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Sample records for dense hexagonal iron

  1. Size and space controlled hexagonal arrays of superparamagnetic iron oxide nanodots: magnetic studies and application

    PubMed Central

    Ghoshal, Tandra; Maity, Tuhin; Senthamaraikannan, Ramsankar; Shaw, Matthew T.; Carolan, Patrick; Holmes, Justin D.; Roy, Saibal; Morris, Michael A.

    2013-01-01

    Highly dense hexagonally arranged iron oxide nanodots array were fabricated using PS-b-PEO self-assembled patterns. The copolymer molecular weight, composition and choice of annealing solvent/s allows dimensional and structural control of the nanopatterns at large scale. A mechanism is proposed to create scaffolds through degradation and/or modification of cylindrical domains. A methodology based on selective metal ion inclusion and subsequent processing was used to create iron oxide nanodots array. The nanodots have uniform size and shape and their placement mimics the original self-assembled nanopatterns. For the first time these precisely defined and size selective systems of ordered nanodots allow careful investigation of magnetic properties in dimensions from 50 nm to 10 nm, which delineate the nanodots are superparamagnetic, well-isolated and size monodispersed. This diameter/spacing controlled iron oxide nanodots systems were demonstrated as a resistant mask over silicon to fabricate densely packed, identical ordered, high aspect ratio silicon nanopillars and nanowire features. PMID:24072037

  2. Mechanism of the body-centered cubic--hexagonal close-packed phase transition in iron.

    PubMed

    Bassett, W A; Huang, E

    1987-11-06

    The transition from body-centered cubic to hexagonal close-packed phase in iron has been studied in a diamond anvil cell with synchrotron radiation. The hexagonal close-packed phase, when it first appears, has a ratio of lattice parameters that is significantly larger than normal. This is attributed to a displacive mechanism that causes a distortion of the hexagonal close-packed structure in a body-centered cubic matrix. The hexagonal close-packed phase adjacent to a boundary with the body-centered cubic phase is stretched in the c direction and compressed in the a direction when it first forms.

  3. Warm dense iron equation of state from quantum molecular dynamics

    NASA Astrophysics Data System (ADS)

    Sjostrom, Travis; Crockett, Scott

    Through quantum molecular dynamics (QMD), utilizing both Kohn-Sham (orbital-based) and orbital-free density functional theory, we calculate the equation of state of warm dense iron in the density range 7-30 g/cm3 and temperatures from 1 to 100 eV. A critical examination of the iron pseudopotential is made, from which we find the previous QMD calculations of Wang et al. [Phys. Rev. E 89, 023101 (2014)] to be in error. Our results also significantly extend the ranges of density and temperature which are attempted in that prior work. We calculate the shock Hugoniot and find very good agreement with experimental results to pressures over 20 TPa. Additionally we have utilized the QMD results to generate a new SESAME tabular equation of state for fluid iron, accurate in the warm dense matter region, and also extending to much broader regions of density and temperature than can be accessed by the QMD alone.

  4. Synthesis of metastable rare-earth-iron mixed oxide with the hexagonal crystal structure

    NASA Astrophysics Data System (ADS)

    Nishimura, Tatsuya; Hosokawa, Saburo; Masuda, Yuichi; Wada, Kenji; Inoue, Masashi

    2013-01-01

    Rare-earth-iron mixed oxides with the rare earth/iron ratio=1 have either orthorhombic (o-REFeO3) or hexagonal (h-REFeO3) structure. h-REFeO3 is a metastable phase and the synthesis of h-REFeO3 is usually difficult. In this work, the crystallization process of the precursors obtained by co-precipitation and Pechini methods was investigated in detail to synthesize h-REFeO3. It was found that the crystallization from amorphous to hexagonal phase and the phase transition from hexagonal to orthorhombic phase occurred at a similar temperature range for rare earth elements with small ionic radii (Er-Lu, Y). For both co-precipitation and Pechini methods, single-phase h-REFeO3 was obtained by shortening the heating time during calcination process. The hexagonal-to-orthorhombic phase transition took place by a nucleation growth mechanism and vermicular morphology of the thus-formed orthorhombic phase was observed. The hexagonal YbFeO3 had higher catalytic activity for C3H8 combustion than orthorhombic YbFeO3.

  5. Anelastic attenuation in cubic and hexagonal iron alloys: implications for the core

    NASA Astrophysics Data System (ADS)

    Redfern, S. A.; Peng, Z.

    2013-12-01

    Grain boundary processes, phase transitions, line defects and point defects may all play a part in controlling the anelastic properties of iron in Earth's core. We have explored the high temperature behaviour of Fe-Ni alloys to investigate the possible role of phase interfaces at phase transitions between cubic phases of iron. The role of point defects has been considered by analogy with previous measurements on hexagonal metals. The mechanical properties of Fe-Ni alloys were studied by torsion pendulum at seismic frequencies from 0.01 to 1 Hz over temperatures from 30 C to 1000 C and atmospheric pressure. The cubic Fe-Ni system undergoes an equilibrium fcc-bcc phase transition for Ni concentration < 5 at.%, but shows a metastable martensitic phase transition from austenite to a distorted bcc martensite when there is more than 5 at.% Ni in the alloy. Mechanical properties show significant variation at the phase transition temperature: significant softening in shear modulus, abrupt change in elastic strain, and massive energy dissipation. Variation in elastic constant as a function of temperature defines the shear modulus, while the volumetric difference between the fcc and bcc structure contributes to a sudden variation in strain at the transition. The movement of interfaces (phase interfaces and martensite variant interfaces) is the key mechanism for anelastic damping at the transition. An intermediate mixture of phases (bcc + fcc or martenste + fcc) was identified over a wide range of temperatures, indicating the importance of phase nucleation process at the transition. For a pure hexagonal iron core there remains the possibility of energy dissipation by an intrinsic atomistic process. While no measurements of anelastic relaxation have been made in hexagonal iron, earlier studies of zirconium and titanium (hexagonal metals).Reorientation of pairs of interstitial atoms or even interstitial-substitutional pairs of atoms provides a mechanism for anelastic relaxation

  6. Magnetic properties of hexagonal closed-packed iron deduced from direct observations in a diamond anvil cell

    PubMed

    Gilder; Glen

    1998-01-02

    The attraction of hexagonal closed packed (hcp) iron to a magnet at 16.9 gigapascals and 261 degrees centigrade suggests that hcp iron is either paramagnetic or ferromagnetic with susceptibilities from 0. 15 to 0.001 and magnetizations from 1800 to 15 amperes per meter. If dominant in Earth's inner core, paramagnetic hcp iron could stabilize the geodynamo.

  7. Thermal conductivity measurements of warm dense iron at the LCLS

    NASA Astrophysics Data System (ADS)

    McKelvey, A.; Jiang, S.; Collins, G.; Shepherd, R.; Hau-Riege, S. P.; Hill, M. P.; Brown, C. R. D.; Floyd, E.; Fyrth, J. D.; Skidmore, J. W.; Hua, R.; Beg, F. N.; Kim, M.; Cho, B.; Lee, J.; King, J.; Freeman, R. R.; Lee, H. J.; Galtier, E.; Audebert, P.; Levy, A.; Ping, Y.

    2016-10-01

    Accurate knowledge of conductivity characteristics in the strongly coupled plasma regime is extremely important for ICF processes such as the onset of hydrodynamic instabilities, thermonuclear burn propagation waves, shell mixing, and efficient x-ray conversion of indirect drive schemes. Recently, an experiment was performed at the LCLS at SLAC to measure the thermal conductivity of warm dense iron. The experiment used 6.8 keV x-rays to differentially heat thin bi-layer Au/Fe targets and establish a prompt temperature gradient at the layer interface. We used a SOP and a FDI to measure the rear layer's time-resolved temperature, expansion velocity, and reflectivity. Data from the time-resolved diagnostics for 100 nm Au and 50 to 100 nm Fe targets will be presented along with analysis and comparison with various models in the strongly coupled plasma regime. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344.

  8. First-principles study of iron spin crossover in the new hexagonal aluminous phase

    NASA Astrophysics Data System (ADS)

    Hsu, Han

    2017-01-01

    The new hexagonal aluminous (NAL) phase, chemical formula A B2C6O12 (A = Na+, K+, Ca2 +; B = Mg2 +, Fe2 +, Fe3 +; C = Al3 +, Si4 +, Fe3 +), is considered a major component (˜20 vol%) of mid-ocean ridge basalt (MORB) under the lower-mantle condition. As MORB can be transported back into the Earth's lower mantle via subduction, a thorough knowledge of the NAL phase is essential to fully understand the fate of subducted MORB and its role in mantle dynamics and heterogeneity. In this Rapid Communication, the complicated spin crossover of the Fe-bearing NAL phase is revealed by a series of local density approximation + self-consistent Hubbard U (LDA+Us c) calculations. Only the ferric iron (Fe3 +) substituting Al/Si in the octahedral (C ) site undergoes a crossover from the high-spin (HS) to the low-spin (LS) state at ˜40 GPa, while iron substituting Mg in the trigonal-prismatic (B ) site remains in the HS state, regardless of its oxidation state (Fe2 + or Fe3 +). The volume/elastic anomalies and the iron nuclear quadrupole splittings determined by calculations are in great agreement with room-temperature experiments. The calculations further predict that the HS-LS transition pressure of the NAL phase barely increases with temperature due to the three nearly degenerate LS states of Fe3 +, suggesting that the elastic anomalies of this mineral can occur at the top lower mantle.

  9. Structural and electrical studies of sol-gel synthesized nanocrystalline hexagonal yttrium iron manganite ceramics

    NASA Astrophysics Data System (ADS)

    Touthang, Jangkhohao; Maisnam, Mamata

    2017-03-01

    Hexagonal yttrium manganites, YMnO3, are interesting materials for their multiferroic behavior. Substituting suitable cations either at the Y-site or Mn-site offers great opportunities to produce a variety of manganites and tune their properties. Nanocrystalline yttrium iron manganites with the compositional formula Y1‑xFexMnO3, x = 0.0, 0.10, 0.15, 0.20 and 0.25, were synthesized by sol-gel autocombustion method. The prepared samples were heated at 1100∘C for 1 h. Another set of samples with compositional formula YFexMn1‑xO3, x = 0.0, 0.10, 0.15, 0.20 and 0.25, were also synthesized by the same method and heated at 1100∘C for 1 h. Various characterizations were done on these manganite systems synthesized by substituting iron at different sites. X-ray diffraction (XRD) technique studied the structure of the samples and analysis of XRD patterns confirmed the formation of hexagonal phase in the samples. Structural parameters such as lattice constants, crystallite size, theoretical density, etc. were determined using the XRD data. The unit cell dimensions have been found to agree with the standard data and the Debye-Scherrer crystallite size obtained from XRD data ranges from 42 nm to 77 nm. The room temperature frequency variations of electrical properties such as dielectric constant, dielectric loss and AC conductivity were measured in the range of 100 Hz-2 MHz and the variations showed a dispersive behavior for all the samples. The various measurements and the results obtained were studied and discussed in the paper.

  10. Lattice dynamics and thermodynamics of hexagonal-close-packed iron at high temperatures and pressures

    NASA Astrophysics Data System (ADS)

    Sha, X.; Cohen, R. E.

    2005-05-01

    We performed linear-response Linear-Muffin-Tin-Orbital (LMTO) calculations to understand and predict the lattice dynamical and thermal properties of hexagonal-close-packed iron at high temperatures and pressures. The phonon dispersion and phonon density of states have been calculated at different volumes and various c/a axial ratios, which show good agreements with available experimental data. We also calculated the thermal conductivity and electrical resistivity at different pressure. We derived the Hemlmholtz free energy functionals based on the LMTO calculations, and have further applied to establish the thermal equation of state, bulk modulus K0, dK0/dT, and thermal expansion coefficients at high pressures and temperatures. The variations of c/a ratios with temperature and pressure have been predicted. We also used the particle-in-cell approach to examine the thermal properties based on tight-binding total energy calculations, and made a detailed comparison with lattice dynamics calculations and experiment. The influence of anharmonic effects has been examined. This work was supported by US Department of Energy ASCI/ASAP subcontract to Caltech, Grant DOE W-7405-ENG-48 (to REC).

  11. Thermoelasticity of Hexagonal Close-Packed Iron from the Phonon Density of States

    NASA Astrophysics Data System (ADS)

    Murphy, Caitlin A.

    This thesis explores the vibrational thermodynamic and thermoelastic properties of pure hexagonal close-packed iron (ε-Fe), in an effort to improve our understanding of the properties of a significant fraction of this remote region of the deep Earth and in turn, better constrain its composition. We determined the Debye sound velocity (vD) at each of our compression points from the low-energy region of the phonon DOS and our in situ measured volumes. In turn, vD is related to the compressional and shear sound velocities via our determined densities and the adiabatic bulk modulus. Our high-statistical quality dataset places a new tight constraint on the density dependence of ε-Fe's sound velocities to outer core pressures. Via comparison with existing data for iron alloys, we investigate how nickel and candidate light elements for the core affect the thermoelastic properties of iron. In addition, we explore the effects of temperature on ε-Fe's sound velocities by applying pressure- and temperature-dependent elastic moduli from theoretical calculations to a finite-strain model. Such models allow for direct comparisons with one-dimensional seismic models of Earth's solid inner core (e.g., the Preliminary Reference Earth Model). Next, the volume dependence of the vibrational free energy is directly related to the vibrational thermal pressure, which we combine with previously reported theoretical values for the electronic and anharmonic thermal pressures to find the total thermal pressure of ε-Fe. In addition, we found a steady increase in the Lamb-Mössbauer factor with compression, which suggests restricted thermal atomic motions at outer core pressures. This behavior is related to the high-pressure melting behavior of ε-Fe via Gilvarry's reformulation of Lindemann's melting criterion, which we used to obtain the shape of ε-Fe's melting curve up to 171 GPa. By anchoring our melting curve shape with experimentally determined melting points and considering thermal

  12. Dense nanocrystalline yttrium iron garnet films formed at room temperature by aerosol deposition

    SciTech Connect

    Johnson, Scooter D. Glaser, Evan R.; Cheng, Shu-Fan; Hite, Jennifer

    2016-04-15

    Highlights: • We deposit yttrium iron garnet films at room temperature using aerosol deposition. • Films are 96% of theoretical density for yttrium iron garnet. • We report magnetic and structural properties post-deposition and post-annealing. • Low-temperature annealing decreases the FMR linewidth. • We discuss features of the FMR spectra at each anneal temperature. - Abstract: We have employed aerosol deposition to form polycrystalline yttrium iron garnet (YIG) films on sapphire at room temperature that are 90–96% dense. We characterize the structural and dynamic magnetic properties of the dense films using scanning electron microscopy, X-ray diffraction, and ferromagnetic resonance techniques. We find that the as-deposited films are pure single-phase YIG formed of compact polycrystallites ∼20 nm in size. The ferromagnetic resonance mode occurs at 2829 G with a linewidth of 308 G. We perform a series of successive anneals up to 1000 °C on a film to explore heat treatment on the ferromagnetic resonance linewidth. We find the narrowest linewidth of 98 G occurs after a 750 °C anneal.

  13. Growth Kinetics of In Situ Fabricated Dense NbC Coatings on Gray Cast Iron

    NASA Astrophysics Data System (ADS)

    Shen, Liuliu; Xu, Yunhua; Zhao, Nana; Zhao, Ziyuan; Zhong, Lisheng; Song, Ke; Cai, Xiaolong; Wang, Juan

    2016-12-01

    In the present study, dense niobium carbide (NbC) coatings are fabricated by in situ techniques on gray cast iron (Fe) substrates at 1150 °C for 5 min, followed by a heat treatment at 990, 1010 and 1030 °C for 5, 10, 15 and 20 min. The microstructure, element composition and metallographic phase of the coating are characterized by scanning electron microscope, energy dispersive spectral and x-ray diffraction, respectively. Results show that the coating consists of NbC and α-Fe phases. NbC coating thickness ranges from 12.51 ± 1.4 to 29.17 ± 2.0 µm depending on the heat treatment temperature and time. In addition, the growth kinetics of dense niobium carbide coatings are estimated. A diffusion model based on Fick's laws is used to explore the carbon diffusion coefficients of the dense NbC coating in the range of heat treatment temperatures in which the experimental results of the kinetics of the niobium carbide coating are in good agreement with those estimated using diffusion model.

  14. Spin crossover and iron-rich dense partial melt in pyrolitic lower mantle

    NASA Astrophysics Data System (ADS)

    Hirose, K.; Tateno, S.

    2012-12-01

    Spin crossover of iron may occur not only in solids but also in melts in the lower mantle. The resulting change in Fe partitioning strongly affects the buoyancy of partial melts near the base of the mantle. Nomura et al. [2011 Nature] measured the Fe partitioning in (Mg0.89Fe0.11)2 SiO4 bulk composition over the entire mantle pressure range, demonstrating that Fe-Mg distribution coefficient KD = ([FePv]/[MgPv]) / ([Femelt]/[Mgmelt]) between (Mg,Fe)SiO3 perovskite and melt dropped from ~0.25 to <0.1 around 76 GPa, resulting in strong Fe-enrichment in melts and thereby dense partial melts in the mid-lower mantle. In contrast, the most recent experiments by Andrault et al. [2012 Nature] found much higher KD and less Fe-enrichment in partial melts formed in primitive mantle composition, suggesting that melt is not dense in the lowermost mantle. Here we extend our measurements in pyrolitic natural mantle (KLB-1 peridotite) bulk composition. The distribution coefficient KD (total Fe/Mg) was determined at 40-180 GPa by a combination of laser-heated diamond-anvil cell experiments and chemical analyses of recovered samples using field-emission-type electron microprobe (FE-EPMA). Our results demonstrate that KD between perovskite and melt is about 0.3 up to 58 GPa, consistent with earlier multi-anvil data. It then dropped to ~0.1 above 68 GPa, indicating strong Fe-enrichment in partial melts. These results are in excellent agreement with those of Nomura et al. [2011], indicating that Fe-rich partial melts are more dense than solids below 1600-km depth in the lower mantle. The observed Fe-enrichment in partial melt above 68 GPa can be explained by a spin crossover of iron in silicate melt, as discussed previously in Nomura et al. [2011].

  15. Structural and optical properties of dense vertically aligned ZnO nanorods grown onto silver and gold thin films by galvanic effect with iron contamination

    SciTech Connect

    Scarpellini, D.; Paoloni, S.; Medaglia, P.G.; Pizzoferrato, R.; Orsini, A.; Falconi, C.

    2015-05-15

    Highlights: • ZnO nanorods were grown on Au and Ag films in aqueous solution by galvanic effect. • The method is prone to metal contamination which can influence the ZnO properties. • Iron doping improves the lattice matching between ZnO and the substrate. • Energy levels of point defects are lowered and the light emission is red-shifted. • Galvanic-induced nucleation starts and proceeds continuously during the growth. - Abstract: Dense arrays of vertically aligned ZnO nanorods have been grown onto either silver or gold seedless substrates trough a simple hydrothermal method by exploiting the galvanic effect between the substrate and metallic parts. The nanorods exhibit larger bases and more defined hexagonal shapes, in comparison with standard non-galvanic wet-chemistry synthesis. X-ray diffraction (XRD) shows that the iron contamination, associated with the galvanic contact, significantly improves the in-plane compatibility of ZnO with the Au and Ag cubic lattice. Photoluminescence (PL) measurements indicate that the contamination does not affect the number density of localized defects, but lowers their energy levels uniformly; differently, the band-edge emission is not altered appreciably. Finally, we have found that the ZnO hetero-nucleation by galvanic effect initiates at different times in different sites of the substrate area. Our results can be useful for the fabrication of high performance piezonanodevices comprising high-density metal-to-ZnO nanoscaled junctions without intermediate polycrystalline layers.

  16. Microstructure and Scratch Resistance of TaC Dense Ceramic Layer on an Iron Matrix

    NASA Astrophysics Data System (ADS)

    Zhao, Nana; Xu, Yunhua; Zhong, Lisheng; Yan, Honghua; Ovcharenko, Vladimir E.

    2016-06-01

    A tantalum carbide dense ceramic layer with a thickness of ~20 μm was produced on the surface of an iron matrix using an in situ technique. The morphology, microstructure, and phase composition of the layer were characterized by means of SEM, TEM, and XRD. The results show fairly agglomerated and uniformly sized (~200 nm) TaC particulates with a face-cantered cubic structure. The values of nano-hardness for the surface and cross section of reinforcing layer can be as high as 29.5 ± 0.6 and 26.7 ± 0.1 GPa, respectively, which were analyzed using a nano-indentation apparatus. Moreover, the scratch resistance of the layer was measured by scratch tests under a progressively increasing load of 0-100 N. A high critical load of 90.4 N is obtained. It is worthy to note that there are only cracking, slight splitting, and small flaking pits (even at the maximum load) all over the whole scratch process, namely the reinforcing layer can protect the iron matrix from serious abrasion effectively. In addition, the excellent scratch resistance and mechanism are discussed in detail.

  17. Hexagonal Platelet-like Magnetite as a Biosignature of Thermophilic Iron-Reducing Bacteria and Its Applications to the Exploration of the Modern Deep, Hot Biosphere and the Emergence of Iron-Reducing Bacteria in Early Precambrian Oceans

    PubMed Central

    2012-01-01

    Abstract Dissimilatory iron-reducing bacteria are able to enzymatically reduce ferric iron and couple to the oxidation of organic carbon. This mechanism induces the mineralization of fine magnetite crystals characterized by a wide distribution in size and irregular morphologies that are indistinguishable from authigenic magnetite. Thermoanaerobacter are thermophilic iron-reducing bacteria that predominantly inhabit terrestrial hot springs or deep crusts and have the capacity to transform amorphous ferric iron into magnetite with a size up to 120 nm. In this study, I first characterize the formation of hexagonal platelet-like magnetite of a few hundred nanometers in cultures of Thermoanaerobacter spp. strain TOR39. Biogenic magnetite with such large crystal sizes and unique morphology has never been observed in abiotic or biotic processes and thus can be considered as a potential biosignature for thermophilic iron-reducing bacteria. The unique crystallographic features and strong ferrimagnetic properties of these crystals allow easy and rapid screening for the previous presence of iron-reducing bacteria in deep terrestrial crustal samples that are unsuitable for biological detection methods and, also, the search for biogenic magnetite in banded iron formations that deposited only in the first 2 billion years of Earth with evidence of life. Key Words: Biosignatures—Magnetite—Iron-reducing bacteria—Deep subsurface biosphere—Banded iron formation. Astrobiology 12, 1100–1108. PMID:23145573

  18. Hexagonal platelet-like magnetite as a biosignature of thermophilic iron-reducing bacteria and its applications to the exploration of the modern deep, hot biosphere and the emergence of iron-reducing bacteria in early precambrian oceans.

    PubMed

    Li, Yi-Liang

    2012-12-01

    Dissimilatory iron-reducing bacteria are able to enzymatically reduce ferric iron and couple to the oxidation of organic carbon. This mechanism induces the mineralization of fine magnetite crystals characterized by a wide distribution in size and irregular morphologies that are indistinguishable from authigenic magnetite. Thermoanaerobacter are thermophilic iron-reducing bacteria that predominantly inhabit terrestrial hot springs or deep crusts and have the capacity to transform amorphous ferric iron into magnetite with a size up to 120 nm. In this study, I first characterize the formation of hexagonal platelet-like magnetite of a few hundred nanometers in cultures of Thermoanaerobacter spp. strain TOR39. Biogenic magnetite with such large crystal sizes and unique morphology has never been observed in abiotic or biotic processes and thus can be considered as a potential biosignature for thermophilic iron-reducing bacteria. The unique crystallographic features and strong ferrimagnetic properties of these crystals allow easy and rapid screening for the previous presence of iron-reducing bacteria in deep terrestrial crustal samples that are unsuitable for biological detection methods and, also, the search for biogenic magnetite in banded iron formations that deposited only in the first 2 billion years of Earth with evidence of life.

  19. Laterally spreading iron, humic-like dissolved organic matter and nutrients in cold, dense subsurface water of the Arctic Ocean

    PubMed Central

    Hioki, Nanako; Kuma, Kenshi; Morita, Yuichirou; Sasayama, Ryouhei; Ooki, Atsushi; Kondo, Yoshiko; Obata, Hajime; Nishioka, Jun; Yamashita, Youhei; Nishino, Shigeto; Kikuchi, Takashi; Aoyama, Michio

    2014-01-01

    The location and magnitude of oceanic iron sources remain uncertain owing to a scarcity of data, particularly in the Arctic Ocean. The formation of cold, dense water in the subsurface layer of the western Arctic Ocean is a key process in the lateral transport of iron, macronutrients, and other chemical constituents. Here, we present iron, humic-like fluorescent dissolved organic matter, and nutrient concentration data in waters above the continental slope and shelf and along two transects across the shelf–basin interface in the western Arctic Ocean. We detected high concentrations in shelf bottom waters and in a plume that extended in the subsurface cold dense water of the halocline layer in slope and basin regions. At σθ = 26.5, dissolved Fe, humic-like fluorescence intensity, and nutrient maxima coincided with N* minima (large negative values of N* indicate significant denitrification within shelf sediments). These results suggest that these constituents are supplied from the shelf sediments and then transported laterally to basin regions. Humic dissolved organic matter probably plays the most important role in the subsurface maxima and lateral transport of dissolved Fe in the halocline layer as natural Fe-binding organic ligand. PMID:25345398

  20. Laterally spreading iron, humic-like dissolved organic matter and nutrients in cold, dense subsurface water of the Arctic Ocean.

    PubMed

    Hioki, Nanako; Kuma, Kenshi; Morita, Yuichirou; Sasayama, Ryouhei; Ooki, Atsushi; Kondo, Yoshiko; Obata, Hajime; Nishioka, Jun; Yamashita, Youhei; Nishino, Shigeto; Kikuchi, Takashi; Aoyama, Michio

    2014-10-27

    The location and magnitude of oceanic iron sources remain uncertain owing to a scarcity of data, particularly in the Arctic Ocean. The formation of cold, dense water in the subsurface layer of the western Arctic Ocean is a key process in the lateral transport of iron, macronutrients, and other chemical constituents. Here, we present iron, humic-like fluorescent dissolved organic matter, and nutrient concentration data in waters above the continental slope and shelf and along two transects across the shelf-basin interface in the western Arctic Ocean. We detected high concentrations in shelf bottom waters and in a plume that extended in the subsurface cold dense water of the halocline layer in slope and basin regions. At σθ = 26.5, dissolved Fe, humic-like fluorescence intensity, and nutrient maxima coincided with N* minima (large negative values of N* indicate significant denitrification within shelf sediments). These results suggest that these constituents are supplied from the shelf sediments and then transported laterally to basin regions. Humic dissolved organic matter probably plays the most important role in the subsurface maxima and lateral transport of dissolved Fe in the halocline layer as natural Fe-binding organic ligand.

  1. Segregation of acid plume pixels from background water pixels, signatures of background water and dispersed acid plumes, and implications for calculation of iron concentration in dense plumes

    NASA Technical Reports Server (NTRS)

    Bahn, G. S.

    1978-01-01

    Two files of data, obtained with a modular multiband scanner, for an acid waste dump into ocean water, were analyzed intensively. Signatures were derived for background water at different levels of effective sunlight intensity, and for different iron concentrations in the dispersed plume from the dump. The effect of increased sunlight intensity on the calculated iron concentration was found to be relatively important at low iron concentrations and relatively unimportant at high values of iron concentration in dispersed plumes. It was concluded that the basic equation for iron concentration is not applicable to dense plumes, particularly because lower values are indicated at the very core of the plume, than in the surrounding sheath, whereas radiances increase consistently from background water to dispersed plume to inner sheath to innermost core. It was likewise concluded that in the dense plume the iron concentration would probably best be measured by the higher wave length radiances, although the suitable relationship remains unknown.

  2. Chlorine Insertion Promoting Iron Reduction in Ba-Fe Hexagonal Perovskites: Effect on the Structural and Magnetic Properties.

    PubMed

    Serrador, Laura; Hernando, María; Martínez, José L; González-Calbet, José M; Varela, Aurea; García-García, F Javier; Parras, Marina

    2016-06-20

    BaFeCl0.13(2)O2.48(2) has been synthesized and studied. A proper tuning of the synthetic route has been designed to stabilize this compound as a single phase. The thermal stability and evolution, along with the magnetic and structural properties are reported here. The crystal structure has been refined from neutron powder diffraction data, and it is of the type (hhchc)2-10H. It is stable up to a temperature of 900 °C, where the composition reads BaFeCl0.13(2)O2.34(2). The study by electron microscopy shows that the crystal structure suffers no changes in the whole BaFeCl0.13(1)O3-y (2.34 ≤ 3 - y ≤ 2.48) compositional range. Refinement of the magnetic structure shows that the Fe is antiferromagneticaly ordered, with the magnetic moment parallel to the ab plane of the hexagonal structure. At higher temperature, a nonreversible phase transition into a (hchc)-4H structure type takes place with overall composition BaFeCl0.13(1)O2.26(1). Microstructural characterization shows that, in some crystals, this phase intergrows with a seemingly cubic related phase. Differences between these two crystalline phases reside in the chlorine content, which keeps constant through the phase transition for the former and disappears for the latter.

  3. SOLUBILITY OF IRON IN METALLIC HYDROGEN AND STABILITY OF DENSE CORES IN GIANT PLANETS

    SciTech Connect

    Wahl, Sean M.; Wilson, Hugh F.; Militzer, Burkhard

    2013-08-20

    The formation of the giant planets in our solar system, and likely a majority of giant exoplanets, is most commonly explained by the accretion of nebular hydrogen and helium onto a large core of terrestrial-like composition. The fate of this core has important consequences for the evolution of the interior structure of the planet. It has recently been shown that H{sub 2}O, MgO, and SiO{sub 2} dissolve in liquid metallic hydrogen at high temperature and pressure. In this study, we perform ab initio calculations to study the solubility of an innermost metallic core. We find dissolution of iron to be strongly favored above 2000 K over the entire pressure range (0.4-4 TPa) considered. We compare with and summarize the results for solubilities on other probable core constituents. The calculations imply that giant planet cores are in thermodynamic disequilibrium with surrounding layers, promoting erosion and redistribution of heavy elements. Differences in solubility behavior between iron and rock may influence evolution of interiors, particularly for Saturn-mass planets. Understanding the distribution of iron and other heavy elements in gas giants may be relevant in understanding mass-radius relationships, as well as deviations in transport properties from pure hydrogen-helium mixtures.

