating a potential in the 1 volt range. 2 figs.

  3. Supported microporous ceramic membranes

    DOEpatents

    Webster, E.; Anderson, M.

    1993-12-14

    A method for the formation of microporous ceramic membranes onto a porous support includes placing a colloidal suspension of metal or metal oxide particles on one side of the porous support and exposing the other side of the porous support to a drying stream of gas or a reactive gas stream so that the particles are deposited on the drying side of the support as a gel. The gel so deposited can be sintered to form a supported ceramic membrane useful for ultrafiltration, reverse osmosis, or molecular sieving having mean pore sizes less than 100 Angstroms. 4 figures.

  4. Supported microporous ceramic membranes

    DOEpatents

    Webster, Elizabeth; Anderson, Marc

    1993-01-01

    A method for permformation of microporous ceramic membranes onto a porous support includes placing a colloidal suspension of metal or metal oxide particles on one side of the porous support and exposing the other side of the porous support to a drying stream of gas or a reactive gas stream so that the particles are deposited on the drying side of the support as a gel. The gel so deposited can be sintered to form a supported ceramic membrane useful for ultrafiltration, reverse osmosis, or molecular sieving having mean pore sizes less than 100 Angstroms.

  5. Capture of alkali during pressurized fluidized-bed combustion using in-bed sorbents

    SciTech Connect

    Mann, M.D.; Ludlow, D.K.

    1997-12-31

    The primary focus of this research was the removal of alkali from PFBC flue gases to a level specified by turbine manufactures. The target level was less than 24 ppbw. Several of the aluminosilicate minerals have the potential to capture alkalis, especially sodium and potassium, under conditions typical of fluid-bed operation. Other goals of this work were to investigate the potential for simultaneously removing SO{sub 2} and Cl from the PFBC gas stream. The initial work focused primarily on one class of sorbents, sodalites, with the goal of determining whether sodalites can be used as an in-bed sorbent to simultaneously remove alkali and sulfur. Thermo gravimetric analysis (TGA) was used to study the mechanism of alkali capture using sodalite. Further testing was performed on a 7.6 cm (3-in.)-diameter pressurized fluid-bed reactor (PFBR). Early results indicated that simultaneous removal of alkali and sulfur and/or chlorine was not practical under the conditions for commercial PFBC operations. Therefore, the focus of the latter part of this work was on sorbents that have been shown to capture alkali in other systems. The effectiveness of bauxite and kaolinite to reduce vapor-phase alkali concentrations was determined. In addition to studying the gettering capability of the sorbent, the impact of the getter on operational performance was evaluated. This evaluation included examining potential agglomeration of bed particles, deposition on heat-transfer surfaces, and the bridging and blinding of ceramic candle filters. The focus of this paper is on the work performed on the PFBR.

  6. Debris-bed friction of hard-bedded glaciers

    NASA Astrophysics Data System (ADS)

    Cohen, D.; Iverson, N. R.; Hooyer, T. S.; Fischer, U. H.; Jackson, M.; Moore, P. L.

    2005-06-01

    Field measurements of debris-bed friction on a smooth rock tablet at the bed of Engabreen, a hard-bedded, temperate glacier in northern Norway, indicated that basal ice containing 10% debris by volume exerted local shear traction of up to 500 kPa. The corresponding bulk friction coefficient between the dirty basal ice and the tablet was between 0.05 and 0.08. A model of friction in which nonrotating spherical rock particles are held in frictional contact with the bed by bed-normal ice flow can account for these measurements if the power law exponent for ice flowing past large clasts is 1. A small exponent (n < 2) is likely because stresses in ice are small and flow is transient. Numerical calculations of the bed-normal drag force on a sphere in contact with a flat bed using n = 1 show that this force can reach values several hundred times that on a sphere isolated from the bed, thus drastically increasing frictional resistance. Various estimates of basal friction are obtained from this model. For example, the shear traction at the bed of a glacier sliding at 20 m a-1 with a geothermally induced melt rate of 0.006 m a-1 and an effective pressure of 300 kPa can exceed 100 kPa. Debris-bed friction can therefore be a major component of sliding resistance, contradicting the common assumption that debris-bed friction is negligible.

  7. Debris-Bed Friction of Hard-Bedded Glaciers

    NASA Astrophysics Data System (ADS)

    Cohen, D.; Iverson, N. R.; Hooyer, T. S.; Fischer, U. H.; Jackson, M.; Moore, P. L.

    2004-12-01

    Field measurements of debris-bed friction on a smooth rock tablet at the bed of Engabreen, a hard-bedded, temperate glacier in northern Norway, indicated that basal ice containing 10% debris by volume exerted local shear traction of up to 500~kPa. The corresponding bulk friction coefficient between the dirty basal ice and the tablet was between 0.05 and 0.08. A model of friction in which non-rotating spherical rock particles are held in frictional contact with the bed by bed-normal ice flow can account for these measurements if ice is Newtonian. Numerical calculations of the bed-normal drag force on a sphere in contact with a flat bed show that this force can reach values several hundred times that on a sphere isolated from the bed, thus drastically increasing frictional resistance. Various estimates of basal friction are obtained from this model. For example, the shear traction at the bed of a 200~m thick glacier sliding at 20~m a-1 with a geothermally induced melt rate of 0.006~m a-1 can exceed 100~kPa. Debris-bed friction can, therefore, be a major component of sliding resistance, contradicting the common assumption that debris-bed friction is negligible.

  8. [Ceramic couplings in orthopedic surgery].

    PubMed

    Thomsen, M; Willmann, G

    2003-01-01

    Ceramic materials have been used as a coupling in total hip arthroplasty since the 1970s to solve the problem of polyethylene particle disease. Several problems with the material and the design have been identified and solved. Using inlays and ceramic heads of the latest generation offers the possibility of reducing the wear rate to as low as 0.001 mm per year. The problem of ceramic fractures is rare. Recently due to the manufacturing process some zirconia ceramic heads have been problematic. New developments with other ceramics are discussed.

  9. Fluidized-bed combustion

    SciTech Connect

    Botros, P E

    1990-04-01

    This report describes the activities of the Morgantown Energy Technology Center's research and development program in fluidized-bed combustion from October 1, 1987, to September 30, 1989. The Department of Energy program involves atmospheric and pressurized systems. Demonstrations of industrial-scale atmospheric systems are being completed, and smaller boilers are being explored. These systems include vortex, multi-solid, spouted, dual-sided, air-cooled, pulsed, and waste-fired fluidized-beds. Combustion of low-rank coal, components, and erosion are being studied. In pressurized combustion, first-generation, combined-cycle power plants are being tested, and second-generation, advanced-cycle systems are being designed and cost evaluated. Research in coal devolatilization, metal wastage, tube corrosion, and fluidization also supports this area. 52 refs., 24 figs., 3 tabs.

  10. Fluidized-bed boilers

    SciTech Connect

    Makansi, J.; Schwieger, B.

    1982-08-01

    Discusses atmospheric fluidized-bed (AFB) boilers with regard to designs available, manufacturers involved, and operating experience. Proven fuel flexibility and satisfactory SO/sub 2/ control without scrubbers make AFB boilers a viable option for industrial steam generation worldwide. Technical concepts on which AFB application is based are a departure from the more familiar methods of burning solid fuels. Behind US thrust for AFB development is the need to burn coal within pollution regulations.

  11. Comet formation in collapsing pebble clouds. What cometary bulk density implies for the cloud mass and dust-to-ice ratio

    NASA Astrophysics Data System (ADS)

    Lorek, S.; Gundlach, B.; Lacerda, P.; Blum, J.

    2016-03-01

    Context. Comets are remnants of the icy planetesimals that formed beyond the ice line in the solar nebula. Growing from μm-sized dust and ice particles to km-sized objects is, however, difficult because of growth barriers and time scale constraints. The gravitational collapse of pebble clouds that formed through the streaming instability may provide a suitable mechanism for comet formation. Aims: We study the collisional compression of silica, ice, and silica/ice-mixed pebbles during gravitational collapse of pebble clouds. Using the initial volume-filling factor and the dust-to-ice ratio of the pebbles as free parameters, we constrain the dust-to-ice mass ratio of the formed comet and the resulting volume-filling factor of the pebbles, depending on the cloud mass. Methods: We use the representative particle approach, which is a Monte Carlo method, to follow cloud collapse and collisional evolution of an ensemble of ice, silica, and silica/ice-mixed pebbles. Therefore, we developed a collision model which takes the various collision properties of dust and ice into account. We study pebbles with a compact size of 1 cm and vary the initial volume-filling factors, φ0, ranging from 0.001 to 0.4. We consider mixed pebbles as having dust-to-ice ratios between 0.5 and 10. We investigate four typical cloud masses, M, between 2.6 × 1014 (very low) and 2.6 × 1023 g (high). Results: Except for the very low-mass cloud (M = 2.6 × 1014 g), silica pebbles are always compressed during the collapse and attain volume-filling factors in the range from ⟨ φ ⟩ V ≈ 0.22 to 0.43, regardless of φ0. Ice pebbles experience no significant compression in very low-mass clouds. They are compressed to values in the range ⟨ φ ⟩ V ≈ 0.11 to 0.17 in low- and intermediate-mass clouds (M = 2.6 × 1017-2.6 × 1020 g); in high-mass clouds (M = 2.6 × 1023 g), ice pebbles end up with ⟨ φ ⟩ V ≈ 0.23. Mixed pebbles obtain filling factors in between the values for pure ice and

