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Sample records for ferromagnetic colloid microprobe

  1. Flocking ferromagnetic colloids

    PubMed Central

    Kaiser, Andreas; Snezhko, Alexey; Aranson, Igor S.

    2017-01-01

    Assemblages of microscopic colloidal particles exhibit fascinating collective motion when energized by electric or magnetic fields. The behaviors range from coherent vortical motion to phase separation and dynamic self-assembly. Although colloidal systems are relatively simple, understanding their collective response, especially under out-of-equilibrium conditions, remains elusive. We report on the emergence of flocking and global rotation in the system of rolling ferromagnetic microparticles energized by a vertical alternating magnetic field. By combing experiments and discrete particle simulations, we have identified primary physical mechanisms, leading to the emergence of large-scale collective motion: spontaneous symmetry breaking of the clockwise/counterclockwise particle rotation, collisional alignment of particle velocities, and random particle reorientations due to shape imperfections. We have also shown that hydrodynamic interactions between the particles do not have a qualitative effect on the collective dynamics. Our findings shed light on the onset of spatial and temporal coherence in a large class of active systems, both synthetic (colloids, swarms of robots, and biopolymers) and living (suspensions of bacteria, cell colonies, and bird flocks). PMID:28246633

  2. Biaxial ferromagnetic liquid crystal colloids

    PubMed Central

    Liu, Qingkun; Ackerman, Paul J.; Lubensky, Tom C.; Smalyukh, Ivan I.

    2016-01-01

    The design and practical realization of composite materials that combine fluidity and different forms of ordering at the mesoscopic scale are among the grand fundamental science challenges. These composites also hold a great potential for technological applications, ranging from information displays to metamaterials. Here we introduce a fluid with coexisting polar and biaxial ordering of organic molecular and magnetic colloidal building blocks exhibiting the lowest symmetry orientational order. Guided by interactions at different length scales, rod-like organic molecules of this fluid spontaneously orient along a direction dubbed “director,” whereas magnetic colloidal nanoplates order with their dipole moments parallel to each other but pointing at an angle to the director, yielding macroscopic magnetization at no external fields. Facile magnetic switching of such fluids is consistent with predictions of a model based on competing actions of elastic and magnetic torques, enabling previously inaccessible control of light. PMID:27601668

  3. Spontaneous liquid crystal and ferromagnetic ordering of colloidal magnetic nanoplates

    PubMed Central

    Shuai, M.; Klittnick, A.; Shen, Y.; Smith, G. P.; Tuchband, M. R.; Zhu, C.; Petschek, R. G.; Mertelj, A.; Lisjak, D.; Čopič, M.; Maclennan, J. E.; Glaser, M. A.; Clark, N. A.

    2016-01-01

    Ferrofluids are familiar as colloidal suspensions of ferromagnetic nanoparticles in aqueous or organic solvents. The dispersed particles are randomly oriented but their moments become aligned if a magnetic field is applied, producing a variety of exotic and useful magnetomechanical effects. A longstanding interest and challenge has been to make such suspensions macroscopically ferromagnetic, that is having uniform magnetic alignment in the absence of a field. Here we report a fluid suspension of magnetic nanoplates that spontaneously aligns into an equilibrium nematic liquid crystal phase that is also macroscopically ferromagnetic. Its zero-field magnetization produces distinctive magnetic self-interaction effects, including liquid crystal textures of fluid block domains arranged in closed flux loops, and makes this phase highly sensitive, with it dramatically changing shape even in the Earth's magnetic field. PMID:26817823

  4. Spontaneous liquid crystal and ferromagnetic ordering of colloidal magnetic nanoplates

    DOE PAGES

    Shuai, M.; Klittnick, A.; Shen, Y.; ...

    2016-01-28

    Ferrofluids are familiar as colloidal suspensions of ferromagnetic nanoparticles in aqueous or organic solvents. The dispersed particles are randomly oriented but their moments become aligned if a magnetic field is applied, producing a variety of exotic and useful magnetomechanical effects. A longstanding interest and challenge has been to make such suspensions macroscopically ferromagnetic, that is having uniform magnetic alignment in the absence of a field. Here we report a fluid suspension of magnetic nanoplates that spontaneously aligns into an equilibrium nematic liquid crystal phase that is also macroscopically ferromagnetic. We find Its zero-field magnetization produces distinctive magnetic self-interaction effects, includingmore » liquid crystal textures of fluid block domains arranged in closed flux loops, and makes this phase highly sensitive, with it dramatically changing shape even in the Earth’s magnetic field.« less

  5. Spontaneous liquid crystal and ferromagnetic ordering of colloidal magnetic nanoplates

    SciTech Connect

    Shuai, M.; Klittnick, A.; Shen, Y.; Smith, G. P.; Tuchband, M. R.; Zhu, C.; Petschek, R. G.; Mertelj, A.; Lisjak, D.; Čopič, M.; Maclennan, J. E.; Glaser, M. A.; Clark, N. A.

    2016-01-28

    Ferrofluids are familiar as colloidal suspensions of ferromagnetic nanoparticles in aqueous or organic solvents. The dispersed particles are randomly oriented but their moments become aligned if a magnetic field is applied, producing a variety of exotic and useful magnetomechanical effects. A longstanding interest and challenge has been to make such suspensions macroscopically ferromagnetic, that is having uniform magnetic alignment in the absence of a field. Here we report a fluid suspension of magnetic nanoplates that spontaneously aligns into an equilibrium nematic liquid crystal phase that is also macroscopically ferromagnetic. We find Its zero-field magnetization produces distinctive magnetic self-interaction effects, including liquid crystal textures of fluid block domains arranged in closed flux loops, and makes this phase highly sensitive, with it dramatically changing shape even in the Earth’s magnetic field.

  6. Spontaneous liquid crystal and ferromagnetic ordering of colloidal magnetic nanoplates

    NASA Astrophysics Data System (ADS)

    Shuai, M.; Klittnick, A.; Shen, Y.; Smith, G. P.; Tuchband, M. R.; Zhu, C.; Petschek, R. G.; Mertelj, A.; Lisjak, D.; Čopič, M.; Maclennan, J. E.; Glaser, M. A.; Clark, N. A.

    2016-01-01

    Ferrofluids are familiar as colloidal suspensions of ferromagnetic nanoparticles in aqueous or organic solvents. The dispersed particles are randomly oriented but their moments become aligned if a magnetic field is applied, producing a variety of exotic and useful magnetomechanical effects. A longstanding interest and challenge has been to make such suspensions macroscopically ferromagnetic, that is having uniform magnetic alignment in the absence of a field. Here we report a fluid suspension of magnetic nanoplates that spontaneously aligns into an equilibrium nematic liquid crystal phase that is also macroscopically ferromagnetic. Its zero-field magnetization produces distinctive magnetic self-interaction effects, including liquid crystal textures of fluid block domains arranged in closed flux loops, and makes this phase highly sensitive, with it dramatically changing shape even in the Earth's magnetic field.

  7. Magnetic domains and defects in ferromagnetic liquid crystal colloids realized with optical patterning

    NASA Astrophysics Data System (ADS)

    Hess, Andrew; Liu, Qingkun; Smalyukh, Ivan

    A promising approach in designing composite materials with unusual physical behavior combines solid nanostructures and orientationally ordered soft matter at the mesoscale. Such composites not only inherit properties of their constituents but also can exhibit emergent behavior, such as ferromagnetic ordering of colloidal metal nanoparticles forming mesoscopic magnetization domains when dispersed in a nematic liquid crystal. Here we demonstrate the optical patterning of domain structures and topological defects in such ferromagnetic liquid crystal colloids which allows for altering their response to magnetic fields. Our findings reveal the nature of the defects in this soft matter system which is different as compared to non-polar nematic and ferromagnetic systems alike. This research was supported by the NSF Grant DMR-1420736.

  8. Static three-dimensional topological solitons in fluid chiral ferromagnets and colloids.

    PubMed

    Ackerman, Paul J; Smalyukh, Ivan I

    2017-04-01

    Three-dimensional (3D) topological solitons are continuous but topologically nontrivial field configurations localized in 3D space and embedded in a uniform far-field background, that behave like particles and cannot be transformed to a uniform state through smooth deformations. Many topologically nontrivial 3D solitonic fields have been proposed. Yet, according to the Hobart-Derrick theorem, physical systems cannot host them, except for nonlinear theories with higher-order derivatives such as the Skyrme-Faddeev model. Experimental discovery of such solitons is hindered by the need for spatial imaging of the 3D fields, which is difficult in high-energy physics and cosmology. Here we experimentally realize and numerically model stationary topological solitons in a fluid chiral ferromagnet formed by colloidal dispersions of magnetic nanoplates. Such solitons have closed-loop preimages-3D regions with a single orientation of the magnetization field. We discuss localized structures with different linking of preimages quantified by topological Hopf invariants. The chirality is found to help in overcoming the constraints of the Hobart-Derrick theorem, like in two-dimensional ferromagnetic solitons, dubbed 'baby skyrmions'. Our experimental platform may lead to solitonic condensed matter phases and technological applications.

  9. Biological colloid engineering: Self-assembly of dipolar ferromagnetic chains in a functionalized biogenic ferrofluid.

    PubMed

    Ruder, Warren C; Hsu, Chia-Pei D; Edelman, Brent D; Schwartz, Russell; Leduc, Philip R

    2012-08-06

    We have studied the dynamic behavior of nanoparticles in ferrofluids consisting of single-domain, biogenic magnetite (Fe(3)O(4)) isolated from Magnetospirillum magnetotacticum (MS-1). Although dipolar chains form in magnetic colloids in zero applied field, when dried upon substrates, the solvent front disorders nanoparticle aggregation. Using avidin-biotin functionalization of the particles and substrate, we generated self-assembled, linear chain motifs that resist solvent front disruption in zero-field. The engineered self-assembly process we describe here provides an approach for the creation of ordered magnetic structures that could impact fields ranging from micro-electro-mechanical systems development to magnetic imaging of biological structures.

  10. The proton (nuclear) microprobe

    NASA Astrophysics Data System (ADS)

    Legge, G. J. F.

    1989-04-01

    The scanning proton microprobe (SPMP) is closely related to the scanning electron microprobe (SEMP) or scanning electron microscope (SEM) with X-ray detector. Though the much greater elemental sensitivity of the SPMP is inherent in the physics, the generally inferior spatial resolution of the SPMP is not inherent and big improvements are possible, As its alternative name would imply, the SPMP is often used with heavier particle beams and with nuclear rather than atomic reactions. Its versatility and quantitative accuracy have justified greater instrumentation and computer power than that associated with other microprobes. It is fast becoming an industrially and commercially important instrument and there are few fields of scientific research in which it has not played a part. Notable contributions have been made in biology, medicine, agriculture, semiconductors, geology, mineralogy, extractive metallurgy, new materials, archaeology, forensic science, catalysis, industrial problems and reactor technology.

  11. Mars Microprobe Entry Analysis

    NASA Technical Reports Server (NTRS)

    Braun, Robert D.; Mitcheltree, Robert A.; Cheatwood, F. McNeil

    1998-01-01

    The Mars Microprobe mission will provide the first opportunity for subsurface measurements, including water detection, near the south pole of Mars. In this paper, performance of the Microprobe aeroshell design is evaluated through development of a six-degree-of-freedom (6-DOF) aerodynamic database and flight dynamics simulation. Numerous mission uncertainties are quantified and a Monte-Carlo analysis is performed to statistically assess mission performance. Results from this 6-DOF Monte-Carlo simulation demonstrate that, in a majority of the cases (approximately 2-sigma), the penetrator impact conditions are within current design tolerances. Several trajectories are identified in which the current set of impact requirements are not satisfied. From these cases, critical design parameters are highlighted and additional system requirements are suggested. In particular, a relatively large angle-of-attack range near peak heating is identified.

  12. Positron microprobe at LLNL

    SciTech Connect

    Asoka, P; Howell, R; Stoeffl, W

    1998-11-01

    The electron linac based positron source at Lawrence Livermore National Laboratory (LLNL) provides the world's highest current beam of keV positrons. We are building a positron microprobe that will produce a pulsed, focused positron beam for 3-dimensional scans of defect size and concentration with sub-micron resolution. The widely spaced and intense positron packets from the tungsten moderator at the end of the 100 MeV LLNL linac are captured and trapped in a magnetic bottle. The positrons are then released in 1 ns bunches at a 20 MHz repetition rate. With a three-stage re-moderation we will compress the cm-sized original beam to a 1 micro-meter diameter final spot on the target. The buncher will compress the arrival time of positrons on the target to less than 100 ps. A detector array with up to 60 BaF2 crystals in paired coincidence will measure the annihilation radiation with high efficiency and low background. The energy of the positrons can be varied from less than 1 keV up to 50 keV.

  13. Electron microprobe mineral analysis guide

    NASA Technical Reports Server (NTRS)

    Brown, R. W.

    1980-01-01

    Electron microprobe mineral analysis guide is a compilation of X-ray tables and spectra recorded from various mineral matrices. Spectra were obtained using electron microprobe, equipped with LiF geared, curved crystal X-ray spectrometers, utilizing typical analytical operating conditions: 15 Kv acceleration potential, 0.02 microampere sample current as measured on a clinopyroxene standard (CP19). Tables and spectra are presented for the majority of elements, fluorine through uranium, occurring in mineral samples from lunar, meteoritic and terrestrial sources. Tables for each element contain relevant analytical information, i.e., analyzing crystal, X-ray peak, background and relative intensity information, X-ray interferences and a section containing notes on the measurement. Originally intended to cover silicates and oxide minerals the tables and spectra have been expanded to cover other mineral phases. Electron microprobe mineral analysis guide is intended as a spectral base to which additional spectra can be added as the analyst encounters new mineral matrices.

  14. High current pulsed positron microprobe

    SciTech Connect

    Howell, R.H.; Stoeffl, W.; Kumar, A.; Sterne, P.A.; Cowan, T.E.; Hartley, J.

    1997-05-01

    We are developing a low energy, microscopically focused, pulsed positron beam for defect analysis by positron lifetime spectroscopy to provide a new defect analysis capability at the 10{sup 10} e{sup +}s{sup -l} beam at the Lawrence Livermore National Laboratory electron linac. When completed, the pulsed positron microprobe will enable defect specific, 3-dimensional maps of defect concentrations with sub-micron resolution of defect location. By coupling these data with first principles calculations of defect specific positron lifetimes and positron implantation profiles we will both map the identity and concentration of defect distributions.

  15. Microscale structure fabrication using microprobe

    NASA Astrophysics Data System (ADS)

    Shinya, Norio; Konno, Takeshi; Egashira, Mitsuru

    1996-05-01

    Using a tungsten micro-probe with a tip of 2 micrometers radius, fine metallic powder particles could be manipulated one by one. By applying low voltage (about 10 V) between the probe and a metallic substrate, the powder particle on the substrate was adsorbed to the tip of probe easily, and by cutting off the voltage the powder particle was desorbed from the tip. Therefore it is possible to arrange powder particles as designed by controlling the voltage and movement of the probe. In addition to the powder particle manipulation, powder particles welding was studied. The tungsten micro-probe was contacted with the powder particle on the metallic substrate, and high voltage (about 10 kV) was applied between the probe and the substrate. It was observed that the glow discharge was caused between the powder particle and the substrate. The contacting parts of the powder particle and the substrate were melted and welded each other. By the manipulation and the welding, micro-structures composed of fine powder particles (about 60 micrometers ) were constructed. Powder particle towers and a micro- actuator were fabricated by way of trial. The results demonstrated the potential of the micro- probe assembly for the fabrication of electronic devices, micromachines and intelligent materials.

  16. Microprobe analysis of chlorpromazine pigmentation

    SciTech Connect

    Benning, T.L.; McCormack, K.M.; Ingram, P.; Kaplan, D.L.; Shelburne, J.D.

    1988-10-01

    We describe the histochemical, ultrastructural, and microanalytical features of a skin biopsy specimen obtained from a patient with chlorpromazine pigmentation. Golden-brown pigment granules were present in the dermis, predominantly in a perivascular arrangement. The granules stained positively with the Fontana-Masson stain for silver-reducing substances and negatively with Perl's stain for iron. Electron microscopy revealed dense inclusion bodies in dermal histiocytes, pericytes, endothelial cells, and Schwann cells, as well as lying free in the extracellular matrix. These ''chlorpromazine bodies'' were quite dense even in unosmicated, unstained ultrathin sections, indicating that the pigmentation is related, at least in part, to the inclusions. Microprobe analysis of the chlorpromazine bodies revealed a striking peak for sulfur, which strongly suggests the presence of the drug or its metabolite within these inclusions.

  17. Colloidal Phenomena.

    ERIC Educational Resources Information Center

    Russel, William B.; And Others

    1979-01-01

    Described is a graduate level engineering course offered at Princeton University in colloidal phenomena stressing the physical and dynamical side of colloid science. The course outline, reading list, and requirements are presented. (BT)

  18. TEAM - Titan Exploration Atmospheric Microprobes

    NASA Astrophysics Data System (ADS)

    Nixon, Conor; Esper, Jaime; Aslam, Shahid; Quilligan, Gerald

    2016-10-01

    The astrobiological potential of Titan's surface hydrocarbon liquids and probable interior water ocean has led to its inclusion as a destination in NASA's "Ocean Worlds" initiative, and near-term investigation of these regions is a high-level scientific goal. TEAM is a novel initiative to investigate the lake and sea environs using multiple dropsondes -scientific probes derived from an existing cubesat bus architecture (CAPE - the Cubesat Application for Planetary Exploration) developed at NASA GSFC. Each 3U probe will parachute to the surface, making atmospheric structure and composition measurements during the descent, and photographing the surface - land, shoreline and seas - in detail. TEAM probes offer a low-cost, high-return means to explore multiple areas on Titan, yielding crucial data about the condensing chemicals, haze and cloud layers, winds, and surface features of the lakes and seas. These microprobes may be included on a near-term New Frontiers class mission to the Saturn system as additional payload, bringing increased scientific return and conducting reconnaissance for future landing zones. In this presentation we describe the probe architecture, baseline payload, flight profile and the unique engineering and science data that can be returned.

  19. Ferromagnetic microswimmer

    NASA Astrophysics Data System (ADS)

    Belovs, M.; Cěbers, A.

    2009-05-01

    The self-propelling motion of the flexible ferromagnetic swimmer is described. Necessary symmetry breaking is achieved by the buckling instability at field inversion. The characteristics of self-propulsion are in good agreement with the numerical calculations of the Floquet multipliers for the ferromagnetic filament under the action of ac magnetic field. In the low frequency range the power stroke of self-propelling motion is similar to that used by the unicellular green algae chlamydomonas and in the high frequency region the self-propulsion is due to the undulation waves propagating from the free ends perpendicularly to ac magnetic field.

  20. Ferromagnetic microswimmer.

    PubMed

    Belovs, M; Cēbers, A

    2009-05-01

    The self-propelling motion of the flexible ferromagnetic swimmer is described. Necessary symmetry breaking is achieved by the buckling instability at field inversion. The characteristics of self-propulsion are in good agreement with the numerical calculations of the Floquet multipliers for the ferromagnetic filament under the action of ac magnetic field. In the low frequency range the power stroke of self-propelling motion is similar to that used by the unicellular green algae chlamydomonas and in the high frequency region the self-propulsion is due to the undulation waves propagating from the free ends perpendicularly to ac magnetic field.

  1. Materials analysis with a nuclear microprobe

    SciTech Connect

    Maggiore, C.J.

    1980-01-01

    The ability to produce focused beams of a few MeV light ions from Van de Graaff accelerators has resulted in the development of nuclear microprobes. Rutherford backscattering, nuclear reactions, and particle-induced x-ray emission are used to provide spatially resolved information from the near surface region of materials. Rutherford backscattering provides nondestructive depth and mass resolution. Nuclear reactions are sensitive to light elements (Z < 15). Particle-induced x-ray analysis is similar to electron microprobe analysis, but 2 orders of magnitude more sensitive. The focused beams are usually produced with specially designed multiplets of magnetic quadrupoles. The LASL microprobe uses a superconducting solenoid as a final lens. The data are acquired by a computer interfaced to the experiment with CAMAC. The characteristics of the information acquired with a nuclear microprobe are discussed; the means of producing the beams of nuclear particles are described; and the limitations and applications of such systems are given.

  2. The ANSTO high energy heavy ion microprobe

    NASA Astrophysics Data System (ADS)

    Siegele, Rainer; Cohen, David D.; Dytlewski, Nick

    1999-10-01

    Recently the construction of the ANSTO High Energy Heavy Ion Microprobe (HIMP) at the 10 MV ANTARES tandem accelerator has been completed. The high energy heavy ion microprobe focuses not only light ions at energies of 2-3 MeV, but is also capable of focusing heavy ions at high energies with ME/ q2 values up to 150 MeV amu and greater. First performance tests and results are reported here.

  3. DS-2 Mars Microprobe Battery

    NASA Technical Reports Server (NTRS)

    Frank, H.; Kindler, A.; Deligiannis, F.; Davies, E.; Blankevoort, J.; Ratnakumar, B. V.; Surampudi, S.

    1999-01-01

    In January of 1999 the NM DS-2 Mars microprobe will be launched to impact on Mars in December. The technical objectives of the missions are to demonstrate: key technologies, a passive atmospheric entry, highly integrated microelectronics which can withstand both low temperatures and high decelerations, and the capability to conduct in-situ, surface and subsurface science data acquisition. The scientific objectives are to determine if ice is present below the Martian surface, measure the local atmospheric pressure, characterize the thermal properties of the martian subsurface soil, and to estimate the vertical temperature gradient of the Martian soil. The battery requirements are 2-4 cell batteries, with voltage of 6-14 volts, capacity of 550 mAh at 80C, and 2Ah at 25C, shelf life of 2.5 years, an operating temperature of 60C and below, and the ability to withstand shock impact of 80,000 g's. The technical challenges and the approach is reviewed. The Li-SOCL2 system is reviewed, and graphs showing the current and voltage is displayed, along with the voltage over discharge time. The problems encountered during the testing were: (1) impact sensitivity, (2) cracking of the seals, and (3) delay in voltage. A new design resulted in no problems in the impact testing phase. The corrective actions for the seal problems involved: (1) pre weld fill tube, (2) an improved heat sink during case to cover weld and (3) change the seal dimensions to reduce stress. To correct the voltage delay problem the solutions involved: (1) drying the electrodes to reduce contamination by water, (2) assemblage of the cells within a week of electrode manufacture, (3) ensure electrolyte purity, and (4) provide second depassivation pulse after landing. The conclusions on further testing were that the battery can: (1) withstand anticipated shock of up to 80,000 g, (2) meet the discharge profile post shock at Mars temperatures, (3) meet the required self discharge rate and (4) meet environmental

  4. Active colloids

    NASA Astrophysics Data System (ADS)

    Aranson, Igor S.

    2013-01-01

    A colloidal suspension is a heterogeneous fluid containing solid microscopic particles. Colloids play an important role in our everyday life, from food and pharmaceutical industries to medicine and nanotechnology. It is useful to distinguish two major classes of colloidal suspensions: equilibrium and active, i.e., maintained out of thermodynamic equilibrium by external electric or magnetic fields, light, chemical reactions, or hydrodynamic shear flow. While the properties of equilibrium colloidal suspensions are fairly well understood, active colloids pose a formidable challenge, and the research is in its early exploratory stage. One of the most remarkable properties of active colloids is the possibility of dynamic self-assembly, a natural tendency of simple building blocks to organize into complex functional architectures. Examples range from tunable, self-healing colloidal crystals and membranes to self-assembled microswimmers and robots. Active colloidal suspensions may exhibit material properties not present in their equilibrium counterparts, e.g., reduced viscosity and enhanced self-diffusivity, etc. This study surveys the most recent developments in the physics of active colloids, both in synthetic and living systems, with the aim of elucidation of the fundamental physical mechanisms governing self-assembly and collective behavior.

  5. Colloidal polypyrrole

    DOEpatents

    Armes, Steven P.; Aldissi, Mahmoud

    1990-01-01

    Processable electrically conductive latex polymer compositions including colloidal particles of an oxidized, polymerized aromatic heterocyclic monomer, a stabilizing effective amount of a vinyl pyridine-containing polymer and dopant anions and a method of preparing such polymer compositions are disclosed.

  6. Hexadecapolar colloids

    NASA Astrophysics Data System (ADS)

    Senyuk, Bohdan; Puls, Owen; Tovkach, Oleh M.; Chernyshuk, Stanislav B.; Smalyukh, Ivan I.

    2016-02-01

    Outermost occupied electron shells of chemical elements can have symmetries resembling that of monopoles, dipoles, quadrupoles and octupoles corresponding to filled s-, p-, d- and f-orbitals. Theoretically, elements with hexadecapolar outer shells could also exist, but none of the known elements have filled g-orbitals. On the other hand, the research paradigm of `colloidal atoms' displays complexity of particle behaviour exceeding that of atomic counterparts, which is driven by DNA functionalization, geometric shape and topology and weak external stimuli. Here we describe elastic hexadecapoles formed by polymer microspheres dispersed in a liquid crystal, a nematic fluid of orientationally ordered molecular rods. Because of conically degenerate boundary conditions, the solid microspheres locally perturb the alignment of the nematic host, inducing hexadecapolar distortions that drive anisotropic colloidal interactions. We uncover physical underpinnings of formation of colloidal elastic hexadecapoles and describe the ensuing bonding inaccessible to elastic dipoles, quadrupoles and other nematic colloids studied previously.

  7. Hexadecapolar colloids

    PubMed Central

    Senyuk, Bohdan; Puls, Owen; Tovkach, Oleh M.; Chernyshuk, Stanislav B.; Smalyukh, Ivan I.

    2016-01-01

    Outermost occupied electron shells of chemical elements can have symmetries resembling that of monopoles, dipoles, quadrupoles and octupoles corresponding to filled s-, p-, d- and f-orbitals. Theoretically, elements with hexadecapolar outer shells could also exist, but none of the known elements have filled g-orbitals. On the other hand, the research paradigm of ‘colloidal atoms' displays complexity of particle behaviour exceeding that of atomic counterparts, which is driven by DNA functionalization, geometric shape and topology and weak external stimuli. Here we describe elastic hexadecapoles formed by polymer microspheres dispersed in a liquid crystal, a nematic fluid of orientationally ordered molecular rods. Because of conically degenerate boundary conditions, the solid microspheres locally perturb the alignment of the nematic host, inducing hexadecapolar distortions that drive anisotropic colloidal interactions. We uncover physical underpinnings of formation of colloidal elastic hexadecapoles and describe the ensuing bonding inaccessible to elastic dipoles, quadrupoles and other nematic colloids studied previously. PMID:26864184

  8. Hexadecapolar Colloids

    DOE PAGES

    Senyuk, Bohdan; Puls, Owen; Tovkach, Oleh M.; ...

    2016-02-11

    Outermost occupied electron shells of chemical elements can have symmetries resembling that of monopoles, dipoles, quadrupoles and octupoles corresponding to filled s-, p-, d- and forbitals. Theoretically, elements with hexadecapolar outer shells could also exist, but none of the known elements have filled g-orbitals. On the other hand, the research paradigm of ‘colloidal atoms’ displays complexity of particle behaviour exceeding that of atomic counterparts, which is driven by DNA functionalization, geometric shape and topology and weak external stimuli. We describe elastic hexadecapoles formed by polymer microspheres dispersed in a liquid crystal, a nematic fluid of orientationally ordered molecular rods. Becausemore » of conically degenerate boundary conditions, the solid microspheres locally perturb the alignment of the nematic host, inducing hexadecapolar distortions that drive anisotropic colloidal interactions. We uncover physical underpinnings of formation of colloidal elastic hexadecapoles and report the ensuing bonding inaccessible to elastic dipoles, quadrupoles and other nematic colloids studied previously.« less

  9. Hexadecapolar Colloids

    SciTech Connect

    Senyuk, Bohdan; Puls, Owen; Tovkach, Oleh M.; Chernyshuk, Stanislav B.; Smalyukh, Ivan I.

    2016-02-11

    Outermost occupied electron shells of chemical elements can have symmetries resembling that of monopoles, dipoles, quadrupoles and octupoles corresponding to filled s-, p-, d- and forbitals. Theoretically, elements with hexadecapolar outer shells could also exist, but none of the known elements have filled g-orbitals. On the other hand, the research paradigm of ‘colloidal atoms’ displays complexity of particle behaviour exceeding that of atomic counterparts, which is driven by DNA functionalization, geometric shape and topology and weak external stimuli. We describe elastic hexadecapoles formed by polymer microspheres dispersed in a liquid crystal, a nematic fluid of orientationally ordered molecular rods. Because of conically degenerate boundary conditions, the solid microspheres locally perturb the alignment of the nematic host, inducing hexadecapolar distortions that drive anisotropic colloidal interactions. We uncover physical underpinnings of formation of colloidal elastic hexadecapoles and report the ensuing bonding inaccessible to elastic dipoles, quadrupoles and other nematic colloids studied previously.

  10. Data acquisition with a nuclear microprobe

    SciTech Connect

    Maggiore, C.

    1980-01-01

    Spatially resolved information from the near surfaces of materials can be obtained with a nuclear microprobe. The spatial resolution is determined by the optics of the instrument and radiation damage in the specimen. Two- and three-dimensional maps of elemental concentration may be obtained from the near surfaces of materials. Data are acquired by repeated scans of a constantly moving beam over the region of interest or by counting for a preset integrated charge at each specimen location.

  11. Biomedical application of the nuclear microprobe

    NASA Astrophysics Data System (ADS)

    Lindh, Ulf

    1987-04-01

    The Studsvik Nuclear Microprobe (SMP) has mainly been devoted to applications in the biomedical field. Its ultimate resolution is reached at 2.9×2.9 μm 2 with a proton current of 100 pA. With this performance the SMP has been used in a wide range of disciplines covering environmental hygiene, toxicology, various aspects of internal medicine and trace element physiology. Examples of recent applications in these fields are described.

  12. Colloidal polyaniline

    DOEpatents

    Armes, Steven P.; Aldissi, Mahmoud

    1990-01-01

    Processable electrically conductive latex polymer compositions including colloidal particles of an oxidized, polymerized amino-substituted aromatic monomer, a stabilizing effective amount of a random copolymer containing amino-benzene type moieties as side chain constituents, and dopant anions, and a method of preparing such polymer compositions are provided.

  13. MicroProbe Small Unmanned Aerial System

    NASA Technical Reports Server (NTRS)

    Bland, Geoffrey; Miles, Ted

    2012-01-01

    The MicroProbe unmanned aerial system (UAS) concept incorporates twin electric motors mounted on the vehicle wing, thus enabling an aerodynamically and environmentally clean nose area for atmospheric sensors. A payload bay is also incorporated in the fuselage to accommodate remote sensing instruments. A key feature of this concept is lightweight construction combined with low flying speeds to minimize kinetic energy and associated hazards, as well as maximizing spatial resolution. This type of aerial platform is needed for Earth science research and environmental monitoring. There were no vehicles of this type known to exist previously.

  14. Laser Microprobe Mass Spectrometry 1: Basic Principles and Performance Characteristics.

    ERIC Educational Resources Information Center

    Denoyer, Eric; And Others

    1982-01-01

    Describes the historical development, performance characteristics (sample requirements, analysis time, ionization characteristics, speciation capabilities, and figures of merit), and applications of laser microprobe mass spectrometry. (JN)

  15. Asymmetric Ferromagnet-Superconductor-Ferromagnet Switch

    SciTech Connect

    Cadden-Zimansky, P.; Bazaliy, Ya.B.; Litvak, L.M.; Jiang, J.S.; Pearson, J.; Gu, J.Y.; You, Chun-Yeol; Beasley, M.R.; Bader, S.D.

    2011-11-04

    In layered ferromagnet-superconductor-ferromagnet F{sub 1} /S/F{sub 2} structures, the critical temperature T{sub c} of the superconductors depends on the magnetic orientation of the ferromagnetic layers F{sub 1} and F{sub 2} relative to each other. So far, the experimentally observed magnitude of change in T{sub c} for structures utilizing weak ferromagnets has been 2 orders of magnitude smaller than is expected from calculations. We theoretically show that such a discrepancy can result from the asymmetry of F/S boundaries, and we test this possibility by performing experiments on structures where F{sub 1} and F{sub 2} are independently varied. Our experimental results indicate that asymmetric boundaries are not the source of the discrepancy. If boundary asymmetry is causing the suppressed magnitude of T{sub c} changes, it may only be possible to detect in structures with thinner ferromagnetic layers.

  16. Soil colloidal behavior

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Recent understanding that organic and inorganic contaminants are often transported via colloidal particles has increased interest in colloid science. The primary importance of colloids in soil science stems from their surface reactivity and charge characteristics. Characterizations of size, shape,...

  17. Self-replication with magnetic dipolar colloids.

    PubMed

    Dempster, Joshua M; Zhang, Rui; Olvera de la Cruz, Monica

    2015-10-01

    Colloidal self-replication represents an exciting research frontier in soft matter physics. Currently, all reported self-replication schemes involve coating colloidal particles with stimuli-responsive molecules to allow switchable interactions. In this paper, we introduce a scheme using ferromagnetic dipolar colloids and preprogrammed external magnetic fields to create an autonomous self-replication system. Interparticle dipole-dipole forces and periodically varying weak-strong magnetic fields cooperate to drive colloid monomers from the solute onto templates, bind them into replicas, and dissolve template complexes. We present three general design principles for autonomous linear replicators, derived from a focused study of a minimalist sphere-dimer magnetic system in which single binding sites allow formation of dimeric templates. We show via statistical models and computer simulations that our system exhibits nonlinear growth of templates and produces nearly exponential growth (low error rate) upon adding an optimized competing electrostatic potential. We devise experimental strategies for constructing the required magnetic colloids based on documented laboratory techniques. We also present qualitative ideas about building more complex self-replicating structures utilizing magnetic colloids.

  18. Aerodynamics of the Mars Microprobe Entry Vehicles

    NASA Technical Reports Server (NTRS)

    Mitcheltree, R. A.; Moss, J. N.; Cheatwood, F. M.; Greene, F. A.; Braun, R. D.

    1997-01-01

    The selection of the unique aeroshell shape for the Mars Microprobes is discussed. A description of its aerodynamics in hypersonic rarefied, hypersonic continuum, supersonic and transonic flow regimes is then presented. This description is based on Direct Simulation Monte Carlo analyses in the rarefied-flow regime, thermochemical nonequilibrium Computational Fluid Dynamics in the hypersonic regime, existing wind tunnel data in the supersonic and transonic regime, additional computational work in the transonic regime, and finally, ballistic range data. The aeroshell is shown to possess the correct combination of aerodynamic stability and drag to convert the probe's initial tumbling attitude and high velocity at atmospheric-interface into the desired surface-impact orientation and velocity.

  19. Ion microprobe, electron microprobe and cathodoluminescence data for Allende inclusions with emphasis on plagioclase chemistry

    NASA Technical Reports Server (NTRS)

    Hutcheon, I. D.; Steele, I. M.; Smith, J. V.; Clayton, R. N.

    1978-01-01

    Three Type B inclusions from the Allende meteorite have been analyzed. A grain-to-grain characterization of mineral chemistry and isotopic content was made possible by the use of a range of techniques, including luminescence and scanning electron microscopy and electron and ion microprobe analysis. Cathodoluminescence was used in fine-grained, optically opaque regions to distinguish between sub-micrometer phases, such as garnet and Si-rich material, subsequently identified by electron probe and scanning electron microscope analyses. Four types of luminescence patterns, due to twinning, primary sector zoning, alteration of boundaries and fractures, and shock effects, were identified in Allende plagioclase. Luminescence color exhibited a strong correlation with Mg content and provided a guide for an electron probe quantitative map of Mg and Na distributions. Ion microprobe studies of individual grains revealed large excesses of Mg-26.

  20. Conductance spectra of asymmetric ferromagnet/ferromagnet/ferromagnet junctions

    NASA Astrophysics Data System (ADS)

    Pasanai, K.

    2017-01-01

    A theory of tunneling spectroscopy of ferromagnet/ferromagnet/ferromagnet junctions was studied. We applied a delta-functional approximation for the interface scattering properties under a one-dimensional system of a free electron approach. The reflection and transmission probabilities were calculated in the ballistic regime, and the conductance spectra were then calculated using the Landauer formulation. The magnetization directions were set to be either parallel (P) or anti-parallel (AP) alignments, for comparison. We found that the conductance spectra was suppressed when increasing the interfacial scattering at the interfaces. Moreover, the electron could exhibit direct transmission when the thickness was rather thin. Thus, there was no oscillation in this case. However, in the case of a thick layer the conductance spectra oscillated, and this oscillation was most prominent when the middle layer thickness increased. In the case of direct transmission, the conductance spectra of P and AP systems were definitely suppressed with increased exchange energy of the middle ferromagnet. This also refers to an increase in the magnetoresistance of the junction. In the case of oscillatory behavior, the positions of the resonance peaks were changed as the exchange energy was changed.

  1. Longitudinal domain wall formation in elongated assemblies of ferromagnetic nanoparticles.

    PubMed

    Varón, Miriam; Beleggia, Marco; Jordanovic, Jelena; Schiøtz, Jakob; Kasama, Takeshi; Puntes, Victor F; Frandsen, Cathrine

    2015-09-29

    Through evaporation of dense colloids of ferromagnetic ~13 nm ε-Co particles onto carbon substrates, anisotropic magnetic dipolar interactions can support formation of elongated particle structures with aggregate thicknesses of 100-400 nm and lengths of up to some hundred microns. Lorenz microscopy and electron holography reveal collective magnetic ordering in these structures. However, in contrast to continuous ferromagnetic thin films of comparable dimensions, domain walls appear preferentially as longitudinal, i.e., oriented parallel to the long axis of the nanoparticle assemblies. We explain this unusual domain structure as the result of dipolar interactions and shape anisotropy, in the absence of inter-particle exchange coupling.

  2. EDITORIAL: Colloidal suspensions Colloidal suspensions

    NASA Astrophysics Data System (ADS)

    Petukhov, Andrei; Kegel, Willem; van Duijneveldt, Jeroen

    2011-05-01

    Special issue in honour of Henk Lekkerkerker's 65th birthday Professor Henk N W Lekkerkerker is a world-leading authority in the field of experimental and theoretical soft condensed matter. On the occasion of his 65th birthday in the summer of 2011, this special issue celebrates his many contributions to science. Henk Lekkerkerker obtained his undergraduate degree in chemistry at the University of Utrecht (1968) and moved to Calgary where he received his PhD in 1971. He moved to Brussels as a NATO fellow at the Université Libre de Bruxelles and was appointed to an assistant professorship (1974), an associate professorship (1977) and a full professorship (1980) in physical chemistry at the Vrije Universiteit Brussel. In 1985 he returned to The Netherlands to take up a professorship at the Van 't Hoff Laboratory, where he has been ever since. He has received a series of awards during his career, including the Onsager Medal (1999) of the University of Trondheim, the Bakhuys Roozeboom Gold Medal (2003) of the Royal Dutch Academy of Arts and Sciences (KNAW), the ECIS-Rhodia European Colloid and Interface Prize (2003), and the Liquid Matter Prize of the European Physical Society (2008). He was elected a member of KNAW in 1996, was awarded an Academy Chair position in 2005, and has held several visiting lectureships. Henk's work focuses on phase transitions in soft condensed matter, and he has made seminal contributions to both the theoretical and experimental aspects of this field. Here we highlight three major themes running through his work, and a few selected publications. So-called depletion interactions may lead to phase separation in colloid-polymer mixtures, and Henk realised that the partitioning of polymer needs to be taken into account to describe the phase behaviour correctly [1]. Colloidal suspensions can be used as model fluids, with the time- and length-scales involved leading to novel opportunities, notably the direct observation of capillary waves at a

  3. Aerothermal Heating Predictions for Mars Microprobe

    NASA Technical Reports Server (NTRS)

    Mitcheltree, R. A.; DiFulvio, M.; Horvath, T. J.; Braun, R. D.

    1998-01-01

    A combination of computational predictions and experimental measurements of the aerothermal heating expected on the two Mars Microprobes during their entry to Mars are presented. The maximum, non-ablating, heating rate at the vehicle's stagnation point (at alpha = 0 degrees) is predicted for an undershoot trajectory to be 194 Watts per square centimeters with associated stagnation point pressure of 0.064 atm. Maximum stagnation point pressure occurs later during the undershoot trajectory and is 0.094 atm. From computations at seven overshoot-trajectory points, the maximum heat load expected at the stagnation point is near 8800 Joules per square centimeter. Heat rates and heat loads on the vehicle's afterbody are much lower than the forebody. At zero degree angle-of-attack, heating over much of the hemi-spherical afterbody is predicted to be less than 2 percent of the stagnation point value. Good qualitative agreement is demonstrated for forebody and afterbody heating between CFD calculations at Mars entry conditions and experimental thermographic phosphor measurements from the Langley 20-Inch Mach 6 Air Tunnel. A novel approach which incorporates six degree-of-freedom trajectory simulations to perform a statistical estimate of the effect of angle-of-attack, and other off-nominal conditions, on heating is included.

  4. Stand-alone microprobe at Livermore

    SciTech Connect

    Antolak, A J; Bench, G S; Brown, T A; Frantz, B R; Grant, P G; Morse, D H; Roberts, M L

    1998-10-02

    Lawrence Livermore National Laboratory (LLNL) and Sandia National Laboratories/California have jointly constructed a new stand-alone microprobe facility. Although the facility was built to develop a method to rapidly locate and determine elemental concentrations of micron scale particulates on various media using PIXE, the facility has found numerous applications in biology and materials science. The facility is located at LLNL and uses a General Ionex Corporation Model 358 duoplasmatron negative ion source, a National Electrostatics Corporation 5SDH-2 tandem accelerator, and an Oxford triplet lens. Features of the system include complete computer control of the beam transport using LabVIEWTM for Macintosh, computer controlled beam collimating and divergence limiting slits, automated sample positioning to micron resolution, and video optics for beam positioning and sample observation. Data collection is accomplished with the simultaneous use of as many as four EG&G Ortec IGLET-XTM X-Ray detectors, digital amplifiers made by X-Ray Instruments and Associates (XIA), and LabVIEWTM for Macintosh acquisition software.

  5. The new nuclear microprobe at Livermore

    NASA Astrophysics Data System (ADS)

    Roberts, M. L.; Bench, G. S.; Heikkinen, D. W.; Morse, D. H.; Bach, P. R.; Pontau, A. E.

    1995-09-01

    Lawrence Livermore National Laboratory (LLNL) and Sandia National Laboratories/California have jointly constructed a new nuclear microprobe beamline. This beamline is located on the LLNL 10 MV tandem accelerator and can be used for multidisciplinary research using PIXE, PIGE, energy loss tomography, or IBS techniques. Distinctive features of the beamline include incorporation of magnet power supplies into the accelerator control system, computer-controlled object and image slits, automated target positioning to sub-micron resolution, and video optics for beam positioning and observation. Mitigation of vibrations was accomplished with vibration isolators and a rigid beamline design while integral beamline shielding was used to shield from stray magnetic fields. Available detectors include a wavelength dispersive X-ray spectrometer, a High-Purity Germanium detector (HPGe), a Lithium-Drifted Silicon X-Ray detector (SiLi), and solid state surface barrier detectors. Along with beamline performance, results from recent measurements on determination of trace impurities in an International Thermonuclear Experimental Reactor (ITER) super conducting wire strand, determination of Ca/Sr ratios in seashells, and determination of minor and trace element concentrations in sperm cells are presented.

  6. Deep Space 2: The Mars Microprobe Mission

    NASA Astrophysics Data System (ADS)

    Smrekar, Suzanne; Catling, David; Lorenz, Ralph; Magalhães, Julio; Moersch, Jeffrey; Morgan, Paul; Murray, Bruce; Presley-Holloway, Marsha; Yen, Albert; Zent, Aaron; Blaney, Diana

    The Mars Microprobe Mission will be the second of the New Millennium Program's technology development missions to planetary bodies. The mission consists of two penetrators that weigh 2.4 kg each and are being carried as a piggyback payload on the Mars Polar Lander cruise ring. The spacecraft arrive at Mars on December 3, 1999. The two identical penetrators will impact the surface at ~190 m/s and penetrate up to 0.6 m. They will land within 1 to 10 km of each other and ~50 km from the Polar Lander on the south polar layered terrain. The primary objective of the mission is to demonstrate technologies that will enable future science missions and, in particular, network science missions. A secondary goal is to acquire science data. A subsurface evolved water experiment and a thermal conductivity experiment will estimate the water content and thermal properties of the regolith. The atmospheric density, pressure, and temperature will be derived using descent deceleration data. Impact accelerometer data will be used to determine the depth of penetration, the hardness of the regolith, and the presence or absence of 10 cm scale layers.

  7. Subgroup report on hard x-ray microprobes

    SciTech Connect

    Ice, G.E.; Barbee, T.; Bionta, R.; Howells, M.; Thompson, A.C.; Yun, W.

    1994-09-01

    The increasing availability of synchrotron x-ray sources has stimulated the development of advanced hard x-ray (E{>=}5 keV) microprobes. New x-ray optics have been demonstrated which show promise for achieving intense submicron hard x-ray probes. These probes will be used for extraordinary elemental detection by x-ray fluorescence/absorption and for microdiffraction to identify phase and strain. The inherent elemental and crystallographic sensitivity of an x-ray microprobe and its inherently nondestructive and penetrating nature makes the development of an advanced hard x-ray microprobe an important national goal. In this workshop state-of-the-art hard x-ray microprobe optics were described and future directions were discussed. Gene Ice, Oak Ridge National Laboratory (ORNL), presented an overview of the current status of hard x-ray microprobe optics and described the use of crystal spectrometers to improve minimum detectable limits in fluorescent microprobe experiments. Al Thompson, Lawrence Berkeley Laboratory (LBL), described work at the Center for X-ray Optics to develop a hard x-ray microprobe based on Kirkpatrick-Baez (KB) optics. Al Thompson also showed the results of some experimental measurements with their KB optics. Malcolm Howells presented a method for bending elliptical mirrors and Troy Barbee commented on the use of graded d spacings to achieve highest efficiency in KB multilayer microfocusing. Richard Bionta, Lawrence Livermore National Laboratory (LLNL), described the development of the first hard x-ray zone plates and future promise of so called {open_quotes}jelly roll{close_quotes} or sputter slice zone plates. Wenbing Yun, Argonne National Laboratory (ANL), described characterization of jelly roll and lithographically produced zone plates and described the application of zone plates to focus extremely narrow bandwidths by nuclear resonance. This report summarizes the presentations of the workshop subgroup on hard x-ray microprobes.

  8. Electrically detected ferromagnetic resonance

    SciTech Connect

    Goennenwein, S. T. B.; Schink, S. W.; Brandlmaier, A.; Boger, A.; Opel, M.; Gross, R.; Keizer, R. S.; Klapwijk, T. M.; Gupta, A.; Huebl, H.; Bihler, C.; Brandt, M. S.

    2007-04-16

    We study the magnetoresistance properties of thin ferromagnetic CrO{sub 2} and Fe{sub 3}O{sub 4} films under microwave irradiation. Both the sheet resistance {rho} and the Hall voltage V{sub Hall} characteristically change when a ferromagnetic resonance (FMR) occurs in the film. The electrically detected ferromagnetic resonance (EDFMR) signals closely match the conventional FMR, measured simultaneously, in both resonance fields and line shapes. The sign and the magnitude of the resonant changes {delta}{rho}/{rho} and {delta}V{sub Hall}/V{sub Hall} can be consistently described in terms of a Joule heating effect. Bolometric EDFMR thus is a powerful tool for the investigation of magnetic anisotropy and magnetoresistive phenomena in ferromagnetic micro- or nanostructures.

  9. What Is a Colloid?

    ERIC Educational Resources Information Center

    Lamb, William G.

    1985-01-01

    Describes the properties of colloids, listing those commonly encountered (such as whipped cream, mayonnaise, and fog). Also presents several experiments using colloids and discusses "Silly Putty," a colloid with viscoelastic properties whose counterintuitive properties result from its mixture of polymers. (DH)

  10. Magnetic Assisted Colloidal Pattern Formation

    NASA Astrophysics Data System (ADS)

    Yang, Ye

    photoacids, which stabilized the structures after the external field was removed. This approach has potential applications in the fabrication of advanced materials. My thesis is arranged as follows. In Chapter 1, I present a brief background of general pattern formation and why I chose to investigate patterns formed in colloidal systems. I also provide a brief review of field-assisted manipulation techniques in order to motivate why I selected magnetic and acoustic field to study colloidal patterns. In chapter 2, I present the theoretical background of magnetic manipulation, which is the main technique used in my research. In this chapter, I will introduce the basic knowledge on magnetic materials and theories behind magnetic manipulation. The underlining thermodynamic mechanisms and theoretical/computational approaches in colloidal pattern formation are also briefly reviewed. In Chapter 3, I focus on using these concepts to study adhesion forces between particle and surfaces. In Chapter 4, I focus on exploring the ground states of colloidal patterns formed from the anti-ferromagnetic interactions of mixtures of particles, as a function of the particle volume fractions. In Chapter 5, I discuss my research on phase transformations of the well-ordered checkerboard phase formed from the equimolar mixture of magnetic and non-magnetic beads in ferrofluid, and I focus mainly on phase transformations in a slowly varying magnetic field. In Chapter 6, I discuss my work on the superimposed magnetic and acoustic field to study patterns formed from monocomponent colloidal suspensions under vertical confinement. Finally, I conclude my thesis in Chapter 7 and discuss future directions and open questions that can be explored in magnetic field directed self-organization in colloidal systems.

  11. Elastic recoil detection analysis on the ANSTO heavy ion microprobe

    NASA Astrophysics Data System (ADS)

    Siegele, R.; Orlic, I.; Cohen, David D.

    2002-05-01

    The heavy ion microprobe at the Australian Nuclear Science and Technology Organisation is capable of focussing heavy ions with an ME/ q2 of up to 100 amu MeV. This makes the microprobe ideally suited for heavy ion elastic recoil detection analysis (ERDA). However, beam currents on a microprobe are usually very small, which requires a detection system with a large solid angle. We apply microbeam heavy ion ERDA using a large solid angle ΔE- E telescope with a gas ΔE detector to layered structures. We demonstrate the capability to measure oxygen and carbon with a lateral resolution of 20 μm, together with determination of the depth of the contamination in thin deposited layers.

  12. Electrohydrodynamically patterned colloidal crystals

    NASA Technical Reports Server (NTRS)

    Hayward, Ryan C. (Inventor); Poon, Hak F. (Inventor); Xiao, Yi (Inventor); Saville, Dudley A. (Inventor); Aksay, Ilhan A. (Inventor)

    2003-01-01

    A method for assembling patterned crystalline arrays of colloidal particles using ultraviolet illumination of an optically-sensitive semiconducting anode while using the anode to apply an electronic field to the colloidal particles. The ultraviolet illumination increases current density, and consequently, the flow of the colloidal particles. As a result, colloidal particles can be caused to migrate from non-illuminated areas of the anode to illuminated areas of the anode. Selective illumination of the anode can also be used to permanently affix colloidal crystals to illuminated areas of the anode while not affixing them to non-illuminated areas of the anode.

  13. Dynamics of magnetic assembly of binary colloidal structures

    NASA Astrophysics Data System (ADS)

    Nogueras-Lara, F.; Rodríguez-Arco, L.; López-López, M. T.

    2015-08-01

    Magnetic field (MF)-directed assembly of colloidal particles provides a step towards the bottom-up manufacturing of smart materials whose properties can be precisely modulated by non-contact forces. Here, we study the MF-directed assembly in binary colloids made up of strong ferromagnetic and diamagnetic microparticles dispersed in ferrofluids. We present observations of the aggregation of pairs and small groups of particles to build equilibrium assemblies. We also develop a theoretical model capable of solving the aggregation dynamics and predicting the particle trajectories, a key factor to understand the physics governing the MF-directed assembly.

  14. Focusing optics for a synchrotron x radiation microprobe

    SciTech Connect

    Ice, G.E.; Sparks, C.J. Jr.

    1983-01-01

    We propose two constant deviation and energy-tunable fluorescent microprobe optical designs which efficiently use x rays available from ending magnets and insertion devices of synchrotron radiation sources. The simpler system consists of a cylindrically bent multilayer to focus the vertical opening angle by in-plane scattering, a fixed radius cylindrically curved multilayer which sagittally focuses the horizontal divergence, and a pinhole to further reduce the beam to microprobe dimensions. A more versatile system has a pair of flat nondispersively arranged diffracting optics followed by crossed elliptical mirrors. These nondispersive combinations can produce a fixed-exit beam. We compare the relative intensity with other optical systems.

  15. Microactuator fabricated by powder particle assemblage using microprobe technology

    NASA Astrophysics Data System (ADS)

    Konno, Takeshi; Egashira, Mitsuru; Shinya, Norio

    1997-06-01

    In the previous paper, preliminary research results on powder particle assemblage technique using a microprobe was reported. It was shown that the technique makes it possible to manipulate powder particles one by one, etch microscopically and weld the powder particle into a substrate or other powder particles. In this work, the welding mechanism of this method and metallurgical properties of welded parts were investigated, and micro- actuators were fabricated by means of powder particle assemblage technique using the microprobe. The results indicated the potentiality of this technique for application to assemblage of micro-machine and micro-devices.

  16. Saturated Zone Colloid Transport

    SciTech Connect

    H. Viswanathan; P. Reimus

    2003-09-05

    Colloid retardation is influenced by the attachment and detachment of colloids from immobile surfaces. This analysis demonstrates the development of parameters necessary to estimate attachment and detachment of colloids and, hence, retardation in both fractured tuff and porous alluvium. Field and experimental data specific to fractured tuff are used for the analysis of colloid retardation in fractured tuff. Experimental data specific to colloid transport in alluvial material from Yucca Mountain as well as bacteriophage field studies in alluvial material, which are thought to be good analogs for colloid transport, are used to estimate attachment and detachment of colloids in the alluvial material. There are no alternative scientific approaches or technical methods for calculating these retardation factors.

  17. Microfluidic colloid filtration

    NASA Astrophysics Data System (ADS)

    Linkhorst, John; Beckmann, Torsten; Go, Dennis; Kuehne, Alexander J. C.; Wessling, Matthias

    2016-03-01

    Filtration of natural and colloidal matter is an essential process in today’s water treatment processes. The colloidal matter is retained with the help of micro- and nanoporous synthetic membranes. Colloids are retained in a “cake layer” – often coined fouling layer. Membrane fouling is the most substantial problem in membrane filtration: colloidal and natural matter build-up leads to an increasing resistance and thus decreasing water transport rate through the membrane. Theoretical models exist to describe macroscopically the hydrodynamic resistance of such transport and rejection phenomena; however, visualization of the various phenomena occurring during colloid retention is extremely demanding. Here we present a microfluidics based methodology to follow filter cake build up as well as transport phenomena occuring inside of the fouling layer. The microfluidic colloidal filtration methodology enables the study of complex colloidal jamming, crystallization and melting processes as well as translocation at the single particle level.

  18. Saturated Zone Colloid Transport

    SciTech Connect

    H. S. Viswanathan

    2004-10-07

    This scientific analysis provides retardation factors for colloids transporting in the saturated zone (SZ) and the unsaturated zone (UZ). These retardation factors represent the reversible chemical and physical filtration of colloids in the SZ. The value of the colloid retardation factor, R{sub col} is dependent on several factors, such as colloid size, colloid type, and geochemical conditions (e.g., pH, Eh, and ionic strength). These factors are folded into the distributions of R{sub col} that have been developed from field and experimental data collected under varying geochemical conditions with different colloid types and sizes. Attachment rate constants, k{sub att}, and detachment rate constants, k{sub det}, of colloids to the fracture surface have been measured for the fractured volcanics, and separate R{sub col} uncertainty distributions have been developed for attachment and detachment to clastic material and mineral grains in the alluvium. Radionuclides such as plutonium and americium sorb mostly (90 to 99 percent) irreversibly to colloids (BSC 2004 [DIRS 170025], Section 6.3.3.2). The colloid retardation factors developed in this analysis are needed to simulate the transport of radionuclides that are irreversibly sorbed onto colloids; this transport is discussed in the model report ''Site-Scale Saturated Zone Transport'' (BSC 2004 [DIRS 170036]). Although it is not exclusive to any particular radionuclide release scenario, this scientific analysis especially addresses those scenarios pertaining to evidence from waste-degradation experiments, which indicate that plutonium and americium may be irreversibly attached to colloids for the time scales of interest. A section of this report will also discuss the validity of using microspheres as analogs to colloids in some of the lab and field experiments used to obtain the colloid retardation factors. In addition, a small fraction of colloids travels with the groundwater without any significant retardation

  19. A thermal microprobe fabricated with wafer-stage processing

    NASA Astrophysics Data System (ADS)

    Zhang, Yongxia; Zhang, Yanwei; Blaser, Juliana; Sriram, T. S.; Enver, Ahsan; Marcus, R. B.

    1998-05-01

    A thermal microprobe has been designed and built for high resolution temperature sensing. The thermal sensor is a thin-film thermocouple junction at the tip of an atomic force microprobe (AFM) silicon probe needle. Only wafer-stage processing steps are used for the fabrication. For high resolution temperature sensing it is essential that the junction be confined to a short distance at the AFM tip. This confinement is achieved by a controlled photoresist coating process. Experiment prototypes have been made with an Au/Pd junction confined to within 0.5 μm of the tip, with the two metals separated elsewhere by a thin insulating oxide layer. Processing begins with double-polished, n-type, 4 in. diameter, 300-μm-thick silicon wafers. Atomically sharp probe tips are formed by a combination of dry and wet chemical etching, and oxidation sharpening. The metal layers are sputtering deposited and the cantilevers are released by a combination of KOH and dry etching. A resistively heated calibration device was made for temperature calibration of the thermal microprobe over the temperature range 25-110 °C. Over this range the thermal outputs of two microprobes are 4.5 and 5.6 μV/K and is linear. Thermal and topographical images are also obtained from a heated tungsten thin film fuse.

  20. Ring around the colloid

    NASA Astrophysics Data System (ADS)

    Cavallaro, Marcello, Jr.; Gharbi, Mohamed A.; Beller, Daniel A.; Čopar, Simon; Shi, Zheng; Kamien, Randall D.; Yang, Shu; Baumgart, Tobias; Stebe, Kathleen J.

    In this work, we show that Janus washers, genus-one colloids with hybrid anchoring conditions, form topologically required defects in nematic liquid crystals. Experiments under crossed polarizers reveal the defect structure to be a rigid disclination loop confined within the colloid, with an accompanying defect in the liquid crystal. When confined to a homeotropic cell, the resulting colloid-defect ring pair tilts relative to the far field director, in contrast to the behavior of toroidal colloids with purely homeotropic anchoring. We show that this tilting behavior can be reversibly suppressed by the introduction of a spherical colloid into the center of the toroid, creating a new kind of multi-shape colloidal assemblage.

  1. Bacteriophage PRD1 and silica colloid transport and recovery in an iron oxide-coated sand aquifer

    USGS Publications Warehouse

    Ryan, J.N.; Elimelech, M.; Ard, R.A.; Harvey, R.W.; Johnson, P.R.

    1999-01-01

    Bacteriophage PRD1 and silica colloids were co-injected into sewage- contaminated and uncontaminated zones of an iron oxide-coated sand aquifer on Cape Cod, MA, and their transport was monitored over distances up to 6 m in three arrays. After deposition, the attached PRD1 and silica colloids were mobilized by three different chemical perturbations (elevated pH, anionic surfactant, and reductant). PRD1 and silica colloids experienced less attenuation in the contaminated zone where adsorbed organic matter and phosphate may be hindering attachment of PRD1 and silica colloids to the iron oxide coatings. The PRD1 collision efficiencies agree well with collision efficiencies predicted by assuming favorable PRD1 deposition on iron oxide coatings for which the surface area coverage was measured by microprobe analysis of sediment thin sections. ?? potentials of the PRD1, silica colloids, and aquifer grains corroborated the transport results, indicating that electrostatic forces dominated the attachment of PRD1 and silica colloids. Elevated pH was the chemical perturbation most effective at mobilizing the attached PRD1 and silica colloids. Elevated surfactant concentration mobilized the attached PRD1 and silica colloids more effectively in the contaminated zone than in the uncontaminated zone.Bacteriophage PRD1 and silica colloids were co-injected into sewage-contaminated and uncontaminated zones of an iron oxide-coated sand aquifer on Cape Cod, MA, and their transport was monitored over distances up to 6 m in three arrays. After deposition, the attached PRD1 and silica colloids were mobilized by three different chemical perturbations (elevated pH, anionic surfactant, and reductant). PRD1 and silica colloids experienced less attenuation in the contaminated zone where adsorbed organic matter and phosphate may be hindering attachment of PRD1 and silica colloids to the iron oxide coatings. The PRD1 collision efficiencies agree well with collision efficiencies predicted by

  2. UZ Colloid Transport Model

    SciTech Connect

    M. McGraw

    2000-04-13

    The UZ Colloid Transport model development plan states that the objective of this Analysis/Model Report (AMR) is to document the development of a model for simulating unsaturated colloid transport. This objective includes the following: (1) use of a process level model to evaluate the potential mechanisms for colloid transport at Yucca Mountain; (2) Provide ranges of parameters for significant colloid transport processes to Performance Assessment (PA) for the unsaturated zone (UZ); (3) Provide a basis for development of an abstracted model for use in PA calculations.

  3. Pituitary Colloid Cyst

    PubMed Central

    Guduk, Mustafa; Sun, Halil Ibrahim; Sav, Murat Aydin; Berkman, Zafer

    2017-01-01

    Abstract Colloid cysts appear most commonly in the third ventricle, their occurrence in the sellar region is uncommon. The authors report a female patient with a pituitary colloid cyst. She was diagnosed incidentally with a sellar lesion by a routine paranasal computed tomography examination performed for planning of a dental implant surgery. Radiologic examinations revealed a pituitary lesion that was removed by transnasal transsphenoidal route. Her pathologic examination revealed that the lesion was a colloid cyst. Although rare, colloid cysts should be considered in the differential diagnosis of pituitary lesions PMID:27792102

  4. Analysis of colloid transport

    SciTech Connect

    Travis, B.J.; Nuttall, H.E.

    1985-12-31

    The population balance methodology is described and applied to the transport and capture of polydispersed colloids in packed columns. The transient model includes particle growth, capture, convective transport, and dispersion. We also follow the dynamic accumulation of captured colloids on the solids. The multidimensional parabolic partial differential equation was solved by a recently enhanced method of characteristics technique. This computational technique minimized numerical dispersion and is computationally very fast. The FORTRAN 77 code ran on a VAX-780 in less than a minute and also runs on an IBM-AT using the Professional FORTRAN compiler. The code was extensively tested against various simplified cases and against analytical models. The packed column experiments by Saltelli et al. were re-analyzed incorporating the experimentally reported size distribution of the colloid feed material. Colloid capture was modeled using a linear size dependent filtration function. The effects of a colloid size dependent filtration factor and various initial colloid size distributions on colloid migration and capture were investigated. Also, we followed the changing colloid size distribution as a function of position in the column. Some simple arguments are made to assess the likelihood of colloid migration at a potential NTS Yucca Mountain waste disposal site. 10 refs., 3 figs., 1 tab.

  5. Fabrication and surface-modification of implantable microprobes for neuroscience studies

    NASA Astrophysics Data System (ADS)

    Cao, H.; Nguyen, C. M.; Chiao, J. C.

    2012-06-01

    In this work implantable micro-probes for central nervous system (CNS) studies were developed on silicon and polyimide substrates. The probes which contained micro-electrode arrays with different surface modifications were designed for implantation in the CNS. The electrode surfaces were modified with nano-scale structures that could greatly increase the active surface area in order to enhance the electrochemical current outputs while maintaining micro-scale dimensions of the electrodes and probes. The electrodes were made of gold or platinum, and designed with different sizes. The silicon probes were modified by silicon nanowires fabricated with the vapor-liquid-solid mechanism at high temperatures. With polyimide substrates, the nanostructure modification was carried out by applying concentrated gold or silver colloid solutions onto the micro-electrodes at room temperature. The surfaces of electrodes before and after modification were observed by scanning electron microscopy. The silicon nanowire-modified surface was characterized by cyclic voltammetry. Experiments were carried out to investigate the improvement in sensing performance. The modified electrodes were tested with H2O2, electrochemical L-glutamate and dopamine. Comparisons between electrodes with and without nanostructure modification were conducted showing that the modifications have enhanced the signal outputs of the electrochemical neurotransmitter sensors.

  6. Interface colloidal robotic manipulator

    DOEpatents

    Aronson, Igor; Snezhko, Oleksiy

    2015-08-04

    A magnetic colloidal system confined at the interface between two immiscible liquids and energized by an alternating magnetic field dynamically self-assembles into localized asters and arrays of asters. The colloidal system exhibits locomotion and shape change. By controlling a small external magnetic field applied parallel to the interface, structures can capture, transport, and position target particles.

  7. Radioactive halos and ion microprobe measurement of Pb isotope ratios

    NASA Technical Reports Server (NTRS)

    Gentry, R. V.

    1974-01-01

    This investigation was to obtain, if possible, the Pb isotope ratios of both lunar and meteoritic troilite grains by utilizing ion microprobe techniques. Such direct in situ measurement of Pb isotope ratios would eliminate contamination problems inherent in wet chemistry separation procedures, and conceivably determine whether lunar troilite grains were of meteoritic origin. For comparison purposes two samples of meteoritic troilite were selected (one from Canyon Diablo) for analysis along with two very small lunar troilite grains (approximately 50-100 microns). It was concluded that the ion microprobe as presently operating, does not permit the in situ measurement of Pb isotope ratios in lunar or meteoritic troilite. On the basis of these experiments no conclusions could be drawn as to the origin of the lunar troilite grains.

  8. Driving magnetic colloidal polymers

    NASA Astrophysics Data System (ADS)

    Dempster, Joshua; Olvera de La Cruz, Monica

    Magnetic colloids are of growing interest for applications such as drug delivery and in vitro tissue growth. Recent experiments have synthesized 1D chains of magnetic colloids into permanent colloidal polymers. We study magnetic colloidal polymers theoretically and computationally under the influence of time-varying external fields and find a rich set of controllable, dynamic conformations. By iterating through a sequence of conformations, these polymers can perform mechanical functions. We discuss possible roles for these polymers beyond those considered for single colloids. This work was supported as part of the Center for Bio-Inspired Energy Science, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award # DE-SC0000989.