  4. DENSE IRON EJECTA AND CORE-COLLAPSE SUPERNOVA EXPLOSION IN THE YOUNG SUPERNOVA REMNANT G11.2-0.3

    SciTech Connect

    Moon, Dae-Sik; Koo, Bon-Chul; Seok, Ji Yeon; Lee, Ho-Gyu; Matthews, Keith; Lee, Jae-Joon; Pyo, Tae-Soo; Hayashi, Masahiko

    2009-09-20

    We present the results of near-infrared spectroscopic observations of dense ({approx}>10{sup 3} cm{sup -3}) iron ejecta in the young core-collapse supernova remnant G11.2-0.3. Five ejecta knots projected to be close to its center show a large dispersion in their Doppler shifts: two knots in the east are blueshifted by more than 1000 km s{sup -1}, while three western knots have relatively small blueshifts of 20-60 km s{sup -1}. This velocity discrepancy may indicate that the western knots have been significantly decelerated or that there exists a systematic velocity difference among the knots. One ejecta filament in the northwestern boundary, on the other hand, is redshifted by {approx}>200 km s{sup -1}, while opposite filament in the southeastern boundary shows a negligible radial motion. Some of the knots and filaments have secondary velocity components, and one knot shows a bow shock-like feature in the velocity structure. The iron ejecta appear to be devoid of strong emission from other heavy elements, such as S, which may attest to the alpha-rich freezeout process in the explosive nucleosynthesis of the core-collapse supernova explosion close to its center. The prominent bipolar distribution of the Fe ejecta in the northwestern and southeastern direction, along with the elongation of the central pulsar wind nebula in the perpendicular direction, is consistent with the interpretation that the supernova exploded primarily along the northwestern and southeastern direction.

  5. Iron and manganese-related magnetic centers in hexagonal silicon carbide: A possible roadmap for spintronic devices

    SciTech Connect

    Machado, W. V. M.; Assali, L. V. C.; Justo, J. F.

    2015-07-28

    The electronic and magnetic properties of manganese- and iron-doped 4H-SiC were investigated by first-principles calculations, using an all electron methodology. The results on stability, spin configurations, formation and transition energies, local magnetic moments, and hyperfine parameters were compared to available theoretical and experimental data. The results indicated that transition metal impurities are energetically more favorable in lattice sites with carbon atoms as their first nearest neighbors, in both substitutional and interstitial configurations, which results from the larger electronegativity of carbon with respect to that of silicon. The analysis of the electronic properties of those impurity centers showed that they could stay in several stable charge states, depending on the Fermi energy level position within the host SiC bandgap. Additionally, by computing the p-d exchange coupling constant, which is related to a spin polarization in the SiC valence band top, we explored the possibility of achieving macroscopic magnetism in SiC. The results indicated that some centers, in both substitutional and interstitial configurations, present reasonably strong magnetic couplings to mediate macroscopic magnetism at high temperatures, which may generate spin polarized currents, leading to applications in spintronic devices.

  6. Iron and manganese-related magnetic centers in hexagonal silicon carbide: A possible roadmap for spintronic devices

    NASA Astrophysics Data System (ADS)

    Machado, W. V. M.; Justo, J. F.; Assali, L. V. C.

    2015-07-01

    The electronic and magnetic properties of manganese- and iron-doped 4H-SiC were investigated by first-principles calculations, using an all electron methodology. The results on stability, spin configurations, formation and transition energies, local magnetic moments, and hyperfine parameters were compared to available theoretical and experimental data. The results indicated that transition metal impurities are energetically more favorable in lattice sites with carbon atoms as their first nearest neighbors, in both substitutional and interstitial configurations, which results from the larger electronegativity of carbon with respect to that of silicon. The analysis of the electronic properties of those impurity centers showed that they could stay in several stable charge states, depending on the Fermi energy level position within the host SiC bandgap. Additionally, by computing the p-d exchange coupling constant, which is related to a spin polarization in the SiC valence band top, we explored the possibility of achieving macroscopic magnetism in SiC. The results indicated that some centers, in both substitutional and interstitial configurations, present reasonably strong magnetic couplings to mediate macroscopic magnetism at high temperatures, which may generate spin polarized currents, leading to applications in spintronic devices.

  7. Formation of Thick Dense Yttrium Iron Garnet Films Using Aerosol Deposition.

    PubMed

    Johnson, Scooter D; Glaser, Evan R; Kub, Fritz J; Eddy, Charles R

    2015-05-15

    Aerosol deposition (AD) is a thick-film deposition process that can produce layers up to several hundred micrometers thick with densities greater than 95% of the bulk. The primary advantage of AD is that the deposition takes place entirely at ambient temperature; thereby enabling film growth in material systems with disparate melting temperatures. This report describes in detail the processing steps for preparing the powder and for performing AD using the custom-built system. Representative characterization results are presented from scanning electron microscopy, profilometry, and ferromagnetic resonance for films grown in this system. As a representative overview of the capabilities of the system, focus is given to a sample produced following the described protocol and system setup. Results indicate that this system can successfully deposit 11 µm thick yttrium iron garnet films that are  > 90% of the bulk density during a single 5 min deposition run. A discussion of methods to afford better control of the aerosol and particle selection for improved thickness and roughness variations in the film is provided.

  8. Formation of Thick Dense Yttrium Iron Garnet Films Using Aerosol Deposition

    PubMed Central

    Johnson, Scooter D.; Glaser, Evan R.; Kub, Fritz J.; Eddy,, Charles R.

    2015-01-01

    Aerosol deposition (AD) is a thick-film deposition process that can produce layers up to several hundred micrometers thick with densities greater than 95% of the bulk. The primary advantage of AD is that the deposition takes place entirely at ambient temperature; thereby enabling film growth in material systems with disparate melting temperatures. This report describes in detail the processing steps for preparing the powder and for performing AD using the custom-built system. Representative characterization results are presented from scanning electron microscopy, profilometry, and ferromagnetic resonance for films grown in this system. As a representative overview of the capabilities of the system, focus is given to a sample produced following the described protocol and system setup. Results indicate that this system can successfully deposit 11 µm thick yttrium iron garnet films that are  > 90% of the bulk density during a single 5 min deposition run. A discussion of methods to afford better control of the aerosol and particle selection for improved thickness and roughness variations in the film is provided. PMID:26067027

  9. Epitaxial Garnets and Hexagonal Ferrites.

    DTIC Science & Technology

    1983-12-01

    Ferrites Lithium Ferrite Magnetostatic Wave Garnets Epitaxy Yttrium Iron Garnet Liquid Phase Epitaxy Hexagonal Ferrite Microwave Signal Processing...epitaxial ferrit ( materials for use in microwave and millirreter-wave signal processing devices. The major emphasis has been on multiple layer...overall objective of this research is to develop epitaxial single crystal ferrite films suitable for microwave and millimeter-wave signal processing at

  10. Epitaxial Garnets and Hexagonal Ferrites.

    DTIC Science & Technology

    1982-04-20

    Iron Garnet Liquid Phase Epitaxy Hexagonal Ferrite microwave Signal Processing Millimeter-Wave 20. ABSTRACT (Continue ani revee arde if necoeermy and...le.’uIfy by block rns.) e objective of this research is to develop new and improved epitauial ferrite materials for use in microwave and millimeter... ferrite films suitable for microwave and millimeter-wave signal processing at frequencies above 1 GHz. The specific tasks are: a. Analyze and develop

  11. Hexagons of the Heart

    ERIC Educational Resources Information Center

    Burkhauser, Beth; Porter, Dave

    2010-01-01

    This article discusses the international interdependence Hexagon Project for Haiti which invites students, ages five through eighteen, to create an image within a hexagonal template and respond to big questions surrounding a global culture of interdependence. The hexagon is a visual metaphor for interdependence, with its potential to infinitely…

  12. Hexagons of the Heart

    ERIC Educational Resources Information Center

    Burkhauser, Beth; Porter, Dave

    2010-01-01

    This article discusses the international interdependence Hexagon Project for Haiti which invites students, ages five through eighteen, to create an image within a hexagonal template and respond to big questions surrounding a global culture of interdependence. The hexagon is a visual metaphor for interdependence, with its potential to infinitely…

  13. Electron and ion dynamics study of iron in warm dense matter regime by time-resolved XAS measurements and from first-principles

    NASA Astrophysics Data System (ADS)

    Ogitsu, T.; Fernandez-Paãella, A.; Correa, A.; Engelhorn, K.; Barbrel, B.; Prendergast, D. G.; Pemmaraju, D.; Beckwith, M.; Kraus, D.; Hamel, S.; Cho, B. I.; Jin, L.; Wong, J.; Heinman, P.; Collins, G. W.; Falcone, R.; Ping, Y.

    2016-10-01

    We present a study of the electron-phonon coupling of warm dense iron upon femtosecond laser excitation by time-resolved x-ray absorption near edge spectroscopy (XANES). The dynamics of iron in electron-ion non-equilibrium conditions was studied using ab-initio density-functional-theory (DFT) simulations combined with the Two Temperature Model (TTM) where spatial inhomogeneity of electron (and ion) temperature(s) due to short ballistic electron transport length in iron was explicitly taken into consideration. Detailed comparison between our simulation results and experiments indicates that the ion temperature dependence on specific heat and on electron-phonon coupling also plays a relevant role in modeling the relaxation dynamics of electrons and ions. These results are the first experimental evidence of the suppression of the electron-phonon coupling factor of a transition metal at electron temperatures ranging 5000- 10000 K. This work was performed under DOE contract DE-AC52-07NA27344 with support from OFES Early Career program and LLNL LDRD program.

  14. Investigation of wetting characteristics of liquid iron on dense MgAION-based ceramics by X-ray sessile drop technique

    NASA Astrophysics Data System (ADS)

    Zhang, Z. T.; Matsushita, T.; Seetharaman, S.; Li, W. C.

    2006-06-01

    The wetting characteristics of liquid iron on dense MgAION-based composite ceramics were investigated using X-ray sessile drop technique. The contact angles were measured on substrates of different composites as functions of temperature and varying partial pressures of oxygen. The results with pure argon gas showed that contact angles kept almost constant in the temperature range 1823 to 1873 K. The contact angle was found to show a slight increase with increasing boron nitride (BN) content in MgAION-BN composites. These are attributed to the higher contact angle between BN substrate and liquid iron drop compared with that obtained for MgAION substrate. When the CO-CO2-Ar gas mixtures were introduced into the system, the contact angle showed an initial quick decrease followed by a slow decrease and then a period of nearly constant contact angle at a given temperature corresponding to the steady-state condition. Even in this case, BN seemed to cause an increase in the equilibrium contact angle. The equilibrium contact angle was found to decrease with increasing temperature. XRD results indicated that the substrate was oxidized and the oxidation products combined with FeO formed by the oxidation of the iron drop to from FeAl2O4 and Mg1-xFex) These were likely to form a ternary FeO-Al2O3-MgO slag or a quaternary slag by combining with B2O3. An interesting observation is that the iron drop moved away from the original site, probably due to the Marangoni effect.

  15. Iron

    MedlinePlus

    Iron is a mineral that our bodies need for many functions. For example, iron is part of hemoglobin, a protein which carries ... It helps our muscles store and use oxygen. Iron is also part of many other proteins and ...

  16. Hexagon solar power panel

    DOEpatents

    Rubin, Irwin

    1978-01-01

    A solar energy panel comprises a support upon which silicon cells are arrayed. The cells are wafer thin and of two geometrical types, both of the same area and electrical rating, namely hexagon cells and hourglass cells. The hourglass cells are composites of half hexagons. A near perfect nesting relationship of the cells achieves a high density packing whereby optimum energy production per panel area is achieved.

  17. Hexagon solar power panel

    NASA Technical Reports Server (NTRS)

    Rubin, I. (Inventor)

    1978-01-01

    A solar energy panel support is described upon which silicon cells are arrayed. The cells are wafer thin and of two geometrical types, both of the same area and electrical rating, namely hexagon cells and hourglass cells. The hourglass cells are composites of half hexagons. A near perfect nesting relationship of the cells achieves a high density packing whereby optimum energy production per panel area is achieved.

  18. Why Hexagonal Basalt Columns?

    PubMed

    Hofmann, Martin; Anderssohn, Robert; Bahr, Hans-Achim; Weiß, Hans-Jürgen; Nellesen, Jens

    2015-10-09

    Basalt columns with their preferably hexagonal cross sections are a fascinating example of pattern formation by crack propagation. Junctions of three propagating crack faces rearrange such that the initial right angles between them tend to approach 120°, which enables the cracks to form a pattern of regular hexagons. To promote understanding of the path on which the ideal configuration can be reached, two periodically repeatable models are presented here involving linear elastic fracture mechanics and applying the principle of maximum energy release rate. They describe the evolution of the crack pattern as a transition from rectangular start configuration to the hexagonal pattern. This is done analytically and by means of three-dimensional finite element simulation. The latter technique reproduces the curved crack path involved in this transition.

  19. Dense Breasts

    MedlinePlus

    ... fatty tissue. On a mammogram, fatty tissue appears dark (radio-lucent) and the glandular and connective tissues ... white on mammography) and non-dense fatty tissue (dark on mammography) using a visual scale and assign ...

  20. Electromagnetic induction of nanoscale zerovalent iron particles accelerates the degradation of chlorinated dense non-aqueous phase liquid: Proof of concept.

    PubMed

    Phenrat, Tanapon; Kumloet, Itsaraphong

    2016-12-15

    In this study, a novel electromagnetically enhanced treatment concept is proposed for in situ remediation of a source zone of chlorinated dense non-aqueous phase liquid (DNAPL) that is slowly dissolved, causing contaminated groundwater for centuries. Here, we used polystyrene sulfonate (PSS)-modified nanoscale zerovalent iron (NZVI) particles (ferromagnetic) in combination with a low frequency (LF) (150 kHz) AC electromagnetic field (EMF) to accelerate the degradation of the DNAPLs via enhanced dissolution and reductive dechlorination. Trichloroethylene (TCE) and tetrachloroethylene (PCE) were used in a bench-scaled evaluation. The PSS-modified NZVI successfully targeted the DNAPL/water interface, as evidenced by the Pickering emulsion formation. Dechlorination of TCE- and PCE-DNAPL was measured by quantifying the by-product formation (acetylene, ethene, and ethane). Without magnetic induction heating (MIH) by LF EMF, PSS-modified NZVI transformed TCE- and PCE-DNAPL to ethene and ethane at the rate constants of 12.19 × 10(-3) and 1.00 × 10(-3) μmol/h/m(2), respectively, following pseudo zero-order reactions. However, four MIH cycles of PSS-NZVI increased the temperature up to 87 °C and increased the rate constants of TCE-DNAPL and PCE-DNAPL up to 14.58 and 58.01 times, respectively, in comparison to the dechlorination rate without MIH. Theoretical analysis suggested that the MIH of the PSS-modified NZVI enhanced the dechlorination of TCE- and PCE-DNAPL via the combination of the enhanced thermal dissolution of DNAPL, the effect of increasing the temperature on the rate constant (the Arrhenius equation), and the accelerated NZVI corrosion. Nevertheless, the effect of the Arrhenius equation was dominant. For the first time, this proof-of-concept study reveals the potential for using polyelectrolyte-modified NZVI coupled with LF EMF as a combined remediation technique for increasing the rate and completeness of in situ chlorinated DNAPL source remediation.

  1. Hexagonal quartz resonator

    DOEpatents

    Peters, Roswell D. M.

    1982-01-01

    A generally flat, relatively thin AT-cut piezoelectric resonator element structured to minimize the force-frequency effect when mounted and energized in a housing. The resonator is in the form of an equilateral hexagon with the X crystallographic axis of the crystal passing through one set of opposing corners with mounting being effected at an adjacent set of corners respectively .+-.60.degree. away from the X axis which thereby results in a substantially zero frequency shift of the operating frequency.

  2. Dynamics of wet granular hexagons

    NASA Astrophysics Data System (ADS)

    Baur, Manuel; Huang, Kai

    2017-03-01

    The collective behavior of vibrated hexagonal disks confined in a monolayer is investigated experimentally. Due to the broken circular symmetry, hexagons prefer to rotate upon sufficiently strong driving. Due to the formation of liquid bridges, short-ranged cohesive interactions are introduced upon wetting. Consequently, a nonequilibrium stationary state with the rotating disks self-organized in a hexagonal structure arises. The bond length of the hexagonal structure is slightly smaller than the circumdiameter of a hexagon, indicating geometric frustration. This investigation provides an example where the collective behavior of granular matter is tuned by the shape of individual particles.

  3. Hexagonalization of correlation functions

    NASA Astrophysics Data System (ADS)

    Fleury, Thiago; Komatsu, Shota

    2017-01-01

    We propose a nonperturbative framework to study general correlation functions of single-trace operators in N = 4 supersymmetric Yang-Mills theory at large N . The basic strategy is to decompose them into fundamental building blocks called the hexagon form factors, which were introduced earlier to study structure constants using integrability. The decomposition is akin to a triangulation of a Riemann surface, and we thus call it hexagonalization. We propose a set of rules to glue the hexagons together based on symmetry, which naturally incorporate the dependence on the conformal and the R-symmetry cross ratios. Our method is conceptually different from the conventional operator product expansion and automatically takes into account multi-trace operators exchanged in OPE channels. To illustrate the idea in simple set-ups, we compute four-point functions of BPS operators of arbitrary lengths and correlation functions of one Konishi operator and three short BPS operators, all at one loop. In all cases, the results are in perfect agreement with the perturbative data. We also suggest that our method can be a useful tool to study conformal integrals, and show it explicitly for the case of ladder integrals.

  4. Comparison of microfabricated hexagonal and lamellar post arrays for DNA electrophoresis

    PubMed Central

    Chen, Zhen; Dorfman, Kevin D.

    2014-01-01

    We used Brownian dynamics simulations to compare DNA separations in microfabricated post arrays containing either hexagonal or lamellar lattices. Contrary to intuition, dense hexagonal arrays with frequent DNA-post collisions do not yield the optimal separation. Rather, hexagonal arrays with pore sizes commensurate with the radius of gyration of the DNA lead to increased separation resolution due to a molecular-weight dependent collision probability that increases with molecular weight. However, when the hexagonal array is too sparse, this advantage is lost due to the low number of collisions. Lamellar lattices, such as the DNA nanofence, appear to be superior to a hexagonal array at the same post density, since the lamellar lattice combines regions for DNA relaxation with locally dense post regions for collisions. The relative advantages of different post array designs are explained in terms of the statistics for the number of collisions and the holdup time, providing guidelines for designing post arrays for separating long DNA. PMID:24132597

  5. Electronic and magnetic properties of Fe and Mn doped two dimensional hexagonal germanium sheets

    SciTech Connect

    Soni, Himadri R. Jha, Prafulla K.

    2014-04-24

    Using first principles density functional theory calculations, the present paper reports systematic total energy calculations of the electronic properties such as density of states and magnetic moment of pristine and iron and manganese doped two dimensional hexagonal germanium sheets.

  6. Hexagonal quartz resonator

    DOEpatents

    Peters, R.D.M.

    1982-11-02

    A generally flat, relatively thin AT-cut piezoelectric resonator element structured to minimize the force-frequency effect when mounted and energized in a housing. The resonator is in the form of an equilateral hexagon with the X crystallographic axis of the crystal passing through one set of opposing corners with mounting being effected at an adjacent set of corners respectively [+-]60[degree] away from the X axis which thereby results in a substantially zero frequency shift of the operating frequency. 3 figs.

  7. Shape-induced frustration of hexagonal order in polyhedral colloids.

    PubMed

    Dullens, Roel P A; Mourad, Maurice C D; Aarts, Dirk G A L; Hoogenboom, Jacob P; Kegel, Willem K

    2006-01-20

    The effect of a nonspherical particle shape and shape polydispersity on the structure of densely packed hard colloidal particles was studied in real space by confocal microscopy. We show that the first layer at the wall of concentrated size-monodisperse but shape-polydisperse polyhedral colloids exhibits significant deviations from a hexagonal lattice. These deviations are identified as bond-orientational fluctuations which lead to percolating "mismatch lines." While the shape-induced geometrical frustration of the hexagonal symmetry suppresses translational order, bond-orientational order is clearly retained, indicating a hexaticlike structure of the polyhedral colloids.

  8. Hexagonal Mirror Array

    NASA Technical Reports Server (NTRS)

    1999-01-01

    NASA's Space Optics Manufacturing Technology Center has been working to expand our view of the universe via sophisticated new telescopes. The Optics Center's goal is to develop low-cost, advanced space optics technologies for the NASA program in the 21st century, including the long-term goal of imaging Earth-like planets in distant solar systems. A segmented array of mirrors was designed by the Space Optics Manufacturing Technology Center for solar the concentrator test stand at the Marshall Space Flight Center (MSFC) for powering solar thermal propulsion engines. Each hexagon mirror has a spherical surface to approximate a parabolic concentrator when combined into the entire 18-foot diameter array. The aluminum mirrors were polished with a diamond turning machine, that creates a glass-like reflective finish on metal. The precision fabrication machinery at the Space Optics Manufacturing Technology Center at MSFC can polish specialized optical elements to a world class quality of smoothness. This image shows optics physicist, Vince Huegele, examining one of the 144-segment hexagonal mirrors of the 18-foot diameter array at the MSFC solar concentrator test stand.

  9. Hexagonal Mirror Array

    NASA Technical Reports Server (NTRS)

    1999-01-01

    NASA's Space Optics Manufacturing Technology Center has been working to expand our view of the universe via sophisticated new telescopes. The Optics Center's goal is to develop low-cost, advanced space optics technologies for the NASA program in the 21st century, including the long-term goal of imaging Earth-like planets in distant solar systems. A segmented array of mirrors was designed by the Space Optics Manufacturing Technology Center for the solar concentrator test stand at the Marshall Space Flight Center (MSFC) for powering solar thermal propulsion engines. Each hexagon mirror has a spherical surface to approximate a parabolic concentrator when combined into the entire 18-foot diameter array. The aluminum mirrors were polished with a diamond turning machine that creates a glass-like reflective finish on metal. The precision fabrication machinery at the Space Optics Manufacturing Technology Center at MSFC can polish specialized optical elements to a world class quality of smoothness. This image shows optics physicist, Vince Huegele, examining one of the 144-segment hexagonal mirrors of the 18-foot diameter array at the MSFC solar concentrator test stand.

  10. Hexagonal Mirror Array

    NASA Technical Reports Server (NTRS)

    1999-01-01

    NASA's Space Optics Manufacturing Technology Center has been working to expand our view of the universe via sophisticated new telescopes. The Optics Center's goal is to develop low-cost, advanced space optics technologies for the NASA program in the 21st century, including the long-term goal of imaging Earth-like planets in distant solar systems. A segmented array of mirrors was designed by the Space Optics Manufacturing Technology Center for solar the concentrator test stand at the Marshall Space Flight Center (MSFC) for powering solar thermal propulsion engines. Each hexagon mirror has a spherical surface to approximate a parabolic concentrator when combined into the entire 18-foot diameter array. The aluminum mirrors were polished with a diamond turning machine, that creates a glass-like reflective finish on metal. The precision fabrication machinery at the Space Optics Manufacturing Technology Center at MSFC can polish specialized optical elements to a world class quality of smoothness. This image shows optics physicist, Vince Huegele, examining one of the 144-segment hexagonal mirrors of the 18-foot diameter array at the MSFC solar concentrator test stand.

  11. Hexagonal Mirror Array

    NASA Technical Reports Server (NTRS)

    1999-01-01

    NASA's Space Optics Manufacturing Technology Center has been working to expand our view of the universe via sophisticated new telescopes. The Optics Center's goal is to develop low-cost, advanced space optics technologies for the NASA program in the 21st century, including the long-term goal of imaging Earth-like planets in distant solar systems. A segmented array of mirrors was designed by the Space Optics Manufacturing Technology Center for the solar concentrator test stand at the Marshall Space Flight Center (MSFC) for powering solar thermal propulsion engines. Each hexagon mirror has a spherical surface to approximate a parabolic concentrator when combined into the entire 18-foot diameter array. The aluminum mirrors were polished with a diamond turning machine that creates a glass-like reflective finish on metal. The precision fabrication machinery at the Space Optics Manufacturing Technology Center at MSFC can polish specialized optical elements to a world class quality of smoothness. This image shows optics physicist, Vince Huegele, examining one of the 144-segment hexagonal mirrors of the 18-foot diameter array at the MSFC solar concentrator test stand.

  12. Hail the Hexagon

    NASA Image and Video Library

    2017-05-08

    Saturn hexagonal polar jet stream is the shining feature of almost every view of the north polar region of Saturn. The region, in shadow for the first part of NASA's Cassini mission, now enjoys full sunlight, which enables Cassini scientists to directly image it in reflected light. Although the sunlight falling on the north pole of Saturn is enough to allow us to image and study the region, it does not provide much warmth. In addition to being low in the sky (just like summer at Earth's poles), the sun is nearly ten times as distant from Saturn as from Earth. This results in the sunlight being only about 1 percent as intense as at our planet. This view looks toward Saturn from about 31 degrees above the ring plane. The image was taken with the Cassini spacecraft wide-angle camera on Jan. 22, 2017 using a spectral filter which preferentially admits wavelengths of near-infrared light centered at 939 nanometers. The view was obtained at a distance of approximately 560,000 miles (900,000 kilometers) from Saturn. Image scale is 33 miles (54 kilometers) per pixel. https://photojournal.jpl.nasa.gov/catalog/PIA21327

  13. An Explanation for Saturn's Hexagon

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2015-08-01

    For over three decades, weve been gathering observations of the mysterious hexagonal cloud pattern encircling Saturns north pole. Now, researchers believe they have a model that can better explain its formation.Fascinating GeometrySaturns northern Hexagon is a cloud band circling Saturns north pole at 78 N, first observed by the Voyager flybys in 198081. This remarkable pattern has now persisted for more than a Saturn year (29.5 Earth years).Eight frames demonstrating the motion within Saturns Hexagon. Click to watch the animation! The view is from a reference frame rotating with Saturn. [NASA/JPL-Caltech/SSI/Hampton University]Observations by Voyager and, more recently, Cassini have helped to identify many key characteristics of this bizarre structure. Two interesting things weve learned are:The Hexagon is associated with an eastward zonal jet moving at more than 200 mph.The cause of the Hexagon is believed to be a jet stream, similar to the ones that we experience on Earth. The path of the jet itself appears to follow the hexagons outline.The Hexagon rotates at roughly the same rate as Saturns overall rotation.While we observe individual storms and cloud patterns moving at different speeds within the Hexagon, the vertices of the Hexagon move at almost exactly the same rotational speed as that of Saturn itself.Attempts to model the formation of the Hexagon with a jet stream have yet to fully reproduce all of the observed features and behavior. But now, a team led by Ral Morales-Juberas of the New Mexico Institute of Mining and Technology believes they have created a model that better matches what we see.Simulating a Meandering JetThe team ran a series of simulations of an eastward, Gaussian-profile jet around Saturns pole. They introduced small perturbations to the jet and demonstrated that, as a result of the perturbations, the jet can meander into a hexagonal shape. With the initial conditions of the teams model, the meandering jet is able to settle into a

  14. Synthesis and assembly of barium-doped iron oxide nanoparticles and nanomagnets.

    PubMed

    Wu, Liheng; Shen, Bo; Sun, Shouheng

    2015-10-21

    A facile organic-phase synthesis of monodisperse barium-doped iron oxide (Ba-Fe-O) nanoparticles (NPs) is reported. The Ba-Fe-O NPs can be converted into hexagonal barium ferrite NPs at 700 °C, showing strong ferromagnetic properties with H(c) reaching 5260 Oe and M(s) at 54 emu g(-1). Moreover, the Ba-Fe-O NPs can be assembled into densely packed magnetic arrays, providing a unique model system for studying nanomagnetism and for nanomagnetic applications.

  15. Hexagonal tessellations in image algebra

    NASA Astrophysics Data System (ADS)

    Eberly, David H.; Wenzel, Dennis J.; Longbotham, Harold G.

    1990-11-01

    In image algebra '' the concept of a coordinate set X is general in that such a set is simply a subset of ndimensional Euclidean space . The standard applications in 2-dimensional image processing use coordinate sets which are rectangular arrays X 72 x ZZm. However some applications may require other geometries for the coordinate set. We look at three such related applications in the context of image algebra. The first application is the modeling of photoreceptors in primate retinas. These receptors are inhomogeneously distributed on the retina. The largest receptor density occurs in the center of the fovea and decreases radially outwards. One can construct a hexagonal tessellation of the retina such that each hexagon contains approximately the same number of receptors. The resulting tessellation called a sunflower heart2 consists of concentric rings of hexagons whose sizes increase as the radius of the ring increases. The second application is the modeling of the primary visual . The neurons are assumed to be uniformly distributed as a regular hexagonal lattice. Cortical neural image coding is modeled by a recursive convolution of the retinal neural image using a special set of filters. The third application involves analysis of a hexagonally-tessellated image where the pixel resolution is variable .