  12. Combustion in fluidized beds

    SciTech Connect

    Dry, F.J.; La Nauze, R.D. )

    1990-07-01

    Circulating fluidized-bed (CFB) combustion systems have become popular since the late 1970s, and, given the current level of activity in the area,it is clear that this technology has a stable future in the boiler market. For standard coal combustion applications, competition is fierce with mature pulverized-fuel-based (PF) technology set to maintain a strong profile. CFB systems, however, can be more cost effective than PF systems when emission control is considered, and, as CFB technology matures, it is expected that an ever-increasing proportion of boiler installations will utilize the CFB concept. CFB systems have advantages in the combustion of low-grade fuels such as coal waste and biomass. In competition with conventional bubbling beds, the CFB boiler often demonstrates superior carbon burn-out efficiency. The key to this combustion technique is the hydrodynamic behavior of the fluidized bed. This article begins with a description of the fundamental fluid dynamic behavior of the CFB system. This is followed by an examination of the combustion process in such an environment and a discussion of the current status of the major CFB technologies.

  13. Tribological properties of structural ceramics

    NASA Technical Reports Server (NTRS)

    Buckley, D. H.; Miyoshi, K.

    1985-01-01

    The tribological and lubricated behavior of both oxide and nonoxide ceramics are reviewed in this chapter. Ceramics are examined in contact with themselves, other harder materials and metals. Elastic, plastic and fracture behavior of ceramics in solid state contact is discussed. The contact load necessary to initiate fracture in ceramics is shown to be appreciably reduced with tangential motion. Both friction and wear of ceramics are anisotropic and relate to crystal structure as has been observed with metals. Grit size effects in two and three body abrasive wear are observed for ceramics. Both free energy of oxide formation and the d valence bond character of metals are related to the friction and wear characteristics for metals in contact with ceramics. Surface contaminants affect friction and adhesive wear. For example, carbon on silicon carbide and chlorine on aluminum oxide reduce friction while oxygen on metal surfaces in contact with ceramics increases friction. Lubrication increases the critical load necessary to initiate fracture of ceramics both in indentation and with sliding or rubbing. Ceramics compositions both as coatings and in composites are described for the high temperature lubrication of both alloys and ceramics.

  14. Light-weight ceramic insulation

    NASA Technical Reports Server (NTRS)

    Hsu, Ming-Ta S. (Inventor); Chen, Timothy S. (Inventor)

    2002-01-01

    Ultra-high temperature, light-weight, ceramic insulation such as ceramic tile is obtained by pyrolyzing a siloxane gel derived from the reaction of at least one organo dialkoxy silane and at least one tetralkoxy silane in an acid or base liquid medium. The reaction mixture of the tetra- and dialkoxy silanes may contain also an effective amount of a mono- or trialkoxy silane to obtain the siloxane gel. The siloxane gel is dried at ambient pressures to form a siloxane ceramic precursor without significant shrinkage. The siloxane ceramic precursor is subsequently pyrolyzed, in an inert atmosphere, to form the black ceramic insulation comprising atoms of silicon, carbon and oxygen. The ceramic insulation, can be characterized as a porous, uniform ceramic tile resistant to oxidation at temperatures ranging as high as 1700.degree. C. and is particularly useful as lightweight tiles for spacecraft and other high-temperature insulation applications.

  15. Metal to ceramic sealed joint

    DOEpatents

    Lasecki, J.V.; Novak, R.F.; McBride, J.R.

    1991-08-27

    A metal to ceramic sealed joint which can withstand wide variations in temperature and maintain a good seal is provided for use in a device adapted to withstand thermal cycling from about 20 to about 1000 degrees C. The sealed joint includes a metal member, a ceramic member having an end portion, and an active metal braze forming a joint to seal the metal member to the ceramic member. The joint is positioned remote from the end portion of the ceramic member to avoid stresses at the ends or edges of the ceramic member. The sealed joint is particularly suited for use to form sealed metal to ceramic joints in a thermoelectric generator such as a sodium heat engine where a solid ceramic electrolyte is joined to metal parts in the system. 11 figures.

  16. Metal to ceramic sealed joint

    DOEpatents

    Lasecki, John V.; Novak, Robert F.; McBride, James R.

    1991-01-01

    A metal to ceramic sealed joint which can withstand wide variations in temperature and maintain a good seal is provided for use in a device adapted to withstand thermal cycling from about 20 to about 1000 degrees C. The sealed joint includes a metal member, a ceramic member having an end portion, and an active metal braze forming a joint to seal the metal member to the ceramic member. The joint is positioned remote from the end portion of the ceramic member to avoid stresses at the ends or edges of the ceramic member. The sealed joint is particularly suited for use to form sealed metal to ceramic joints in a thermoelectric generator such as a sodium heat engine where a solid ceramic electrolyte is joined to metal parts in the system.

  17. Moving Bed Granular Bed Filter Development Program. Topical report, September 1994

    SciTech Connect

    Haas, J.C.; Prudhomme, J.W.; Wilson, K.W.

    1994-09-01

    Five test arrangements have been designed to support the Granular Bed Filter Development Program as defined in the Test Plan. The first arrangement is a 3.6 ft. diameter half filter, with a glass covering along the cross section to allow visual examination of the granular alumina material passing through the filter. The second test arrangement is a 3.6 ft diameter full size filter having refractory lining to simulate actual surface roughness conditions. The third test arrangement will examine filter geometry scale up by testing a 6.0 ft. diameter full size filter. The fourth Test Arrangement consists of a small 12 inch diameter fluidizer to measure the minimum fluidization velocity of the 7 m (approx. size) alumina material to be used in the filter assemblies. The last Test Unit is used to evaluation relative abrasion characteristics of potential refractory and ceramic materials to be installed in high abrasion areas in the pneumatic transport piping.

  18. An exploration hydrogeochemical study at the giant Pebble porphyry Cu-Au-Mo deposit, Alaska, USA, using high-resolution ICP-MS

    USGS Publications Warehouse

    Eppinger, Robert G.; Fey, David L.; Giles, Stuart A.; Kelley, Karen D.; Smith, Steven M.

    2012-01-01

    A hydrogeochemical study using high resolution ICP-MS was undertaken at the giant Pebble porphyry Cu-Au-Mo deposit and surrounding mineral occurrences. Surface water and groundwater samples from regional background and the deposit area were collected at 168 sites. Rigorous quality control reveals impressive results at low nanogram per litre (ng/l) levels. Sites with pH values below 5.1 are from ponds in the Pebble West area, where sulphide-bearing rubble crop is thinly covered. Relative to other study area waters, anomalous concentrations of Cu, Cd, K, Ni, Re, the REE, Tl, SO42− and F− are present in water samples from Pebble West. Samples from circum-neutral waters at Pebble East and parts of Pebble West, where cover is much thicker, have anomalous concentrations of Ag, As, In, Mn, Mo, Sb, Th, U, V, and W. Low-level anomalous concentrations for most of these elements were also found in waters surrounding nearby porphyry and skarn mineral occurrences. Many of these elements are present in low ng/l concentration ranges and would not have been detected using traditional quadrupole ICP-MS. Hydrogeochemical exploration paired with high resolution ICP-MS is a powerful new tool in the search for concealed deposits.

  19. The Control of semaphorin-1a-mediated reverse signaling by opposing pebble and RhoGAPp190 functions in drosophila.

    PubMed

    Jeong, Sangyun; Juhaszova, Katarina; Kolodkin, Alex L

    2012-11-21

    Transmembrane semaphorins (Semas) serve evolutionarily conserved guidance roles, and some function as both ligands and receptors. However, the molecular mechanisms underlying the transduction of these signals to the cytoskeleton remain largely unknown. We have identified two direct regulators of Rho family small GTPases, pebble (a Rho guanine nucleotide exchange factor [GEF]) and RhoGAPp190 (a GTPase activating protein [GAP]), that show robust interactions with the cytoplasmic domain of the Drosophila Sema-1a protein. Neuronal pebble and RhoGAPp190 are required to control motor axon defasciculation at specific pathway choice points and also for target recognition during Drosophila neuromuscular development. Sema-1a-mediated motor axon defasciculation is promoted by pebble and inhibited by RhoGAPp190. Genetic analyses show that opposing pebble and RhoGAPp190 functions mediate Sema-1a reverse signaling through the regulation of Rho1 activity. Therefore, pebble and RhoGAPp190 transduce transmembrane semaphorin-mediated guidance cue information that regulates the establishment of neuronal connectivity during Drosophila development.