  9. Microprobe analyses of glasses and minerals from Luna-16 soil

    NASA Technical Reports Server (NTRS)

    Brown, R. W.; Harmon, R. S.; Jakes, P.; Reid, A. M.; Ridley, W. I.; Warner, J. L.

    1971-01-01

    Electron microprobe analyses are presented for nine elements in 250 glasses and 434 pyroxenes, eight elements in 113 olivines, and six elements in 354 feldspars, 35 spinels, and 159 ilmenites. All grains are from the 125-425 micron fraction of horizon A and horizon D soil from the Luna 16 sample. A norm is presented for each glass analysis and the structural formula is calculated for each mineral analysis.

  10. Magnetically controlled ferromagnetic swimmers

    PubMed Central

    Hamilton, Joshua K.; Petrov, Peter G.; Winlove, C. Peter; Gilbert, Andrew D.; Bryan, Matthew T.; Ogrin, Feodor Y.

    2017-01-01

    Microscopic swimming devices hold promise for radically new applications in lab-on-a-chip and microfluidic technology, diagnostics and drug delivery etc. In this paper, we demonstrate the experimental verification of a new class of autonomous ferromagnetic swimming devices, actuated and controlled solely by an oscillating magnetic field. These devices are based on a pair of interacting ferromagnetic particles of different size and different anisotropic properties joined by an elastic link and actuated by an external time-dependent magnetic field. The net motion is generated through a combination of dipolar interparticle gradient forces, time-dependent torque and hydrodynamic coupling. We investigate the dynamic performance of a prototype (3.6 mm) of the ferromagnetic swimmer in fluids of different viscosity as a function of the external field parameters (frequency and amplitude) and demonstrate stable propulsion over a wide range of Reynolds numbers. We show that the direction of swimming has a dependence on both the frequency and amplitude of the applied external magnetic field, resulting in robust control over the speed and direction of propulsion. This paves the way to fabricating microscale devices for a variety of technological applications requiring reliable actuation and high degree of control. PMID:28276490

  11. Metallic quantum ferromagnets

    NASA Astrophysics Data System (ADS)

    Brando, M.; Belitz, D.; Grosche, F. M.; Kirkpatrick, T. R.

    2016-04-01

    An overview of quantum phase transitions (QPTs) in metallic ferromagnets, discussing both experimental and theoretical aspects, is given. These QPTs can be classified with respect to the presence and strength of quenched disorder: Clean systems generically show a discontinuous, or first-order, QPT from a ferromagnetic to a paramagnetic state as a function of some control parameter, as predicted by theory. Disordered systems are much more complicated, depending on the disorder strength and the distance from the QPT. In many disordered materials the QPT is continuous, or second order, and Griffiths-phase effects coexist with QPT singularities near the transition. In other systems the transition from the ferromagnetic state at low temperatures is to a different type of long-range order, such as an antiferromagnetic or a spin-density-wave state. In still other materials a transition to a state with glasslike spin dynamics is suspected. The review provides a comprehensive discussion of the current understanding of these various transitions and of the relation between experiment and theory.

  12. Precessing Ferromagnetic Needle Magnetometer.

    PubMed

    Jackson Kimball, Derek F; Sushkov, Alexander O; Budker, Dmitry

    2016-05-13

    A ferromagnetic needle is predicted to precess about the magnetic field axis at a Larmor frequency Ω under conditions where its intrinsic spin dominates over its rotational angular momentum, Nℏ≫IΩ (I is the moment of inertia of the needle about the precession axis and N is the number of polarized spins in the needle). In this regime the needle behaves as a gyroscope with spin Nℏ maintained along the easy axis of the needle by the crystalline and shape anisotropy. A precessing ferromagnetic needle is a correlated system of N spins which can be used to measure magnetic fields for long times. In principle, by taking advantage of rapid averaging of quantum uncertainty, the sensitivity of a precessing needle magnetometer can far surpass that of magnetometers based on spin precession of atoms in the gas phase. Under conditions where noise from coupling to the environment is subdominant, the scaling with measurement time t of the quantum- and detection-limited magnetometric sensitivity is t^{-3/2}. The phenomenon of ferromagnetic needle precession may be of particular interest for precision measurements testing fundamental physics.

  13. Magnetically controlled ferromagnetic swimmers

    NASA Astrophysics Data System (ADS)

    Hamilton, Joshua K.; Petrov, Peter G.; Winlove, C. Peter; Gilbert, Andrew D.; Bryan, Matthew T.; Ogrin, Feodor Y.

    2017-03-01

    Microscopic swimming devices hold promise for radically new applications in lab-on-a-chip and microfluidic technology, diagnostics and drug delivery etc. In this paper, we demonstrate the experimental verification of a new class of autonomous ferromagnetic swimming devices, actuated and controlled solely by an oscillating magnetic field. These devices are based on a pair of interacting ferromagnetic particles of different size and different anisotropic properties joined by an elastic link and actuated by an external time-dependent magnetic field. The net motion is generated through a combination of dipolar interparticle gradient forces, time-dependent torque and hydrodynamic coupling. We investigate the dynamic performance of a prototype (3.6 mm) of the ferromagnetic swimmer in fluids of different viscosity as a function of the external field parameters (frequency and amplitude) and demonstrate stable propulsion over a wide range of Reynolds numbers. We show that the direction of swimming has a dependence on both the frequency and amplitude of the applied external magnetic field, resulting in robust control over the speed and direction of propulsion. This paves the way to fabricating microscale devices for a variety of technological applications requiring reliable actuation and high degree of control.

  14. Spherical chamber effective solution for multipurpose nuclear microprobe

    NASA Astrophysics Data System (ADS)

    Pelicon, P.; Simčič, J.; Jakšić, M.; Medunić, Z.; Naab, F.; McDaniel, F. D.

    2005-04-01

    Vacuum chambers for multipurpose nuclear microprobes must provide for the installation and servicing of several detection systems operating simultaneously, as well as sample visual control and mechanical manipulation. Detectors for X-rays, scattered ions, nuclear reaction products, secondary electrons, secondary luminescence and optical microscopes are mounted at the angles preferably larger than 120° with respect to the beam direction. Their positioning should not increase the space in the region between the ion lens and the focal point of the microprobe. Spherical chambers presented here effectively solve this problem and offer, at the same time, ports for gamma-ray detector, annular microscope, easy manual access in the sample region, ports for vertical and horizontal sample positioning and manipulation, as well as STIM and ERDA detectors at forward scattering angles and the Faraday cup. The basic construction, resulting in the three different but similar chamber designs at three nuclear microprobes worldwide, are presented. Current installation details, comments on the performance and suggested improvements are given.

  15. Longitudinal domain wall formation in elongated assemblies of ferromagnetic nanoparticles

    PubMed Central

    Varón, Miriam; Beleggia, Marco; Jordanovic, Jelena; Schiøtz, Jakob; Kasama, Takeshi; Puntes, Victor F.; Frandsen, Cathrine

    2015-01-01

    Through evaporation of dense colloids of ferromagnetic ~13 nm ε-Co particles onto carbon substrates, anisotropic magnetic dipolar interactions can support formation of elongated particle structures with aggregate thicknesses of 100–400 nm and lengths of up to some hundred microns. Lorenz microscopy and electron holography reveal collective magnetic ordering in these structures. However, in contrast to continuous ferromagnetic thin films of comparable dimensions, domain walls appear preferentially as longitudinal, i.e., oriented parallel to the long axis of the nanoparticle assemblies. We explain this unusual domain structure as the result of dipolar interactions and shape anisotropy, in the absence of inter-particle exchange coupling. PMID:26416297

  16. Possibility of ferromagnetic neutron matter

    NASA Astrophysics Data System (ADS)

    Hashimoto, Koji

    2015-04-01

    We study ferromagnetism at high density of neutrons in the QCD hadron phase, by using the simplest chiral effective model incorporating magnetic fields and the chiral anomaly. Under the assumption of spatial homogeneity, we calculate the energy density as a function of neutron density, with a magnetization and a neutral pion condensation in the style of Dautry and Neyman. We find that at a high density the energy of the ferromagnetic order is lower than that of the ordinary neutron matter, and the reduction effect is enhanced by the anomaly. Compared to the inhomogeneous phase with the alternating layer structure, our ferromagnetic phase turns out to be unfavored. However, once an axial vector meson condensation is taken into account in our simplest model, the ferromagnetic energy density is lowered significantly, which still leaves some room for a possible realization of a QCD ferromagnetic phase and ferromagnetic magnetars.

  17. Correlated petrographic, electron microprobe, and ion microprobe studies of selected primitive and processed phase assemblages in meteorites

    NASA Technical Reports Server (NTRS)

    Albee, Arden L.

    1993-01-01

    During the past three years we have received support to continue our research in elucidating the formation and alteration histories of selected meteoritic materials by a combination of petrographic, trace element, and isotopic analyses employing optical and scanning electron microscopes and electron and ion microprobes. The awarded research funds enabled the P.I. to attend the annual LPSC, the co-I to devote approximately 15 percent of his time to the research proposed in the grant, and partial support for a visiting summer post-doctoral fellow to conduct electron microprobe analyses of meteoritic samples in our laboratory. The research funds, along with support from the NASA Education Initiative awarded to P.I. G. Wasserburg, enabled the co-I to continue a mentoring program with inner-city minority youth. The support enabled us to achieve significant results in the five projects that we proposed (in addition to the Education Initiative), namely: studies of the accretional and post-accretional alteration and thermal histories in CV meteorites, characterization of periclase-bearing Fremdlinge in CV meteorites, characterization of Ni-Pt-Ge-Te-rich Fremdlinge in CV meteorites in an attempt to determine the constraints they place on the petrogenetic and thermal histories of their host CAI's, correlated electron and ion microprobe studies of silicate and phosphate inclusions in the Colomera meteorite in an attempt to determine the petrogenesis of the IE iron meteorites, and development of improved instrumental and correction procedures for improved accuracy of analysis of meteoritic materials with the electron microprobe. This grant supported, in part or whole, 18 publications so far by our research team, with at least three more papers anticipated. The list of these publications is included. The details of the research results are briefly summarized.

  18. Lock and key colloids.

    PubMed

    Sacanna, S; Irvine, W T M; Chaikin, P M; Pine, D J

    2010-03-25

    New functional materials can in principle be created using colloids that self-assemble into a desired structure by means of a programmable recognition and binding scheme. This idea has been explored by attaching 'programmed' DNA strands to nanometre- and micrometre- sized particles and then using DNA hybridization to direct the placement of the particles in the final assembly. Here we demonstrate an alternative recognition mechanism for directing the assembly of composite structures, based on particles with complementary shapes. Our system, which uses Fischer's lock-and-key principle, employs colloidal spheres as keys and monodisperse colloidal particles with a spherical cavity as locks that bind spontaneously and reversibly via the depletion interaction. The lock-and-key binding is specific because it is controlled by how closely the size of a spherical colloidal key particle matches the radius of the spherical cavity of the lock particle. The strength of the binding can be further tuned by adjusting the solution composition or temperature. The composite assemblies have the unique feature of having flexible bonds, allowing us to produce flexible dimeric, trimeric and tetrameric colloidal molecules as well as more complex colloidal polymers. We expect that this lock-and-key recognition mechanism will find wider use as a means of programming and directing colloidal self-assembly.

  19. Frequency mixer having ferromagnetic film

    DOEpatents

    Khitun, Alexander; Roshchin, Igor V.; Galatsis, Kosmas; Bao, Mingqiang; Wang, Kang L.

    2016-03-29

    A frequency conversion device, which may include a radiofrequency (RF) mixer device, includes a substrate and a ferromagnetic film disposed over a surface of the substrate. An insulator is disposed over the ferromagnetic film and at least one microstrip antenna is disposed over the insulator. The ferromagnetic film provides a non-linear response to the frequency conversion device. The frequency conversion device may be used for signal mixing and amplification. The frequency conversion device may also be used in data encryption applications.

  20. Proton beam micromachined resolution standards for nuclear microprobes

    NASA Astrophysics Data System (ADS)

    Watt, F.; Rajta, I.; van Kan, J. A.; Bettiol, A. A.; Osipowicz, T.

    2002-05-01

    The quest for smaller spot sizes has long been the goal of many nuclear microprobe groups worldwide, and consequently there is a need for good quality resolution standards. Such standards have to be consistent with the accurate measurement of state-of-the-art nuclear microbeam spot sizes, i.e. 400 nm for high current applications such as Rutherford backscattering spectrometry and proton-induced X-ray emission, and 100 nm for low current applications such as scanning transmission ion microscopy or ion beam-induced charge. The criteria for constructing a good quality nuclear microprobe resolution standard is therefore demanding: the standard has to be three dimensional with a smooth surface, have an edge definition better than the state-of-the-art beam spot resolutions, and exhibit vertical side walls. Proton beam micromachining (PBM) is a new technique of high potential for the manufacture of precise 3D microstructures. Recent developments have shown that metallic microstructures (nickel and copper) can be formed from these microshapes. Prototype nickel PBM resolution standards have been manufactured at the Research Centre for Nuclear Microscopy, NUS and these new standards are far superior to the 2000 mesh gold grids currently in use by many groups in terms of surface smoothness, vertical walls and edge definition. Results of beam resolution tests using the new PBM standards with the OM2000 microprobe end station/HVEE Singletron system have yielded spot sizes of 290 nm×450 nm for a 50 pA beam of 2 MeV protons.

  1. Preparation of ultra small samples for optical and microprobe analysis

    NASA Technical Reports Server (NTRS)

    Inman, C. S.

    1973-01-01

    This paper describes a simple but satisfactory new method for the preparation of tiny, varied and specialized specimens for electron or ion-microprobe analysis developed over the past five years. Microtektites, individual chondrules, single grains, blebs from lunar samples and meteoritic minerals have been prepared by this technique. A description of the preparation of these usually difficult samples from the initial mounting through the various polishing steps to their final polish is presented in detail. The procedures used to prevent any contamination of these specimens by the polishing agents and to prevent cross contamination to the other samples used for geochronology studies are presented.

  2. Design considerations for an x-ray microprobe

    SciTech Connect

    Howells, M.R.; Hastings, J.B.

    1982-01-01

    The optical design of a fluorescent microprobe covering the x-ray region from 2 to 16 keV is considered for the NSLS x-ray ring. The limit on detectability is from total flux (photons/..mu..m/sup 2/) and several design choices are considered to match the optical system to the storage ring to maximize throughput. The tradeoffs in image quality and energy resolution of these designs have been considered and within these constraints two firm proposals are presented.

  3. An X-ray microprobe facility using synchrotron radiation.

    PubMed

    Gordon, B M; Jones, K W; Hanson, A L; Pounds, J G; Rivers, M L; Spanne, P; Sutton, S R

    1990-01-01

    An X-ray microprobe for trace elemental analysis at micrometer spatial resolutions, using synchrotron radiation (SR), is under development. The facility consists of two beamlines, one including a 1:1 focusing mirror and the other an 8:1 ellipsoidal mirror. At present, "white light" is used for excitation of the characteristic X-ray fluorescence lines. Sensitivities in thin biological samples are in the range of 2-20 fg in 100 microns2 areas in 5 min irradiation times. Scanning techniques, as well as microtomography and chemical speciation, are discussed. Application to a specific biomedical study is included.

  4. An x-ray microprobe facility using synchrotron radiation

    SciTech Connect

    Gordon, B.M.; Jones, K.W.; Hanson, A.L.; Pounds, J.G.; Rivers, M.L.; Spanne, P.; Sutton, S.R.

    1989-01-01

    A x-ray microprobe for trace elemental analysis at micrometer spatial resolutions using synchrotron radiation (SR) is under development. The facility consists of two beamlines, one including a 1:1 focusing mirror and the other an 8:1 ellipsoidal mirror. At present ''white light''' is used for excitation of the characteristic x-ray fluorescence lines. Sensitivities in thin biological samples are in the range of 2-20 fg in 100 ..mu..m/sup 2/ areas in 5 min irradiation times. Scanning techniques as well as microtomography and chemical speciation are discussed. Application to a specific biomedical study is included. 13 refs., 2 figs.

  5. Electrostatic microprobe for determining charge domains on surfaces.

    PubMed

    Fletcher, Robert A

    2015-11-01

    An electrostatic microprobe was developed to measure charge on wipes and various test surfaces. The device is constructed on an optical microscope platform utilizing a computer controlled XY stage. Test surfaces can be optically imaged to identify microscopic features that can be correlated to the measured charge domain maps. The ultimate goal is to quantify charge on wipe cloths to determine the influence of electrostatic forces on wipe sampling efficiency. We found that certain wipe materials do not extensively charge while others accumulate charge by making contact with other surfaces (through the triboelectric effect). Charge domains are found to be nonuniform.

  6. Elemental mapping of biological samples using a scanning proton microprobe

    NASA Astrophysics Data System (ADS)

    Watt, F.; Grime, G. W.

    1988-03-01

    Elemental mapping using a scanning proton microprobe (SPM) can be a powerful technique for probing trace elements in biology, allowing complex interfaces to be studied in detail, identifying contamination and artefacts present in the specimen, and in certain circumstances obtaining indirect chemical information. Examples used to illustrate the advantages of the technique include the elemental mapping of growing pollen tubes, honey bee brain section, a mouse macrophage cell, human liver section exhibiting primary biliary cirrhosis, and the attack by a mildew fungus on a pea leaf.

  7. A High Resolution Microprobe Study of EETA79001 Lithology C

    NASA Technical Reports Server (NTRS)

    Schrader, Christian M.; Cohen, B. A.; Donovan, J. J.; Vicenzi, E. P.

    2010-01-01

    Antarctic meteorite EETA79001 has received substantial attention for possibly containing a component of Martian soil in its impact glass (Lithology C) [1]. The composition of Martian soil can illuminate near-surface processes such as impact gardening [2] and hydrothermal and volcanic activity [3,4]. Impact melts in meteorites represent our most direct samples of Martian regolith. We present the initial findings from a high-resolution electron microprobe study of Lithology C from Martian meteorite EETA79001. As this study develops we aim to extract details of a potential soil composition and to examine Martian surface processes using elemental ratios and correlations.

  8. Spin Pumping in Ferromagnetic Multilayers

    NASA Astrophysics Data System (ADS)

    Taniguchi, Tomohiro; Imamura, Hiroshi

    We present a brief review of our recent study on spin pumping in ferromagnetic multilayers. First, we present theoretical models describing spin pumping induced by ferromagnetic resonance (FMR). Then we apply the spin-pumping theory to FMR in ferromagnetic multilayers and show that the line width of the FMR spectrum depends on the thickness of the ferromagnetic metal layer which is not in resonance. We also show that the penetration depths of transverse spin current in ferromagnetic metals can be determined by analyzing the line width of the FMR spectrum. The obtained penetration depths of the transverse spin current were 3.7 nm for Py, 2.5 nm for CoFe, 12.0 nm for CoFeB, and 1.7 nm for Co, respectively.

  9. Super-achromatic microprobe for ultrahigh-resolution endoscopic OCT imaging at 800 nm (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Yuan, Wu; Alemohammad, Milad; Yu, Xiaoyun; Yu, Shaoyong; Li, Xingde

    2016-03-01

    In this paper, we report a super-achromatic microprobe made with fiber-optic ball lens to enable ultrahigh-resolution endoscopic OCT imaging. An axial resolution of ~2.4 µm (in air) can be achieved with a 7-fs Ti:Sapphire laser. The microprobe has minimal astigmatism which affords a high transverse resolution of ~5.6 µm. The miniaturized microprobe has an outer diameter of ~520 µm including the encasing metal guard and can be used to image small luminal organs. The performance of the ultrahigh-resolution OCT microprobe was demonstrated by imaging rat esophagus, guinea pig esophagus, and mouse rectum in vivo.

  10. Sampling colloids and colloid-associated contaminants in ground water

    USGS Publications Warehouse

    Backhus, Debera A.; Ryan, Joseph N.; Groher, Daniel M.; MacFarlane, John K.; Gschwend, Philip M.

    1993-01-01

    It has recently been recognized that mobile colloids may affect the transport of contaminants in ground water. To determine the significance of this process, knowledge of both the total mobile load (dissolved + colloid-associated) and the dissolved concentration of a ground-water contaminant must be obtained. Additional information regarding mobile colloid characteristics and concentrations are required to predict accurately the fate and effects of contaminants at sites where significant quantities of colloids are found. To obtain this information, a sampling scheme has been designed and refined to collect mobile colloids while avoiding the inclusion of normally immobile subsurface and well-derived solids. The effectiveness of this sampling protocol was evaluated at a number of contaminated and pristine sites.The sampling results indicated that slow, prolonged pumping of ground water is much more effective at obtaining ground-water samples that represent in situ colloid populations than bailing. Bailed samples from a coal tar-contaminated site contained 10–100 times greater colloid concentrations and up to 750 times greater polycyclic aromatic hydrocarbon concentrations as were detected in slowly pumped samples. The sampling results also indicated that ground-water colloid concentrations should be monitored in the field to determine the adequacy of purging if colloid and colloid-associated contaminants are of interest. To avoid changes in the natural ground-water colloid population through precipitation or coagulation, in situ ground-water chemistry conditions must be preserved during sampling and storage. Samples collected for determination of the total mobile load of colloids and low-solubility contaminants must not be filtered because some mobile colloids are removed by this process. Finally, suggestions that mobile colloids are present in ground water at any particular site should be corroborated with auxiliary data, such as colloid levels in

  11. Spherical colloidal photonic crystals.

    PubMed

    Zhao, Yuanjin; Shang, Luoran; Cheng, Yao; Gu, Zhongze

    2014-12-16

    CONSPECTUS: Colloidal photonic crystals (PhCs), periodically arranged monodisperse nanoparticles, have emerged as one of the most promising materials for light manipulation because of their photonic band gaps (PBGs), which affect photons in a manner similar to the effect of semiconductor energy band gaps on electrons. The PBGs arise due to the periodic modulation of the refractive index between the building nanoparticles and the surrounding medium in space with subwavelength period. This leads to light with certain wavelengths or frequencies located in the PBG being prohibited from propagating. Because of this special property, the fabrication and application of colloidal PhCs have attracted increasing interest from researchers. The most simple and economical method for fabrication of colloidal PhCs is the bottom-up approach of nanoparticle self-assembly. Common colloidal PhCs from this approach in nature are gem opals, which are made from the ordered assembly and deposition of spherical silica nanoparticles after years of siliceous sedimentation and compression. Besides naturally occurring opals, a variety of manmade colloidal PhCs with thin film or bulk morphology have also been developed. In principle, because of the effect of Bragg diffraction, these PhC materials show different structural colors when observed from different angles, resulting in brilliant colors and important applications. However, this angle dependence is disadvantageous for the construction of some optical materials and devices in which wide viewing angles are desired. Recently, a series of colloidal PhC materials with spherical macroscopic morphology have been created. Because of their spherical symmetry, the PBGs of spherical colloidal PhCs are independent of rotation under illumination of the surface at a fixed incident angle of the light, broadening the perspective of their applications. Based on droplet templates containing colloidal nanoparticles, these spherical colloidal PhCs can be

  12. Ferromagnet / superconductor oxide superlattices

    NASA Astrophysics Data System (ADS)

    Santamaria, Jacobo

    2006-03-01

    The growth of heterostructures combining oxide materials is a new strategy to design novel artificial multifunctional materials with interesting behaviors ruled by the interface. With the (re)discovery of colossal magnetoresistance (CMR) materials, there has been renewed interest in heterostructures involving oxide superconductors and CMR ferromagnets where ferromagnetism (F) and superconductivity (S) compete within nanometric distances from the interface. In F/S/F structures involving oxides, interfaces are especially complex and various factors like interface disorder and roughness, epitaxial strain, polarity mismatch etc., are responsible for depressed magnetic and superconducting properties at the interface over nanometer length scales. In this talk I will focus in F/S/F structures made of YBa2Cu3O7 (YBCO) and La0.7Ca0.3MnO3 (LCMO). The high degree of spin polarization of the LCMO conduction band, together with the d-wave superconductivity of the YBCO make this F/S system an adequate candidate for the search of novel spin dependent effects in transport. We show that superconductivity at the interface is depressed by various factors like charge transfer, spin injection or ferromagnetic superconducting proximity effect. I will present experiments to examine the characteristic distances of the various mechanisms of superconductivity depression. In particular, I will discuss that the critical temperature of the superconductor depends on the relative orientation of the magnetization of the F layers, giving rise to a new giant magnetoresistance effect which might be of interest for spintronic applications. Work done in collaboration with V. Peña^1, Z. Sefrioui^1, J. Garcia-Barriocanal^1, C. Visani^1, D. Arias^1, C. Leon^1 , N. Nemes^2, M. Garcia Hernandez^2, S. G. E. te Velthuis^3, A. Hoffmann^3, M. Varela^4, S. J. Pennycook^4. Work supported by MCYT MAT 2005-06024, CAM GR- MAT-0771/2004, UCM PR3/04-12399 Work at Argonne supported by the Department of Energy, Basic

  13. Coexistence of superconductivity and ferromagnetism in ferromagnetic metals.

    PubMed

    Karchev, N I; Blagoev, K B; Bedell, K S; Littlewood, P B

    2001-01-29

    We address the question of coexistence of superconductivity and ferromagnetism. Using a field theoretical approach we study a one-fermion effective model of a ferromagnetic superconductor in which the quasiparticles responsible for the ferromagnetism form the Cooper pairs as well. For the first time we solve self-consistently the mean-field equations for the superconducting gap and the spontaneous magnetization. We discuss the physical features which are different in this model and the standard BCS model and consider their experimental consequences.

  14. Nuclear microprobe applications to radioactive waste management basic research

    NASA Astrophysics Data System (ADS)

    Trocellier, P.; Badillo, V.; Barré, N.; Bois, L.; Cachoir, C.; Gallien, J. P.; Guilbert, S.; Mercier, F.; Tiffreau, C.

    1999-10-01

    Radioactive waste management is one of the major technical and scientific challenge to be solved by industrialized countries near the beginning of the 21st century. Relevant questions arise about the extrapolation of the long term-behavior of materials from waste package, engineered barriers and near field repository. Whatever the strategical option might be, wet atmosphere or water intrusion through the different barriers constitute the two main remobilization factors for radionuclides in the geosphere and the biosphere. The study of solid alteration processes and elemental sorption phenomena on mineral surfaces is one of the most efficient basic research approaches to assess the long term performance of waste materials. Ion beam analysis and more recently nuclear microprobe techniques have been applied to investigate exchange mechanisms near representative solid/liquid interfaces such as glass/deionized water, uranium dioxide/granitic or clay water or mineral surface/aqueous solution doped with chemical elements analogue to actinide or fission products. This paper intends to describe the different works that have been carried out in Saclay using the nuclear microprobe facility. The coupling of μRBS, μPIXE and μNRA permits to determine the evolution of the surface composition induced by chemical reactions involved. Complementary observation of solid morphology and solution analysis allows to obtain a complete elemental balance on exchange processes.

  15. Applications of the nuclear microprobe in planetary science

    NASA Astrophysics Data System (ADS)

    Vis, R. D.

    1997-07-01

    Nuclear microprobes have been used in a variety of studies on extra-terrestrial materials. Although by far the most used analytical technique is micro-PIXE, valuable contributions have also been given to planetary science using other methods available among the suite of analytical techniques provided by the microprobe. Also a few studies of the application of synchrotron radiation to planetary science has been published. Research aims are either to get a full analysis of very small objects such as cosmic dust or to extract elemental profiles over areas of interest. In the latter case, these distributions may give insight into the temperature history of the objects studied. In this way single crystals, chondrules in ordinary chondrites but also phase transitions in iron-meteorites have been investigated. Being by far the oldest objects available for research and being conserved for billions of years without serious wearing and erosion as would happen on earth, their detailed studies provide knowledge about the early history of the solar system and on primary geological processes.

  16. Ferromagnetic thin films

    DOEpatents

    Krishnan, K.M.

    1994-12-20

    A ferromagnetic [delta]-Mn[sub 1[minus]x]Ga[sub x] thin film having perpendicular anisotropy is described which comprises: (a) a GaAs substrate, (b) a layer of undoped GaAs overlying said substrate and bonded thereto having a thickness ranging from about 50 to about 100 nanometers, (c) a layer of [delta]-Mn[sub 1[minus]x]Ga[sub x] overlying said layer of undoped GaAs and bonded thereto having a thickness ranging from about 20 to about 30 nanometers, and (d) a layer of GaAs overlying said layer of [delta]-Mn[sub 1[minus]x]Ga[sub x] and bonded thereto having a thickness ranging from about 2 to about 5 nanometers, wherein x is 0.4[+-]0.05. 7 figures.

  17. Ferromagnetic thin films

    DOEpatents

    Krishnan, Kannan M.

    1994-01-01

    A ferromagnetic .delta.-Mn.sub.1-x Ga.sub.x thin film having perpendicular anisotropy is described which comprises: (a) a GaAs substrate, (b) a layer of undoped GaAs overlying said substrate and bonded thereto having a thickness ranging from about 50 to about 100 nanometers, (c) a layer of .delta.-Mn.sub.1-x Ga.sub.x overlying said layer of undoped GaAs and bonded thereto having a thickness ranging from about 20 to about 30 nanometers, and (d) a layer of GaAs overlying said layer of .delta.-Mn.sub.1-x Ga.sub.x and bonded thereto having a thickness ranging from about 2 to about 5 nanometers, wherein x is 0.4 .+-.0.05.

  18. Quantum hall ferromagnets

    NASA Astrophysics Data System (ADS)

    Kumar, Akshay

    We study several quantum phases that are related to the quantum Hall effect. Our initial focus is on a pair of quantum Hall ferromagnets where the quantum Hall ordering occurs simultaneously with a spontaneous breaking of an internal symmetry associated with a semiconductor valley index. In our first example ---AlAs heterostructures--- we study domain wall structure, role of random-field disorder and dipole moment physics. Then in the second example ---Si(111)--- we show that symmetry breaking near several integer filling fractions involves a combination of selection by thermal fluctuations known as "order by disorder" and a selection by the energetics of Skyrme lattices induced by moving away from the commensurate fillings, a mechanism we term "order by doping". We also study ground state of such systems near filling factor one in the absence of valley Zeeman energy. We show that even though the lowest energy charged excitations are charge one skyrmions, the lowest energy skyrmion lattice has charge > 1 per unit cell. We then broaden our discussion to include lattice systems having multiple Chern number bands. We find analogs of quantum Hall ferromagnets in the menagerie of fractional Chern insulator phases. Unlike in the AlAs system, here the domain walls come naturally with gapped electronic excitations. We close with a result involving only topology: we show that ABC stacked multilayer graphene placed on boron nitride substrate has flat bands with non-zero local Berry curvature but zero Chern number. This allows access to an interaction dominated system with a non-trivial quantum distance metric but without the extra complication of a non-zero Chern number.

  19. RABBIT: an electron microprobe data-reduction program using empirical corrections

    USGS Publications Warehouse

    Goff, Fraser E.

    1977-01-01

    RABBIT is a FORTRAN IV computer Program that uses Bence-Albee empirical corrections for the reduction of electron microprobe data of silicates, oxides, sulphates, carbonates, and phosphates. RABBIT efficiently reduces large volumes of data collected on 3-11 channel microprobes.

  20. Molecular microanalysis of pathological specimens in situ with a laser-Raman microprobe.

    PubMed

    Abraham, J L; Etz, E S

    1979-11-09

    A laser-Raman microprobe has been used to identify microscopic inclusions of silicone polymer in standard paraffin sections of lymph node. This example of organic chemical microanalysis in situ in pathological tissue represents an extension of microanalytical capabilities from elemental analysis, performed with electron and ion microprobes, to compound-specific molecular microanalysis.

  1. Motor-based microprobe powered by bio-assembled catalase for motion detection of DNA.

    PubMed

    Xie, Yuzhe; Fu, Shizhe; Wu, Jie; Lei, Jianping; Ju, Huangxian

    2017-01-15

    A motor-based microprobe is proposed using a tubular microengine powered by bio-assembled enzyme as catalyst and exploited for washing-free detection of DNA through motion readout. The microprobe is fabricated by assembling a catalase layer on the inner surface of poly(3,4-ethylenedioxythiophene)/Au (PEDOT/Au) microtube through DNA conjugate, which is responsible for the biocatalytic bubble propulsion. The sensing concept of the microprobe relies on the target-induced release of catalase through the DNA strand-replacement hybridization, which decreases the amount of enzyme assembled on microtube to slow down the movement of the microprobe. Therefore, the motion speed is negatively correlated with the target concentration. At the optimal conditions, the microprobe can conveniently distinguish the concentration of specific DNA in a range of 0.5-10µM without any washing and separation step. This microprobe can be prepared in batch with good reproducibility and stability, and its motion speed can be conveniently visualized by optical microscope. The proposed motor-based microprobe and its dynamic sensing method provide a novel platform for the development of intelligent microprobe and clinical diagnostic strategy.

  2. Development and applications of an epifluorescence module for synchrotron x-ray fluorescence microprobe imaging

    SciTech Connect

    Miller, Lisa M.; Smith, Randy J.; Ruppel, Meghan E.; Ott, Cassandra H.; Lanzirotti, Antonio

    2005-06-15

    Synchrotron x-ray fluorescence (XRF) microprobe is a valuable analysis tool for imaging trace element composition in situ at a resolution of a few microns. Frequently, epifluorescence microscopy is beneficial for identifying the region of interest. To date, combining epifluorescence microscopy with x-ray microprobe has involved analyses with two different microscopes. We report the development of an epifluorescence module that is integrated into a synchrotron XRF microprobe beamline, such that visible fluorescence from a sample can be viewed while collecting x-ray microprobe images simultaneously. This unique combination has been used to identify metal accumulation in Alzheimer's disease plaques and the mineral distribution in geological samples. The flexibility of this accessory permits its use on almost any synchrotron x-ray fluorescence microprobe beamline and applications in many fields of science can benefit from this technology.

  3. Topological properties of ferromagnetic superconductors

    DOE PAGES

    Cheung, Alfred K. C.; Raghu, S.

    2016-04-27

    Here, a variety of heavy fermion superconductors, such as UCoGe, UGe2, and URhGe exhibit a striking coexistence of bulk ferromagnetism and superconductivity. In the first two materials, the magnetic moment decreases with pressure, and vanishes at a ferromagnetic quantum critical point (qcp). Remarkably, the superconductivity in UCoGe varies smoothly with pressure across the qcp and exists in both the ferromagnetic and paramagnetic regimes. We argue that in UCoGe, spin-orbit interactions stabilize a time-reversal invariant odd-parity superconductor in the high pressure paramagnetic regime. Based on a simple phenomenological model, we predict that the transition from the paramagnetic normal state to themore » phase where superconductivity and ferromagnetism coexist is a first-order transition.« less

  4. Topological properties of ferromagnetic superconductors

    SciTech Connect

    Cheung, Alfred K. C.; Raghu, S.

    2016-04-27

    Here, a variety of heavy fermion superconductors, such as UCoGe, UGe2, and URhGe exhibit a striking coexistence of bulk ferromagnetism and superconductivity. In the first two materials, the magnetic moment decreases with pressure, and vanishes at a ferromagnetic quantum critical point (qcp). Remarkably, the superconductivity in UCoGe varies smoothly with pressure across the qcp and exists in both the ferromagnetic and paramagnetic regimes. We argue that in UCoGe, spin-orbit interactions stabilize a time-reversal invariant odd-parity superconductor in the high pressure paramagnetic regime. Based on a simple phenomenological model, we predict that the transition from the paramagnetic normal state to the phase where superconductivity and ferromagnetism coexist is a first-order transition.

  5. Non-ferromagnetic overburden casing

    DOEpatents

    Vinegar, Harold J.; Harris, Christopher Kelvin; Mason, Stanley Leroy

    2010-09-14

    Systems, methods, and heaters for treating a subsurface formation are described herein. At least one system for electrically insulating an overburden portion of a heater wellbore is described. The system may include a heater wellbore located in a subsurface formation and an electrically insulating casing located in the overburden portion of the heater wellbore. The casing may include at least one non-ferromagnetic material such that ferromagnetic effects are inhibited in the casing.

  6. The Elusive Organic Ferromagnet

    NASA Astrophysics Data System (ADS)

    Letts, Nathan Percy

    A new thermally stable triplet, hexa(adamantylmethylene)hexaazatritetralin dication (ACH_2)HAT^ {+2} has been prepared as a test of the Breslow-McConnell model for organic ferromagnetism. Liquid helium Curie studies to 7.5 K are consistent with it being a ground state triplet or nearly degenerate triplet. Salts of (ACH_2)HAT were isolated and characterized as tests of the Wudl and Torrance models for an organic ferromagnet. Magnetic susceptibility studies were done on (ACH_2)HAT ^{+1}BF_4^ {-1}, (ACH_2)HAT ^{+1}SbF_6 ^{-1}, (ACH_2)HAT ^{+1}PF_6 ^{-1}, (ACH_2)HAT ^{+1.6}(SbF_6 ^{-1})_{1.6}, and (ACH_2)HAT^{+2 }(SbF_6^{-1}) _2. All are paramagnetic solids. The mixed valence compound shows antiferromagnetic interactions, which would be consistent with weakly interacting radicals. It was not a ferrimagnet as predicted by the Buchachenko model. Without a crystal structure it is impossible to know whether this is a valid test of these models. The parent compound H_6HAT was isolated and characterized. Two new discotic liquid crystals were synthesized by preparing the dodecanoyl and palmitoyl derivatives of H_6HAT. They show only narrow mesophases (2 and 5 degrees, respectively). Lastly semiempirical calculations were done on the following antiaromatic systems with D_{rm nh} symmetry: cyclopropenyl anion, cyclobutadiene, cyclopentadienyl cation and benzene dication. They all demonstrated triplet ground states by 37.0, 14.4, 7.0 and 6.8 kcal/mol, respectively. Stacks of the cyclopropenyl anion and radical were also high spin including the infinite chain. In the infinite chain the monomer (C_3H_3) _2^{-1} quartet is the ground state by 14.7 kcal/mol. Stacks in the cyclopentadienyl series are not high spin, but the trimer (C_5 H_5)_3^{+2} is a ground state quartet by 7.0 kcal/mol. The spin state of the cyclopentadienyl trimer is consistent with a Buchachenko model ferrimagnetic stack.

  7. Ferromagnetism beyond Lieb's theorem

    NASA Astrophysics Data System (ADS)

    Costa, Natanael C.; Mendes-Santos, Tiago; Paiva, Thereza; Santos, Raimundo R. dos; Scalettar, Richard T.

    2016-10-01

    The noninteracting electronic structures of tight-binding models on bipartite lattices with unequal numbers of sites in the two sublattices have a number of unique features, including the presence of spatially localized eigenstates and flat bands. When a uniform on-site Hubbard interaction U is turned on, Lieb proved rigorously that at half-filling (ρ =1 ) the ground state has a nonzero spin. In this paper we consider a "CuO2 lattice" (also known as "Lieb lattice," or as a decorated square lattice), in which "d orbitals" occupy the vertices of the squares, while "p orbitals" lie halfway between two d orbitals; both d and p orbitals can accommodate only up to two electrons. We use exact determinant quantum Monte Carlo (DQMC) simulations to quantify the nature of magnetic order through the behavior of correlation functions and sublattice magnetizations in the different orbitals as a function of U and temperature; we have also calculated the projected density of states, and the compressibility. We study both the homogeneous (H) case, Ud=Up , originally considered by Lieb, and the inhomogeneous (IH) case, Ud≠Up . For the H case at half-filling, we found that the global magnetization rises sharply at weak coupling, and then stabilizes towards the strong-coupling (Heisenberg) value, as a result of the interplay between the ferromagnetism of like sites and the antiferromagnetism between unlike sites; we verified that the system is an insulator for all U . For the IH system at half-filling, we argue that the case Up≠Ud falls under Lieb's theorem, provided they are positive definite, so we used DQMC to probe the cases Up=0 ,Ud=U and Up=U ,Ud=0 . We found that the different environments of d and p sites lead to a ferromagnetic insulator when Ud=0 ; by contrast, Up=0 leads to to a metal without any magnetic ordering. In addition, we have also established that at density ρ =1 /3 , strong antiferromagnetic correlations set in, caused by the presence of one fermion on each

  8. Development of an x-ray microprobe using synchrotron radiation

    NASA Astrophysics Data System (ADS)

    Thompson, Albert C.; Chapman, Karen L.; Underwood, James H.

    1993-01-01

    An X-ray microprobe is being built that will use a bending magnet port on the new Advanced Light Source (ALS) at the Lawrence Berkeley Laboratory. A pair of elliptical multi-layer mirrors will be used to focus and monochromatize the white radiation beam from the synchrotron. A beam spot size of 1 micrometers X 1 micrometers will be produced with a bandwidth of 1 keV at 10 keV. The energy of the beam will be variable from 3 keV to 12 keV. With a counting time of 30 sec it should be possible to simultaneously measure femtogram amounts of elements from potassium to zinc.

  9. Micro Electron MicroProbe and Sample Analyzer

    NASA Technical Reports Server (NTRS)

    Manohara, Harish; Bearman, Gregory; Douglas, Susanne; Bronikowski, Michael; Urgiles, Eduardo; Kowalczyk, Robert; Bryson, Charles

    2009-01-01

    A proposed, low-power, backpack-sized instrument, denoted the micro electron microprobe and sample analyzer (MEMSA), would serve as a means of rapidly performing high-resolution microscopy and energy-dispersive x-ray spectroscopy (EDX) of soil, dust, and rock particles in the field. The MEMSA would be similar to an environmental scanning electron microscope (ESEM) but would be much smaller and designed specifically for field use in studying effects of geological alteration at the micrometer scale. Like an ESEM, the MEMSA could be used to examine uncoated, electrically nonconductive specimens. In addition to the difference in size, other significant differences between the MEMSA and an ESEM lie in the mode of scanning and the nature of the electron source.

  10. Implementation of ionoluminescence in the AGLAE scanning external microprobe

    NASA Astrophysics Data System (ADS)

    Pichon, L.; Calligaro, T.; Gonzalez, V.; Lemasson, Q.; Moignard, B.; Pacheco, C.

    2015-04-01

    The scope of this work is to present the implementation of an IBIL imaging system in the scanning external microprobe of the AGLAE facility so as to correlate luminescence and composition maps provided by PIXE, RBS and PIGE. The challenging integration of the optical spectrometer, due to incompatibility of acquisition timings and data formats with the other IBA channels has motivated the development of a specific acquisition system. This article details the IBIL setup and explains the technical solutions retained for the coupling of IBIL with IBA techniques in order to produce fast and large IBIL-IBA maps. The IBIL maps stored in the same format as the PIXE, RBS and PIGE ones can be visualised and compared using the dedicated AGLAEmap program or the PyMCA processing package. An example of such a coupled mapping on Mesoamerican jade is presented to emphasise the interest of performing simultaneously IBA and IBIL large mappings.

  11. Secondary ion collection and transport system for ion microprobe

    DOEpatents

    Ward, James W.; Schlanger, Herbert; McNulty, Jr., Hugh; Parker, Norman W.

    1985-01-01

    A secondary ion collection and transport system, for use with an ion microprobe, which is very compact and occupies only a small working distance, thereby enabling the primary ion beam to have a short focal length and high resolution. Ions sputtered from the target surface by the primary beam's impact are collected between two arcuate members having radii of curvature and applied voltages that cause only ions within a specified energy band to be collected. The collected ions are accelerated and focused in a transport section consisting of a plurality of spaced conductive members which are coaxial with and distributed along the desired ion path. Relatively high voltages are applied to alternate transport sections to produce accelerating electric fields sufficient to transport the ions through the section to an ion mass analyzer, while lower voltages are applied to the other transport sections to focus the ions and bring their velocity to a level compatible with the analyzing apparatus.

  12. The Oxford scanning proton microprobe: A medical diagnostic application

    NASA Astrophysics Data System (ADS)

    Watt, F.; Grime, G. W.; Takacs, J.; Vaux, D. J. T.

    1984-04-01

    Primary biliary cirrhosis (PBC) is a disease characterised by progressive destruction of small intrahepatic bile ducts, cholestasis, and high levels of copper within the liver. The Oxford 1 μm scanning proton microprobe (SPM) has been used to construct elemental maps of a 7 μm section of diseased liver at several different magnifications. The results of these investigations have shown that the copper is distributed in small deposits ( < 5 μm) at specific locations in the liver. Further there appears to be a 1:1 atomic correlation between copper and sulphur, indicating the presence of an inorganic salt or a protein with approximately equal numbers of copper and sulphur atoms.

  13. Nuclear microprobe analysis of lead profile in crocodile bones

    NASA Astrophysics Data System (ADS)

    Orlic, I.; Siegele, R.; Hammerton, K.; Jeffree, R. A.; Cohen, D. D.

    2003-09-01

    Elevated concentrations of lead were found in Australian free ranging saltwater crocodile ( Crocodylus porosus) bone and flesh. Lead shots were found as potential source of lead in these animals. ANSTO's heavy ion nuclear microprobe was used to measure the distribution of Pb in a number of bones and osteoderms. The aim was to find out if elevated Pb concentration remains in growth rings and if the concentration is correlated with the blood levels recorded at the time. Results of our study show a very distinct distribution of accumulated Pb in bones and osteoderms as well as good correlation with the level of lead concentration in blood. To investigate influence of ion species on detection limits measurements of the same sample were performed by using 3 MeV protons, 9 MeV He ions and 20 MeV carbon ions. Peak to background ratios, detection limits and the overall 'quality' of obtained spectra are compared and discussed.

  14. Analysis of biological materials using a nuclear microprobe

    NASA Astrophysics Data System (ADS)

    Mulware, Stephen Juma

    The use of nuclear microprobe techniques including: Particle induced x-ray emission (PIXE) and Rutherford backscattering spectrometry (RBS) for elemental analysis and quantitative elemental imaging of biological samples is especially useful in biological and biomedical research because of its high sensitivity for physiologically important trace elements or toxic heavy metals. The nuclear microprobe of the Ion Beam Modification and Analysis Laboratory (IBMAL) has been used to study the enhancement in metal uptake of two different plants. The roots of corn (Zea mays) have been analyzed to study the enhancement of iron uptake by adding Fe (II) or Fe(III) of different concentrations to the germinating medium of the seeds. The Fe uptake enhancement effect produced by lacing the germinating medium with carbon nanotubes has also been investigated. The aim of this investigation is to ensure not only high crop yield but also Fe-rich food products especially from calcareous soil which covers 30% of world's agricultural land. The result will help reduce iron deficiency anemia, which has been identified as the leading nutritional disorder especially in developing countries by the World Health Organization. For the second plant, Mexican marigold (Tagetes erecta ), the effect of an arbuscular mycorrhizal fungi (Glomus intraradices ) for the improvement of lead phytoremediation of lead contaminated soil has been investigated. Phytoremediation provides an environmentally safe technique of removing toxic heavy metals (like lead), which can find their way into human food, from lands contaminated by human activities like mining or by natural disasters like earthquakes. The roots of Mexican marigold have been analyzed to study the role of arbuscular mycorrhizal fungi in enhancement of lead uptake from the contaminated rhizosphere.

  15. Tactile 3D microprobe system with exchangeable styli

    NASA Astrophysics Data System (ADS)

    Balzer, Felix G.; Hausotte, Tino; Dorozhovets, Nataliya; Manske, Eberhard; Jäger, Gerd

    2011-09-01

    Over the past decade a trend of component miniaturization can be observed both in industry and in the laboratory, which involves an increasing demand for nanopositioning and nanomeasuring machines as well as for miniature tactile probes for measuring complex three-dimensional objects. The challenge is that these components—for example, diesel injectors, microgears and small optics—feature dimensions in the micrometre range with associated dimensional tolerances below 100 nm. For this reason, a significant number of research projects have dealt with microprobes for performing the dimensional measurements of microstructures with the goal of achieving measurement uncertainties in the nanometre range. This paper introduces an updated version of a 3D microprobe with an optical detection system developed at the Institute of Process Measurement and Sensor Technology. It consists of a measuring head and a separate probe system. The mechanical design of the probe system has been completely overhauled to enable the exchange of the stylus separately from the flexure elements. This is very important for the determination of the probing sphere's roundness deviations. The silicon membranes used in the first system design are therefore replaced by metal membranes. A new design of these membranes, optimized for isotropic probing forces and locking parasitic movements, is presented. Regarding the measuring head, the optical design has been redesigned to eliminate disruptive interference on the quadrant photodiode used for deflection measurement and to improve adjustment. Its dimensioning is discussed, especially the influence of the laser beam diameter on the interference contrast due to the parallel misalignment of the collimated laser beam. Initial measurement results are presented to prove functionality.

  16. Deep Space 2: The Mars Microprobe Project and Beyond

    NASA Astrophysics Data System (ADS)

    Smrekar, S. E.; Gavit, S. A.

    1998-01-01

    The Mars Microprobe Project, or Deep Space 2 (DS2), is the second of the New Millennium Program planetary missions and is designed to enable future space science network missions through flight validation of new technologies. A secondary goal is the collection of meaningful science data. Two micropenetrators will be deployed to carry out surface and subsurface science. The penetrators are being carried as a piggyback payload on the Mars Polar Lander cruise ring and will be launched in January 1999. The microprobe has no active control, attitude determination, or propulsive systems. It is a single stage from separation until landing and will passively orient itself due to its aerodynamic design. The aeroshell will be made of a nonerosive heat shield material, Silicon impregnated Reusable Ceramic Ablator(SIRCA), developed at Ames Research Center. The aeroshell shatters on impact, at which time the probe separates into an aftbody that remains at the surface and a forebody that penetrates into the subsurface. Each probe has a total mass of up to 3 kg, including the aeroshell. The impact velocity will be about 180 meters per second. The forebody will experience up to 30,000 g's and penetrate between 0.3 and 2 meters, depending on the ice content of the soil. The aftbody deceleration will be up to 80,000 g. The penetrators arrive in December 1999. The landing ellipse latitude range is 73 deg-77 deg S. The longitude will be selected by the Mars Surveyor Project to place the lander on the polar layered deposits in the range of 180 deg -230 deg W. The two micropenetrators are likely to land within 100 km of the Mars Surveyor Lander, on the polar deposits. The likely arrival date is Ls = 256, late southern spring. The nominal mission lasts 2 days. A science team was selected in April 1998.

  17. Viscosity of colloidal suspensions

    SciTech Connect

    Cohen, E.G.D.; Schepper, I.M. de

    1995-12-31

    Simple expressions are given for the effective Newtonian viscosity as a function of concentration as well as for the effective visco-elastic response as a function of concentration and imposed frequency, of monodisperse neutral colloidal suspensions over the entire fluid range. The basic physical mechanisms underlying these formulae are discussed. The agreement with existing experiments is very good.

  18. Nucleation in food colloids

    NASA Astrophysics Data System (ADS)

    Povey, Malcolm J. W.

    2016-12-01

    Nucleation in food colloids has been studied in detail using ultrasound spectroscopy. Our data show that classical nucleation theory (CNT) remains a sound basis from which to understand nucleation in food colloids and analogous model systems using n-alkanes. Various interpretations and modifications of CNT are discussed with regard to their relevance to food colloids. Much of the evidence presented is based on the ultrasound velocity spectrometry measurements which has many advantages for the study of nucleating systems compared to light scattering and NMR due to its sensitivity at low solid contents and its ability to measure true solid contents in the nucleation and early crystal growth stages. Ultrasound attenuation spectroscopy also responds to critical fluctuations in the induction region. We show, however, that a periodic pressure fluctuation such as a quasi-continuous (as opposed to a pulse comprising only a few pressure cycles) ultrasound field can alter the nucleation process, even at very low acoustic intensity. Thus care must be taken when using ultrasound techniques that the measurements do not alter the studied processes. Quasi-continuous ultrasound fields may enhance or suppress nucleation and the criteria to determine such effects are derived. The conclusions of this paper are relevant to colloidal systems in foods, pharmaceuticals, agro-chemicals, cosmetics, and personal products.

  19. PREFACE: Half Metallic Ferromagnets

    NASA Astrophysics Data System (ADS)

    Dowben, Peter

    2007-08-01

    Since its introduction by de Groot and colleagues in the early 1980s [1], the concept of half metallic ferromagnetism has attracted great interest. Idealized, half-metals have only one spin channel for conduction: the spin-polarized band structure exhibits metallic behavior for one spin channel, while the other spin band structure exhibits a gap at the Fermi level. Due to the gap for one spin direction, the density of states at the Fermi level has, theoretically, 100 & spin polarization. This gap in the density of states in one spin at the Fermi level, for example ↓ so N↓ (EF) = 0, also causes the resistance of that channel to go to infinity. At zero or low temperatures, the nonquasiparticle density of states (electron correlation effects), magnons and spin disorder reduce the polarization from the idealized 100 & polarization. At higher temperatures magnon-phonon coupling and irreversible compositional changes affect polarization further. Strategies for assessing and reducing the effects of finite temperatures on the polarization are now gaining attention. The controversies surrounding the polarization stability of half metallic ferromagnets are not, however, limited to the consideration of finite temperature effects alone. While many novel half metallic materials have been predicted, materials fabrication can be challenging. Defects, surface and interface segregation, and structural stability can lead to profound decreases in polarization, but can also suppress long period magnons. There is a 'delicate balance of energies required to obtain half metallic behaviour: to avoid spin flip scattering, tiny adjustments in atomic positions might occur so that a gap opens up in the other spin channel' [2]. When considering 'spintronics' devices, a common alibi for the study of half metallic systems, surfaces and interfaces become important. Free enthalpy differences between the surface and the bulk will lead to spin minority surface and interface states, as well as

  20. Magnetorheology of hybrid colloids obtained by spin-coating and classical rheometry

    NASA Astrophysics Data System (ADS)

    Aslam, Raheema; Shahrivar, Keshvad; de Vicente, Juan; González-Viñas, Wenceslao

    2016-07-01

    Hybrid colloids composed of micron-sized ferromagnetic (carbonyl iron) and diamagnetic (silica) particles suspended in cyclohexanone, behave as, non-Newtonian, magnetorheological fluids. We measure and compare the magnetic field-dependent viscosity of hybrid diluted colloids using spin-coating and conventional magnetorheometry. We extend a previously developed model for simple colloids to this kind of hybrid colloids. As in the previous model, the viscosity of the colloidal suspension under applied fields can be derived from the surface coverage of the dry spin-coated deposits for each type of particles, and from the viscosity of the colloid at zero field. Also, our results allow us to obtain the evaporation rate of the solvent as a function of the rotation speed. Finally, we also measure the viscosity of the same suspension with a torsional parallel plate magnetorheometer under uniaxial DC magnetic fields aligned in the velocity gradient direction of a steady shearing flow. The experimental results under different conditions and the effect of each component on the magnetorheological properties of the resulting colloid are discussed. Standard spin-coating technique can be used both to characterize smart materials—complex fluids as well as to fabricate films with arbitrary solvents by tuning their viscosity by means of external fields.

  1. COLLOIDS. Colloidal matter: Packing, geometry, and entropy.

    PubMed

    Manoharan, Vinothan N

    2015-08-28

    Colloidal particles with well-controlled shapes and interactions are an ideal experimental system for exploring how matter organizes itself. Like atoms and molecules, these particles form bulk phases such as liquids and crystals. But they are more than just crude analogs of atoms; they are a form of matter in their own right, with complex and interesting collective behavior not seen at the atomic scale. Their behavior is affected by geometrical or topological constraints, such as curved surfaces or the shapes of the particles. Because the interactions between the particles are often short-ranged, we can understand the effects of these constraints using geometrical concepts such as packing. The geometrical viewpoint gives us a window into how entropy affects not only the structure of matter, but also the dynamics of how it forms.

  2. Colloidal Double Quantum Dots

    PubMed Central

    2016-01-01

    Conspectus Pairs of coupled quantum dots with controlled coupling between the two potential wells serve as an extremely rich system, exhibiting a plethora of optical phenomena that do not exist in each of the isolated constituent dots. Over the past decade, coupled quantum systems have been under extensive study in the context of epitaxially grown quantum dots (QDs), but only a handful of examples have been reported with colloidal QDs. This is mostly due to the difficulties in controllably growing nanoparticles that encapsulate within them two dots separated by an energetic barrier via colloidal synthesis methods. Recent advances in colloidal synthesis methods have enabled the first clear demonstrations of colloidal double quantum dots and allowed for the first exploratory studies into their optical properties. Nevertheless, colloidal double QDs can offer an extended level of structural manipulation that allows not only for a broader range of materials to be used as compared with epitaxially grown counterparts but also for more complex control over the coupling mechanisms and coupling strength between two spatially separated quantum dots. The photophysics of these nanostructures is governed by the balance between two coupling mechanisms. The first is via dipole–dipole interactions between the two constituent components, leading to energy transfer between them. The second is associated with overlap of excited carrier wave functions, leading to charge transfer and multicarrier interactions between the two components. The magnitude of the coupling between the two subcomponents is determined by the detailed potential landscape within the nanocrystals (NCs). One of the hallmarks of double QDs is the observation of dual-color emission from a single nanoparticle, which allows for detailed spectroscopy of their properties down to the single particle level. Furthermore, rational design of the two coupled subsystems enables one to tune the emission statistics from single

  3. Colloidal Double Quantum Dots.

    PubMed

    Teitelboim, Ayelet; Meir, Noga; Kazes, Miri; Oron, Dan

    2016-05-17

    Pairs of coupled quantum dots with controlled coupling between the two potential wells serve as an extremely rich system, exhibiting a plethora of optical phenomena that do not exist in each of the isolated constituent dots. Over the past decade, coupled quantum systems have been under extensive study in the context of epitaxially grown quantum dots (QDs), but only a handful of examples have been reported with colloidal QDs. This is mostly due to the difficulties in controllably growing nanoparticles that encapsulate within them two dots separated by an energetic barrier via colloidal synthesis methods. Recent advances in colloidal synthesis methods have enabled the first clear demonstrations of colloidal double quantum dots and allowed for the first exploratory studies into their optical properties. Nevertheless, colloidal double QDs can offer an extended level of structural manipulation that allows not only for a broader range of materials to be used as compared with epitaxially grown counterparts but also for more complex control over the coupling mechanisms and coupling strength between two spatially separated quantum dots. The photophysics of these nanostructures is governed by the balance between two coupling mechanisms. The first is via dipole-dipole interactions between the two constituent components, leading to energy transfer between them. The second is associated with overlap of excited carrier wave functions, leading to charge transfer and multicarrier interactions between the two components. The magnitude of the coupling between the two subcomponents is determined by the detailed potential landscape within the nanocrystals (NCs). One of the hallmarks of double QDs is the observation of dual-color emission from a single nanoparticle, which allows for detailed spectroscopy of their properties down to the single particle level. Furthermore, rational design of the two coupled subsystems enables one to tune the emission statistics from single photon

  4. Biological Effects in Coral Biomineralization: The Ion-Microprobe Revolution

    NASA Astrophysics Data System (ADS)

    Meibom, A.

    2004-12-01

    Scleractinian corals are among the most prolific biomineralizing organisms on Earth and massive, reef-building corals are used extensively as proxies for past variations in the global climate. It is therefore of wide interest to understand the degree to which biological versus inorganic processes control the chemistry of the coral skeleton. Early workers considered aragonitic coral skeleton formation to be a purely physiochemical process. More recent studies have increasingly emphasized the role of a skeletal organic matrix, or intercalated organic macro-molecules that control the macroscopic shape and size of the growing crystals. It is now well established that organic compounds play a key role in controlling the morphology of crystals in a wide variety of calcium carbonate biomineralization processes by binding to specific sites, thereby causing direction-specific binding energies on the crystal surfaces. Macro-molecules, such as aspartic acid-rich or glutamic proteins and sulfated polysaccharides, are known to be embedded within the aragonitic skeletal components of coral. In addition, endosymbiotic algae and the layer of cells adjacent to the mineralizing surface, the calicoblastic ectoderm, are believed to play important roles in driving and controlling hermatypic coral skeletogenesis. However, until recently, further progress has been somewhat limited because it was not possible to obtain chemical analyses of the coral skeleton with sufficiently high spatial resolution and sensitivity to correlate chemical variations with the micrometer scale organization of its different structural components. The recent emergence of new ion microprobe technology is changing this situation radically. Conventional ion microprobe and laser ablation techniques have already contributed substantially to our knowledge about the micro-distribution of key trace elements such as B, Mg, Sr, Ba and U. However, with the development of the NanoSIMS, a newly designed ion microprobe

  5. The Perils of Electron Microprobe Analysis of Apatite

    NASA Astrophysics Data System (ADS)

    Henderson, C. E.; Essene, E. J.; Wang, K. L.; Zhang, Y.

    2010-12-01

    Accurate electron microprobe analysis of apatite is problematic, especially for F and Cl, whose concentrations are essential in calculating a non-analyzable OH component. The issues include beam-induced sample damage and temporal variation of F and Cl X-rays; both effects are mainly dependent on beam current, beam spot size and apatite orientation [1]. To establish a rigorous analytical procedure, several oriented apatite samples, including the well-known Durango and Wilberforce fluorapatites, were analyzed for a large suite of elements, including oxygen. Careful X-ray spectroscopy was performed, including selection of appropriate analytical standards, background measurement positions and comparison of area peak factors. Polarized infrared spectra on oriented apatite samples were also collected for complementary information. The results show that when apatite samples are oriented with the c-axis parallel to the electron beam, there is significant nonlinear variation (an increase or decrease, depending on measurement conditions) of F and Cl X-ray intensities during analyses, and systematically higher-than-expected F apparent concentrations, despite the careful selection of electron beam conditions from a series of X-ray time scans and zero-time count rate extrapolation. On the other hand, when the electron beam is oriented perpendicular to the c-axis, with a ≤ 15 nA beam current and a ≥ 5 µm diameter defocused beam, F and Cl X-ray intensities do not vary or vary slowly and predictably with time, yielding quantitative analysis results for the Durango and Wilberforce apatites (both containing little OH) which are in good agreement with published wet chemical analyses. Furthermore, the OH and CO2 contents inferred for three other analyzed apatite samples are roughly consistent with infrared analyses. For example, for an apatite from Silver Crater Mine in Ontario, significant deficiency in the P site, as well as extra F, was inferred from microprobe analyses

  6. Fractal nematic colloids

    PubMed Central

    Hashemi, S. M.; Jagodič, U.; Mozaffari, M. R.; Ejtehadi, M. R.; Muševič, I.; Ravnik, M.

    2017-01-01

    Fractals are remarkable examples of self-similarity where a structure or dynamic pattern is repeated over multiple spatial or time scales. However, little is known about how fractal stimuli such as fractal surfaces interact with their local environment if it exhibits order. Here we show geometry-induced formation of fractal defect states in Koch nematic colloids, exhibiting fractal self-similarity better than 90% over three orders of magnitude in the length scales, from micrometers to nanometres. We produce polymer Koch-shaped hollow colloidal prisms of three successive fractal iterations by direct laser writing, and characterize their coupling with the nematic by polarization microscopy and numerical modelling. Explicit generation of topological defect pairs is found, with the number of defects following exponential-law dependence and reaching few 100 already at fractal iteration four. This work demonstrates a route for generation of fractal topological defect states in responsive soft matter. PMID:28117325

  7. Fractal nematic colloids

    NASA Astrophysics Data System (ADS)

    Hashemi, S. M.; Jagodič, U.; Mozaffari, M. R.; Ejtehadi, M. R.; Muševič, I.; Ravnik, M.

    2017-01-01

    Fractals are remarkable examples of self-similarity where a structure or dynamic pattern is repeated over multiple spatial or time scales. However, little is known about how fractal stimuli such as fractal surfaces interact with their local environment if it exhibits order. Here we show geometry-induced formation of fractal defect states in Koch nematic colloids, exhibiting fractal self-similarity better than 90% over three orders of magnitude in the length scales, from micrometers to nanometres. We produce polymer Koch-shaped hollow colloidal prisms of three successive fractal iterations by direct laser writing, and characterize their coupling with the nematic by polarization microscopy and numerical modelling. Explicit generation of topological defect pairs is found, with the number of defects following exponential-law dependence and reaching few 100 already at fractal iteration four. This work demonstrates a route for generation of fractal topological defect states in responsive soft matter.

  8. Fractal nematic colloids.

    PubMed

    Hashemi, S M; Jagodič, U; Mozaffari, M R; Ejtehadi, M R; Muševič, I; Ravnik, M

    2017-01-24

    Fractals are remarkable examples of self-similarity where a structure or dynamic pattern is repeated over multiple spatial or time scales. However, little is known about how fractal stimuli such as fractal surfaces interact with their local environment if it exhibits order. Here we show geometry-induced formation of fractal defect states in Koch nematic colloids, exhibiting fractal self-similarity better than 90% over three orders of magnitude in the length scales, from micrometers to nanometres. We produce polymer Koch-shaped hollow colloidal prisms of three successive fractal iterations by direct laser writing, and characterize their coupling with the nematic by polarization microscopy and numerical modelling. Explicit generation of topological defect pairs is found, with the number of defects following exponential-law dependence and reaching few 100 already at fractal iteration four. This work demonstrates a route for generation of fractal topological defect states in responsive soft matter.