  16. DENSE MEDIUM CYCLONE OPTIMIZATON

    SciTech Connect

    Gerald H. Luttrell; Chris J. Barbee; Peter J. Bethell; Chris J. Wood

    2005-06-30

    Dense medium cyclones (DMCs) are known to be efficient, high-tonnage devices suitable for upgrading particles in the 50 to 0.5 mm size range. This versatile separator, which uses centrifugal forces to enhance the separation of fine particles that cannot be upgraded in static dense medium separators, can be found in most modern coal plants and in a variety of mineral plants treating iron ore, dolomite, diamonds, potash and lead-zinc ores. Due to the high tonnage, a small increase in DMC efficiency can have a large impact on plant profitability. Unfortunately, the knowledge base required to properly design and operate DMCs has been seriously eroded during the past several decades. In an attempt to correct this problem, a set of engineering tools have been developed to allow producers to improve the efficiency of their DMC circuits. These tools include (1) low-cost density tracers that can be used by plant operators to rapidly assess DMC performance, (2) mathematical process models that can be used to predict the influence of changes in operating and design variables on DMC performance, and (3) an expert advisor system that provides plant operators with a user-friendly interface for evaluating, optimizing and trouble-shooting DMC circuits. The field data required to develop these tools was collected by conducting detailed sampling and evaluation programs at several industrial plant sites. These data were used to demonstrate the technical, economic and environmental benefits that can be realized through the application of these engineering tools.

  17. Bioenhanced dissolution of dense non-aqueous phase of trichloroethylene as affected by iron reducing conditions: model systems and environmental samples.

    PubMed

    Paul, Laiby; Smolders, Erik

    2015-01-01

    The anaerobic biotransformation of trichloroethylene (TCE) can be affected by competing electron acceptors such as Fe (III). This study assessed the role of Fe (III) reduction on the bioenhanced dissolution of TCE dense non-aqueous phase liquid (DNAPL). Columns were set up as 1-D diffusion cells consisting of a lower DNAPL layer, a layer with an aquifer substratum and an upper water layer that is regularly refreshed. The substrata used were either inert sand or sand coated with 2-line ferrihydrite (HFO) or two environmental Fe (III) containing samples. The columns were inoculated with KB-1 and were repeatedly fed with formate. In none of the diffusion cells, vinyl chloride or ethene was detected while dissolved and extractable Fe (II) increased strongly during 60 d of incubation. The cis-DCE concentration peaked at 4.0 cm from the DNAPL (inert sand) while it was at 3.4 cm (sand+HFO), 1.7 cm and 2.5 cm (environmental samples). The TCE concentration gradients near the DNAPL indicate that the DNAPL dissolution rate was larger than that in an abiotic cell by factors 1.3 (inert sand), 1.0 (sand+HFO) and 2.2 (both environmental samples). This results show that high bioavailable Fe (III) in HFO reduces the TCE degradation by competitive Fe (III) reduction, yielding lower bioenhanced dissolution. However, Fe (III) reduction in environmental samples was not reducing TCE degradation and the dissolution factor was even larger than that of inert sand. It is speculated that physical factors, e.g. micro-niches in the environmental samples protect microorganisms from toxic concentrations of TCE. Copyright © 2014 Elsevier Ltd. All rights reserved.

  18. Plea for Iron Astrochemistry

    SciTech Connect

    Mostefaoui, T. A.; Benmerad, B.; Kerkar, M.

    2010-10-31

    Iron is a key element and compound in living bodies. It is the most abundant refractory element and has the most stable nucleus in the Universe. Also, elemental Iron has a relevant abundance in the interstellar medium and dense clouds, it can be in gas phase or included in dust particles. During this talk, I shall explain why this special interest in Iron and shall give a brief explanation about its origin and the interstellar nucleosynthesis. After this I'll detail the rich chemistry that Iron can be involved in the interstellar medium, dense clouds with several species.

  19. Graphene on hexagonal boron nitride

    NASA Astrophysics Data System (ADS)

    Yankowitz, Matthew; Xue, Jiamin; LeRoy, B. J.

    2014-07-01

    The field of graphene research has developed rapidly since its first isolation by mechanical exfoliation in 2004. Due to the relativistic Dirac nature of its charge carriers, graphene is both a promising material for next-generation electronic devices and a convenient low-energy testbed for intrinsically high-energy physical phenomena. Both of these research branches require the facile fabrication of clean graphene devices so as not to obscure its intrinsic physical properties. Hexagonal boron nitride has emerged as a promising substrate for graphene devices as it is insulating, atomically flat and provides a clean charge environment for the graphene. Additionally, the interaction between graphene and boron nitride provides a path for the study of new physical phenomena not present in bare graphene devices. This review focuses on recent advancements in the study of graphene on hexagonal boron nitride devices from the perspective of scanning tunneling microscopy with highlights of some important results from electrical transport measurements.

  20. Process for the synthesis of iron powder

    DOEpatents

    Not Available

    1982-03-06

    A process for preparing iron powder suitable for use in preparing the iron-potassium perchlorate heat-powder fuel mixture used in thermal batteries, comprises preparing a homogeneous, dense iron oxide hydroxide precipitate by homogeneous precipitation from an aqueous mixture of a ferric salt, formic or sulfuric acid, ammonium hydroxide and urea as precipitating agent; and then reducing the dense iron oxide hydroxide by treatment with hydrogen to prepare the iron powder.

  1. Process for the synthesis of iron powder

    DOEpatents

    Welbon, William W.

    1983-01-01

    A process for preparing iron powder suitable for use in preparing the iron-potassium perchlorate heat-powder fuel mixture used in thermal batteries, comprises preparing a homogeneous, dense iron oxide hydroxide precipitate by homogeneous precipitation from an aqueous mixture of a ferric salt, formic or sulfuric acid, ammonium hydroxide and urea as precipitating agent; and then reducing the dense iron oxide hydroxide by treatment with hydrogen to prepare the iron powder.

  2. Process for the synthesis of iron powder

    DOEpatents

    Welbon, W.W.

    1983-11-08

    A process for preparing iron powder suitable for use in preparing the iron-potassium perchlorate heat-powder fuel mixture used in thermal batteries, comprises preparing a homogeneous, dense iron oxide hydroxide precipitate by homogeneous precipitation from an aqueous mixture of a ferric salt, formic or sulfuric acid, ammonium hydroxide and urea as precipitating agent; and then reducing the dense iron oxide hydroxide by treatment with hydrogen to prepare the iron powder. 2 figs.

  3. Hexagonal OsB2: Sintering, microstructure and mechanical properties

    DOE PAGES

    Xie, Zhilin; Lugovy, Mykola; Orlovskaya, Nina; ...

    2015-02-07

    In this study, the metastable high pressure ReB2-type hexagonal OsB2 bulk ceramics was produced by spark plasma sintering. The phase composition, microstructure, and mechanical behavior of the sintered OsB2 were studied by X-ray diffraction, optical microscopy, TEM, SEM, EDS, and nanoindentation. The produced ceramics was rather porous and contained a mixture of hexagonal (~80 wt.%) and orthorhombic (~20 wt.%) phases as identified by X-ray diffraction and EBSD analysis. Two boron-rich phases, which do not contain Os, were also identified by TEM and SEM/EDS analysis. Nanoindentation measurements yielded a hardness of 31 ± 9 GPa and Young’s modulus of 574 ±more » 112 GPa, indicating that the material is rather hard and very stiff; but, it is very prone to crack formation and propagation, which is indicative of a very brittle nature of this material. Improvements in the sintering regime are required in order to produce dense, homogeneous and single phase hexagonal OsB2 bulk ceramics.« less

  4. Dense topological spaces and dense continuity

    NASA Astrophysics Data System (ADS)

    Aldwoah, Khaled A.

    2013-09-01

    There are several attempts to generalize (or "widen") the concept of topological space. This paper uses equivalence relations to generalize the concept of topological space via the concept of equivalence relations. By the generalization, we can introduce from particular topology on a nonempty set X many new topologies, we call anyone of these new topologies a dense topology. In addition, we formulate some simple properties of dense topologies and study suitable generalizations of the concepts of limit points, closeness and continuity, as well as Jackson, Nörlund and Hahn dense topologies.

  5. Ferroelectricity of multiferroic hexagonal TmMnO3 ceramics synthesized under high pressure

    NASA Astrophysics Data System (ADS)

    Wang, L. J.; Feng, S. M.; Zhu, J. L.; Yu, R. C.; Jin, C. Q.; Yu, W.; Wang, X. H.; Li, L. T.

    2007-10-01

    Dense hexagonal TmMnO3 ceramics were synthesized by solid-state reaction technique combined with high-pressure treatment which significantly increased the density of ceramic samples. The crystal structure of the hexagonal TmMnO3 oxide was refined by using Rietveld analysis based on powder x-ray diffraction experiment. We observed obvious dielectric peaks through dielectric measurement on the specimen subjected to postannealing in oxygen atmosphere. A ferroelectric-paraelectric transition around 348°C is identified. Polarization-electric field hysteresis (P-E ) loop measurement proved the ferroelectricity of the sample at room temperature.

  6. Electrodeposited Silver Nanoparticles Patterned Hexagonally for SERS

    SciTech Connect

    Gu, Geun Hoi; Lee, Sue Yeone; Suh, Jung Sang

    2010-08-06

    We have fabricated hexagonally patterned silver nanoparticles for surface-enhanced Raman scattering (SERS) by electrodepositing silver on the surface of an aluminum plate prepared by completely removing the oxide from anodic aluminum oxide (AAO) templates. Even after completely removing the oxide, well-ordered hexagonal patterns, similar to the shape of graphene, remained on the surface of the aluminum plate. The borders of the hexagonal pattern protruded up to form sorts of nano-mountains at both the sides and apexes of the hexagon, with the apexes protruding even more significantly than the sides. The aluminum plate prepared by completely removing the oxide has been used in the preparation of SERS substrates by sputter-coating of gold or silver on it. Instead of sputter-coating, here we have electro-deposited silver on the aluminum plate. When silver was electro-deposited on the plate, silver nanoparticles were made along the hexagonal margins.

  7. Atoms in dense plasmas

    SciTech Connect

    More, R.M.

    1986-01-01

    Recent experiments with high-power pulsed lasers have strongly encouraged the development of improved theoretical understanding of highly charged ions in a dense plasma environment. This work examines the theory of dense plasmas with emphasis on general rules which govern matter at extreme high temperature and density. 106 refs., 23 figs.

  8. Bronze-mean hexagonal quasicrystal.

    PubMed

    Dotera, Tomonari; Bekku, Shinichi; Ziherl, Primož

    2017-10-01

    The most striking feature of conventional quasicrystals is their non-traditional symmetry characterized by icosahedral, dodecagonal, decagonal or octagonal axes. The symmetry and the aperiodicity of these materials stem from an irrational ratio of two or more length scales controlling their structure, the best-known examples being the Penrose and the Ammann-Beenker tiling as two-dimensional models related to the golden and the silver mean, respectively. Surprisingly, no other metallic-mean tilings have been discovered so far. Here we propose a self-similar bronze-mean hexagonal pattern, which may be viewed as a projection of a higher-dimensional periodic lattice with a Koch-like snowflake projection window. We use numerical simulations to demonstrate that a disordered variant of this quasicrystal can be materialized in soft polymeric colloidal particles with a core-shell architecture. Moreover, by varying the geometry of the pattern we generate a continuous sequence of structures, which provide an alternative interpretation of quasicrystalline approximants observed in several metal-silicon alloys.

  9. Bronze-mean hexagonal quasicrystal

    NASA Astrophysics Data System (ADS)

    Dotera, Tomonari; Bekku, Shinichi; Ziherl, Primož

    2017-10-01

    The most striking feature of conventional quasicrystals is their non-traditional symmetry characterized by icosahedral, dodecagonal, decagonal or octagonal axes. The symmetry and the aperiodicity of these materials stem from an irrational ratio of two or more length scales controlling their structure, the best-known examples being the Penrose and the Ammann-Beenker tiling as two-dimensional models related to the golden and the silver mean, respectively. Surprisingly, no other metallic-mean tilings have been discovered so far. Here we propose a self-similar bronze-mean hexagonal pattern, which may be viewed as a projection of a higher-dimensional periodic lattice with a Koch-like snowflake projection window. We use numerical simulations to demonstrate that a disordered variant of this quasicrystal can be materialized in soft polymeric colloidal particles with a core-shell architecture. Moreover, by varying the geometry of the pattern we generate a continuous sequence of structures, which provide an alternative interpretation of quasicrystalline approximants observed in several metal-silicon alloys.

  10. Thermally induced fluid reversed hexagonal (H(II)) mesophase.

    PubMed

    Amar-Yuli, Idit; Wachtel, Ellen; Shalev, Deborah E; Moshe, Hagai; Aserin, Abraham; Garti, Nissim

    2007-12-06

    In the present study we characterized the microstructures of the Lc and HII phases in a glycerol monooleate (GMO)/tricaprylin (TAG)/water mixture as a function of temperature. We studied the factors that govern the formation of a low-viscosity HII phase at relatively elevated temperatures (>35 degrees C). This phase has very valuable physical characteristics and properties. The techniques used were differential scanning calorimetry (DSC), wide- and small-angle X-ray scattering (WAXS and SAXS, respectively), NMR (self-diffusion and (2)H NMR), and Fourier transform infrared (FTIR) spectroscopies. The reverse hexagonal phase exhibited relatively rapid flow of water in the inner channels within the densely packed cylindrical aggregates of GMO with TAG molecules located in the interstices. The existence of two water diffusion peaks reflects the existence of both mobile water and hydration water at the GMO-water interface (hydrogen exchange between the GMO hydroxyls and water molecules). Above 35 degrees C, the sample became fluid yet hexagonal symmetry was maintained. The fluidity of the HII phase is explained by a significant reduction in the domain size and also perhaps cylinder length. This phenomenon was characterized by higher mobility of the GMO, lower mobility of the water, and a significant dehydration process.

  11. Hydrogen in Iron at High Pressures and Temperatures

    NASA Astrophysics Data System (ADS)

    Hirao, N.; Ohtani, E.; Kondo, T.; Takemura, K.; Kikegawa, T.; Isshiki, M.

    2002-12-01

    Seismic data indicate both the inner and outer core of the Earth is less dense than pure iron at core pressures and temperatures. The density deficit suggests that light elements as iron compounds are contained in the inner and outer core. The preferred candidates for the light element are hydrogen, sulfur, oxygen, silicon, and carbon. The possibility that hydrogen was dissolved into the Earth's core was proposed 25 years ago [1] and experimental works show that H has many qualities that make it a good candidate for the light element in the core [i.e. 2, 3]. However, information on iron hydride is limited and the crystal structure and the stability of iron hydride, including the equilibrium solubility of hydrogen, is unknown at higher temperatures and higher pressures. We carried out in situ X-ray diffraction experiments using electrically heated diamond-anvil cells (DACs) in order to determine the phase relation and equation of state on iron hydride. A series of experiments was performed on samples of iron and hydrogen loaded into DACs. X-ray diffraction patterns of iron hydride were collected using monochromatic synchrotron x-ray radiation and the imaging plate at the BL-13A beamline at the Photon Factory, National Laboratory for High Energy Physics (KEK). Pressure was determined by the ruby fluorescence method. As a preliminary result, we found that iron hydride which has a double hexagonal close-packed structure is stable the temperature between 300 K and 654 K at about 15 GPa. A second-order Birch-Murnaghan equation of state fitted to the pressure-volume data yields the isothermal bulk modulus of 129 (+/-2) GPa and zero-pressure volume of 56.0 (+/-0.3) Å3, assuming the pressure derivative of bulk modulus of 4. The results are in a good agreement with those reported by Badding et al. [1991]. The composition FeHx with x=0.88 (+/-0.03) at zero-pressure, which seems to be constant up to 25 GPa at room temperature, is obtained using the volume of iron hydride, hcp

  12. Synthesis of Hexagonal FeMnP Thin Films from a Single-Source Molecular Precursor.

    PubMed

    Leitner, Andrew P; Schipper, Desmond E; Chen, Jing-Han; Colson, Adam C; Rusakova, Irene; Kumar Rai, Binod; Morosan, Emilia; Whitmire, Kenton Herbert

    2017-03-08

    The first heterobimetallic phosphide thin film containing iron, manganese, and phosphorus derived from the single-source precursor FeMn(CO)8(μ-PH2) has been prepared using a home-built metal-organic chemical vapor deposition apparatus. The thin film contains the same ratio of iron, manganese, and phosphorus as the initial precursor. The film becomes oxidized when deposited on a quartz substrate whereas the film deposited on an alumina substrate provides a more homogeneous product. Powder X-ray diffraction confirms the formation of metastable, hexagonal FeMnP phase that was previously only observed at temperatures above 1200 ºC. Selected area electron diffraction on single crystals isolated from the films were indexed to the hexagonal phase. The effective moment of the films (µeff = 3.68µB) matches the previously reported theoretical value for the metastable hexagonal phase whereas the more stable orthorhombic phase is known to be antiferromagnetic. These results not only demonstrate the successful synthesis of a bimetallic, ternary thin film from a single-source precursor, but also the first low temperature approach to the hexagonal phase of FeMnP.

  13. New hexagonal structure for silicon atoms

    NASA Astrophysics Data System (ADS)

    Naji, S.; Belhaj, A.; Labrim, H.; Benyoussef, A.; El Kenz, A.

    2012-11-01

    Motivated by recent experimental and theoretical works on silicene and its derived materials and based on the exceptional Lie algebra G2 we propose a new hexagonal symmetry producing the (√3 × √3)R30° superstructure for silicon atoms. The principal hexagonal unit cell contains twelve atoms instead of the usual structure involving only six ones and it is associated with the G2 root system. In this silicon atom configuration appears two hexagons of unequal side length at angle 30°. This atomic structure can be tessellated to exhibit two superstructures (1 × 1) and (√3 × √3)R30° on the same atomic sheet. To test this double hexagonal structure, we perform a numerical study using Ab-initio calculations based on FPLO9.00-34 code. We observe that the usual silicon electronic properties and the lattice parameters of planar geometry are modified. In particular, the corresponding material becomes a conductor rather than zero gaped semi-conductor arising in single hexagonal structure. Although the calculation is done for silicon atoms, we expect that this structure could be adapted to all two dimensional materials having a single hexagonal flat geometry.

  14. Polyfunctional bioceramics based on calcium phosphate and M-type hexagonal ferrite for medical applications

    NASA Astrophysics Data System (ADS)

    Tkachenko, M. V.; Ol'khovik, L. P.; Kamzin, A. S.; Keshri, S.

    2014-01-01

    Magnetic biologically active ceramics based on calcium phosphate with a content of M-type hexagonal ferrite (HF) particles varying from 10 to 50 wt % has been synthesized and characterized. It has been found that the ceramics synthesized consists of a biocompatible carbonated hydroxyapatite (CHA) with the matrix containing M-type HF particles, leading to the magnetic characteristics of the ceramics synthesized being significantly higher than those of iron-oxide-modified bioglass ceramics used in medicine.

  15. Dense array expressions

    NASA Astrophysics Data System (ADS)

    Wilson, Joseph N.; Chen, LiangMing

    1999-10-01

    Various researchers have realized the value of implementing loop fusion to evaluate dense (pointwise) array expressions. Recently, the method of template metaprogramming in C++ has been used to significantly speed-up the evaluation of array expressions, allowing C++ programs to achieve performance comparable to or better than FORTRAN for numerical analysis applications. Unfortunately, the template metaprogramming technique suffers from several limitations in applicability, portability, and potential performance. We present a framework for evaluating dense array expressions in object-oriented programming languages. We demonstrate how this technique supports both common subexpression elimination and threaded implementation and compare its performance to object-library and hand-generated code.

  16. IR Spectroscopy of PANHs in Dense Clouds

    NASA Astrophysics Data System (ADS)

    Allamandola, Louis; Mattioda, Andrew; Sandford, Scott

    2008-03-01

    Interstellar PAHs are likely to be frozen into ice mantles on dust grains in dense clouds. These PAHs will produce IR absorption bands, not emission features. A couple of very weak absorption features in ground based spectra of a few objects in dense clouds may be due to PAHs. It is now thought that aromatic molecules in which N atoms are substituted for a few of the C atoms in a PAH's hexagonal skeletal network (PANHs) may well be as abundant and ubiquitous throughout the interstellar medium as PAHs. Spaceborne observations in the 5 to 8 um region, the region in which PAH spectroscopy is rich, reveal unidentified new bands and significant variation from object to object. It is not possible to analyze these observations because lab spectra of PANHs and PAHs condensed in realistic interstellar ice analogs are lacking. This lab data is necessary to interpret observations because, in ice mantles, the surrounding molecules affect PANH and PAH IR band positions, widths, profiles, and intrinsic strengths. Further, PAHs (and PANHs?) are readily ionized in pure H2O ice, further altering the spectrum. This proposal starts to address this situation by studying the IR spectra of PANHs frozen in laboratory ice analogs that reflect the composition of the interstellar ices observed in dense clouds. Thanks to Spitzer Cycle-4 support, we are now measuring the spectra of PAHs in interstellar ice analogs to provide laboratory spectra that can be used to interpret IR observations. Here we propose to extend this work to PANHs. We will measure the spectra of these interstellar ice analogs containing PANHs before and after ionization and determine the band strengths of neutral and ionized PANHs in these ices. This will enable a quantitative assessment of the role that PANHs can play in the 5-8 um spectrum of dense clouds and address the following two fundamental questions associated with dense cloud spectroscopy and chemistry: 1- Can PANHs be detected in dense clouds? 2- Are PANH ions

  17. Thermally induced microstrain broadening in hexagonal zinc

    SciTech Connect

    Lawson, Andrew C; Valdez, James A; Roberts, Joyce A; Leineweber, Andreas; Mittemeijer, E J; Kreher, W

    2008-01-01

    Neutron powder-diffraction experiments on polycrystalline hexagonal zinc show considerable temperature-dependent line broadening. Whereas as-received zinc at 300 K exhibits narrow reflections, during cooling to a minimum temperature of 10K considerable line-broadening appears, which largely disappears again during reheating. The line broadening may be ascribed to microstrains induced by thermal microstresses due to the anisotropy of the thermal expansion (shrinkage) of hexagonal zinc. Differences between the thermal microstrains and theoretical predictions considering elastic deformation of the grains can be explained by plastic deformation and surface effects.

  18. Disclinations in square and hexagonal patterns.

    PubMed

    Golovin, A A; Nepomnyashchy, A A

    2003-05-01

    We report the observation of defects with fractional topological charges (disclinations) in square and hexagonal patterns as numerical solutions of several generic equations describing many pattern-forming systems: Swift-Hohenberg equation, damped Kuramoto-Sivashinsky equation, as well as nonlinear evolution equations describing large-scale Rayleigh-Benard and Marangoni convection in systems with thermally nearly insulated boundaries. It is found that disclinations in square and hexagonal patterns can be stable when nucleated from special initial conditions. The structure of the disclinations is analyzed by means of generalized Cross-Newell equations.

  19. Saturnian north polar region: a triangle inside the hexagon?

    NASA Astrophysics Data System (ADS)

    Kochemasov, Gennady G.

    2010-05-01

    The famous and "mysterious" stable hexagon structure around the North Pole of Saturn was earlier interpreted as projections of faces of a structural tetrahedron [1]. This "hidden" simplest Plato's polyhedron is a result of an interference of four fundamental (wave 1) warping waves having in any rotating celestial body four directions: orthogonal and diagonal. Origin of the warping waves in any celestial body is due to their movements in elliptical keplerian orbits with periodically changing accelerations. The structural tetrahedron is an intrinsic geometric feature marking the celestial bodies ubiquitous tectonic dichotomy as in a tetrahedron always there is an opposition of a face (expansion) and a vertex (contraction). In the saturnian case the tetrahedron shows a face at the north and a vertex at the south. Morphologically this is manifested by the hexagon and opposing it in the south a vertex. Blue and pink hues of the northern and southern hemispheres also underline the tectonic dichotomy. These geometric expressions are enforced by a subtle dark equilateral triangle appearing in the image PIA11682 also around the north pole and inside the hexagon (the triangle side is about 15000 km long). One angle of the triangle is clearly visible, another one just shows itself and the third one is barely distinguished. The sides of the triangle are not strait lines but slightly broken amidst lines what makes the triangle appear a bit hexagonal (spherical) and the angle is a bit bigger than 60 degrees of a classical equilateral triangle (~70 degrees). The central part of the triangle is not imaged (a black hole in the PIA11682). This image also confirms that the wide northern polar region is also densely "peppered" with bright cloudy more or less isometric spots on average 400 to 800 km across as in other latitudinal belts of Saturn [2, 3, 4]. Earlier they were observed in IR wavelengths, now they show themselves in visible wavelengths. Their origin and size were

  20. The single crystal elastic constants of hexagonal SiC to 1000 C

    NASA Technical Reports Server (NTRS)

    Li, Z.; Bradt, R. C.

    1988-01-01

    The relationships between the sound velocities in the cubic and hexagonal crystal structures and the tensor transformations for the two structures are applied to determine the elastic stiffnesses for the hexagonal structures of SiC to 1000 C. These results are then applied to calculate the polycrystalline elastic moduli, E and G, and their temperature variations. The calculated values for E and G at 20 C are 420 and 180 GPa; for (dE/dT) and (dG/dT), the values are -0.020 and -0.007 GPa/C, respectively.These agree well with published experimental values for E and G of dense polycrystalline alpha silicon carbides.

  1. An orthogonal oriented quadrature hexagonal image pyramid

    NASA Technical Reports Server (NTRS)

    Watson, Andrew B.; Ahumada, Albert J., Jr.

    1987-01-01

    An image pyramid has been developed with basis functions that are orthogonal, self-similar, and localized in space, spatial frequency, orientation, and phase. The pyramid operates on a hexagonal sample lattice. The set of seven basis functions consist of three even high-pass kernels, three odd high-pass kernels, and one low-pass kernel. The three even kernels are identified when rotated by 60 or 120 deg, and likewise for the odd. The seven basis functions occupy a point and a hexagon of six nearest neighbors on a hexagonal sample lattice. At the lowest level of the pyramid, the input lattice is the image sample lattice. At each higher level, the input lattice is provided by the low-pass coefficients computed at the previous level. At each level, the output is subsampled in such a way as to yield a new hexagonal lattice with a spacing sq rt 7 larger than the previous level, so that the number of coefficients is reduced by a factor of 7 at each level. The relationship between this image code and the processing architecture of the primate visual cortex is discussed.

  2. A composite nodal finite element for hexagons

    SciTech Connect

    Hennart, J.P.; Mund, E.H. |; Valle, E. Del

    1997-10-01

    A nodal algorithm for the solution of the multigroup diffusion equations in hexagonal arrays is analyzed. Basically, the method consists of dividing each hexagon into four quarters and mapping the hexagon quarters onto squares. The resulting boundary value problem on a quadrangular domain is solved in primal weak formulation. Nodal finite element methods like the Raviart-Thomas RTk schemes provide accurate analytical expansions of the solution in the hexagons. Transverse integration cannot be performed on the equations in the quadrangular domain as simply as it is usually done on squares because these equations have essentially variable coefficients. However, by considering an auxiliary problem with constant coefficients (on the same quadrangular domain) and by using a preconditioning approach, transverse integration can be performed as for rectangular geometry. A description of the algorithm is given for a one-group diffusion equation. Numerical results are presented for a simple model problem with a known analytical solution and for k{sub eff} evaluations of some benchmark problems proposed in the literature. For the analytical problem, the results indicate that the theoretical convergence orders of RTk schemes (k = 0,1) are obtained, yielding accurate solutions at the expense of a few preconditioning iterations.

  3. Hexagonal ferrites for millimeter wave applications

    NASA Astrophysics Data System (ADS)

    Polk, Donald E.; Hathaway, Kristl B.

    1993-01-01

    A review of the work accomplished on this contract is presented. A review of the physics of hexagonal ferrite materials and the effective linewidth concept and the detailed overall research plan are contained in the original proposal document. The focus of the program was on the effective linewidth in millimeter wave materials, including planar hexagonal ferrite Y-type materials, uniaxial M-type materials, and thin ferromagnetic transition metal and alloy films. The key idea in the original proposal was that the ferromagnetic resonance (FMR) linewidth in hexagonal ferrites is dominated by inhomogeneous and two-magnon scattering losses and that off-resonance measurements of the effective linewidth would (1) show that the FMR losses do not represent the intrinsic losses, and (2) that the intrinsic losses are significantly lower. This basic idea was verified. Results were obtained on the off-resonance far-field effective linewidth in planar Zn-Y hexagonal ferrite single crystal platelets, single crystal spheres of Ba- and Sr-hexaferrite materials, and permalloy thin films. Three papers on these results were published.

  4. 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.

  5. 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.

  6. 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.

  7. Powdered Hexagonal Boron Nitride Reducing Nanoscale Wear

    NASA Astrophysics Data System (ADS)

    Chkhartishvili, L.; Matcharashvili, T.; Esiava, R.; Tsagareishvili, O.; Gabunia, D.; Margiev, B.; Gachechiladze, A.

    2013-05-01

    A morphology model is suggested for nano-powdered hexagonal boron nitride that can serve as an effective solid additive to liquid lubricants. It allows to estimate the specific surface, that is a hard-to-measure parameter, based on average size of powder particles. The model can be used also to control nanoscale wear processes.

  8. Hexagonal and Pentagonal Fractal Multiband Antennas

    NASA Technical Reports Server (NTRS)

    Tang, Philip W.; Wahid, Parveen

    2005-01-01

    Multiband dipole antennas based on hexagonal and pentagonal fractals have been analyzed by computational simulations and functionally demonstrated in experiments on prototypes. These antennas are capable of multiband or wide-band operation because they are subdivided into progressively smaller substructures that resonate at progressively higher frequencies by virtue of their smaller dimensions. The novelty of the present antennas lies in their specific hexagonal and pentagonal fractal configurations and the resonant frequencies associated with them. These antennas are potentially applicable to a variety of multiband and wide-band commercial wireless-communication products operating at different frequencies, including personal digital assistants, cellular telephones, pagers, satellite radios, Global Positioning System receivers, and products that combine two or more of the aforementioned functions. Perhaps the best-known prior multiband antenna based on fractal geometry is the Sierpinski triangle antenna (also known as the Sierpinski gasket), shown in the top part of the figure. In this antenna, the scale length at each iteration of the fractal is half the scale length of the preceding iteration, yielding successive resonant frequencies related by a ratio of about 2. The middle and bottom parts of the figure depict the first three iterations of the hexagonal and pentagonal fractals along with typical dipole-antenna configuration based on the second iteration. Successive resonant frequencies of the hexagonal fractal antenna have been found to be related by a ratio of about 3, and those of the pentagonal fractal antenna by a ratio of about 2.59.

