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Sample records for activated diffusion brazing

  1. Development of the activated diffusion brazing process for fabrication of finned shell to strut turbine blades

    NASA Technical Reports Server (NTRS)

    Wilbers, L. G.; Berry, T. F.; Kutchera, R. E.; Edmonson, R. E.

    1971-01-01

    The activated diffusion brazing process was developed for attaching TD-NiCr and U700 finned airfoil shells to matching Rene 80 struts obstructing the finned cooling passageways. Creep forming the finned shells to struts in combination with precise preplacement of brazing alloy resulted in consistently sound joints, free of cooling passageway clogging. Extensive tensile and stress rupture testing of several joint orientation at several temperatures provided a critical assessment of joint integrity of both material combinations. Trial blades of each material combination were fabricated followed by destructive metallographic examination which verified high joint integrity.

  2. Diffusion barriers in modified air brazes

    DOEpatents

    Weil, Kenneth Scott; Hardy, John S; Kim, Jin Yong; Choi, Jung-Pyung

    2013-04-23

    A method for joining two ceramic parts, or a ceramic part and a metal part, and the joint formed thereby. The method provides two or more parts, a braze consisting of a mixture of copper oxide and silver, a diffusion barrier, and then heats the braze for a time and at a temperature sufficient to form the braze into a bond holding the two or more parts together. The diffusion barrier is an oxidizable metal that forms either a homogeneous component of the braze, a heterogeneous component of the braze, a separate layer bordering the braze, or combinations thereof. The oxidizable metal is selected from the group Al, Mg, Cr, Si, Ni, Co, Mn, Ti, Zr, Hf, Pt, Pd, Au, lanthanides, and combinations thereof.

  3. Diffusion barriers in modified air brazes

    DOEpatents

    Weil, Kenneth Scott; Hardy, John S.; Kim, Jin Yong; Choi, Jung-Pyung

    2010-04-06

    A method for joining two ceramic parts, or a ceramic part and a metal part, and the joint formed thereby. The method provides two or more parts, a braze consisting of a mixture of copper oxide and silver, a diffusion barrier, and then heats the braze for a time and at a temperature sufficient to form the braze into a bond holding the two or more parts together. The diffusion barrier is an oxidizable metal that forms either a homogeneous component of the braze, a heterogeneous component of the braze, a separate layer bordering the braze, or combinations thereof. The oxidizable metal is selected from the group Al, Mg, Cr, Si, Ni, Co, Mn, Ti, Zr, Hf, Pt, Pd, Au, lanthanides, and combinations thereof.

  4. Theory and modeling of active brazing.

    SciTech Connect

    van Swol, Frank B.; Miller, James Edward; Lechman, Jeremy B.; Givler, Richard C.

    2013-09-01

    Active brazes have been used for many years to produce bonds between metal and ceramic objects. By including a relatively small of a reactive additive to the braze one seeks to improve the wetting and spreading behavior of the braze. The additive modifies the substrate, either by a chemical surface reaction or possibly by alloying. By its nature, the joining process with active brazes is a complex nonequilibrium non-steady state process that couples chemical reaction, reactant and product diffusion to the rheology and wetting behavior of the braze. Most of the these subprocesses are taking place in the interfacial region, most are difficult to access by experiment. To improve the control over the brazing process, one requires a better understanding of the melting of the active braze, rate of the chemical reaction, reactant and product diffusion rates, nonequilibrium composition-dependent surface tension as well as the viscosity. This report identifies ways in which modeling and theory can assist in improving our understanding.

  5. Thin-film diffusion brazing of titanium alloys

    NASA Technical Reports Server (NTRS)

    Mikus, E. B.

    1972-01-01

    A thin film diffusion brazing technique for joining titanium alloys by use of a Cu intermediate is described. The method has been characterized in terms of static and dynamic mechanical properties on Ti-6Al-4V alloy. These include tensile, fracture toughness, stress corrosion, shear, corrosion fatigue, mechanical fatigue and acoustic fatigue. Most of the properties of titanium joints formed by thin film diffusion brazing are equal or exceed base metal properties. The advantages of thin film diffusion brazing over solid state diffusion bonding and brazing with conventional braze alloys are discussed. The producibility advantages of this process over others provide the potential for producing high efficiency joints in structural components of titanium alloys for the minimum cost.

  6. In-process oxidation protection in fluxless brazing or diffusion bonding of aluminum alloys

    NASA Technical Reports Server (NTRS)

    Okelly, K. P.; Featherston, A. B.

    1974-01-01

    Aluminum is cleaned of its oxide coating and is sealed immediately with polymeric material which makes it suitable for fluxless brazing or diffusion bonding. Time involved between cleaning and brazing is no longer critical factor.

  7. Elevated temperature creep properties for selected active metal braze alloys

    SciTech Connect

    Stephens, J.J.

    1997-02-01

    Active metal braze alloys reduce the number of processes required for the joining of metal to ceramic components by eliminating the need for metallization and/or Ni plating of the ceramic surfaces. Titanium (Ti), V, and Zr are examples of active element additions which have been used successfully in such braze alloys. Since the braze alloy is expected to accommodate thermal expansion mismatch strains between the metal and ceramic materials, a knowledge of its elevated temperature mechanical properties is important. In particular, the issue of whether or not the creep strength of an active metal braze alloy is increased or decreased relative to its non-activated counterpart is important when designing new brazing processes and alloy systems. This paper presents a survey of high temperature mechanical properties for two pairs of conventional braze alloys and their active metal counterparts: (a) the conventional 72Ag-28Cu (Cusil) alloy, and the active braze alloy 62.2Ag- 36.2Cu-1.6Ti (Cusil ABA), and (b) the 82Au-18Ni (Nioro) alloy and the active braze alloy Mu-15.5M-0.75Mo-1.75V (Nioro ABA). For the case of the Cusil/Cusil ABA pair, the active metal addition contributes to solid solution strengthening of the braze alloy, resulting in a higher creep strength as compared to the non-active alloy. In the case of the Nioro/Nioro ABA pair, the Mo and V additions cause the active braze alloy to have a two-phase microstructure, which results in a reduced creep strength than the conventional braze alloy. The Garofalo sinh equation has been used to quantitatively describe the stress and temperature dependence of the deformation behavior. It will be observed that the effective stress exponent in the Garofalo sinh equation is a function of the instantaneous value of the stress argument.

  8. Microstructural development of diffusion-brazed austenitic stainless steel to magnesium alloy using a nickel interlayer

    SciTech Connect

    Elthalabawy, Waled M.; Khan, Tahir I.

    2010-07-15

    The differences in physical and metallurgical properties of stainless steels and magnesium alloys make them difficult to join using conventional fusion welding processes. Therefore, the diffusion brazing of 316L steel to magnesium alloy (AZ31) was performed using a double stage bonding process. To join these dissimilar alloys, the solid-state diffusion bonding of 316L steel to a Ni interlayer was carried out at 900 deg. C followed by diffusion brazing to AZ31 at 510 deg. C. Metallographic and compositional analyses show that a metallurgical bond was achieved with a shear strength of 54 MPa. However, during the diffusion brazing stage B{sub 2} intermetallic compounds form within the joint and these intermetallics are pushed ahead of the solid/liquid interface during isothermal solidification of the joint. These intermetallics had a detrimental effect on joint strengths when the joint was held at the diffusion brazing temperature for longer than 20 min.

  9. Method of fluxless brazing and diffusion bonding of aluminum containing components

    NASA Technical Reports Server (NTRS)

    Featherston, A. B.; Okelly, K. P. (Inventor)

    1976-01-01

    A method of diffusion bonding and fluxless brazing of aluminum containing components is reported. The aluminum surfaces are freed of any aluminum oxide coating and are coated with a polymeric sealer which can be thermally removed leaving essentially no residue. The polymeric sealer is being removed in a substantially oxygen free environment, and the aluminum components are then being brazed or diffusion bonded without the use of a flux to remove oxide coating.

  10. Diffusion bonding and brazing of high purity copper for linear collider accelerator structures

    NASA Astrophysics Data System (ADS)

    Elmer, J. W.; Klingmann, J.; van Bibber, K.

    2001-05-01

    Diffusion bonding and brazing of high purity copper were investigated to develop procedures for joining precision machined copper components for the Next Linear Collider (NLC). Diffusion bonds were made over a range of temperatures from 400 °C to 1000 °C, under two different loading conditions [3.45 kPa (0.5 psi) and 3.45 MPa (500 psi)], and on two different diamond machined surface finishes. Brazes were made using pure silver, pure gold, and gold-nickel alloys, and different heating rates produced by both radiation and induction heating. Braze materials were applied by both physical vapor deposition (PVD) and conventional braze alloy shims. Results of the diffusion bonding experiments showed that bond strengths very near that of the copper base metal could be made at bonding temperatures of 700 °C or higher at 3.45 MPa bonding pressure. At lower temperatures, only partial strength diffusion bonds could be made. At low bonding pressures (3.45 kPa), full strength bonds were made at temperatures of 800 °C and higher, while no bonding (zero strength) was observed at temperatures of 700 °C and lower. Observations of the fracture surfaces of the diffusion bonded samples showed the effects of surface finish on the bonding mechanism. These observations clearly indicate that bonding began by point asperity contact, and flatter surfaces resulted in a higher percentage of bonded area under similar bonding conditions. Results of the brazing experiments indicated that pure silver worked very well for brazing under both conventional and high heating rate scenarios. Similarly, pure silver brazed well for both the PVD layers and the braze alloy shims. The gold and gold-containing brazes had problems, mainly due to the high diffusivity of gold in copper. These problems led to the necessity of overdriving the temperature to ensure melting, the presence of porosity in the joint, and very wide braze joints. Based on the overall findings of this study, a two-step joining method

  11. Microstructural and Mechanical Characterization of Actively Brazed Alumina Specimens

    SciTech Connect

    Hosking, F.M.; Cadden, C.H.; Stephens, J.J.; Glass, S.J.; Yang, N.Y.C.; Vianco, P.V.; Walker, C.A.

    1999-08-26

    Alumina (94 and 99.8% grade compositions) was brazed directly to itself with gold-based active brazing alloys (ABA's) containing vanadium additions of 1,2 and 3 weight percent. The effects of brazing conditions on the joint properties were investigated. Wetting behavior, interfacial reactions, microstructure, hermeticity and tensile strength were determined. Wetting was fair to good for the ABA and base material combinations. Microanalysis identified a discontinuous Al-V-O spinel reaction product at the alumina-braze interface. Tensile strength results for 94% alumina were uniformly good and generally not sensitive to the vanadium concentration, with tensile values of 85-105 MPa. There was more variability in the 99.8% alumina strength results, with values ranging from 25-95 MPa. The highest vanadium concentration (3 wt. %) yielded the highest joint strength for the brazed 99.8% alumina. Failures in the 99.8% alumina samples occurred at the braze-alumina interface, while the 94% alumina specimens exhibited fracture of the ceramic substrate.

  12. Chemical elements diffusion in the stainless steel components brazed with Cu-Ag alloy

    NASA Astrophysics Data System (ADS)

    Voiculescu, I.; Geanta, V.; Vasile, I. M.; Binchiciu, E. F.; Winestoock, R.

    2016-06-01

    The paper presents the study of diffusion of chemical elements through a brazing joint, between two thin components (0.5mm) made of stainless steel 304. An experimental brazing filler material has been used for brazing stainless steel component and then the diffusion phenomenon has been studied, in terms of chemical element displacement from the brazed separation interface. The filler material is in the form of a metal rod coated with ceramic slurry mixture of minerals, containing precursors and metallic powders, which can contribute to the formation of deposit brazed. In determining the distance of diffusion of chemical elements, on both sides of the fusion line, were performed measurements of the chemical composition using electron microscopy SEM and EDX spectrometry. Metallographic analysis of cross sections was performed with the aim of highlight the microstructural characteristics of brazed joints, for estimate the wetting capacity, adherence of filler metal and highlight any imperfections. Analyzes performed showed the penetration of alloying elements from the solder (Ag, Cu, Zn and Sn) towards the base material (stainless steel), over distances up to 60 microns.

  13. Active Metal Brazing and Characterization of Brazed Joints in Titanium to Carbon-Carbon Composites

    NASA Technical Reports Server (NTRS)

    Singh, M.; Shpargel, T. P.; Morscher, G. N.; Asthana, R.

    2006-01-01

    The Ti-metal/C-C composite joints were formed by reactive brazing with three commercial brazes, namely, Cu-ABA, TiCuNi, and TiCuSiI. The joint microstructures were examined using optical microscopy and scanning electron microscopy (SEM) coupled with energy dispersive spectrometry (EDS). The results of the microstructure analysis indicate solute redistribution across the joint and possible metallurgical bond formation via interdiffusion, which led to good wetting and spreading. A tube-on-plate tensile test was used to evaluate joint strength of Ti-tube/ C-C composite joints. The load-carrying ability was greatest for the Cu-ABA braze joint structures. This system appeared to have the best braze spreading which resulted in a larger braze/C-C composite bonded area compared to the other two braze materials. Also, joint loadcarrying ability was found to be higher for joint structures where the fiber tows in the outer ply of the C-C composite were aligned perpendicular to the tube axis when compared to the case where fiber tows were aligned parallel to the tube axis.

  14. Nanoparticle-Assisted Diffusion Brazing of Metal Microchannel Arrays: Nanoparticle Synthesis, Deposition, and Characterization

    NASA Astrophysics Data System (ADS)

    Eluri, Ravindranadh T.

    Microchannel process technology (MPT) offers several advantages to the field of nanomanufacturing: 1) improved process control over very short time intervals owing to shorter diffusional distances; and 2) reduced reactor size due to high surface area to volume ratios and enhanced heat and mass transfer. The objective of this thesis was to consider how nanomaterials, produced in part using MPT, could be used to solve problems associated with the fabrication of MPT devices. Specifically, many MPT devices are produced using transient liquid-phase brazing involving an electroplated interlayer consisting of a brazing alloy designed for melting temperature suppression. Unfortunately, these alloys can form brittle secondary phases which significantly reduce bond strength. In contrast, prior efforts have shown that it is possible to leverage the size-dependent properties of nanomaterials to suppress brazing temperatures. In this prior work, thin films of off-the-shelf elemental nanoparticles were used as interlayers yielding joints with improved mechanical properties. In the present investigation, efforts have been made to characterize the synthesis and deposition of various elemental nanoparticle suspensions for use in the transient liquid-phase brazing of aluminum and stainless steel. Advances were used to demonstrate the nanoparticle-assisted diffusion brazing of a microchannel array. In the first section, a silver nanoparticle (AgNP) interlayer was produced for the diffusion brazing of heat exchanger aluminum. Efforts are made to examine the effect of braze filler particle size (˜5 nm and ˜50 nm) and processing parameters (heating rate: 5ºC/min and 25ºC/min; brazing temperature: 550ºC and 570ºC) on thin coupons of diffusion-brazed 3003 Al. A tensile strength of 69.7 MPa was achieved for a sample brazed at 570°C for 30 min under 1 MPa with an interlayer thickness of approximately 7 microm. Further suppression of the brazing temperature to 500ºC was achieved by

  15. Brazing of the Tore Supra actively cooled Phase III Limiter

    SciTech Connect

    Nygren, R.E.; Walker, C.A.; Lutz, T.J.; Hosking, F.M.; McGrath, R.T.

    1993-12-31

    The head of the water-cooled Tore Supra Phase 3 Limiter is a bank of 14 round OFHC copper tubes, curved to fit the plasma radius, onto which several hundred pyrolytic graphite (PG) tiles and a lesser number of carbon fiber composite tiles are brazed. The small allowable tolerances for fitting the tiles to the tubes and mating of compound curvatures made the brazing and fabrication extremely challenging. The paper describes the fabrication process with emphasis on the procedure for brazing. In the fixturing for vacuum furnace brazing, the tiles were each independently clamped to the tube with an elaborate set of window frame clamps. Braze quality was evaluated with transient heating tests. Some rebrazing was necessary.

  16. Detached Melt Nucleation during Diffusion Brazing of a Technical Ni-based Superalloy: A Phase-Field Study

    NASA Astrophysics Data System (ADS)

    Böttger, B.; Apel, M.; Laux, B.; Piegert, S.

    2015-06-01

    Advanced solidification processes like welding, soldering, and brazing are often characterized by their specific solidification conditions. But they also may include different types of melting processes which themselves are strongly influenced by the initial microstructures and compositions of the applied materials and therefore are decisive for the final quality and mechanical properties of the joint. Such melting processes are often not well- understood because - compared to other fields of solidification science - relatively little research has been done on melting by now. Also, regarding microstructure simulation, melting has been strongly neglected in the past, although this process is substantially different from solidification due to the reversed diffusivities of the involved phases. In this paper we present phase-field simulations showing melting, solidification and precipitation of intermetallic phases during diffusion brazing of directionally solidified and heat-treated high-alloyed Ni- based gas turbine blade material using different boron containing braze alloys. Contrary to the common belief, melting of the base material is not always planar and can be further accompanied by detached nucleation and growth of a second liquid phase inside the base material leading to polycrystalline morphologies of the joint after solidification. These findings are consistent with results from brazed laboratory samples, which were characterized by EDX and optical microscopy, and can be explained in terms of specific alloy thermodynamics and inter-diffusion kinetics. Consequences of the gained new understanding for brazing of high- alloyed materials are discussed.

  17. Active Metal Brazing of Carbon-Carbon Composites to Titanium

    NASA Technical Reports Server (NTRS)

    Singh, M.; Shpargel, T. P.; Morscher, G.; Asthana, R.

    2004-01-01

    The Ti-metal/C-C composite joints were formed by reactive brazing with three commercial brazes, namely, Cu-ABA, TiCuNi, and TiCuSil. The joint microstructures were examined using optical microscopy, and scanning electron microscopy (SEM) coupled with energy dispersive spectrometry (EDS). The results of the microstructure analysis indicate solute redistribution across the joint which led to good wetting, spreading, and metallurgical bond formation via interdiffusion.

  18. Melting Point Depression and Fast Diffusion in Nanostructured Brazing Fillers Confined Between Barrier Nanolayers

    NASA Astrophysics Data System (ADS)

    Kaptay, G.; Janczak-Rusch, J.; Jeurgens, L. P. H.

    2016-05-01

    Successful brazing using Cu-based nanostructured brazing fillers at temperatures much below the bulk melting temperature of Cu was recently demonstrated (Lehmert et al. in, Mater Trans 56:1015-1018, 2015). The Cu-based nano-fillers are composed of alternating nanolayers of Cu and a permeable, non-wetted AlN barrier. In this study, a thermodynamic model is derived to estimate the melting point depression (MPD) in such Cu/AlN nano-multilayers (NMLs) as function of the Cu nanolayer thickness. Depending on the melting route, the model predicts a MPD range of 238-609 K for Cu10nm/AlN10nm NMLs, which suggests a heterogeneous pre-melting temperature range of 750-1147 K (476-874 °C), which is consistent with experimental observations. As suggested by basic kinetic considerations, the observed Cu outflow to the NML surface at the temperatures of 723-1023 K (450-750 °C) can also be partially rationalized by fast solid-state diffusion of Cu along internal interfaces, especially for the higher temperatures.

  19. Brazing technique

    DOEpatents

    Harast, Donald G.

    1986-01-01

    A method of brazing comprises sand blasting the surfaces of the components to be brazed with particles of a brazing material to clean the surfaces and to embed brazing material in the surfaces, applying the brazing material to the surfaces, and heating the brazing material to form a brazement between the components.

  20. Fluxless Brazing and Heat Treatment of a Plate-Fin Sandwich Actively Cooled Panel

    NASA Technical Reports Server (NTRS)

    Beuyukian, C. S.

    1978-01-01

    The processes and techniques used to fabricate plate-fin sandwich actively cooled panels are presented. The materials were 6061 aluminum alloy and brazing sheet having clad brazing alloy. The panels consisted of small scale specimens, fatigue specimens, and a large 0.61 m by 1.22 m test panel. All panels were fluxless brazed in retorts in heated platen presses while exerting external pressure to assure intimate contact of details. Distortion and damage normally associated with that heat treatment were minimized by heat treating without fixtures and solution quenching in an organic polymer solution. The test panel is the largest fluxless brazed and heat treated panel of its configuration known to exist.

  1. Microstructure of arc brazed and diffusion bonded joints of stainless steel and SiC reinforced aluminum matrix composite

    NASA Astrophysics Data System (ADS)

    Elßner, M.; Weis, S.; Grund, T.; Wagner, G.; Habisch, S.; Mayr, P.

    2016-03-01

    Joint interfaces of aluminum and stainless steel often exhibit intermetallics of Al-Fe, which limit the joint strength. In order to reduce these brittle phases in joints of aluminum matrix composites (AMC) and stainless steel, diffusion bonding and arc brazing are used. Due to the absence of a liquid phase, diffusion welding can reduce the formation of these critical in- termetallics. For this joining technique, the influence of surface treatments and adjusted time- temperature-surface-pressure-regimes is investigated. On the other hand, arc brazing offers the advantage to combine a localized heat input with the application of a low melting filler and was conducted using the system Al-Ag-Cu. Results of the joining tests using both approaches are described and discussed with regard to the microstructure of the joints and the interfaces.

  2. Nondestructive test of brazed cooling tubes of prototype bolometer camera housing using active infrared thermography.

    PubMed

    Tahiliani, Kumudni; Pandya, Santosh P; Pandya, Shwetang; Jha, Ratneshwar; Govindarajan, J

    2011-01-01

    The active infrared thermography technique is used for assessing the brazing quality of an actively cooled bolometer camera housing developed for steady state superconducting tokamak. The housing is a circular pipe, which has circular tubes vacuum brazed on the periphery. A unique method was adopted to monitor the temperature distribution on the internal surface of the pipe. A stainless steel mirror was placed inside the pipe and the reflected IR radiations were viewed using an IR camera. The heat stimulus was given by passing hot water through the tubes and the temperature distribution was monitored during the transient phase. The thermographs showed a significant nonuniformity in the brazing with a contact area of around 51%. The thermography results were compared with the x-ray radiographs and a good match between the two was observed. Benefits of thermography over x-ray radiography testing are emphasized. PMID:21280850

  3. Coating system to permit direct brazing of ceramics

    DOEpatents

    Cadden, Charles H.; Hosking, F. Michael

    2003-01-01

    This invention relates to a method for preparing the surface of a ceramic component that enables direct brazing using a non-active braze alloy. The present invention also relates to a method for directly brazing a ceramic component to a ceramic or metal member using this method of surface preparation, and to articles produced by using this brazing method. The ceramic can be high purity alumina. The method comprises applying a first coating of a silicon-bearing oxide material (e.g. silicon dioxide or mullite (3Al.sub.2 O.sub.3.2SiO.sub.2) to the ceramic. Next, a thin coating of active metal (e.g. Ti or V) is applied. Finally, a thicker coating of a non-active metal (e.g. Au or Cu) is applied. The coatings can be applied by physical vapor deposition (PVD). Alternatively, the active and non-active metals can be co-deposited (e.g. by sputtering a target made of mullite). After all of the coatings have been applied, the ceramic can be fired at a high temperature in a non-oxidizing environment to promote diffusion, and to enhance bonding of the coatings to the substrate. After firing, the metallized ceramic component can be brazed to other components using a conventional non-active braze alloy. Alternatively, the firing and brazing steps can be combined into a single step. This process can replace the need to perform a "moly-manganese" metallization step.

  4. New concept in brazing metallic honeycomb panels

    NASA Technical Reports Server (NTRS)

    Carter, P. D.; Layton, R. E.; Stratton, F. W.

    1973-01-01

    Aluminum oxide coating provides surface which will not be wetted by brazing alloy and which stops metallic diffusion welding of tooling materials to part being produced. This method eliminates loss of tooling materials and parts from braze wetting and allows fall-apart disassembly of tooling after brazing.

  5. BRAZING ALLOYS

    DOEpatents

    Donnelly, R.G.; Gilliland, R.G.; Slaughter, G.M.

    1962-02-20

    A brazing alloy is described which, in the molten state, is characterized by excellent wettability and flowability and is capable of forming a corrosion-resistant brazed joint. At least one component of said joint is graphite and the other component is a corrosion-resistant refractory metal. The brazing alloy consists essentially of 40 to 90 wt % of gold, 5 to 35 wt% of nickel, and 1 to 45 wt% of tantalum. (AEC)

  6. Active Metal Brazing and Adhesive Bonding of Titanium to C/C Composites for Heat Rejection System

    NASA Technical Reports Server (NTRS)

    Singh, M.; Shpargel, Tarah; Cerny, Jennifer

    2006-01-01

    Robust assembly and integration technologies are critically needed for the manufacturing of heat rejection system (HRS) components for current and future space exploration missions. Active metal brazing and adhesive bonding technologies are being assessed for the bonding of titanium to high conductivity Carbon-Carbon composite sub components in various shapes and sizes. Currently a number of different silver and copper based active metal brazes and adhesive compositions are being evaluated. The joint microstructures were examined using optical microscopy, and scanning electron microscopy (SEM) coupled with energy dispersive spectrometry (EDS). Several mechanical tests have been employed to ascertain the effectiveness of different brazing and adhesive approaches in tension and in shear that are both simple and representative of the actual system and relatively straightforward in analysis. The results of these mechanical tests along with the fractographic analysis will be discussed. In addition, advantages, technical issues and concerns in using different bonding approaches will also be presented.

  7. Laser Brazing of High Temperature Braze Alloy

    NASA Technical Reports Server (NTRS)

    Gao, Y. P.; Seaman, R. F.; McQuillan, T. J.; Martiens, R. F.

    2000-01-01

    The Space Shuttle Main Engine (SSME) consists of 1080 conical tubes, which are furnace brazed themselves, manifolds, and surrounding structural jacket making almost four miles of braze joints. Subsequent furnace braze cycles are performed due to localized braze voids between the coolant tubes. SSME nozzle experiences extremely high heat flux (180 mW/sq m) during hot fire. Braze voids between coolant tubes may result in hot combustion gas escape causing jacket bulges. The nozzle can be disqualified for flight or result in mission failure if the braze voids exceed the limits. Localized braze processes were considered to eliminate braze voids, however, damage to the parent materials often prohibited use of such process. Being the only manned flight reusable rocket engine, it has stringent requirement on the braze process. Poor braze quality or damage to the parent materials limits the nozzle service life. The objective of this study was to develop a laser brazing process to provide quality, localized braze joints without adverse affect on the parent materials. Gold (Au-Cu-Ni-Pd-Mn) based high temperature braze alloys were used in both powder and wire form. Thin section iron base superalloy A286 tube was used as substrate materials. Different Laser Systems including CO2 (10.6 micrometers, 1kW), ND:YAG (1.06 micrometers, 4kW). and direct diode laser (808nm. 150W) were investigated for brazing process. The laser process variables including wavelength. laser power, travel speed and angle of inclination were optimized according to bead geometry and braze alloy wetting at minimum heat input level, The properties of laser brazing were compared to that of furnace brazing. Microhardness profiles were used for braze joint property comparison between laser and furnace brazing. The cooling rate of laser brazing was compared to furnace brazing based on secondary dendritic arm spacing, Both optical and Scanning Electron Microscope (SEM) were used to evaluate the microstructures of

  8. BRAZING ALLOYS

    DOEpatents

    Donnelly, R.G.; Gilliland, R.G.; Slaughter, G.M.

    1963-02-26

    A brazing alloy which, in the molten state, is characterized by excellent wettability and flowability, said alloy being capable of forming a corrosion resistant brazed joint wherein at least one component of said joint is graphite and the other component is a corrosion resistant refractory metal, said alloy consisting essentially of 20 to 50 per cent by weight of gold, 20 to 50 per cent by weight of nickel, and 15 to 45 per cent by weight of molybdenum. (AEC)

  9. Improved brazing technique

    DOEpatents

    Harast, D.G.

    1984-01-27

    A method of brazing comprises sand blasting the surfaces of the components to be brazed with particles of a brazing material to clean the surfaces and to embed brazing material in the surfaces, applying the brazing material to the surfaces, and heating the brazing material to form a brazement between the components.

  10. Method for brazing together planar and nonplanar metal members

    DOEpatents

    Hammersand, Fred G.; Witkowski, Anthony J.

    1985-01-01

    The invention relates to a method and apparatus for brazing two metal members together, at least one of which is nonplanar, in a brazing furnace using a substantially pure brazing material. The method comprises the steps of utilizing a brazing fixture to hold the two metal members in tangential relation to one another along a portion of each member so that a cavity is formed adjacent to the contacting portions. A braze material is then positioned within the cavity. The braze fixture, the metal members, and the braze material are then placed in a brazing furnace. A heat shield is then placed over the braze fixture, the metal members, and the braze material to shield the braze material from direct furnace radiation. The furnace temperature is linearly increased at a rate of about 180.degree. C. per hour until a temperature of 350.degree. C. is achieved. Heat is transferred by conduction from the metal members to the braze material to cause the braze material to melt. Some material from the metal members slowly diffuses into the braze material forming a braze joint. The furnace is rapidly cooled to room temperature using nitrogen gas. The brazed assemblies made according to this method are superior to assemblies formed by heliarc welding.

  11. Reversible brazing process

    DOEpatents

    Pierce, Jim D.; Stephens, John J.; Walker, Charles A.

    1999-01-01

    A method of reversibly brazing surfaces together. An interface is affixed to each surface. The interfaces can be affixed by processes such as mechanical joining, welding, or brazing. The two interfaces are then brazed together using a brazing process that does not defeat the surface to interface joint. Interfaces of materials such as Ni-200 can be affixed to metallic surfaces by welding or by brazing with a first braze alloy. The Ni-200 interfaces can then be brazed together using a second braze alloy. The second braze alloy can be chosen so that it minimally alters the properties of the interfaces to allow multiple braze, heat and disassemble, rebraze cycles.

  12. Microstructural and Mechanical Evaluation of a Cu-Based Active Braze Alloy to Join Silicon Nitride Ceramics

    NASA Technical Reports Server (NTRS)

    Singh, M.; Asthana, Rajiv; Varela, F. M.; Martinez-Fernandez, J.

    2010-01-01

    Self-joining of St. Gobain Si3N4 (NT-154) using a ductile Cu-Al-Si-Ti active braze (Cu-ABA) was demonstrated. A reaction zone approx.2.5-3.5 microns thick) developed at the interface after 30 min brazing at 1317 K. The interface was enriched in Ti and Si. The room temperature compressive shear strengths of Si3N4/Si3N4 and Inconel/Inconel joints (the latter created to access baseline data for use with the proposed Si3N4/Inconel joints) were 140+/-49MPa and 207+/-12MPa, respectively. High-temperature shear tests were performed at 1023K and 1073 K, and the strength of the Si3N4/Si3N4 and Inconel/Inconel joints were determined. The joints were metallurgically well-bonded for temperatures above 2/3 of the braze solidus. Scanning and transmission electron microscopy studies revealed a fine grain microstructure in the reaction layer, and large grains in the inner part of the joint with interfaces being crack-free. The observed formation of Ti5Si3 and AlN at the joint interface during brazing is discussed.

  13. Active Metal Brazing and Characterization of Brazed Joints in C-C and C-SiC Composites to Copper-Clad-Molybdenum System

    NASA Technical Reports Server (NTRS)

    Singh, M.; Asthana, R.

    2008-01-01

    Carbon/carbon composites with CVI and resin-derived matrices, and C/SiC composites reinforced with T-300 carbon fibers in a CVI SiC matrix were joined to Cu-clad Mo using two Ag-Cu braze alloys, Cusil-ABA (1.75% Ti) and Ticusil (4.5% Ti). The brazed joints revealed good interfacial bonding, preferential precipitation of Ti at the composite/braze interface, and a tendency toward delamination in resin-derived C/C composite. Extensive braze penetration of the inter-fiber channels in the CVI C/C composites was observed. The Knoop microhardness (HK) distribution across the C/C joints indicated sharp gradients at the interface, and a higher hardness in Ticusil than in Cusil-ABA. For the C/SiC composite to Cu-clad-Mo joints, the effect of composite surface preparation revealed that ground samples did not crack whereas unground samples cracked. Calculated strain energy in brazed joints in both systems is comparable to the strain energy in a number of other ceramic/metal systems. Theoretical predictions of the effective thermal resistance suggest that such joined systems may be promising for thermal management applications.

  14. Microstructural evolution and ductile phase toughening in brazed joints

    NASA Astrophysics Data System (ADS)

    Philips, Noah Robinson

    In typical brazed joints, melting point depressants degrade the structural robustness by concentrating as brittle phases into continuous seams along the centerline. The objective of this dissertation is to sufficiently understand the mechanisms governing the microstructure of a typical braze that approaches for modifying the fabrication to eliminate brittleness can be identified and demonstrated. A characterization of a quaternary braze (Nicrobraze 31) used for stainless steel bonds, containing P and Si melting point depressants, reveals that the thermochemical interactions governing the microstructure include dissolution/reprecipitation, solid-state diffusion, and solidification. It is shown that the Si can be incorporated into a solid solution gamma-Ni(Fe, Si) phase that forms by reprecipitation. A fracture toughness test for intermediate toughness materials is developed to quantify the performance of brazed joints. The test configuration is a wedge driven DCB (Double Cantilever Beam), with design guided by analytical solutions for the energy release rate and compliance. The fracture resistance of a typical braze joint is found to be significantly greater than that for the intermetallic constituents. Approximately half of the toughening is attributed to plastic stretch of the ductile phase within the eutectic. The remainder is attributed to dissipation within a plastic zone that forms in the primary gamma-Ni(Fe, Si) regions. Heat treatments are presented that use ductile phase toughening to mitigate the effect of brittle intermetallics in a Ni-based braze alloy. The development of this beneficial microstructure is based on an understanding of the transient dissolution and isothermal solidification phenomena. By rapid cooling after a short brazing time, gamma-Ni(Fe, Si) is redistributed to the midline where it disrupts the intermetallics and forms a network of ductile ligaments upon fracture. Reinforcement by the modified ductile phase nearly doubles the toughness

  15. Active Brazing of C/C Composite to Copper by AgCuTi Filler Metal

    NASA Astrophysics Data System (ADS)

    Zhang, Kexiang; Xia, Lihong; Zhang, Fuqin; He, Lianlong

    2016-05-01

    Brazing between the carbon-fiber-reinforced carbon composite (C/C composite) and copper has gained increasing interest because of its important application in thermal management systems in nuclear fusion reactors and in the aerospace industry. In order to examine the "interfacial shape effect" on the mechanical properties of the joint, straight and conical interfacial configurations were designed and machined on the surface of C/C composites before joining to copper using an Ag-68.8Cu-4.5Ti (wt pct) alloy. The microstructure and interfacial microchemistry of C/C composite/AgCuTi/Cu brazed joints were comprehensively investigated by using high-resolution transmission electron microscopy. The results indicate that the joint region of both straight and conical joints can be described as a bilayer. Reaction products of Cu3Ti3O and γ-TiO were formed near the copper side in a conical interface joint, while no reaction products were found in the straight case. The effect of Ag on the interfacial reaction was discussed, and the formation mechanism of the joints during brazing was proposed. On the basis of the detailed microstructure presented, the mechanical performance of the brazed joints was discussed in terms of reaction and morphology across the joint.

  16. BRAZE BONDING OF COLUMBIUM

    DOEpatents

    Heestand, R.L.; Picklesimer, M.L.

    1962-07-31

    A method of brazing niobium parts together is described. The surfaces of the parts to be brazed together are placed in abutting relationship with a brazing alloy disposed adjacent. The alloy consists essentially of, by weight, 12 to 25% niobium, 0.5 to 5% molybdenum, and the balance zirconium, The alloy is heated to at least its melting point to braze the parts together. The brazed joint is then cooled. The heating, melting and cooling take place in an inert atmosphere. (AEC)

  17. Brazing graphite to graphite

    DOEpatents

    Peterson, George R.

    1976-01-01

    Graphite is joined to graphite by employing both fine molybdenum powder as the brazing material and an annealing step that together produce a virtually metal-free joint exhibiting properties similar to those found in the parent graphite. Molybdenum powder is placed between the faying surfaces of two graphite parts and melted to form molybdenum carbide. The joint area is thereafter subjected to an annealing operation which diffuses the carbide away from the joint and into the graphite parts. Graphite dissolved by the dispersed molybdenum carbide precipitates into the joint area, replacing the molybdenum carbide to provide a joint of virtually graphite.

  18. Microstructure and Performance of Kovar/Alumina Joints Made with Silver-Copper Base Active Metal Braze Alloys

    SciTech Connect

    STEPHENS, JOHN J.; VIANCO,PAUL T.; HLAVA,PAUL F.; WALKER,CHARLES A.

    1999-12-15

    Poor hermeticity performance was observed for Al{sub 2}O{sub 3}-Al{sub 2}O{sub 3} ceramic-ceramic joints having a Kovar{trademark} alloy interlayer. The active Ag-Cu-Ti filler metal was used to braze the substrates together. The Ti active element was scavenged from the filler metal by the formation of a (Fe, Ni, Co){sub x}Ti phase (x= 2-3) that prevented development of a continuous Ti{sub x}O{sub y} layer at the filler metal/Al{sub 2}O{sub 3} interface. Altering the process parameters did not circumvent the scavenging of Ti. Molybdenum barrier layers 1000, 2500, or 5000 {angstrom} thick on the Kovar{trademark} surfaces successfully allowed Ti{sub x}O{sub y} formation at the filler metal/Al{sub 2}O{sub 3} interface and hermetic joints. The problems with the Ag-Cu-Ti filler metal for Kovar{trademark}/Al{sub 2}O{sub 3} braze joints led to the evaluation of a Ag-Cu-Zr filler metal. The Zr (active element) in Ag-Cu-Zr filler metal was not susceptible to the scavenging problem.

  19. Fluxless aluminum brazing

    DOEpatents

    Werner, W.J.

    1974-01-01

    This invention relates to a fluxless brazing alloy for use in forming brazed composites made from members of aluminum and its alloys. The brazing alloy consists of 35-55% Al, 10--20% Si, 25-60% Ge; 65-88% Al, 2-20% Si, 2--18% In; 65--80% Al, 15-- 25% Si, 5- 15% Y. (0fficial Gazette)

  20. Design of a braze alloy for fast epitaxial brazing of superalloys

    NASA Astrophysics Data System (ADS)

    Piegert, S.; Laux, B.; Rösier, J.

    2012-07-01

    For the repair of directionally solidified turbine components made of nickel-based superalloys, a new high-temperature brazing method has been developed. Utilising heterogeneous nucleation on the crack surface, the microstructure of the base material can be reproduced, i.e. single crystallinity can be maintained. In contrast to commonly used eutectic braze alloys, such as nickel-boron or nickel-silicon systems, the process is not diffusion controlled but works with a consolute binary base system. The currently applied epitaxial brazing methods rely on isothermal solidification diffusing the melting point depressants into the base material until their concentration is reduced so that the liquid braze solidifies. Contrary, the identified Ni-Mn consolute system enables a temperature driven epitaxial solidification resulting in substantially reduced process duration. The development of the braze alloys was assisted using the CALPHAD software Thermo-Calc. The solidification behaviour was estimated by kinetic calculations with realistic boundary conditions. Finally, the complete system, including braze alloy as well as substrate material, was modelled by means of DICTRA. Subsequently, the thermodynamic properties of the braze alloys were experimentally analysed by DSC measurements. For brazing experiments 300 μm wide parallel gaps were used. Complete epitaxial solidification, i.e. the absence of high-angle grain boundaries, could be achieved within brazing times being up to two orders of magnitude shorter compared to diffusion brazing processes. Theoretically and experimentally evaluated process windows reveal similar shapes. However, a distinct shift has to be stated which can be ascribed to the limited accuracy of the underlying thermodynamic databases.

  1. Oxide film on 5052 aluminium alloy: Its structure and removal mechanism by activated CsF-AlF3 flux in brazing

    NASA Astrophysics Data System (ADS)

    Xiao, Bing; Wang, Dongpo; Cheng, Fangjie; Wang, Ying

    2015-05-01

    The oxide-film structure on the 5052 Al alloy and the film-removal mechanism by activated CsF-AlF3 flux in brazing were studied. Characterisation of the oxide film shows that thermally activated Mg, segregated from the alloy's interior, was significantly enriched and oxidised during medium-temperature brazing. Thus, the outer oxide surface consisted of the amorphous MgO-like phase, and the interior of the oxide film comprised mainly the amorphous MgO-like phase and dispersely distributed and less-ordered MgAl2O4. The MgO-like phase was the main obstacle to oxide removal in brazing. The activated ZnCl2-containing CsF-AlF3 flux effectively removed the oxide film, and the 5052 Al alloy was successfully brazed by the Zn-Al filler metal and activated flux. When Zn2+ in the molten flux permeated the oxide film through cracks, its chemical reaction with the Al substrate loosened the oxide film, which was eventually pushed out as the filler metal spread over the alloy surface.

  2. Evaluation of methods for nondestructive testing of brazed joints

    NASA Technical Reports Server (NTRS)

    Kanno, A.

    1968-01-01

    Evaluation of nondestructive methods of testing brazed joints reveals that ultrasonic testing is effective in the detection of nonbonds in diffusion bonded samples. Radiography provides excellent resolutions of void or inclusion defects, and the neutron radiographic technique shows particular advantage for brazing materials containing cadmium.

  3. Brazing method produces solid-solution bond between refractory metals

    NASA Technical Reports Server (NTRS)

    1965-01-01

    Brazing two refractory metals by diffusion bonding minimizes distortion and avoids excessive grain growth in the metals. This method requires the selection of an interface metal that forms intermediate low-melting eutectics or solid solutions with the metals to be brazed.

  4. Weld braze technique

    DOEpatents

    Kanne, Jr., William R.; Kelker, Jr., John W.; Alexander, Robert J.

    1982-01-01

    High-strength metal joints are formed by a combined weld-braze technique. A hollow cylindrical metal member is forced into an undersized counterbore in another metal member with a suitable braze metal disposed along the bottom of the counterbore. Force and current applied to the members in an evacuated chamber results in the concurrent formation of the weld along the sides of the counterbore and a braze along the bottom of the counterbore in one continuous operation.

  5. Vacuum brazing of high volume fraction SiC particles reinforced aluminum matrix composites

    NASA Astrophysics Data System (ADS)

    Cheng, Dongfeng; Niu, Jitai; Gao, Zeng; Wang, Peng

    2015-03-01

    This experiment chooses A356 aluminum matrix composites containing 55% SiC particle reinforcing phase as the parent metal and Al-Si-Cu-Zn-Ni alloy metal as the filler metal. The brazing process is carried out in vacuum brazing furnace at the temperature of 550°C and 560°C for 3 min, respectively. The interfacial microstructures and fracture surfaces are investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy spectrum analysis (EDS). The result shows that adequacy of element diffusion are superior when brazing at 560°C, because of higher activity and liquidity. Dislocations and twins are observed at the interface between filler and composite due to the different expansion coefficient of the aluminum alloy matrix and SiC particles. The fracture analysis shows that the brittle fracture mainly located at interface of filler and composites.

  6. Brazing of Stainless Steels to Yttria Stabilized Zirconia (YSZ) Using Silver -Base Brazes

    NASA Technical Reports Server (NTRS)

    Singh, Mrityunjay; Shpargel, Tarah P.; Asthana, Rajiv

    2005-01-01

    Three silver-base brazes containing either noble metal palladium (Palcusil-10 and Palcusil-15) or active metal titanium (Ticusil) were evaluated for high-temperature oxidation resistance, and their effectiveness in joining yttria stabilized zirconia (YSZ) to a corrosion-resistant ferritic stainless steel. Thermogravimetric analysis (TGA), and optical- and scanning electron microscopy (SEM) coupled with energy dispersive spectrometry (EDS) were used to evaluate the braze oxidation behavior and the structure and chemistry of the YSZ/braze/steel joints. The effect of the braze type and processing conditions on the interfacial microstructure and composition of the joint regions is discussed with reference to the chemical changes that occur at the interface. It was found that chemical interdiffusion of the constituents of YSZ, steel and the brazes led to compositional changes and/or interface reconstruction, and metallurgically sound joints.

  7. Brazing Dissimilar Metals

    NASA Technical Reports Server (NTRS)

    Krotz, Phillip D.; Davis, William M.; Wisner, Daniel L.

    1996-01-01

    Brazing effective technique for joining ordinary structural metals to brittle, low-thermal-expansion refractory metals. Specifically, brazing process established for joining copper or nickel flanges to ends of vacuum-plasma-sprayed tungsten tubes and for joining stainless-steel flanges to ends of tubes made of alloy of molybdenum with 40 percent of rhenium.

  8. Composition and method for brazing graphite to graphite

    DOEpatents

    Taylor, Albert J.; Dykes, Norman L.

    1984-01-01

    The present invention is directed to a brazing material for joining graphite structures that can be used at temperatures up to about 2800.degree. C. The brazing material formed of a paste-like composition of hafnium carbide and uranium oxide with a thermosetting resin. The uranium oxide is converted to uranium dicarbide during the brazing operation and then the hafnium carbide and uranium dicarbide form a liquid phase at a temperature about 2600.degree. C. with the uranium diffusing and vaporizing from the joint area as the temperature is increased to about 2800.degree. C. so as to provide a brazed joint consisting essentially of hafnium carbide. This brazing temperature for hafnium carbide is considerably less than the eutectic temperature of hafnium carbide of about 3150.degree. C. The brazing composition also incorporates the thermosetting resin so that during the brazing operation the graphite structures may be temporarily bonded together by thermosetting the resin so that machining of the structures to final dimensions may be completed prior to the completion of the brazing operation. The resulting brazed joint is chemically and thermally compatible with the graphite structures joined thereby and also provides a joint of sufficient integrity so as to at least correspond with the strength and other properties of the graphite.

  9. Composition and method for brazing graphite to graphite

    DOEpatents

    Taylor, A.J.; Dykes, N.L.

    1982-08-10

    A brazing material is described for joining graphite structures that can be used up to 2800/sup 0/C. The brazing material is formed of a paste-like composition of hafnium carbide and uranium oxide with a thermosetting resin. The uranium oxide is converted to uranium dicarbide during the brazing operation and then the hafnium carbide and uranium dicarbide form a liquid phase at a temperature about 2600/sup 0/C with the uranium diffusing and vaporizing from the joint area as the temperature is increased to about 2800/sup 0/C so as to provide a brazed joint consisting essentially of hafnium carbide. The resulting brazed joint is chemically and thermally compatible with the graphite structures.

  10. METHOD OF BRAZING

    DOEpatents

    Patriarca, P.; Slaughter, G.M.

    1962-11-27

    A method of joining metal surfaces is given. Surfaces having nickel or iron as the base metal are joined together with a brazing composition consisting of 80% nickel, 10% phosphorus, and 10% chromium. (AEC)

  11. Joining Ceramics By Brazing

    NASA Technical Reports Server (NTRS)

    Chiaramonte, Francis P.; Sudsina, Michael W.

    1992-01-01

    Certain ceramic materials tightly bond together by brazing with suitable alloys. Enables fabrication of parts of wide variety of shapes from smaller initial pieces of ceramics produced directly in only limited variety of shapes.

  12. A New Vacuum Brazing Route for Niobium-316L Stainless Steel Transition Joints for Superconducting RF Cavities

    NASA Astrophysics Data System (ADS)

    Kumar, Abhay; Ganesh, P.; Kaul, R.; Bhatnagar, V. K.; Yedle, K.; Ram Sankar, P.; Sindal, B. K.; Kumar, K. V. A. N. P. S.; Singh, M. K.; Rai, S. K.; Bose, A.; Veerbhadraiah, T.; Ramteke, S.; Sridhar, R.; Mundra, G.; Joshi, S. C.; Kukreja, L. M.

    2015-02-01

    The paper describes a new approach for vacuum brazing of niobium-316L stainless steel transition joints for application in superconducting radiofrequency cavities. The study exploited good wettability of titanium-activated silver-base brazing alloy (CuSil-ABA®), along with nickel as a diffusion barrier, to suppress brittle Fe-Nb intermetallic formation, which is well reported during the established vacuum brazing practice using pure copper filler. The brazed specimens displayed no brittle intermetallic layers on any of its interfaces, but instead carried well-distributed intermetallic particles in the ductile matrix. The transition joints displayed room temperature tensile and shear strengths of 122-143 MPa and 80-113 MPa, respectively. The joints not only exhibited required hermeticity (helium leak rate <1.1 × 10-10 mbar l/s) for service in ultra-high vacuum but also withstood twelve hour degassing heat treatment at 873 K (suppresses Q-disease in niobium cavities), without any noticeable degradation in the microstructure and the hermeticity. The joints retained their leak tightness even after undergoing ten thermal cycles between the room temperature and the liquid nitrogen temperature, thereby establishing their ability to withstand service-induced low cycle fatigue conditions. The study proposes a new lower temperature brazing route to form niobium-316L stainless steel transition joints, with improved microstructural characteristics and acceptable hermeticity and mechanical properties.

  13. Weld-brazing of titanium

    NASA Technical Reports Server (NTRS)

    Bales, T. T.; Royster, D. M.; Arnold, W. E., Jr.

    1974-01-01

    A joining process, designated weld-brazing, which combines resistance spotwelding and brazing has been developed at the NASA Langley Research Center. Resistance spot-welding is employed to position and align the parts and to establish a suitable faying surface gap for brazing; it contributes to the integrity of the joint. Brazing enhances the properties of the joint and reduces the stress concentrations normally associated with spotwelds. Ti-6Al-4V titanium alloy joints have been fabricated using 3003 aluminum braze both in a vacuum furnace and in a retort containing an inert gas environment.

  14. METHOD OF BRAZING BERYLLIUM

    DOEpatents

    Hanks, G.S.; Keil, R.W.

    1963-05-21

    A process is described for brazing beryllium metal parts by coating the beryllium with silver (65- 75 wt%)-aluminum alloy using a lithium fluoride (50 wt%)-lithium chloride flux, and heating the coated joint to a temperature of about 700 un. Concent 85% C for about 10 minutes. (AEC)

  15. Method for controlling brazing

    DOEpatents

    Hosking, F. Michael; Hall, Aaron C.; Givler, Richard C.; Walker, Charles A.

    2006-08-01

    A method for making a braze joint across a discontinuity in a work piece using alternating current. A filler metal is pre-placed at a location sufficiently close to the discontinuity such that, when an alternating current is applied across a work piece to heat the work piece and melt the filler metal, the filler metal is drawn into the discontinuity. The alternating current is maintained for a set residence time, generally less than 10 seconds and more particularly less than 3 seconds. The alternating current is then altered, generally by reducing the current and/or voltage such that the filler metal can solidify to form a braze joint of desired quality and thickness.

  16. Failure Assessment of Brazed Structures

    NASA Technical Reports Server (NTRS)

    Flom, Yuri

    2012-01-01

    Despite the great advances in analytical methods available to structural engineers, designers of brazed structures have great difficulties in addressing fundamental questions related to the loadcarrying capabilities of brazed assemblies. In this chapter we will review why such common engineering tools as Finite Element Analysis (FEA) as well as many well-established theories (Tresca, von Mises, Highest Principal Stress, etc) don't work well for the brazed joints. This chapter will show how the classic approach of using interaction equations and the less known Coulomb-Mohr failure criterion can be employed to estimate Margins of Safety (MS) in brazed joints.

  17. Vacuum Brazing of Accelerator Components

    NASA Astrophysics Data System (ADS)

    Singh, Rajvir; Pant, K. K.; Lal, Shankar; Yadav, D. P.; Garg, S. R.; Raghuvanshi, V. K.; Mundra, G.

    2012-11-01

    Commonly used materials for accelerator components are those which are vacuum compatible and thermally conductive. Stainless steel, aluminum and copper are common among them. Stainless steel is a poor heat conductor and not very common in use where good thermal conductivity is required. Aluminum and copper and their alloys meet the above requirements and are frequently used for the above purpose. The accelerator components made of aluminum and its alloys using welding process have become a common practice now a days. It is mandatory to use copper and its other grades in RF devices required for accelerators. Beam line and Front End components of the accelerators are fabricated from stainless steel and OFHC copper. Fabrication of components made of copper using welding process is very difficult and in most of the cases it is impossible. Fabrication and joining in such cases is possible using brazing process especially under vacuum and inert gas atmosphere. Several accelerator components have been vacuum brazed for Indus projects at Raja Ramanna Centre for Advanced Technology (RRCAT), Indore using vacuum brazing facility available at RRCAT, Indore. This paper presents details regarding development of the above mentioned high value and strategic components/assemblies. It will include basics required for vacuum brazing, details of vacuum brazing facility, joint design, fixturing of the jobs, selection of filler alloys, optimization of brazing parameters so as to obtain high quality brazed joints, brief description of vacuum brazed accelerator components etc.

  18. Finding Brazing Voids by Holography

    NASA Technical Reports Server (NTRS)

    Galluccio, R.

    1986-01-01

    Vibration-induced interference fringes reveal locations of defects. Holographic apparatus used to view object while vibrated ultrasonically. Interference fringes in hologram reveal brazing defects. Holographic technique locates small voids in large brazed joints. Identifies unbrazed regions 1 in. to second power (6 cm to the second power) or less in area.

  19. Dissimilar joint characteristics of SiC and WC-Co alloy by laser brazing

    NASA Astrophysics Data System (ADS)

    Nagatsuka, K.; Sechi, Y.; Nakata, K.

    2012-08-01

    SiC and WC-Co alloys were joined by laser brazing with an active braze metal. The braze metal based on eutectic Ag-Cu alloy with additional Ti as an active element ranging from 0 to 2.8 mass% was sandwiched by the SiC block and WC-Co alloy plate. The brazing was carried out by selective laser beam irradiation on the WC-Co alloy plate. The content of Ti in the braze metal was required to exceed 0.6 mass% in order to form a brazed joint with a measurable shear strength. The shear strength increased with increasing Ti content up to 2.3 mass%Ti and decreased with a higher content.

  20. Interfacial metallurgy study of brazed joints between tungsten and fusion related materials for divertor design

    NASA Astrophysics Data System (ADS)

    Zhang, Yuxuan; Galloway, Alexander; Wood, James; Robbie, Mikael Brian Olsson; Easton, David; Zhu, Wenzhong

    2014-11-01

    In the developing DEMO divertor, the design of joints between tungsten to other fusion related materials is a significant challenge as a result of the dissimilar physical metallurgy of the materials to be joined. This paper focuses on the design and fabrication of dissimilar brazed joints between tungsten and fusion relevant materials such as EUROFER 97, oxygen-free high thermal conductivity (OFHC) Cu and SS316L using a gold based brazing foil. The main objectives are to develop acceptable brazing procedures for dissimilar joining of tungsten to other fusion compliant materials and to advance the metallurgical understanding within the interfacial region of the brazed joint. Four different butt-type brazed joints were created and characterised, each of which were joined with the aid of a thin brazing foil (Au80Cu19Fe1, in wt.%). Microstructural characterisation and elemental mapping in the transition region of the joint was undertaken and, thereafter, the results were analysed as was the interfacial diffusion characteristics of each material combination produced. Nano-indentation tests are performed at the joint regions and correlated with element composition information in order to understand the effects of diffused elements on mechanical properties. The experimental procedures of specimen fabrication and material characterisation methods are presented. The results of elemental transitions after brazing are reported. Elastic modulus and nano-hardness of each brazed joints are reported.

  1. Brazing of Stainless Steel to Yttria-Stabilized Zirconia Using Gold-Based Brazes for Solid Oxide Fuel Cell Applications

    NASA Technical Reports Server (NTRS)

    Singh, M.; Shpargel, T. P.; Asthana, R.

    2007-01-01

    Two gold-base active metal brazes (gold-ABA and gold-ABA-V) were evaluated for oxidation resistance to 850 C, and used to join yttria-stabilized zirconia (YSZ) to a corrosion-resistant ferritic stainless steel for possible use in solid oxide fuel cells. Thermogravimetric analysis and optical microscopy and scanning electron microscopy coupled with energy-dispersive spectroscopy were used to evaluate the braze oxidation behavior, and microstructure and composition of the YSZ/braze/steel joints. Both gold-ABA and gold-ABA-V exhibited nearly linear oxidation kinetics at 850 C, with gold-ABA-V showing faster oxidation than gold-ABA. Both brazes produced metallurgically sound YSZ/steel joints due to chemical interactions of Ti and V with the YSZ and steel substrates.

  2. Thermally stable diamond brazing

    DOEpatents

    Radtke, Robert P.

    2009-02-10

    A cutting element and a method for forming a cutting element is described and shown. The cutting element includes a substrate, a TSP diamond layer, a metal interlayer between the substrate and the diamond layer, and a braze joint securing the diamond layer to the substrate. The thickness of the metal interlayer is determined according to a formula. The formula takes into account the thickness and modulus of elasticity of the metal interlayer and the thickness of the TSP diamond. This prevents the use of a too thin or too thick metal interlayer. A metal interlayer that is too thin is not capable of absorbing enough energy to prevent the TSP diamond from fracturing. A metal interlayer that is too thick may allow the TSP diamond to fracture by reason of bending stress. A coating may be provided between the TSP diamond layer and the metal interlayer. This coating serves as a thermal barrier and to control residual thermal stress.

  3. Welding, brazing, and soldering handbook

    NASA Technical Reports Server (NTRS)

    Kilgore, A. B.; Koehler, M. L.; Metzler, J. W.; Sturges, S. R.

    1969-01-01

    Handbook gives information on the selection and application of welding, brazing, and soldering techniques for joining various metals. Summary descriptions of processes, criteria for process selection, and advantages of different methods are given.

  4. Brazing titanium to stainless steel

    NASA Technical Reports Server (NTRS)

    Batista, R. I.

    1980-01-01

    Titanium and stainless-steel members are usually joined mechanically for lack of any other effective method. New approach using different brazing alloy and plating steel member with nickel resolves problem. Process must be carried out in inert atmosphere.

  5. Effective diffusion of confined active Brownian swimmers.

    PubMed

    Sandoval, Mario; Dagdug, Leornardo

    2014-12-01

    We theoretically find the effect of confinement and thermal fluctuations on the diffusivity of a spherical active swimmer moving inside a two-dimensional narrow cavity of general shape. The explicit formulas for the effective diffusion coefficient of a swimmer moving inside two particular cavities are presented. We also compare our analytical results with Brownian dynamics simulations and we obtain excellent agreement. PMID:25615133

  6. Laser activated diffuse discharge switch

    DOEpatents

    Christophorou, Loucas G.; Hunter, Scott R.

    1988-01-01

    The invention is a gas mixture for a diffuse discharge switch which is capable of changing from a conducting state to an insulating state in the presence of electrons upon the introduction of laser light. The mixture is composed of a buffer gas such as nitrogen or argon and an electron attaching gas such as C.sub.6 H.sub.5 SH, C.sub.6 H.sub.5 SCH.sub.3, CH.sub.3 CHO and CF.sub.3 CHO wherein the electron attachment is brought on by indirect excitation of molecules to long-lived states by exposure to laser light.

  7. Diffusion in active suspension of microswimmers

    NASA Astrophysics Data System (ADS)

    Climent, Eric; Delmotte, Blaise; Plouraboue, Franck; Keaveny, Eric; Martin, Matthieu; Rafai, Salima; Peyla, Philippe; Bertin, Eric; IMFT Team; IC Team; LiPhy Team

    2015-11-01

    The presence of microswimmers in a fluid generates flow agitation due to multi-body hydrodynamic interactions. This agitation of the fluid leads to random trajectories of passive tracers particles and the swimmers themselves, and from a macroscopic point view, it can be interpreted as a diffusive mechanism. By means of experiments (videomicroscopy of suspensions of chlamydomonas reinhardtii)and numerical simulations (Stokesian fluid populated with squirmers), we investigate the evolution of the effective diffusion coefficient when the volumetric concentration of the active suspension varies. By comparing the experimental and numerical results, we quantify the role of active swimming on the measured diffusion and identify the physical mechanisms that lead to diffusion enhancement. Our results aim to provide a better understanding of how swimming organisms affect micron-scale transport in the environment.

  8. Silver-hafnium braze alloy

    DOEpatents

    Stephens, Jr., John J.; Hosking, F. Michael; Yost, Frederick G.

    2003-12-16

    A binary allow braze composition has been prepared and used in a bonded article of ceramic-ceramic and ceramic-metal materials. The braze composition comprises greater than approximately 95 wt % silver, greater than approximately 2 wt % hafnium and less than approximately 4.1 wt % hafnium, and less than approximately 0.2 wt % trace elements. The binary braze alloy is used to join a ceramic material to another ceramic material or a ceramic material, such as alumina, quartz, aluminum nitride, silicon nitride, silicon carbide, and mullite, to a metal material, such as iron-based metals, cobalt-based metals, nickel-based metals, molybdenum-based metals, tungsten-based metals, niobium-based metals, and tantalum-based metals. A hermetic bonded article is obtained with a strength greater than 10,000 psi.

  9. Vertical diffusivities of active and passive tracers

    NASA Astrophysics Data System (ADS)

    Canuto, V. M.; Cheng, Y.; Howard, A. M.

    The climate models that include a carbon-cycle need the vertical diffusivity of a passive tracer. Since an expression for the latter is not available, it has been common practice to identify it with that of salt. The identification is questionable since T, S are active, not passive tracers. We present the first derivation of the diffusivity of a passive tracer in terms of Ri (Richardson number) and R ρ (density ratio, ratio of salinity over temperature z-gradients). The following results have emerged: The passive tracer diffusivity is an algebraic function of Ri, R ρ. In doubly stable regimes (DS, ∂ T/∂z > 0, ∂S/∂ z < 0), the passive scalar diffusivity is nearly the same as that of salt/heat for any values of R ρ < 0 and Ri > 0. In DC regimes (diffusive convection, ∂ T/∂ z < 0, ∂ S/∂ z < 0, R ρ > 1), the passive scalar diffusivity is larger than that of salt. At Ri = O(1), it can be more than twice as large. In SF regimes (salt fingers, ∂ T/∂ z > 0, ∂ S/∂ z > 0, R ρ < 1), the passive scalar diffusivity is smaller than that of salt. At Ri = O(1), it can be less than half of it. The passive tracer diffusivity predicted at the location of NATRE (North Atlantic Tracer Release Experiment) is discussed. Perhaps the most relevant conclusion is that the common identification of the tracer diffusivity with that of salt is valid only in DS regimes. In the Southern Ocean, where there is the largest CO 2 absorption, the dominant regime is diffusive convection discussed in (c) above.

  10. Vertical Diffusivities of Active and Passive Tracers

    NASA Technical Reports Server (NTRS)

    Canuto, V. M.; Cheng, Y.; Howard, A. M.

    2010-01-01

    The climate models that include a carbon-cycle need the vertical diffusivity of a passive tracer. Since an expression for the latter is not available, it has been common practice to identify it with that of salt. The identification is questionable since T, S are active, not passive tracers. We present the first derivation of the diffusivity of a passive tracer in terms of Ri (Richardson number) and Rq (density ratio, ratio of salinity over temperature z-gradients). The following results have emerged: (a) The passive tracer diffusivity is an algebraic function of Ri, Rq. (b) In doubly stable regimes (DS, partial derivative of T with respect to z > 0, partial derivative of S with respect to z < 0), the passive scalar diffusivity is nearly the same as that of salt/heat for any values of Rq < 0 and Ri > 0. (c) In DC regimes (diffusive convection, partial derivative of T with respect to z < 0, partial derivative of S with respect to z < 0, Rq > 1), the passive scalar diffusivity is larger than that of salt. At Ri = O(1), it can be more than twice as large. (d) In SF regimes (salt fingers, partial derivative of T with respect to z > 0, partial derivative of S with respect to z > 0, Rq < 1), the passive scalar diffusivity is smaller than that of salt. At Ri = O(1), it can be less than half of it. (e) The passive tracer diffusivity predicted at the location of NATRE (North Atlantic Tracer Release Experiment) is discussed. (f) Perhaps the most relevant conclusion is that the common identification of the tracer diffusivity with that of salt is valid only in DS regimes. In the Southern Ocean, where there is the largest CO2 absorption, the dominant regime is diffusive convection discussed in (c) above.

  11. The Effect of Braze Interlayer Thickness on the Mechanical Strength of Alumina Brazed with Ag-CuO Braze Alloys

    SciTech Connect

    Erskine, Kevin M.; Meier, Alan; Joshi, Vineet V.; Pilgrim, Steven M.

    2014-12-01

    The effect of braze interlayer thickness on the strength of alumina brazed with silver-copper oxide reactive air braze (RAB) alloys was evaluated using a four point bend test configuration. The brazed samples had an average fracture strength of 180 MPa or approximately 60 percent of the average monolithic alumina strength. The joint strength values obtained exceeded the yield strength and ultimate tensile strength of the silver interlayer indicating strong ceramic to metal adhesion and the development of a triaxial stress state in the braze interlayer. The average fracture strength was relatively constant (190 ± 60 MPa) in the thickness range of 0.030 mm to 0.230 mm for all test conditions. The braze fracture strength then decreased down to 100 ± 30 MPa as the braze thickness increased from 0.230 mm to 0.430 mm indicating a loss of triaxial constraint with increasing interlayer thickness. In addition, four different fracture modes were observed.