  9. Colloidal Covalent Organic Frameworks

    PubMed Central

    2017-01-01

    Covalent organic frameworks (COFs) are two- or three-dimensional (2D or 3D) polymer networks with designed topology and chemical functionality, permanent porosity, and high surface areas. These features are potentially useful for a broad range of applications, including catalysis, optoelectronics, and energy storage devices. But current COF syntheses offer poor control over the material’s morphology and final form, generally providing insoluble and unprocessable microcrystalline powder aggregates. COF polymerizations are often performed under conditions in which the monomers are only partially soluble in the reaction solvent, and this heterogeneity has hindered understanding of their polymerization or crystallization processes. Here we report homogeneous polymerization conditions for boronate ester-linked, 2D COFs that inhibit crystallite precipitation, resulting in stable colloidal suspensions of 2D COF nanoparticles. The hexagonal, layered structures of the colloids are confirmed by small-angle and wide-angle X-ray scattering, and kinetic characterization provides insight into the growth process. The colloid size is modulated by solvent conditions, and the technique is demonstrated for four 2D boronate ester-linked COFs. The diameter of individual COF nanoparticles in solution is monitored and quantified during COF growth and stabilization at elevated temperature using in situ variable-temperature liquid cell transmission electron microscopy imaging, a new characterization technique that complements conventional bulk scattering techniques. Solution casting of the colloids yields a free-standing transparent COF film with retained crystallinity and porosity, as well as preferential crystallite orientation. Collectively this structural control provides new opportunities for understanding COF formation and designing morphologies for device applications. PMID:28149954

  10. Increasing entropy for colloidal stabilization

    PubMed Central

    Mo, Songping; Shao, Xuefeng; Chen, Ying; Cheng, Zhengdong

    2016-01-01

    Stability is of paramount importance in colloidal applications. Attraction between colloidal particles is believed to lead to particle aggregation and phase separation; hence, stability improvement can be achieved through either increasing repulsion or reducing attraction by modifying the fluid medium or by using additives. Two traditional mechanisms for colloidal stability are electrostatic stabilization and steric stabilization. However, stability improvement by mixing attractive and unstable particles has rarely been considered. Here, we emphasize the function of mixing entropy in colloidal stabilization. Dispersion stability improvement is demonstrated by mixing suspensions of attractive nanosized titania spheres and platelets. A three-dimensional phase diagram is proposed to illustrate the collaborative effects of particle mixing and particle attraction on colloidal stability. This discovery provides a novel method for enhancing colloidal stability and opens a novel opportunity for engineering applications. PMID:27872473

  11. Equilibrium Shape of Colloidal Crystals.

    PubMed

    Sehgal, Ray M; Maroudas, Dimitrios

    2015-10-27

    Assembling colloidal particles into highly ordered configurations, such as photonic crystals, has significant potential for enabling a broad range of new technologies. Facilitating the nucleation of colloidal crystals and developing successful crystal growth strategies require a fundamental understanding of the equilibrium structure and morphology of small colloidal assemblies. Here, we report the results of a novel computational approach to determine the equilibrium shape of assemblies of colloidal particles that interact via an experimentally validated pair potential. While the well-known Wulff construction can accurately capture the equilibrium shape of large colloidal assemblies, containing O(10(4)) or more particles, determining the equilibrium shape of small colloidal assemblies of O(10) particles requires a generalized Wulff construction technique which we have developed for a proper description of equilibrium structure and morphology of small crystals. We identify and characterize fully several "magic" clusters which are significantly more stable than other similarly sized clusters.

  12. Increasing entropy for colloidal stabilization

    NASA Astrophysics Data System (ADS)

    Mo, Songping; Shao, Xuefeng; Chen, Ying; Cheng, Zhengdong

    2016-11-01

    Stability is of paramount importance in colloidal applications. Attraction between colloidal particles is believed to lead to particle aggregation and phase separation; hence, stability improvement can be achieved through either increasing repulsion or reducing attraction by modifying the fluid medium or by using additives. Two traditional mechanisms for colloidal stability are electrostatic stabilization and steric stabilization. However, stability improvement by mixing attractive and unstable particles has rarely been considered. Here, we emphasize the function of mixing entropy in colloidal stabilization. Dispersion stability improvement is demonstrated by mixing suspensions of attractive nanosized titania spheres and platelets. A three-dimensional phase diagram is proposed to illustrate the collaborative effects of particle mixing and particle attraction on colloidal stability. This discovery provides a novel method for enhancing colloidal stability and opens a novel opportunity for engineering applications.

  13. Microwave properties of ferromagnetic nanostructures.

    PubMed

    Valenzuela, R; Alvarez, G; Mata-Zamora, M E

    2008-06-01

    A review of the dynamic properties of nanostructured ferromagnetic materials at microwave frequencies (1-40 GHz) is presented. Since some confusion has recently appeared between giant magnetoimpedance (GMI) and ferromagnetic resonance (FMR), a detailed analysis is made in order to establish their differences. A brief review of a novel microwave absorption mode, the low-field microwave absorption (LFA) is then presented, together with a discussion about its similarities with GMI. Recent results on high-frequency measurements on nanogranular thin films and FMR in nanowire arrays are finally addressed.

  14. Theory of disordered Heisenberg ferromagnets

    NASA Technical Reports Server (NTRS)

    Stubbs, R. M.

    1973-01-01

    A Green's function technique is used to calculate the magnetic properties of Heisenberg ferromagnets in which the exchange interactions deviate randomly in strength from the mean interaction. Systems of sc, bcc, and fcc topologies and of general spin values are treated. Disorder produces marked effects in the density of spin wave states, in the form of enhancement of the low-energy density and extension of the energy band to higher values. The spontaneous magnetization and the Curie temperature decrease with increasing disorder. The effects of disorder are shown to be more pronounced in the ferromagnetic than in the paramagnetic phase.

  15. Nuclear micro-probe analysis of Arabidopsis thaliana leaves

    NASA Astrophysics Data System (ADS)

    Ager, F. J.; Ynsa, M. D.; Domínguez-Solís, J. R.; López-Martín, M. C.; Gotor, C.; Romero, L. C.

    2003-09-01

    Phytoremediation is a cost-effective plant-based approach for remediation of soils and waters which takes advantage of the remarkable ability of some plants to concentrate elements and compounds from the environment and to metabolize various molecules in their tissues, such as toxic heavy metals and organic pollutants. Nowadays, phytoremediation technology is becoming of paramount importance when environmental decontamination is concerned, due to the emerging knowledge of its physiological and molecular mechanisms and the new biological and engineering strategies designed to optimize and improve it. In addition, the feasibility of using plants for environmental cleanup has been confirmed by many different trials around the world. Arabidopsis thaliana plants can be used for basic studies to improve the technology on phytoremediation. Making use of nuclear microscopy techniques, in this paper we study leaves of wild type and transgenic A. thaliana plants grown in a cadmium-rich environment under different conditions. Micro-PIXE, RBS and SEM analyses, performed on the scanning proton micro-probe at the CNA in Seville (Spain), prove that cadmium is preferentially sequestered in the central region of epidermal trichome and allow comparing the effects of genetic modifications.

  16. Identification of cosmogenic argon components in Allende by laser microprobe

    NASA Technical Reports Server (NTRS)

    Kirschbaum, C.

    1986-01-01

    New techniques are presented for using a laser microprobe to determine the spallation argon systematics of calcium-aluminum inclusions. The Ar-38(s) amounts determined for melilite and anorthite in a coarse-grained inclusion from Allende are 2.9 x 10 to the -8th and 1.3 x 10 to the -8th cc/g, respectively. The ratio of the amounts is consistent with the calcium contents of these two minerals. The Ar-38(s) amount determined for a fine-grained inclusion from Allende is 1.1 x 10 to the -8th cc/g. Calcium and potassium amounts were determined from irradiated samples of the same inclusions so that production of Ar-38 from calcium during the cosmic ray exposure of Allende could be determined for these samples. The production observed was 12.4 + or - 2.1 x 10 to the -8th cc STP Ar-38/g Ca for the coarse-grained inclusion and 9.9 + or - 2.4 cc STP Ar-38/g Ca for the fine-grained inclusion. No evidence of unusual exposure was observed in the two inclusions studied.

  17. Enhanced Raman Microprobe Imaging of Single-Wall Carbon Nanotubes

    NASA Technical Reports Server (NTRS)

    Hadjiev, V. G.; Arepalli, S.; Nikolaev, P.; Jandl, S.; Yowell, L.

    2003-01-01

    We explore Raman microprobe capabilities to visualize single wall carbon nanotubes (SWCNTs). Although this technique is limited to a micron scale, we demonstrate that images of individual SWCNTs, bundles or their agglomerates can be generated by mapping Raman active elementary excitations. We measured the Raman response from carbon vibrations in SWCNTs excited by confocal scanning of a focused laser beam. Carbon vibrations reveal key characteristics of SWCNTs as nanotube diameter distribution (radial breathing modes, RBM, 100-300 cm(exp -1)), presence of defects and functional groups (D-mode, 1300-1350 cm(exp -1)), strain and oxidation states of SWCNTs, as well as metallic or semiconducting character of the tubes encoded in the lineshape of the G-modes at 1520-1600 cm(exp - 1). In addition, SWCNTs are highly anisotropic scatterers. The Raman response from a SWCNT is maximal for incident light polarization parallel to the tube axis and vanishing for perpendicular directions. We show that the SWCNT bundle shape or direction can be determined, with some limitations, from a set of Raman images taken at two orthogonal directions of the incident light polarization.

  18. Application of the Karlsruhe proton microprobe to medical samples

    NASA Astrophysics Data System (ADS)

    Heck, D.; Rokita, E.

    1984-04-01

    The Karlsruhe nuclear microprobe was used in the investigation of healthy and malign tissue of animals and men. Target preparation tests showed that cryofixation of the tissue before cutting with a microtome and succeeding lyophilization of the slices gave reliable results. The slices were mounted on backing foils of Formvar the thickness of which varied between 30 and 50 {μg}/{cm 2}. For irradiation we tested various patterns generated by the 3 MeV proton beam by sweeping in one or two dimensions. Most of the data were collected in line-scan mode, where 256 equidistant irradiation dots of 3 × 10 μm 2 formed a line of 750 μm length at beam currents of 250 pA. The target thickness was determined simultaneously by proton elastic scattering in all cases. Radial concentration profiles of degenerated human arteries (atherosclerosis) showed a remarkable increase of Ca, partly correlated with local maxima of the Zn content, when compared with non-degenerated capillaries. Microtome cuts across a Morris Hepatoma 7777 cancer grown in a rat leg were investigated to correlate the concentration shifts of some trace elements in malign tissue with single cells.

  19. Light stable isotope analysis of meteorites by ion microprobe

    NASA Technical Reports Server (NTRS)

    Mcsween, Harry Y., Jr.

    1994-01-01

    The main goal was to develop the necessary secondary ion mass spectrometer (SIMS) techniques to use a Cameca ims-4f ion microprobe to measure light stable isotope ratios (H, C, O and S) in situ and in non-conducting mineral phases. The intended application of these techniques was the analysis of meteorite samples, although the techniques that have been developed are equally applicable to the investigation of terrestrial samples. The first year established techniques for the analysis of O isotope ratios (delta O-18 and delta O-17) in conducting mineral phases and the measurement of S isotope ratios (delta S-34) in a variety of sulphide phases. In addition, a technique was developed to measure delta S-34 values in sulphates, which are insulators. Other research undertaken in the first year resulted in SIMS techniques for the measurement of wide variety of trace elements in carbonate minerals, with the aim of understanding the nature of alteration fluids in carbonaceous chondrites. In the second year we developed techniques for analyzing O isotope ratios in nonconducting mineral phases. These methods are potentially applicable to the measurement of other light stable isotopes such as H, C and S in insulators. Also, we have further explored the analytical techniques used for the analysis of S isotopes in sulphides by analyzing troilite in a number of L and H ordinary chondrites. This was done to see if there was any systematic differences with petrological type.

  20. The nuclear microprobe: An insight of applications in cell biology

    NASA Astrophysics Data System (ADS)

    Moretto, Ph.; Llabador, Y.

    1997-07-01

    During the last five years, the evolution of biomedical research based upon nuclear microprobe analysis has followed the development of experimental models of cultured or isolated cells. Fundamental studies of cellular mechanisms have been approached by means of in vitro assays associated with single cell analysis. Within those groups which are involved in such programs, special emphasis has been placed on cell culture and processing techniques which fulfill the methodological requirements for intracellular ion beam analysis. Great efforts have been orientated towards the improvement of normalization procedures. It is now possible to provide reliable quantitative results expressed in such units that they can be easily cross-checked using conventional methods. Imaging techniques have been also developed for the identification of the analyzed structures. In this paper, different domains of cell biology which have been addressed during the last years are reviewed. Studies dealing with cellular physiology and pharmacology are briefly presented as are also those related to the role of trace elements. Topics under development in our group as well as ongoing investigations will be also evoked.

  1. Colloidal Metamaterials at Optical Frequencies

    DTIC Science & Technology

    2014-07-18

    AFRL-OSR-VA-TR-2014-0184 Colloidal Metamaterials at Optical Frequencies Jennifer Dionne LELAND STANFORD JUNIOR UNIV CA Final Report 07/18/2014...Prescribed by ANSI Std. Z39.18 Colloidal Metamaterials at Optical Frequencies Annual Report, June 30, 2014 A. Investigators PI: Jennifer Dionne...team has combined theoretical and experimental methods to produce a colloidally -synthesized metamaterial fluid, or “metafluid,” exhibiting strong

  2. Dating Archean zircon by ion microprobe: New light on an old problem

    NASA Technical Reports Server (NTRS)

    Williams, I. S.; Kinny, P. D.; Black, L. P.; Compston, W.; Froude, D. O.; Ireland, T. R.

    1985-01-01

    Ion microprobe analysis of zircons from three sites (Watersmeet Dome in northern Michigan, Mount Sones in eastern Antarctica, and Mount Narryer in western Australia) is discussed. Implications of the results to Archean geochronology and early Earth crust composition are addressed.

  3. Optimum Design of Cantilevered Microprobes for Inspecting Lcd Panels and Measurement of Contacting Forces

    NASA Astrophysics Data System (ADS)

    Kim, Cheol; Kim, Kwang-Joong

    Fine pitch microprobe arrays are microneedle-like probes for inspecting the pixels of LCD panels or IC. They are usually made of multi-layers of metallic, nonmetallic, or combination of the two. The design requirement for a contacting force is less than 2 gf and a deflection should be less than 100 µm. Many microprobe shapes satisfying the design requirements are possible. A cantilever-type microprobe having many needles was chosen and optimized in this study. Several candidate shapes were chosen using topology and shape optimization technique subjected to design requirements. Then, the microprobe arrays were fabricated using the process applied for MEMS fabrication and they were made of BeNi, BeCu, or Si. The contact probing forces and deflections were measured for checking the results from optimum design by newly developed measuring equipment in our laboratory. Numerical and experimental results were compared and both showed a good correlation.

  4. Novel room temperature ferromagnetic semiconductors

    SciTech Connect

    Gupta, Amita

    2004-06-01

    Today's information world, bits of data are processed by semiconductor chips, and stored in the magnetic disk drives. But tomorrow's information technology may see magnetism (spin) and semiconductivity (charge) combined in one 'spintronic' device that exploits both charge and 'spin' to carry data (the best of two worlds). Spintronic devices such as spin valve transistors, spin light emitting diodes, non-volatile memory, logic devices, optical isolators and ultra-fast optical switches are some of the areas of interest for introducing the ferromagnetic properties at room temperature in a semiconductor to make it multifunctional. The potential advantages of such spintronic devices will be higher speed, greater efficiency, and better stability at a reduced power consumption. This Thesis contains two main topics: In-depth understanding of magnetism in Mn doped ZnO, and our search and identification of at least six new above room temperature ferromagnetic semiconductors. Both complex doped ZnO based new materials, as well as a number of nonoxides like phosphides, and sulfides suitably doped with Mn or Cu are shown to give rise to ferromagnetism above room temperature. Some of the highlights of this work are discovery of room temperature ferromagnetism in: (1) ZnO:Mn (paper in Nature Materials, Oct issue, 2003); (2) ZnO doped with Cu (containing no magnetic elements in it); (3) GaP doped with Cu (again containing no magnetic elements in it); (4) Enhancement of Magnetization by Cu co-doping in ZnO:Mn; (5) CdS doped with Mn, and a few others not reported in this thesis. We discuss in detail the first observation of ferromagnetism above room temperature in the form of powder, bulk pellets, in 2-3 mu-m thick transparent pulsed laser deposited films of the Mn (<4 at. percent) doped ZnO. High-resolution transmission electron microscopy (HRTEM) and electron energy loss spectroscopy (EELS) spectra recorded from 2 to 200nm areas showed homogeneous distribution of Mn substituting

  5. Spin Seebeck effect in a weak ferromagnet

    NASA Astrophysics Data System (ADS)

    Arboleda, Juan David; Arnache Olmos, Oscar; Aguirre, Myriam Haydee; Ramos, Rafael; Anadon, Alberto; Ibarra, Manuel Ricardo

    2016-06-01

    We report the observation of room temperature spin Seebeck effect (SSE) in a weak ferromagnetic normal spinel Zinc Ferrite (ZFO). Despite the weak ferromagnetic behavior, the measurements of the SSE in ZFO show a thermoelectric voltage response comparable with the reported values for other ferromagnetic materials. Our results suggest that SSE might possibly originate from the surface magnetization of the ZFO.

  6. Magnetorheology of hybrid colloids measured by spin coating and classical rheometry

    NASA Astrophysics Data System (ADS)

    Muhammad Aslam, Raheema; Shahrivar, Keshwad; Álvarez-Manzaneda, Juan De Vicente; González-Viñas, Wenceslao

    Hybrid colloids composed of micron-sized ferromagnetic and diamagnetic particles constitute a promising category of magnetorheological fluids with enhanced field-induced apparent yield stress. However, the physical mechanism explaining this stress enhancement is currently lacking. For the first time, we measure and compare the magnetic field-dependent viscosity of hybrid diluted colloids using spin-coating and magnetorheometry. In the former technique, a magnetic field is applied during the spin coating of the colloidal suspension involving evaporation of the solvent. The viscosity of the colloidal suspension at applied field can be derived from the surface coverage of the dry spin-coated deposits and from the viscosity of the colloid at zero field. In the latter, its viscosity is measured with a torsional parallel plate magnetorheometer under uniaxial magnetic fields aligned in the gradient direction of a steady shearing flow. The experimental results under different conditions and the effect of each component on the magnetorheological properties of the resulting colloid will be discussed. This work is partly supported by the Spanish MINECO (FIS201454101-P).

  7. An x-ray microprobe beam line for trace element analysis

    SciTech Connect

    Gordon, B.M.; Hanson, A.L.; Jones, K.W.; Kwiatek, W.M.; Long, G.J.; Pounds, J.G.; Schidlovsky, G.; Spanne, P.; Rivers, M.L.; Sutton, S.R.

    1987-01-01

    The application of synchrotron radiation to an x-ray microprobe for trace element analysis is a complementary and natural extension of existing microprobe techniques using electrons, protons, and heavier ions as excitation sources for x-ray fluorescence. The ability to focus charged particles leads to electron microprobes with spatial resolutions in the sub-micrometer range and down to 100 ppM detection limits and proton microprobes with micrometer resolution and ppM detection limits. The characteristics of synchrotron radiation that prove useful for microprobe analysis include a broad and continuous energy spectrum, a relatively small amount of radiation damage compared to that deposited by charged particles, a highly polarized source which reduces background scattered radiation in an appropriate counting geometry, and a small vertical divergence angle of approx.0.2 mrad which allows for focussing of the light beam into a small spot with high flux. The features of a dedicated x-ray microprobe beam line developed at the National Synchrotron Light Source (NSLS) are described. 4 refs., 3 figs.

  8. Interplay Between Ferromagnetism and Superconductivity

    NASA Astrophysics Data System (ADS)

    Linder, Jacob; Sudbø, Asle

    This chapter presents results on transport properties of hybrid structures where the interplay between ferromagnetism and superconductivity plays a central role. In particular, the appearance of so-called odd-frequency pairing in such structures is investigated in detail. The basic physics of superconductivity in such structures is presented, and the quasiclassical theory of Greens functions with appropriate boundary conditions is given. Results for superconductor∣ferromagnet bilayers as well as magnetic Josephson junctions and spin valves are presented. Further phenomena that are studied include transport in the presence of inhomogenous magnetic textures, spin-Josephon effect, and crossed Andreev reflection. We also investigate the possibility of intrinsic coexistence of ferromagnetism and superconductivity, as reported in a series of uranium-based heavy-fermion compounds. The nature of such a coexistence and the resulting superconducting order parameter is discussed along with relevant experimental results. We present a thermodynamic treatment for a model of a ferromagnetic supercondcutor and moreover suggest ways to experimentally determine the pairing symmetry of the superconducting gap, in particular by means of conductance spectroscopy.

  9. From Nagaoka's Ferromagnetism to Flat-Band Ferromagnetism and Beyond --- An Introduction to Ferromagnetism in the Hubbard Model ---

    NASA Astrophysics Data System (ADS)

    Tasaki, H.

    1998-04-01

    It is believed that strong ferromagnetic interactions in some solids are generated by subtle interplay between quantum many-body effects and spin-independent Coulomb interactions between electrons. It is a challenging problem to verify this scenario in the Hubbard model, which is an idealized model for strongly interacting electrons in a solid. Nagaoka's ferromagnetism is a well-known rigorous example of ferromagnetism in the Hubbard model. It deals with the limiting situation in which there is one fewer electron than in the half-filling and the on-site Coulomb interaction is infinitely large. There are relatively new rigorous examples of ferromagnetism in Hubbard models called flat-band ferromagnetism. Flat-band ferromagnetism takes place in carefully prepared models in which the lowest bands (in the single-electron spectra) are ``flat.'' Usually, these two approaches are regarded as two complimentary routes to ferromagnetism in the Hubbard model. In the present paper we describe Nagaoka's ferromagnetism and flat-band ferromagnetism in detail, giving all the necessary background as well as complete (but elementary) mathematical proofs. By studying an intermediate model called the long-range hopping model, we also demonstrate that there is indeed a deep relation between these two seemingly different approaches to ferromagnetism. We further discuss some attempts to go beyond these approaches. We briefly discuss recent rigorous example of ferromagnetism in the Hubbard model which has neither infinitely large parameters nor completely flat bands. We give preliminary discussion regarding possible experimental realizations of the (nearly-)flat-band ferromagnetism. Finally, we focus on some theoretical attempts to understand metallic ferromagnetism. We discuss three artificial one-dimensional models in which the existence of metallic ferromagnetism can be easily proved. We have tried to make the present paper as self-contained as possible, keeping in mind readers who are

  10. Electron Microprobe Analysis Techniques for Accurate Measurements of Apatite

    NASA Astrophysics Data System (ADS)

    Goldoff, B. A.; Webster, J. D.; Harlov, D. E.

    2010-12-01

    Apatite [Ca5(PO4)3(F, Cl, OH)] is a ubiquitous accessory mineral in igneous, metamorphic, and sedimentary rocks. The mineral contains halogens and hydroxyl ions, which can provide important constraints on fugacities of volatile components in fluids and other phases in igneous and metamorphic environments in which apatite has equilibrated. Accurate measurements of these components in apatite are therefore necessary. Analyzing apatite by electron microprobe (EMPA), which is a commonly used geochemical analytical technique, has often been found to be problematic and previous studies have identified sources of error. For example, Stormer et al. (1993) demonstrated that the orientation of an apatite grain relative to the incident electron beam could significantly affect the concentration results. In this study, a variety of alternative EMPA operating conditions for apatite analysis were investigated: a range of electron beam settings, count times, crystal grain orientations, and calibration standards were tested. Twenty synthetic anhydrous apatite samples that span the fluorapatite-chlorapatite solid solution series, and whose halogen concentrations were determined by wet chemistry, were analyzed. Accurate measurements of these samples were obtained with many EMPA techniques. One effective method includes setting a static electron beam to 10-15nA, 15kV, and 10 microns in diameter. Additionally, the apatite sample is oriented with the crystal’s c-axis parallel to the slide surface and the count times are moderate. Importantly, the F and Cl EMPA concentrations are in extremely good agreement with the wet-chemical data. We also present EMPA operating conditions and techniques that are problematic and should be avoided. J.C. Stormer, Jr. et al., Am. Mineral. 78 (1993) 641-648.

  11. Electron microprobe observations of PB diffusion in metamorphosed detrital monazites

    NASA Astrophysics Data System (ADS)

    Suzuki, K.; Adachi, M.; Kajizuka, I.

    1994-12-01

    Electron microprobe analyses have been made on monazite grains from paragneiss samples in the andalusite-sillimanite transition (620 +/- 15 C) and sillimanite-orthoclase (680 +/- 15 C) zones of the Cretaceous Ryoke metamorphic belt, southwest Japan. Monazites from pelitic gneisses are of metamorphic origin, euhedral to subhedral and chronologically homogeneous, giving chemical Th-U-total Pb isochron (CHIME) ages of 98.8 +/- 3.3 - 98.0 +/- 3.2 Ma. Two psammitic gneisses of individual metamorphic grade contain both metamorphic monazite grains and detrital ones as old as ca. 1700 Ma. Most detrital monazite grains are heterogeneous in the ThO2 and UO2 concentrations and have multiple or single rims as young as ca. 100 Ma. Several detrital monazite grains are well rounded in form, exhibit homogeneous Th and U distributions and show a Pb diffusion profile in the margin. The width of the diffusion zones is approximately constant throughout grains from each psammitic gneiss: 18-22 micrometers for 620 C and 48-58 micrometers for 680 C. Assuming the isothermal diffusion of Pb from homogeneous monazite spheres during a 5 Ma duration of peak metamorphism, we obtain diffusion coefficients of 1.9 (+/- 0.3) x 10-21 and 1.5 (+/- 0.3) x 10-20 sq cm/s at 620 C and 680 C, respectively. These data derive an activation energy of 2.44 (+2.85/-1.26) x 105 J/mol and a frequency factor of 3.4 x 10-7 (8.5 x 10-12 - 2.2 x 107 sq cm/s, taking account of uncertainties of +/- 15 C in the temperatures and of +/- 20% in the diffusion coefficients. The diffusion parameters obtained from natural samples in this study provide a reliable insight into the closure temperature for Pb in monazite that has been poorly understood so far.

  12. Carbon p electron ferromagnetism in silicon carbide

    DOE PAGES

    Wang, Yutian; Liu, Yu; Wang, Gang; ...

    2015-03-11

    Ferromagnetism can occur in wide-band gap semiconductors as well as in carbon-based materials when specific defects are introduced. It is thus desirable to establish a direct relation between the defects and the resulting ferromagnetism. Here, we contribute to revealing the origin of defect-induced ferromagnetism using SiC as a prototypical example. We show that the long-range ferromagnetic coupling can be attributed to the p electrons of the nearest-neighbor carbon atoms around the VSiVC divacancies. Thus, the ferromagnetism is traced down to its microscopic electronic origin.

  13. Carbon p electron ferromagnetism in silicon carbide

    SciTech Connect

    Wang, Yutian; Liu, Yu; Wang, Gang; Anwand, Wolfgang; Jenkins, Catherine A.; Arenholz, Elke; Munnik, Frans; Gordan, Ovidiu D.; Salvan, Georgeta; Zahn, Dietrich R. T.; Chen, Xiaolong; Gemming, Sibylle; Helm, Manfred; Zhou, Shengqiang

    2015-03-11

    Ferromagnetism can occur in wide-band gap semiconductors as well as in carbon-based materials when specific defects are introduced. It is thus desirable to establish a direct relation between the defects and the resulting ferromagnetism. Here, we contribute to revealing the origin of defect-induced ferromagnetism using SiC as a prototypical example. We show that the long-range ferromagnetic coupling can be attributed to the p electrons of the nearest-neighbor carbon atoms around the VSiVC divacancies. Thus, the ferromagnetism is traced down to its microscopic electronic origin.

  14. Colloids in water from a subsurface fracture in granitic rock, Grimsel Test Site, Switzerland

    NASA Astrophysics Data System (ADS)

    Degueldre, C.; Baeyens, B.; Goerlich, W.; Riga, J.; Verbist, J.; Stadelmann, P.

    1989-03-01

    The characterization of colloids from the Grimsel Test Site granitic groundwater has been carried out after concentrating the natural colloids by diaultrafiltration in situ and in the laboratory. A 2-year-long study has shown little variation in the chemistry of the Grimsel water ( T = 285 K, pH = 9.6) and a calculation of saturation indices indicates that quartz and fluorite are slightly oversaturated in the in situ conditions ( log P( CO2)/ atm. = -5.5). Scanning electron microscope (SEM) investigations indicate a colloid concentration of approximately 10 10 particles (40 to 1000 nm) per litre. On the basis electron spectroscopy for chemical analysis (ESCA), transmission electron microscopy (TEM), energy dispersive X-ray spectrometry (EDS), electron energy loss spectrometry (EELS), and laser microprobe mass analysis (LAMMA), the particles are a mixture of organic (C, N, O, (S)) and inorganic (Si, Ca, S and to a lesser extent Mg, Sr and Ba) materials. The alpha specific activity in the colloidal phase is less than 0.5 mBq · 1 -1. The mode of formation is discussed together with the size distribution and the concentration.

  15. Spin pumping in Ferromagnet-Topological Insulator-Ferromagnet Heterostructures

    PubMed Central

    Baker, A. A.; Figueroa, A. I.; Collins-McIntyre, L. J.; van der Laan, G.; Hesjedal, T.

    2015-01-01

    Topological insulators (TIs) are enticing prospects for the future of spintronics due to their large spin-orbit coupling and dissipationless, counter-propagating conduction channels in the surface state. However, a means to interact with and exploit the topological surface state remains elusive. Here, we report a study of spin pumping at the TI-ferromagnet interface, investigating spin transfer dynamics in a spin-valve like structure using element specific time-resolved x-ray magnetic circular dichroism, and ferromagnetic resonance. Gilbert damping increases approximately linearly with increasing TI thickness, indicating efficient behaviour as a spin sink. However, layer-resolved measurements suggest that a dynamic coupling is limited. These results shed new light on the spin dynamics of this novel material class, and suggest great potential for TIs in spintronic devices, through their novel magnetodynamics that persist even up to room temperature. PMID:25601364

  16. Isotope shift of the ferromagnetic transition temperature in itinerant ferromagnets

    NASA Astrophysics Data System (ADS)

    Yanagisawa, Takashi; Hase, Izumi; Odagiri, Kosuke

    2017-02-01

    We present a theory of the isotope effect of the Curie temperature Tc in itinerant ferromagnets. The isotope effect in ferromagnets occurs via the electron-phonon vertex correction and the effective attractive interaction mediated by the electron-phonon interaction. The decrease of the Debye frequency increases the relative strength of the Coulomb interaction, which results in a positive isotope shift of Tc when the mass M of an atom increases. Following this picture, we evaluate the isotope effect of Tc by using the Stoner theory and a spin-fluctuation theory. When Tc is large enough as large as or more than 100 K, the isotope effect on Tc can be measurable. Recently, precise measurements on the oxygen isotope effect on Tc have been performed for itinerant ferromagnet SrRuO3 with Tc ∼ 160 K. A clear isotope effect has been observed with the positive shift of Tc ∼ 1 K by isotope substitution (16O →18O). This experimental result is consistent with our theory.

  17. Superconducting magnetoresistance in ferromagnet/superconductor/ferromagnet trilayers.

    PubMed

    Stamopoulos, D; Aristomenopoulou, E

    2015-08-26

    Magnetoresistance is a multifaceted effect reflecting the diverse transport mechanisms exhibited by different kinds of plain materials and hybrid nanostructures; among other, giant, colossal, and extraordinary magnetoresistance versions exist, with the notation indicative of the intensity. Here we report on the superconducting magnetoresistance observed in ferromagnet/superconductor/ferromagnet trilayers, namely Co/Nb/Co trilayers, subjected to a parallel external magnetic field equal to the coercive field. By manipulating the transverse stray dipolar fields that originate from the out-of-plane magnetic domains of the outer layers that develop at coercivity, we can suppress the supercurrent of the interlayer. We experimentally demonstrate a scaling of the magnetoresistance magnitude that we reproduce with a closed-form phenomenological formula that incorporates relevant macroscopic parameters and microscopic length scales of the superconducting and ferromagnetic structural units. The generic approach introduced here can be used to design novel cryogenic devices that completely switch the supercurrent 'on' and 'off', thus exhibiting the ultimate magnetoresistance magnitude 100% on a regular basis.

  18. Seal device for ferromagnetic containers

    DOEpatents

    Meyer, Ross E.; Jason, Andrew J.

    1994-01-01

    A temporary seal or patch assembly prevents the escape of contents, e.g., fluids and the like, from within a container having a breach therethrough until the contents can be removed and/or a repair effected. A frame that supports a sealing bladder can be positioned over the breach and the frame is then attached to the container surface, which must be of a ferromagnet material, by using switchable permanent magnets. The permanent magnets are designed to have a first condition that is not attracted to the ferromagnetic surface and a second conditions whereby the magnets are attracted to the surface with sufficient force to support the seal assembly on the surface. Latching devices may be attached to the frame and engage the container surface with hardened pins to prevent the lateral movement of the seal assembly along the container surface from external forces such as fluid drag or gravity.

  19. Seal device for ferromagnetic containers

    DOEpatents

    Meyer, R.E.; Jason, A.J.

    1994-10-18

    A temporary seal or patch assembly prevents the escape of contents, e.g., fluids and the like, from within a container having a breach there through until the contents can be removed and/or a repair effected. A frame that supports a sealing bladder can be positioned over the breach and the frame is then attached to the container surface, which must be of a ferromagnet material, by using switchable permanent magnets. The permanent magnets are designed to have a first condition that is not attracted to the ferromagnetic surface and a second conditions whereby the magnets are attracted to the surface with sufficient force to support the seal assembly on the surface. Latching devices may be attached to the frame and engage the container surface with hardened pins to prevent the lateral movement of the seal assembly along the container surface from external forces such as fluid drag or gravity. 10 figs.

  20. Physics of colloidal suspensions

    NASA Astrophysics Data System (ADS)

    Huang, Jiping

    Colloidal suspensions are complex fluids that consist of mesoscopic particles suspended in a solvent, e.g. water, oil, etc. In this thesis, the objective is to investigate the four aspects of colloidal suspensions: electrorotation, dielectrophoresis, dielectric dispersion spectrum, and nonlinear alternating current (AC) response. The traditional theories failed to fit the recent experimental data, and hence, for the purpose of a better fitting, we aim to develop new theories. In addition, our theories also predicted some new phenomena which are expected to be verified in experiments. Electrorotation has been increasingly employed as a sensitive tool for non-invasive studies of a broad variety of microparticles, ranging from living cells to spores and seeds, as well as synthetic materials. In order to analyze the abundant experimental data, we extend here the existing theory by taking into account crucial elements, such as inhomogeneities, multipolar interactions, nonspherical shapes as well as many-body (local-field) effects. Good agreement is shown between our theoretical results and the experimental data. Dielectrophoresis is typically used for micromanipulation and separation of biological cellular size particles, and it has recently been successfully applied to submicron size particles as well. Specific applications include diverse problems in medicine, colloidal science and nanotechnology. To analyze the recent experimental observations, we present a theory which includes the effects of both charging and multipolar interactions. Our theoretical results are favorably compared with the recent experimental observations. Recent experiments revealed that the dielectric dispersion spectrum of fission yeast cells in a suspension was mainly composed of two sub-dispersions. The low-frequency sub-dispersion depended on the cell length, while the high-frequency one was independent of it. However, the existing theory does not fit the experimental data. Hence, we here put

  1. Light-structured colloidal assemblies

    NASA Astrophysics Data System (ADS)

    Aubret, Antoine; Mena, Youssef; Ramananarivo, Sophie; Sacanna, Stefano; Palacci, Jeremie; Palacci lab Team; Sacanna lab Team

    2016-11-01

    Self-propelled particles (SPP) are a key tool since they are of relative simplicity as compared to biological micro-entities and provide a higher level of control. They can convert an energy source into motion and work, and exhibit surprising non-equilibrium behavior. In our work, we focus on the manipulation of colloids using light. We exploit osmotic and phoretic effects to act on single and ensemble of colloids. The key mechanism relies on the photocatalytic decomposition of hydrogen peroxide using hematite, which triggers the motion of colloids around it when illuminated. We use hematite particles and particles with photocatalytic inclusions (i.e. SPP). We first show that the interactions between hematite and colloidal tracers can be tuned by adjusting the chemical environment. Furthermore, we report a phototaxic behavior (migration in light gradient) of the particles. From this, we explore the effect of spatio-temporal modulation of the light to control the motion of colloids at the single particle level, and to generate self-assembled colloidal structures through time and space. The so-formed structures are maintained by phoretic and hydrodynamic forces resulting from the motion of each particles. Ultimately, a dynamic light modulation may be a route for the creation of active colloidal motion on a collective scale through the synchronization of the individual motions of SPP. This work is supported by NSF CAREER DMR 1554724.

  2. Ferromagnetic viscoelastic liquid crystalline materials

    NASA Astrophysics Data System (ADS)

    Schlesier, Cristina; Shibaev, Petr; McDonald, Scott

    2012-02-01

    Novel ferromagnetic liquid crystalline materials were designed by mixing ferromagnetic nanoparticles with glass forming oligomers and low molar mass liquid crystals. The matrix in which nanoparticles are embedded is highly viscous that reduces aggregation of nanoparticles and stabilizes the whole composition. Mechanical and optical properties of the composite material are studied in the broad range of nanoparticle concentrations. The mechanical properties of the viscoelastic composite material resemble those of chemically crosslinked elastomers (elasticity and reversibility of deformations). The optical properties of ferromagnetic cholesteric materials are discussed in detail. It is shown that application of magnetic field leads to the shift of the selective reflection band of the cholesteric material and dramatically change its color. Theoretical model is suggested to account for the observed effects; physical properties of the novel materials and liquid crystalline elastomers are compared and discussed. [1] P.V. Shibaev, C. Schlesier, R. Uhrlass, S. Woodward, E. Hanelt, Liquid Crystals, 37, 1601 (2010) [2] P.V. Shibaev, R. Uhrlass, S. Woodward, C. Schlesier, Md R. Ali, E. Hanelt, Liquid Crystals, 37, 587 (2010)

  3. In vivo monitoring of nanosphere onsite delivery using fiber optic microprobe

    NASA Astrophysics Data System (ADS)

    Lo, Leu-Wei; Yang, Chung-Shi

    2005-02-01

    To recognize the information of ischemia-induced blood vessel permeability would be valuable to formulate the drugs for optimal local delivery, we constructed an implantable needle type fiber-optic microprobe for the monitoring of in vivo fluorescent substances in anesthetized rats. This fiber-optic microprobe was composed of coaxial optical fibers and catheterized using a thin wall tubing of stainless steel (~400 um O.D. and ~300 um I.D.). The central fiber, with 100 um core diameter and 20 um cladding, coated with a 30 um layer of gold, was surrounded by 10 fibers with 50 um cores. The central fiber carried the light from the 488 nm Argon laser to the tissue while the surrounding fibers collected the emitted fluorescence to the detector. When the fiber-optic microprobe was placed in the solutions containing various concentrations of fluorescent nanospheres (20 nm), either with or without 10% lipofundin as optical phantom, nanosphere concentration-dependent responses of the fluorescence intensity were observed. The microprobe was then implanted into the liver and the brain of anesthetized rats to monitor the in situ extravasation of pre-administered fluorescent nanospheres from vasculature following the ischemic insults. Both the hepatic and cerebral ischemic insults showed immediate increases of the extracellular 20 nm fluorescent nanospheres. The implantable fiber-optic microprobe constructed in present study provides itself as a minimally-invasive technique capable of investigating the vascular permeability for in vivo nanosphere delivery in both ischemic liver and brain.

  4. The NeuroMedicator—a micropump integrated with silicon microprobes for drug delivery in neural research

    NASA Astrophysics Data System (ADS)

    Spieth, S.; Schumacher, A.; Kallenbach, C.; Messner, S.; Zengerle, R.

    2012-06-01

    The NeuroMedicator is a micropump integrated with application-specific silicon microprobes aimed for drug delivery in neural research with small animals. The micropump has outer dimensions of 11 × 15 × 3 mm3 and contains 16 reservoirs each having a capacity of 0.25 µL. Thereby, the reservoirs are interconnected in a pearl-chain-like manner and are connected to two 8 mm long silicon microprobes. Each microprobe has a cross-sectional area of 250 × 250 µm2 and features an integrated drug delivery channel of 50 × 50 µm2 with an outlet of 25 µm in diameter. The drug is loaded to the micropump prior to implantation. After implantation, individual 0.25 µL portions of drug can be sequentially released by short heating pulses applied to a polydimethylsiloxane (PDMS) layer containing Expancel® microspheres. Due to local, irreversible thermal expansion of the elastic composite material, the drug is displaced from the reservoirs and released through the microprobe outlet directly to the neural tissue. While implanted, leakage of drug by diffusion occurs due to the open microprobe outlets. The maximum leakage within the first three days after implantation is calculated to be equivalent to 0.06 µL of drug solution.

  5. Clathrate colloidal crystals

    NASA Astrophysics Data System (ADS)

    Lin, Haixin; Lee, Sangmin; Sun, Lin; Spellings, Matthew; Engel, Michael; Glotzer, Sharon C.; Mirkin, Chad A.

    2017-03-01

    DNA-programmable assembly has been used to deliberately synthesize hundreds of different colloidal crystals spanning dozens of symmetries, but the complexity of the achieved structures has so far been limited to small unit cells. We assembled DNA-modified triangular bipyramids (~250-nanometer long edge, 177-nanometer short edge) into clathrate architectures. Electron microscopy images revealed that at least three different structures form as large single-domain architectures or as multidomain materials. Ordered assemblies, isostructural to clathrates, were identified with the help of molecular simulations and geometric analysis. These structures are the most sophisticated architectures made via programmable assembly, and their formation can be understood based on the shape of the nanoparticle building blocks and mode of DNA functionalization.

  6. Microfluidic control using colloidal devices.

    PubMed

    Terray, Alex; Oakey, John; Marr, David W M

    2002-06-07

    By manipulating colloidal microspheres within customized channels, we have created micrometer-scale fluid pumps and particulate valves. We describe two positive-displacement designs, a gear and a peristaltic pump, both of which are about the size of a human red blood cell. Two colloidal valve designs are also demonstrated, one actuated and one passive, for the direction of cells or small particles. The use of colloids as both valves and pumps will allow device integration at a density far beyond what is currently achievable by other approaches and may provide a link between fluid manipulation at the macro- and nanoscale.

  7. Microfluidic Control Using Colloidal Devices

    NASA Astrophysics Data System (ADS)

    Terray, Alex; Oakey, John; Marr, David W. M.

    2002-06-01

    By manipulating colloidal microspheres within customized channels, we have created micrometer-scale fluid pumps and particulate valves. We describe two positive-displacement designs, a gear and a peristaltic pump, both of which are about the size of a human red blood cell. Two colloidal valve designs are also demonstrated, one actuated and one passive, for the direction of cells or small particles. The use of colloids as both valves and pumps will allow device integration at a density far beyond what is currently achievable by other approaches and may provide a link between fluid manipulation at the macro- and nanoscale.

  8. Viscosity Control of the Dynamic Self-Assembly in Ferromagnetic Suspensions

    NASA Astrophysics Data System (ADS)

    Piet, D. L.; Straube, A. V.; Snezhko, A.; Aranson, I. S.

    2013-05-01

    Recent studies of dynamic self-assembly in ferromagnetic colloids suspended in liquid-air or liquid-liquid interfaces revealed a rich variety of dynamic structures ranging from linear snakes to axisymmetric asters, which exhibit novel morphology of the magnetic ordering accompanied by large-scale hydrodynamic flows. Based on controlled experiments and first principles theory, we argue that the transition from snakes to asters is governed by the viscosity of the suspending liquid where less viscous liquids favor snakes and more viscous, asters. By obtaining analytic solutions of the time-averaged Navier-Stokes equations, we gain insight into the role of mean hydrodynamic flows and an overall balance of forces governing the self-assembly. Our results illustrate that the viscosity can be used to control the outcome of the dynamic self-assembly in magnetic colloidal suspensions.

  9. Colloid labelled with radionuclide and method

    DOEpatents

    Atcher, R.W.; Hines, J.J.

    1990-11-13

    A ferric hydroxide colloid having an alpha-emitting radionuclide essentially on the outer surfaces and a method of forming same. The method includes oxidizing a ferrous hydroxide to ferric hydroxide in the presence of a preselected radionuclide to form a colloid having the radionuclide on the outer surface thereof, and thereafter washing the colloid, and suspending the washed colloid in a suitable solution. The labelled colloid is useful in cancer therapy and for the treatment of inflamed joints. No Drawings

  10. Method of making colloid labeled with radionuclide

    DOEpatents

    Atcher, Robert W.; Hines, John J.

    1991-01-01

    A ferric hydroxide colloid having an alpha-emitting radionuclide essentially on the outer surfaces and a method of forming same. The method includes oxidizing a ferrous hydroxide to ferric hydroxide in the presence of a preselected radionuclide to form a colloid having the radionuclide on the outer surface thereof, and thereafter washing the colloid, and suspending the washed colloid in a suitable solution. The labelled colloid is useful in cancer therapy and for the treatment of inflamed joints.

  11. Colloid labelled with radionuclide and method

    DOEpatents

    Atcher, Robert W.; Hines, John J.

    1990-01-01

    A ferric hydroxide colloid having an alpha-emitting radionuclide essentially on the outer surfaces and a method of forming same. The method includes oxidizing a ferrous hydroxide to ferric hydroxide in the presence of a preselected radionuclide to form a colloid having the radionuclide on the outer surface thereof, and thereafter washing the colloid, and suspending the washed colloid in a suitable solution. The labelled colloid is useful in cancer therapy and for the treatment of inflamed joints.

  12. Boron analysis by electron microprobe using MoB4C layered synthetic crystals

    USGS Publications Warehouse

    McGee, J.J.; Slack, J.F.; Herrington, C.R.

    1991-01-01

    Preliminary electron microprobe studies of B distribution in minerals have been carried out using MoB4C-layered synthetic crystals to improve analytical sensitivity for B. Any microprobe measurements of the B contents of minerals using this crystal must include analyses for Cl to assess and correct for the interference of Cl X-rays on the BK?? peak. Microprobe analyses for B can be made routinely in tourmaline and other B-rich minerals, and minor B contents also can be determined in common rock-forming minerals. Incorporation of unusually high B contents in minerals other than borosilicates has been discovered in prograde and retrograde minerals in tourmalinites from the Broken Hill district, Australia, and may reflect high B activities produced during the metamorphism of tourmaline-rich rocks. -from Authors

  13. The Debrecen Scanning Nuclear Microprobe and its Applications in Biology and Environmental Science

    SciTech Connect

    Kertesz, Zsofia

    2007-11-26

    Nuclear microscopy is one of the most powerful tools which are able to determine quantitative trace element distributions in complex samples on a microscopic scale. The advantage of nuclear microprobes are that different ion beam analytical techniques, like PIXE, RBS, STIM and NRA can be applied at the same time allowing the determination of the sample structure, major, minor and trace element distribution simultaneously.In this paper a nuclear microprobe setup developed for the microanalysis of thin complex samples of organic matrix at the Debrecen Scanning Nuclear Microprobe Facility is presented. The application of nuclear microscopy in life sciences is shown through an example, the study of penetration of TiO{sub 2} nanoparticles of bodycare cosmetics in skin layers.

  14. Colloidal nanomaterial-based immunoassay.

    PubMed

    Teste, Bruno; Descroix, Stephanie

    2012-06-01

    Nanomaterials have been widely developed for their use in nanomedicine, especially for immunoassay-based diagnosis. In this review we focus on the use of nanomaterials as a nanoplatform for colloidal immunoassays. While conventional heterogeneous immunoassays suffer from mass transfer limitations and consequently long assay time, colloidal immunosupports allow target capture in the entire volume, thus speeding up reaction kinetics and shortening assay time. Owing to their wide range of chemical and physical properties, nanomaterials are an interesting candidate for immunoassay development. The most popular colloidal nanomaterials for colloidal immunoassays will be discussed, as well as their influence on immune reactions. Recent advances in nanomaterial applications for different formats of immunoassays will be reported, such as nanomaterial-based indirect immunoassays, optical-based agglutination immunoassays, resonance energy transfer-based immunoassays and magnetic relaxation-based immunoassays. Finally, the future of using nanomaterials for homogeneous immunoassays dedicated to clinical diagnosis will be discussed.

  15. On the Absence of Ferromagnetism in Typical 2D Ferromagnets

    SciTech Connect

    Biskup, Marek

    2010-04-06

    We consider the Ising systems in d dimensions with nearest-neighbor ferromagnetic interactions and long-range repulsive (antiferromagnetic) interactions that decay with power s of the distance. The physical context of such models is discussed; primarily this is d = 2 and s = 3 where, at long distances, genuine magnetic interactions between genuine magnetic dipoles are of this form.We prove that when the power of decay lies above d and does not exceed d + 1, then for all temperatures the spontaneous magnetization is zero. In contrast, we also show that for powers exceeding d + 1 (with d {ge} 2) magnetic order can occur.

  16. Ferromagnetism in α-Mn nanorods

    NASA Astrophysics Data System (ADS)

    Tiwary, Chandra Sekhar; Bhowmick, Somnath; Prakash, Abhinav; Chakrabarti, Ramananda; Biswas, Krishanu; Chattopadhyay, Kamanio

    2017-02-01

    The present investigation reports the first experimental evidence of ferromagnetism in the cryomilled pure α-Mn nano-rods. Cryomilling of Mn powder at liquid nitrogen temperature leads to the formation of long nanorods of α-Mn. The detailed electron microscopy reveals that the nanorods grow along [ 1 1 ¯ 2 ] directions with surfaces bounded by {110} planes of FCC α-Mn. The magnetic measurements indicate ferromagnetic hysteresis loops, suggesting typical ferromagnetic order. The ab-initio density functional theory calculations indicate that the ferromagnetic response originates from the under coordinated surface atoms.

  17. Mechanical Failure in Colloidal Gels

    NASA Astrophysics Data System (ADS)

    Kodger, Thomas Edward

    When colloidal particles in a dispersion are made attractive, they aggregate into fractal clusters which grow to form a space-spanning network, or gel, even at low volume fractions. These gels are crucial to the rheological behavior of many personal care, food products and dispersion-based paints. The mechanical stability of these products relies on the stability of the colloidal gel network which acts as a scaffold to provide these products with desired mechanical properties and to prevent gravitational sedimentation of the dispersed components. Understanding the mechanical stability of such colloidal gels is thus of crucial importance to predict and control the properties of many soft solids. Once a colloidal gel forms, the heterogeneous structure bonded through weak physical interactions, is immediately subject to body forces, such as gravity, surface forces, such as adhesion to a container walls and shear forces; the interplay of these forces acting on the gel determines its stability. Even in the absence of external stresses, colloidal gels undergo internal rearrangements within the network that may cause the network structure to evolve gradually, in processes known as aging or coarsening or fail catastrophically, in a mechanical instability known as syneresis. Studying gel stability in the laboratory requires model colloidal system which may be tuned to eliminate these body or endogenous forces systematically. Using existing chemistry, I developed several systems to study delayed yielding by eliminating gravitational stresses through density matching and cyclic heating to induce attraction; and to study syneresis by eliminating adhesion to the container walls, altering the contact forces between colloids, and again, inducing gelation through heating. These results elucidate the varied yet concomitant mechanisms by which colloidal gels may locally or globally yield, but then reform due to the nature of the physical, or non-covalent, interactions which form

  18. Recent advances in laser microprobe mass analysis (LAMMA) of inner ear tissue

    SciTech Connect

    Meyer zum Gottesberge-Orsulakova, A.; Kaufmann, R.

    1985-01-01

    Maintenance of ionic gradients within the various fluids compartments of the inner ear requires transport active cellular systems at different locations. LAMMA analysis is ideally suited for detection of ions in microquantity on cellular levels overcoming many technical difficulties. The present paper summarizes the results of microprobe analysis obtained with laser induced mass spectrometry (LAMMA) supplemented by X-ray microprobe analysis of epithelial cell layers adjacent to the endolymphatic space in the cochlear duct, in the vestibular organ and in the endolymphatic sac. The possible role of inner ear as well as ocular melanin in the mechanisms of active ion transport is discussed.

  19. Core Community Specifications for Electron Microprobe Operating Systems: Software, Quality Control, and Data Management Issues

    NASA Technical Reports Server (NTRS)

    Fournelle, John; Carpenter, Paul

    2006-01-01

    Modem electron microprobe systems have become increasingly sophisticated. These systems utilize either UNIX or PC computer systems for measurement, automation, and data reduction. These systems have undergone major improvements in processing, storage, display, and communications, due to increased capabilities of hardware and software. Instrument specifications are typically utilized at the time of purchase and concentrate on hardware performance. The microanalysis community includes analysts, researchers, software developers, and manufacturers, who could benefit from exchange of ideas and the ultimate development of core community specifications (CCS) for hardware and software components of microprobe instrumentation and operating systems.

  20. An x-ray microprobe using focussing optics with a synchrotron radiation source

    SciTech Connect

    Thompson, A.C.; Underwood, J.H.; Wu, Y.; Giauque, R.D.

    1989-01-01

    An x-ray microprobe can be used to produce maps of the concentration of elements in a sample. Synchrotron radiation provides x-ray beams with enough intensity and collimation to make possible elemental images with femtogram sensitivity. The use of focussing x-ray mirrors made from synthetic multilayers with a synchrotron x-ray beam allows beam spot sizes of less than 10 /mu/m /times/ 10 /mu/m to be produced. Since minimal sample preparation is required and a vacuum environment is not necessary, there will be a wide variety of applications for such microprobes. 8 refs., 6 figs.

  1. Optimal Parameters of High Energy Ion Microprobe Systems Comprised of Lafayette Lenses

    NASA Astrophysics Data System (ADS)

    Dymnikov, Alexander D.; Glass, Gary A.; Rout, Bibhudutta; Dias, Johnny F.

    2009-03-01

    High energy optimal ion microprobes comprised of new compact magnetic quadrupole lenses (Lafayette Quadrupole Lens) are numerically investigated. The smallest beam spot size and appropriate radii of object and divergence slits are presented for different emittances and compared with the corresponding parameters of the Oxford triplet for the same total length. The parameters of the calculated microprobes include demagnification, the magnetic field in the lenses and the coefficients of spherical and chromatic aberrations for several quadrupole system configurations including the doublet, the Lafayette symmetric triplet, the Russian magnetic quadruplets and sextuplets.

  2. Proton microprobe analysis of zinc in skeletal tissues. [Proton induced x-ray emission analysis

    SciTech Connect

    Doty, S B; Jones, K W; Kraner, H W; Shroy, R E; Hanson, A L

    1980-06-01

    A proton microprobe with windowless exit port was used to study zinc distributions in various types of skeletal tissues. The use of an external beam facilitated positioning of the targets for examination of particular points of interest. The proton microprobe is uniquely suited to this work since it combines high sensitivity for zinc determinations in thick samples with good spatial resolution. Measurements on rat and rabbit Achilles tendon showed a significant increase in zinc concentrations as the beam moved from the unmineralized collagen into the mineralized attachment site. Cartilage gave a similar result, with calcified cartilage having a greater zinc level than the articular surface on unmineralized epiphyseal cartilage.

  3. Polymer SU-8 Based Microprobes for Neural Recording and Drug Delivery

    NASA Astrophysics Data System (ADS)

    Altuna, Ane; Fernandez, Luis; Berganzo, Javier

    2015-06-01

    This manuscript makes a reflection about SU-8 based microprobes for neural activity recording and drug delivery. By taking advantage of improvements in microfabrication technologies and using polymer SU-8 as the only structural material, we developed several microprobe prototypes aimed to: a) minimize injury in neural tissue, b) obtain high-quality electrical signals and c) deliver drugs at a micrometer precision scale. Dedicated packaging tools have been developed in parallel to fulfill requirements concerning electric and fluidic connections, size and handling. After these advances have been experimentally proven in brain using in vivo preparation, the technological concepts developed during consecutive prototypes are discussed in depth now.

  4. Aggregation of Heterogeneously Charged Colloids.

    PubMed

    Dempster, Joshua M; Olvera de la Cruz, Monica

    2016-06-28

    Patchy colloids are attractive as programmable building blocks for metamaterials. Inverse patchy colloids, in which a charged surface is decorated with patches of the opposite charge, are additionally noteworthy as models for heterogeneously charged biological materials such as proteins. We study the phases and aggregation behavior of a single charged patch in an oppositely charged colloid with a single-site model. This single-patch inverse patchy colloid model shows a large number of phases when varying patch size. For large patch sizes we find ferroelectric crystals, while small patch sizes produce cross-linked gels. Intermediate values produce monodisperse clusters and unusual worm structures that preserve finite ratios of area to volume. The polarization observed at large patch sizes is robust under extreme disorder in patch size and shape. We examine phase-temperature dependence and coexistence curves and find that large patch sizes produce polarized liquids, in contrast to mean-field predictions. Finally, we introduce small numbers of unpatched charged colloids. These can either suppress or encourage aggregation depending on their concentration and the size of the patches on the patched colloids. These effects can be exploited to control aggregation and to measure effective patch size.

  5. Electron transport in ferromagnetic nanostructures

    NASA Astrophysics Data System (ADS)

    Lee, Sungbae

    As the size of a physical system decreases toward the nanoscale, quantum mechanical effects such as the discretization of energy levels and the interactions of the electronic spins become readily observable. To understand what happens within submicrometer scale samples is one of the goals of modern condensed matter physics. Electron transport phenomena drew a lot of attention over the past two decades or so, not only because quantum corrections to the classical transport theory, but also they allow us to probe deeply into the microscopic nature of the system put to test. Although a significant amount of research was done in the past and thus extended our understanding in this field, most of these works were concentrated on simpler examples. Electron transport in strongly correlated systems is still a field that needs to be explored more thoroughly. In fact, experimental works that have been done so far to characterize coherence physics in correlated systems such as ferromagnetic metals are far from conclusive. One reason ferromagnetic samples draw such attention is that there exist correlations that lead to excitations (e.g. spin waves, domain wall motions) not present in normal metals, and these new environmental degrees of freedom can have profound effects on decoherence processes. In this thesis, three different types of magnetic samples were examined: a band ferromagnetism based metallic ferromagnet, permalloy, a III-V diluted ferromagnetic semiconductor with ferromagnetism from a hole-mediated exchange interaction, and magnetite nanocrystals and films. The first observation of time-dependent universal conductance fluctuations (TD-UCF) in permalloy is presented and our observations lead to three major conclusions. First, the cooperon contribution to the conductance is suppressed in this material. This is consistent with some theoretical expectations, and implies that weak localization will be suppressed as well. Second, we see evidence that domain wall motion

  6. Spin-orbit ferromagnetic resonance

    NASA Astrophysics Data System (ADS)

    Ferguson, Andrew

    2013-03-01

    In conventional magnetic resonance techniques the magnitude and direction of the oscillatory magnetic field are (at least approximately) known. This oscillatory field is used to probe the properties of a spin ensemble. Here, I will describe experiments that do the inverse. I will discuss how we use a magnetic resonance technique to map out the current-induced effective magnetic fields in the ferromagnetic semiconductors (Ga,Mn)As and (Ga,Mn)(As,P). These current-induced fields have their origin in the spin-orbit interaction. Effective magnetic fields are observed with symmetries which resemble the Dresselhaus and Rashba spin-orbit interactions and which depend on the diagonal and off-diagonal strain respectively. Ferromagnetic semiconductor materials of different strains, annealing conditions and concentrations are studied and the results compared with theoretical calculations. Our original study measured the rectification voltage coming from the product of the oscillatory magnetoresistance, during magnetisation precession, and the alternating current. More recently we have developed an impedance matching technique which enables us to extract microwave voltages from these high resistance (10 k Ω) samples. In this way we measure the microwave voltage coming from the product of the oscillating magneto-resistance and a direct current. The direct current is observed to affect the magnetisation precession, indicating that anti-damping as well as field-like torques can originate from the spin-orbit interaction.

  7. Voltage control of ferromagnetic resonance

    NASA Astrophysics Data System (ADS)

    Zhou, Ziyao; Peng, Bin; Zhu, Mingmin; Liu, Ming

    2016-05-01

    Voltage control of magnetism in multiferroics, where the ferromagnetism and ferroelectricity are simultaneously exhibiting, is of great importance to achieve compact, fast and energy efficient voltage controllable magnetic/microwave devices. Particularly, these devices are widely used in radar, aircraft, cell phones and satellites, where volume, response time and energy consumption is critical. Researchers realized electric field tuning of magnetic properties like magnetization, magnetic anisotropy and permeability in varied multiferroic heterostructures such as bulk, thin films and nanostructure by different magnetoelectric (ME) coupling mechanism: strain/stress, interfacial charge, spin-electromagnetic (EM) coupling and exchange coupling, etc. In this review, we focus on voltage control of ferromagnetic resonance (FMR) in multiferroics. ME coupling-induced FMR change is critical in microwave devices, where the electric field tuning of magnetic effective anisotropic field determines the tunability of the performance of microwave devices. Experimentally, FMR measurement technique is also an important method to determine the small effective magnetic field change in small amount of magnetic material precisely due to its high sensitivity and to reveal the deep science of multiferroics, especially, voltage control of magnetism in novel mechanisms like interfacial charge, spin-EM coupling and exchange coupling.

  8. Spin waves of ferromagnetic films

    NASA Astrophysics Data System (ADS)

    Arias, Rodrigo

    The spin wave modes of ferromagnetic films have been studied for a long time experimentally as well as theoretically: initially magnetostatic and later dipole-exchange modes. Theoretically dipole-exchange modes have been solved exactly numerically for some configurations and boundary conditions, and there are approximations of their frequency dispersion relations based on infinite series solutions and perturbation theory, valid for arbitrary orientations of an applied magnetic field, and for boundary conditions that allow varying degrees of pinning. A theoretical method that allows to determine with ease the exact frequency dispersion relations of the dipole-exchange modes is presented: it is required to solve numerically a 6x6 linear eigenvalue problem at each wavevector of interest; the spin wave modes inside or outside the sample may be plotted. Analogous calculations may be done to determine magnetostatic modes in detail. The method corresponds to a generalization of Green's theorem to the problem of determining the dipole-exchange modes of a ferromagnetic film: convolution integral equations for the magnetization and magnetostatic potential are derived on the surfaces of the film that become simple local algebraic equations in Fourier space, or for specific wavevectors. This work was supported by Project ICM FP10-061-F-FIC, Chile, and Center for the Development of Nanoscience and Nanotechnology CEDENNA FB0807 (Chile).

  9. High-speed microprobe for roughness measurements in high-aspect-ratio microstructures

    NASA Astrophysics Data System (ADS)

    Doering, Lutz; Brand, Uwe; Bütefisch, Sebastian; Ahbe, Thomas; Weimann, Thomas; Peiner, Erwin; Frank, Thomas

    2017-03-01

    Cantilever-type silicon microprobes with an integrated tip and a piezoresistive signal read out have successfully proven to bridge the gap between scanning force microscopy and stylus profilometry. Roughness measurements in high-aspect-ratio microstructures (HARMS) with depths down to 5 mm and widths down to 50 µm have been demonstrated. To improve the scanning speed up to 15 mm s‑1, the wear of the tip has to be reduced. The atomic layer deposition (ALD) technique with alumina (Al2O3) has been tested for this purpose. Repeated wear measurements with coated and uncoated microprobe cantilevers have been carried out on a roughness standard at a speed of 15 mm s‑1. The tip shape and the wear have been measured using a new probing tip reference standard containing rectangular silicon grooves with widths from 0.3 µm to 3 µm. The penetration depth of the microprobe allows one to measure the wear of the tip as well as the tip width and the opening angle of the tip. The roughness parameters obtained on the roughness standard during wear experiments agree well with the reference values measured with a calibrated stylus instrument, nevertheless a small amount of wear still is observable. Further research is necessary in order to obtain wear resistant microprobe tips for non-destructive inspection of microstructures in industry and microform measurements, for example in injection nozzles.

  10. On the analysis of neonatal hamster tooth germs with the photon microprobe at Daresbury, UK

    NASA Astrophysics Data System (ADS)

    Tros, G. H. J.; Van Langevelde, F.; Vis, R. D.

    1990-04-01

    Complementary to the micro-PIXE experiments performed on hamster tooth germs to elucidate the role of fluoride during the growth, the photon microprobe at Daresbury was used to obtain information on the distribution of Zn. The germs of fluoride-administered hamsters, together with a control group, were analyzed with the micro-synchrotron radiation fluorescence method (micro-SXRF).

  11. Strain in UHMWPE for orthopaedic use studied by Raman microprobe spectroscopy.

    PubMed

    Kyomoto, Masayuki; Miwa, Yasutake; Pezzotti, Giuseppe

    2007-01-01

    Ultra-high-molecular-weight polyethylene (UHMWPE) has been the most popular bearing material against both metal and ceramic counter-faces in total hip and knee joint replacements. Therefore, it is desirable to clarify the complex phenomena occurring both in vivo and in vitro, using highly sensitive analytical techniques. However, conventional analytical techniques used so far suffer from destructive measurements, lack of precision and/or intricate techniques. In the present study, the physical and chemical properties of both conventional UHMWPE (PE) and highly cross-linked UHMWPE (CLPE) were investigated by Raman microprobe spectroscopy, which combines the advantages of high precision and non-destructive measurements. It was found that the strain of UHMWPE can be evaluated by a change in the full width at half maximum (FWHM) of a selected Raman band (located at around 1127 cm(-1)), and that these spectroscopic strain coefficients were (0.42 +/- 0.01) x 10(-2) cm(-1)/% elongation and (0.48 +/- 0.01) x 10(-2) cm(-1)/% elongation for PE and CLPE (100 kGy), respectively. The difference in the crystalline nature between PE and CLPE was also confirmed by Raman microprobe spectroscopy. In addition, the Raman microprobe spectroscopy technique enabled us to obtain hyperspectral images of strain and crystallinity on a microscopic scale. Thus, Raman microprobe spectroscopy is a very effective method for analyzing UHMWPE for orthopaedic use.

  12. Hydrogen in ferromagnetic semiconductors for planar spintronics

    NASA Astrophysics Data System (ADS)

    Farshchi, Rouin

    This dissertation documents the use of hydrogen for controlling electrical and magnetic properties of ferromagnetic semiconductors, particularly GaMnAs. With minimal structural perturbation, hydrogen forms complexes with Mn acceptors and renders them neutral, thereby substantially increasing electrical resistivity and removing ferromagnetism. A major finding presented herein is that laser annealing can be used to controllably dissociate the Mn-H complexes and restore ferromagnetism. Structural, electrical, and magnetic effects of the laser activation process are thoroughly explored through experiments and numerical modeling. Local laser activation with tightly-focused ultra-short laser pulses allows for high-resolution direct-writing of ferromagnetic patterns in semiconductors, introducing a new paradigm for device design. Prospects for laser formation of high-temperature phases in ferromagnetic semiconductors are investigated. Finally, several device concepts incorporating the laser activation process are discussed as building blocks towards planar all-semiconductor spintronics.