  9. Formation and stability of dense arrays of Au nanoclusters on hexagonal boron nitride/Rh(111)

    NASA Astrophysics Data System (ADS)

    Patterson, Matthew C.; Habenicht, Bradley F.; Kurtz, Richard L.; Liu, Li; Xu, Ye; Sprunger, Phillip T.

    2014-05-01

    We have studied the nucleation and growth of Au clusters at submonolayer and greater coverages on the h-BN nanomesh grown on Rh(111) by means of scanning tunneling microscopy (STM), x-ray photoelectron spectroscopy (XPS), and density functional theory (DFT). STM reveals that submonolayer Au deposited at 115 K nucleates within the nanomesh pores and remains confined to the pores even after warming to room temperature. Whereas there is a propensity of monoatomic high islands at low temperature, upon annealing, bi- and multilayer Au clusters emerge. Deposition of higher coverages of Au similarly results in Au clusters primarily confined to the nanomesh pores at room temperature. XPS analysis of core-level electronic states in the deposited Au shows strong final-state effects induced by restricted particle size dominating for low Au coverage, with indications that larger Au clusters are negatively charged by interaction through the h-BN monolayer. DFT calculations suggest that the structure of the Au clusters transitions from monolayer to bilayer at a size between 30 and 37 atoms per cluster, in line with our experiment. Bader charge analysis supports the negative charge state of deposited Au.

  10. Anisotropic Hexagonal Boron Nitride Nanomaterials - Synthesis and Applications

    SciTech Connect

    Han,W.Q.

    2008-08-01

    rhombohedral system consists of three-layered units: ABCABC..., whose honeycomb layers are arranged in a shifted phase, like as those of graphite. Reflecting its weak interlayer bond, the h-BN can be cleaved easily along its layers, and hence, is widely used as a lubricant material. The material is stable up to a high temperature of 2300 C before decomposition sets in [2] does not fuse a nitrogen atmosphere of 1 atm, and thus, is applicable as a refractory material. Besides having such properties, similar to those of graphite, the material is transparent, and acts as a good electric insulator, especially at high temperatures (10{sup 6} {Omega}m at 1000 C) [1]. c-BN and w-BN are tetrahedrally linked BN. The former has a cubic sphalerite-type structure, and the latter has a hexagonal wurtzite-type structure. c-BN is the second hardest known material (the hardest is diamond), the so-called white diamond. It is used mainly for grinding and cutting industrial ferrous materials because it does not react with molten iron, nickel, and related alloys at high temperatures whereas diamond does [1]. It displays the second highest thermal conductivity (6-9 W/cm.deg) after diamond. This chapter focuses principally upon information about h-BN nanomaterials, mainly BN nanotubes (BNNTs), porous BN, mono- and few-layer-BN sheets. There are good reviews book chapters about c-BN in [1, 4-6].

  11. Dense Plasma Focus Modeling

    SciTech Connect

    Li, Hui; Li, Shengtai; Jungman, Gerard; Hayes-Sterbenz, Anna Catherine

    2016-08-31

    The mechanisms for pinch formation in Dense Plasma Focus (DPF) devices, with the generation of high-energy ions beams and subsequent neutron production over a relatively short distance, are not fully understood. Here we report on high-fidelity 2D and 3D numerical magnetohydrodynamic (MHD) simulations using the LA-COMPASS code to study the pinch formation dynamics and its associated instabilities and neutron production.

  12. Fragility in dense suspensions

    NASA Astrophysics Data System (ADS)

    Mari, Romain; Cates, Mike

    Dense suspensions can jam under shear when the volume fraction of solid material is large enough. In this work we investigate the mechanical properties of shear jammed suspensions with numerical simulations. In particular, we address the issue of the fragility of these systems, i.e., the type of mechanical response (elastic or plastic) they show when subject to a mechanical load differing from the one applied during their preparation history.

  13. Are energy dense diets also nutrient dense?

    PubMed

    Nicklas, Theresa A; O'Neil, Carol E; Mendoza, Jason; Liu, Yan; Zakeri, Issa F; Berenson, Gerald S

    2008-10-01

    Some beverages are nutrient dense, but they are often excluded from nutrient density calculations. The purpose of this study was to assess whether the energy-nutrient association changed when beverages were included in these calculations. Applying a cross-sectional design, a 24-hour dietary recall was collected on each participant. Subjects/ 440 young adults (ages 19-28 years) in Bogalusa, Louisiana participated in this study. Mean nutrient intakes and food group consumption were examined across the energy density (ED) tertiles using two calculation methods: one with food and all beverages (excluding water) (ED1) and one including food and only energy containing beverages (ED2). Regression models were used and multiple comparisons were performed using the Tukey-Kramer procedure. A p-value < 0.05 was considered to be significant. With increasing ED, there was a significant increase in the consumption of total meats (ED1 p < 0.05; ED2 p < 0.01). In contrast, there was a significant decrease in consumption of fruits/juices (ED1 p < 0.01; ED2 p < 0.0001), vegetables (ED1 p < 0.01; ED2 p < 0.05), beverages (both p < 0.0001) and total sweets with increasing ED (both p < 0.0001). There was a significantly higher mean intake of total protein (grams) (ED2 p < 0.0001), amino acids (ED1 histidine/leucine p < 0.05; ED2 p < 0.0001), and total fat (grams) (ED1 p < 0.0001; ED2 p < 0.0001) with higher ED compared to lower ED. The percent energy from protein (ED1 p < 0.05; ED2 p < 0.0001), total fat (both p < 0.001) and saturated fatty acids (both p < 0.0001) significantly increased and the percent energy from carbohydrate (both p < 0.0001) and sucrose (both p < 0.0001) significantly decreased with increasing ED. This study suggests that ED may influence the ND of the diet depending on whether energy containing beverages are included or excluded in the analysis.

  14. Are Energy Dense Diets Also Nutrient Dense?

    PubMed Central

    Nicklas, Theresa A.; O’Neil, Carol E.; Mendoza, Jason; Liu, Yan; Zakeri, Issa F.; Berenson, Gerald S.

    2009-01-01

    Objective Some beverages are nutrient dense, but they are often excluded from nutrient density calculations. The purpose of this study was to assess whether the energy-nutrient association changed when beverages were included in these calculations. Design Applying a cross-sectional design, a 24-hour dietary recall was collected on each participant. Subjects/Setting 440 young adults (ages 19–28 years) in Bogalusa, Louisiana participated in this study. Statistical Analysis Mean nutrient intakes and food group consumption were examined across the energy density (ED) tertiles using two calculation methods: one with food and all beverages (excluding water) (ED1) and one including food and only energy containing beverages (ED2). Regression models were used and multiple comparisons were performed using the Tukey-Kramer procedure. A p-value < 0.05 was considered to be significant. Results With increasing ED, there was a significant increase in the consumption of total meats (ED1 p < 0.05; ED2 p < 0.01). In contrast, there was a significant decrease in consumption of fruits/juices (ED1 p < 0.01; ED2 p < 0.0001), vegetables (ED1 p < 0.01; ED2 p < 0.05), beverages (both p < 0.0001) and total sweets with increasing ED (both p < 0.0001). There was a significantly higher mean intake of total protein (grams) (ED2 p < 0.0001), amino acids (ED1 histidine/leucine p < 0.05; ED2 p < 0.0001), and total fat (grams) (ED1 p < 0.0001; ED2 p < 0.0001) with higher ED compared to lower ED. The percent energy from protein (ED1 p < 0.05; ED2 p < 0.0001), total fat (both p < 0.001) and saturated fatty acids (both p < 0.0001) significantly increased and the percent energy from carbohydrate (both p < 0.0001) and sucrose (both p < 0.0001) significantly decreased with increasing ED. Conclusion This study suggests that ED may influence the ND of the diet depending on whether energy containing beverages are included or excluded in the analysis. PMID:18845705

  15. Chain hexagonal cacti with the extremal eccentric distance sum.

    PubMed

    Qu, Hui; Yu, Guihai

    2014-01-01

    Eccentric distance sum (EDS), which can predict biological and physical properties, is a topological index based on the eccentricity of a graph. In this paper we characterize the chain hexagonal cactus with the minimal and the maximal eccentric distance sum among all chain hexagonal cacti of length n, respectively. Moreover, we present exact formulas for EDS of two types of hexagonal cacti.

  16. Chain Hexagonal Cacti with the Extremal Eccentric Distance Sum

    PubMed Central

    Qu, Hui

    2014-01-01

    Eccentric distance sum (EDS), which can predict biological and physical properties, is a topological index based on the eccentricity of a graph. In this paper we characterize the chain hexagonal cactus with the minimal and the maximal eccentric distance sum among all chain hexagonal cacti of length n, respectively. Moreover, we present exact formulas for EDS of two types of hexagonal cacti. PMID:24741365

  17. Fabrication and infrared-transmission properties of monolayer hexagonal-close-packed metallic nanoshells

    NASA Astrophysics Data System (ADS)

    Chen, Jing; Xu, Rongqing; Liu, Zhengqi; Tang, Chaojun; Chen, Zhuo; Wang, Zhenlin

    2013-06-01

    This paper presents a novel method for fabricating a monolayer of hexagonal-close-packed metallic nanoshells with a small opening, based on a combination of a porous polymer template and a nanocrystal-seeded electroless plating technique. Light transmission spectra of the metallic nanoshell arrays are measured, which show that light can transmit through the dense particle assemblies via excitations of a variety of surface-plasmons (SPs). Further numerical simulations confirm these transmission resonances and reveal that they are attributed to the excitations of localized quadrupolar spherelike and Fano-type hybridized SP modes supported by the specific structure. The present metallic microstructure could find applications in plasmonics.

  18. Four-channel optical demultiplexer based on hexagonal photonic crystal ring resonators

    NASA Astrophysics Data System (ADS)

    Fallahi, Vahid; Seifouri, Mahmood; Olyaee, Saeed; Alipour-Banaei, Hamed

    2017-08-01

    In this paper, photonic crystal ring resonators with hexagonal lattice structure are used to design a four-channel optical demultiplexer. The structure size, the average transfer coefficient, the quality factor, and the channel spacing are equal to 424.5 µm2, 95.8%, 1943, and 2 nm, respectively. The average crosstalk is also computed to be -18.11 dB. In this study, the plane wave expansion (PWE) and finite-difference time-domain (FDTD) methods are used, respectively, to characterize the photonic bandgap and to investigate the optical behavior of the structure. The proposed design can be used in dense wavelength division multiplexing (DWDM) systems.

  19. How iron controls iron.

    PubMed

    Kühn, Lukas C

    2009-12-01

    Cells regulate iron homeostasis by posttranscriptional regulation of proteins responsible for iron uptake and storage. This requires RNA-binding activity of iron-regulatory proteins, IRP1 and IRP2. Two studies recently published in Science by Vashisht et al. (2009) and Salahudeen et al. (2009) reveal how cells adjust IRP2 activity.

  20. Electron-electron scattering and thermal conductivity of ɛ-iron at Earth’s core conditions

    NASA Astrophysics Data System (ADS)

    Pourovskii, L. V.; Mravlje, J.; Georges, A.; Simak, S. I.; Abrikosov, I. A.

    2017-07-01

    The electronic state and transport properties of hot dense iron are of the utmost importance for the understanding of Earth’s interior. Combining state-of-the-art density functional and dynamical mean field theories we study the impact of electron correlations on the electrical and thermal resistivity of hexagonal close-packed ɛ-Fe at Earth’s core conditions and show that the electron-electron scattering in ɛ-Fe exhibit a nearly perfect Fermi-liquid (FL) behavior. Accordingly, the quadratic dependence of the scattering rate, typical of FLs, leads to a modification of the Wiedemann-Franz law and suppresses the thermal conductivity with respect to the electrical one. The consequence is a significant increase of the electron-electron thermal resistivity, which is found to be of comparable magnitude to the electron-phonon one.

  1. Multilayer hexagonal silicon forming in slit nanopore.

    PubMed

    He, Yezeng; Li, Hui; Sui, Yanwei; Qi, Jiqiu; Wang, Yanqing; Chen, Zheng; Dong, Jichen; Li, Xiongying

    2015-10-05

    The solidification of two-dimensional liquid silicon confined to a slit nanopore has been studied using molecular dynamics simulations. The results clearly show that the system undergoes an obvious transition from liquid to multilayer hexagonal film with the decrease of temperature, accompanied by dramatic change in potential energy, atomic volume, coordination number and lateral radial distribution function. During the cooling process, some hexagonal islands randomly appear in the liquid first, then grow up to grain nuclei, and finally connect together to form a complete polycrystalline film. Moreover, it is found that the quenching rate and slit size are of vital importance to the freezing structure of silicon film. The results also indicate that the slit nanopore induces the layering of liquid silicon, which further induces the slit size dependent solidification behavior of silicon film with different electrical properties.

  2. Discrete breathers in hexagonal dusty plasma lattices

    SciTech Connect

    Koukouloyannis, V.; Kourakis, I.

    2009-08-15

    The occurrence of single-site or multisite localized vibrational modes, also called discrete breathers, in two-dimensional hexagonal dusty plasma lattices is investigated. The system is described by a Klein-Gordon hexagonal lattice characterized by a negative coupling parameter epsilon in account of its inverse dispersive behavior. A theoretical analysis is performed in order to establish the possibility of existence of single as well as three-site discrete breathers in such systems. The study is complemented by a numerical investigation based on experimentally provided potential forms. This investigation shows that a dusty plasma lattice can support single-site discrete breathers, while three-site in phase breathers could exist if specific conditions, about the intergrain interaction strength, would hold. On the other hand, out of phase and vortex three-site breathers cannot be supported since they are highly unstable.

  3. Synthesis of silicon carbide hexagonal nanoprisms

    NASA Astrophysics Data System (ADS)

    Wu, R. B.; Yang, G. Y.; Pan, Y.; Chen, J. J.

    2007-02-01

    SiC hexagonal nanoprisms have been prepared by a reaction of multiwall carbon nanotubes and Si vapor in an Astro furnace at 1450 °C for 3 h. The polytype, morphology, crystal structure of the nanoprisms were studied by X-ray powder diffraction, scanning electron microscopy and high resolution transmission electron microscopy, showing their hexagonal nanoprism shapes with a 3C-SiC single crystal structure with a diameter of about 100 nm and 2 μm in length. The photoluminescence spectrum of the nanoprisms exhibits a significant blue-shift relative to bulk 3C-SiC and other nanostructured SiC. The possible growth mechanism that controls the nanostructure formation is also analysed.

  4. Hexagonal Ferrites for Millimeter Wave Applications

    DTIC Science & Technology

    1993-01-07

    single crystal platelets, single crystal spheres of Ba- and Sr- hexaferrite materials, and permalloy thin films. Three papers on these results have been...effective linewidth in planar Zn-Y hexagonal ferrite single crystal platelets, single crystal spheres of Ba- and Sr- hexaferrite materials, and...basic thesis of the original proposal - that the measured linewidth in single crystal hexaferrites (1) may contain significant contributions related to

  5. Dense cold baryonic matter

    NASA Astrophysics Data System (ADS)

    Stavinskiy, A. V.

    2017-09-01

    A possibility of studying cold nuclear matter on the Nuclotron-NICA facility at baryonic densities characteristic of and higher than at the center of a neutron star is considered based on the data from cumulative processes. A special rare-event kinematic trigger for collisions of relativistic ions is proposed for effective selection of events accompanied by production of dense baryonic systems. Possible manifestations of new matter states under these unusual conditions and an experimental program for their study are discussed. Various experimental setups are proposed for these studies, and a possibility of using experimental setups at the Nuclotron-NICA facility for this purpose is considered.

  6. The reconstructed edges of the hexagonal BN.

    PubMed

    Zhao, Ruiqi; Gao, Junfeng; Liu, Zhongfan; Ding, Feng

    2015-06-07

    As an important two-dimensional material which shows exceptional mechanical and chemical stability, superior electronic properties, along with broad applications, the hexagonal-BN (h-BN) has drawn great attention recently. Here we report a systematic study on the structural stability, electronic and magnetic properties of various h-BN edges, including both bare and hydrogen-terminated ones. It is found that along the armchair (AC) direction, the pristine edge is the most stable one because of the formation of a triple B≡N bond, while, along the zigzag (ZZ) directions, the reconstructed ones, ZZB + N and ZZN57 are more stable. The pristine edges are more stable in bare BN in most cases if saturated with hydrogen. By applying the theory of Wulff construction, we predicted that an unpassivated BN domain prefers the hexagonal shape enclosed with bare AC edges i.e., AC-Ns, AC, AC-Bs if the feedstock varies from N-rich to B-rich. However, the evolution from ZZN edged triangular domain, to hexagonal domain enclosed with AC edges, and ZZB edged triangle may occur if the edges are terminated by hydrogen atoms. Further calculation shows that these edges present rich type-dependent properties and thus are important for various applications. This theoretical study showed that controlling the morphologies of BN domains and BN edges is crucial for various applications.

  7. Dense Axion Stars

    NASA Astrophysics Data System (ADS)

    Mohapatra, Abhishek; Braaten, Eric; Zhang, Hong

    2016-03-01

    If the dark matter consists of axions, gravity can cause them to coalesce into axion stars, which are stable gravitationally bound Bose-Einstein condensates of axions. In the previously known axion stars, gravity and the attractive force between pairs of axions are balanced by the kinetic pressure. If the axion mass energy is mc2 =10-4 eV, these dilute axion stars have a maximum mass of about 10-14M⊙ . We point out that there are also dense axion stars in which gravity is balanced by the mean-field pressure of the axion condensate. We study axion stars using the leading term in a systematically improvable approximation to the effective potential of the nonrelativistic effective field theory for axions. Using the Thomas-Fermi approximation in which the kinetic pressure is neglected, we find a sequence of new branches of axion stars in which gravity is balanced by the mean-field interaction energy of the axion condensate. If mc2 =10-4 4 eV, the first branch of these dense axion stars has mass ranging from about 10-11M⊙ toabout M⊙.

  8. Dense Axion Stars.

    PubMed

    Braaten, Eric; Mohapatra, Abhishek; Zhang, Hong

    2016-09-16

    If the dark matter particles are axions, gravity can cause them to coalesce into axion stars, which are stable gravitationally bound systems of axions. In the previously known solutions for axion stars, gravity and the attractive force between pairs of axions are balanced by the kinetic pressure. The mass of these dilute axion stars cannot exceed a critical mass, which is about 10^{-14}M_{⊙} if the axion mass is 10^{-4}  eV. We study axion stars using a simple approximation to the effective potential of the nonrelativistic effective field theory for axions. We find a new branch of dense axion stars in which gravity is balanced by the mean-field pressure of the axion Bose-Einstein condensate. The mass on this branch ranges from about 10^{-20}M_{⊙} to about M_{⊙}. If a dilute axion star with the critical mass accretes additional axions and collapses, it could produce a bosenova, leaving a dense axion star as the remnant.

  9. Dense suspension splash

    NASA Astrophysics Data System (ADS)

    Dodge, Kevin M.; Peters, Ivo R.; Ellowitz, Jake; Schaarsberg, Martin H. Klein; Jaeger, Heinrich M.; Zhang, Wendy W.

    2014-11-01

    Impact of a dense suspension drop onto a solid surface at speeds of several meters-per-second splashes by ejecting individual liquid-coated particles. Suppression or reduction of this splash is important for thermal spray coating and additive manufacturing. Accomplishing this aim requires distinguishing whether the splash is generated by individual scattering events or by collective motion reminiscent of liquid flow. Since particle inertia dominates over surface tension and viscous drag in a strong splash, we model suspension splash using a discrete-particle simulation in which the densely packed macroscopic particles experience inelastic collisions but zero friction or cohesion. Numerical results based on this highly simplified model are qualitatively consistent with observations. They also show that approximately 70% of the splash is generated by collective motion. Here an initially downward-moving particle is ejected into the splash because it experiences a succession of low-momentum-change collisions whose effects do not cancel but instead accumulate. The remainder of the splash is generated by scattering events in which a small number of high-momentum-change collisions cause a particle to be ejected upwards. Current Address: Physics of Fluids Group, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands.

  10. Dense Suspension Splash

    NASA Astrophysics Data System (ADS)

    Zhang, Wendy; Dodge, Kevin M.; Peters, Ivo R.; Ellowitz, Jake; Klein Schaarsberg, Martin H.; Jaeger, Heinrich M.

    2014-03-01

    Upon impact onto a solid surface at several meters-per-second, a dense suspension plug splashes by ejecting liquid-coated particles. We study the mechanism for splash formation using experiments and a numerical model. In the model, the dense suspension is idealized as a collection of cohesionless, rigid grains with finite surface roughness. The grains also experience lubrication drag as they approach, collide inelastically and rebound away from each other. Simulations using this model reproduce the measured momentum distribution of ejected particles. They also provide direct evidence supporting the conclusion from earlier experiments that inelastic collisions, rather than viscous drag, dominate when the suspension contains macroscopic particles immersed in a low-viscosity solvent such as water. Finally, the simulations reveal two distinct routes for splash formation: a particle can be ejected by a single high momentum-change collision. More surprisingly, a succession of small momentum-change collisions can accumulate to eject a particle outwards. Supported by NSF through its MRSEC program (DMR-0820054) and fluid dynamics program (CBET-1336489).

  11. Dense Axion Stars

    NASA Astrophysics Data System (ADS)

    Braaten, Eric; Mohapatra, Abhishek; Zhang, Hong

    2016-09-01

    If the dark matter particles are axions, gravity can cause them to coalesce into axion stars, which are stable gravitationally bound systems of axions. In the previously known solutions for axion stars, gravity and the attractive force between pairs of axions are balanced by the kinetic pressure. The mass of these dilute axion stars cannot exceed a critical mass, which is about 10-14M⊙ if the axion mass is 10-4 eV . We study axion stars using a simple approximation to the effective potential of the nonrelativistic effective field theory for axions. We find a new branch of dense axion stars in which gravity is balanced by the mean-field pressure of the axion Bose-Einstein condensate. The mass on this branch ranges from about 10-20M⊙ to about M⊙ . If a dilute axion star with the critical mass accretes additional axions and collapses, it could produce a bosenova, leaving a dense axion star as the remnant.

  12. Warm dense crystallography

    NASA Astrophysics Data System (ADS)

    Valenza, Ryan A.; Seidler, Gerald T.

    2016-03-01

    The intense femtosecond-scale pulses from x-ray free electron lasers (XFELs) are able to create and interrogate interesting states of matter characterized by long-lived nonequilibrium semicore or core electron occupancies or by the heating of dense phases via the relaxation cascade initiated by the photoelectric effect. We address here the latter case of "warm dense matter" (WDM) and investigate the observable consequences of x-ray heating of the electronic degrees of freedom in crystalline systems. We report temperature-dependent density functional theory calculations for the x-ray diffraction from crystalline LiF, graphite, diamond, and Be. We find testable, strong signatures of condensed-phase effects that emphasize the importance of wide-angle scattering to study nonequilibrium states. These results also suggest that the reorganization of the valence electron density at eV-scale temperatures presents a confounding factor to achieving atomic resolution in macromolecular serial femtosecond crystallography (SFX) studies at XFELs, as performed under the "diffract before destroy" paradigm.

  13. Hexagonal OsB2: Sintering, microstructure and mechanical properties

    SciTech Connect

    Xie, Zhilin; Lugovy, Mykola; Orlovskaya, Nina; Graule, Thomas; Kuebler, Jakob; Mueller, Martin; Gao, Huili; Radovic, Miladin; Cullen, David A.

    2015-02-07

    In this study, the metastable high pressure ReB2-type hexagonal OsB2 bulk ceramics was produced by spark plasma sintering. The phase composition, microstructure, and mechanical behavior of the sintered OsB2 were studied by X-ray diffraction, optical microscopy, TEM, SEM, EDS, and nanoindentation. The produced ceramics was rather porous and contained a mixture of hexagonal (~80 wt.%) and orthorhombic (~20 wt.%) phases as identified by X-ray diffraction and EBSD analysis. Two boron-rich phases, which do not contain Os, were also identified by TEM and SEM/EDS analysis. Nanoindentation measurements yielded a hardness of 31 ± 9 GPa and Young’s modulus of 574 ± 112 GPa, indicating that the material is rather hard and very stiff; but, it is very prone to crack formation and propagation, which is indicative of a very brittle nature of this material. Improvements in the sintering regime are required in order to produce dense, homogeneous and single phase hexagonal OsB2 bulk ceramics.

  14. Thermal conductivity of hexagonal Si and hexagonal Si nanowires from first-principles

    NASA Astrophysics Data System (ADS)

    Raya-Moreno, Martí; Aramberri, Hugo; Seijas-Bellido, Juan Antonio; Cartoixà, Xavier; Rurali, Riccardo

    2017-07-01

    We calculate the thermal conductivity, κ, of the recently synthesized hexagonal diamond (lonsdaleite) Si using first-principles calculations and solving the Boltzmann Transport Equation. We find values of κ which are around 40% lower than in the common cubic diamond polytype of Si. The trend is similar for [111] Si nanowires, with reductions of the thermal conductivity that are even larger than in the bulk in some diameter range. The Raman active modes are identified, and the role of mid-frequency optical phonons that arise as a consequence of the reduced symmetry of the hexagonal lattice is discussed. We also show briefly that popular classic potentials used in molecular dynamics might not be suited to describe hexagonal polytypes, discussing the case of the Tersoff potential.

  15. Iron Chelation

    MedlinePlus

    ... iron overload and need treatment. What is iron overload? Iron chelation therapy is used when you have ... may want to perform: How quickly does iron overload happen? This is different for each person. It ...

  16. Solubilization of nutraceuticals into reverse hexagonal mesophases.

    PubMed

    Amar-Yuli, Idit; Aserin, Abraham; Garti, Nissim

    2008-08-21

    The solubilization of four bioactive molecules with different polarities, in three reverse hexagonal (HII) systems has been investigated. The three HII systems were a typical reverse hexagonal composed of glycerol monooleate (GMO)/tricaprylin/water and two fluid hexagonal systems containing either 2.75 wt % Transcutol or ethanol as a fourth component. The phase behavior of the liquid crystalline phases in the presence of ascorbic acid, ascorbyl palmitate, D-alpha-tocopherol and D-alpha-tocopherol acetate were determined by small-angle X-ray scattering (SAXS) and optical microscopy. Differential scanning calorimetry (DSC) and Fourier-transform infrared (FT-IR) techniques were utilized to follow modifications in the thermal behavior and in the vibrations of different functional groups upon solubilizing the bioactive molecules. The nature of each guest molecule (in both geometry and polarity) together with the different HII structures (typical and fluids) determined the corresponding phase behavior, swelling or structural transformations and its location in the HII structures. Ascorbic acid was found to act as a chaotropic guest molecule, localized in the water-rich core and at the interface. The AP was also a chaotropic guest molecule with its head located in the vicinity of the GMO headgroup while its tail embedded close to the surfactant tail. D-alpha-tocopherol and D-alpha-tocopherol acetate were incorporated between the GMO tails; however, the D-alpha-tocopherol was located closer to the interface. Once Transcutol or ethanol was present and upon guest molecule incorporation, partial migration was detected.

  17. Wargaming in Both Rectilinear and Hexagonal Spaces

    NASA Technical Reports Server (NTRS)

    Hoover, Alex

    2012-01-01

    There are two main approaches to managing wargame entity interactions (movement, line of sight, area of effect, etc) freespace and gridded In the freespace approach, the units exist as entities in a continuous volume of (usually) Cartesian 3D space. They move in any direction (based on interaction with "terrain" that occupies the same space) and interact with each other based on references and displacements from their position in that space. In the gridded approach, space is broken up into (usually regular) shaped pieces. Units are considered to occupy the entire volume of one of these pieces, movement, line of sight, and other interactions are based on the relationships among the spaces rather than the absolute positions of the units themselves. Both approaches have advantages and drawbacks. The general issue that this discussion has addressed is that there is no "perfect" approach to implementing a wargaming battlespace. Each of them (and this extends to others not discussed) has different sets of advantages and disadvantages. Nothing will change that basic nature of the various approaches, nor would it be desirable to do so. Along with the advantages, the challenges define the feel of the game and focus the thinking of the players on certain aspects and away from others. The proposed approach to combining square and hexagonal approaches, which we will call the rhombus interface, leverages rhombuses constructed from equilateral triangles into which the hexagon can be decomposed to bridge the gap between the approaches, maintain relative consistency between the two as much as possible, and provide most of the feel of the hexagonal approach.

  18. Method for exfoliation of hexagonal boron nitride

    NASA Technical Reports Server (NTRS)

    Lin, Yi (Inventor); Connell, John W. (Inventor)

    2012-01-01

    A new method is disclosed for the exfoliation of hexagonal boron nitride into mono- and few-layered nanosheets (or nanoplatelets, nanomesh, nanoribbons). The method does not necessarily require high temperature or vacuum, but uses commercially available h-BN powders (or those derived from these materials, bulk crystals) and only requires wet chemical processing. The method is facile, cost efficient, and scalable. The resultant exfoliated h-BN is dispersible in an organic solvent or water thus amenable for solution processing for unique microelectronic or composite applications.

  19. Geometrical Optics of Dense Aerosols

    SciTech Connect

    Hay, Michael J.; Valeo, Ernest J.; Fisch, Nathaniel J.