  12. INVESTIGATION OF A NOVEL AIR BRAZING COMPOSITION FOR HIGH-TEMPERATURE, OXIDATION-RESISTANT CERAMIC JOINING

    SciTech Connect

    Weil, K. Scott; Hardy, John S.; Darsell, Jens T.

    2004-01-30

    One of the challenges in developing a useful ceramic joining technique is in producing a joint that offers good strength under high temperature and highly oxidizing operating conditions. Unfortunately many of the commercially available active metal ceramic brazing alloys exhibit oxidation behaviors which are unacceptable for use in a high temperature application. We have developed a new approach to ceramic brazing, referred to as air brazing, that employs an oxide wetting agent dissolved in a molten noble metal solvent, in this case CuO in Ag, such that acceptable wetting behavior occurs on a number of ceramic substrates. In an effort to explore how to increase the operating temperature of this type of braze, we have investigated the effect of ternary palladium additions on the wetting characteristics of our standard Ag-CuO air braze composition

  13. Weld-brazing - a new joining process. [combination resistance spot welding and brazing of titanium alloys

    NASA Technical Reports Server (NTRS)

    Bales, T. T.; Royster, D. M.; Arnold, W. E., Jr.

    1972-01-01

    A joining process designated weld brazing which combines resistance spot welding and brazing has been developed. Resistance spot welding is used to position and align the parts as well as to establish a suitable faying surface gap for brazing. Fabrication is then completed by capillary flow of the braze alloy into the joint. The process has been used successfully to fabricate Ti-6Al-4V titanium alloy joints using 3003 aluminum braze alloy. Test results obtained on single overlap and hat-stiffened structural specimens show that weld brazed joints are superior in tensile shear, stress rupture, fatigue, and buckling than joint fabricated by spotwelding or brazing. Another attractive feature of the process is that the brazed joints is hermetically sealed by the braze material.

  14. Stress level evaluation of thin films under thermal loading from a brazing process

    SciTech Connect

    Wang, Z.; Kuzay, T.M.

    1996-06-01

    X-ray front end beamline windows are made of thin beryllium foil that is commonly brazed or diffusion bonded onto a copper frame. In the brazing process, due to differences in the thermal expansion coefficient of the beryllium and copper materials, the beryllium film ends up in a state of very high level compression stress after cooling from 700{degrees}C (the brazing temperature) to room temperature. This makes the thin Be foil deform into a dome-shaped structure due to the usual asymmetrical geometry of the window. This paper studies the brazing process using a finite element method and explains the reason for such phenomena. Recommendations are offered for possible improvement in the bonding process of beryllium to the window block.

  15. Determining Enzyme Activity by Radial Diffusion

    ERIC Educational Resources Information Center

    Davis, Bill D.

    1977-01-01

    Discusses advantages of radial diffusion assay in determining presence of enzyme and/or rough approximation of amount of enzyme activities. Procedures are included for the preparation of starch-agar plates, and the application and determination of enzyme. Techniques using plant materials (homogenates, tissues, ungerminated embryos, and seedlings)…

  16. Simulation based analysis of laser beam brazing

    NASA Astrophysics Data System (ADS)

    Dobler, Michael; Wiethop, Philipp; Schmid, Daniel; Schmidt, Michael

    2016-03-01

    Laser beam brazing is a well-established joining technology in car body manufacturing with main applications in the joining of divided tailgates and the joining of roof and side panels. A key advantage of laser brazed joints is the seam's visual quality which satisfies highest requirements. However, the laser beam brazing process is very complex and process dynamics are only partially understood. In order to gain deeper knowledge of the laser beam brazing process, to determine optimal process parameters and to test process variants, a transient three-dimensional simulation model of laser beam brazing is developed. This model takes into account energy input, heat transfer as well as fluid and wetting dynamics that lead to the formation of the brazing seam. A validation of the simulation model is performed by metallographic analysis and thermocouple measurements for different parameter sets of the brazing process. These results show that the multi-physical simulation model not only can be used to gain insight into the laser brazing process but also offers the possibility of process optimization in industrial applications. The model's capabilities in determining optimal process parameters are exemplarily shown for the laser power. Small deviations in the energy input can affect the brazing results significantly. Therefore, the simulation model is used to analyze the effect of the lateral laser beam position on the energy input and the resulting brazing seam.

  17. Effective diffusion of confined active Brownian swimmers

    NASA Astrophysics Data System (ADS)

    Sandoval, Mario; Dagdug, Leonardo

    2014-11-01

    We find theoretically the effect of confinement and thermal fluctuations, on the diffusivity of a spherical active swimmer moving inside a two-dimensional narrow cavity of general shape. The explicit formulas for the effective diffusion coefficient of a swimmer moving inside two particular cavities are presented. We also compare our analytical results with Brownian Dynamics simulations and we obtain excellent agreement. L.D. thanks Consejo Nacional de Ciencia y Tecnologia (CONACyT) Mexico, for partial support by Grant No. 176452. M. S. thanks CONACyT and Programa de Mejoramiento de Profesorado (PROMEP) for partially funding this work under Grant No. 103.5/13/6732.

  18. Experimental study of W-Eurofer laser brazing for divertor application

    NASA Astrophysics Data System (ADS)

    Munez, C. J.; Garrido, M. A.; Rams, J.; Ureña, A.

    2011-11-01

    This work can be considered as a preliminary evaluation of the potential of laser brazing for joining tungsten based alloys to reduced activation ferritic-martensitic steels (Eurofer). Brazing of tungsten and EUROFER alloys using a 55Ni-45Ti alloy as a brazer and a high power diode laser (HPDL) as a power source has been investigated. The brazed joints showed solidified pools with good superficial aspect and a high degree of wettability with the both parent sheets, presumably because of the active effect of titanium. Metallurgical brazeability was investigated and nanoindentation measurements were done to evaluate local hardening and stiffness effects associated to dilution phenomena.

  19. Diffusion of torqued active Brownian particles

    NASA Astrophysics Data System (ADS)

    Sevilla, Francisco J.

    An analytical approach is used to study the diffusion of active Brownian particles that move at constant speed in three-dimensional space, under the influence of passive (external) and active (internal) torques. The Smoluchowski equation for the position distribution of the particles is obtained from the Kramer-Fokker-Planck equation corresponding to Langevin equations for active Brownian particles subject to torques. In addition of giving explicit formulas for the mean square-displacement, the non-Gaussian behavior is analyzed through the kurtosis of the position distribution that exhibits an oscillatory behavior in the short-time limit. FJS acknowledges support from PAPIIT-UNAM through the grant IN113114

  20. Competitive Wetting in Active Brazes

    SciTech Connect

    Chandross, Michael Evan

    2014-05-01

    We found that the wetting and spreading of molten filler materials (pure Al, pure Ag, and AgAl alloys) on a Kovar ™ (001) substrate was studied with molecular dynamics simulations. A suite of different simulations was used to understand the effects on spreading rates due to alloying as well as reactions with the substrate. Moreover, the important conclusion is that the presence of Al in the alloy enhances the spreading of Ag, while the Ag inhibits the spreading of Al.

  1. Brazing of beryllium for structural applications

    NASA Technical Reports Server (NTRS)

    Vogan, J. W.

    1972-01-01

    Progress made in fabricating a beryllium compression tube structure and a stiffened beryllium panel. The compression tube was 7.6cm in diameter and 30.5cm long with titanium end fittings. The panel was 203cm long and stiffened with longitudinal stringers. Both units were assembled by brazing with BAg-18 braze alloy. The detail parts were fabricated by hot forming 0.305cm beryllium sheet and the brazing parameters established.

  2. Fluxless Brazing of Large Structural Panels

    NASA Technical Reports Server (NTRS)

    Beuyukian, C. S.

    1982-01-01

    Fluxless brazing is used in fabricating aluminum structural panels that withstand high internal pressure. Aluminum sheet of structural thickness with 4045 aluminum/silicon-braze-alloy cladding is brazed to corrugated "fin stock" having channels 0.001 inch (0.03mm) high by same width. Process is carried out in an inert (argon) atmosphere in a retort furnace. Filler bars are used in some channels to prevent fin stock from collapsing as pressure is applied.

  3. Brazing Inconel 625 Using the Copper Foil

    NASA Astrophysics Data System (ADS)

    Chen, Wen-Shiang; Wang, Cheng-Yen; Shiue, Ren-Kae

    2013-12-01

    Brazing Inconel 625 (IN-625) using the copper foil has been investigated in this research. The brazed joint is composed of nanosized CrNi3 precipitates and Cr/Mo/Nb/Ni quaternary compound in the Cu/Ni-rich matrix. The copper filler 50 μm in thickness is enough for the joint filling. However, the application of Cu foil 100 μm in thickness has little effect on the shear strength of the brazed joint. The specimen brazed at 1433 K (1160 °C) for 1800 seconds demonstrates the best shear strength of 470 MPa, and its fractograph is dominated by ductile dimple fracture with sliding marks. Decreasing the brazing temperature slightly decreases the shear strength of the brazed joint due to the presence of a few isolated solidification shrinkage voids smaller than 15 μm. Increasing the brazing temperature, especially for the specimen brazed at 1473 K (1200 °C), significantly deteriorates the shear strength of the joint below 260 MPa because of coalescence of isothermal solidification shrinkage voids in the joint. The Cu foil demonstrates potential in brazing IN-625 for industrial application.

  4. Thermal resilient multiple jaw braze fixture

    DOEpatents

    Ney, Robert; Perrone, Alex J.

    1995-07-11

    A braze fixture has side walls forming a cavity with an opening to receive a stack of parts to be brazed. Sidewalls of the housing have a plurality of bearing receiving openings into which bearing rods or jaws are inserted to align the stacked elements of the workpiece. The housing can also have view ports to allow a visual check of the alignment. Straps or wires around the fixture are selected to have thermal characteristics similar to the thermal characteristics of the workpiece undergoing brazing. The straps or wires make physical contact with the bearing rods thereby causing bearing rods to maintain the workpiece in proper alignment throughout the entire brazing cycle.

  5. Susceptor heating device for electron beam brazing

    DOEpatents

    Antieau, Susan M.; Johnson, Robert G. R.

    1999-01-01

    A brazing device and method are provided which locally apply a controlled amount of heat to a selected area, within a vacuum. The device brazes two components together with a brazing metal. A susceptor plate is placed in thermal contact with one of the components. A serrated pedestal supports the susceptor plate. When the pedestal and susceptor plate are in place, an electron gun irradiates an electron beam at the susceptor plate such that the susceptor plate is sufficiently heated to transfer heat through the one component and melt the brazing metal.

  6. Mechanical design of ceramic beam tube braze joints for NOvA kicker magnets

    SciTech Connect

    Ader, C.R.; Reilly, R.E.; Wilson, J.H.; /Fermilab

    2010-05-01

    The NO?A Experiment will construct a detector optimized for electron neutrino detection in the existing NuMI neutrino beam. The NuMI beam line is capable of operating at 400 kW of primary beam power and the upgrade will allow up to 700 kW. Ceramic beam tubes are utilized in numerous kicker magnets in different accelerator rings at Fermi National Accelerator Laboratory. Kovar flanges are brazed onto each beam tube end, since kovar and high alumina ceramic have similar expansion curves. The tube, kovar flange, end piece, and braze foil alloy brazing material are stacked in the furnace and then brazed. The most challenging aspect of fabricating kicker magnets in recent years have been making hermetic vacuum seals on the braze joints between the ceramic and flange. Numerous process variables can influence the robustness of conventional metal/ceramic brazing processes. The ceramic-filler metal interface is normally the weak layer when failure does not occur within the ceramic. Differences between active brazing filler metal and the moly-manganese process will be discussed along with the applicable results of these techniques used for Fermilab production kicker tubes.

  7. Vacuum brazing beryllium to Monel

    SciTech Connect

    Glenn, T.G.; Grotsky, V.K.; Keller, D.L.

    1982-10-01

    The tensile strength of beryllium to Monel vacuum furnace brazed joints was studied. The filler used was the 72% Ag-28%Cu(BAg-8) alloy. The strength of these joints, which require the use of a titanium hydride powder or physical vapor deposited titanium wetting agent on the beryllium, was found to approach the yield strength of the base metals. Strength was found to be reduced by the interaction of increased titanium hydride quantity and brazing time. Metallographic and scanning electron microscope (SEM) studies correlated these effects with microstructure. The formation of the brittle copper-beryllium delta phase was found to require conditions of high brazing temperature and the presence of a reservoir of the copper-containing filler such as found in fillet areas. Two other filler metals: pure silver, and a 60% Ag-30% Cu-10%Sn (BAg-17) alloy were shown to be acceptable alternatives to the BAg-8 alloy in cases where the filler metal can be preplaced between the base metal surfaces.

  8. Weld-brazing of titanium. [resistance spot welding combined with brazing

    NASA Technical Reports Server (NTRS)

    Bales, T. T.; Royster, D. M.; Arnold, W. E., Jr.

    1973-01-01

    A joining process, designated weld-brazing, which combines resistance spot-welding and brazing has been developed at the NASA Langley Research Center. Resistance spot-welding is employed to position and aline the parts and to establish a suitable faying surface gap for brazing and contributes to the integrity of the joint. Brazing enhances the properties of the joint and reduces the stress concentrations normally associated with spotwelds. Ti-6Al-4V titanium alloy joints have been fabricated using 3003 aluminum braze both in a vaccum furnace and in a retort containing an inert gas environment.

  9. Brazed Joints Design and Allowables: Discuss Margins of Safety in Critical Brazed Structures

    NASA Technical Reports Server (NTRS)

    FLom, Yury

    2009-01-01

    This slide presentation tutorial discusses margins of safety in critical brazed structures. It reviews: (1) the present situation (2) definition of strength (3) margins of safety (4) design allowables (5) mechanical testing (6) failure criteria (7) design flowchart (8) braze gap (9) residual stresses and (10) delayed failures. This presentation addresses the strength of the brazed joints, the methods of mechanical testing, and our ability to evaluate the margins of safety of the brazed joints as it applies to the design of critical and expensive brazed assemblies.

  10. Laser beam brazing of car body and aircraft components

    SciTech Connect

    Haferkamp, H.; Kreutzburg, K.

    1994-12-31

    At present, when brazing car body components for the automotive industry, manual flame brazing is mostly used. The advantage of brazing as compared to welding, is the lower hardness of the braze metal, making postmachining easier. But manual flame brazing also shows several main disadvantages, such as pores within the seam and a high thermal influence on the workpiece. Therefore, investigations on laser beam brazing concerning the reduction of the technological and economical disadvantages of the flame brazing process were carried out. Laser beam brazing of aluminum alloys is also a main topic of this presentation. The fundamental research in brazing mild steel was done on lap joints. The investigations about brazing mild steel and aluminum alloys have demonstrated that it is possible to braze these metals using laser beam radiation. Laser beam brazing of 3-dimensional mild steel components requires a special program for the brazing sequence, and new specifications in design and fabrication. But comparing seams made by laser beam brazing to manual flame brazing show that there are advantages to using the automated laser process. Laser beam brazing of aluminum alloys makes it possible to join metals with poor brazeability, although brazing conditions lead to a slight melting of the gap sides.

  11. Supergranule Diffusion and Active Region Decay

    NASA Technical Reports Server (NTRS)

    Hathaway, David H.; Choudhary, Debi Prasad

    2004-01-01

    Models of the Sun's magnetic dynamo include turbulent diffusion to parameterize the effects of convective motions on the evolution of the Sun's magnetic field. Supergranules are known to dominate the evolution of the surface magnetic field structure as evidenced by the structure of both the active and quiet magnetic network. However, estimates for the dif hivity attributed to su perymules differ by an order of magnitude from about 100 km sup2/s to more than 1000 km sup2/s. We examine this question of the e i v i t y using three merent approaches. 1) We study the decay of more than 30,000 active regions by determining the rate of change in the sunspot area of each active region from day-to-day. 2) We study the decay of a single isolated active region near the time of solar minimum by examining the magnetic field evolution over five solar rotations fiom SOHOMDI magnetograms obtained at 96-minute intervals. 3) We study the characteristics of supergranules that influence the estimates of their diffusive properties - flow speeds and lifetimes as functions of size - fiom SOHO/MDI Dopplergrams.

  12. Dissimilar laser brazing of h-BN and WC-Co alloy in Ar atmosphere without evacuation process

    NASA Astrophysics Data System (ADS)

    Sechi, Y.; Nagatsuka, K.; Nakata, K.

    2012-08-01

    Laser brazing with Ti as an active element in Ag-Cu alloy braze metal has been successfully applied to dissimilar joining of h-BN and WC-Co alloy in Ar (99.999% purity) gas flow atmosphere without any evacuation process. Good wettability of the braze metal with h-BN and WC-Co alloy were confirmed by the observation and structural analysis of the interface by electron probe micro-analysis and scanning acoustic microscopy. The oxidation of titanium was not observed and this showed that the laser brazing with titanium as an active element in braze metal could be performed even in an Ar gas flow atmosphere without an evacuation process using a high-vacuum furnace.

  13. Braze alloys for high temperature service

    NASA Technical Reports Server (NTRS)

    Lindberg, R. A.; Mckisson, R. L.; Erwin, G., Jr.

    1973-01-01

    Two groups of refractory metal compositions have been developed that are very useful as high temperature brazing alloys for sealing between ceramic and metal parts. Each group consists of various compositions of three selected refractory metals which, when combined, have characteristics required of good braze alloys.

  14. Automatic-Control System for Safer Brazing

    NASA Technical Reports Server (NTRS)

    Stein, J. A.; Vanasse, M. A.

    1986-01-01

    Automatic-control system for radio-frequency (RF) induction brazing of metal tubing reduces probability of operator errors, increases safety, and ensures high-quality brazed joints. Unit combines functions of gas control and electric-power control. Minimizes unnecessary flow of argon gas into work area and prevents electrical shocks from RF terminals. Controller will not allow power to flow from RF generator to brazing head unless work has been firmly attached to head and has actuated micro-switch. Potential shock hazard eliminated. Flow of argon for purging and cooling must be turned on and adjusted before brazing power applied. Provision ensures power not applied prematurely, causing damaged work or poor-quality joints. Controller automatically turns off argon flow at conclusion of brazing so potentially suffocating gas does not accumulate in confined areas.

  15. Braze alloy spreading on steel

    NASA Technical Reports Server (NTRS)

    Siewert, T. A.; Heine, R. W.; Lagally, M. G.

    1978-01-01

    Scanning electron microscopy (SEM) and Auger electron microscopy (AEM) were employed to observe elemental surface decomposition resulting from the brazing of a copper-treated steel. Two types of steel were used for the study, stainless steel (treated with a eutectic silver-copper alloy), and low-carbon steel (treated with pure copper). Attention is given to oxygen partial pressure during the processes; a low enough pressure (8 x 10 to the -5th torr) was found to totally inhibit the spreading of the filler material at a fixed heating cycle. With both types of steel, copper treatment enhanced even spreading at a decreased temperature.

  16. Structure of Vacuum Brazed BNi-5 Joint of Inconel 718

    NASA Astrophysics Data System (ADS)

    Grushko, B.; Weiss, B. Z.

    1984-04-01

    Structural investigations of the brazed joint of Inconel 718 with BNi-5 filler metal were carried out on specimens with geometries simulating a real joint. Three identification methods applied in parallel were used. Fused and solidified filler metal showed the presence of at least four microstructural components: the dominant γ-solid solution, two binary eutectics (G phase + γ) and (θ-phase + γ @#@), and prismatic objects identified as cr-phase. The influence of brazing time and temperature was studied with specimens heated in accordance with three different thermal regimes. The Ni-base γ-phase solidifies in dendritic form and contains Cr, Fe, Nb, and Mo, the concentrations of which are dependent on the thermal regime and on the distance from the former liquid-solid interface. The intermetallics (G, 0) and the matrix form binary and ternary eutectics. In overheated brazed joints the filler metal penetrates into the grain boundaries of the base metal, resulting in the formation of new phases. The dominant phase was identified as a hexagonal Laves phase (λ,). The diffusion zone in the base metal can be divided into two subregions. In subregion I the precipitating phase is a Nb-rich G-phase, while in subregion II, the depth of which can be directly related to the width of the gap, preferentially oriented carbides of Nb and Ti are formed. The phase formation in the BNi-5 brazing of Inconel 718 may be described by a quasi-quarternary diagram on the Ni-Cr-Nb-Si system.

  17. 46 CFR 56.75-20 - Brazing qualification.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 46 Shipping 2 2010-10-01 2010-10-01 false Brazing qualification. 56.75-20 Section 56.75-20 Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) MARINE ENGINEERING PIPING SYSTEMS AND APPURTENANCES Brazing § 56.75-20 Brazing qualification. (a) The qualification of the performance of brazers and brazing operators shall be in...

  18. Surface preparation for high purity alumina ceramics enabling direct brazing in hydrogen atmospheres

    DOEpatents

    Cadden, Charles H.; Yang, Nancy Yuan Chi; Hosking, Floyd M.

    2001-01-01

    The present invention relates to a method for preparing the surface of a high purity alumina ceramic or sapphire specimen that enables direct brazing in a hydrogen atmosphere using an active braze alloy. The present invention also relates to a method for directly brazing a high purity alumina ceramic or sapphire specimen to a ceramic or metal member using this method of surface preparation, and to articles produced by this brazing method. The presence of silicon, in the form of a SiO.sub.2 -containing surface layer, can more than double the tensile bond strength in alumina ceramic joints brazed in a hydrogen atmosphere using an active Au-16Ni-0.75 Mo-1.75V filler metal. A thin silicon coating applied by PVD processing can, after air firing, produce a semi-continuous coverage of the alumina surface with a SiO.sub.2 film. Room temperature tensile strength was found to be proportional to the fraction of air fired surface covered by silicon-containing films. Similarly, the ratio of substrate fracture versus interface separation was also related to the amount of surface silicon present prior to brazing. This process can replace the need to perform a "moly-manganese" metallization step.

  19. Tensile fracture characterization of braze joined copper-to-CFC coupon assemblies

    NASA Astrophysics Data System (ADS)

    Trester, P. W.; Valentine, P. G.; Johnson, W. R.; Chin, E.; Reis, E. E.; Colleraine, A. P.

    1996-10-01

    A vacuum brazing process was used to join a broad spectrum of carbon-fiber reinforced carbon matrix composite (CFC) materials, machined into cylindrical coupons, between coupons of oxygen-free copper, the braze alloy was a copper-base alloy which contained only low activation elements (Al, Si, and Ti) relative to a titanium baseline specification. This demonstration was of particular importance for plasma facing components (PFCs) under design for use in the Tokamak Physics Experiment (TPX); the braze investigation was conducted by General Atomics for the Princeton Plasma Physics Laboratory. A tensile test of each brazed assembly was conducted. The results from the braze processing, testing, and fracture characterization studies of this reporting support the use of CFC's of varied fiber architecture and matrix processing in PFC designs for TPX. Further, the copper braze alloy investigated is now considered to be a viable candidate for a low-activation bond design. The prediction of plasma disruption-induced loads on the PFCs in TPX requires that joint strength between CFC tiles and their copper substrate be considered in design analysis and CFC selection.

  20. Characterization of Brazed Joints of C-C Composite to Cu-clad-Molybdenum

    NASA Technical Reports Server (NTRS)

    Singh, M.; Asthana, R.

    2008-01-01

    Carbon-carbon composites with either pitch+CVI matrix or resin-derived matrix were joined to copper-clad molybdenum using two active braze alloys, Cusil-ABA (1.75% Ti) and Ticusil (4.5% Ti). The brazed joints revealed good interfacial bonding, preferential precipitation of Ti at the composite/braze interface, and a tendency toward de-lamination in resin-derived C-C composite due to its low inter-laminar shear strength. Extensive braze penetration of the inter-fiber channels in the pitch+CVI C-C composites was observed. The relatively low brazing temperatures (<950 C) precluded melting of the clad layer and restricted the redistribution of alloying elements but led to metallurgically sound composite joints. The Knoop microhardness (HK) distribution across the joint interfaces revealed sharp gradients at the Cu-clad-Mo/braze interface and higher hardness in Ticusil (approx.85-250 HK) than in Cusil-ABA (approx.50-150 HK). These C-C/Cu-clad-Mo joints with relatively low thermal resistance may be promising for thermal management applications.

  1. Failure Assessment Diagram for Titanium Brazed Joints

    NASA Technical Reports Server (NTRS)

    Flom, Yury; Jones, Justin S.; Powell, Mollie M.; Puckett, David F.

    2011-01-01

    The interaction equation was used to predict failure in Ti-4V-6Al joints brazed with Al 1100 filler metal. The joints used in this study were geometrically similar to the joints in the brazed beryllium metering structure considered for the ATLAS telescope. This study confirmed that the interaction equation R(sub sigma) + R(sub Tau) = 1, where R(sub sigma) and R(sub Tau)are normal and shear stress ratios, can be used as conservative lower bound estimate of the failure criterion in ATLAS brazed joints as well as for construction of the Failure Assessment Diagram (FAD).

  2. Direct metal brazing to cermet feedthroughs

    DOEpatents

    Not Available

    1982-07-29

    An improved method for brazing metallic components to a cermet surface in an alumina substrate eliminates the prior art metallized layer over the cermet via and adjoining alumina surfaces. Instead, a nickel layer is applied over the cermet surface only and metallic components are brazed directly to this nickel coated cermet surface. As a result, heretofore unachievable tensile strength joints are produced. In addition, cermet vias with their brazed metal components can be spaced more closely in the alumina substrate because of the elimination of the prior art metallized alumina surfaces.

  3. Direct metal brazing to cermet feedthroughs

    DOEpatents

    Hopper, Jr., Albert C.

    1984-12-18

    An improved method for brazing metallic components to a cermet surface in an alumina substrate eliminates the prior art metallized layer over the cermet via and adjoining alumina surfaces. Instead, a nickel layer is applied over the cermet surface only and metallic components are brazed directly to this nickel coated cermet surface. As a result, heretofore unachievable tensile strength joints are produced. In addition, cermet vias with their brazed metal components can be spaced more closely in the alumina substrate because of the elimination of the prior art metallized alumina surfaces.

  4. Development of brazing process for W-EUROFER joints using Cu-based fillers

    NASA Astrophysics Data System (ADS)

    de Prado, J.; Sánchez, M.; Ureña, A.

    2016-02-01

    A successful joint between W and EUROFER using high temperature brazing technique has been achieved for structural application in future fusion power plants. Cu-based powder alloy mixed with a polymeric binder has been used as filler. Microstructural analysis of the joints revealed that the joint consisted mainly of primary phases and acicular structures in a Cu matrix. Interaction between EUROFER and filler took place at the interface giving rise to several Cu-Ti-Fe rich layers. A loss of hardness at the EUROFER substrate close to the joint due to a diffusion phenomenon during brazing cycle was measured; however, the joints had an adequate shear strength value.

  5. Brazing SiC/SiC Composites to Metals

    NASA Technical Reports Server (NTRS)

    Steffier, Wayne S.

    2004-01-01

    Experiments have shown that active brazing alloys (ABAs) can be used to join SiC/SiC composite materials to metals, with bond strengths sufficient for some structural applications. The SiC/SiC composite coupons used in the experiments were made from polymerbased SiC fiber preforms that were chemical-vapor-infiltrated with SiC to form SiC matrices. Some of the metal coupons used in the experiments were made from 304 stainless steel; others were made from oxygen-free, high-conductivity copper. Three ABAs were chosen for the experiments: two were chosen randomly from among a number of ABAs that were on hand at the time; the third ABA was chosen because its titanium content (1.25 percent) is less than those of the other two ABAs (1.75 and 4.5 percent, respectively) and it was desired to evaluate the effect of reducing the titanium content, as described below. The characteristics of ABAs that are considered to be beneficial for the purpose of joining SiC/SiC to metal include wettability, reactivity, and adhesion to SiC-based ceramics. Prior to further development, it was verified that the three chosen ABAs have these characteristics. For each ABA, suitable vacuum brazing process conditions were established empirically by producing a series of (SiC/SiC)/ABA wetting samples. These samples were then sectioned and subjected to scanning electron microscopy (SEM) and energy-dispersive x-ray spectrometry (EDS) for analysis of their microstructures and compositions. Specimens for destructive mechanical tests were fabricated by brazing of lap joints between SiC/SiC coupons 1/8-in. (.3.2- mm) thick and, variously, stainless steel or copper tabs. The results of destructive mechanical tests and the SEM/EDS analysis were used to guide the development of a viable method of brazing the affected materials.

  6. The diffusion-active permeable reactive barrier

    NASA Astrophysics Data System (ADS)

    Schwarz, Alex O.; Rittmann, Bruce E.

    2010-03-01

    Using the biogeochemical model CCBATCH, which we expanded to include transport processes, we study a novel approach for the treatment of aquifers contaminated with toxic concentrations of metals, the diffusion-active permeable reactive barrier (DAPRB), which is based on generation of sulfide by Sulfate Reducing Bacteria (SRB) as the groundwater moves through a layered treatment zone. In the DAPRB, layers of low conductivity (low-K) containing reactive materials are intercalated between layers of high conductivity (high-K) that transport the groundwater across the barrier. Because diffusion dominates transport in the reactive layers, microbial communities can take advantage there of the chemical-gradient mechanism for protection from toxicants. The ideal sulfidic DAPRB design includes particulate organic matter (POM) and solid sulfate mineral inside the reactive (low-K) layer. This leads to sulfate reduction and the formation of sulfide ligands that complex with toxic metals, such as Zn 2+ in the high-K layer. We perform a theoretical biogeochemical analysis of the ideal configuration of a DAPRB for treatment of Zn-contaminated groundwater. Our analysis using the expanded CCBATCH confirms the gradient-resistance mechanism for bio-protection, with the ZnS bio-sink forming at the intersection of the Zn and sulfide plumes inside the high-K layers of the DAPRB. The detailed DAPRB analysis also shows that total alkalinity and pH distributions are representative footprints of the two key biogeochemical processes taking place, sulfidogenesis and Zn immobilization as sulfide mineral. This is so because these two reactions consume or produce acidic hydrogen and alkalinity. Additionally, because Zn immobilization is due to ZnS mineral precipitation, the ZnS mineral distribution is a good indicator for the bio-sink. Bio-sinks are located for the most part within the high-K layers, and their exact position depends on the relative magnitude of metal and sulfide fluxes. Finally

  7. Compound characterization of laser brazed SiC-steel joints using tungsten reinforced SnAgTi-alloys

    NASA Astrophysics Data System (ADS)

    Südmeyer, I.; Rohde, M.; Fürst, T.

    2010-02-01

    With the help of a CO2-laser (λ = 10.64 μm) Silicon carbide (Trade name: Ekasic-F, Comp: ESK Ceramics) has been brazed to commercial steel (C45E, Matnr. 1.1191) using SnAgTi-filler alloys. The braze pellets were dry pressed based on commercially available powders and polished to a thickness of 300 μm. The SnAgTi-fractions were varied with the objective of improving the compound strength. Furthermore, tungsten reinforced SnAgTi-fillers were examined with regard to the shear strength of the ceramic/steel joints. Polished microsections of SnAgTi-pellets were investigated before brazing in order to evaluate the particle distribution and to detect potential porosities using optical microscopy. The brazing temperature and the influence of the reinforcing particles on the active braze filler were determined by measurements with a differential scanning calorimeter (DSC). After brazing. the ceramic-steel joints were characterized by scanning electron micrographs and EDX-analysis. Finally the mechanical strength of the braze-joints was determined by shear tests.

  8. Photospheric Magnetic Diffusion by Measuring Moments of Active Regions

    NASA Astrophysics Data System (ADS)

    Engell, Alexander; Longcope, D.

    2013-07-01

    Photospheric magnetic surface diffusion is an important constraint for the solar dynamo. The HMI Active Region Patches (HARPs) program automatically identify all magnetic regions above a certain flux. In our study we measure the moments of ARs that are no longer actively emerging and can thereby give us good statistical constraints on photospheric diffusion. We also present the diffusion properties as a function of latitude, flux density, and single polarity (leading or following) within each HARP.

  9. Ultrasonics permits brazing complex stainless steel assembly without flux

    NASA Technical Reports Server (NTRS)

    Baker, W. H.

    1967-01-01

    Ultrasonic vibration of an assembly of stainless steel instrumentation tubes ensures brazing without flux. Vibration with an ultrasonic transducer permits the brazing material to flow down each tube in contact with a seal plug installed in a pressure vessel wall.

  10. Aluminum core structures brazed without use of flux

    NASA Technical Reports Server (NTRS)

    1966-01-01

    Aluminum alloy face sheets are brazed to aluminum alloy honeycomb cores without using corrosive flux by means of one or three methods. The completed brazed structure has the high-strength characteristics of heat treated aluminum alloys.

  11. Refractory metals welded or brazed with tungsten inert gas equipment

    NASA Technical Reports Server (NTRS)

    Wisner, J. P.

    1965-01-01

    Appropriate brazing metals and temperatures facilitate the welding or brazing of base metals with tungsten inert gas equipment. The highest quality bond is obtained when TIG welding is performed in an inert atmosphere.

  12. Tungsten wire and tubing joined by nickel brazing

    NASA Technical Reports Server (NTRS)

    1965-01-01

    Thin tungsten wire and tungsten tubing are brazed together using a contacting coil of nickel wire heated to its melting point in an inert-gas atmosphere. This method is also effective for brazing tungsten to tungsten-rhenium parts.

  13. Surface diffusion activation energy determination using ion beam microtexturing

    NASA Technical Reports Server (NTRS)

    Rossnagel, S. M.; Robinson, R. S.

    1982-01-01

    The activation energy for impurity atom (adatom) surface diffusion can be determined from the temperature dependence of the spacing of sputter cones. These cones are formed on the surface during sputtering while simultaneously adding impurities. The impurities form clusters by means of surface diffusion, and these clusters in turn initiate cone formation. Values are given for the surface diffusion activation energies for various materials on polycrystalline Cu, Al, Pb, Au, and Ni. The values for different impurity species on each of these substrates are approximately independent of impurity species within the experimental uncertainty, suggesting the absence of strong chemical bonding effects on the diffusion.

  14. Braze Process Optimization Involving Conventional Metal/Ceramic Brazing with 50Au-50Cu Alloy

    SciTech Connect

    MALIZIA JR.,LOUIS A.; MEREDITH,KEITH W.; APPEL,DANIEL B.; MONROE,SAUNDRA L.; BURCHETT,STEVEN N.; STEPHENS JR.,JOHN J.

    1999-12-15

    Numerous process variables can influence the robustness of conventional metal/ceramic brazing processes. Experience with brazing of hermetic vacuum components has identified the following parameters as influencing the outcome of hydrogen furnace brazed Kovar{trademark} to metallized alumina braze joints: (a) Mo-Mn metallization thickness, sinter fire temperature and porosity (b) Nil plate purity, thickness, and sinter firing conditions (c) peak process temperature, time above liquidus and (d) braze alloy washer thickness. ASTM F19 tensile buttons are being used to investigate the above parameters. The F19 geometry permits determination of both joint hermeticity and tensile strength. This presentation will focus on important lessons learned from the tensile button study: (A) the position of the Kovar{trademark} interlayer can influence the joint tensile strength achieved--namely, off-center interlayers can lead to residual stress development in the ceramic and degrade tensile strength values. Finite element analysis has been used to demonstrate the expected magnitude in strength degradation as a function of misalignment. (B) Time above liquidus (TAL) and peak temperature can influence the strength and alloying level of the resulting braze joint. Excessive TAL or peak temperatures can lead to overbraze conditions where all of the Ni plate is dissolved. (C) Metallize sinter fire processes can influence the morphology and strength obtained from the braze joints.

  15. Union would facilitate joining of tubing, minimize braze contamination

    NASA Technical Reports Server (NTRS)

    Terril, A. E.

    1966-01-01

    Union assembly provides a fluidtight joint between two lengths of tubing and minimizes introduction of braze contaminants into the tubing. The union contains two brazing preforms separated by a metal ring that serves as a dam for the molten brazing alloy.

  16. Communication: Memory effects and active Brownian diffusion.

    PubMed

    Ghosh, Pulak K; Li, Yunyun; Marchegiani, Giampiero; Marchesoni, Fabio

    2015-12-01

    A self-propelled artificial microswimmer is often modeled as a ballistic Brownian particle moving with constant speed aligned along one of its axis, but changing direction due to random collisions with the environment. Similarly to thermal noise, its angular randomization is described as a memoryless stochastic process. Here, we speculate that finite-time correlations in the orientational dynamics can affect the swimmer's diffusivity. To this purpose, we propose and solve two alternative models. In the first one, we simply assume that the environmental fluctuations governing the swimmer's propulsion are exponentially correlated in time, whereas in the second one, we account for possible damped fluctuations of the propulsion velocity around the swimmer's axis. The corresponding swimmer's diffusion constants are predicted to get, respectively, enhanced or suppressed upon increasing the model memory time. Possible consequences of this effect on the interpretation of the experimental data are discussed. PMID:26646861

  17. Communication: Memory effects and active Brownian diffusion

    NASA Astrophysics Data System (ADS)

    Ghosh, Pulak K.; Li, Yunyun; Marchegiani, Giampiero; Marchesoni, Fabio

    2015-12-01

    A self-propelled artificial microswimmer is often modeled as a ballistic Brownian particle moving with constant speed aligned along one of its axis, but changing direction due to random collisions with the environment. Similarly to thermal noise, its angular randomization is described as a memoryless stochastic process. Here, we speculate that finite-time correlations in the orientational dynamics can affect the swimmer's diffusivity. To this purpose, we propose and solve two alternative models. In the first one, we simply assume that the environmental fluctuations governing the swimmer's propulsion are exponentially correlated in time, whereas in the second one, we account for possible damped fluctuations of the propulsion velocity around the swimmer's axis. The corresponding swimmer's diffusion constants are predicted to get, respectively, enhanced or suppressed upon increasing the model memory time. Possible consequences of this effect on the interpretation of the experimental data are discussed.

  18. Communication: Memory effects and active Brownian diffusion

    SciTech Connect

    Ghosh, Pulak K.; Li, Yunyun; Marchegiani, Giampiero; Marchesoni, Fabio

    2015-12-07

    A self-propelled artificial microswimmer is often modeled as a ballistic Brownian particle moving with constant speed aligned along one of its axis, but changing direction due to random collisions with the environment. Similarly to thermal noise, its angular randomization is described as a memoryless stochastic process. Here, we speculate that finite-time correlations in the orientational dynamics can affect the swimmer’s diffusivity. To this purpose, we propose and solve two alternative models. In the first one, we simply assume that the environmental fluctuations governing the swimmer’s propulsion are exponentially correlated in time, whereas in the second one, we account for possible damped fluctuations of the propulsion velocity around the swimmer’s axis. The corresponding swimmer’s diffusion constants are predicted to get, respectively, enhanced or suppressed upon increasing the model memory time. Possible consequences of this effect on the interpretation of the experimental data are discussed.

  19. ZIRCONIUM-TITANIUM-BERYLLIUM BRAZING ALLOY

    DOEpatents

    Gilliland, R.G.; Patriarca, P.; Slaughter, G.M.; Williams, L.C.

    1962-06-12

    A new and improved ternary alloy is described which is of particular utility in braze-bonding parts made of a refractory metal selected from Group IV, V, and VI of the periodic table and alloys containing said metal as a predominating alloying ingredient. The brazing alloy contains, by weight, 40 to 50 per cent zirconium, 40 to 50 per cent titanium, and the balance beryllium in amounts ranging from 1 to 20 per cent, said alloy having a melting point in the range 950 to 1400 deg C. (AEC)

  20. Effects of Different Braze Materials and Composite Substrates on Composite/Ti Joints

    NASA Technical Reports Server (NTRS)

    Morscher, Gregory N.; Singh, Mrityunjay; Asthana, Rajiv; Shpargel, Tarah

    2007-01-01

    An ever increasing number of applications require robust joining technologies of dissimilar materials. In this study, three types of ceramic composites (C-C, C-SiC, and SiC-SiC) were vacuum brazed to commercially pure Ti using the Cusil-ABA (63 Ag - 35.5 Cu - 1.75 Ti) active metal braze alloy. The study also compared composite specimens as-fabricated and after surface grinding/polishing. A butt-strap tensile shear strength test was used to evaluate the joined structures at room temperature, 270 and 500 C. The elevated temperatures represent possible use temperatures for some heat rejection type applications. Joint strength will be discussed in light of braze wetting and spreading properties, composite properties, and test temperature.

  1. One-step brazing process to join CFC composites to copper and copper alloy

    NASA Astrophysics Data System (ADS)

    Salvo, Milena; Casalegno, Valentina; Rizzo, Stefano; Smeacetto, Federico; Ferraris, Monica; Merola, Mario

    2008-02-01

    The aim of this work is to develop a new single-step brazing technique to join carbon fibre reinforced carbon composite (CFC) to pure copper (Cu) and copper alloy (CuCrZr) for nuclear fusion applications. In order to increase the wettability of CFC by a copper-based brazing alloy containing no active metal, the composite surface was modified by direct reaction with chromium, which forms a carbide layer and allows a large reduction of the contact angle. After the CFC surface modification, the commercial Gemco ® alloy (Cu/Ge) was successfully used to braze CFC to pure copper and pure copper to CuCrZr by the same heat treatment. The shear strength of the CFC/Cu joints measured by single lap shear tests at room temperature was (34 ± 4) MPa, comparable to the values obtained by other joining processes and higher than the intrinsic CFC shear strength.

  2. Effect of Composite Substrates on the Mechanical Behavior of Brazed Joints in Metal-Composite System

    NASA Technical Reports Server (NTRS)

    Singh, M.; Morscher, Gregory N.; Shpargel, Tarah; Asthana, Rajiv

    2006-01-01

    Advanced composite components are being considered for a wide variety of demanding applications in aerospace, space exploration, and ground based systems. A number of these applications require robust integration technologies to join dissimilar materials (metalcomposites) into complex structural components. In this study, three types of composites (C-C, C-SiC, and SiC-SiC) were vacuum brazed to commercially pure Ti using the active metal braze alloy Cusil-ABA (63Ag-35.3Cu-1.75Ti). Composite substrates with as fabricated and polished surfaces were used for brazing. The microstructure and composition of the joint, examined using scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS), showed sound metallurgical bonding in all systems. The butt strap tensile (BST) test was performed on bonded specimens at room and elevated temperatures. Effect of substrate composition, interlaminar properties, and surface roughness on the mechanical properties and failure behavior of joints will be discussed.

  3. Methods to Predict Stresses in Cutting Inserts Brazed Using Iron-Carbon Brazing Alloy

    NASA Astrophysics Data System (ADS)

    Konovodov, V. V.; Valentov, A. V.; Retuynskiy, O. Yu; Esekuev, Sh B.

    2016-04-01

    This work describes a method for predicting residual and operating stresses in a flat-form tool insert made of tungsten free carbides brazed using iron-carbon alloy. According to the studies’ results it is concluded that the recommendations relating to the limitation of a melting point of tool brazing alloys (950-1100°C according to different data) are connected with a negative impact on tools as a composite made of dissimilar materials rather than on hard alloys as a tool material. Due to the cooling process stresses inevitably occur in the brazed joint of dissimilar materials, and these stresses increase with the higher solidification temperature of the brazing alloy.

  4. Gold-nickel-titanium brazing alloy

    DOEpatents

    Mizuhara, Howard

    1995-01-03

    A brazing alloy in accordance with this invention has the following composition, by weight: 91 to 99 gold, 0.5 to 7% nickel; 0.10 to 2% titanium. Alternatively, with palladium present, the composition is as follows, by weight: 83 to 96% gold; 3 to 10% palladium; 0.5 to 5% nickel; 0.10 to 2% titanium.

  5. Gold-nickel-titanium brazing alloy

    DOEpatents

    Mizuhara, Howard

    1990-07-03

    A brazing alloy in accordance with this invention has the following composition, by weight: 91 to 99% gold, 0.5 to 7% nickel; 0.10 to 2% titanium. Alternatively, with palladium present, the composition is as follows, by weight: 83 to 96% gold; 3 to 10% palladium; 0.5 to 5% nickel; 0.10 to 2% titanium.

  6. Nondestructive testing of brazed rocket engine components

    NASA Technical Reports Server (NTRS)

    Adams, C. J.; Hagemaier, D. J.; Meyer, J. A.

    1968-01-01

    Report details study made of nondestructive radiographic, ultrasonic, thermographic, and leak test methods used to inspect and evaluate the quality of the various brazed joints in liquid-propellant rocket engine components and assemblies. Descriptions of some of the unique equipment and methods developed are included.

  7. Brazed bipolar plates for PEM fuel cells

    DOEpatents

    Neutzler, Jay Kevin

    1998-01-01

    A liquid-cooled, bipolar plate separating adjacent cells of a PEM fuel cell comprising corrosion-resistant metal sheets brazed together so as to provide a passage between the sheets through which a dielectric coolant flows. The brazement comprises a metal which is substantially insoluble in the coolant.

  8. Brazed bipolar plates for PEM fuel cells

    DOEpatents

    Neutzler, J.K.

    1998-07-07

    A liquid-cooled, bipolar plate separating adjacent cells of a PEM fuel cell comprises corrosion-resistant metal sheets brazed together so as to provide a passage between the sheets through which a dielectric coolant flows. The brazement comprises a metal which is substantially insoluble in the coolant. 6 figs.

  9. Welding/brazing for Space Station repair

    NASA Technical Reports Server (NTRS)

    Dickinson, David W.; Babel, H. W.; Conaway, H. R.; Hooper, W. H.

    1990-01-01

    Viewgraphs on welding/brazing for space station repair are presented. Topics covered include: fabrication and repair candidates; debris penetration of module panel; welded repair patch; mechanical assembly of utility fluid line; space station utility systems; Soviet aerospace fabrication - an overview; and processes under consideration.

  10. Nickel-chromium-silicon brazing filler metal

    DOEpatents

    Martini, Angelo J.; Gourley, Bruce R.

    1976-01-01

    A brazing filler metal containing, by weight percent, 23-35% chromium, 9-12% silicon, a maximum of 0.15% carbon, and the remainder nickel. The maximum amount of elements other than those noted above is 1.00%.

  11. Thermal and Fluid Flow Brazing Simulations

    SciTech Connect

    HOSKING, FLOYD MICHAEL; GIANOULAKIS,STEVEN E.; GIVLER,RICHARD C.; SCHUNK,P. RANDALL

    1999-12-15

    The thermal response of fixtured parts in a batch-type brazing furnace can require numerous, time-consuming development runs before an acceptable furnace schedule or joint design is established. Powerful computational simulation tools are being developed to minimize the required number of verification experiments, improve furnace throughput, and increase product yields. Typical furnace simulations are based on thermal, fluid flow, and structural codes that incorporate the fundamental physics of the brazing process. The use of massively parallel computing to predict furnace and joint-level responses is presented. Measured and computed data are compared. Temperature values are within 1-270 of the expected peak brazing temperature for different loading conditions. Sensitivity studies reveal that the thermal response is more sensitive to the thermal boundary conditions of the heating enclosure than variability y in the materials data. Braze flow simulations predict fillet geometry and free surface joint defects. Dynamic wetting conditions, interfacial reactions, and solidification structure add a high degree of uncertainty to the flow results.

  12. Brazing of photocathode RF gun structures in Hydrogen atmosphere: Process qualification, effect of brazing on RF properties and vacuum compatibility

    NASA Astrophysics Data System (ADS)

    Kak, Ajay; Kulshreshtha, P.; Lal, Shankar; Kaul, Rakesh; Ganesh, P.; Pant, K. K.; Abhinandan, Lala

    2012-11-01

    In this paper, we report on the development of a brazing process for an ultra-high vacuum (UHV) compatible photocathode RF gun structure developed at our Centre. The choice of brazing alloy and its form, brazing clearance between parts to be joined and the brazing cycle adopted have been qualified through metallographic examination of identical joints on an OFE copper prototype that was cut open after brazing. The quality of brazed joint not only affects the UHV compatibility of the gun, but also influences the RF parameters finally achieved. A 2-D electromagnetic code, SUPERFISH, was used to predict the variation in RF parameters before and after brazing considering actual brazing clearances provided between the parts to be joined. Results obtained from low power RF measurements on the brazed gun structure confirm the integrity of the brazed joints and show good agreement with those predicted by electromagnetic simulations. The brazed gun structure has been leak-tested and pumped down to a vacuum level limited by the vacuum compatibility of the flange-fittings employed in the setup.

  13. Emission measure distribution for diffuse regions in solar active regions

    SciTech Connect

    Subramanian, Srividya; Tripathi, Durgesh; Klimchuk, James A.; Mason, Helen E.

    2014-11-01

    Our knowledge of the diffuse emission that encompasses active regions is very limited. In this paper we investigate two off-limb active regions, namely, AR 10939 and AR 10961, to probe the underlying heating mechanisms. For this purpose, we have used spectral observations from Hinode/EIS and employed the emission measure (EM) technique to obtain the thermal structure of these diffuse regions. Our results show that the characteristic EM distributions of the diffuse emission regions peak at log T = 6.25 and the coolward slopes are in the range 1.4-3.3. This suggests that both low- as well as high-frequency nanoflare heating events are at work. Our results provide additional constraints on the properties of these diffuse emission regions and their contribution to the background/foreground when active region cores are observed on-disk.

  14. Development of the weld-braze joining process

    NASA Technical Reports Server (NTRS)

    Bales, T. T.; Royster, D. M.; Arnold, W. E., Jr.

    1973-01-01

    A joining process, designated weld-brazing, was developed which combines resistance spot welding and brazing. Resistance spot welding is used to position and aline the parts, as well as to establish a suitable faying-surface gap for brazing. Fabrication is then completed at elevated temperature by capillary flow of the braze alloy into the joint. The process was used successfully to fabricate Ti-6Al-4V alloy joints by using 3003 aluminum braze alloy and should be applicable to other metal-braze systems. Test results obtained on single-overlap and hat-stiffened panel specimens show that weld-brazed joints were superior in tensile shear, stress rupture, fatigue, and buckling compared with joints fabricated by conventional means. Another attractive feature of the process is that the brazed joint is hermetically sealed by the braze material, which may eliminate many of the sealing problems encountered with riveted or spot welded structures. The relative ease of fabrication associated with the weld-brazing process may make it cost effective over conventional joining techniques.

  15. Temperature Activated Diffusion of Radicals through Ion Implanted Polymers.

    PubMed

    Wakelin, Edgar A; Davies, Michael J; Bilek, Marcela M M; McKenzie, David R

    2015-12-01

    Plasma immersion ion implantation (PIII) is a promising technique for immobilizing biomolecules on the surface of polymers. Radicals generated in a subsurface layer by PIII treatment diffuse throughout the substrate, forming covalent bonds to molecules when they reach the surface. Understanding and controlling the diffusion of radicals through this layer will enable efficient optimization of this technique. We develop a model based on site to site diffusion according to Fick's second law with temperature activation according to the Arrhenius relation. Using our model, the Arrhenius exponential prefactor (for barrierless diffusion), D0, and activation energy, EA, for a radical to diffuse from one position to another are found to be 3.11 × 10(-17) m(2) s(-1) and 0.31 eV, respectively. The model fits experimental data with a high degree of accuracy and allows for accurate prediction of radical diffusion to the surface. The model makes useful predictions for the lifetime over which the surface is sufficiently active to covalently immobilize biomolecules and it can be used to determine radical fluence during biomolecule incubation for a range of storage and incubation temperatures so facilitating selection of the most appropriate parameters. PMID:26562064

  16. Applying Taguchi Methods To Brazing Of Rocket-Nozzle Tubes

    NASA Technical Reports Server (NTRS)

    Gilbert, Jeffrey L.; Bellows, William J.; Deily, David C.; Brennan, Alex; Somerville, John G.

    1995-01-01

    Report describes experimental study in which Taguchi Methods applied with view toward improving brazing of coolant tubes in nozzle of main engine of space shuttle. Dr. Taguchi's parameter design technique used to define proposed modifications of brazing process reducing manufacturing time and cost by reducing number of furnace brazing cycles and number of tube-gap inspections needed to achieve desired small gaps between tubes.

  17. Evaluation of Brazed Joints Using Failure Assessment Diagram

    NASA Technical Reports Server (NTRS)

    Flom, Yury

    2012-01-01

    Fitness-for service approach was used to perform structural analysis of the brazed joints consisting of several base metal / filler metal combinations. Failure Assessment Diagrams (FADs) based on tensile and shear stress ratios were constructed and experimentally validated. It was shown that such FADs can provide a conservative estimate of safe combinations of stresses in the brazed joints. Based on this approach, Margins of Safety (MS) of the brazed joints subjected to multi-axial loading conditions can be evaluated..

  18. The story of laser brazing technology

    NASA Astrophysics Data System (ADS)

    Hoffmann, Peter; Dierken, Roland

    2012-03-01

    This article gives an overview on the development of laser brazing technology as a new joining technique for car body production. The story starts with fundamental research work at German institutes in 1993, continues with the first implementations in automobile production in 1998, gives examples of applications since then and ends with an outlook. Laser brazing adapted design of joints and boundary conditions for a safe processing are discussed. Besides a better understanding for the sensitivity of the process against joint irregularities and misalignment, the key to successful launch was an advanced system technology. Different working heads equipped with wire feeding device, seam tracking system or tactile sensors for an automated teaching are presented in this paper. Novel laser heads providing a two beam technology will allow improved penetration depth of the filler wire and a more ecological processing by means of energy consumption.

  19. Diffusion of passive particles in active suspensions

    NASA Astrophysics Data System (ADS)

    Mussler, Matthias; Rafai, Salima; John, Thomas; Peyla, Philippe; Wagner, Christian

    2013-11-01

    We study how an active suspension consisting of a definite volume fraction of the microswimmer Chlamydomonas Reinhardtii modifies the Brownian movement of small to medium size microspheres. We present measurements and simulations of trajectories of microspheres with a diameter of 20 μm in suspensions of Chlamydomonas Reinhardtii, a so called ``puller,'' and show that the mean squared displacement of such trajectories consist of parabolic and a linear part. The linear part is due to the hydrodynamic noise of the microswimmers while the parabolic part is a consequence of directed motion events that occur randomly, when a microsphere is transported by a microswimmer on a timescale that is in higher order of magnitude than the Brownian like hydrodynamic interaction. In addition, we theoretically describe this effect with a dimensional analysis that takes the force dipole model used to describe ``puller'' like Chlamydomonas Reinhardtii into account.

  20. Ultrasonic scanning system for inspection of brazed tube joints

    NASA Technical Reports Server (NTRS)

    Haynes, J. L.; Maurer, N. A.

    1972-01-01

    An ultrasonic scanning system used to inspect and evaluate in-place brazed tube joints is considered. The system was designed, developed, and built especially for nondestructive testing and was selected because of its known response to brazing defects not associated with material density changes. The scan system is capable of scanning brazed joints in union, tee, elbow and cross configuration of 3/16-inch through 5/8-inch diameters. It is capable of detecting brazed defects as small as 0.008 by 0.010-inch, which exceeds the 0.015-inch diameter defect resolution required by specification.

  1. Thermal fatigue and oxidation data for alloy/braze combinations

    NASA Technical Reports Server (NTRS)

    Hill, V. L.; Humphreys, V. E.

    1977-01-01

    Thermal fatigue and oxidation data were obtained for 62 brazed specimens of 3 iron-, 3 nickel-, and 1 cobalt-base alloy. Fluidized bed thermal cycling was conducted over the range 740/25 C employing 10 cm long single-edge wedge specimens. Immersion time was always 4 minutes in each bed. Types of test specimens employed in the program include those with brazed overlays on the specimen radius, those butt brazed at midspan and those with a brazed foil overlay on the specimen radius. Of the 18 braze overlay specimens, 5 generated fatigue cracks by 7000 cycles. Thermal cracking of butt brazed specimens occurred exclusively through the butt braze. Of the 23 butt brazed specimens, 7 survived 11,000 thermal cycles without cracking. Only 2 of the 21 foil overlaid specimens exhibiting cracking in 7,000 cycles. Blistering of the foil did occur for 2 alloys by 500 cycles. Oxidation of the alloy/braze combination was limited at the test maximum test temperature of 740 C.

  2. Brazing of copper to stainless steel with a low-silver-content brazing filler metal

    NASA Astrophysics Data System (ADS)

    Fukikoshi, Tatsuya; Watanabe, Yūki; Miyazawa, Yasuyuki; Kanasaki, Fumio

    2014-08-01

    The brazing of copper to stainless steel (SUS304 JIS) was performed using a low- silver-content brazing filler metal, Ag-50Cu, under an Ar gas atmosphere with a conventional furnace, owing to the potential economic benefits of using low-silver-content filler metals. The brazeability of the low-silver-content brazing filler metal to copper and SUS304 was investigated. A good joint was obtained, and a drastic dissolution reaction occurred at the copper side. Molten BAg8 penetrated along the crystal grain boundary of the copper base metal when BAg8 was used as the filler metal. This was caused by the dissolution of Ni from the stainless steel into the molten filler metal. Ag-50Cu, which was investigated in this work, can be used instead of BAg8 filler metal.

  3. Several braze filler metals for joining an oxide-dispersion-strengthened nickel-chromium-aluminum alloy

    NASA Technical Reports Server (NTRS)

    Gyorgak, C. A.

    1975-01-01

    An evaluation was made of five braze filler metals for joining an aluminum-containing oxide dispersion-strengthened (ODS) alloy, TD-NiCrAl. All five braze filler metals evaluated are considered suitable for joining TD-NiCrAl in terms of wettability and flow. Also, the braze alloys appear to be tolerant of slight variations in brazing procedures since joints prepared by three sources using three of the braze filler metals exhibited similar brazing characteristics and essentially equivalent 1100 C stress-rupture properties in a brazed butt-joint configuration. Recommendations are provided for brazing the aluminum-containing ODS alloys.

  4. Development of Brazing Technology for Use in High- Temperature Gas Separation Equipment

    SciTech Connect

    Weil, K.S.; Hardy, J.S.; Kim, J.Y.

    2003-04-23

    The development of high-temperature electrochemical devices such as oxygen and hydrogen separators, fuel gas reformers, solid oxide fuel cells, and chemical sensors is part of a rapidly expanding segment of the solid state technology market. These devices employ an ionic conducting ceramic as the active membrane that establishes the electrochemical potential of the device, either under voltage (i.e. to carry out gas separation) or under chemical gradient (to develop an electrical potential and thereby generate electrical power). Because the device operates under an ionic gradient that develops across the electrolyte, hermiticity across this layer is paramount. That is, not only must this thin ceramic membrane be dense with no interconnected porosity, but it must be connected to the rest of the device, typically constructed from a heat resistant alloy, with a high-temperature, gas-tight seal. A significant engineering challenge in fabricating these devices is how to effectively join the thin electrochemically active membrane to the metallic body of the device such that the resulting seal is hermetic, rugged, and stable during continuous high temperature operation. Active metal brazing is the typical method of joining ceramic and metal engineering components. It employs a braze alloy that contains one or more reactive elements, often titanium, which will chemically reduce the ceramic faying surface and greatly improve its wetting behavior and adherence with the braze. However, recent studies of these brazes for potential use in fabricating high-temperature electrochemical devices revealed problems with interfacial oxidation and subsequent joint failure [1,2]. Specifically, it was found that the introduction of the ceramic electrolyte and/or heat resistant metal substrate dramatically affects the inherent oxidation behavior of the braze, often in a deleterious manner. These conclusions pointed to the need for an oxidation resistant, high-temperature ceramic

  5. Braze Development of Graphite Fiber for Use in Phase Change Material Heat Sinks

    NASA Technical Reports Server (NTRS)

    Quinn, Gregory; Gleason, Brian; Beringer, Woody; Stephen, Ryan

    2010-01-01

    Hamilton Sundstrand (HS), together with NASA Johnson Space Center, developed methods to metallurgically join graphite fiber to aluminum. The goal of the effort was to demonstrate improved thermal conductance, tensile strength and manufacturability compared to existing epoxy bonded techniques. These improvements have the potential to increase the performance and robustness of phase change material heat sinks that use graphite fibers as an interstitial material. Initial work focused on evaluating joining techniques from 4 suppliers, each consisting of a metallization step followed by brazing or soldering of one inch square blocks of Fibercore graphite fiber material to aluminum end sheets. Results matched the strength and thermal conductance of the epoxy bonded control samples, so two suppliers were down-selected for a second round of braze development. The second round of braze samples had up to a 300% increase in strength and up to a 132% increase in thermal conductance over the bonded samples. However, scalability and repeatability proved to be significant hurdles with the metallization approach. An alternative approach was pursued which used nickel and active braze allows to prepare the carbon fibers for joining with aluminum. This approach was repeatable and scalable with improved strength and thermal conductance when compared with epoxy bonding.

  6. Diffusion welding tool

    NASA Technical Reports Server (NTRS)

    Milam, T. B.

    1973-01-01

    Tool allows flat plate diffusion welding to be done in standard brazing furnace. Weld is achieved using high water pressure applied by hand-operated positive-displacement pump. Good welds have been obtained between nickel and nickel-base alloy plates at temperature of 1200 K and water pressure of 13.8 million N/sq m.

  7. Silver-palladium braze alloy recovered from masking materials

    NASA Technical Reports Server (NTRS)

    Cierniak, R.; Colman, G.; De Carlo, F.

    1966-01-01

    Method for recovering powdered silver-palladium braze alloy from an acrylic spray binder and rubber masking adhesive used in spray brazing is devised. The process involves agitation and dissolution of masking materials and recovery of suspended precious metal particles on a filter.

  8. 46 CFR 56.30-30 - Brazed joints.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... Pressure Vessel Code (incorporated by reference; see 46 CFR 56.01-2) are satisfied at the highest... 46 Shipping 2 2012-10-01 2012-10-01 false Brazed joints. 56.30-30 Section 56.30-30 Shipping COAST... Selection and Limitations of Piping Joints § 56.30-30 Brazed joints. (a) General (refer also to subpart...

  9. 46 CFR 56.30-30 - Brazed joints.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... Pressure Vessel Code (incorporated by reference; see 46 CFR 56.01-2) are satisfied at the highest... 46 Shipping 2 2013-10-01 2013-10-01 false Brazed joints. 56.30-30 Section 56.30-30 Shipping COAST... Selection and Limitations of Piping Joints § 56.30-30 Brazed joints. (a) General (refer also to subpart...

  10. 46 CFR 56.30-30 - Brazed joints.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... Pressure Vessel Code (incorporated by reference; see 46 CFR 56.01-2) are satisfied at the highest... 46 Shipping 2 2014-10-01 2014-10-01 false Brazed joints. 56.30-30 Section 56.30-30 Shipping COAST... Selection and Limitations of Piping Joints § 56.30-30 Brazed joints. (a) General (refer also to subpart...

  11. 46 CFR 56.30-30 - Brazed joints.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... Pressure Vessel Code (incorporated by reference; see 46 CFR 56.01-2) are satisfied at the highest... 46 Shipping 2 2010-10-01 2010-10-01 false Brazed joints. 56.30-30 Section 56.30-30 Shipping COAST... Selection and Limitations of Piping Joints § 56.30-30 Brazed joints. (a) General (refer also to subpart...

  12. 46 CFR 56.30-30 - Brazed joints.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... Pressure Vessel Code (incorporated by reference; see 46 CFR 56.01-2) are satisfied at the highest... 46 Shipping 2 2011-10-01 2011-10-01 false Brazed joints. 56.30-30 Section 56.30-30 Shipping COAST... Selection and Limitations of Piping Joints § 56.30-30 Brazed joints. (a) General (refer also to subpart...

  13. Evaluation of Margins of Safety in Brazed Joints

    NASA Technical Reports Server (NTRS)

    Flom, Yury; Wang, Len; Powell, Mollie M.; Soffa, Matthew A.; Rommel, Monica L.

    2009-01-01

    One of the essential steps in assuring reliable performance of high cost critical brazed structures is the assessment of the Margin of Safety (MS) of the brazed joints. In many cases the experimental determination of the failure loads by destructive testing of the brazed assembly is not practical and cost prohibitive. In such cases the evaluation of the MS is performed analytically by comparing the maximum design loads with the allowable ones and incorporating various safety or knock down factors imposed by the customer. Unfortunately, an industry standard methodology for the design and analysis of brazed joints has not been developed. This paper provides an example of an approach that was used to analyze an AlBeMet 162 (38%Be-62%Al) structure brazed with the AWS BAlSi-4 (Al-12%Si) filler metal. A practical and conservative interaction equation combining shear and tensile allowables was developed and validated to evaluate an acceptable (safe) combination of tensile and shear stresses acting in the brazed joint. These allowables are obtained from testing of standard tensile and lap shear brazed specimens. The proposed equation enables the assessment of the load carrying capability of complex brazed joints subjected to multi-axial loading.

  14. Tube dimpling tool assures accurate dip-brazed joints

    NASA Technical Reports Server (NTRS)

    Beuyukian, C. S.; Heisman, R. M.

    1968-01-01

    Portable, hand-held dimpling tool assures accurate brazed joints between tubes of different diameters. Prior to brazing, the tool performs precise dimpling and nipple forming and also provides control and accurate measuring of the height of nipples and depth of dimples so formed.

  15. Split glass tube assures quality in electron beam brazing

    NASA Technical Reports Server (NTRS)

    Kressin, W. J.