  20. Optical nanosensors for chemical analysis inside single living cells. 2. Sensors for pH and calcium and the intracellular application of PEBBLE sensors.

    PubMed

    Clark, H A; Kopelman, R; Tjalkens, R; Philbert, M A

    1999-11-01

    Optical nanosensors, or PEBBLEs (probes encapsulated by biologically localized embedding), have been produced for intracellular measurements of pH and calcium. Five varieties of pH-sensitive sensors and three different calcium-selective sensors are presented and discussed. Each sensor combines an ion-selective fluorescent indicator and an ion-insensitive internal standard entrapped within an acrylamide polymeric matrix. Calibrations and linear ranges are presented for each sensor. The photobleaching of dyes incorporated into PEBBLEs is comparable to that of the respective free dye that is incorporated within the matrix. These PEBBLE sensors are fully reversible over many measurements. The leaching of fluorescent indicator from the polymer is less than 50% over a 48-h period (note that a typical application time is only a few hours). The PEBBLE sensors have also been applied to intracellular analysis of the calcium flux in the cytoplasm of neural cells during the mitochondrial permeability transition. Specifically, a distinct difference is noted between cells of different types (astrocyte vs neuron-derived cells) with respect to their response to the toxicant m-dinitrobenzene (DNB). Use of PEBBLE sensors permits the quantitative discrimination of subtle differences between the ability of human SY5Y neuroblastoma and C6 glioma to respond to challenge with DNB. Specifically, measurement of intracellular calcium, the precursor to cell death, has been achieved.

  1. A pebbles accretion model with chemistry and implications for the Solar system

    NASA Astrophysics Data System (ADS)

    Ali-Dib, Mohamad

    2017-02-01

    We investigate the chemical composition of the Solar system's giant planets atmospheres using a physical formation model with chemistry. The model incorporate disc evolution, pebbles and gas accretion, type I and II migration, simplified disc photoevaporation and Solar system chemical measurements. We track the chemical compositions of the formed giant planets and compare them to the observed values. Two categories of models are studied: with and without disc chemical enrichment via photoevaporation (PE). Predictions for the oxygen and nitrogen abundances, core masses and total amount of heavy elements for the planets are made for each case. We find that in the case without disc PE, both Jupiter and Saturn will have a small residual core and comparable total amounts of heavy elements in the envelopes. We predict oxygen abundances enrichments in the same order as carbon, phosphorus and sulfur for both planets. Cometary nitrogen abundances does not allow us to easily reproduce Jupiter's nitrogen observations. In the case with disc PE, less core erosion is needed to reproduce the chemical composition of the atmospheres, so both planets will end up with possibly more massive residual cores and higher total mass of heavy elements. It is also significantly easier to reproduce Jupiter's nitrogen abundance. No single disc was found to form both Jupiter and Saturn with all their constraints in the case without photoevaporation. No model was able to fit the constraints on Uranus and Neptune, hinting towards a more complicated formation mechanism for these planets. The predictions of these models should be compared to the upcoming Juno measurements to better understand the origins of the Solar system giant planets.

  2. Revision of the Western Australian pebble-mimic dragon species-group (Tympanocryptis cephalus: Reptilia: Agamidae).

    PubMed

    Doughty, Paul; Kealley, Luke; Shoo, Luke P; Melville, Jane

    2015-11-03

    Recent work on species complexes of the pebble-mimic dragons of the Australian genus Tympanocryptis has greatly clarified evolutionary relationships among taxa and also indicated that species diversity has been severely underestimated. Here we provide a morphological and molecular appraisal of variation in the T. cephalus species-group and find evidence for recognizing five species-level lineages from Western Australia. Four species-level lineages are strongly supported with a combined mitochondrial and nuclear DNA Bayesian analysis (a fifth population from the Gascoyne region lacked tissue samples). Morphologically, we found subtle, yet consistent, differences among the populations in scalation, color and pattern. True T. cephalus Günther is restricted to the coastal Pilbara region and characterized by five dark blotches on the dorsum, keeled ventrals, and other characters. Two other lineages within the Pilbara, from the Hamersley range and Fortescue/northern Pilbara region, differed from T. cephalus senso stricto by possessing a more elongate body and a plain dorsum. Furthermore, the Hamersley lineage differed from the Fortescue lineage by possessing slightly more reddish coloration and feeble keeling on the snout. Although there are few specimens and no tissue samples available for the Gascoyne population, these individuals are larger, have rugose scales on the snout, and possess scattered enlarged tubercles with three large blotches on the dorsum. The name T. cephalus gigas Mitchell is available for this population. The most widespread lineage, and the one best represented in collections and in field guides, occurs throughout central Western Australia. These Goldfield populations are characterized by a protruding snout, narrow rostral, and uniform reddish-brown coloration, often with a dark wash. Based on the genetic and morphological differences, we redescribe T. cephalus, resurrect and elevate T. gigas to a full species and designate a neotype for this taxon

  3. The epithelial-mesenchymal transition of the Drosophila mesoderm requires the Rho GTP exchange factor Pebble.

    PubMed

    Smallhorn, Masha; Murray, Michael J; Saint, Robert

    2004-06-01

    Drosophila pebble (pbl) encodes a Rho-family GTP exchange factor (GEF) required for cytokinesis. The accumulation of high levels of PBL protein during interphase and the developmentally regulated expression of pbl in mesodermal tissues suggested that the primary cytokinetic mutant phenotype might be masking other roles. Using various muscle differentiation markers, we found that Even skipped (EVE) expression in the dorsal mesoderm is greatly reduced in pbl mutant embryos. EVE expression in the dorsalmost mesodermal cells is induced in response to DPP secreted by the dorsal epidermal cells. Further analysis revealed that this phenotype is likely to be a consequence of an earlier defect. pbl mutant mesodermal cells fail to undergo the normal epithelial-mesenchymal transition (EMT) and dorsal migration that follows ventral furrow formation. This phenotype is not a secondary consequence of failed cytokinesis, as it is rescued by a mutant form of pbl that does not rescue the cytokinetic defect. In wild-type embryos, newly invaginated cells at the lateral edges of the mesoderm extend numerous protrusions. In pbl mutant embryos, however, cells appear more tightly adhered to their neighbours and extend very few protrusions. Consistent with the dependence of the mesoderm EMT and cytokinesis on actin organisation, the GTP exchange function of the PBL RhoGEF is required for both processes. By contrast, the N-terminal BRCT domains of PBL are required only for the cytokinetic function of PBL. These studies reveal that a novel PBL-mediated intracellular signalling pathway operates in mesodermal cells during the transition from an epithelial to migratory mesenchymal morphology during gastrulation.

  4. FILTER COMPONENT ASSESSMENT--CERAMIC CANDLES--

    SciTech Connect

    M.A. Alvin

    2004-04-23

    Efforts at Siemens Westinghouse Power Corporation (SWPC) have been focused on development of hot gas filter systems as an enabling technology for advanced coal and biomass-based gas turbine power generation applications. SWPC has been actively involved in the development of advanced filter materials and component configuration, has participated in numerous surveillance programs characterizing the material properties and microstructure of field tested filter elements, and has undertaken extended, accelerated filter life testing programs. This report summarizes the results of SWPC's filter component assessment efforts, identifying the performance and stability of porous monolithic, fiber reinforced, and filament wound ceramic hot gas candle filters, potentially for {ge}3 years of viable pressurized fluidized-bed combustion (PFBC) service operating life.

  5. Microporous alumina ceramic membranes

    DOEpatents

    Anderson, M.A.; Guangyao Sheng.

    1993-05-04

    Several methods are disclosed for the preparation microporous alumina ceramic membranes. For the first time, porous alumina membranes are made which have mean pore sizes less than 100 Angstroms and substantially no pores larger than that size. The methods are based on improved sol-gel techniques.

  6. Coated ceramic breeder materials

    DOEpatents

    Tam, Shiu-Wing; Johnson, Carl E.

    1987-04-07

    A breeder material for use in a breeder blanket of a nuclear reactor is disclosed. The breeder material comprises a core material of lithium containing ceramic particles which has been coated with a neutron multiplier such as Be or BeO, which coating has a higher thermal conductivity than the core material.

  7. Silicon carbide ceramic production

    NASA Technical Reports Server (NTRS)

    Suzuki, K.; Shinohara, N.

    1984-01-01

    A method to produce sintered silicon carbide ceramics in which powdery carbonaceous components with a dispersant are mixed with silicon carbide powder, shaped as required with or without drying, and fired in nonoxidation atmosphere is described. Carbon black is used as the carbonaceous component.

  8. Microporous alumina ceramic membranes

    DOEpatents

    Anderson, Marc A.; Sheng, Guangyao

    1993-01-01

    Several methods are disclosed for the preparation microporous alumina ceramic membranes. For the first time, porous alumina membranes are made which have mean pore sizes less than 100 Angstroms and substantially no pores larger than that size. The methods are based on improved sol-gel techniques.