    2013-04-24

    Assembling a free-standing, sharp-edged slab of homogeneous material that is much denser than gas, but much more rare ed than a solid, is an outstanding technological challenge. The solution may lie in focusing a dense aerosol to assume this geometry. However, whereas the geometrical optics of dilute aerosols is a well-developed fi eld, the dense aerosol limit is mostly unexplored. Yet controlling the geometrical optics of dense aerosols is necessary in preparing such a material slab. Focusing dense aerosols is shown here to be possible, but the nite particle density reduces the eff ective Stokes number of the flow, a critical result for controlled focusing. __________________________________________________

  20. Nanocrystalline hexagonal diamond formed from glassy carbon

    NASA Astrophysics Data System (ADS)

    Shiell, Thomas. B.; McCulloch, Dougal G.; Bradby, Jodie E.; Haberl, Bianca; Boehler, Reinhard; McKenzie, David. R.

    2016-11-01

    Carbon exhibits a large number of allotropes and its phase behaviour is still subject to significant uncertainty and intensive research. The hexagonal form of diamond, also known as lonsdaleite, was discovered in the Canyon Diablo meteorite where its formation was attributed to the extreme conditions experienced during the impact. However, it has recently been claimed that lonsdaleite does not exist as a well-defined material but is instead defective cubic diamond formed under high pressure and high temperature conditions. Here we report the synthesis of almost pure lonsdaleite in a diamond anvil cell at 100 GPa and 400 °C. The nanocrystalline material was recovered at ambient and analysed using diffraction and high resolution electron microscopy. We propose that the transformation is the result of intense radial plastic flow under compression in the diamond anvil cell, which lowers the energy barrier by “locking in” favourable stackings of graphene sheets. This strain induced transformation of the graphitic planes of the precursor to hexagonal diamond is supported by first principles calculations of transformation pathways and explains why the new phase is found in an annular region. Our findings establish that high purity lonsdaleite is readily formed under strain and hence does not require meteoritic impacts.

  1. Nanocrystalline hexagonal diamond formed from glassy carbon.

    PubMed

    Shiell, Thomas B; McCulloch, Dougal G; Bradby, Jodie E; Haberl, Bianca; Boehler, Reinhard; McKenzie, David R

    2016-11-29

    Carbon exhibits a large number of allotropes and its phase behaviour is still subject to significant uncertainty and intensive research. The hexagonal form of diamond, also known as lonsdaleite, was discovered in the Canyon Diablo meteorite where its formation was attributed to the extreme conditions experienced during the impact. However, it has recently been claimed that lonsdaleite does not exist as a well-defined material but is instead defective cubic diamond formed under high pressure and high temperature conditions. Here we report the synthesis of almost pure lonsdaleite in a diamond anvil cell at 100 GPa and 400 °C. The nanocrystalline material was recovered at ambient and analysed using diffraction and high resolution electron microscopy. We propose that the transformation is the result of intense radial plastic flow under compression in the diamond anvil cell, which lowers the energy barrier by "locking in" favourable stackings of graphene sheets. This strain induced transformation of the graphitic planes of the precursor to hexagonal diamond is supported by first principles calculations of transformation pathways and explains why the new phase is found in an annular region. Our findings establish that high purity lonsdaleite is readily formed under strain and hence does not require meteoritic impacts.

  2. Nanocrystalline hexagonal diamond formed from glassy carbon

    SciTech Connect

    Shiell, Thomas. B.; McCulloch, Dougal G.; Bradby, Jodie E.; Haberl, Bianca; Boehler, Reinhard; McKenzie, David. R.

    2016-11-29

    Carbon exhibits a large number of allotropes and its phase behaviour is still subject to signifcant uncertainty and intensive research. The hexagonal form of diamond, also known as lonsdaleite, was discovered in the Canyon Diablo meteorite where its formation was attributed to the extreme conditions experienced during the impact. However, it has recently been claimed that lonsdaleite does not exist as a well-defned material but is instead defective cubic diamond formed under high pressure and high temperature conditions. Here we report the synthesis of almost pure lonsdaleite in a diamond anvil cell at 100GPa and 400 C. The nanocrystalline material was recovered at ambient and analysed using difraction and high resolution electron microscopy. We propose that the transformation is the result of intense radial plastic fow under compression in the diamond anvil cell, which lowers the energy barrier by locking in favourable stackings of graphene sheets. This strain induced transformation of the graphitic planes of the precursor to hexagonal diamond is supported by frst principles calculations of transformation pathways and explains why the new phase is found in an annular region. Furthermore, our findings establish that high purity lonsdaleite is readily formed under strain and hence does not require meteoritic impacts.

  3. Nanocrystalline hexagonal diamond formed from glassy carbon

    PubMed Central

    Shiell, Thomas. B.; McCulloch, Dougal G.; Bradby, Jodie E.; Haberl, Bianca; Boehler, Reinhard; McKenzie, David. R.

    2016-01-01

    Carbon exhibits a large number of allotropes and its phase behaviour is still subject to significant uncertainty and intensive research. The hexagonal form of diamond, also known as lonsdaleite, was discovered in the Canyon Diablo meteorite where its formation was attributed to the extreme conditions experienced during the impact. However, it has recently been claimed that lonsdaleite does not exist as a well-defined material but is instead defective cubic diamond formed under high pressure and high temperature conditions. Here we report the synthesis of almost pure lonsdaleite in a diamond anvil cell at 100 GPa and 400 °C. The nanocrystalline material was recovered at ambient and analysed using diffraction and high resolution electron microscopy. We propose that the transformation is the result of intense radial plastic flow under compression in the diamond anvil cell, which lowers the energy barrier by “locking in” favourable stackings of graphene sheets. This strain induced transformation of the graphitic planes of the precursor to hexagonal diamond is supported by first principles calculations of transformation pathways and explains why the new phase is found in an annular region. Our findings establish that high purity lonsdaleite is readily formed under strain and hence does not require meteoritic impacts. PMID:27897174

  4. Nanocrystalline hexagonal diamond formed from glassy carbon

    DOE PAGES

    Shiell, Thomas. B.; McCulloch, Dougal G.; Bradby, Jodie E.; ...

    2016-11-29

    Carbon exhibits a large number of allotropes and its phase behaviour is still subject to signifcant uncertainty and intensive research. The hexagonal form of diamond, also known as lonsdaleite, was discovered in the Canyon Diablo meteorite where its formation was attributed to the extreme conditions experienced during the impact. However, it has recently been claimed that lonsdaleite does not exist as a well-defned material but is instead defective cubic diamond formed under high pressure and high temperature conditions. Here we report the synthesis of almost pure lonsdaleite in a diamond anvil cell at 100GPa and 400 C. The nanocrystalline materialmore » was recovered at ambient and analysed using difraction and high resolution electron microscopy. We propose that the transformation is the result of intense radial plastic fow under compression in the diamond anvil cell, which lowers the energy barrier by locking in favourable stackings of graphene sheets. This strain induced transformation of the graphitic planes of the precursor to hexagonal diamond is supported by frst principles calculations of transformation pathways and explains why the new phase is found in an annular region. Furthermore, our findings establish that high purity lonsdaleite is readily formed under strain and hence does not require meteoritic impacts.« less

  5. Two-dimensional hexagonal semiconductors beyond graphene

    NASA Astrophysics Data System (ADS)

    Nguyen, Bich Ha; Hieu Nguyen, Van

    2016-12-01

    The rapid and successful development of the research on graphene and graphene-based nanostructures has been substantially enlarged to include many other two-dimensional hexagonal semiconductors (THS): phosphorene, silicene, germanene, hexagonal boron nitride (h-BN) and transition metal dichalcogenides (TMDCs) such as MoS2, MoSe2, WS2, WSe2 as well as the van der Waals heterostructures of various THSs (including graphene). The present article is a review of recent works on THSs beyond graphene and van der Waals heterostructures composed of different pairs of all THSs. One among the priorities of new THSs compared to graphene is the presence of a non-vanishing energy bandgap which opened up the ability to fabricate a large number of electronic, optoelectronic and photonic devices on the basis of these new materials and their van der Waals heterostructures. Moreover, a significant progress in the research on TMDCs was the discovery of valley degree of freedom. The results of research on valley degree of freedom and the development of a new technology based on valley degree of freedom-valleytronics are also presented. Thus the scientific contents of the basic research and practical applications os THSs are very rich and extremely promising.

  6. Dense Deposit Disease

    PubMed Central

    Smith, Richard J.H; Harris, Claire L.; Pickering, Matthew C.

    2011-01-01

    Dense deposit disease (DDD) is an orphan disease that primarily affects children and young adults without sexual predilection. Studies of its pathophysiology have shown conclusively that it is caused by fluid-phase dysregulation of the alternative pathway of complement, however the role played by genetics and autoantibodies like C3 nephritic factors must be more thoroughly defined if we are to make an impact in the clinical management of this disease. There are currently no mechanism-directed therapies to offer affected patients, half of whom progress to end stage renal failure disease within 10 years of diagnosis. Transplant recipients face the dim prospect of disease recurrence in their allografts, half of which ultimately fail. More detailed genetic and complement studies of DDD patients may make it possible to identify protective factors prognostic for naïve kidney and transplant survival, or conversely risk factors associated with progression to renal failure and allograft loss. The pathophysiology of DDD suggests that a number of different treatments warrant consideration. As advances are made in these areas, there will be a need to increase healthcare provider awareness of DDD by making resources available to clinicians to optimize care for DDD patients. PMID:21601923

  7. Ariel's Densely Pitted Surface

    NASA Technical Reports Server (NTRS)

    1986-01-01

    This mosaic of the four highest-resolution images of Ariel represents the most detailed Voyager 2 picture of this satellite of Uranus. The images were taken through the clear filter of Voyager's narrow-angle camera on Jan. 24, 1986, at a distance of about 130,000 kilometers (80,000 miles). Ariel is about 1,200 km (750 mi) in diameter; the resolution here is 2.4 km (1.5 mi). Much of Ariel's surface is densely pitted with craters 5 to 10 km (3 to 6 mi) across. These craters are close to the threshold of detection in this picture. Numerous valleys and fault scarps crisscross the highly pitted terrain. Voyager scientists believe the valleys have formed over down-dropped fault blocks (graben); apparently, extensive faulting has occurred as a result of expansion and stretching of Ariel's crust. The largest fault valleys, near the terminator at right, as well as a smooth region near the center of this image, have been partly filled with deposits that are younger and less heavily cratered than the pitted terrain. Narrow, somewhat sinuous scarps and valleys have been formed, in turn, in these young deposits. It is not yet clear whether these sinuous features have been formed by faulting or by the flow of fluids.

    JPL manages the Voyager project for NASA's Office of Space Science.

  8. Mercury's Densely Cratered Surface

    NASA Technical Reports Server (NTRS)

    1974-01-01

    Mariner 10 took this picture (FDS 27465) of the densely cratered surface of Mercury when the spacecraft was 18,200 kilometers (8085 miles) from the planet on March 29. The dark line across top of picture is a 'dropout' of a few TV lines of data. At lower left, a portion of a 61 kilometer (38 mile) crater shows a flow front extending across the crater floor and filling more than half of the crater. The smaller, fresh crater at center is about 25 kilometers (15 miles) in diameter. Craters as small as one kilometer (about one-half mile) across are visible in the picture.

    The Mariner 10 mission, managed by the Jet Propulsion Laboratory for NASA's Office of Space Science, explored Venus in February 1974 on the way to three encounters with Mercury-in March and September 1974 and in March 1975. The spacecraft took more than 7,000 photos of Mercury, Venus, the Earth and the Moon.

    Image Credit: NASA/JPL/Northwestern University

  9. An X-ray scattering study of flow-aligned samples of a lyotropic liquid-crystalline hexagonal phase

    NASA Astrophysics Data System (ADS)

    Impéror-Clerc, M.; Davidson, P.

    Large flow-aligned samples of the hexagonal mesophase of the (sodium dodecylsulfate, pentanol, water) ternary system were produced by merely sucking the material into flat glass capillaries. These samples were examined by polarized light microscopy and X-ray scattering. In the plane of the hexagonal lattice, the `` -mosaic'' is only because the dense (10) hexagonal planes lie parallel to the flat glass plates of the capillaries. In contrast, the `` -mosaic'' of the C6 axis reaches 5-10 because the samples undergo a thermomechanical instability of the columns already investigated by Oswald et al. in detail on the (C12EO6, H2O) system. Anisotropic thermal diffuse scattering is observed around the Bragg peaks and its description in the frame of an elastic continuum model provides estimates of the elastic constants. On heating the samples, we observed a clear splitting of four of the (10) hexagonal lattice reflections. This splitting is the defining signature of the thermomechanical instability by which the columns form zig-zags. The fact that two of the (10) reflections are not affected by the instability demonstrates that it is confined to the plane of the capillary. The influence of temperature on the thermomechanical instability was also studied in detail.

  10. Conductive dense hydrogen

    NASA Astrophysics Data System (ADS)

    Eremets, M.; Troyan, I.

    2012-12-01

    Hydrogen at ambient pressures and low temperatures forms a molecular crystal which is expected to display metallic properties under megabar pressures. This metal is predicted to be superconducting with a very high critical temperature Tc of 200-400 K. The superconductor may potentially be recovered metastably at ambient pressures, and it may acquire a new quantum state as a metallic superfluid and a superconducting superfluid. Recent experiments performed at low temperatures T < 100 K showed that at record pressures of 300 GPa, hydrogen remains in the molecular state and is an insulator with a band gap of appr 2 eV. Given our current experimental and theoretical understanding, hydrogen is expected to become metallic at pressures of 400-500 GPa, beyond the current limits of static pressures achievable using diamond anvil cells. We found that at room temperature and pressure > 220 GPa, new Raman modes arose, providing evidence for the transformation to a new opaque and electrically conductive phase IV. Above 260 GPa, in the next phase V, hydrogen reflected light well. Its resistance was nearly temperature-independent over a wide temperature range, down to 30 K, indicating that the hydrogen was metallic. Releasing the pressure induced the metallic phase to transform directly into molecular hydrogen with significant hysteresis at 200 GPa and 295 K. These data were published in our paper: M. I. Eremets and I. A. Troyan "Conductive dense hydrogen." Nature Materials 10: 927-931. We will present also new results on hydrogen: phase diagram with phases IV and V determined in P,T domain up to 300 GPa and 350 K. We will also discuss possible structures of phase IV based on our Raman and infrared measurements up to 300 GPa.

  11. Oxygen ion-conducting dense ceramic

    DOEpatents

    Balachandran, Uthamalingam; Kleefisch, Mark S.; Kobylinski, Thaddeus P.; Morissette, Sherry L.; Pei, Shiyou

    1997-01-01

    Preparation, structure, and properties of mixed metal oxide compositions containing at least strontium, cobalt, iron and oxygen are described. The crystalline mixed metal oxide compositions of this invention have, for example, structure represented by Sr.sub..alpha. (Fe.sub.1-x Co.sub.x).sub..alpha.+.beta. O.sub..delta. where x is a number in a range from 0.01 to about 1, .alpha. is a number in a range from about 1 to about 4, .beta. is a number in a range upward from 0 to about 20, and .delta. is a number which renders the compound charge neutral, and wherein the composition has a non-perovskite structure. Use of the mixed metal oxides in dense ceramic membranes which exhibit oxygen ionic conductivity and selective oxygen separation, are described as well as their use in separation of oxygen from an oxygen-containing gaseous mixture.

  12. Oxygen ion-conducting dense ceramic

    DOEpatents

    Balachandran, Uthamalingam; Kleefisch, Mark S.; Kobylinski, Thaddeus P.; Morissette, Sherry L.; Pei, Shiyou

    1996-01-01

    Preparation, structure, and properties of mixed metal oxide compositions containing at least strontium, cobalt, iron and oxygen are described. The crystalline mixed metal oxide compositions of this invention have, for example, structure represented by Sr.sub..alpha. (Fe.sub.1-x Co.sub.x).sub..alpha.+.beta. O.sub..delta. where x is a number in a range from 0.01 to about 1, .alpha. is a number in a range from about 1 to about 4, .beta. is a number in a range upward from 0 to about 20, and .delta. is a number which renders the compound charge neutral, and wherein the composition has a non-perovskite structure. Use of the mixed metal oxides in dense ceramic membranes which exhibit oxygen ionic conductivity and selective oxygen separation, are described as well as their use in separation of oxygen from an oxygen-containing gaseous mixture.

  13. Hexagonal boron nitride and water interaction parameters.

    PubMed

    Wu, Yanbin; Wagner, Lucas K; Aluru, Narayana R

    2016-04-28

    The study of hexagonal boron nitride (hBN) in microfluidic and nanofluidic applications at the atomic level requires accurate force field parameters to describe the water-hBN interaction. In this work, we begin with benchmark quality first principles quantum Monte Carlo calculations on the interaction energy between water and hBN, which are used to validate random phase approximation (RPA) calculations. We then proceed with RPA to derive force field parameters, which are used to simulate water contact angle on bulk hBN, attaining a value within the experimental uncertainties. This paper demonstrates that end-to-end multiscale modeling, starting at detailed many-body quantum mechanics and ending with macroscopic properties, with the approximations controlled along the way, is feasible for these systems.

  14. The hexagon hypothesis: Six disruptive scenarios.

    PubMed

    Burtles, Jim

    2015-01-01

    This paper aims to bring a simple but effective and comprehensive approach to the development, delivery and monitoring of business continuity solutions. To ensure that the arguments and principles apply across the board, the paper sticks to basic underlying concepts rather than sophisticated interpretations. First, the paper explores what exactly people are defending themselves against. Secondly, the paper looks at how defences should be set up. Disruptive events tend to unfold in phases, each of which invites a particular style of protection, ranging from risk management through to business continuity to insurance cover. Their impact upon any business operation will fall into one of six basic scenarios. The hexagon hypothesis suggests that everyone should be prepared to deal with each of these six disruptive scenarios and it provides them with a useful benchmark for business continuity.

  15. Hexagonal boron nitride and water interaction parameters

    NASA Astrophysics Data System (ADS)

    Wu, Yanbin; Wagner, Lucas K.; Aluru, Narayana R.

    2016-04-01

    The study of hexagonal boron nitride (hBN) in microfluidic and nanofluidic applications at the atomic level requires accurate force field parameters to describe the water-hBN interaction. In this work, we begin with benchmark quality first principles quantum Monte Carlo calculations on the interaction energy between water and hBN, which are used to validate random phase approximation (RPA) calculations. We then proceed with RPA to derive force field parameters, which are used to simulate water contact angle on bulk hBN, attaining a value within the experimental uncertainties. This paper demonstrates that end-to-end multiscale modeling, starting at detailed many-body quantum mechanics and ending with macroscopic properties, with the approximations controlled along the way, is feasible for these systems.

  16. Quantum emission from hexagonal boron nitride monolayers

    NASA Astrophysics Data System (ADS)

    Tran, Toan Trong; Bray, Kerem; Ford, Michael J.; Toth, Milos; Aharonovich, Igor

    2016-01-01

    Artificial atomic systems in solids are widely considered the leading physical system for a variety of quantum technologies, including quantum communications, computing and metrology. To date, however, room-temperature quantum emitters have only been observed in wide-bandgap semiconductors such as diamond and silicon carbide, nanocrystal quantum dots, and most recently in carbon nanotubes. Single-photon emission from two-dimensional materials has been reported, but only at cryogenic temperatures. Here, we demonstrate room-temperature, polarized and ultrabright single-photon emission from a colour centre in two-dimensional hexagonal boron nitride. Density functional theory calculations indicate that vacancy-related defects are a probable source of the emission. Our results demonstrate the unprecedented potential of van der Waals crystals for large-scale nanophotonics and quantum information processing.

  17. Quantum emission from hexagonal boron nitride monolayers

    NASA Astrophysics Data System (ADS)

    Aharonovich, Igor; Tran, Toantrong; Bray, Kerem; Ford, Michael J.; Toth, Milos; MTEE Collaboration

    Artificial atomic systems in solids are widely considered the leading physical system for a variety of quantum technologies, including quantum communications, computing and metrology. To date, however, room-temperature quantum emitters have only been observed in wide-bandgap semiconductors such as diamond and silicon carbide, nanocrystal quantum dots, and most recently in carbon nanotubes. Here, we demonstrate room-temperature, polarized single-photon emission from a colour centre in two-dimensional hexagonal boron nitride. The emitters emit at the red and the near infrared spectral range and exhibit narrowband ultra bright emission (~full width at half maximum of below 10 nm with more than three million counts/s). Density functional theory calculations indicate that vacancy-related defects are a probable source of the emission. Our results demonstrate the unprecedented potential of van der Waals crystals for large-scale nanophotonics and quantum information processing.

  18. Structural domain walls in polar hexagonal manganites

    NASA Astrophysics Data System (ADS)

    Kumagai, Yu

    2014-03-01

    The domain structure in the multiferroic hexagonal manganites is currently intensely investigated, motivated by the observation of intriguing sixfold topological defects at their meeting points [Choi, T. et al,. Nature Mater. 9, 253 (2010).] and nanoscale electrical conductivity at the domain walls [Wu, W. et al., Phys. Rev. Lett. 108, 077203 (2012).; Meier, D. et al., Nature Mater. 11, 284 (2012).], as well as reports of coupling between ferroelectricity, magnetism and structural antiphase domains [Geng, Y. et al., Nano Lett. 12, 6055 (2012).]. The detailed structure of the domain walls, as well as the origin of such couplings, however, was previously not fully understood. In the present study, we have used first-principles density functional theory to calculate the structure and properties of the low-energy structural domain walls in the hexagonal manganites [Kumagai, Y. and Spaldin, N. A., Nature Commun. 4, 1540 (2013).]. We find that the lowest energy domain walls are atomically sharp, with {210}orientation, explaining the orientation of recently observed stripe domains and suggesting their topological protection [Chae, S. C. et al., Phys. Rev. Lett. 108, 167603 (2012).]. We also explain why ferroelectric domain walls are always simultaneously antiphase walls, propose a mechanism for ferroelectric switching through domain-wall motion, and suggest an atomistic structure for the cores of the sixfold topological defects. This work was supported by ETH Zurich, the European Research Council FP7 Advanced Grants program me (grant number 291151), the JSPS Postdoctoral Fellowships for Research Abroad, and the MEXT Elements Strategy Initiative to Form Core Research Center TIES.

  19. Formation of hexagonal 9R silicon polytype by ion implantation

    NASA Astrophysics Data System (ADS)

    Korolev, D. S.; Nikolskaya, A. A.; Krivulin, N. O.; Belov, A. I.; Mikhaylov, A. N.; Pavlov, D. A.; Tetelbaum, D. I.; Sobolev, N. A.; Kumar, M.

    2017-08-01

    Transmission electron-microscopy examination revealed the appearance of a hexagonal silicon (9R polytype) inclusions in the subsrface silicon layer upon ion implantation and subsequent heat treatment of the SiO2/Si structure. The formation of this hexagonal phase is stimulated by mechanical stresses arising in the heterophase system in the course of ion implantation.

  20. Iron Test

    MedlinePlus

    ... are used together to detect and help diagnose iron deficiency or iron overload. In people with anemia , these ... help determine whether the condition is due to iron deficiency or another cause, such as chronic blood loss ...

  1. Comparison of presumptive blood test kits including hexagon OBTI.

    PubMed

    Johnston, Emma; Ames, Carole E; Dagnall, Kathryn E; Foster, John; Daniel, Barbara E

    2008-05-01

    Four presumptive blood tests, Hexagon OBTI, Hemastix(R), Leucomalachite green (LMG), and Kastle-Meyer (KM) were compared for their sensitivity in the identification of dried bloodstains. Stains of varying blood dilutions were subjected to each presumptive test and the results compared. The Hexagon OBTI buffer volume was also reduced to ascertain whether this increased the sensitivity of the kit. The study found that Hemastix(R) was the most sensitive test for trace blood detection. Only with the reduced buffer volume was the Hexagon OBTI kit as sensitive as the LMG and KM tests. However, the Hexagon OBTI kit has the advantage of being a primate specific blood detection kit. This study also investigated whether the OBTI buffer within the kit could be utilized for DNA profiling after presumptive testing. The results show that DNA profiles can be obtained from the Hexagon OBTI kit buffer directly.

  2. Elastic and mechanical properties of hexagonal diamond under pressure

    NASA Astrophysics Data System (ADS)

    Güler, E.; Güler, M.

    2015-05-01

    Hexagonal diamond is the harder and stiffer alternative of traditional cubic diamond for today's technology. Although several theoretical attempts have been performed to understand the ground-state elastic properties of hexagonal diamond, little is known about the high-pressure elastic properties of this key material. Unlike previous theoretical methods, we report the application of second-generation reactive bond order potential for the first time to elaborate the pressure-dependent properties of hexagonal diamond in conjunction with geometry optimization calculations up to 500 GPa. Pressure dependency of density, five independent elastic constants, bulk, shear and Young moduli, Poisson ratio, elastic wave velocities, anisotropy parameter, Kleinman parameter, and stability conditions of hexagonal diamond were evaluated. Overall, considered properties of hexagonal diamond display evident increments under pressure, and their ground-state values are in reasonable agreement with available theoretical data.

  3. Saturn's Hexagon as Summer Solstice Approaches

    NASA Image and Video Library

    2017-05-24

    These natural color views from NASA's Cassini spacecraft compare the appearance of Saturn's north-polar region in June 2013 and April 2017. In both views, Saturn's polar hexagon dominates the scene. The comparison shows how clearly the color of the region changed in the interval between the two views, which represents the latter half of Saturn's northern hemisphere spring. In 2013, the entire interior of the hexagon appeared blue. By 2017, most of the hexagon's interior was covered in yellowish haze, and only the center of the polar vortex retained the blue color. The seasonal arrival of the sun's ultraviolet light triggers the formation of photochemical aerosols, leading to haze formation. The general yellowing of the polar region is believed to be caused by smog particles produced by increasing solar radiation shining on the polar region as Saturn approached the northern summer solstice on May 24, 2017. Scientists are considering several ideas to explain why the center of the polar vortex remains blue while the rest of the polar region has turned yellow. One idea is that, because the atmosphere in the vortex's interior is the last place in the northern hemisphere to be exposed to spring and summer sunlight, smog particles have not yet changed the color of the region. A second explanation hypothesizes that the polar vortex may have an internal circulation similar to hurricanes on Earth. If the Saturnian polar vortex indeed has an analogous structure to terrestrial hurricanes, the circulation should be downward in the eye of the vortex. The downward circulation should keep the atmosphere clear of the photochemical smog particles, and may explain the blue color. Images captured with Cassini's wide-angle camera using red, green and blue spectral filters were combined to create these natural-color views. The 2013 view (left in the combined view), was captured on June 25, 2013, when the spacecraft was about 430,000 miles (700,000 kilometers) away from Saturn. The

  4. Ultracold Quantum Gases in Hexagonal Optical Lattices

    NASA Astrophysics Data System (ADS)

    Sengstock, Klaus

    2010-03-01

    Hexagonal structures occur in a vast variety of systems, ranging from honeycombs of bees in life sciences to carbon nanotubes in material sciences. The latter, in particular its unfolded two-dimensional layer -- Graphene -- has rapidly grown to one of the most discussed topics in condensed-matter physics. Not only does it show proximity to various carbon-based materials but also exceptional properties owing to its unusual energy spectrum. In quantum optics, ultracold quantum gases confined in periodic light fields have shown to be very general and versatile instruments to mimic solid state systems. However, so far nearly all experiments were performed in cubic lattice geometries only. Here we report on the first experimental realization of ultracold quantum gases in a state-dependent, two-dimensional, Graphene-like optical lattice with hexagonal symmetry. The lattice is realized via a spin-dependent optical lattice structure with alternating σ^+ and σ^- -sites and thus constitutes a so called `magnetic'-lattice with `antiferromagnetic'-structure. Atoms with different spin orientation can be loaded to specific lattice sites or -- depending on the parameters -- to the whole lattice. As a consequence e.g. superpositions of a superfluid spin component with a different spin component in the Mott-insulating phase can be realized as well as spin-dependent transport properties, disorder etc. After preparing an antiferromagnetically ordered state we e.g. measure sustainable changes of the transport properties of the atoms. This manifests in a significant reduction of the tunneling as compared to a single-component system. We attribute this observation to a partial tunneling blockade for one spin component induced by population in another spin component localized at alternating lattice sites. Within a Gutzwiller-Ansatz we calculate the phase diagrams for the mixed spin-states and find very good agreement with our experimental results. Moreover, by state-resolved recording

  5. Microcrystalline hexagonal tungsten bronze. 2. Dehydration dynamics.

    PubMed

    Luca, Vittorio; Griffith, Christopher S; Hanna, John V

    2009-07-06

    Low-temperature (25-600 degrees C) thermal transformations have been studied for hydrothermally prepared, microcrystalline hexagonal tungsten bronze (HTB) phases A(x)WO(3+x/2).zH(2)O as a function of temperature, where A is an exchangeable cation (in this case Na(+) or Cs(+)) located in hexagonal structural tunnels. Thermal treatment of the as-prepared sodium- and cesium-exchanged phases in air were monitored using a conventional laboratory-based X-ray diffractometer, while thermal transformations in vacuum were studied using synchrotron X-ray and neutron diffraction. Concurrent thermogravimetric, diffuse reflectance infrared (DRIFT), and (23)Na and (133)Cs magic angle spinning (MAS) NMR spectroscopic studies have also been undertaken. For the cesium variant, cell volume contraction occurred from room temperature to about 350 degrees C, the regime in which water was "squeezed" out of tunnel sites. This was followed by a lattice expansion in the 350-600 degrees C temperature range. Over the entire temperature range, a net thermal contraction was observed, and this was the result of an anisotropic change in the cell dimensions which included a shortening of the A-O2 bond length. These changes explain why Cs(+) ions are locked into tunnel positions at temperatures as low as 400 degrees C, subsequently inducing a significant reduction in Cs(+) extractability under low pH (nitric acid) conditions. The changing Cs(+) speciation as detected by (133)Cs MAS NMR showed a condensation from multiple Cs sites, presumably associated with differing modes of Cs(+) hydration in the tunnels, to a single Cs(+) environment upon thermal transformation and water removal. While similar lattice contraction was observed for the as-prepared sodium variant, the smaller radius of Na(+) caused it to be relatively easily removed with acid in comparison to the Cs(+) variant. From (23)Na MAS NMR studies of the parent material, complex Na(+) speciation was observed with dehydrated and various

  6. Effective elastic properties of two dimensional multiplanar hexagonal nanostructures

    NASA Astrophysics Data System (ADS)

    Mukhopadhyay, T.; Mahata, A.; Adhikari, S.; Asle Zaeem, M.