    1966-01-01

    Sealed enclosure of heat-resistant glass tubing and silicone rubber molds provide good visibility for electron beam brazing of metal tubes in an inert gas atmosphere. The glass tubing and rubber molds, which are bonded together, are easily applied to and removed from the brazing area by operation of a clamp.

  16. Reactive Boride Brazing on Low-Alloy Automotive Grade Steel

    NASA Astrophysics Data System (ADS)

    Palanisamy, B.; Upadhyaya, A.

    2011-11-01

    Brazing is a widely used process to improve the performance of steels used in automotive applications. The substrate material is often exposed to harsh conditions in these applications and may affect the service life of the component. Reactive boride brazing aims to improve the mechanical properties of the substrate material by forming a ceramic-metal composite coating in a single-step process in situ. In this study, sintered Ancor 4300 low-alloy steel is used as the substrate with chromium-rich braze and chromium-lean braze materials. The mechanical properties of the brazed samples were studied in detail using microindentation hardness measurements and the transverse rupture test. The results indicate that the brazed superlayer has a 10 times higher hardness. There was a significant improvement in the transverse rupture strength of the steel brazed with the chromium-rich boride as compared to the pure substrate material. In an effort to reduce processing time, green compacts of the substrate were also directly brazed and yielded favorable results.

  17. Failure Assessment Diagram for Brazed 304 Stainless Steel Joints

    NASA Technical Reports Server (NTRS)

    Flom, Yory

    2011-01-01

    Interaction equations were proposed earlier to predict failure in Albemet 162 brazed joints. Present study demonstrates that the same interaction equations can be used for lower bound estimate of the failure criterion in 304 stainless steel joints brazed with silver-based filler metals as well as for construction of the Failure Assessment Diagrams (FAD).

  18. Mechanical characterization and modeling of brazed EUROFER-tungsten-joints

    NASA Astrophysics Data System (ADS)

    Chehtov, T.; Aktaa, J.; Kraft, O.

    2007-08-01

    Within the scope of the European fusion power plant study for development of a He-cooled divertor, a tungsten-steel joint has been considered. A preferable joining technique is high temperature brazing. Brazed joints of dissimilar materials suffer from a mismatch in coefficients of thermal expansion. The components of the joint are exposed to mechanical and cyclic thermal loads which give rise to development of high stresses and could lead to failure. Brazed joints of tungsten alloy and ferritic-martensitic steel using different brazing filler materials were studied both experimentally and theoretically. Finite element computations have been performed to calculate the stress distribution and to investigate their evolution within the course of the operational thermal load. Sample joint specimen have been brazed, investigated with respect to their microstructure, and mechanically characterized by performing bend and notched bar impact testing at different temperatures. Some plastic deformation and relatively low impact energies were measured.

  19. Control of Interfacial Reactivity Between ZrB2 and Ni-Based Brazing Alloys

    NASA Astrophysics Data System (ADS)

    Valenza, F.; Muolo, M. L.; Passerone, A.; Cacciamani, G.; Artini, C.

    2012-05-01

    Transition metals diborides (Ti,Zr,Hf)B2 play a key role in applications where stability at extremely high temperatures and damage tolerance are required; however, much research has still to be done to optimize the joining of these materials to themselves or to other high-temperature materials. In this study, the reactivity at the solid-liquid interface between ZrB2 ceramics and Ni-based brazing alloys has been addressed; it is shown how the reactivity and the dissolution of the solid phase can be controlled and even suppressed by adjusting the brazing alloy composition on the basis of thermodynamic calculations. Wetting experiments on ZrB2 ceramics by Ni, Ni-B 17 at.%, and Ni-B 50 at.% were performed at 1500 and 1200 °C by the sessile drop technique. The obtained interfaces were characterized by optical microscopy and SEM-EDS, and interpreted by means of the ad hoc-calculated B-Ni-Zr ternary diagram. A correlation among microstructures, substrate dissolution, shape of the drops, spreading kinetics, and the phase diagram was found. The effect on the interfacial reactivity of Si3Ni4 used as a sintering aid and issues related to Si diffusion into the brazing alloy are discussed as well.

  20. Residual Stress in Brazing of Submicron Al2O3 to WC-Co

    NASA Astrophysics Data System (ADS)

    Grunder, T.; Piquerez, A.; Bach, M.; Mille, P.

    2016-07-01

    This study evaluated the residual stresses induced by brazing and grinding submicron Al2O3, using different methods. Energy dispersive x-ray spectrometry analysis (EDX) of 72Ag-Cu filler and filler/WC-Co interface showed evidence of atomic diffusion and possible formation of titanium oxide layers between the joint and the bonding materials. An analytical model supported by the finite element method (FEM) based on strain determination due to the difference in variation of thermal expansion was used to assess the stress distribution at the coupling interface and in bulk materials. The model took into account the evolution of the Young's modulus and of the thermal expansion with temperature. The model could be used to follow strain and stress evolutions of the bonded materials during the cooling cycle. The maximum stress rose above -300 MPa at the center of the 100 × 100 × 3 mm ceramic plates. The residual stresses on the external surface of ceramic were investigated by x-ray diffraction (XRD) and indentation fracture method (IFM). After brazing and grinding the plate, the principal stresses were 128.1 and 94.9 MPa, and the shear stress was -20.1 MPa. Microscopic examination revealed grain pull-out promoted by the global residual stresses induced by the brazing and grinding processes. The surface stresses evaluated by the different methods were reasonably correlated.

  1. Residual Stress in Brazing of Submicron Al2O3 to WC-Co

    NASA Astrophysics Data System (ADS)

    Grunder, T.; Piquerez, A.; Bach, M.; Mille, P.

    2016-06-01

    This study evaluated the residual stresses induced by brazing and grinding submicron Al2O3, using different methods. Energy dispersive x-ray spectrometry analysis (EDX) of 72Ag-Cu filler and filler/WC-Co interface showed evidence of atomic diffusion and possible formation of titanium oxide layers between the joint and the bonding materials. An analytical model supported by the finite element method (FEM) based on strain determination due to the difference in variation of thermal expansion was used to assess the stress distribution at the coupling interface and in bulk materials. The model took into account the evolution of the Young's modulus and of the thermal expansion with temperature. The model could be used to follow strain and stress evolutions of the bonded materials during the cooling cycle. The maximum stress rose above -300 MPa at the center of the 100 × 100 × 3 mm ceramic plates. The residual stresses on the external surface of ceramic were investigated by x-ray diffraction (XRD) and indentation fracture method (IFM). After brazing and grinding the plate, the principal stresses were 128.1 and 94.9 MPa, and the shear stress was -20.1 MPa. Microscopic examination revealed grain pull-out promoted by the global residual stresses induced by the brazing and grinding processes. The surface stresses evaluated by the different methods were reasonably correlated.

  2. Preliminary results on the development of vacuum-brazed joints for cyrogenic wind tunnel aerofoil models

    SciTech Connect

    Wigley, D.A.; Lawing, P.L.; Sandefur, P.G.

    1982-01-01

    Initial trials carried out at the NASA Langley Research Center in the investigation of cryogenic wind tunnel joint construction demonstrated that diffusion-assisted brazed joints could be formed in 17-4 PH, 15-5 PH, AISI-type 347, and Nitronic 40 stainless steels using electrodeposited copper as the bonding agent. Subsequent work has concentrated on 15-5 PH and Nitronic 40 using thin foils of pure copper and Nicrobraz LM, a commercially available nickel-based alloy containing boron and silicon melting point depressants. This paper summarizes the work carried out to understand and evaluate these bonds and their metallurgical characteristics. The results indicate that a high-strength void-free bond can be formed by the vacuum brazing of stainless steels using copper- and nickel-based filler alloys. The Nitronic 40 brazed joints show strengths in excess of the yield strengths of the parent metal. The poor toughness of 15-5 PH stainless steel at cryogenic temperatures tends to disqualify its use in critical areas of low-temperature aerofoil models.

  3. Flaw Tolerance in Lap Shear Brazed Joints. Part 1

    NASA Technical Reports Server (NTRS)

    Flom, Yury; Wang, Li-Qin

    2003-01-01

    Furnace brazing is a joining process used in the aerospace and other industries to produce strong permanent and hermetic structural joints. As in any joining process, brazed joints have various imperfections and defects. At the present time, our understanding of the influence of the internal defects on the strength of the brazed joints is not adequate. The goal of this 3-part investigation is to better understand the properties and failure mechanisms of the brazed joints containing defects. This study focuses on the behavior of the brazed lap shear joints because of their importance in manufacturing aerospace structures. In Part 1, an average shear strength capability and failure modes of the single lap joints are explored. Stainless steel specimens brazed with pure silver are tested in accordance with the AWS C3.2 standard. Comparison of the failure loads and the ultimate shear strength with the Finite Element Analysis (FEA) of the same specimens as a function of the overlap widths shows excellent correlation between the experimental and calculated values for the defect-free lap joints. A damage zone criterion is shown to work quite well in understanding the failure of the braze joints. In Part 2, the findings of the Part 1 will be verified on the larger test specimens. Also, various flaws will be introduced in the test specimens to simulate lack of braze coverage in the lap joints. Mechanical testing and FEA will be performed on these joints to verify that behavior of the flawed ductile lap joints is similar to joints with a reduced braze area. Finally, in Part 3, the results obtained in Parts 1 and 2 will be applied to the actual brazed structure to evaluate the load-carrying capability of a structural lap joint containing discontinuities. In addition, a simplified engineering procedure will be offered for the laboratory testing of the lap shear specimens.

  4. Active diffusion positions the nucleus in mouse oocytes.

    PubMed

    Almonacid, Maria; Ahmed, Wylie W; Bussonnier, Matthias; Mailly, Philippe; Betz, Timo; Voituriez, Raphaël; Gov, Nir S; Verlhac, Marie-Hélène

    2015-04-01

    In somatic cells, the position of the cell centroid is dictated by the centrosome. The centrosome is instrumental in nucleus positioning, the two structures being physically connected. Mouse oocytes have no centrosomes, yet harbour centrally located nuclei. We demonstrate how oocytes define their geometric centre in the absence of centrosomes. Using live imaging of oocytes, knockout for the formin 2 actin nucleator, with off-centred nuclei, together with optical trapping and modelling, we discover an unprecedented mode of nucleus positioning. We document how active diffusion of actin-coated vesicles, driven by myosin Vb, generates a pressure gradient and a propulsion force sufficient to move the oocyte nucleus. It promotes fluidization of the cytoplasm, contributing to nucleus directional movement towards the centre. Our results highlight the potential of active diffusion, a prominent source of intracellular transport, able to move large organelles such as nuclei, providing in vivo evidence of its biological function. PMID:25774831

  5. Rene 95 brazed joint metallurgical program

    NASA Technical Reports Server (NTRS)

    Gay, C.; Givens, J.; Mastrorroco, S.; Sterman, A.

    1972-01-01

    This metallurgical program was specifically conducted for the establishment of material properties required for the design of the LF460 fan. The LF460 lift fan is an advanced 18:1 high thrust to weight single stage design. It has a turbine attached to the outer flowpath of the fan blade tip which minimizes the axial depth of the fan. Advanced lightweight attachment designs are employed in this concept to achieve minimum mass polar moments of inertia which are required for good aircraft flight response control. The design features which are unique to this advanced LF460 lift fan are the 0.010 inch thin Udimet 700 alloy integral tip turbine design, minimum weight braze attachment of the turbine to the fan blade, and the high strength and elevated temperature capability of the Rene'95 alloy for the fan blade. The data presented in this report show that the LF460 fan rotor design is feasible and that the design stresses and margins of safety were more than adequate. Prior to any production application, however, additional stress rupture/shear lap joints should be run in order to establish a firm 1200 F stress rupture curve for the CM50 braze metal.

  6. Cathodic ARC surface cleaning prior to brazing

    SciTech Connect

    Dave, V. R.; Hollis, K. J.; Castro, R. G.; Smith, F. M.; Javernick, D. A.

    2002-01-01

    Surface cleanliness is one the critical process variables in vacuum furnace brazing operations. For a large number of metallic components, cleaning is usually accomplished either by water-based alkali cleaning, but may also involve acid etching or solvent cleaning / rinsing. Nickel plating may also be necessary to ensure proper wetting. All of these cleaning or plating technologies have associated waste disposal issues, and this article explores an alternative cleaning process that generates minimal waste. Cathodic arc, or reserve polarity, is well known for welding of materials with tenacious oxide layers such as aluminum alloys. In this work the reverse polarity effect is used to clean austenitic stainless steel substrates prior to brazing with Ag-28%Cu. This cleaning process is compared to acid pickling and is shown to produce similar wetting behavior as measured by dynamic contact angle experiments. Additionally, dynamic contact angle measurements with water drops are conducted to show that cathodic arc cleaning can remove organic contaminants as well. The process does have its limitations however, and alloys with high titanium and aluminum content such as nickel-based superalloys may still require plating to ensure adequate wetting.

  7. Innovation diffusion on time-varying activity driven networks

    NASA Astrophysics Data System (ADS)

    Rizzo, Alessandro; Porfiri, Maurizio

    2016-01-01

    Since its introduction in the 1960s, the theory of innovation diffusion has contributed to the advancement of several research fields, such as marketing management and consumer behavior. The 1969 seminal paper by Bass [F.M. Bass, Manag. Sci. 15, 215 (1969)] introduced a model of product growth for consumer durables, which has been extensively used to predict innovation diffusion across a range of applications. Here, we propose a novel approach to study innovation diffusion, where interactions among individuals are mediated by the dynamics of a time-varying network. Our approach is based on the Bass' model, and overcomes key limitations of previous studies, which assumed timescale separation between the individual dynamics and the evolution of the connectivity patterns. Thus, we do not hypothesize homogeneous mixing among individuals or the existence of a fixed interaction network. We formulate our approach in the framework of activity driven networks to enable the analysis of the concurrent evolution of the interaction and individual dynamics. Numerical simulations offer a systematic analysis of the model behavior and highlight the role of individual activity on market penetration when targeted advertisement campaigns are designed, or a competition between two different products takes place.

  8. Brazing ZrO{sub 2} ceramic to Ti–6Al–4V alloy using NiCrSiB amorphous filler foil: Interfacial microstructure and joint properties

    SciTech Connect

    Cao, J.; Song, X.G.; Li, C.; Zhao, L.Y.; Feng, J.C.

    2013-07-15

    Reliable brazing of ZrO{sub 2} ceramic and Ti–6Al–4V alloy was achieved using NiCrSiB amorphous filler foil. The interfacial microstructure of ZrO{sub 2}/Ti–6Al–4V joints was characterized by scanning electron microscope, energy dispersive spectrometer and micro-focused X-ray diffractometer. The effects of brazing temperature on the interfacial microstructure and joining properties of brazed joints were investigated in detail. Active Ti of Ti–6Al–4V alloy dissolved into molten filler metal and reacted with ZrO{sub 2} ceramic to form a continuous TiO reaction layer, which played an important role in brazing. Various reaction phases including Ti{sub 2}Ni, Ti{sub 5}Si{sub 3} and β-Ti were formed in brazed joints. With an increasing of brazing temperature, the TiO layer thickened gradually while the Ti{sub 2}Ni amount reduced. Shear test indicated that brazed joints tend to fracture at the interface between ZrO{sub 2} ceramic and brazing seam or Ti{sub 2}Ni intermetallic layer. The maximum average shear strength reached 284.6 MPa when brazed at 1025 °C for 10 min. - Graphical Abstract: Interfacial microstructure of ZrO{sub 2}/TC4 joint brazed using NiCrSiB amorphous filler foil was: ZrO{sub 2}/TiO/Ti{sub 2}Ni + β-Ti + Ti{sub 5}Si{sub 3}/β-Ti/Widmanstätten structure/TC4. - Highlights: • Brazing of ZrO{sub 2} ceramic and Ti-6Al-4V alloy was achieved. • Interfacial microstructure was TiO/Ti{sub 2}Ni + β + Ti{sub 5}Si{sub 3}/β/Widmanstätten structure. • The formation of TiO produced the darkening effect of ZrO{sub 2} ceramic. • The highest joining strength of 284.6MPa was obtained.

  9. Plasma Spray for Difficult-To-Braze Alloys

    NASA Technical Reports Server (NTRS)

    Brennan, A.

    1982-01-01

    Nickel plating on surfaces makes brazing easier for some alloys. Sometimes nickel plating may not be feasible because of manufacturing sequence, size of hardware, or lack of suitable source for nickel plating. Alternative surface preparation in such cases is to grit-blast surface lightly and then plasma-spray 1 1/2 to 2 mils of fine nickel powder or braze-alloy material directly on surface. Powder is sprayed from plasma gun, using argon as carrier gas to prevent oxidation of nickel or braze alloy.

  10. Braze system and method for reducing strain in a braze joint

    SciTech Connect

    Cadden, Charles H.; Goods, Steven H.; Prantil, Vincent C.

    2004-05-11

    A system for joining a pair of structural members having widely differing coefficients of thermal expansion is disclosed. A mechanically "thick" foil is made by dispersing a refractory metal powder, such as molybdenum, niobium, tantalum, or tungsten into a quantity of a liquid, high expansion metal such as copper, silver, or gold, casting an ingot of the mixture, and then cutting sections of the ingot about 1 mm thick to provide the foil member. These foil members are shaped, and assembled between surfaces of structural members for joining, together with a layer of a braze alloy on either side of the foil member capable of wetting both the surfaces of the structural members and the foil. The assembled body is then heated to melt the braze alloy and join the assembled structure. The foil member subsequently absorbs the mechanical strain generated by the differential contraction of the cooling members that results from the difference in the coefficients of thermal expansion of the members.

  11. Brazing of Carbon Carbon Composites to Cu-clad Molybdenum for Thermal Management Applications

    NASA Technical Reports Server (NTRS)

    Singh, M.; Asthana, R.; Shpargel, T> P.

    2007-01-01

    Advanced carbon carbon composites were joined to copper-clad molybdenum (Cu/Mo) using four active metal brazes containing Ti (Cu ABA, Cusin-1 ABA, Ticuni, and Ticusil) for potential use in thermal management applications. The brazed joints were characterized using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and Knoop microhardness measurements across the joint region. Metallurgically sound C-C/Cu/Mo joints, devoid of interfacial cracks formed in all cases. The joint interfaces were preferentially enriched in Ti, with Cu ABA joints exhibiting the largest interfacial Ti concentrations. The microhardness measurements revealed hardness gradients across the joint region, with a peak hardness of 300-350 KHN in Cusin-1 ABA and Ticusil joints and 200-250 KHN in Cu ABA and Ticuni joints, respectively.

  12. Soldering and brazing safety guide: A handbook on space practice for those involved in soldering and brazing

    NASA Astrophysics Data System (ADS)

    This manual provides those involved in welding and brazing with effective safety procedures for use in performance of their jobs. Hazards exist in four types of general soldering and brazing processes: (1) cleaning; (2) application of flux; (3) application of heat and filler metal; and (4) residue cleaning. Most hazards during those operations can be avoided by using care, proper ventilation, protective clothing and equipment. Specific process hazards for various methods of brazing and soldering are treated. Methods to check ventilation are presented as well as a check of personal hygiene and good maintenance practices are stressed. Several emergency first aid treatments are described.

  13. Enhanced diffusion in shock activated Be-Al interfaces

    SciTech Connect

    Staudhammer, K.P.

    1997-05-01

    Enhanced diffusion of aluminum in shock activated beryllium has been observed. Cylindrical samples of aluminum coated beryllium rods were axisymetrically loaded up to 40 GPa and a total residual strain of up to 6.7%. The defect microstructure produced by both the shock wave and strain enabled the transport of aluminum in beryllium to exceed its equilibrium solid state saturation. This {open_quotes}super saturated{close_quotes} aluminum, upon heating exsolves out at relatively low temperatures and forms very strong interfaces with pressure mated components.

  14. Fabrication and Characterization of Brazed Joints for SiC-Metallic Systems Utilizing Refractory Metals

    NASA Technical Reports Server (NTRS)

    Coddington, Bryan; Asthana, Rajiv; Halbig, Michael C.; Singh, M.

    2011-01-01

    Metal to ceramic joining plays a key role for the integration of ceramics into many nuclear, ground and aero based technologies. In order to facilitate these technologies, the active metal brazing of silicon carbide (CVD beta-SiC, 1.1 mm thick, and hot-pressed alpha-SiC, 3 mm thick) to the refractory metals molybdenum and tungsten using active braze alloys was studied. The joint microstructure, composition, and microhardness were evaluated by optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and Knoop hardness testing. The braze alloys, Cusil-ABA, Ticusil and Copper-ABA, all formed sound joints with excellent wetting and chemical bonding with the SiC substrate. Despite the close thermal expansion match between the metal substrates and SiC, hairline cracks formed in alpha-SiC while beta-SiC showed no signs of residual stress cracking. The use of ductile interlayers to reduce the effect from residual stresses was investigated and joints formed with copper as an interlayer produced crack free systems utilizing both CVD and hot-pressed SiC.

  15. Low vapor pressure braze alloys for thermionic energy converters

    NASA Technical Reports Server (NTRS)

    Bair, V. L.

    1976-01-01

    The evaluation of cesium diode electrode materials called for braze fillers with very low vapor pressures and a wide range of melting points. Binary alloys of low vapor pressure refractory metals were chosen to fill this need. These alloys of Th, Zr, Hf, Ru, Nb, Ir, Mo, Ta, Os, Re, and W have reported melting point minima or eutectics from 1,510 K to above 3,000 K. Preliminary data are compiled on the use of several of these braze alloys. Melting points and surface wetting on a Ta base are given. Results of brazing Ir, LaB6, Nb, Re, W, and Zr-22 wt % ZrO2 materials into Ta and Nb-1% Zr bases are presented. Current braze usage is summarized.

  16. Failure Assessment of Stainless Steel and Titanium Brazed Joints

    NASA Technical Reports Server (NTRS)

    Flom, Yury A.

    2012-01-01

    Following successful application of Coulomb-Mohr and interaction equations for evaluation of safety margins in Albemet 162 brazed joints, two additional base metal/filler metal systems were investigated. Specimens consisting of stainless steel brazed with silver-base filler metal and titanium brazed with 1100 Al alloy were tested to failure under combined action of tensile, shear, bending and torsion loads. Finite Element Analysis (FEA), hand calculations and digital image comparison (DIC) techniques were used to estimate failure stresses and construct Failure Assessment Diagrams (FAD). This study confirms that interaction equation R(sub sigma) + R(sub tau) = 1, where R(sub sigma) and R(sub t u) are normal and shear stress ratios, can be used as conservative lower bound estimate of the failure criterion in stainless steel and titanium brazed joints.

  17. Reactive Brazing of Carbon-Carbon Composites to Titanium

    NASA Technical Reports Server (NTRS)

    Shpargel, Tarah; Singh, M.; Morscher, Gregory; Asthana, Rajiv

    2004-01-01

    The Ti-metal/C-C composite joints were formed by reactive brazing with three commercial brazes, namely, Cu-ABA, TiCuNi, and TiCuSil. The joint microstructures were examined using optical microscopy, and scanning electron microscopy (SEM) coupled with energy dispersive spectrometry (EDS). The results of the microstructure analysis indicate solute redistribution across the joint and possible metallurgical bond formation via interdiffusion, which led to good wetting and spreading.

  18. Improved Assembly for Gas Shielding During Welding or Brazing

    NASA Technical Reports Server (NTRS)

    Gradl, Paul; Baker, Kevin; Weeks, Jack

    2009-01-01

    An improved assembly for inert-gas shielding of a metallic joint is designed to be useable during any of a variety of both laser-based and traditional welding and brazing processes. The basic purpose of this assembly or of a typical prior related assembly is to channel the flow of a chemically inert gas to a joint to prevent environmental contamination of the joint during the welding or brazing process and, if required, to accelerate cooling upon completion of the process.

  19. Ceramic-to-metal stator vane assembly with braze

    DOEpatents

    Chase, Donna J.; Fang, Ho T.; Irwin, Craig W.; Schienle, James L.

    1995-01-01

    A stator vane assembly for a gas turbine engine that includes a plurality of circumferentially spaced ceramic vanes, each of which has an inner and outer ceramic shroud, and a ceramic post extending from one of the shrouds, and a metallic platform having a plurality of circumferentially spaced recesses. The posts are inserted into a metallic sleeve and then brazed. The brazed sleeves are then mounted in the recesses. A method for assembling these components to form the stator assembly is also described.

  20. Diffuse optical imaging of brain activation to joint attention experience.

    PubMed

    Zhu, Banghe; Yadav, Nitin; Rey, Gustavo; Godavarty, Anuradha

    2009-08-24

    In the early development of social cognition and language, infants tend to participate in face-to-face interactions engaging in joint attention exchanges. Joint attention is vital to social competence at all ages, lacking which is a primary feature to distinguish autistic from non-autistic population. In this study, diffuse optical imaging is used for the first time to investigate the joint attention experience in normal adults. Imaging studies were performed in the frontal regions of the brain (BA9 and BA10) in order to study the differences in the brain activation in response to video clips corresponding to joint attention based skills. The frontal regions of the brain were non-invasively imaged using a novel optical cap coupled to a frequency-domain optical imaging system. The statistical analysis from 11 normal adult subjects, with three repetitions from each subject, indicated that the averaged changes in the cerebral blood oxygenation levels were different under the joint and non-joint attention based stimulus. The preliminary studies demonstrate the feasibility of implementing diffuse optical imaging towards autism-related research to study the brain activation in response to socio-communication skills. PMID:19447278

  1. Activity and diffusion of metals in binary aluminum alloys

    SciTech Connect

    Jao, C. S.

    1980-12-01

    To determine the activity of zinc in Zn-Al alloys, the electromotive force (emf) of the cell: Zn/ZnCl/sub 2/-KC1 (eut)/Zn,Al was measured at temperatures between 569.5 K (296.5C) and 649.5 K (376.5C). The applicability of a two-suffix Margules equation was demonstrated, in good agreement with theoretical expectations. The diffusion coefficient of Zn in Al determined from a planar diffusion model for the experimental data was about 3 x 10/sup -10/ cm/sup 2//sec to 2 x 10/sup -9/ cm/sup 2//sec in the range of temperature studied. This is higher than that found in the literature. The most plausible reason appears to be the high alumina concentration in the working electrode because of partial oxidation. Oxidation of the alloying metals was the primary cause of poor alloying between calcium/or zinc and aluminum, thereby frustrating similar measurements at a Ca-Al/or Zn-Al alloy. The literature on the activity of calcium and zinc is aluminum is reviewed.

  2. Reducing inadvertent alloying of metal/ceramic brazes

    SciTech Connect

    Stephens, J.J.; Hlava, P.F.

    1992-12-31

    Inadvertent alloying of Cu braze metal can compromise metal/ceramic seals. Electron microprobe analyses have quantified alloying of Cu brazes in metal/ceramic feedthroughs. Pin material and processing parameters above 1084C both affect alloying levels. Using either Kovar or Ni-plated 316L stainless steel pins limits alloying compared to Palco pins. Minimizing the time during which the braze is molten also avoids excessive alloying. The original thickness of the Ni plating on the Mo-Mn metallization of the ceramic also influences the alloying content of these brazes. Metal/ceramic brazes made with long brazing cycles, Mo-Mn metallization, and Kovar components grow a layer of Mo{sub 6}(Fe{sub 3.5}CO{sub 3.5}){sub 7} on the metallization. Layer thicknesses observed do not appear to compromise joint integrity. Ni additions of approximately 10 and 20 wt.% to Cu apparently increases the stress required for stress relaxation during cooldown. to maintain creep rates required for stress relaxation during cooldown. Relative to unalloyed Cu, this strengthening effect tends to increase as temperature is decreased.

  3. A new low-melting-point aluminum braze

    SciTech Connect

    Jacobson, D.M.; Humpston, G.; Sangha, S.P.S.

    1996-08-01

    Most high-strength aluminum engineering alloys cannot be joined by brazing because they either degrade or melt at the temperature at which commercially available aluminum brazes are used. Previous efforts to develop aluminum brazing filler metal alloys with a significantly reduced melting point have tended to be frustrated by poor mechanical properties of the alloys, corrosion of the joints or the high cost, toxicity or volatility of the constituent materials. This paper describes the development and assessment of a new brazing alloy with a composition of 73Al-20Cu-2Ni-55I (wt-%), which has been designed to overcome these limitations. A joining process has been devised for fluxless brazing of aluminum engineering alloys using the new filler metal for use in both inert gas and vacuum furnaces. The production of ductile foil preforms and roll-clad base metals is described together with preliminary results of mechanical property assessments and corrosion resistance trials. These results are highly encouraging and point to promising new applications for aluminum brazing technology.

  4. Electron Beam Welder Used to Braze Sapphire to Platinum

    NASA Technical Reports Server (NTRS)

    Forsgren, Roger C.; Vannuyen, Thomas

    1998-01-01

    A new use for electron beam brazing was recently developed by NASA Lewis Research Center's Manufacturing Engineering Division. This work was done to fabricate a fiberoptic probe (developed by Sentec Corporation) that could measure high temperatures less than 600 deg C of vibrating machinery, such as in jet engine combustion research. Under normal circumstances, a sapphire fiber would be attached to platinum by a ceramic epoxy. However, no epoxies can adhere ceramic fibers to platinum under such high temperatures and vibration. Also, since sapphire and platinum have different thermal properties, the epoxy bond is subjected to creep over time. Therefore, a new method had to be developed that would permanently and reliably attach a sapphire fiber to platinum. Brazing a sapphire fiber to a platinum shell. The fiber-optic probe assembly consists of a 0.015-in.-diameter sapphire fiber attached to a 0.25-in.-long, 0.059-in.-diameter platinum shell. Because of the small size of this assembly, electron beam brazing was chosen instead of conventional vacuum brazing. The advantage of the electron beam is that it can generate a localized heat source in a vacuum. Gold reactive braze was used to join the sapphire fiber and the platinum. Consequently, the sapphire fiber was not affected by the total heat needed to braze the components together.

  5. Brazing Refractory Metals Used In High-Temperature Nuclear Instrumentation

    SciTech Connect

    A. J. Palmer; C. J. Woolstenhulme

    2009-06-01

    As part of the U. S. Department of Energy (DOE) sponsored Next Generation Nuclear Project (NGNP) currently ongoing at Idaho National Laboratory (INL), the irradiation performance of candidate high-temperature gas reactor fuels and materials is being evaluated at INL’s Advanced Test Reactor (ATR). The design of the first Advanced Gas Reactor (AGR 1) experiment, currently being irradiated in the ATR, required development of special techniques for brazing niobium and molybdenum. Brazing is one technique used to join refractory metals to each other and to stainless steel alloys. Although brazing processes are well established, it is difficult to braze niobium, molybdenum, and most other refractory metals because they quickly develop adherent oxides when exposed to room-temperature air. Specialized techniques and methods were developed by INL to overcome these obstacles. This paper describes the techniques developed for removing these oxides, as well as the ASME Section IX-qualified braze procedures that were developed as part of the AGR-1 project. All brazes were made using an induction coil with an inert or reducing atmosphere at low pressure. Other parameters, such as filler metals, fluxes used, and general setup procedures, are also discussed.

  6. Brazing open cell reticulated copper foam to stainless steel tubing with vacuum furnace brazed gold/indium alloy plating

    DOEpatents

    Howard, Stanley R.; Korinko, Paul S.

    2008-05-27

    A method of fabricating a heat exchanger includes brush electroplating plated layers for a brazing alloy onto a stainless steel tube in thin layers, over a nickel strike having a 1.3 .mu.m thickness. The resultant Au-18 In composition may be applied as a first layer of indium, 1.47 .mu.m thick, and a second layer of gold, 2.54 .mu.m thick. The order of plating helps control brazing erosion. Excessive amounts of brazing material are avoided by controlling the electroplating process. The reticulated copper foam rings are interference fit to the stainless steel tube, and in contact with the plated layers. The copper foam rings, the plated layers for brazing alloy, and the stainless steel tube are heated and cooled in a vacuum furnace at controlled rates, forming a bond of the copper foam rings to the stainless steel tube that improves heat transfer between the tube and the copper foam.

  7. Diffuse γ-Ray Emission from Misaligned Active Galactic Nuclei

    NASA Astrophysics Data System (ADS)

    Di Mauro, M.; Calore, F.; Donato, F.; Ajello, M.; Latronico, L.

    2014-01-01

    Active galactic nuclei (AGNs) with jets seen at small viewing angles are the most luminous and abundant objects in the γ-ray sky. AGNs with jets misaligned along the line of sight appear fainter in the sky but are more numerous than the brighter blazars. We calculate the diffuse γ-ray emission due to the population of misaligned AGNs (MAGNs) unresolved by the Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope (Fermi). A correlation between the γ-ray luminosity and the radio-core luminosity is established and demonstrated to be physical by statistical tests, as well as compatible with upper limits based on Fermi-LAT data for a large sample of radio-loud MAGNs. We constrain the derived γ-ray luminosity function by means of the source-count distribution of the radio galaxies detected by the Fermi-LAT. We finally calculate the diffuse γ-ray flux due to the whole MAGN population. Our results demonstrate that MAGNs can contribute from 10% up to nearly the entire measured isotropic gamma-ray background. We evaluate a theoretical uncertainty on the flux of almost an order of magnitude.

  8. Diffuse γ-ray emission from misaligned active galactic nuclei

    SciTech Connect

    Di Mauro, M.; Donato, F.; Calore, F.; Ajello, M.; Latronico, L.

    2014-01-10

    Active galactic nuclei (AGNs) with jets seen at small viewing angles are the most luminous and abundant objects in the γ-ray sky. AGNs with jets misaligned along the line of sight appear fainter in the sky but are more numerous than the brighter blazars. We calculate the diffuse γ-ray emission due to the population of misaligned AGNs (MAGNs) unresolved by the Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope (Fermi). A correlation between the γ-ray luminosity and the radio-core luminosity is established and demonstrated to be physical by statistical tests, as well as compatible with upper limits based on Fermi-LAT data for a large sample of radio-loud MAGNs. We constrain the derived γ-ray luminosity function by means of the source-count distribution of the radio galaxies detected by the Fermi-LAT. We finally calculate the diffuse γ-ray flux due to the whole MAGN population. Our results demonstrate that MAGNs can contribute from 10% up to nearly the entire measured isotropic gamma-ray background. We evaluate a theoretical uncertainty on the flux of almost an order of magnitude.

  9. Microstructure and mechanical properties of joints in sintered SiC fiber-bonded ceramics brazed with Ag Cu Ti alloy

    SciTech Connect

    Singh, Mrityunjay; Asthana, Rajiv; Ishikawa, Toshihiro; Matsunaga, Tadashi; Lin, Hua-Tay

    2012-01-01

    Active metal brazing of a new high thermal conductivity sintered SiC-polycrystalline fiber-bonded ceramic (SA-Tyrannohexs) has been carried out using a Ti-containing Ag Cu active braze alloy (Cusil-ABAs). The brazed composite joints were characterized using scanning electron microscopy coupled with energy-dispersive X-ray spectrometry (SEM EDS). The results show that this material can be successfully joined using judiciously selected off-the shelf active braze alloys to yield metallurgically sound joints possessing high integrity. Uniform and continuous joints were obtained irrespective of differences in the fiber orientation in the substrate material. Detailed interfacial microanalysis showed that the titanium reacts with C and Si to form TiC layer and a Ti Si compound, respectively. Furthermore, the evaluation of shear strength of the joints was also conducted at ambient and elevated temperatures in air using the single-lap offset (SLO) shear test. The perpendicular-type SA-Tyrannohex joints exhibited apparent shear strengths of about 42 MPa and 25 MPa at 650 1C and 750 1C, respectively. The fracture at the higher temperature occurred at the interface between the reactionformed TiC layer and braze. This might be caused by generation of stress intensity when a shear stress was applied, according to m-FEA simulation results.

  10. Microstructure and Mechanical Properties of Joints in Sintered SiC Fiber-Bonded Ceramics Brazed with Ag-Cu-Ti Alloy

    SciTech Connect

    Singh, Mrityunjay; Matsunaga, Tadashi; Lin, Hua-Tay; Asthana, Rajiv; Ishikawa, Toshihiro

    2012-01-01

    Active metal brazing of a new high thermal conductivity sintered SiC-polycrystalline fiber-bonded ceramic (SA-Tyrannohex{reg_sign}) has been carried out using a Ti-containing Ag-Cu active braze alloy (Cusil-ABA{reg_sign}). The brazed composite joints were characterized using scanning electron microscopy coupled with energy-dispersive X-ray spectrometry (SEM-EDS). The results show that this material can be successfully joined using judiciously selected off-the shelf active braze alloys to yield metallurgically sound joints possessing high integrity. Uniform and continuous joints were obtained irrespective of differences in the fiber orientation in the substrate material. Detailed interfacial microanalysis showed that the titanium reacts with C and Si to form TiC layer and a Ti-Si compound, respectively. Furthermore, the evaluation of shear strength of the joints was also conducted at ambient and elevated temperatures in air using the single-lap offset (SLO) shear test. The perpendicular-type SA-Tyrannohex joints exhibited apparent shear strengths of about 42 MPa and 25 MPa at 650 C and 750 C, respectively. The fracture at the higher temperature occurred at the interface between the reaction-formed TiC layer and braze. This might be caused by generation of stress intensity when a shear stress was applied, according to {mu}-FEA simulation results.

  11. Thermochemical Analysis of Phases Formed at the Interface of a Mg alloy-Ni-plated Steel Joint during Laser Brazing

    NASA Astrophysics Data System (ADS)

    Nasiri, Ali M.; Chartrand, Patrice; Weckman, David C.; Zhou, Norman Y.

    2013-04-01

    The thermodynamic stability of precipitated phases at the steel-Ni-Mg alloy interface during laser brazing of Ni-plated steel to AZ31B magnesium sheet using AZ92 magnesium alloy filler wire has been evaluated using FactSage thermochemical software. Assuming local chemical equilibrium at the interface, the chemical activity-temperature-composition relationships of intermetallic compounds that might form in the steel-Ni interlayer-AZ92 magnesium alloy system in the temperature range of 873 K to 1373 K (600 °C to 1100 °C) were estimated using the Equilib module of FactSage. The results provided better understanding of the phases that might form at the interface of the dissimilar metal joints during the laser brazing process. The addition of a Ni interlayer between the steel and the Mg brazing alloy was predicted to result in the formation of the AlNi, Mg2Ni, and Al3Ni2 intermetallic compounds at the interface, depending on the local maximum temperature. This was confirmed experimentally by laser brazing of Ni electro-plated steel to AZ31B-H24 magnesium alloy using AZ92 magnesium alloy filler wire. As predicted, the formation of just AlNi and Mg2Ni from a monotectic and eutectic reaction, respectively, was observed near the interface.

  12. Compressive Strength Evaluation in Brazed ZrO2/Ti6Al4V Joints Using Finite Element Analysis

    NASA Astrophysics Data System (ADS)

    Sharma, Ashutosh; Kee, Se Ho; Jung, Flora; Heo, Yongku; Jung, Jae Pil

    2016-04-01

    This study aims to synthesize and evaluate the compressive strength of the ZrO2/Ti-6Al-4V joint brazed using an active metal filler Ag-Cu-Sn-Ti, and its application to dental implants assuring its reliability to resist the compressive failure in the actual oral environment. The brazing was performed at a temperature of 750 °C for 30 min in a vacuum furnace under 5 × 10-6 Torr atmosphere. The microstructure of the brazed joint showed the presence of an Ag-rich matrix and a Cu-rich phase, and Cu-Ti intermetallic compounds were observed along the Ti-6Al-4V bonded interface. The compressive strength of the brazed ZrO2/Ti-6Al-4V joint was measured by EN ISO 14801 standard test method. The measured compressive strength of the joint was ~1477 MPa—a value almost five times that of existing dental cements. Finite element analysis also confirmed the high von Mises stress values. The compressive strains in the samples were found concentrated near the Ti-6Al-4V position, matching with the position of the real fractured sample. These results suggest extremely significant compressive strength in ZrO2/Ti-6Al-4V joints using the Ag-Cu-Sn-Ti filler. It is believed that a highly reliable dental implant can be processed and designed using the results of this study.

  13. Compressive Strength Evaluation in Brazed ZrO2/Ti6Al4V Joints Using Finite Element Analysis

    NASA Astrophysics Data System (ADS)

    Sharma, Ashutosh; Kee, Se Ho; Jung, Flora; Heo, Yongku; Jung, Jae Pil

    2016-05-01

    This study aims to synthesize and evaluate the compressive strength of the ZrO2/Ti-6Al-4V joint brazed using an active metal filler Ag-Cu-Sn-Ti, and its application to dental implants assuring its reliability to resist the compressive failure in the actual oral environment. The brazing was performed at a temperature of 750 °C for 30 min in a vacuum furnace under 5 × 10-6 Torr atmosphere. The microstructure of the brazed joint showed the presence of an Ag-rich matrix and a Cu-rich phase, and Cu-Ti intermetallic compounds were observed along the Ti-6Al-4V bonded interface. The compressive strength of the brazed ZrO2/Ti-6Al-4V joint was measured by EN ISO 14801 standard test method. The measured compressive strength of the joint was ~1477 MPa—a value almost five times that of existing dental cements. Finite element analysis also confirmed the high von Mises stress values. The compressive strains in the samples were found concentrated near the Ti-6Al-4V position, matching with the position of the real fractured sample. These results suggest extremely significant compressive strength in ZrO2/Ti-6Al-4V joints using the Ag-Cu-Sn-Ti filler. It is believed that a highly reliable dental implant can be processed and designed using the results of this study.

  14. Online monitoring of the laser brazing of titanium overlap joints

    NASA Astrophysics Data System (ADS)

    Schmitt, R.; Vielhaber, K.; Donst, D.; Klocke, F.

    2007-06-01

    Image processing and thermography for its own are very versatile and established measurement techniques for many years. However, the combination of these two measurement technologies opens a new field of applications. The online monitoring of the laser-brazing of titanium overlap joints is such a new application. The laser brazing process for overlap joining of formed titanium sheets for the production of heat exchangers is presently being investigated at the Fraunhofer IPT. In comparison to conventional furnace brazing the laser brazing technology decreases substantially the heat impact and thus reduces the thermal material damage in the parts due to local selective heating in a laser beam focal spot. Even though the process is stable, errors in the brazing seam such as pores or unacceptable material oxidation can occur. To ensure a high quality an online process monitoring or even process control is necessary. But since the surface remains unchanged during this brazing process no geometrical inspection of the surface can be conducted. Therefore today's quality assurance performs x-ray or destructive testing. This paper demonstrates how the use of thermography in combination with image processing allows a machine integrated online monitoring of the laser brazing process. First the basic principals are presented which cover the fields of heat coupling, heat transmission and heat distribution as well as the temperature emission of light and the spectral properties of the laser beam shaping optic and so lead to the optical set-up. Then analysis algorithms are derived which characterize the process, detect process failures and make a seam tracking possible.

  15. Air Brazing: A New Method of Ceramic-Ceramic and Ceramic-Metal Joining

    SciTech Connect

    Weil, K. Scott; Darsell, Jens T.; Kim, Jin Yong

    2011-10-01

    A new method of ceramic-ceramic and ceramic-metal joining has emerged over the past several years. Referred to as air brazing, the technique was originally designed and developed for use in fabricating high-temperature solid-state electrochemical devices such as planar SOFCs and oxygen and hydrogen concentrators. The primary advantage of air brazing is that a predominantly metallic joint can be formed directly in air without need of an inert cover gas or the use of surface reactive fluxes. The resulting bond is hermetic, offers excellent room temperature strength, and is inherently resistant to oxidation at high temperature. The key to developing a successful filler metal composition for air brazing is to identify a metal oxide wetting agent that is mutually soluble in a molten noble metal solvent. One particular oxide-metal combination that appears readily suited for this purpose is CuOx-Ag, a system originally of interest in the development of silver clad cuprate-based superconductors. Studies of the equilibrium phases studies in this system indicate that there are two invariant points in the pseudobinary CuOx-Ag phase diagram around which new braze compositions can be developed: 1) a monotectic reaction at 969±1°C, where CuO and a Ag-rich liquid L1 coexist with a second CuOx-rich liquid phase L2 at a composition of xAg/(xAg + xCu) = 0.10±0.03 Ag and 2) a eutectic reaction at 942±1°C, where CuO and Ag coexist with L1 at a composition of xAg/(xAg + xCu) = 0.99±0.005. Specifically, near-eutectic Ag-CuO filler metal compositions have shown good promise in joining electrochemically active ceramics such as yttria-stabilized zirconia, lanthanum strontium manganite, and barium strontium cobalt ferrite, as well as alumina and magnesia. More recently it has been found that various ternary additions can further improve the wetting characteristics of these filler metals, increase their potential operating temperatures, and/or increase the resulting strength of the

  16. Direct use geothermal applications for brazed plate heat exchangers

    SciTech Connect

    Rafferty, K.

    1993-02-01

    Brazed plate heat exchanger were placed in three geothermal fluids (Klamath Falls, OR; Boise, ID; and Pagosa Springs, CO) in order to determine the effect of H{sub 2}S on braze material. Based on subsequent analysis, it appears that the rate of corrosion of the braze material is much slower than corrosion of copper tube materials in the same fluids. Minimum expected life of the heat exchangers based on these corrosion rates is reported to be 12 years in fluids of less than 1 ppm H{sub 2}S and 10 years in fluids of less than 5 ppm. Based on these expected lives, and using a 3% inflation rate and 8% discount rate, brazed plate heat exchangers are a clear economic choice in which the capital cost is 50% or less of the cost of a plate and frame heat exchanger for the same duty. Due to their single pass design, brazed plate heat exchangers are generally limited to approach temperatures of 10{degree} or greater. Size limitations restrict applications to 100 gpm and/or 200 ft{sup 2} heat transfer surface area.

  17. 49 CFR 178.50 - Specification 4B welded or brazed steel cylinders.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 49 Transportation 3 2014-10-01 2014-10-01 false Specification 4B welded or brazed steel cylinders... FOR PACKAGINGS Specifications for Cylinders § 178.50 Specification 4B welded or brazed steel cylinders. (a) Type, size, and service pressure. A DOT 4B is a welded or brazed steel cylinder with...

  18. 49 CFR 178.50 - Specification 4B welded or brazed steel cylinders.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 49 Transportation 3 2011-10-01 2011-10-01 false Specification 4B welded or brazed steel cylinders... FOR PACKAGINGS Specifications for Cylinders § 178.50 Specification 4B welded or brazed steel cylinders. (a) Type, size, and service pressure. A DOT 4B is a welded or brazed steel cylinder with...

  19. 49 CFR 178.50 - Specification 4B welded or brazed steel cylinders.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 49 Transportation 3 2012-10-01 2012-10-01 false Specification 4B welded or brazed steel cylinders... FOR PACKAGINGS Specifications for Cylinders § 178.50 Specification 4B welded or brazed steel cylinders. (a) Type, size, and service pressure. A DOT 4B is a welded or brazed steel cylinder with...

  20. Inert-gas welding and brazing enclosure fabricated from sheet plastic

    NASA Technical Reports Server (NTRS)

    Wisner, J. P.

    1965-01-01

    Custom-fabricated plastic bag maintains an inert-gas atmosphere for welding and brazing certain metals. The bag fits over part of the workpieces and the welding and brazing tools. It is also used for metal brazing and fusion plating which require an inert-gas atmosphere.

  1. Substrate Effects on the High Temperature Oxidation Behavior of a Gold-Based Braze Filler Metal

    SciTech Connect

    Weil, K. Scott; Rice, Joseph P.

    2005-06-30

    Oxidation testing was conducted on a commercial gold-based braze alloy, Gold ABA, and on zirconia and stainless steel joining couples prepared using this braze filler metal. Preliminary results reveal that both substrates play a significant role in determining the overall oxidation resistance of the brazed joint.

  2. Process for forming unusually strong joints between metals and ceramics by brazing at temperatures that do not exceed 750/sup 0/C

    DOEpatents

    Hammond, J.P.; David, S.A.; Woodhouse, J.J.

    1984-12-04

    This invention is a process for joining metals to ceramics to form very strong bonds using low brazing temperature, i.e., less than 750/sup 0/C, and particularly for joining nodular cast iron to partially stabilized zirconia. The process provides that the ceramic be coated with an active metal, such as titanium, that can form an intermetallic with a low melting point brazing alloy such as 60Ag-30Cu-10Sn. The nodular cast iron is coated with a noncarbon containing metal, such as copper, to prevent carbon in the nodular cast iron from dissolving in the brazing alloy. These coated surfaces can be brazed together with the brazing alloy between at less than 750/sup 0/C to form a very strong joint. An even stronger bond can be formed if a transition piece is used between the metal and ceramic. It is preferred for the transition piece to have a coefficient of thermal expansion compatible with the coefficient of thermal expansion of the ceramic, such as titanium.

  3. Process for forming unusually strong joints between metals and ceramics by brazing at temperatures that do no exceed 750 degree C.

    DOEpatents

    Hammond, Joseph P.; David, Stan A.; Woodhouse, John J.

    1986-01-01

    This invention is a process for joining metals to ceramics to form very strong bonds using low brazing temperature, i.e., less than 750.degree. C., and particularly for joining nodular cast iron to partially stabilized zirconia. The process provides that the ceramic be coated with an active metal, such as titanium, that can form an intermetallic with a low melting point brazing alloy such as 60Ag-30Cu-10Sn. The nodular cast iron is coated with a noncarbon containing metal, such as copper, to prevent carbon in the nodular cast iron from dissolving in the brazing alloy. These coated surfaces can be brazed together with the brazing alloy between at less than 750.degree. C. to form a very strong joint. An even stronger bond can be formed if a transition piece is used between the metal and ceramic. It is preferred for the transition piece to have a coefficient of thermal compatible with the coefficient of thermal expansion of the ceramic, such as titanium.

  4. A review of oxide, silicon nitride, and silicon carbide brazing

    SciTech Connect

    Santella, M.L.; Moorhead, A.J.

    1987-01-01

    There is growing interest in using ceramics for structural applications, many of which require the fabrication of components with complicated shapes. Normal ceramic processing methods restrict the shapes into which these materials can be produced, but ceramic joining technology can be used to overcome many of these limitations, and also offers the possibility for improving the reliability of ceramic components. One method of joining ceramics is by brazing. The metallic alloys used for bonding must wet and adhere to the ceramic surfaces without excessive reaction. Alumina, partially stabilized zirconia, and silicon nitride have high ionic character to their chemical bonds and are difficult to wet. Alloys for brazing these materials must be formulated to overcome this problem. Silicon carbide, which has some metallic characteristics, reacts excessively with many alloys, and forms joints of low mechanical strength. The brazing characteristics of these three types of ceramics, and residual stresses in ceramic-to-metal joints are briefly discussed.

  5. Two-beam Laser Brazing of Thin Sheet Steel for Automotive Industry Using Cu-base Filler Material

    NASA Astrophysics Data System (ADS)

    Mittelstädt, C.; Seefeld, T.; Reitemeyer, D.; Vollertsen, F.

    This work shows the potential of two-beam laser brazing for joining both Zn-coated steel and 22MnB5. Brazing of Zn-coated steel sheets using Cu-Si filler wire is already state of the art in car manufacturing. New press-hardened steels like 22MnB5 are more and more used in automotive industry, offering high potential to save costs and improve structural properties (reduced weight / higher stiffness). However, for joining of these ultra-high strength steels investigations are mandatory. In this paper, a novel approach using a two-beam laser brazing process and Cu-base filler material is presented. The use of Cu-base filler material leads to a reduced heat input, compared to currently applied welding processes, which may result in benefits concerning distortion, post processing and tensile strength of the joint. Reliable processing at desired high speeds is attained by means of laser-preheating. High feed rates prevent significant diffusion of copper into the base material.

  6. Computational simulations and experimental validation of a furnace brazing process

    SciTech Connect

    Hosking, F.M.; Gianoulakis, S.E.; Malizia, L.A.

    1998-12-31

    Modeling of a furnace brazing process is described. The computational tools predict the thermal response of loaded hardware in a hydrogen brazing furnace to programmed furnace profiles. Experiments were conducted to validate the model and resolve computational uncertainties. Critical boundary conditions that affect materials and processing response to the furnace environment were determined. {open_quotes}Global{close_quotes} and local issues (i.e., at the furnace/hardware and joint levels, respectively) are discussed. The ability to accurately simulate and control furnace conditions is examined.

  7. Particle diffusion in active fluids is non-monotonic in size.

    PubMed

    Patteson, Alison E; Gopinath, Arvind; Purohit, Prashant K; Arratia, Paulo E

    2016-02-28

    We experimentally investigate the effect of particle size on the motion of passive polystyrene spheres in suspensions of Escherichia coli. Using particles covering a range of sizes from 0.6 to 39 microns, we probe particle dynamics at both short and long time scales. In all cases, the particles exhibit super-diffusive ballistic behavior at short times before eventually transitioning to diffusive behavior. Surprisingly, we find a regime in which larger particles can diffuse faster than smaller particles: the particle long-time effective diffusivity exhibits a peak in particle size, which is a deviation from classical thermal diffusion. We also find that the active contribution to particle diffusion is controlled by a dimensionless parameter, the Péclet number. A minimal model qualitatively explains the existence of the effective diffusivity peak and its dependence on bacterial concentration. Our results have broad implications on characterizing active fluids using concepts drawn from classical thermodynamics. PMID:26797039

  8. Brazing Inconel 625 Using Two Ni/(Fe)-Based Amorphous Filler Foils

    NASA Astrophysics Data System (ADS)

    Chen, Wen-Shiang; Shiue, Ren-Kae

    2012-07-01

    For MBF-51 filler, the brazed joint consists of interfacial grain boundary borides, coarse Nb6Ni16Si7, and Ni/Cr-rich matrix. In contrast, the VZ-2106 brazed joint is composed of interfacial Nb6Ni16Si7 precipitates as well as grain boundary borides, coarse Nb6Ni16Si7, and Ni/Cr/Fe-rich matrix. The maximum tensile strength of 443 MPa is obtained from the MBF-51 brazed specimen. The tensile strengths of VZ-2106 brazed joints are approximately 300 MPa. Both amorphous filler foils demonstrate potential in brazing IN-625 substrate.

  9. Diffusion properties of active particles with directional reversal

    NASA Astrophysics Data System (ADS)

    Großmann, R.; Peruani, F.; Bär, M.

    2016-04-01

    The diffusion properties of self-propelled particles which move at constant speed and, in addition, reverse their direction of motion repeatedly are investigated. The internal dynamics of particles triggering these reversal processes is modeled by a stochastic clock. The velocity correlation function as well as the mean squared displacement is investigated and, furthermore, a general expression for the diffusion coefficient for self-propelled particles with directional reversal is derived. Our analysis reveals the existence of an optimal, finite rotational noise amplitude which maximizes the diffusion coefficient. We comment on the relevance of these results with regard to biological systems and suggest further experiments in this context.

  10. Interfacial Microstructure Evolution and Shear Strength of Titanium Sandwich Structures Fabricated by Brazing

    NASA Astrophysics Data System (ADS)

    Wang, Wentao; Fan, Minyu; Li, Jinlong; Tao, Jie

    2016-03-01

    The corrugated sandwich structure, consisting of a CP Ti (commercially pure titanium) core between two Ti-6Al-4V face sheets, was brazed using pasty Ti-37.5Zr-15Cu-10Ni as filler alloy, at the temperature of 870°C for 5, 10, 20, and 30 min. The effect of brazing time on the microstructure and elemental distribution of the brazed joints was examined by means of SEM, EDS, and XRD analyses. It was found that various intermetallic phases were formed in the brazed joints, following a brazing time of 5 min, and their contents were decreased by the increment of brazing time, while prolonged brazing time resulted in a fine, acicular Widmanstätten microstructure throughout the entire joint. In addition, shear testing was performed in the brazed corrugated specimens in order to indirectly assess the quality of the joints. The debonding between CP Ti and Ti-6Al-4V was observed in the specimen brazed for 5 min and the fracture of the CP Ti corrugated core occurred after 30 min of brazing time. Additionally, when brazed for 10 min or 20 min, brittle intermetallic compounds in the joints and the grain growth of the base metal were controllable. Therefore, the sandwich structures failed without debonding in the joints or fracture within the base metal, demonstrating a good combination of strength and ductility.

  11. Active Teaching of Diffusion through History of Science, Computer Animation and Role Playing

    ERIC Educational Resources Information Center

    Krajsek, Simona Strgulc; Vilhar, Barbara

    2010-01-01

    We developed and tested a lesson plan for active teaching of diffusion in secondary schools (grades 10-13), which stimulates understanding of the thermal (Brownian) motion of particles as the principle underlying diffusion. During the lesson, students actively explore the Brownian motion through microscope observations of irregularly moving small…

  12. Influences of Nozzle Material on Laser Droplet Brazing Joints with Cu89Sn11 Preforms

    NASA Astrophysics Data System (ADS)

    Stein, Stefan; Heberle, Johannes; Gürtler, Franz Josef; Cvecek, Kristian; Roth, Stephan; Schmidt, Michael

    This paper presents latest results on the influences of nozzle material and geometry on the electromechanical contacting of sensitive piezoceramic actuator modules. Two nozzle types have been investigated,a standard WC/Co nozzle which is used for soldering applications and a novelceramic nozzle. Applications for active piezoceramic components integrated in structural parts are e.g. active damping, energy harvesting, or monitoring of vibrations and material failure. Anup to now unsolved problem is the electrical contacting of such components without damaging the conductor or the metallization of the ceramic substrate. Since piezoelectric components are to be integrated into structures made of casted aluminum, requirements are high mechanical strength and temperature resistance. Within this paper a method forcontacting piezoceramic modules is presented. A spherical braze preform of tin bronze Cu89Sn11 with a diameter of 600 μm is located in a ceramic nozzle and is subsequently melted by a laser pulse. The liquid solder is ejected from the nozzlevia nitrogen overpressure and wets the surface of the metallization pad and the Cu-wire, resulting in a brazing joint after solidification. The process is called laser droplet brazing (LDB). To asses the thermal evolution during one cycle WC/Co and ZTA have been simulated numerically for two different geometries enabling a proposition weather the geometry or the material properties have a significant influence on the thermal load during one cycle. To evaluate the influence of the nozzle on the joint the positioning accuracy, joint height and detachment times have been evaluated. Results obtained with the ZTA nozzle show comparable positioning accuracies to a WC/Co nozzle with a lower standard deviation of solder detachment time.

  13. Activation of bone remodeling after fatigue: differential response to linear microcracks and diffuse damage.

    PubMed

    Herman, B C; Cardoso, L; Majeska, R J; Jepsen, K J; Schaffler, M B

    2010-10-01

    Recent experiments point to two predominant forms of fatigue microdamage in bone: linear microcracks (tens to a few hundred microns in length) and "diffuse damage" (patches of diffuse stain uptake in fatigued bone comprised of clusters of sublamellar-sized cracks). The physiological relevance of diffuse damage in activating bone remodeling is not known. In this study microdamage amount and type were varied to assess whether linear or diffuse microdamage has similar effects on the activation of intracortical resorption. Activation of resorption was correlated to the number of linear microcracks (Cr.Dn) in the bone (R(2)=0.60, p<0.01). In contrast, there was no activation of resorption in response to diffuse microdamage alone. Furthermore, there was no significant change in osteocyte viability in response to diffuse microdamage, suggesting that osteocyte apoptosis, which is known to activate remodeling at typical linear microcracks in bone, does not result from sublamellar damage. These findings indicate that inability of diffuse microdamage to activate resorption may be due to lack of a focal injury response. Finally, we found that duration of loading does not affect the remodeling response. In conclusion, our data indicate that osteocytes activate resorption in response to linear microcracks but not diffuse microdamage, perhaps due to lack of a focal injury-induced apoptotic response. PMID:20633708

  14. Field installed brazed thermocouple feedthroughs for high vacuum experiments

    NASA Astrophysics Data System (ADS)

    Anderson, P. M.; Messick, C.

    1983-12-01

    In order to reduce the occurrence of vacuum leaks and to increase the availability of the DIII vacuum vessel for experimental operation, effort was applied to developing a vacuum-tight brazed feedthrough system for sheathed thermocouples, stainless steel sheathed conductor cables and tubes for cooling fluids. This brazed technique is a replacement for elastomer O ring sealed feedthroughs that have proven vulnerable to leaks caused by thermal cycling, etc. To date, about 200 feedthroughs were used. Up to 91 were grouped on a single conflat flange mounted in a bulkhead connector configuration which facilitates installation and removal. Investigation was required to select a suitable braze alloy, flux and installation procedure. Braze alloy selection was challenging since the alloy was required to have: (1) melting temperature in excess of the 250 C (482 F) bakeout temperature; (2) no high vapor pressure elements; (3) good wetting properties when used in air with acceptable flux; and (4) good wettability to 300 series stainless steel and Inconel.

  15. More About Brazing Or Welding NiAl Without Filler

    NASA Technical Reports Server (NTRS)

    Moore, Thomas J.; Kalinowski, Joseph M.

    1996-01-01

    Two reports present additional information about two processes for joining, brazing, or welding workpieces made of nickel aluminide alloys, without use of filler metal. Joining processes involve uniform heating in vacuum-controlled furnace. Eliminates internal thermal gradients in workpieces joined and greatly reduces tendency toward cracking.

  16. 46 CFR 56.75-20 - Brazing qualification.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... brazing operators shall be in accordance with the requirements of part C, Section IX of the ASME Boiler and Pressure Vessel Code (incorporated by reference; see 46 CFR 56.01-2) and part 57 of this... Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) MARINE ENGINEERING PIPING SYSTEMS...

  17. 46 CFR 56.75-20 - Brazing qualification.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... brazing operators shall be in accordance with the requirements of part C, section IX of the ASME Boiler and Pressure Vessel Code (incorporated by reference; see 46 CFR 56.01-2) and part 57 of this... Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) MARINE ENGINEERING PIPING SYSTEMS...

  18. 46 CFR 56.75-20 - Brazing qualification.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... brazing operators shall be in accordance with the requirements of part C, Section IX of the ASME Boiler and Pressure Vessel Code (incorporated by reference; see 46 CFR 56.01-2) and part 57 of this... Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) MARINE ENGINEERING PIPING SYSTEMS...

  19. 46 CFR 56.75-20 - Brazing qualification.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... brazing operators shall be in accordance with the requirements of part C, section IX of the ASME Boiler and Pressure Vessel Code (incorporated by reference; see 46 CFR 56.01-2) and part 57 of this... Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) MARINE ENGINEERING PIPING SYSTEMS...

  20. Low-energy gamma ray inspection of brazed aluminum joints

    NASA Technical Reports Server (NTRS)

    Brown, J. A.

    1967-01-01

    Americium 241 serves as a suitable radioisotope /gamma ray source/ and exposure probe for radiographic inspection of brazed aluminum joints in areas of limited accessibility. The powdered isotope is contained in a sealed capsule mounted at the end of a spring-loaded pushrod in the probe assembly.

  1. Computation of Rate Constants for Diffusion of Small Ligands to and from Buried Protein Active Sites.

    PubMed

    Wang, P-H; De Sancho, D; Best, R B; Blumberger, J

    2016-01-01

    The diffusion of ligands to actives sites of proteins is essential to enzyme catalysis and many cellular signaling processes. In this contribution we review our recently developed methodology for calculation of rate constants for diffusion and binding of small molecules to buried protein active sites. The diffusive dynamics of the ligand obtained from molecular dynamics simulation is coarse grained and described by a Markov state model. Diffusion and binding rate constants are then obtained either from the reactive flux formalism or by fitting the time-dependent population of the Markov state model to a phenomenological rate law. The method is illustrated by applications to diffusion of substrate and inhibitors in [NiFe] hydrogenase, CO-dehydrogenase, and myoglobin. We also discuss a recently developed sensitivity analysis that allows one to identify hot spots in proteins, where mutations are expected to have the strongest effects on ligand diffusion rates. PMID:27497172

  2. Wetting and spreading behavior of molten brazing filler metallic alloys on metallic substrate

    NASA Astrophysics Data System (ADS)

    Kogi, Satoshi; Kajiura, Tetsurou; Hanada, Yukiakira; Miyazawa, Yasuyuki

    2014-08-01

    Wetting and spreading of molten brazing filler material are important factors that influence the brazing ability of a joint to be brazed. Several investigations into the wetting ability of a brazing filler alloy and its surface tension in molten state, in addition to effects of brazing time and temperature on the contact angle, have been carried out. In general, dissimilar-metals brazing technology and high-performance brazed joint are necessities for the manufacturing field in the near future. Therefore, to address this requirement, more such studies on wetting and spreading of filler material are required for a deeper understanding. Generally, surface roughness and surface conditions affect spreading of molten brazing filler material during brazing. Wetting by and interfacial reactions of the molten brazing filler material with the metallic substrate, especially, affect strongly the spreading of the filler material. In this study, the effects of surface roughness and surface conditions on the spreading of molten brazing filler metallic alloys were investigated. Ag-(40-x)Cu-xIn and Ag- (40-x)Cu-xSn (x=5, 10, 15, 20, 25) alloys were used as brazing filler materials. A mild-steel square plate (S45C (JIS); side: 30 mm; thickness: 3mm) was employed as the substrate. A few surfaces with varying roughness were prepared using emery paper. Brazing filler material and metallic base plate were first washed with acetone, and then a flux was applied to them. The filler, 50 mg, was placed on the center of the metallic base with the flux. A spreading test was performed under Ar gas using an electrically heated furnace, after which, the original spreading area, defined as the sessile drop area, and the apparent spreading area, produced by the capillary grooves, were both evaluated. It was observed that the spreading area decreased with increasing In and Sn content.