  9. Microwave processing of ceramics

    SciTech Connect

    Katz, J.D.

    1993-01-01

    Recent work in the areas of microwave processing and joining of ceramics is briefly reviewed. Advantages and disadvantages of microwave processing as well as some of the current issues in the field are discussed. Current state and potential for future commercialization of this technology is also addressed.

  10. Microwave processing of ceramics

    SciTech Connect

    Katz, J.D.

    1993-04-01

    Recent work in the areas of microwave processing and joining of ceramics is briefly reviewed. Advantages and disadvantages of microwave processing as well as some of the current issues in the field are discussed. Current state and potential for future commercialization of this technology is also addressed.

  11. OXYGEN TRANSPORT CERAMIC MEMBRANES

    SciTech Connect

    Dr. Sukumar Bandopadhyay; Dr. Nagendra Nagabhushana

    2001-05-01

    The mechanical properties of model systems were analyzed. A reasonably accurate finite element model was implemented and a rational metric to predict the strength of ceramic/metal concentrical joints was developed. The mode of failure of the ceramic/metal joints was determined and the importance of the mechanical properties of the braze material was assessed. Thermal cycling experiments were performed on the model systems and the results were discussed. Additionally, experiments using the concept of placing diffusion barriers on the ceramic surface to limit the extent of the reaction with the braze were performed. It was also observed that the nature and morphology of the reaction zone depends greatly on the nature of the perovskite structure being used. From the experiments, it is observed that the presence of Cr in the Fe-occupied sites decreases the tendency of Fe to segregate and to precipitate out of the lattice. In these new experiments, Ni was observed to play a major role in the decomposition of the ceramic substrate.

  12. OXYGEN TRANSPORT CERAMIC MEMBRANES

    SciTech Connect

    Dr. Sukumar Bandopadhyay; Dr. Nagendfra Nagabhushana

    2001-07-01

    The mechanical properties of model systems were analyzed. A reasonably accurate finite element model was implemented and a rational metric to predict the strength of ceramic/metal concentrical joints was developed. The mode of failure of the ceramic/metal joints was determined and the importance of the mechanical properties of the braze material was assessed. Thermal cycling experiments were performed on the model systems and the results were discussed. Additionally, experiments using the concept of placing diffusion barriers on the ceramic surface to limit the extent of the reaction with the braze were performed. It was also observed that the nature and morphology of the reaction zone depends greatly on the nature of the perovskite structure being used. From the experiments, it is observed that the presence of Cr in the Fe-occupied sites decreases the tendency of Fe to segregate and to precipitate out of the lattice. In these new experiments, Ni was observed to play a major role in the decomposition of the ceramic substrate.

  13. Ceramic Coating Method

    DTIC Science & Technology

    2002-07-02

    platinum, protactinium , rhenium, chemically stable in oxygen or other oxidizing atmospheres. rhodium; ruthenium, samarium, scandium, silicon, tantalum; 20...high "mismatch" platinum, protactinium , rhenium, and tantalum braze layer, 30 between ceramic (e.g., A12O3 or ZrO2 ) and carbon steel, the lower-melting

  14. Durability of ceramic filters

    SciTech Connect

    Alvin, M.A.; Tressler, R.E.; Lippert, T.E.; Diaz, E.S.; Smeltzer, E.E.

    1994-10-01

    The objectives of this program are to identify the potential long-term thermal/chemical effects that advanced coal-based power generating systems have on the stability of porous ceramic filter materials, as well as to assess the influence of these effects on filter operating performance and life.

  15. Coated ceramic breeder materials

    DOEpatents

    Tam, Shiu-Wing; Johnson, Carl E.

    1987-01-01

    A breeder material for use in a breeder blanket of a nuclear reactor is disclosed. The breeder material comprises a core material of lithium containing ceramic particles which has been coated with a neutron multiplier such as Be or BeO, which coating has a higher thermal conductivity than the core material.

  16. Refractory ceramic fibers

    Integrated Risk Information System (IRIS)

    Refractory ceramic fibers ; CASRN Not found Human health assessment information on a chemical substance is included in the IRIS database only after a comprehensive review of toxicity data , as outlined in the IRIS assessment development process . Sections I ( Health Hazard Assessments for Noncarcino

  17. Ceramic Laser Materials

    SciTech Connect

    Soules, T F; Clapsaddle, B J; Landingham, R L; Schaffers, K I

    2005-02-15

    Transparent ceramic materials have several major advantages over single crystals in laser applications, not the least of which is the ability to make large aperture parts in a robust manufacturing process. After more than a decade of working on making transparent YAG:Nd, Japanese workers have recently succeeded in demonstrating samples that performed as laser gain media as well as their single crystal counterparts. Since then several laser materials have been made and evaluated. For these reasons, developing ceramic laser materials is the most exciting and futuristic materials topic in today's major solid-state laser conferences. We have established a good working relationship with Konoshima Ltd., the Japanese producer of the best ceramic laser materials, and have procured and evaluated slabs designed by us for use in our high-powered SSHCL. Our measurements indicate that these materials will work in the SSHCL, and we have nearly completed retrofitting the SSHCL with four of the largest transparent ceramic YAG:Nd slabs in existence. We have also begun our own effort to make this material and have produced samples with various degrees of transparency/translucency. We are in the process of carrying out an extensive design-of-experiments to establish the significant process variables for making transparent YAG. Finally because transparent ceramics afford much greater flexibility in the design of lasers, we have been exploring the potential for much larger apertures, new materials, for example for the Mercury laser, other designs for SSHL, such as, edge pumping designs, slabs with built in ASE suppression, etc. This work has just beginning.

  18. Ceramic tubesheet design analysis

    SciTech Connect

    Mallett, R.H.; Swindeman, R.W.

    1996-06-01

    A transport combustor is being commissioned at the Southern Services facility in Wilsonville, Alabama to provide a gaseous product for the assessment of hot-gas filtering systems. One of the barrier filters incorporates a ceramic tubesheet to support candle filters. The ceramic tubesheet, designed and manufactured by Industrial Filter and Pump Manufacturing Company (EF&PM), is unique and offers distinct advantages over metallic systems in terms of density, resistance to corrosion, and resistance to creep at operating temperatures above 815{degrees}C (1500{degrees}F). Nevertheless, the operational requirements of the ceramic tubesheet are severe. The tubesheet is almost 1.5 m in (55 in.) in diameter, has many penetrations, and must support the weight of the ceramic filters, coal ash accumulation, and a pressure drop (one atmosphere). Further, thermal stresses related to steady state and transient conditions will occur. To gain a better understanding of the structural performance limitations, a contract was placed with Mallett Technology, Inc. to perform a thermal and structural analysis of the tubesheet design. The design analysis specification and a preliminary design analysis were completed in the early part of 1995. The analyses indicated that modifications to the design were necessary to reduce thermal stress, and it was necessary to complete the redesign before the final thermal/mechanical analysis could be undertaken. The preliminary analysis identified the need to confirm that the physical and mechanical properties data used in the design were representative of the material in the tubesheet. Subsequently, few exploratory tests were performed at ORNL to evaluate the ceramic structural material.

  19. Ceramic oxide powders and the formation thereof

    DOEpatents

    Katz, J.L.; Chenghung Hung.

    1993-12-07

    Ceramic oxide powders and a method for their preparation. Ceramic oxide powders are obtained using a flame process whereby two or more precursors of ceramic oxides are introduced into a counterflow diffusion flame burner wherein said precursors are converted into ceramic oxide powders. The morphology, particle size, and crystalline form of the ceramic oxide powders are determined by process conditions. 14 figures.

  20. Ceramic oxide powders and the formation thereof

    DOEpatents

    Katz, Joseph L.; Hung, Cheng-Hung

    1993-01-01

    Ceramic oxide powders and a method for their preparation. Ceramic oxide powders are obtained using a flame process whereby two or more precursors of ceramic oxides are introduced into a counterflow diffusion flame burner wherein said precursors are converted into ceramic oxide powders. The morphology, particle size, and crystalline form of the ceramic oxide powders are determined by process conditions.

  1. Oxidation and Corrosion of Ceramics and Ceramic Matrix Composites

    NASA Technical Reports Server (NTRS)

    Jacobson, Nathan S.; Opila, Elizabeth J.; Lee, Kang N.

    2000-01-01

    Ceramics and ceramic matrix composites are candidates for numerous applications in high temperature environments with aggressive gases and possible corrosive deposits. There is a growing realization that high temperature oxidation and corrosion issues must be considered. There are many facets to these studies, which have been extensively covered in some recent reviews. The focus of this paper is on current research, over the past two years. In the authors' view, the most important oxidation and corrosion studies have focused on four major areas during this time frame. These are; (I) Oxidation of precursor-based ceramics; (II) Studies of the interphase material in ceramic matrix composites; (III) Water vapor interactions with ceramics, particularly in combustion environments; and (IV) Development of refractory oxide coatings for silicon-based ceramics. In this paper, we shall explore the most current work in each of these areas.