    2017-06-01

    A generalized analytical approach is presented to derive closed-form formulae for the elastic moduli of hexagonal multiplanar nano-structures. Hexagonal nano-structural forms are common for various materials. Four different classes of materials (single layer) from a structural point of view are proposed to demonstrate the validity and prospective application of the developed formulae. For example, graphene, an allotrope of carbon, consists of only carbon atoms to form a honeycomb like hexagonal lattice in a single plane, while hexagonal boron nitride (hBN) consists of boron and nitrogen atoms to form the hexagonal lattice in a single plane. Unlike graphene and hBN, there are plenty of other materials with hexagonal nano-structures that have the atoms placed in multiple planes such as stanene (consists of only Sn atoms) and molybdenum disulfide (consists of two different atoms: Mo and S). The physics based high-fidelity analytical model developed in this article are capable of obtaining the elastic properties in a computationally efficient manner for wide range of such materials with hexagonal nano-structures that are broadly classified in four classes from structural viewpoint. Results are provided for materials belonging to all the four classes, wherein a good agreement between the elastic moduli obtained using the proposed formulae and available scientific literature is observed.

  7. Selective MBE growth of hexagonal networks of trapezoidal and triangular GaAs nanowires on patterned (1 1 1)B substrates

    NASA Astrophysics Data System (ADS)

    Tamai, Isao; Hasegawa, Hideki

    2007-04-01

    As a combination of novel hardware architecture and novel system architecture for future ultrahigh-density III-V nanodevice LSIs, the authors' group has recently proposed a hexagonal binary decision diagram (BDD) quantum circuit approach where gate-controlled path switching BDD node devices for a single or few electrons are laid out on a hexagonal nanowire network to realize a logic function. In this paper, attempts are made to establish a method to grow highly dense hexagonal nanowire networks for future BDD circuits by selective molecular beam epitaxy (MBE) on (1 1 1)B substrates. The (1 1 1)B orientation is suitable for BDD architecture because of the basic three-fold symmetry of the BDD node device. The growth experiments showed complex evolution of the cross-sectional structures, and it was explained in terms of kinetics determining facet boundaries. Straight arrays of triangular nanowires with 60 nm base width as well as hexagonal arrays of trapezoidal nanowires with a node density of 7.5×10 6 cm -2 were successfully grown with the aid of computer simulation. The result shows feasibility of growing high-density hexagonal networks of GaAs nanowires with precise control of the shape and size.

  8. Hexagonal boron-nitride nanomesh magnets

    NASA Astrophysics Data System (ADS)

    Ohata, C.; Tagami, R.; Nakanishi, Y.; Iwaki, R.; Nomura, K.; Haruyama, J.

    2016-09-01

    The formation of magnetic and spintronic devices using two-dimensional (2D) atom-thin layers has attracted attention. Ferromagnetisms (FMs) arising from zigzag-type atomic structure of edges of 2D atom-thin materials have been experimentally observed in graphene nanoribbons, hydrogen (H)-terminated graphene nanomeshes (NMs), and few-layer oxygen (O)-terminated black phosphorus NMs. Herein, we report room-temperature edge FM in few-layer hexagonal boron-nitride (hBN) NMs. O-terminated hBNNMs annealed at 500 °C show the largest FM, while it completely disappears in H-terminated hBNNMs. When hBNNMs are annealed at other temperatures, amplitude of the FM significantly decreases. These are highly in contrast to the case of graphene NMs but similar to the cases of black phosphorus NM and suggest that the hybridization of the O atoms with B(N) dangling bonds of zigzag pore edges, formed at the 500 °C annealing, strongly contribute to this edge FM. Room-temperature FM realizable only by exposing hBNNMs into air opens the way for high-efficiency 2D flexible magnetic and spintronic devices without the use of rare magnetic elements.

  9. Mathematical Foundation for Plane Covering Using Hexagons

    NASA Technical Reports Server (NTRS)

    Johnson, Gordon G.

    1999-01-01

    This work is to indicate the development and mathematical underpinnings of the algorithms previously developed for covering the plane and the addressing of the elements of the covering. The algorithms are of interest in that they provides a simple systematic way of increasing or decreasing resolution, in the sense that if we have the covering in place and there is an image superimposed upon the covering, then we may view the image in a rough form or in a very detailed form with minimal effort. Such ability allows for quick searches of crude forms to determine a class in which to make a detailed search. In addition, the addressing algorithms provide an efficient way to process large data sets that have related subsets. The algorithms produced were based in part upon the work of D. Lucas "A Multiplication in N Space" which suggested a set of three vectors, any two of which would serve as a bases for the plane and also that the hexagon is the natural geometric object to be used in a covering with a suggested bases. The second portion is a refinement of the eyeball vision system, the globular viewer.

  10. Instability of vibrational modes in hexagonal lattice

    NASA Astrophysics Data System (ADS)

    Korznikova, Elena A.; Bachurin, Dmitry V.; Fomin, Sergey Yu.; Chetverikov, Alexander P.; Dmitriev, Sergey V.

    2017-02-01

    The phenomenon of modulational instability is investigated for all four delocalized short-wave vibrational modes recently found for the two-dimensional hexagonal lattice with the help of a group-theoretic approach. The polynomial pair potential with hard-type quartic nonlinearity ( β-FPU potential with β > 0) is used to describe interactions between atoms. As expected for the hard-type anharmonic interactions, for all four modes the frequency is found to increase with the amplitude. Frequency of the modes I and III bifurcates from the upper edge of the phonon spectrum, while that of the modes II and IV increases from inside the spectrum. It is also shown that the considered model supports spatially localized vibrational mode called discrete breather (DB) or intrinsic localized mode. DB frequency increases with the amplitude above the phonon spectrum. Two different scenarios of the mode decay were revealed. In the first scenario (for modes I and III), development of the modulational instability leads to a formation of long-lived DBs that radiate their energy slowly until thermal equilibrium is reached. In the second scenario (for modes II and IV) a transition to thermal oscillations of atoms is observed with no formation of DBs.

  11. Bootstrapping the Three-Loop Hexagon

    SciTech Connect

    Dixon, Lance J.; Drummond, James M.; Henn, Johannes M.; /Humboldt U., Berlin /Santa Barbara, KITP

    2011-11-08

    We consider the hexagonal Wilson loop dual to the six-point MHV amplitude in planar N = 4 super Yang-Mills theory. We apply constraints from the operator product expansion in the near-collinear limit to the symbol of the remainder function at three loops. Using these constraints, and assuming a natural ansatz for the symbol's entries, we determine the symbol up to just two undetermined constants. In the multi-Regge limit, both constants drop out from the symbol, enabling us to make a non-trivial confirmation of the BFKL prediction for the leading-log approximation. This result provides a strong consistency check of both our ansatz for the symbol and the duality between Wilson loops and MHV amplitudes. Furthermore, we predict the form of the full three-loop remainder function in the multi-Regge limit, beyond the leading-log approximation, up to a few constants representing terms not detected by the symbol. Our results confirm an all-loop prediction for the real part of the remainder function in multi-Regge 3 {yields} 3 scattering. In the multi-Regge limit, our result for the remainder function can be expressed entirely in terms of classical polylogarithms. For generic six-point kinematics other functions are required.

  12. Hyperbolic phonon polaritons in hexagonal boron nitride

    NASA Astrophysics Data System (ADS)

    Dai, Siyuan

    2015-03-01

    Uniaxial materials whose axial and tangential permittivities have opposite signs are referred to as indefinite or hyperbolic media. While hyperbolic responses are normally achieved with metamaterials, hexagonal boron nitride (hBN) naturally possesses this property due to the anisotropic phonons in the mid-infrared. Using scattering-type scanning near-field optical microscopy, we studied polaritonic phenomena in hBN. We performed infrared nano-imaging of highly confined and low-loss hyperbolic phonon polaritons in hBN. The polariton wavelength was shown to be governed by the hBN thickness according to a linear law persisting down to few atomic layers [Science, 343, 1125-1129 (2014)]. Additionally, we carried out the modification of hyperbolic response in heterostructures comprised of a mononlayer graphene deposited on hBN. Electrostatic gating of the top graphene layer allows for the modification of wavelength and intensity of hyperbolic phonon polaritons in bulk hBN. The physics of the modification originates from the plasmon-phonon coupling in the hyperbolic medium. Furthermore, we demonstrated the ``hyperlens'' for subdiffractional imaging and focusing using a slab of hBN.

  13. Ab-initio study of hexagonal apatites

    NASA Astrophysics Data System (ADS)

    Calderin, Lazaro; Stott, Malcom J.

    2001-03-01

    A silicon stabilized mixture of calcium phosphate phases has been recognized as playing an important role in actively resorbable coatings and in ceramics as bone materials. The nature of this material is being investigated using a variety of techniques including a combination of crystallographic analysis of measured x-ray diffraction spectra, and ab initio quantum mechanics simulations. We have used all-electron, density functional based calculations to investigate a group of hexagonal apatites. The fully relaxed crystallographic structures of hydroxyapatite, and related apatites have been obtained. We will present the results and discuss the nature of the bonding in these materials. The x-ray diffraction pattern and the infra-red spectra have also been obtained and will be compared with experiment. Acknowledgments:This work is part of a collaboration with the Applied Ceramics group of M.Sayer, and with Millenium Biologix Inc. Support of the NSERC of Canada through the award of a Co-operative R & D grant to the collaboration is acknowledged.

  14. Pyramidal Image-Processing Code For Hexagonal Grid

    NASA Technical Reports Server (NTRS)

    Watson, Andrew B.; Ahumada, Albert J., Jr.

    1990-01-01

    Algorithm based on processing of information on intensities of picture elements arranged in regular hexagonal grid. Called "image pyramid" because image information at each processing level arranged in hexagonal grid having one-seventh number of picture elements of next lower processing level, each picture element derived from hexagonal set of seven nearest-neighbor picture elements in next lower level. At lowest level, fine-resolution of elements of original image. Designed to have some properties of image-coding scheme of primate visual cortex.

  15. Nylon flocked swab severely reduces Hexagon Obti sensibility.

    PubMed

    Frippiat, Christophe; De Roy, Gilbert; Fontaine, Louis-Marie; Dognaux, Sophie; Noel, Fabrice; Heudt, Laeticia; Lepot, Laurent

    2015-02-01

    Hexagon Obti immunological blood test and flocked swab are widely used in forensic laboratories. Nevertheless, up to now, no compatibility tests have been published between sampling with the ethylene oxide treated flocked swab and the Hexagon Obti blood detection strip. In this study, we investigated this compatibility. Our work shows that sampling with ethylene oxide treated flocked swab reduces by a factor of at least 100 the detection threshold of blood using the Hexagon Obti immunological test. Copyright © 2014 Elsevier Ireland Ltd. All rights reserved.

  16. Pyramidal Image-Processing Code For Hexagonal Grid

    NASA Technical Reports Server (NTRS)

    Watson, Andrew B.; Ahumada, Albert J., Jr.

    1990-01-01

    Algorithm based on processing of information on intensities of picture elements arranged in regular hexagonal grid. Called "image pyramid" because image information at each processing level arranged in hexagonal grid having one-seventh number of picture elements of next lower processing level, each picture element derived from hexagonal set of seven nearest-neighbor picture elements in next lower level. At lowest level, fine-resolution of elements of original image. Designed to have some properties of image-coding scheme of primate visual cortex.

  17. Calculation of refractive-index distribution of hexagonal GRIN lenses

    NASA Astrophysics Data System (ADS)

    Zhou, Zigang; Zhang, Ren; Chen, Kai

    2007-12-01

    The GRIN lens is widely used in optical communication and imaging systems. Its array can be used to design integrated optic imaging system, especially for hexagonal GRIN. In this paper, the analytic solution of refractive-index distribution of regularly hexagonal GRIN was obtained by separating variables and transforming coordinate. Having been simulated and compared, the correctness of this analytic solution was proved qualitatively and quantitatively. It has great benefit for further research of regular hexagonal GRIN lens and compound eye imaging system. Furthermore, a universal solution of the refractive-index distribution of a regular N-gon (N is even) lens was obtained by this method.

  18. 2-D photonic crystals microcavity filters based on hexagonal lattice structures embedded in ridge waveguides

    NASA Astrophysics Data System (ADS)

    Jugessur, A. S.; Pottier, P.; De La Rue, R. M.; Kirk, A. G.

    2005-09-01

    Compact photonic crystal (PhC) microcavity filters in a ridge waveguide format could play a useful role for wavelength division multiplexing (WDM) and de-multiplexing functionality in dense integrated photonic circuits. The microcavity filters are embedded in ridge waveguides with high lateral refractive-index contrast because good lateral confinement and efficient coupling of light into the device can be achieved using this established waveguide technology. However, this configuration leads to significant modal mismatch at the interfaces between the PhC and waveguide sections, contributing to reflection losses and reduced transmission over much of the useful spectrum. By the same token, mode-matching features consisting of two rows of PhC holes with a different filling factor and displaced to mirror-image positions with respect to the outer two rows of the main PhC mirrors have been implemented to enhance the optical transmission by more than a factor of two. Furthermore, an increase in Q-factor (more than 100 %) is achieved by the addition of two further rows of PhC holes on either side of the microcavity. Moreover, Bragg-grating concepts have been applied in several other filter designs using the same hexagonal PhC lattice configuration, in an attempt to control the filter response. This work involves the design, fabrication (using electron-beam lithography and reactive ion etching) and characterization of such hexagonal-lattice PhC microcavity filters embedded in ridge waveguides.

  19. 14. DETAIL OF ROOF SUPPORT BEAMS BRACED AGAINST HEXAGONAL WOODEN ...

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

    14. DETAIL OF ROOF SUPPORT BEAMS BRACED AGAINST HEXAGONAL WOODEN COMPRESSION RING AT TOP OF CENTRAL ROOF TRUSS. - Saratoga Gas Light Company, Gasholder No. 2, Niagara Mohawk Power Corporation Substation Facility, intersection of Excelsior & East Avenues, Saratoga Springs, NY

  20. Hydrogen bonding in the hexagonal ice surface.

    PubMed

    Barnett, Irene Li; Groenzin, Henning; Shultz, Mary Jane

    2011-06-16

    A recently developed technique in sum frequency generation spectroscopy, polarization angle null (or PAN-SFG), is applied to two orientations of the prism face of hexagonal ice. It is found that the vibrational modes of the surface are similar in different faces. As in the basal face, the prism face of ice contains five dominant resonances: 3096, 3146, 3205, 3253, and 3386 cm(-1). On the basal face, the reddest resonance occurs at 3098 cm(-1); within the bandwidth, the same as the prism face. On both the prism and basal faces, this mode contains a significant quadrupole component and is assigned to the bilayer stitching hydrogen bonds. The bluest of the resonances, 3386 cm(-1), occurs slightly blue-shifted at 3393 cm(-1) in the basal face. The prism face has two orientations: one with the optic or c axis in the input plane (the plane formed by the surface normal and the interrogating beam propagation) and one with the c axis perpendicular to the input plane. The 3386 cm(-1) mode has significant intensity only with the c axis in the input plane. On the basis of these orientation characteristics, the 3386 cm(-1) mode is assigned to double-donor molecules in either the top half bilayer or in the lower half bilayer. On the basis of frequency considerations, it is assigned to double-donor molecules in the top half bilayer. These are water molecules containing a nonbonded lone pair. In addition to identification of the components of the broad hydrogen-bonded region, PAN-SFG measures the tangential vs longitudinal content of the vibrational modes. In accord with previous suggestions, the lower frequency modes are predominantly tangential, whereas the higher frequency modes are mainly longitudinal. On the prism face, the 3386 cm(-1) mode is entirely longitudinal.

  1. Optoelectronic properties of hexagonal boron nitride epilayers

    NASA Astrophysics Data System (ADS)

    Cao, X. K.; Majety, S.; Li, J.; Lin, J. Y.; Jiang, H. X.

    2013-01-01

    This paper summarizes recent progress primarily achieved in authors' laboratory on synthesizing hexagonal boron nitride (hBN) epilayers by metal organic chemical vapor deposition (MCVD) and studies of their structural and optoelectronic properties. The structural and optical properties of hBN epilayers have been characterized by x-ray diffraction (XRD) and photoluminescence (PL) studies and compared to the better understood wurtzite AIN epilayers with a comparable energy bandgap. These MOCVD grown hBN epilayers exhibit highly efficient band-edge PL emission lines centered at around 5.5 eVat room temperature. The band-edge emission of hBN is two orders of magnitude higher than that of high quality AlN epilayers. Polarization-resolved PL spectroscopy revealed that hEN epilayers are predominantly a surface emission material, in which the band-edge emission with electric field perpendicular to the c-axis (Eemi⊥c) is about 1.7 times stronger than the component along the c-axis (Eemillc). This is in contrast to AIN, in which the band­ edge emission is known to be polarized along the c-axis, (Eemillc). Based on the graphene optical absorption concept, the estimated band-edge absorption coefficient of hBN is about 7x105 cm-1, which is more than 3 times higher than the value for AlN (~2x105 cm-1 . The hBN epilayer based photodetectors exhibit a sharp cut-off wavelength around 230 nm, which coincides with the band-edge PL emission peak and virtually no responses in the long wavelengths. The dielectric strength of hBN epilayers exceeds that of AlN and is greater than 4.5 MV/cm based on the measured result for an hBN epilayer released from the host sapphire substrate.

  2. Electrical contact to carbon nanotubes encapsulated in hexagonal boron nitride

    NASA Astrophysics Data System (ADS)

    Huang, Jhao-Wun; Pan, Cheng; Tran, Son; Taniguchi, Takashi; Bockrath, Marc; Lau, Jeanie

    2015-03-01

    Hexagonal boron nitride has been an excellent platform for low dimensional materials. We have fabricated ultra clean single-walled carbon nanotube(SWNT) devices encapsulated in hexagonal boron nitride by a dry transfer technique. Contacts to the SWNTs were made by reactive ion etching to expose the ends of SWNTs, followed by metal deposition. Ohmic contacts to SWNTs were achieved. We will discuss the quality of the contacts using different combinations of metals and present latest transport data.

  3. Structural and electronic properties of hexagonal yttrium trihydride

    SciTech Connect

    Wang, Y.; Chou, M.Y. )

    1995-03-15

    The structural and electronic properties of yttrium trihydride with metal atoms in the hexagonal-close-packed (hcp) structure are studied by the pseudopotential method within the local-density-functional approximation (LDA). It is found that the hydrogen positions within the metal lattice have a major role in determining these properties. Calculations confirmed that hexagonal YH[sub 3] with unusual wavelike hydrogen displacements (space group [ital D][sub 3[ital d

  4. Synthesis and Characterization of Hexagonal Boron Nitride (h- BN) Films

    DTIC Science & Technology

    2014-01-09

    Synthesis 1. Diborane- ammonia (B2H6-NH3- gases): Early results with these precursors were published in 2012. 5 Briefly, LPCVD growth of h-BN in a hot-wall...Approved for public release; distribution is unlimited. Synthesis and Characterization of Hexagonal Boron Nitride (h- BN) Films. The views, opinions and...1 ABSTRACT Number of Papers published in peer-reviewed journals: Synthesis and Characterization of Hexagonal Boron Nitride (h-BN) Films. Report Title

  5. The charge and spin transport properties in hexagonal silicene nanorings

    NASA Astrophysics Data System (ADS)

    Xu, N.; Zhang, H. Y.; Wu, X. Q.; Chen, Q.; Ding, J. W.

    2017-09-01

    Based on the tight-binding model, charge and spin transport properties of hexagonal silicene rings are investigated within the nonequilibrium Green’s function technique. The effects of external electric, magnetic and exchange fields are taken into account. The calculated results reveal that the hexagonal silicene nanorings act as a controllable spin filter. The near-perfect spin polarization can be achieved by adjusting the electric, magnetic and exchange fields. The calculated results offer new possibilities for silicene ring based spin nanodevices.

  6. Solar concentrating properties of truncated hexagonal, pyramidal and circular cones

    NASA Technical Reports Server (NTRS)

    Burkhard, D. G.; Strobel, G. L.; Shealy, D. L.

    1978-01-01

    The solar concentrating properties of specularly reflecting truncated pyramidal, hexagonal, and circular cones are evaluated. Pyramidal and hexagonal configurations are discussed with reference to the concentration factor as a function of half apex angle and the length of the side over the width, and to the irradiance distribution. Expressions are derived for the concentration factor and the irradiance at the base of a circular cone when the sunlight is incident normal to the aperture and for oblique incidence.

  7. Epitaxial Hexagonal Ferrites for Millimeter Wave Tunable Filters.

    DTIC Science & Technology

    1982-12-13

    anisotropy fields which, in effect, provide built-in biasing. The result is that ferrite components, similar to those used in microwave systems, can operate... method for growing hexagonal ferrites in the form of single crystal layers on non-magnetic, trAnsparmat subsrates - . The LPE method circumvents... method , single crystal hexagonal ferrites which are superior in quality to those grown by conventional methods . In order to have a more specific goal

  8. Hexagonal Organic Nanopillar Array from Melamine-Cyanuric Acid Complex

    PubMed Central

    Ji, Hai-Feng; Xu, Xiaohe

    2010-01-01

    We report a well-defined, organic, hexagonal nanopillar array on gold surface. The array was prepared from a cyanuric acid-melamine complex by mean of a sequential mixing on a gold surface. These nanopillars had uniform diameters of 200–400 nm and 1 µm in length. They were well facetted with hexagonal cross-sections. The nanopillars had a crystalline structure, and the pillars exhibited a layered texture in the longitudinal direction. PMID:20205460

  9. Synthesis of Fe-MCM-41 Using Iron Ore Tailings as the Silicon and Iron Source.

    PubMed

    Li, Xin; Yu, Honghao; He, Yan; Xue, Xiangxin

    2012-01-01

    Highly ordered Fe-MCM-41 molecular sieve was successfully synthesized by using n-hexadecyl-trimethyl ammonium bromide (CTAB) as the template and the iron ore tailings (IOTs) as the silicon and iron source. X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), diffuse reflectance UV-visible spectroscopy, (29)Si magic-angle spinning (MAS) nuclear magnetic resonance (NMR), and nitrogen adsorption/desorption were used to characterize the samples. The results showed that the mesoporous materials had highly ordered 2-dimensional hexagonal structure. The synthesized sample had high surface area, and part of iron atoms is retained in the framework with formation of tetrahedron after removal of the template by calcinations. The results obtained in the present work demonstrate the feasibility of employing iron ore tailings as a potential source of silicon and iron to produce Fe-MCM-41 mesoporous materials.

  10. Synthesis of Fe-MCM-41 Using Iron Ore Tailings as the Silicon and Iron Source

    PubMed Central

    Li, Xin; Yu, Honghao; He, Yan; Xue, Xiangxin

    2012-01-01

    Highly ordered Fe-MCM-41 molecular sieve was successfully synthesized by using n-hexadecyl-trimethyl ammonium bromide (CTAB) as the template and the iron ore tailings (IOTs) as the silicon and iron source. X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), diffuse reflectance UV-visible spectroscopy, 29Si magic-angle spinning (MAS) nuclear magnetic resonance (NMR), and nitrogen adsorption/desorption were used to characterize the samples. The results showed that the mesoporous materials had highly ordered 2-dimensional hexagonal structure. The synthesized sample had high surface area, and part of iron atoms is retained in the framework with formation of tetrahedron after removal of the template by calcinations. The results obtained in the present work demonstrate the feasibility of employing iron ore tailings as a potential source of silicon and iron to produce Fe-MCM-41 mesoporous materials. PMID:22567574

  11. Parametric bleaching of dense plasmas

    NASA Astrophysics Data System (ADS)

    Gradov, O. M.; Ramazashvili, R. R.

    1981-11-01

    A mechanism is proposed for the nonlinear bleaching of a dense plasma slab. In this new mechanism, the electromagnetic wave incident on the plasma decays into plasma waves and then reappears as a result of the coalescence of the plasma waves at the second boundary of the slab.

  12. Strain-induced extrinsic high-temperature ferromagnetism in the Fe-doped hexagonal barium titanate.

    PubMed

    Zorko, A; Pregelj, M; Gomilšek, M; Jagličić, Z; Pajić, D; Telling, M; Arčon, I; Mikulska, I; Valant, M

    2015-01-09

    Diluted magnetic semiconductors possessing intrinsic static magnetism at high temperatures represent a promising class of multifunctional materials with high application potential in spintronics and magneto-optics. In the hexagonal Fe-doped diluted magnetic oxide, 6H-BaTiO3-δ, room-temperature ferromagnetism has been previously reported. Ferromagnetism is broadly accepted as an intrinsic property of this material, despite its unusual dependence on doping concentration and processing conditions. However, the here reported combination of bulk magnetization and complementary in-depth local-probe electron spin resonance and muon spin relaxation measurements, challenges this conjecture. While a ferromagnetic transition occurs around 700 K, it does so only in additionally annealed samples and is accompanied by an extremely small average value of the ordered magnetic moment. Furthermore, several additional magnetic instabilities are detected at lower temperatures. These coincide with electronic instabilities of the Fe-doped 3C-BaTiO3-δ pseudocubic polymorph. Moreover, the distribution of iron dopants with frozen magnetic moments is found to be non-uniform. Our results demonstrate that the intricate static magnetism of the hexagonal phase is not intrinsic, but rather stems from sparse strain-induced pseudocubic regions. We point out the vital role of internal strain in establishing defect ferromagnetism in systems with competing structural phases.

  13. Strain-Induced Extrinsic High-Temperature Ferromagnetism in the Fe-Doped Hexagonal Barium Titanate

    PubMed Central

    Zorko, A.; Pregelj, M.; Gomilšek, M.; Jagličić, Z.; Pajić, D.; Telling, M.; Arčon, I.; Mikulska, I.; Valant, M.

    2015-01-01

    Diluted magnetic semiconductors possessing intrinsic static magnetism at high temperatures represent a promising class of multifunctional materials with high application potential in spintronics and magneto-optics. In the hexagonal Fe-doped diluted magnetic oxide, 6H-BaTiO3-δ, room-temperature ferromagnetism has been previously reported. Ferromagnetism is broadly accepted as an intrinsic property of this material, despite its unusual dependence on doping concentration and processing conditions. However, the here reported combination of bulk magnetization and complementary in-depth local-probe electron spin resonance and muon spin relaxation measurements, challenges this conjecture. While a ferromagnetic transition occurs around 700 K, it does so only in additionally annealed samples and is accompanied by an extremely small average value of the ordered magnetic moment. Furthermore, several additional magnetic instabilities are detected at lower temperatures. These coincide with electronic instabilities of the Fe-doped 3C-BaTiO3-δ pseudocubic polymorph. Moreover, the distribution of iron dopants with frozen magnetic moments is found to be non-uniform. Our results demonstrate that the intricate static magnetism of the hexagonal phase is not intrinsic, but rather stems from sparse strain-induced pseudocubic regions. We point out the vital role of internal strain in establishing defect ferromagnetism in systems with competing structural phases. PMID:25572803

  14. High-Pressure Polymorph of Iron.

    PubMed

    Takahashi, T; Bassett, W A

    1964-07-31

    An x-ray diffraction study of iron under pressure has shown that alpha-iron (body-centered cubic) transforms to hexagonal-close-packing (designated epsilon-iron) at 130 kb, room temperature. The volume change for the transformation is -0.20 +/- 0.03 cm2/ mole. The slope for the gamma-epsilon phase boundary has been calculated to be 2 +/- 1 degrees C/kb. The molar volume of iron decreases from 7.10 cm3/mole (density = 7.85 g/cm(3)) at room pressure to 6.10 +/- 0.08 cm(3)/mole (density = 9.1 +/- 0.1 g/cm(3)) at 200 kb and room temperature. The extrapolation of the gamma-epsilon phase boundary, consistent with shock wave data, suggests that it may have an influence on the properties of the earth's core.

  15. Polyfunctional bioceramics modified by M-type hexagonal ferrite particles for medical applications

    NASA Astrophysics Data System (ADS)

    Tkachenko, M. V.; Ol'Khovik, L. P.; Kamzin, A. S.

    2011-06-01

    Magnetic bioceramics based on Ca5(PO4)3OH hydroxyapatite and M-type hexagonal ferrite (HF) microcrystals has been synthesized and characterized. The material consists of a biocompatible apatite matrix containing dispersed M-type HF particles. The latter component makes the magnetic characteristics of synthesized ceramics significantly higher as compared to those of iron-oxide-modified bioglass ceramics currently used in medicine. These properties increase the efficiency and prospects of using the new bioceramics in medicine, in particular, for the hyperthermal treatment of malignant tumors. Thus, a new class of materials is created, which combine the necessary biocompatibility and biological activity of Ca5(PO4)3OH hydroxyapatite and high magnetic characteristics of M-type HF microcrystals.