  3. Copper Gas Diffusers For Purging Line-Focus Laser Welds

    NASA Technical Reports Server (NTRS)

    Fonteyne, Steve L.; Hosking, Timothy J.; Shelley, D. Mark

    1996-01-01

    Modified flow diffusers built for inert-gas purging of welds made with 5-kW CO(2) lasers operating with line-focus optics in conduction mode instead of with point-focus optics in customary keyhole mode. Diffusers made of copper components brazed together, robust enough to withstand strong reflections of line-focused laser energy.

  4. Perturbative path-integral study of active- and passive-tracer diffusion in fluctuating fields

    NASA Astrophysics Data System (ADS)

    Démery, Vincent; Dean, David S.

    2011-07-01

    We study the effective diffusion constant of a Brownian particle linearly coupled to a thermally fluctuating scalar field. We use a path-integral method to compute the effective diffusion coefficient perturbatively to lowest order in the coupling constant. This method can be applied to cases where the field is affected by the particle (an active tracer) and cases where the tracer is passive. Our results are applicable to a wide range of physical problems, from a protein diffusing in a membrane to the dispersion of a passive tracer in a random potential. In the case of passive diffusion in a scalar field, we show that the coupling to the field can, in some cases, speed up the diffusion corresponding to a form of stochastic resonance. Our results on passive diffusion are also confirmed via a perturbative calculation of the probability density function of the particle in a Fokker-Planck formulation of the problem. Numerical simulations on simplified systems corroborate our results.

  5. Evaluation of Superplastic Forming and Weld-brazing for Fabrication of Titanium Compression Panels

    NASA Technical Reports Server (NTRS)

    Royster, D. M.; Bales, T. T.; Davis, R. C.

    1985-01-01

    The two titanium processing procedures, superplastic forming and weld brazing, are successfully combined to fabricate titanium skin stiffened structural panels. Stiffeners with complex shapes are superplastically formed using simple tooling. These stiffeners are formed to the desired configuration and required no additional sizing or shaping following removal from the mold. The weld brazing process by which the stiffeners are attached to the skins utilize spot welds to maintain alignment and no additional tooling is required for brazing. The superplastic formed/weld brazed panels having complex shaped stiffeners develop up to 60 percent higher buckling strengths than panels with conventional shaped stiffeners. The superplastic forming/weld brazing process is successfully scaled up to fabricate full size panels having multiple stiffeners. The superplastic forming/weld brazing process is also successfully refined to show its potential for fabricating multiple stiffener compression panels employing unique stiffener configurations for improved structural efficiency.

  6. Improved Wetting of Mixed Ionic/Electronic Conductors Used in Electrochemical Devices with Ternary Reactive Air Braze Filler Metals

    SciTech Connect

    Hardy, John S; Kim, Jin Yong Y; Thomsen, Ed C; Weil, K Scott

    2007-01-19

    This paper reports on the wetting behavior, reactivity, and long-term electrical conductance of a series of ternary filler metals being considered for brazing lanthanum strontium cobalt ferrite (LSCF) based oxygen separation membranes. Mixed ionic/electronic conducting perovskite oxides such as LSCF and various doped barium cerates are currently being considered for use in high-temperature electrochemical devices such as oxygen and hydrogen concentrators and solid oxide fuel cells. However to take full advantage of the unique properties of these materials, reliable joining techniques need to be developed. Furthermore, if the proposed joining technique were to yield a hermetic ceramic-to-metal junction that was also electrically conductive, it would additionally benefit the device by allowing current to be drawn from or carried to the electrochemically active mixed conducting oxide component without requiring an separate current collector. A newly developed brazing technique known as air brazing is one such method of joining. In its present form, air brazing uses a silver-copper oxide based filler metal that can be melted directly in air to form a compliant joint that is electrically conductive. Recently, it has been shown that the addition of titania can enhance the wetting behavior of Ag-CuO filler metals on alumina. Here the effect of this wetting agent on the surface wettability, long-term electrical resistance at 750°C, and reactivity with La0.6Sr0.4Co0.2Fe0.8O3- (LSCF-6428 or LSCF) substrates is discussed.

  7. DEVELOPMENT OF AN ACTIVE PERSONAL OZONE SAMPLER USING A HOLLOW TUBE DIFFUSION DENUDER

    EPA Science Inventory

    Personal, microenvironmental and indoor ozone monitoring is currently conducted using a lightweight, inexpensive sampling device. lthough the passive device is adequate for many studies, we are developing a relatively ight weight active hollow tube diffusion denuder system which ...

  8. Braze material for joining ceramic to metal and ceramic to ceramic surfaces and joined ceramic to metal and ceramic to ceramic article

    DOEpatents

    Hunt, T.K.; Novak, R.F.

    1991-05-07

    An improved active metal braze filler material is provided in which the coefficient of thermal expansion of the braze filler is more closely matched with that of the ceramic and metal, or two ceramics, to provide ceramic to metal, or ceramic to ceramic, sealed joints and articles which can withstand both high temperatures and repeated thermal cycling without failing. The braze filler material comprises a mixture of a material, preferably in the form of a powder, selected from the group consisting of molybdenum, tungsten, silicon carbide and mixtures thereof, and an active metal filler material selected from the group consisting of alloys or mixtures of nickel and titanium, alloys or mixtures of nickel and zirconium, alloys or mixtures of nickel, titanium, and copper, alloys or mixtures of nickel, titanium, and zirconium, alloys or mixtures of niobium and nickel, alloys or mixtures of niobium and zirconium, alloys or mixtures of niobium and titanium, alloys or mixtures of niobium, titanium, and nickel, alloys or mixtures of niobium, zirconium, and nickel, and alloys or mixtures of niobium, titanium, zirconium, and nickel. The powder component is selected such that its coefficient of thermal expansion will effect the overall coefficient of thermal expansion of the braze material so that it more closely matches the coefficients of thermal expansion of the ceramic and metal parts to be joined. 3 figures.

  9. Braze material for joining ceramic to metal and ceramic to ceramic surfaces and joined ceramic to metal and ceramic to ceramic article

    DOEpatents

    Hunt, Thomas K.; Novak, Robert F.

    1991-01-01

    An improved active metal braze filler material is provided in which the coefficient of thermal expansion of the braze filler is more closely matched with that of the ceramic and metal, or two ceramics, to provide ceramic to metal, or ceramic to ceramic, sealed joints and articles which can withstand both high temperatures and repeated thermal cycling without failing. The braze filler material comprises a mixture of a material, preferably in the form of a powder, selected from the group consisting of molybdenum, tungsten, silicon carbide and mixtures thereof, and an active metal filler material selected from the group consisting of alloys or mixtures of nickel and titanium, alloys or mixtures of nickel and zirconium, alloys or mixtures of nickel, titanium, and copper, alloys or mixtures of nickel, titanium, and zirconium, alloys or mixtures of niobium and nickel, alloys or mixtures of niobium and zirconium, alloys or mixtures of niobium and titanium, alloys or mixtures of niobium, titanium, and nickel, alloys or mixtures of niobium, zirconium, and nickel, and alloys or mixtures of niobium, titanium, zirconium, and nickel. The powder component is selected such that its coefficient of thermal expansion will effect the overall coefficient of thermal expansion of the braze material so that it more closely matches the coefficients of thermal expansion of the ceramic and metal parts to be joined.

  10. Kinetics of water vapor diffusion in activated carbon

    NASA Astrophysics Data System (ADS)

    Kurmasheva, D. M.; Kapralov, P. O.; Travkin, V. D.; Artemov, V. G.; Tikhonov, V. I.; Volkov, A. A.

    2014-05-01

    We describe an experimental method for studying rapid processes of water vapor sorption by fine-dispersed and porous materials. The concentration of gas-phase water molecules is detected during adsorption by a laser-diode spectrometer. The kinetic pressure curves are recorded in a time window of 10-1 to 103 s and are analyzed using analogy of the diffusion flow with the electric current in a branched RC circuit. The proposed model establishes the relation between the kinetics curves being measured and the structural parameters of the medium.

  11. Low vapor pressure braze alloys for thermionic energy converters

    NASA Technical Reports Server (NTRS)

    Bair, V. L.

    1976-01-01

    Preliminary results in the use of some low-vapor-pressure braze alloys are reported; these are binary alloys of refractory metals (Th, Zr, Hf, Ru, Nb, Ir, Mo, Ta, Os, Re, W) with vapor pressures below 0.1 nanotorr at 1500 K or 10 microtorr at 2000 K. The melting point minima or eutectics of the alloys range from 1510 K to above 3000 K. Melting points and surface wetting on a Ta base are given. Results are presented on brazing of Ir, LaB6, Nb, Re, W, and ZrO2 (with 22 wt % Zr) into a Ta base or a Nb-1% Zr base. The results are applicable in electrode screening programs for thermionic cesium diodes.

  12. Corrosion Testing of Brazed Space Station IATCS Materials

    NASA Technical Reports Server (NTRS)

    Pohlman, Matthew J.; Varisik, Jerry; Steele, John W.; Golden, Johnny L.; Boyce, William E.; Pedley, Michael D.

    2004-01-01

    Increased nickel concentrations in the IATCS coolant prompted a study of the corrosion rates of nickel-brazed heat exchangers in the system. The testing has shown that corrosion is occurring in a silicon-rich intermetallic phase in the braze filler of coldplates and heat exchangers as the result of a decrease in the coolant pH brought about by cabin carbon dioxide permeation through polymeric flexhoses. Similar corrosion is occurring in the EMU de-ionized water loop. Certain heat exchangers and coldplates have more silicon-rich phase because of their manufacturing method, and those units produce more nickel corrosion product. Silver biocide additions did not induce pitting corrosion at silver precipitate sites.

  13. New hermetic sealing material for vacuum brazing of stainless steels

    NASA Astrophysics Data System (ADS)

    Hildebrandt, S.; Wiehl, G.; Silze, F.

    2016-03-01

    For vacuum brazing applications such as in vacuum interrupter industry Hermetic Sealing Materials (HSM) with low partial pressure are widely used. AgCu28 dominates the hermetic sealing market, as it has a very good wetting behavior on copper and metallized ceramics. Within recent decades wetting on stainless steel has become more and more important. However, today the silver content of HSMs is more in focus than in the past decades, because it has the biggest impact on the material prices. Umicore Technical Materials has developed a new copper based HSM, CuAg40Ga10. The wettability on stainless steel is significantly improved compared to AgCu28 and the total silver content is reduced by almost 44%. In this article the physical properties of the alloy and its brazed joints will be presented compared to AgCu28.

  14. Separation and Sealing of a Sample Container Using Brazing

    NASA Technical Reports Server (NTRS)

    Bar-Cohen, Yoseph; Rivellini, Tommaso P.; Wincentsen, James E.; Gershman, Robert

    2007-01-01

    A special double-wall container and a process for utilizing the container are being developed to enable (1) acquisition of a sample of material in a dirty environment that may include a biological and/or chemical hazard; (2) sealing a lid onto the inner part of the container to hermetically enclose the sample; (3) separating the resulting hermetic container from the dirty environment; and (4) bringing that hermetic container, without any biological or chemical contamination of its outer surface, into a clean environment. The process is denoted S(exp 3)B (separation, seaming, and sealing using brazing) because sealing of the sample into the hermetic container, separating the container from the dirty environment, and bringing the container with a clean outer surface into the clean environment are all accomplished simultaneously with a brazing operation.

  15. Flight service evaluation of two aluminum-brazed titanium spoilers

    NASA Technical Reports Server (NTRS)

    Boyer, R. R.

    1984-01-01

    The long-term service evaluation of two aluminum-brazed titanium (ABTi) honeycomb flight spoilers was concluded. The two spoilers had about 7.5 years of commercial flight experience on All Nippon Airways Model 737 aircraft. All Nippon Airways was selected because Japan has one of the most severe marine-industrial environments in the world. The results indicated that both flight spoilers still had the same load-carrying capability as when they were originally installed. No direct evidence of any corrosion was observed on either spoiler. Another significant accomplishment of this effort was the development of a braze design for efficiently distributing point loads from the fittings and skin into the honeycomb core.

  16. Effects of service environments on aluminum-brazed titanium (ABTi)

    NASA Technical Reports Server (NTRS)

    Cotton, W. L.

    1978-01-01

    Aluminum brazed titanium (ABTi) structures were evaluated during prolonged exposure to extreme environments: elevated temperature exposure to airline service fluids, hydraulic fluid, and seawater, followed by laboratory corrosion tests. Solid-face and perforated face honeycomb sandwich panel specimens, stressed panel assemblies, and faying surface brazed joints were tested. The corrosion resistance of ABTi is satisfactory for commercial airline service. Unprotected ABTi proved inherently resistant to attack by all of the extreme service aircraft environments except: seawater at 700 K (800 F) and above, dripping phosphate ester hydraulic fluid at 505 K (450 F), and a marine environment at ambient temperature. The natural oxides and deposits present on titanium surfaces in airline service provide protection against hot salt corrosion pitting. Coatings are required to protect titanium dripping phosphate ester fluid at elevated temperatures and to protect exposed acoustic honeycomb parts against corrosion in a marine environment.

  17. Effect of Temperature and Sheet Temper on Isothermal Solidification Kinetics in Clad Aluminum Brazing Sheet

    NASA Astrophysics Data System (ADS)

    Benoit, Michael J.; Whitney, Mark A.; Wells, Mary A.; Winkler, Sooky

    2016-07-01

    Isothermal solidification (IS) is a phenomenon observed in clad aluminum brazing sheets, wherein the amount of liquid clad metal is reduced by penetration of the liquid clad into the core. The objective of the current investigation is to quantify the rate of IS through the use of a previously derived parameter, the Interface Rate Constant (IRC). The effect of peak temperature and initial sheet temper on IS kinetics were investigated. The results demonstrated that IS is due to the diffusion of silicon (Si) from the liquid clad layer into the solid core. Reduced amounts of liquid clad at long liquid duration times, a roughened sheet surface, and differences in resolidified clad layer morphology between sheet tempers were observed. Increased IS kinetics were predicted at higher temperatures by an IRC model as well as by experimentally determined IRC values; however, the magnitudes of these values are not in good agreement due to deficiencies in the model when applied to alloys. IS kinetics were found to be higher for sheets in the fully annealed condition when compared with work-hardened sheets, due to the influence of core grain boundaries providing high diffusivity pathways for Si diffusion, resulting in more rapid liquid clad penetration.

  18. Effect of Temperature and Sheet Temper on Isothermal Solidification Kinetics in Clad Aluminum Brazing Sheet

    NASA Astrophysics Data System (ADS)

    Benoit, Michael J.; Whitney, Mark A.; Wells, Mary A.; Winkler, Sooky

    2016-09-01

    Isothermal solidification (IS) is a phenomenon observed in clad aluminum brazing sheets, wherein the amount of liquid clad metal is reduced by penetration of the liquid clad into the core. The objective of the current investigation is to quantify the rate of IS through the use of a previously derived parameter, the Interface Rate Constant (IRC). The effect of peak temperature and initial sheet temper on IS kinetics were investigated. The results demonstrated that IS is due to the diffusion of silicon (Si) from the liquid clad layer into the solid core. Reduced amounts of liquid clad at long liquid duration times, a roughened sheet surface, and differences in resolidified clad layer morphology between sheet tempers were observed. Increased IS kinetics were predicted at higher temperatures by an IRC model as well as by experimentally determined IRC values; however, the magnitudes of these values are not in good agreement due to deficiencies in the model when applied to alloys. IS kinetics were found to be higher for sheets in the fully annealed condition when compared with work-hardened sheets, due to the influence of core grain boundaries providing high diffusivity pathways for Si diffusion, resulting in more rapid liquid clad penetration.

  19. Ultrasonic guided wave inspection of Inconel 625 brazed lap joints

    NASA Astrophysics Data System (ADS)

    Comot, Pierre; Bocher, Philippe; Belanger, Pierre

    2016-04-01

    The aerospace industry has been investigating the use of brazing for structural joints, as a mean of reducing cost and weight. There therefore is a need for a rapid, robust, and cost-effective non-destructive testing method for evaluating the structural integrity of the joints. The mechanical strength of brazed joints depends mainly on the amount of brittle phases in their microstructure. Ultrasonic guided waves offer the possibility of detecting brittle phases in joints using spatio-temporal measurements. Moreover, they offer the opportunity to inspect complex shape joints. This study focused on the development of a technique based on ultrasonic guided waves for the inspection of Inconel 625 lap joints brazed with BNi-2 filler metal. A finite element model of a lap joint was used to optimize the inspection parameters and assess the feasibility of detecting the amount of brittle phases in the joint. A finite element parametric study simulating the input signal shape, the center frequency, and the excitation direction was performed. The simulations showed that the ultrasonic guided wave energy transmitted through, and reflected from, the joints was proportional to the amount of brittle phases in the joint.

  20. Mechanistic understanding of aerosol emissions from a brazing operation.

    PubMed

    Zimmer, A T; Biswas, P

    2000-01-01

    Welding operations produce gaseous and aerosol by-products that can have adverse health effects. A laboratory furnace study was conducted to aid understanding of the chemical and aerosol behavior of a widely used, self-fluxing brazing alloy (89% Cu, 6% Ag, 5% P) that is also used with a supplemental fluxing compound to prevent oxidation at the molten metal surface. The results indicate that the aerosols generated by the alloy are transient (produced over a short duration of time) and are associated with mass transfer of phosphorus species from the molten metal surface to the surrounding gas. In contrast, when the alloy was used in conjunction with the supplemental fluxing compound, a relatively nontransient, submicron-size aerosol was generated that was several orders of magnitude higher in concentration. Thermodynamic equilibrium analysis suggests that fluoride (a major constituent in the fluxing compound) played a significant role in reacting with the brazing alloy metals to form gas phase metal fluoride compounds that had high vapor pressures when compared with their elemental or oxide forms. As these metal-fluoride vapors cooled, submicron-size particles were formed mainly through nucleation and condensation growth processes. In addition, the equilibrium results revealed the potential formation of severe pulmonary irritants (HF and BF3) from heating the supplemental fluxing compound. These results demonstrated the importance of fluxing compounds in the formation of brazing fumes, and suggest that fluxing compounds could be selected that serve their metallurgical intention and suppress the formation of aerosols. PMID:10885884

  1. Dispersed metal-toughened ceramics and ceramic brazing

    SciTech Connect

    Moorhead, A.J.; Tiegs, T.N.; Lauf, R.J.

    1983-01-01

    An alumina (Al/sub 2/O/sub 3/) based material that contains approximately 1 vol % finely dispersed platinum or chromium was developed for use in high temperature thermal-shock resistant electrical insulators. The work at ORNL is divided into two areas: (1) development of DMT ceramics; and (2) development of brazing filler metals suitable for making ceramic-to-ceramic and ceramic-to-metal brazements. The DMT ceramics and brazements are intended for service at elevated temperatures and at high stress levels in the dirty environments of advanced heat engines. The development and characterization of DMT ceramics includes processing (powder preparation, densification and heat treatment) and detailed measurement of mechanical and physical properties (strength, fracture toughness, and thermal conductivity). The brazing work includes: (1) the formulation and melting of small quantities of experimental brazing filler metals; (2) evaluation of the wetting and bonding behavior of these filler metals on Al/sub 2/O/sub 3/, partially stabilized zirconia and ..cap alpha..-SiC in a sessile drop apparatus; and (3) determine the short-term strength and fracture toughness of brazements.

  2. Cognitive activity, cognitive function, and brain diffusion characteristics in old age.

    PubMed

    Arfanakis, Konstantinos; Wilson, Robert S; Barth, Christopher M; Capuano, Ana W; Vasireddi, Anil; Zhang, Shengwei; Fleischman, Debra A; Bennett, David A

    2016-06-01

    The objective of this work was to test the hypotheses that a) more frequent cognitive activity in late life is associated with higher brain diffusion anisotropy and lower trace of the diffusion tensor, and b) brain diffusion characteristics partially mediate the association of late life cognitive activity with cognition. As part of a longitudinal cohort study, 379 older people without dementia rated their frequency of participation in cognitive activities, completed a battery of cognitive function tests, and underwent diffusion tensor imaging. We used tract-based spatial statistics to test the association between late life cognitive activity and brain diffusion characteristics. Clusters with statistically significant findings defined regions of interest in which we tested the hypothesis that diffusion characteristics partially mediate the association of late life cognitive activity with cognition. More frequent cognitive activity in late life was associated with higher level of global cognition after adjustment for age, sex, education, and indicators of early life cognitive enrichment (p = 0.001). More frequent cognitive activity was also related to higher fractional anisotropy in the left superior and inferior longitudinal fasciculi, left fornix, and corpus callosum, and lower trace in the thalamus (p < 0.05, FWE-corrected). After controlling for fractional anisotropy or trace from these regions, the regression coefficient for the association of late life cognitive activity with cognition was reduced by as much as 26 %. These findings suggest that the association of late life cognitive activity with cognition may be partially mediated by brain diffusion characteristics. PMID:25982658

  3. Diffusion of GPI-anchored proteins is influenced by the activity of dynamic cortical actin

    PubMed Central

    Saha, Suvrajit; Lee, Il-Hyung; Polley, Anirban; Groves, Jay T.; Rao, Madan; Mayor, Satyajit

    2015-01-01

    Molecular diffusion at the surface of living cells is believed to be predominantly driven by thermal kicks. However, there is growing evidence that certain cell surface molecules are driven by the fluctuating dynamics of cortical cytoskeleton. Using fluorescence correlation spectroscopy, we measure the diffusion coefficient of a variety of cell surface molecules over a temperature range of 24–37°C. Exogenously incorporated fluorescent lipids with short acyl chains exhibit the expected increase of diffusion coefficient over this temperature range. In contrast, we find that GPI-anchored proteins exhibit temperature-independent diffusion over this range and revert to temperature-dependent diffusion on cell membrane blebs, in cells depleted of cholesterol, and upon acute perturbation of actin dynamics and myosin activity. A model transmembrane protein with a cytosolic actin-binding domain also exhibits the temperature-independent behavior, directly implicating the role of cortical actin. We show that diffusion of GPI-anchored proteins also becomes temperature dependent when the filamentous dynamic actin nucleator formin is inhibited. However, changes in cortical actin mesh size or perturbation of branched actin nucleator Arp2/3 do not affect this behavior. Thus cell surface diffusion of GPI-anchored proteins and transmembrane proteins that associate with actin is driven by active fluctuations of dynamic cortical actin filaments in addition to thermal fluctuations, consistent with expectations from an “active actin-membrane composite” cell surface. PMID:26378258

  4. HIGH TEMPERATURE BRAZING ALLOY FOR JOINT Fe-Cr-Al MATERIALS AND AUSTENITIC AND FERRITIC STAINLESS STEELS

    DOEpatents

    Cost, R.C.

    1958-07-15

    A new high temperature brazing alloy is described that is particularly suitable for brazing iron-chromiumaluminum alloys. It consists of approximately 20% Cr, 6% Al, 10% Si, and from 1.5 to 5% phosphorus, the balance being iron.

  5. Anomalous diffusion of an ellipsoid in quasi-2D active fluids

    NASA Astrophysics Data System (ADS)

    Peng, Yi; Yang, Ou; Tang, Chao; Cheng, Xiang

    Enhanced diffusion of a tracer particle is a unique feature in active fluids. Here, we studied the diffusion of an ellipsoid in a free-standing film of E. coli. Particle diffusion is linearly enhanced at low bacterial concentrations, whereas a non-linear enhancement is observed at high bacterial concentrations due to the giant fluctuation. More importantly, we uncover an anomalous coupling between the translational and rotational degrees of freedom that is strictly prohibited in the classical Brownian diffusion. Combining experiments with theoretical modeling, we show that such an anomaly arises from the stretching flow induced by the force dipole of swimming bacteria. Our work illustrates a novel universal feature of active matter and transforms the understanding of fundamental transport processes in microbiological systems. ACS Petroleum Research Fund #54168-DNI9, NSF Faculty Early Career Development Program, DMR-1452180.

  6. Active galaxies and the diffuse Gamma-Ray background

    NASA Technical Reports Server (NTRS)

    Kazanas, D.; Protheroe, R. J.

    1983-01-01

    A model for the origin of relativistic particles and gamma rays in active galactic nuclei and quasars, together with recent HEAO-1 observations of the spectra of active galaxies from 2 to 165 keV, provide the basis for a reexamination of the nature of the extragalactic gamma ray background. Active galaxies account for the observed background if their X-ray spectra steepen to E.021 above 100 keV, as observed in Cen-A, together with a further steepening to E.021 as a result of absorption of gamma rays by photon-photon pair production interactions with X-ray photons. The compactness of active galaxies required to give this steepening is consistent with estimates of their typical luminosity and radius.

  7. Ceruminal diffusion activities and ceruminolytic characteristics of otic preparations – an in-vitro study

    PubMed Central

    2013-01-01

    Background An in-vitro setup was established in order to determine a) the diffusion activities of eight otic preparations (Aurizon®, Eas Otic®, Epi Otic®, Otifree®, Otomax®, Panolog®, Posatex®, Surolan®) through synthetic cerumen, and b) the ceruminolytic capacity and impregnation effects of these products. The main lipid classes of canine cerumen produced with moderate, non-purulent otitis externa were determined by thin layer chromatography and were subsequently used to produce a standardised synthetic cerumen (SCC). SCC was filled into capillary tubes, all of which were loaded with six commercially available multipurpose otic medications and two ear cleaners, each mixed with two markers in two experimental setups. These two marker compounds (Oil red O and marbofloxacin) were chosen, since they exhibit different physicochemical drug characteristics by which it is possible to determine and verify the diffusion activity of different types of liquids (i.e. the otic preparations). A synthetic cerumen described in the literature (JSL) was also used for comparison as its lipid composition was different to SCC. The diffusion activities of the otic preparations through both types of synthetic cerumen were studied over 24 hours. A second in-vitro experiment determined both the ceruminolytic activity and impregnation effect of the otic preparations by comparing the weight loss or weight gain after repeated incubation of JSL. Results Canine cerumen is mainly composed of triglycerides, sterol esters, fatty acid esters and squalene. The diffusion experiments showed a high diffusion efficacy along with a high impregnation effect for one test product. All the other products exhibited a lower diffusion activity with a mild to moderate impregnation effect. A mild ceruminolytic activity was observed for the two ear cleaners but not for any of the otic medications. Conclusions The present study demonstrates that there are significant differences in the diffusion

  8. Direct and fast detection of neuronal activation in the human brain with diffusion MRI

    PubMed Central

    Le Bihan, Denis; Urayama, Shin-ichi; Aso, Toshihiko; Hanakawa, Takashi; Fukuyama, Hidenao

    2006-01-01

    Using MRI, we found that a slowly diffusing water pool was expanding (1.7 ± 0.3%) upon activation on the human visual cortex at the detriment of a faster diffusing pool. The time course of this water phase transition preceded the activation-triggered vascular response detected by usual functional MRI by several seconds. The observed changes in water diffusion likely reflect early biophysical events that take place in the activated cells, such as cell swelling and membrane expansion. Although the exact mechanisms remain to clarify, access to such an early and direct physiological marker of cortical activation with MRI will provide opportunities for functional neuroimaging of the human brain. PMID:16702549

  9. Volatile species in halide-activated-diffusion coating packs

    NASA Technical Reports Server (NTRS)

    Bianco, Robert; Rapp, Robert A.; Jacobson, Nathan S.

    1992-01-01

    An atmospheric pressure sampling mass spectrometer was used to identify the vapor species generated in a halide-activated cementation pack. Pack powder mixtures containing a Cr-Al binary masteralloy powder, an NH4Cl activator salt, and either ZrO2 or Y2O3 (or neither) were analyzed at 1000 C. Both the equilibrium calculations for the pack and mass spectrometer results indicated that volatile AlCl(x) and CrCl(y) species were generated by the pack powder mixture; in packs containing the reactive element oxide, volatile ZrCl(z) and YCl(w) species were formed by the conversion of their oxide sources.

  10. Recent experience in the fabrication and brazing of ceramic beam tubes for kicker magnets at FNAL

    SciTech Connect

    Ader, C.R.; Jensen, C.; Reilly, R.; Snee, D.; Wilson, J.H.; /Fermilab

    2008-06-01

    Ceramic beam tubes are utilized in numerous kicker magnets in different accelerator rings at Fermi National Accelerator Laboratory. Kovar flanges are brazed onto each beam tube end, since kovar and high alumina ceramic have similar expansion curves. The tube, kovar flange, end piece, and braze foil (titanium/incusil) alloy brazing material are stacked in the furnace and then brazed in the furnace at 1000 C. The ceramic specified is 99.8% Alumina, Al{sub 2}O{sub 3}, a strong recrystallized high-alumina fabricated by slip casting. Recent experience at Fermilab with the fabrication and brazing of these tubes has brought to light numerous problems including tube breakage and cracking and also the difficulty of brazing the tube to produce a leak-tight joint. These problems may be due to the ceramic quality, voids in the ceramic, thinness of the wall, and micro-cracks in the ends which make it difficult to braze because it cannot fill tiny surface cracks which are caused by grain pullout during the cutting process. Solutions which are being investigated include lapping the ends of the tubes before brazing to eliminate the micro-cracks and also metallization of the tubes.

  11. Substrate Effects on the High Temperature Oxidation Behavior of a Gold-Based Braze Filler Metal

    SciTech Connect

    Weil, K. Scott; Rice, Joseph P.

    2005-06-01

    Oxidation testing was conducted on a commercial gold-based braze alloy, Gold ABA®, and on zirconia/stainless steel couples joined using this filler metal. Preliminary results reveal that both substrates play a significant role in determining the overall oxidation behavior of the brazed joint.

  12. Educational activities for the diffusion of scientific culture

    NASA Astrophysics Data System (ADS)

    Ferlet, Roger

    2015-08-01

    Considering there is a divorce between science and culture, we suggest activities such as trails of mathematical/astronomical knowledge and vision of scientific teaching and education, that are aiming ata global, citizen dialogue, at reviving a truly human culture integrating science, and at answering all kinds of obscurantism/fundamentalism.

  13. Development of brazing foils to join monocrystalline tungsten alloys with ODS-EUROFER steel

    NASA Astrophysics Data System (ADS)

    Kalin, B. A.; Fedotov, V. T.; Sevrjukov, O. N.; Kalashnikov, A. N.; Suchkov, A. N.; Moeslang, A.; Rohde, M.

    2007-08-01

    Results on rapidly solidified filler metals for brazing W with W and monocrystalline W with EUROFER steel (FS) are presented. Rapidly quenched powder-type filler metals based on Ti bal-V-Cr-Be were developed to braze polycrystalline W with monocrystalline W. In addition, Fe bal-Ta-Ge-Si-B-Pd alloys were developed to braze monocrystalline W with FS for helium gas cooled divertors and plasma-facing components. The W to FS brazed joints were fabricated under vacuum at 1150 °C, using a Ta spacer of 0.1 mm in thickness to account for the different thermal expansions. The monocrystalline tungsten as well as the related brazed joints withstood 30 cycles between 750 °C/20 min and air cooling/3-5 min.

  14. Effects of two ergonomic improvements in brazing coils of air-handler units.

    PubMed

    Loo, H S; Yeow, Paul H P

    2015-11-01

    The research aims to address the physically loading task and quality and productivity problems in the brazing of coils of air-handler units. Eight operators participated in two intervention studies conducted in a factory in Malaysia to compare the status quo brazing with (1) the use of a new twin-brazing torch that replaced the single-brazing gun and (2) brazing in a sitting position. The outcome measures are related to quality, productivity, monetary costs, body postures and symptoms. After baseline, Interventions I and II were applied for 3 months respectively. The results show a 58.9% quality improvement, 140% productivity increase and 113 times ROI. There was also a reduction in poor work postures e.g. in the raising of the arms and shoulders; bending, twisting and extending of the neck; and bending of left and right wrists, and the back. This research can be replicated in other factories that share similar processes. PMID:26154237

  15. Antioxidant Activity and Glucose Diffusion Relationship of Traditional Medicinal Antihyperglycemic Plant Extracts

    PubMed Central

    Asgharpour, Fariba; Pouramir, Mahdi; Khalilpour, Asieh; Asgharpour Alamdar, Sobgol; Rezaei, Mehrasa

    2013-01-01

    Plants with hypoglycemic properties are important in the treatment of diabetes. One of the mechanisms in reducing blood glucose is preventing the digestive absorption of glucose. The aim of this study was to evaluate the antioxidant properties of some traditional medicinal plants collected from different regions of Iran and their effects on glucose diffusion decrease. The amounts of phenolic compounds, total flavonoids, total polysaccharides, antioxidant activity and lipid peroxidation were determined respectively by folin ciocalteu, querceting, sulfuric acid, FRAP and thiobarbituric acid - reactive substanses (TBARS) in eleven confirmed traditional antihyperglycemic medicinal plants prepared at 50g/l concentrations using the boiling method. Phenolic compounds of Eucalyptus globules (100.8± 0.01 mg /g), total flavonoids content of Juglans regia (16.9± 0.01 mg /g) and total polysaccharide amount of Allium satirum (0.28± 0.05) were the highest. Significant relationship was observed between the polyphenols and flavonoids (p <0.05). The grape seed extract showed the highest antioxidant activity (133± 0.02 mg/g) together with decreased glucose diffusion as well as increased polyphenols (p <0.05), but the increase in antioxidant activity was not related to glucose diffusion. Antihyperglycemic plant extracts containing higher polyphenols showed more efficiently in vitro glucose diffusion decrease, but no significant relationship was observed between antioxidant activity increase and glucose diffusion. PMID:24551809

  16. Visualizing repetitive diffusion activity of double-strand RNA binding proteins by single molecule fluorescence assays.

    PubMed

    Koh, Hye Ran; Wang, Xinlei; Myong, Sua

    2016-08-01

    TRBP, one of double strand RNA binding proteins (dsRBPs), is an essential cofactor of Dicer in the RNA interference pathway. Previously we reported that TRBP exhibits repetitive diffusion activity on double strand (ds)RNA in an ATP independent manner. In the TRBP-Dicer complex, the diffusion mobility of TRBP facilitates Dicer-mediated RNA cleavage. Such repetitive diffusion of dsRBPs on a nucleic acid at the nanometer scale can be appropriately captured by several single molecule detection techniques. Here, we provide a step-by-step guide to four different single molecule fluorescence assays by which the diffusion activity of dsRBPs on dsRNA can be detected. One color assay, termed protein induced fluorescence enhancement enables detection of unlabeled protein binding and diffusion on a singly labeled RNA. Two-color Fluorescence Resonance Energy Transfer (FRET) in which labeled dsRBPs is applied to labeled RNA, allows for probing the motion of protein along the RNA axis. Three color FRET reports on the diffusion movement of dsRBPs from one to the other end of RNA. The single molecule pull down assay provides an opportunity to collect dsRBPs from mammalian cells and examine the protein-RNA interaction at single molecule platform. PMID:27012177

  17. Non-classical size-dependent particle diffusion in active fluids

    NASA Astrophysics Data System (ADS)

    Gopinath, Arvind; Patteson, Alison; Arratia, Paulo

    2015-11-01

    We experimentally investigate the effect of particle size on the motion of passive polystyrene spheres in suspensions of Escherchia coli, a flagellated bacterium that is approximately 2 microns long and swims using a sequence of runs punctuated by tumbles. Using particles covering a range of sizes from 0.6 to 39 microns, we probe particle dynamics at both short and long time scales. In all cases, the particles exhibit super-diffusive ballistic behavior at short times before eventually transitioning to diffusive behavior. Surprisingly, the long-time hydrodynamic effective diffusivity is non-monotonic with particle size; an anomalous response that is fundamentally different from classical thermal diffusion. Consistent with recent theory, we find that for fixed bacterial type, the active contribution to particle diffusion can be predicted by a single dimensionless parameter, the Peclét number. Combining our experimental results, we propose a minimal model that allows us to predict the requirements for a peak in the diffusivity as well as the location and magnitude of the peak as a function of particle size and bacterial concentration. Our results have broad implications on characterizing active fluids using concepts drawn from classical (passive) thermodynamics. This work was supported by NSF-DMR-1104705 and NSF-CBET-1437482.

  18. Non-monotonic size-dependent particle diffusion in active fluids

    NASA Astrophysics Data System (ADS)

    Patteson, Alison; Gopinath, Arvind; Arratia, Paulo

    We experimentally investigate the effect of particle size on the motion of passive polystyrene spheres in suspensions of Escherchia coli. Using particles covering a range of sizes from 0.6 to 39 microns, we probe particle dynamics at both short and long time scales. In all cases, the particles exhibit super-diffusive ballistic behavior at short times before eventually transitioning to diffusive behavior. Surprisingly, the long-time hydrodynamic effective diffusivity exhibits a peak in particle size; an anomalous response that is fundamentally different from classical thermal diffusion. Consistent with recent theory, we find that the active contribution to particle diffusion is controlled by a dimensionless parameter, the Peclet number. We propose a minimal model that allows us to predict the requirements for a peak in the diffusivity as well as the magnitude of the peak as a function of particle size and bacterial concentration. Our results have broad implications on characterizing active fluids using concepts drawn from classical thermodynamics. NSF-DMR-1104705 and NSF-CBET-1437482.

  19. Active galaxies and the diffuse gamma-ray background

    NASA Technical Reports Server (NTRS)

    Kazanas, D.; Protheroe, R. J.

    1983-01-01

    Active galaxies are shown to account for the observed gamma ray background radiation if a steepening of the spectra above about 100 keV is present. An analytical model is discussed in which protons undergo Fermi acceleration at a shock in a spherical accretion flow onto a massive black hole. Relativistic protons with power law spectra, nuclear interactions producing gamma rays from neutal pion decay and electrons from pion-mu meson-electron decay, with a power law spectrum above several hundred MeV, synchrotron and inverse Compton losses steepening the electron spectrum, a photon spectrum close to the pion gamma spectrum and a high-energy gamma ray spectrum steepened by photon-photon pair production interactions with X rays are covered in the model. Comparisons are made with HEAO 2 data on active galaxies, which have estimated luminosities and radii consistent with the compactness necessary for producing the steepening predicted by the model. The active galaxies spectra would be described by a spherical accretion-shock model.

  20. Active diffusion and microtubule-based transport oppose myosin forces to position organelles in cells

    PubMed Central

    Lin, Congping; Schuster, Martin; Guimaraes, Sofia Cunha; Ashwin, Peter; Schrader, Michael; Metz, Jeremy; Hacker, Christian; Gurr, Sarah Jane; Steinberg, Gero

    2016-01-01

    Even distribution of peroxisomes (POs) and lipid droplets (LDs) is critical to their role in lipid and reactive oxygen species homeostasis. How even distribution is achieved remains elusive, but diffusive motion and directed motility may play a role. Here we show that in the fungus Ustilago maydis ∼95% of POs and LDs undergo diffusive motions. These movements require ATP and involve bidirectional early endosome motility, indicating that microtubule-associated membrane trafficking enhances diffusion of organelles. When early endosome transport is abolished, POs and LDs drift slowly towards the growing cell end. This pole-ward drift is facilitated by anterograde delivery of secretory cargo to the cell tip by myosin-5. Modelling reveals that microtubule-based directed transport and active diffusion support distribution, mobility and mixing of POs. In mammalian COS-7 cells, microtubules and F-actin also counteract each other to distribute POs. This highlights the importance of opposing cytoskeletal forces in organelle positioning in eukaryotes. PMID:27251117

  1. Active diffusion and microtubule-based transport oppose myosin forces to position organelles in cells

    NASA Astrophysics Data System (ADS)

    Lin, Congping; Schuster, Martin; Guimaraes, Sofia Cunha; Ashwin, Peter; Schrader, Michael; Metz, Jeremy; Hacker, Christian; Gurr, Sarah Jane; Steinberg, Gero

    2016-06-01

    Even distribution of peroxisomes (POs) and lipid droplets (LDs) is critical to their role in lipid and reactive oxygen species homeostasis. How even distribution is achieved remains elusive, but diffusive motion and directed motility may play a role. Here we show that in the fungus Ustilago maydis ~95% of POs and LDs undergo diffusive motions. These movements require ATP and involve bidirectional early endosome motility, indicating that microtubule-associated membrane trafficking enhances diffusion of organelles. When early endosome transport is abolished, POs and LDs drift slowly towards the growing cell end. This pole-ward drift is facilitated by anterograde delivery of secretory cargo to the cell tip by myosin-5. Modelling reveals that microtubule-based directed transport and active diffusion support distribution, mobility and mixing of POs. In mammalian COS-7 cells, microtubules and F-actin also counteract each other to distribute POs. This highlights the importance of opposing cytoskeletal forces in organelle positioning in eukaryotes.

  2. Active diffusion and microtubule-based transport oppose myosin forces to position organelles in cells.

    PubMed

    Lin, Congping; Schuster, Martin; Guimaraes, Sofia Cunha; Ashwin, Peter; Schrader, Michael; Metz, Jeremy; Hacker, Christian; Gurr, Sarah Jane; Steinberg, Gero

    2016-01-01

    Even distribution of peroxisomes (POs) and lipid droplets (LDs) is critical to their role in lipid and reactive oxygen species homeostasis. How even distribution is achieved remains elusive, but diffusive motion and directed motility may play a role. Here we show that in the fungus Ustilago maydis ∼95% of POs and LDs undergo diffusive motions. These movements require ATP and involve bidirectional early endosome motility, indicating that microtubule-associated membrane trafficking enhances diffusion of organelles. When early endosome transport is abolished, POs and LDs drift slowly towards the growing cell end. This pole-ward drift is facilitated by anterograde delivery of secretory cargo to the cell tip by myosin-5. Modelling reveals that microtubule-based directed transport and active diffusion support distribution, mobility and mixing of POs. In mammalian COS-7 cells, microtubules and F-actin also counteract each other to distribute POs. This highlights the importance of opposing cytoskeletal forces in organelle positioning in eukaryotes. PMID:27251117

  3. Corrosion of Ti-STS dissimilar joints brazed by a Ag interlayer and Ag-Cu-(Pd) alloy fillers

    NASA Astrophysics Data System (ADS)

    Lee, M. K.; Park, J. J.; Lee, G. J.; Lee, J. G.; Kim, D. W.; Lim, C. H.; Rhee, C. K.; Lee, Y. B.; Lee, J. K.; Hong, S. J.

    2011-02-01

    Corrosion behavior of dissimilar brazed joints between titanium Gr. 2 (Ti) and S31254 stainless steel (STS) was investigated. For the study, a Ag interlayer and two Ag-base eutectic alloys, 72Ag-28Cu and 66.2Ag-25.8Cu-8Pd (wt.%), were introduced as a diffusion control layer and fillers, respectively, between the base materials. The joints commonly had a layered structure of Ti(base)/TiAg/Ag solid solution/STS(base), but the one brazed by the Ag-Cu-Pd filler was slightly alloyed with the noble Pd elements over the Ag-rich solid solution region. A series of corrosion test experiments in a sea water revealed that a corrosion of TiAg layer and a stress-induced cracking at the TiAg/Ag solid solution interface were dominant due to a galvanic attack, but notably the Ti-STS dissimilar joint's resistance to corrosion was significantly improved by alloying the Pd in the joint. The corrosion behavior of such dissimilar metal joints was discussed based on galvanic corrosion effect.

  4. Assessment of Activity of Crohn Disease by Diffusion-Weighted Magnetic Resonance Imaging.

    PubMed

    Li, Xue-Hua; Sun, Can-Hui; Mao, Ren; Zhang, Zhong-Wei; Jiang, Xiao-Song; Pui, Margaret H; Chen, Min-Hu; Li, Zi-Ping

    2015-10-01

    To assess the diagnostic efficacy of diffusion-weighted MR imaging (DWI) for evaluating inflammatory activity in patients with Crohn's disease (CD). A total of 47 CD patients underwent MR enterography (MRE) and DWI using 3 b values of 50, 400, and 800 s/mm. Apparent diffusion coefficients (ADCs) of inflamed and normal bowel wall were calculated. The conventional MRE findings and DWI signal intensities were qualitatively scored from 0 to 3. The correlation between Crohn disease activity index (CDAI) and both ADCs and magnetic resonance imaging scores was analyzed. Receiver-operating characteristic curve analysis was used to determine the diagnostic accuracy of CD activity. Of the 47 patients, 25 were active CD (CDAI≥150) and 22 were inactive (CDAI<150). Diffusion-weighted MR imaging and MRE + DWI scores of active CD were significantly higher than that of inactive CD (both P < 0.001). Apparent diffusion coefficients in inflamed segments of active CD were lower than that of inactive CD (P < 0.001). The DWI scores (r = 0.74, P < 0.001), ADCs (r = -0.71, P < 0.001), MRE scores (r = 0.54, P < 0.001), and MRE + DWI scores (r = 0.66, P < 0.001) were all correlated with CDAI. The areas under the receiver-operating characteristics curves for ADCs, DWI scores, MRE scores, and MRE + DWI scores ranged from 0.83 to 0.98. The threshold ADC value of 1.17 × 10 mm/s allowed differentiation of active from inactive CD with 100% sensitivity and 88% specificity. Diffusion-weighted MR imaging and ADC correlated with CD activity, and had excellent diagnostic accuracy for differentiating active from inactive CD. PMID:26512584

  5. Standard operating procedure: Gas atmosphere MELCO brazing furnace

    SciTech Connect

    Waller, C.R.

    1988-08-01

    A hydrogen and argon gas atmosphere furnace facility using electric furnaces is located at the Clinton P. Anderson Meson Physics Facility (LAMPF). This furnace system was acquired to handle smaller jobs with a more rapid response time than was possible with the larger furnaces. Accelerator- and experimental-related components best assembled by atmosphere brazing techniques are routinely processed by this facility in addition to special heat treatment and bakeout heats. The detailed operation sequence and description of the MELCO furnace system are covered by this report. This document is to augment LA-10231-SOP, which describes the operation of the large furnace systems. 6 figs.

  6. Design data for brazed Rene 41 honeycomb sandwich

    NASA Technical Reports Server (NTRS)

    Hepler, A. K.; Arnquist, J.; Koetje, E. L.; Esposito, J. J.; Lindsay, V. E. J.; Swegle, A. R.

    1981-01-01

    Strength data, creep data and residual strength data after cyclic thermal exposure were obtained at temperatures from 78 K to 1144 K (-320 F to 1600 F). The influences of face thickness, core depth, core gage, cell size and thermal/stress exposure conditions on the mechanical design properties were investigated. A braze alloy and process was developed that is adequate to fully develop the strength of the honeycomb core while simultaneously solution treating and aging the Rene 41 fact sheets. New test procedures and test specimen configurations were developed to avoid excessive thermal stresses during cyclic thermal exposure.

  7. Service evaluation of aluminum-brazed titanium (ABTi). [aircraft structures

    NASA Technical Reports Server (NTRS)

    Elrod, S. D.

    1981-01-01

    Long term creep-rupture, flight service and jet engine exhaust tests on aluminum-brazed titanium (ABTi), originally initiated under the DOT/SST follow-on program, were completed. These tests included exposure to natural airline service environments for up to 6 years. The results showed that ABTi has adequate corrosion resistance for long time commercial airplane structural applications. Special precautions are required for those sandwich structures designed for sound attenuation that utilize perforated skins. ABTi was also shown to have usable creep-rupture strength and to be metallurgically stable at temperatures up to 425 C (800 F).

  8. An Overview of Follow-On Testing Activities of the A-3 Subscale Diffuser Test Project

    NASA Technical Reports Server (NTRS)

    Ryan, James E.

    2009-01-01

    An overview of NASA Stennis Space Center's (SSC) A-3 Subscale Diffuser Test (SDT) Project is presented. The original scope of the SDT Project, conducted from April 2007 to January 2008, collected data to support mitigation of risk associated with design and procurement activities of the A-3 Test Stand Project, an effort to construct a simulated altitude test facility at SSC in support of NASA's Constellation Program. Follow-on tests were conducted from May 2008 through August 2009, utilizing the SDT test setup as a testbed for additional risk mitigation activities. Included are descriptions of the Subscale Diffuser (SD) test article, the test facility configuration, and test approaches.

  9. Experiments and simulation on diffusion and activation of codoped with arsenic and phosphorous germanium

    SciTech Connect

    Tsouroutas, P.; Tsoukalas, D.; Bracht, H.

    2010-07-15

    We report arsenic and phosphorus diffusion experiments and activation related phenomena in codoped germanium substrates utilizing conventional thermal annealing. Chemical profiles were obtained by secondary ion mass spectroscopy, sheet resistance was estimated by the Van der Pauw method. Our study covers the temperature range from 600 to 750 deg. C. We accurately described the dopant profiles with a quadratic dependence of the dopants diffusion coefficient on the free electron concentration. In our simulations we considered the dopant pile-up near the surface and dopant loss owing to outdiffusion during the annealing. Although the double donor codoping technique exhibited no advantage over monodoping with P concerning the level of activation and junction depth, it was interesting to observe the different diffusion behavior of the two dopants. Whereas the diffusion of As indicates a retardation under codoping the diffusion of P remains either unaffected or is slightly enhanced by codoping. The activation level of the codoped samples remains lower compared to the respective monodoped samples, except for the highest annealing temperature.

  10. Performance of active feedforward control systems in non-ideal, synthesized diffuse sound fields.

    PubMed

    Misol, Malte; Bloch, Christian; Monner, Hans Peter; Sinapius, Michael

    2014-04-01

    The acoustic performance of passive or active panel structures is usually tested in sound transmission loss facilities. A reverberant sending room, equipped with one or a number of independent sound sources, is used to generate a diffuse sound field excitation which acts as a disturbance source on the structure under investigation. The spatial correlation and coherence of such a synthesized non-ideal diffuse-sound-field excitation, however, might deviate significantly from the ideal case. This has consequences for the operation of an active feedforward control system which heavily relies on the acquisition of coherent disturbance source information. This work, therefore, evaluates the spatial correlation and coherence of ideal and non-ideal diffuse sound fields and considers the implications on the performance of a feedforward control system. The system under consideration is an aircraft-typical double panel system, equipped with an active sidewall panel (lining), which is realized in a transmission loss facility. Experimental results for different numbers of sound sources in the reverberation room are compared to simulation results of a comparable generic double panel system excited by an ideal diffuse sound field. It is shown that the number of statistically independent noise sources acting on the primary structure of the double panel system depends not only on the type of diffuse sound field but also on the sample lengths of the processed signals. The experimental results show that the number of reference sensors required for a defined control performance exhibits an inverse relationship to control filter length. PMID:25234987

  11. Diffuse elevated MIBG activity in the renal parenchyma caused by compromised renal blood flow.

    PubMed

    Liu, Bin; Codreanu, Ion; Yang, Jigang; Servaes, Sabah; Zhuang, Hongming

    2014-11-01

    Increased metaiodobenzylguanidine (MIBG) activity in the kidneys is usually focal and commonly attributed to radioactive urine accumulation in the renal pelvis. Hereby, we present 2 cases of abnormal diffuse MIBG activity in the kidneys caused by compromised renal blood flow. The patterns should be differentiated from physiologic renal MIBG activity, especially when the uptake is relatively symmetric as well as from regional MIBG-avid disease. PMID:24999702

  12. Thermally activated diffusion of magnesium from bioapatite crystals

    NASA Astrophysics Data System (ADS)

    Danil'Chenko, S. N.; Kulik, A. N.; Pavlenko, P. A.; Kalinichenko, T. G.; Bugai, A. N.; Chemeris, I. I.; Sukhodub, L. F.

    2006-05-01

    We have attempted to use heat treatment followed by ultrasonic treatment to separate the apatite from the non-apatite components of bone mineral in samples from different animals. The Mg content and the Ca/P ratio in the temperature range 560°C-720°C in the samples before and after ultrasonic treatment were determined by electron-probe x-ray microanalysis. Furthermore, we used atomic absorption spectrometry to measure the Mg content in powdered bone samples only after annealing and in distilled water, which was the “sonication” medium. We obtained evidence for thermally activated transition of Mg from a structurally bound state to a labile state at 680°C-720°C. At the same temperature, the Ca-deficient apatite is transformed to stoichiometric apatite. The data presented are evidence that crystals of Ca-deficient bioapatite are surrounded by Ca-enriched surface layers. As a result of thermal transformations at 680°C-720°C, all the Mg in the biomineral is found in the non-apatite environment surrounding the crystals and is removed by ultrasonic treatment, while the surface-localized Ca penetrates into the apatite lattice, restoring its stoichiometry.

  13. Perturbative path-integral study of active- and passive-tracer diffusion in fluctuating fields.

    PubMed

    Démery, Vincent; Dean, David S

    2011-07-01

    We study the effective diffusion constant of a Brownian particle linearly coupled to a thermally fluctuating scalar field. We use a path-integral method to compute the effective diffusion coefficient perturbatively to lowest order in the coupling constant. This method can be applied to cases where the field is affected by the particle (an active tracer) and cases where the tracer is passive. Our results are applicable to a wide range of physical problems, from a protein diffusing in a membrane to the dispersion of a passive tracer in a random potential. In the case of passive diffusion in a scalar field, we show that the coupling to the field can, in some cases, speed up the diffusion corresponding to a form of stochastic resonance. Our results on passive diffusion are also confirmed via a perturbative calculation of the probability density function of the particle in a Fokker-Planck formulation of the problem. Numerical simulations on simplified systems corroborate our results. PMID:21867153

  14. Modeling of slow glutamate diffusion and AMPA receptor activation in the cerebellar glomerulus.

    PubMed

    Saftenku, E E

    2005-06-01

    Synaptic conductances are influenced markedly by the geometry of the space surrounding the synapse since the transient glutamate concentration in the synaptic cleft is determined by this geometry. Our paper is an attempt to understand the reasons for slow glutamate diffusion in the cerebellar glomerulus, a structure situated around the enlarged mossy fiber terminal in the cerebellum and surrounded by a glial sheath. For this purpose, analytical expressions for glutamate diffusion in the glomerulus were considered in models with two-, three-, and fractional two-three-dimensional (2D-3D) geometry with an absorbing boundary. The time course of average glutamate concentration in the synaptic cleft of the mossy fiber-granule cell connection was calculated for both direct release of glutamate from the same synaptic unit, and for cumulative spillover of glutamate from neighboring release sites. Several kinetic schemes were examined, and the parameters of the diffusion models were estimated by identifying theoretical activation of AMPA receptors with direct release and spillover components of published experimental AMPA receptor-mediated EPSCs. For model selection, the correspondence of simulated paired-pulse ratio and EPSC increase after prevention of desensitization to experimental values were also taken into consideration. Our results suggest at least a 7- to 10-fold lower apparent diffusion coefficient of glutamate in the porous medium of the glomerulus than in water. The modeling of glutamate diffusion in the 2D-3D geometry gives the best fit of experimental EPSCs. We show that it could be only partly explained by normal diffusion of glutamate in the complex geometry of the glomerulus. We assume that anomalous diffusion of glutamate occurs in the glomerulus. A good match of experimental estimations and theoretical parameters, obtained in the simulations that use an approximation of anomalous diffusion by a solution for fractional Brownian motion, confirms our

  15. Theory of activated penetrant diffusion in viscous fluids and colloidal suspensions.

    PubMed

    Zhang, Rui; Schweizer, Kenneth S

    2015-10-14

    We heuristically formulate a microscopic, force level, self-consistent nonlinear Langevin equation theory for activated barrier hopping and non-hydrodynamic diffusion of a hard sphere penetrant in very dense hard sphere fluid matrices. Penetrant dynamics is controlled by a rich competition between force relaxation due to penetrant self-motion and collective matrix structural (alpha) relaxation. In the absence of penetrant-matrix attraction, three activated dynamical regimes are predicted as a function of penetrant-matrix size ratio which are physically distinguished by penetrant jump distance and the nature of matrix motion required to facilitate its hopping. The penetrant diffusion constant decreases the fastest with size ratio for relatively small penetrants where the matrix effectively acts as a vibrating amorphous solid. Increasing penetrant-matrix attraction strength reduces penetrant diffusivity due to physical bonding. For size ratios approaching unity, a distinct dynamical regime emerges associated with strong slaving of penetrant hopping to matrix structural relaxation. A crossover regime at intermediate penetrant-matrix size ratio connects the two limiting behaviors for hard penetrants, but essentially disappears if there are strong attractions with the matrix. Activated penetrant diffusivity decreases strongly with matrix volume fraction in a manner that intensifies as the size ratio increases. We propose and implement a quasi-universal approach for activated diffusion of a rigid atomic/molecular penetrant in a supercooled liquid based on a mapping between the hard sphere system and thermal liquids. Calculations for specific systems agree reasonably well with experiments over a wide range of temperature, covering more than 10 orders of magnitude of variation of the penetrant diffusion constant. PMID:26472397

  16. Theory of activated penetrant diffusion in viscous fluids and colloidal suspensions

    NASA Astrophysics Data System (ADS)

    Zhang, Rui; Schweizer, Kenneth S.

    2015-10-01

    We heuristically formulate a microscopic, force level, self-consistent nonlinear Langevin equation theory for activated barrier hopping and non-hydrodynamic diffusion of a hard sphere penetrant in very dense hard sphere fluid matrices. Penetrant dynamics is controlled by a rich competition between force relaxation due to penetrant self-motion and collective matrix structural (alpha) relaxation. In the absence of penetrant-matrix attraction, three activated dynamical regimes are predicted as a function of penetrant-matrix size ratio which are physically distinguished by penetrant jump distance and the nature of matrix motion required to facilitate its hopping. The penetrant diffusion constant decreases the fastest with size ratio for relatively small penetrants where the matrix effectively acts as a vibrating amorphous solid. Increasing penetrant-matrix attraction strength reduces penetrant diffusivity due to physical bonding. For size ratios approaching unity, a distinct dynamical regime emerges associated with strong slaving of penetrant hopping to matrix structural relaxation. A crossover regime at intermediate penetrant-matrix size ratio connects the two limiting behaviors for hard penetrants, but essentially disappears if there are strong attractions with the matrix. Activated penetrant diffusivity decreases strongly with matrix volume fraction in a manner that intensifies as the size ratio increases. We propose and implement a quasi-universal approach for activated diffusion of a rigid atomic/molecular penetrant in a supercooled liquid based on a mapping between the hard sphere system and thermal liquids. Calculations for specific systems agree reasonably well with experiments over a wide range of temperature, covering more than 10 orders of magnitude of variation of the penetrant diffusion constant.

  17. Theory of activated penetrant diffusion in viscous fluids and colloidal suspensions

    SciTech Connect

    Zhang, Rui; Schweizer, Kenneth S.

    2015-10-14

    We heuristically formulate a microscopic, force level, self-consistent nonlinear Langevin equation theory for activated barrier hopping and non-hydrodynamic diffusion of a hard sphere penetrant in very dense hard sphere fluid matrices. Penetrant dynamics is controlled by a rich competition between force relaxation due to penetrant self-motion and collective matrix structural (alpha) relaxation. In the absence of penetrant-matrix attraction, three activated dynamical regimes are predicted as a function of penetrant-matrix size ratio which are physically distinguished by penetrant jump distance and the nature of matrix motion required to facilitate its hopping. The penetrant diffusion constant decreases the fastest with size ratio for relatively small penetrants where the matrix effectively acts as a vibrating amorphous solid. Increasing penetrant-matrix attraction strength reduces penetrant diffusivity due to physical bonding. For size ratios approaching unity, a distinct dynamical regime emerges associated with strong slaving of penetrant hopping to matrix structural relaxation. A crossover regime at intermediate penetrant-matrix size ratio connects the two limiting behaviors for hard penetrants, but essentially disappears if there are strong attractions with the matrix. Activated penetrant diffusivity decreases strongly with matrix volume fraction in a manner that intensifies as the size ratio increases. We propose and implement a quasi-universal approach for activated diffusion of a rigid atomic/molecular penetrant in a supercooled liquid based on a mapping between the hard sphere system and thermal liquids. Calculations for specific systems agree reasonably well with experiments over a wide range of temperature, covering more than 10 orders of magnitude of variation of the penetrant diffusion constant.

  18. Development of optimum process parameters and a study of the effects of surface roughness on brazing of copper

    NASA Astrophysics Data System (ADS)

    Zaharinie, Tuan; Huda, Zainul; Izuan, Mohd Faaliq; Hamdi, Mohammed

    2015-03-01

    Brazing experiments on commercially-pure copper plates, using brazing filler metal (MBF-2005), are conducted at temperatures in the range of 650-750 °C for time-durations in the range of 5-15 min. Shear tests for braze-joints involved use of a universal testing machine. Based on the shear-test results, a new brazing cycle has been developed that corresponds to the greatest shear strength of the braze-joint. The brazing cycle has been performed under a controlled dry-argon atmosphere in a tube furnace. Microscopic observations were made by use of both optical and electron microscopes; whereas surface roughness measurements were made by using a TR100 Surface Roughness Tester. It is found that successful brazing and good wetting can be achieved by the least voids by using an average surface roughness (Ra value) for the base material.

  19. A Compendium of Brazed Microstructures For Fission Power Systems Applications

    NASA Technical Reports Server (NTRS)

    Locci, Ivan E.; Bowman, Cheryl L.

    2012-01-01

    NASA has been supporting design studies and technology development for fission-based power systems that could provide power to an outpost on the Moon, Mars, or an asteroid. Technology development efforts have included fabrication and evaluation of components used in a Stirling engine power conversion system. This investigation is part of the development of several braze joints crucial for the heat exchanger transfer path from a hot-side heat exchanger to a Stirling engine heat acceptor. Dissimilar metal joints are required to impart both mechanical strength and thermal path integrity for a heater head of interest. Preliminary design work for the heat exchanger involved joints between low carbon stainless steel to Inconel 718, where the 316L stainless steel would contain flowing liquid metal NaK while Inconel 718, a stronger alloy, would be used as structural reinforcement. This paper addressed the long-term microstructural stability of various braze alloys used to join 316L stainless steel heater head to the high conductivity oxygen-free copper acceptor to ensure the endurance of the critical metallic components of this sophisticated heat exchanger. The bonding of the 316L stainless steel heater head material to a copper heat acceptor is required to increase the heat-transfer surface area in contact with flowing He, which is the Stirling engine working fluid.

  20. Flaw Tolerance In Lap Shear Brazed Joints. Part 2

    NASA Technical Reports Server (NTRS)

    Wang, Len; Flom, Yury

    2003-01-01

    This paper presents results of the second part of an on-going effort to gain better understanding of defect tolerance in braze joints. In the first part of this three-part series, we mechanically tested and modeled the strength of the lap joints as a function of the overlap distance. A failure criterion was established based on the zone damage theory, which predicts the dependence of the lap joint shear strength on the overlap distance, based on the critical size of a finite damage zone or an overloaded region in the joint. In this second part of the study, we experimentally verified the applicability of the damage zone criterion on prediction of the shear strength of the lap joint and introduced controlled flaws into the lap joints. The purpose of the study was to evaluate the lap joint strength as a function of flaw size and its location through mechanical testing and nonlinear finite element analysis (FEA) employing damage zone criterion for definition of failure. The results obtained from the second part of the investigation confirmed that the failure of the ductile lap shear brazed joints occurs when the damage zone reaches approximately 10% of the overlap width. The same failure criterion was applicable to the lap joints containing flaws.

  1. Quorum activation at a distance: spatiotemporal patterns of gene regulation from diffusion of an autoinducer signal

    NASA Astrophysics Data System (ADS)

    Dilanji, Gabriel; Langebrake, Jessica; Deleenheer, Patrick; Hagen, Stephen J.

    2012-02-01

    Bacteria in colonies coordinate gene regulation through the exchange of diffusible signal molecules known as autoinducers (AI). This ``quorum signaling'' often occurs in physically heterogeneous and spatially extended environments such as biofilms. Under these conditions the space and time scales for diffusion of the signal limit the range and timing of effective gene regulation. We expect that spatial and temporal patterns of gene expression will reflect physical environmental constraints as well as nonlinear transcriptional activation and feedback within the gene regulatory system. We have combined experiments and modeling to investigate how these spatiotemporal patterns develop. We embed engineered plasmid/GFP quorum sensor strains or wild type strains in a long narrow agar lane, and then introduce AI signal at one terminus of the lane. Diffusion of the AI initiates reporter expression along the length of the lane, extending to macroscopic distances of mm-cm. Resulting patterns are captured quantitatively by a mathematical model that incorporates logistic growth of the population, diffusion of AI, and nonlinear transcriptional activation. Our results show that a diffusing quorum signal can coordinate gene expression over distances of order 1cm on time scales of order 10 hrs.