  13. Colloids in the vicinity of landfills

    NASA Astrophysics Data System (ADS)

    Baumann, T.; Fruhstorfer, P.; Klein, T.; Niessner, R.

    2003-04-01

    Waste disposals without adequate landfill liner system are a source of contaminants and colloids. In order to assess the effects of the presence of colloids on the transport of heavy metal ions, the colloids at three landfill sites were characterized with regard to their chemical and mineralogical composition, their size distribution, and the concentration of heavy metal ions associated to the colloids. It can be shown that the pattern of the colloids inside and outside of the landfill is different in all examined parameters, e.g. inside of the disposal we find organic colloids and salt particles, whereas the groundwater downstream of the disposal contains mainly iron-colloids and carbonatic particles. Therefore a direct transfer of colloids from the landfill to the aquifer seems unlikely. Changes of the hydrochemical (mainly redox) and hydrodynamic conditions contribute to this behaviour. The association of heavy metal ions to colloids shows an interesting pattern: High concentrations are present in solution and associated to smaller (< 10 nm) and larger (> 1 μm) colloids, whereas the colloids in between show only small concentrations. This finding has some impact on the assessment of colloidal transport processes, since it suggests, that the more mobile colloids do not carry high concentrations of heavy metal ions.

  14. Modeling of ferromagnetic semiconductor devices for spintronics

    NASA Astrophysics Data System (ADS)

    Lebedeva, N.; Kuivalainen, P.

    2003-06-01

    We develop physical models for magnetic semiconductor devices, where a part of the device structure consists of a ferromagnetic semiconductor layer. First we calculate the effect of the exchange interaction between the charge carrier spins and the spins of the localized magnetic electrons on the electronic states, recombination processes, and charge transport in ferromagnetic semiconductors such as (Ga,Mn)As. Taking into account, e.g., the splitting of the conduction and valence bands due to the exchange interaction, we model the electrical characteristics of the basic magnetic semiconductor devices such as Schottky diodes consisting of a nonmagnetic metal/ferromagnetic semiconductor interface, pn diodes consisting of a ferromagnetic/nonmagnetic junction and bipolar transistors having a ferromagnetic emitter. The models predict that at temperatures close to the Curie temperature TC the electrical properties of the magnetic semiconductor devices become strongly dependent on the average spin polarization of the magnetic atoms. A feature in the models is that many device parameters such as diffusion lengths or potential barriers become spin dependent in magnetic semiconductor devices. In a ferromagnetic Schottky diode the sensitivity of the device current I to the external magnetic field may be as large as (∂I/∂B)I-1≈1/T at temperatures close to TC. In a ferromagnetic pn diode both the ideal and recombination currents become magnetic field dependent. In a ferromagnetic bipolar transistor the current gain shows the same sensitivity to the spin polarization as the dc current in the ferromagnetic pn diodes. According to our model calculations optimal structures showing the largest magnetization dependence of the electrical characteristics in III-V ferromagnetic semiconductor devices would be those where the magnetic side of the junction is of n type.

  15. Resonance frequency in ferromagnetic superlattices

    NASA Astrophysics Data System (ADS)

    Qiu, Rong-ke; Huang, An-dong; Li, Da; Zhang, Zhi-dong

    2011-10-01

    The resonance frequency in two-layer and three-layer ferromagnetic superlattices is studied, using the Callen's Green function method, the Tyablikov decoupling approximation and the Anderson-Callen decoupling approximation. The effects of interlayer exchange coupling, anisotropy, external magnetic field and temperature on the resonance frequency are investigated. It is found that the resonance frequencies increase with increasing external magnetic field. In a parameter region of the asymmetric system, each sublayer corresponds to its own resonance frequency. The anisotropy of a sublayer affects only the resonance frequency corresponding to this sublayer. The stronger the anisotropy, the higher is the resonance frequency. The interlayer exchange coupling affects only the resonance frequencies belonging to the sublayers connected by it. The stronger the interlayer exchange coupling, the higher are the resonance frequencies. All the resonance frequencies decrease as the reduced temperature increases. The results direct the method to enhance and adjust the resonance frequency of magnetic multilayered materials with a wide band.

  16. Intrinsic ferromagnetism in hexagonal boron nitride nanosheets

    SciTech Connect

    Si, M. S.; Gao, Daqiang E-mail: xueds@lzu.edu.cn; Yang, Dezheng; Peng, Yong; Zhang, Z. Y.; Xue, Desheng E-mail: xueds@lzu.edu.cn; Liu, Yushen; Deng, Xiaohui; Zhang, G. P.

    2014-05-28

    Understanding the mechanism of ferromagnetism in hexagonal boron nitride nanosheets, which possess only s and p electrons in comparison with normal ferromagnets based on localized d or f electrons, is a current challenge. In this work, we report an experimental finding that the ferromagnetic coupling is an intrinsic property of hexagonal boron nitride nanosheets, which has never been reported before. Moreover, we further confirm it from ab initio calculations. We show that the measured ferromagnetism should be attributed to the localized π states at edges, where the electron-electron interaction plays the role in this ferromagnetic ordering. More importantly, we demonstrate such edge-induced ferromagnetism causes a high Curie temperature well above room temperature. Our systematical work, including experimental measurements and theoretical confirmation, proves that such unusual room temperature ferromagnetism in hexagonal boron nitride nanosheets is edge-dependent, similar to widely reported graphene-based materials. It is believed that this work will open new perspectives for hexagonal boron nitride spintronic devices.

  17. Intrinsic ferromagnetism in hexagonal boron nitride nanosheets.

    PubMed

    Si, M S; Gao, Daqiang; Yang, Dezheng; Peng, Yong; Zhang, Z Y; Xue, Desheng; Liu, Yushen; Deng, Xiaohui; Zhang, G P

    2014-05-28

    Understanding the mechanism of ferromagnetism in hexagonal boron nitride nanosheets, which possess only s and p electrons in comparison with normal ferromagnets based on localized d or f electrons, is a current challenge. In this work, we report an experimental finding that the ferromagnetic coupling is an intrinsic property of hexagonal boron nitride nanosheets, which has never been reported before. Moreover, we further confirm it from ab initio calculations. We show that the measured ferromagnetism should be attributed to the localized π states at edges, where the electron-electron interaction plays the role in this ferromagnetic ordering. More importantly, we demonstrate such edge-induced ferromagnetism causes a high Curie temperature well above room temperature. Our systematical work, including experimental measurements and theoretical confirmation, proves that such unusual room temperature ferromagnetism in hexagonal boron nitride nanosheets is edge-dependent, similar to widely reported graphene-based materials. It is believed that this work will open new perspectives for hexagonal boron nitride spintronic devices.

  18. Intrinsic ferromagnetism in hexagonal boron nitride nanosheets

    NASA Astrophysics Data System (ADS)

    Si, M. S.; Gao, Daqiang; Yang, Dezheng; Peng, Yong; Zhang, Z. Y.; Xue, Desheng; Liu, Yushen; Deng, Xiaohui; Zhang, G. P.

    2014-05-01

    Understanding the mechanism of ferromagnetism in hexagonal boron nitride nanosheets, which possess only s and p electrons in comparison with normal ferromagnets based on localized d or f electrons, is a current challenge. In this work, we report an experimental finding that the ferromagnetic coupling is an intrinsic property of hexagonal boron nitride nanosheets, which has never been reported before. Moreover, we further confirm it from ab initio calculations. We show that the measured ferromagnetism should be attributed to the localized π states at edges, where the electron-electron interaction plays the role in this ferromagnetic ordering. More importantly, we demonstrate such edge-induced ferromagnetism causes a high Curie temperature well above room temperature. Our systematical work, including experimental measurements and theoretical confirmation, proves that such unusual room temperature ferromagnetism in hexagonal boron nitride nanosheets is edge-dependent, similar to widely reported graphene-based materials. It is believed that this work will open new perspectives for hexagonal boron nitride spintronic devices.

  19. Colloids and Nucleation

    NASA Technical Reports Server (NTRS)

    Ackerson, Bruce

    1997-01-01

    The objectives of the work funded under this grant were to develop a microphotographic technique and use it to monitor the nucleation and growth of crystals of hard colloidal spheres. Special attention is given to the possible need for microgravity studies in future experiments. A number of persons have been involved in this work. A masters student, Keith Davis, began the project and developed a sheet illumination apparatus and an image processing system for detection and analysis. His work on a segmentation program for image processing was sufficient for his master's research and has been published. A post doctoral student Bernie Olivier and a graduate student Yueming He, who originally suggested the sheet illumination, were funded by another source but along with Keith made photographic series of several samples (that had been made by Keith Davis). Data extraction has been done by Keith, Bernie, Yueming and two undergraduates employed on the grant. Results are published in Langmuir. These results describe the sheet lighting technique as one which illuminates not only the Bragg scattering crystal, but all the crystals. Thus, accurate crystal counts can be made for nucleation rate measurements. The strange crystal length scale reduction, observed in small angle light scattering (SALS) studies, following the initial nucleation and growth period, has been observed directly. The Bragg scattering (and dark) crystal size decreases in the crossover region. This could be an effect due to gravitational forces or due to over- compression of the crystal during growth. Direct observations indicate a complex morphology for the resulting hard sphere crystals. The crystal edges are fairly sharp but the crystals have a large degree of internal structure. This structure is a result of (unstable) growth and not aggregation. As yet unpublished work compares growth exponents data with data obtained by SALS. The nucleation rate density is determined over a broad volume fraction range

  20. Multifunctional Sn- and Fe-Codoped In2O3 Colloidal Nanocrystals: Plasmonics and Magnetism.

    PubMed

    Tandon, Bharat; Shanker, G Shiva; Nag, Angshuman

    2014-07-03

    We prepared Fe- and Sn-codoped colloidal In2O3 nanocrystals (∼6 nm). Sn doping provides free electrons in the conduction band, originating localized surface plasmon resonance (LSPR) and electrical conductivity. The LSPR band can be tuned between 2000 and >3000 nm, depending on the extent and kind of dopant ions. Fe doping, on the other hand, provides unpaired electrons, resulting in weak ferromagnetism at room temperature. Fe doping shifts the LSPR band of 10% Sn-doped In2O3 nanocrystals to a longer wavelength along with a reduction in intensity, suggesting trapping of charge carriers around the dopant centers, whereas Sn doping increases the magnetization of 10% Fe-doped In2O3 nanocrystals, probably because of the free electron mediated interactions between distant magnetic ions. The combination of plasmonics and magnetism, in addition to electronic conductivity and visible-light transparency, is a unique feature of our colloidal codoped nanocrystals.

  1. Angular and Linear Momentum of Excited Ferromagnets

    NASA Astrophysics Data System (ADS)

    Yan, Peng; Kamra, Akashdeep; Cao, Yunshan; Bauer, Gerrit

    2014-03-01

    The angular momentum vector of a Heisenberg ferromagnet with isotropic exchange interaction is conserved, while under uniaxial crystalline anisotropy the projection of the total spin along the easy axis is a constant of motion. Using Noether's theorem, we prove that these conservation laws persist in the presence of dipole-dipole interactions. However, spin and orbital angular momentum are not conserved separately anymore. We also define the linear momentum of ferromagnetic textures. We illustrate the general principles with special reference to spin transfer torques and identify the emergence of a non-adiabatic effective field acting on domain walls in ferromagnetic insulators

  2. Amorphous RE–Fe–B–Na colloidal nanoparticles: High temperature solution synthesis and magnetic properties

    SciTech Connect

    Jia, Li-Ping; Yan, Bing

    2015-04-15

    Graphical abstract: RE–Fe–B–Na (RE = Nd–Er) colloidal nanoparticles by high-temperature solution synthesis are ultra-small monodisperse and air-stable amorphous, whose size and magnetic dependence are studied. - Highlights: • RE–Fe–B–Na nanoparticles are obtained by high-temperature solution synthesis. • These colloidal nanoparticles are monodisperse and size controlled. • The magnetism dependence and possible magnetic coupling mechanism are studied. - Abstract: RE–Fe–B–Na (RE = Nd–Er) colloidal nanoparticles are prepared by high-temperature solution synthesis. These nanoparticles are ultra-small monodisperse, air-stable and amorphous, whose particle size and magnetic property are characterized by transmission electron microscope and superconducting quantum interference device. Taking Nd–Fe–B–Na nanoparticle as an example, it is found that the particle size can be controlled in less than 7 nm. Besides, the magnetic properties of RE–Fe–B–Na colloidal nanoparticles can be compared for different rare earth elements. Based on the bulk ferromagnetic coupling, other possible magnetic coupling mechanism is discussed.

  3. Colloid characterization and quantification in groundwater samples

    SciTech Connect

    K. Stephen Kung

    2000-06-01

    This report describes the work conducted at Los Alamos National Laboratory for studying the groundwater colloids for the Yucca Mountain Project in conjunction with the Hydrologic Resources Management Program (HRMP) and the Underground Test Area (UGTA) Project. Colloidal particle size distributions and total particle concentration in groundwater samples are quantified and characterized. Colloid materials from cavity waters collected near underground nuclear explosion sites by HRMP field sampling personnel at the Nevada Test Site (NTS) were quantified. Selected colloid samples were further characterized by electron microscope to evaluate the colloid shapes, elemental compositions, and mineral phases. The authors have evaluated the colloid size and concentration in the natural groundwater sample that was collected from the ER-20-5 well and stored in a 50-gallon (about 200-liter) barrel for several months. This groundwater sample was studied because HRMP personnel have identified trace levels of radionuclides in the water sample. Colloid results show that even though the water sample had filtered through a series of Millipore filters, high-colloid concentrations were identified in all unfiltered and filtered samples. They had studied the samples that were diluted with distilled water and found that diluted samples contained more colloids than the undiluted ones. These results imply that colloids are probably not stable during the storage conditions. Furthermore, results demonstrate that undesired colloids have been introduced into the samples during the storage, filtration, and dilution processes. They have evaluated possible sources of colloid contamination associated with sample collection, filtrating, storage, and analyses of natural groundwaters. The effects of container types and sample storage time on colloid size distribution and total concentration were studied to evaluate colloid stability by using J13 groundwater. The data suggests that groundwater samples

  4. Solid colloidal optical wavelength filter

    DOEpatents

    Alvarez, Joseph L.

    1992-01-01

    A solid colloidal optical wavelength filter includes a suspension of spheal particles dispersed in a coagulable medium such as a setting plastic. The filter is formed by suspending spherical particles in a coagulable medium; agitating the particles and coagulable medium to produce an emulsion of particles suspended in the coagulable medium; and allowing the coagulable medium and suspended emulsion of particles to cool.

  5. Dynamics of evaporative colloidal patterning

    NASA Astrophysics Data System (ADS)

    Kaplan, C. Nadir; Wu, Ning; Mandre, Shreyas; Aizenberg, Joanna; Mahadevan, L.

    2015-09-01

    Drying suspensions often leave behind complex patterns of particulates, as might be seen in the coffee stains on a table. Here, we consider the dynamics of periodic band or uniform solid film formation on a vertical plate suspended partially in a drying colloidal solution. Direct observations allow us to visualize the dynamics of band and film deposition, where both are made of multiple layers of close packed particles. We further see that there is a transition between banding and filming when the colloidal concentration is varied. A minimal theory of the liquid meniscus motion along the plate reveals the dynamics of the banding and its transition to the filming as a function of the ratio of deposition and evaporation rates. We also provide a complementary multiphase model of colloids dissolved in the liquid, which couples the inhomogeneous evaporation at the evolving meniscus to the fluid and particulate flows and the transition from a dilute suspension to a porous plug. This allows us to determine the concentration dependence of the bandwidth and the deposition rate. Together, our findings allow for the control of drying-induced patterning as a function of the colloidal concentration and evaporation rate.

  6. Physics of Colloids in Space

    NASA Technical Reports Server (NTRS)

    Weitz, Dave; Weeks, Eric; Gasser, Urs; Dinsmore, Tony; Mawley, Suliana; Segre, Phil; Cipelletti, Lucia

    2000-01-01

    This talk will present recent results from ground-based research to support the "Physics of Colloids in Space" project which is scheduled to fly in the ISS approximately one year from now. In addition, results supporting future planned flights will be discussed.

  7. Microbial effects on colloidal agglomeration

    SciTech Connect

    Hersman, L.

    1995-11-01

    Colloidal particles are known to enhance the transport of radioactive metals through soil and rock systems. This study was performed to determine if a soil microorganism, isolated from the surface samples collected at Yucca Mountain, NV, could affect the colloidal properties of day particles. The agglomeration of a Wyoming bentonite clay in a sterile uninoculated microbial growth medium was compared to the agglomeration in the medium inoculated with a Pseudomonas sp. In a second experiment, microorganisms were cultured in the succinate medium for 50 h and removed by centrifugation. The agglomeration of the clay in this spent was compared to sterile uninoculated medium. In both experiments, the agglomeration of the clay was greater than that of the sterile, uninoculated control. Based on these results, which indicate that this microorganism enhanced the agglomeration of the bentonite clay, it is possible to say that in the presence of microorganisms colloidal movement through a rock matrix could be reduced because of an overall increase in the size of colloidal particle agglomerates. 32 refs.

  8. Enhanced colloidal stability of hydroxyapatite

    NASA Astrophysics Data System (ADS)

    Borum, La Rhonda Terese

    Hydroxyapatite, Ca10(PO4)6(OH) 2 is the most thermodynamically stable calcium phosphate in physiological environments. Hence, it is the main inorganic mineral found in bone and teeth. Its colloidal stability, however, is poor because hydroxyapatite (HAp) particles exhibit sediment formation upon standing at short time periods, where agglomerates form and lead to non-homogeneous suspensions. Surface modification is a promising method to tailor the colloidal stability of hydroxyapatite for biomaterial applications. Three techniques to modify the HAp surface and enhance the colloidal stability of HAp were investigated. Modified particles were characterized by methods sensitive to surface chemistry changes, such as sedimentation studies, diffuse reflectance Fourier transform infrared spectroscopy (DRIFT), Brunauer-Emmett-Teller (BET) surface area, and electrophoresis. Sedimentation studies demonstrated how effective each technique was in improving the colloidal stability of hydroxyapatite particles. Electrophoresis provided information on electrostatic interactions within each system. The first technique entailed an esterification reaction of the HAp surface with dodecyl alcohol at elevated temperatures. DRIFT results showed that dodecyl groups from the alcohol replaced acidic hydroxyl and phosphate sites on the HAp surface, giving rise to enhanced colloidal stability through steric interactions in ethanol suspensions. TGA curves gave insight to the degree of esterification for the esterified particles. Higher reaction temperatures give rise to a higher degree of esterification resulting in better colloidal stability. The second technique applied a silica coating on the HAp surface by the hydrolysis of tetraethyl orthosilicate in ethanol. Silica was coated onto the HAp surface at 5--75 wt% loading amounts. A combination of acid dissolution and x-ray diffraction (XRD), along with BET showed that the silica coating is complete at 50 wt% silica loading. The silica coating

  9. Assembling non-ferromagnetic materials to ferromagnetic architectures using metal-semiconductor interfaces

    NASA Astrophysics Data System (ADS)

    Ma, Ji; Liu, Chunting; Chen, Kezheng

    2016-09-01

    In this work, a facile and versatile solution route was used to fabricate room-temperature ferromagnetic fish bone-like, pteridophyte-like, poplar flower-like, cotton-like Cu@Cu2O architectures and golfball-like Cu@ZnO architecture. The ferromagnetic origins in these architectures were found to be around metal-semiconductor interfaces and defects, and the root cause for their ferromagnetism lay in charge transfer processes from metal Cu to semiconductors Cu2O and ZnO. Owing to different metallization at their interfaces, these architectures exhibited different ferromagnetic behaviors, including coercivity, saturation magnetization as well as magnetic interactions.

  10. Assembling non-ferromagnetic materials to ferromagnetic architectures using metal-semiconductor interfaces

    PubMed Central

    Ma, Ji; Liu, Chunting; Chen, Kezheng

    2016-01-01

    In this work, a facile and versatile solution route was used to fabricate room-temperature ferromagnetic fish bone-like, pteridophyte-like, poplar flower-like, cotton-like Cu@Cu2O architectures and golfball-like Cu@ZnO architecture. The ferromagnetic origins in these architectures were found to be around metal-semiconductor interfaces and defects, and the root cause for their ferromagnetism lay in charge transfer processes from metal Cu to semiconductors Cu2O and ZnO. Owing to different metallization at their interfaces, these architectures exhibited different ferromagnetic behaviors, including coercivity, saturation magnetization as well as magnetic interactions. PMID:27680286

  11. Heat dissipation due to ferromagnetic resonance in a ferromagnetic metal monitored by electrical resistance measurement

    SciTech Connect

    Yamanoi, Kazuto; Yokotani, Yuki; Kimura, Takashi

    2015-11-02

    The heat dissipation due to the resonant precessional motion of the magnetization in a ferromagnetic metal has been investigated. We demonstrated that the temperature during the ferromagnetic resonance can be simply detected by the electrical resistance measurement of the Cu strip line in contact with the ferromagnetic metal. The temperature change of the Cu strip due to the ferromagnetic resonance was found to exceed 10 K, which significantly affects the spin-current transport. The influence of the thermal conductivity of the substrate on the heating was also investigated.

  12. Effective Forces Between Colloidal Particles

    NASA Technical Reports Server (NTRS)

    Tehver, Riina; Banavar, Jayanth R.; Koplik, Joel

    1999-01-01

    Colloidal suspensions have proven to be excellent model systems for the study of condensed matter and its phase behavior. Many of the properties of colloidal suspensions can be investigated with a systematic variation of the characteristics of the systems and, in addition, the energy, length and time scales associated with them allow for experimental probing of otherwise inaccessible regimes. The latter property also makes colloidal systems vulnerable to external influences such as gravity. Experiments performed in micro-ravity by Chaikin and Russell have been invaluable in extracting the true behavior of the systems without an external field. Weitz and Pusey intend to use mixtures of colloidal particles with additives such as polymers to induce aggregation and form weak, tenuous, highly disordered fractal structures that would be stable in the absence of gravitational forces. When dispersed in a polarizable medium, colloidal particles can ionize, emitting counterions into the solution. The standard interaction potential in these charged colloidal suspensions was first obtained by Derjaguin, Landau, Verwey and Overbeek. The DLVO potential is obtained in the mean-field linearized Poisson-Boltzmann approximation and thus has limited applicability. For more precise calculations, we have used ab initio density functional theory. In our model, colloidal particles are charged hard spheres, the counterions are described by a continuum density field and the solvent is treated as a homogeneous medium with a specified dielectric constant. We calculate the effective forces between charged colloidal particles by integrating over the solvent and counterion degrees of freedom, taking into account the direct interactions between the particles as well as particle-counterion, counterion-counterion Coulomb, counterion entropic and correlation contributions. We obtain the effective interaction potential between charged colloidal particles in different configurations. We evaluate two

  13. Conserved momenta of a ferromagnetic soliton

    SciTech Connect

    Tchernyshyov, Oleg

    2015-12-15

    Linear and angular momenta of a soliton in a ferromagnet are commonly derived through the application of Noether’s theorem. We show that these quantities exhibit unphysical behavior: they depend on the choice of a gauge potential in the spin Lagrangian and can be made arbitrary. To resolve this problem, we exploit a similarity between the dynamics of a ferromagnetic soliton and that of a charged particle in a magnetic field. For the latter, canonical momentum is also gauge-dependent and thus unphysical; the physical momentum is the generator of magnetic translations, a symmetry combining physical translations with gauge transformations. We use this analogy to unambiguously define conserved momenta for ferromagnetic solitons. General considerations are illustrated on simple models of a domain wall in a ferromagnetic chain and of a vortex in a thin film.

  14. Conserved momenta of a ferromagnetic soliton

    NASA Astrophysics Data System (ADS)

    Tchernyshyov, Oleg

    2015-12-01

    Linear and angular momenta of a soliton in a ferromagnet are commonly derived through the application of Noether's theorem. We show that these quantities exhibit unphysical behavior: they depend on the choice of a gauge potential in the spin Lagrangian and can be made arbitrary. To resolve this problem, we exploit a similarity between the dynamics of a ferromagnetic soliton and that of a charged particle in a magnetic field. For the latter, canonical momentum is also gauge-dependent and thus unphysical; the physical momentum is the generator of magnetic translations, a symmetry combining physical translations with gauge transformations. We use this analogy to unambiguously define conserved momenta for ferromagnetic solitons. General considerations are illustrated on simple models of a domain wall in a ferromagnetic chain and of a vortex in a thin film.

  15. Colloid particle size-dependent dispersivity

    NASA Astrophysics Data System (ADS)

    Chrysikopoulos, C. V.; Katzourakis, V. E.

    2014-12-01

    Laboratory and field studies have demonstrated that dispersion coefficients evaluated by fitting advection-dispersion transport models to nonreactive tracer breakthrough curves do not adequately describe colloid transport under the same flow field conditions. Here an extensive laboratory study was undertaken to assess whether the dispersivity, which traditionally has been considered to be a property of the porous medium, is dependent on colloid particle size and interstitial velocity. A total of 49 colloid transport experiments were performed in columns packed with glass beads under chemically unfavorable colloid attachment conditions. Nine different colloid diameters, and various flow velocities were examined. The breakthrough curves were successfully simulated with a mathematical model describing colloid transport in homogeneous, water saturated porous media. The results demonstrated that the dispersivity is positively correlated with colloid particle size, and increases with increasing velocity.

  16. Nonequilibrium interfaces in colloidal fluids

    NASA Astrophysics Data System (ADS)

    Bier, Markus; Arnold, Daniel

    2013-12-01

    The time-dependent structure, interfacial tension, and evaporation of an oversaturated colloid-rich (liquid) phase in contact with an undersaturated colloid-poor (vapor) phase of a colloidal dispersion is investigated theoretically during the early-stage relaxation, where the interface is relaxing towards a local equilibrium state while the bulk phases are still out of equilibrium. Since systems of this type exhibit a clear separation of colloidal and solvent relaxation time scales with typical times of interfacial tension measurements in between, they can be expected to be suitable for analogous experimental studies, too. The major finding is that, irrespective of how much the bulk phases differ from two-phase coexistence, the interfacial structure and the interfacial tension approach those at two-phase coexistence during the early-stage relaxation process. This is a surprising observation since it implies that the relaxation towards global equilibrium of the interface is not following but preceding that of the bulk phases. Scaling forms for the local chemical potential, the flux, and the dissipation rate exhibit qualitatively different leading order contributions depending on whether an equilibrium or a nonequilibrium system is considered. The degree of nonquilibrium between the bulk phases is found to not influence the qualitative relaxation behavior (i.e., the values of power-law exponents), but to determine the quantitative deviation of the observed quantities from their values at two-phase coexistence. Whereas the underlying dynamics differs between colloidal and molecular fluids, the behavior of quantities such as the interfacial tension approaching the equilibrium values during the early-stage relaxation process, during which nonequilibrium conditions of the bulk phases are not changed, can be expected to occur for both types of systems.

  17. Automatic system for single ion/single cell irradiation based on Cracow microprobe

    NASA Astrophysics Data System (ADS)

    Veselov, O.; Polak, W.; Lekki, J.; Stachura, Z.; Lebed, K.; Styczeń, J.; Ugenskiene, R.

    2006-05-01

    Recently, the Cracow ion microprobe has found its new application as a single ion hit facility (SIHF), allowing precise irradiations of living cells by a controlled number of ions. The instrument enables a broad field of research, such as survival studies, adaptive response investigations, bystander effect, inverse dose-rate effect, low-dose hypersensitivity, etc. This work presents principles of construction and operation of the SIHF based on the Cracow microprobe. We discuss some crucial features of optical, positioning, and blanking systems, including self-developed software responsible for semiautomatic cell recognition, for precise positioning of cells, and for controlling the irradiation process. We also show some tests carried out to determine the efficiency of the whole system and of its segments. In addition, we present results of the first irradiation measurements performed with living cells.

  18. Ion microscope and ion microprobe analysis under oxygen, cesium and gallium bombardment

    NASA Astrophysics Data System (ADS)

    Migeon, H.-N.; Saldi, F.; Gao, Y.; Schuhmacher, M.

    1995-05-01

    This article concentrates on dynamic SIMS analysis using a magnetic sector instrument at micron and sub-micron resolutions with the ion microscope and ion microprobe modes. The advantages and drawbacks of both alternatives for recording measurements in laterally heterogeneous specimens are highlighted expecially concerning transmission and acquisition times. The ionization efficiencies and matrix effects under oxygen, cesium and gallium bombardment are compared. The ion microscope is shown to provide fast acquisition times owing to the parallel detection of the entire analyzed area and the most adequate mode for lateral resolutions above 1 [mu]m, whereas the ion microprobe provides better sensitivity and is best suited for high resolution. Combining cesium and oxygen ion sources provides, in most cases, a better ionization efficiency than the gallium beam but all three sources induce matrix effects which are shown to be much less critical using cationized species.

  19. Thermal Hysteresis of Interface Biased Ferromagnetic Dots

    DTIC Science & Technology

    2007-12-27

    superparamagnetic at a temperature smaller than the bulk ordering temperature.1 A possible way to combat the super - paramagnetic limit is to take advantage...of the magnetic cou- pling between the nanoparticle and a thermally stable mag- netic system. This has been investigated by growing arrays of...ferromagnetic FM nanoparticles on an antiferromagnetic AFM substrate.2–4 Arrays of single-domain fine ferromagnetic particles are currently under

  20. Barkhausen Noise Analysis and Ferromagnetic Materials

    DTIC Science & Technology

    1989-12-01

    MTL TR 89-108 AD BARKHAUSEN NOISE ANALYSIS ANDV SFERROMAGNETIC MATERIALS DOUGLAS J. STRAND MATERIEL DURABILIW BRANCH DTIC ELECTE December 1989 FEB...PERIOD COVERED Final Report BARKHAUSEN NOISE ANALYSIS AND FERROMAGNETIC MATERIALS . PERFORMING OR. REPORT NUMBER 7. AUTHOR(s) 6. CONTRACT OR GRANT...K Y WORDS (Conmw on Mm, jA& fneceiar and id&nfy bl Wock ;,,mb) Barkhausen Noise Analysis Residual stress TOW missile Ferromagnetic Hysteresis

  1. Ion beam induced charge characterisation of a silicon microdosimeter using a heavy ion microprobe

    NASA Astrophysics Data System (ADS)

    Cornelius, Iwan; Siegele, Rainer; Rosenfeld, Anatoly B.; Cohen, David D.

    2002-05-01

    An ion beam induced charge (IBIC) facility has been added to the existing capabilities of the ANSTO heavy ion microprobe and the results of the first measurements are presented. Silicon on insulator (SOI) diode arrays with microscopic junction sizes have recently been proposed as microdosimeters for hadron therapy. A 20 MeV carbon beam was used to perform IBIC imaging of a 10 μm thick SOI device.

  2. DSMC Simulations of Blunt Body Flows for Mars Entries: Mars Pathfinder and Mars Microprobe Capsules

    NASA Technical Reports Server (NTRS)

    Moss, James N.; Wilmoth, Richard G.; Price, Joseph M.

    1997-01-01

    The hypersonic transitional flow aerodynamics of the Mars Pathfinder and Mars Microprobe capsules are simulated with the direct simulation Monte Carlo method. Calculations of axial, normal, and static pitching coefficients were obtained over an angle of attack range comparable to actual flight requirements. Comparisons are made with modified Newtonian and free-molecular-flow calculations. Aerothermal results were also obtained for zero incidence entry conditions.

  3. Quantum-well-laser mirror degradation investigated by microprobe optical spectroscopy

    NASA Astrophysics Data System (ADS)

    Corvasce, C.; Spagnolo, Vincenzo; Scamarcio, Gaetano; Lugara, M.; Adduci, F.; Ferrara, Michele; Sibilano, Michele; Pellegrino, Sergio; del Giudice, Massimo; Re, M. G.

    1995-11-01

    A study of facet degradation of InGaAs quantum well lasers is reported. We tune up a Raman and photoluminescence micro-probe technique for determining the crystal structure and the temperature profile of the cladding layer, in steps of approximately 1 micrometer, with a temperature resolution better than 1 degree Kelvin. The cladding layer composition and cross- section temperature profile have been monitored during operation. A clear correlation between the facet degradation and the type of protective coating is found.

  4. Trace Element Zoning and Incipient Metamictization in a Lunar Zircon: Application of Three Microprobe Techniques

    NASA Technical Reports Server (NTRS)

    Wopenka, Brigitte; Jollife, Bradley L.; Zinner, Ernst; Kremser, Daniel T.

    1996-01-01

    We have determined major (Si, Zr, Hf), minor (Al, Y, Fe, P), and trace element (Ca, Sc, Ti, Ba, REE, Th, U) concentrations and Raman spectra of a zoned, 200 microns zircon grain in lunar sample 14161,7069, a quartz monzodiorite breccia collected at the Apollo 14 site. Analyses were obtained on a thin section in situ with an ion microprobe, an electron microprobe, and a laser Raman microprobe. The zircon grain is optically zoned in birefringence, a reflection of variable (incomplete) metamictization resulting from zo- nation in U and Th concentrations. Variations in the concentrations of U and Th correlate strongly with those of other high-field-strength trace elements and with changes in Raman spectral parameters. Concentrations of U and Th range from 21 to 55 ppm and 6 to 31 ppm, respectively, and correlate with lower Raman peak intensities, wider Raman peaks, and shifted Si-O peak positions. Concentrations of heavy rare earth elements range over a factor of three to four and correlate with intensities of fluorescence peaks. Correlated variations in trace element concentrations reflect the original magmatic differentiation of the parental melt approx. 4 b.y. ago. Degradation of the zircon structure, as reflected by the observed Raman spectral parameters, has occurred in this sample over a range of alpha-decay event dose from approx. 5.2 x 10(exp 14) to 1.4 x 10(exp 15) decay events per milligram of zircon, as calculated from the U and Th concentrations. This dose is well below the approx. 10(exp 16) events per milligram cumulative dose that causes complete metamictization and indicates that laser Raman microprobe spectroscopy is an analytical technique that is very sensitive to the radiation-induced damage in zircon.

  5. A High-Speed Detector System for X-ray Fluorescence Microprobes.

    SciTech Connect

    Siddons,P.D.; Dragone, A.; De Geronimo, g.; Kuczewski, A.; Kuczewski, J.; O

    2006-10-29

    We have developed a high-speed system for collecting x-ray fluorescence microprobe data, based on ASICs developed at BNL and high-speed processors developed by CSIRO. The system can collect fluorescence data in a continuous raster scan mode, and present elemental images in real time using Ryan's Dynamic Analysis algorithm. We will present results from a 32-element prototype array illustrating the concept. The final instrument will have 384 elements arranged in a square array around a central hole.

  6. Topological magnon bands in ferromagnetic star lattice.

    PubMed

    Owerre, S A

    2017-05-10

    The experimental observation of topological magnon bands and thermal Hall effect in a kagomé lattice ferromagnet Cu(1-3, bdc) has inspired the search for topological magnon effects in various insulating ferromagnets that lack an inversion center allowing a Dzyaloshinskii-Moriya (DM) spin-orbit interaction. The star lattice (also known as the decorated honeycomb lattice) ferromagnet is an ideal candidate for this purpose because it is a variant of the kagomé lattice with additional links that connect the up-pointing and down-pointing triangles. This gives rise to twice the unit cell of the kagomé lattice, and hence more interesting topological magnon effects. In particular, the triangular bridges on the star lattice can be coupled either ferromagnetically or antiferromagnetically which is not possible on the kagomé lattice ferromagnets. Here, we study DM-induced topological magnon bands, chiral edge modes, and thermal magnon Hall effect on the star lattice ferromagnet in different parameter regimes. The star lattice can also be visualized as the parent material from which topological magnon bands can be realized for the kagomé and honeycomb lattices in some limiting cases.

  7. Nuclear microprobe analysis of 14N and its application to the study of ammonium-bearing minerals

    NASA Astrophysics Data System (ADS)

    Mosbah, M.; Bastoul, A.; Cuney, M.; Pironon, J.

    1993-05-01

    Nuclear microprobe technique has been applied to the study of ammonium-bearing feldspar, biotite and muscovite crystals selected from metamorphosed black shales and pegmatite veins cross-cutting the shales sampled in the Central Jebilet (Morocco). 14N is easily detected by the nuclear reactions (d, p 0) and (d, α 0) with deuteron energy > 1.6 MeV for a better detection limit ( 14N ⩽ 50 ppm) . The experimental procedure has been developed and is detailed herein. TiN has been used for calibration. The nitrogen content measured in feldspar, biotite and muscovite crystals by the nuclear microprobe is perfectly consistent with quantitative nitrogen analysis by catharometry and semiquantitative analysis by Fourier transform infrared microspectrometry. The nuclear microprobe results can be used to calibrate complementary methods such as ion microprobe and IR microspectrometry.

  8. Trace elemental analysis of bituminuos coals using the Heidelberg proton microprobe

    USGS Publications Warehouse

    Chen, J.R.; Kneis, H.; Martin, B.; Nobiling, R.; Traxel, K.; Chao, E.C.T.; Minkin, J.A.

    1981-01-01

    Trace elements in coal can occur as components of either the organic constituents (macerals) or the inorganic constituents (minerals). Studies of the concentrations and distribution of the trace elements are vital to understanding the geochemical millieu in which the coal was formed and in evaluating the attempts to recover rare but technologically valuable metals. In addition, information on the trace element concentrations is important in predicting the environmental impact of burning particular coals, as many countries move toward greater utilization of coal reserves for energy production. Traditionally, the optical and the electron microscopes and more recently the electron microprobe have been used in studying the components of coal. The proton-induced X-ray emission (PIXE) microprobe offers a new complementary approach with an order of magnitude or more better minimum detection limit. We present the first measurements with a PIXE microprobe of the trace element concentrations of bituminous coal samples. Elemental analyses of the coal macerals-vitrinite, exinite, and inertinite-are discussed for three coal samples from the Eastern U.S.A., three samples from the Western U.S.A., and one sample from the Peoples Republic of China. ?? 1981.

  9. Ion microprobe measurement of strontium isotopes in calcium carbonate with application to salmon otoliths

    USGS Publications Warehouse

    Weber, P.K.; Bacon, C.R.; Hutcheon, I.D.; Ingram, B.L.; Wooden, J.L.

    2005-01-01

    The ion microprobe has the capability to generate high resolution, high precision isotopic measurements, but analysis of the isotopic composition of strontium, as measured by the 87Sr/ 86Sr ratio, has been hindered by isobaric interferences. Here we report the first high precision measurements of 87Sr/ 86Sr by ion microprobe in calcium carbonate samples with moderate Sr concentrations. We use the high mass resolving power (7000 to 9000 M.R.P.) of the SHRIMP-RG ion microprobe in combination with its high transmission to reduce the number of interfering species while maintaining sufficiently high count rates for precise isotopic measurements. The isobaric interferences are characterized by peak modeling and repeated analyses of standards. We demonstrate that by sample-standard bracketing, 87Sr/86Sr ratios can be measured in inorganic and biogenic carbonates with Sr concentrations between 400 and 1500 ppm with ???2??? external precision (2??) for a single analysis, and subpermil external precision with repeated analyses. Explicit correction for isobaric interferences (peak-stripping) is found to be less accurate and precise than sample-standard bracketing. Spatial resolution is ???25 ??m laterally and 2 ??m deep for a single analysis, consuming on the order of 2 ng of material. The method is tested on otoliths from salmon to demonstrate its accuracy and utility. In these growth-banded aragonitic structures, one-week temporal resolution can be achieved. The analytical method should be applicable to other calcium carbonate samples with similar Sr concentrations. Copyright ?? 2005 Elsevier Ltd.

  10. Use of X-ray microprobe to diagnose bone tissue demineralization after caffeine administration.

    PubMed

    Tomaszewski, Marek; Olchowik, Grazyna; Tomaszewska, Monika; Burdan, Franciszek

    2012-10-08

    Caffeine is a methylxanthine which permeates the placenta. In studies on animals, it has been shown to produce teratogenic and embryotoxic effects in large doses. The objective of this study was to assess the influence of caffeine on the development of bone tissue, with particular reference to elemental bone composition using an X-ray microprobe. The research was conducted on rats. The fertilized females were randomly divided into an experimental and a control group. The experimental group was given caffeine orally in 30 mg/day doses from the 8th to the 21st day of pregnancy, while the control group was given water. The fetuses were used to assess the growth and mineralization of the skeleton. On the basis of double dyeing, a qualitative analysis of the bone morphology and mineralization was conducted. For calcium and potassium analysis, an X-ray microprobe was used. In 67 fetuses from the experimental group, changes in skeleton staining with the alcian-alizarin method were noticed. The frequency of the development of variants in the experimental group was statistically higher. In the experimental group,a significant decrease in the calcium level, as well as an increase in the potassium level, was observed. The X-ray microprobe's undoubted advantage is that is offers a quick qualitative and quantitative analysis of the elemental composition of the examined samples. Employing this new technique may furnish us with new capabilities when investigating the essence of the pathology process.

  11. Quantitative elemental imaging of octopus stylets using PIXE and the nuclear microprobe

    NASA Astrophysics Data System (ADS)

    Doubleday, Zoë; Belton, David; Pecl, Gretta; Semmens, Jayson

    2008-01-01

    By utilising targeted microprobe technology, the analysis of elements incorporated within the hard bio-mineralised structures of marine organisms has provided unique insights into the population biology of many species. As hard structures grow, elements from surrounding waters are incorporated effectively providing a natural 'tag' that is often unique to the animal's particular location or habitat. The spatial distribution of elements within octopus stylets was investigated, using the nuclear microprobe, to assess their potential for determining dispersal and population structure in octopus populations. Proton Induced X-ray Emission (PIXE) was conducted using the Dynamic Analysis method and GeoPIXE software package, which produced high resolution, quantitative elemental maps of whole stylet cross-sections. Ten elements were detected within the stylets which were heterogeneously distributed throughout the microstructure. Although Ca decreased towards the section edge, this trend was consistent between individuals and remained homogeneous in the inner region of the stylet, and thus appears a suitable internal standard for future microprobe analyses. Additional analyses used to investigate the general composition of the stylet structure suggested that they are amorphous and largely organic, however, there was some evidence of phosphatic mineralisation. In conclusion, this study indicates that stylets are suitable for targeted elemental analysis, although this is currently limited to the inner hatch region of the microstructure.

  12. Study of microstructure and silicon segregation in cast iron using color etching and electron microprobe analysis

    SciTech Connect

    Vazehrad, S.; Diószegi, A.

    2015-06-15

    An investigation on silicon segregation of lamellar, compacted and nodular graphite iron was carried out by applying a selective, immersion color etching and a modified electron microprobe to study the microstructure. The color etched micrographs of the investigated cast irons by revealing the austenite phase have provided data about the chronology and mechanism of microstructure formation. Moreover, electron microprobe has provided two dimensional segregation maps of silicon. A good agreement was found between the segregation profile of silicon in the color etched microstructure and the silicon maps achieved by electron microprobe analysis. However, quantitative silicon investigation was found to be more accurate than color etching results to study the size of the eutectic colonies. - Highlights: • Sensitivity of a color etchant to silicon segregation is quantitatively demonstrated. • Si segregation measurement by EMPA approved the results achieved by color etching. • Color etched micrographs provided data about solidification mechanism in cast irons. • Austenite grain boundaries were identified by measuring the local Si concentration.

  13. Colloid Straining within Saturated Heterogeneous Porous Media

    NASA Astrophysics Data System (ADS)

    Porubcan, A.; Walczak, J.; Xu, S.

    2008-12-01

    A thorough understanding of colloid movement in the subsurface system is critical to the assessment of groundwater pollution by pathogenic bacteria and colloid-bound contaminants. It is increasingly recognized that straining, a process that occurs when the pore space is too small to allow for a particle's passage, represents an important process in colloid immobilization within groundwater systems. Previously published studies have focused on the kinetics of colloid straining within sand packs composed of uniform mineral grains. Natural aquifers, however, are usually characterized by physically heterogeneous sediments. In this study, we conducted column transport experiments with carboxylated latex particles and quartz sand to investigate the impact of sediment texture (i.e., the size distribution of mineral grains) on colloid straining kinetics. The quartz sands used in the experiment were thoroughly cleaned and the strong repulsive interactions between colloid particles and quartz sands resulted in minimal physicochemical deposition so the straining kinetics can be quantified unambiguously. Sand packs of different textures were prepared by mixing sands of various sizes (mesh sizes of 20-25, 35-40 and 60-70). Our results suggested that the ratio of colloid size and the median sand grain size was insufficient to predict colloid straining within heterogeneous sediments. Soil texture, which was related to the size distribution of the sand grains, must be considered. A relationship between colloid straining kinetics and the heterogeneity of porous media that can be useful for the prediction of colloid transport within heterogeneous sediments was presented.

  14. What happens when pharmaceuticals meet colloids.

    PubMed

    Xing, Yingna; Chen, Xijuan; Zhuang, Jie; Chen, Xin

    2015-12-01

    Pharmaceuticals (PCs) have been widely detected in natural environment due to agricultural application of reclaimed water, sludge and animal wastes. Their potential risks to various ecosystems and even to human health have caused great concern; however, little was known about their environmental behaviors. Colloids (such as clays, metal oxides, and particulate organics) are kind of substances that are active and widespread in the environment. When PCs meet colloids, their interaction may influence the fate, transport, and toxicity of PCs. This review summarizes the progress of studies on the role of colloids in mediating the environmental behaviors of PCs. Synthesized results showed that colloids can adsorb PCs mainly through ion exchange, complexation and non-electrostatic interactions. During this process the structure of colloids and the stability of PCs may be changed. The adsorbed PCs may have higher risks to induce antibiotic resistance; besides, their transport may also be altered considering they have great chance to move with colloids. Solution conditions (such as pH, ionic strength, and cations) could influence these interactions between PCs and colloids, as they can change the forms of PCs and alter the primary forces between PCs and colloids in the solution. It could be concluded that PCs in natural soils could bind with colloids and then co-transport during the processes of irrigation, leaching, and erosion. Therefore, colloid-PC interactions need to be understood for risk assessment of PCs and the best management practices of various ecosystems (such as agricultural and wetland systems).

  15. Stable colloids in molten inorganic salts

    NASA Astrophysics Data System (ADS)

    Zhang, Hao; Dasbiswas, Kinjal; Ludwig, Nicholas B.; Han, Gang; Lee, Byeongdu; Vaikuntanathan, Suri; Talapin, Dmitri V.

    2017-02-01

    A colloidal solution is a homogeneous dispersion of particles or droplets of one phase (solute) in a second, typically liquid, phase (solvent). Colloids are ubiquitous in biological, chemical and technological processes, homogenizing highly dissimilar constituents. To stabilize a colloidal system against coalescence and aggregation, the surface of each solute particle is engineered to impose repulsive forces strong enough to overpower van der Waals attraction and keep the particles separated from each other. Electrostatic stabilization of charged solutes works well in solvents with high dielectric constants, such as water (dielectric constant of 80). In contrast, colloidal stabilization in solvents with low polarity, such as hexane (dielectric constant of about 2), can be achieved by decorating the surface of each particle of the solute with molecules (surfactants) containing flexible, brush-like chains. Here we report a class of colloidal systems in which solute particles (including metals, semiconductors and magnetic materials) form stable colloids in various molten inorganic salts. The stability of such colloids cannot be explained by traditional electrostatic and steric mechanisms. Screening of many solute–solvent combinations shows that colloidal stability can be traced to the strength of chemical bonding at the solute–solvent interface. Theoretical analysis and molecular dynamics modelling suggest that a layer of surface-bound solvent ions produces long-ranged charge-density oscillations in the molten salt around solute particles, preventing their aggregation. Colloids composed of inorganic particles in inorganic melts offer opportunities for introducing colloidal techniques to solid-state science and engineering applications.

  16. Integrated Laser Microprobe (U-Th)/He and U/Pb Dating of Titanite and Zircon

    NASA Astrophysics Data System (ADS)

    Horne, A.; Van Soest, M. C.; Hodges, K. V.; Tripathy-Lang, A.

    2014-12-01

    The application of laser technologies for high spatial resolution dating has proven to be an important advancement in (U-Th)/He thermochronology. Excimer laser microprobes have been used to successfully date high U+Th minerals and are an especially promising way to determine the distribution of (U-Th)/He zircon ages in detrital sedimentary samples. We have also found that another detrital mineral, titanite, may be amenable to this method as well. While titanite contains lower concentrations of parent isotopes than zircon, and consequently less radiogenic 4He, its typically larger grain size allows for these characteristics to be mitigated by the use of larger laser beam diameters during the ablation process. With the integrated use of ICPMS, an established method for U/Pb geochronology, this phase of the laser microprobe (U-Th)/He technique can be modified slightly to enable (U-Th)/He and U/Pb 'double' dating of detrital samples. Here we present a proof of concept study demonstrating the viability of integrated laser microprobe (U-Th)/He and U/Pb through dating Oligocene Fish Canyon tuff titanite and zircon from Colorado. Our use of a well characterized sample with established (U-Th)/He and U/Pb dates allows us to fully evaluate the utility of this technique. By selecting medium- to fine-grained crystals we are able to simulate a realistic, uni-modal detrital sample. Using our modified laser microprobe approach, we are able to reproduce the expected age modes with an analytical imprecision roughly twice that of more established methods, a difference that has little practical effect on geologic interpretations. Additionally, we believe that the technique could prove a viable method for double dating detrital rutile and apatite, so long as characteristically lower U+Th concentrations in these minerals are balanced by appropriately scaled ablation pits in an aliquot unbiased by the need for larger detrital grains. Ultimately, integrated laser microprobe U/Pb and (U

  17. Analytic studies of colloid transport in fractured porous media

    SciTech Connect

    Hwang, Y.; Chambre, P.L.; Lee, W.W.L.; Pigford, T.H.

    1989-11-01

    We analyze the interactive migration of radioactive colloids and solute in fractured rock. Two possible interactions between radionuclides as colloids and as solute are considered: solute sorption on nonradioactive colloids to form pseudocolloids, and dissolution of radioactive colloids. Previous studies have discussed the formation and transport of colloids in porous media, including removal of colloids by filtration and sedimentation. Colloids can migrate faster than solute because of weaker sorption on stationary solids and because of hydrochromatography of colloid particles in flow channels. However, the migration of colloids and pseudocolloids can be retarded by the interaction of colloids with solute, and the migration of solute in local equilibrium with colloids can be more rapid than if colloids were not present. Here we present a new quantative analysis to predict the interactive migration of colloids and solute in porous and fractured media. 4 figs.

  18. Chancellor Water Colloids: Characterization and Radionuclide Association

    SciTech Connect

    Abdel-Fattah, Amr I.

    2012-06-18

    Concluding remarks about this paper are: (1) Gravitational settling, zeta potential, and ultrafiltration data indicate the existence of a colloidal phase of both the alpha and beta emitters in the Chancellor water; (2) The low activity combined with high dispersion homogeneity of the Chancellor water indicate that both alpha and beta emitters are not intrinsic colloids; (3) Radionuclides in the Chancellor water, particularly Pu, coexist as dissolved aqueous and sorbed phases - in other words the radionuclides are partitioned between the aqueous phase and the colloidal phase; (4) The presence of Pu as a dissolved species in the aqueous phase, suggests the possibility of Pu in the (V) oxidation state - this conclusion is supported by the similarity of the k{sub d} value of Pu determined in the current study to that determined for Pu(V) sorbed onto smectite colloids, and the similar electrokinetic behavior of the Chancellor water colloids to smectite colloids; (5) About 50% of the Pu(V) is in the aqueous phase and 50% is sorbed on colloids (mass concentration of colloids in the Chancellor water is 0.12 g/L); (6) The k{sub d} of the Pu and the beta emitters (fission products) between aqueous and colloidal phases in the Chancellor water is {approx}8.0 x 10{sup 3} mL/g using two different activity measurement techniques (LSC and alpha spectroscopy); (7) The gravitational settling and size distributions of the association colloids indicate that the properties (at least the physical ones) of the colloids to which the alpha emitters are associated with seem to be different that the properties of the colloids to which the beta emitters are associated with - the beta emitters are associated with very small particles ({approx}50 - 120 nm), while the alpha emitters are associated with relatively larger particles; and (8) The Chancellor water colloids are extremely stable under the natural pH and ionic strength conditions, indicating high potential for transport in the

  19. Designing Colloidal Molecules with Microfluidics

    PubMed Central

    Shen, Bingqing; Ricouvier, Joshua; Malloggi, Florent

    2016-01-01

    The creation of new colloidal materials involves the design of functional building blocks. Here, a microfluidic method for designing building blocks one by one, at high throughput, with a broad range of shapes is introduced. The method exploits a coupling between hydrodynamic interactions and depletion forces that controls the configurational dynamics of droplet clusters traveling in microfluidic channels. Droplet clusters can be solidified in situ with UV. By varying the flow parameters, clusters are prescribed a given size, geometry, chemical and/or magnetic heterogeneities enabling local bonding. Compact structures (chains, triangles, diamonds, tetrahedrons,...) and noncompact structures, such as crosses and T, difficult to obtain with current techniques are produced. Size dispersions are small (2%) and throughputs are high (30 000 h−1). The work opens a new pathway, based on microfluidics, for designing colloidal building blocks with a potential to enable the creation of new materials. PMID:27840804

  20. Predicting crystals of Janus colloids

    NASA Astrophysics Data System (ADS)

    Vissers, Teun; Preisler, Zdeněk; Smallenburg, Frank; Dijkstra, Marjolein; Sciortino, Francesco

    2013-04-01

    We present a numerical study on the phase diagram for a simple model of Janus colloids, including ordered and disordered structures. Using a range of techniques, we generate a set of crystal structures and investigate their relative stability field in the pressure-temperature and temperature-density planes by means of free-energy calculations and thermodynamic integration schemes. We find that despite the Janus colloids' simple architecture, they form stable crystal structures with complicated bond-topologies on an underlying face-centered-cubic or hexagonal-close-packed lattice. In addition, we find a phase consisting of wrinkled bilayer sheets, competing with both the fluid and the crystal phases. We detect a metastable gas-liquid coexistence which displays a micellization-driven re-entrant behavior.

  1. Electrokinetic properties of polymer colloids

    NASA Technical Reports Server (NTRS)

    Micale, F. J.; Fuenmayor, D. Y.

    1986-01-01

    The surface of polymer colloids, especially polystyrene latexes, were modified for the purpose of controlling the electrokinetic properties of the resulting colloids. Achievement required a knowledge of electrical double layer charging mechanism, as a function of the electrolyte conditions, at the polymer/water interface. The experimental approach is to control the recipe formulation in the emulsion polymerization process so as to systematically vary the strong acid group concentration on the surface of the polymer particles. The electrophoretic mobility of these model particles will then be measured as a function of surface group concentration and as a function of electrolyte concentration and type. An effort was also made to evaluate the electrophoretic mobility of polystyrene latexes made in space and to compare the results with latexes made on the ground.

  2. Colloids at Curved Fluid Interfaces

    NASA Astrophysics Data System (ADS)

    Stebe, Kathleen

    2016-11-01

    Fluid interfaces are remarkable sites for colloidal assembly. When a colloid attaches to a fluid interface, it distorts a region around it; this distortion has an associated capillary energy, the product of its area and interfacial tension. The particle's capillary energy depends on the local interface curvature. By molding the interface, we can define curvature fields that drive microparticles along pre-determined paths. This example captures the emergent nature of the interactions. We discuss curvature fields as analogues to external electro-magnetic fields, and define curvatures that drive particles to well-defined locations, and to equilibrium sites far from boundaries. Particle-particle and particle-curvature interactions can guide particles into structures via interaction among many particles. This work demonstrates the potential importance of curvature capillary interactions in schemes to make reconfigurable materials, since interfaces and their associated capillary energy landscapes can be readily reconfigured. Analogies in other soft systems will be described. Support acknowledged from NSF DMR 1607878.

  3. Thermophoresis of charged colloidal particles.

    PubMed

    Fayolle, Sébastien; Bickel, Thomas; Würger, Alois

    2008-04-01

    Thermally induced particle flow in a charged colloidal suspension is studied in a fluid-mechanical approach. The force density acting on the charged boundary layer is derived in detail. From Stokes' equation with no-slip boundary conditions at the particle surface, we obtain the particle drift velocity and the thermophoretic transport coefficients. The results are discussed in view of previous work and available experimental data.

  4. Dynamics of evaporative colloidal patterning

    NASA Astrophysics Data System (ADS)

    Mahadevan, L.; Kaplan, C. Nadir; Wu, Ning; Mandre, Shreyas; Aizenberg, Joanna

    2014-11-01

    Evaporating suspensions of colloidal particles lead to the formation of a variety of patterns, ranging from rings left behind a coffee drop to periodic bands or uniform solid films deposited on a substrate suspended vertically in a container of the colloidal solution. To characterize the transition between different types of patterns, we develop minimal models of the liquid meniscus deformation due to the evaporation and colloidal deposition. A complementary multiphase model allows us to investigate the detailed dynamics of patterning in a drying solvent. This approach couples the inhomogeneous evaporation at the evolving liquid-air interface to the dynamics inside the suspension, i.e. the liquid flow, local variations of the particle concentration, and the propagation of the deposition front where the solute forms a wet, incompressible porous medium at high concentrations. The results of our theory are in good agreement with direct observations. This research was supported by the Air Force Office of Scientific Research (AFOSR) under Award FA9550-09-1-0669-DOD35CAP and the Kavli Institute for Bionano Science and Technology at Harvard University.

  5. Three-dimensional colloidal lithography.

    PubMed

    Nagai, Hironori; Poteet, Austen; Zhang, Xu A; Chang, Chih-Hao

    2017-03-24

    Light interactions with colloidal particles can generate a variety of complex three-dimensional (3D) intensity patterns, which can be utilized for nanolithography. The study of particle-light interactions can add more types of intensity patterns by manipulating key factors. Here we investigate a novel 3D nanolithography technique using colloidal particles under two-beam coherent illuminations. The fabricated 3D nanostructures are hollow, nested within periodic structures, and possess multiple chamber geometry. The effects of incident angles and particle size on the fabricated nanostructures were examined. The relative phase shift between particle position and interference pattern is identified as another significant parameter influencing the resultant nanostructures. A numerical model has been developed to show the evolution of nanostructure geometry with phase shifts, and experimental studies confirm the simulation results. Through the introduction of single colloidal particles, the fabrication capability of Lloyd's mirror interference can now be extended to fabrication of 3D nanostructure with complex shell geometry. The fabricated hollow nanostructures with grating background could find potential applications in the area of photonics, drug delivery, and nanofluidics.

  6. Three-dimensional colloidal lithography

    NASA Astrophysics Data System (ADS)

    Nagai, Hironori; Poteet, Austen; Zhang, Xu A.; Chang, Chih-Hao

    2017-03-01

    Light interactions with colloidal particles can generate a variety of complex three-dimensional (3D) intensity patterns, which can be utilized for nanolithography. The study of particle–light interactions can add more types of intensity patterns by manipulating key factors. Here we investigate a novel 3D nanolithography technique using colloidal particles under two-beam coherent illuminations. The fabricated 3D nanostructures are hollow, nested within periodic structures, and possess multiple chamber geometry. The effects of incident angles and particle size on the fabricated nanostructures were examined. The relative phase shift between particle position and interference pattern is identified as another significant parameter influencing the resultant nanostructures. A numerical model has been developed to show the evolution of nanostructure geometry with phase shifts, and experimental studies confirm the simulation results. Through the introduction of single colloidal particles, the fabrication capability of Lloyd’s mirror interference can now be extended to fabrication of 3D nanostructure with complex shell geometry. The fabricated hollow nanostructures with grating background could find potential applications in the area of photonics, drug delivery, and nanofluidics.

  7. Emergent incommensurate correlations in frustrated ferromagnetic spin-1 chains

    NASA Astrophysics Data System (ADS)

    Lee, Hyeong Jun; Choi, MooYoung; Jeon, Gun Sang

    2017-01-01

    We study frustrated ferromagnetic spin-1 chains, where the ferromagnetic nearest-neighbor coupling competes with the antiferromagnetic next-nearest-neighbor coupling. We use the density-matrix renormalization group to obtain the ground states. Through the analysis of spin-spin correlations we identify the double Haldane phase as well as the ferromagnetic phase. It is shown that the ferromagnetic coupling leads to incommensurate correlations in the double Haldane phase. Such short-range correlations transform continuously into the ferromagnetic instability at the transition to the ferromagnetic phase. We also compare the results with the spin-1/2 and classical spin systems and discuss the string orders in the system.

  8. Crystallization of DNA-coated colloids

    PubMed Central

    Wang, Yu; Wang, Yufeng; Zheng, Xiaolong; Ducrot, Étienne; Yodh, Jeremy S.; Weck, Marcus; Pine, David J.

    2015-01-01

    DNA-coated colloids hold great promise for self-assembly of programmed heterogeneous microstructures, provided they not only bind when cooled below their melting temperature, but also rearrange so that aggregated particles can anneal into the structure that minimizes the free energy. Unfortunately, DNA-coated colloids generally collide and stick forming kinetically arrested random aggregates when the thickness of the DNA coating is much smaller than the particles. Here we report DNA-coated colloids that can rearrange and anneal, thus enabling the growth of large colloidal crystals from a wide range of micrometre-sized DNA-coated colloids for the first time. The kinetics of aggregation, crystallization and defect formation are followed in real time. The crystallization rate exhibits the familiar maximum for intermediate temperature quenches observed in metallic alloys, but over a temperature range smaller by two orders of magnitude, owing to the highly temperature-sensitive diffusion between aggregated DNA-coated colloids. PMID:26078020

  9. Nanostructured colloidal crystals from forced hydrolysis methods.

    PubMed

    Otal, Eugenio H; Granada, Mara; Troiani, Horacio E; Cánepa, Horacio; Walsöe de Reca, Noemí E

    2009-08-18

    In this work, an original route for ZnO nanostructured spherical colloids and their assembly into colloidal crystals are presented. The temporal evolution of crystal size and shape was followed by X-ray diffraction and the colloids size distribution by scanning electron microscopy. These spherical colloids showed a change in their size dispersion with aging time. Early stage suspensions, with a narrow size distribution, were settled to the bottom and dried with a slow evaporation rate to obtain colloidal crystals. This original route provides a new material for future applications in opalline photonic crystals, with a dielectric constant higher than that of classical materials (silica and latex). Moreover, this route means an improvement of previously reported data from the literature since it involves a one-pot strategy and room-temperature colloid assembly.

  10. Crystallization of DNA-coated colloids

    NASA Astrophysics Data System (ADS)

    Wang, Yu; Wang, Yufeng; Zheng, Xiaolong; Ducrot, Étienne; Yodh, Jeremy S.; Weck, Marcus; Pine, David J.

    2015-06-01

    DNA-coated colloids hold great promise for self-assembly of programmed heterogeneous microstructures, provided they not only bind when cooled below their melting temperature, but also rearrange so that aggregated particles can anneal into the structure that minimizes the free energy. Unfortunately, DNA-coated colloids generally collide and stick forming kinetically arrested random aggregates when the thickness of the DNA coating is much smaller than the particles. Here we report DNA-coated colloids that can rearrange and anneal, thus enabling the growth of large colloidal crystals from a wide range of micrometre-sized DNA-coated colloids for the first time. The kinetics of aggregation, crystallization and defect formation are followed in real time. The crystallization rate exhibits the familiar maximum for intermediate temperature quenches observed in metallic alloys, but over a temperature range smaller by two orders of magnitude, owing to the highly temperature-sensitive diffusion between aggregated DNA-coated colloids.

  11. Ferromagnetism in Hubbard models: Low density route

    SciTech Connect

    Mueller-Hartmann, E.

    1995-05-01

    Thirty years ago the Hubbard model was introduced by Gutzwiller, Hubbard and Kanamori with the main purpose of mimicking the ferromagnetism of transition metals. Soon after, Nagaoka and Thouless pointed out a basic mechanism for ferromagnetism in strongly correlated electron systems by studying the motion of a single hole in a half-filled Hubbard model. This important work was hoped to shed light onto metallic ferromagnetism from the low doping regime. Unfortunately, this low doping route towards ferromagnetism has not been successful as far as rigorous results for finite doping concentrations are concerned. In the work presented, we start from the opposite limit of low particle concentrations. In this limit we provide the first proof of a fully polarized metallic ground state for a Hubbard model. The proof proceeds by mapping Hubbard {open_quotes}zigzag{close_quotes} chains onto a continuum model with an additional degree of freedom and local first Hund`s rule coupling. For this model the maximum total spin multiplet is shown to be the unique ground state for infinite Hubbard coupling. Our proof may open a low density route towards the understanding of the ferromagnetism of Hubbard models.

  12. Metallic ferromagnetism in the Kondo lattice

    PubMed Central

    Yamamoto, Seiji J.; Si, Qimiao

    2010-01-01

    Metallic magnetism is both ancient and modern, occurring in such familiar settings as the lodestone in compass needles and the hard drive in computers. Surprisingly, a rigorous theoretical basis for metallic ferromagnetism is still largely missing. The Stoner approach perturbatively treats Coulomb interactions when the latter need to be large, whereas the Nagaoka approach incorporates thermodynamically negligible holes into a half-filled band. Here, we show that the ferromagnetic order of the Kondo lattice is amenable to an asymptotically exact analysis over a range of interaction parameters. In this ferromagnetic phase, the conduction electrons and local moments are strongly coupled but the Fermi surface does not enclose the latter (i.e., it is “small”). Moreover, non-Fermi-liquid behavior appears over a range of frequencies and temperatures. Our results provide the basis to understand some long-standing puzzles in the ferromagnetic heavy fermion metals, and raise the prospect for a new class of ferromagnetic quantum phase transitions. PMID:20798053

  13. Superconductivity in the ferromagnetic semiconductor samarium nitride

    NASA Astrophysics Data System (ADS)

    Anton, E.-M.; Granville, S.; Engel, A.; Chong, S. V.; Governale, M.; Zülicke, U.; Moghaddam, A. G.; Trodahl, H. J.; Natali, F.; Vézian, S.; Ruck, B. J.