  2. Coal Bed Methane Primer

    SciTech Connect

    Dan Arthur; Bruce Langhus; Jon Seekins

    2005-05-25

    During the second half of the 1990's Coal Bed Methane (CBM) production increased dramatically nationwide to represent a significant new source of income and natural gas for many independent and established producers. Matching these soaring production rates during this period was a heightened public awareness of environmental concerns. These concerns left unexplained and under-addressed have created a significant growth in public involvement generating literally thousands of unfocused project comments for various regional NEPA efforts resulting in the delayed development of public and fee lands. The accelerating interest in CBM development coupled to the growth in public involvement has prompted the conceptualization of this project for the development of a CBM Primer. The Primer is designed to serve as a summary document, which introduces and encapsulates information pertinent to the development of Coal Bed Methane (CBM), including focused discussions of coal deposits, methane as a natural formed gas, split mineral estates, development techniques, operational issues, producing methods, applicable regulatory frameworks, land and resource management, mitigation measures, preparation of project plans, data availability, Indian Trust issues and relevant environmental technologies. An important aspect of gaining access to federal, state, tribal, or fee lands involves education of a broad array of stakeholders, including land and mineral owners, regulators, conservationists, tribal governments, special interest groups, and numerous others that could be impacted by the development of coal bed methane. Perhaps the most crucial aspect of successfully developing CBM resources is stakeholder education. Currently, an inconsistent picture of CBM exists. There is a significant lack of understanding on the parts of nearly all stakeholders, including industry, government, special interest groups, and land owners. It is envisioned the Primer would being used by a variety of

  3. Bed Rest Muscular Atrophy

    NASA Technical Reports Server (NTRS)

    Greenleaf, John E.

    2000-01-01

    A major debilitating response from prolonged bed rest (BR) is muscle atrophy, defined as a "decrease in size of a part of tissue after full development has been attained: a wasting away of tissue as from disuse, old age, injury or disease". Part of the complicated mechanism for the dizziness, increased body instability, and exaggerated gait in patients who arise immediately after BR may be a result of not only foot pain, but also of muscular atrophy and associated reduction in lower limb strength. Also, there seems to be a close association between muscle atrophy and bone atrophy. A discussion of many facets of the total BR homeostatic syndrome has been published. The old adage that use determines form which promotes function of bone (Wolff's law) also applies to those people exposed to prolonged BR (without exercise training) in whom muscle atrophy is a consistent finding. An extreme case involved a 16-year-old boy who was ordered to bed by his mother in 1932: after 50 years in bed he had "a lily-white frame with limbs as thin as the legs of a ladder-back chair". These findings emphasize the close relationship between muscle atrophy and bone atrophy. In addition to loss of muscle mass during deconditioning, there is a significant loss of muscle strength and a decrease in protein synthesis. Because the decreases in force (strength) are proportionately greater than those in fiber size or muscle cross-sectional area, other contributory factors must be involved; muscle fiber dehydration may be important.

  4. Fluidized-bed sorbents

    SciTech Connect

    Gangwal, S.K.; Gupta, R.P.

    1994-10-01

    The objectives of this project are to identify and demonstrate methods for enhancing long-term chemical reactivity and attrition resistance of zinc oxide-based mixed metal-oxide sorbents for desulfurization of hot coal-derived gases in a high-temperature, high-pressure (HTHP) fluidized-bed reactor. In this program, regenerable ZnO-based mixed metal-oxide sorbents are being developed and tested. These include zinc ferrite, zinc titanate, and Z-SORB sorbents. The Z-SORB sorbent is a proprietary sorbent developed by Phillips Petroleum Company (PPCo).

  5. Biparticle fluidized bed reactor

    DOEpatents

    Scott, C.D.; Marasco, J.A.

    1996-02-27

    A fluidized bed reactor system is described which utilizes a fluid phase, a retained fluidized primary particulate phase, and a migratory second particulate phase. The primary particulate phase is a particle such as a gel bead containing an immobilized biocatalyst. The secondary and tertiary particulate phases, continuously introduced and removed simultaneously in the cocurrent and countercurrent mode, act in a role such as a sorbent to continuously remove a product or by-product constituent from the fluid phase. Means for introducing and removing the sorbent phases include feed screw mechanisms and multivane slurry valves. 3 figs.

  6. Biparticle fluidized bed reactor

    DOEpatents

    Scott, C.D.; Marasco, J.A.

    1995-04-25

    A fluidized bed reactor system utilizes a fluid phase, a retained fluidized primary particulate phase, and a migratory second particulate phase. The primary particulate phase is a particle such as a gel bead containing an immobilized biocatalyst. The secondary particulate phase, continuously introduced and removed in either cocurrent or countercurrent mode, acts in a secondary role such as a sorbent to continuously remove a product or by-product constituent from the fluid phase. Introduction and removal of the sorbent phase is accomplished through the use of feed screw mechanisms and multivane slurry valves. 3 figs.

  7. Biparticle fluidized bed reactor

    DOEpatents

    Scott, Charles D.

    1993-01-01

    A fluidized bed reactor system which utilizes a fluid phase, a retained fluidized primary particulate phase, and a migratory second particulate phase. The primary particulate phase is a particle such as a gel bead containing an immobilized biocatalyst. The secondary particulate phase, continuously introduced and removed in either cocurrent or countercurrent mode, acts in a secondary role such as a sorbent to continuously remove a product or by-product constituent from the fluid phase. Introduction and removal of the sorbent phase is accomplished through the use of feed screw mechanisms and multivane slurry valves.

  8. Biparticle fluidized bed reactor

    DOEpatents

    Scott, Charles D.; Marasco, Joseph A.

    1996-01-01

    A fluidized bed reactor system which utilizes a fluid phase, a retained fluidized primary particulate phase, and a migratory second particulate phase. The primary particulate phase is a particle such as a gel bead containing an immobilized biocatalyst. The secondary and tertiary particulate phases, continuously introduced and removed simultaneously in the cocurrent and countercurrent mode, act in a role such as a sorbent to continuously remove a product or by-product constituent from the fluid phase. Means for introducing and removing the sorbent phases include feed screw mechanisms and multivane slurry valves.

  9. Biparticle fluidized bed reactor

    DOEpatents

    Scott, Charles D.; Marasco, Joseph A.

    1995-01-01

    A fluidized bed reactor system utilizes a fluid phase, a retained fluidized primary particulate phase, and a migratory second particulate phase. The primary particulate phase is a particle such as a gel bead containing an immobilized biocatalyst. The secondary particulate phase, continuously introduced and removed in either cocurrent or countercurrent mode, acts in a secondary role such as a sorbent to continuously remove a product or by-product constituent from the fluid phase. Introduction and removal of the sorbent phase is accomplished through the use of feed screw mechanisms and multivane slurry valves.

  10. Biparticle fluidized bed reactor

    DOEpatents

    Scott, C.D.

    1993-12-14

    A fluidized bed reactor system which utilizes a fluid phase, a retained fluidized primary particulate phase, and a migratory second particulate phase is described. The primary particulate phase is a particle such as a gel bead containing an immobilized biocatalyst. The secondary particulate phase, continuously introduced and removed in either cocurrent or countercurrent mode, acts in a secondary role such as a sorbent to continuously remove a product or by-product constituent from the fluid phase. Introduction and removal of the sorbent phase is accomplished through the use of feed screw mechanisms and multivane slurry valves. 3 figures.

  11. Particle bed reactor modeling

    NASA Technical Reports Server (NTRS)

    Sapyta, Joe; Reid, Hank; Walton, Lew

    1993-01-01

    The topics are presented in viewgraph form and include the following: particle bed reactor (PBR) core cross section; PBR bleed cycle; fuel and moderator flow paths; PBR modeling requirements; characteristics of PBR and nuclear thermal propulsion (NTP) modeling; challenges for PBR and NTP modeling; thermal hydraulic computer codes; capabilities for PBR/reactor application; thermal/hydralic codes; limitations; physical correlations; comparison of predicted friction factor and experimental data; frit pressure drop testing; cold frit mask factor; decay heat flow rate; startup transient simulation; and philosophy of systems modeling.

  12. Bed drain cover assembly for a fluidized bed

    DOEpatents

    Comparato, Joseph R.; Jacobs, Martin

    1982-01-01

    A loose fitting movable cover plate (36), suitable for the severe service encountered in a fluidized bed combustor (10), restricts the flow of solids into the combustor drain lines (30) during shutdown of the bed. This cover makes it possible to empty spent solids from the bed drain lines which would otherwise plug the piping between the drain and the downstream metering device. This enables use of multiple drain lines each with a separate metering device for the control of solids flow rate.

  13. Fluidized Bed Steam Reformer (FBSR) monolith formation

    SciTech Connect

    Jantzen, C.M.