  2. Diffusion of point defects in crystalline silicon using the kinetic activation-relaxation technique method

    NASA Astrophysics Data System (ADS)

    Trochet, Mickaël; Béland, Laurent Karim; Joly, Jean-François; Brommer, Peter; Mousseau, Normand

    2015-06-01

    We study point-defect diffusion in crystalline silicon using the kinetic activation-relaxation technique (k-ART), an off-lattice kinetic Monte Carlo method with on-the-fly catalog building capabilities based on the activation-relaxation technique (ART nouveau), coupled to the standard Stillinger-Weber potential. We focus more particularly on the evolution of crystalline cells with one to four vacancies and one to four interstitials in order to provide a detailed picture of both the atomistic diffusion mechanisms and overall kinetics. We show formation energies, activation barriers for the ground state of all eight systems, and migration barriers for those systems that diffuse. Additionally, we characterize diffusion paths and special configurations such as dumbbell complex, di-interstitial (IV-pair+2I) superdiffuser, tetrahedral vacancy complex, and more. This study points to an unsuspected dynamical richness even for this apparently simple system that can only be uncovered by exhaustive and systematic approaches such as the kinetic activation-relaxation technique.

  3. An Introduction to Biological Modeling Using Coin Flips to Predict the Outcome of a Diffusion Activity

    ERIC Educational Resources Information Center

    Butcher, Greg Q.; Rodriguez, Juan; Chirhart, Scott; Messina, Troy C.

    2016-01-01

    In order to increase students' awareness for and comfort with mathematical modeling of biological processes, and increase their understanding of diffusion, the following lab was developed for use in 100-level, majors/non-majors biology and neuroscience courses. The activity begins with generation of a data set that uses coin-flips to replicate…

  4. Comparison of the antibacterial activity of chelating agents using the agar diffusion method

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The agar diffusion assay was used to examine antibacterial activity of 2 metal chelators. Concentrations of 0 to 40 mM of ethylenediaminetetraacetic acid (EDTA) and ethylenediamine-N,N’-disuccinic acid (EDDS) were prepared in 1.0 M potassium hydroxide (KOH). The pH of the solutions was adjusted to 1...

  5. Extending the Diffuse Layer Model of Surface Acidity Behavior: III. Estimating Bound Site Activity Coefficients

    EPA Science Inventory

    Although detailed thermodynamic analyses of the 2-pK diffuse layer surface complexation model generally specify bound site activity coefficients for the purpose of accounting for those non-ideal excess free energies contributing to bound site electrochemical potentials, in applic...

  6. Active-Site Hydration and Water Diffusion in Cytochrome P450cam: A Highly Dynamic Process

    SciTech Connect

    Miao, Yinglong; Baudry, Jerome Y

    2011-01-01

    Long-timescale molecular dynamics simulations (300 ns) are performed on both the apo- (i.e., camphor-free) and camphor-bound cytochrome P450cam (CYP101). Water diffusion into and out of the protein active site is observed without biased sampling methods. During the course of the molecular dynamics simulation, an average of 6.4 water molecules is observed in the camphor-binding site of the apo form, compared to zero water molecules in the binding site of the substrate-bound form, in agreement with the number of water molecules observed in crystal structures of the same species. However, as many as 12 water molecules can be present at a given time in the camphor-binding region of the active site in the case of apo-P450cam, revealing a highly dynamic process for hydration of the protein active site, with water molecules exchanging rapidly with the bulk solvent. Water molecules are also found to exchange locations frequently inside the active site, preferentially clustering in regions surrounding the water molecules observed in the crystal structure. Potential-of-mean-force calculations identify thermodynamically favored trans-protein pathways for the diffusion of water molecules between the protein active site and the bulk solvent. Binding of camphor in the active site modifies the free-energy landscape of P450cam channels toward favoring the diffusion of water molecules out of the protein active site.

  7. Strength testing of Ti-vapor-coated silicon nitride braze joints

    SciTech Connect

    Santella, M.L.

    1994-09-01

    Sintered silicon nitride was vacuum brazed to itself at 1130{degree}C with a Au-25Ni-25Pd wt % filler metal. Wetting was obtained by coating the Si{sub 3}N{sub 4} surfaces with titanium prior to brazing by electron beam evaporation. The brazed joints were virtually free of porosity. Metallographic analysis showed that Ti reacted with the Si{sub 3}N{sub 4}, to form a TiN reaction layer during brazing. Small amounts of Si and Ti dissolved in the filler metal layers but they did not appear to influence the mechanical properties of the braze layer. Flexure bars were made from the brazed coupons and tested at room temperature, 600C, 700C, and 800C in air. At 700C and below, fracture of the test bars occurred in the Si{sub 3}N{sub 4}, either near the brazed surfaces or at some distance into the monolithic material. The measured strength of joint specimens decreased slightly with increasing test temperature, and generally exceeded the intrinsic braze filler metal strength in this temperature range. It was also found that lapping the Si{sub 3}N{sub 4}, prior to Ti coating reduced the number of near-surface flaws and produced joints with higher average strength and lower scatter than those left in a ground condition. Specimens tested at 800C had very low strengths, and this behavior was related to the microstructure at the brazed Si{sub 3}N{sub 4} surfaces.

  8. Vacuum Brazing of Beryllium Copper Components for the National Ignition Facility

    SciTech Connect

    Tyhurst, C.C.; Cunningham, M.A.

    2002-06-04

    A process for vacuum brazing beryllium copper anode assemblies was required for the Plasma Electrode Pockels Cell System, or PEPC, a component for the National Ignition Facility (NIF). Initial problems with the joint design and wettability of the beryllium copper drove some minor design changes. Brazing was facilitated by plating the joint surface of the beryllium copper rod with silver 0.0006 inch thick. Individual air sampling during processing and swipe tests of the furnace interior after brazing revealed no traceable levels of beryllium.

  9. Brazing of refractory, superalloy, and composite materials for Space Shuttle applications.

    NASA Technical Reports Server (NTRS)

    Beuyukian, C. S.

    1972-01-01

    Research work concerning the metallic portion of the shuttle-orbiter heat shield (expected to experience temperatures up to 2500 F) is described. The five metals being evaluated are TD-Ni-Cr, Cb-C129Y, Cb752, Hayes 188, and Inconel 625. Brazing techniques whereby pairs of these materials are joined into thin-membered assemblies for heat shield applications are described. Results obtained with the vacuum-furnace brazing process are examined. In addition, the use of brazed aluminum-boron metal-matrix-contoured composite structures for heat shield applications is evaluated.

  10. Imaging hypothalamic activity using diffusion weighted magnetic resonance imaging in the mouse and human brain.

    PubMed

    Lizarbe, Blanca; Benítez, Ania; Sánchez-Montañés, Manuel; Lago-Fernández, Luis F; Garcia-Martin, María L; López-Larrubia, Pilar; Cerdán, Sebastián

    2013-01-01

    Hypothalamic appetite regulation is a vital homeostatic process underlying global energy balance in animals and humans, its disturbances resulting in feeding disorders with high morbidity and mortality. The objective evaluation of appetite remains difficult, very often restricted to indirect measurements of food intake and body weight. We report here, the direct, non-invasive visualization of hypothalamic activation by fasting using diffusion weighted magnetic resonance imaging, in the mouse brain as well as in a preliminary study in the human brain. The brain of fed or fasted mice or humans were imaged at 7 or 1.5 Tesla, respectively, by diffusion weighted magnetic resonance imaging using a complete range of b values (10diffusion weighted image data sets were registered and analyzed pixel by pixel using a biexponential model of diffusion, or a model-free Linear Discriminant Analysis approach. Biexponential fittings revealed statistically significant increases in the slow diffusion parameters of the model, consistent with a neurocellular swelling response in the fasted hypothalamus. Increased resolution approaches allowed the detection of increases in the diffusion parameters within the Arcuate Nucleus, Ventromedial Nucleus and Dorsomedial Nucleus. Independently, Linear Discriminant Analysis was able to classify successfully the diffusion data sets from mice and humans between fed and fasted states. Present results are consistent with increased glutamatergic neurotransmission during orexigenic firing, a process resulting in increased ionic accumulation and concomitant osmotic neurocellular swelling. This swelling response is spatially extendable through surrounding astrocytic networks until it becomes MRI detectable. Present findings open new avenues for the direct, non-invasive, evaluation of appetite disorders and other hypothalamic pathologies helping potentially in the development of the corresponding therapies. PMID:23000787

  11. Influence of BOLD Contributions to Diffusion fMRI Activation of the Visual Cortex

    PubMed Central

    Williams, Rebecca J.; Reutens, David C.; Hocking, Julia

    2016-01-01

    Reliance on the hemodynamic response as a surrogate marker of neural activity imposes an intrinsic limit on the spatial specificity of functional MRI. An alternative approach based on diffusion-weighted functional MRI (DfMRI) has been reported as a contrast less reliant on hemodynamic effects, however current evidence suggests that both hemodynamic and unique neural sources contribute to the diffusion signal. Here we compare activation patterns obtained with the standard blood oxygenation level-dependent (BOLD) contrast to DfMRI in order to gain a deeper understanding of how the BOLD proportion contributes to the observable diffusion signal. Both individual and group-level activation patterns obtained with DfMRI and BOLD to a visual field stimulation paradigm were analyzed. At the individual level, the DfMRI contrast showed a strong, positive relationship between the volumes of cortex activated in response to quadrant- and hemi-field visual stimulation. This was not observed in the corresponding BOLD experiment. Overall, the DfMRI response indicated less between-subject variability, with random effects analyses demonstrating higher statistical values at the peak voxel for DfMRI. Furthermore, the spatial extent of the activation was more restricted to the primary visual region for DfMRI than BOLD. However, the diffusion signal was sensitive to the hemodynamic response in a manner dependent on experimental manipulation. It was also limited by its low signal-to-noise ratio (SNR), demonstrating lower sensitivity than BOLD. Together these findings both support DfMRI as a contrast that bears a closer spatial relationship to the underlying neural activity than BOLD, and raise important caveats regarding its utilization. Models explaining the DfMRI signal change need to consider the dynamic vascular contributions that may vary with neural activity. PMID:27445654

  12. Thermally Activated Point Defect Diffusion in Methylammonium Lead Trihalide: Anisotropic and Ultrahigh Mobility of Iodine.

    PubMed

    Delugas, P; Caddeo, C; Filippetti, A; Mattoni, A

    2016-07-01

    We study the diffusion of point defects in crystalline methylammonium lead halide (MAPI) at finite temperatures by using all-atoms molecular dynamics. We find that, for what concerns intrinsic defects, iodine diffusion is by far the dominant mechanism of ionic transport in MAPI, with diffusivities as high as 7.4 × 10(-7) and 4.3 × 10(-6) cm(2) s(-1) at 300 K and single activation energies of 0.24 and 0.10 eV, for interstitials and vacancies, respectively. The comparison with common covalent and oxide crystals reveals the ultrahigh mobility of defects in MAPI. Though at room temperature the vacancies are about 1 order of magnitude more diffusive, the anisotropic interstitial dynamics increases more rapidly with temperature, and it can be dominant at high temperatures. Present results are fully consistent with the involvement of iodide ions in hysteresis and have implications for improvement of the material quality by better control of defect diffusion. PMID:27237630

  13. Ultrasonic inspection of brazed titanium samples with complex shape

    NASA Astrophysics Data System (ADS)

    Bamberg, J.; Steinhauser, L.

    The ultrasonic technique of inspecting the completeness of brazed titanium joints of complex shape in aircraft engines is examined. The metal dies used for the inspection of titanium parts can be made of aluminum alloy because the longitudinal sound velocity of both materials is nearly the same. The two aluminum dies with an interposed turbine blade dummy are shown. The experiments indicate that a gap of 1.5 mm is sufficient for a broadband 5 MHz pulse. The smallest detected defect with axicon lenses was about 2 mm in diameter. The variation in the transmitted ultrasonic signal through junctions without defects was smaller than 3 dB. A C-scan of a titanium blade dummy with the two cavities inside is shown.

  14. Exchange diffusion, active transport, and diffusional components of transbranchial Na and cl fluxes.

    PubMed

    Kirschner, L B; Howe, D

    1981-05-01

    Sodium efflux across the gills of the sculpin Leptocottus armatus average about 900 mumol.100 g-1.h-1 in seawater (SW). When external Na+ was replaced by Tris [tris(hydroxymethyl)aminomethane] the efflux dropped about 35% and the voltage across the gill (TEP) decreased from +20.3 to -2.3 mV. The electrical change accounted, almost exactly, for the diminution of efflux, suggesting that most, if not all, of the Na+ efflux in this fish is diffusive. Chloride efflux in SW was about 300 mumol.100 g-1.h-1. When external Cl- was replaced by gluconate, efflux fell to about one-half the SW value. This could not be due to a change in TEP and is therefore attributed to exchange diffusion. Injection of thiocyanate further reduced the efflux to about 15% of the SW rate. This fraction of the total efflux is active extrusion. The remaining efflux (exchange and active transport eliminated) is diffusive. It is also shown that substitution of gluconate for chloride reduces the activity coefficient for Na+. A small decrease in TEP, noted in this substitution, can be explained by the activity change. A few experiments with isethionate suggest that it does not have this effect and hence is a better chloride substitute in single-ion replacement experiments. PMID:7235052

  15. Isoconversion effective activation energy profiles by variable temperature diffuse reflection infrared spectroscopy.

    PubMed

    White, Daniel R; White, Robert L

    2008-01-01

    Thermal process characterization based on calculating effective activation energies from variable temperature diffuse reflection infrared spectroscopy (VT-DRIFTS) measurements is demonstrated. Experimental factors that affect the accuracies of activation energy values are outlined. Infrared radiation scattering efficiency, thermal conductivity, and inertness towards chemical reactions are factors that should be considered when selecting an appropriate diluent for preparing samples. The Kubelka-Munk representation is superior to apparent absorbance when baseline variations in spectra measured at different temperatures can be minimized. Variable-temperature infrared spectral features, such as integrated absorption band area, can be used to compute isoconversion effective activation energies, provided that measured quantities are proportional to species concentrations. PMID:18230216

  16. Copper-phosphorus alloys offer advantages in brazing copper

    SciTech Connect

    Rupert, W.D.

    1996-05-01

    Copper-phosphorus brazing alloys are used extensively for joining copper, especially refrigeration and air-conditioning copper tubing and electrical conductors. What is the effect of phosphorus when alloyed with copper? The following are some of the major effects: (1) It lowers the melt temperature of copper (a temperature depressant). (2) It increases the fluidity of the copper when in the liquid state. (3) It acts as a deoxidant or a fluxing agent with copper. (4) It lowers the ductility of copper (embrittles). There is a misconception that silver improves the ductility of the copper-phosphorus alloys. In reality, silver added to copper acts in a similar manner as phosphorus. The addition of silver to copper lowers the melt temperature (temperature depressant) and decreases the ductility. Fortunately, the rate and amount at which silver lowers copper ductility is significantly less than that of phosphorus. Therefore, taking advantage of the temperature depressant property of silver, a Ag-Cu-P alloy can be selected at approximately the same melt temperature as a Cu-P alloy, but at a lower phosphorus content. The lowering of the phosphorus content actually makes the alloy more ductile, not the silver addition. A major advantage of the copper-phosphorus alloys is the self-fluxing characteristic when joining copper to copper. They may also be used with the addition of a paste flux on brass, bronze, and specialized applications on silver, tungsten and molybdenum. Whether it is selection of the proper BCuP alloy or troubleshooting an existing problem, the suggested approach is a review of the desired phosphorus content in the liquid metal and how it is being altered during application. In torch brazing, a slight change in the oxygen-fuel ratio can affect the joint quality or leak tightness.

  17. Some possible filler alloys with low vapor pressures for refractory-metal brazing

    NASA Technical Reports Server (NTRS)

    Morris, J. F.

    1973-01-01

    A compilation of eutectics and melting-point minima for binary combinations of metals having vapor pressures below 10 to the minus 10th power torr at 1500 degrees K and .00005 torr at 2000 degree K is presented. These compositions and others near them on their phase diagrams are potential special brazing fillers for refractory metals. Some possible problems and advantages for fusion bonds of such mixtures are indicated. Evaluations of brazing fillers containing refractory metals are reported.

  18. Study of the possibility of using solar radiant energy for welding and brazing metals

    NASA Technical Reports Server (NTRS)

    Dvernyakov, V. S.; Frantsevich, I. N.; Pasichnyy, V. V.; Shiganov, N. A.; Korunov, Y. I.; Kasich-Pilipenko, I. Y.

    1974-01-01

    The solar spectrum at the surface of the earth is analyzed. A facility for creating concentrated solar radiant energy flux is described, and data on its energetic capabilities are presented. The technology of solar welding by the fusion technique and joining by high-temperature brazing is examined. The use of concentrated solar radiant energy for welding and brazing metals and alloys is shown. The results of mechanical tests and microscopic and macroscopic studies are presented.

  19. Development of plasma MIG brazing process for dissimilar metal joining of aluminum to steel

    NASA Astrophysics Data System (ADS)

    Tashiro, Shinichi; Tanaka, Manabu

    2014-08-01

    This study aims to develop a new brazing process employing plasma MIG. Because the energy density of the plasma produced by the plasma electrode is low, the base metal can be heated extensively without melting of the base metal, consequently improving the wettability of bead. This paper discussed the dissimilar metal joining of aluminum to steel by plasma MIG brazing process. Fracture occurred at the HAZ in the aluminum plate at 80 MPa.

  20. The effect of excimer laser pretreatment on diffusion and activation of boron implanted in silicon

    SciTech Connect

    Monakhov, E.V.; Svensson, B.G.; Linnarsson, M.K.; La Magna, A.; Italia, M.; Privitera, V.; Fortunato, G.; Cuscuna, M.; Mariucci, L.

    2005-11-07

    We have investigated the effect of excimer laser annealing (ELA) on transient enhanced diffusion (TED) and activation of boron implanted in Si during subsequent rapid thermal annealing (RTA). It is observed that ELA with partial melting of the implanted region causes reduction of TED in the region that remains solid during ELA, where the diffusion length of boron is reduced by a factor of {approx}4 as compared to the as-implanted sample. This is attributed to several mechanisms such as liquid-state annealing of a fraction of the implantation induced defects, introduction of excess vacancies during ELA, and solid-state annealing of the defects beyond the maximum melting depth by the heat wave propagating into the Si wafer. The ELA pretreatment provides a substantially improved electrical activation of boron during subsequent RTA.

  1. Disk Diffusion Assay to Assess the Antimicrobial Activity of Marine Algal Extracts.

    PubMed

    Desbois, Andrew P; Smith, Valerie J

    2015-01-01

    Marine algae are a relatively untapped source of bioactive natural products, including those with antimicrobial activities. The ability to assess the antimicrobial activity of cell extracts derived from algal cultures is vital to identifying species that may produce useful novel antibiotics. One assay that is used widely for this purpose is the disk diffusion assay due to its simplicity, rapidity, and low cost. Moreover, this assay gives output data that are easy to interpret and can be used to screen many samples at once irrespective of the solvent used during preparation. In this chapter, a step-by-step protocol for performing a disk diffusion assay is described. The assay is particularly well suited to testing algal cell extracts and fractions resulting from separation through bioassay-guided approaches. PMID:26108520

  2. Diffused Intra-Oocyte Hydrogen Peroxide Activates Myeloperoxidase and Deteriorates Oocyte Quality

    PubMed Central

    Khan, Sana N.; Shaeib, Faten; Najafi, Tohid; Kavdia, Mahendra; Gonik, Bernard; Saed, Ghassan M.; Goud, Pravin T.; Abu-Soud, Husam M.

    2015-01-01

    Hydrogen peroxide (H2O2) is a relatively long-lived signaling molecule that plays an essential role in oocyte maturation, implantation, as well as early embryonic development. Exposure to relatively high levels of H2O2 functions efficiently to accelerate oocyte aging and deteriorate oocyte quality. However, little precise information exists regarding intra-oocyte H2O2 concentrations, and its diffusion to the oocyte milieu. In this work, we utilized an L-shaped amperometric integrated H2O2-selective probe to directly and quantitatively measure the real-time intra-oocyte H2O2 concentration. This investigation provides an exact measurement of H2O2 in situ by reducing the possible loss of H2O2 caused by diffusion or reactivity with other biological systems. This experiment suggests that the intra-oocyte H2O2 levels of oocytes obtained from young animals are reasonably high and remained constant during the procedure measurements. However, the intra-oocyte H2O2 concentration dropped significantly (40-50% reduction) in response to catalase pre-incubation, suggesting that the measurements are truly H2O2 based. To further confirm the extracellular diffusion of H2O2, oocytes were incubated with myeloperoxidase (MPO), and the diffused H2O2 triggered MPO chlorinating activity. Our results show that the generated hypochlorous acid (HOCl) facilitated the deterioration in oocyte quality, a process that could be prevented by pre-incubating the oocytes with melatonin, which was experimentally proven to be oxidized utilizing HPLC methods. This study is the first to demonstrate direct quantitative measurement of intracellular H2O2, and its extracellular diffusion and activation of MPO as well as its impact on oocyte quality. These results may help in designing more accurate treatment plans in assisted reproduction under inflammatory conditions. PMID:26197395

  3. Alterations in Daytime and Nighttime Activity in Piglets after Focal and Diffuse Brain Injury.

    PubMed

    Olson, Emily; Badder, Carlie; Sullivan, Sarah; Smith, Colin; Propert, Kathleen; Margulies, Susan S

    2016-04-15

    We have developed and implemented a noninvasive, objective neurofunctional assessment for evaluating the sustained effects of traumatic brain injury (TBI) in piglets with both diffuse and focal injury types. Derived from commercial actigraphy methods in humans, this assessment continuously monitors the day/night activity of piglets using close-fitting jackets equipped with tri-axial accelerometers to monitor movements of the thorax. Acceleration metrics were correlated (N = 7 naïve piglets) with video images to define values associated with a range of activities, from recumbancy (rest) to running. Both focal (N = 8) and diffuse brain injury (N = 9) produced alterations in activity that were significant 4 days post-TBI. Compared to shams (N = 6) who acclimated to the animal facility 4 days after an anesthesia experience by blurring the distinction between day and night activity, post-TBI time-matched animals had larger fractions of inactive periods during the daytime than nighttime, and larger fractions of active time in the night were spent in high activity (e.g., constant walking, intermittent running) than during the day. These persistent disturbances in rest and activity are similar to those observed in human adults and children post-TBI, establishing actigraphy as a translational metric, used in both humans and large animals, for assessment of injury severity, progressions, and intervention. PMID:26414329

  4. Solubility and Dissolution Rate of Ni Base Alloy to Molten Ag-Cu-Pd Brazing Filler

    NASA Astrophysics Data System (ADS)

    Ikeshoji, Toshi-Taka; Watanabe, Yuki; Suzumura, Akio; Yamazaki, Takahisa

    During the brazing process of the rocket engine’s nozzle skirt assembly made from Fe-Ni based super alloy pipes with Pd based brazing filler, the erosion corrosion pits were sometimes engraved on those pipes’ surface. The corrosion is considered to be assisted by the dynamic flow of the molten brazing filler. In order to estimate the amount of erosion corrosion and to prevent it, the solubility and the dissolution rate of Ni to the molten Ag-Cu-Pd brazing filler are measured experimentally. The Ni crucible poured with the Ag-Cu-Pd brazing filler was heated up to 1320K and quenched after the various keeping time. The microstructure of the solidified brazing filler part’s cross sections was observed, and the amount of the dissolved Ni was estimated using the image processing technique. The solubility was about 5.53mass%and the initial dissolution rate was 6.28 × 10-3mass%/s. Using these data, more elaborate dynamic flow simulation will be able to conduct.

  5. JOINING OF MOLYBDENUM DISILICIDE TO STAINLESS STEEL USING AMORPHOUS METAL BRAZES-RESIDUAL STRESS ANALYSIS

    SciTech Connect

    VAIDYA, RAJENDRA U; KAUTZ, DOUGLAS D.; GALLEGOS, DAVID E.

    2007-01-30

    Molybdenum disilicide (MoSi{sub 2})/stainless steel 316 L jOints were produced by high temperature brazing using a cobalt-based metallic-glass (METGLAS{trademark} 2714A). Successful joining was completed in two different ways; either by feeding excess braze into the braze gap upon heating or by constraining the MoSi{sub 2}/stainiess steel assembly with an alumina (Al{sub 2}O{sub 3}) fixture during the heating cycle. These steps were necessary to ensure the production of a high quality void free joint. Residual stress measurements were completed on these joints. Indentation results show higher tensile residual stresses in the stainless steel for the joint with the external constraint, in comparison to the unconstrained state. In contrast, the compressive residual stresses In the MoSi{sub 2} (as measured by X-ray diffraction) were lower in the constrained state relative to the unconstrained state. These results and a lack of residual stress balance indicate that the stress state in the braze is significantly different under the two joining conditions and the volume of the braze plays an important role in the development of the residual stresses. Push-out tests carried out on these joints gave higher joint strengths in the unconstrained as compared to the constrained condition. The results of this study have important implications on the selection of the appropriate joining process (use of constraint versus extra braze).

  6. Multidrug efflux transporter activity in sea urchin embryos:Does localization provide a diffusive advantage?

    NASA Astrophysics Data System (ADS)

    Song, Xianfeng; Setayeshgar, Sima; Cole, Bryan; Hamdoun, Amro; Epel, David

    2008-03-01

    Experiments have shown upregulation of multidrug efflux transporter activity approximately 30 min after fertilization in the sea urchin embryo [1]. These ATP-hydrolyzing transporter proteins pump moderately hydrophobic molecules out of the cell and represent the cell's first line of defense againstexogenous toxins. It has also been shown that transporters are moved in vesicles along microfilaments and localized to tips of microvilli prior to activation. We have constructed a geometrically realistic model of the embryo, including microvilli, to explore the functional role of this localization in the efficient elimination of toxins from the standpoint of diffusion. We compute diffusion of toxins in extracellular, membrane and intracellular spaces coupled with transporter activity, using experimentally derived values for physical parameters. For transporters uniformly distributed along microvilli and tip-localized transporters we compare regions in parameter space where each distribution provides diffusive advantage, and comment on the physically expected conditions. [1] A. M. Hamdoun, G. N. Cherr, T. A. Roepke and D. Epel, Developmental Biology 276 452 (2004).

  7. Study of microparticles' anomalous diffusion in active bath using speckle light fields (Presentation Recording)

    NASA Astrophysics Data System (ADS)

    Pince, Ercag; Sabareesh, Sabareesh K. P.; Volpe, Giorgio; Gigan, Sylvain; Volpe, Giovanni S.

    2015-08-01

    Particles undergoing a stochastic motion within a disordered medium is a ubiquitous physical and biological phenomenon. Examples can be given from organelles as molecular machines of cells performing physical tasks in a populated cytoplasm to human mobility in patchy environment at larger scales. Our recent results showed that it is possible to use the disordered landscape generated by speckle light fields to perform advanced manipulation tasks at the microscale. Here, we use speckle light fields to study the anomalous diffusion of micron size silica particles (5 μm) in the presence of active microswimmers. The microswimmers we used in the experiments are motile bacteria, Escherichia coli (E.coli). They constitute an active background constantly agitating passive silica particles within complex optical potentials. The speckle fields are generated by mode mixing inside a multimode optical fiber where a small amount of incident laser power (maximum power = 12 μW/μm2) is needed to obtain an effective random landscape pattern for the purpose of optical manipulation. We experimentally show how complex potentials contribute to the anomalous diffusion of silica particles undergoing collisions with swimming bacteria. We observed an enhanced diffusion of particles interacting with the active bath of E.coli inside speckle light fields: this effect can be tuned and controlled by varying the intensity and the statistical properties of the speckle pattern. Potentially, these results could be of interest for many technological applications, such as the manipulation of microparticles inside optically disordered media of biological interests.

  8. Electrically active centers formed in silicon during the high-temperature diffusion of boron and aluminum

    SciTech Connect

    Sobolev, N. A.; Loshachenko, A. S.; Poloskin, D. S.; Shek, E. I.

    2013-02-15

    The parameters of electrically active centers formed during the high-temperature diffusion of boron and aluminum into silicon in various media are studied by the Hall method and capacitance spectroscopy. It is found that the variation in the resistivity of the n base of the structures with p-n junctions fabricated in the study is controlled by the formation of three donor levels Q1, E4, and Q3 with the energies E{sub c} - 0.31, E{sub c} - 0.27, and E{sub c} - 0.16 eV. Diffusion in a chlorine-containing atmosphere introduces only a single level E4, but its concentration is 2.5 times lower, compared with diffusion in air. The values of the ionization energy of the Q3 level, measured under equilibrium (Hall effect) and nonequilibrium (capacitance spectroscopy) conditions, almost coincide. The deepest level E1 with an energy of E{sub c} - 0.54 eV, formed upon diffusion in both media, has no effect on the resistivity in the n base of the structures.

  9. The impact of probe size on measurements of diffusion in active microrheology.

    PubMed

    Hoh, Nicholas J; Zia, Roseanna N

    2016-08-21

    We present a framework to elucidate the influence of polydispersity on flow-induced diffusion in active microrheology. A colloidal probe particle is driven through a suspension of hydrodynamically interacting background particles, where the probe may be larger or smaller than the bath particles. The thermodynamic size of the particles may be greater than their hydrodynamic size; the hydrodynamic sizes can be identical with thermodynamic sizes that differ, or vice versa, or a combination of both. The diffusive behavior is set entirely and dually by the proximity with which two particles can approach one another, and by the extent to which this minimum approach distance is occupied by the hydrodynamic size of the forced particle. We find that reducing the size of the probe reduces flow-induced diffusion when hydrodynamic interactions are weak but increases flow-induced diffusion when hydrodynamic interactions are strong-regardless of the strength of external forcing. This behavior owes its origins to a rich evolution of the dominance of hydrodynamic and entropic forces with changes in the relative hydrodynamic and thermodynamic sizes of the particles. PMID:27442485

  10. Mechanical properties of Inconel 718 and Nickel 201 alloys after thermal histories simulating brazing and high temperature service

    SciTech Connect

    James, W.F.

    1985-09-01

    An experimental investigation was made to evaluate two nickel base alloys (Nickel-201 and Inconel-718) in three heat treated conditions. These conditions were: (1) annealed; (2) after thermal exposure simulating a braze cycle; and (3) after a thermal exposure simulating a braze cycle plus one operational lifetime of high temperature service. For the Nickel-201, two different braze cycle temperatures were evaluated. A braze cycle utilizing a lower braze temperature resulted in less grain growth for Nickel-201 than the standard braze cycle used for joining Nickel-201 to Inconel-718. It was determined, however, that Nickel-201, was marginal for temperatures investigated due to large grain growth. After the thermal exposures described above, the mechanical properties of Nickel-201 were degraded, whereas similar exposure on Inconel-718 actually strengthened the material compared with the annealed condition. The investigation included tensile tests at both room temperature and elevated temperatures, stress-rupture tests, and metallographic examination.

  11. Mechanical properties of Inconel 718 and Nickel 201 alloys after thermal histories simulating brazing and high temperature service

    NASA Technical Reports Server (NTRS)

    James, W. F.

    1985-01-01

    An experimental investigation was made to evaluate two nickel base alloys (Nickel-201 and Inconel-718) in three heat treated conditions. These conditions were: (1) annealed; (2) after thermal exposure simulating a braze cycle; and (3) after a thermal exposure simulating a braze cycle plus one operational lifetime of high temperature service. For the Nickel-201, two different braze cycle temperatures were evaluated. A braze cycle utilizing a lower braze temperature resulted in less grain growth for Nickel-201 than the standard braze cycle used for joining Nickel-201 to Inconel-718. It was determined, however, that Nickel-201, was marginal for temperatures investigated due to large grain growth. After the thermal exposures described above, the mechanical properties of Nickel-201 were degraded, whereas similar exposure on Inconel-718 actually strengthened the material compared with the annealed condition. The investigation included tensile tests at both room temperature and elevated temperatures, stress-rupture tests, and metallographic examination.

  12. Braze alloy process and strength characterization studies for 18 nickel grade 200 maraging steel with application to wind tunnel models

    NASA Technical Reports Server (NTRS)

    Bradshaw, James F.; Sandefur, Paul G., Jr.; Young, Clarence P., Jr.

    1991-01-01

    A comprehensive study of braze alloy selection process and strength characterization with application to wind tunnel models is presented. The applications for this study include the installation of stainless steel pressure tubing in model airfoil sections make of 18 Ni 200 grade maraging steel and the joining of wing structural components by brazing. Acceptable braze alloys for these applications are identified along with process, thermal braze cycle data, and thermal management procedures. Shear specimens are used to evaluate comparative shear strength properties for the various alloys at both room and cryogenic (-300 F) temperatures and include the effects of electroless nickel plating. Nickel plating was found to significantly enhance both the wetability and strength properties for the various braze alloys studied. The data are provided for use in selecting braze alloys for use with 18 Ni grade 200 steel in the design of wind tunnel models to be tested in an ambient or cryogenic environment.

  13. An Asymptotic Analysis of a 2-D Model of Dynamically Active Compartments Coupled by Bulk Diffusion

    NASA Astrophysics Data System (ADS)

    Gou, J.; Ward, M. J.

    2016-04-01

    A class of coupled cell-bulk ODE-PDE models is formulated and analyzed in a two-dimensional domain, which is relevant to studying quorum-sensing behavior on thin substrates. In this model, spatially segregated dynamically active signaling cells of a common small radius ɛ ≪ 1 are coupled through a passive bulk diffusion field. For this coupled system, the method of matched asymptotic expansions is used to construct steady-state solutions and to formulate a spectral problem that characterizes the linear stability properties of the steady-state solutions, with the aim of predicting whether temporal oscillations can be triggered by the cell-bulk coupling. Phase diagrams in parameter space where such collective oscillations can occur, as obtained from our linear stability analysis, are illustrated for two specific choices of the intracellular kinetics. In the limit of very large bulk diffusion, it is shown that solutions to the ODE-PDE cell-bulk system can be approximated by a finite-dimensional dynamical system. This limiting system is studied both analytically, using a linear stability analysis and, globally, using numerical bifurcation software. For one illustrative example of the theory, it is shown that when the number of cells exceeds some critical number, i.e., when a quorum is attained, the passive bulk diffusion field can trigger oscillations through a Hopf bifurcation that would otherwise not occur without the coupling. Moreover, for two specific models for the intracellular dynamics, we show that there are rather wide regions in parameter space where these triggered oscillations are synchronous in nature. Unless the bulk diffusivity is asymptotically large, it is shown that a diffusion-sensing behavior is possible whereby more clustered spatial configurations of cells inside the domain lead to larger regions in parameter space where synchronous collective oscillations between the small cells can occur. Finally, the linear stability analysis for these cell

  14. An Asymptotic Analysis of a 2-D Model of Dynamically Active Compartments Coupled by Bulk Diffusion

    NASA Astrophysics Data System (ADS)

    Gou, J.; Ward, M. J.

    2016-08-01

    A class of coupled cell-bulk ODE-PDE models is formulated and analyzed in a two-dimensional domain, which is relevant to studying quorum-sensing behavior on thin substrates. In this model, spatially segregated dynamically active signaling cells of a common small radius ɛ ≪ 1 are coupled through a passive bulk diffusion field. For this coupled system, the method of matched asymptotic expansions is used to construct steady-state solutions and to formulate a spectral problem that characterizes the linear stability properties of the steady-state solutions, with the aim of predicting whether temporal oscillations can be triggered by the cell-bulk coupling. Phase diagrams in parameter space where such collective oscillations can occur, as obtained from our linear stability analysis, are illustrated for two specific choices of the intracellular kinetics. In the limit of very large bulk diffusion, it is shown that solutions to the ODE-PDE cell-bulk system can be approximated by a finite-dimensional dynamical system. This limiting system is studied both analytically, using a linear stability analysis and, globally, using numerical bifurcation software. For one illustrative example of the theory, it is shown that when the number of cells exceeds some critical number, i.e., when a quorum is attained, the passive bulk diffusion field can trigger oscillations through a Hopf bifurcation that would otherwise not occur without the coupling. Moreover, for two specific models for the intracellular dynamics, we show that there are rather wide regions in parameter space where these triggered oscillations are synchronous in nature. Unless the bulk diffusivity is asymptotically large, it is shown that a diffusion-sensing behavior is possible whereby more clustered spatial configurations of cells inside the domain lead to larger regions in parameter space where synchronous collective oscillations between the small cells can occur. Finally, the linear stability analysis for these cell

  15. Activated microglia in acute encephalopathy with biphasic seizures and late reduced diffusion.

    PubMed

    Fujita, Yuji; Takanashi, Jun-Ichi; Takei, Haruka; Ota, Setsuo; Fujii, Katsunori; Sakuma, Hiroshi; Hayashi, Masaharu

    2016-07-15

    Acute encephalopathy with biphasic seizures and late reduced diffusion (AESD) is the most common subtype of infectious pediatric encephalopathy in Japan. The exact pathogenesis of and the best therapeutic strategy for AESD are uncertain. We firstly performed a brain biopsy in a 2-year-old boy with AESD associated with RS viral infection, which revealed activated ameoboid microglia accumulation around degenerated neuron, and astrogliosis in the affected cortex. Glutamate released from activated microglia may play an important role in the pathogenesis of AESD, which is compatible with the previous report of magnetic resonance spectroscopy showing elevated glutamate. PMID:27288783

  16. Using a Simple Apparatus to Measure Direct and Diffuse Photosynthetically Active Radiation at Remote Locations

    PubMed Central

    Cruse, Michael J.; Kucharik, Christopher J.; Norman, John M.

    2015-01-01

    Plant canopy interception of photosynthetically active radiation (PAR) drives carbon dioxide (CO2), water and energy cycling in the soil-plant-atmosphere system. Quantifying intercepted PAR requires accurate measurements of total incident PAR above canopies and direct beam and diffuse PAR components. While some regional data sets include these data, e.g. from Atmospheric Radiation Measurement (ARM) Program sites, they are not often applicable to local research sites because of the variable nature (spatial and temporal) of environmental variables that influence incoming PAR. Currently available instrumentation that measures diffuse and direct beam radiation separately can be cost prohibitive and require frequent adjustments. Alternatively, generalized empirical relationships that relate atmospheric variables and radiation components can be used but require assumptions that increase the potential for error. Our goal here was to construct and test a cheaper, highly portable instrument alternative that could be used at remote field sites to measure total, diffuse and direct beam PAR for extended time periods without supervision. The apparatus tested here uses a fabricated, solar powered rotating shadowband and other commercially available parts to collect continuous hourly PAR data. Measurements of total incident PAR had nearly a one-to-one relationship with total incident radiation measurements taken at the same research site by an unobstructed point quantum sensor. Additionally, measurements of diffuse PAR compared favorably with modeled estimates from previously published data, but displayed significant differences that were attributed to the important influence of rapidly changing local environmental conditions. The cost of the system is about 50% less than comparable commercially available systems that require periodic, but not continual adjustments. Overall, the data produced using this apparatus indicates that this instrumentation has the potential to support

  17. Using a simple apparatus to measure direct and diffuse photosynthetically active radiation at remote locations.

    PubMed

    Cruse, Michael J; Kucharik, Christopher J; Norman, John M

    2015-01-01

    Plant canopy interception of photosynthetically active radiation (PAR) drives carbon dioxide (CO2), water and energy cycling in the soil-plant-atmosphere system. Quantifying intercepted PAR requires accurate measurements of total incident PAR above canopies and direct beam and diffuse PAR components. While some regional data sets include these data, e.g. from Atmospheric Radiation Measurement (ARM) Program sites, they are not often applicable to local research sites because of the variable nature (spatial and temporal) of environmental variables that influence incoming PAR. Currently available instrumentation that measures diffuse and direct beam radiation separately can be cost prohibitive and require frequent adjustments. Alternatively, generalized empirical relationships that relate atmospheric variables and radiation components can be used but require assumptions that increase the potential for error. Our goal here was to construct and test a cheaper, highly portable instrument alternative that could be used at remote field sites to measure total, diffuse and direct beam PAR for extended time periods without supervision. The apparatus tested here uses a fabricated, solar powered rotating shadowband and other commercially available parts to collect continuous hourly PAR data. Measurements of total incident PAR had nearly a one-to-one relationship with total incident radiation measurements taken at the same research site by an unobstructed point quantum sensor. Additionally, measurements of diffuse PAR compared favorably with modeled estimates from previously published data, but displayed significant differences that were attributed to the important influence of rapidly changing local environmental conditions. The cost of the system is about 50% less than comparable commercially available systems that require periodic, but not continual adjustments. Overall, the data produced using this apparatus indicates that this instrumentation has the potential to support

  18. Short timescale inkjet ink component diffusion: an active part of the absorption mechanism into inkjet coatings.

    PubMed

    Lamminmäki, T T; Kettle, J P; Puukko, P J T; Ridgway, C J; Gane, P A C

    2012-01-01

    The structures of inkjet coatings commonly contain a high concentration of fine diameter pores together with a large pore volume capacity. To clarify the interactive role of the porous structure and the coincidentally occurring swelling of binder during inkjet ink vehicle imbibition, coating structures were studied in respect to their absorption behaviour for polar and non-polar liquid. The absorption measurement was performed using compressed pigment tablets, based on a range of pigment types and surface charge polarity, containing either polyvinyl alcohol (PVOH) or styrene acrylic latex (SA) as the binder, by recording the liquid uptake with a microbalance. The results indicate that, at the beginning of liquid uptake, at times less than 2 s, the small pores play the dominant role with respect to the inkjet ink vehicle imbibition. Simultaneously, water molecules diffuse into and within the hydrophilic PVOH binder causing binder swelling, which diminishes the number of active small pores and reduces the diameter of remaining pores, thus slowing the capillary flow as a function of time. The SA latex does not absorb the vehicle, and therefore the dominating phenomenon is then capillary absorption. However, the diffusion coefficient of the water vapour across separately prepared PVOH and SA latex films seems to be quite similar. In the PVOH, the polar liquid diffuses into the polymer network, whereas in the SA latex the hydrophobic nature prevents the diffusion into the polymer matrix and there exists surface diffusion. At longer timescale, permeation flow into the porous coating dominates as the resistive term controlling the capillary driven liquid imbibition rate. PMID:21981972

  19. Transcriptional Activity in Diplotene Larch Microsporocytes, with Emphasis on the Diffuse Stage

    PubMed Central

    Kołowerzo-Lubnau, Agnieszka; Niedojadło, Janusz; Świdziński, Michał; Bednarska-Kozakiewicz, Elżbieta; Smoliński, Dariusz J.

    2015-01-01

    Manuscript provides insights into the biology of long-lived plants, different from Arabidopsis, tomato or grass species that are widely studied. In the European larch the diplotene stage lasts approximately 5 months and it is possible to divide it into several substages and to observe each of them in details. The diplotene stage is a period of intensive microsporocyte growth associated with the synthesis and accumulation of different RNA and proteins. Larch microsporocytes display changes in chromatin morphology during this stage, alternating between 4 short stages of chromatin condensation (contraction) and 5 longer diffusion (relaxation) stages. The occurrence of a diplotene diffusion stage has been observed in many plant species. Interestingly, they have also been observed during spermiogenesis and oogenesis in animals. The aim of this study was to examine whether chromatin relaxation during the diplotene is accompanied by the synthesis and maturation of mRNA. The results reveal a correlation between the diffusion and chromatin decondensation, transcriptional activity. We also found decreasing amount of poly(A) mRNA synthesis in the consecutive diffusion stages. During the early diffusion stages, mRNA is intensively synthesized. In the nuclei large amounts of RNA polymerase II, and high levels of snRNPs were observed. In the late diffusion stages, the synthesized mRNA is not directly subjected to translation but it is stored in the nucleus, and later transported to the cytoplasm and translated. In the last diffusion stage, the level of poly(A) RNA is low, but that of splicing factors is still high. It appears that the mRNA synthesized in early stages is used during the diplotene stage and is not transmitted to dyad and tetrads. In contrast, splicing factors accumulate and are most likely transmitted to the dyad and tetrads, where they are used after the resumption of intense transcription. Similar meiotic process were observed during oogenesis in animals. This

  20. Technical Consultation of the International Space Station (ISS) Internal Active Thermal Control System (IATCS) Cooling Water Chemistry

    NASA Technical Reports Server (NTRS)

    Gentz, Steven J.; Rotter, Hank A.; Easton, Myriam; Lince, Jeffrey; Park, Woonsup; Stewart, Thomas; Speckman, Donna; Dexter, Stephen; Kelly, Robert

    2005-01-01

    The Internal Active Thermal Control System (IATCS) coolant exhibited unexpected chemical changes during the first year of on-orbit operation following the launch and activation in February 2001. The coolant pH dropped from 9.3 to below the minimum specification limit of 9.0, and re-equilibrated between 8.3 and 8.5. This drop in coolant pH was shown to be the result of permeation of CO2 from the cabin into the coolant via Teflon flexible hoses which created carbonic acid in the fluid. This unexpected diffusion was the result of having a cabin CO2 partial pressure higher than the ground partial pressure (average 4.0 mmHg vs. less than 0.2 mmHg). This drop in pH was followed by a concurrent increasing coolant nickel concentration. No other metal ions were observed in the coolant and based on previous tests, the source of nickel ion was thought to be the boron nickel (BNi) braze intermetallics used in the construction of HXs and cold plates. Specifically, BNi2 braze alloy was used for the IATCS IFHX and BNi3 braze alloy was used for the IATCS Airlock Servicing and Performance Checkout Unit (SPCU) HX and cold plates. Given the failure criticality of the HXs, a Corrosion Team was established by the IATCS CWG to determine the impact of the nickel corrosion on hardware performance life.

  1. Modeling and experiments on diffusion and activation of phosphorus in germanium

    SciTech Connect

    Tsouroutas, P.; Tsoukalas, D.; Zergioti, I.; Cherkashin, N.; Claverie, A.

    2009-05-01

    We report on phosphorus diffusion and activation related phenomena in germanium. We have used both conventional thermal processing and laser annealing by pulsed nanosecond Nd:YAG laser. Chemical profiles were obtained by secondary-ion-mass spectroscopy, sheet resistance was estimated by the van der Pauw method, and structural defects were monitored by transmission electron microscopy. Our study covers the temperature range from 440 to 750 deg. C, and we were able to efficiently simulate the dopant profiles within that temperature range, taking into account a quadratic dependence of the P diffusion coefficient on the free electron concentration. To achieve that we have taken into account dopant activation dependence on temperature as well as dopant pile-up near the surface and dopant loss owing to outdiffusion during the annealing. A combined laser thermal treatment above the melting threshold prior to conventional annealing allowed the elimination of the implantation damage, so we could perceive the influence of defects on both transient dopant diffusion and outdiffusion.

  2. The effect of biological activity on soil water retention and diffusivity

    NASA Astrophysics Data System (ADS)

    Choudhury, Burhan U.; Ferraris, Stefano; Ashton, Rhys W.; Powlson, David S.; Whalley, William R.

    2016-04-01

    Root exudates of both living and artificial origins are known to affect various rhizosphere microbial and micro-faunal activities. However, information on effects on root exudates on soil hydraulic properties responsible for water transmission and distribution in the vadose zone is inadequate, especially in dry soils. To study the effect of artificial root exudates (carbohydrate, amino acids and organic acids mixture) on soil water retention and diffusion process, a laboratory experiment was carried out using soil cores filled with air dried 2-mm sieved loamy sand soils of Cambric Arenosol subclass. Root exudates at three concentrations (1.25, 2.5 & 5.0 g C kg‑1 dry soil) were added and the soil cores were saturated in distilled water for 48 hours at 20 oC together with a control. To determine whether microbes have any influence on diffusivity, two additional treatments with sterilization of microbes using mercuric chloride solution (0.10%) in root exudates (2.5 g C kg‑1 dry soil) and distilled water saturated soil cores were studied. The water in the soil cores was allowed to evaporate at constant temperature (20 ± 1oC) and at a relative humidity of 0.3. The evaporation loss in terms of volumetric water content in the core was measured regularly until the water content was constant with time. Soil water diffusivity was determined numerically. To determine the water retention properties, soils were saturated and incubated for 14 days at 20 oC with the same six treatments and retention curves were generated for 8 different suctions, ranging from 0.01 bars to 15 bars. Results revealed that evaporation from soil cores, initially at a uniform moisture content of saturation, initially decreased linearly with the square root of time. The rate of decrease was gradual in the root exudate treated soils but more rapid in soils treated to stop microbial activity. Addition of root exudates considerably decreased the diffusivity compared to a control treatment. By stopping

  3. Chemical activity induces dynamical force with global structure in a reaction-diffusion-convection system.

    PubMed

    Mahara, Hitoshi; Okada, Koichi; Nomura, Atsushi; Miike, Hidetoshi; Sakurai, Tatsunari

    2009-07-01

    We found a rotating global structure induced by the dynamical force of local chemical activity in a thin solution layer of excitable Belousov-Zhabotinsky reaction coupled with diffusion. The surface flow and deformation associated with chemical spiral waves (wavelength about 1 mm) represents a global unidirectional structure and a global tilt in the entire Petri dish (100 mm in diameter), respectively. For these observations, we scanned the condition of hierarchal pattern selection. From this result, the bromomalonic acid has an important role to induce the rotating global structure. An interaction between a reaction-diffusion process and a surface-tension-driven effect leads to such hierarchal pattern with different scales. PMID:19658764

  4. Prediction of motor outcomes and activities of daily living function using diffusion tensor tractography in acute hemiparetic stroke patients

    PubMed Central

    Imura, Takeshi; Nagasawa, Yuki; Inagawa, Tetsuji; Imada, Naoki; Izumi, Hiroaki; Emoto, Katsuya; Tani, Itaru; Yamasaki, Hiroyuki; Ota, Yuichiro; Oki, Shuichi; Maeda, Tadanori; Araki, Osamu

    2015-01-01

    [Purpose] The efficacy of diffusion tensor imaging in the prediction of motor outcomes and activities of daily living function remains unclear. We evaluated the most appropriate diffusion tensor parameters and methodology to determine whether the region of interest- or tractography-based method was more useful for predicting motor outcomes and activities of daily living function in stroke patients. [Subjects and Methods] Diffusion tensor imaging data within 10 days after stroke onset were collected and analyzed for 25 patients. The corticospinal tract was analyzed. Fractional anisotropy, number of fibers, and apparent diffusion coefficient were used as diffusion tensor parameters. Motor outcomes and activities of daily living function were evaluated on the same day as diffusion tensor imaging and at 1 month post-onset. [Results] The fractional anisotropy value of the affected corticospinal tract significantly correlated with the motor outcome and activities of daily living function within 10 days post-onset and at 1 month post-onset. Tthere were no significant correlations between other diffusion tensor parameters and motor outcomes or activities of daily living function. [Conclusion] The fractional anisotropy value of the affected corticospinal tract obtained using the tractography-based method was useful for predicting motor outcomes and activities of daily living function in stroke patients. PMID:26157225

  5. Thermodynamics of copper-nickel alloys containing aluminum, silicon, titanium, and chromium relative to their use in ceramic brazing

    SciTech Connect

    Williams, R.O.

    1984-11-01

    By varying the copper-to-nickel ratio the activity coefficients of Al, Si, Ti, and Cr can be varied over a wide range. Thus to a degree one can tailor the behavior of such alloys for usefulness in brazing ceramics. Further, considerable amounts of these active elements can be present while the ability of carbon to reduce the surface oxide film in a high-vacuum system is retained. The critical aluminum concentrations required to prevent the formation of SiO/sub 2/, TiO, or Cr/sub 2/O/sub 3/ by reaction with Al/sub 2/O/sub 3/ are calculated. The simultaneous presence of the four active additions will presumably promote wetting without making the surface deoxidation more difficult.

  6. Tensile Creep Properties of the 50Au-50Cu Braze Alloy

    SciTech Connect

    Stephens, J.J.

    1999-05-28

    The 50Au-50CU (wt.%) alloy is a solid-solution strengthened braze alloy used extensively in conventional, hermetic metal/ceramic brazing applications where low vapor pressure is a requirement. Typical metal/ceramic base materials would be KovarTM alloy and metallized and Ni-plated 94% alumina ceramic. The elevated temperature mechanical properties are important for permitting FEA evaluation of residual stresses in metal/ceramic brazes given specific geometries and braze cooldown profiles. For material with an atomic composition of 76.084 at.% CL 23.916 Au (i.e., on the Cu-rich side of Cu3Au) that was annealed for 2 hr. at 750°C and water quenched a Garofalo sinh equation was found to adequately characterize the minimum strain rate data over the temperature mnge 450-850°C. At lower temperatures (250 arid 350°C), a conventional power law equation was found to characterize the data. For samples held long periods of time at 375°C (96 hrs.) and slowly cooled to room temperature, a slight strengthening reaction was observed: with the stress necessary to reach the same strain rate increasing by about 15% above the baseline annealed and quenched data. X-ray diffiction indicates that the 96 hr at 375°C + slow cool condition does indeed order. The microhardness of the ordered samples indicates a value of 94.5 VHN, compared to 93.7 VHN for the baseline annealed and quenched (disordered FCC) samples. From a brazing perspective, the relative sluggishness of this ordering reaction does not appear to pose a problem for braze joints cooled at reasonable rates following brazing.

  7. Diffusion and chemical activity of Zr-Sn and Zr-Ti systems

    SciTech Connect

    Zee, R.H.; Watters, J.F.; Davidson, R.D.

    1986-11-15

    A modified evaporation method was used to determine the diffusion coefficients and the emission rates of Sn and Ti in Zr-Sn and Zr-Ti, respectively, at temperatures between 1605 and 1970 K. Results show that both Sn and Ti diffuse in their respective alloys via a vacancy mechanism. Comparison with data in the literature reveals that the activation energy for diffusion of Sn in Zr-Sn, with Sn content between 3 and 5 at.X is relatively constant from 1200 to 1970 K. From the measured emission rates, values of 103 and 98 kcal/mol were obtained for the enthalpies of sublimation for Sn and Ti in their alloys. With a comparison of the solute vapor pressures with those of the pure elements, partial molar free energies, entropies, and enthalpies for the two systems were determined in the temperature range investigated. The Zr-Sn system shows a very large negative heat of formation (-33 kcal/mol) whereas the Zr-Ti system behaves quite ideally, in agreement with phase-diagram predictions.

  8. A convergent diffusion and social marketing approach for disseminating proven approaches to physical activity promotion.

    PubMed

    Dearing, James W; Maibach, Edward W; Buller, David B

    2006-10-01

    Approaches from diffusion of innovations and social marketing are used here to propose efficient means to promote and enhance the dissemination of evidence-based physical activity programs. While both approaches have traditionally been conceptualized as top-down, center-to-periphery, centralized efforts at social change, their operational methods have usually differed. The operational methods of diffusion theory have a strong relational emphasis, while the operational methods of social marketing have a strong transactional emphasis. Here, we argue for a convergence of diffusion of innovation and social marketing principles to stimulate the efficient dissemination of proven-effective programs. In general terms, we are encouraging a focus on societal sectors as a logical and efficient means for enhancing the impact of dissemination efforts. This requires an understanding of complex organizations and the functional roles played by different individuals in such organizations. In specific terms, ten principles are provided for working effectively within societal sectors and enhancing user involvement in the processes of adoption and implementation. PMID:16979466

  9. Iterative weighted average diffusion as a novel external force in the active contour model

    NASA Astrophysics Data System (ADS)

    Mirov, Ilya S.; Nakhmani, Arie

    2016-03-01

    The active contour model has good performance in boundary extraction for medical images; particularly, Gradient Vector Flow (GVF) active contour model shows good performance at concavity convergence and insensitivity to initialization, yet it is susceptible to edge leaking, deep and narrow concavities, and has some issues handling noisy images. This paper proposes a novel external force, called Iterative Weighted Average Diffusion (IWAD), which used in tandem with parametric active contours, provides superior performance in images with high values of concavity. The image gradient is first turned into an edge image, smoothed, and modified with enhanced corner detection, then the IWAD algorithm diffuses the force at a given pixel based on its 3x3 pixel neighborhood. A forgetting factor, φ, is employed to ensure that forces being spread away from the boundary of the image will attenuate. The experimental results show better behavior in high curvature regions, faster convergence, and less edge leaking than GVF when both are compared to expert manual segmentation of the images.

  10. High sensitivity detectors for measurement of diffusion, emanation and low activity of radon

    SciTech Connect

    Mamedov, Fadahat; Štekl, Ivan; Smolek, Karel; Čermák, Pavel

    2013-08-08

    Today's underground experiments require ultra-low background conditions. One of the most important source of background is radon. It is necessary to suppress it and consequently to detect very low radon concentration. In the frame of SuperNEMO collaboration experimental setups for measurement of low radon activity, radon diffusion through shielding foils and radon emanation from construction materials have been constructed in IEAP CTU in Prague and the obtained results are presented. The application of Timepix device in radon detection is briefly discussed.

  11. Brain activation and connectivity of social cognition using diffuse optical imaging

    NASA Astrophysics Data System (ADS)

    Zhu, Banghe; Godavarty, Anuradha

    2009-02-01

    In the current research, diffuse optical imaging (DOI) is used for the first time towards studies related to sociocommunication impairments, which is a characteristic feature of autism. DOI studies were performed on normal adult volunteers to determine the differences in the brain activation (cognitive regions) in terms of the changes in the cerebral blood oxygenation levels in response to joint and non-joint attention based stimulus (i.e. socio-communicative paradigms shown as video clips). Functional connectivity models are employed to assess the extent of synchronization between the left and right pre-frontal regions of the brain in response to the above stimuli.

  12. An electrically-activated dynamic tissue-equivalent phantom for assessment of diffuse optical imaging systems.

    PubMed

    Hebden, Jeremy C; Brunker, Joanna; Correia, Teresa; Price, Ben D; Gibson, Adam P; Everdell, N L

    2008-01-21

    A novel design of solid dynamic phantom with tissue-like optical properties is presented, which contains variable regions of contrast which are activated electrically. Reversible changes in absorption are produced by localized heating of targets impregnated with thermochromic pigment. A portable, battery-operated prototype has been constructed, and its optical and temporal characteristics have been investigated. The phantom has been developed as a means of assessing the performance of diffuse optical imaging systems, such as those used to monitor haemodynamic changes in the brain and other tissues. Images of the phantom have been reconstructed using data acquired with a continuous wave optical topography system. PMID:18184989

  13. An electrically-activated dynamic tissue-equivalent phantom for assessment of diffuse optical imaging systems

    NASA Astrophysics Data System (ADS)

    Hebden, Jeremy C.; Brunker, Joanna; Correia, Teresa; Price, Ben D.; Gibson, Adam P.; Everdell, N. L.

    2008-01-01

    A novel design of solid dynamic phantom with tissue-like optical properties is presented, which contains variable regions of contrast which are activated electrically. Reversible changes in absorption are produced by localized heating of targets impregnated with thermochromic pigment. A portable, battery-operated prototype has been constructed, and its optical and temporal characteristics have been investigated. The phantom has been developed as a means of assessing the performance of diffuse optical imaging systems, such as those used to monitor haemodynamic changes in the brain and other tissues. Images of the phantom have been reconstructed using data acquired with a continuous wave optical topography system.

  14. Periodic patterning of the Drosophila eye is stabilized by the diffusible activator Scabrous

    PubMed Central

    Gavish, Avishai; Shwartz, Arkadi; Weizman, Abraham; Schejter, Eyal; Shilo, Ben-Zion; Barkai, Naama

    2016-01-01

    Generation of periodic patterns is fundamental to the differentiation of multiple tissues during development. How such patterns form robustly is still unclear. The Drosophila eye comprises ∼750 units, whose crystalline order is set during differentiation of the eye imaginal disc: an activation wave sweeping across the disc is coupled to lateral inhibition, sequentially selecting pro-neural cells. Using mathematical modelling, here we show that this template-based lateral inhibition is highly sensitive to spatial variations in biochemical parameters and cell sizes. We reveal the basis of this sensitivity, and suggest that it can be overcome by assuming a short-range diffusible activator. Clonal experiments identify Scabrous, a previously implicated inhibitor, as the predicted activator. Our results reveal the mechanism by which periodic patterning in the fly eye is stabilized against spatial variations, highlighting how the need to maintain robustness shapes the design of patterning circuits. PMID:26876750

  15. Cryogenic performance of slotted brazed Rene 41 honeycomb panels

    NASA Technical Reports Server (NTRS)

    Hepler, A. K.; Swegle, A. R.

    1982-01-01

    Two brazed Rene 41 honeycomb panels that would incorporate a frame element were designed, fabricated and tested. The panels were representative of the lower surface of an advanced space transportation vehicle. The first panel was a two span panel supported by a center frame and on edges parallel to it. The second panel was a two span panel supported by a center frame and on edges parallel to it. The second panel was a three span panel supported on two frames and on edges parallel to the frames. Each panel had its outer skin slotted to reduce the thermal stresses of the panel skins. The first panel was tested under simulated boost conditions that included liquid hydrogen exposure of the frame and inner skin and radiant heat to 478K on the outer skins. The first panel was tested to investigate the effect of thermal stresses in skins and core caused by the panel being restrained by a cold integral frame and to observe the effects of frost formation and possible liquid air development in and around outer skin slots.

  16. Corrosion Behavior of Aluminum-Steel Weld-Brazing Joint

    NASA Astrophysics Data System (ADS)

    Shi, Yu; Li, Jie; Zhang, Gang; Huang, Jiankang; Gu, Yufen

    2016-05-01

    Dissimilar metals of 1060 aluminum and galvanized steel were joined with a lap joint by pulsed double-electrode gas metal arc weld brazing with aluminum-magnesium and aluminum-silicon filler metals. The corrosion behavior of the weld joints was investigated with immersion corrosion and electrochemical corrosion tests, and the corrosion morphology of the joints was analyzed with scanning electron microscopy (SEM). Galvanic corrosion was found to occur when the samples were immersed in corrosive media, and the corrosion rate of joints was increased with increased heat input of the workpiece. Comparison of the corrosion properties of weld joints with different filler wires indicated that the corrosion rate of weld joints with aluminum-silicon filler wire was larger than that of weld joints with aluminum-magnesium filler wire. Results also showed that the zinc-rich zone of weld joints was prone to corrosion. The corrosion behavior of zinc-rich zone was analyzed with SEM equipped with an energy-dispersive x-ray spectroscopy analysis system based on the test results.

  17. ``Long-life`` aluminium brazing alloys for automotive radiators -- a ten-year retrospective

    SciTech Connect

    Scott, A.C.; Woods, R.A.

    1998-12-31

    A class of corrosion-resistant brazing sheet materials, generally referred to as ``long-life alloys,`` has been in widespread use in brazed aluminum automobile radiators for over ten years. K319 tube material was initially introduced in 1986 to address the problem of road-salt-induced, outside-in corrosion of tubes in vacuum-brazed aluminum radiators, The development history, metallurgy, and field performance of long-life radiator brazing sheet are reviewed. This material utilizes the familiar sacrificial layer concept to improve corrosion resistance; however, it is unusual in that the layer is not introduced by conventional cladding means during sheet manufacture, but rather develops in situ by metallurgical transformations which occur during the brazing cycle. The sacrificial layer, about 25 mV anodic to the core alloy, increases by an order of magnitude the time-to-perforation of radiator tube sheet tested in cyclic acidified salt spray (SWAAT), which mimics the corrosion morphology observed in the field. Radiators examined after ten years of field service show excellent corrosion resistance, as predicted by SWAAT.

  18. Development of rapidly quenched brazing foils to join tungsten alloys with ferritic steel

    NASA Astrophysics Data System (ADS)

    Kalin, B. A.; Fedotov, V. T.; Sevrjukov, O. N.; Moeslang, A.; Rohde, M.

    2004-08-01

    Results on rapidly solidified filler metals for tungsten brazing are presented. A rapidly quenched foil-type filler metal based on Ni bal-15Cr-4Mo-4Fe-(0.5-1.0)V-7.5Si-1.5B was developed to braze tungsten to ferritic/martensitic Crl3Mo2NbVB steel (FS) for helium gas cooled divertors and plasma facing components. Polycrystalline W-2CeO 2 and monocrystalline pure tungsten were brazed to the steel under vacuum at 1150 °C, using a 0.5 mm thick foil spacer made of a 50Fe-50Ni alloy. As a result of thermocycling tests (100 cycles between 700 °C/20 min and air-water cooling/3-5 min) on brazed joints, tungsten powder metallurgically processed W-2CeO 2 failed due to residual stresses, whereas the brazed joint with zone-melted monocrystalline tungsten withstood the thermocycling tests.

  19. Microwave induced plasma (MIP) brazing of silicon nitride to stainless steel

    SciTech Connect

    Samandi, M.; Bate, M.; Donnan, R.; Miyake, S.

    1996-12-31

    In an attempt to accelerate the process of joining of metals to ceramics, a new rapid brazing technology has been developed. In this process, referred to as Microwave Induced Plasma (MIP) brazing, a microwave plasma is used to rapidly heat the ceramic and metal to the melting temperature of the reactive braze material. The heating rate obtained by MIP could be many times faster than those achieved by conventional resistive heating in a tube furnace. The fast heating rate has no detrimental effect on the joint quality and in fact results in the formation of a thick interfacial film suggesting significant interdiffusion between the braze and ceramic, possibly stimulated by the microwave radiation. In this paper the experimental arrangement of the MIP system is described. The unique capability of the MIP heating is demonstrated by successful joining of hot pressed nitride to stainless steel using reactive metal brazing. The results of microstructural characterization of the joints carried out by SEM and EDS will also be presented.