    2016-07-01

    Conventional wisdom expects that making semiconductors ferromagnetic requires doping with magnetic ions and that superconductivity cannot coexist with magnetism. However, recent concerted efforts exploring new classes of materials have established that intrinsic ferromagnetic semiconductors exist and that certain types of strongly correlated metals can be ferromagnetic and superconducting at the same time. Here we show that the trifecta of semiconducting behavior, ferromagnetism, and superconductivity can be achieved in a single material. Samarium nitride (SmN) is a well-characterized intrinsic ferromagnetic semiconductor, hosting strongly spin-ordered 4 f electrons below a Curie temperature of 27 K. We have now observed that it also hosts a superconducting phase below 4 K when doped to electron concentrations above 1021cm-3 . The large exchange splitting of the conduction band in SmN favors equal-spin triplet pairing with p -wave symmetry. Significantly, superconductivity is enhanced in superlattices of gadolinium nitride (GdN) and SmN. An analysis of the robustness of such a superconducting phase against disorder leads to the conclusion that the 4 f bands are crucial for superconductivity, making SmN a heavy-fermion-type superconductor.

  14. Does colloid shape affect detachment of colloids by a moving air-water interface?

    PubMed

    Aramrak, Surachet; Flury, Markus; Harsh, James B; Zollars, Richard L; Davis, Howard P

    2013-05-14

    Air-water interfaces interact strongly with colloidal particles by capillary forces. The magnitude of the interaction force depends on, among other things, the particle shape. Here, we investigate the effects of particle shape on colloid detachment by a moving air-water interface. We used hydrophilic polystyrene colloids with four different shapes (spheres, barrels, rods, and oblong disks), but otherwise identical surface properties. The nonspherical shapes were created by stretching spherical microspheres on a film of polyvinyl alcohol (PVA). The colloids were then deposited onto the inner surface of a glass channel. An air bubble was introduced into the channel and passed through, thereby generating a receding followed by an advancing air-water interface. The detachment of colloids by the air-water interfaces was visualized with a confocal microscope, quantified by image analysis, and analyzed statistically to determine significant differences. For all colloid shapes, the advancing air-water interface caused pronounced colloid detachment (>63%), whereas the receding interface was ineffective in colloid detachment (<1.5%). Among the different colloid shapes, the barrels were most readily removed (94%) by the advancing interface, followed by the spheres and oblong disks (80%) and the rods (63%). Colloid detachment was significantly affected by colloid shape. The presence of an edge, as it occurs in a barrel-shaped colloid, promoted colloid detachment because the air-water interface is being pinned at the edge of the colloid. This suggests that the magnitude of colloid mobilization and transport in porous media is underestimated for edged particles and overestimated for rodlike particles when a sphere is used as a model colloid.

  15. Dynamic Colloidal Stabilization by Nanoparticle Halos

    NASA Astrophysics Data System (ADS)

    Karanikas, S.; Louis, A. A.

    2004-12-01

    We explore the conditions under which colloids can be stabilized by the addition of smaller particles. The largest repulsive barriers between colloids occur when the added particles repel each other with soft interactions, leading to an accumulation near the colloid surfaces. At lower densities these layers of mobile particles (nanoparticle halos) result in stabilization, but when too many are added, the interactions become attractive again. We systematically study these effects—accumulation repulsion, reentrant attraction, and bridging—by accurate integral equation techniques.

  16. Transformative Colloidal Nanomaterials for Mid- Infrared Devices

    DTIC Science & Technology

    2015-06-11

    SECURITY CLASSIFICATION OF: The grant focused on the Photoluminescence efficiency of HgTe colloidal quantum dots. The photoluminescence quantum yield...of HgTe colloidal quantum dots was measured from 1800 to 6500 cm-1 . There is a steep drop at low energy consistent with the generic gap law...Distribution Unlimited Final Report: Transformative Colloidal Nanomaterials for Mid- Infrared Devices The views, opinions and/or findings contained in this

  17. Binodal Colloidal Aggregation Test - 4: Polydispersion

    NASA Technical Reports Server (NTRS)

    Chaikin, Paul M.

    2008-01-01

    Binodal Colloidal Aggregation Test - 4: Polydispersion (BCAT-4-Poly) will use model hard-spheres to explore seeded colloidal crystal nucleation and the effects of polydispersity, providing insight into how nature brings order out of disorder. Crewmembers photograph samples of polymer and colloidal particles (tiny nanoscale spheres suspended in liquid) that model liquid/gas phase changes. Results will help scientists develop fundamental physics concepts previously cloaked by the effects of gravity.

  18. Thermophoresis of colloids by mesoscale simulations.

    PubMed

    Lüsebrink, Daniel; Yang, Mingcheng; Ripoll, Marisol

    2012-07-18

    The motion of a colloid induced by a temperature gradient is simulated by means of multiparticle collision dynamics, a mesoscale simulation technique. Two algorithms to quantify the thermophoretic behavior are employed and contrasted. The validity of the methods is verified as a function of the temperature gradient, system size, and algorithm parameters. The variation of the solvent-colloid interaction from attractive to purely repulsive interestingly results in the change of the colloid behavior from thermophobic to thermophilic.

  19. Binary Colloidal Alloy Test Conducted on Mir

    NASA Technical Reports Server (NTRS)

    Hoffmann, Monica I.; Ansari, Rafat R.

    1999-01-01

    Colloids are tiny (submicron) particles suspended in fluid. Paint, ink, and milk are examples of colloids found in everyday life. The Binary Colloidal Alloy Test (BCAT) is part of an extensive series of experiments planned to investigate the fundamental properties of colloids so that scientists can make colloids more useful for technological applications. Some of the colloids studied in BCAT are made of two different sized particles (binary colloidal alloys) that are very tiny, uniform plastic spheres. Under the proper conditions, these colloids can arrange themselves in a pattern to form crystals. These crystals may form the basis of new classes of light switches, displays, and optical devices. Windows made of liquid crystals are already in the marketplace. These windows change their appearance from transparent to opaque when a weak electric current is applied. In the future, if the colloidal crystals can be made to control the passage of light through them, such products could be made much more cheaply. These experiments require the microgravity environment of space because good quality crystals are difficult to produce on Earth because of sedimentation and convection in the fluid. The BCAT experiment hardware included two separate modules for two different experiments. The "Slow Growth" hardware consisted of a 35-mm camera with a 250- exposure photo film cartridge. The camera was aimed toward the sample module, which contained 10 separate colloid samples. A rack of small lights provided backlighting for the photographs. The BCAT hardware was launched on the shuttle and was operated aboard the Russian space station Mir by American astronauts John Blaha and David Wolf (launched September 1996 and returned January 1997; reflown September 1997 and returned January 1998). To begin the experiment, one of these astronauts would mix the samples to disperse the colloidal particles and break up any crystals that might have already formed. Once the samples were mixed and

  20. Colloid Titration--A Rapid Method for the Determination of Charged Colloid.

    ERIC Educational Resources Information Center

    Ueno, Keihei; Kina, Ken'yu

    1985-01-01

    "Colloid titration" is a volumetric method for determining charged polyelectrolytes in aqueous solutions. The principle of colloid titration, reagents used in the procedure, methods of endpoint detection, preparation of reagent solutions, general procedure used, results obtained, and pH profile of colloid titration are considered. (JN)

  1. Collective motion in populations of colloidal bots

    NASA Astrophysics Data System (ADS)

    Bartolo, Denis

    One of the origins of active matter physics was the idea that flocks, herds, swarms and shoals could be quantitatively described as emergent ordered phases in self-driven materials. From a somehow dual perspective, I will show how to engineer active materials our of colloidal flocks. I will show how to motorize colloidal particles capable of sensing the orientation of their neighbors and how to handle them in microfluidic chips. These populations of colloidal bots display a non-equilibrium transition toward collective motion. A special attention will be paid to the robustness of the resulting colloidal flocks with respect to geometrical frustration and to quenched disorder.

  2. Colloid Coalescence with Focused X Rays

    SciTech Connect

    Weon, B. M.; Kim, J. T.; Je, J. H.; Yi, J. M.; Wang, S.; Lee, W.-K.

    2011-07-01

    We show direct evidence that focused x rays enable us to merge polymer colloidal particles at room temperature. This phenomenon is ascribed to the photochemical scission of colloids with x rays, reducing the molecular weight, glass transition temperature, surface tension, and viscosity of colloids. The observation of the neck bridge growth with time shows that the x-ray-induced colloid coalescence is analogous to viscoelastic coalescence. This finding suggests a feasible protocol of photonic nanofabrication by sintering or welding of polymers, without thermal damage, using x-ray photonics.

  3. Surface spin polarization induced ferromagnetic Ag nanoparticles

    NASA Astrophysics Data System (ADS)

    Shih, Po-Hsun; Li, Wen-Hsien; Wu, Sheng Yun

    2016-05-01

    We report on the observation of ferromagnetic spin polarized moments in 4.5 nm Ag nanoparticles. Both ferromagnetic and diamagnetic responses to an applied magnetic field were detected. The spin polarized moments shown under non-linear thermoinduced magnetization appeared on the surface atoms, rather than on all the atoms in particles. The saturation magnetization departed substantially from the Bloch T3/2-law, showing the existence of magnetic anisotropy. The Heisenberg ferromagnetic spin wave model for Ha-aligned moments was then employed to identify the magnetic anisotropic energy gap of ~0.12 meV. Our results may be understood by assuming the surface magnetism model, in which the surface atoms give rise to polarized moments while the core atoms produce diamagnetic responses.

  4. Simple and advanced ferromagnet/molecule spinterfaces

    NASA Astrophysics Data System (ADS)

    Gruber, M.; Ibrahim, F.; Djedhloul, F.; Barraud, C.; Garreau, G.; Boukari, S.; Isshiki, H.; Joly, L.; Urbain, E.; Peter, M.; Studniarek, M.; Da Costa, V.; Jabbar, H.; Bulou, H.; Davesne, V.; Halisdemir, U.; Chen, J.; Xenioti, D.; Arabski, J.; Bouzehouane, K.; Deranlot, C.; Fusil, S.; Otero, E.; Choueikani, F.; Chen, K.; Ohresser, P.; Bertran, F.; Le Fèvre, P.; Taleb-Ibrahimi, A.; Wulfhekel, W.; Hajjar-Garreau, S.; Wetzel, P.; Seneor, P.; Mattana, R.; Petroff, F.; Scheurer, F.; Weber, W.; Alouani, M.; Beaurepaire, E.; Bowen, M.

    2016-10-01

    Spin-polarized charge transfer between a ferromagnet and a molecule can promote molecular ferromagnetism 1, 2 and hybridized interfacial states3, 4. Observations of high spin-polarization of Fermi level states at room temperature5 designate such interfaces as a very promising candidate toward achieving a highly spin-polarized, nanoscale current source at room temperature, when compared to other solutions such as half-metallic systems and solid-state tunnelling over the past decades. We will discuss three aspects of this research. 1) Does the ferromagnet/molecule interface, also called an organic spinterface, exhibit this high spin-polarization as a generic feature? Spin-polarized photoemission experiments reveal that a high spin-polarization of electronics states at the Fermi level also exist at the simple interface between ferromagnetic cobalt and amorphous carbon6. Furthermore, this effect is general to an array of ferromagnetic and molecular candidates7. 2) Integrating molecules with intrinsic properties (e.g. spin crossover molecules) into a spinterface toward enhanced functionality requires lowering the charge transfer onto the molecule8 while magnetizing it1,2. We propose to achieve this by utilizing interlayer exchange coupling within a more advanced organic spinterface architecture. We present results at room temperature across the fcc Co(001)/Cu/manganese phthalocyanine (MnPc) system9. 3) Finally, we discuss how the Co/MnPc spinterface's ferromagnetism stabilizes antiferromagnetic ordering at room temperature onto subsequent molecules away from the spinterface, which in turn can exchange bias the Co layer at low temperature10. Consequences include tunnelling anisotropic magnetoresistance across a CoPc tunnel barrier11. This augurs new possibilities to transmit spin information across organic semiconductors using spin flip excitations12.

  5. Magnetic pinning in superconductor-ferromagnet multilayers

    SciTech Connect

    Bulaevskii, L. N.; Chudnovsky, E. M.; Maley, M. P.

    2000-05-01

    We argue that superconductor/ferromagnet multilayers of nanoscale period should exhibit strong pinning of vortices by the magnetic domain structure in magnetic fields below the coercive field when ferromagnetic layers exhibit strong perpendicular magnetic anisotropy. The estimated maximum magnetic pinning energy for single vortex in such a system is about 100 times larger than the pinning energy by columnar defects. This pinning energy may provide critical currents as high as 10{sup 6}-10{sup 7} A/cm{sup 2} at high temperatures (but not very close to T{sub c}) at least in magnetic fields below 0.1 T. (c) 2000 American Institute of Physics.

  6. Surface ferromagnetism in close-packed structures

    NASA Astrophysics Data System (ADS)

    Sanchez, J. M.; Morán-López, J. L.

    The temperature-magnetic field equilibrium phase diagram for the (111) surface of an fcc spin- {1}/{2} Ising ferromagnet is calculated using the tetrahedron aproximation of the cluster variation method. Among the new features found in the model is a triple point corresponding to a ferromagnetic first-order phase transition at zero field. Some characteristics of the model, such as the increase in the surface transition temperature with the magnetic field, may be relevant to recent observations in Gd(0001) by Weller and Alvarado.

  7. Wellhead with non-ferromagnetic materials

    DOEpatents

    Hinson, Richard A [Houston, TX; Vinegar, Harold J [Bellaire, TX

    2009-05-19

    Wellheads for coupling to a heater located in a wellbore in a subsurface formation are described herein. At least one wellhead may include a heater located in a wellbore in a subsurface formation; and a wellhead coupled to the heater. The wellhead may be configured to electrically couple the heater to one or more surface electrical components. The wellhead may include at least one non-ferromagnetic material such that ferromagnetic effects are inhibited in the wellhead. Systems and methods for using such wellheads for treating a subsurface formation are described herein.

  8. Domain-wall guided nucleation of superconductivity in hybrid ferromagnet-superconductor-ferromagnet layered structures.

    PubMed

    Gillijns, W; Aladyshkin, A Yu; Lange, M; Van Bael, M J; Moshchalkov, V V

    2005-11-25

    Domain-wall superconductivity is studied in a superconducting Nb film placed between two ferromagnetic Co/Pd multilayers with perpendicular magnetization. The parameters of top and bottom ferromagnetic films are chosen to provide different coercive fields, so that the magnetic domain structure of the ferromagnets can be selectively controlled. From the dependence of the critical temperature Tc on the applied magnetic field H, we have found evidence for domain-wall superconductivity in this three-layered F/S/F structure for different magnetic domain patterns. The phase boundary, calculated numerically for this structure from the linearized Ginzburg-Landau equation, is in good agreement with the experimental data.

  9. Quantitative simultaneous multi-element microprobe analysis using combined wavelength and energy dispersive systems

    NASA Technical Reports Server (NTRS)

    Walter, L. S.; Doan, A. S., Jr.; Wood, F. M., Jr.; Bredekamp, J. H.

    1972-01-01

    A combined WDS-EDS system obviates the severe X-ray peak overlap problems encountered with Na, Mg, Al and Si common to pure EDS systems. By application of easily measured empirical correction factors for pulse pile-up and peak overlaps which are normally observed in the analysis of silicate minerals, the accuracy of analysis is comparable with that expected for WDS electron microprobe analyses. The continuum backgrounds are subtracted for the spectra by a spline fitting technique based on integrated intensities between the peaks. The preprocessed data are then reduced to chemical analyses by existing data reduction programs.

  10. Ion microprobe magnesium isotope analysis of plagioclase and hibonite from ordinary chondrites

    NASA Astrophysics Data System (ADS)

    Hinton, R. W.; Bischoff, A.

    1984-03-01

    In a search for 26Mg excesses generated by 26Al decay the authors analysed four Al-rich objects from the type 3 ordinary chondrites using an ion microprobe. They report here the presence of 26Mg excesses of up to 100% in an unusually pure hibonite clast from the Dhajala chondrite; this 26Mg excess is the first to be found in an ordinary chondrite. No 26Mg excesses were observed in the three plagioclase-bearing chondrules analysed. It is concluded that 26Al may not have been sufficiently plentiful to act as a major heat source in condensed Solar System bodies.

  11. Ion microprobe magnesium isotope analysis of plagioclase and hibonite from ordinary chondrites

    NASA Technical Reports Server (NTRS)

    Hinton, R. W.; Bischoff, A.

    1984-01-01

    Ion and electron microprobes were used to examine Mg-26 excesses from Al-26 decay in four Al-rich objects from the type 3 ordinary hibonite clast in the Dhajala chondrite. The initial Al-26/Al-27 ratio was actually significantly lower than Al-rich inclusions in carbonaceous chondrites. Also, no Mg-26 excesses were found in three plagioclase-bearing chondrules that were also examined. The Mg-26 excesses in the hibonite chondrites indicated a common origin for chondrites with the excesses. The implied Al-26 content in a proposed parent body could not, however, be confirmed as a widespread heat source in the early solar system.

  12. Electron microprobe evaluation of terrestrial basalts for whole-rock K-Ar dating

    USGS Publications Warehouse

    Mankinen, E.A.; Brent, Dalrymple G.

    1972-01-01

    Four basalt samples for whole-rock K-Ar dating were analyzed with an electron microprobe to locate potassium concentrations. Highest concentrations of potassium were found in those mineral phases which were the last to crystallize. The two reliable samples had potassium concentrated in fine-grained interstitial feldspar and along grain boundaries of earlier formed plagioclase crystals. The two unreliable samples had potassium concentrated in the glassy matrix, demonstrating the ineffectiveness of basaltic glass as a retainer of radiogenic argon. In selecting basalt samples for whole-rock K-Ar dating, particular emphasis should be placed on determining the nature and condition of the fine-grained interstitial phases. ?? 1972.

  13. Electron microprobe analysis of trace elements in minerals at 10 PPM concentrations

    NASA Technical Reports Server (NTRS)

    Mckay, G. A.; Seymour, R. S.

    1982-01-01

    An improved technique is developed for measuring backgrounds during trace element analysis of crystals and glass using electron microprobes. This technique overcomes major difficulties encountered with conventional techniques, such as the problem of obtaining the net X-ray intensity of the characteristic emission line of interest with sufficient precision and accuracy, as well as the error due to the inability to directly measure the intensity at the wavelength of the characteristic line on the sample being analyzed. It is shown that this technique can yield reproducible results to within 4 ppm in olivine, and has a minimum uncertainty and detection limit of 10 ppm Nd in olivine.

  14. The Role of the Ion Microprobe in Solid-Earth Geochemistry

    NASA Astrophysics Data System (ADS)

    Hauri, E. H.

    2002-12-01

    Despite the early success of the electron microprobe in taking petrology to the micron scale, and the widespread use of mass spectrometers in geochemistry and geochronology, it was not until the mid-1970s that the ion microprobe came into its own as an in situ analytical tool in the Earth sciences. Despite this inauspicious beginning, secondary ion mass spectrometry (SIMS) was widely advertised as a technology that would eventually eclipse thermal ion mass spectrometry (TIMS) in isotope geology. However this was not to happen. While various technical issues in SIMS such as interferences and matrix effects became increasingly clear, an appreciation grew for the complimentary abilities of SIMS and TIMS that, even with the advent of ICP-MS, continues to this day. Today the ion microprobe is capable of abundance measurements in the parts-per-billion range across nearly the entire periodic table, and SIMS stable isotope data quality is now routinely crossing the 1 per mil threshold, all at the micron scale. Much of this success is due to the existence of multi-user community facilities for SIMS research, and the substantial efforts of interested scientists to understand the fundamentals of sputtered ion formation and their application to geochemistry. Recent discoveries of evidence for the existence of ancient crust and oceans, the emergence of life on Earth, the large-scale cycling of surficial materials into the deep Earth, and illumination of fundamental high-pressure phenomena have all been made possible by SIMS, and these (and many more) discoveries owe a debt to the vision of creating and supporting multi-user community facilities for SIMS. The ion microprobe remains an expensive instrument to purchase and maintain, yet it is also exceedingly diverse in application. Major improvements in SIMS, indeed in all mass spectrometry, are visible on the near horizon. Yet the geochemical community cannot depend on commercial manufacturers alone to design and build the next

  15. $ANBA; a rapid, combined data acquisition and correction program for the SEMQ electron microprobe

    USGS Publications Warehouse

    McGee, James J.

    1983-01-01

    $ANBA is a program developed for rapid data acquisition and correction on an automated SEMQ electron microprobe. The program provides increased analytical speed and reduced disk read/write operations compared with the manufacturer's software, resulting in a doubling of analytical throughput. In addition, the program provides enhanced analytical features such as averaging, rapid and compact data storage, and on-line plotting. The program is described with design philosophy, flow charts, variable names, a complete program listing, and system requirements. A complete operating example and notes to assist in running the program are included.

  16. X-ray microprobe measurements of the chemical compositions of ALH84001 carbonate globules

    SciTech Connect

    Flynn, G.J.; Sutton, S.R.; Keller, L.P.

    2004-01-28

    We measured minor element contents of carbonate from ALH84001 and report trends in tbe Ca, V, Mn and Sr in carbonate and the associated magnetite bands. McKay et al. suggested that carbonate globules in the ALH84001 meteorite from Mars contained evidence consistent with the development of bacterial life early in the history of Mars. This result provoked an extensive study of the ALH84001 meteorite. More recently Thomas-Keprta et al. have published a study showing that the magnetite associated with carbonate rims are of the size and shape produced by terrestrial bacteria. This paper has revived interest in ALH84001. The typical ALH84001 carbonate globule consists of four regions: a core of Fe-rich carbonate, a thin magnetite-rich band, a rim of Mn-rich carbonate, and another thin magnetite-rich band. Trace element analysis of each of these phases may allow us to address several important questions about these carbonates: (1) The origin of the magnetite-rich bands in the ALH84001 carbonate globules. If the magnetites are derived from the underlying carbonate through thermal decomposition (as proposed by Golden et al.), then we expect to see 'inherited' trace elements in these magnetite bands. (2) The origin of the rim carbonate, by determining whether the carbonate in the core has the same trace elements as the rim carbonates. (3) The age of the rim carbonate. Borg et al. dated the formation of the rim carbonate using the Rb/Sr chronometer. Borg et al. performed their measurements on an aliquot of what they called a high-Rb, low-Sr carbonate separate from the rim. We previously measured the trace element contents of chips from core and rim carbonates from an ALH84001 carbonate globule using an X-Ray Microprobe on Beamline X26A at the National Synchrotron Light Source. These measurements showed the rim carbonate had a very low Rb content, with Sr>>Rb, inconsistent with the {approx}5 ppm Rb reported by Borg et al. in the sample they dated by the Rb/Sr chronometer. The

  17. Colloid transport in dual-permeability media.

    PubMed

    Leij, Feike J; Bradford, Scott A

    2013-07-01

    It has been widely reported that colloids can travel faster and over longer distances in natural structured porous media than in uniform structureless media used in laboratory studies. The presence of preferential pathways for colloids in the subsurface environment is of concern because of the increased risks for disease caused by microorganisms and colloid-associated contaminants. This study presents a model for colloid transport in dual-permeability media that includes reversible and irreversible retention of colloids and first-order exchange between the aqueous phases of the two regions. The model may also be used to describe transport of other reactive solutes in dual-permeability media. Analytical solutions for colloid concentrations in aqueous and solid phases were obtained using Laplace transformation and matrix decomposition. The solutions proved convenient to assess the effect of model parameters on the colloid distribution. The analytical model was used to describe effluent concentrations for a bromide tracer and 3.2- or 1-μm-colloids that were observed after transport through a composite 10-cm long porous medium made up of a cylindrical lens or core of sand and a surrounding matrix with sand of a different grain size. The tracer data were described very well and realistic estimates were obtained for the pore-water velocity in the two flow domains. An accurate description was also achieved for most colloid breakthrough curves. Dispersivity and retention parameters were typically greater for the larger 3.2-μm-colloids while both reversible and irreversible retention rates tended to be higher for the finer sands than the coarser sand. The relatively small sample size and the complex flow pattern in the composite medium made it difficult to reach definitive conclusions regarding transport parameters for colloid transport.

  18. Itinerant ferromagnetism in a two-dimensional atomic gas

    SciTech Connect

    Conduit, G. J.

    2010-10-15

    Motivated by the first experimental evidence of ferromagnetic behavior in a three-dimensional ultracold atomic gas, we explore the possibility of itinerant ferromagnetism in a trapped two-dimensional atomic gas. Firstly, we develop a formalism that demonstrates how quantum fluctuations drive the ferromagnetic reconstruction first order, and consider the consequences of an imposed population imbalance. Secondly, we adapt this formalism to elucidate the key experimental signatures of ferromagnetism in a realistic trapped geometry.

  19. Temperature limited heater utilizing non-ferromagnetic conductor

    DOEpatents

    Vinegar,; Harold J. , Harris; Kelvin, Christopher [Houston, TX

    2012-07-17

    A heater is described. The heater includes a ferromagnetic conductor and an electrical conductor electrically coupled to the ferromagnetic conductor. The ferromagnetic conductor is positioned relative to the electrical conductor such that an electromagnetic field produced by time-varying current flow in the ferromagnetic conductor confines a majority of the flow of the electrical current to the electrical conductor at temperatures below or near a selected temperature.

  20. The hydrodynamics of colloidal gelation.

    PubMed

    Varga, Zsigmond; Wang, Gang; Swan, James

    2015-12-14

    Colloidal gels are formed during arrested phase separation. Sub-micron, mutually attractive particles aggregate to form a system spanning network with high interfacial area, far from equilibrium. Models for microstructural evolution during colloidal gelation have often struggled to match experimental results with long standing questions regarding the role of hydrodynamic interactions. In nearly all models, these interactions are neglected entirely. In the present work, we report simulations of gelation with and without hydrodynamic interactions between the suspended particles executed in HOOMD-blue. The disparities between these simulations are striking and mirror the experimental-theoretical mismatch in the literature. The hydrodynamic simulations agree with experimental observations, however. We explore a simple model of the competing transport processes in gelation that anticipates these disparities, and conclude that hydrodynamic forces are essential. Near the gel boundary, there exists a competition between compaction of individual aggregates which suppresses gelation and coagulation of aggregates which enhances it. The time scale for compaction is mildly slowed by hydrodynamic interactions, while the time scale for coagulation is greatly accelerated. This enhancement to coagulation leads to a shift in the gel boundary to lower strengths of attraction and lower particle concentrations when compared to models that neglect hydrodynamic interactions. Away from the gel boundary, differences in the nearest neighbor distribution and fractal dimension persist within gels produced by both simulation methods. This result necessitates a fundamental rethinking of how dynamic, discrete element models for gelation kinetics are developed as well as how collective hydrodynamic interactions influence the arrest of attractive colloidal dispersions.

  1. Ferromagnetic Conducting Lignosulfonic Acid-doped Polyaniline Nanocomposites

    NASA Technical Reports Server (NTRS)

    Viswansthan, Tito (Inventor); Berry, Brian (Inventor)

    2004-01-01

    A conductive ferromagnetic composition of matter comprising sulfonated lignin or a sulfonated polyflavonoid, or derivatives thereof, and ferromagnetic iron oxide particles is disclosed. Among the uses of the composition is to shield electromagnetic radiation. The ferromagnetic iron oxide particles of the composition are surprisingly stable to acid, and are easily and inexpensively formed from iron cations in solution.

  2. Ferromagnets as pure spin current generators and detectors

    SciTech Connect

    Qu, Danru; Miao, Bingfeng; Chien, Chia -Ling; Huang, Ssu -Yen

    2015-09-08

    Provided is a spintronics device. The spintronics can include a ferromagnetic metal layer, a positive electrode disposed on a first surface portion of the ferromagnetic metal layer, and a negative electrode disposed on a second surface portion of the ferromagnetic metal.

  3. Patchy particles using colloidal caps

    NASA Astrophysics Data System (ADS)

    Middleton, Christine; Pine, David

    2015-03-01

    We present a method for making patchy particles functionalized with single stranded sticky end DNA only on their patches. This is done by adding ``spherical cap'' particles as patches to spherical colloids using the depletion interaction. The caps are then functionalized with single stranded DNA using copper-free click chemistry. Due to being attached only by depletion, the patches diffuse on the surface of the particle. The patchy particles can then interact with each other in a specific, directional way through the mobile, DNA functionalized patches.

  4. Corralled Colloids in Four Dimensions

    NASA Astrophysics Data System (ADS)

    Anthony, Stephen; Kim, Minsu; Granick, Steve

    2008-03-01

    Three colloidal particles were placed in small corrals and the strong correlations between their translation and rotation were quantified using the optical anisotropy of MOON (Modulated Optical Nanoprobes) particles to simultaneously measure their translation and rotation in an optical microscope. This system represents the simplest system which can capture one of the relevant components of multi-body interactions, the fact that while two particles can freely rotate together (like gears), once a third particle (or gear) is added there is no universally favorable set of rotations. This simple multi-body system provides a paradigm of how rotation influences translation and vice-versa.

  5. Active colloids at liquid-liquid interfaces: dynamic self-assembly and functionality

    NASA Astrophysics Data System (ADS)

    Snezhko, Alexey; Aranson, Igor

    2012-02-01

    Self-assembled materials must actively consume energy and remain out of equilibrium in order to support structural complexity and functional diversity. Colloids of interacting particles suspended at liquid-liquid interfaces and maintained out of equilibrium by external alternating electromagnetic fields develop nontrivial collective dynamics and self-assembly. We use ferromagnetic colloidal micro-particles (so the magnetic moment is fixed in each particle and interactions between colloids is highly anisotropic and directional) suspended over an interface of two immiscible liquids and energized by vertical alternating magnetic fields to demonstrate novel dynamic and active self-assembled structures (``asters'') which are not accessible through thermodynamic assembly. Structures are attributed to the interplay between surface waves, generated at the liquid/liquid interface by the collective response of magnetic microparticles to the alternating magnetic field, and hydrodynamic fields induced in the boundary layers of both liquids forming the interface. Two types of magnetic order are reported. We demonstrate that asters develop self-propulsion in the presence of a small in-plane dc magnetic field. We show that asters can capture, transport, and position target microparticles.

  6. Colloidal Electrolytes and the Critical Micelle Concentration

    ERIC Educational Resources Information Center

    Knowlton, L. G.

    1970-01-01

    Describes methods for determining the Critical Micelle Concentration of Colloidal Electrolytes; methods described are: (1) methods based on Colligative Properties, (2) methods based on the Electrical Conductivity of Colloidal Electrolytic Solutions, (3) Dye Method, (4) Dye Solubilization Method, and (5) Surface Tension Method. (BR)

  7. Binary Colloidal Alloy Test-5: Aspheres

    NASA Technical Reports Server (NTRS)

    Chaikin, Paul M.; Hollingsworth, Andrew D.

    2008-01-01

    The Binary Colloidal Alloy Test - 5: Aspheres (BCAT-5-Aspheres) experiment photographs initially randomized colloidal samples (tiny nanoscale spheres suspended in liquid) in microgravity to determine their resulting structure over time. BCAT-5-Aspheres will study the properties of concentrated systems of small particles when they are identical, but not spherical in microgravity..

  8. Colloid transport in dual-permeability media

    Technology Transfer Automated Retrieval System (TEKTRAN)

    It has been widely reported that colloids can travel faster and over longer distances in natural structured porous media than in uniform structureless media used in laboratory studies. The presence of preferential pathways for colloids in the subsurface environment is of concern because of the incre...

  9. Proximity effect and its enhancement by ferromagnetism in high-temperature superconductor-ferromagnet structures.

    PubMed

    Volkov, A F; Efetov, K B

    2009-02-20

    We consider a bilayer consisting of a d-wave layered superconductor and diffusive ferromagnet with a domain wall (DW). The c axis in the superconductor and DW in the ferromagnet are assumed to be perpendicular to the interface. We demonstrate that in such a heterostructure the inhomogeneous exchange field enhances the proximity effect. It is shown that, whereas in the absence of the exchange field the d-wave condensate decays in the normal metal on the mean free path l, the superconductivity penetrates the ferromagnet along the DW over much larger distances. This happens because the presence of the DW results in a generation of an odd-frequency triplet s-wave component of the condensate. The phenomenon discovered here may help to explain a recent experiment on high-temperature superconductor-ferromagnet bilayers.

  10. Structural transitions in condensed colloidal virus phases

    NASA Astrophysics Data System (ADS)

    Schmidt, Nathan; Barr, Steve; Udit, Andrew; Gutierrez, Leonardo; Nguyen, Thanh; Finn, M. G.; Luijten, Erik; Wong, Gerard

    2010-03-01

    Analogous to monatomic systems colloidal phase behavior is entirely determined by the interaction potential between particles. This potential can be tuned using solutes such as multivalent salts and polymers with varying affinity for the colloids to create a hierarchy of attractions. Bacteriophage viruses are a naturally occurring type of colloidal particle with characteristics difficult to achieve by laboratory synthesis. They are monodisperse, nanometers in size, and have heterogeneous surface charge distributions. We use the MS2 and Qbeta bacteriophages (diameters 27-28nm) to understand the interplay between different attraction mechanisms on nanometer-sized colloids. Small Angle X-ray Scattering (SAXS) is used to characterize the inter-particle interaction between colloidal viruses using several polymer species and different salt types.

  11. Optical effects of charges in colloidal solutions

    NASA Astrophysics Data System (ADS)

    Chang, Railing; Chung, Hung-Yi; Chen, Chih-Wei; Chiang, Hai-Pang; Leung, P. T.

    2017-04-01

    The optical response of charged polymeric and metallic colloids is investigated using effective medium theories for composite systems of nanoparticles. Based on the Bohren-Hunt theory for generalized Mie scattering from charged particles, an effective quasi-static dielectric function previously obtained is applied to the present study to characterize the response from the various colloidal particles. It is found that such effects are more prominent for polymeric and nonmetallic colloidal solutions in general. In addition, the effects of clustering among the colloidal particles are also studied via a fractal model available from the literature. Detailed numerical studies of the dependence of these effects on the amount of extraneous charge, as well as on the geometry and volume fraction of the colloidal particles are presented.

  12. Finding the Curie Temperature for Ferromagnetic Materials

    ERIC Educational Resources Information Center

    Kizowski, Czeslaw; Budzik, Sylwia; Cebulski, Jozef

    2007-01-01

    The laboratory exercise described in this paper is based on a well-known qualitative demonstration of Curie temperature. A long ferromagnetic wire, in the form of a spiral, is attracted to a strong permanent magnet placed near its midpoint (see Fig. 1). The temperature of the wire is increased by passing a current through it. When the temperature…

  13. Magnetic profiles in ferromagnetic/superconducting superlattices.

    SciTech Connect

    te Velthuis, S. G. E.; Hoffmann, A.; Santamaria, J.; Materials Science Division; Univ. Complutense de Madrid

    2007-02-28

    The interplay between ferromagnetism and superconductivity has been of longstanding fundamental research interest to scientists, as the competition between these generally mutually exclusive types of long-range order gives rise to a rich variety of physical phenomena. A method of studying these exciting effects is by investigating artificially layered systems, i.e. alternating deposition of superconducting and ferromagnetic thin films on a substrate, which enables a straight-forward combination of the two types of long-range order and allows the study of how they compete at the interface over nanometer length scales. While originally studies focused on low temperature superconductors interchanged with metallic ferromagnets, in recent years the scope has broadened to include superlattices of high T{sub c} superconductors and colossal magnetoresistance oxides. Creating films where both the superconducting as well as the ferromagnetic layers are complex oxide materials with similar crystal structures (Figure 1), allows the creation of epitaxial superlattices, with potentially atomically flat and ordered interfaces.

  14. Lattice effects on ferromagnetism in perovskite ruthenates.

    PubMed

    Cheng, J-G; Zhou, J-S; Goodenough, John B

    2013-08-13

    Ferromagnetism and its evolution in the orthorhombic perovskite system Sr(1-x)Ca(x)RuO3 have been widely believed to correlate with structural distortion. The recent development of high-pressure synthesis of the Ba-substituted Sr(1-y)Ba(y)RuO3 makes it possible to study ferromagnetism over a broader phase diagram, which includes the orthorhombic Imma and the cubic phases. However, the chemical substitutions introduce the A-site disorder effect on Tc, which complicates determination of the relationship between ferromagnetism and structural distortion. By clarifying the site disorder effect on Tc in several unique series of ruthenates in which the average bond length remains the same but the bond-length variance varies, we are able to demonstrate a parabolic curve of Tc versus mean bond length . A much higher Tc ∼ 177 K than that found in orthorhombic SrRuO3 can be obtained from the curve at a bond length , which makes the geometric factor t = /(√2) ∼ 1. This result reveals not only that the ferromagnetism in the ruthenates is extremely sensitive to the lattice strain, but also that it has an important implication for exploring the structure-property relationship in a broad range of oxides with perovskite or a perovskite-related structure.

  15. Ferromagnetic resonance probe liftoff suppression apparatus

    DOEpatents

    Davis, Thomas J.; Tomeraasen, Paul L.

    1985-01-01

    A liftoff suppression apparatus utilizing a liftoff sensing coil to sense the amount a ferromagnetic resonance probe lifts off the test surface during flaw detection and utilizing the liftoff signal to modulate the probe's field modulating coil to suppress the liftoff effects.

  16. Magnetic and Electrical Properties of Ferromagnetic Semiconductors,

    DTIC Science & Technology

    magnetism and of the mechanism of the electronic conductivity of ferromagnetic semiconductors in connection with their chemical composition and crystalline ... structure . The basic groups of oxide compounds of 4f- and 3d-transition metals with maximum spin values were selected for the studies in this work. The

  17. Late Pleistocene granodiorite beneath Crater Lake caldera, Oregon, dated by ion microprobe

    USGS Publications Warehouse

    Bacon, C.R.; Persing, H.M.; Wooden, J.L.; Ireland, T.R.

    2000-01-01

    Variably melted granodiorite blocks ejected during the Holocene caldera-forming eruption of Mount Mazama were plucked from the walls of the climactic magma chamber ~15 km depth. Ion-microprobe U-Pb dating of zircons from two unmelted granodiorite blocks with SHRIMP RG (sensitive high-resolution ion microprobe-reverse geometry) gives a nominal 238U/206Pb age of 101+78-80 ka, or 174+89-115 ka when adjusted for an initial 230Th deficit. SHRIMP RG U-Th measurements on a subset of the zircons yield a 230Th/238U isochron age of 112 ?? 24 ka, considered to be the best estimate of the time of solidification of the pluton. These results suggest that the granodiorite is related to andesite and dacite of Mount Mazama and not to magmas of the climactic eruption. The unexposed granodiorite has an area of at least 28 km2. This young, shallow pluton was emplaced in virtually the same location where a similarly large magma body accumulated and powered violent explosive eruptions ~7700 yr ago, resulting in collapse of Crater Lake caldera.

  18. Characterisation of a ΔE E particle telescope using the ANSTO heavy ion microprobe

    NASA Astrophysics Data System (ADS)

    Siegele, Rainer; Reinhard, Mark; Prokopovich, Dale; Ionescu, Mihail; Cohen, David D.; Rosenfeld, Anatoly B.; Cornelius, Iwan M.; Wroe, Andrew; Lerch, Michael L. F.; Fazzi, A.; Pola, A.; Agosteo, S.

    2007-07-01

    Semiconductor planar processing technology has spurned the development of novel radiation detectors with applications in space, high energy physics, medical diagnostics, radiation protection and cancer therapy. The ANSTO heavy ion microprobe, which allows a wide range of ions to be focused into spot sizes of a few micrometers in diameter, has proven to be an essential tool for characterising these detectors using the Ion Beam Induced Charge (IBIC) imaging technique. The use of different ions and the wide range of available energies on the heavy ion microprobe, allows the testing of these devices with ionising particles associated with different values of linear energy transfer (LET). Quadruple coincidence measurements have been used to map the charge collection characteristics of a monolithic ΔE E telescope. This was done through simultaneous measurement of the spatial coordinates of the microbeam relative to the sample and the response of both detector elements. The resulting charge collection maps were used to better understand the functionality of the device as well as to ascertain ways in which future device designs could be modified to improve performance.

  19. Probe-AMPH—A spreadsheet program to classify microprobe-derived amphibole analyses

    NASA Astrophysics Data System (ADS)

    Tindle, A. G.; Webb, P. C.

    1994-10-01

    A Microsoft Excel™ spreadsheet program has been developed to calculate structural formulae of microprobe-derived amphibole analyses and determine classification parameters according to the International Mineralogical Association scheme for amphibole nomenclature. The program has been tested in the determination of formulae and classification of 138 amphibole analyses from the literature. Of these, the small percentage (14%) of discrepancies were determined mainly to be the result of (i) differences between measured (wet chemical) and estimated values for FeO and Fe2O3 and (ii) differences inherent in summing structural formula of microprobe data to 23 oxygens and wet chemical data to 24 oxygens. The program has been developed for the Apple Macintosh but a PC version also is available. Spreadsheet implementations of four published geobarometers based on the total aluminium content of certain calcic amphiboles also are presented. These geobarometers are applicable to metaluminous plutonic (and associated volcanic) rocks containing the assemblage amphibole-biotite-quartz-plagioclase-(orthoclase)-sphene-FeTi oxides and apply to a pressure range of 2.5-13 kbar.

  20. Electron Microprobe Analyses of Lithic Fragments and Their Minerals from Luna 20 Fines

    NASA Technical Reports Server (NTRS)

    Conrad, G. H.; Hlava, P. F.; Green, J. A.; Moore, R. B.; Moreland, G.; Dowty, E.; Prinz, M.; Keil, K.; Nehru, C. E.; Bunch, T. E.

    1973-01-01

    The bulk analyses (determined with the broad beam electron microprobe technique) of lithic fragments are given in weight percentages and are arranged according to the rock classification. Within each rock group the analyses are arranged in order of increasing FeO content. Thin section and lithic fragment numbers are given at the top of each column of analysis and correspond to the numbers recorded on photo mosaics on file in the Institute of Meteoritics. CIPW molecular norms are given for each analysis. Electron microprobe mineral analyses (given in oxide weight percentages), structural formulae and molecular end member values are presented for plagioclase, olivine, pyroxene and K-feldspar. The minerals are selected mostly from lithic fragments that were also analyzed for bulk composition. Within each mineral group the analyses are presented according to the section number and lithic fragment number. Within each lithic fragment the mineral analyses are arranged as follows: Plagioclase in order of increasing CaO; olivine and pyroexene in order of increasing FeO; and K-feldspar in order of increasing K2O. The mineral grains are identified at the top of each column of analysis by grain number and lithic fragment number.

  1. Development of Ultra Low Temperature, Impact Resistant Lithium Battery for the Mars Microprobe

    NASA Technical Reports Server (NTRS)

    Frank, H.; Deligiannis, F.; Davies, E.; Ratnakumar, Bugga V.; Surampudi, S.; Russel, P. G.; Reddy, T. B.

    1998-01-01

    The requirements of the power source for the Mars Microprobe, to be backpacked on the Mars 98 Spacecraft, are fairly demanding, with survivability to a shock of the order of 80,000 g combined with an operational requirement at -80 C. Development of a suitable power system, based on primary lithium-thionyl chloride is underway for the last eighteen months, together with Yardney Technical Products Inc., Pawcatuck, CT. The battery consists of 4 cells of 2 Ah capacity at 25 C, of which at least 25 % would be available at -80 C, at a moderate rate of C/20. Each probe contains two batteries and two such probes will be deployed. The selected cell is designed around an approximate 1/2 "D" cells, with flat plate electrodes. Significant improvements to the conventional Li-SOCl2 cell include: (a) use of tetrachlorogallate salt instead of aluminate for improved low temperature performance and reduced voltage delay, (b) optimization of the salt concentration, and (c) modification of the cell design to develop shock resistance to 80,000 g. We report here results from our several electrical performance tests, mission simulation tests, microcalorimetry and AC impedance studies, and Air gun tests. The cells have successfully gone through mission-enabling survivability and performance tests for the Mars Microprobe penetrator.

  2. Study of the toughening mechanisms in bone and biomimetic hydroxyapatite materials using Raman microprobe spectroscopy.

    PubMed

    Pezzotti, Giuseppe; Sakakura, Seiji

    2003-05-01

    A Raman microprobe spectroscopy characterization of microscopic fracture mechanisms is presented for a natural hydroxyapatite material (cortical bovine femur) and two synthetic hydroxyapatite-based materials with biomimetic structures-a hydroxyapatite skeleton interpenetrated with a metallic (silver) or a polymeric (nylon-6) phase. In both the natural and synthetic materials, a conspicuous amount of toughening arose from a microscopic crack-bridging mechanism operated by elasto-plastic stretching of unbroken second-phase ligaments along the crack wake. This mechanism led to a rising R-curve behavior. An additional micromechanism, responsible for stress relaxation at the crack tip, was recognized in the natural bone material and was partly mimicked in the hydroxyapatite/silver composite. This crack-tip mechanism conspicuously enhanced the cortical bone material resistance to fracture initiation. A piezo-spectroscopic technique, based on a microprobe measurement of 980 cm(-1) Raman line of hydroxyapatite, enabled us to quantitatively assess in situ the microscopic stress fields developed during fracture both at the crack tip and along the crack wake. Using the Raman piezo-spectroscopy technique, toughening mechanisms were assessed quantitatively and rationally related to the macroscopic fracture characteristics of hydroxyapatite-based materials.

  3. Ion microprobe mass analysis of plagioclase from 'non-mare' lunar samples

    NASA Technical Reports Server (NTRS)

    Meyer, C., Jr.; Anderson, D. H.; Bradley, J. G.

    1974-01-01

    The ion microprobe was used to measure the composition and distribution of trace elements in lunar plagioclase, and these analyses are used as criteria in determining the possible origins of some nonmare lunar samples. The Apollo 16 samples with metaclastic texture and high-bulk trace-element contents contain plagioclase clasts with extremely low trace-element contents. These plagioclase inclusions represent unequilibrated relicts of anorthositic, noritic, or troctolitic rocks that have been intermixed as a rock flour into the KREEP-rich matrix of these samples. All of the plagioclase-rich inclusions which were analyzed in the KREEP-rich Apollo 14 breccias were found to be rich in trace elements. This does not seem to be consistent with the interpretation that the Apollo 14 samples represent a pre-Imbrium regolith, because such an ancient regolith should have contained many plagioclase clasts with low trace-element contents more typical of plagioclase from the pre-Imbrium crust. Ion-microprobe analyses for Ba and Sr in large plagioclase phenocrysts in 14310 and 68415 are consistent with the bulk compositions of these rocks and with the known distribution coefficients for these elements. The distribution coefficient for Li (basaltic liquid/plagioclase) was measured to be about 2.

  4. In situ ion microprobe U-Pb dating and REE abundances of a carboniferous conodont

    NASA Astrophysics Data System (ADS)

    Sano, Yuji; Terada, Kentaro

    We report here in situ ion microprobe U-Pb dating of a conodont micro-fossil using an ion microprobe method. Thirteen spots on the single fragment of the Carboniferous conodont (size: approximately 800 µm × 100 µm) yield a 238U/206Pb isochron age of 323±36 Ma and a Tera-Wasserburg concordia intercept age of 332±44 Ma in a three-dimensional 238U/206Pb-207Pb/206 Pb-204Pb/206Pb diagram. These ages are consistent with the depositional and early diagenetic ages of the fossil in its host Mississippian sedimentary sequence within experimental error. The success of the method depends on the chemical fractionation of U from Pb within a hundred-µm length scale and the consequent variations in Pb isotopic compositions due to radioactive decay. Shale-normalized rare earth element (REE) abundances of two spots on the same sample show flat patterns from light REE to middle REE and decreases from middle REE to heavy REE with negative anomalies of both Ce and Eu. The REE characteristics are significantly different from those of Devonian conodonts reported by other workers, suggesting discrepant redox states and/or formation environments.

  5. Colloid Transport and Retention in Fractured Media

    SciTech Connect

    McCarthy, J.F.

    2001-02-01

    The goal of this project was to identify the chemical and physical factors that control the transport of colloids in fractured materials, and develop a generalized capability to predict colloid attachment and detachment based on hydraulic factors (head, flow rate), physical processes and structure (fracture aperture, matrix porosity), and chemical properties (surface properties of colloids, solution chemistry, and mineralogy of fracture surfaces). Both aqueous chemistry and physical structure of geologic formations influenced transport. Results of studies at all spatial scales reached consensus on the importance of several key controlling variables: (1) colloid retention is dominated by chemical conditions favoring colloid-wall interactions; (2) even in the presence of conditions favorable to colloid collection, deposited colloids are remobilized over long times and this process contributes substantially to the overall extent of transport; (3) diffusive exchange between water-conducting fractures and finer fractures and pores acts to ''buffer'' the effects of the major fracture network structure, and reduces predictive uncertainties. Predictive tools were developed that account for fundamental mechanisms of colloid dynamics in fracture geometry, and linked to larger-scale processes in networks of fractures. The results of our study highlight the key role of physical and hydrologic factors, and processes of colloid remobilization that are potentially of even greater importance to colloid transport in the vadose zone than in saturated conditions. We propose that this work be extended to focus on understanding vadose zone transport processes so that they can eventually be linked to the understanding and tools developed in our previous project on transport in saturated groundwater systems.

  6. PROTON MICROPROBE ANALYSIS OF TRACE-ELEMENT VARIATIONS IN VITRINITES IN THE SAME AND DIFFERENT COAL BEDS.

    USGS Publications Warehouse

    Minkin, J.A.; Chao, E.C.T.; Blank, Herma; Dulong, F.T.

    1987-01-01

    The PIXE (proton-induced X-ray emission) microprobe can be used for nondestructive, in-situ analyses of areas as small as those analyzed by the electron microprobe, and has a sensitivity of detection as much as two orders of magnitude better than the electron microprobe. Preliminary studies demonstrated that PIXE provides a capability for quantitative determination of elemental concentrations in individual coal maceral grains with a detection limit of 1-10 ppm for most elements analyzed. Encouraged by the earlier results, we carried out the analyses reported below to examine trace element variations laterally (over a km range) as well as vertically (cm to m) in the I and J coal beds in the Upper Cretaceous Ferron Sandstone Member of the Mancos Shale in central Utah, and to compare the data with the data from two samples of eastern coals of Pennsylvanian age.

  7. Gel trapping of dense colloids.

    PubMed

    Laxton, Peter B; Berg, John C

    2005-05-01

    Phase density differences in sols, foams, or emulsions often lead to sedimentation or creaming, causing problems for materials where spatial uniformity over extended periods of time is essential. The problem may be addressed through the use of rheology modifiers in the continuous phase. Weak polymer gels have found use for this purpose in the food industry where they appear to be capable of trapping dispersoid particles in a three-dimensional matrix while displaying water-like viscosities at low shear. Attempts to predict sedimentation stability in terms of particle properties (size, shape, density difference) and gel yield stress have led to qualitative success for suspensions of large particles. The effect of particle size, however, in particular the case in which colloidal dimensions are approached, has not been investigated. The present work seeks to determine useful stability criteria for colloidal dispersions in terms of readily accessible viscoelastic descriptors. Results are reported for systems consisting of 12 microm poly(methyl methacrylate) (PMMA) spheres dispersed in aqueous gellan gum. Monovalent salt concentration is varied to control rheological properties, and sedimentation/centrifugation experiments are performed to determine dispersion stability. Necessary conditions for stability consist of a minimum yield stress together with a value of tan delta less than unity.

  8. Synthesis of substantially monodispersed colloids

    NASA Technical Reports Server (NTRS)

    Klabunde, Kenneth J. (Inventor); Stoeva, Savka (Inventor); Sorensen, Christopher (Inventor)

    2003-01-01

    A method of forming ligated nanoparticles of the formula Y(Z).sub.x where Y is a nanoparticle selected from the group consisting of elemental metals having atomic numbers ranging from 21-34, 39-52, 57-83 and 89-102, all inclusive, the halides, oxides and sulfides of such metals, and the alkali metal and alkaline earth metal halides, and Z represents ligand moieties such as the alkyl thiols. In the method, a first colloidal dispersion is formed made up of nanoparticles solvated in a molar excess of a first solvent (preferably a ketone such as acetone), a second solvent different than the first solvent (preferably an organic aryl solvent such as toluene) and a quantity of ligand moieties; the first solvent is then removed under vacuum and the ligand moieties ligate to the nanoparticles to give a second colloidal dispersion of the ligated nanoparticles solvated in the second solvent. If substantially monodispersed nanoparticles are desired, the second dispersion is subjected to a digestive ripening process. Upon drying, the ligated nanoparticles may form a three-dimensional superlattice structure.

  9. Kinetically guided colloidal structure formation

    PubMed Central

    Hecht, Fabian M.; Bausch, Andreas R.

    2016-01-01

    The self-organization of colloidal particles is a promising approach to create novel structures and materials, with applications spanning from smart materials to optoelectronics to quantum computation. However, designing and producing mesoscale-sized structures remains a major challenge because at length scales of 10–100 μm equilibration times already become prohibitively long. Here, we extend the principle of rapid diffusion-limited cluster aggregation (DLCA) to a multicomponent system of spherical colloidal particles to enable the rational design and production of finite-sized anisotropic structures on the mesoscale. In stark contrast to equilibrium self-assembly techniques, kinetic traps are not avoided but exploited to control and guide mesoscopic structure formation. To this end the affinities, size, and stoichiometry of up to five different types of DNA-coated microspheres are adjusted to kinetically control a higher-order hierarchical aggregation process in time. We show that the aggregation process can be fully rationalized by considering an extended analytical DLCA model, allowing us to produce mesoscopic structures of up to 26 µm in diameter. This scale-free approach can easily be extended to any multicomponent system that allows for multiple orthogonal interactions, thus yielding a high potential of facilitating novel materials with tailored plasmonic excitation bands, scattering, biochemical, or mechanical behavior. PMID:27444018

  10. Depth Probing Soft X-ray Microprobe (DPSXRM) for High Resolution Probing of Earth's Microstructural Samples

    NASA Astrophysics Data System (ADS)

    Dikedi, P. N.

    2015-12-01

    The Cambrian explosion; occurrence of landslides in very dry weather conditions; rockslides; dead, shriveled-up and crumbled leaves possessing fossil records with the semblance of well preserved, flat leaves; abundance of trilobite tracks in lower and higher rock layers; and sailing stones are enigmas demanding demystifications. These enigmas could be elucidated when data on soil structure, texture and strength are provided by some device with submicrometre accuracy; for these and other reasons, the design of a Depth Probing Soft X-ray Microprobe (DPSXRM), is being proposed; it is expected to deliver soft X-rays, at spatial resolution, ϛ≥600nm and to probe at the depth of 0.5m in 17s. The microprobe is portable compared to a synchrotron radiation facility (Diamond Light Source has land size of 43,300m2); spatial resolution,ϛ , of the DPSXRM surpasses those of the X-ray Fluorescence microanalysis (10µm), electron microprobe (1-3µm) and ion microprobe (5->30µm); the DPSXRM has allowance for multiple targets. Vanadium and Manganese membranes are proposed owing to respective 4.952KeV VKα1 and 5.899KeV MnKα1 X-rays emitted, which best suits micro-probing of Earth's microstructural samples. Compound systems like the Kirk-Patrick and Baez and Wolter optics, aspheric mirrors like elliptical and parabolic optics, small apertures and Abbe sine condition are employed to reduce or remove astigmatism, obliquity, comatic and spherical aberrations—leading to good image quality. Results show that 5.899KeV MnKα1 and 4.952KeV VKα1 soft X-rays will travel a distance of 2.75mm to form circular patches of radii 2.2mm and 2.95mm respectively. Zone plate with nth zone radius of 1.5mm must be positioned 1.5mm and 2mm from the electron gun if circular patches must be formed from 4.952KeV VKα1 and 5.899KeV MnKα1 soft X-rays respectively. The focal lengths of 0.25μm≤ƒ≤1.50μm and 0.04μm≤ƒ≤0.2μm covered by 4.952KeV VKα1 and 5.899KeV Mn Kα1 soft X-Rays, will

  11. Achieving High-Temperature Ferromagnetic Topological Insulator

    NASA Astrophysics Data System (ADS)

    Katmis, Ferhat

    Topological insulators (TIs) are insulating materials that display conducting surface states protected by time-reversal symmetry, wherein electron spins are locked to their momentum. This unique property opens new opportunities for creating next-generation electronic and spintronic devices, including TI-based quantum computation. Introducing ferromagnetic order into a TI system without compromising its distinctive quantum coherent features could lead to a realization of several predicted novel physical phenomena. In particular, achieving robust long-range magnetic order at the TI surface at specific locations without introducing spin scattering centers could open up new possibilities for devices. Here, we demonstrate topologically enhanced interface magnetism by coupling a ferromagnetic insulator (FMI) to a TI (Bi2Se3); this interfacial ferromagnetism persists up to room temperature, even though the FMI (EuS) is known to order ferromagnetically only at low temperatures (<17 K). The induced magnetism at the interface resulting from the large spin-orbit interaction and spin-momentum locking feature of the TI surface is found to greatly enhance the magnetic ordering (Curie) temperature of the TI/FMI bilayer system. Due to the short range nature of the ferromagnetic exchange interaction, the time-reversal symmetry is broken only near the surface of a TI, while leaving its bulk states unaffected. The topological magneto-electric response originating in such an engineered TI could allow for an efficient manipulation of the magnetization dynamics by an electric field, providing an energy efficient topological control mechanism for future spin-based technologies. Work supported by MIT MRSEC through the MRSEC Program of NSF under award number DMR-0819762, NSF Grant DMR-1207469, the ONR Grant N00014-13-1-0301, and the STC Center for Integrated Quantum Materials under NSF grant DMR-1231319.

  12. Use of a beta microprobe system to measure arterial input function in PET via an arteriovenous shunt in rats

    PubMed Central

    2011-01-01

    Background Kinetic modeling of physiological function using imaging techniques requires the accurate measurement of the time-activity curve of the tracer in plasma, known as the arterial input function (IF). The measurement of IF can be achieved through manual blood sampling, the use of small counting systems such as beta microprobes, or by derivation from PET images. Previous studies using beta microprobe systems to continuously measure IF have suffered from high background counts. Methods In the present study, a light-insensitive beta microprobe with a temporal resolution of up to 1 s was used in combination with a pump-driven femoral arteriovenous shunt to measure IF in rats. The shunt apparatus was designed such that the placement of the beta microprobe was highly reproducible. The probe-derived IF was compared to that obtained from manual sampling at 5-s intervals and IF derived from a left ventricle VOI in a dynamic PET image of the heart. Results Probe-derived IFs were very well matched to that obtained by "gold standard" manual blood sampling, but with an increased temporal resolution of up to 1 s. The area under the curve (AUC) ratio between probe- and manually derived IFs was 1.07 ± 0.05 with a coefficient of variation of 0.04. However, image-derived IFs were significantly underestimated compared to the manually sampled IFs, with an AUC ratio of 0.76 ± 0.24 with a coefficient of variation of 0.32. Conclusions IF derived from the beta microprobe accurately represented the IF as measured by blood sampling, was reproducible, and was more accurate than an image-derived technique. The use of the shunt removed problems of tissue-background activity, and the use of a light-tight probe with minimal gamma sensitivity refined the system. The probe/shunt apparatus can be used in both microprobe and PET studies. PMID:22214227

  13. Plutonium and Cesium Colloid Mediated Transport

    NASA Astrophysics Data System (ADS)

    Boukhalfa, H.; Dittrich, T.; Reimus, P. W.; Ware, D.; Erdmann, B.; Wasserman, N. L.; Abdel-Fattah, A. I.

    2013-12-01

    Plutonium and cesium have been released to the environment at many different locations worldwide and are present in spent fuel at significant levels. Accurate understanding of the mechanisms that control their fate and transport in the environment is important for the management of contaminated sites, for forensic applications, and for the development of robust repositories for the disposal of spent nuclear fuel and nuclear waste. Plutonium, which can be present in the environment in multiple oxidations states and various chemical forms including amorphous oxy(hydr)oxide phases, adsorbs/adheres very strongly to geological materials and is usually immobile in all its chemical forms. However, when associated with natural colloids, it has the potential to migrate significant distances from its point of release. Like plutonium, cesium is not very mobile and tends to remain adhered to geological materials near its release point, although its transport can be enhanced by natural colloids. However, the reactivity of plutonium and cesium are very different, so their colloid-mediated transport might be significantly different in subsurface environments. In this study, we performed controlled experiments in two identically-prepared columns; one dedicated to Pu and natural colloid transport experiments, and the other to Cs and colloid experiments. Multiple flow-through experiments were conducted in each column, with the effluent solutions being collected and re-injected into the same column two times to examine the persistence and scaling behavior of the natural colloids, Pu and Cs. The data show that that a significant fraction of colloids were retained in the first elution through each column, but the eluted colloids collected from the first run transported almost conservatively in subsequent runs. Plutonium transport tracked natural colloids in the first run but deviated from the transport of natural colloids in the second and third runs. Cesium transport tracked natural

  14. Determination of trace element mineral/liquid partition coefficients in melilite and diopside by ion and electron microprobe techniques

    NASA Technical Reports Server (NTRS)

    Kuehner, S. M.; Laughlin, J. R.; Grossman, L.; Johnson, M. L.; Burnett, D. S.

    1989-01-01

    The applicability of ion microprobe (IMP) for quantitative analysis of minor elements (Sr, Y, Zr, La, Sm, and Yb) in the major phases present in natural Ca-, Al-rich inclusions (CAIs) was investigated by comparing IMP results with those of an electron microprobe (EMP). Results on three trace-element-doped glasses indicated that it is not possible to obtain precise quantitative analysis by using IMP if there are large differences in SiO2 content between the standards used to derive the ion yields and the unknowns.

  15. Electron microprobe study of lunar and planetary zoned plagioclase feldspars: An analytical and experimental study of zoning in plagioclase

    NASA Technical Reports Server (NTRS)

    Smith, R. K.; Lofgren, G. E.

    1982-01-01

    Natural and experimentally grown zoned plagioclase feldspars were examined by electron microprobe. The analyses revealed discontinuous, sector, and oscillary chemical zoning superimposed on continuous normal or reverse zoning trends. Postulated mechanisms for the origin of zoning are based on either physical changes external to the magma (P, T, H2O saturation) or kinetic changes internal to the magma (diffusion, supersaturation, growth rate). Comparison of microprobe data on natural zoned plagioclase with zoned plagioclase grown in controlled experiments show that it may be possible to distinguish zonal development resulting from physio-chemical changes to the bulk magma from local kinetic control on the growth of individual crystals.

  16. Ion and laser microprobes applied to the measurement of corrosion-produced hydrogen on a microscopic scale

    NASA Technical Reports Server (NTRS)

    Gray, H. R.

    1971-01-01

    An ion microprobe and a laser microprobe were used to measure concentrations of corrosion-produced hydrogen on a microscopic scale. Hydrogen concentrations of several thousand ppm were measured by both analytical techniques below the fracture surfaces of hot-salt stress-corroded titanium alloy specimens. This segregation of hydrogen below fracture surfaces supports a previously proposed theory that corrosion-produced hydrogen is responsible for hot-salt stress-corrosion embrittlement and cracking of titanium alloys. These advanced analytical techniques suggest great potential for many areas of stress-corrosion and hydrogen embrittlement research, quality control, and field inspection applications.

  17. A generalized description of aquatic colloidal interactions: The three-colloidal component approach

    SciTech Connect

    Buffle, J.; Wilkinson, K.J.; Stoll, S.; Filella, M.; Zhang, J.

    1998-10-01

    This paper describes several possible interactions among the different types of organic and inorganic aquatic colloids, based on present knowledge of their size, electric charge, and conformation. The physico-chemical properties of the different groups of colloids are described. Emphasis is placed on the various types of organic components, including fulvic compounds. Subsequently, the role of each colloid class is discussed with respect to homoaggregation (aggregation within a given colloid class) and heteroaggregation (aggregation among different colloid types). On the basis of a synthesis of literature reports, microscopic observations of natural colloids, experimental results obtained with model systems, and numerical simulations, it is concluded that the formation of aggregates in aquatic systems can be understood by mainly considering the roles of three types of colloids: (1) compact inorganic colloids; (2) large, rigid biopolymers; and (3) either the soil-derived fulvic compounds or their equivalent in pelagic waters, aquagenic refractory organic matter. In most natural aquatic systems, the small fulvic compounds will stabilize the inorganic colloids whereas the rigid biopolymers will destabilize them. The concentration of stable colloids in a particular aquatic system will depend on the relative proportions of these three components.

  18. Fluid-fluid demixing curves for colloid-polymer mixtures in a random colloidal matrix

    NASA Astrophysics Data System (ADS)

    Annunziata, Mario Alberto; Pelissetto, Andrea

    2011-12-01

    We study fluid-fluid phase separation in a colloid-polymer mixture adsorbed in a colloidal porous matrix close to the θ point. For this purpose we consider the Asakura-Oosawa model in the presence of a quenched matrix of colloidal hard spheres. We study the dependence of the demixing curve on the parameters that characterize the quenched matrix, fixing the polymer-to-colloid size ratio to 0.8. We find that, to a large extent, demixing curves depend only on a single parameter f, which represents the volume fraction which is unavailable to the colloids. We perform Monte Carlo simulations for volume fractions f equal to 40% and 70%, finding that the binodal curves in the polymer and colloid packing-fraction plane have a small dependence on disorder. The critical point instead changes significantly: for instance, the colloid packing fraction at criticality increases with increasing f. Finally, we observe for some values of the parameters capillary condensation of the colloids: a bulk colloid-poor phase is in chemical equilibrium with a colloid-rich phase in the matrix.

  19. Colloid Transport in Saturated Porous Media: Elimination of Attachment Efficiency in a New Colloid Transport Model

    SciTech Connect

    Landkamer, Lee L.; Harvey, Ronald W.; Scheibe, Timothy D.; Ryan, Joseph N.