  16. Intrinsic magnetic properties of hexagonal LuFeO{sub 3} and the effects of nonstoichiometry

    SciTech Connect

    Moyer, Jarrett A. E-mail: schlom@cornell.edu; Schiffer, Peter; Misra, Rajiv; Mundy, Julia A.; Brooks, Charles M.; Heron, John T.; Muller, David A.; Schlom, Darrell G. E-mail: schlom@cornell.edu

    2014-01-01

    We used oxide molecular-beam epitaxy in a composition-spread geometry to deposit hexagonal LuFeO{sub 3} (h-LuFeO{sub 3}) thin films with a monotonic variation in the Lu/Fe cation ratio, creating a mosaic of samples that ranged from iron rich to lutetium rich. We characterized the effects of composition variation with x-ray diffraction, atomic force microscopy, scanning transmission electron microscopy, and superconducting quantum interference device magnetometry. After identifying growth conditions leading to stoichiometric film growth, an additional sample was grown with a rotating sample stage. From this stoichiometric sample, we determined stoichiometric h-LuFeO{sub 3} to have a T{sub N} = 147 K and M{sub s} = 0.018 μ{sub B}/Fe.

  17. The extended family of hexagonal molybdenum oxide

    SciTech Connect

    Hartl, Monika; Daemen, Luke; Lunk, J H; Hartl, H; Frisk, A T; Shendervich, I; Mauder, D; Feist, M; Eckelt, R

    2009-01-01

    Over the last 40 years, a large number of isostructural compounds in the system MoO{sub 3}-NH{sub 3}-H{sub 2}O have been published. The reported molecular formulae of 'hexagonal molybdenum oxide' (HEMO) varied from MoO{sub 3}, MoO{sub 3} {center_dot} 0.33NH{sub 3}, MoO{sub 3} {center_dot} nH{sub 2}O (0.09 {le} n {le} 0.69) to MoO{sub 3} {center_dot} mNH{sub 3} {center_dot} nH{sub 2}O (0.09 {le} m {le} 0.20; 0.18 {le} n {le} 0.60). Samples, prepared by the acidification route, were investigated using thermal analysis coupled on-line to a mass spectrometer for evolved gas analysis; X-ray powder diffraction; Fourier Transform Infrared, Raman and Magic-Angle-Spinning {sup 1}H-NMR spectroscopy; Incoherent Inelastic Neutron Scattering. The X-ray study of a selected monocrystal confirmed the presence of the well-known framework of edge-sharing MoO{sub 6} octahedra: Space group P6{sub 3}/m, a = 10.527(1), c =3.7245(7) {angstrom}, {gamma} = 120{sup o}. The structure of the synthesized samples can best be described by the structural formula (NH{sub 4})[Mo{sub x}{open_square}{sub 1/2+p/2}(O{sub 3x + 1/2-p/2})(OH){sub p}] {center_dot} yH{sub 2}O (x 5.9-7.1; p {approx} 0.1; y = 1.2-2.6), which is consistent with the existence of one vacancy for 12-15 molybdenum sites. The 'chimie douce' reaction of MoO{sub 3} {center_dot} 0.155NH{sub 3} {center_dot} 0.440H{sub 2}O with a 1:1 mixture of NO/NO{sub 2} at 100 C resulted in the synthesis of MoO{sub 3} {center_dot} 0.539H{sub 2}O. Tailored nano-sized molybdenum powders can be produced using HEMO as precursor.

  18. Warm Dense Matter: An Overview

    SciTech Connect

    Kalantar, D H; Lee, R W; Molitoris, J D

    2004-04-21

    This document provides a summary of the ''LLNL Workshop on Extreme States of Materials: Warm Dense Matter to NIF'' which was held on 20, 21, and 22 February 2002 at the Wente Conference Center in Livermore, CA. The warm dense matter regime, the transitional phase space region between cold material and hot plasma, is presently poorly understood. The drive to understand the nature of matter in this regime is sparking scientific activity worldwide. In addition to pure scientific interest, finite temperature dense matter occurs in the regimes of interest to the SSMP (Stockpile Stewardship Materials Program). So that obtaining a better understanding of WDM is important to performing effective experiments at, e.g., NIF, a primary mission of LLNL. At this workshop we examined current experimental and theoretical work performed at, and in conjunction with, LLNL to focus future activities and define our role in this rapidly emerging research area. On the experimental front LLNL plays a leading role in three of the five relevant areas and has the opportunity to become a major player in the other two. Discussion at the workshop indicated that the path forward for the experimental efforts at LLNL were two fold: First, we are doing reasonable baseline work at SPLs, HE, and High Energy Lasers with more effort encouraged. Second, we need to plan effectively for the next evolution in large scale facilities, both laser (NIF) and Light/Beam sources (LCLS/TESLA and GSI) Theoretically, LLNL has major research advantages in areas as diverse as the thermochemical approach to warm dense matter equations of state to first principles molecular dynamics simulations. However, it was clear that there is much work to be done theoretically to understand warm dense matter. Further, there is a need for a close collaboration between the generation of verifiable experimental data that can provide benchmarks of both the experimental techniques and the theoretical capabilities. The conclusion of this

  19. Radiative properties of dense nanofluids.

    PubMed

    Wei, Wei; Fedorov, Andrei G; Luo, Zhongyang; Ni, Mingjiang

    2012-09-01

    The radiative properties of dense nanofluids are investigated. For nanofluids, scattering and absorbing of electromagnetic waves by nanoparticles, as well as light absorption by the matrix/fluid in which the nanoparticles are suspended, should be considered. We compare five models for predicting apparent radiative properties of nanoparticulate media and evaluate their applicability. Using spectral absorption and scattering coefficients predicted by different models, we compute the apparent transmittance of a nanofluid layer, including multiple reflecting interfaces bounding the layer, and compare the model predictions with experimental results from the literature. Finally, we propose a new method to calculate the spectral radiative properties of dense nanofluids that shows quantitatively good agreement with the experimental results.

  20. Boundary Preserving Dense Local Regions.

    PubMed

    Kim, Jaechul; Grauman, Kristen

    2015-05-01

    We propose a dense local region detector to extract features suitable for image matching and object recognition tasks. Whereas traditional local interest operators rely on repeatable structures that often cross object boundaries (e.g., corners, scale-space blobs), our sampling strategy is driven by segmentation, and thus preserves object boundaries and shape. At the same time, whereas existing region-based representations are sensitive to segmentation parameters and object deformations, our novel approach to robustly sample dense sites and determine their connectivity offers better repeatability. In extensive experiments, we find that the proposed region detector provides significantly better repeatability and localization accuracy for object matching compared to an array of existing feature detectors. In addition, we show our regions lead to excellent results on two benchmark tasks that require good feature matching: weakly supervised foreground discovery and nearest neighbor-based object recognition.

  1. HEXAGONAL ARRAY STRUCTURE FOR 2D NDE APPLICATIONS

    SciTech Connect

    Dziewierz, J.; Ramadas, S. N.; Gachagan, A.; O'Leary, R. L.

    2010-02-22

    This paper describes a combination of simulation and experimentation to evaluate the advantages offered by utilizing a hexagonal shaped array element in a 2D NDE array structure. The active material is a 1-3 connectivity piezoelectric composite structure incorporating triangular shaped pillars--each hexagonal array element comprising six triangular pillars. A combination of PZFlex, COMSOL and Matlab has been used to simulate the behavior of this device microstructure, for operation around 2.25 MHz, with unimodal behavior and low levels of mechanical cross-coupling predicted. Furthermore, the application of hexagonal array elements enables the array aperture to increase by approximately 30%, compared to a conventional orthogonal array matrix and hence will provide enhanced volumetric coverage and SNR. Prototype array configurations demonstrate good corroboration of the theoretically predicted mechanical cross-coupling between adjacent array elements (approx23 dB).

  2. Multilayer DNA Origami Packed on Hexagonal and Hybrid Lattices

    PubMed Central

    Ke, Yonggang; Voigt, Niels V.; Gothelf, Kurt V.; Shih, William M.

    2012-01-01

    “Scaffolded DNA origami” has been proven to be a powerful and efficient approach to construct two-dimensional or three-dimensional objects with great complexity. Multilayer DNA origami has been demonstrated with helices packing along either honeycomb-lattice geometry or square-lattice geometry. Here we report successful folding of multilayer DNA origami with helices arranged on a close-packed hexagonal lattice. This arrangement yields a higher density of helical packing and therefore higher resolution of spatial addressing than has been shown previously. We also demonstrate hybrid multilayer DNA origami with honeycomb-lattice, square-lattice, and hexagonal lattice packing of helices all in one design. The availability of hexagonal close packing of helices extends our ability to build complex structures using DNA nanotechnology. PMID:22187940

  3. Stabilization of 4H hexagonal phase in gold nanoribbons

    PubMed Central

    Fan, Zhanxi; Bosman, Michel; Huang, Xiao; Huang, Ding; Yu, Yi; Ong, Khuong P.; Akimov, Yuriy A.; Wu, Lin; Li, Bing; Wu, Jumiati; Huang, Ying; Liu, Qing; Eng Png, Ching; Lip Gan, Chee; Yang, Peidong; Zhang, Hua

    2015-01-01

    Gold, silver, platinum and palladium typically crystallize with the face-centred cubic structure. Here we report the high-yield solution synthesis of gold nanoribbons in the 4H hexagonal polytype, a previously unreported metastable phase of gold. These gold nanoribbons undergo a phase transition from the original 4H hexagonal to face-centred cubic structure on ligand exchange under ambient conditions. Using monochromated electron energy-loss spectroscopy, the strong infrared plasmon absorption of single 4H gold nanoribbons is observed. Furthermore, the 4H hexagonal phases of silver, palladium and platinum can be readily stabilized through direct epitaxial growth of these metals on the 4H gold nanoribbon surface. Our findings may open up new strategies for the crystal phase-controlled synthesis of advanced noble metal nanomaterials. PMID:26216712

  4. Density functional theory study of hexagonal carbon phases.

    PubMed

    Wang, Zhibin; Gao, Faming; Li, Na; Qu, Nianrui; Gou, Huiyang; Hao, Xianfeng

    2009-06-10

    It is reported frequently that the new carbon phases may be harder than diamond (Wang et al 2004 Proc. Natl Acad. Sci. 101 13699 and Mao et al 2003 Science 302 425). However, the mechanism is still unclear. In this paper we systematically investigate the structural, electronic, and mechanical properties of the diamond polytypes using first-principles density functional calculations. The results show that the bulk modulus and shear modulus for the hexagonal form of diamond approach those of diamond, suggesting they might be hard and low compressibility materials. According to the semiempirical method for hardness based on the Mulliken overlap population, the hardnesses for hexagonal forms have been evaluated and compared to diamond. The results indicate that these phases are superhard. More importantly, the bonds in some specific directions of the hexagonal phases are harder than those in diamond, which may lead to the noticeable indentation marks on the diamond anvils observed in experiments.

  5. New approach for direct chemical synthesis of hexagonal Co nanoparticles

    NASA Astrophysics Data System (ADS)

    Abel, Frank M.; Tzitzios, Vasilis; Hadjipanayis, George C.

    2016-02-01

    In this paper, we explore the possibility of producing hexagonal Cobalt nanoparticles, with high saturation magnetization by direct chemical synthesis. The nanoparticles were synthesized by reduction of anhydrous cobalt (II) chloride by NaBH4 in tetraglyme at temperatures in the range of 200-270 °C under a nitrogen-hydrogen atmosphere. The reactions were done at high temperatures to allow for the formation of as-made hexagonal cobalt. The size of the particles was controlled by the addition of different surfactants. The best magnetic properties so far were obtained on spherical hexagonal Co nanoparticles with an average size of 45 nm, a saturation magnetization of 143 emu/g and coercivity of 500 Oe. the saturation magnetization and coercivity were further improved by annealing the Co nanoparticles leading to saturation magnetization of 160 emu/g and coercivity of 540 Oe.

  6. Ab initio engineering of materials with stacked hexagonal tin frameworks

    PubMed Central

    Shao, Junping; Beaufils, Clément; Kolmogorov, Aleksey N.

    2016-01-01

    The group-IV tin has been hypothesized to possess intriguing electronic properties in an atom-thick hexagonal form. An attractive pathway of producing sizable 2D crystallites of tin is based on deintercalation of bulk compounds with suitable tin frameworks. Here, we have identified a new synthesizable metal distannide, NaSn2, with a 3D stacking of flat hexagonal layers and examined a known compound, BaSn2, with buckled hexagonal layers. Our ab initio results illustrate that despite being an exception to the 8-electron rule, NaSn2 should form under pressures easily achievable in multi-anvil cells and remain (meta)stable under ambient conditions. Based on calculated Z2 invariants, the predicted NaSn2 may display topologically non-trivial behavior and the known BaSn2 could be a strong topological insulator. PMID:27387140

  7. Hexagonal cobalt carbide formed by carbon ion implantation

    NASA Astrophysics Data System (ADS)

    Liu, B. X.; Wang, J.; Fang, Z. Z.

    1991-05-01

    Thin films of ferromagnetic metals, i.e., bcc Fe, hcp Co, and fcc Ni, were subjected to 50-keV carbon ion implantation at room temperature. At the dose of 2.5×1017 ions/cm2, the formation of hexagonal Fe3C and Ni3C phases was confirmed by transmission electron microscopy selected area electron diffraction patterns; and more interestingly a similar pattern for Co was also observed for the first time. The phase was identified as hexagonal Co3C with a=2.685 Å and c=4.335 Å based on the spacings and intensities of the diffraction rings. The carbide formation was also confirmed by Auger electron spectra. The stoichiometry of the hexagonal structure may be extended in the range of Co3-2C as estimated from the experiments performed up to the dose of 9×1017 ions/cm2.

  8. Ab initio engineering of materials with stacked hexagonal tin frameworks

    NASA Astrophysics Data System (ADS)

    Shao, Junping; Beaufils, Clément; Kolmogorov, Aleksey N.

    2016-07-01

    The group-IV tin has been hypothesized to possess intriguing electronic properties in an atom-thick hexagonal form. An attractive pathway of producing sizable 2D crystallites of tin is based on deintercalation of bulk compounds with suitable tin frameworks. Here, we have identified a new synthesizable metal distannide, NaSn2, with a 3D stacking of flat hexagonal layers and examined a known compound, BaSn2, with buckled hexagonal layers. Our ab initio results illustrate that despite being an exception to the 8-electron rule, NaSn2 should form under pressures easily achievable in multi-anvil cells and remain (meta)stable under ambient conditions. Based on calculated Z2 invariants, the predicted NaSn2 may display topologically non-trivial behavior and the known BaSn2 could be a strong topological insulator.

  9. Backscattering by hexagonal ice crystals of cirrus clouds.

    PubMed

    Borovoi, Anatoli; Konoshonkin, Alexander; Kustova, Natalia

    2013-08-01

    Light backscattering by randomly oriented hexagonal ice crystals of cirrus clouds is considered within the framework of the physical-optics approximation. The fine angular structure of all elements of the Mueller matrix in the vicinity of the exact backward direction is first calculated and discussed. In particular, an approximate equation for the differential scattering cross section is obtained. Its simple spectral dependence is discussed. Also, a hollow of the linear depolarization ratio around the exact backward direction inherent to the long hexagonal columns is revealed.

  10. Electronic properties of hexagonal gallium phosphide: A DFT investigation

    SciTech Connect

    Kumar, Vipin; Shah, Esha V.; Roy, Debesh R.

    2016-05-23

    A detail density functional investigation is performed to develop hexagonal 2D gallium phosphide material. The geometry, band structure and density of states (total and projected) of 2D hexagonal GaP are reported in detail. It is heartening to note that the developed material is identified as an indirect band gap semiconductor. The indirect gap for this material is predicted as 1.97 eV at K-Γ, and a direct gap of 2.28 eV at K point is achieved, which is very close to the reported direct band gap for zinc blende and buckled structures of GaP.

  11. Communication: Water on hexagonal boron nitride from diffusion Monte Carlo

    NASA Astrophysics Data System (ADS)

    Al-Hamdani, Yasmine S.; Ma, Ming; Alfè, Dario; von Lilienfeld, O. Anatole; Michaelides, Angelos

    2015-05-01

    Despite a recent flurry of experimental and simulation studies, an accurate estimate of the interaction strength of water molecules with hexagonal boron nitride is lacking. Here, we report quantum Monte Carlo results for the adsorption of a water monomer on a periodic hexagonal boron nitride sheet, which yield a water monomer interaction energy of -84 ± 5 meV. We use the results to evaluate the performance of several widely used density functional theory (DFT) exchange correlation functionals and find that they all deviate substantially. Differences in interaction energies between different adsorption sites are however better reproduced by DFT.

  12. Communication: Water on hexagonal boron nitride from diffusion Monte Carlo.

    PubMed

    Al-Hamdani, Yasmine S; Ma, Ming; Alfè, Dario; von Lilienfeld, O Anatole; Michaelides, Angelos

    2015-05-14

    Despite a recent flurry of experimental and simulation studies, an accurate estimate of the interaction strength of water molecules with hexagonal boron nitride is lacking. Here, we report quantum Monte Carlo results for the adsorption of a water monomer on a periodic hexagonal boron nitride sheet, which yield a water monomer interaction energy of -84 ± 5 meV. We use the results to evaluate the performance of several widely used density functional theory (DFT) exchange correlation functionals and find that they all deviate substantially. Differences in interaction energies between different adsorption sites are however better reproduced by DFT.

  13. Communication: Water on hexagonal boron nitride from diffusion Monte Carlo

    SciTech Connect

    Al-Hamdani, Yasmine S.; Ma, Ming; Michaelides, Angelos; Alfè, Dario; Lilienfeld, O. Anatole von

    2015-05-14

    Despite a recent flurry of experimental and simulation studies, an accurate estimate of the interaction strength of water molecules with hexagonal boron nitride is lacking. Here, we report quantum Monte Carlo results for the adsorption of a water monomer on a periodic hexagonal boron nitride sheet, which yield a water monomer interaction energy of −84 ± 5 meV. We use the results to evaluate the performance of several widely used density functional theory (DFT) exchange correlation functionals and find that they all deviate substantially. Differences in interaction energies between different adsorption sites are however better reproduced by DFT.

  14. Optical Emission in Hexagonal SiGe Nanowires.

    PubMed

    Cartoixà, Xavier; Palummo, Maurizia; Hauge, Håkon Ikaros T; Bakkers, Erik P A M; Rurali, Riccardo

    2017-08-09

    Recent advances in the synthetic growth of nanowires have given access to crystal phases that in bulk are only observed under extreme pressure conditions. Here, we use first-principles methods based on density functional theory and many-body perturbation theory to show that a suitable mixing of hexagonal Si and hexagonal Ge yields a direct bandgap with an optically permitted transition. Comparison of the calculated radiative lifetimes with typical values of nonradiative recombination mechanisms indicates that optical emission will be the dominant recombination mechanism. These findings pave the way to the development of silicon-based optoelectronic devices, thus far hindered by the poor light emission efficiency of cubic Si.

  15. Hexagonal Pixels and Indexing Scheme for Binary Images

    NASA Technical Reports Server (NTRS)

    Johnson, Gordon G.

    2004-01-01

    A scheme for resampling binaryimage data from a rectangular grid to a regular hexagonal grid and an associated tree-structured pixel-indexing scheme keyed to the level of resolution have been devised. This scheme could be utilized in conjunction with appropriate image-data-processing algorithms to enable automated retrieval and/or recognition of images. For some purposes, this scheme is superior to a prior scheme that relies on rectangular pixels: one example of such a purpose is recognition of fingerprints, which can be approximated more closely by use of line segments along hexagonal axes than by line segments along rectangular axes. This scheme could also be combined with algorithms for query-image-based retrieval of images via the Internet. A binary image on a rectangular grid is generated by raster scanning or by sampling on a stationary grid of rectangular pixels. In either case, each pixel (each cell in the rectangular grid) is denoted as either bright or dark, depending on whether the light level in the pixel is above or below a prescribed threshold. The binary data on such an image are stored in a matrix form that lends itself readily to searches of line segments aligned with either or both of the perpendicular coordinate axes. The first step in resampling onto a regular hexagonal grid is to make the resolution of the hexagonal grid fine enough to capture all the binaryimage detail from the rectangular grid. In practice, this amounts to choosing a hexagonal-cell width equal to or less than a third of the rectangular- cell width. Once the data have been resampled onto the hexagonal grid, the image can readily be checked for line segments aligned with the hexagonal coordinate axes, which typically lie at angles of 30deg, 90deg, and 150deg with respect to say, the horizontal rectangular coordinate axis. Optionally, one can then rotate the rectangular image by 90deg, then again sample onto the hexagonal grid and check for line segments at angles of 0deg, 60deg

  16. The Discrete Fourier Transform on hexagonal remote sensing image

    NASA Astrophysics Data System (ADS)

    Li, Yalu; Ben, Jin; Wang, Rui; Du, Lingyu

    2016-11-01

    Global discrete grid system will subdivide the earth recursively to form a multi-resolution grid hierarchy with no Overlap and seamless which help build global uniform spatial reference datum and multi-source data processing mode which takes the position as the object and in the aspect of data structure supports the organization, process and analysis of the remote sensing big data. This paper adopts the base transform to realize the mutual transformation of square pixel and hexagonal pixel. This paper designs the corresponding discrete Fourier transform algorithm for any lattice. Finally, the paper show the result of the DFT of the remote sensing image of the hexagonal pixel.

  17. Temperature and composition of Saturn's polar hot spots and hexagon.

    PubMed

    Fletcher, L N; Irwin, P G J; Orton, G S; Teanby, N A; Achterberg, R K; Bjoraker, G L; Read, P L; Simon-Miller, A A; Howett, C; de Kok, R; Bowles, N; Calcutt, S B; Hesman, B; Flasar, F M

    2008-01-04

    Saturn's poles exhibit an unexpected symmetry in hot, cyclonic polar vortices, despite huge seasonal differences in solar flux. The cores of both vortices are depleted in phosphine gas, probably resulting from subsidence of air into the troposphere. The warm cores are present throughout the upper troposphere and stratosphere at both poles. The thermal structure associated with the marked hexagonal polar jet at 77 degrees N has been observed for the first time. Both the warm cyclonic belt at 79 degrees N and the cold anticyclonic zone at 75 degrees N exhibit the hexagonal structure.

  18. Constructing Dense Graphs with Unique Hamiltonian Cycles

    ERIC Educational Resources Information Center

    Lynch, Mark A. M.

    2012-01-01

    It is not difficult to construct dense graphs containing Hamiltonian cycles, but it is difficult to generate dense graphs that are guaranteed to contain a unique Hamiltonian cycle. This article presents an algorithm for generating arbitrarily large simple graphs containing "unique" Hamiltonian cycles. These graphs can be turned into dense graphs…

  19. Probing Cold Dense Nuclear Matter

    NASA Astrophysics Data System (ADS)

    Subedi, R.; Shneor, R.; Monaghan, P.; Anderson, B. D.; Aniol, K.; Annand, J.; Arrington, J.; Benaoum, H.; Benmokhtar, F.; Boeglin, W.; Chen, J.-P.; Choi, Seonho; Cisbani, E.; Craver, B.; Frullani, S.; Garibaldi, F.; Gilad, S.; Gilman, R.; Glamazdin, O.; Hansen, J.-O.; Higinbotham, D. W.; Holmstrom, T.; Ibrahim, H.; Igarashi, R.; de Jager, C. W.; Jans, E.; Jiang, X.; Kaufman, L. J.; Kelleher, A.; Kolarkar, A.; Kumbartzki, G.; LeRose, J. J.; Lindgren, R.; Liyanage, N.; Margaziotis, D. J.; Markowitz, P.; Marrone, S.; Mazouz, M.; Meekins, D.; Michaels, R.; Moffit, B.; Perdrisat, C. F.; Piasetzky, E.; Potokar, M.; Punjabi, V.; Qiang, Y.; Reinhold, J.; Ron, G.; Rosner, G.; Saha, A.; Sawatzky, B.; Shahinyan, A.; Širca, S.; Slifer, K.; Solvignon, P.; Sulkosky, V.; Urciuoli, G. M.; Voutier, E.; Watson, J. W.; Weinstein, L. B.; Wojtsekhowski, B.; Wood, S.; Zheng, X.-C.; Zhu, L.

    2008-06-01

    The protons and neutrons in a nucleus can form strongly correlated nucleon pairs. Scattering experiments, in which a proton is knocked out of the nucleus with high-momentum transfer and high missing momentum, show that in carbon-12 the neutron-proton pairs are nearly 20 times as prevalent as proton-proton pairs and, by inference, neutron-neutron pairs. This difference between the types of pairs is due to the nature of the strong force and has implications for understanding cold dense nuclear systems such as neutron stars.

  20. Probing cold dense nuclear matter.

    PubMed

    Subedi, R; Shneor, R; Monaghan, P; Anderson, B D; Aniol, K; Annand, J; Arrington, J; Benaoum, H; Benmokhtar, F; Boeglin, W; Chen, J-P; Choi, Seonho; Cisbani, E; Craver, B; Frullani, S; Garibaldi, F; Gilad, S; Gilman, R; Glamazdin, O; Hansen, J-O; Higinbotham, D W; Holmstrom, T; Ibrahim, H; Igarashi, R; de Jager, C W; Jans, E; Jiang, X; Kaufman, L J; Kelleher, A; Kolarkar, A; Kumbartzki, G; Lerose, J J; Lindgren, R; Liyanage, N; Margaziotis, D J; Markowitz, P; Marrone, S; Mazouz, M; Meekins, D; Michaels, R; Moffit, B; Perdrisat, C F; Piasetzky, E; Potokar, M; Punjabi, V; Qiang, Y; Reinhold, J; Ron, G; Rosner, G; Saha, A; Sawatzky, B; Shahinyan, A; Sirca, S; Slifer, K; Solvignon, P; Sulkosky, V; Urciuoli, G M; Voutier, E; Watson, J W; Weinstein, L B; Wojtsekhowski, B; Wood, S; Zheng, X-C; Zhu, L

    2008-06-13

    The protons and neutrons in a nucleus can form strongly correlated nucleon pairs. Scattering experiments, in which a proton is knocked out of the nucleus with high-momentum transfer and high missing momentum, show that in carbon-12 the neutron-proton pairs are nearly 20 times as prevalent as proton-proton pairs and, by inference, neutron-neutron pairs. This difference between the types of pairs is due to the nature of the strong force and has implications for understanding cold dense nuclear systems such as neutron stars.

  1. Probing Cold Dense Nuclear Matter

    SciTech Connect

    Subedi, Ramesh; Shneor, R.; Monaghan, Peter; Anderson, Bryon; Aniol, Konrad; Annand, John; Arrington, John; Benaoum, Hachemi; Benmokhtar, Fatiha; Bertozzi, William; Boeglin, Werner; Chen, Jian-Ping; Choi, Seonho; Cisbani, Evaristo; Craver, Brandon; Frullani, Salvatore; Garibaldi, Franco; Gilad, Shalev; Gilman, Ronald; Glamazdin, Oleksandr; Hansen, Jens-Ole; Higinbotham, Douglas; Holmstrom, Timothy; Ibrahim, Hassan; Igarashi, Ryuichi; De Jager, Cornelis; Jans, Eddy; Jiang, Xiaodong; Kaufman, Lisa; Kelleher, Aidan; Kolarkar, Ameya; Kumbartzki, Gerfried; LeRose, John; Lindgren, Richard; Liyanage, Nilanga; Margaziotis, Demetrius; Markowitz, Pete; Marrone, Stefano; Mazouz, Malek; Meekins, David; Michaels, Robert; Moffit, Bryan; Perdrisat, Charles; Piasetzky, Eliazer; Potokar, Milan; Punjabi, Vina; Qiang, Yi; Reinhold, Joerg; Ron, Guy; Rosner, Guenther; Saha, Arunava; Sawatzky, Bradley; Shahinyan, Albert; Sirca, Simon; Slifer, Karl; Solvignon, Patricia; Sulkosky, Vince; Sulkosky, Vincent; Sulkosky, Vince; Sulkosky, Vincent; Urciuoli, Guido; Voutier, Eric; Watson, John; Weinstein, Lawrence; Wojtsekhowski, Bogdan; Wood, Stephen; Zheng, Xiaochao; Zhu, Lingyan

    2008-06-01

    The protons and neutrons in a nucleus can form strongly correlated nucleon pairs. Scattering experiments, in which a proton is knocked out of the nucleus with high-momentum transfer and high missing momentum, show that in carbon-12 the neutron-proton pairs are nearly 20 times as prevalent as proton-proton pairs and, by inference, neutron-neutron pairs. This difference between the types of pairs is due to the nature of the strong force and has implications for understanding cold dense nuclear systems such as neutron stars.

  2. SUPPORTED DENSE CERAMIC MEMBRANES FOR OXYGEN SEPARATION

    SciTech Connect

    Timothy L. Ward

    2000-06-30

    . This successfully reduced cracking, however the films retained open porosity. The investigation of this concept will be continued in the final year of the project. Investigation of a metal organic chemical vapor deposition (MOCVD) method for defect mending in dense membranes was also initiated. An appropriate metal organic precursor (iron tetramethylheptanedionate) was identified whose deposition can be controlled by access to oxygen at temperatures in the 280-300 C range. Initial experiments have deposited iron oxide, but only on the membrane surface; thus refinement of this method will continue.

  3. Optically transparent dense colloidal gels

    PubMed Central

    Zupkauskas, M.; Lan, Y.; Joshi, D.; Ruff, Z.