  20. Brazing of Stainless Steels to Yttria Stabilized Zirconia (YSZ) for Solid Oxide Fuel Cells

    NASA Technical Reports Server (NTRS)

    Shpargel, Tarah P.; Needham, Robert J.; Singh, M.; Kung, Steven C.

    2005-01-01

    Recently, there has been a great deal of interest in research, development, and commercialization of solid oxide fuel cells. Joining and sealing are critical issues that will need to be addressed before SOFC's can truly perform as expected. Ceramics and metals can be difficult to join together, especially when the joint must withstand up to 900 C operating temperature of the SOFC's. The goal of the present study is to find the most suitable braze material for joining of yttria stabilized zirconia (YSZ) to stainless steels. A number of commercially available braze materials TiCuSil, TiCuNi, Copper-ABA, Gold-ABA, and Gold-ABA-V have been evaluated. The oxidation behavior of the braze materials and steel substrates in air was also examined through thermogravimetric analysis. The microstructure and composition of the brazed regions have been examined by optical and scanning electron microscopy and EDS analysis. Effect of braze composition and processing conditions on the interfacial microstructure and composition of the joint regions will be presented.

  1. Hydrogen activation, diffusion, and clustering on CeO₂(111): a DFT+U study.

    PubMed

    Fernández-Torre, Delia; Carrasco, Javier; Ganduglia-Pirovano, M Verónica; Pérez, Rubén

    2014-07-01

    We present a comprehensive density functional theory+U study of the mechanisms underlying the dissociation of molecular hydrogen, and diffusion and clustering of the resulting atomic species on the CeO2(111) surface. Contrary to a widely held view based solely on a previous theoretical prediction, our results show conclusively that H2 dissociation is an activated process with a large energy barrier ~1.0 eV that is not significantly affected by coverage or the presence of surface oxygen vacancies. The reaction proceeds through a local energy minimum--where the molecule is located close to one of the surface oxygen atoms and the H-H bond has been substantially weaken by the interaction with the substrate--, and a transition state where one H atom is attached to a surface O atom and the other H atom sits on-top of a Ce(4+) ion. In addition, we have explored how several factors, including H coverage, the location of Ce(3+) ions as well as the U value, may affect the chemisorption energy and the relative stability of isolated OH groups versus pair and trimer structures. The trimer stability at low H coverages and the larger upward relaxation of the surface O atoms within the OH groups are consistent with the assignment of the frequent experimental observation by non-contact atomic force and scanning tunneling microscopies of bright protrusions on three neighboring surface O atoms to a triple OH group. The diffusion path of isolated H atoms on the surface goes through the adsorption on-top of an oxygen in the third atomic layer with a large energy barrier of ~1.8 eV. Overall, the large energy barriers for both, molecular dissociation and atomic diffusion, are consistent with the high activity and selectivity found recently in the partial hydrogenation of acetylene catalyzed by ceria at high H2/C2H2 ratios. PMID:25005299

  2. Modeling of moisture diffusivity, activation energy and energy consumption in fluidized bed drying of rough rice

    NASA Astrophysics Data System (ADS)

    Khanali, Majid; Banisharif, Alireza; Rafiee, Shahin

    2016-01-01

    The present work was an attempt to assess the effective moisture diffusivity, activation energy, and energy consumption of rough rice in a batch fluidized bed dryer. Drying experiments were conducted at drying air temperatures of 50, 60, and 70 °C, superficial fluidization velocities of 2.3, 2.5, and 2.8 m/s, and solids holdup of 1.32 kg. Drying kinetics showed that the whole fluidized bed drying of rough rice occurred in the falling rate period. The effective moisture diffusivity was described by an Arrhenius equation. The evaluated effective moisture diffusivity increased with drying air temperature and superficial fluidization velocity and was found to vary from 4.78 × 10-11 to 1.364 × 10-10 m2/s with R2 higher than 0.9643. The activation energy and the pre-exponential factor of Arrhenius equation were found to be in the range of 36.59-44.31 kJ/mol and 4.71 × 10-5-7.15 × 10-4 m2/s, respectively. Both maximum values of the specific energy consumption of 74.73 MJ/kg and the total energy need of 12.43 MJ were obtained at 60 °C drying air temperature and 2.8 m/s superficial fluidization velocity. Both minimum values of the specific energy consumption of 29.98 MJ/kg and the total energy need of 4.85 MJ were obtained under drying air temperature of 70 °C and superficial fluidization velocity of 2.3 m/s.

  3. Evaluation of diffusion and dilution methods to determine the antibacterial activity of plant extracts.

    PubMed

    Klancnik, Anja; Piskernik, Sasa; Jersek, Barbara; Mozina, Sonja Smole

    2010-05-01

    The aim of this study was to evaluate diffusion and dilution methods for determining the antibacterial activity of plant extracts and their mixtures. Several methods for measurement of the minimal inhibitory concentration (MIC) of a plant extract are available, but there is no standard procedure as there is for antibiotics. We tested different plant extracts, their mixtures and phenolic acids on selected gram-positive (Staphylococcus aureus, Bacillus cereus, and Listeria monocytogenes) and gram-negative bacteria (Escherichia coli O157:H7, Salmonella Infantis, Campylobacter jejuni, Campylobacter coli) with the disk diffusion, agar dilution, broth microdilution and macrodilution methods. The disk diffusion method was appropriate only as a preliminary screening test prior to quantitative MIC determination with dilution methods. A comparison of the results for MIC obtained by agar dilution and broth microdilution was possible only for gram-positive bacteria, and indicated the latter as the most accurate way of assessing the antimicrobial effect. The microdilution method with TTC (2,3,5-triphenyl tetrazolium chloride) or INT (2-p-iodophenyl-3-p-nitrophenyl-5-phenyl tetrazolium chloride) to indicate the viability of aerobic bacteria was found to be the best alternative approach, while only ATP determination was appropriate for microaerophilic Campylobacter spp. Using survival curves the kinetics of bacterial inactivation on plant extract exposure was followed for 24h and in this way the MIC values determined by the microdilution method were confirmed as the concentrations of extracts that inhibited bacterial growth. We suggest evaluation of the antibacterial activity of plant extracts using the broth microdilution method as a fast screening method for MIC determination and the macrodilution method at selected MIC values to confirm bacterial inactivation. Campylobacter spp. showed a similar sensitivity to plant extracts as the tested gram-positive bacteria, but S

  4. THE FERMI BUBBLES: SUPERSONIC ACTIVE GALACTIC NUCLEUS JETS WITH ANISOTROPIC COSMIC-RAY DIFFUSION

    SciTech Connect

    Yang, H.-Y. K.; Ruszkowski, M.; Ricker, P. M.; Zweibel, E.; Lee, D.

    2012-12-20

    The Fermi Gamma-Ray Space Telescope reveals two large bubbles in the Galaxy, which extend nearly symmetrically {approx}50 Degree-Sign above and below the Galactic center. Using three-dimensional (3D) magnetohydrodynamic simulations that self-consistently include the dynamical interaction between cosmic rays (CRs) and thermal gas and anisotropic CR diffusion along the magnetic field lines, we show that the key characteristics of the observed gamma-ray bubbles and the spatially correlated X-ray features in the ROSAT 1.5 keV map can be successfully reproduced by recent jet activity from the central active galactic nucleus. We find that after taking into account the projection of the 3D bubbles onto the sky the physical heights of the bubbles can be much smaller than previously thought, greatly reducing the formation time of the bubbles to about a Myr. This relatively small bubble age is needed to reconcile the simulations with the upper limit of bubble ages estimated from the cooling time of high-energy electrons. No additional physical mechanisms are required to suppress large-scale hydrodynamic instabilities because the evolution time is too short for them to develop. The simulated CR bubbles are edge-brightened, which is consistent with the observed projected flat surface brightness distribution. Furthermore, we demonstrate that the sharp edges of the observed bubbles can be due to anisotropic CR diffusion along magnetic field lines that drape around the bubbles during their supersonic expansion, with suppressed perpendicular diffusion across the bubble surface. Possible causes of the slight bends of the Fermi bubbles to the west are also discussed.

  5. Critical Issues for Producing UHTC-Brazed Joints: Wetting and Reactivity

    NASA Astrophysics Data System (ADS)

    Passerone, A.; Muolo, M. L.; Valenza, F.

    2016-03-01

    A brief survey is presented of the most important interaction phenomena occurring at the solid-liquid interfaces in metal-ceramic systems at high temperatures, with special attention to the most recent developments concerning wetting and joining transition metals diborides. These phenomena are described and discussed from both the experimental and theoretical points of view in relation to joining ceramic and metal-ceramic systems by means of processes in the presence of a liquid phase (brazing, TLPB etc.). It is shown that wetting and the formation of interfacial dissolution regions are the results of the competition between different phenomena: dissolution of the ceramic in the liquid phase, reaction and formation of new phases at the solid-liquid interface, and drop spreading along the substrate surface. We emphasize the role of phase diagrams to support both the design of the experiments and the choice of active alloying elements, and to interpret the evolution of the system in relation to temperature and composition. In this respect, the sessile-drop technique has been shown to be helpful in assessing critical points of newly calculated phase diagrams. These studies are essential for the design of joining processes, for the creation of composite materials, and are of a particular relevance when applied to UHTC materials.

  6. 75 FR 52037 - Welding, Cutting and Brazing Standard; Extension of the Office of Management and Budget's (OMB...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-08-24

    ... Order No. 5-2007 (67 FR 31160). Signed at Washington, DC, on August 16, 2010. David Michaels, Assistant... Occupational Safety and Health Administration Welding, Cutting and Brazing Standard; Extension of the Office of... the information collection requirements contained in the Welding, Cutting and Brazing Standard (29...

  7. Diffusion-Weighted MRI Reflects Proliferative Activity in Primary CNS Lymphoma

    PubMed Central

    Meyer, Jonas; Gawlitza, Matthias; Frydrychowicz, Clara; Müller, Wolf; Preuss, Matthias; Bure, Lionel; Quäschling, Ulf; Hoffmann, Karl-Titus; Surov, Alexey

    2016-01-01

    Purpose To investigate if apparent diffusion coefficient (ADC) values within primary central nervous system lymphoma correlate with cellularity and proliferative activity in corresponding histological samples. Materials and Methods Echo-planar diffusion-weighted magnetic resonance images obtained from 21 patients with primary central nervous system lymphoma were reviewed retrospectively. Regions of interest were drawn on ADC maps corresponding to the contrast enhancing parts of the tumors. Biopsies from all 21 patients were histologically analyzed. Nuclei count, total nuclei area and average nuclei area were measured. The proliferation index was estimated as Ki-67 positive nuclei divided by total number of nuclei. Correlations of ADC values and histopathologic parameters were determined statistically. Results Ki-67 staining revealed a statistically significant correlation with ADCmin (r = -0.454, p = 0.038), ADCmean (r = -0.546, p = 0.010) and ADCmax (r = -0.515, p = 0.017). Furthermore, ADCmean correlated in a statistically significant manner with total nucleic area (r = -0.500, p = 0.021). Conclusion Low ADCmin, ADCmean and ADCmax values reflect a high proliferative activity of primary cental nervous system lymphoma. Low ADCmean values—in concordance with several previously published studies—indicate an increased cellularity within the tumor. PMID:27571268

  8. Facilitation of polymer looping and giant polymer diffusivity in crowded solutions of active particles

    NASA Astrophysics Data System (ADS)

    Shin, Jaeoh; Cherstvy, Andrey G.; Kim, Won Kyu; Metzler, Ralf

    2015-11-01

    We study the dynamics of polymer chains in a bath of self-propelled particles (SPP) by extensive Langevin dynamics simulations in a two-dimensional model system. Specifically, we analyse the polymer looping properties versus the SPP activity and investigate how the presence of the active particles alters the chain conformational statistics. We find that SPPs tend to extend flexible polymer chains, while they rather compactify stiffer semiflexible polymers, in agreement with previous results. Here we show that higher activities of SPPs yield a higher effective temperature of the bath and thus facilitate the looping kinetics of a passive polymer chain. We explicitly compute the looping probability and looping time in a wide range of the model parameters. We also analyse the motion of a monomeric tracer particle and the polymer’s centre of mass in the presence of the active particles in terms of the time averaged mean squared displacement, revealing a giant diffusivity enhancement for the polymer chain via SPP pooling. Our results are applicable to rationalising the dimensions and looping kinetics of biopolymers at constantly fluctuating and often actively driven conditions inside biological cells or in suspensions of active colloidal particles or bacteria cells.

  9. Identification of prefrontal cortex (BA10) activation while performing Stroop test using diffuse optical tomography

    NASA Astrophysics Data System (ADS)

    Khadka, Sabin; Chityala, Srujan R.; Tian, Fenghua; Liu, Hanli

    2011-03-01

    Stroop test is commonly used as a behavior-testing tool for psychological examinations that are related to attention and cognitive control of the human brain. Studies have shown activations in Broadmann area 10 (BA10) of prefrontal cortex (PFC) during attention and cognitive process. The use of diffuse optical tomography (DOT) for human brain mapping is becoming more prevalent. In this study we expect to find neural correlates between the performed cognitive tasks and hemodynamic signals detected by a DOT system. Our initial observation showed activation of oxy-hemoglobin concentration in BA 10, which is consistent with some results seen by positron emission tomography (PET) and functional magnetic resonance imaging (fMRI). Our study demonstrates the possibility of combining DOT with Stroop test to quantitatively investigate cognitive functions of the human brain at the prefrontal cortex.

  10. Numerical Analysis of Residual Stress for Copper Base Brazed Stainless Steel Plate-Fin Structure

    NASA Astrophysics Data System (ADS)

    Xie, Qiaoyun; Ling, Xiang

    2010-07-01

    Copper base stainless steel plate-fin structure has been widely used as a heat exchanger in many fields. The nonlinear thermal reaction on the residual stress in brazing process of the plate-fin structure was studied in this paper. A finite element model (FEM) was proposed to simulate the heat transfer and the sequential residual stress generated in the plate-fin and filler metals based on thermal elastic-plastic theory. By the stress distribution in four paths marked in the structure obtained from FEM results, it is found that the maximum residual tensile stress occurs in the brazed joint next to the plate side and a crack would initiate in this region. Also, the first principle stresses of reference nodes were calculated and the conclusion is consistent with the simulation results. These results would provide some constructive instructions in the practical brazing procedure.

  11. Basic principles of creating a new generation of high- temperature brazing filler alloys

    NASA Astrophysics Data System (ADS)

    Kalin, B. A.; Suchkov, A. N.

    2016-04-01

    The development of new materials is based on the formation of a structural-phase state providing the desired properties by selecting the base and the complex of alloying elements. The development of amorphous filler alloys for a high-temperature brazing has its own features that are due to the limited life cycle and the production method of brazing filler alloys. The work presents a cycle of analytical and experimental materials science investigations including justification of the composition of a new amorphous filler alloy for brazing the products from zirconium alloys at the temperature of no more than 800 °C and at the unbrazing temperature of permanent joints of more than 1200 °C. The experimental alloys have been used for manufacture of amorphous ribbons by rapid quenching, of which the certification has been made by X-ray investigations and a differential-thermal analysis. These ribbons were used to obtain permanent joints from the spacer grid cells (made from the alloy Zr-1% Nb) of fuel assemblies of the thermal nuclear reactor VVER-440. The brazed samples in the form of a pair of cells have been exposed to corrosion tests in autoclaves in superheated water at a temperature of 350 °C, a pressure of 160 MPa and duration of up to 6,000 h. They have been also exposed to destructive tests using a tensile machine. The experimental results obtained have made it possible to propose and patent a brazing filler alloy of the following composition: Zr-5.5Fe-(2.5-3.5)Be-1Nb-(5-8)Cu-2Sn-0.4Cr-(0.5-1.0)Ge. Its melting point is 780 °C and the recommended brazing temperature is 800°C.

  12. Theory of simple biochemical ``shape recognition'' via diffusion from activator coated nanoshapes

    NASA Astrophysics Data System (ADS)

    Daniels, D. R.

    2008-09-01

    Inspired by recent experiments, we model the shape sensitivity, via a typical threshold initiation response, of an underlying complex biochemical reaction network to activator coated nanoshapes. Our theory re-emphasizes that shape effects can be vitally important for the onset of functional behavior in nanopatches and nanoparticles. For certain critical or particular shapes, activator coated nanoshapes do not evoke a threshold response in a complex biochemical network setting, while for different critical or specific shapes, the threshold response is rapidly achieved. The model thus provides a general theoretical understanding for how activator coated nanoshapes can enable a chemical system to perform simple "shape recognition," with an associated "all or nothing" response. The novel and interesting cases of the chemical response due to a nanoshape that shrinks with time is additionally considered, as well as activator coated nanospheres. Possible important applications of this work include the initiation of blood clotting by nanoshapes, nanoshape effects in nanocatalysis, physiological toxicity to nanoparticles, as well as nanoshapes in nanomedicine, drug delivery, and T cell immunological response. The aim of the theory presented here is that it inspires further experimentation on simple biochemical shape recognition via diffusion from activator coated nanoshapes.

  13. Evaluation of Muscle Activities in Human Forearms under Exercises by Diffuse Optical Tomography

    NASA Astrophysics Data System (ADS)

    Tanikawa, Yukari; Gao, Feng; Miyakawa, Michio; Kiryu, Toru; Kizuka, Tomohiro; Endo, Yasuomi; Okawa, Shinpei; Yamada, Yukio

    During the forearm exercise, it is generally understood that the inner muscles work for the task, and the outer muscles work to fix the joints for the efficient work of the inner muscles. For evaluation of the exercise, quantitative measurement of inner muscle activities is necessary. Electromyograph (EMG) and oxygen monitoring using continuous-wave near-infrared spectroscopy (CW-NIRS) have been used for the evaluation because both of them are the modalities of safe, portable and noninvasive measurements of muscle activities. However, these modalities can show the qualitative changes in the muscle activities in the vicinity of the skin surface. Time-resolved diffuse optical tomography (TR-DOT) can quantitatively provide tomographic images of the changes in the oxygenation state of the whole muscles. In vivo experiments of TR-DOT were performed for human forearms under handgrip exercises, and DOT images of the changes in the oxygenation state of the forearms were reconstructed using the algorithm based on the modified generalized pulsed spectrum technique. The DOT images are compared with the MR-images, and it is shown that the activities of the inner muscles of the forearms were active during the handgrip excises.

  14. Protein dynamics from structural ensembles: Diffusive and activated contributions in a linear mode description

    NASA Astrophysics Data System (ADS)

    Copperman, Jeremy; Guenza, Marina

    2015-03-01

    We have developed a coarse-grained linear Langevin equation for protein dynamics, which describes proteins as semiflexible objects collapsed into the free energy well representing the folded state of the protein. Fundamental to this approach is the inclusion of internal dissipation, absent in any rigid-body hydrodynamical modeling scheme. The normal mode analytical solution naturally separates into global modes describing the anisotropic tumbling of the object, and internal modes which contain both diffusive and activated glass-like contributions. We show how cooperativity in the dynamical modes is related to the energy barriers to mode diffusion. While molecular dynamic simulations generate the most accurate structural ensembles, we show how sets of NMR conformers can be used to generate the structural ensemble needed as input to the theory, making the approach truly predictive in nature. Results are in good agreement when compared with both nuclear magnetic resonance relaxation, and time correlation functions calculated from molecular dynamic simulations. This material is based upon work partially supported by the National Science Foundation under Grant CHE-1362500.

  15. Theory of diffusion of active particles that move at constant speed in two dimensions.

    PubMed

    Sevilla, Francisco J; Gómez Nava, Luis A

    2014-08-01

    Starting from a Langevin description of active particles that move with constant speed in infinite two-dimensional space and its corresponding Fokker-Planck equation, we develop a systematic method that allows us to obtain the coarse-grained probability density of finding a particle at a given location and at a given time in arbitrary short-time regimes. By going beyond the diffusive limit, we derive a generalization of the telegrapher equation. Such generalization preserves the hyperbolic structure of the equation and incorporates memory effects in the diffusive term. While no difference is observed for the mean-square displacement computed from the two-dimensional telegrapher equation and from our generalization, the kurtosis results in a sensible parameter that discriminates between both approximations. We carry out a comparative analysis in Fourier space that sheds light on why the standard telegrapher equation is not an appropriate model to describe the propagation of particles with constant speed in dispersive media. PMID:25215711

  16. Tracking the activity-dependent diffusion of synaptic proteins using restricted photoconversion of Dendra2

    PubMed Central

    Cassé, Frédéric; Martin, Stéphane

    2015-01-01

    Spines are small protrusions on dendritic membranes receiving inputs from axonal termini. They consist in a head connected to the dendritic shaft by a narrow neck and contain multiple synaptic proteins that interact in a coordinated manner to allow for synaptic communication. This process involves many proteins that are moving in and out spines. However, comparing this synaptodendritic movement in basal and stimulated conditions is very challenging. Here we describe an elegant method to measure the activity-dependent diffusion of synaptic proteins using Dendra2 photoconversion. We provide a successful method to obtain Dendra2-photoconverted images and a step-by-step procedure to analyze the data. This live-imaging approach may also apply to investigate the diffusion of proteins across other subcellular compartments or organelles including but not restricted to, nucleus, nucleolus, ER, or vesicular structures. Once the imaging system is set up, data can be acquired in 1–30 min and analyzed in approximately 1–4 h. PMID:26441538

  17. Modeling meiotic chromosome pairing: nuclear envelope attachment, telomere-led active random motion, and anomalous diffusion

    NASA Astrophysics Data System (ADS)

    Marshall, Wallace F.; Fung, Jennifer C.

    2016-04-01

    The recognition and pairing of homologous chromosomes during meiosis is a complex physical and molecular process involving a combination of polymer dynamics and molecular recognition events. Two highly conserved features of meiotic chromosome behavior are the attachment of telomeres to the nuclear envelope and the active random motion of telomeres driven by their interaction with cytoskeletal motor proteins. Both of these features have been proposed to facilitate the process of homolog pairing, but exactly what role these features play in meiosis remains poorly understood. Here we investigate the roles of active motion and nuclear envelope tethering using a Brownian dynamics simulation in which meiotic chromosomes are represented by a Rouse polymer model subjected to tethering and active forces at the telomeres. We find that tethering telomeres to the nuclear envelope slows down pairing relative to the rates achieved by unattached chromosomes, but that randomly directed active forces applied to the telomeres speed up pairing dramatically in a manner that depends on the statistical properties of the telomere force fluctuations. The increased rate of initial pairing cannot be explained by stretching out of the chromosome conformation but instead seems to correlate with anomalous diffusion of sub-telomeric regions.

  18. BRAZING OF POROUS ALUMINA TO MONOLITHIC ALUMINA WITH Ag-CuO and Ag-V2O5 ALLOYS

    SciTech Connect

    Lamb, M. C.; Camardello, Sam J.; Meier, Alan; Weil, K. Scott; Hardy, John S.

    2005-01-31

    The feasibility of joining porous alumina (Al{sub 2}O{sub 3}) bodies to monolithic Al{sub 2}O{sub 3} using Ag-CuO and Ag-V{sub 2}O{sub 5} alloys via reactive air brazing (RAB) was examined for a nanoporous filter application. Brazing for these systems is complicated by the conflicting requirements of satisfactory wetting to fill the braze gap, while minimizing the infiltration of the porous body. By varying the firing time, temperature, and initial powder size, porous bodies with a range of pore microstructures were fabricated. The wettability was evaluated via sessile drop testing on monolithic substrates and porous body infiltration. Porous Al{sub 2}O{sub 3}/monolithic Al{sub 2}O{sub 3} brazed samples were fabricated, and the microstructures were evaluated. Both systems exhibited satisfactory wetting for brazing, but two unique types of brazing behavior were observed. In the Ag-CuO system, the braze alloy infiltrated a short distance into the porous body. For these systems, the microstructures indicated satisfactory filling of the brazed gap and a sound joint regardless of the processing conditions. The Ag-V{sub 2}O{sub 5} alloys brazed joints exhibited a strong dependence on the amount of V{sub 2}O{sub 5} available. For Ag-V{sub 2}O{sub 5} alloys with large V{sub 2}O{sub 5} additions, the braze alloy aggressively infiltrated the porous body and significantly depleted the Ag from the braze region resulting in poor bonding and large gaps within the joint. With small additions of V{sub 2}O{sub 5}, the Ag infiltrated the porous body until the V{sub 2}O{sub 5} was exhausted and the Ag remaining at the braze interlayer bonded with the Al{sub 2}O{sub 3}. Based on these results, the Ag-CuO alloys have the best potential for brazing porous Al{sub 2}O{sub 3} to monolithic Al{sub 2}O{sub 3}.

  19. Mechanical Property and Corrosion Resistance Evaluations of Ti-6Al-7Nb Alloy Brazed with Bulk Metallic Glasses

    SciTech Connect

    Miura, E.; Kato, H.; Ogata, Toshiaki; Nishiyama, Nobuyuki; Specht, Eliot D; Shiraishi, Takanobu; Inoue, A.; Hisatsune, K.

    2007-01-01

    Exploitation of metallic glass as new brazing filler for Ti-based biomedical alloy was attempted. Ti-6Al-7Nb was used as a brazed material, and candidates of bulk metallic glass brazing filler were Cu60Hf25Ti15, Mg65Cu25Gd10, Zr55Cu30Al10Ni5 and Pd40Cu30P20Ni10. Convergence infrared-ray brazing was conducted for brazing Ti-6Al-7Nb/metallic glass in Ar atmosphere. After brazing, hardness measurement, X-ray tomography, cross-sectional observation, artificial saliva immersion test and tensile test were performed to evaluate brazability, mechanical property and corrosion resistance of the obtained brazing joints. The results of brazing using these metallic glass fillers show that all the metallic glasses were brazable to Ti-6Al-7Nb except for Mg65Cu25Gd10. Mg65Cu25Gd10, Cu60Hf25Ti15 and their joints collapsed rapidly during immersion test. Zr55Cu30Al10Ni5 joint was the best in terms of degradation resistance; however, tensile strength was inferior to the conventional one. Pd40Cu30Ni10P20 filler and Zr55Cu30Al10Ni5 filler and their joints did not show any collapse or tarnish during the immersion test. Pd40Cu30Ni10P20 joint showed the excellent properties in terms of both corrosion resistance and tensile strength, which were superior to a joint brazed using Ti-15Cu-25Ni conventional filler. X-ray tomograph indicates that fracture tends to occur in the vicinity of the brazing interface after tensile test. The brazed metallic glass fillers were fully crystallized, excluding Pd40Cu30Ni10P20 filler. Pd40Cu30Ni10P20 brazed filler contained mapleleaf like primary dendrite, peritectoid and a few microns interfacial reaction layer in glassy matrix. The results indicated that Pd40Cu30Ni10P20 is promising brazing filler for dental or biomaterial devices.

  20. Health Promotion Efforts as Predictors of Physical Activity in Schools: An Application of the Diffusion of Innovations Model

    ERIC Educational Resources Information Center

    Glowacki, Elizabeth M.; Centeio, Erin E.; Van Dongen, Daniel J.; Carson, Russell L.; Castelli, Darla M.

    2016-01-01

    Background: Implementing a comprehensive school physical activity program (CSPAP) effectively addresses public health issues by providing opportunities for physical activity (PA). Grounded in the Diffusion of Innovations model, the purpose of this study was to identify how health promotion efforts facilitate opportunities for PA. Methods: Physical…

  1. Phosphorous transient enhanced diffusion suppression and activation enhancement with cluster carbon co-implantation

    SciTech Connect

    Nakashima, Yoshiki; Hamamoto, Nariaki; Nagayama, Tsutomu; Koga, Yuji; Umisedo, Sei; Kawamura, Yasunori; Hashimoto, Masahiro; Onoda, Hiroshi

    2012-11-06

    Carbon co-implantation is well known as an effective method for suppressing boron/phosphorous transient enhanced diffusion (TED). Germanium pre-amorphization implantation (PAI) is usually applied prior to carbon co-implantation for suppressing channeling tail of dopants. In this study, cluster carbon was applied instead of the combination of germanium PAI and monomer carbon co-implantation prior to phosphorous implantation. Dependence of phosphorous activation and TED on amorphous layer thickness, carbon dose, carbon distribution and substrate temperature have been investigated. Cluster carbon implantation enables thick amorphous layer formation and TED suppression at the same time and low temperature implantation enhances the ability of amorphous layer formation so that shallow junction and low Rs can be achieved without Ge implantation.

  2. An agar diffusion study comparing the antimicrobial activity of Nanoseal with some other endodontic sealers.

    PubMed

    Aal-Saraj, Ali Burak; Ariffin, Zaihan; Masudi, Sam'an Malik

    2012-08-01

    The aim of this study was to evaluate the antimicrobial activity of a new experimental nano-hydroxyapatite epoxy resin-based sealer (Nanoseal) with several other commercially available sealers; AH26, Tubliseal, Sealapex and Roekoseal against Enterococcus faecalis, Pseudomonas aeruginosa, Streptococcus mutans, Streptococcus sobrinus and Escherichia coli for up to 7 days. Agar diffusion was used in this study. Fifty Muller-Hinton agar plates were prepared and divided into five experimental groups (n = 10), for each micro-organism. Another 10 agar plates were used as positive and negative controls. Endodontic sealers were tested against each micro-organism. Inhibition zones produced were recorded. The results of this study showed that all test materials exhibited inhibition zones towards the tested micro-organisms for 7 days except for Roekoseal, which showed no inhibition zones. Nanoseal and AH26 exhibited similar zones of inhibition. Significant difference was found between Nanoseal and the other tested sealers (P < 0.001). PMID:22827817

  3. Real space mapping of ionic diffusion and electrochemical activity in energy storage and conversion materials

    DOEpatents

    Kalinin, Sergei V; Balke, Nina; Kumar, Amit; Dudney, Nancy J; Jesse, Stephen

    2014-05-06

    A method and system for probing mobile ion diffusivity and electrochemical reactivity on a nanometer length scale of a free electrochemically active surface includes a control module that biases the surface of the material. An electrical excitation signal is applied to the material and induces the movement of mobile ions. An SPM probe in contact with the surface of the material detects the displacement of mobile ions at the surface of the material. A detector measures an electromechanical strain response at the surface of the material based on the movement and reactions of the mobile ions. The use of an SPM tip to detect local deformations allows highly reproducible measurements in an ambient environment without visible changes in surface structure. The measurements illustrate effective spatial resolution comparable with defect spacing and well below characteristic grain sizes of the material.

  4. Outflowing Diffuse Gas in the Active Galactic Nucleus of NGC 1068

    NASA Astrophysics Data System (ADS)

    Geballe, T. R.; Mason, R. E.; Oka, T.

    2015-10-01

    Spectra of the archetypal Type II Seyfert galaxy NGC 1068 in a narrow wavelength interval near 3.7 μm have revealed a weak absorption feature due to two lines of the molecular ion {{{H}}}3+. The observed wavelength of the feature corresponds to a velocity of -70 km s-1 relative to the systemic velocity of the galaxy, implying an outward flow from the nucleus along the line of sight. The absorption by H{}3+ along with the previously known broad hydrocarbon absorption at 3.4μm are probably formed in diffuse gas that is in close proximity to the continuum source, i.e., within a few tens of parsecs of the central engine. Based on that conclusion and the measured H{}3+ absorption velocity and with the assumption of a spherically symmetric wind we estimate a rate of mass outflow from the active galactic nucleus of ˜1 M⊙ yr-1.

  5. Microstructural Development and Mechanical Properties for Reactive Air Brazing of ZTA to Ni Alloys using Ag-CuO Braze Alloys

    SciTech Connect

    Prevost, Erica; DeMarco, A.Joseph; MacMichael, Beth; Joshi, Vineet V.; Meier, Alan; Hoffman, John W.; Walker, William J.

    2014-12-01

    Reactive air brazing (RAB) is a potential joining technique to join metal alloys to ceramics for a variety of applications. In the current study, nickel (Ni) alloys were heat treated to form an oxide layer prior to RAB joining to zirconia toughened alumina (ZTA). The Ni alloys evaluated were Nicrofer 6025 HT, Inconel 600, Inconel 693, Haynes 214 and Inconel 601. The ZTA studied had compositions of 0 to 15 wt% zirconia and 0 to 14 wt% glass. Four point-bend tests were performed to evaluate the joint strength of ZTA/ZTA and ZTA/nickel alloys brazed with Ag-2wt% CuO braze alloys. It was determined that the joint strength is not a function of the ZTA composition, but that the strength is a strong function of the chemistry and microstructure of the oxide layer formed on the nickel alloy. It was determined that an increase in the aluminum content of the Ni alloy resulted in an increase of the thickness of alumina in the oxide layer and was directly proportional to the bond strength with the exception of Inconel 601 which exhibited relatively high joint strengths even though it had a relatively low aluminum content.

  6. Use of blood-pool imaging in evaluation of diffuse activity patterns in technetium-99m pyrophosphate myocardial scintigraphy.

    PubMed

    Cowley, M J; Mantle, J A; Rogers, W J; Russell, R O; Rackley, C E; Logic, J R

    1979-06-01

    It has been suggested that diffuse Tc-99m pyrophosphate precordial activity may be due to persistent blood-pool activity in routine delayed views during myocardial imaging. To answer this question, we reviewed myocardial scintigrams recorded 60--90 min following the injection of 12--15 mCi of Tc-99m pyrophosphate for the presence of diffuse precordial activity, and compared these with early images of the blood pool in 265 patients. Diffuse activity in the delayed images was identified in 48 patients: in 20 with acute myocardial infarction and in 28 with no evidence of it. Comparison of these routine delayed images with early views of the blood pool revealed two types of patterns. In patients with acute infarction, 95% had delayed images that were distinguishable from blood pool either because the activity was smaller than the early blood pool, or by the presence of localized activity superimposed on diffuse activity identical to blood pool. In those without infarction, 93% had activity distribution in routine delayed views matching that in the early blood-pool images. The usefulness of the diffuse TcPPi precordial activity in myocardial infarction is improved when early blood-pool imaging is used to exclude persistence of blood-pool activity as its cause. Moreover, it does not require additional amounts of radioactivity nor complex computer processing, a feature that may be of value in the community hospital using the technique to "rule out" infarction 24--72 hr after onset of suggestive symptoms. PMID:231644

  7. Boron activation and diffusion in silicon and strained silicon-on-insulator by rapid thermal and flash lamp annealings

    NASA Astrophysics Data System (ADS)

    Lanzerath, F.; Buca, D.; Trinkaus, H.; Goryll, M.; Mantl, S.; Knoch, J.; Breuer, U.; Skorupa, W.; Ghyselen, B.

    2008-08-01

    We present experimental results on the activation and diffusion behaviors of boron in silicon-on-insulator and strained silicon-on-insulator using standard rapid thermal processing treatments as well as flash lamp annealing. After boron implantation at different doses and at a low energy of 1 keV, samples were annealed to activate the dopants, and secondary ion mass spectrometry and Hall measurements were carried out to determine boron diffusion and the amount of activated dopants, respectively. In contrast to rapid thermal annealing, flash lamp annealing enables the activation without significant diffusion of dopants. In addition, we investigated the effect of coating the samples with antireflection layers to increase the absorbed energy during flash annealing. As a result, the activation was increased significantly to values comparable with the activation obtained with standard annealing. Furthermore, the relation between the observed boron diffusion and activation as a function of the implantation and annealing parameters is discussed in terms of the kinetics of the defects involved in these processes.

  8. Interfacial diffusion behavior in Ni-BaTiO 3 MLCCs with ultra-thin active layers

    NASA Astrophysics Data System (ADS)

    Gong, Huiling; Wang, Xiaohui; Tian, Zhibin; Zhang, Hui; Li, Longtu

    2014-03-01

    The interfacial structure and diffusion behavior between the dielectric layers (BaTiO3) and internal electrode layers (Ni) in X5R-type multilayer ceramic capacitors (MLCCs, from -55°C to 85°C, at a temperature capacitance coefficient within ±15%) with ultra-thin active layers ( T = 1-3 µm) have been investigated by several microstructural techniques (SEM/TEM/HRTEM) with energy-dispersive x-ray spectroscopy (EDS). In the MLCC samples with different active layer thicknesses (1-3 µm), weak interfacial diffusion was observed between BaTiO3 and Ni. It was also found that the diffusion capability of Ni into the BaTiO3 layer was stronger than that of BaTiO3 to the Ni electrode, which indicated that the diffusion of Ni was the dominant factor for the interfacial diffusion behavior in the ultra-thin layered MLCCs. The mechanism of Ni diffusion is discussed in this study as well.

  9. Thermal Diffusivity of Reduced Activation Ferritic/Martensitic Steel Determined by the Time Domain Photoacoustic Piezoelectric Technique

    NASA Astrophysics Data System (ADS)

    Zhao, Binxing; Wang, Yafei; Gao, Chunming; Sun, Qiming; Wang, Pinghuai

    2015-06-01

    The thermal diffusivity of reduced activation ferritic/martensitic steel (CLF-1), which is recognized as the primary candidate structural material for the test blanket module of the international thermal-nuclear experimental reactor, has been studied by the time-domain (TD) photoacoustic piezoelectric (PAPE) technique. The TD PAPE model based on a simplified thermoelastic theory under square-wave modulated laser excitation is presented, relating the TD PAPE signal to the modulation frequency, thermal diffusivity, and other material parameters. Thermal diffusivities of reference samples such as copper and nickel were measured and analyzed, by which the validity of the technique is verified. The thermal diffusivity of the CLF-1 sample was measured to be , which is at a medium level among the ordinary steel materials ( to and has decent heat-dissipation ability. The results show that the TD PAPE technique can provide a fast and economic way for the investigation of the thermophysical properties of fusion reactor structural materials.

  10. Correlation established between heat transfer and ultrasonic transmission properties of copper braze bonds

    NASA Technical Reports Server (NTRS)

    Dinovi, R. A.

    1967-01-01

    Measuring and correlating the thermal conductivity and ultrasonic transmission of seven hot-brazed-bonded copper plates established a relationship between heat transfer and ultrasonic transmission properties of the bonds. This relationship permits the prediction of heat transfer characteristics from ultrasonic transmission tests.

  11. Ultrasonics used for high-precision nondestructive inspection of brazed joints

    NASA Technical Reports Server (NTRS)

    Peterson, R. M.

    1971-01-01

    Technique detects voids greater than or equal to 0.1016 cm in braze depths of 0.254 cm, detecting voids of smaller dimensions is possible. Internal design ensures control of beam's water path length to within 0.635 cm, this length is critical to system's accuracy.

  12. Method for braze-joining spirally wound tapes to inner walls of heat exchanger tubes

    DOEpatents

    Garrison, Melton E.

    1984-01-01

    The present invention is directed to a method of fabricating heat exchanger tubes in which twisted tapes are utilized for promoting turbulence and heat transfer. The method of the present invention provides for the brazing of the tapes to the inner walls of the tubes for enhancing heat transfer between the fluid within the conduit and a fluid medium outside of the conduit by conduction through the tape. The braze joint of the present invention is coextensive with the tape over the entire length thereof within the conduit. The practice of the present invention is achieved by placing a filler wire of brazing metal along the tape at a location removed from the side walls and then heating the conduit and tape sufficiently to effect the displacement of the filler metal by wicking to the contact point between the tape and the conduit wall to form a braze joint coextensive with the length of the tape within the conduit. This arrangement provides maximum heat transfer and assures that the tape is in contact with the conduit over the entire common length thereof.

  13. Method for braze-joining spirally wound tapes to inner walls of heat exchanger tubes

    DOEpatents

    Garrison, M.E.

    1982-09-03

    The present invention is directed to a method of fabricating heat exchanger tubes in which twisted tapes are utilized for promoting turbulence and heat transfer. The method of the present invention provides for the brazing of the tapes to the inner walls of the tubes for enhancing heat transfer between the fluid within the conduit and a fluid medium outside of the conduit by conduction through the tape. The braze joint of the present invention is coextensive with the tape over the entire length thereof within the conduit. The practice of the present invention is achieved by placing a filler wire of brazing metal along the tape at a location removed from the side walls and then heating the conduit and tape sufficiently to effect the displacement of the filler metal by wicking to the contact point between the tape and the conduit wall to form a braze joint coextensive with the length of the tape within the conduit. This arrangement provides maximum heat transfer and assures that the tape is in contact with the conduit over the entire common length thereof.

  14. Braze Development of Graphite Fiber for Use in Phase Change Material Heat Sinks

    NASA Technical Reports Server (NTRS)

    Quinn, Gregory; Beringer, Woody; Gleason, Brian; Stephan, Ryan

    2011-01-01

    Hamilton Sundstrand (HS), together with NASA Johnson Space Center, developed methods to metallurgically join graphite fiber to aluminum. The goal of the effort was to demonstrate improved thermal conductance, tensile strength and manufacturability compared to existing epoxy bonded techniques. These improvements have the potential to increase the performance and robustness of phase change material heat sinks that use graphite fibers as an interstitial material. Initial work focused on evaluating joining techniques from four suppliers, each consisting of a metallization step followed by brazing or soldering of one inch square blocks of Fibercore graphite fiber material to aluminum end sheets. Results matched the strength and thermal conductance of the epoxy bonded control samples, so two suppliers were down-selected for a second round of braze development. The second round of braze samples had up to a 300% increase in strength and up to a 132% increase in thermal conductance over the bonded samples. However, scalability and repeatability proved to be significant hurdles with the metallization approach. An alternative approach was pursued which used a nickel braze allow to prepare the carbon fibers for joining with aluminum. Initial results on sample blocks indicate that this approach should be repeatable and scalable with good strength and thermal conductance when compared with epoxy bonding.

  15. Nondestructive testing for braze voids in thin panels by use of special coatings

    NASA Technical Reports Server (NTRS)

    Gibson, J. C.

    1972-01-01

    Application of commercial coating to exterior of sandwich panel structures for determining presence of voids in brazed plates is discussed. Procedure for applying coating material and method of conducting nondestructive tests are explained. Illustrations are included to show appearance of voids.

  16. Brazing retort manifold design concept may minimize air contamination and enhance uniform gas flow

    NASA Technical Reports Server (NTRS)

    Ruppe, E. P.

    1966-01-01

    Brazing retort manifold minimizes air contamination, prevents gas entrapment during purging, and provides uniform gas flow into the retort bell. The manifold is easily cleaned and turbulence within the bell is minimized because all manifold construction lies outside the main enclosure.

  17. 49 CFR 178.51 - Specification 4BA welded or brazed steel cylinders.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 49 Transportation 3 2012-10-01 2012-10-01 false Specification 4BA welded or brazed steel cylinders. 178.51 Section 178.51 Transportation Other Regulations Relating to Transportation (Continued) PIPELINE AND HAZARDOUS MATERIALS SAFETY ADMINISTRATION, DEPARTMENT OF TRANSPORTATION (CONTINUED) SPECIFICATIONS FOR PACKAGINGS Specifications...

  18. 49 CFR 178.55 - Specification 4B240ET welded or brazed cylinders.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 49 Transportation 3 2013-10-01 2013-10-01 false Specification 4B240ET welded or brazed cylinders. 178.55 Section 178.55 Transportation Other Regulations Relating to Transportation (Continued) PIPELINE AND HAZARDOUS MATERIALS SAFETY ADMINISTRATION, DEPARTMENT OF TRANSPORTATION (CONTINUED) SPECIFICATIONS FOR PACKAGINGS Specifications for...

  19. Training Materials Sourcebook. Welding, Brazing, and Flame-Cutting. Voc./Tec. Resources Series Number 2.

    ERIC Educational Resources Information Center

    Canadian Commission of Employment and Immigration, Ottawa (Ontario).

    Second in a resource series (see note), this annotated bibliography provides detailed information on training curriculum and instructional materials for welding, brazing, and flame-cutting. The materials are divided into thirty-fie sections by topic and type. Specific topic areas include gas and arc welding; arc welding; oxyacetylene welding and…

  20. Skylab experiment performance evaluation manual. Appendix G: Experiment M552 exothermic brazing (MSFC)

    NASA Technical Reports Server (NTRS)

    Thomas, O. H., Jr.

    1973-01-01

    Analyses for Experiment M552, Exothermic Brazing (MSFC), to be used for evaluating the performance of the Skylab corollary experiments under preflight, inflight, and post-flight conditions are presented. Experiment contingency plan workaround procedure and malfunction analyses are presented in order to assist in making the experiment operationally successful.

  1. Copper-silver-titanium filler metal for direct brazing of structural ceramics

    DOEpatents

    Moorhead, Arthur J.

    1987-01-01

    A method of joining ceramics and metals to themselves and to one another is described using a brazing filler metal consisting essentially of 35 to 50 atomic percent copper, 15 to 50 atomic percent silver and 10 to 45 atomic percent titanium. This method produces strong joints that can withstand high service temperatures and oxidizing environments.

  2. Copper-silver-titanium-tin filler metal for direct brazing of structural ceramics

    DOEpatents

    Moorhead, Arthur J.

    1988-04-05

    A method of joining ceramics and metals to themselves and to one another at about 800.degree. C. is described using a brazing filler metal consisting essentially of 35 to 50 at. % copper, 40 to 50 at. % silver, 1 to 15 at. % titanium, and 2 to 8 at. % tin. This method produces strong joints that can withstand high service temperatures and oxidizing environments.

  3. Micro-nano filler metal foil on vacuum brazing of SiCp/Al composites

    NASA Astrophysics Data System (ADS)

    Wang, Peng; Gao, Zeng; Niu, Jitai

    2016-06-01

    Using micro-nano (Al-5.25Si-26.7Cu)- xTi (wt%, x = 1.0, 1.5, 2.0, 2.5 and 3.0) foils as filler metal, the research obtained high-performance joints of aluminum matrix composites with high SiC particle content (60 vol%, SiCp/Al-MMCs). The effect of brazing process and Ti content on joint properties was investigated, respectively. The experimental results indicate that void free dense interface between SiC particle and metallic brazed seam with C-Al-Si-Ti product was readily obtained, and the joint shear strength enhanced with increasing brazing temperature from 560 to 580 °C or prolonging soaking time from 10 to 90 min. Sound joints with maximum shear strength of 112.5 MPa was achieved at 580 °C for soaking time of 90 min with (Al-5.25Si-26.7Cu)-2Ti filler, where Ti(AlSi)3 intermetallic is in situ strengthening phase dispersed in the joint and fracture occured in the filler metal layer. In this research, the beneficial effect of Ti addition into filler metal on improving wettability between SiC particle and metallic brazed seam was demonstrated, and capable welding parameters were broadened for SiCp/Al-MMCs with high SiC particle content.

  4. High temperature silver-palladium-copper oxide air braze filler metal

    NASA Astrophysics Data System (ADS)

    Darsell, Jens Tommy

    The Ag-CuO system is currently being investigated as the basis for an air braze filler metal alloy to be used in SOFC components. The system is of interest because unlike most braze alloys, it is capable of wetting a variety of ceramic materials while being applied in an air. This thesis work examined modification of Ag-CuO filler metal system by alloying with palladium to increase the use temperature of the resulting air braze alloy. Thermal analysis was performed to track changes in the solidus and liquidus temperatures for these alloys and determine equilibrium phase present as a function of temperature and composition. Sessile drop experiments were performed to investigate the effect of palladium addition on braze wetability. The influence of copper-oxide and palladium contents on brazed joint strength was characterized by a combination of four-point bend testing and fractography. From combined thermal analysis and quenched data it was found that both the liquidus and solidus increase with increasing palladium content, and the silver-rich miscibility gap boundary could be shifted by the addition of palladium. This was employed as a tool to study the effects of two-liquid phase formation on wetting behavior. In addition, a mass loss likely attributable to silver volatilization is observed in the Pd-modified filler metals when heated over ˜1100°C. As volatilization should be avoided, the ternary alloys should be limited to 15mol% Pd. It was found by sessile drop wetting experiments that there is a definitive change in wetting behavior that corresponds directly to the miscibility gap boundary for the Pd-Ag-CuO system. The first order transition tracks with changes in the miscibility gap boundary that can be induced by increasing palladium content. This is the first experimental evidence of critical point wetting behavior reported for a metal-oxide system and further confirms that critical point wetting theory is universal. Four-point bend testing and

  5. Active bio-based food-packaging: Diffusion and release of active substances through and from cellulose nanofiber coating toward food-packaging design.

    PubMed

    Lavoine, Nathalie; Guillard, Valérie; Desloges, Isabelle; Gontard, Nathalie; Bras, Julien

    2016-09-20

    Cellulose nanofibers (CNFs) were recently investigated for the elaboration of new functional food-packaging materials. Their nanoporous network was especially of interest for controlling the release of active species. Qualitative release studies were conducted, but quantification of the diffusion phenomenon observed when the active species are released from and through CNF coating has not yet been studied. Therefore, this work aims to model CNF-coated paper substrates as controlled release system for food-packaging using release data obtained for two model molecules, namely caffeine and chlorhexidine digluconate. The applied mathematical model - derived from Fickian diffusion - was validated for caffeine only. When the active species chemically interacts with the release device, another model is required as a non-predominantly diffusion-controlled release was observed. From caffeine modeling data, a theoretical active food-packaging material was designed. The use of CNFs as barrier coating was proved to be the ideal material configuration that best meets specifications. PMID:27261728

  6. Topographic localization of brain activation in diffuse optical imaging using spherical wavelets

    PubMed Central

    Abdelnour, F; Schmidt, B; Huppert, T J

    2009-01-01

    Diffuse optical imaging is a non-invasive technique that uses near-infrared light to measure changes in brain activity through an array of sensors placed on the surface of the head. Compared to functional MRI, optical imaging has the advantage of being portable while offering the ability to record functional changes in both oxy- and deoxy-hemoglobin within the brain at a high temporal resolution. However, the reconstruction of accurate spatial images of brain activity from optical measurements represents an ill-posed and underdetermined problem that requires regularization. These reconstructions benefit from incorporating prior information about the underlying spatial structure and function of the brain. In this work, we describe a novel image reconstruction approach which uses surface-based wavelets derived from structural MRI to incorporate high-resolution anatomical and structural prior information about the brain. This surface-based approach is used to approximate brain activation patterns through the reconstruction and presentation of topographical (two-dimensional) maps of brain activation directly onto the folded surface of the cortex. The set of wavelet coefficients is directly estimated by a truncated singular-value decomposition based pseudo-inversion of the wavelet projection of the optical forward model. We use a reconstruction metric based on Shannon entropy which quantifies the sparse loading of the wavelet coefficients and is used to determine the optimal truncation and regularization of this inverse model. In this work, examples of the performance of this model are illustrated for several cases of numerical simulation and experimental data with comparison to functional magnetic resonance imaging. PMID:19809125

  7. Topographic localization of brain activation in diffuse optical imaging using spherical wavelets.

    PubMed

    Abdelnour, F; Schmidt, B; Huppert, T J

    2009-10-21

    Diffuse optical imaging is a non-invasive technique that uses near-infrared light to measure changes in brain activity through an array of sensors placed on the surface of the head. Compared to functional MRI, optical imaging has the advantage of being portable while offering the ability to record functional changes in both oxy- and deoxy-hemoglobin within the brain at a high temporal resolution. However, the reconstruction of accurate spatial images of brain activity from optical measurements represents an ill-posed and underdetermined problem that requires regularization. These reconstructions benefit from incorporating prior information about the underlying spatial structure and function of the brain. In this work, we describe a novel image reconstruction approach which uses surface-based wavelets derived from structural MRI to incorporate high-resolution anatomical and structural prior information about the brain. This surface-based approach is used to approximate brain activation patterns through the reconstruction and presentation of topographical (two-dimensional) maps of brain activation directly onto the folded surface of the cortex. The set of wavelet coefficients is directly estimated by a truncated singular-value decomposition based pseudo-inversion of the wavelet projection of the optical forward model. We use a reconstruction metric based on Shannon entropy which quantifies the sparse loading of the wavelet coefficients and is used to determine the optimal truncation and regularization of this inverse model. In this work, examples of the performance of this model are illustrated for several cases of numerical simulation and experimental data with comparison to functional magnetic resonance imaging. PMID:19809125

  8. Evaluating a three dimensional model of diffuse photosynthetically active radiation in maize canopies

    NASA Astrophysics Data System (ADS)

    Wang, Xiping; Guo, Yan; Li, Baoguo; Wang, Xiyong; Ma, Yuntao

    2006-07-01

    Diffuse photosynthetically active radiation (DPAR) is important during overcast days and for plant parts shaded from the direct beam radiation. Simulation of DPAR interception by individual plant parts of a canopy, separately from direct beam photosynthetically active radiation (PAR), may give important insights into plant ecology. This paper presents a model to simulate the interception of DPAR in plant canopies. A sub-model of a virtual maize canopy was reconstructed. Plant surfaces were represented as small triangular facets positioned according to three-dimensionally (3D) digitized data collected in the field. Then a second sub-model to simulate the 3D DPAR distribution in the canopy was developed by dividing the sky hemisphere into a grid of fine cells that allowed for the anisotropic distribution of DPAR over the sky hemisphere. This model, DSHP (Dividing Sky Hemisphere with Projecting), simulates which DSH (Divided Sky Hemisphere) cells are directly visible from a facet in the virtual canopy, i.e. not obscured by other facets. The DPAR reaching the center of a facet was calculated by summing the amounts of DPAR present in every DSH cell. The distribution of DPAR in a canopy was obtained from the calculated DPARs intercepted by all facets in the canopy. This DSHP model was validated against DPAR measurements made in an actual maize ( Zea mays L.) canopy over selected days during the early filling stage. The simulated and measured DPAR at different canopy depths showed a good agreement with a R 2 equaling 0.78 ( n=120).

  9. Active Brownian motion of emulsion droplets: Coarsening dynamics at the interface and rotational diffusion.

    PubMed

    Schmitt, M; Stark, H

    2016-08-01

    A micron-sized droplet of bromine water immersed in a surfactant-laden oil phase can swim (S. Thutupalli, R. Seemann, S. Herminghaus, New J. Phys. 13 073021 (2011). The bromine reacts with the surfactant at the droplet interface and generates a surfactant mixture. It can spontaneously phase-separate due to solutocapillary Marangoni flow, which propels the droplet. We model the system by a diffusion-advection-reaction equation for the mixture order parameter at the interface including thermal noise and couple it to fluid flow. Going beyond previous work, we illustrate the coarsening dynamics of the surfactant mixture towards phase separation in the axisymmetric swimming state. Coarsening proceeds in two steps: an initially slow growth of domain size followed by a nearly ballistic regime. On larger time scales thermal fluctuations in the local surfactant composition initiates random changes in the swimming direction and the droplet performs a persistent random walk, as observed in experiments. Numerical solutions show that the rotational correlation time scales with the square of the inverse noise strength. We confirm this scaling by a perturbation theory for the fluctuations in the mixture order parameter and thereby identify the active emulsion droplet as an active Brownian particle. PMID:27562831

  10. Altered activation of innate immunity associates with white matter volume and diffusion in first-episode psychosis.

    PubMed

    Mäntylä, Teemu; Mantere, Outi; Raij, Tuukka T; Kieseppä, Tuula; Laitinen, Hanna; Leiviskä, Jaana; Torniainen, Minna; Tuominen, Lauri; Vaarala, Outi; Suvisaari, Jaana

    2015-01-01

    First-episode psychosis (FEP) is associated with inflammatory and brain structural changes, but few studies have investigated whether systemic inflammation associates with brain structural changes in FEP. Thirty-seven FEP patients (median 27 days on antipsychotic medication), and 19 matched controls were recruited. Serum levels of 38 chemokines and cytokines, and cardiovascular risk markers were measured at baseline and 2 months later. We collected T1- and diffusion-weighted MRIs with a 3 T scanner from the patients at baseline. We analyzed the association of psychosis-related inflammatory markers with gray and white matter (WM) volume using voxel-based morphometry and WM diffusion using tract-based spatial statistics with whole-brain and region-of-interest (ROI) analyses. FEP patients had higher CCL22 and lower TGFα, CXCL1, CCL7, IFN-α2 and ApoA-I than controls. CCL22 decreased significantly between baseline and 2 months in patients but was still higher than in controls. The association between inflammatory markers and FEP remained significant after adjusting for age, sex, smoking and BMI. We did not observe a correlation of inflammatory markers with any symptoms or duration of antipsychotic treatment. Baseline CCL22 levels correlated negatively with WM volume and positively with mean diffusivity and radial diffusivity bilaterally in the frontal lobes in ROI analyses. Decreased serum level of ApoA-I was associated with smaller volume of the medial temporal WM. In whole-brain analyses, CCL22 correlated positively with mean diffusivity and radial diffusivity, and CXCL1 associated negatively with fractional anisotropy and positively with mean diffusivity and radial diffusivity in several brain regions. This is the first report to demonstrate an association between circulating chemokine levels and WM in FEP patients. Interestingly, CCL22 has been previously implicated in autoimmune diseases associated with WM pathology. The results suggest that an altered activation

  11. Diffusive transport parameters of deuterium through China reduced activation ferritic-martensitic steels

    NASA Astrophysics Data System (ADS)

    Wang, Bo; Liu, Lingbo; Xiang, Xin; Rao, Yongchu; Ye, Xiaoqiu; Chen, Chang An

    2016-03-01

    Reduced Activation Ferritic/Martensitic (RAFM) steels have been considered as the most promising candidate structure materials for a fusion reactor. In the recent decades, two new types of RAFM steels, called China Low Activation Martensitic (CLAM) steel and China Low-activation Ferritic (CLF-1) steel, have been developed. The gas evolution permeation technique has been used to investigate diffusive transport parameters of deuterium through CLAM and CLF-1 over the temperature range 623 ∼ 873 K at deuterium pressure of 105 Pa. The resultant transport parameters are: Φ (mol. m-1 s-1 Pa-1/2) = 5.40 × 10-8 exp (-46.8 (kJ. mol-1)/RT), D(m2 s-1) = 3.81 × 10-7 exp(-24.0(kJ. mol-1)/RT) and S (mol. m-3 Pa-1/2) = 1.42 × 10-1 exp(-22.8(kJ. mol-1)/RT) for CLAM; while Φ(mol m-1 s-1 Pa-1/2) = 1.76 × 10-8 exp(-43.9(kJ. mol-1)/RT), D(m2. s-1) = 1.02 × 10-7 exp(-16.9(kJ. mol-1)/RT) and S(mol. m-1 Pa-1/2) = 1.73 × 10-1 exp(-27.0(kJ. mol-1) /RT) for CLF-1. The results show that CLAM is more permeable than CLF-1, thus it is easier for hydrogen isotopes to transport and be removed.

  12. Cromolyn as surface active drug (surfadrug): Effect of the self-association on diffusion and percutaneous permeation.

    PubMed

    Tavano, Lorena; Nicoletta, Fiore Pasquale; Picci, Nevio; Muzzalupo, Rita

    2016-03-01

    Cromolyn sodium, or disodium cromoglycate (CS), is a surface active drug: a pharmacologically active compound with an amphiphilic nature. At certain conditions it is able to self-associate in several kind of supramolecular aggregates. Since CS could play the role of both carrier and drug, bypassing the use of additional excipients and increasing the system biocompatibility, the effects of cromolyn self-aggregates on diffusion and percutaneous permeation across rabbit ear skin were investigated. Niosomes (vesicular systems, 0.5wt% of CS), monomeric and isotropic solutions (0.5 and 5wt% of CS), nematic (15wt% of CS) and hexagonal phases (30wt% of CS) were selected as supramolecular systems and tested as transdermal delivery systems. Results demonstrated that CS was able to form vesicular structures of about 500nm of diameter and this formulation gave the higher percutaneous permeation profile (systemic action), while isotropic solution and liquid crystals mesophases acted as slower release reservoir of drug on the skin surface (local action), as confirmed by diffusion coefficients. Diffusion rates through a synthetic membrane were dependent both on CS concentration present into the formulations and on its structural organization: maximum diffusion was noticed with isotropic solution, a lower amount of diffused cromolyn sodium was achieved by hexagonal phase. Consequently, CS appears as a versatile surfadrug as, depending on the disease degree, it is possible to modulate its permeation profile by choosing the most appropriate formulation. PMID:26705827

  13. Neuronal activity mediated regulation of glutamate transporter GLT-1 surface diffusion in rat astrocytes in dissociated and slice cultures.

    PubMed

    Al Awabdh, Sana; Gupta-Agarwal, Swati; Sheehan, David F; Muir, James; Norkett, Rosalind; Twelvetrees, Alison E; Griffin, Lewis D; Kittler, Josef T

    2016-07-01

    The astrocytic GLT-1 (or EAAT2) is the major glutamate transporter for clearing synaptic glutamate. While the diffusion dynamics of neurotransmitter receptors at the neuronal surface are well understood, far less is known regarding the surface trafficking of transporters in subcellular domains of the astrocyte membrane. Here, we have used live-cell imaging to study the mechanisms regulating GLT-1 surface diffusion in astrocytes in dissociated and brain slice cultures. Using GFP-time lapse imaging, we show that GLT-1 forms stable clusters that are dispersed rapidly and reversibly upon glutamate treatment in a transporter activity-dependent manner. Fluorescence recovery after photobleaching and single particle tracking using quantum dots revealed that clustered GLT-1 is more stable than diffuse GLT-1 and that glutamate increases GLT-1 surface diffusion in the astrocyte membrane. Interestingly, the two main GLT-1 isoforms expressed in the brain, GLT-1a and GLT-1b, are both found to be stabilized opposed to synapses under basal conditions, with GLT-1b more so. GLT-1 surface mobility is increased in proximity to activated synapses and alterations of neuronal activity can bidirectionally modulate the dynamics of both GLT-1 isoforms. Altogether, these data reveal that astrocytic GLT-1 surface mobility, via its transport activity, is modulated during neuronal firing, which may be a key process for shaping glutamate clearance and glutamatergic synaptic transmission. GLIA 2016;64:1252-1264. PMID:27189737

  14. Development of carbon free diffusion layer for activated carbon air cathode of microbial fuel cells.

    PubMed

    Yang, Wulin; Kim, Kyoung-Yeol; Logan, Bruce E

    2015-12-01

    The fabrication of activated carbon air cathodes for larger-scale microbial fuel cells requires a diffusion layer (DL) that is highly resistant to water leakage, oxygen permeable, and made using inexpensive materials. A hydrophobic polyvinylidene fluoride (PVDF) membrane synthesized using a simple phase inversion process was examined as a low cost ($0.9/m(2)), carbon-free DL that prevented water leakage at high pressure heads compared to a polytetrafluoroethylene/carbon black DL ($11/m(2)). The power density produced with a PVDF (20%, w/v) DL membrane of 1400±7mW/m(2) was similar to that obtained using a wipe DL [cloth coated with poly(dimethylsiloxane)]. Water head tolerance reached 1.9m (∼19kPa) with no mesh supporter, and 2.1m (∼21kPa, maximum testing pressure) with a mesh supporter, compared to 0.2±0.05m for the wipe DL. The elimination of carbon black from the DL greatly simplified the fabrication procedure and further reduced overall cathode costs. PMID:26342345

  15. Risk of COPD with obstruction in active smokers with normal spirometry and reduced diffusion capacity.

    PubMed

    Harvey, Ben-Gary; Strulovici-Barel, Yael; Kaner, Robert J; Sanders, Abraham; Vincent, Thomas L; Mezey, Jason G; Crystal, Ronald G

    2015-12-01

    Smokers are assessed for chronic obstructive pulmonary disease (COPD) using spirometry, with COPD defined by the Global Initiative for Chronic Obstructive Lung Disease (GOLD) as airflow limitation that is not fully reversible with bronchodilators. There is a subset of smokers with normal spirometry (by GOLD criteria), who have a low diffusing capacity of the lung for carbon monoxide (DLCO), a parameter linked to emphysema and small airway disease. The natural history of these "normal spirometry/low DLCO" smokers is unknown.From a cohort of 1570 smokers in the New York City metropolitian area, all of whom had normal spirometry, two groups were randomly selected for lung function follow-up: smokers with normal spirometry/normal DLCO (n=59) and smokers with normal spirometry/low DLCO (n=46). All had normal history, physical examination, complete blood count, urinalysis, HIV status, α1-antitrypsin level, chest radiography, forced expiratory volume in 1 s (FEV1), forced vital capacity (FVC), FEV1/FVC ratio and total lung capacity. Throughout the study, all continued to be active smokers.In the normal spirometry/normal DLCO group assessed over 45±20 months, 3% developed GOLD-defined COPD. In contrast, in the normal spirometry/low DLCO group, followed over 41±31 months, 22% developed GOLD-defined COPD.Despite appearing "normal" according to GOLD, smokers with normal spirometry but low DLCO are at significant risk of developing COPD with obstruction to airflow. PMID:26541521

  16. A simple and efficient diffusion technique for assay of endo β-1,4-xylanase activity

    PubMed Central

    Samanta, A.K.; Kolte, Atul P.; Senani, S.; Sridhar, Manpal.; Jayapal, Natasha.