    2013-05-11

    A new colloid transport model is introduced that is conceptually simple but captures the essential features of complicated attachment and detachment behavior of colloids when conditions of secondary minimum attachment exist. This model eliminates the empirical concept of collision efficiency; the attachment rate is computed directly from colloid filtration theory. Also, a new paradigm for colloid detachment based on colloid population heterogeneity is introduced. Assuming the dispersion coefficient can be estimated from tracer behavior, this model has only two fitting parameters: (1) the fraction of colloids that attach irreversibly and (2) the rate at which reversibly attached colloids leave the surface. These two parameters were correlated to physical parameters that control colloid transport such as the depth of the secondary minimum and pore water velocity. Given this correlation, the model serves as a heuristic tool for exploring the influence of physical parameters such as surface potential and fluid velocity on colloid transport. This model can be extended to heterogeneous systems characterized by both primary and secondary minimum deposition by simply increasing the fraction of colloids that attach irreversibly.

  20. Colloid transport and retention in unsaturated porous media: effect of colloid input concentration.

    PubMed

    Zhang, Wei; Morales, Verónica L; Cakmak, M Ekrem; Salvucci, Anthony E; Geohring, Larry D; Hay, Anthony G; Parlange, Jean-Yves; Steenhuis, Tammo S

    2010-07-01

    Colloids play an important role in facilitating transport of adsorbed contaminants in soils. Recent studies showed that under saturated conditions colloid retention was a function of its concentration. It is unknown if this is the case under unsaturated conditions. In this study, the effect of colloid concentration on colloid retention was investigated in unsaturated columns by increasing concentrations of colloid influents with varying ionic strength. Colloid retention was observed in situ by bright field microscopy and quantified by measuring colloid breakthrough curves. In our unsaturated experiments, greater input concentrations resulted in increased colloid retention at ionic strength above 0.1 mM, but not in deionized water (i.e., 0 mM ionic strength). Bright field microscope images showed that colloid retention mainly occurred at the solid-water interface and wedge-shaped air-water-solid interfaces, whereas the retention at the grain-grain contacts was minor. Some colloids at the air-water-solid interfaces were rotating and oscillating and thus trapped. Computational hydrodynamic simulation confirmed that the wedge-shaped air-water-solid interface could form a "hydrodynamic trap" by retaining colloids in its low velocity vortices. Direct visualization also revealed that colloids once retained acted as new retention sites for other suspended colloids at ionic strength greater than 0.1 mM and thereby could explain the greater retention with increased input concentrations. Derjaguin-Landau-Verwey-Overbeek (DLVO) energy calculations support this concept. Finally, the results of unsaturated experiments were in agreement with limited saturated experiments under otherwise the same conditions.

  1. Polymer-Induced Depletion Interaction and Its Effect on Colloidal Sedimentation in Colloid-Polymer Mixtures

    NASA Technical Reports Server (NTRS)

    Tong, Penger

    1996-01-01

    In this paper we focus on the polymer-induced depletion attraction and its effect on colloidal sedimentation in colloid-polymer mixtures. We first report a small angle neutron scattering (SANS) study of the depletion effect in a mixture of hard-sphere-like colloid and non-adsorbing polymer. Then we present results of our recent sedimentation measurements in the same colloid-polymer mixture. A key parameter in controlling the sedimentation of heavy colloidal particles is the interparticle potential U(tau), which is the work required to bring two colloidal particles from infinity to a distance tau under a give solvent condition. This potential is known to affect the average settling velocity of the particles and experimentally one needs to have a way to continuously vary U(tau) in order to test the theory. The interaction potential U(tau) can be altered by adding polymer molecules into the colloidal suspension. In a mixture of colloid and non-adsorbing polymer, the potential U(tau) can develop an attractive well because of the depletion effect, in that the polymer chains are expelled from the region between two colloidal particles when their surface separation becomes smaller than the size of the polymer chains. The exclusion of polymer molecules from the space between the colloidal particles leads to an unbalanced osmotic pressure difference pushing the colloidal particles together, which results in an effective attraction between the two colloidal particles. The polymer-induced depletion attraction controls the phase stability of many colloid-polymer mixtures, which are directly of interest to industry.

  2. Room temperature ferromagnetism in Teflon due to carbon dangling bonds.

    PubMed

    Ma, Y W; Lu, Y H; Yi, J B; Feng, Y P; Herng, T S; Liu, X; Gao, D Q; Xue, D S; Xue, J M; Ouyang, J Y; Ding, J

    2012-03-06

    The ferromagnetism in many carbon nanostructures is attributed to carbon dangling bonds or vacancies. This provides opportunities to develop new functional materials, such as molecular and polymeric ferromagnets and organic spintronic materials, without magnetic elements (for example, 3d and 4f metals). Here we report the observation of room temperature ferromagnetism in Teflon tape (polytetrafluoroethylene) subjected to simple mechanical stretching, cutting or heating. First-principles calculations indicate that the room temperature ferromagnetism originates from carbon dangling bonds and strong ferromagnetic coupling between them. Room temperature ferromagnetism has also been successfully realized in another polymer, polyethylene, through cutting and stretching. Our findings suggest that ferromagnetism due to networks of carbon dangling bonds can arise in polymers and carbon-based molecular materials.

  3. Photochemical manipulation of colloidal structures in liquid-crystal colloids

    NASA Astrophysics Data System (ADS)

    Yamamoto, T.; Tabe, Y.; Yokoyama, H.

    2007-05-01

    We investigated photochemical manipulation of physical properties and colloidal structures in liquid-crystal (LC) colloids containing azobenzene compounds. In a LC suspension where polymeric particles were dispersed in a host LC, we achieved photochemical control of light-scattering properties of the suspension. In a nematic phase, when the suspension was sandwiched with two glass plates, the film became opaque. This would be attributable to an appearance of both multidomain structures of LC alignment and mismatches of refractive indices between the materials. The opaque state turned into a transparent one when a nematic-to-isotropic phase transition was induced by the trans-to-cis photoisomerization of the azo-dye. This will result from a disappearance of both the multidomain structures and the refractive-index mismatches in the isotropic phase. The transparent film went back into the initial opaque film when the nematic phase was obtained by the cis-to-trans photoisomerization. In a LC emulsion in which glycerol or water droplets were dispersed in liquid crystals, we examined photochemical change of defect structures and inter-droplet distances by the photochemical manner. At the initial state, Saturn ring and hedgehog defects were formed around the droplets. For the glycerol droplets, we observed structural transformations between Saturn ring and boojums on irradiation with ultra-violet and visible light. For the water droplets, the inter-droplet distances varied by changing defect size on the irradiation. These phenomena would result from modulation of anchoring conditions of the droplets by the photoisomerization of the azo-dyes.

  4. Quantification of hydrophobic interaction affinity of colloids

    NASA Astrophysics Data System (ADS)

    Saini, G.; Nasholm, N.; Wood, B. D.

    2009-12-01

    Colloids play an important role in a wide variety of disciplines, including water and wastewater treatment, subsurface transport of metals and organic contaminants, migration of fines in oil reservoirs, biocolloid (virus and bacteria) transport in subsurface, and are integral to laboratory transport studies. Although the role of hydrophobicity in adhesion and transport of colloids, particularly bacteria, is well known; there is scarcity of literature regarding hydrophobicity measurement of non-bacterial colloids and other micron-sized particles. Here we detail an experimental approach based on differential partitioning of colloids between two liquid phases (hydrocarbon and buffer) as a measure of the hydrophobic interaction affinity of colloids. This assay, known as Microbial adhesion to hydrocarbons or MATH, is frequently used in microbiology and bacteriology for quantifying the hydrophobicity of microbes. Monodispersed colloids and particles, with sizes ranging from 1 micron to 33 micron, were used for the experiments. A range of hydrophobicity values were observed for different particles. The hydrophobicity results are also verified against water contact angle measurements of these particles. This liquid-liquid partitioning assay is quick, easy-to-perform and requires minimal instrumentation. Estimation of the hydrophobic interaction affinity of colloids would lead to a better understanding of their adhesion to different surfaces and subsequent transport in porous media.

  5. Structural evolution of Colloidal Gels under Flow

    NASA Astrophysics Data System (ADS)

    Boromand, Arman; Maia, Joao; Jamali, Safa

    Colloidal suspensions are ubiquitous in different industrial applications ranging from cosmetic and food industries to soft robotics and aerospace. Owing to the fact that mechanical properties of colloidal gels are controlled by its microstructure and network topology, we trace the particles in the networks formed under different attraction potentials and try to find a universal behavior in yielding of colloidal gels. Many authors have implemented different simulation techniques such as molecular dynamics (MD) and Brownian dynamics (BD) to capture better picture during phase separation and yielding mechanism in colloidal system with short-ranged attractive force. However, BD neglects multi-body hydrodynamic interactions (HI) which are believed to be responsible for the second yielding of colloidal gels. We envision using dissipative particle dynamics (DPD) with modified depletion potential and hydrodynamic interactions, as a coarse-grain model, can provide a robust simulation package to address the gel formation process and yielding in short ranged-attractive colloidal systems. The behavior of colloidal gels with different attraction potentials under flow is examined and structural fingerprints of yielding in these systems will be discussed.

  6. [The colloid milium: An observation associated with trichinosis].

    PubMed

    Okhremchuk, Ilona; Abed, Safia; Nguyen, Anh Tuan; Brandone, Nicolas; Morand, Jean-Jacques

    2016-04-01

    The colloid milium has four clinical forms: adult colloid milium, juvenile colloid milium, paracolloid (or nodular colloid degeneration) and pigmented colloid milium. We report the case of an adult colloid milium in a man of 56, who presented episodes of diffuse pruritus associated with myalgia and digestive disorders, indicative of trichinosis. He also developed gradually over the past 10 years, yellowish injuries in the mandibles and neck for whom histology objectified a colloid milium. Etiology and treatment are still unknown; association with a trichinosis is probably coincidental.

  7. Colloidal Synthesis of Gold Semishells

    PubMed Central

    Rodríguez-Fernández, Denis; Pérez-Juste, Jorge; Pastoriza-Santos, Isabel; Liz-Marzán, Luis M

    2012-01-01

    This work describes a novel and scalable colloid chemistry strategy to fabricate gold semishells based on the selective growth of gold on Janus silica particles (500 nm in diameter) partly functionalized with amino groups. The modulation of the geometry of the Janus silica particles allows us to tune the final morphology of the gold semishells. This method also provides a route to fabricating hollow gold semishells through etching of the silica cores with hydrofluoric acid. The optical properties were characterized by visible near-infrared (vis-NIR) spectroscopy and compared with simulations performed using the boundary element method (BEM). These revealed that the main optical features are located beyond the NIR region because of the large core size. PMID:24551496

  8. Diffusiophoretic Focusing of Suspended Colloids

    NASA Astrophysics Data System (ADS)

    Shi, Nan; Nery-Azevedo, Rodrigo; Abdel-Fattah, Amr I.; Squires, Todd M.

    2016-12-01

    Using a microfluidic system to impose and maintain controlled, steady-state multicomponent p H and electrolyte gradients, we present systems where the diffusiophoretic migration of suspended colloids leads them to focus at a particular position, even in steady-state gradients. We show that naively superpositing effects of each gradient may seem conceptually and qualitatively reasonable, yet is invalid due to the coupled transport of these multicomponent electrolytes. In fact, reformulating the classic theories in terms of the flux of each species (rather than local gradients) reveals rather stringent conditions that are necessary for diffusiophoretic focusing in steady gradients. Either particle surface properties must change as a function of local composition in solution (akin to isoelectric focusing in electrophoresis), or chemical reactions must occur between electrolyte species, for such focusing to be possible. The generality of these findings provides a conceptual picture for understanding, predicting, or designing diffusiophoretic systems.

  9. Oxyhydroxy Silicate Colloids: A New Type of Waterborne Actinide(IV) Colloids

    PubMed Central

    Weiss, Stephan; Hennig, Christoph; Brendler, Vinzenz; Ikeda‐Ohno, Atsushi

    2016-01-01

    Abstract At the near‐neutral and reducing aquatic conditions expected in undisturbed ore deposits or in closed nuclear waste repositories, the actinides Th, U, Np, and Pu are primarily tetravalent. These tetravalent actinides (AnIV) are sparingly soluble in aquatic systems and, hence, are often assumed to be immobile. However, AnIV could become mobile if they occur as colloids. This review focuses on a new type of AnIV colloids, oxyhydroxy silicate colloids. We herein discuss the chemical characteristics of these colloids and the potential implication for their environmental behavior. The binary oxyhydroxy silicate colloids of AnIV could be potentially more mobile as a waterborne species than the well‐known mono‐component oxyhydroxide colloids. PMID:27957406

  10. Three-dimensional ultrasonic colloidal crystals

    NASA Astrophysics Data System (ADS)

    Caleap, Mihai; Drinkwater, Bruce W.

    2016-05-01

    Colloidal assembly represents a powerful method for the fabrication of functional materials. In this article, we describe how acoustic radiation forces can guide the assembly of colloidal particles into structures that serve as microscopic elements in novel acoustic metadevices or act as phononic crystals. Using a simple three-dimensional orthogonal system, we show that a diversity of colloidal structures with orthorhombic symmetry can be assembled with megahertz-frequency (MHz) standing pressure waves. These structures allow rapid tuning of acoustic properties and provide a new platform for dynamic metamaterial applications.

  11. Transport in charged colloids driven by thermoelectricity.

    PubMed

    Würger, Alois

    2008-09-05

    We study the thermal diffusion coefficient D{T} of a charged colloid in a temperature gradient, and find that it is to a large extent determined by the thermoelectric response of the electrolyte solution. The thermally induced salinity gradient leads in general to a strong increase with temperature. The difference of the heat of transport of coions and counterions gives rise to a thermoelectric field that drives the colloid to the cold or to the warm, depending on the sign of its charge. Our results provide an explanation for recent experimental findings on thermophoresis in colloidal suspensions.

  12. Linear colloidal crystal arrays by electrohydrodynamic printing

    NASA Astrophysics Data System (ADS)

    Poon, H. F.; Saville, D. A.; Aksay, I. A.

    2008-09-01

    We use electrohydrodynamic jets of colloidal suspensions to produce arrays of colloidal crystalline stripes on surfaces. A critical factor in maintaining a stable jet is the distance of separation between the nozzle and the surface. Colloidal crystalline stripes are produced as two wetting lines of the deployed suspension merge during drying. To ensure that the two wetting lines merge, the "deployed-line-width" to "particle size" ratio is kept below a critical value so that the capillary forces overcome the frictional forces between the particles and the substrate.

  13. Food colloids research: historical perspective and outlook.

    PubMed

    Dickinson, Eric

    2011-06-09

    Trends and past achievements in the field of food colloids are reviewed. Specific mention is made of advances in knowledge and understanding in the areas of (i) structure and rheology of protein gels, (ii) properties of adsorbed protein layers, (iii) functionality derived from protein-polysaccharide interactions, and (iv) oral processing of food colloids. Amongst ongoing experimental developments, the technique of particle tracking for monitoring local dynamics and microrheology of food colloids is highlighted. The future outlook offers exciting challenges with expected continued growth in research into digestion processes, encapsulation, controlled delivery, and nanoscience.

  14. Aggregation and Gelation of Anisometric Colloidal Particles

    NASA Astrophysics Data System (ADS)

    Mohraz, Ali; Solomon, Michael J.

    2002-11-01

    The quiescent and flow-induced structure and dynamics of colloidal aggregates and gels of anisometric particles are studied by means of static and dynamic light scattering. Ground-based studies of weak gels are possible due to the submicron size of the boehmite rod suspensions investigated; however, microgravity conditions would be required for more general studies. The properties of colloidal rod suspensions are compared to typical properties of spherical particle gels to understand the role of anisotropic excluded volume on gel structure and dynamics. The structure and dynamics of colloidal aggregates and gels have long been of scientific and technological interest; however, most research has focused on suspensions of spherical particles. Yet, aggregates and gels of anisometric particles - colloidal rods and platelets - may exhibit structure and dynamics that are quite different from spherical colloids. For example, suspensions of colloidal rods gel at extremely low volume fractions and form birefringent sediments. The rheology of solutions and gels of colloidal rods and platelets differs dramatically from that of colloidal spheres. Scientifically, studies with anisometric particles offer the opportunity to assess the role of anisotropic excluded volume and particle orientation in aggregates and gels. Technologically, anisometric colloids find use in a wide range of materials such as ceramics, polymer nanocomposites, well-bore drilling fluids and magnetic storage media. Model colloidal boehmite rods of approximately monodisperse dimension and aspect ratio have been synthesized according to the method of Philipse and coworkers. In aqueous solution, these materials undergo gelation upon the addition of divalent salt. By means of a novel grafting reaction and procedure for solvent refractive index matching, the rods have also been dispersed in mixed organic solvents. In this case, gelation is induced by means of depletion interaction. We report the effect of

  15. A colloidal quantum dot spectrometer

    NASA Astrophysics Data System (ADS)

    Bao, Jie; Bawendi, Moungi G.

    2015-07-01

    Spectroscopy is carried out in almost every field of science, whenever light interacts with matter. Although sophisticated instruments with impressive performance characteristics are available, much effort continues to be invested in the development of miniaturized, cheap and easy-to-use systems. Current microspectrometer designs mostly use interference filters and interferometric optics that limit their photon efficiency, resolution and spectral range. Here we show that many of these limitations can be overcome by replacing interferometric optics with a two-dimensional absorptive filter array composed of colloidal quantum dots. Instead of measuring different bands of a spectrum individually after introducing temporal or spatial separations with gratings or interference-based narrowband filters, a colloidal quantum dot spectrometer measures a light spectrum based on the wavelength multiplexing principle: multiple spectral bands are encoded and detected simultaneously with one filter and one detector, respectively, with the array format allowing the process to be efficiently repeated many times using different filters with different encoding so that sufficient information is obtained to enable computational reconstruction of the target spectrum. We illustrate the performance of such a quantum dot microspectrometer, made from 195 different types of quantum dots with absorption features that cover a spectral range of 300 nanometres, by measuring shifts in spectral peak positions as small as one nanometre. Given this performance, demonstrable avenues for further improvement, the ease with which quantum dots can be processed and integrated, and their numerous finely tuneable bandgaps that cover a broad spectral range, we expect that quantum dot microspectrometers will be useful in applications where minimizing size, weight, cost and complexity of the spectrometer are critical.

  16. Colloid-Facilitated Transport of Radionuclides through the Vadose Zone

    SciTech Connect

    Flury, Markus; Harsh, James B.; Zachara, John M.; McCarthy, John F.; Lichtner, Peter C.

    2006-05-31

    This project seeks to improve the basic understanding of the role of colloids in facilitating the transport of contaminants in the vadose zone. We focus on three major thrusts: (1) thermodynamic stability and mobility of colloids formed by reactions of sediments with highly alkaline tank waste solutions, (2) colloid-contaminant interactions, and (3) in-situ colloid mobilization and colloid facilitated contaminant transport occurring in both contaminated and uncontaminated Hanford sediments.

  17. Polarity inversion of ζ-potential in concentrated colloidal dispersions.

    PubMed

    Manzanilla-Granados, Héctor M; Jiménez-Ángeles, Felipe; Lozada-Cassou, Marcelo

    2011-10-27

    A concentrated colloidal dispersion is studied by applying an integral equations theory to the colloidal primitive model fluid. Important effects, attributed to large size and charge and to the finite concentration of colloidal particles, are found. We observe a polarity inversion of ζ-potential for concentrated colloidal dispersions, while it is not present for a single colloidal particle at infinite dilution. An excellent qualitative agreement between our theoretical predictions and our computer simulations is observed.

  18. Tuning ferromagnetism by varying ion beam profiles

    NASA Astrophysics Data System (ADS)

    Hariwal, Rajesh V.; Malik, Hitendra K.; Asokan, K.

    2017-02-01

    Present study demonstrates a novel technique to tune the ferromagnetism at room temperature by varying the ion beam profiles from 3 to 7 mm during Carbon ion implantation in ZnO matrix and keeping other beam parameters constant. The interaction of implanted C ions with host ZnO matrix at different profiles result in variable ferromagnetism from 0.75 to 3.0  ×  10‑4 emu gm‑1 due to difference in the induced radiation pressure. Similar variation is also observed in the optical bandgap from 3.35 to 3.24 eV for different beam profiles. This study shows that the material properties can be tuned and controlled by the variation of beam profiles during the ion implantation.

  19. Transport in ferromagnet/superconductor spin valves

    NASA Astrophysics Data System (ADS)

    Moen, Evan; Valls, Oriol T.

    2017-02-01

    We consider charge transport properties in realistic, fabricable, ferromagnet/superconductor spin valves having a layered structure F1/N /F2/S , where F1 and F2 denote the ferromagnets, S the superconductor, and N the normal-metal spacer usually inserted in actual devices. Our calculation is fully self-consistent, as required to ensure that conservation laws are satisfied. We include the effects of scattering at all the interfaces. We obtain results for the device conductance G , as a function of bias voltage, for all values of the angle ϕ between the magnetizations of the F1 and F2 layers and a range of realistic values for the material and geometrical parameters in the sample. We discuss, in the context of our results for G , the relative influence of all parameters on the spin valve properties. We also study the spin current and the corresponding spin-transfer torque in F1/F2/S structures.

  20. Helical glasses near ferromagnetic quantum criticality

    NASA Astrophysics Data System (ADS)

    Thomson, S. J.; Krüger, F.; Green, A. G.

    2013-06-01

    We study the effects of quenched charge disorder on the phase reconstruction near itinerant ferromagnetic quantum critical points in three spatial dimensions. Combining a Replica-disorder average with a fermionic version of the quantum order-by-disorder mechanism, we show that weak disorder destabilizes the ferromagnetic state and enhances the susceptibility towards incommensurate, spiral magnetic ordering. The Goldstone modes of the spiral phase are governed by a 3d-XY model. The induced disorder in the pitch of the spiral generates a random anisotropy for the Goldstone modes, inducing vortex lines in the phase of the helical order and rendering the magnetic correlations short ranged with a strongly anisotropic correlation length.

  1. Angle sensing with ferromagnetic nanowire arrays

    NASA Astrophysics Data System (ADS)

    Tannous, C.; Gieraltowski, J.

    2014-01-01

    Hysteresis loops and Ferromagnetic Resonance (FMR) linewidths of Nickel ferromagnetic nanowire arrays are measured versus angle θH between the applied magnetic field angle and the common nanowire axis. Using Preisach analysis, we extract from the hysteresis loop an interaction parameter σi that strongly depends on θH. Extending the analysis to FMR lineshapes, we deduce a strong dependence of the FMR field linewidth ΔH on θH through the interaction parameter σi. Existence of a link between static (hysteresis) and dynamic (FMR) cases through θH might be exploited in contactless absolute angle sensing devices that could compete with inductive, Hall, and magnetoresistive devices.

  2. A wavelength dispersive detector for synchrotron x-ray fluorescence microprobe analysis (abstract)

    NASA Astrophysics Data System (ADS)

    Rivers, Mark L.; Sutton, Stephen R.

    1995-02-01

    The synchrotron x-ray fluorescence (SXRF) microprobe has proven to be a valuable tool for trace element research. It permits analysis down to a few parts per million of many elements in a spot size of less than 10 μm. Existing SXRF microprobes are using energy dispersive detectors (EDS), either Si(Li) or intrinsic Ge diodes. Such detectors have the advantage of collecting the entire fluorescence spectrum at once. They can also be positioned to collect a relatively large solid angle. However, EDS detectors suffer from several significant problems: resolution at Fe Kα is about 150 eV, which is roughly 60 times the natural linewidth; the maximum count rate is less than 20 000 counts/s in the entire spectrum; there is significant low-energy background due to scattering and incomplete charge collection in the device. For geochemical analyses these limitations preclude trace element analyses in the presence of a large amount of a high atomic number element: for example, trace element studies of galena (PbS) and zircon (ZrSiO4), or measurements of Cr or Ti in minerals with more than a few percent Fe or Mn. The poor energy resolution prevents the measurement of small amounts of rare-earth elements in samples with significant concentrations of first-row transition elements. Wavelength dispersive spectrometers, based upon Bragg diffraction from a bent crystal, have several distinct advantages over EDS detectors. The resolution at Fe Kα is about 10 eV, or only 4 times the natural linewidth. This permits the analysis of rare-earth elements and also lowers the background which improves detection limits to the 0.1 ppm range. The WDS spectrometer only detects a single energy at once, so it is possible to measure trace elements in the presence of intense fluorescence of a major element. We have installed a commercial wavelength dispersive spectrometer (model WDX-3PC from Microspec Corp., Fremont, CA) on the X-26A microprobe beamline at the NSLS. The spectrometer can scan the

  3. Hg diffusion in books of XVIII and XIX centuries by synchrotron microprobe

    NASA Astrophysics Data System (ADS)

    Pessanha, S.; Carvalho, M. L.; Manso, M.; Guilherme, A.; Marques, A. F.; Perez, C. A.

    2009-08-01

    The pigment vermilion (HgS) was used to color the fore edge, tail and head of books. Dissemination and quantification of Hg present in the ink used to color books from XVIII and XIX centuries are reported. Mercury is a very toxic element for the human body, therefore it is extremely important to know whether Hg tends to disseminate throughout the paper or stays confined to the borders of the books with less danger for readers. Synchrotron X-ray microprobe was used to evaluate Hg dissemination from the border to the centre of the paper sheet. The diffusion pattern of Hg was compared with the results obtained by a portable X-ray fluorescence spectrometer and mean quantitative calculations were obtained by a stationary X-ray fluorescence system with triaxial geometry. The results showed high concentrations of Hg in the external regions, but no diffusion was observed for the inner parts of the paper.

  4. Tetramine dichloro-palladium subcellular localization in the kidney: electron microprobe study.

    PubMed

    Berry, J P

    1987-01-01

    Palladium salt has been used for some time in experimental therapy protocols; with this in mind, we carried out a study of the effect of tetramine dichloro-palladium (soluble salt) upon kidney cells. Using an electron microprobe, we were able to detect the presence of palladium associated with sulfur and iron in the lysosomes of the proximal tubule cells. Our results were compared with those obtained using Cis-diaminedichloro-platinum (Cis-DDP), an anti-cancer drug used in the treatment of diverse tumors. The mechanism of intralysosomal concentration of palladium as a non soluble salt associated with sulfur appeared to be related to local sulfatase activity. Finally, iron concentration appeared to be related to the inhibition process of erythropoiesis.

  5. Transparent intracortical microprobe array for simultaneous spatiotemporal optical stimulation and multichannel electrical recording.

    PubMed

    Lee, Joonhee; Ozden, Ilker; Song, Yoon-Kyu; Nurmikko, Arto V

    2015-12-01

    Optogenetics, the selective excitation or inhibition of neural circuits by light, has become a transformative approach for dissecting functional brain microcircuits, particularly in in vivo rodent models, owing to the expanding libraries of opsins and promoters. Yet there is a lack of versatile devices that can deliver spatiotemporally patterned light while performing simultaneous sensing to map the dynamics of perturbed neural populations at the network level. We have created optoelectronic actuator and sensor microarrays that can be used as monolithic intracortical implants, fabricated from an optically transparent, electrically highly conducting semiconductor ZnO crystal. The devices can perform simultaneous light delivery and electrical readout in precise spatial registry across the microprobe array. We applied the device technology in transgenic mice to study light-perturbed cortical microcircuit dynamics and their effects on behavior. The functionality of this device can be further expanded to optical imaging and patterned electrical microstimulation.

  6. LASER MICROPROBE **4**0Ar/**3**9Ar DATING OF MINERAL GRAINS IN SITU.

    USGS Publications Warehouse

    Sutter, J.F.; Hartung, J.B.

    1984-01-01

    A laser-microprobe attached to a mass spectrometer for **4**0Ar/**3**9Ar age determination of single mineral grains in geological materials has been made operational at the US Geological Survey, Reston, VA. This microanalytical technique involves focusing a pulsed laser beam onto a sample contained in an ultra-high vacuum chamber attached to a rare-gas mass spectrometer. Argon in the neutron-irradiated sample is released by heating with the laser pulse and its isotopic composition is measured to yield an **4**0Ar/**3**9Ar age. Laser probe **4**0Ar/**3**9Ar ages of single mineral grains measured in situ can aid greatly in understanding the chronology of many geological situations where datable minerals are present but are not physically separable in quantities needed for conventional age dating.

  7. Applications to cultural heritage diagnostics at the new nuclear microprobe beam line at CEDAD

    NASA Astrophysics Data System (ADS)

    Calcagnile, L.; Quarta, G.; Demortier, G.; Maruccio, L.; D'Elia, M.

    2009-06-01

    A nuclear microprobe beam line has been installed at CEDAD (Centre for Dating and Diagnostics), University of Salento, Lecce, Italy. The beam line is connected to the -30° port of the high energy switching magnet of a 3 MV HVEE 4130HC Tandetron accelerator. It is based on an Oxford Microbeam magnetic quadrupole triplet and its general features are presented. The results of functional tests are presented showing how a lateral spatial resolution as low as ˜2 μm has been achieved in vacuum by analysing standard reference material. The results obtained in the analysis of ancient radiocarbon dated biological tissues are presented for the identification and distribution of toxic elements such as Pb.

  8. Microprobe Evaluations of Grain Boundary Segregation in KM4 and IN100

    NASA Technical Reports Server (NTRS)

    Gabb, T. P.; Smith, J. W.

    2001-01-01

    Turbine disk alloys subjected to fatigue cycles with dwells at high temperatures and stresses can fail by cracking along grain boundaries. This could be due to concentrated creep deformation or environmental attack at grain boundaries. It would be important to identify any chemical segregation along grain boundaries to aid understanding of this intergranular failure mode. The objective of this study was to evaluate the degree of chemical segregation present at the grain boundaries of two disk alloys, KM4 and IN 100. An electron microprobe employing wavelength dispersive x-ray chemical analyses was used to characterize the chemistry along multiple grain boundaries in metallographically prepared samples of each alloy. Some degrees of boron, chromium, and cobalt enrichment of grain boundaries were observed in each alloy.

  9. Application of laser microprobe (LAMMA 1000) to "fingerprinting" of coal constituents in bituminous coal

    USGS Publications Warehouse

    Lyons, P.C.; Hercules, D.M.; Morelli, J.J.; Sellers, G.A.; Mattern, D.; Thompson-Rizer, C. L.; Brown, F.W.; Millay, M.A.

    1987-01-01

    A laser microprobe (LAMMA-1000) microchemical analysis of vitrinites of different morphologies but similar reflectances within the same bituminous coal bed indicates distinct "fingerprint" spectra. The banded form of vitrinite contains Li, Ti, Ba, Sr, F, and Cl which were not detected in the nonbanded vitrinite. These differences may indicate a different plant source or the introduction of these elements from fluids mobilized during diagenesis. The nonbanded vitrinite (called corpocollinite), which was contained in a pyrite coal-ball seed fern permineralization of Myeloxylon, may have been protected from influx of these elements due to entrapment by pyrite during an early peat stage. An ion at M/Z 65, which is characteristic of the banded vitrinite, may indicate C5H5+ and, perhaps a difference in the chemical structure of the two vitrinites. These results demonstrate that "fingerprint" spectra can be obtained from vitrinite macerals by LAMMA and that these "fingerprints" have genetic implications. ?? 1987.

  10. Electron microprobe analyses of Ca, S, Mg and P distribution in incisors of Spacelab-3 rats

    NASA Technical Reports Server (NTRS)

    Rosenberg, G. D.; Simmons, D. J.

    1985-01-01

    The distribution of Ca, S, Mg and P was mapped within the incisors of Spacelab-3 rats using an electron microprobe. The data indicate that Flight rats maintained in orbit for 7 days have significantly higher Ca/Mg ratios in dentin due to both higher Ca and lower Mg content than in dentin of ground-based Controls. There is no statistical difference in distribution of either P or S within Fligth animals and Controls, but there is clear indication that, for P at least, the reason is the greater variability of the Control data. These results are consistent with those obtained on a previous NASA/COSMOS flight of 18.5 days duration, although they are not pronounced. The results further suggest that continuously growing rat incisors provide useful records of the effects of weightlessness on Ca metabolism.

  11. Volatility in the lunar crust: Trace element analyses of lunar minerals by PIXE proton microprobe

    NASA Technical Reports Server (NTRS)

    Norman, M. D.; Griffin, W. L.; Ryan, C. G.

    1993-01-01

    In situ determination of mineral compositions using microbeam techniques can characterize magma compositions through mineral-melt partitioning, and be used to investigate fine-grained or rare phases which cannot be extracted for analysis. Abundances of Fe, Mn, Sr, Ga, Zr, Y, Nb, Zn, Cu, Ni, Se, and Sb were determined for various mineral phases in a small number of lunar highlands rocks using the PIXE proton microprobe. Sr/Ga ratios of plagioclase and Mn/Zn ratios of mafic silicates show that the ferroan anorthosites and Mg-suite cumulates are depleted in volatile lithophile elements to about the same degree compared with chondrites and the Earth. This links the entire lunar crust to common processes or source compositions. In contrast, secondary sulfides in Descartes breccia clasts are enriched in chalcophile elements such as Cu, Zn, Ni, Se, and Sb, and represent a potential resource in the lunar highlands.

  12. Garnet/high-silica rhyolite trace element partition coefficients measured by ion microprobe

    USGS Publications Warehouse

    Sisson, T.W.; Bacon, C.R.

    1992-01-01

    Garnet/liquid trace element partition coefficients have been measured in situ by ion microprobe in a rhyolite from Monache Mountain, California. Partition coefficients are reported for La, Ce, Nd, Sm, Dy, Er, Yb, Sc, Ti, V, Cr, Sr, Y, and Zr. The in situ analyses avoid the problem of contamination of the garnet phase by trace element-rich accessory minerals encountered in traditional bulk phenocryst/matrix partitioning studies. The partitioning pattern for the rare earth elements (REEs, excluding Eu) is smooth and rises steeply from the light to the heavy REEs with no sharp kinks or changes in slope, unlike patterns for garnet /silicic liquid REE partitioning determined by bulk methods. This difference suggests that the previous determinations by bulk methods are in error, having suffered from contamination of the phenocryst separates. ?? 1992.

  13. Out-of-plane magnetoresistance in ferromagnet/graphene/ferromagnet spin-valve junctions

    NASA Astrophysics Data System (ADS)

    Park, Jae-Hyun; Lee, Hu-Jong

    2014-04-01

    Out-of-plane spin-injection and detection through naturally stacked graphene layers were investigated in ferromagnet/graphene/ferromagnet (FGF) junctions. We obtained a maximum magnetoresistance (MR) of 4.6% at T =4.2 K in the junction of a four-layer graphene insertion, having a very small area-junction-resistance product of 0.2 Ωμm2. According to resistance-temperature and current-voltage characteristics, the graphene layer in the FGF junction acted as a metal-like insertion rather than as an insulating barrier. A lower value for the interfacial spin asymmetry coefficient (γ =0.25±0.05) obtained from the fitting of variations with interfacial resistance implies that the spin-injection efficiency along the out-of-plane direction was reduced by spin-flip scattering at graphene/ferromagnet interfaces. Our results showed that highly transparent graphene/ferromagnet interfaces with crystalline ferromagnet (FM) electrodes are required to achieve higher spin-injection efficiency through the graphene layer in a FGF junction along the out-of-plane direction.

  14. Hierarchical Modeling of Ferromagnetic SMAs and Composites

    DTIC Science & Technology

    2006-01-01

    Gururaja 5e. TASK NUMBER 5f. WORK UNIT NUMBER 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 8 . PERFORMING ORGANIZATION REPORT NUMBER Department of...Release DistribUtion, Unlimited 13 . SUPPLEMENTARY NOTES 20060309 061 14. ABSTRACT Ferromagnetic shape memory alloys (FSMA) are key active materials for...PAGE 19b. TELEPHONE NUMBER (include area code) Standard Form 298 (Rev. 8 -98) Prescribed by ANSI Std. Z39.18 Table of Contents

  15. Multifunctional ferromagnetic disks for modulating cell function

    PubMed Central

    Vitol, Elina A.; Novosad, Valentyn; Rozhkova, Elena A.

    2013-01-01

    In this work, we focus on the methods for controlling cell function with ferromagnetic disk-shaped particles. We will first review the history of magnetically assisted modulation of cell behavior and applications of magnetic particles for studying physical properties of a cell. Then, we consider the biological applications of the microdisks such as the method for induction of cancer cell apoptosis, controlled drug release, hyperthermia and MRI imaging. PMID:23766544

  16. Ferromagnetism in doped or undoped spintronics nanomaterials

    NASA Astrophysics Data System (ADS)

    Qiang, You

    2010-10-01

    Much interest has been sparked by the discovery of ferromagnetism in a range of oxide doped and undoped semiconductors. The development of ferromagnetic oxide semiconductor materials with giant magnetoresistance (GMR) offers many advantages in spintronics devices for future miniaturization of computers. Among them, TM-doped ZnO is an extensively studied n-type wide-band-gap (3.36 eV) semiconductor with a tremendous interest as future mini-computer, blue light emitting, and solar cells. In this talk, Co-doped ZnO and Co-doped Cu2O semiconductor nanoclusters are successfully synthesized by a third generation sputtering-gas-aggregation cluster technique. The Co-doped nanoclusters are ferromagnetic with Curie temperature above room temperature. Both of Co-doped nanoclusters show positive magnetoresistance (PMR) at low temperature, but the amplitude of the PMRs shows an anomalous difference. For similar Co doping concentration at 5 K, PMR is greater than 800% for Co-doped ZnO but only 5% for Co-doped Cu2O nanoclusters. Giant PMR in Co-doped ZnO which is attributed to large Zeeman splitting effect has a linear dependence on applied magnetic field with very high sensitivity, which makes it convenient for the future spintronics applications. The small PMR in Co-doped Cu2O is related to its vanishing density of states at Fermi level. Undoped Zn/ZnO core-shell nanoparticle gives high ferromagnetic properties above room temperature due to the defect induced magnetization at the interface.

  17. Coarsening and percolation in a disordered ferromagnet

    NASA Astrophysics Data System (ADS)

    Corberi, Federico; Cugliandolo, Leticia F.; Insalata, Ferdinando; Picco, Marco

    2017-02-01

    By studying numerically the phase-ordering kinetics of a two-dimensional ferromagnetic Ising model with quenched disorder (either random bonds or random fields) we show that a critical percolation structure forms at an early stage. This structure is then rendered more and more compact by the ensuing coarsening process. Our results are compared to the nondisordered case, where a similar phenomenon is observed, and they are interpreted within a dynamical scaling framework.

  18. Prosthetic Tool For Holding Small Ferromagnetic Parts

    NASA Technical Reports Server (NTRS)

    Norton, William E.; Carden, James R.; Belcher, Jewell G., Jr.; Vest, Thomas W.

    1995-01-01

    Tool attached to prosthetic hand or arm enables user to hold nails, screws, nuts, rivets, and other small ferromagnetic objects on small magnetic tip. Device adjusted to hold nail or screw at proper angle for hammering or for use of screwdriver, respectively. Includes base connector with threaded outer surface and lower male member inserted in standard spring-action, quick-connect/quick-disconnect wrist adapter on prosthetic hand or arm.

  19. Raman characterization of bulk ferromagnetic nanostructured graphite

    NASA Astrophysics Data System (ADS)

    Pardo, Helena; Divine Khan, Ngwashi; Faccio, Ricardo; Araújo-Moreira, F. M.; Fernández-Werner, Luciana; Makarova, Tatiana; Mombrú, Álvaro W.

    2012-08-01

    Raman spectroscopy was used to characterize bulk ferromagnetic graphite samples prepared by controlled oxidation of commercial pristine graphite powder. The G:D band intensity ratio, the shape and position of the 2D band and the presence of a band around 2950 cm-1 showed a high degree of disorder in the modified graphite sample, with a significant presence of exposed edges of graphitic planes as well as a high degree of attached hydrogen atoms.

  20. Ferromagnetic nanoparticles suspensions in twisted nematic

    NASA Astrophysics Data System (ADS)

    Cîrtoaje, Cristina; Petrescu, Emil; Stan, Cristina; Creangă, Dorina

    2016-05-01

    Ferromagnetic nanoparticles insertions in nematic liquid crystals (NLC) in twisted configuration are studied and a theoretical model is proposed to explain the results. Experimental observation revealed that nanoparticles tend to overcrowd in long strings parallel to the rubbing direction of the alignment substrate of the LC cell. Their behavior under external field was studied and their interaction with their nematic host is described using elastic continuum theory.

  1. The laser microprobe: a technique for extracting carbon, nitrogen, and oxygen from solid samples for isotopic measurements.

    NASA Astrophysics Data System (ADS)

    Franchi, I. A.; Wright, I. P.; Gibson, E. K., Jr.; Pillinger, C. T.

    1986-03-01

    The laser microprobe extraction technique has been adapted for the determination of concentrations and stable isotopic compositions of carbon, nitrogen, and oxygen. Initial studies on the distribution of nitrogen in an iron meteorite (Uwet) and a carbonaceous chondrite (Murchison) have been undertaken.

  2. U/Th dating by SHRIMP RG ion-microprobe mass spectrometry using single ion-exchange beads

    USGS Publications Warehouse

    Bischoff, J.L.; Wooden, J.; Murphy, F.; Williams, Ross W.

    2005-01-01

    We present a new analytical method for U-series isotopes using the SHRIMP RG (Sensitive High mass Resolution Ion MicroProbe) mass spectrometer that utilizes the preconcentration of the U-series isotopes from a sample onto a single ion-exchange bead. Ion-microprobe mass spectrometry is capable of producing Th ionization efficiencies in excess of 2%. Analytical precision is typically better than alpha spectroscopy, but not as good as thermal ionization mass spectroscopy (TIMS) and inductively coupled plasma multicollector mass spectrometry (ICP-MS). Like TIMS and ICP-MS the method allows analysis of small samples sizes, but also adds the advantage of rapidity of analysis. A major advantage of ion-microprobe analysis is that U and Th isotopes are analyzed in the same bead, simplifying the process of chemical separation. Analytical time on the instrument is ???60 min per sample, and a single instrument-loading can accommodate 15-20 samples to be analyzed in a 24-h day. An additional advantage is that the method allows multiple reanalyses of the same bead and that samples can be archived for reanalysis at a later time. Because the ion beam excavates a pit only a few ??m deep, the mount can later be repolished and reanalyzed numerous times. The method described of preconcentrating a low concentration sample onto a small conductive substrate to allow ion-microprobe mass spectrometry is potentially applicable to many other systems. Copyright ?? 2005 Elsevier Ltd.

  3. Heavy ion microprobes: a unique tool for bystander research and other radiobiological applications

    NASA Astrophysics Data System (ADS)

    Voss, K. O.; Fournier, C.; Taucher-Scholz, G.

    2008-07-01

    The risk assessment for low doses of high linear energy transfer (LET) radiation has been challenged by a growing body of experimental evidence showing that non-irradiated bystander cells can receive signals from irradiated cells to elicit a variety of cellular responses. These may be significant for radiation protection but also for radiation therapy using heavy ions. Charged particle microbeams for radiobiological application provide a unique means to address these issues by allowing the precise irradiation of single cells with a counted numbers of ions. Here, we focus specifically on heavy ion microbeam facilities currently in use for biological purposes, describing their technical features and biological results. Typically, ion species up to argon are used for targeted biological irradiation at the vertically collimated microbeam at JAEA (Takasaki, Japan). At the SNAKE microprobe in Munich, mostly oxygen ions have been used in a horizontal focused beam line for cell targeting. At GSI (Darmstadt), a horizontal microprobe with a focused beam for defined targeting using ion species up to uranium is operational. The visualization of DNA damage response proteins relocalizing to defined sites of ion traversal has been accomplished at the three heavy ion microbeam facilities described above and is used to study mechanistic aspects of heavy ion effects. However, bystander studies have constituted the main focus of biological applications. While for cell inactivation and effects on cell cycle progression a response of non-targeted cells has been described at JAEA and GSI, respectively, in part controversial results have been obtained for the induction of DNA damage measured by double-strand formation or at the cytogenetic level. The results emphasize the influence of the cellular environment, and standardization of experimental conditions for cellular studies at different facilities as well as the investigation of bystander effects in tissue will be the aims of future

  4. Fabrication of an 8:1 ellipsoidal mirror for a synchrotron x-ray microprobe

    SciTech Connect

    Jones, K.W.; Takacs, P.Z.; Hastings, J.B.; Casstevens, J.M.; Pionke, C.D.

    1987-01-11

    The fabrication of an 8:1 demagnifying ellipsoidal mirror to be used for an x-ray microprobe at the National Synchrotron Light Source X-26 beam port is described. The design aim was to produce a mirror that could be used over the photon energy range from about 3 to 17 keV. The 300-mm long mirror was required to operate at a grazing angle of 5 mr. The semimajor axis was 4500 mm and the semiminor axis 14.142 mm. Surface roughness of 1 nm or less and slope errors of 1 arc second parallel to the long axis and 200 arc seconds parallel to the short direction were specified. Production of the first electroless nickel-coated aluminum mirror using a diamond-turning technique has been completed. The mirror meets the 1 arc sec surface figure specification except for areas near the ends of the mirror. The reasons for these deviations arise from subtle details of the diamond-turning process which have not been fully incorporated in to the computer program that controls the diamond-turning machines. Further work in computer correction of repeatable errors of the diamond-turning machine can eliminate the waviness at the ends of the mirror. The diamond-turned mirror surface was not fully polished under this effort and therefore does not meet the roughness specification; however, surface smoothness of a fully polished cylindrical mirror manufactured using the same techniques does not meet the specification. It can be concluded that it is now technically feasible to meet the required specifications for the mirror and that the x-ray microprobe based on its use can be achieved.

  5. Challenge to Electron Microprobe Analysis by Nano-features in Geo-materials

    NASA Astrophysics Data System (ADS)

    Ma, C.; Rossman, G. R.

    2007-12-01

    With current high-resolution analytical scanning electron microscope and transmission electron microscope technology, nano-features (i.e., inclusions, exsolutions, pores) are being discovered in many common geo- materials routinely analyzed by EPMA. Most EPMA instruments have a thermionic electron gun with a tungsten "hairpin" type filament and operate at such high probe currents that they do not produce the high resolution imaging that field emission SEMs do. Such nano-features present difficulties to electron microprobe analysis of the host materials. It is an accuracy issue. Presented here are a few examples. Nano-inclusions like magnetite or pyroxene are common in volcanic glass. Massive rose quartz contains nano-fibers of a dumortierite-related phase that is pink, which is the cause of rose color and optical star effects. Blue quartz has nano-inclusions of ilmenite. Nano-exsolutions and nano-inclusions occur in some feldspars (moonstone and sunstone). Nano- pores in corundum and opals are observed. Thin coatings of nanocrystals on grains of hematite bring Al and P (or As) into the analytical picture. In each of these cases, electron microprobe analyses of host materials were contaminated or affected by the nano-features. For a complete analytical description of a geo-material it is necessary to first examine probe samples under an optical microscope (400× minimum) and a FE-SEM. If the sample contains nano-features, it would then be necessary to combine FIB and TEM-EDS-EELS to comprehensively analyze the host composition.

  6. An X-Ray Microprobe for In-Situ Stone and Wood Characterization

    NASA Astrophysics Data System (ADS)

    Lovoi, P.; Asmus, J. F.

    NonDestructive Testing (NDT) has become an essential ingredient in the conservation of artworks and in the preservation of historic buildings. In many instances it is necessary to characterize the underlying strata of an artistic or historic object in order to plan technical conservation measures, to understand its history, to authenticate it, or to search for hidden features. X-ray and gamma-ray radiography as well as infrared imaging have been ubiquitous in conservation practice for generations. Recent decades have also seen the introduction of ultrasonic imaging, thermovision, x-ray fluorescence, neutron activation analyses, holographic interferometry, isotopic and trace element analyses, the electron microprobe, the laser microprobe, microwave impulse radar, eddy current imaging, and fiber-optic imaging. Unfortunately, for mainstream conservation and preservation some of these technologies are too costly or difficult to be implemented in any general way. In other instances penetration is too superficial or signals from the depth of interest are masked by interferences. Nevertheless, sufficiently important problems have arisen to warrant the utilization of each of the above NDT technologies as well as still others. A new diagnostic device has been introduced into the conservation field. Stone characterization analyses are reported using miniature x-ray devices that can be inserted into cracks and holes in specimens of interest. The family of x-ray tubes employed in these studies range in diameter from 1 to 6 mm. Operating voltages up to 50 kV are available. Electrical power and cooling are delivered through a flexible cable that has a bend diameter of less than 3 cm. Thus, it was possible to insert the x-ray tube into small holes and cracks in marble stones. In this manner radiographs of the outer strata of stones (and embedded metal pins) have been produced without having to transmit through the entire thickness of large blocks. It should also be possible to

  7. Fabrication of wear-resistant silicon microprobe tips for high-speed surface roughness scanning devices

    NASA Astrophysics Data System (ADS)

    Wasisto, Hutomo Suryo; Yu, Feng; Doering, Lutz; Völlmeke, Stefan; Brand, Uwe; Bakin, Andrey; Waag, Andreas; Peiner, Erwin

    2015-05-01

    Silicon microprobe tips are fabricated and integrated with piezoresistive cantilever sensors for high-speed surface roughness scanning systems. The fabrication steps of the high-aspect-ratio silicon microprobe tips were started with photolithography and wet etching of potassium hydroxide (KOH) resulting in crystal-dependent micropyramids. Subsequently, thin conformal wear-resistant layer coating of aluminum oxide (Al2O3) was demonstrated on the backside of the piezoresistive cantilever free end using atomic layer deposition (ALD) method in a binary reaction sequence with a low thermal process and precursors of trimethyl aluminum and water. The deposited Al2O3 layer had a thickness of 14 nm. The captured atomic force microscopy (AFM) image exhibits a root mean square deviation of 0.65 nm confirming the deposited Al2O3 surface quality. Furthermore, vacuum-evaporated 30-nm/200-nm-thick Au/Cr layers were patterned by lift-off and served as an etch mask for Al2O3 wet etching and in ICP cryogenic dry etching. By using SF6/O2 plasma during inductively coupled plasma (ICP) cryogenic dry etching, micropillar tips were obtained. From the preliminary friction and wear data, the developed silicon cantilever sensor has been successfully used in 100 fast measurements of 5- mm-long standard artifact surface with a speed of 15 mm/s and forces of 60-100 μN. Moreover, the results yielded by the fabricated silicon cantilever sensor are in very good agreement with those of calibrated profilometer. These tactile sensors are targeted for use in high-aspect-ratio microform metrology.

  8. ICP Source with Immersed Ferromagnetic Inductor

    NASA Astrophysics Data System (ADS)

    Godyak, Valery

    2013-09-01

    Inductively coupled plasma (ICP) sources have found a wide range of applications in various areas of plasma science and technology. Among different ICP topology, ICPs with immersed inductors have benefits (compared to ICPs with helical side or flat top inductors) of better coupling and electromagnetic (EM) field self-screening by the plasma surrounding the inductor. This allows for EM-free otter plasma boundary, thus making an ICP chamber entirely of metal or glass, with no EM radiation outside the plasma. It's been long known that ICP enhanced with ferromagnetic core immersed inductor is applicable in rf light sources and has demonstrated good performance. In this presentation we report a detailed experimental study of the electrical and plasma characteristics of compact ICPs with immersed ferromagnetic inductors in argon and xenon gas. The extremely high plasma transfer efficiency of this plasma source has been demonstrated in a wide range of gas pressure and rf power. A compact plasma cathode built with ICP having an immersed ferromagnetic inductor, and operating at 70-200 W has shown high power transfer efficiency of 97%, and electron emission efficiency of 25 mA/W. These data are superior compared to those demonstrated for other plasma cathodes.

  9. Tunable Magnon Weyl Points in Ferromagnetic Pyrochlores.

    PubMed

    Mook, Alexander; Henk, Jürgen; Mertig, Ingrid

    2016-10-07

    The dispersion relations of magnons in ferromagnetic pyrochlores with Dzyaloshinskii-Moriya interaction are shown to possess Weyl points, i. e., pairs of topologically nontrivial crossings of two magnon branches with opposite topological charge. As a consequence of their topological nature, their projections onto a surface are connected by magnon arcs, thereby resembling closely Fermi arcs of electronic Weyl semimetals. On top of this, the positions of the Weyl points in reciprocal space can be tuned widely by an external magnetic field: rotated within the surface plane, the Weyl points and magnon arcs are rotated as well; tilting the magnetic field out of plane shifts the Weyl points toward the center Γ[over ¯] of the surface Brillouin zone. The theory is valid for the class of ferromagnetic pyrochlores, i. e., three-dimensional extensions of topological magnon insulators on kagome lattices. In this Letter, we focus on the (111) surface, identify candidates of established ferromagnetic pyrochlores which apply to the considered spin model, and suggest experiments for the detection of the topological features.

  10. Spin polarization in half-metallic ferromagnets

    NASA Astrophysics Data System (ADS)

    Biasini, M.; Mills, A. P., Jr.

    2005-03-01

    Ferromagnetic contacts for spin injection and analysis are key components determining the performance of spintronic devices. For practical applications the materials for these contacts should have a high electron spin polarization at the Fermi surface (FS) at room temperature. We need to develop suitable new high Curie-temperature ferromagnets from the class of half metallic compounds that are theoretically ideal for spintronics [1]. We point out that a polarized slow positron probe combined with the two-dimensional angular correlation of annihilation radiation (2D-ACAR) technique [2] would allow unambiguous, direct, room-temperature determinations of the spin polarization of the conducting electrons at the FS of important candidate spintronic ferromagnetic thin films and single crystals. The electron spin polarization at the FS may be deduced directly from the amplitudes of the discontinuities in the electron occupation number at the Fermi momentum for two directions of the polarization of a positron probe relative to the saturating magnetic field direction [3]. Work supported in part by NSF grants DMR 0216927 and PHY 0140382 and by DOD/DARPA/DMEA, Award DMEA90-02-2-0216. [1] I. Zutic et al., Rev. Mod. Phys. 76, 323 (2004).[2] S. Berko, in Positron Solid-State Physics, Brant and Dupasquier, eds. (North-Holland, 1983) p. 64.[3] K. E. H. M. Hanssen et al., Phys. Rev. B 42, 1533 (1990).

  11. Robust ferromagnetism carried by antiferromagnetic domain walls

    NASA Astrophysics Data System (ADS)

    Hirose, Hishiro T.; Yamaura, Jun-Ichi; Hiroi, Zenji

    2017-02-01

    Ferroic materials, such as ferromagnetic or ferroelectric materials, have been utilized as recording media for memory devices. A recent trend for downsizing, however, requires an alternative, because ferroic orders tend to become unstable for miniaturization. The domain wall nanoelectronics is a new developing direction for next-generation devices, in which atomic domain walls, rather than conventional, large domains themselves, are the active elements. Here we show that atomically thin magnetic domain walls generated in the antiferromagnetic insulator Cd2Os2O7 carry unusual ferromagnetic moments perpendicular to the wall as well as electron conductivity: the ferromagnetic moments are easily polarized even by a tiny field of 1 mT at high temperature, while, once cooled down, they are surprisingly robust even in an inverse magnetic field of 7 T. Thus, the magnetic domain walls could serve as a new-type of microscopic, switchable and electrically readable magnetic medium which is potentially important for future applications in the domain wall nanoelectronics.

  12. Role of reversible susceptibility in ferromagnetic hysteresis

    NASA Astrophysics Data System (ADS)

    Schneider, Carl S.

    2002-05-01

    An equation of state based upon saturation magnetization, Ms, coercive field, Hc, and the reversible susceptibility function of magnetization is proposed for ferromagnetic hysteresis. Reversible susceptibility divided by the initial susceptibility is the anisotropy function of magnetization, χr, ranging from one in the demagnetized state to zero at saturation, and varying with magnetic history. Its dependence on scaled magnetization, m=M/Ms on the interval (-1,1) varies with material, allowing characterization of anisotropy classes. Precise measurements have been made of reversible susceptibility, initial and saturate magnetization curves, and loops for Orthonol™, annealed 3% nickel steel and as-received 1018 steel, representing crystals, isotropic polycrystals and composite ferromagnets, respectively. Magnetization change is the product of the reversible susceptibility, change in the applied field and the cooperative function due to domain interactions. This function is 1+βm for the virgin curve with half this slope from any reversal, where β=Ms/XiHc is the hysteresis coefficient. Variation of β for 1018 steel is due to distributed coercivities, and causes sigmoid B(H) curves. In the scaled field representation, where h=H/Hc, the cooperative function is 1/(1-hχr), a hyperbolic field dependence smeared by the anisotropy function. Constant anisotropy causes closed hysteresis loops, while variable anisotropy causes creeping of cycled asymmetric loops. In ferromagnetism, 1/χ=1/χr-h, normal scaled reluctivity is reduced from its reversible value by the scaled field.

  13. Dilute ferromagnetic semiconductors: Physics and spintronic structures

    NASA Astrophysics Data System (ADS)

    Dietl, Tomasz; Ohno, Hideo

    2014-01-01

    This review compiles results of experimental and theoretical studies on thin films and quantum structures of semiconductors with randomly distributed Mn ions, which exhibit spintronic functionalities associated with collective ferromagnetic spin ordering. Properties of p-type Mn-containing III-V as well as II-VI, IV-VI, V2-VI3, I-II-V, and elemental group IV semiconductors are described, paying particular attention to the most thoroughly investigated system (Ga,Mn)As that supports the hole-mediated ferromagnetic order up to 190 K for the net concentration of Mn spins below 10%. Multilayer structures showing efficient spin injection and spin-related magnetotransport properties as well as enabling magnetization manipulation by strain, light, electric fields, and spin currents are presented together with their impact on metal spintronics. The challenging interplay between magnetic and electronic properties in topologically trivial and nontrivial systems is described, emphasizing the entangled roles of disorder and correlation at the carrier localization boundary. Finally, the case of dilute magnetic insulators is considered, such as (Ga,Mn)N, where low-temperature spin ordering is driven by short-ranged superexchange that is ferromagnetic for certain charge states of magnetic impurities.

  14. Robust ferromagnetism carried by antiferromagnetic domain walls

    PubMed Central

    Hirose, Hishiro T.; Yamaura, Jun-ichi; Hiroi, Zenji

    2017-01-01

    Ferroic materials, such as ferromagnetic or ferroelectric materials, have been utilized as recording media for memory devices. A recent trend for downsizing, however, requires an alternative, because ferroic orders tend to become unstable for miniaturization. The domain wall nanoelectronics is a new developing direction for next-generation devices, in which atomic domain walls, rather than conventional, large domains themselves, are the active elements. Here we show that atomically thin magnetic domain walls generated in the antiferromagnetic insulator Cd2Os2O7 carry unusual ferromagnetic moments perpendicular to the wall as well as electron conductivity: the ferromagnetic moments are easily polarized even by a tiny field of 1 mT at high temperature, while, once cooled down, they are surprisingly robust even in an inverse magnetic field of 7 T. Thus, the magnetic domain walls could serve as a new-type of microscopic, switchable and electrically readable magnetic medium which is potentially important for future applications in the domain wall nanoelectronics. PMID:28195565

  15. Biocompatible Ferromagnetic Cr-Trihalide Monolayers

    NASA Astrophysics Data System (ADS)

    Sun, Qiang

    Cr with an electronic configuration of 3d54s1 possesses the largest atomic magnetic moment (6µB) of all elements in the 3d transition metal series. Furthermore, the trivalent chromium (Cr3+) is biocompatible and is widely found in food and supplements. Here using first principles calculations combined with Monte Carlo simulations based on Ising model, we systematically study a class of 2D ferromagnetic monolayers CrX3 (X = Cl, Br, I). The feasibility of exfoliation from their layered bulk phase is confirmed by the small cleavage energy and high in-plane stiffness. Spin-polarized calculations, combined with self consistently determined Hubbard U that accounts for strong correlation energy, demonstrate that CrX3 (X =Cl, Br, I) monolayers are ferromagnetic and Cr is trivalent and carries a magnetic moment of 3µB, the resulting Cr3+ ions are biocompatible. The corresponding Curie temperatures for CrCl3 CrBr3 CrI3 are are found to 66, 86, and 107 K, respectively, which can be increased to 323, 314, 293 K by hole doping. The biocompatibility and ferromagnetism render these Cr-containing trichalcogenide monolayers unique for applications.

  16. Tunable Magnon Weyl Points in Ferromagnetic Pyrochlores

    NASA Astrophysics Data System (ADS)

    Mook, Alexander; Henk, Jürgen; Mertig, Ingrid

    2016-10-01

    The dispersion relations of magnons in ferromagnetic pyrochlores with Dzyaloshinskii-Moriya interaction are shown to possess Weyl points, i. e., pairs of topologically nontrivial crossings of two magnon branches with opposite topological charge. As a consequence of their topological nature, their projections onto a surface are connected by magnon arcs, thereby resembling closely Fermi arcs of electronic Weyl semimetals. On top of this, the positions of the Weyl points in reciprocal space can be tuned widely by an external magnetic field: rotated within the surface plane, the Weyl points and magnon arcs are rotated as well; tilting the magnetic field out of plane shifts the Weyl points toward the center Γ ¯ of the surface Brillouin zone. The theory is valid for the class of ferromagnetic pyrochlores, i. e., three-dimensional extensions of topological magnon insulators on kagome lattices. In this Letter, we focus on the (111) surface, identify candidates of established ferromagnetic pyrochlores which apply to the considered spin model, and suggest experiments for the detection of the topological features.

  17. Robust ferromagnetism carried by antiferromagnetic domain walls.

    PubMed

    Hirose, Hishiro T; Yamaura, Jun-Ichi; Hiroi, Zenji

    2017-02-14

    Ferroic materials, such as ferromagnetic or ferroelectric materials, have been utilized as recording media for memory devices. A recent trend for downsizing, however, requires an alternative, because ferroic orders tend to become unstable for miniaturization. The domain wall nanoelectronics is a new developing direction for next-generation devices, in which atomic domain walls, rather than conventional, large domains themselves, are the active elements. Here we show that atomically thin magnetic domain walls generated in the antiferromagnetic insulator Cd2Os2O7 carry unusual ferromagnetic moments perpendicular to the wall as well as electron conductivity: the ferromagnetic moments are easily polarized even by a tiny field of 1 mT at high temperature, while, once cooled down, they are surprisingly robust even in an inverse magnetic field of 7 T. Thus, the magnetic domain walls could serve as a new-type of microscopic, switchable and electrically readable magnetic medium which is potentially important for future applications in the domain wall nanoelectronics.

  18. Quantum oscillations in magnetically doped colloidal nanocrystals.

    PubMed

    Ochsenbein, Stefan T; Gamelin, Daniel R

    2011-02-01

    Progress in the synthesis of colloidal quantum dots has recently provided access to entirely new forms of diluted magnetic semiconductors, some of which may find use in quantum computation. The usefulness of a spin qubit is defined by its Rabi frequency, which determines the operation time, and its coherence time, which sets the error correction window. However, the spin dynamics of magnetic impurity ions in colloidal doped quantum dots remain entirely unexplored. Here, we use pulsed electron paramagnetic resonance spectroscopy to demonstrate long spin coherence times of ∼0.9 µs in colloidal ZnO quantum dots containing the paramagnetic dopant Mn(2+), as well as Rabi oscillations with frequencies ranging between 2 and 20 MHz depending on microwave power. We also observe electron spin echo envelope modulations of the Mn(2+) signal due to hyperfine coupling with protons outside the quantum dots, a situation unique to the colloidal form of quantum dots, and not observed to date.

  19. Luminol chemiluminescence catalysed by colloidal platinum nanoparticles.

    PubMed

    Xu, Sheng-Liang; Cui, Hua

    2007-01-01

    Platinum colloids prepared by the reduction of hexachloroplatinic acid with citrate in the presence of different stabilizers were found to enhance the chemiluminescence (CL) of the luminol-H(2)O(2) system, and the most intensive CL signals were obtained with citrate-protected Pt colloids synthesized with citrate as both a reductant and a stabilizer. Light emission was intense and reproducible. Transmission electron microscopy and X-ray photoelectron spectroscopy studies were conducted before and after the CL reaction to investigate the possible CL enhancement mechanism. It is suggested that this CL enhancement is attributed to the catalysis of platinum nanoparticles, which could accelerate the electron-transfer process and facilitate the CL radical generation in aqueous solution. The effects of Pt colloids prepared by the hydroborate reduction were also investigated. The application of the luminol-H(2)O(2)-Pt colloids system was exploited for the determination of compounds such as uric acid, ascorbic acid, phenols and amino acids.

  20. Computer simulations of charged colloids in confinement.

    PubMed

    Puertas, Antonio M; de las Nieves, F Javier; Cuetos, Alejandro

    2015-02-15

    We study by computer simulations the interaction between two similarly charged colloidal particles confined between parallel planes, in salt free conditions. Both the colloids and ions are simulated explicitly, in a fine-mesh lattice, and the electrostatic interaction is calculated using Ewald summation in two dimensions. The internal energy is measured by setting the colloidal particles at a given position and equilibrating the ions, whereas the free energy is obtained introducing a bias (attractive) potential between the colloids. Our results show that upon confining the system, the internal energy decreases, resulting in an attractive contribution to the interaction potential for large charges and strong confinement. However, the loss of entropy of the ions is the dominant mechanism in the interaction, irrespective of the confinement of the system. The interaction potential is therefore repulsive in all cases, and is well described by the DLVO functional form, but effective values have to be used for the interaction strength and Debye length.

  1. A Course in Colloid and Surface Science.

    ERIC Educational Resources Information Center

    Scamehorn, John F.

    1984-01-01

    Describes a course for chemical engineers, chemists, and petroleum engineers that focuses on colloid and surface science. Major topic areas in the course include capillarity, surface thermodynamics, adsorption contact angle, micelle formation, solubilization in micelles, emulsions, foams, and applications. (JN)

  2. Self-similarity in active colloid motion

    NASA Astrophysics Data System (ADS)

    Constant, Colin; Sukhov, Sergey; Dogariu, Aristide

    The self-similarity of displacements among randomly evolving systems has been used to describe the foraging patterns of animals and predict the growth of financial systems. At micron scales, the motion of colloidal particles can be analyzed by sampling their spatial displacement in time. For self-similar systems in equilibrium, the mean squared displacement increases linearly in time. However, external forces can take the system out of equilibrium, creating active colloidal systems, and making this evolution more complex. A moment scaling spectrum of the distribution of particle displacements quantifies the degree of self-similarity in the colloid motion. We will demonstrate that, by varying the temporal and spatial characteristics of the external forces, one can control the degree of self-similarity in active colloid motion.