    2007-07-01

    Fluidized Bed Steam Reforming (FBSR) is being considered as an alternative technology for the immobilization of a wide variety of aqueous high sodium containing radioactive wastes at various DOE facilities in the United States. The addition of clay, charcoal, and a catalyst as co-reactants converts aqueous Low Activity Wastes (LAW) to a granular or 'mineralized' waste form while converting organic components to CO{sub 2} and steam, and nitrate/nitrite components, if any, to N{sub 2}. The waste form produced is a multiphase mineral assemblage of Na-Al-Si (NAS) feldspathoid minerals with cage-like structures that atomically bond radionuclides like Tc-99 and anions such as SO{sub 4}, I, F, and Cl. The granular product has been shown to be as durable as LAW glass. Shallow land burial requires that the mineralized waste form be able to sustain the weight of soil overburden and potential intrusion by future generations. The strength requirement necessitates binding the granular product into a monolith. FBSR mineral products were formulated into a variety of monoliths including various cements, Ceramicrete, and hydro-ceramics. All but one of the nine monoliths tested met the <2 g/m{sup 2} durability specification for Na and Re (simulant for Tc-99) when tested using the Product Consistency Test (PCT; ASTM C1285). Of the nine monoliths tested the cements produced with 80-87 wt% FBSR product, the Ceramicrete, and the hydro-ceramic produced with 83.3 wt% FBSR product, met the compressive strength and durability requirements for an LAW waste form. (authors)

  14. Integrally cored ceramic investment casting mold fabricated by ceramic stereolithography

    NASA Astrophysics Data System (ADS)

    Bae, Chang-Jun

    Superalloy airfoils are produced by investment casting (IC), which uses ceramic cores and wax patterns with ceramic shell molds. Hollow cored superalloy airfoils in a gas turbine engine are an example of complex IC parts. The complex internal hollow cavities of the airfoil are designed to conduct cooling air through one or more passageways. These complex internal passageways have been fabricated by a lost wax process requiring several processing steps; core preparation, injection molding for wax pattern, and dipping process for ceramic shell molds. Several steps generate problems such as high cost and decreased accuracy of the ceramic mold. For example, costly tooling and production delay are required to produce mold dies for complex cores and wax patterns used in injection molding, resulting in a big obstacle for prototypes and smaller production runs. Rather than using separate cores, patterns, and shell molds, it would be advantageous to directly produce a mold that has the casting cavity and the ceramic core by one process. Ceramic stereolithography (CerSLA) can be used to directly fabricate the integrally cored ceramic casting mold (ICCM). CerSLA builds ceramic green objects from CAD files from many thin liquid layers of powder in monomer, which are solidified by polymerization with a UV laser, thereby "writing" the design for each slice. This dissertation addresses the integrally cored casting ceramic mold (ICCM), the ceramic core with a ceramic mold shell in a single patternless construction, fabricated by ceramic stereolithography (CerSLA). CerSLA is considered as an alternative method to replace lost wax processes, for small production runs or designs too complex for conventional cores and patterns. The main topic is the development of methods to successfully fabricate an ICCM by CerSLA from refractory silica, as well as related issues. The related issues are the segregation of coarse fused silica powders in a layer, the degree of segregation parameter to

  15. Ceramic Stereolithography: Additive Manufacturing for Ceramics by Photopolymerization

    NASA Astrophysics Data System (ADS)

    Halloran, John W.

    2016-07-01

    Ceramic stereolithography and related additive manufacturing methods involving photopolymerization of ceramic powder suspensions are reviewed in terms of the capabilities of current devices. The practical fundamentals of the cure depth, cure width, and cure profile are related to the optical properties of the monomer, ceramic, and photo-active components. Postpolymerization steps, including harvesting and cleaning the objects, binder burnout, and sintering, are discussed and compared with conventional methods. The prospects for practical manufacturing are discussed.

  16. Grain boundaries in ceramics and ceramic-metal interfaces

    SciTech Connect

    Clarke, D.R.; Wolf, D.

    1986-01-01

    Three interfaces exist: the crystal-crystal grain boundary in very pure single-phase ceramics, the crystal-glass-crystal grain boundary in most single-phase and polyphase ceramics, and the ceramic-metal interface. It is needed to correlate their structure and adhesion/failure. Methods for studying the bonding, interfacial structure, and fracture and adhesion are discussed, and recommendations are given. 42 refs. (DLC)

  17. Geological analysis of aeromagnetic data from southwestern Alaska: implications for exploration in the area of the Pebble porphyry Cu-Au-Mo deposit

    USGS Publications Warehouse

    Anderson, Eric D.; Hitzman, Murray W.; Monecke, Thomas; Bedrosian, Paul A.; Shah, Anjana K.; Kelley, Karen D.

    2013-01-01

    Aeromagnetic data are used to better understand the geology and mineral resources near the Late Cretaceous Pebble porphyry Cu-Au-Mo deposit in southwestern Alaska. The reduced-to-pole (RTP) transformation of regional-scale aeromagnetic data shows that the Pebble deposit is within a cluster of magnetic anomaly highs. Similar to Pebble, the Iliamna, Kijik, and Neacola porphyry copper occurrences are in magnetic highs that trend northeast along the crustal-scale Lake Clark fault. A high-amplitude, short- to moderate-wavelength anomaly is centered over the Kemuk occurrence, an Alaska-type ultramafic complex. Similar anomalies are found west and north of Kemuk. A moderate-amplitude, moderate-wavelength magnetic low surrounded by a moderate-amplitude, short-wavelength magnetic high is associated with the gold-bearing Shotgun intrusive complex. The RTP transformation of the district-scale aeromagnetic data acquired over Pebble permits differentiation of a variety of Jurassic to Tertiary magmatic rock suites. Jurassic-Cretaceous basalt and gabbro units and Late Cretaceous biotite pyroxenite and granodiorite rocks produce magnetic highs. Tertiary basalt units also produce magnetic highs, but appear to be volumetrically minor. Eocene monzonite units have associated magnetic lows. The RTP data do not suggest a magnetite-rich hydrothermal system at the Pebble deposit. The 10-km upward continuation transformation of the regional-scale data shows a linear northeast trend of magnetic anomaly highs. These anomalies are spatially correlated with Late Cretaceous igneous rocks and in the Pebble district are centered over the granodiorite rocks genetically related to porphyry copper systems. The spacing of these anomalies is similar to patterns shown by the numerous porphyry copper deposits in northern Chile. These anomalies are interpreted to reflect a Late Cretaceous magmatic arc that is favorable for additional discoveries of Late Cretaceous porphyry copper systems in southwestern

  18. Seal between metal and ceramic conduits

    DOEpatents

    Underwood, Richard Paul; Tentarelli, Stephen Clyde

    2015-02-03

    A seal between a ceramic conduit and a metal conduit of an ion transport membrane device consisting of a sealing surface of ceramic conduit, a sealing surface of ceramic conduit, a single gasket body, and a single compliant interlayer.

  19. Pressurized fluidized bed reactor

    DOEpatents

    Isaksson, J.

    1996-03-19

    A pressurized fluid bed reactor power plant includes a fluidized bed reactor contained within a pressure vessel with a pressurized gas volume between the reactor and the vessel. A first conduit supplies primary gas from the gas volume to the reactor, passing outside the pressure vessel and then returning through the pressure vessel to the reactor, and pressurized gas is supplied from a compressor through a second conduit to the gas volume. A third conduit, comprising a hot gas discharge, carries gases from the reactor, through a filter, and ultimately to a turbine. During normal operation of the plant, pressurized gas is withdrawn from the gas volume through the first conduit and introduced into the reactor at a substantially continuously controlled rate as the primary gas to the reactor. In response to an operational disturbance of the plant, the flow of gas in the first, second, and third conduits is terminated, and thereafter the pressure in the gas volume and in the reactor is substantially simultaneously reduced by opening pressure relief valves in the first and third conduits, and optionally by passing air directly from the second conduit to the turbine. 1 fig.

  20. Pressurized fluidized bed reactor

    DOEpatents

    Isaksson, Juhani

    1996-01-01

    A pressurized fluid bed reactor power plant includes a fluidized bed reactor contained within a pressure vessel with a pressurized gas volume between the reactor and the vessel. A first conduit supplies primary gas from the gas volume to the reactor, passing outside the pressure vessel and then returning through the pressure vessel to the reactor, and pressurized gas is supplied from a compressor through a second conduit to the gas volume. A third conduit, comprising a hot gas discharge, carries gases from the reactor, through a filter, and ultimately to a turbine. During normal operation of the plant, pressurized gas is withdrawn from the gas volume through the first conduit and introduced into the reactor at a substantially continuously controlled rate as the primary gas to the reactor. In response to an operational disturbance of the plant, the flow of gas in the first, second, and third conduits is terminated, and thereafter the pressure in the gas volume and in the reactor is substantially simultaneously reduced by opening pressure relief valves in the first and third conduits, and optionally by passing air directly from the second conduit to the turbine.