    2011-01-01

    Endo-β-1, 4-xylanases is thought to be of great significance for several industries namely paper, pharmaceuticals, food, feed etc. in addition to better utilization of lignocellulosic biomass. The present investigation was aimed to develop an easy, simple and efficient assay technique for endo-β-1, 4-xylanases secreted by the aerobic fungi. Under the proposed protocol, 9 g/L xylan containing agar was prepared in 100 mM phosphate buffer at different pH (4.5, 5.5 and 6.5). The sterilized xylan agar was dispensed in 90 mm petri dishes. 100 µl of culture supernatant of 12 fungal isolates was added to the wells and left overnight at 31±10C. The petri dishes were observed for zone of clearance by naked eye and diameter was measured. Congo red solution (1 g/L) was applied over the petri dishes as per the established protocol and thereafter plates were flooded with 1M Sodium chloride solution for the appearance of zone of clearance. The diameter for zone of clearance by the proposed method and the established protocol was almost identical and ranged from 21 to 42 mm at different pH depending upon the activity of endo-β-1, 4-xylanases. Change of pH towards alkaline side enabled similar or marginal decrease of diameter for the zone of clearance in most of the fungal isolates. The specific activities of these fungal isolates varied from 1.85 to 11.47 IU/mg protein. The present investigation revealed that the proposed simple diffusion technique gave similar results as compared to the established Congo red assay for endo-β-1, 4-xylanases. Moreover, the present technique avoided the cumbersome steps of staining by Congo red and de-staining by sodium chloride. PMID:24031763

  17. User-oriented batch reactor solutions to the homogeneous surface diffusion model for different activated carbon dosages.

    PubMed

    Zhang, Qiong; Crittenden, John; Hristovski, Kiril; Hand, David; Westerhoff, Paul

    2009-04-01

    This paper presents a simplified approach and user-oriented solutions to the homogeneous surface diffusion model (HSDM) equations for determining the surface diffusivity using a batch reactor system. Once the surface diffusivity is known, this model could also be used to estimate the performance of activated carbon (AC) applications as a function of contact time. In addition, fixed-bed performance can be predicted using the user-oriented solutions to the HSDM for fixed beds. The step-by-step procedure for determining surface diffusion coefficients of an activated carbon adsorber, which was initially developed by Hand, Crittenden and Thacker in 1983 for a carbon dose where C(equilibrium)/C(0)=0.5, is modified to allow calculations for different carbon dosages. This modification provides solutions to the HSDM equations for different activated carbon dosages. The solutions to the HSDM framework are provided as simplified algebraic equations suitable for quick and easy estimations of D(S). The excel spread sheet is provided in the supplemental information and a detailed example is discussed. PMID:19249812

  18. Neuronal activity mediated regulation of glutamate transporter GLT‐1 surface diffusion in rat astrocytes in dissociated and slice cultures

    PubMed Central

    Al Awabdh, Sana; Gupta‐Agarwal, Swati; Sheehan, David F.; Muir, James; Norkett, Rosalind; Twelvetrees, Alison E.; Griffin, Lewis D.

    2016-01-01

    The astrocytic GLT‐1 (or EAAT2) is the major glutamate transporter for clearing synaptic glutamate. While the diffusion dynamics of neurotransmitter receptors at the neuronal surface are well understood, far less is known regarding the surface trafficking of transporters in subcellular domains of the astrocyte membrane. Here, we have used live‐cell imaging to study the mechanisms regulating GLT‐1 surface diffusion in astrocytes in dissociated and brain slice cultures. Using GFP‐time lapse imaging, we show that GLT‐1 forms stable clusters that are dispersed rapidly and reversibly upon glutamate treatment in a transporter activity‐dependent manner. Fluorescence recovery after photobleaching and single particle tracking using quantum dots revealed that clustered GLT‐1 is more stable than diffuse GLT‐1 and that glutamate increases GLT‐1 surface diffusion in the astrocyte membrane. Interestingly, the two main GLT‐1 isoforms expressed in the brain, GLT‐1a and GLT‐1b, are both found to be stabilized opposed to synapses under basal conditions, with GLT‐1b more so. GLT‐1 surface mobility is increased in proximity to activated synapses and alterations of neuronal activity can bidirectionally modulate the dynamics of both GLT‐1 isoforms. Altogether, these data reveal that astrocytic GLT‐1 surface mobility, via its transport activity, is modulated during neuronal firing, which may be a key process for shaping glutamate clearance and glutamatergic synaptic transmission. GLIA 2016;64:1252–1264 PMID:27189737

  19. Diffusion Bonding Beryllium to Reduced Activation Ferritic Martensitic Steel: Development of Processes and Techniques

    NASA Astrophysics Data System (ADS)

    Hunt, Ryan Matthew

    Only a few materials are suitable to act as armor layers against the thermal and particle loads produced by magnetically confined fusion. These candidates include beryllium, tungsten, and carbon fiber composites. The armor layers must be joined to the plasma facing components with high strength bonds that can withstand the thermal stresses resulting from differential thermal expansion. While specific joints have been developed for use in ITER (an experimental reactor in France), including beryllium to CuCrZr as well as tungsten to stainless steel interfaces, joints specific to commercially relevant fusion reactors are not as well established. Commercial first wall components will likely be constructed front Reduced Activation Ferritic Martensitic (RAFM) steel, which will need to be coating with one of the three candidate materials. Of the candidates, beryllium is particularly difficult to bond, because it reacts during bonding with most elements to form brittle intermetallic compounds. This brittleness is unacceptable, as it can lead to interface crack propagation and delamination of the armor layer. I have attempted to overcome the brittle behavior of beryllium bonds by developing a diffusion bonding process of beryllium to RAFM steel that achieves a higher degree of ductility. This process utilized two bonding aids to achieve a robust bond: a. copper interlayer to add ductility to the joint, and a titanium interlayer to prevent beryllium from forming unwanted Be-Cu intermetallics. In addition, I conducted a series of numerical simulations to predict the effect of these bonding aids on the residual stress in the interface. Lastly, I fabricated and characterized beryllium to ferritic steel diffusion bonds using various bonding parameters and bonding aids. Through the above research, I developed a process to diffusion bond beryllium to ferritic steel with a 150 M Pa tensile strength and 168 M Pa shear strength. This strength was achieved using a Hot Isostatic

  20. Wetting and Mechanical Performance of Zirconia Brazed with Silver/Copper Oxide and Silver/Vanadium Oxide Alloys

    SciTech Connect

    Sinnamon, Kathleen E.; Meier, Alan; Joshi, Vineet V.

    2014-12-01

    The wetting behavior and mechanical strength of silver/copper oxide and silver/vanadium oxide braze alloys were investigated for both magnesia-stabilized and yttria-stabilized (Mg-PSZ and Y-TZP) transformation toughened zirconia substrates. The temperatures investigated were 1000 to 1100°C, with oxide additions of 1 to 10 weight percent V2O5 or CuO, and hold times of 0.9 to 3.6 ks. Increasing either the isothermal hold temperature or time had a distinctly negative effect on the joint strength. The maximum strengths for both braze alloys were obtained for 5 wt. % oxide additions at 1050°C with a hold time of 0.9 ks. The Mg-PSZ/Ag-CuO system exhibited a average fracture strength of 255 MPa (45% of the reported monolithic strength), and the Y-TZP/Ag-CuO system had an average fracture strength of 540 MPa (30% of the reported monolithic strength). The fracture strengths were lower for the Ag-V2O5 braze alloys, with fracture strengths of approximately 180 MPa (30% of the monolithic strength) for Mg-PSZ versus approximately 160 MPa (10% of the monolithic strength) for Y-TZP. No interfacial products were observed in low magnification SEM analysis for the brazing alloys containing V2O5 additions, while there were interfacial products present for brazes prepared with CuO additions in the braze alloy.

  1. CORRELATIONS FOR THE DETERMINATION OF SURFACE DIFFUSIVITIES OF ORGANIC CHEMICALS ADSORBED ONTO GRANULAR ACTIVATED CARBON

    EPA Science Inventory

    Differential column batch reactor (DCBR) experiments in organic-free water were conducted for the following volatile organic compounds (VOCs): trichloroethene, tetrachloroethene, cis-1,2 dichlorethene, and toluene. Surface diffusion was required to explain the rate of uptake for ...

  2. Methane Uptake in a Semi-Arid Grassland Affected by Elevated CO2 and Warming: Role of Methanotroph Activity and Gas Diffusion

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Semiarid rangelands represent a significant global sink for methane (CH4) where methane uptake is controlled by methanotroph activity and the diffusivity of CH4 into the soil. Because increasing soil moisture causes diffusivity to fall but methanotroph activity to rise, methane uptake rates show a h...

  3. Mechanical and microstructural behavior of brazed aluminum / stainless steel mixed joints

    NASA Astrophysics Data System (ADS)

    Fedorov, V.; Weis, S.; Wagner, G.

    2016-03-01

    There is a requirement to combine different materials such as aluminum and stainless steel in industrial applications like automotive heat exchangers. Brazing offers the possibility to reduce the joining temperature in comparison to welding due to the lower liquidus temperature of the fillers. In the present work, the mechanical and microstructural behavior of aluminum / stainless steel mixed joints is investigated. The specimens are produced by induction brazing using an AlSi10filler and a non-corrosive flux. To evaluate the mechanical properties of the joints, tensile tests at elevated temperatures are carried out. Additionally, long-term thermal exposure experiments are done in order to investigate the changes in the microstructure.

  4. Brazing as a Means of Sealing Ceramic Membranes for use in Advanced Coal Gasification Processes

    SciTech Connect

    Weil, K. Scott; Hardy, John S.; Rice, Joseph P.; Kim, Jin Yong Y.

    2006-01-02

    Coal is potentially a very inexpensive source of clean hydrogen fuel for use in fuel cells, turbines, and various process applications. To realize its potential however, efficient, low-cost gas separation systems are needed to provide high purity oxygen to enhance the coal gasification reaction and to extract hydrogen from the resulting gas product stream. Several types of inorganic membranes are being developed for hydrogen or oxygen separation, including porous alumina, transition metal oxide perovskites, and zirconia. One of the key challenges in developing solid-state membrane based gas separation systems is in hermetically joining the membrane to the metallic body of the separation device. In an effort to begin addressing this issue, a new brazing concept has been developed, referred to as reactive air brazing. This paper discusses the details of this joining technique and illustrates its use in bonding a wide variety of materials, including alumina, lanthanum strontium cobalt ferrite, and yttria stabilized zirconia.

  5. Brazing as a Means of Sealing Ceramic Membranes for Use in Advanced Coal Gasification Processes

    SciTech Connect

    Weil, K. Scott; Hardy, John S.; Rice, Joseph P.; Kim, Jin Yong

    2006-01-31

    Coal is a potentially a very inexpensive source of clean hydrogen fuel for use in fuel cells, turbines, and various process applications. To realize its potential however, efficient, low-cost gas separation systems are needed to provide high purity oxygen to enhance the coal gasification reaction and to extract hydrogen from the resulting gas product stream. Several types of inorganic membranes are being developed for hydrogen or oxygen separation, including porous alumina, transition metal oxide perovskites, and zirconia. One of the key challenges in developing solid-state membrane based gas separation systems is in hermetically joining the membrane to the metallic body of the separation device. In an effort to begin addressing this issue, a new brazing concept has been developed, referred to as reactive air brazing. This paper discusses the details of this joining technique and illustrates its use in bonding a wide variety of materials, including alumina, lanthanum strontium cobalt ferrite, and yttria stabilized zirconia.

  6. Ultrasonic scanning system for in-place inspection of brazed tube joints

    NASA Technical Reports Server (NTRS)

    Haynes, J. L.; Wages, C. G.; Haralson, H. S. (Inventor)

    1973-01-01

    A miniaturized ultrasonic scanning system for nondestructive in-place, non-immersion testing of brazed joints in stainless-steel tubing is described. The system is capable of scanning brazed tube joints, with limited clearance access, in 1/4 through 5/8 inch union, tee, elbow and cross configurations. The system has the capability to detect defective conditions now associated with material density changes in addition to those which are depended upon density variations. The system includes a miniaturized scanning head assembly that fits around a tube joint and rotates the transducer around and down the joint in a continuous spiral motion. The C-scan recorder is similar in principle to conventional models except that it was specially designed to track the continuous spiral scan of the tube joint. The scanner and recorder can be operated with most commercially available ultrasonic flaw detectors.

  7. High-Power Comparison Among Brazed, Clamped and Electroformed X-Band Cavities

    SciTech Connect

    Spataro, B.; Alesini, D.; Chimenti, V.; Dolgashev, V.; Higashi, Y.; Migliorati, M.; Mostacci, A.; Parodi, R.; Tantawi, S.G.; Yeremian, A.D.; /SLAC

    2012-04-25

    We report the building procedure of X-band copper structures using the electroforming and electroplating techniques. These techniques allow the deposition of copper layers on a suitable die and they can be used to build RF structures avoiding the high temperature brazing step in the standard technique. We show the constructed prototypes and low power RF measurements and discuss the results of the high power tests at SLAC National Accelerator Laboratory.

  8. Mechanical Characterization of Reactively Brazed Metal-Composite Joints for Heat Rejection Systems

    NASA Technical Reports Server (NTRS)

    Morscher, Gregory N.; Asthana, Rajiv; Singh, Mrityunjay; Shpargel, Tarah

    2005-01-01

    The joining of metal tubes to composite plates is required for heat-rejection components in several space applications. Currently a number of different braze compositions are being evaluated as to their effectiveness. Such tube-plate configurations cannot be represented by traditional methods of testing, e.g., lap joints. The joined region is not between two flat surfaces, but rather between a flat surface and a curved surface. Therefore, several tests have been employed to ascertain the effectiveness of the different braze approaches in tension and in shear that are both simple and representative of the actual system and relatively straightforward in analysis. The results of these "tube tests" will be discussed for the three different braze compositions, Cu-ABA, Ti-Cu-Sil, and Ti-Cu-Ni. In addition, fracture analysis of the failed joints was performed and offers insights into the cause of joint failure and the distinctions which need to be made between the "strength" of a joint versus the "load carrying ability" of a joint.

  9. Fabrication and evaluation of superplastically formed/weld-brazed corrugated compression panels with beaded webs

    NASA Technical Reports Server (NTRS)

    Royster, D. M.; Davis, R. C.; Shinn, J. M., Jr.; Bales, T. T.; Wiant, H. R.

    1985-01-01

    A study was made to investigate the feasibility of superplastically forming corrugated panels with beaded webs and to demonstrate the structural integrity of these panels by testing. The test panels in the study consist of superplastically formed titanium alloy Ti-6Al-4V half-hat elements that are joined by weld-brazing to titanium alloy Ti-6Al-4V caps to form either single-corrugation compression panels or multiple-corrugation compression panels. Stretching and subsequent thinning of the titanium sheet during superplastic forming is reduced by approximately 35 percent with a shallow half-hat die concept instead of a deep die concept and results in a more uniform thickness across the beaded webs. The complete panels are tested in end compression at room temperature and the results compared with analysis. The heavily loaded panels failed at loads approaching the yield strength of the titanium material. At maximum load, the caps wrinkled locally accompanied with separation of the weld-braze joint in the wrinkle. None of the panels tested, however, failed catastrophically in the weld-braze joint. Experimental test results are in good agreement with structural analysis of the panels.

  10. A historical perspective on the lateral diffusion model of GTPase activation and related coupling of membrane signaling proteins

    PubMed Central

    Liebman, Paul A

    2014-01-01

    Aspects of our discovery of lateral diffusion of the G protein coupled receptor (GPCR) rhodopsin and that a single activated rhodopsin can non-covalently catalyze GTP binding to thousands of GTPases per second on rod disk membranes via this diffusion are summarized herein. Rapid GTPase coupling to membrane-bound phosphodiesterase (PDE) further amplifies the signal via cGMP hydrolysis, essential to visual transduction. Important generalizations from this work are that biomembranes can uniquely concentrate, orient for reaction and provide a solvent appropriate to rapid, powerful and appropriately controlled sequential interaction of signaling proteins. Of equal importance to function is timely control and termination of such powerful amplification via receptor phosphorylation (quenching) and arrestin binding. Downstream kinetic modulation by GTPase activating proteins (GAPs) and regulators of G protein signaling (RGS) and related mechanisms as well as limitations set by membrane domain fencing, structural protein binding etc. can be essential in relevant systems. PMID:25279248

  11. Economic value analysis of the return from the Korean astronaut program and the science culture diffusion activity in Korea

    NASA Astrophysics Data System (ADS)

    Yi, Soyeon; Jang, Hyun-Jin; Lee, Hyo Suk; Yu, Jong-Phil; Kim, Soyeon; Lee, Joohee; Hur, Hee-Young

    2013-06-01

    In this study, we analyze the economic effects from the Korean Astronaut Program (KAP) and the subsequent Science Culture Diffusion Activity (SCDA). Korea has had a huge practical effect on the development of science and technology and has increased international awareness of Korea by producing Korea's first astronaut. There has also been a large, ripple effect on space related industries. In addition, the KAP has exercised a far-reaching influence on Korean society and culture by boosting all science and engineering and inspiring national pride. After the KAP, astronauts' outreach activities, such as lectures for the general public; interviews on television, newspapers and magazines; participating in children's science camps; and distributing publications and DVDs about astronaut program for general public, were instituted for diffusing science culture. Thus, positive effects such as the promotion of Korea's level of technology, student interest in science and engineering fields, and the expansion of the industrial base were reinforced after the KAP. This study is aimed at evaluating the economic significance and the value of return through analyzing the effects of the KAP and the subsequent Science Culture Diffusion Activity.

  12. A Minimum Energy Fit Method to Reconstruct Photospheric Velocity and Magnetic Diffusivity in Active Regions from Observed Magnetograms and Dopplergrams

    NASA Astrophysics Data System (ADS)

    Tremblay, Benoit; Vincent, Alain

    2015-02-01

    We introduce MEF-R, a generalization of the minimum energy fit (MEF; Longcope, Astrophys. J. 612, 1181, 2004) to a non-ideal (resistive) gas. The new technique requires both vector magnetograms and Doppler velocities as input fields. However, in the case of active regions observed only with the Michelson-Doppler Imager (MDI) onboard the Solar and Heliospheric Observatory (SOHO) such as AR 9077, we have only access to line-of-sight magnetograms. We reconstruct two-dimensional maps of the magnetic diffusivity η( x, y) together with velocity components v x ( x, y), v y ( x, y), and v z ( x, y) under the linear force-free magnetic field approximation. Computed maps for v z ( x, y) very well match the Doppler velocities v r ( x, y). We find the average value < η>≈108 m2 s-1 with a standard deviation of ≈ 1010 m2 s-1. Such high values of η( x, y) are to be expected at some places since our magnetic diffusivity is actually eddy-diffusivity. Inside AR 9077, the maps of η( x, y) do not resemble closely the maps from classical models of the magnetic diffusivity, but they are closer to η as a function of temperature than to η as a function of electric current density.

  13. COMPARISON OF 24H AVERAGE VOC MONITORING RESULTS FOR RESIDENTIAL INDOOR AND OUTDOOR AIR USING CARBOPACK X-FILLED DIFFUSIVE SAMPLERS AND ACTIVE SAMPLING - A PILOT STUDY

    EPA Science Inventory

    Analytical results obtained by thermal desorption GC/MS for 24h diffusive sampling of 11 volatile organic compounds (VOCs) are compared with results of time-averaged active sampling at a known constant flow rate. Air samples were collected with co-located duplicate diffusive samp...

  14. Development of rapidly quenched nickel-based non-boron filler metals for brazing corrosion resistant steels

    NASA Astrophysics Data System (ADS)

    Ivannikov, A.; Kalin, B.; Suchkov, A.; Penyaz, M.; Yurlova, M.

    2016-04-01

    Corrosion-resistant steels are stably applied in modern rocket and nuclear technology. Creating of permanent joints of these steels is a difficult task that can be solved by means of welding or brazing. Recently, the use rapidly quenched boron-containing filler metals is perspective. However, the use of such alloys leads to the formation of brittle borides in brazing zone, which degrades the corrosion resistance and mechanical properties of the compounds. Therefore, the development of non-boron alloys for brazing stainless steels is important task. The study of binary systems Ni-Be and Ni-Si revealed the perspective of replacing boron in Ni-based filler metals by beryllium, so there was the objective of studying of phase equilibrium in the system Ni-Be-Si. The alloys of the Ni-Si-Be with different contents of Si and Be are considered in this paper. The presence of two low-melting components is revealed during of their studying by methods of metallography analysis and DTA. Microhardness is measured and X-ray diffraction analysis is conducted for a number of alloys of Ni-Si-Be. The compositions are developed on the basis of these data. Rapidly quenched brazing alloys can be prepared from these compositions, and they are suitable for high temperature brazing of steels.

  15. Investigation of the electrochemically active surface area and lithium diffusion in graphite anodes by a novel OsO4 staining method

    NASA Astrophysics Data System (ADS)

    Pfaffmann, Lukas; Birkenmaier, Claudia; Müller, Marcus; Bauer, Werner; Mitsch, Tim; Feinauer, Julian; Krämer, Yvonne; Scheiba, Frieder; Hintennach, Andreas; Schleid, Thomas; Schmidt, Volker; Ehrenberg, Helmut

    2016-03-01

    Negative electrodes of lithium-ion batteries generally consist of graphite-based active materials. In order to realize batteries with a high current density and therefore accelerated charging processes, the intercalation of lithium and the diffusion processes of these carbonaceous materials must be understood. In this paper, we visualized the electrochemical active surface area for three different anode materials using a novel OsO4 staining method in combination with scanning electron microscopy techniques. The diffusion behavior of these three anode materials is investigated by potentiostatic intermittent titration technique measurements. From those we determine the diffusion coefficient with and without consideration of the electrochemical active surface area.

  16. Interactive effects of physical activity and APOE-ε4 on white matter tract diffusivity in healthy elders.

    PubMed

    Smith, J Carson; Lancaster, Melissa A; Nielson, Kristy A; Woodard, John L; Seidenberg, Michael; Durgerian, Sally; Sakaie, Ken; Rao, Stephen M

    2016-05-01

    Older adult apolipoprotein-E epsilon 4 (APOE-ε4) allele carriers vary considerably in the expression of clinical symptoms of Alzheimer's disease (AD), suggesting that lifestyle or other factors may offer protection from AD-related neurodegeneration. We recently reported that physically active APOE-ε4 allele carriers exhibit a stable cognitive trajectory and protection from hippocampal atrophy over 18months compared to sedentary ε4 allele carriers. The aim of this study was to examine the interactions between genetic risk for AD and physical activity (PA) on white matter (WM) tract integrity, using diffusion tensor imaging (DTI) MRI, in this cohort of healthy older adults (ages of 65 to 89). Four groups were compared based on the presence or absence of an APOE-ε4 allele (High Risk; Low Risk) and self-reported frequency and intensity of leisure time physical activity (PA) (High PA; Low PA). As predicted, greater levels of PA were associated with greater fractional anisotropy (FA) and lower radial diffusivity in healthy older adults who did not possess the APOE-ε4 allele. However, the effects of PA were reversed in older adults who were at increased genetic risk for AD, resulting in significant interactions between PA and genetic risk in several WM tracts. In the High Risk-Low PA participants, who had exhibited episodic memory decline over the previous 18-months, radial diffusivity was lower and fractional anisotropy was higher, compared to the High Risk-High PA participants. In WM tracts that subserve learning and memory processes, radial diffusivity (DR) was negatively correlated with episodic memory performance in physically inactive APOE-ε4 carriers, whereas DR was positively correlated with episodic memory performance in physically active APOE-ε4 carriers and the two Low Risk groups. The common model of demyelination-induced increase in radial diffusivity cannot directly explain these results. Rather, we hypothesize that PA may protect APOE-ε4 allele

  17. Polymer structure and the compensation effect of the diffusion pre-exponential factor and activation energy of a permeating solute.

    PubMed

    Zheng, Ju-Meng; Qiu, Jun; Madeira, Luis M; Mendes, Adélio

    2007-03-22

    In the present work, the relation between the pre-exponential factor and the apparent activation energy of diffusion, ln D(0) = alpha + betaE(D), so-called compensation effect, is re-examined and critically discussed for diffusion of gases in rubbery and glassy polymers. In principle, the above equation could be derived from the enthalpy-entropy compensation in the framework of the transition state theory. However, one should consider the influence of the jump length term contained in the pre-exponential factor, which may be affected by permeating species and polymer properties. We found that parameter alpha depends on penetrant size and polymer properties, such as local chain mobility and free volume. This can be interpreted by the fact that the jump length is affected by both penetrant and polymer properties. Finally, methods for estimating the jump length are discussed. PMID:17316040

  18. Active monitoring of formaldehyde diffusion into histological tissues with digital acoustic interferometry.

    PubMed

    Bauer, Daniel R; Stevens, Benjamin; Chafin, David; Theiss, Abbey P; Otter, Michael

    2016-01-01

    The preservation of certain labile cancer biomarkers with formaldehyde-based fixatives can be considerably affected by preanalytical factors such as quality of fixation. Currently, there are no technologies capable of quantifying a fixative's concentration or the formation of cross-links in tissue specimens. This work examined the ability to detect formalin diffusion into a histological specimen in real time. As formaldehyde passively diffused into tissue, an ultrasound time-of-flight (TOF) shift of several nanoseconds was generated due to the distinct sound velocities of formalin and exchangeable fluid within the tissue. This signal was resolved with a developed digital acoustic interferometry algorithm, which compared the phase differential between signals and computed the absolute TOF with subnanosecond precision. The TOF was measured repeatedly across the tissue sample for several hours until diffusive equilibrium was realized. The change in TOF from 6-mm thick ex vivo human tonsil fit a single-exponential decay ([Formula: see text]) with rate constants that varied drastically spatially between 2 and 10 h ([Formula: see text]) due to substantial heterogeneity. This technology may prove essential to personalized cancer diagnostics by documenting and tracking biospecimen preanalytical fixation, guaranteeing their suitability for diagnostic assays, and speeding the workflow in clinical histopathology laboratories. PMID:26866049

  19. Random Vibration Tests for Prediction of Fatigue Life of Diffuser Structure for Gas Dynamic Laser

    NASA Astrophysics Data System (ADS)

    Maurer, O. F.; Banaszak, D. L.

    1980-01-01

    Static and dynamic strain measurements which were taken during test stand operations of the gas dynamic laser (GDL) for the AF Airborne Laser Laboratory indicated that higher than expected vibrational stress levels may possibly limit the fatigue life of the laser structure. Particularly the diffuser sidewall structure exhibited large amplitude random vibrations which were excited by the internal gas flow. The diffuser structure consists of two layers of brazed stainless steel, AISI-347, panels. Cooling ducts were milled into the outer face sheet. These in turn are backed by the inner face sheet. So called T-rail stiffeners silver-brazed to the outer face sheets add the required stiffness and divide the sidewall into smaller rectangular plate sections.

  20. Mechanical performance of reactive-air-brazed (RAB) ceramic/metal joints for solid oxide fuel cells at ambient temperature

    NASA Astrophysics Data System (ADS)

    Kuhn, B.; Wetzel, F. J.; Malzbender, J.; Steinbrech, R. W.; Singheiser, L.

    Mechanical integrity of the sealants in planar SOFC stacks is a key prerequisite for reliable operation. In this respect joining with metals rather than brittle glass-ceramics is considered to have advantages. Hence, as one of the joining solutions for SOFCs of planar design, reactive air brazing of ceramic cells into metallic frames gains increasing interest. Fracture experiments are carried out to characterize fracture energy and failure mechanisms of silver-based reactive-air-brazes, used for joining the zirconia electrolytes of anode supported planar cells with metallic Crofer22APU frames. The specimens are mechanically tested in notched beam bending geometry. In-situ observation in optical and SEM resolution reveals specific failure mechanisms. The influence of braze formulation and associated interfacial reactions on the crack path location is addressed. Discussion of the results focuses in particular on the role of oxide scale formation.

  1. An Ag based brazing system with a tunable thermal expansion for the use as sealant for solid oxide cells

    NASA Astrophysics Data System (ADS)

    Kiebach, Ragnar; Engelbrecht, Kurt; Grahl-Madsen, Laila; Sieborg, Bertil; Chen, Ming; Hjelm, Johan; Norrman, Kion; Chatzichristodoulou, Christodoulos; Hendriksen, Peter Vang

    2016-05-01

    An Ag-Al2TiO5 composite braze was developed and successfully tested as seal for solid oxide cells. The thermo-mechanical properties of the Ag-Al2TiO5 system and the chemical compatibility between this composite braze and relevant materials used in stacks were characterized and the leak rates as a function of the operation temperature were measured. The thermal expansion coefficient in the Ag-Al2TiO5 system can be tailored by varying the amount of the ceramic filler. The brazing process can be carried out in air, the joining partners showed a good chemical stability and sufficient low leak rates were demonstrated. Furthermore, the long-term stability of the Ag-Al2TiO5 composite braze was studied under relevant SOFC and SOEC conditions. The stability of brazed Crofer/Ag-Al2TiO5/NiO-YSZ assemblies in reducing atmosphere and in pure oxygen was investigated over 500 h at 850 °C. Additionally, a cell component test was performed to investigate the durability of the Ag-Al2TiO5 seal when exposed to dual atmosphere. The seals performed well over 900 h under electrolysis operation conditions (-0.5 A cm2, 850 °C), and no cell degradation related to the Ag-Al2TiO5 sealing was found, indicating that the developed braze system is applicable for the use in SOFC/SOEC stacks.

  2. Erosion of tungsten and its brazed joints with bronze irradiated by pulsed deuterium plasma flows

    NASA Astrophysics Data System (ADS)

    Yakushin, V.; Polsky, V.; Kalin, B.; Dzhumaev, P.; Polyansky, A.; Sevryukov, O.; Suchkov, A.; Fedotov, V.

    2013-11-01

    This work presents results on erosion of mono- and polycrystalline tungsten and its brazed joints with bronze substrates under irradiation by high-temperature pulsed (τp ˜ 20 μs) deuterium plasma flows, with a power density q = 19-66 GW/m2 and pulses numbering from 2 to 10, simulating the expected plasma disruptions and ELMs in fusion reactors. The surface erosion and heat resistance of tungsten and brazed joints were investigated by scanning electron microscopy, and erosion coefficients were determined by target mass loss. It is found that for both types of tungsten the surface starts to significantly crack even under relatively weak irradiation regimes (q = 19 GW/m2, N = 2), at which point surface melting is not observed. Local melting becomes visible with an increase of q up to 25 GW/m2. In addition, there is formation of blisters with a typical size of 1-2 μm on the surface of monocrystalline samples and craters up to 2 μm in diameter on polycrystalline samples. In addition, craters ˜10-30 μm in diameter are formed on defects similar to those observed under unipolar arcs. At that point, the erosion coefficients change to within ranges of 0.2-0.7 × 10-5 kg/J m2. It is found that at q = 50 GW/m2, the brazed joints of monocrystalline tungsten with bronze of Cu-0.6% Cr-0.08% Zr have the highest heat resistance.

  3. Potential and limitations of microanalysis SEM techniques to characterize borides in brazed Ni-based superalloys

    SciTech Connect

    Ruiz-Vargas, J.; Siredey-Schwaller, N.; Noyrez, P.; Mathieu, S.; Bocher, P.; and others

    2014-08-15

    Brazed Ni-based superalloys containing complex phases of different Boron contents remain difficult to characterize at the micrometer scale. Indeed Boron is a light element difficult to measure precisely. The state-of-the-art microanalysis systems have been tested on a single crystal MC2 based metal brazed with BNi-2 alloy to identify boride precipitates. Effort has been made to evaluate the accuracy in Boron quantitation. Energy-dispersive and wavelength-dispersive X-ray spectroscopy attached to a Scanning Electron Microscope have first been used to determine the elemental composition of Boron-free phases, and then applied to various types of borides. Results have been compared to the ones obtained using a dedicated electron probe microanalysis, considered here as the reference technique. The most accurate method to quantify Boron using EDS is definitely by composition difference. A precision of 5 at.% could be achieved with optimized data acquisition and post-processing schemes. Attempts that aimed at directly quantifying Boron with various standards using EDS or coupled EDS/WDS gave less accurate results. Ultimately, Electron Backscatter Diffraction combined with localized EDS analysis has proved invaluable in conclusively identifying micrometer sized boride precipitates; thus further improving the characterization of brazed Ni-based superalloys. - Highlights: • We attempt to accurately identify Boron-rich phases in Ni-based superalloys. • EDS, WDS, EBSD systems are tested for accurate identification of these borides. • Results are compared with those obtained by electron probe microanalysis. • Boron was measured with EDS by composition difference with a precision of 5 at. %. • Additional EBSD in phase identification mode conclusively identifies the borides.

  4. Adhesive bonding and brazing of nanocrystalline diamond foil onto different substrate materials

    NASA Astrophysics Data System (ADS)

    Lodes, Matthias A.; Sailer, Stefan; Rosiwal, Stefan M.; Singer, Robert F.

    2013-10-01

    Diamond coatings are used in heavily stressed industrial applications to reduce friction and wear. Hot-filament chemical vapour deposition (HFCVD) is the favourable coating method, as it allows a coating of large surface areas with high homogeneity. Due to the high temperatures occurring in this CVD-process, the selection of substrate materials is limited. With the desire to coat light materials, steels and polymers a new approach has been developed. First, by using temperature-stable templates in the HFCVD and stripping off the diamond layer afterwards, a flexible, up to 150 μm thick and free standing nanocrystalline diamond foil (NCDF) can be produced. Afterwards, these NCDF can be applied on technical components through bonding and brazing, allowing any material as substrate. This two-step process offers the possibility to join a diamond layer on any desired surface. With a modified scratch test and Rockwell indentation testing the adhesion strength of NCDF on aluminium and steel is analysed. The results show that sufficient adhesion strength is reached both on steel and aluminium. The thermal stress in the substrates is very low and if failure occurs, cracks grow undercritically. Adhesion strength is even higher for the brazed samples, but here crack growth is critical, delaminating the diamond layer to some extent. In comparison to a sample directly coated with diamond, using a high-temperature CVD interlayer, the brazed as well as the adhesively bonded samples show very good performance, proving their competitiveness. A high support of the bonding layer could be identified as crucial, though in some cases a lower stiffness of the latter might be acceptable considering the possibility to completely avoid thermal stresses which occur during joining at higher temperatures.

  5. Tensile properties of thin Au-Ni brazes between strong base materials

    SciTech Connect

    Tolle, M.C.; Kassner, M.E. )

    1991-12-01

    It has long been known that when relatively strong base materials are joined by thin, soft, interlayer metals such as with brazing or various solid state joining processes, the ultimate tensile strength (UTS) of the bond may be several factors higher than the UTS of the bulk, or unconstrained, interlayer metals. However, earlier work reported by the authors confirmed that delayed or creep'' failure of the bond may occur at stresses much less than the UTS. It was found that for thin silver interlayers, prepared by brazing and physical vapor deposition (PVD), joining elastically deforming base materials (i.e. no measurable plastic deformation occurs in the base metal at the applied stresses), the ambient (and near-ambient) temperature time to failure is controlled by the creep rate of the silver interlayer which is determined by the effective stress within the interlayer. The plastic deformation within the interlayer causes cavity nucleation which continues until the concentration of nuclei is sufficiently high to lead to instability and eventual failure. The delayed failure may be accelerated by base material creep resulting from the effective stress in the base material. Plastic deformation in the base metal causes corresponding deformation in the interlayer, and cavities nucleate as with elastic base metal case. The delayed failure phenomenon was confirmed by the authors only for silver interlayers; other compositions were not tested. In this study, maraging steel was joined with an Au-Ni braze alloy with 57.5 at. % Au and 42.5 at. % Ni. The microstructure is expected to be a refined two-phase (spinodal) alloy with higher strength than the PVD silver of our previous investigation.

  6. Tensile properties of thin Au-Ni brazes between strong base materials

    SciTech Connect

    Tolle, M.C.; Kassner, M.E.

    1991-12-01

    It has long been known that when relatively strong base materials are joined by thin, soft, interlayer metals such as with brazing or various solid state joining processes, the ultimate tensile strength (UTS) of the bond may be several factors higher than the UTS of the bulk, or unconstrained, interlayer metals. However, earlier work reported by the authors confirmed that delayed or ``creep`` failure of the bond may occur at stresses much less than the UTS. It was found that for thin silver interlayers, prepared by brazing and physical vapor deposition (PVD), joining elastically deforming base materials (i.e. no measurable plastic deformation occurs in the base metal at the applied stresses), the ambient (and near-ambient) temperature time to failure is controlled by the creep rate of the silver interlayer which is determined by the effective stress within the interlayer. The plastic deformation within the interlayer causes cavity nucleation which continues until the concentration of nuclei is sufficiently high to lead to instability and eventual failure. The delayed failure may be accelerated by base material creep resulting from the effective stress in the base material. Plastic deformation in the base metal causes corresponding deformation in the interlayer, and cavities nucleate as with elastic base metal case. The delayed failure phenomenon was confirmed by the authors only for silver interlayers; other compositions were not tested. In this study, maraging steel was joined with an Au-Ni braze alloy with 57.5 at. % Au and 42.5 at. % Ni. The microstructure is expected to be a refined two-phase (spinodal) alloy with higher strength than the PVD silver of our previous investigation.

  7. SPECTRAL INDEX STUDIES OF THE DIFFUSE RADIO EMISSION IN ABELL 2256: IMPLICATIONS FOR MERGER ACTIVITY

    SciTech Connect

    Kale, Ruta; Dwarakanath, K. S. E-mail: dwaraka@rri.res.i

    2010-08-01

    We present a multi-wavelength analysis of the merging rich cluster of galaxies, Abell 2256 (A2256). We have observed A2256 at 150 MHz using the Giant Metrewave Radio Telescope and successfully detected the diffuse radio halo and the relic emission over a {approx}1.2 Mpc{sup 2} extent. Using this 150 MHz image and the images made using archival observations from the Very Large Array (VLA; 1369 MHz) and the Westerbrok Synthesis Radio Telescope (WSRT; 330 MHz), we have produced spectral index images of the diffuse radio emission in A2256. These spectral index images show a distribution of flat spectral index (S {proportional_to} {nu}{sup {alpha}}, {alpha} in the range -0.7 to -0.9) plasma in the region NW of the cluster center. Regions showing steep spectral indices ({alpha} in the range -1.0 to -2.3) are toward the SE of the cluster center. These spectral indices indicate synchrotron lifetimes for the relativistic plasmas in the range 0.08-0.4 Gyr. We interpret this spectral behavior as resulting from a merger event along the direction SE to NW within the last 0.5 Gyr or so. A shock may be responsible for the NW relic in A2256 and the megaparsec scale radio halo toward the SE is likely to be generated by the turbulence injected by mergers. Furthermore, the diffuse radio emission shows spectral steepening toward lower frequencies. This low-frequency spectral steepening is consistent with a combination of spectra from two populations of relativistic electrons created at two epochs (two mergers) within the last {approx}0.5 Gyr. Earlier interpretations of the X-ray and the optical data also suggested that there were two mergers in Abell 2256 in the last 0.5 Gyr, consistent with the current findings. Also highlighted in this study is the futility of correlating the average temperatures of thermal gas and the average spectral indices of diffuse radio emission in the respective clusters.

  8. Modeling moisture diffusivity, activation energy and specific energy consumption of squash seeds in a semi fluidized and fluidized bed drying.

    PubMed

    Chayjan, Reza Amiri; Salari, Kamran; Abedi, Qasem; Sabziparvar, Ali Akbar

    2013-08-01

    This study investigated thin layer drying of squash seeds under semi fluidized and fluidized bed conditions with initial moisture content about 83.99% (d.b.). An experimental fluidized bed dryer was also used in this study. Air temperature levels of 50, 60, 70 and 80 °C were applied in drying samples. To estimate the drying kinetic of squash seed, seven mathematical models were used to fit the experimental data of thin layer drying. Among the applied models, Two-term model has the best performance to estimate the thin layer drying behavior of the squash seeds. Fick's second law in diffusion was used to determine the effective moisture diffusivity of squash seeds. The range of calculated values of effective moisture diffusivity for drying experiments were between 0.160 × 10(-9) and 0.551 × 10(-10) m(2)/s. Moisture diffusivity values decreased as the input air temperature decreased. Activation energy values were found to be between 31.94 and 34.49 kJ/mol for 50 °C to 80 °C, respectively. The specific energy consumption for squash seeds was calculated at the boundary of 0.783 × 10(6) and 2.303 × 10(6) kJ/kg. Increasing in drying air temperature in different bed conditions led to decrease in specific energy value. Results showed that applying the semi fluidized bed condition is more effective for convective drying of squash seeds. The aforesaid drying characteristics are useful to select the best operational point of fluidized bed dryer and to precise design of system. PMID:24425968

  9. Exploring Shifts in Middle School Learners' Modeling Activity While Generating Drawings, Animations, and Computational Simulations of Molecular Diffusion

    NASA Astrophysics Data System (ADS)

    Wilkerson-Jerde, Michelle H.; Gravel, Brian E.; Macrander, Christopher A.

    2015-04-01

    Modeling and using technology are two practices of particular interest to K-12 science educators. These practices are inextricably linked among professionals, who engage in modeling activity with and across a variety of representational technologies. In this paper, we explore the practices of five sixth-grade girls as they generated models of smell diffusion using drawing, stop-motion animation, and computational simulation during a multi-day workshop. We analyze video, student discourse, and artifacts to address the questions: In what ways did learners' modeling practices, reasoning about mechanism, and ideas about smell shift as they worked across this variety of representational technologies? And, what supports enabled them to persist and progress in the modeling activity? We found that the girls engaged in two distinct modeling cycles that reflected persistence and deepening engagement in the task. In the first, messing about, they focused on describing and representing many ideas related to the spread of smell at once. In the second, digging in, they focused on testing and revising specific mechanisms that underlie smell diffusion. Upon deeper analysis, we found these cycles were linked to the girls' invention of "oogtom," a representational object that encapsulated many ideas from the first cycle and allowed the girls to restart modeling with the mechanistic focus required to construct simulations. We analyze the role of activity design, facilitation, and technological infrastructure in this pattern of engagement over the course of the workshop and discuss implications for future research, curriculum design, and classroom practice.

  10. Density-functional calculations of prefactors and activation energies for H diffusion in BaZrO3

    NASA Astrophysics Data System (ADS)

    Sundell, Per G.; Björketun, Mårten E.; Wahnström, Göran

    2007-09-01

    Density-functional calculations are used to investigate hydrogen diffusion in the solid-state proton conductor BaZrO3 . Activation energies and prefactors for the rate of proton transfer and reorientation are evaluated for a defect-free region of this simple cubic perovskite-structured oxide. Both semiclassical over-barrier jumps and phonon-assisted tunneling transitions between sites are considered. It is found that the classical barriers for the elementary transfer and reorientation steps are both of the order of 0.2eV . The quantum-mechanical zero-point motion effects are found to be sizable, to effectively reduce the barrier heights, and to make the prefactors similar for the transfer and reorientation steps. The Flynn-Stoneham model [Phys. Rev. B 1, 3966 (1970)] of phonon-assisted tunneling yields an activation energy of around 0.2eV and a very small prefactor for proton transfer, whereas the corresponding adiabatic model gives a similar activation energy but a much larger prefactor. It is suggested that the effect of other defects such as dopants has to be included for a proper description of hydrogen diffusion in this material.

  11. Challenge and opportunity in evaluating a diffusion-based active bystanding prevention program: Green Dot in high schools.

    PubMed

    Cook-Craig, Patricia G; Coker, Ann L; Clear, Emily R; Garcia, Lisandra S; Bush, Heather M; Brancato, Candace J; Williams, Corrine M; Fisher, Bonnie S

    2014-10-01

    Increasing attention has recently been paid to the development of prevention programs designed to actively engage bystanders in prevention efforts to reduce the risk of sexual and dating violence; yet, few evaluations have been conducted. Our proposed plan to rigorously evaluate a randomized intervention trial of the Green Dot bystander program as it is implemented in high schools across Kentucky is presented. We highlight the value of measuring violence victimization and perpetration outcomes, capturing actual and observed student bystander behaviors, and testing the diffusion of Green Dot training through students' social networks. PMID:25255794

  12. Note: Magnification of a polarization angle with a Littrow layout brazed grating

    SciTech Connect

    Sasao, H. Kubo, H.; Kawano, Y.; Itami, K.; Arakawa, H.

    2014-08-15

    A new method to magnify a small polarization angle with brazed gratings has been developed. In the method, difference in diffraction efficiency for S and P polarization components is used. The magnification dependence on the incident angle can be small by arranging the grating in Littrow layout. A magnification with a factor ∼2.7 has been demonstrated for a 10.6 μm CO{sub 2} laser beam as expected from a calculation. The method is applicable in many polarimetry fields.

  13. Simulation and experiment of packaging of the fibre Bragg grating sensors using brazing/soldering methods

    NASA Astrophysics Data System (ADS)

    Wen, Changjin; Li, Yulong; Hu, Ronghua; Xu, Jianning

    2016-08-01

    To manufacture fibre Bragg grating (FBG) transducer, finite element model simulation and experimental verification of packaging of the FBG by brazing/soldering were investigated. The packaging processes and their impacts on the wavelength change of FBG were analysed. Simulation results showed that the Bragg wavelength of packaged FBG shifted down a level of ~10 nm. For experimental verification, temperature sensitivity of the packaged FBG was enhanced about twice of the bare FBG, while its spectrum was well preserved. The Bragg wavelength was shifted down a level of ~10 nm which was in accordance with the simulation.

  14. Investigation of welding and brazing of molybdenum and TZM alloy tubes

    NASA Technical Reports Server (NTRS)

    Lundblad, Wayne E.

    1991-01-01

    This effort involved investigating the welding and brazing techniques of molybdenum tubes to be used as cartridges in the crystal growth cartridge. Information is given in the form of charts and photomicrographs. It was found that the recrystallization temperature of molybdenum can be increased by alloying it with 0.5 percent titanium and 0.1 percent zirconium. Recrystallization temperatures for this alloy, known as TZM, become significant around 2500 F. A series of microhardness tests were run on samples of virgin and heat soaked TZM. The test results are given in tabular form. It was concluded that powder metallurgy TZM may be an acceptable cartridge material.

  15. Automating a precision braze paste dispensing operation using non- contact sensing

    SciTech Connect

    Schmitt, D; Novak, J; Maslakowski, J; Thiele, A

    1993-01-01

    This paper describes a collaborative effort between Sandia National Laboratories and the Rocketdyne Division of Rockwell International Corporation to develop an automated braze paste dispensing system for rocket engine nozzle manufacturing. The motivation for automating this manufacturing process is to reduce the amount of labor and excess material required. A critical requirement for this system is the automatic location of key nozzle features using non-contact sensors. Sandia has demonstrated that the low-cost Multi-Axis Seam Tracking (MAST) capacitive sensor can be used to accurately locate the nozzle surface and tube gaps.

  16. Using the EZ-Diffusion Model to Score a Single-Category Implicit Association Test of Physical Activity

    PubMed Central

    Rebar, Amanda L.; Ram, Nilam; Conroy, David E.

    2014-01-01

    Objective The Single-Category Implicit Association Test (SC-IAT) has been used as a method for assessing automatic evaluations of physical activity, but measurement artifact or consciously-held attitudes could be confounding the outcome scores of these measures. The objective of these two studies was to address these measurement concerns by testing the validity of a novel SC-IAT scoring technique. Design Study 1 was a cross-sectional study, and study 2 was a prospective study. Method In study 1, undergraduate students (N = 104) completed SC-IATs for physical activity, flowers, and sedentary behavior. In study 2, undergraduate students (N = 91) completed a SC-IAT for physical activity, self-reported affective and instrumental attitudes toward physical activity, physical activity intentions, and wore an accelerometer for two weeks. The EZ-diffusion model was used to decompose the SC-IAT into three process component scores including the information processing efficiency score. Results In study 1, a series of structural equation model comparisons revealed that the information processing score did not share variability across distinct SC-IATs, suggesting it does not represent systematic measurement artifact. In study 2, the information processing efficiency score was shown to be unrelated to self-reported affective and instrumental attitudes toward physical activity, and positively related to physical activity behavior, above and beyond the traditional D-score of the SC-IAT. Conclusions The information processing efficiency score is a valid measure of automatic evaluations of physical activity. PMID:25484621

  17. Reduce Confusion about Diffusion.

    ERIC Educational Resources Information Center

    Hebrank, Mary R.

    1997-01-01

    Presents activities that allow students to explore the fundamental but poorly understood concept of diffusion by appealing to their kinesthetic senses first, then challenging their analytical skills as they try to deduce the mathematical principle involved. Presents a computer simulation of diffusion and discusses diffusion's limitations and…

  18. Perianal Fistula With and Without Abscess: Assessment of Fistula Activity Using Diffusion-Weighted Magnetic Resonance Imaging

    PubMed Central

    Bakan, Selim; Olgun, Deniz Cebi; Kandemirli, Sedat Giray; Tutar, Onur; Samanci, Cesur; Dikici, Suleyman; Simsek, Osman; Rafiee, Babak; Adaletli, Ibrahim; Mihmanli, Ismail

    2015-01-01

    Background: Magnetic resonance imaging (MRI) is highly accurate for the depiction of both the primary tract of fistula and abscesses, in patients with perianal disease. In addition, MRI can be used to evaluate the activity of fistulas, which is a significant factor for determining the therapeutic strategy. Objectives: This study aimed to determine the usefulness of diffusion-weighted (DW) MRI for assessing activity and visibility of perianal fistula. Patients and Methods: Fifty-three patients with 56 perianal fistulas were included in the current retrospective study. The T2-weighted imaging (T2WI) and DWMRI were performed and apparent diffusion coefficient (ADC) values of fistulas were measured. Fistulas were classified into two groups: only perianal fistulas and fistulas accompanied by abscess. Fistulas were also classified into two groups, based on clinical findings: positive inflammatory activity (PIA) and negative inflammatory activity (NIA). Results: Mean ADC value (mm2/s) of PIA group was significantly lower than that of NIA group, regarding lesions in patients with abscess-associated fistulas (1.371 × 10-3 ± 0.168 × 10-3 vs. 1.586 × 10-3 ± 0.136 × 10-3; P = 0.036). No statistically significant difference was found in mean ADC values between PIA and NIA groups, in patients with only perianal fistulas (P = 0.507). Perianal fistula visibility was greater with combined evaluation of T2WI and DWMRI than with T2WI, for two reviewers (P = 0.046 and P = 0.014). Conclusion: The DWMRI is a useful technique for evaluating activity of fistulas with abscess. Perianal fistula visibility is greater with combined T2WI and DWMRI than T2WI alone. PMID:26715982

  19. Diffusion bonding aeroengine components

    NASA Astrophysics Data System (ADS)

    Fitzpatrick, G. A.; Broughton, T.

    1988-10-01

    The use of diffusion bonding processes at Rolls-Royce for the manufacture of titanium-alloy aircraft engine components and structures is described. A liquid-phase diffusion bonding process called activated diffusion bonding has been developed for the manufacture of the hollow titanium wide chord fan blade. In addition, solid-state diffusion bonding is being used in the manufacture of hollow vane/blade airfoil constructions mainly in conjunction with superplastic forming and hot forming techniques.

  20. Preparation of antioxidant active films based on chitosan: diffusivity study of α-tocopherol into food simulants.

    PubMed

    Otero-Pazos, P; Sendón, R; Blanco-Fernandez, B; Blanco-Dorado, S; Alvarez-Lorenzo, C; Concheiro, A; Angulo, I; Paseiro-Losada, P; Rodríguez-Bernaldo de Quirós, A

    2016-06-01

    New active films based on chitosan and polycaprolactone blends and containing α-tocopherol were designed for food packaging applications. Mechanical properties, stability against temperature and swelling degree in 50 % ethanol (v/v) were evaluated. Migration kinetics of α-tocopherol from the developed films into butter and food simulants [50 % ethanol (v/v), 95 % ethanol (v/v), and isooctane] at different temperatures were studied. α-Tocopherol was quantified in the food simulants by means of high performance liquid chromatography with diode-array detection at 292 nm. The proposed method exhibited a good sensitivity with a limit of detection of 0.1 mg/L. The kinetics release of α-tocopherol was characterized by determining the partition and the diffusion coefficients by using a mathematical modeling based on Fick's Second Law. The diffusion coefficients obtained ranged between 1.03 × 10(-13) and 2.24 × 10(-12) cm(2)/s for 95 % ethanol (v/v) at 4 and 20 °C, respectively. Developed films maintained the antioxidant activity for more than 20 days. PMID:27478238

  1. The Effect of Post-grinding Heat Treatment of Alumina and Ag-Cu-Ti Braze Preform Thickness on the Microstructure and Mechanical Properties of Alumina-to-Alumina-Brazed Joints

    NASA Astrophysics Data System (ADS)

    Kassam, Tahsin Ali; Nadendla, Hari Babu; Ludford, Nicholas; Buisman, Iris

    2016-05-01

    Alumina-to-alumina-brazed joints were formed using 96.0 and 99.7 wt.% Al2O3 and TICUSIL® (68.8Ag-26.7Cu-4.5Ti wt.%) preforms of different thicknesses. Brazing was conducted in a vacuum of 1 × 10-5 mbar at 850 °C for 10 minutes. Joint strengths were evaluated using four-point bend testing and were compared to flexural strengths of standard test bars. Post-grinding heat treatment, performed at 1550 °C for 1 hour, did not affect the average surface roughness or grain size of either grades of alumina but affected their average flexural strengths with a small increase for 96.0 wt.% Al2O3 and a small decrease for 99.7 wt.% Al2O3. As the TICUSIL® preform thickness was increased from 50 to 100 µm, the average strengths of both 96.0 and 99.7 wt.% Al2O3 brazed joints improved. Joints made using 100-µm-thick TICUSIL® preforms predominantly consisted of Cu-Ti phases which formed due to excess Ti in the interlayers and non-uniform Ag-rich outflow. Brazed joints of 96.0 wt.% Al2O3 made using 100-µm-thick TICUSIL® preforms achieved an average joint strength of 238 MPa with consistent failure in the ceramic.

  2. Investigating the effect of solvent boiling temperature on the active layer morphology of diffusive bilayer solar cells

    NASA Astrophysics Data System (ADS)

    Vohra, Varun; Dörling, Bernhard; Higashimine, Koichi; Murata, Hideyuki

    2016-01-01

    Using chlorobenzene as a base solvent for the deposition of the poly(3-hexylthiophene-2,5-diyl) (P3HT) layer in P3HT:phenyl-C61-butyric acid methyl ester diffusive bilayer solar cells, we investigate the effect of adding of small amounts of high-boiling-point solvents with similar chemical structures on the resulting active layer morphologies. The results demonstrate that the crystallinity of the P3HT films as well as the vertical donor-acceptor gradient in the active layer can be tuned by this approach. The use of high-boiling-point solvents improved all photovoltaic parameters and resulted in a 32% increase in power conversion efficiency.

  3. Some properties of low-vapor-pressure braze alloys for thermionic converters

    NASA Technical Reports Server (NTRS)

    Bair, V. L.

    1978-01-01

    Density, dc electrical resistivity, thermal conductivity, and linear thermal expansion are measured for arc-melted rod-shaped samples of binary eutectics of Zr, Hf, Ru, Nb, Ir, Mo, Ta, Os, Re, and W selected as very-low-pressure braze fillers for thermionic converters. The first two properties are measured at 296 K for Zr-21.7 at% Ru, Zr-13 wt% W, Zr-19 wt% W, Zr-22.3 at% Nb, Nb-66.9 at% Ru, Hf-25.3 wt% Re, Zr-25.7 at% Ta, Hf-22.5 at% W, and Nb-35 wt% Mo. The last property is measured from 293 K to 2/3 melting point for specified alloys of different compositions. Resistivities of 0.000055 to 0.000181 ohm-cm are observed with the alloys having resistivities about ten times that of the less resistive constituent metal and about three times that of the more resistive constituent metal, except for Zr-19 wt% W and Nb-35 wt% Mo (greater resistivities). Thermal expansion coefficients vary from 0.000006 to 0.0000105/K. All brazes exhibit linear thermal expansion near that of their constituent metals.

  4. Preparation and Properties of a Novel Al-Si-Ge-Zn Filler Metal for Brazing Aluminum

    NASA Astrophysics Data System (ADS)

    Niu, Zhiwei; Huang, Jihua; Yang, Hao; Chen, Shuhai; Zhao, Xingke

    2015-06-01

    The study is concerned with developing a filler metal with low melting temperature and good processability for brazing aluminum and its alloys. For this purpose, a novel Al-Si-Ge-Zn alloy was prepared according to Al-Si-Ge and Al-Si-Zn ternary phase diagrams. The melting characteristics, microstructures, wettability, and processing property of the alloy were investigated. The results showed that the melting temperature range of the novel filler metal was 505.2-545.1 °C, and the temperature interval between the solidus and the liquidus was 39.9 °C. Compared with a common Al-Si-Ge alloy, it had smaller and better dispersed β-GeSi solid solution precipitates, and the Zn-rich phases distributed on the boundary of the β-GeSi precipitates. The novel filler metal has good processability and good wettability with Al. There was one obvious transition layer with a thin α-Al solid solution between the filler metal and base metal, which is favorable to improve the strength of brazing joint.

  5. Phase constitution in the interfacial region of laser penetration brazed magnesium–steel joints

    SciTech Connect

    Miao, Yugang; Han, Duanfeng Xu, Xiangfang; Wu, Bintao

    2014-07-01

    The phase constitution in the interfacial region of laser penetration brazed magnesium–steel joints was investigated using electron microscopy. From the distribution of elements, the transition zone was mainly composed of elements Mg and Fe along with some Al and O. Furthermore, the transition layer consisted mainly of intermetallic compounds and metal oxides. The compounds were identified as Al-rich phases, such as Mg{sub 17}Al{sub 12}, Mg{sub 2}Al{sub 3}, FeAl and Fe{sub 4}Al{sub 13}. More noteworthy was that the thickness of the transition layer was determined by Fe–Al compounds. The presence of FeAl and Fe{sub 4}Al{sub 13} was a result of the complex processes that were associated with the interfacial reaction of solid steel and liquid Mg–Al alloy. - Highlights: • A technology of laser penetration brazed Mg alloy and steel has been developed. • The interface of Mg/Fe dissimilar joints was investigated using electron microscopy. • The transition layer consisted of intermetallic compounds and metal oxides. • Moreover, the thickness of transition layer was determined by Fe/Al compounds. • The presence of FeAl and Fe{sub 4}Al{sub 13} was associated with the interfacial reaction.

  6. Elevated temperature behavior of superplastically formed/weld-brazed titanium compression panels having advanced shaped stiffeners

    NASA Technical Reports Server (NTRS)

    Royster, D. M.; Bales, T. T.

    1983-01-01

    The 316 C (600 F) buckling behavior of superplastically formed/weld-brazed titanium compression panels having advanced shaped stiffeners was investigated. Fabrication of the advanced shaped stiffeners was made possible by the increased formability afforded by the superplasticity characteristics of the titanium alloy Ti-6Al-4V. Stiffeners having the configurations of a conventional hat, a beaded web, a modified beaded web, a ribbed web, and a stepped web were investigated. The data from the panel tests include load-shortening curves, local buckling strengths, and failure loads. The superplastic formed/weld-brazed panels with the ribbed web and stepped web stiffeners developed 25 and 27 percent higher buckling strengths at 316 C (600 F) than panels with conventionally shaped stiffeners. The buckling load reductions for panels tested at 316 C (600 F), compared with panels tested at room temperature, were in agreement with predictions based on titanium material property data. The advantage that higher buckling loads can be readily achieved by superplastically forming of advanced stiffener shapes was demonstrated. Application of these advanced stiffener shapes offers the potential to achieve substantial weight savings in aerospace vehicles.

  7. Effect of mechanical milling on Ni-TiH{sub 2} powder alloy filler metal for brazing TiAl intermetallic alloy: The microstructure and joint's properties

    SciTech Connect

    He Peng Liu Duo; Shang Erjing; Wang Ming

    2009-01-15

    A TiH{sub 2}-50 wt.% Ni powder alloy was mechanically milled in an argon gas atmosphere using milling times up to 480 min. A TiAl intermetallic alloy was joined by vacuum furnace brazing using the TiH{sub 2}-50 wt.% Ni powder alloy as the filler metal. The effect of mechanical milling on the microstructure and shear strength of the brazed joints was investigated. The results showed that the grains of TiH{sub 2}-50 wt.% Ni powder alloy were refined and the fusion temperature decreased after milling. A sound brazing seam was obtained when the sample was brazed at 1140 deg. C for 15 min using filler metal powder milled for 120 min. The interfacial zones of the specimens brazed with the milled filler powder were thinner and the shear strength of the joint was increased compared to specimens brazed with non-milled filler powder. A sample brazed at 1180 deg. C for 15 min using TiH{sub 2}-50 wt.% Ni powder alloy milled for 120 min exhibited the highest shear strength at both room and elevated temperatures.

  8. Microstructure and Mechanical Properties of Plasma Arc Brazed AISI 304L Stainless Steel and Galvanized Steel Plates

    NASA Astrophysics Data System (ADS)

    Jin, Yajuan; Li, Ruifeng; Yu, Zhishui; Wang, Yu

    2016-04-01

    Plasma arc brazing is used to join the AISI 304L stainless steel and galvanized steel plate butt joints with the CuSi3Mn1 filler wire. The effect of parameters on weld surface appearance, interfacial microstructure, and composition distribution in the joint was studied. The microhardness and mechanical tests were conducted to determine the mechanical properties of the welded specimens. The results indicated that good appearance, bead shape, and sufficient metallurgical bonding could be obtained when the brazing process was performed with a wire feeding speed of 0.8 m/min, plasma gas flow rate of 3.0 l/min, welding current of 100 A, and welding speed of 27 cm/min. During plasma arc brazing process, the top corner of the stainless steel and galvanized steel plate were heated and melted, and the melted quantity of stainless steel was much more than that of the galvanized steel due to the thermal conductivity coefficient difference between the dissimilar materials. The microhardness test results shows that the microhardness value gradually increased from the side of the galvanized steel to the stainless steel in the joint, and it is good for improving the mechanical properties of joint. The tensile strength was a little higher than that of the brazing filler, and the fracture position of weld joint was at the base metal of galvanized steel plate.

  9. 78 FR 53159 - Standard for Welding, Cutting, and Brazing; Extension of the Office of Management and Budget's...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-08-28

    ... Paperwork Reduction Act of 1995 (44 U.S.C. 3506 et seq.) and Secretary of Labor's Order No. 1-2012 (77 FR... Occupational Safety and Health Administration Standard for Welding, Cutting, and Brazing; Extension of the... Budget's (OMB) approval of the information collection requirements contained in the Standard for...

  10. Manufacturing and High Heat Flux Testing of Brazed Flat-Type W/CuCrZr Plasma Facing Components

    NASA Astrophysics Data System (ADS)

    Lian, Youyun; Liu, Xiang; Feng, Fan; Chen, Lei; Cheng, Zhengkui; Wang, Jin; Chen, Jiming

    2016-02-01

    Water-cooled flat-type W/CuCrZr plasma facing components with an interlayer of oxygen-free copper (OFC) have been developed by using vacuum brazing route. The OFC layer for the accommodation of thermal stresses was cast onto the surface of W at a temperature range of 1150 °C-1200 °C in a vacuum furnace. The W/OFC cast tiles were vacuum brazed to a CuCrZr heat sink at 940 °C using the silver-free filler material CuMnSiCr. The microstructure, bonding strength, and high heat flux properties of the brazed W/CuCrZr joint samples were investigated. The W/Cu joint exhibits an average tensile strength of 134 MPa, which is about the same strength as pure annealed copper. High heat flux tests were performed in the electron beam facility EMS-60. Experimental results indicated that the brazed W/CuCrZr mock-up experienced screening tests of up to 15 MW/m2 and cyclic tests of 9 MW/m2 for 1000 cycles without visible damage. supported by National Natural Science Foundation of China (No. 11205049) and the National Magnetic Confinement Fusion Science Program of China (No. 2011GB110004)

  11. The Effect of TiO2 on the Wetting Behavior of Silver-copper Oxide Braze Filler Metals

    SciTech Connect

    Weil, K. Scott; Kim, Jin Yong Y.; Hardy, John S.; Darsell, Jens T.

    2006-03-01

    A series of silver-copper oxide ceramic brazing alloys was compositionally modified by doping with small amounts of titania. Subsequent contact angle measurements indicate that concentrations as low as 0.5 mol% TiO2 can significantly enhance wettability over a wide range of binary Ag-CuOx compositions.

  12. Study on the Microstructure and Wettability of an Al-Cu-Si Braze Containing Small Amounts of Rare Earth Erbium

    NASA Astrophysics Data System (ADS)

    Shi, Yaowu; Yu, Yang; Li, Yapeng; Xia, Zhidong; Lei, Yongping; Li, Xiaoyan; Guo, Fu

    2009-04-01

    The effect of adding small amounts of rare earth Er on the microstructure of an Al-Cu-Si braze alloy has been investigated. Several Al-20Cu-7Si braze alloys containing various contents of Er were prepared, and their melting temperature, microstructure, hardness, and wettability in contact with 3003 aluminum alloy substrates were determined. The results indicate that the constituents of the microstructure of Al-20Cu-7Si-Er braze alloys are similar to those in the Al-20Cu-7Si alloy, and comprise of solid solutions of aluminum, silicon, and the intermetallic compound CuAl2. When the Er content increases, the size of the Al phase decreases, and the needle-like Si phase is thickened, and transformed to a blocky shape. Moreover, small amounts of Er can improve the wettability and hardness of the Al-20Cu-7Si braze alloy; however, the melting temperature of the Al-20Cu-7Si alloy does not change.