  3. Thin film interference of colloidal thin films.

    PubMed

    Cong, Hailin; Cao, Weixiao

    2004-09-14

    A stairlike colloidal crystal thin film composed of poly(styrene-methyl methacrylate-acrylic acid) (P(St-MMA-AA)) monodispersed colloids was fabricated on an inclined silicon substrate. Different bright colors were observed on the various parts of the film with different layers as white light irradiated perpendicularly on it. The relationship between the colors and layers of the film was investigated and discussed according to the principle of thin film interference. On the basis of the phenomenon of thin film interference, a one-layer colloidal film having uniform color was researched and it would display diverse colors before and after swollen by styrene (St). A circular stairlike colloidal film was achieved to mimic the colors of the peacock tail feather.

  4. Hemorrhagic Colloid Cyst Presenting with Acute Hydrocephaly

    PubMed Central

    Akhavan, Reza; Zandi, Behrouz; Pezeshki-Rad, Masoud; Farrokh, Donya

    2017-01-01

    Colloid cysts are benign slow-growing cystic lesions located on the roof of the third ventricle that usually present with symptoms related to gradual rise of intracranial pressure. They mostly remain asymptomatic and sometimes grow progressively and cause diverse symptoms associated with increased intracranial pressure such as headache, diplopia, and sixth cranial nerve palsy. Here we report a 47-year-old female who presented to the emergency department with acute severe headache and nausea/vomiting. On MRI examination acute hydrocephaly due to hemorrhagic colloid cyst was detected. Acute hemorrhage in colloid cysts is extremely rare and may present with symptoms of acute increase in the intracranial pressure. Intracystic hemorrhage is very rarely reported as a complication of colloid cyst presenting with paroxysmal symptoms of acute hydrocephaly. PMID:28210514

  5. Sulfonated nanoporous colloidal films and membranes

    NASA Astrophysics Data System (ADS)

    Smith, Joanna Jane

    The objective of this thesis is to describe the preparation and investigation of a new class of proton-conducting membrane materials, namely, nanoporous colloidal membranes whose proton conductivity results from the nanopore surface modification with organic molecules carrying acid functionalities. Both the proton transport and ion transport were studied in nanoporous silica colloidal crystals that were surface modified with sulfonic groups. First, the transport of ions was studied through sulfonated silica colloidal films that were supported on platinum electrodes using cyclic voltammetry. The surface of self-assembled nanoporous silica colloidal crystalline films was sulfonated using 1,3-propanesultone. We found that the flux of anions through the sulfonated colloidal films is reduced, while the flux of cations is increased, compared to the unmodified colloidal films. Second, the proton transport in free-standing assemblies of surface-sulfonated silica nanospheres, either randomly packed or self-assembled into a close-packed arrangement, were studied. It was demonstrated that colloidal assemblies prepared using surface-sulfonated silica nanospheres posses proton conductivity that depends on the ordering of the material, temperature and relative humidity. Based on the comparison between the close-packed and disordered assemblies made of the same spheres, we conclude that the increase in structural organization of the self-assembled colloidal materials leads to increased proton conductivity and better water retention. Next free-standing colloidal membranes with a relatively large area and no mechanical defects were prepared by sintering silica colloidal films. The sintered membranes were then surface rehydroxylated, which restores the surface silanol groups, and then can be chemically modified. Finally, sintered self-assembled nanoporous silica colloidal crystals were modified with poly(sulfopropyl-methacrylate) (pSPM) and poly(stryrenesulfonic acid) (pSSA) brushes

  6. Colloid Thrusters, Physics, Fabrication and Performance

    DTIC Science & Technology

    2005-11-17

    Murray, Paulo Lozano and Manuel Martinez-Sanchez, "Mass Spectrometric Analysis of Colloid Thruster Ion Emission from Selected Propellants", JOURNAL...OF PROPULSION AND POWER Vol. 21, No. 3, May-June 2005. 21. Paulo Lozano and Manuel Martinez-Sanchez, "Ionic liquid ion sources: characterization of...externally wetted emitters", Journal of Colloid and Interface Science 282 (2005) 415-421. 22. Paulo Lozano and Manuel Martinez-Sanchez, "Efficiency

  7. Colloid milium: a rare cutaneous deposition disease.

    PubMed

    Rahman, Simeen Ber; Arfan Ul Bari; Mumtaz, Nadeem

    2008-04-01

    Colloid milium is a rare degenerative skin disorder known by the development of small translucent, yellowish brown pappular nodules or plaques, generally located in sun exposed areas. Clinically they are of two types, adult and juvenile type. We present a case of adult type Colloid milium in a 60 years old female patient with clinical and histological findings unmistakable of the condition. She was treated with IPL. (Intense Pulsed Light) laser following unsatisfactory response with dermabrasion.

  8. Linked topological colloids in a nematic host.

    PubMed

    Martinez, Angel; Hermosillo, Leonardo; Tasinkevych, Mykola; Smalyukh, Ivan I

    2015-04-14

    Geometric shape and topology of constituent particles can alter many colloidal properties such as Brownian motion, self-assembly, and phase behavior. Thus far, only single-component building blocks of colloids with connected surfaces have been studied, although topological colloids, with constituent particles shaped as freestanding knots and handlebodies of different genus, have been recently introduced. Here we develop a topological class of colloids shaped as multicomponent links. Using two-photon photopolymerization, we fabricate colloidal microparticle analogs of the classic examples of links studied in the field of topology, the Hopf and Solomon links, which we disperse in nematic fluids that possess orientational ordering of anisotropic rod-like molecules. The surfaces of these particles are treated to impose tangential or perpendicular boundary conditions for the alignment of liquid crystal molecules, so that they generate a host of topologically nontrivial field and defect structures in the dispersing nematic medium, resulting in an elastic coupling between the linked constituents. The interplay between the topologies of surfaces of linked colloids and the molecular alignment field of the nematic host reveals that linking of particle rings with perpendicular boundary conditions is commonly accompanied by linking of closed singular defect loops, laying the foundations for fabricating complex composite materials with interlinking-based structural organization.

  9. Tunable Time-Dependent Colloidal Interactions

    NASA Astrophysics Data System (ADS)

    Bergman, Andrew M.; Rogers, W. Benjamin; Manoharan, Vinothan N.

    Self-assembly of colloidal particles can be driven by changes in temperature, density, or the concentration of solutes, and it is even possible to program the thermal response and equilibrium phase transitions of such systems. It is still difficult, however, to tune how the self-assembly process varies in time. We demonstrate control over the time-dependence of colloidal interactions, using DNA-functionalized colloidal particles with binding energies that are set by the concentration of a free linker strand in solution. We control the rate at which this free strand is consumed using a catalytic DNA reaction, whose rate is governed by the concentration of a catalyst strand. Varying the concentration of the linker, its competitor, and the catalyst at a fixed temperature, we can tune the rate and degree of the formation of colloidal aggregates and their following disassembly. Close to the colloidal melting point, the timescales of these out-of-equilibrium assembly and disassembly processes are determined by the rate of the catalytic reaction. Far below the colloidal melting point, however, the effects from varying our linker and competitor concentrations dominate.

  10. Inventions Utilizing Microfluidics and Colloidal Particles

    NASA Technical Reports Server (NTRS)

    Marr, David W.; Gong, Tieying; Oakey, John; Terray, Alexander V.; Wu, David T.

    2009-01-01

    Several related inventions pertain to families of devices that utilize microfluidics and/or colloidal particles to obtain useful physical effects. The families of devices can be summarized as follows: (1) Microfluidic pumps and/or valves wherein colloidal-size particles driven by electrical, magnetic, or optical fields serve as the principal moving parts that propel and/or direct the affected flows. (2) Devices that are similar to the aforementioned pumps and/or valves except that they are used to manipulate light instead of fluids. The colloidal particles in these devices are substantially constrained to move in a plane and are driven to spatially order them into arrays that function, variously, as waveguides, filters, or switches for optical signals. (3) Devices wherein the ultra-laminar nature of microfluidic flows is exploited to effect separation, sorting, or filtering of colloidal particles or biological cells in suspension. (4) Devices wherein a combination of confinement and applied electrical and/or optical fields forces the colloidal particles to become arranged into three-dimensional crystal lattices. Control of the colloidal crystalline structures could be exploited to control diffraction of light. (5) Microfluidic devices, incorporating fluid waveguides, wherein switching of flows among different paths would be accompanied by switching of optical signals.

  11. Colloids with high-definition surface structures.

    PubMed

    Chen, Hsien-Yeh; Rouillard, Jean-Marie; Gulari, Erdogan; Lahann, Joerg

    2007-07-03

    Compared with the well equipped arsenal of surface modification methods for flat surfaces, techniques that are applicable to curved, colloidal surfaces are still in their infancy. This technological gap exists because spin-coating techniques used in traditional photolithographic processes are not applicable to the curved surfaces of spherical objects. By replacing spin-coated photoresist with a vapor-deposited, photodefinable polymer coating, we have now fabricated microstructured colloids with a wide range of surface patterns, including asymmetric and chiral surface structures, that so far were typically reserved for flat substrates. This high-throughput method can yield surface-structured colloidal particles at a rate of approximately 10(7) to 10(8) particles per operator per day. Equipped with spatially defined binding pockets, microstructured colloids can engage in programmable interactions, which can lead to directed self-assembly. The ability to create a wide range of colloids with both simple and complex surface patterns may contribute to the genesis of previously unknown colloidal structures and may have important technological implications in a range of different applications, including photonic and phononic materials or chemical sensors.

  12. Colloids with high-definition surface structures

    PubMed Central

    Chen, Hsien-Yeh; Rouillard, Jean-Marie; Gulari, Erdogan; Lahann, Joerg

    2007-01-01

    Compared with the well equipped arsenal of surface modification methods for flat surfaces, techniques that are applicable to curved, colloidal surfaces are still in their infancy. This technological gap exists because spin-coating techniques used in traditional photolithographic processes are not applicable to the curved surfaces of spherical objects. By replacing spin-coated photoresist with a vapor-deposited, photodefinable polymer coating, we have now fabricated microstructured colloids with a wide range of surface patterns, including asymmetric and chiral surface structures, that so far were typically reserved for flat substrates. This high-throughput method can yield surface-structured colloidal particles at a rate of ≈107 to 108 particles per operator per day. Equipped with spatially defined binding pockets, microstructured colloids can engage in programmable interactions, which can lead to directed self-assembly. The ability to create a wide range of colloids with both simple and complex surface patterns may contribute to the genesis of previously unknown colloidal structures and may have important technological implications in a range of different applications, including photonic and phononic materials or chemical sensors. PMID:17592149

  13. Estuarine mixing behavior of colloidal organic carbon and colloidal mercury in Galveston Bay, Texas.

    PubMed

    Lee, Seyong; Han, Seunghee; Gill, Gary A

    2011-06-01

    Mercury (Hg) in estuarine water is distributed among different physical phases (i.e. particulate, colloidal, and truly dissolved). This phase speciation influences the fate and cycling of Hg in estuarine systems. However, limited information exists on the estuarine distribution of colloidal phase Hg, mainly due to the technical difficulties involved in measuring it. In the present study, we determined Hg and organic carbon levels from unfiltered, filtered (<0.45 μm), colloidal (10 kDa-0.45 μm), and truly dissolved (<10 kDa) fractions of Galveston Bay surface water in order to understand the estuarine mixing behavior of Hg species as well as interactions of Hg with colloidal organic matter. For the riverine end-member, the colloidal fraction comprised 43 ± 11% of the total dissolved Hg pool and decreased to 17 ± 8% in brackish water. In the estuarine mixing zone, dissolved Hg and colloidal organic carbon showed non-conservative removal behavior, particularly in the low salinity (<15 ppt) region. This removal may be caused by salt-induced coagulation of colloidal matter and consequent removal of dissolved Hg. The particle-water interaction, K(d) ([particulate Hg (mol kg(-1))]/[dissolved Hg (mol L(-1))]) of Hg decreased as particle concentration increased, while the particle-water partition coefficient based on colloidal Hg and the truly dissolved Hg fraction, K(c) ([colloidal Hg (mol kg(-1))]/[truly dissolved Hg (mol L(-1))]) of Hg remained constant as particle concentration increased. This suggests that the particle concentration effect is associated with the amount of colloidal Hg, increasing in proportion to the amount of suspended particulate matter. This work demonstrates that, colloidal organic matter plays an important role in the transport, particle-water partitioning, and removal of dissolved Hg in estuarine waters.

  14. Micromagnetic modeling of the shielding properties of nanoscale ferromagnetic layers

    NASA Astrophysics Data System (ADS)

    Iskandarova, I. M.; Knizhnik, A. A.; Popkov, A. F.; Potapkin, B. V.; Stainer, Q.; Lombard, L.; Mackay, K.

    2016-09-01

    Ferromagnetic shields are widely used to concentrate magnetic fields in a target region of space. Such shields are also used in spintronic nanodevices such as magnetic random access memory and magnetic logic devices. However, the shielding properties of nanostructured shields can differ considerably from those of macroscopic samples. In this work, we investigate the shielding properties of nanostructured NiFe layers around a current line using a finite element micromagnetic model. We find that thin ferromagnetic layers demonstrate saturation of magnetization under an external magnetic field, which reduces the shielding efficiency. Moreover, we show that the shielding properties of nanoscale ferromagnetic layers strongly depend on the uniformity of the layer thickness. Magnetic anisotropy in ultrathin ferromagnetic layers can also influence their shielding efficiency. In addition, we show that domain walls in nanoscale ferromagnetic shields can induce large increases and decreases in the generated magnetic field. Therefore, ferromagnetic shields for spintronic nanodevices require careful design and precise fabrication.

  15. Nonlinear motion of coupled magnetic vortices in ferromagnetic/non-magnetic/ferromagnetic trilayer

    SciTech Connect

    Jun, Su-Hyeong; Shim, Je-Ho; Oh, Suhk-Kun; Yu, Seong-Cho; Kim, Dong-Hyun; Mesler, Brooke; Fischer, Peter

    2009-07-05

    We have investigated a coupled motion of two vortex cores in ferromagnetic/nonmagnetic/ferromagnetic trilayer cynliders by means of micromagnetic simulation. Dynamic motion of two vortex with parallel and antiparallel relative chiralities of curling spins around the vortex cores have been examined after excitation by 1-ns pulsed external field. With systematic variation in non-magnetic spacer layer thickness from 0 to 20 nm, the coupling between two cores becomes significant as the spacer becomes thinner. Significant coupling leads to a nonlinear chaotic coupled motion of two vortex cores for the parallel chiralities and a faster coupled gyrotropic oscillation for the antiparallel chiralities.

  16. Engineering of frustration in colloidal artificial ices realized on microfeatured grooved lattices

    PubMed Central

    Ortiz-Ambriz, Antonio; Tierno, Pietro

    2016-01-01

    Artificial spin ice systems, namely lattices of interacting single domain ferromagnetic islands, have been used to date as microscopic models of frustration induced by lattice topology, allowing for the direct visualization of spin arrangements and textures. However, the engineering of frustrated ice states in which individual spins can be manipulated in situ and the real-time observation of their collective dynamics remain both challenging tasks. Inspired by recent theoretical advances, here we realize a colloidal version of an artificial spin ice system using interacting polarizable particles confined to lattices of bistable gravitational traps. We show quantitatively that ice-selection rules emerge in this frustrated soft matter system by tuning the strength of the pair interactions between the microscopic units. Via independent control of particle positioning and dipolar coupling, we introduce monopole-like defects and strings and use loops with defined chirality as an elementary unit to store binary information. PMID:26830629

  17. Colloid's influences on microalgae growth as a potential environmental factor

    NASA Astrophysics Data System (ADS)

    Zhao, Xinhuai; Zhang, Zhengbin; Liu, Liansheng

    2003-09-01

    The role of colloid as “colloid pump” in the ocean is well known. The important influence of colloid in seawater on the growth of microalga was found in our 1999 2000 study. Colloid concentrates were obtained by employing a cross-flow filtration system to ultrafilter seawater (which had been pre-filtrated by 0.45 μm acetate cellulose membrane) successively with different membranes. Ultrafiltration retentions (we called them colloid concentrates) together with control sample (seawater without colloid) were then inoculated with two species of microalgae and cultivated in selected conditions. Monitoring of microalgae growth during cultivation showed that all colloid concentrates had obvious influence on the growth of the microalgae studied. Addition of Fe(OH)3 colloid or organic colloid (protein or carbohydrate) to the control sample enhanced the microalgae’s growth.

  18. Ferromagnetic resonance in FeCoNi electroplated wires

    NASA Astrophysics Data System (ADS)

    García-Miquel, H.; Bhagat, S. M.; Lofland, S. E.; Kurlyandskaya, G. V.; Svalov, A. V.

    2003-08-01

    We have investigated the microwave properties (ferromagnetic resonance and ferromagnetic antiresonance) of FeCoNi magnetic tubes created by electroplating on CuBe wire. Important parameters such as the g factor, magnetization, anisotropy field, and damping parameter were obtained from the measurements. One sample, prepared by a method which entails rf-sputtering deposition of an additional FeNi layer, shows a clear ferromagnetic antiresonance.

  19. Magnetic resonance in ferromagnetic films, multilayers and nanoparticle composites

    NASA Astrophysics Data System (ADS)

    Noginova, Natalia; Bates, Brittany; Greene, Nicole

    2014-03-01

    Incorporation of magnetic materials into metamaterial systems provides an opportunity to tune microwave permeability with external magnetic field. We studied magnetically dependent microwave properties of polymer composites with iron oxide nanoparticles, ferromagnetic films and ferromagnetic/dielectric multilayers. We show that the permeability of such systems can be magnetically tuned from positive to negative values in the range of ferromagnetic resonance, strongly affecting wave propagation. Strong changes in mu-metal permeability in low field range provides an additional possibility of tuning.

  20. Quantum transport in ferromagnetic graphene: Role of Berry curvature

    SciTech Connect

    Chowdhury, Debashree; Basu, Banasri

    2014-12-10

    The magnetic effects in ferromagnetic graphene basically depend on the principle of exchange interaction when ferromagntism is induced by depositing an insulator layer on graphene. Here we deal with the consequences of non-uniformity in the exchange coupling strength of the ferromagnetic graphene. We discuss how the in- homogeneity in the coordinate and momentum of the exchange vector field can provide interesting results in the conductivity analysis of the ferromagnetic graphene. Our analysis is based on the Kubo formalism of quantum transport.

  1. Statistical thermodynamics of charge-stabilized colloids

    NASA Astrophysics Data System (ADS)

    Torres Valderrama, A.

    2008-06-01

    This thesis is a theoretical study of equilibrium statistical thermodynamic properties of colloidal systems in which electrostatic interactions play a dominant role, namely, charge-stabilized colloidal suspensions. Such systems are fluids consisting of a mixture of a large number of mesoscopic particles and microscopic ions which interact via the Coulomb force, suspended in a molecular fluid. Quantum statistical mechanics is essential to fully understand the properties and stability of such systems. A less fundamental but for many purposes, sufficient description, is provided by classical statistical mechanics. In such approximation the system is considered as composed of a great number of charged classical particles with additional hard-core repulsions. The kinetic energy or momentum integrals become independent Gaussians, and hence their contribution to the free energy can be trivially evaluated. The contribution of the potential energy to the free energy on the other hand, depends upon the configuration of all the particles and becomes highly non-trivial due to the long-range character of the Coulomb force and the extremely different length scales involved in the problem. Using the microscopic model described above, we focus on the calculation of equilibrium thermodynamic properties (response functions), correlations (structure factors), and mechanical properties (forces and stresses), which can be measured in experiments and computed by Monte Carlo simulations. This thesis is divided into three parts. In part I, comprising chapters 2 and 3, we focus on finite-thickness effects in colloidal platelets and rigid planar membranes. In chapter 2 we study electrolyte-mediated interactions between two of such colloidal objects. Several aspects of these interactions are considered including the nature (attractive or repulsive) of the force between the objects, the osmotic properties for different types of surfaces and image charge effects. In part II, which includes

  2. The dynamics of an edge dislocation in a ferromagnetic crystals

    NASA Astrophysics Data System (ADS)

    Dezhin, V. V.; Nechaev, V. N.

    2016-08-01

    The system of equations describing the bending vibrations of the dislocation in the ferromagnetic crystal is written. Elastic and magnetostrictive properties of the ferromagnetic crystals are considered isotropic. The linearization of the resulting system produced a relatively small contribution to the magnetization from the influence of dislocation. In the linear approximation of the dislocation displacement system of equation describing vibrations of a ferromagnetic crystal with an edge dislocation is obtained. The equation of motion of an edge dislocation in a ferromagnetic crystal is found.

  3. Colloids and polymers in random colloidal matrices: Demixing under good-solvent conditions

    NASA Astrophysics Data System (ADS)

    Annunziata, Mario Alberto; Pelissetto, Andrea

    2012-10-01

    We consider a simplified coarse-grained model for colloid-polymer mixtures, in which polymers are represented as monoatomic molecules interacting by means of pair potentials. We use it to study polymer-colloid segregation in the presence of a quenched matrix of colloidal hard spheres. We fix the polymer-to-colloid size ratio to 0.8 and consider matrices such that the fraction f of the volume that is not accessible to the colloids due to the matrix is equal to 40%. As in the Asakura-Oosawa-Vrij (AOV) case, we find that binodal curves in the polymer and colloid volume-fraction plane have a small dependence on disorder. As for the position of the critical point, the behavior differs from that observed in the AOV case: While the critical colloid volume fraction is essentially the same in the bulk and in the presence of the matrix, the polymer volume fraction at criticality increases as f increases. At variance with the AOV case, no capillary colloid condensation or evaporation is generically observed.

  4. Colloids and polymers in random colloidal matrices: demixing under good-solvent conditions.

    PubMed

    Annunziata, Mario Alberto; Pelissetto, Andrea

    2012-10-01

    We consider a simplified coarse-grained model for colloid-polymer mixtures, in which polymers are represented as monoatomic molecules interacting by means of pair potentials. We use it to study polymer-colloid segregation in the presence of a quenched matrix of colloidal hard spheres. We fix the polymer-to-colloid size ratio to 0.8 and consider matrices such that the fraction f of the volume that is not accessible to the colloids due to the matrix is equal to 40%. As in the Asakura-Oosawa-Vrij (AOV) case, we find that binodal curves in the polymer and colloid volume-fraction plane have a small dependence on disorder. As for the position of the critical point, the behavior differs from that observed in the AOV case: While the critical colloid volume fraction is essentially the same in the bulk and in the presence of the matrix, the polymer volume fraction at criticality increases as f increases. At variance with the AOV case, no capillary colloid condensation or evaporation is generically observed.

  5. Colloidal Gelation-2 and Colloidal Disorder-Order Transition-2 Investigations Conducted on STS-95

    NASA Technical Reports Server (NTRS)

    Hoffmann, Monica T.

    2000-01-01

    The Colloidal Gelation-2 (CGEL 2) and Colloidal Disorder-Order Transition-2 (CDOT 2) investigations flew on Space Shuttle Discovery mission STS-95 (also known as the John Glenn Mission). These investigations were part of a series of colloid experiments designed to help scientists answer fundamental science questions and reduce the trial and error involved in developing new and better materials. Industries dealing with semiconductors, electro-optics, ceramics, and composites are just a few that may benefit from this knowledge. The goal of the CGEL 2 investigation was to study the fundamental properties of colloids to help scientists better understand their nature and make them more useful for technology. Colloids consist of very small (submicron) particles suspended in a fluid. They play a critical role in the technology of this country, finding uses in materials ranging from paints and coatings to drugs, cosmetics, food, and drink. Although these products are routinely produced and used, there are still many aspects of their behavior about which scientists know little. Understanding their structures may allow scientists to manipulate the physical properties of colloids (a process called "colloidal engineering") to produce new materials and products. Colloid research may even improve the processing of known products to enhance their desirable properties.

  6. Colloids in the River Inn

    NASA Astrophysics Data System (ADS)

    Ueckert, Martina; Baumann, Thomas

    2014-05-01

    In the light of an increasing number of technical applications using nanoparticles and reports of adverse effects of engineered nanoparticles, research on the occurrence and stability of particles in all compartments has to be intensified. Colloids in river water represent the geologic setting, environmental conditions, and the anthropogenic use in its catchment. The river not only acts as a sink for nanoparticles but also as the source term due to exchange in the hyporheic zone and in bank filtration setups. The concentration, size distribution and elemental composition of particles in the River Inn were studied from the source in the Swiss Alps to the river mouth at Passau. Samples were collected after each tributary from a sub-catchment and filtered on-site. The elemental composition was determined after acid digestion with ICP/MS. SEM/EDX analyses provided morphological and elemental information for single particles. A complementary chemical analysis of the river water was performed to assess the geochemical stability of indvidual particles. Particles in the upper, rural parts mainly reveal changes in the geological setting of the tributary catchments. Not unexpectedly, particles originating from crystalline rocks, were more stable than particles originating from calcareous rocks. Anthropogenic and industrial influences increase in the lower parts. This went together with a change of the size distribution, an increase of the number of organic particles, and a decrease of the microfauna. Interestingly, specific leisure activities in a sub-catchment, like extensive downhill skiing, manifest itself in the particle composition.

  7. Drying of thin colloidal films

    NASA Astrophysics Data System (ADS)

    Routh, Alexander F.

    2013-04-01

    When thin films of colloidal fluids are dried, a range of transitions are observed and the final film profile is found to depend on the processes that occur during the drying step. This article describes the drying process, initially concentrating on the various transitions. Particles are seen to initially consolidate at the edge of a drying droplet, the so-called coffee-ring effect. Flow is seen to be from the centre of the drop towards the edge and a front of close-packed particles passes horizontally across the film. Just behind the particle front the now solid film often displays cracks and finally the film is observed to de-wet. These various transitions are explained, with particular reference to the capillary pressure which forms in the solidified region of the film. The reasons for cracking in thin films is explored as well as various methods to minimize its effect. Methods to obtain stratified coatings through a single application are considered for a one-dimensional drying problem and this is then extended to two-dimensional films. Different evaporative models are described, including the physical reason for enhanced evaporation at the edge of droplets. The various scenarios when evaporation is found to be uniform across a drying film are then explained. Finally different experimental techniques for examining the drying step are mentioned and the article ends with suggested areas that warrant further study.

  8. Self-Pinning by Colloids Confined at a Contact Line

    NASA Astrophysics Data System (ADS)

    Weon, Byung Mook; Je, Jung Ho

    2013-01-01

    Colloidal particles suspended in a fluid usually inhibit complete wetting of the fluid on a solid surface and cause pinning of the contact line, known as self-pinning. We show differences in spreading and drying behaviors of pure and colloidal droplets using optical and confocal imaging methods. These differences come from spreading inhibition by colloids confined at a contact line. We propose a self-pinning mechanism based on spreading inhibition by colloids. We find a good agreement between the mechanism and the experimental result taken by directly tracking individual colloids near the contact lines of evaporating colloidal droplets.

  9. Seismic stress mobilization of natural colloids in a porous rock

    SciTech Connect

    Roberts, Peter M; Abdel-fattah, Amr I

    2008-01-01

    Stress oscillations at 26 Hz enhanced the release of natural micro-particles (colloids) in a porous rock sample. Micron-scale effects were induced by meter-scale wavelengths. The results are attributed to altering the release rate coefficient for colloids trapped in pores. The rate change did not depend on colloid size and thus is not due to altering colloid-pore-wall interactions. Enhanced colloid detachment from pore walls and flushing from dead-end pores are likely mechanisms. This phenomenon could impact a broad range of physical sciences involving colloid dynamics and porous transport.

  10. MicroPET Outperforms Beta-Microprobes in Determining Neuroreceptor Availability under Pharmacological Restriction for Cold Mass Occupancy

    PubMed Central

    Glorie, Dorien; Servaes, Stijn; Verhaeghe, Jeroen; Wyckhuys, Tine; Wyffels, Leonie; Vanderveken, Olivier; Stroobants, Sigrid; Staelens, Steven

    2017-01-01

    Both non-invasive micro-positron emission tomography (μPET) and in situ beta-microprobes have the ability to determine radiotracer kinetics and neuroreceptor availability in vivo. Beta-microprobes were proposed as a cost-effective alternative to μPET, but literature revealed conflicting results most likely due to methodological differences and inflicted tissue damage. The current study has three main objectives: (i) evaluate the theoretical advantages of beta-microprobes; (ii) perform μPET imaging to assess the impact of (beta-micro)probe implantation on relative tracer delivery (R1) and receptor occupancy (non-displaceable binding potential, BPND) in the rat brain; and (iii) investigate whether beta-microprobe recordings produce robust results when a pharmacological restriction for cold mass dose (tracer dose condition) is imposed. We performed acquisitions (n = 61) in naive animals, dummy probe implanted animals (outer diameter: 0.75 and 1.00 mm) and beta-microprobe implanted animals (outer diameter: 0.75 mm) using two different radiotracers with high affinity for the striatum: [11C]raclopride (n = 29) and [11C]ABP688 (n = 32). In addition, acquisitions were completed with or without an imposed restriction for cold mass occupancy. We estimated BPND and R1 values using the simplified reference tissue method (SRTM). [11C]raclopride dummy μPET BPND (0.75 mm: −13.01 ± 0.94%; 1.00 mm: −13.89 ± 1.20%) and R1 values (0.75 mm: −29.67 ± 4.94%; 1.00 mm: −39.07 ± 3.17%) significantly decreased at the implant side vs. the contralateral intact side. A similar comparison for [11C]ABP688 dummy μPET, demonstrated significantly (p < 0.05) decreased BPND (−19.09 ± 2.45%) and R1 values (−38.12 ± 6.58%) in the striatum with a 1.00 mm implant, but not with a 0.75 mm implant. Particularly in tracer dose conditions, despite lower impact of partial volume effects, beta-microprobes proved unfit to produce representative results due to tissue destruction associated

  11. 230Th-U dating of surficial deposits using the ion microprobe (SHRIMP-RG): A microstratigraphic perspective

    USGS Publications Warehouse

    Maher, K.; Wooden, J.L.; Paces, J.B.; Miller, D.M.

    2007-01-01

    We used the sensitive high-resolution ion microprobe reverse-geometry (SHRIMP-RG) to date pedogenic opal using the 230Th-U system. Due to the high-spatial resolution of an ion microprobe (typically 30 ??m), regions of pure opal within a sample can be targeted and detrital material can be avoided. In addition, because the technique is non-destructive, the sample can be preserved for other types of analyses including electron microprobe or other stable isotope or trace element ion microprobe measurements. The technique is limited to material with U concentrations greater than ???50 ppm. However, the high spatial resolution, small sample requirements, and the ability to avoid detrital material make this technique a suitable technique for dating many Pleistocene deposits formed in semi-arid environments. To determine the versatility of the method, samples from several different deposits were analyzed, including silica-rich pebble coatings from pedogenic carbonate horizons, a siliceous sinter deposit, and opaline silica deposited as a spring mound. U concentrations for 30-??m-diameter spots ranged from 50 to 1000 ppm in these types of materials. The 230Th/232Th activity ratios also ranged from ???100 to 106, eliminating the need for detrital Th corrections that reduce the precision of traditional U-Th ages for many milligram- and larger-sized samples. In pedogenic material, layers of high-U opal (ca. 500 ppm) are commonly juxtaposed next to layers of calcite with much lower U concentrations (1-2 ppm). If these types of samples are not analyzed using a technique with the appropriate spatial resolution, the ages may be strongly biased towards the age of the opal. Comparison with standard TIMS (Thermal Ionization Mass Spectrometry) measurements from separate microdrilled samples suggests that although the analytical precision of the ion microprobe (SHRIMP-RG) measurements is less than TIMS, the high spatial resolution results in better accuracy in the age determination for

  12. MicroPET Outperforms Beta-Microprobes in Determining Neuroreceptor Availability under Pharmacological Restriction for Cold Mass Occupancy.

    PubMed

    Glorie, Dorien; Servaes, Stijn; Verhaeghe, Jeroen; Wyckhuys, Tine; Wyffels, Leonie; Vanderveken, Olivier; Stroobants, Sigrid; Staelens, Steven

    2017-01-01

    Both non-invasive micro-positron emission tomography (μPET) and in situ beta-microprobes have the ability to determine radiotracer kinetics and neuroreceptor availability in vivo. Beta-microprobes were proposed as a cost-effective alternative to μPET, but literature revealed conflicting results most likely due to methodological differences and inflicted tissue damage. The current study has three main objectives: (i) evaluate the theoretical advantages of beta-microprobes; (ii) perform μPET imaging to assess the impact of (beta-micro)probe implantation on relative tracer delivery (R1) and receptor occupancy (non-displaceable binding potential, BPND) in the rat brain; and (iii) investigate whether beta-microprobe recordings produce robust results when a pharmacological restriction for cold mass dose (tracer dose condition) is imposed. We performed acquisitions (n = 61) in naive animals, dummy probe implanted animals (outer diameter: 0.75 and 1.00 mm) and beta-microprobe implanted animals (outer diameter: 0.75 mm) using two different radiotracers with high affinity for the striatum: [(11)C]raclopride (n = 29) and [(11)C]ABP688 (n = 32). In addition, acquisitions were completed with or without an imposed restriction for cold mass occupancy. We estimated BPND and R1 values using the simplified reference tissue method (SRTM). [(11)C]raclopride dummy μPET BPND (0.75 mm: -13.01 ± 0.94%; 1.00 mm: -13.89 ± 1.20%) and R1 values (0.75 mm: -29.67 ± 4.94%; 1.00 mm: -39.07 ± 3.17%) significantly decreased at the implant side vs. the contralateral intact side. A similar comparison for [(11)C]ABP688 dummy μPET, demonstrated significantly (p < 0.05) decreased BPND (-19.09 ± 2.45%) and R1 values (-38.12 ± 6.58%) in the striatum with a 1.00 mm implant, but not with a 0.75 mm implant. Particularly in tracer dose conditions, despite lower impact of partial volume effects, beta-microprobes proved unfit to produce representative results due to tissue destruction associated with

  13. Magnetic and magnetoresistive properties of half-metallic ferromagnetic and charge ordered modified ferromagnetic manganite nanoparticles

    NASA Astrophysics Data System (ADS)

    Das, Kalipada; Das, I.

    2017-03-01

    In our present study, we address in detail magnetic and magneto-transport properties of well known half metallic La0.67Sr0.33MnO3 (LSMO) and charge order suppressed ferromagnetic La0.48Ca0.52MnO3 (LCMO) nanoparticles. The average particle size for LSMO and LCMO is ˜20 nm and ˜25 nm, respectively. With respect to their magnetic properties, both compounds exhibit ferromagnetic behavior, whereas they markedly differ in their magneto-transport characteristics. The magnetoresistive properties of LSMO nanoparticles indicate low field magnetoresistance and tendency for saturation at higher field values. In addition to the sharp low field magnetoresistance, we have achieved significantly large magnetoresistance at higher values of external magnetic field for the ferromagnetic LCMO nanoparticles. To address such anomalous behavior in these two different classes of ferromagnetic materials, we introduce the re-entrant core-shell type structure formation in charge ordered nanoparticles (LCMO) when charge ordering is completely suppressed.

  14. Vanishing magnetic interactions in ferromagnetic thin films.

    PubMed

    Dunn, J Hunter; Karis, O; Andersson, C; Arvanitis, D; Carr, R; Abrikosov, I A; Sanyal, B; Bergqvist, L; Eriksson, O

    2005-06-03

    We have used element-specific hysteresis measurements, based on the x-ray magnetic circular dichroism technique, to investigate magnetic trilayer structures composed of Fe and Ni layers. Within a critical regime we have discovered a class of structures in which the exchange interaction, the mechanism responsible for the macroscopic magnetism, can become vanishingly small. The experimental observations are supported by first principles theory and are explained as arising from a cancellation of several competing magnetic interactions. Hence, we have discovered a system with a novel exchange interaction between magnetic layers in direct contact that replaces the conventional exchange interaction in ferromagnets.

  15. Spin transport in half-metallic ferromagnets

    NASA Astrophysics Data System (ADS)

    Ohnuma, Y.; Matsuo, M.; Maekawa, S.

    2016-11-01

    We theoretically investigate spin transport in half-metallic ferromagnets at finite temperatures. The side-jump and skew-scattering contributions to spin Hall conductivity are derived using the Kubo formula. The electron-magnon interaction causes a finite density of states in the energy gap of the minority-spin band and induces spin Hall conductivity. We show that spin Hall conductivity is proportional to T3 /2, with T being temperature, and is sensitive to T . We propose that spin Hall conductivity may be a tool to study the minority-spin state.

  16. Ferromagnetic resonance in submicron permalloy stripes

    NASA Astrophysics Data System (ADS)

    Skorohodov, E. V.; Gorev, R. V.; Yakubov, R. R.; Demidov, E. S.; Khivintsev, Yu. V.; Filimonov, Yu. A.; Mironov, V. L.

    2017-02-01

    We present systematic experimental investigation and micromagnetic simulation of ferromagnetic resonance (FMR) in planar rectangular permalloy microstripes. The experimental microwave absorption was studied for different sample orientations in an external magnetic field. To analyze the FMR modes we developed the algorithm for the simulation of spectrum and spatial distribution of magnetization oscillations in dependence on swept external magnetic field based on numerical solution of Landau-Lifshitz-Gilbert equation. It was shown good agreement between experimental and model FMR spectra that enables the reliable visualization for spatial distributions of oscillating magnetization in modes of spin-wave resonances for different excitation conditions.

  17. Ferromagnetism in metals at finite temperatures

    SciTech Connect

    Gyorffy, B.L.; Staunton, J.B.; Stocks, G.M.

    1984-01-01

    The conventional spin-polarized band theory is well known to give a reasonable description of the magnetic ground states of metals. Here it is generalized to finite temperatures. The resulting theory is the first first-principles theory of the ferromagnetic phase transition in metals. It is a mean-field theory. For iron we find T/sub c/ = 1250 K and chi/sup -1/(q = 0) follows a Curie-Weiss law. We also report on our results for the wave-vector dependent susceptibility chi(q) which is a measure of magnetic short-range order above T/sub c/.

  18. Thorite in an Apollo 12 granite fragment and age determination using the electron microprobe

    NASA Astrophysics Data System (ADS)

    Seddio, Stephen M.; Jolliff, Bradley L.; Korotev, Randy L.; Carpenter, Paul K.

    2014-06-01

    We present the first quantitative compositional analysis of thorite in a lunar sample. The sample, a granitic assemblage, also contains monazite and yttrobetafite grains, all with concentrations of U, Th, and Pb sufficiently high to determine reliably with the electron microprobe. The assemblage represents the first documented occurrence of these three minerals together and only the second reported occurrence of thorite in a lunar rock. Sample 12023,147-10 is a small, monomict rock fragment recovered from an Apollo 12 regolith sample. It comprises graphic intergrowths of K-feldspar and quartz, and plagioclase and quartz, along with minor or accessory hedenbergite, fayalite, ilmenite, zircon, yttrobetafite, thorite, monazite, and Fe metal. Thorite, ideally ThSiO4, occurs in the assemblage adjacent to quartz and plagioclase, and includes a 12% xenotime ([Y,HREE]PO4) component. From quantitative electron-probe microanalysis (EPMA) of Th, U, and Pb in thorite, assuming that all of the measured Pb is radiogenic, we calculate an age of 3.87 ± 0.03 Ga. Yttrobetafite and monazite, which contain lesser concentrations of U, Th, and Pb than the thorite, yield ages of 3.78 ± 0.06 Ga and 3.9 ± 0.3 Ga, respectively. These dates are consistent with formation of the granitic material around 3.8-3.9 Ga, possibly associated with, or after, the formation of the Imbrium basin. This age falls within a group of younger ages for granitic samples, measured mainly by ion microprobe analysis of zircon, compared to a suite of older ages, ca. 4.20-4.32 Ga, also from zircons (Meyer et al., 1996). A 3.8-3.9 Ga age may reflect an origin following the Imbrium event whereby granitic melt formed as a result of heating and melting, and was mobilized and emplaced along an Imbrium-related ring-fracture system. Silicic volcanic or exposed intrusive materials occur in several circum-Imbrium locations such as the Mairan and Gruithuisen Domes and in ejecta excavated by Aristarchus crater. Perhaps

  19. Electron Microprobe Analysis of Fe2+/Fe3+ in Minerals With low Total Iron Concentrations

    NASA Astrophysics Data System (ADS)

    Creighton, S. D.; Matveev, S.; Stachel, T.; Luth, R. W.

    2004-12-01

    The development of the `flank method' by Höfer et al. (1994) has made it possible to quantify ferrous and ferric iron concentrations in minerals using the electron microprobe. The flank method makes use of the changes in both the wavelength and intensity of soft Fe Lα and Fe Lβ X-ray emission lines of minerals containing Fe3+ and Fe2+.By measuring at energies off the peak maxima (on the peaksAƒAøAøâ_sA¬Aøâ_zAø flanks) the differences due to variable ferric iron ratios are maximized, thus making the flank method much more sensitive than methods relying on either peak shifts or peak area ratios. Using a correction for self-absorption, the Fe3+/Fe2+ ratio of minerals may be accurately and precisely determined. The original flank method was developed for minerals with high total iron concentration e.g. Fe-rich garnet end-members (almandine, andradite, and skiagite), and Fe-oxides (wüstite). To make it applicable to minerals with total iron concentrations of less than 10 wt.% as is common in mantle-derived minerals, we have modified, in three ways, the flank method to significantly improve the precision. Firstly, we have increased the number of analyses per mineral grain to 400 thereby providing a far more representative mean. Secondly, because it is necessary to accurately reproduce the exact position of the spectrometer crystal for each flank measurement, we have eliminated the need to reposition the spectrometer by serially measuring each flank position. Thirdly, we compensate for instrumental drift by measuring two 10 μ m by 10 μ m grids (1 μ m spot size and spacing) for both flank positions. Each mineral grain is measured sequentially, collecting 200 analyses on the first flank position. The procedure is identically repeated for measurements on the second flank position. The elapsed time between each grid measurement is the same for all samples and drift for either flank position is eliminated by averaging. Using these modifications to the flank

  20. Gaining Precision and Accuracy on Microprobe Trace Element Analysis with the Multipoint Background Method

    NASA Astrophysics Data System (ADS)

    Allaz, J. M.; Williams, M. L.; Jercinovic, M. J.; Donovan, J. J.

    2014-12-01

    Electron microprobe trace element analysis is a significant challenge, but can provide critical data when high spatial resolution is required. Due to the low peak intensity, the accuracy and precision of such analyses relies critically on background measurements, and on the accuracy of any pertinent peak interference corrections. A linear regression between two points selected at appropriate off-peak positions is a classical approach for background characterization in microprobe analysis. However, this approach disallows an accurate assessment of background curvature (usually exponential). Moreover, if present, background interferences can dramatically affect the results if underestimated or ignored. The acquisition of a quantitative WDS scan over the spectral region of interest is still a valuable option to determine the background intensity and curvature from a fitted regression of background portions of the scan, but this technique retains an element of subjectivity as the analyst has to select areas in the scan, which appear to represent background. We present here a new method, "Multi-Point Background" (MPB), that allows acquiring up to 24 off-peak background measurements from wavelength positions around the peaks. This method aims to improve the accuracy, precision, and objectivity of trace element analysis. The overall efficiency is amended because no systematic WDS scan needs to be acquired in order to check for the presence of possible background interferences. Moreover, the method is less subjective because "true" backgrounds are selected by the statistical exclusion of erroneous background measurements, reducing the need for analyst intervention. This idea originated from efforts to refine EPMA monazite U-Th-Pb dating, where it was recognised that background errors (peak interference or background curvature) could result in errors of several tens of million years on the calculated age. Results obtained on a CAMECA SX-100 "UltraChron" using monazite

  1. Colloidal domain lithography in multilayers with perpendicular anisotropy: an experimental study and micromagnetic simulations.

    PubMed

    Kuświk, Piotr; Sveklo, Iosif; Szymański, Bogdan; Urbaniak, Maciej; Stobiecki, Feliks; Ehresmann, Arno; Engel, Dieter; Mazalski, Piotr; Maziewski, Andrzej; Jagielski, Jacek

    2012-11-30

    Currently, much attention is being paid to patterned multilayer systems in which there exists a perpendicular magnetic anisotropy, because of their potential applications in spintronics devices and in a new generation of magnetic storage media. To further improve their performance, different patterning techniques can be used, which render them suitable also for other applications. Here we show that He(+) 10 keV and Ar(+) 100 keV ion bombardment of (Ni(80)Fe(20)-2 nm/Au-2 nm/Co-0.6 nm/Au-2 nm)(10) multilayers through colloidal mask enables magnetic patterning of regularly arranged cylindrical magnetic domains, with perpendicular anisotropy, embedded in a non-ferromagnetic matrix or in a ferromagnetic matrix with magnetization oriented along the normal. These domains form an almost perfect two-dimensional hexagonal lattice with a submicron period and a large correlation length in a continuous and flat multilayer system. The magnetic anisotropy of these artificial domains remains unaffected by the magnetic patterning process, however the magnetization configuration of such a system depends on the magnetic properties of the matrix. The micromagnetic simulations were used to explain some of the features of the investigated patterned structures.

  2. Rheological properties of Cubic colloidal suspensions

    NASA Astrophysics Data System (ADS)

    Boromand, Arman; Maia, Joao

    2016-11-01

    Colloidal and non-colloidal suspensions are ubiquitous in many industrial application. There are numerous studies on these systems to understand and relate their complex rheological properties to their microstructural evolution under deformation. Although most of the experimental and simulation studies are centered on spherical particles, in most of the industrial applications the geometry of the colloidal particles deviate from the simple hard sphere and more complex geometries exist. Recent advances in microfabrication paved the way to fabricate colloidal particles with complex geometries for applications in different areas such as drug delivery where the fundamental understanding of their dynamics has remained unexplored. In this study, using dissipative particle dynamics, we investigate the rheological properties of cubic (superball) particles which are modeled as the cluster of core-modified DPD particles. Explicit representation of solvent particles in the DPD scheme will conserve the full hydrodynamic interactions between colloidal particles. Rheological properties of these cubic suspensions are investigated in the dilute and semi-dilute regimes. The Einstein and Huggins coefficients for these particles with different superball exponent will be calculate which represent the effect of single particle's geometry and multibody interactions on viscosity, respectively. The response of these suspensions is investigated under simple shear and oscillatory shear where it is shown that under oscillation these particles tend to form crystalline structure giving rise to stronger shear-thinning behavior recently measured experimentally.

  3. Quasicrystalline tilings with nematic colloidal platelets

    PubMed Central

    Dontabhaktuni, Jayasri; Ravnik, Miha; Žumer, Slobodan

    2014-01-01

    Complex nematic fluids have the remarkable capability for self-assembling regular colloidal structures of various symmetries and dimensionality according to their micromolecular orientational order. Colloidal chains, clusters, and crystals were demonstrated recently, exhibiting soft-matter functionalities of robust binding, spontaneous chiral symmetry breaking, entanglement, shape-driven and topological driven assembly, and even memory imprinting. However, no quasicrystalline structures were found. Here, we show with numerical modeling that quasicrystalline colloidal lattices can be achieved in the form of original Penrose P1 tiling by using pentagonal colloidal platelets in layers of nematic liquid crystals. The tilings are energetically stabilized with binding energies up to 2500 kBT for micrometer-sized platelets and further allow for hierarchical substitution tiling, i.e., hierarchical pentagulation. Quasicrystalline structures are constructed bottom-up by assembling the boat, rhombus, and star maximum density clusters, thus avoiding other (nonquasicrystalline) stable or metastable configurations of platelets. Central to our design of the quasicrystalline tilings is the symmetry breaking imposed by the platelet shape and the surface anchoring conditions at the colloidal platelets, which are misaligning and asymmetric over two perpendicular mirror planes. Finally, the design of the quasicrystalline tilings as platelets in nematic liquid crystals is inherently capable of a continuous variety of length scales of the tiling, ranging over three orders of magnitude in the typical length (from to ), which could allow for the design of quasicrystalline photonics at multiple frequency ranges. PMID:24550269

  4. Colloid-polymer mixtures under slit confinement.

    PubMed

    Pérez-Ramírez, Allan; Figueroa-Gerstenmaier, Susana; Odriozola, Gerardo

    2017-03-14

    We report a NVT molecular dynamic study of colloid-polymer mixtures under slit confinement. For this purpose, we are employing the Asakura-Oosawa model for studying colloidal particles, polymer coils, and hard walls as the external confining field. The colloid-polymer size ratio, q, is varied in the range 1⩾q⩾0.4 and the confinement distance, H, in 10σc⩾H⩾3σc, σc being the colloidal diameter. Vapor-liquid coexistence properties are assessed, from which phase diagrams are built. The obtained data fulfill the corresponding states law for a constant H when q is varied. The shift of the polymer and colloidal chemical potentials of coexistence follows a linear relationship with (H-σc)(-1) for H≳4σc. The confined vapor-liquid interfaces can be fitted with a semicircular line of curvature (H-σc)(-1), from which the contact angle can be obtained. We observe complete wetting of the confining walls for reservoir polymer concentrations above and close to the critical value, and partial wetting for reservoir polymer concentrations above and far from it.

  5. Colloids with continuously tunable surface charge.

    PubMed

    van Ravensteijn, Bas G P; Kegel, Willem K

    2014-09-09

    In this paper, we present a robust way to tune the surface potential of polystyrene colloids without changing the pH, ionic strength, etc. The colloids are composed of a cross-linked polystyrene core and a cross-linked vinylbenzyl chloride layer. Besides the chlorine groups, the particle surface contains sulfate/sulfonate groups (arising from the polymerization initiators) that provide a negative surface potential. Performing a Menschutkin reaction on the surface chlorine groups with tertiary amines allows us to introduce quaternary, positively charged amines. The overall charge on the particles is then determined by the ratio between the sulfate/sulfonate moieties and the quaternary amines. Using this process, we were able to invert the charge in a continuous manner without losing colloidal stability upon passing the isoelectric point. The straightforward reaction mechanism together with the fact that the reaction could be quenched rapidly resulted in a colloidal system in which the ζ potential can be tuned between -80 and 45 mV. As proof of principle, the positively charged particles were used in heterocoagulation experiments with nanometer- and micrometer-sized negatively charged silica particles to create geometrically well-defined colloidal (nano) clusters.

  6. Colloid-polymer mixtures under slit confinement

    NASA Astrophysics Data System (ADS)

    Pérez-Ramírez, Allan; Figueroa-Gerstenmaier, Susana; Odriozola, Gerardo

    2017-03-01

    We report a NVT molecular dynamic study of colloid-polymer mixtures under slit confinement. For this purpose, we are employing the Asakura-Oosawa model for studying colloidal particles, polymer coils, and hard walls as the external confining field. The colloid-polymer size ratio, q, is varied in the range 1 ⩾q ⩾0.4 and the confinement distance, H, in 10 σc ⩾H ⩾3 σc , σc being the colloidal diameter. Vapor-liquid coexistence properties are assessed, from which phase diagrams are built. The obtained data fulfill the corresponding states law for a constant H when q is varied. The shift of the polymer and colloidal chemical potentials of coexistence follows a linear relationship with (H-σc ) -1 for H ≳4 σc . The confined vapor-liquid interfaces can be fitted with a semicircular line of curvature (H-σc ) -1, from which the contact angle can be obtained. We observe complete wetting of the confining walls for reservoir polymer concentrations above and close to the critical value, and partial wetting for reservoir polymer concentrations above and far from it.

  7. Interparticle interactions and polarization effects in colloids

    SciTech Connect

    Hayter, J.B.

    1987-01-01

    The physics of simple colloidal systems is usually dominated by three independent length scales: the particle size, the average interparticle distance, and the range of the interparticle potential. The dispersed particles typically have characteristic dimensions in the range 5 to 100 nm, often with spherical or cylindrical symmetry. Dispersion densities vary over volume fractions ranging from 0.5 to 10/sup -4/, with the corresponding mean interparticle distances ranging from about 1 to 10 diameters (in spherical systems). The interaction potential may be very short ranged (hard sphere), very long ranged (Coulomb or dipolar), or anywhere in between (screened Coulomb), and the correlations exhibited in the dispersion may be gas-like, liquid-like or crystalline, depending on the range of the potential relative to the interparticle distance. This rich phase behavior is responsible for the remarkable importance of colloidal studies in many areas of condensed matter physics and biophysics, but it poses often intractable problems in developing the statistical mechanical descriptions necessary for an understanding of scattering data from colloids. This paper will review the considerable recent progress in this field, in the context of SANS experiments on colloids in which the potentials are dominated by either screened Coulomb or magnetic dipolar interactions; in the case of magnetic colloids (ferrofluids), the use of polarization analysis will also be discussed. 32 refs., 4 figs.

  8. Method for electrohydrodynamically assembling patterned colloidal structures

    NASA Technical Reports Server (NTRS)

    Trau, Mathias (Inventor); Aksay, Ilhan A. (Inventor); Saville, Dudley A. (Inventor)

    1999-01-01

    A method apparatus is provided for electrophoretically depositing particles onto an electrode, and electrohydrodynamically assembling the particles into crystalline structures. Specifically, the present method and apparatus creates a current flowing through a solution to cause identically charged electrophoretically deposited colloidal particles to attract each other over very large distances (<5 particle diameters) on the surface of electrodes to form two-dimensional colloidal crystals. The attractive force can be created with both DC and AC fields and can modulated by adjusting either the field strength or frequency of the current. Modulating this lateral attraction between the particles causes the reversible formation of two-dimensional fluid and crystalline colloidal states on the electrode surface. Further manipulation allows for the formation of two or three-dimensional colloidal crystals, as well as more complex designed structures. Once the required structures are formed, these three-dimension colloidal crystals can be permanently frozen or glued by controlled coagulation induced by to the applied field to form a stable crystalline structure.

  9. Apparatus for electrohydrodynamically assembling patterned colloidal structures

    NASA Technical Reports Server (NTRS)

    Trau, Mathias (Inventor); Aksay, Ilhan A. (Inventor); Saville, Dudley A. (Inventor)

    2000-01-01

    A method apparatus is provided for electrophoretically depositing particles onto an electrode, and electrohydrodynamically assembling the particles into crystalline structures. Specifically, the present method and apparatus creates a current flowing through a solution to cause identically charged electrophoretically deposited colloidal particles to attract each other over very large distances (<5 particle diameters) on the surface of electrodes to form two-dimensional colloidal crystals. The attractive force can be created with both DC and AC fields and can modulated by adjusting either the field strength or frequency of the current. Modulating this lateral attraction between the particles causes the reversible formation of two-dimensional fluid and crystalline colloidal states on the electrode surface. Further manipulation allows for the formation of two or three-dimensional colloidal crystals, as well as more complex designed structures. Once the required structures are formed, these three-dimension colloidal crystals can be permanently frozen or glued by controlled coagulation induced by to the applied field to form a stable crystalline structure.

  10. Critical Zone Weathering and Your Smartphone: Understanding How Mineral Decomposition and Colloid Redistribution Can Generate Rare Earth Element Deposits

    NASA Astrophysics Data System (ADS)

    Bern, C.; Foley, N.

    2014-12-01

    Rare earth elements (REE's) are crucial in the manufacture of smartphones and many other high tech devices. Increasing global demand and relatively narrow geographic sourcing have promoted interest in understanding REE deposit genesis and distribution. Highly weathered, clay-hosted, ion-exchange type deposits in southern China are the source of much of the world's production of the more valuable heavy REEs. Such deposits form as REE-bearing minerals weather and REEs released to solution in ionic form are retained by negatively charged exchange sites on clay minerals. We are investigating the potential for ion-exchange REE deposits in the Piedmont of the southeastern United States, where slow erosion rates have preserved thick (up to 20 m) regolith, as required for such deposits. The Liberty Hill pluton outcrops as coarse-grained biotite-amphibole granite and quartz monzonite over nearly 400 km2 in South Carolina, and has an age of 305 Ma (new SHRIMP ion microprobe zircon age). In weathered profiles over the pluton, ion-exchangeable REE content ranges from 8 to 580 ppm and accounts for 2 to 80% of bulk REE content. Elemental and heavy mineral distributions suggest the wide ranging differences in leachability may be attributable to the amount and distribution of resistant REE-bearing phases (e.g., monazite) relative to more easily weathered phases (e.g., allanite) in the parent granite. The REEs show little mobility within the regolith, indicating the effectiveness of the ion-exchange retention mechanism. In contrast, vertical redistribution of colloidal material shows maximum accumulations at ~1 m depth, as traced by the newly developed dual-phase (colloids vs. solution) mass balance model. The contrast suggests redistributed colloidal material has minimal influence on REE mobilization or retention. Conditions and processes necessary for ion-exchange REE deposit development exist in the Piedmont, but their presence will depend upon favorable parent rock mineralogy.

  11. U-Pb geochronology of zircons form lunar Breccia 73217 using a sensitive high mass-resolution ion microprobe

    NASA Astrophysics Data System (ADS)

    Compston, W.; Williams, I. S.; Meyer, C.

    1984-02-01

    U-Pb age determinations on four lunar zircons from existing thin-sections of one highland breccia, 73217, using the recently constructed ion microprobe SHRIMP, are reported. The analytical reproducibility of SHRIMP is demonstrated, and procedures for measuring Pb/U, Th/U, and corecting for initial Pb are explained. Electron microprobe analyses for the zircons are also are reported. The results show that the four zircons survived the lunar cataclysm without any identifiable effects on their U-Pb systematics. All four indicate a single age of 4356 +23 or -14 m.y. The zircons have experienced small variable amounts of Pb loss since crystallization, from almost zero up to about 10 percent. If this occurred during one later event, then age of the latter is between 1100 and 2300 m.y.

  12. The BioCAT Microprobe for X-Ray Fluorescence Imaging, MicroXAFS and Microdiffraction Studies on Biological Samples

    SciTech Connect

    Barrea, R.A.; Gore, D.; Kondrashkina, E.; Weng, T.; Heurich, R.; Vukonich, M.; Orgel, J.; Davidson, M.; Collingwood, J.F.; Mikhaylova, A.; Irving, T.C.

    2007-07-31

    Microbeam capabilities have been recently added to the Biophysics Collaborative Access Team (BioCAT) beamline 18-ID at the Advanced Photon Source to allow x-ray elemental mapping, micro x-ray absorption fine structure and microdiffraction studies on biological samples. The microprobe setup comprises a pair of platinum coated silicon KB mirrors; a sample holder mounted in a high precision positioner (100 nm accuracy); fluorescence detectors including a Si drift detector, Fe and Zn Bent Laue analyzers and a Ge detector; and a CCD detector for micro-diffraction experiments. The energy range of the microprobe is from 3.5 keV up to 17 keV. The fast scanning capabilities of the Bio-CAT beamline facilitate rapid acquisition of x-ray elemental images and micro-XAFS spectra. This paper reports the results of commissioning the KB mirror system and its performance in initial x-ray fluorescence mapping and micro-diffraction studies.

  13. Targeted irradiation of biological cells using an ion microprobe - Why a small beam spot is not sufficient for success

    NASA Astrophysics Data System (ADS)

    Fischer, B. E.; Voss, K.-O.; Du, G.

    2009-06-01

    When people plan to adapt their ion microprobe for the targeted irradiation of biological cells, they often claim that they expect a targeting accuracy in the range of their beam spot diameter, because they assume that reaching a sub-μm beam spot is the most difficult part of the job. Although many microprobes have now a beam spot diameter of some hundred nano-meters or less, nobody reached a targeting accuracy below 1 μm. Besides obvious reasons, like mechanical or thermal instabilities, there is a more difficult problem to overcome: one still needs a light microscope to locate both the microbeam and the cells to be irradiated, and there are various light-optical effects, which can give misleading information about the position of the beam and the cells.

  14. U-Pb geochronology of zircons form lunar Breccia 73217 using a sensitive high mass-resolution ion microprobe

    NASA Technical Reports Server (NTRS)

    Compston, W.; Williams, I. S.; Meyer, C.

    1984-01-01

    U-Pb age determinations on four lunar zircons from existing thin-sections of one highland breccia, 73217, using the recently constructed ion microprobe SHRIMP, are reported. The analytical reproducibility of SHRIMP is demonstrated, and procedures for measuring Pb/U, Th/U, and corecting for initial Pb are explained. Electron microprobe analyses for the zircons are alsoar reported. The results show that the four zircons survived the lunar cataclysm without any identifiable effects on their U-Pb systematics. All four indicate a single age of 4356 +23 or -14 m.y. The zircons have experienced small variable amounts of Pb loss since crystallization, from almost zero up to about 10 percent. If this occurred during one later event, then age of the latter is between 1100 and 2300 m.y.

  15. Laser-excited fluorescence of rare earth elements in fluorite: Initial observations with a laser Raman microprobe

    USGS Publications Warehouse

    Burruss, R.C.; Ging, T.G.; Eppinger, R.G.; Samson, a.M.

    1992-01-01

    Fluorescence emission spectra of three samples of fluorite containing 226-867 ppm total rare earth elements (REE) were excited by visible and ultraviolet wavelength lines of an argon ion laser and recorded with a Raman microprobe spectrometer system. Narrow emission lines ( 0.9 for Eu2+ and 0.99 for Er3+. Detection limits for three micrometer spots are about 0.01 ppm Eu2+ and 0.07 ppm Er3+. These limits are less than chondrite abundance for Eu and Er, demonstrating the potential microprobe analytical applications of laser-excited fluorescence of REE in fluorite. However, application of this technique to common rock-forming minerals may be hampered by competition between fluorescence emission and radiationless energy transfer processes involving lattice phonons. ?? 1992.

  16. Apollo 15 rake sample microbreccias and non-mare rocks: Bulk rock, mineral and glass electron microprobe analyses

    NASA Technical Reports Server (NTRS)

    Hlava, P. F.; Green, J. A.; Prinz, M.; Nehru, C. E.; Keil, K.; Dowty, E.; Bunch, T. E.

    1972-01-01

    Quantitative electron microprobe data of Apollo 15 nonmare rake samples are presented. Bulk analyses of lithic fragments in the nomare rocks (expressed in oxide weight-percent) and the corresponding CIPW molecular norms are given. The mineralogy of the rocks and lithic fragments are also given; structural formulae for complete analyses and molecular end-members for all mineral analyses are included. The mineral analyses include pyroxene, olivine, plagioclase, barian K-feldspar, spinel and ilmenite, cobaltian metallic nickel-iron as well as SiO2-K2O-rich residual glass. Electron micropobe analyses (oxide weight percent) of glasses in loose fines and microbreccia samples and their CIPW molecular norms are presented along with electron microprobe data on bulk, mineral, and matrix glass from chondrules.

  17. U-Pb geochronology of zircons form lunar Breccia 73217 using a sensitive high mass-resolution ion microprobe

    SciTech Connect

    Compston, W.; Williams, I.S.

    1984-02-15

    U-Pb age determinations on four lunar zircons from existing thin-sections of one highland breccia, 73217, using the recently constructed ion microprobe SHRIMP, are reported. The analytical reproducibility of SHRIMP is demonstrated, and procedures for measuring Pb/U, Th/U, and corecting for initial Pb are explained. Electron microprobe analyses for the zircons are also reported. The results show that the four zircons survived the lunar cataclysm without any identifiable effects on their U-Pb systematics. All four indicate a single age of 4356 +23 or -14 m.y. The zircons have experienced small variable amounts of Pb loss since crystallization, from almost zero up to about 10 percent. If this occurred during one later event, then age of the latter is between 1100 and 2300 m.y. 18 references.

  18. Asymmetric Distribution of Metals in the Xenopus Laevis Oocyte: a Synchrotron X-Ray Fluorescence Microprobe Study

    SciTech Connect

    Popescu, B.F.Gh.; Belak, Z.R.; Ignatyev, K.; Ovsenek, N.; Nichol, H.

    2009-06-04

    The asymmetric distribution of many components of the Xenopus oocyte, including RNA, proteins, and pigment, provides a framework for cellular specialization during development. During maturation, Xenopus oocytes also acquire metals needed for development, but apart from zinc, little is known about their distribution. Synchrotron X-ray fluorescence microprobe was used to map iron, copper, and zinc and the metalloid selenium in a whole oocyte. Iron, zinc, and copper were asymmetrically distributed in the cytoplasm, while selenium and copper were more abundant in the nucleus. A zone of high copper and zinc was seen in the animal pole cytoplasm. Iron was also concentrated in the animal pole but did not colocalize with zinc, copper, or pigment accumulations. This asymmetry of metal deposition may be important for normal development. Synchrotron X-ray fluorescence microprobe will be a useful tool to examine how metals accumulate and redistribute during fertilization and embryonic development.

  19. Asymmetri Distribution of Metals in the Xenopus Laevis Oocyte: a Synchrotron X-Ray Fluorescence Microprobe Study

    SciTech Connect

    Popescu, B.F.G.; Belak, Z.R.; Ignatyev, K.; Ovsenek, N.; Nichol, H.; /Saskatchewan U. /SLAC, SSRL

    2009-04-29

    The asymmetric distribution of many components of the Xenopus oocyte, including RNA, proteins, and pigment, provides a framework for cellular specialization during development. During maturation, Xenopus oocytes also acquire metals needed for development, but apart from zinc, little is known about their distribution. Synchrotron X-ray fluorescence microprobe was used to map iron, copper, and zinc and the metalloid selenium in a whole oocyte. Iron, zinc, and copper were asymmetrically distributed in the cytoplasm, while selenium and copper were more abundant in the nucleus. A zone of high copper and zinc was seen in the animal pole cytoplasm. Iron was also concentrated in the animal pole but did not colocalize with zinc, copper, or pigment accumulations. This asymmetry of metal deposition may be important for normal development. Synchrotron X-ray fluorescence microprobe will be a useful tool to examine how metals accumulate and redistribute during fertilization and embryonic development.

  20. Partitioning of Zr and Nb between coexisting opaque phases in lunar rocks _ Determined by quantitative proton microprobe analysis

    NASA Astrophysics Data System (ADS)

    Blank, H.; El Goresy, A.; Janicke, J.; Nobiling, R.; Traxel, K.