  1. Impact on Granular Beds

    NASA Astrophysics Data System (ADS)

    van der Meer, Devaraj

    2017-01-01

    The impact of an object on a granular solid is an ubiquitous phenomenon in nature, the scale of which ranges from the impact of a raindrop onto sand all the way to that of a large asteroid on a planet. Despite the obvious relevance of these impact events, the study of the underlying physics mechanisms that guide them is relatively young, with most work concentrated in the past decade. Upon impact, an object starts to interact with a granular bed and experiences a drag force from the sand. This ultimately leads to phenomena such as crater formation and the creation of a transient cavity that upon collapse may cause a jet to appear from above the surface of the sand. This review provides an overview of research that targets these phenomena, from the perspective of the analogous but markedly different impact of an object on a liquid. It successively addresses the drag an object experiences inside a granular bed, the expansion and collapse of the cavity created by the object leading to the formation of a jet, and the remarkable role played by the air that resides within the pores between the grains.

  2. Ceramic hot-gas filter

    DOEpatents

    Connolly, Elizabeth Sokolinski; Forsythe, George Daniel; Domanski, Daniel Matthew; Chambers, Jeffrey Allen; Rajendran, Govindasamy Paramasivam

    1999-01-01

    A ceramic hot-gas candle filter having a porous support of filament-wound oxide ceramic yarn at least partially surrounded by a porous refractory oxide ceramic matrix, and a membrane layer on at least one surface thereof. The membrane layer may be on the outer surface, the inner surface, or both the outer and inner surface of the porous support. The membrane layer may be formed of an ordered arrangement of circularly wound, continuous filament oxide ceramic yarn, a ceramic filler material which is less permeable than the filament-wound support structure, or some combination of continuous filament and filler material. A particularly effective membrane layer features circularly wound filament with gaps intentionally placed between adjacent windings, and a filler material of ceramic particulates uniformly distributed throughout the gap region. The filter can withstand thermal cycling during backpulse cleaning and is resistant to chemical degradation at high temperatures.

  3. Ceramic hot-gas filter

    DOEpatents

    Connolly, E.S.; Forsythe, G.D.; Domanski, D.M.; Chambers, J.A.; Rajendran, G.P.

    1999-05-11

    A ceramic hot-gas candle filter is described having a porous support of filament-wound oxide ceramic yarn at least partially surrounded by a porous refractory oxide ceramic matrix, and a membrane layer on at least one surface thereof. The membrane layer may be on the outer surface, the inner surface, or both the outer and inner surface of the porous support. The membrane layer may be formed of an ordered arrangement of circularly wound, continuous filament oxide ceramic yarn, a ceramic filler material which is less permeable than the filament-wound support structure, or some combination of continuous filament and filler material. A particularly effective membrane layer features circularly wound filament with gaps intentionally placed between adjacent windings, and a filler material of ceramic particulates uniformly distributed throughout the gap region. The filter can withstand thermal cycling during back pulse cleaning and is resistant to chemical degradation at high temperatures.

  4. Fast fluidized bed steam generator

    DOEpatents

    Bryers, Richard W.; Taylor, Thomas E.

    1980-01-01

    A steam generator in which a high-velocity, combustion-supporting gas is passed through a bed of particulate material to provide a fluidized bed having a dense-phase portion and an entrained-phase portion for the combustion of fuel material. A first set of heat transfer elements connected to a steam drum is vertically disposed above the dense-phase fluidized bed to form a first flow circuit for heat transfer fluid which is heated primarily by the entrained-phase fluidized bed. A second set of heat transfer elements connected to the steam drum and forming the wall structure of the furnace provides a second flow circuit for the heat transfer fluid, the lower portion of which is heated by the dense-phase fluidized bed and the upper portion by the entrained-phase fluidized bed.

  5. Safeguards-by-Design: Guidance for High Temperature Gas Reactors (HTGRs) With Pebble Fuel

    SciTech Connect

    Philip Casey Durst; Mark Schanfein

    2012-08-01

    The following is a guidance document from a series prepared for the U.S. Department of Energy (DOE) National Nuclear Security Administration (NNSA), under the Next Generation Safeguards Initiative (NGSI), to assist facility designers and operators in implementing international Safeguards-by-Design (SBD). SBD has two main objectives: (1) to avoid costly and time consuming redesign work or retrofits of new nuclear fuel cycle facilities and (2) to make the implementation of international safeguards more effective and efficient at such facilities. In the long term, the attainment of these goals would save industry and the International Atomic Energy Agency (IAEA) time, money, and resources and be mutually beneficial. This particular safeguards guidance document focuses on pebble fuel high temperature gas reactors (HTGR). The purpose of the IAEA safeguards system is to provide credible assurance to the international community that nuclear material and other specified items are not diverted from peaceful nuclear uses. The safeguards system consists of the IAEA’s statutory authority to establish safeguards; safeguards rights and obligations in safeguards agreements and additional protocols; and technical measures implemented pursuant to those agreements. Of foremost importance is the international safeguards agreement between the country and the IAEA, concluded pursuant to the Treaty on the Non-Proliferation of Nuclear Weapons (NPT). According to a 1992 IAEA Board of Governors decision, countries must: notify the IAEA of a decision to construct a new nuclear facility as soon as such decision is taken; provide design information on such facilities as the designs develop; and provide detailed design information based on construction plans at least 180 days prior to the start of construction, and on "as-built" designs at least 180 days before the first receipt of nuclear material. Ultimately, the design information will be captured in an IAEA Design Information

  6. The aluminum phosphate zone in the Peace River area, land-pebble phosphate field, Florida

    USGS Publications Warehouse

    Cathcart, James B.

    1953-01-01

    The Peace River area, comprising T. 30 and 31 S., R. 24 and 25 E., contains a thicker and more persistent aluminum phosphate zone, and one that is higher in P2O5 and uranium content than is known elsewhere in the land-pebble phosphate district. This report has been prepared to bring together all of the information on the aluminum phosphate zone in the area where the first plant to treat this material will probably be located. The area may be divided into three physiographic units, (1) the ridge, (2) the flatwoods, and (3) the valley. Maps showing distribution and grade of the aluminum phosphate zone indicate that the zone is thin or absent in the ridge unit, thickest and most persistent, and of the best grade in P2O5 and uranium in the flatwoods unit, and absent or very low in grade in the valley unit. Maps of thickness and of chemical composition show that even in favorable areas there are places where the aluminum phosphate zone is missing or of questionable economic importance. The distribution maps also show that areas of high P2O5 and high uranium content coincide closely. Areas containing thick aluminum phosphate material usually have high uranium and P2O5 contents. It is estimated that an average of 13,000 tons per day of aluminum phosphate material might be mined from this area. This figure is based on the probable amount of time, per year, that mining would be in favorable ground. When all mines in the area are in favorable ground, the tonnage per day might be about 23,000 tons. Tonnages of aluminum phosphate material have been computed for about 36 percent of the area of T. 30 S., R. 25 E., and for 18 percent of the area of T. 31 S., R. 25 E. The total inferred tonnage is about 150,000,000 short tons, with an average grade of 0.012 percent U3O8.

  7. Fluidized bed boiler feed system

    DOEpatents

    Jones, Brian C.

    1981-01-01

    A fluidized bed boiler feed system for the combustion of pulverized coal. Coal is first screened to separate large from small particles. Large particles of coal are fed directly to the top of the fluidized bed while fine particles are first mixed with recycled char, preheated, and then fed into the interior of the fluidized bed to promote char burnout and to avoid elutriation and carryover.

  8. Testing Ceramics for Diesel Engines

    NASA Technical Reports Server (NTRS)

    Schneider, H. W.

    1985-01-01

    Adaptation of diesel engine allows prestressed ceramic materials evaluated under realistic pressure, temperature, and stress without introducing extraneous stress. Ceramic specimen part of prechamber of research engine. Specimen held in place by clamp, introduces required axial compressive stress. Specimen -- cylindrical shell -- surrounded by chamber vented or pressurized to introduce requisite radial stress in ceramic. Pressure chamber also serves as safety shield in case speimen disintegrates. Materials under consideration as cylinder liners for diesel engines.

  9. Processing method for superconducting ceramics

    DOEpatents

    Bloom, Ira D.; Poeppel, Roger B.; Flandermeyer, Brian K.

    1993-01-01

    A process for preparing a superconducting ceramic and particularly YBa.sub.2 Cu.sub.3 O.sub.7-.delta., where .delta. is in the order of about 0.1-0.4, is carried out using a polymeric binder which decomposes below its ignition point to reduce carbon residue between the grains of the sintered ceramic and a nonhydroxylic organic solvent to limit the problems with water or certain alcohols on the ceramic composition.

  10. Processing method for superconducting ceramics

    DOEpatents

    Bloom, Ira D.; Poeppel, Roger B.; Flandermeyer, Brian K.

    1993-02-02

    A process for preparing a superconducting ceramic and particularly YBa.sub.2 Cu.sub.3 O.sub.7-.delta., where .delta. is in the order of about 0.1-0.4, is carried out using a polymeric binder which decomposes below its ignition point to reduce carbon residue between the grains of the sintered ceramic and a nonhydroxylic organic solvent to limit the problems with water or certain alcohols on the ceramic composition.