  13. Active unsteady aerodynamic suppression of rotating stall in an incompressible flow centrifugal compressor with vaned diffuser

    NASA Technical Reports Server (NTRS)

    Lawless, Patrick B.; Fleeter, Sanford

    1991-01-01

    A mathematical model is developed to analyze the suppression of rotating stall in an incompressible flow centrifugal compressor with a vaned diffuser, thereby addressing the important need for centrifugal compressor rotating stall and surge control. In this model, the precursor to to instability is a weak rotating potential velocity perturbation in the inlet flow field that eventually develops into a finite disturbance. To suppress the growth of this potential disturbance, a rotating control vortical velocity disturbance is introduced into the impeller inlet flow. The effectiveness of this control is analyzed by matching the perturbation pressure in the compressor inlet and exit flow fields with a model for the unsteady behavior of the compressor. To demonstrate instability control, this model is then used to predict the control effectiveness for centrifugal compressor geometries based on a low speed research centrifugal compressor. These results indicate that reductions of 10 to 15 percent in the mean inlet flow coefficient at instability are possible with control waveforms of half the magnitude of the total disturbance at the inlet.

  14. Theory of activated glassy relaxation, mobility gradients, surface diffusion, and vitrification in free standing thin films

    SciTech Connect

    Mirigian, Stephen E-mail: smirigian@gmail.com; Schweizer, Kenneth S. E-mail: smirigian@gmail.com

    2015-12-28

    We have constructed a quantitative, force level, statistical mechanical theory for how confinement in free standing thin films introduces a spatial mobility gradient of the alpha relaxation time as a function of temperature, film thickness, and location in the film. The crucial idea is that relaxation speeds up due to the reduction of both near-surface barriers associated with the loss of neighbors in the local cage and the spatial cutoff and dynamical softening near the vapor interface of the spatially longer range collective elasticity cost for large amplitude hopping. These two effects are fundamentally coupled. Quantitative predictions are made for how an apparent glass temperature depends on the film thickness and experimental probe technique, the emergence of a two-step decay and mobile layers in time domain measurements, signatures of confinement in frequency-domain dielectric loss experiments, the dependence of film-averaged relaxation times and dynamic fragility on temperature and film thickness, surface diffusion, and the relationship between kinetic experiments and pseudo-thermodynamic measurements such as ellipsometry.

  15. Helicobacter pylori Couples Motility and Diffusion to Actively Create a Heterogeneous Complex Medium in Gastric Mucus

    NASA Astrophysics Data System (ADS)

    Mirbagheri, Seyed Amir; Fu, Henry Chien

    2016-05-01

    Helicobacter pylori swims through mucus gel by generating ammonia that locally neutralizes the acidic gastric environment, turning nearby gel into a fluid pocket. The size of the fluid zone is important for determining the physics of the motility: in a large zone swimming occurs as in a fluid through hydrodynamic principles, while in a very small zone the motility could be strongly influenced by nonhydrodynamic cell-mucus interactions including chemistry and adhesion. Here, we calculate the size of the fluid pocket. We model how swimming depends on the de-gelation range using a Taylor sheet swimming through a layer of Newtonian fluid bounded by a Brinkman fluid. Then, we model how the de-gelation range depends on the swimming speed by considering the advection-diffusion of ammonia exuded from a translating sphere. Self-consistency between both models determines the values of the swimming speed and the de-gelation range. We find that H. pylori swims through mucus as if unconfined, in a large pocket of Newtonian fluid.

  16. Generalized acoustic energy density based active noise control in single frequency diffuse sound fields.

    PubMed

    Xu, Buye; Sommerfeldt, Scott D

    2014-09-01

    In a diffuse sound field, prior research has established that a secondary source can theoretically achieve perfect cancellation at an error microphone in the far field of the secondary source. However, the sound pressure level is generally only reduced in a small zone around the error sensor, and at a distance half of a wavelength away from the error sensor, the averaged sound pressure level will be increased by more than 10 dB. Recently an acoustic energy quantity, referred to as the generalized acoustic energy density (GED), has been introduced. The GED is obtained by using a weighting factor in the formulation of total acoustic energy density. Different values of the weighting factor can be chosen for different applications. When minimizing the GED at the error sensor, one can adjust the weighting factor to increase the spatial extent of the "quiet zone" and to achieve a desired balance between the degree of attenuation in the quiet zone and the total energy added into the sound field. PMID:25190386

  17. Theory of activated glassy relaxation, mobility gradients, surface diffusion, and vitrification in free standing thin films.

    PubMed

    Mirigian, Stephen; Schweizer, Kenneth S

    2015-12-28

    We have constructed a quantitative, force level, statistical mechanical theory for how confinement in free standing thin films introduces a spatial mobility gradient of the alpha relaxation time as a function of temperature, film thickness, and location in the film. The crucial idea is that relaxation speeds up due to the reduction of both near-surface barriers associated with the loss of neighbors in the local cage and the spatial cutoff and dynamical softening near the vapor interface of the spatially longer range collective elasticity cost for large amplitude hopping. These two effects are fundamentally coupled. Quantitative predictions are made for how an apparent glass temperature depends on the film thickness and experimental probe technique, the emergence of a two-step decay and mobile layers in time domain measurements, signatures of confinement in frequency-domain dielectric loss experiments, the dependence of film-averaged relaxation times and dynamic fragility on temperature and film thickness, surface diffusion, and the relationship between kinetic experiments and pseudo-thermodynamic measurements such as ellipsometry. PMID:26723700

  18. Theory of activated glassy relaxation, mobility gradients, surface diffusion, and vitrification in free standing thin films

    NASA Astrophysics Data System (ADS)

    Mirigian, Stephen; Schweizer, Kenneth S.

    2015-12-01

    We have constructed a quantitative, force level, statistical mechanical theory for how confinement in free standing thin films introduces a spatial mobility gradient of the alpha relaxation time as a function of temperature, film thickness, and location in the film. The crucial idea is that relaxation speeds up due to the reduction of both near-surface barriers associated with the loss of neighbors in the local cage and the spatial cutoff and dynamical softening near the vapor interface of the spatially longer range collective elasticity cost for large amplitude hopping. These two effects are fundamentally coupled. Quantitative predictions are made for how an apparent glass temperature depends on the film thickness and experimental probe technique, the emergence of a two-step decay and mobile layers in time domain measurements, signatures of confinement in frequency-domain dielectric loss experiments, the dependence of film-averaged relaxation times and dynamic fragility on temperature and film thickness, surface diffusion, and the relationship between kinetic experiments and pseudo-thermodynamic measurements such as ellipsometry.

  19. Vacuum brazing of alumina ceramic to titanium for biomedical implants using pure gold as the filler metal

    NASA Astrophysics Data System (ADS)

    Siddiqui, Mohammad S.

    One of the many promising applications of metal/ceramic joining is in biomedical implantable devices. This work is focused on vacuum brazing of C.P titanium to 96% alumina ceramic using pure gold as the filler metal. A novel method of brazing is developed where resistance heating of C.P titanium is done inside a thermal evaporator using a Ta heating electrode. The design of electrode is optimized using Ansys resistive heating simulations. The materials chosen in this study are biocompatible and have prior history in implantable devices approved by FDA. This research is part of Boston Retinal implant project to make a biocompatible implantable device (www.bostonretina.org). Pure gold braze has been used in the construction of single terminal feedthrough in low density hermetic packages utilizing a single platinum pin brazed to an alumina or sapphire ceramic donut (brazed to a titanium case or ferrule for many years in implantable pacemakers. Pure gold (99.99%) brazing of 96% alumina ceramic with CP titanium has been performed and evaluated in this dissertation. Brazing has been done by using electrical resistance heating. The 96% alumina ceramic disk was manufactured by high temperature cofired ceramic (HTCC) processing while the Ti ferrule and gold performs were purchased from outside. Hermetic joints having leak rate of the order of 1.6 x 10-8 atm-cc/ sec on a helium leak detector were measured. Alumina ceramics made by HTCC processing were centreless grounded utilizing 800 grit diamond wheel to provide a smooth surface for sputtering of a thin film of Nb. Since pure alumina demonstrates no adhesion or wetting to gold, an adhesion layer must be used on the alumina surface. Niobium (Nb), Tantalum (Ta) and Tungsten (W) were chosen for evaluation since all are refractory (less dissolution into molten gold), all form stable oxides (necessary for adhesion to alumina) and all are readily thin film deposited as metals. Wetting studies are also performed to determine the

  20. Formation of α-alumina scales in the Fe-Al(Cr) diffusion coating on China low activation martensitic steel

    NASA Astrophysics Data System (ADS)

    Zhan, Qin; Zhao, Weiwei; Yang, Hongguang; Hatano, Yuji; Yuan, Xiaoming; Nozaki, Teo; Zhu, Xinxin

    2015-09-01

    To study the formation mechanism of stable α-Al2O3 scales, the oxidation behavior of Fe-Al(Cr) diffusion coating on China low activation martensitic steel has been investigated under the oxygen partial pressure ranging from 1 to 20,000 Pa at 1253 K. A single, continuous Al2O3 scale with the maximum thickness of about 2000 nm was formed on the Fe-Al(Cr) diffusion layer. The phase transformation of alumina scales on the surface of Fe-Al(Cr) layer was studied at different oxidation times ranging from 3 to 180 min. With the increase in oxygen partial pressure, the phase transformation time of α-Al2O3 is decreased. The metastable γ-Al2O3 and transition α-(Al0.948Cr0.052)2O3 phases were formed in the earlier oxidation process and finally transformed to the stable α-Al2O3 phase, which were detected by grazing incidence angle X-ray diffraction and confirmed by transmission electron microscopy. This implies that Cr shows the third element effect and serves as a template for the nucleation of the stable α-Al2O3.

  1. Brazing of ceramic and graphite to metal in the fabrication of ICRF (ion cyclotron range of frequencies) antenna and feedthrough components

    SciTech Connect

    Schechter, D.E.; Sluss, F.; Hoffman, D.J.

    1987-01-01

    Fabrication of some of the more critical components of ion cyclotron range of frequencies (ICRF) antenna and feedthrough assemblies has involved the brazing of alumina ceramic and graphite to various metals. Copper end pieces have been successfully brazed to alumina cylinders for use in feedthroughs for TEXTOR and in feedthroughs and capacitors for a Tokamak Fusion Test Reactor (TFTR) antenna. Copper-plated Inconel rods and tubes have been armored with graphite for construction of Faraday shields on antennas for Doublet III-D and TFTR. Details of brazing procedures and test results, including rf performance, mechanical strength, and thermal capabilities, are presented. 14 figs.

  2. Increasing Ti-6Al-4V brazed joint strength equal to the base metal by Ti and Zr amorphous filler alloys

    SciTech Connect

    Ganjeh, E.; Sarkhosh, H.; Bajgholi, M.E.; Khorsand, H.; Ghaffari, M.

    2012-09-15

    Microstructural features developed along with mechanical properties in furnace brazing of Ti-6Al-4V alloy using STEMET 1228 (Ti-26.8Zr-13Ni-13.9Cu, wt.%) and STEMET 1406 (Zr-9.7Ti-12.4Ni-11.2Cu, wt.%) amorphous filler alloys. Brazing temperatures employed were 900-950 Degree-Sign C for the titanium-based filler and 900-990 Degree-Sign C for the zirconium-based filler alloys, respectively. The brazing time durations were 600, 1200 and 1800 s. The brazed joints were evaluated by ultrasonic test, and their microstructures and phase constitutions analyzed by metallography, scanning electron microscopy and X-ray diffraction analysis. Since microstructural evolution across the furnace brazed joints primarily depends on their alloying elements such as Cu, Ni and Zr along the joint. Accordingly, existence of Zr{sub 2}Cu, Ti{sub 2}Cu and (Ti,Zr){sub 2}Ni intermetallic compounds was identified in the brazed joints. The chemical composition of segregation region in the center of brazed joints was identical to virgin filler alloy content which greatly deteriorated the shear strength of the joints. Adequate brazing time (1800 s) and/or temperature (950 Degree-Sign C for Ti-based and 990 Degree-Sign C for Zr-based) resulted in an acicular Widmanstaetten microstructure throughout the entire joint section due to eutectoid reaction. This microstructure increased the shear strength of the brazed joints up to the Ti-6Al-4V tensile strength level. Consequently, Ti-6Al-4V can be furnace brazed by Ti and Zr base foils produced excellent joint strengths. - Highlights: Black-Right-Pointing-Pointer Temperature or time was the main factors of controlling braze joint strength. Black-Right-Pointing-Pointer Developing a Widmanstaetten microstructure generates equal strength to base metal. Black-Right-Pointing-Pointer Brittle intermetallic compounds like (Ti,Zr){sub 2}Ni/Cu deteriorate shear strength. Black-Right-Pointing-Pointer Ti and Zr base filler alloys were the best choice for brazing Ti

  3. Pore Pressure Diffusion as a possible mechanism for the Ag. Ioanis 2001 earthquake swarm activity (Gulf of Corinth, Central Greece).

    NASA Astrophysics Data System (ADS)

    Vallianatos, F.; Michas, G.; Papadakis, G.; Sammonds, P.

    2012-04-01

    The Gulf of Corinth rift (Central Greece) is one of the most seismotectonically active areas in Europe (Ambraseys and Jackson, 1990; 1997), with an important continental N-S extension of about 13 mm/yr and 6 mm/yr at the west and east part respectively (Clarke et al., 1997a). The seismicity of the area includes 5 main earthquakes of magnitude greater than 5.8 since 1960. In the western part of the rift, where the extension reaches its maximum value, earthquake swarms are often being observed (Bourouis and Cornet, 2009). Such an earthquake crisis has been occurred on 2001 at the southern margin of the west part of the rift. The crisis lasted about 100 days with a major event the Ag. Ioanis earthquake (4.3 Mw) on 8th of April 2001 (Pacchiani and Lyon-Caen, 2010). The possible relation between fluids flow and the observed earthquake swarms at the west part of the Gulf of Corinth rift has been discussed in the works of Bourouis and Cornet (2009) and Pacchiani and Lyon-Caen (2010). In the present work we examine the spatiotemporal properties of the Ag. Ioanis 2001 earthquake swarm, using data from the CRL network (http://crlab.eu/). We connect these properties to a mechanism due to pore pressure diffusion (Shapiro et al., 1997) and we estimate the hydraulic diffusivity and the permeability of the surrounding rocks. A back front of the seismicity (Parotidis et al., 2004) is also been observed, related to the migration of seismicity and the development of a quiescence region near the area of the initial pore pressure perturbation. Moreover, anisotropy of the hydraulic diffusivity has been observed, revealing the heterogeneity of the surrounding rocks and the fracture systems. This anisotropy is consistent in direction with the fault zone responsible for the Ag. Ioanis earthquake (Pacchiani and Lyon-Caen, 2010). Our results indicate that fluids flow and pore pressure perturbations are possible mechanisms for the initiation and the evolution of the Ag. Ioanis 2001

  4. Influence of different brazing and welding methods on tensile strength and microhardness of orthodontic stainless steel wire.

    PubMed

    Bock, Jens Johannes; Fraenzel, Wolfgang; Bailly, Jacqueline; Gernhardt, Christian Ralf; Fuhrmann, Robert Andreas Werner

    2008-08-01

    The aim of this study was to compare the mechanical strength and microhardness of joints made by conventional brazing and tungsten inert gas (TIG) and laser welding. A standardized end-to-end joint configuration of the orthodontic wire material in spring hard quality was used. The joints were made using five different methods: brazing (soldering > 450 degrees C) with universal silver solder, two TIG, and two laser welders. Laser parameters and welding conditions were used according to the manufacturers' guidance. The tensile strengths were measured with a universal testing machine (Zwick 005). The microhardness measurements were carried out with a hardness tester (Zwick 3202). Data were analysed using one-way analysis of variance and Bonferroni's post hoc correction (P < 0.05). In all cases, brazing joints ruptured at low levels of tensile strength (198 +/- 146 MPa). Significant differences (P < 0.001) between brazing and TIG or laser welding were found. The highest means were observed for TIG welding (699-754 MPa). Laser welding showed a significantly lower mean tensile strength (369-520 MPa) compared with TIG welding. Significant differences (P < 0.001) were found between the original orthodontic wire and the mean microhardness at the centre of the welded area. The mean microhardness differed significantly between brazing (1.99 GPa), TIG (2.22-2.39 GPa) and laser welding (2.21-2.68 GPa). For orthodontic purposes, laser and TIG welding are solder-free alternatives to joining metal. TIG welding with a lower investment cost is comparable with laser welding. However, while expensive, the laser technique is a sophisticated and simple method. PMID:18617503

  5. Atomic structure and thermophysical properties of molten silver-copper oxide air braze alloys

    NASA Astrophysics Data System (ADS)

    Hardy, John Steven

    The Ag-CuOx materials system is the basis for a family of filler alloys used in a recently developed ceramic-metal joining technique referred to as air brazing, which is a brazing process that can be carried out in ambient air rather than under the vacuum or inert to reducing gas conditions required for conventional brazing methods. This research was conducted to elucidate the atomic coordination and selected thermophysical properties of these materials as a function of temperature when they are in the salient liquid state in air, since this is when the critical steps of wetting and spreading occur in the joining process. A series of alloys was selected spanning the entire length of the phase diagram including the pure end members, Ag and CuOx; alloys that form the two constituent single phase liquids; and alloys for which the two liquid phases coexist in the miscibility gap of the phase diagram. The oxygen content of the liquid alloys in air was measured using thermogravimetry. The oxidative weight gain of 99.999% pure metallic precursors was measured while simultaneously accounting for the concurrent silver volatility using a method that was developed in the course of the study. The surface tension and mass density were measured using the maximum bubble pressure method. The number density was calculated based on the information gained from the oxygen content and mass density measurements. For compositions that were amenable to laser heating, containerless high energy x-ray scattering measurements of the liquid atomic coordination were performed using a synchrotron beamline, an aerodynamic levitator, and laser heating. For the remaining compositions x-ray scattering measurements were performed in a beamline-compatible furnace. The two liquid phases that form in this materials system have distinct atomic coordinations characterized by an average of nearly two-fold coordinated ionic metal-oxygen pairs in the CuOx-rich liquid and nearly eight-fold coordinated atomic

  6. Association and Diffusion of Nutrition and Physical Activity Policies on the State and District Level

    ERIC Educational Resources Information Center

    Taber, Daniel R.; Chriqui, Jamie F.; Chaloupka, Frank J.

    2012-01-01

    Background: School district wellness policies designed to reduce obesity and promote student health and well-being often lack specific requirements or any mandate that schools comply with the policy. Researchers, educators, and policymakers have called for states to take an active role in shaping district policies. The objective of this study was…

  7. Hydrogen activation, diffusion, and clustering on CeO{sub 2}(111): A DFT+U study

    SciTech Connect

    Fernández-Torre, Delia

    2014-07-07

    We present a comprehensive density functional theory+U study of the mechanisms underlying the dissociation of molecular hydrogen, and diffusion and clustering of the resulting atomic species on the CeO{sub 2}(111) surface. Contrary to a widely held view based solely on a previous theoretical prediction, our results show conclusively that H{sub 2} dissociation is an activated process with a large energy barrier ∼1.0 eV that is not significantly affected by coverage or the presence of surface oxygen vacancies. The reaction proceeds through a local energy minimum – where the molecule is located close to one of the surface oxygen atoms and the H–H bond has been substantially weaken by the interaction with the substrate –, and a transition state where one H atom is attached to a surface O atom and the other H atom sits on-top of a Ce{sup 4+} ion. In addition, we have explored how several factors, including H coverage, the location of Ce{sup 3+} ions as well as the U value, may affect the chemisorption energy and the relative stability of isolated OH groups versus pair and trimer structures. The trimer stability at low H coverages and the larger upward relaxation of the surface O atoms within the OH groups are consistent with the assignment of the frequent experimental observation by non-contact atomic force and scanning tunneling microscopies of bright protrusions on three neighboring surface O atoms to a triple OH group. The diffusion path of isolated H atoms on the surface goes through the adsorption on-top of an oxygen in the third atomic layer with a large energy barrier of ∼1.8 eV. Overall, the large energy barriers for both, molecular dissociation and atomic diffusion, are consistent with the high activity and selectivity found recently in the partial hydrogenation of acetylene catalyzed by ceria at high H{sub 2}/C{sub 2}H{sub 2} ratios.

  8. 2-165 keV observations of active galaxies and the diffuse background

    NASA Technical Reports Server (NTRS)

    Rothschild, R. E.; Baity, W. A.; Gruber, D. E.; Matteson, J. L.; Peterson, L. E.; Mushotzky, R. F.

    1983-01-01

    HEAO 1 spectral observations of 12 active galaxies in the 12-165 keV and 2-50 keV ranges are reported. The spectra of these galaxies in the 2-165 keV range are well represented by a single power law model; within experimental uncertainties a narrow dispersion in power law index attributable to the individual galaxies is observed, while the 2-165 keV luminosities of these galaxies ranged from 3 x 10 to the 43rd to 3 x 10 to the 45th ergs/s. An apparent universality of the spectral form is found which can be interpreted as due to a common electron distribution with a temperature of tens of keV in the Compton scattering region or as a common nonthermal power-law distribution generating the observed flux through synchrotron-Compton processes. The data indicate that relativistic particles are likely to be responsible for the X-rays from cores of active galaxies through synchroton-Compton processes. In addition, it is noted that only weak number evolution, if any at all, is present in active galaxies.

  9. Diffusion barriers in the kinetics of water vapor adsorption/desorption on activated carbons

    SciTech Connect

    Harding, A.W.; Foley, N.J.; Thomas, K.M.; Norman, P.R.; Francis, D.C.

    1998-07-07

    The adsorption of water vapor on a highly microporous coconut-shell-derived carbon and a mesoporous wood-derived carbon was studied. These carbons were chosen as they had markedly different porous structures. The adsorption and desorption characteristics of water vapor on the activated carbons were investigated over the relative pressure range p/p{degree} = 0--0.9 for temperatures in the range 285--313 K in a static water vapor system. The adsorption isotherms were analyzed using the Dubinin-Serpinski equation, and this provided an assessment of the polarity of the carbons. The kinetics of water vapor adsorption and desorption were studied with different amounts of preadsorbed water for set changes in pressure relative to the saturated vapor pressure (p/p{degree}). The adsorption kinetics for each relative pressure step were compared and used to calculate the activation energies for the vapor pressure increments. The kinetic results are discussed in relation to their relative position on the equilibrium isotherm and the adsorption mechanism of water vapor on activated carbons.

  10. Constitutive activation of the DNA damage response pathway as a novel therapeutic target in diffuse large B-cell lymphoma

    PubMed Central

    Derenzini, Enrico; Agostinelli, Claudio; Imbrogno, Enrica; Iacobucci, Ilaria; Casadei, Beatrice; Brighenti, Elisa; Righi, Simona; Fuligni, Fabio; Di Rorà, Andrea Ghelli Luserna; Ferrari, Anna; Martinelli, Giovanni; Pileri, Stefano; Zinzani, Pier Luigi

    2015-01-01

    The recent finding that MYC-driven cancers are sensitive to inhibition of the DNA damage response (DDR) pathway, prompted us to investigate the role of DDR pathway as therapeutic target in diffuse large B-cell lymphoma (DLBCL), which frequently overexpresses the MYC oncogene. In a preliminary immunohistochemical study conducted on 99 consecutive DLBCL patients, we found that about half of DLBCLs showed constitutive expression of the phosphorylated forms of checkpoint kinases (CHK) and CDC25c, markers of DDR activation, and of phosphorylated histone H2AX (γH2AX), marker of DNA damage and genomic instability. Constitutive γH2AX expression correlated with c-MYC levels and DDR activation, and defined a subset of tumors characterised by poor outcome. Next, we used the CHK inhibitor PF-0477736 as a tool to investigate whether the inhibition of the DDR pathway might represent a novel therapeutic approach in DLBCL. Submicromolar concentrations of PF-0477736 hindered proliferation in DLBCL cell lines with activated DDR pathway. These results were fully recapitulated with a different CHK inhibitor (AZD-7762). Inhibition of checkpoint kinases induced rapid DNA damage accumulation and apoptosis in DLBCL cell lines and primary cells. These data suggest that pharmacologic inhibition of DDR through targeting of CHK kinases may represent a novel therapeutic strategy in DLBCL. PMID:25544753

  11. Constitutive activation of the DNA damage response pathway as a novel therapeutic target in diffuse large B-cell lymphoma.

    PubMed

    Derenzini, Enrico; Agostinelli, Claudio; Imbrogno, Enrica; Iacobucci, Ilaria; Casadei, Beatrice; Brighenti, Elisa; Righi, Simona; Fuligni, Fabio; Ghelli Luserna Di Rorà, Andrea; Ferrari, Anna; Martinelli, Giovanni; Pileri, Stefano; Zinzani, Pier Luigi

    2015-03-30

    The recent finding that MYC-driven cancers are sensitive to inhibition of the DNA damage response (DDR) pathway, prompted us to investigate the role of DDR pathway as therapeutic target in diffuse large B-cell lymphoma (DLBCL), which frequently overexpresses the MYC oncogene. In a preliminary immunohistochemical study conducted on 99 consecutive DLBCL patients, we found that about half of DLBCLs showed constitutive expression of the phosphorylated forms of checkpoint kinases (CHK) and CDC25c, markers of DDR activation, and of phosphorylated histone H2AX (γH2AX), marker of DNA damage and genomic instability. Constitutive γH2AX expression correlated with c-MYC levels and DDR activation, and defined a subset of tumors characterised by poor outcome. Next, we used the CHK inhibitor PF-0477736 as a tool to investigate whether the inhibition of the DDR pathway might represent a novel therapeutic approach in DLBCL. Submicromolar concentrations of PF-0477736 hindered proliferation in DLBCL cell lines with activated DDR pathway. These results were fully recapitulated with a different CHK inhibitor (AZD-7762). Inhibition of checkpoint kinases induced rapid DNA damage accumulation and apoptosis in DLBCL cell lines and primary cells. These data suggest that pharmacologic inhibition of DDR through targeting of CHK kinases may represent a novel therapeutic strategy in DLBCL. PMID:25544753

  12. Structural Design and Preliminary Evaluation of a Lightweight, Brazed, Air-Cooled Turbine Rotor Assembly

    NASA Technical Reports Server (NTRS)

    Meyer, Andre J., Jr.; Morgan, William C.

    1958-01-01

    A lightweight turbine rotor assembly was devised, and components were evaluated in a full-scale jet engine. Thin sheet-metal airfoils were brazed to radial fingers that were an integral part of a number of thin disks composing the turbine rotor. Passages were provided between the disks and in the blades for air cooling. The computed weight of the assembly was 50 percent less than that of a similar turbine of normal construction used in a conventional turbojet engine. Two configurations of sheet-metal test blades simulating the manner of attachment were fabricated and tested in a turbojet engine at rated speed and temperature. After 8-1/2 hours of operation pieces broke loose from the tip sections of the better blades. Severe cracking produced by vibration was determined as the cause of failure. Several methods of overcoming the vibration problem are suggested.

  13. Design and fabrication of brazed Rene 41 honeycomb sandwich structural panels for advanced space transportation systems

    NASA Technical Reports Server (NTRS)

    Hepler, A. K.; Swegle, A. R.

    1981-01-01

    The design and fabrication of two large brazed Rene 41 honeycomb panels, the establishment of a test plan, the design and fabrication of a test fixture to subject the panels to cyclic thermal gradients and mechanical loads equivalent to those imposed on an advanced space transportation vehicle during its boost and entry trajectories are discussed. The panels will be supported at four points, creating three spans. The outer spans are 45.7 cm (18 in.) and the center span 76.2 cm (30 in). Specimen width is 30.5 cm (12 in.). The panels were primarily designed by boost conditions simulated by subjecting the panels to liquid nitrogen, 77K (-320 F) on one side and 455K (360 F) on the other side and by mechanically imposing loads representing vehicle fuel pressure loads. Entry conditions were simulated by radiant heating to 1034K (1400 F). The test program subjected the panels to 500 boost thermal conditions. Results are presented.

  14. Heat transfer and flow characteristics of automotive brazed aluminum heat exchangers

    SciTech Connect

    Chang, Y.J.; Wang, C.C.; Chang, W.J.

    1994-12-31

    Extensive experiments on the heat transfer and pressure-drop characteristics of automotive brazed aluminum heat exchangers were carried out. In the present study, 18 samples of louvered-fin heat exchangers with different geometrical parameters, including tube width, louver length, louver pitch, fin height, and fin pitch, were tested in an induced open wind tunnel. Results are presented as plots of friction factor and Colburn j-factor against Reynolds number based on the volumetric hydraulic diameter in the range of 200 to 1,600. The comparisons between the Sahnoun and Webb model and the present test data are reported and good agreement was found. By introducing a finning factor, a simpler correlation of the Colburn j-factor is obtained. The heat transfer data for the Colburn j-factor are correlated within 10%, and those for the friction factor are within 15%.

  15. Nonlinear thermal and structural analysis of a brazed solar-central-receiver panel

    SciTech Connect

    Napolitano, L.M. Jr.; Kanouff, M.P.

    1981-07-01

    One part of the evaluation program for a molten sodium central receiver was to be a test of a reduced-scale panel at Sandia's Central Receiver Test Facility in Albuquerque. The panel incorporates a new way of joining tubes - brazing to intermediate filler strips - which can affect the panel's lifetime. To calculate the stresses and strains for the worst-case section of the experimental panel, we have done a nonlinear elastic-plastic analysis with the MARC finite element computer code, which takes the temperature dependence of the material properties into account. From the results, tube design lifetimes are predicted. The analysis shows that concerns for cracking and reduction in lifetime are warranted, but a more detailed fracture analysis is necessary to determine whether there is a stable-crack-growth problem.

  16. Diffuse neutrino intensity from the inner jets of active galactic nuclei: Impacts of external photon fields and the blazar sequence

    NASA Astrophysics Data System (ADS)

    Murase, Kohta; Inoue, Yoshiyuki; Dermer, Charles D.

    2014-07-01

    We study high-energy neutrino production in inner jets of radio-loud active galactic nuclei (AGN), taking into account effects of external photon fields and the blazar sequence. We show that the resulting diffuse neutrino intensity is dominated by quasar-hosted blazars, in particular, flat spectrum radio quasars, and that PeV-EeV neutrino production due to photohadronic interactions with broadline and dust radiation is unavoidable if the AGN inner jets are ultrahigh-energy cosmic-ray (UHECR) sources. Their neutrino spectrum has a cutoff feature around PeV energies since target photons are due to Lyα emission. Because of infrared photons provided by the dust torus, neutrino spectra above PeV energies are too hard to be consistent with the IceCube data unless the proton spectral index is steeper than 2.5, or the maximum proton energy is ≲100 PeV. Thus, the simple model has difficulty in explaining the IceCube data. For the cumulative neutrino intensity from blazars to exceed ˜10-8 GeV cm-2 s-1 sr-1, their local cosmic-ray energy generation rate would be ˜10-100 times larger than the local UHECR emissivity but is comparable to the averaged γ-ray blazar emissivity. Interestingly, future detectors such as the Askaryan Radio Array can detect ˜0.1-1 EeV neutrinos even in more conservative cases, allowing us to indirectly test the hypothesis that UHECRs are produced in the inner jets. We find that the diffuse neutrino intensity from radio-loud AGN is dominated by blazars with γ-ray luminosity of ≳1048 erg s-1, and the arrival directions of their ˜1-100 PeV neutrinos correlate with the luminous blazars detected by Fermi.

  17. Distinct isoform of FABP7 revealed by screening for retroelement-activated genes in diffuse large B-cell lymphoma.

    PubMed

    Lock, Frances E; Rebollo, Rita; Miceli-Royer, Katharine; Gagnier, Liane; Kuah, Sabrina; Babaian, Artem; Sistiaga-Poveda, Maialen; Lai, C Benjamin; Nemirovsky, Oksana; Serrano, Isabel; Steidl, Christian; Karimi, Mohammad M; Mager, Dixie L

    2014-08-26

    Remnants of ancient transposable elements (TEs) are abundant in mammalian genomes. These sequences harbor multiple regulatory motifs and hence are capable of influencing expression of host genes. In response to environmental changes, TEs are known to be released from epigenetic repression and to become transcriptionally active. Such activation could also lead to lineage-inappropriate activation of oncogenes, as one study described in Hodgkin lymphoma. However, little further evidence for this mechanism in other cancers has been reported. Here, we reanalyzed whole transcriptome data from a large cohort of patients with diffuse large B-cell lymphoma (DLBCL) compared with normal B-cell centroblasts to detect genes ectopically expressed through activation of TE promoters. We have identified 98 such TE-gene chimeric transcripts that were exclusively expressed in primary DLBCL cases and confirmed several in DLBCL-derived cell lines. We further characterized a TE-gene chimeric transcript involving a fatty acid-binding protein gene (LTR2-FABP7), normally expressed in brain, that was ectopically expressed in a subset of DLBCL patients through the use of an endogenous retroviral LTR promoter of the LTR2 family. The LTR2-FABP7 chimeric transcript encodes a novel chimeric isoform of the protein with characteristics distinct from native FABP7. In vitro studies reveal a dependency for DLBCL cell line proliferation and growth on LTR2-FABP7 chimeric protein expression. Taken together, these data demonstrate the significance of TEs as regulators of aberrant gene expression in cancer and suggest that LTR2-FABP7 may contribute to the pathogenesis of DLBCL in a subgroup of patients. PMID:25114248

  18. Distinct isoform of FABP7 revealed by screening for retroelement-activated genes in diffuse large B-cell lymphoma

    PubMed Central

    Lock, Frances E.; Rebollo, Rita; Miceli-Royer, Katharine; Gagnier, Liane; Kuah, Sabrina; Babaian, Artem; Sistiaga-Poveda, Maialen; Lai, C. Benjamin; Nemirovsky, Oksana; Serrano, Isabel; Steidl, Christian; Karimi, Mohammad M.; Mager, Dixie L.

    2014-01-01

    Remnants of ancient transposable elements (TEs) are abundant in mammalian genomes. These sequences harbor multiple regulatory motifs and hence are capable of influencing expression of host genes. In response to environmental changes, TEs are known to be released from epigenetic repression and to become transcriptionally active. Such activation could also lead to lineage-inappropriate activation of oncogenes, as one study described in Hodgkin lymphoma. However, little further evidence for this mechanism in other cancers has been reported. Here, we reanalyzed whole transcriptome data from a large cohort of patients with diffuse large B-cell lymphoma (DLBCL) compared with normal B-cell centroblasts to detect genes ectopically expressed through activation of TE promoters. We have identified 98 such TE-gene chimeric transcripts that were exclusively expressed in primary DLBCL cases and confirmed several in DLBCL-derived cell lines. We further characterized a TE-gene chimeric transcript involving a fatty acid-binding protein gene (LTR2-FABP7), normally expressed in brain, that was ectopically expressed in a subset of DLBCL patients through the use of an endogenous retroviral LTR promoter of the LTR2 family. The LTR2-FABP7 chimeric transcript encodes a novel chimeric isoform of the protein with characteristics distinct from native FABP7. In vitro studies reveal a dependency for DLBCL cell line proliferation and growth on LTR2-FABP7 chimeric protein expression. Taken together, these data demonstrate the significance of TEs as regulators of aberrant gene expression in cancer and suggest that LTR2-FABP7 may contribute to the pathogenesis of DLBCL in a subgroup of patients. PMID:25114248

  19. M-CSF receptor mutations in hereditary diffuse leukoencephalopathy with spheroids impair not only kinase activity but also surface expression

    SciTech Connect

    Hiyoshi, Masateru; Hashimoto, Michihiro; Yukihara, Mamiko; Bhuyan, Farzana; Suzu, Shinya

    2013-11-01

    Highlights: •Many mutations were identified in Fms as a putative genetic cause of HDLS. •All of the mutations tested severely impair the kinase activity. •Most of the mutations also impair the trafficking to the cell surface. •These defects further suggest that HDLS is caused by a loss of Fms function. -- Abstract: The tyrosine kinase Fms, the cell surface receptor for M-CSF and IL-34, is critical for microglial proliferation and differentiation in the brain. Recently, a number of mutations have been identified in Fms as a putative genetic cause of hereditary diffuse leukoencephalopathy with spheroids (HDLS), implying an important role of microglial dysfunction in HDLS pathogenesis. In this study, we initially confirmed that 11 mutations, which reside within the ATP-binding or major tyrosine kinase domain, caused a severe impairment of ligand-induced Fms auto-phosphorylation. Intriguingly, we found that 10 of the 11 mutants also showed a weak cell surface expression, which was associated with a concomitant increase in the low molecular weight hypo-N-glycosylated immature gp130Fms-like species. Indeed, the mutant proteins heavily accumulated to the Golgi-like perinuclear regions. These results indicate that all of the Fms mutations tested severely impair the kinase activity and most of the mutations also impair the trafficking to the cell surface, further suggesting that HDLS is caused by the loss of Fms function.

  20. Simultaneous EEG and diffuse optical imaging of seizure-related hemodynamic activity in the newborn infant brain

    NASA Astrophysics Data System (ADS)

    Hebden, Jeremy C.; Cooper, Robert J.; Gibson, Adam; Everdell, Nick; Austin, Topun

    2012-06-01

    An optical imaging system has been developed which uses measurements of diffusely reflected near-infrared light to produce maps of changes in blood flow and oxygenation occurring within the cerebral cortex. Optical sources and detectors are coupled to the head via an array of optical fibers, on a probe held in contact with the scalp, and data is collected at a rate of 10 Hz. A clinical electroencephalography (EEG) system has been integrated with the optical system to enable simultaneous observation of electrical and hemodynamic activity in the cortex of neurologically compromised newborn infants diagnosed with seizures. Studies have made a potentially critically important discovery of previously unknown transient hemodynamic events in infants treated with anticonvulsant medication. We observed repeated episodes of small increases in cortical oxyhemoglobin concentration followed by a profound decrease in 3 of 4 infants studied, each with cerebral injury who presented with neonatal seizures. This was not accompanied by clinical or EEG seizure activity and was not present in nineteen matched controls. The underlying cause of these changes is currently unknown. We tentatively suggest that our results may be associated with a phenomenon known as cortical spreading depolarization, not previously observed in the infant brain.

  1. Genomic analysis of diffuse intrinsic pontine gliomas identifies three molecular subgroups and recurrent activating ACVR1 mutations

    PubMed Central

    Buczkowicz, Pawel; Hoeman, Christine; Rakopoulos, Patricia; Pajovic, Sanja; Letourneau, Louis; Dzamba, Misko; Morrison, Andrew; Lewis, Peter; Bouffet, Eric; Bartels, Ute; Zuccaro, Jennifer; Agnihotri, Sameer; Ryall, Scott; Barszczyk, Mark; Chornenkyy, Yevgen; Bourgey, Mathieu; Bourque, Guillaume; Montpetit, Alexandre; Cordero, Francisco; Castelo-Branco, Pedro; Mangerel, Joshua; Tabori, Uri; Ho, King Ching; Huang, Annie; Taylor, Kathryn R.; Mackay, Alan; Bendel, Anne E; Nazarian, Javad; Fangusaro, Jason R; Karajannis, Matthias A.; Zagzag, David; Foreman, Nicholas K.; Donson, Andrew; Hegert, Julia V.; Smith, Amy; Chan, Jennifer; Lafay-Cousin, Lucy; Dunn, Sandra; Hukin, Juliette; Dunham, Chris; Scheinemann, Katrin; Michaud, Jean; Zelcer, Shayna; Ramsay, David; Cain, Jason; Brennan, Cameron; Souweidane, Mark M.; Jones, Chris; Allis, C. David; Brudno, Michael; Becher, Oren; Hawkins, Cynthia

    2014-01-01

    Diffuse Intrinsic Pontine Glioma (DIPG) is a fatal brain cancer that arises in the brainstem of children with no effective treatment and near 100% fatality. The failure of most therapies can be attributed to the delicate location of these tumors and choosing therapies based on assumptions that DIPGs are molecularly similar to adult disease. Recent studies have unraveled the unique genetic make-up of this brain cancer with nearly 80% harboring a K27M-H3.3 or K27M-H3.1 mutation. However, DIPGs are still thought of as one disease with limited understanding of the genetic drivers of these tumors. To understand what drives DIPGs we integrated whole-genome-sequencing with methylation, expression and copy-number profiling, discovering that DIPGs are three molecularly distinct subgroups (H3-K27M, Silent, MYCN) and uncovering a novel recurrent activating mutation in the activin receptor ACVR1, in 20% of DIPGs. Mutations in ACVR1 were constitutively activating, leading to SMAD phosphorylation and increased expression of downstream activin signaling targets ID1 and ID2. Our results highlight distinct molecular subgroups and novel therapeutic targets for this incurable pediatric cancer. PMID:24705254

  2. Combining energy and Laplacian regularization to accurately retrieve the depth of brain activity of diffuse optical tomographic data

    NASA Astrophysics Data System (ADS)

    Chiarelli, Antonio M.; Maclin, Edward L.; Low, Kathy A.; Mathewson, Kyle E.; Fabiani, Monica; Gratton, Gabriele

    2016-03-01

    Diffuse optical tomography (DOT) provides data about brain function using surface recordings. Despite recent advancements, an unbiased method for estimating the depth of absorption changes and for providing an accurate three-dimensional (3-D) reconstruction remains elusive. DOT involves solving an ill-posed inverse problem, requiring additional criteria for finding unique solutions. The most commonly used criterion is energy minimization (energy constraint). However, as measurements are taken from only one side of the medium (the scalp) and sensitivity is greater at shallow depths, the energy constraint leads to solutions that tend to be small and superficial. To correct for this bias, we combine the energy constraint with another criterion, minimization of spatial derivatives (Laplacian constraint, also used in low resolution electromagnetic tomography, LORETA). Used in isolation, the Laplacian constraint leads to solutions that tend to be large and deep. Using simulated, phantom, and actual brain activation data, we show that combining these two criteria results in accurate (error <2 mm) absorption depth estimates, while maintaining a two-point spatial resolution of <24 mm up to a depth of 30 mm. This indicates that accurate 3-D reconstruction of brain activity up to 30 mm from the scalp can be obtained with DOT.

  3. Genomic analysis of diffuse intrinsic pontine gliomas identifies three molecular subgroups and recurrent activating ACVR1 mutations.

    PubMed

    Buczkowicz, Pawel; Hoeman, Christine; Rakopoulos, Patricia; Pajovic, Sanja; Letourneau, Louis; Dzamba, Misko; Morrison, Andrew; Lewis, Peter; Bouffet, Eric; Bartels, Ute; Zuccaro, Jennifer; Agnihotri, Sameer; Ryall, Scott; Barszczyk, Mark; Chornenkyy, Yevgen; Bourgey, Mathieu; Bourque, Guillaume; Montpetit, Alexandre; Cordero, Francisco; Castelo-Branco, Pedro; Mangerel, Joshua; Tabori, Uri; Ho, King Ching; Huang, Annie; Taylor, Kathryn R; Mackay, Alan; Bendel, Anne E; Nazarian, Javad; Fangusaro, Jason R; Karajannis, Matthias A; Zagzag, David; Foreman, Nicholas K; Donson, Andrew; Hegert, Julia V; Smith, Amy; Chan, Jennifer; Lafay-Cousin, Lucy; Dunn, Sandra; Hukin, Juliette; Dunham, Chris; Scheinemann, Katrin; Michaud, Jean; Zelcer, Shayna; Ramsay, David; Cain, Jason; Brennan, Cameron; Souweidane, Mark M; Jones, Chris; Allis, C David; Brudno, Michael; Becher, Oren; Hawkins, Cynthia

    2014-05-01

    Diffuse intrinsic pontine glioma (DIPG) is a fatal brain cancer that arises in the brainstem of children, with no effective treatment and near 100% fatality. The failure of most therapies can be attributed to the delicate location of these tumors and to the selection of therapies on the basis of assumptions that DIPGs are molecularly similar to adult disease. Recent studies have unraveled the unique genetic makeup of this brain cancer, with nearly 80% found to harbor a p.Lys27Met histone H3.3 or p.Lys27Met histone H3.1 alteration. However, DIPGs are still thought of as one disease, with limited understanding of the genetic drivers of these tumors. To understand what drives DIPGs, we integrated whole-genome sequencing with methylation, expression and copy number profiling, discovering that DIPGs comprise three molecularly distinct subgroups (H3-K27M, silent and MYCN) and uncovering a new recurrent activating mutation affecting the activin receptor gene ACVR1 in 20% of DIPGs. Mutations in ACVR1 were constitutively activating, leading to SMAD phosphorylation and increased expression of the downstream activin signaling targets ID1 and ID2. Our results highlight distinct molecular subgroups and novel therapeutic targets for this incurable pediatric cancer. PMID:24705254

  4. Activity of the human visual cortex measured non-invasively by diffusing-wave spectroscopy

    NASA Astrophysics Data System (ADS)

    Jaillon, Franck; Li, Jun; Dietsche, Gregor; Elbert, Thomas; Gisler, Thomas

    2007-05-01

    Activity of the human visual cortex, elicited by steady-state flickering at 8Hz, is non-invasively probed by multi-speckle diffusingwave spectroscopy (DWS). Parallel detection of the intensity fluctuations of statistically equivalent, but independent speckles allows to resolve stimulation-induced changes in the field autocorrelation of multiply scattered light of less than 2%. In a group of 9 healthy subjects we find a faster decay of the field autocorrelation function during the stimulation periods for data measured with a long-distance probe (30mm source-receiver distance) at 2 positions over the occipital cortex (t-test: t(8) = -2.672, p = 0.028 < 0.05 for position 1, t(8) = -2.874, p = 0.021 < 0.05 for position 2). In contrast, no statistically significant change is seen when a short-distance probe (16mm source-receiver distance) is used (t-test: t(8) = -2.043, p = 0.075 > 0.05 for position 1, t(8) = -2.146, p = 0.064 > 0.05 for position 2). The enhanced dynamics observed with DWS is positively correlated with the functional increase of blood volume in the visual cortex, while the heartbeat rate is not affected by stimulation. Our results indicate that the DWS signal from the visual cortex is governed by the regional cerebral blood flow velocity.

  5. Epidemic spreading with activity-driven awareness diffusion on multiplex network.

    PubMed

    Guo, Quantong; Lei, Yanjun; Jiang, Xin; Ma, Yifang; Huo, Guanying; Zheng, Zhiming

    2016-04-01

    There has been growing interest in exploring the interplay between epidemic spreading with human response, since it is natural for people to take various measures when they become aware of epidemics. As a proper way to describe the multiple connections among people in reality, multiplex network, a set of nodes interacting through multiple sets of edges, has attracted much attention. In this paper, to explore the coupled dynamical processes, a multiplex network with two layers is built. Specifically, the information spreading layer is a time varying network generated by the activity driven model, while the contagion layer is a static network. We extend the microscopic Markov chain approach to derive the epidemic threshold of the model. Compared with extensive Monte Carlo simulations, the method shows high accuracy for the prediction of the epidemic threshold. Besides, taking different spreading models of awareness into consideration, we explored the interplay between epidemic spreading with awareness spreading. The results show that the awareness spreading can not only enhance the epidemic threshold but also reduce the prevalence of epidemics. When the spreading of awareness is defined as susceptible-infected-susceptible model, there exists a critical value where the dynamical process on the awareness layer can control the onset of epidemics; while if it is a threshold model, the epidemic threshold emerges an abrupt transition with the local awareness ratio α approximating 0.5. Moreover, we also find that temporal changes in the topology hinder the spread of awareness which directly affect the epidemic threshold, especially when the awareness layer is threshold model. Given that the threshold model is a widely used model for social contagion, this is an important and meaningful result. Our results could also lead to interesting future research about the different time-scales of structural changes in multiplex networks. PMID:27131489

  6. Epidemic spreading with activity-driven awareness diffusion on multiplex network

    NASA Astrophysics Data System (ADS)

    Guo, Quantong; Lei, Yanjun; Jiang, Xin; Ma, Yifang; Huo, Guanying; Zheng, Zhiming

    2016-04-01

    There has been growing interest in exploring the interplay between epidemic spreading with human response, since it is natural for people to take various measures when they become aware of epidemics. As a proper way to describe the multiple connections among people in reality, multiplex network, a set of nodes interacting through multiple sets of edges, has attracted much attention. In this paper, to explore the coupled dynamical processes, a multiplex network with two layers is built. Specifically, the information spreading layer is a time varying network generated by the activity driven model, while the contagion layer is a static network. We extend the microscopic Markov chain approach to derive the epidemic threshold of the model. Compared with extensive Monte Carlo simulations, the method shows high accuracy for the prediction of the epidemic threshold. Besides, taking different spreading models of awareness into consideration, we explored the interplay between epidemic spreading with awareness spreading. The results show that the awareness spreading can not only enhance the epidemic threshold but also reduce the prevalence of epidemics. When the spreading of awareness is defined as susceptible-infected-susceptible model, there exists a critical value where the dynamical process on the awareness layer can control the onset of epidemics; while if it is a threshold model, the epidemic threshold emerges an abrupt transition with the local awareness ratio α approximating 0.5. Moreover, we also find that temporal changes in the topology hinder the spread of awareness which directly affect the epidemic threshold, especially when the awareness layer is threshold model. Given that the threshold model is a widely used model for social contagion, this is an important and meaningful result. Our results could also lead to interesting future research about the different time-scales of structural changes in multiplex networks.

  7. NASA/DOD Aerospace Knowledge Diffusion Research Project. Paper 6: Aerospace knowledge diffusion in the academic community: A report of phase 3 activities of the NASA/DOD Aerospace Knowledge Diffusion Research Project

    NASA Technical Reports Server (NTRS)

    Pinelli, Thomas E.; Kennedy, John M.

    1990-01-01

    Descriptive and analytical data regarding the flow of aerospace-based scientific and technical information (STI) in the academic community are presented. An overview is provided of the Federal Aerospace Knowledge Diffusion Research Project, illustrating a five-year program on aerospace knowledge diffusion. Preliminary results are presented of the project's research concerning the information-seeking habits, practices, and attitudes of U.S. aerospace engineering and science students and faculty. The type and amount of education and training in the use of information sources are examined. The use and importance ascribed to various information products by U.S. aerospace faculty and students including computer and other information technology is assessed. An evaluation of NASA technical reports is presented and it is concluded that NASA technical reports are rated high in terms of quality and comprehensiveness, citing Engineering Index and IAA as the most frequently used materials by faculty and students.

  8. Chromosome instability in diffuse large B cell lymphomas is suppressed by activation of the noncanonical NF-κB pathway

    PubMed Central

    Ramachandiran, Sampath; Adon, Arsene; Guo, Xiangxue; Wang, Yi; Wang, Huichen; Chen, Zhengjia; Kowalski, Jeanne; Sunay, Ustun R.; Young, Andrew N.; Brown, Theresa; Mar, Jessica C.; Du, Yuhong; Fu, Haian; Mann, Karen P.; Natkunam, Yasodha; Boise, Lawrence H.; Saavedra, Harold I.; Lossos, Izidore S.; Bernal-Mizrachi, Leon

    2016-01-01

    Diffuse large B cell lymphoma (DLBCL) is the most common form of lymphoma in the United States. DLBCL comprises biologically distinct subtypes including germinal center-like (GCB) and activated-B-cell-like DLBCL (ABC). The most aggressive type, ABC-DLBCL, displays dysregulation of both canonical and noncanonical NF-κB pathway as well as genomic instability. Although, much is known about the tumorigenic roles of the canonical NF-kB pathway, the precise role of the noncanonical NF-kB pathway remains unknown. Here we show that activation of the noncanonical NF-κB pathway regulates chromosome stability, DNA damage response and centrosome duplication in DLBCL. Analysis of 92 DLBCL samples revealed that activation of the noncanonical NF-κB pathway is associated with low levels of DNA damage and centrosome amplification. Inhibiting the noncanonical pathway in lymphoma cells uncovered baseline DNA damage and prevented doxorubicin-induced DNA damage repair. In addition, it triggered centrosome amplification and chromosome instability, indicated by anaphase bridges, multipolar spindles and chromosome missegregation. We determined that the noncanonical NF-κB pathway execute these functions through the regulation of GADD45α and REDD1 in a p53-independent manner, while it collaborates with p53 to regulate cyclin G2 expression. Furthermore, this pathway regulates GADD45α, REDD1 and cyclin G2 through direct binding of NF-κB sites to their promoter region. Overall, these results indicate that the noncanonical NF-κB pathway plays a central role in maintaining genome integrity in DLBCL. Our data suggests that inhibition of the noncanonical NF-kB pathway should be considered as an important component in DLBCL therapeutic approach. PMID:25359525

  9. Use of agar diffusion assay to measure bactericidal activity of alkaline salts of fatty acids against bacteria associated with poultry processing

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The agar diffusion assay was used to examine antibacterial activity of alkaline salts of caproic, caprylic, capric, lauric, and myristic acids. A 0.5M concentration of each fatty acid was dissolved in 1.0 M potassium hydroxide (KOH), and pH of the mixtures was adjusted to 10.5 with citric acid. Solu...

  10. Use of agar diffusion assay to evaluate bactericidal activity of formulations of alkaline salts of fatty acids against bacteria associated with poultry processing

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The agar diffusion assay was used to examine antibacterial activity of alkaline salts of fatty acids (FA). Wells in agar media seeded with bacteria were filled with FA-potassium hydroxide (KOH) solutions, plates were incubated, and zones of inhibition were measured. The relationship between bacteric...

  11. Bonding of Cf/SiC composite to Invar alloy using an active cement, Ag-Cu eutectic and Cu interlayer

    NASA Astrophysics Data System (ADS)

    Lei, Zhao; Xiaohong, Li; Jinbao, Hou; Qiang, Sun; Fuli, Zhang

    2012-10-01

    The interfacial microstructures and mechanical properties of the joints formed by active cement added brazing in vacuum of Cf/SiC composite to Invar alloy, using Ag-Cu eutectic alloy and pure copper foil as braze alloy and interlayer respectively, were investigated. CuTi, Cu4Ti3, Fe2Ti and the reaction layer of TiC and Si were the predominant components at the joint interface. The maximum shear strength of the joint was 77 MPa for brazing at 850 °C for 15 min. The results show that active cement added brazing in vacuum using Ag-Cu eutectic alloy and Cu interlayer can be used successfully for joining Cf/SiC composites to Invar alloy.

  12. Linking biofilm growth to fouling and aeration performance of fine-pore diffuser in activated sludge.

    PubMed

    Garrido-Baserba, Manel; Asvapathanagul, Pitiporn; McCarthy, Graham W; Gocke, Thomas E; Olson, Betty H; Park, Hee-Deung; Al-Omari, Ahmed; Murthy, Sudhir; Bott, Charles B; Wett, Bernhard; Smeraldi, Joshua D; Shaw, Andrew R; Rosso, Diego

    2016-03-01

    Aeration is commonly identified as the largest contributor to process energy needs in the treatment of wastewater and therefore garners significant focus in reducing energy use. Fine-pore diffusers are the most common aeration system in municipal wastewater treatment. These diffusers are subject to fouling and scaling, resulting in loss in transfer efficiency as biofilms form and change material properties producing larger bubbles, hindering mass transfer and contributing to increased plant energy costs. This research establishes a direct correlation and apparent mechanistic link between biofilm DNA concentration and reduced aeration efficiency caused by biofilm fouling. Although the connection between biofilm growth and fouling has been implicit in discussions of diffuser fouling for many years, this research provides measured quantitative connection between the extent of biofouling and reduced diffuser efficiency. This was clearly established by studying systematically the deterioration of aeration diffusers efficiency during a 1.5 year period, concurrently with the microbiological study of the biofilm fouling in order to understand the major factors contributing to diffuser fouling. The six different diffuser technologies analyzed in this paper included four different materials which were ethylene-propylene-diene monomer (EPDM), polyurethane, silicone and ceramic. While all diffusers foul eventually, some novel materials exhibited fouling resistance. The material type played a major role in determining the biofilm characteristics (i.e., growth rate, composition, and microbial density) which directly affected the rate and intensity at what the diffusers were fouled, whereas diffuser geometry exerted little influence. Overall, a high correlation between the increase in biofilm DNA and the decrease in αF was evident (CV < 14.0 ± 2.0%). By linking bacterial growth with aeration efficiency, the research was able to show quantitatively the causal connection

  13. Constitutive NF-κB Activation Underlines Major Mechanism of Drug Resistance in Relapsed Refractory Diffuse Large B Cell Lymphoma

    PubMed Central

    2015-01-01

    Diffuse large B cell lymphoma (DLBCL) is the most common subtype of B cell non-Hodgkin's lymphoma (NHL), encompassing 30–40% of the estimated 70,000 cases of NHL in 2014 in the USA. Despite major improvements with immune-chemotherapy, the fraction of patients who still succumb to a refractory or relapsed disease remains high. This review addresses whether the better understanding of the biology of DLBCL defines new therapeutic avenues that may overcome the emerging resistance of this disease to traditional immune-chemotherapy, such as rituximab in combination with traditional chemotherapy agents. Emerging targeted therapy for relapsed refractory DLBCL encompasses more complex molecular abnormalities involving signaling pathways other than NF-κB as mechanism of resistance to immune-chemotherapy. Our review suggests that NF-κB pathway is an important crossroad where other pathways converge as phenotype of resistance that emerges in patients who fail frontline and salvage immune-chemotherapy. Future efforts should aim at targeting the role of NF-κB resistance in clinical trials, where novel agents like lenalidomide and proteasome inhibitors with established activity in this perspective will be an important component in combination therapy, along with new monoclonal antibody, BTK-inhibitors, and other novel therapy agents. PMID:25984532

  14. Inhibition of COP9-signalosome (CSN) deneddylating activity and tumor growth of diffuse large B-cell lymphomas by doxycycline

    PubMed Central

    Pulvino, Mary; Chen, Luojing; Oleksyn, David; Li, Jing; Compitello, George; Rossi, Randy; Spence, Stephen; Balakrishnan, Vijaya; Jordan, Craig; Poligone, Brian; Casulo, Carla; Burack, Richard; Shapiro, Joel L.; Bernstein, Steven; Friedberg, Jonathan W.; Deshaies, Raymond J.; Land, Hartmut; Zhao, Jiyong

    2015-01-01

    In searching for small-molecule compounds that inhibit proliferation and survival of diffuse large B-cell lymphoma (DLBCL) cells and may, therefore, be exploited as potential therapeutic agents for this disease, we identified the commonly used and well-tolerated antibiotic doxycycline as a strong candidate. Here, we demonstrate that doxycycline inhibits the growth of DLBCL cells both in vitro and in mouse xenograft models. In addition, we show that doxycycline accumulates in DLBCL cells to high concentrations and affects multiple signaling pathways that are crucial for lymphomagenesis. Our data reveal the deneddylating activity of COP-9 signalosome (CSN) as a novel target of doxycycline and suggest that doxycycline may exert its effects in DLBCL cells in part through a CSN5-HSP90 pathway. Consistently, knockdown of CSN5 exhibited similar effects as doxycycline treatment on DLBCL cell survival and HSP90 chaperone function. In addition to DLBCL cells, doxycycline inhibited growth of several other types of non-Hodgkin lymphoma cells in vitro. Together, our results suggest that doxycycline may represent a promising therapeutic agent for DLBCL and other non-Hodgkin lymphomas subtypes. PMID:26142707

  15. Activation of less affected corticospinal tract and poor motor outcome in hemiplegic pediatric patients: a diffusion tensor tractography imaging study

    PubMed Central

    Kim, Jin Hyun; Son, Su Min

    2015-01-01

    The less affected hemisphere is important in motor recovery in mature brains. However, in terms of motor outcome in immature brains, no study has been reported on the less affected corticospinal tract in hemiplegic pediatric patients. Therefore, we examined the relationship between the condition of the less affected corticospinal tract and motor function in hemiplegic pediatric patients. Forty patients with hemiplegia due to perinatal or prenatal injury (13.7 ± 3.0 months) and 40 age-matched typically developing controls were recruited. These patients were divided into two age-matched groups, the high functioning group (20 patients) and the low functioning group (20 patients) using functional level of hemiplegia scale. Diffusion tensor tractography images showed that compared with the control group, the patient group of the less affected corticospinal tract showed significantly increased fiber number and significantly decreased fractional anisotropy value. Significantly increased fiber number and significantly decreased fractional anisotropy value in the low functioning group were observed than in the high functioning group. These findings suggest that activation of the less affected hemisphere presenting as increased fiber number and decreased fractional anisotropy value is related to poor motor function in pediatric hemiplegic patients. PMID:26889198

  16. Reduced-Temperature Transient-Liquid-Phase Bonding of AluminaUsing a Ag-Cu-Based Brazing Alloy

    SciTech Connect

    Hong, Sung Moo; Glaeser, Andreas M.

    2005-12-19

    The mechanical properties and microstructural evolution ofmetal-ceramic bonds produced using a transient liquid phase (TLP) aredescribed. Alumina (Al2O3) was joined at 500 degrees C, 600 degrees C,and 700 degrees C using a multilayer In/Cusil-ABA (R) (commercialcopper-silver eutectic brazing alloy)/In interlayer. The introduction ofthin In cladding layers allows the system to bond at much lowertemperatures than those typically used for brazing with Cusil-ABA (R),thereby protecting temperature-sensitive components. After chemicalhomogenization, the interlayers retain an operating temperature rangesimilar to that of the brazed joints. TLP bonds made at 500 degrees C,600 degrees C, and 700 degrees C with holding times ranging from as lowas 1.5 h to 24 h had average fracture strengths above 220 MPa. Theeffects of bonding temperature and time on fracture strength aredescribed. Preliminary analysis of the interlayers shows that the Ag-Inor Cu-In intermetallic phases do not form. Considerations unique tosystems with two-phase core layers are discussed. Experiments usingsingle-crystal sapphire indicate rapid formation of a reaction layer at700 degrees C, suggesting the possibility of making strong bonds usinglower temperatures and/or shorter processing times.

  17. Investigating Diffusion with Technology

    ERIC Educational Resources Information Center

    Miller, Jon S.; Windelborn, Augden F.

    2013-01-01

    The activities described here allow students to explore the concept of diffusion with the use of common equipment such as computers, webcams and analysis software. The procedure includes taking a series of digital pictures of a container of water with a webcam as a dye slowly diffuses. At known time points, measurements of the pixel densities…

  18. Holographic diffusers

    NASA Astrophysics Data System (ADS)

    Wadle, Stephen; Wuest, Daniel; Cantalupo, John; Lakes, Roderic S.

    1994-01-01

    Holographic diffusers are prepared using silver halide (Agfa 8E75 and Kodak 649F) and photopolymer (Polaroid DMP 128 and DuPont 600, 705, and 150 series) media. It is possible to control the diffusion angle in three ways: by selection of the properties of the source diffuser, by control of its subtended angle, and by selection of the holographic medium. Several conventional diffusers based on refraction or scattering of light are examined for comparison.

  19. Diffusion MRI

    NASA Astrophysics Data System (ADS)

    Fukuyama, Hidenao

    Recent advances of magnetic resonance imaging have been described, especially stressed on the diffusion sequences. We have recently applied the diffusion sequence to functional brain imaging, and found the appropriate results. In addition to the neurosciences fields, diffusion weighted images have improved the accuracies of clinical diagnosis depending upon magnetic resonance images in stroke as well as inflammations.

  20. Direct imaging of thermally-activated grain-boundary diffusion in Cu/Co/IrMn/Pt exchange-bias structures using atom-probe tomography

    SciTech Connect

    Letellier, F.; Lardé, R.; Le Breton, J.-M.; Akmaldinov, K.; Auffret, S.; Dieny, B.; Baltz, V.

    2014-11-28

    Magnetic devices are often subject to thermal processing steps, such as field cooling to set exchange bias and annealing to crystallize amorphous magnetic electrodes. These processing steps may result in interdiffusion and the subsequent deterioration of magnetic properties. In this study, we investigated thermally-activated diffusion in Cu/Co/IrMn/Pt exchange biased polycrystalline thin-film structures using atom probe tomography. Images taken after annealing at 400 °C for 60 min revealed Mn diffusion into Co grains at the Co/IrMn interface and along Pt grain boundaries for the IrMn/Pt stack, i.e., a Harrison type C regime. Annealing at 500 °C showed further Mn diffusion into Co grains. At the IrMn/Pt interface, annealing at 500 °C led to a type B behavior since Mn diffusion was detected both along Pt grain boundaries and also into Pt grains. The deterioration of the films' exchange bias properties upon annealing was correlated to the observed diffusion. In particular, the topmost Pt capping layer thickness turned out to be crucial since a faster deterioration of the exchange bias properties for thicker caps was observed. This is consistent with the idea that Pt acts as a getter for Mn, drawing Mn out of the IrMn layer.