    1984-04-01

    The chemical partitioning among coexisting opaque phases of various assemblages in different lunar rocks from several landing sites is studied using electron microprobe techniques for major and minor elements and proton microprobe analyses for trace elements. In Apollo 17 rocks, the partitioning of Zr between armalcolite and ilmenite is determined in rocks showing different crystallization sequences. In olivine porphyritic basalts, Zr partitions in favor of armalcolite, probably due to equilibration between armalcolite and ilmenite achieved by the reactions involving armalcolite. Apollo 15 basalts contain ulvoespinel/ilmenite-bearing assemblages of entirely different origins: (1) subsolidus reactions leading to 'exosolution' of ilmenite from ulvoespinel and (2) isobarically invariant reaction leading to formation of ilmenite + fayalite as a result of the reaction between ulvoespinel + silica.

  1. Magneto-optical studies of ultrathin ferromagnetic films

    SciTech Connect

    Bader, S.D.

    1992-01-01

    The focus of this paper is on surface magnetic anisotropy of 3d ferromagnetic transition metals. While the exchange interaction is responsible for the net magnetization associated with ferromagnetism, it is the magnetic anisotropy energetics that determine the direction of that magnetization with respect to the crystallographic axes and to the shape of the sample.

  2. Influence of heteroaggregation processes between intrinsic colloids and carrier colloids on cerium(III) mobility through fractured carbonate rocks.

    PubMed

    Tran, Emily; Klein Ben-David, Ofra; Teutch, Nadya; Weisbrod, Noam

    2016-09-01

    Colloid facilitated transport of radionuclides has been implicated as a major transport vector for leaked nuclear waste in the subsurface. Sorption of radionuclides onto mobile carrier colloids such as bentonite and humic acid often accelerates their transport through saturated rock fractures. Here, we employ column studies to investigate the impact of intrinsic, bentonite and humic acid colloids on the transport and recovery of Ce(III) through a fractured chalk core. Ce(III) recovery where either bentonite or humic colloids were added was 7.7-26.9% Ce for all experiments. Greater Ce(III) recovery was observed when both types of carrier colloids were present (25.4-37.4%). When only bentonite colloids were present, Ce(III) appeared to be fractionated between chemical sorption to the bentonite colloid surfaces and heteroaggregation of bentonite colloids with intrinsic carbonate colloids, precipitated naturally in solution. However, scanning electron microscope (SEM) images and colloid stability experiments reveal that in suspensions of humic acid colloids, colloid-facilitated Ce(III) migration results only from the latter attachment mechanism rather than from chemical sorption. This observed heteroaggregation of different colloid types may be an important factor to consider when predicting potential mobility of leaked radionuclides from geological repositories for spent fuel located in carbonate rocks.

  3. Colloidal crystallization of colloidal silica modified with ferrocenyl group-contained polymers in organic solvents.

    PubMed

    Yoshinaga, Kohji; Shigeta, Maki; Komune, Seishu; Mouri, Emiko; Nakai, Akemi

    2007-01-15

    Surface modification of colloidal silica with ferrocenyl-grafted polymer and colloidal crystallization of the particles in organic solvent were studied. Poly(methyl methacrylate-co-vinylferrocene)-grafted silica never formed colloidal crystals in polar solvent, such as acetone, acetonitrile, ethanol and N,N-dimethylformamide (DMF), while poly(methyl methacrylate-co-ferrocenyl acrylate)-grafted silica gave colloidal crystallization in DMF. The particles prepared by grafting of poly(N,N-dimethylacrylamide-co-vinylferrocene), with vinylferrocene (Vfc) mole fraction of 1/13 and 1/23, were observed to give the crystallization in ethanol and DMF over particle volume fraction of 0.058. Further, silica modified with copolymer of Vfc and N-vinyl-2-pyrrolidone, N-vinylcarbazole or N-isopropylacrylamide formed colloidal crystals in ethanol and DMF. Especially, poly(N-isopropylacrylamide-co-Vfc)-grafted silica, which was composed of the highest mole fraction of vinylferrocene, 1/3, afforded colloidal crystallization in ethanol over particle volume fraction of 0.053. Relatively high polar vinylferrocene copolymer grafting of silica resulted in colloidal polymerization in organic solvents.

  4. Testing system for ferromagnetic shape memory microactuators.

    PubMed

    Ganor, Y; Shilo, D; Messier, J; Shield, T W; James, R D

    2007-07-01

    Ferromagnetic shape memory alloys are a class of smart materials that exhibit a unique combination of large strains and fast response when exposed to magnetic field. Accordingly, these materials have significant potential in motion generation applications such as microactuators and sensors. This article presents a novel experimental system that measures the dynamic magnetomechanical behavior of microscale ferromagnetic shape memory specimens. The system is comprised of an alternating magnetic field generator (AMFG) and a mechanical loading and sensing system. The AMFG generates a dynamic magnetic field that periodically alternates between two orthogonal directions to facilitate martensitic variant switching and to remotely achieve a full magnetic actuation cycle, without the need of mechanical resetting mechanisms. Moreover, the AMFG is designed to produce a magnetic field that inhibits 180 degrees magnetization domain switching, which causes energy loss without strain generation. The mechanical loading and sensing system maintains a constant mechanical load on the measured specimen by means of a cantilever beam, while the displacement is optically monitored with a resolution of approximately 0.1 microm. Preliminary measurements using Ni(2)MnGa single crystal specimens, with a cross section of 100x100 microm(2), verified their large actuation strains and established their potential to become a material of great importance in microactuation technology.

  5. Ferromagnetic properties of manganese doped iron silicide

    NASA Astrophysics Data System (ADS)

    Ruiz-Reyes, Angel; Fonseca, Luis F.; Sabirianov, Renat

    We report the synthesis of high quality Iron silicide (FeSi) nanowires via Chemical Vapor Deposition (CVD). The materials exhibits excellent magnetic response at room temperature, especially when doped with manganese showing values of 2.0 X 10-04 emu for the FexMnySi nanowires. SEM and TEM characterization indicates that the synthesized nanowires have a diameter of approximately 80nm. MFM measurements present a clear description of the magnetic domains when the nanowires are doped with manganese. Electron Diffraction and XRD measurements confirms that the nanowires are single crystal forming a simple cubic structure with space group P213. First-principle calculations were performed on (111) FeSi surface using the Vienna ab initio simulation package (VASP). The exchange correlations were treated under the Ceperley-Alder (CA) local density approximation (LDA). The Brillouin Zone was sampled with 8x8x1 k-point grid. A total magnetic moment of about 10 μB was obtained for three different surface configuration in which the Iron atom nearest to the surface present the higher magnetization. To study the effect of Mn doping, Fe atom was replaced for a Mn. Stronger magnetization is presented when the Mn atom is close to the surface. The exchange coupling constant have been evaluated calculating the energy difference between the ferromagnetic and anti-ferromagnetic configurations.

  6. Applications of a theory of ferromagnetic hysteresis

    SciTech Connect

    Hodgdon, M.L.

    1988-01-01

    The differential equation B = ..cap alpha../vertical/ bar H /vertical bar/(f(H) - B) + Hg(H) and a set of restrictions on the material functions f and g yield a theory of rate independent hyseresis for isoperm ferromagnetic materials. A modification based on exchanging the positions of B and H in the differential equation and on allowing for the dependence of the material functions on H extends the theory to rate dependent, nonisoperm materials. The theory and its extension exhibit all of the important features of ferromagnetic hysteresis, including the existence and stability of minor loops. Both are well suited for use in numerical field solving codes. Examples in which the material functions are simple combinations of analytic functions are presented here for MnZn ferrite, NiZn ferrite, NiFe tape, and CoCr thin film. Also presented is a procedure for constructing a two dimensional vector model that yields bell-shaped and M-shaped curves for graphs of the angular variation of the coercive field.

  7. Intertwined nematic orders in a frustrated ferromagnet

    NASA Astrophysics Data System (ADS)

    Iqbal, Yasir; Ghosh, Pratyay; Narayanan, Rajesh; Kumar, Brijesh; Reuther, Johannes; Thomale, Ronny

    2016-12-01

    We investigate the quantum phases of the frustrated spin-1/2 J1-J2-J3 Heisenberg model on the square lattice with ferromagnetic J1 and antiferromagnetic J2 and J3 interactions. Using the pseudofermion functional renormalization group technique, we find an intermediate paramagnetic phase located between classically ordered ferromagnetic, stripy antiferromagnetic, and incommensurate spiral phases. We observe that quantum fluctuations lead to significant shifts of the spiral pitch angles compared to the classical limit. By computing the response of the system with respect to various spin rotation and lattice symmetry-breaking perturbations, we identify a complex interplay between different nematic spin states in the paramagnetic phase. While retaining time-reversal invariance, these phases either break spin-rotation symmetry, lattice-rotation symmetry, or a combination of both. We therefore propose the J1-J2-J3 Heisenberg model on the square lattice as a paradigmatic example where different intimately connected types of nematic orders emerge in the same model.

  8. Thermal fluctuations in superconductor/ferromagnet nanostripes

    NASA Astrophysics Data System (ADS)

    Nasti, U.; Parlato, L.; Ejrnaes, M.; Cristiano, R.; Taino, T.; Myoren, H.; Sobolewski, Roman; Pepe, G.

    2015-07-01

    Thermal fluctuations in hybrid superconductor/ferromagnetic NbN /NiCu bilayers, as well as in pure superconducting NbN, two-dimensional (2D), nanostripes, have been investigated in order to understand the origin of dark counts in superconducting nanostripes when operated as single-photon detectors in the temperature range from 4.2 to 8 K . In 2D superconductors, the dynamics of vortex motion play a significant role in the formation of a transient normal state, leading to dark-count events in current-biased nanostripes. By introducing a weak ferromagnetic overlayer on top of pure NbN, we managed to control the vortex dynamics, which subsequently enabled us to differentiate between several proposed theoretical models. In particular, a 6 -nm-thick NiCu film grown on top of 8 -nm-thick NbN nanostripes led to an enhanced critical current density in the resulting nanostructure, as well as significantly lowered fluctuation rates, as compared to pure NbN structures, leading to reduced dark counts. The enhancement of pinning in NbN /NiCu bilayers provided evidence that thermal excitations of single vortices (vortex hopping) near the edge of a 2D nanostripe were the dominant mechanism of the observed dark-count transients. On the other hand, in pure NbN the leading source of thermal fluctuations was the current-assisted thermal unbinding of vortex-antivortex pairs.

  9. Hornblende-melt trace-element partitioning measured by ion microprobe

    USGS Publications Warehouse

    Sisson, T.W.

    1994-01-01

    Trace-element abundances were measured in situ by ion microprobe in five samples of hornblende and melt ranging from basaltic andesite to high-silica rhyolite. Except for one sample, for which quench overgrowth or disequilibrium is suspected, the abundance ratios show systematic inter-element and inter-sample variations, and probably approach true partition coefficients. Apparent partition coefficients are reported for La, Ce, Nd, Sm, Dy, Er, Yb, Sc, Ti, V, Cr, Sr, Y and Zr. Rare-earth elements (REE) and Y form smooth convex-upward partitioning patterns that rise to higher D-values and become increasingly convex in more evolved samples. Apparent partition coefficients for REE, Y, Ti, V and Cr can be parameterized as functions of the distribution of Ca between hornblende and melt, giving expressions to predict hornblende-melt trace-element partitioning values. These expressions are used to show that heavy REE-enriched hornblende/whole-rock REE abundance patterns in granitoids may result from partial re-equilibration of hornblende and late-stage residual liquids rather than from anomalous partitioning values.

  10. Ion microprobe elemental analyses of impact features on interplanetary dust experiment sensor surfaces

    NASA Technical Reports Server (NTRS)

    Hunter, Jerry L.; Wortman, Jim J.; Griffis, Dieter P.; Simon, Charles G.

    1991-01-01

    Hypervelocity impact features on several of the electro-active dust sensors utilized in the Interplanetary Dust Experiment (IDE) were subjected to elemental analysis using an ion microprobe. The negatively biased dust sensor surfaces acted as ion traps for cations produced in the plasma plumes of impacting particles. Impactor residue surrounds most impact features to two or three feature diameters. After etching away a layer of carbonaceous/silicaceous surface contamination, low mass resolution elemental survey scans are used to tentatively identify the presence of impactor debris. High mass resolution two-dimensional elemental maps and three dimensional depth profiling of the feature and surrounding area show the distribution and relative composition of the debris. The location of these sensors on the six primary Long Duration Exposure Facility (LDEF) sides provides a unique opportunity to further define the debris environment. Researchers applied the same techniques to impact and contaminant features on a set of ultra-pure, highly polished single crystal germanium wafer witness plates that were mounted on row 12 and exposed to the environment during the entire mission.

  11. Investigation of elemental distribution in human femoral head by PIXE and SRXRF microprobe

    NASA Astrophysics Data System (ADS)

    Zhang, Y. X.; Wang, Y. S.; Zhang, Y. P.; Zhang, G. L.; Huang, Y. Y.; He, W.

    2007-07-01

    In order to study the distribution and possible degenerative processes inducing the loss of inorganic substances in bone and to provide a scientific basis for the prevention and therapy of osteoporosis, proton induced X-ray emission (PIXE) method is used for the determination of elemental concentrations in femoral heads from five autopsies and seven patients with femoral neck fractures. Synchrotron radiation X-ray fluorescence (SRXRF) microprobe analysis technique is used to scan a slice of the femoral head from its periphery to its center, via cartilage, compact and spongy zones. The specimen preparation and experiment procedure are described in detail. The results show that the concentrations of P, Ca, Fe, Cu, Sr in the control group are higher than those in the patient group, but the concentrations of S, K, Zn, Mn are not significantly different. The quantitative results of elemental distribution, such as Ca, P, K, Fe, Zn, Sr and Pb in bone slice tissue including cartilage, substantial compact and substantial spongy, are investigated. The data obtained show that the concentrations of Ca, P, K, (the major elements of bone composition), are obviously low in both spongy and cartilage zones in the patient group, but there are no remarkable differences in the compact zone. Combined with the correlations between P, K, Zn, Sr and Ca, the loss mechanism of minerals and the physiological functions of some metal elements in bone are also discussed.

  12. Application of a nuclear microprobe to the study of calcified tissues

    NASA Astrophysics Data System (ADS)

    Coote, Graeme E.; Vickridge, Ian C.

    1988-03-01

    The mineral fraction of calcified tissue is largely calcium hydroxyapatite (bones and teeth) or calcium carbonate (shells and fish otoliths). Apatite has such a strong affinity for fluoride ions that the F/Ca ratio can vary markedly with position in a bone or tooth, depending on the amount of fluoride present at the time of calcification or partial recrystallization. New biological information can be obtained by introducing extra fluoride into the diet of an animal and using a microprobe later to scan sections of bones or teeth. In suitable burial sites extra fluoride is introduced after death, and the new distribution may have applications in forensic science and archaeology. Fish otoliths are also of interest since a new carbonate layer is formed each day and the distribution of trace elements may record some aspects of the fish's life history. Results from the following studies are presented: fluorine distributions in the teeth of sheep which ingested extra fluoride for known periods; distributions of calcium and fluorine in femurs of rats which drank water high in fluoride for periods from 2 to 15 weeks; calcium and fluorine distributions in artificially-prepared lesions in tooth enamel; diffusion profiles in archaeological human teeth and animal bones; patterns in the strontium/calcium ratio in sectioned otoliths of several species of fish.

  13. Improving the quantification at high spatial resolution using a field emission electron microprobe

    NASA Astrophysics Data System (ADS)

    Pinard, P. T.; Richter, S.

    2014-03-01

    The capabilities of field emitter electron microprobes to perform quantitative measurements at high spatial resolution are discussed. Using Fe-Cr-C particles in a bearing steel (SAE 52100) as example, a generic procedure was established to find the optimal analytical conditions (beam energy, beam current and acquisition time). The influence of these parameters on the accuracy, precision and spatial resolution was evaluated using experimental measurements and Monte Carlo simulations. A quantification procedure was developed for soft X-ray lines, taking into account the overlap of high order X-ray lines and background anomalies. The accuracy of Ka- and La-lines was verified using reference materials. A relationship between experimental and simulated X-ray intensities was determined to evaluate the measurement precision. The spatial resolution of each X-ray line was calculated from the simulated lateral and depth X-ray intensity distribution using simulations integrating experimentally measured beam diameters. The optimal analytical conditions for the studied sample were found to be 5 keV, 10 nA and 10 s acquisition time. Further specialized techniques to improve the spatial resolution are presented: focused ion beam preparation of thin lamella and wedge, and Monte Carlo based reconstruction. The feasibility of the latter to quantify features smaller than the X-ray emission volume was demonstrated.

  14. Development of an external beam nuclear microprobe on the Aglae facility of the Louvre museum

    NASA Astrophysics Data System (ADS)

    Calligaro, T.; Dran, J.-C.; Ioannidou, E.; Moignard, B.; Pichon, L.; Salomon, J.

    2000-03-01

    The external beam line of our facility has been recently equipped with the focusing system previously mounted on a classical nuclear microprobe. When using a 0.1 μm thick Si 3N 4 foil for the exit window and flowing helium on the sample under analysis, a beam spot as small as 10 μm is attainable at a distance of 3 mm from the window. Elemental micromapping is performed by mechanical scanning. An electronic device has been designed which allows XY scanning by moving the sample under the beam by steps down to 0.1 μm. Beam monitoring is carried out by means of the weak X-ray signal emitted by the exit foil and detected by a specially designed Si(Li) detector cooled by Peltier effect. The characteristics of external beams of protons and alpha particles are evaluated by means of resonance scanning and elemental mapping of a grid. An example of application is presented, dealing with elemental micro-mapping of inclusions in gemstones.

  15. Experimental and numerical analysis of the temperature distribution of injection molded products using protruding microprobes.

    PubMed

    Liu, Shih-Jung; Ho, Chia-Wei

    2011-05-01

    Injection molding has been one of the most important polymer processing methods for manufacturing plastic parts. In the process, the temperature is an important parameter that influences process features such as cycle times, crystallization rates, degree of crystallinity, melt flow properties, and molded product qualities. This study aims to, experimentally and numerically, examine the three-dimensional temperature distribution along the melt flow path of injection molded parts. A special experimental set-up, which includes an injection mold equipped with protruding microprobes for guiding embedded thermocouples, was designed and built to measure the temperature field along the flow path, i.e., inside the runner and the cavity, of injection molded products. The experimental results suggested that the disturbance induced by the probes remained negligible and precise temperature profiles could be measured at various positions inside the cavity. A significant increase of melt temperature was found to result from the viscous dissipation of the polymeric materials in the runner. Additionally, a commercially available code was employed to simulate and predict the temperature variation in injection molded parts. It was shown that the numerical simulation predicted better the temperature distributions inside the cavity than those along the runner.

  16. Nuclear microprobe study of TiO 2-penetration in the epidermis of human skin xenografts

    NASA Astrophysics Data System (ADS)

    Kertész, Zs.; Szikszai, Z.; Gontier, E.; Moretto, P.; Surlève-Bazeille, J.-E.; Kiss, B.; Juhász, I.; Hunyadi, J.; Kiss, Á. Z.

    2005-04-01

    Titanium-dioxide is a widely used physical photoprotective component of various cosmetic products. However, very few experiments have been carried out on its penetration through the human epidermal barrier and its possible biological effects in vivo and in vitro. In the frame of the NANODERM EU5 project, the penetration of TiO2-nanoparticles through the epidermis of human foreskin grafts transplanted into SCID mice was investigated in the Debrecen and Bordeaux nuclear microprobe laboratories using combined IBA techniques. Transmission electron microscope studies of the same samples were also carried out in the DMPFCS laboratory. The skin grafts were treated with a hydrophobic emulsion containing micronised TiO2-nanoparticles in occlusion, for different time periods. Quantitative elemental concentrations and distributions have been determined in 14-16 μm thick freeze-dried sections obtained from quick frozen punch biopsies using STIM, PIXE and RBS analytical methods. Using both microscopic methods, we have observed nanoparticles having penetrated into the corneocyte layers of stratum corneum by direct visualisation in TEM and via their chemical fingerprint in PIXE. The human skin xenograft has proved to be a model particularly well adapted to such penetration studies.

  17. Experimental and numerical analysis of the temperature distribution of injection molded products using protruding microprobes

    NASA Astrophysics Data System (ADS)

    Liu, Shih-Jung; Ho, Chia-Wei

    2011-05-01

    Injection molding has been one of the most important polymer processing methods for manufacturing plastic parts. In the process, the temperature is an important parameter that influences process features such as cycle times, crystallization rates, degree of crystallinity, melt flow properties, and molded product qualities. This study aims to, experimentally and numerically, examine the three-dimensional temperature distribution along the melt flow path of injection molded parts. A special experimental set-up, which includes an injection mold equipped with protruding microprobes for guiding embedded thermocouples, was designed and built to measure the temperature field along the flow path, i.e., inside the runner and the cavity, of injection molded products. The experimental results suggested that the disturbance induced by the probes remained negligible and precise temperature profiles could be measured at various positions inside the cavity. A significant increase of melt temperature was found to result from the viscous dissipation of the polymeric materials in the runner. Additionally, a commercially available code was employed to simulate and predict the temperature variation in injection molded parts. It was shown that the numerical simulation predicted better the temperature distributions inside the cavity than those along the runner.

  18. Pyroxene-high silica rhyolite trace element partition coefficients measured by ion microprobe

    NASA Astrophysics Data System (ADS)

    Sisson, T. W.

    1991-06-01

    Pyroxene-liquid trace element partition coefficients have been measured in situ by ion microprobe in high silica rhyolites. Partition coefficients are reported for La, Ce, Nd, Sm, Dy, Er, Yb, Sc, Ti, V, Cr, Sr, Y, and Zr. The in situ analyses avoid the problem of contamination of the pyroxene phase by trace element-rich accessory mineral inclusions encountered in traditional bulk phenocryst-glass partitioning studies. Pyroxenes and glasses which have been analyzed are typical of high silica rhyolites worldwide. The samples analyzed are Bishop Tuff, California (augite, hypersthene); Sierra La Primavera, Mexico (ferrohedenbergite); and two samples of the Huckleberry Ridge Tuff, Wyoming (ferroaugite). Rare earth element (REE) partition coefficient patterns are convex-upward and resemble patterns determined in less silicic bulk compositions. Partition coefficients for the REEs Sr, Zr, and Cr show correlations with the Mg# of clinopyroxene, suggesting that crystal composition influences the fine structure of partitioning patterns. The overall similarity of partitioning patterns between samples indicates that the partition coefficients determined in this study can be generally applied in the geochemical modeling of high silica rhyolites.

  19. Development of a bio-PIXE setup at the Debrecen scanning proton microprobe

    NASA Astrophysics Data System (ADS)

    Kertész, Zs.; Szikszai, Z.; Uzonyi, I.; Simon, A.; Kiss, Á. Z.

    2005-04-01

    On the growing need of an accurate, quantitative method for the analysis of thin biological tissues down to the cell level, a measurement setup and data evaluating system has been developed at the Debrecen scanning proton microprobe facility, using its unique capability of the PIXE-PIXE technique. Quantitative elemental concentrations and true elemental maps from C to U can be produced in the case of thin (10-50 μm), inhomogeneous samples of organic matrix with a 2 μm lateral resolution. The method is based on the combined application of on-axis STIM and PIXE-PIXE ion beam analytical techniques. STIM spectra and maps are used to determine the morphology and the area density of the samples. PIXE spectra and maps of an ultra thin windowed and a conventional Be-windowed Si(Li) X-ray detectors are used to quantify concentrations and distributions of elements in the C to Fe (light and medium) and S to U (medium and heavy) atomic number regions, separately. For cross-checking the validation of the obtained data in a few cases RBS technique was used simultaneously. The application of the new bio-PIXE method is shown through an example, the study of the penetration and clearance of ultra-fine particles containing heavy metals (TiO2) of physical bodycare cosmetics in different layers of skin within the frame of the NANODERM EU5 project.

  20. Granulation in amine-storage organelles of mouse megakaryocytes: X-ray microprobe analysis and radioautography.

    PubMed

    Daimon, T; Kawai, K; Uchida, K

    1995-02-01

    The mechanisms and the processes of the storage of bivalent cations, ATP and 5-hydroxytryptamine (5HT) in the precursors of the amine-storage organelles of megakaryocytes were studied at the electron microscopic level. Although the precursors of the amine-storage organelles in the megakaryocytes fixed with glutaraldehyde and osmium tetroxide were empty, the electron opaque granules were observed in these organelles of the freeze-substituted megakaryocytes cut onto ethylene glycol. X-ray microprobe analysis demonstrated that they contained P, Mg and Ca. Quantitative differences in bivalent cations in the granules were not observed between megakaryocytes and blood platelets. Electron opaque uranaffin-reaction products were observed in the precursors of the amine-storage organelles of the megakaryocytes after treatment with the uranaffin reaction for ATP. However, few chromaffin positive granules were observed in the precursors of the amine-storage organelles after the chromaffin reaction for monoamines. Radioautographic analysis demonstrated that blood platelets avidly took up 3H-5HT but megakaryocytes were not able to accumulate 3H-5HT in vivo. These results indicate that megakaryocytes do not yet acquire the well developed uptake system of 5HT in vivo, while they readily accumulate cations and ATP in the precursors of the amine-storage organelles.

  1. Development of a High Resolution-High Sensitivity Ion Microprobe Facility for Cosmochemical Applications

    NASA Technical Reports Server (NTRS)

    McKeegan, Kevin D.

    1998-01-01

    NASA NAGW-4112 has supported development of the CAMECA ims 1270 ion microprobe at UCLA for applications in cosmochemistry. The instrument has been brought to an operational status and techniques developed for accurate, precise microbeam analysis of oxygen isotope ratios in polished thin-sections. We made the first oxygen isotopic (delta(18)O and delta(17)O) measurements of rare mafic silicates in the most chemically primitive meteorites, the a chondrites (Leshin et al., 1997). The results have implications for both high temperature processing in the nebula and low-T aqueous alteration on the CI asteroid. We have performed measurements of oxygen isotopic compositions of magnetite and co-existing olivine from carbonaceous (Choi et al., 1997) and unequilibrated ordinary chondrites (Choi et al., in press). This work has identified a significant new oxygen isotope reservoir in the early solar system: water characterized by a very high Delta(17)) value of approx. 5 % per thousand. We have determined the spatial distributions of oxygen isotopic anomalies in all major mineral phases of a type B CAI from Allende. We have also studied an unusual fractionated CAI from Leoville and made the first oxygen isotopic measurements in rare CAIs from ordinary chondrites.

  2. The biological research programme of the nuclear microprobe at the National Accelerator Centre, Faure

    NASA Astrophysics Data System (ADS)

    Prozesky, V. M.; Pineda, C. A.; Mesjasz-Przybylowicz, J.; Przybylowicz, W. J.; Churms, C. L.; Springhorn, K. A.; Moretto, Ph; Michelet, C.; Chikte, U.; Wenzl, P.

    2000-03-01

    The nuclear microprobe (NMP) unit of the National Accelerator Centre (NAC) has initiated a focused research programme on studies of biological material, ranging from applications in medicine to agriculture and botany. During this period a state-of-the-art cryo-preparation laboratory was also developed. This research programme has resulted in a wide range of projects, and has shown how well suited the NMP is for studies of biological material in general. This paper reports on some of the problems and demands in this field, as well as some of the results obtained using particle induced X-ray spectroscopy (PIXE) and Rutherford backscattering (RBS). True elemental imaging is routinely performed using the dynamic analysis (DA) method, which forms part of the GeoPIXE suite of programmes. A collaborative project, together with the CENBG group of Bordeaux-Gradignan in France, on the development of a facility with the aim of studying effects of single-events of radiation in living cells was recently established and is discussed.

  3. Nuclear microprobe studies of elemental distributions in dormant seeds of Burkea africana

    NASA Astrophysics Data System (ADS)

    Witkowski, E. T. F.; Weiersbye-Witkowski, I. M.; Przybyłowicz, W. J.; Mesjasz-Przybyłowicz, J.

    1997-07-01

    Seed nutrient stores are vital post-germination for the establishment of seedlings in harsh and unpredictable environments. Plants of nutrient-poor environments allocate a substantial proportion of total acquired nutrients to reproduction (i.e. seeds). We propose that differential allocation of mineral resources to specific seed tissues is an indication of a species germination and establishment strategy. Burkea africana Hook is a leguminous tree typical of broad-leaved nutrient-poor savannas in southern Africa. Elemental distributions in dormant B. africana seed structures were obtained using the true elemental imaging system (Dynamic Analysis) of the NAC Van de Graaff nuclear microprobe. Raster scans of 3.0 MeV protons were complemented by simultaneous BS and PIXE point analyses. Mineral nutrient concentrations varied greatly between seed tissues. Elevated levels of metals known to play an important role as plant enzyme co-factors were found in the seed lens and embryonic axis. Distributions of most of these metals (Ca, Mn, Fe and Zn, but not K or Cu) were positively correlated with embryonic P distribution, and probably represent phytin deposits. The distribution of metals within seed structures is 'patchy' due to their complexation with P as electron-dense globoid phytin crystals, which constrains the interpretation of PIXE point analyses.

  4. Direct ion microprobe U-Pb dating of fossil tooth of a Permian shark

    NASA Astrophysics Data System (ADS)

    Sano, Yuji; Terada, Kentaro

    1999-12-01

    We report here direct ion microprobe dating of fossil tooth (dentine) of a Permian fresh-water shark, Orthacanthus senckenbergianus using the SHRIMP instrument recently installed at Hiroshima University. Fifteen spots on the small sample (approximately 2 mm×1 mm) indicate a 238U/ 206Pb isochron age of 266±18 Ma and a Tera-Wasserburg concordia intercept age of 266±24 Ma in a three-dimensional 238U/ 206Pb- 207Pb/ 206Pb- 204Pb/ 206Pb diagram. These Permian ages are consistent with a 235U/ 207Pb age of 453±170 Ma and a 232Th- 208Pb age of 235±310 Ma, suggesting indistinguishable depositional and early diagenetic ages of the fossil in its sedimentary sequences. The success of the method depends on the chemical fractionation of uranium from lead in a specimen a few hundred microns in size and the consequent variations in lead isotopic compositions due to radioactive decay.

  5. Ion microprobe analyses of aluminous lunar glasses - A test of the 'rock type' hypothesis

    NASA Technical Reports Server (NTRS)

    Meyer, C., Jr.

    1978-01-01

    Previous soil survey investigations found that there are natural groupings of glass compositions in lunar soils and that the average major element composition of some of these groupings is the same at widely separated lunar landing sites. This led soil survey enthusiasts to promote the hypothesis that the average composition of glass groupings represents the composition of primary lunar 'rock types'. In this investigation the trace element composition of numerous aluminous glass particles was determined by the ion microprobe method as a test of the above mentioned 'rock type' hypothesis. It was found that within any grouping of aluminous lunar glasses by major element content, there is considerable scatter in the refractory trace element content. In addition, aluminous glasses grouped by major elements were found to have different average trace element contents at different sites (Apollo 15, 16 and Luna 20). This evidence argues that natural groupings in glass compositions are determined by regolith processes and may not represent the composition of primary lunar 'rock types'.

  6. Using Synchrotron X-ray Fluorescence Microprobes in the Study of Metal Homeostasis in Plants

    SciTech Connect

    Punshon, T.; Guerinot, M; Lanzirotti, A

    2009-01-01

    Background and Aims: This Botanical Briefing reviews the application of synchrotron X-ray fluorescence (SXRF) microprobes to the plant sciences; how the technique has expanded our knowledge of metal(loid) homeostasis, and how it can be used in the future. Scope: The use of SXRF microspectroscopy and microtomography in research on metal homeostasis in plants is reviewed. The potential use of SXRF as part of the ionomics toolbox, where it is able to provide fundamental information on the way that plants control metal homeostasis, is recommended. Conclusions: SXRF is one of the few techniques capable of providing spatially resolved in-vivo metal abundance data on a sub-micrometre scale, without the need for chemical fixation, coating, drying or even sectioning of samples. This gives researchers the ability to uncover mechanisms of plant metal homeostasis that can potentially be obscured by the artefacts of sample preparation. Further, new generation synchrotrons with smaller beam sizes and more sensitive detection systems will allow for the imaging of metal distribution within single living plant cells. Even greater advances in our understanding of metal homeostasis in plants can be gained by overcoming some of the practical boundaries that exist in the use of SXRF analysis.

  7. Processing of electron microprobe data from the analysis of altered cementitious materials

    SciTech Connect

    Bertron, A. Escadeillas, G.; Parseval, P. de; Duchesne, J.

    2009-10-15

    The purpose of this paper is to present a method for processing electron microprobe data coming from the analysis of degraded cementitious materials. The application domain is that of cement matrices exposed to attack by aggressive media inducing the leaching of one or more chemical elements from the cement paste - typically attacked by neutral or acid aqueous environments. As raw data obtained from electron probe microanalysis (EPMA) come in the form of relative quantities of elements, the aim of the processing is to obtain the absolute variation of the specimen's chemical composition in the degraded zone and consequently to allow a better understanding of the degradation mechanisms by the aggressive environment under consideration. This method was designed for degraded specimens in which the porosity was not filled with resin before the EPMA. The method uses the titanium content of the cement matrix as a control, this element being stable during attack by neutral or acidic media. The method is described in detail using the example of the attack of cement pastes by a mix of several organic acids (notably acetic acid) at pH 4. The use of EPMA for sound and altered cement pastes is also validated. The application domain of the correction method is discussed.

  8. Age Dating from Electron Microprobe Analyses of U, Th, and Pb: Geological Advantages and Analytical Difficulties.

    PubMed

    Bowles, John F W

    2015-10-01

    Electron microprobe analysis of U, Th, and Pb in naturally occurring minerals can indicate their age. Where the Pb is entirely due to the radioactive decay of U and Th, the time since mineral formation or equilibration can be calculated. Uraninite (UO2), monazite (REE PO4), zircon (ZrSiO4), and xenotime (YPO4) have been used, the latter containing U and/or Th in minor proportions. Any stable U- or Th-bearing phase can be considered. Careful analysis is required with attention to interferences, background measurement, detection limits, and Pb-free sample preparation. Extended counting times (600 s) at a probe current >200 nA are recommended. Ages can be determined from uraninite older than 2 Ma for a Pb detection limit of 0.02% and up to 700-1,000 Ma, after which Pb can be lost from the structure. The youngest monazite ages permitted by the Pb detection limit are 50-100 Ma and ages greater than 3,000 Ma have been determined. The method does not provide the detail of isotopic methods, but results can be obtained more readily. Examples show dating of cheralite ((Ca,Ce)(Th,Ce)(PO4)2), a rock containing primary and secondary UO2, and a suite of detrital uraninite grains that formed a part of a mineral exploration program.

  9. Laser microprobe study of cosmic dust (IDPs) and potential source materials

    NASA Technical Reports Server (NTRS)

    Gibson, E. K., Jr.; Sommer, M. S., II

    1986-01-01

    The study of cosmic dust or interplanetary dust particles (IDP) can provide vital information about primitive materials derived primarily from comets and asteroids along with a small unknown fraction from the nearby interstellar medium. The study of these particles can enhance our understanding of comets along with the decoding of the history of the early solar system. In addition the study of the cosmic dust for IDP particles can assist in the elucidation of the cosmic history of the organogenic elements which are vital to life processes. Studies to date on these particles have shown that they are complex, heterogeneous assemblages of both amorphous and crystalline components. In order to understand the nature of these particles, any analytical measurements must be able to distinguish between the possible sources of these particles. A study was undertaken using a laser microprobe interfaced to a quadrupole mass spectrometer for the analysis of the volatile components present in cosmic dust particles, terrestrial contaminants present in the upper atmosphere, and primitive carbonaceous chondrites. From the study of the volatiles released from the carbonaceous materials it is hoped that one could distinguish between components and sources in the IDP particles analyzed. The technique is briefly described and results for the CI, CM, and CV chondrites and cosmic dust particle W7027B8 are presented.

  10. X-ray Microprobe Investigation of Iron During a Simulated Silicon Feedstock Extraction Process

    NASA Astrophysics Data System (ADS)

    Bernardis, Sarah; Fakra, Sirine C.; Dal Martello, Elena; Larsen, Rune B.; Newman, Bonna K.; Fenning, David P.; Di Sabatino, Marisa; Buonassisi, Tonio

    2016-12-01

    Elemental silicon is extracted through carbothermic reduction from silicon-bearing raw feedstock materials such as quartz and quartzites. We investigate the micron-scale distribution and valence state of iron, a deleterious impurity in several iron-sensitive applications, in hydrothermal quartz samples of industrial relevance during a laboratory-scale simulated reduction process. We use X-ray diffraction to inspect the quartz structural change and synchrotron-based microprobe techniques to monitor spatial distribution and oxidation state of iron. In the untreated quartz, most of the iron is embedded in foreign minerals, both as ferric (Fe3+, e.g., in muscovite) and ferrous (Fe2+, e.g., as in biotite) iron. Upon heating the quartz to 1273 K (1000 °C) under industrial-like conditions in a CO(g) environment, iron is found in ferrous (Fe2+) particles. At this temperature, its chemical state is influenced by mineral decomposition and melting processes, whereas at higher temperatures it is influenced by the silicate melts. As the quartz grains partially transform to cristobalite 1873 K (1600 °C), iron diffuses towards liquid-solid interfaces forming ferrous clusters. Silica is liquid at 2173 K (1900 °C) and the iron migrates towards the interfaces between gas phases and the silicate liquid.

  11. A LSO β microprobe for measuring input functions for quantitative small animal PET

    NASA Astrophysics Data System (ADS)

    Maramraju, S.; Stoll, S.; Woody, C.; Schlyer, D.; Schiffer, W.; Lee, D.; Dewey, S.; Vaska, P.

    2007-02-01

    A miniature scintillation microprobe has been developed to measure the input function in live rodents for use in longitudinal, quantitative PET studies. The probe consists of a small lutetium oxyorthosilicate (LSO) crystal measuring typically 0.3-0.5 mm diameter ×0.5-2 mm in length that is used to directly detect positrons in the blood or tissue. The probe has a sensitivity of 10-30 Hz/μCi/cm 3 and is primarily sensitive to short-range positrons emitted by labeled radiotracers in the blood. The sensitivity to γ-ray background can be minimized using a variable threshold in the readout to discriminate between positrons and γ's. The probe was implanted in one of the tail veins of a Sprague-Dawley rat and the input function was measured for the injection of 0.8 mCi of FDG in the other tail vein. The probe exhibits a fast time response that is able to quickly and accurately measure the concentration of 18F circulating in the bloodstream. Additional tests were also carried out to study the probe's sensitivity to γ-ray background.

  12. Electrochemical reduction of chlorophyll in colloidal solutions

    SciTech Connect

    Suponeva, E.P.; Kadoshnikova, I.G.; Kazakova, A.A.; Kiselev, B.A.

    1986-02-01

    This paper discusses determining the energy yield of the photochemical reaction. The authors investigated the peculiarities of the electrochemical reduction of Chl in the colloidal state, where the elements of the molecular organization of the pigments in the reaction centers of photosynthesis are simulated and, as a result, the lifetime of Chl.- is substantially increased. Polarograms of a colloidal solution of Chl ''a'' in aqueous buffer solution contining less than 5% acetone are presented. The adsorption spectra were measured on a spectrophotometer and the fluorescence spectra were recorded on a setup assembled on the basis of RM-w and FEU-30 monochromators. The results obtained are evidence of the ability of Chl for spontaneous formation of molecular associates in aqueous medium, which are characterized by hindrance of the protonation of Chl.- in comparison with monomeric Chl at a high rate of exchange of an electron between the eletrode and the colloidal particle and between molecules in the volume of the particle.

  13. Spin Dynamics of Charged Colloidal Quantum Dots

    NASA Astrophysics Data System (ADS)

    Stern, N. P.

    2005-03-01

    Colloidal semiconductor quantum dots are promising structures for controlling spin phenomena because of their highly size- tunable physical properties, ease of manufacture, and nanosecond-scale spin lifetimes at room temperature. Recent experiments have succeeded in controlling the charging of the lowest electronic state of colloidal quantum dots ootnotetextC. Wang, B. L. Wehrenberg, C. Y. Woo, and P. Guyot-Sionnest, J. Phys. Chem B 108, 9027 (2004).. Here we use time-resolved Faraday rotation measurements in the Voigt geometry to investigate the spin dynamics of colloidal CdSe quantum dot films in both a charged and uncharged state at room temperature. The charging of the film is controlled by applying a voltage in an electrochemical cell and is confirmed by absorbance measurements. Significant changes in the spin precession are observed upon charging, reflecting the voltage- controlled electron occupation of the quantum dot states and filling of surface states.

  14. Targeted delivery of colloids by swimming bacteria

    NASA Astrophysics Data System (ADS)

    Koumakis, N.; Lepore, A.; Maggi, C.; di Leonardo, R.

    2013-10-01

    The possibility of exploiting motile microorganisms as tiny propellers represents a fascinating strategy for the transport of colloidal cargoes. However, delivery on target sites usually requires external control fields to steer propellers and trigger cargo release. The need for a constant feedback mechanism prevents the design of compact devices where biopropellers could perform their tasks autonomously. Here we show that properly designed three-dimensional (3D) microstructures can define accumulation areas where bacteria spontaneously and efficiently store colloidal beads. The process is stochastic in nature and results from the rectifying action of an asymmetric energy landscape over the fluctuating forces arising from collisions with swimming bacteria. As a result, the concentration of colloids over target areas can be strongly increased or depleted according to the topography of the underlying structures. Besides the significance to technological applications, our experiments pose some important questions regarding the structure of stationary probability distributions in non-equilibrium systems.

  15. Colloidal Disorder-Order Transition (CDOT-2)

    NASA Technical Reports Server (NTRS)

    2004-01-01

    This is an image of a colloidal crystal from the CDOT-2 investigation flown on STS-95. There are so many colloidal particles in this sample that it behaves like a glass. In the laboratory on Earth, the sample remained in an amorphous state, showing no sign of crystal growth. In microgravity the sample crystallized in 3 days, as did the other glassy colloidal samples examined in the CDOT-2 experiment. During the investigation, crystallization occurred in samples that had a volume fraction (number of particles per total volume) larger than the formerly reported glass transition of 0.58. This has great implications for theories of the structural glass transition. These crystals were strong enough to survive space shuttle re-entry and landing.

  16. Manipulating semiconductor colloidal stability through doping.

    PubMed

    Fleharty, Mark E; van Swol, Frank; Petsev, Dimiter N

    2014-10-10

    The interface between a doped semiconductor material and electrolyte solution is of considerable fundamental interest, and is relevant to systems of practical importance. Both adjacent domains contain mobile charges, which respond to potential variations. This is exploited to design electronic and optoelectronic sensors, and other enabling semiconductor colloidal materials. We show that the charge mobility in both phases leads to a new type of interaction between semiconductor colloids suspended in aqueous electrolyte solutions. This interaction is due to the electrostatic response of the semiconductor interior to disturbances in the external field upon the approach of two particles. The electrostatic repulsion between two charged colloids is reduced from the one governed by the charged groups present at the particles surfaces. This type of interaction is unique to semiconductor particles and may have a substantial effect on the suspension dynamics and stability.

  17. Shape-shifting colloids via stimulated dewetting

    PubMed Central

    Youssef, Mena; Hueckel, Theodore; Yi, Gi-Ra; Sacanna, Stefano

    2016-01-01

    The ability to reconfigure elementary building blocks from one structure to another is key to many biological systems. Bringing the intrinsic adaptability of biological systems to traditional synthetic materials is currently one of the biggest scientific challenges in material engineering. Here we introduce a new design concept for the experimental realization of self-assembling systems with built-in shape-shifting elements. We demonstrate that dewetting forces between an oil phase and solid colloidal substrates can be exploited to engineer shape-shifting particles whose geometry can be changed on demand by a chemical or optical signal. We find this approach to be quite general and applicable to a broad spectrum of materials, including polymers, semiconductors and magnetic materials. This synthetic methodology can be further adopted as a new experimental platform for designing and rapidly prototyping functional colloids, such as reconfigurable micro swimmers, colloidal surfactants and switchable building blocks for self-assembly. PMID:27426418

  18. Manipulating colloidal assemblies with active dopants

    NASA Astrophysics Data System (ADS)

    Ramananarivo, Sophie; Palacci, Jeremie

    2016-11-01

    The dynamics of a densely packed 2D layer of colloids can be significantly altered upon introducing a small amount of active microparticles. Those motile intruders drive the system out-of-equilibrium, which produces a variety of new complex phenomena such as the accentuation of density heterogeneities or the reorganization of crystalline colloidal structures. We investigate the altered dynamics of the passive spheres, as well as the behavior of micro-swimmers propelling in such crowded environment where interactions with passive obstacles or other active units become important. Ultimately, understanding and controlling such mixed systems could open new routes toward activity-assisted manipulation of colloids, potentially guiding the design of materials able to self-anneal their defects.

  19. Convection of a stratified colloidal suspension

    SciTech Connect

    Cherepanov, I. N.; Smorodin, B. L.

    2013-11-15

    The convection of a colloidal suspension, which is a binary mixture of a carrier medium with an admixture of nanoparticles having a large positive thermal diffusion parameter, has been studied for the case of the heating of a horizontal cell from below and periodic conditions at the vertical boundaries corresponding to the experimental situation of ring channels. Bifurcation diagrams have been constructed for vibrational and monotonic regimes of the convection of the colloidal mixture. The time dependences of the maximum stream function and the stream function at a fixed point of the cell, as well as the spatial distributions of the concentration field of the colloid admixture, have been obtained. It has been shown that a stable regime of traveling waves exists in a certain region of the parameters of the problem (Boltzmann and Rayleigh numbers characterizing the gravitational stratification and intensity of the thermal effect, respectively)

  20. Colloids in food: ingredients, structure, and stability.

    PubMed

    Dickinson, Eric

    2015-01-01

    This article reviews progress in the field of food colloids with particular emphasis on advances in novel functional ingredients and nanoscale structuring. Specific aspects of ingredient development described here are the stabilization of bubbles and foams by the protein hydrophobin, the emulsifying characteristics of Maillard-type protein-polysaccharide conjugates, the structural and functional properties of protein fibrils, and the Pickering stabilization of dispersed droplets by food-grade nanoparticles and microparticles. Building on advances in the nanoscience of biological materials, the application of structural design principles to the fabrication of edible colloids is leading to progress in the fabrication of functional dispersed systems-multilayer interfaces, multiple emulsions, and gel-like emulsions. The associated physicochemical insight is contributing to our mechanistic understanding of oral processing and textural perception of food systems and to the development of colloid-based strategies to control delivery of nutrients during food digestion within the human gastrointestinal tract.

  1. Plasmonic films based on colloidal lithography.

    PubMed

    Ai, Bin; Yu, Ye; Möhwald, Helmuth; Zhang, Gang; Yang, Bai

    2014-04-01

    This paper reviews recent advances in the field of plasmonic films fabricated by colloidal lithography. Compared with conventional lithography techniques such as electron beam lithography and focused ion beam lithography, the unconventional colloidal lithography technique with advantages of low-cost and high-throughput has made the fabrication process more efficient, and moreover brought out novel films that show remarkable surface plasmon features. These plasmonic films include those with nanohole arrays, nanovoid arrays and nanoshell arrays with precisely controlled shapes, sizes, and spacing. Based on these novel nanostructures, optical and sensing performances can be greatly enhanced. The introduction of colloidal lithography provides not only efficient fabrication processes but also plasmonic films with unique nanostructures, which are difficult to be fabricated by conventional lithography techniques.

  2. Dynamic Assembly of Magnetic Colloidal Vortices

    SciTech Connect

    Mohorič, Tomaž; Kokot, Gašper; Osterman, Natan; Snezhko, Alexey; Vilfan, Andrej; Babič, Dušan; Dobnikar, Jure

    2016-04-29

    Magnetic colloids in external time-dependent fields are subject to complex induced many-body interactions governing their self-assembly into a variety of equilibrium and out-of-equilibrium structures such as chains, networks, suspended membranes, and colloidal foams. Here, we report experiments, simulations, and theory probing the dynamic assembly of superparamagnetic colloids in precessing external magnetic fields. Within a range of field frequencies, we observe dynamic large-scale structures such as ordered phases composed of precessing chains, ribbons, and rotating fluidic vortices. We show that the structure formation is inherently coupled to the buildup of torque, which originates from internal relaxation of induced dipoles and from transient correlations among the particles as a result of short-lived chain formation. We discuss in detail the physical properties of the vortex phase and demonstrate its potential in particle-coating applications.

  3. Energy transport velocity in bidispersed magnetic colloids

    NASA Astrophysics Data System (ADS)

    Bhatt, Hem; Patel, Rajesh; Mehta, R. V.

    2012-07-01

    Study of energy transport velocity of light is an effective background for slow, fast, and diffuse light and exhibits the photonic property of the material. We report a theoretical analysis of magnetic field dependent resonant behavior in forward-backward anisotropy factor, light diffusion constant, and energy transport velocity for bidispersed magnetic colloids. A bidispersed magnetic colloid is composed of micrometer size magnetic spheres dispersed in a magnetic nanofluid consisting of magnetic nanoparticles in a nonmagnetic liquid carrier. Magnetic Mie resonances and reduction in energy transport velocity accounts for the possible delay (longer dwell time) by field dependent resonant light transport. This resonant behavior of light in bidispersed magnetic colloids suggests a novel magnetophotonic material.

  4. Shape-shifting colloids via stimulated dewetting

    NASA Astrophysics Data System (ADS)

    Youssef, Mena; Hueckel, Theodore; Yi, Gi-Ra; Sacanna, Stefano

    2016-07-01

    The ability to reconfigure elementary building blocks from one structure to another is key to many biological systems. Bringing the intrinsic adaptability of biological systems to traditional synthetic materials is currently one of the biggest scientific challenges in material engineering. Here we introduce a new design concept for the experimental realization of self-assembling systems with built-in shape-shifting elements. We demonstrate that dewetting forces between an oil phase and solid colloidal substrates can be exploited to engineer shape-shifting particles whose geometry can be changed on demand by a chemical or optical signal. We find this approach to be quite general and applicable to a broad spectrum of materials, including polymers, semiconductors and magnetic materials. This synthetic methodology can be further adopted as a new experimental platform for designing and rapidly prototyping functional colloids, such as reconfigurable micro swimmers, colloidal surfactants and switchable building blocks for self-assembly.

  5. The x ray microprobe determination of chromium oxidation state in olivine from lunar basalt and kimberlitic diamonds

    NASA Technical Reports Server (NTRS)

    Sutton, S. R.; Bajt, S.; Rivers, M. L.; Smith, J. V.

    1993-01-01

    The synchrotron x-ray microprobe is being used to obtain oxidation state information on planetary materials with high spatial resolution. Initial results on chromium in olivine from various sources including laboratory experiments, lunar basalt, and kimberlitic diamonds are reported. The lunar olivine was dominated by Cr(2+) whereas the diamond inclusions had Cr(2+/Cr(3+) ratios up to about 0.3. The simpliest interpretation is that the terrestrial olivine crystallized in a more oxidizing environment than the lunar olivine.

  6. Nuclear microprobe investigation of the effects of ionization and displacement damage in vertical, high voltage GaN diodes

    DOE PAGES

    Vizkelethy, G.; King, M. P.; Aktas, O.; ...

    2016-12-02

    Radiation responses of high-voltage, vertical gallium-nitride (GaN) diodes were investigated using Sandia National Laboratories’ nuclear microprobe. Effects of the ionization and the displacement damage were studied using various ion beams. We found that the devices show avalanche effect for heavy ions operated under bias well below the breakdown voltage. Here, the displacement damage experiments showed a surprising effect for moderate damage: the charge collection efficiency demonstrated an increase instead of a decrease for higher bias voltages.

  7. Heat-driven spin transport in a ferromagnetic metal

    SciTech Connect

    Xu, Yadong; Yang, Bowen; Tang, Chi; Jiang, Zilong; Shi, Jing; Schneider, Michael; Whig, Renu

    2014-12-15

    As a non-magnetic heavy metal is attached to a ferromagnet, a vertically flowing heat-driven spin current is converted to a transverse electric voltage, which is known as the longitudinal spin Seebeck effect (SSE). If the ferromagnet is a metal, this voltage is also accompanied by voltages from two other sources, i.e., the anomalous Nernst effect in both the ferromagnet and the proximity-induced ferromagnetic boundary layer. By properly identifying and carefully separating those different effects, we find that in this pure spin current circuit the additional spin current drawn by the heavy metal generates another significant voltage by the ferromagnetic metal itself which should be present in all relevant experiments.

  8. Itinerant ferromagnetism in an interacting Fermi gas with mass imbalance

    SciTech Connect

    Keyserlingk, C. W. von; Conduit, G. J.

    2011-05-15

    We study the emergence of itinerant ferromagnetism in an ultracold atomic gas with a variable mass ratio between the up- and down-spin species. Mass imbalance breaks the SU(2) spin symmetry, leading to a modified Stoner criterion. We first elucidate the phase behavior in both the grand canonical and canonical ensembles. Second, we apply the formalism to a harmonic trap to demonstrate how a mass imbalance delivers unique experimental signatures of ferromagnetism. These could help future experiments to better identify the putative ferromagnetic state. Furthermore, we highlight how a mass imbalance suppresses the three-body loss processes that handicap the formation of a ferromagnetic state. Finally, we study the time-dependent formation of the ferromagnetic phase following a quench in the interaction strength.

  9. Room-temperature ferromagnetism in cerium dioxide powders

    SciTech Connect

    Rakhmatullin, R. M. Pavlov, V. V.; Semashko, V. V.; Korableva, S. L.

    2015-08-15

    Room-temperature ferromagnetism is detected in a CeO{sub 2} powder with a grain size of about 35 nm and a low (<0.1 at %) manganese and iron content. The ferromagnetism in a CeO{sub 2} sample with a submicron crystallite size and the same manganese and iron impurity content is lower than in the nanocrystalline sample by an order of magnitude. Apart from ferromagnetism, both samples exhibit EPR spectra of localized paramagnetic centers, the concentration of which is lower than 0.01 at %. A comparative analysis of these results shows that the F-center exchange (FCE) mechanism cannot cause ferromagnetism. This conclusion agrees with the charge-transfer ferromagnetism model proposed recently.

  10. Phosphate binding by natural iron-rich colloids in streams.

    PubMed

    Baken, Stijn; Moens, Claudia; van der Grift, Bas; Smolders, Erik

    2016-07-01

    Phosphorus (P) in natural waters may be bound to iron (Fe) bearing colloids. However, the natural variation in composition and P binding strength of these colloids remain unclear. We related the composition of "coarse colloids" (colloids in the 0.1-1.2 μm size range) in 47 Belgian streams to the chemical properties of the streamwater. On average, 29% of the P in filtered (<1.2 μm) samples of these streams is present in coarse colloids. The concentration of Fe-rich colloids in streams decreases with increasing water hardness and pH. The P bearing colloids in these streams mostly consist of Fe hydroxyphosphates and of Fe oxyhydroxides with surface adsorbed P, which is underpinned by geochemical speciation calculations. In waters with molar P:Fe ratios above 0.5, only a minor part of the P is bound to coarse colloids. In such waters, the colloids have molar P:Fe ratios between 0.2 and 1 and are, therefore, nearly saturated with P. Conversely, in streams with molar P:Fe ratios below 0.1, most of the P is bound to Fe-rich colloids. Equilibration of synthetic and natural Fe and P bearing colloids with a zero sink reveals that colloids with low molar P:Fe ratios contain mostly nonlabile P, whereas P-saturated colloids contain mostly labile P which can be released within 7 days. Equilibration at a fixed free orthophosphate activity shows that the Fe-rich colloids may bind only limited P through surface adsorption, in the range of 0.02-0.04 mol P (mol Fe)(-1). The P:Fe ratios measured in naturally occurring Fe and P bearing colloids is clearly higher (between 0.05 and 1). These colloids are therefore likely formed by coprecipitation of P during oxidation of Fe(II), which leads to the formation of Fe hydroxyphosphate minerals.

  11. Highly Elastic and Self-Healing Composite Colloidal Gels.

    PubMed

    Diba, Mani; Wang, Huanan; Kodger, Thomas E; Parsa, Shima; Leeuwenburgh, Sander C G

    2017-03-01

    Composite colloidal gels are formed by the pH-induced electrostatic assembly of silica and gelatin nanoparticles. These injectable and moldable colloidal gels are able to withstand substantial compressive and tensile loads, and exhibit a remarkable self-healing efficiency. This study provides new, critical insight into the structural and mechanical properties of composite colloidal gels and opens up new avenues for practical application of colloidal gels.

  12. Colloid straining within saturated heterogeneous porous media.

    PubMed

    Porubcan, Alexis A; Xu, Shangping

    2011-02-01

    The transport of 0.46 μm, 2.94 μm, 5.1 μm and 6.06 μm latex particles in heterogeneous porous media prepared from the mixing of 0.78 mm, 0.46 mm and 0.23 mm quartz sands was investigated through column transport experiments. It was observed that the 0.46 μm particles traveled conservatively within the heterogeneous porous media, suggesting that under the experimental conditions employed in this research the strong repulsive interactions between the negatively charged latex particles and the clean quartz sands led to minimal colloid immobilization due to physicochemical filtration. The immobilization of the 2.94 μm, 5.1 μm and 6.06 μm latex particles was thus attributed to colloid straining. Experimental results showed that the straining of colloidal particles within heterogeneous sand mixtures increased when the fraction of finer sands increased. The mathematical model that was developed and tested based on results obtained using uniform sands (Xu et al., 2006) was found to be able to describe colloid straining within heterogeneous porous media. Examination of the relationship between the best-fit values of the clean-bed straining rate coefficients (k(0)) and the ratio of colloid diameter (d(p)) and sand grain size (d(g)) indicated that when number-average sizes were used to represent the size of the heterogeneous porous media, there existed a consistent relationship for both uniform sands and heterogeneous sand mixtures. Similarly, the use of the number-averaged sizes for the heterogeneous porous media produced a uniform relationship between the colloid straining capacity term (λ) and the ratio of d(p)/d(g) for all the sand treatments.

  13. Chemical and Isotopic Analysis of Trace Organic Matter on Meteorites and Interstellar Dust Using a Laser Microprobe Instrument

    NASA Technical Reports Server (NTRS)

    Zare, Richard N.; Boyce, Joseph M. (Technical Monitor)

    2001-01-01

    Polycyclic Aromatic Hydrocarbons (PAHs) are of considerable interest today because they are ubiquitous on Earth and in the interstellar medium (ISM). In fact, about 20% of cosmic carbon in the galaxy is estimated to be in the form of PAHs. Investigation of these species has obvious uses for determining the cosmochemistry of the solar system. Work in this laboratory has focused on four main areas: 1) Mapping the spatial distribution of PAHs in a variety of meteoritic samples and comparing this distribution with mineralogical features of the meteorite to determine whether a correlation exists between the two. 2) Developing a method for detection of fullerenes in extraterrestrial samples using microprobe Laser Desorption Ionization Mass Spectroscopy and utilizing this technique to investigate fullerene presence, while exploring the possibility of spatially mapping the fullerene distribution in these samples through in situ detection. 3) Investigating a possible formation pathway for meteoritic and ancient terrestrial kerogen involving the photochemical reactions of PAHs with alkanes under prebiotic and astrophysically relevant conditions. 4) Studying reaction pathways and identifying the photoproducts generated during the photochemical evolution of PAH-containing interstellar ice analogs as part of an ongoing collaboration with researchers at the Astrochemistry Lab at NASA Ames. All areas involve elucidation of the solar system formation and chemistry using microprobe Laser Desorption Laser Ionization Mass Spectrometry. A brief description of microprobe Laser Desorption Ionization Mass Spectroscopy, which allows selective investigation of subattomole levels of organic species on the surface of a sample at 10-40 micrometer spatial resolution, is given.

  14. A hard x-ray scanning microprobe for fluorescence imaging and microdiffraction at the Advanced Photon Source

    SciTech Connect

    Cai, L.; Lai, B.; Yun, W.; Ilinski, P.; Legnini, D.; Maser, J.; Rodrigues, W.

    1999-11-02

    A hard x-ray scanning microprobe based on zone plate optics and undulator radiation, in the energy region from 6 to 20 keV, has reached a focal spot size (FWHM) of 0.15 {micro}m (v) x 0.6 {micro}m (h), and a photon flux of 4 x 10{sup 9} photons/sec/0.01%BW. Using a slit 44 meters upstream to create a virtual source, a circular beam spot of 0.15 {micro}m in diameter can be obtained with a photon flux of one order of magnitude less. During fluorescence mapping of trace elements in a single human ovarian cell, the microprobe exhibited an imaging sensitivity for Pt (L{sub a} line) of 80 attograms/{micro}m{sup 2} for a count rate of 10 counts per second. The x-ray microprobe has been used to map crystallographic strain and multiquantum well thickness in micro-optoelectronic devices produced with the selective area growth technique.

  15. Pair Potential of Charged Colloidal Stars

    NASA Astrophysics Data System (ADS)

    Huang, F.; Addas, K.; Ward, A.; Flynn, N. T.; Velasco, E.; Hagan, M. F.; Dogic, Z.; Fraden, S.

    2009-03-01

    We report on the construction of colloidal stars: 1μm polystyrene beads grafted with a dense brush of 1μm long and 10 nm wide charged semiflexible filamentous viruses. The pair interaction potentials of colloidal stars are measured using an experimental implementation of umbrella sampling, a technique originally developed in computer simulations in order to probe rare events. The influence of ionic strength and grafting density on the interaction is measured. Good agreements are found between the measured interactions and theoretical predictions based upon the osmotic pressure of counterions.

  16. Fabrication of anisotropic multifunctional colloidal carriers

    NASA Astrophysics Data System (ADS)

    Jerri, Huda A.

    The field of colloidal assembly has grown tremendously in recent years, although the direct or template-assisted methods used to fabricate complex colloidal constructions from monodisperse micro- and nanoparticles have been generally demonstrated on model materials. In this work, novel core particle syntheses, particle functionalizations and bottom-up assembly techniques are presented to create functional colloidal devices. Using particle lithography, high-information colloidal vectors have been developed and modified with imaging and targeting agents. Localized nanoscale patches have been reliably positioned on microparticles to serve as foundations for further chemical or physical modifications. Site-specific placement of RGD targeting ligands has been achieved in these lithographed patches. Preferential uptake of these targeted vectors by RGD-specific 3T3 fibroblasts was verified using confocal laser scanning microscopy. A transition was made from the functionalization of model imaging core particles to the lithography of colloidal cartridges, in an effort to construct colloidal syringes with specialized, programmable release profiles. A variety of functional, pH-sensitive fluorescent cores were engineered to respond to solution conditions. When triggered, the diverse composite core microparticles and reservoir microcapsules released embedded fluorescent moieties such as dye molecules, and fluorophore-conjugated nanoparticles. The microcapsules, created using layer-by-layer polyelectrolyte deposition on sacrificial templates, were selectively modified with a robust coating. The pH-responsive anisotropic reservoir microcapsules were extremely stable in solution, and exhibited a "Lazarus" functionality of rehydrating to their original state following desiccation. A snapshot of focused-release of core constituents through the lone opening in colloidal monotremes has been obtained by anisotropically-functionalizing degradable cores with barrier shells. Additionally

  17. Colloidal-gold electrosensor measuring device

    DOEpatents

    Wegner, S.; Harpold, M.A.; McCaffrey, T.M.; Morris, S.E.; Wojciechowski, M.; Zhao, J.; Henkens, R.W.; Naser, N.; O`Daly, J.P.

    1995-11-21

    The present invention provides a new device for use in measuring lead levels in biological and environmental samples. Using square wave coulometry and colloidal gold particles impregnated on carbon electrodes, the present invention provides a rapid, reliable, portable and inexpensive means of detecting low lead levels. The colloidal gold modified electrodes have microelectrode array characteristics and produce significantly higher stripping detection signals for lead than are produced at bulk gold electrode surfaces. The method is effective in determining levels of lead down to at least 5 {micro}g/dL in blood samples as small as 10 {micro}L. 9 figs.

  18. Dynamics of Colloidal Disorder-Order Transition

    NASA Technical Reports Server (NTRS)

    2001-01-01

    Experiments with colloidal solutions of plastic microspheres suspended in a liquid serve as models of how molecules interact and form crystals. For the Dynamics of Colloidal Disorder-Order Transition (CDOT) experiment, Paul Chaikin of Princeton University has identified effects that are attributable to Earth's gravity and demonstrated that experiments are needed in the microgravity of orbit. Space experiments have produced unexpected dendritic (snowflake-like) structures. To date, the largest hard sphere crystal grown is a 3 mm single crystal grown at the cool end of a ground sample. At least two more additional flight experiments are plarned aboard the International Space Station. This image is from a video downlink.

  19. Colloidal-gold electrosensor measuring device

    DOEpatents

    Wegner, Steven; Harpold, Michael A.; McCaffrey, Terence M.; Morris, Susan E.; Wojciechowski, Marek; Zhao, Junguo; Henkens, Robert W.; Naser, Najih; O'Daly, John P.

    1995-01-01

    The present invention provides a new device for use in measuring lead levels in biological and environmental samples. Using square wave coulometry and colloidal gold particles impregnated on carbon electrodes, the present invention provides a rapid, reliable, portable and inexpensive means of detecting low lead levels. The colloidal gold modified electrodes have microelectrode array characteristics and produce significantly higher stripping detection signals for lead than are produced at bulk gold electrode surfaces. The method is effective in determining levels of lead down to at least 5 .mu.g/dL in blood samples as small as 10 .mu.L.

  20. Anisotropic elasticity of experimental colloidal Wigner crystals.

    PubMed

    Russell, Emily R; Spaepen, Frans; Weitz, David A

    2015-03-01

    Colloidal particles interacting via a long-range repulsion can, in contrast to hard-sphere systems, exhibit crystalline ordering at low volume fraction. Here we experimentally investigate the structure and properties of such "colloidal Wigner crystals." We find a body-centered-cubic crystalline phase at volume fractions of ϕ≳15%, which exhibits large fluctuations of individual particles from their average positions. We determine the three independent crystalline elastic constants and find that these crystals are very compliant and highly anisotropic.