  11. Tailored Ceramics for Laser Applications

    SciTech Connect

    Hollingsworth, Joel

    2007-12-10

    Transparent ceramics match or exceed the performance of single-crystal materials in laser applications, with a more-robust fabrication process. Controlling the distribution of optical dopants in transparent ceramics would allow qualitative improvements in amplifier slab design by allowing gain and loss to be varied within the material. My work aims to achieve a controlled pattern or gradient of dopant prior to sintering, in order to produce tailored ceramics.

  12. Ceramic composite coating

    DOEpatents

    Wicks, G.G.

    1997-01-21

    A thin, room-temperature-curing, ceramic composite for coating and patching metal substrates comprises a sol gel silica glass matrix filled with finely ground particles or fibers, preferably alumina. The sol gel glass is made by adding ethanol to water to form a first mixture, then separately adding ethanol to tetraethyl orthosilicate to form a second mixture, then slowly adding the first to the second mixture to make a third mixture, and making a slurry by adding the finely ground particles or fibers to the third mixture. The composite can be applied by spraying, brushing or trowelling. If applied to patch fine cracks, densification of the ceramic composite may be obtained to enhance sealing by applying heat during curing.

  13. Ceramic composite coating

    DOEpatents

    Wicks, George G.

    1997-01-01

    A thin, room-temperature-curing, ceramic composite for coating and patching etal substrates comprises a sol gel silica glass matrix filled with finely ground particles or fibers, preferably alumina. The sol gel glass is made by adding ethanol to water to form a first mixture, then separately adding ethanol to tetraethyl orthosilicate to form a second mixture, then slowly adding the first to the second mixture to make a third mixture, and making a slurry by adding the finely ground particles or fibers to the third mixture. The composite can be applied by spraying, brushing or trowelling. If applied to patch fine cracks, densification of the ceramic composite may be obtained to enhance sealing by applying heat during curing.

  14. Ceramic Composite Thin Films

    NASA Technical Reports Server (NTRS)

    Ruoff, Rodney S. (Inventor); Stankovich, Sasha (Inventor); Dikin, Dmitriy A. (Inventor); Nguyen, SonBinh T. (Inventor)

    2013-01-01

    A ceramic composite thin film or layer includes individual graphene oxide and/or electrically conductive graphene sheets dispersed in a ceramic (e.g. silica) matrix. The thin film or layer can be electrically conductive film or layer depending the amount of graphene sheets present. The composite films or layers are transparent, chemically inert and compatible with both glass and hydrophilic SiOx/silicon substrates. The composite film or layer can be produced by making a suspension of graphene oxide sheet fragments, introducing a silica-precursor or silica to the suspension to form a sol, depositing the sol on a substrate as thin film or layer, at least partially reducing the graphene oxide sheets to conductive graphene sheets, and thermally consolidating the thin film or layer to form a silica matrix in which the graphene oxide and/or graphene sheets are dispersed.

  15. Ceramics for fusion applications

    SciTech Connect

    Clinard, F.W. Jr.

    1986-01-01

    Ceramics are required for a variety of uses in both near-term fusion devices and in commercial powerplants. These materials must retain adequate structural and electrical properties under conditions of neutron, particle, and ionizing irradiation; thermal and applied stresses; and physical and chemical sputtering. Ceramics such as Al/sub 2/O/sub 3/, MgAl/sub 2/O/sub 4/, BeO, Si/sub 3/N/sub 4/ and SiC are currently under study for fusion applications, and results to date show widely-varying response to the fusion environment. Materials can be identified today which will meet initial operating requirements, but improvements in physical properties are needed to achieve satisfactory lifetimes for critical applications.

  16. Ceramic fabrication R D

    SciTech Connect

    Not Available

    1990-01-01

    This project is separated into three tasks. The first task is a design and modeling effort to be carried out by MSE, Inc. The purpose of this task is to develop and analyze designs for various cohesive ceramic fabrication (CCF) components, including an MHD electrode for strategic defense initiative (SDI) applications and a high stress, low cost, reinforced ceramic component for armor applications. The MHD electrode design is substantially completed. A layered structure composed of molybdenum disilicide graded with quartz glass has been designed and analyzed using finite element methods. The design demonstrates the fabrication capabilities of the CCF process. The high stress, armor application component will be silicon carbide reinforced alumina in thick plates. 2 refs., 4 figs., 1 tab.

  17. Debris-bed friction of hard-bedded glaciers

    USGS Publications Warehouse

    Cohen, D.; Iverson, N.R.; Hooyer, T.S.; Fischer, U.H.; Jackson, M.; Moore, P.L.

    2005-01-01

    [1] Field measurements of debris-bed friction on a smooth rock tablet at the bed of Engabreen, a hard-bedded, temperate glacier in northern Norway, indicated that basal ice containing 10% debris by volume exerted local shear traction of up to 500 kPa. The corresponding bulk friction coefficient between the dirty basal ice and the tablet was between 0.05 and 0.08. A model of friction in which nonrotating spherical rock particles are held in frictional contact with the bed by bed-normal ice flow can account for these measurements if the power law exponent for ice flowing past large clasts is 1. A small exponent (n < 2) is likely because stresses in ice are small and flow is transient. Numerical calculations of the bed-normal drag force on a sphere in contact with a flat bed using n = 1 show that this force can reach values several hundred times that on a sphere isolated from the bed, thus drastically increasing frictional resistance. Various estimates of basal friction are obtained from this model. For example, the shear traction at the bed of a glacier sliding at 20 m a-1 with a geothermally induced melt rate of 0.006 m a-1 and an effective pressure of 300 kPa can exceed 100 kPa. Debris-bed friction can therefore be a major component of sliding resistance, contradicting the common assumption that debris-bed friction is negligible. Copyright 2005 by the American Geophysical Union.

  18. A pebbles accretion model with chemistry and implications for the solar system in the lights of Juno

    NASA Astrophysics Data System (ADS)

    Ali-Dib, Mohamad

    2016-10-01

    The chemical compositions of the solar system giant planets are a major source of informations on their origins. Since the measurements by the Galileo probe, multiple models have been put forward to try and explain the noble gases enrichment in Jupiter. The most discussed among these are its formation in the outer cold nebula and its formation in a partially photoevaporated disk. In this work I couple a pebbles accretion model to the disk's chemistry and photoevaporation in order to make predictions from both scenarios and compare them to the upcoming Juno measurements. The model include pebbles and gas accretion, type I and II migration, photoevaporation and chemical measurements from meteorites, comets and disks. Population synthesis simulations are used to explore the models free parameters (planets initial conditions), where then the results are narrowed down using the planets chemical, dynamical and core mass costraints. We end up with a population that fits all of the constrains. These are then used to predict the oxygen abundance and core mass in Jupiter, to be compared to results of Juno. Same calculations are also done for Saturn and Neptune for comparison. I will present the results from these simulations as well as the predictions from all of the different models.Ali-Dib, M. (2016ab, submitted to MNRAS)

  19. Diversification patterns of pebble-mimic dragons are consistent with historical disruption of important habitat corridors in arid Australia.

    PubMed

    Shoo, L P; Rose, R; Doughty, P; Austin, J J; Melville, J

    2008-08-01

    The pebble-mimic dragon lineage of Tympanocryptis is widely distributed in the stony, or 'gibber', deserts of Australia but is noticeably absent from intersecting areas of sand deserts. Past fluctuations in the extent and configuration of sandy desert habitat barriers are likely to have been an import factor promoting genetic differentiation in this group. We sequenced a approximately 1400bp region of mitochondrial DNA and a approximately 1400bp nuclear gene (RAG-1) to investigate phylogeographic structuring of species of pebble-mimic dragons. Our topology indicates an early split in this lineage between eastern and western parts of the arid zone that probably dates to the mid-Miocene. This split corresponds directly with large expanses of contemporary sandy habitat in the form of Great Sandy and Great Victoria Deserts. Our data indicate that this biogeographic barrier established very early on in the development of the arid zone and has persisted to present. Additional genetic structuring in the absence of recognized barriers suggests that an expanded view of potential habitat barriers in the arid zone is required.

  20. Fluidized bed deposition of diamond

    DOEpatents

    Laia, Jr., Joseph R.; Carroll, David W.; Trkula, Mitchell; Anderson, Wallace E.; Valone, Steven M.

    1998-01-01

    A process for coating a substrate with diamond or diamond-like material including maintaining a substrate within a bed of particles capable of being fluidized, the particles having substantially uniform dimensions and the substrate characterized as having different dimensions than the bed particles, fluidizing the bed of particles, and depositing a coating of diamond or diamond-like material upon the substrate by chemical vapor deposition of a carbon-containing precursor gas mixture, the precursor gas mixture introduced into the fluidized bed under conditions resulting in excitation mechanisms sufficient to form the diamond coating.