    2017-01-01

    Traditionally it has been difficult to study the porous structure of dense colloidal gels and (macro) molecular transport through them simply because of the difference in refractive index between the colloid material and the continuous fluid phase surrounding it, rendering the samples opaque even at low colloidal volume fractions. Here, we demonstrate a novel colloidal gel that can be refractive index-matched in aqueous solutions owing to the low refractive index of fluorinated latex (FL)-particles (n = 1.37). Synthesizing them from heptafluorobutyl methacrylate using emulsion polymerization, we demonstrate that they can be functionalized with short DNA sequences via a dense brush-layer of polystyrene-b-poly(ethylene oxide) block-copolymers (PS-PEO). The block-copolymer, holding an azide group at the free PEO end, was grafted to the latex particle utilizing a swelling–deswelling method. Subsequently, DNA was covalently attached to the azide-end of the block copolymer via a strain-promoted alkyne–azide click reaction. For comparison, we present a structural study of single gels made of FL-particles only and composite gels made of a percolating FL-colloid gel coated with polystyrene (PS) colloids. Further we demonstrate that the diffusivity of tracer colloids dispersed deep inside a refractive index matched FL-colloidal gel can be measured as function of the local confinement using Dynamic Differential Microscopy (DDM). PMID:28970935

  4. Magnetism in Dense Quark Matter

    NASA Astrophysics Data System (ADS)

    Ferrer, Efrain J.; de la Incera, Vivian

    We review the mechanisms via which an external magnetic field can affect the ground state of cold and dense quark matter. In the absence of a magnetic field, at asymptotically high densities, cold quark matter is in the Color-Flavor-Locked (CFL) phase of color superconductivity characterized by three scales: the superconducting gap, the gluon Meissner mass, and the baryonic chemical potential. When an applied magnetic field becomes comparable with each of these scales, new phases and/or condensates may emerge. They include the magnetic CFL (MCFL) phase that becomes relevant for fields of the order of the gap scale; the paramagnetic CFL, important when the field is of the order of the Meissner mass, and a spin-one condensate associated to the magnetic moment of the Cooper pairs, significant at fields of the order of the chemical potential. We discuss the equation of state (EoS) of MCFL matter for a large range of field values and consider possible applications of the magnetic effects on dense quark matter to the astrophysics of compact stars.

  5. Dense crystalline packings of ellipsoids

    NASA Astrophysics Data System (ADS)

    Jin, Weiwei; Jiao, Yang; Liu, Lufeng; Yuan, Ye; Li, Shuixiang

    2017-03-01

    An ellipsoid, the simplest nonspherical shape, has been extensively used as a model for elongated building blocks for a wide spectrum of molecular, colloidal, and granular systems. Yet the densest packing of congruent hard ellipsoids, which is intimately related to the high-density phase of many condensed matter systems, is still an open problem. We discover an unusual family of dense crystalline packings of self-dual ellipsoids (ratios of the semiaxes α : √{α }:1 ), containing 24 particles with a quasi-square-triangular (SQ-TR) tiling arrangement in the fundamental cell. The associated packing density ϕ exceeds that of the densest known SM2 crystal [ A. Donev et al., Phys. Rev. Lett. 92, 255506 (2004), 10.1103/PhysRevLett.92.255506] for aspect ratios α in (1.365, 1.5625), attaining a maximal ϕ ≈0.758 06 ... at α = 93 /64 . We show that the SQ-TR phase derived from these dense packings is thermodynamically stable at high densities over the aforementioned α range and report a phase diagram for self-dual ellipsoids. The discovery of the SQ-TR crystal suggests organizing principles for nonspherical particles and self-assembly of colloidal systems.

  6. Algebraic signal processing theory: 2-D spatial hexagonal lattice.

    PubMed

    Pünschel, Markus; Rötteler, Martin

    2007-06-01

    We develop the framework for signal processing on a spatial, or undirected, 2-D hexagonal lattice for both an infinite and a finite array of signal samples. This framework includes the proper notions of z-transform, boundary conditions, filtering or convolution, spectrum, frequency response, and Fourier transform. In the finite case, the Fourier transform is called discrete triangle transform. Like the hexagonal lattice, this transform is nonseparable. The derivation of the framework makes it a natural extension of the algebraic signal processing theory that we recently introduced. Namely, we construct the proper signal models, given by polynomial algebras, bottom-up from a suitable definition of hexagonal space shifts using a procedure provided by the algebraic theory. These signal models, in turn, then provide all the basic signal processing concepts. The framework developed in this paper is related to Mersereau's early work on hexagonal lattices in the same way as the discrete cosine and sine transforms are related to the discrete Fourier transform-a fact that will be made rigorous in this paper.

  7. Lattice-Polarity-Driven Epitaxy of Hexagonal Semiconductor Nanowires.

    PubMed

    Wang, Ping; Yuan, Ying; Zhao, Chao; Wang, Xinqiang; Zheng, Xiantong; Rong, Xin; Wang, Tao; Sheng, Bowen; Wang, Qingxiao; Zhang, Yongqiang; Bian, Lifeng; Yang, Xuelin; Xu, Fujun; Qin, Zhixin; Li, Xinzheng; Zhang, Xixiang; Shen, Bo

    2016-02-10

    Lattice-polarity-driven epitaxy of hexagonal semiconductor nanowires (NWs) is demonstrated on InN NWs. In-polarity InN NWs form typical hexagonal structure with pyramidal growth front, whereas N-polarity InN NWs slowly turn to the shape of hexagonal pyramid and then convert to an inverted pyramid growth, forming diagonal pyramids with flat surfaces and finally coalescence with each other. This contrary growth behavior driven by lattice-polarity is most likely due to the relatively lower growth rate of the (0001̅) plane, which results from the fact that the diffusion barriers of In and N adatoms on the (0001) plane (0.18 and 1.0 eV, respectively) are about 2-fold larger in magnitude than those on the (0001̅) plane (0.07 and 0.52 eV), as calculated by first-principles density functional theory (DFT). The formation of diagonal pyramids for the N-polarity hexagonal NWs affords a novel way to locate quantum dot in the kink position, suggesting a new recipe for the fabrication of dot-based devices.

  8. A low cost route to hexagonal mesostructured carbon molecular sieves.

    PubMed

    Kim, S S; Pinnavaia, T J

    2001-12-07

    A mesoporous carbon molecular sieve with a hexagonal framework structure (denoted C-MSU-H) has been prepared using a MSU-H silica template that can be assembled from a low cost soluble silicate precursor at near-neutral pH conditions.

  9. Synthesis and photocatalytic activity of porous bismuth oxychloride hexagonal prisms.

    PubMed

    Ding, Liyong; Chen, Huan; Wang, Qingqian; Zhou, Tengfei; Jiang, Qingqing; Yuan, Yuhong; Li, Jinlin; Hu, Juncheng

    2016-01-18

    Porous BiOCl hexagonal prisms have been successfully prepared through a simple solvothermal route. These novel BiOCl HPs with porous structures are assembled from nanoparticles and exhibit high activity and selectivity toward the photocatalytic aerobic oxidation of benzyl alcohol to benzaldehyde and degradation of methyl orange.

  10. Liquid phase deposition synthesis of hexagonal molybdenum trioxide thin films

    SciTech Connect

    Deki, Shigehito; Beleke, Alexis Bienvenu; Kotani, Yuki; Mizuhata, Minoru

    2009-09-15

    Hexagonal molybdenum trioxide thin films with good crystallinity and high purity have been fabricated by the liquid phase deposition (LPD) technique using molybdic acid (H{sub 2}MoO{sub 4}) dissolved in 2.82% hydrofluoric acid (HF) and H{sub 3}BO{sub 3} as precursors. The crystal was found to belong to a hexagonal hydrate system MoO{sub 3}.nH{sub 2}O (napprox0.56). The unit cell lattice parameters are a=10.651 A, c=3.725 A and V=365.997 A{sup 3}. Scanning electron microscope (SEM) images of the as-deposited samples showed well-shaped hexagonal rods nuclei that grew and where the amount increased with increase in reaction time. X-ray photon electron spectroscopy (XPS) spectra showed a Gaussian shape of the doublet of Mo 3d core level, indicating the presence of Mo{sup 6+} oxidation state in the deposited films. The deposited films exhibited an electrochromic behavior by lithium intercalation and deintercalation, which resulted in coloration and bleaching of the film. Upon dehydration at about 450 deg. C, the hexagonal MoO{sub 3}.nH{sub 2}O was transformed into the thermodynamically stable orthorhombic phase. - Abstract: SEM photograph of typical h-MoO{sub 3}.nH{sub 2}O thin film nuclei obtained after 36 h at 40 deg. C by the LPD method. Display Omitted

  11. Epitaxial hexagonal materials on IBAD-textured substrates

    DOEpatents

    Matias, Vladimir; Yung, Christopher

    2017-08-15

    A multilayer structure including a hexagonal epitaxial layer, such as GaN or other group III-nitride (III-N) semiconductors, a <111> oriented textured layer, and a non-single crystal substrate, and methods for making the same. The textured layer has a crystalline alignment preferably formed by the ion-beam assisted deposition (IBAD) texturing process and can be biaxially aligned. The in-plane crystalline texture of the textured layer is sufficiently low to allow growth of high quality hexagonal material, but can still be significantly greater than the required in-plane crystalline texture of the hexagonal material. The IBAD process enables low-cost, large-area, flexible metal foil substrates to be used as potential alternatives to single-crystal sapphire and silicon for manufacture of electronic devices, enabling scaled-up roll-to-roll, sheet-to-sheet, or similar fabrication processes to be used. The user is able to choose a substrate for its mechanical and thermal properties, such as how well its coefficient of thermal expansion matches that of the hexagonal epitaxial layer, while choosing a textured layer that more closely lattice matches that layer.

  12. Photogrammetric processing of hexagon stereo data for change detection studies

    NASA Astrophysics Data System (ADS)

    Padmanabha, E. Anantha; Shashivardhan Reddy, P.; Narender, B.; Muralikrishnan, S.; Dadhwal, V. K.

    2014-11-01

    Hexagon satellite data acquired as a part of USA Corona program has been declassified and is accessible to general public. This image data was acquired in high resolution much before the launch of civilian satellites. However the non availability of interior and exterior orientation parameters is the main bottle neck in photogrammetric processing of this data. In the present study, an attempt was made to orient and adjust Hexagon stereo pair through Rigorous Sensor Model (RSM) and Rational Function Models (RFM). The study area is part of Western Ghats in India. For rigorous sensor modelling an arbitrary camera file is generated based on the information available in the literature and few assumptions. A terrain dependent RFM was generated for the stereo data using Cartosat-1 reference data. The model accuracy achieved for both RSM and RFM was better than one pixel. DEM and orthoimage were generated with a spacing of 50 m and Ground Sampling Distance (GSD) of 6 m to carry out the change detection with a special emphasis on water bodies with reference to recent Cartosat-1 data. About 72 new water bodies covering an area of 2300 hectares (23 sq. km) were identified in Cartosat-1 orthoimage that were not present in Hexagon data. The image data from various Corona programs like Hexagon provide a rich source of information for temporal studies. However photogrammetric processing of the data is a bit tedious due to lack of information about internal sensor geometry.

  13. On the Structure of a New Superhard Hexagonal Carbon Phase

    NASA Astrophysics Data System (ADS)

    Zhang, Bin; Liang, Yongcheng; Guo, Zaoyang; Bordas, Stéphane

    2010-05-01

    Molecular dynamics simulations show that graphite will transform into a superhard phase under cold compression. Recent experiments show that there is a sp3-rich hexagonal carbon polymorph (a0 = 2.496 Å, c0 = 4.123 Å) with a bulk modulus of 447 GPa and average density about 3.6 g/cm3, restricted to the space group of P-62c (No. 190), but the detailed atomic structure was not obtained [Wang et al., P. Natl. Acad. Sci. 101(38), 13699]. Here we set carbon atoms occupying P-62c 4f Wyckoff positions of P-62c, and calculate the total energy of the different structures changing the internal parameter z by first-principles calculations using geometry optimisation algorithm in CASTEP code, which shows that the stable structures in energy (at local minimum points) are hexagonal carbon (z = 1/4) and hexagonal diamond (z = 1/16). The calculated mechanical properties and lattice parameters of the structure P-62c 4f (z = 1/4) are in good agreement with those of the new hexagonal carbon proposed by Wang et al., which indicates that the atomic structure is a possible candidate.

  14. On the Penrose and Taylor–Socolar hexagonal tilings

    PubMed Central

    Lee, Jeong-Yup; Moody, Robert V.

    2017-01-01

    The intimate relationship between the Penrose and the Taylor–Socolar tilings is studied, within both the context of double hexagon tiles and the algebraic context of hierarchical inverse sequences of triangular lattices. This unified approach produces both types of tilings together, clarifies their relationship and offers straightforward proofs of their basic properties. PMID:28447596

  15. TOILET ROOM IN THE PROJECTION BOOTH. NOTE THE HEXAGONAL FLOOR ...

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

    TOILET ROOM IN THE PROJECTION BOOTH. NOTE THE HEXAGONAL FLOOR TILES WITH ACCENTED BORDER AND GLAZED WALL TILES, ALL OF WHICH WERE ORIGINAL/ TYPICAL IN TOILET ROOMS IN THIS FACILITY VIEW FACING NORTHWEST - U.S. Naval Base, Pearl Harbor, Theater, Hornet Avenue between Enterprise & Pokomoke Streets, Pearl City, Honolulu County, HI

  16. Microwave Loss Properties of Hexagonal Ferrites for Millimeter Wave Applications.

    DTIC Science & Technology

    1986-03-15

    concerns the magnetic loss. Previous ferromagnetic resonance (FMR) linewidth data indicated that these losses were too large for efficient device... magnetic and dielectric materials measurement facility at Colorado State University and one to extend the measurements reported herein to the actual...reprint of the article, "Off Resonance Relaxation in Hexagonal Ferrites", which was presented at the International Conference on Magnetics , San

  17. Characterization of the secondary flow in hexagonal ducts

    NASA Astrophysics Data System (ADS)

    Marin, O.; Vinuesa, R.; Obabko, A. V.; Schlatter, P.

    2016-12-01

    In this work we report the results of DNSs and LESs of the turbulent flow through hexagonal ducts at friction Reynolds numbers based on centerplane wall shear and duct half-height Reτ,c ≃ 180, 360, and 550. The evolution of the Fanning friction factor f with Re is in very good agreement with experimental measurements. A significant disagreement between the DNS and previous RANS simulations was found in the prediction of the in-plane velocity, and is explained through the inability of the RANS model to properly reproduce the secondary flow present in the hexagon. The kinetic energy of the secondary flow integrated over the cross-sectional area yz decreases with Re in the hexagon, whereas it remains constant with Re in square ducts at comparable Reynolds numbers. Close connection between the values of Reynolds stress u w ¯ on the horizontal wall close to the corner and the interaction of bursting events between the horizontal and inclined walls is found. This interaction leads to the formation of the secondary flow, and is less frequent in the hexagon as Re increases due to the 120∘ aperture of its vertex, whereas in the square duct the 90∘ corner leads to the same level of interaction with increasing Re. Analysis of turbulence statistics at the centerplane and the azimuthal variance of the mean flow and the fluctuations shows a close connection between hexagonal ducts and pipe flows, since the hexagon exhibits near-axisymmetric conditions up to a distance of around 0.15DH measured from its center. Spanwise distributions of wall-shear stress show that in square ducts the 90∘ corner sets the location of a high-speed streak at a distance zv+≃50 from it, whereas in hexagons the 120∘ aperture leads to a shorter distance of zv+≃38 . At these locations the root mean square of the wall-shear stresses exhibits an inflection point, which further shows the connections between the near-wall structures and the large-scale motions in the outer flow.

  18. Characterization of the secondary flow in hexagonal ducts

    SciTech Connect

    Marin, O.; Vinuesa, R.; Obabko, A. V.; Schlatter, P.

    2016-12-06

    In this work we report the results of DNSs and LESs of the turbulent flow through hexagonal ducts at friction Reynolds numbers based on centerplane wall shear and duct half-height Reτ,c ≃ 180, 360, and 550. The evolution of the Fanning friction factor f with Re is in very good agreement with experimental measurements. A significant disagreement between the DNS and previous RANS simulations was found in the prediction of the in-plane velocity, and is explained through the inability of the RANS model to properly reproduce the secondary flow present in the hexagon. The kinetic energy of the secondary flow integrated over the cross-sectional area < K >yz decreases with Re in the hexagon, whereas it remains constant with Re in square ducts at comparable Reynolds numbers. Close connection between the values of Reynolds stress uw¯ on the horizontal wall close to the corner and the interaction of bursting events between the horizontal and inclined walls is found. This interaction leads to the formation of the secondary flow, and is less frequent in the hexagon as Re increases due to the 120° aperture of its vertex, whereas in the square duct the 90° corner leads to the same level of interaction with increasing Re. Analysis of turbulence statistics at the centerplane and the azimuthal variance of the mean flow and the fluctuations shows a close connection between hexagonal ducts and pipe flows, since the hexagon exhibits near-axisymmetric conditions up to a distance of around 0.15DH measured from its center. Spanwise distributions of wall-shear stress show that in square ducts the 90° corner sets the location of a high-speed streak at a distance z+v≃50 from it, whereas in hexagons the 120° aperture leads to a shorter distance of z+v≃38. Finally, at these locations the root mean square of the wall-shear stresses exhibits an inflection point, which

  19. Characterization of the secondary flow in hexagonal ducts

    DOE PAGES

    Marin, O.; Vinuesa, R.; Obabko, A. V.; ...

    2016-12-06

    In this work we report the results of DNSs and LESs of the turbulent flow through hexagonal ducts at friction Reynolds numbers based on centerplane wall shear and duct half-height Reτ,c ≃ 180, 360, and 550. The evolution of the Fanning friction factor f with Re is in very good agreement with experimental measurements. A significant disagreement between the DNS and previous RANS simulations was found in the prediction of the in-plane velocity, and is explained through the inability of the RANS model to properly reproduce the secondary flow present in the hexagon. The kinetic energy of the secondary flowmore » integrated over the cross-sectional area < K >yz decreases with Re in the hexagon, whereas it remains constant with Re in square ducts at comparable Reynolds numbers. Close connection between the values of Reynolds stress uw¯ on the horizontal wall close to the corner and the interaction of bursting events between the horizontal and inclined walls is found. This interaction leads to the formation of the secondary flow, and is less frequent in the hexagon as Re increases due to the 120° aperture of its vertex, whereas in the square duct the 90° corner leads to the same level of interaction with increasing Re. Analysis of turbulence statistics at the centerplane and the azimuthal variance of the mean flow and the fluctuations shows a close connection between hexagonal ducts and pipe flows, since the hexagon exhibits near-axisymmetric conditions up to a distance of around 0.15DH measured from its center. Spanwise distributions of wall-shear stress show that in square ducts the 90° corner sets the location of a high-speed streak at a distance z+v≃50 from it, whereas in hexagons the 120° aperture leads to a shorter distance of z+v≃38. Finally, at these locations the root mean square of the wall-shear stresses exhibits an inflection point, which further shows the connections between the near-wall structures and the large-scale motions in the outer flow.« less

  20. Iron refractory iron deficiency anemia

    PubMed Central

    De Falco, Luigia; Sanchez, Mayka; Silvestri, Laura; Kannengiesser, Caroline; Muckenthaler, Martina U.; Iolascon, Achille; Gouya, Laurent; Camaschella, Clara; Beaumont, Carole

    2013-01-01

    Iron refractory iron deficiency anemia is a hereditary recessive anemia due to a defect in the TMPRSS6 gene encoding Matriptase-2. This protein is a transmembrane serine protease that plays an essential role in down-regulating hepcidin, the key regulator of iron homeostasis. Hallmarks of this disease are microcytic hypochromic anemia, low transferrin saturation and normal/high serum hepcidin values. The anemia appears in the post-natal period, although in some cases it is only diagnosed in adulthood. The disease is refractory to oral iron treatment but shows a slow response to intravenous iron injections and partial correction of the anemia. To date, 40 different Matriptase-2 mutations have been reported, affecting all the functional domains of the large ectodomain of the protein. In vitro experiments on transfected cells suggest that Matriptase-2 cleaves Hemojuvelin, a major regulator of hepcidin expression and that this function is altered in this genetic form of anemia. In contrast to the low/undetectable hepcidin levels observed in acquired iron deficiency, in patients with Matriptase-2 deficiency, serum hepcidin is inappropriately high for the low iron status and accounts for the absent/delayed response to oral iron treatment. A challenge for the clinicians and pediatricians is the recognition of the disorder among iron deficiency and other microcytic anemias commonly found in pediatric patients. The current treatment of iron refractory iron deficiency anemia is based on parenteral iron administration; in the future, manipulation of the hepcidin pathway with the aim of suppressing it might become an alternative therapeutic approach. PMID:23729726

  1. Freezing resistance of high iron phoasphoaluminate cement

    NASA Astrophysics Data System (ADS)

    Zhang, S. X.; Lu, L. C.; Wang, S. D.; Zhao, P. Q.; Gong, C. C.

    2017-03-01

    The influence of freeze-thaw cycle on the mechanical properties of high iron phoasphoaluminate cement was investigated in the present study. The visual examination was conducted to evaluate the surface damage. The deterioration considering the weight loss, modulus loss of relative dynamic elastic and strength loss of mortar were also investigated. The morphology of hydration products were analysed by SEM. Compared with ordinary Portland cement and sulphoaluminate cement, the frost resistance of high iron phosphoraluminate cement is better. Hydration products of high iron phoasphoaluminate cement contain sheet crystals, and a lot of gel form a dense three-dimensional network structure, which results in a lower porosity. Different from ordinary Portland cement, the hydration product of high iron phoasphoaluminate cement does not contain Ca(OH)2, and low alkalinity reduces its osmotic pressure. The lower porosity and osmotic pressure are the two main reasons which causes in the higher frost resistance of high iron phoasphoaluminate cement.

  2. Serum iron test

    MedlinePlus

    ... test if you have: Signs of low iron (iron deficiency) Signs of too much iron Anemia caused by ... Brittenham GM. Disorders of iron homeostasis: iron deficiency and ... Basic Principles and Practice . 6th ed. Philadelphia, PA: ...

  3. DPIS for warm dense matter

    SciTech Connect

    Kondo, K.; Kanesue, T.; Horioka, K.; Okamura, M.

    2010-05-23

    Warm Dense Matter (WDM) offers an challenging problem because WDM, which is beyond ideal plasma, is in a low temperature and high density state with partially degenerate electrons and coupled ions. WDM is a common state of matter in astrophysical objects such as cores of giant planets and white dwarfs. The WDM studies require large energy deposition into a small target volume in a shorter time than the hydrodynamical time and need uniformity across the full thickness of the target. Since moderate energy ion beams ({approx} 0.3 MeV/u) can be useful tool for WDM physics, we propose WDM generation using Direct Plasma Injection Scheme (DPIS). In the DPIS, laser ion source is connected to the Radio Frequency Quadrupole (RFQ) linear accelerator directly without the beam transport line. DPIS with a realistic final focus and a linear accelerator can produce WDM.

  4. Uniformly dense polymeric foam body

    DOEpatents

    Whinnery, Jr., Leroy

    2003-07-15

    A method for providing a uniformly dense polymer foam body having a density between about 0.013 g/cm.sup.3 to about 0.5 g/cm.sup.3 is disclosed. The method utilizes a thermally expandable polymer microsphere material wherein some of the microspheres are unexpanded and some are only partially expanded. It is shown that by mixing the two types of materials in appropriate ratios to achieve the desired bulk final density, filling a mold with this mixture so as to displace all or essentially all of the internal volume of the mold, heating the mold for a predetermined interval at a temperature above about 130.degree. C., and then cooling the mold to a temperature below 80.degree. C. the molded part achieves a bulk density which varies by less then about .+-.6% everywhere throughout the part volume.

  5. Velocity coherence in dense cores

    NASA Astrophysics Data System (ADS)

    Goodman, Alyssa A.; Barranco, Joseph A.; Wilner, David J.; Heyer, Mark H.

    1997-02-01

    At the meeting, we presented a summary of two papers which support the hypothesis that the molecular clouds which contain star-forming low-mass dense cores are self-similar in nature on size scales larger than an inner scale, Rcoh, and that within Rcoh, the cores are ``coherent,'' in that their filling factor is large and they are characterized by a very small, roughly constant, mildly supersonic velocity dispersion. We expect these two papers, by Barranco & Goodman [1] and Goodman, Barranco, Wilner, & Heyer, to appear in the Astrophysical Journal within the coming year. Here, we present a short summary of our results. The interested reader is urged to consult the on-line version of this work at cfa-www.harvard.edu/~agoodman/vel_coh.html [2].

  6. Neutrino Oscillations in Dense Matter

    NASA Astrophysics Data System (ADS)

    Lobanov, A. E.

    2017-03-01

    A modification of the electroweak theory, where the fermions with the same electroweak quantum numbers are combined in multiplets and are treated as different quantum states of a single particle, is proposed. In this model, mixing and oscillations of particles arise as a direct consequence of the general principles of quantum field theory. The developed approach enables one to calculate the probabilities of the processes taking place in the detector at long distances from the particle source. Calculations of higher-order processes, including computation of the contributions due to radiative corrections, can be performed in the framework of the perturbation theory using the regular diagram technique. As a result, the analog to the Dirac-Schwinger equation of quantum electrodynamics describing neutrino oscillations and its spin rotation in dense matter can be obtained.

  7. Viscoelastic behavior of dense microemulsions

    NASA Astrophysics Data System (ADS)

    Cametti, C.; Codastefano, P.; D'arrigo, G.; Tartaglia, P.; Rouch, J.; Chen, S. H.

    1990-09-01

    We have performed extensive measurements of shear viscosity, ultrasonic absorption, and sound velocity in a ternary system consisting of water-decane-sodium di(2-ethylhexyl)sulfo- succinate(AOT), in the one-phase region where it forms a water-in-oil microemulsion. We observe a rapid increase of the static shear viscosity in the dense microemulsion region. Correspondingly the sound absorption shows unambiguous evidence of a viscoelastic behavior. The absorption data for various volume fractions and temperatures can be reduced to a universal curve by scaling both the absorption and the frequency by the measured static shear viscosity. The sound absorption can be interpreted as coming from the high-frequency tail of the viscoelastic relaxation, describable by a Cole-Cole relaxation formula with unusually small elastic moduli.

  8. Extended thermodynamics of dense gases

    NASA Astrophysics Data System (ADS)

    Arima, T.; Taniguchi, S.; Ruggeri, T.; Sugiyama, M.

    2012-11-01

    We study extended thermodynamics of dense gases by adopting the system of field equations with a different hierarchy structure to that adopted in the previous works. It is the theory of 14 fields of mass density, velocity, temperature, viscous stress, dynamic pressure, and heat flux. As a result, most of the constitutive equations can be determined explicitly by the caloric and thermal equations of state. It is shown that the rarefied-gas limit of the theory is consistent with the kinetic theory of gases. We also analyze three physically important systems, that is, a gas with the virial equations of state, a hard-sphere system, and a van der Waals fluid, by using the general theory developed in the former part of the present work.

  9. Synthesis, characterization, shape evolution, and optical properties of copper sulfide hexagonal bifrustum nanocrystals

    NASA Astrophysics Data System (ADS)

    Jia, Baorui; Qin, Mingli; Jiang, Xuezhi; Zhang, Zili; Zhang, Lin; Liu, Ye; Qu, Xuanhui

    2013-03-01

    The hexagonal bifrustum-shaped copper sulfide (CuS) nanocrystals were selectively and facilely synthesized by a hydrothermal method for the first time at 120 °C. The products were characterized by X-ray diffraction, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, transmission electron microscopy, ultraviolet-visible (UV-Vis) spectroscopy, and photoluminescence spectroscopy. The results showed that the CuS hexagonal bifrustum nanocrystal was bounded by two top hexagons with edge length of about 50-70 nm and twelve lateral trapezoids with a base of about 100 nm and that the length of each hexagonal bifrustum was about 250 nm. Tetradecylamine (TDA), as an effective capping agent, was found to be critical for this special shape. Using different amounts of TDA, two kinds of CuS hexagonal bifrustum nanocrystals were obtained: "lender hexagonal bifrustum" and "pancake hexagonal bifrustum." Furthermore, we studied the formation mechanism of hexagonal bifrustum, which is related to the intrinsic crystalline structure of CuS and Ostwald ripening. And, the results revealed that the CuS nanocrystal evolved from hexagonal plate to hexagonal bifrustum and finally to hexagonal bipyramid as the heating time increased. The UV-Vis absorption spectrum showed that these CuS hexagonal bifrustum nanocrystals exhibited strong absorption in the near-infrared region and had a potential application for photothermal therapy and photocatalysis.

  10. Iron release from corroded iron pipes in drinking water distribution systems: effect of dissolved oxygen.

    PubMed

    Sarin, P; Snoeyink, V L; Bebee, J; Jim, K K; Beckett, M A; Kriven, W M; Clement, J A

    2004-03-01

    Iron release from corroded iron pipes is the principal cause of "colored water" problems in drinking water distribution systems. The corrosion scales present in corroded iron pipes restrict the flow of water, and can also deteriorate the water quality. This research was focused on understanding the effect of dissolved oxygen (DO), a key water quality parameter, on iron release from the old corroded iron pipes. Corrosion scales from 70-year-old galvanized iron pipe were characterized as porous deposits of Fe(III) phases (goethite (alpha-FeOOH), magnetite (Fe(3)O(4)), and maghemite (alpha-Fe(2)O(3))) with a shell-like, dense layer near the top of the scales. High concentrations of readily soluble Fe(II) content was present inside the scales. Iron release from these corroded pipes was investigated for both flow and stagnant water conditions. Our studies confirmed that iron was released to bulk water primarily in the ferrous form. When DO was present in water, higher amounts of iron release was observed during stagnation in comparison to flowing water conditions. Additionally, it was found that increasing the DO concentration in water during stagnation reduced the amount of iron release. Our studies substantiate that increasing the concentration of oxidants in water and maintaining flowing conditions can reduce the amount of iron release from corroded iron pipes. Based on our studies, it is proposed that iron is released from corroded iron pipes by dissolution of corrosion scales, and that the microstructure and composition of corrosion scales are important parameters that can influence the amount of iron released from such systems.

  11. The performance of dense medium processes

    SciTech Connect

    Horsfall, D.W.

    1993-12-31

    Dense medium washing in baths and cyclones is widely carried out in South Africa. The paper shows the reason for the preferred use of dense medium processes rather than gravity concentrators such as jigs. The factors leading to efficient separation in baths are listed and an indication given of the extent to which these factors may be controlled and embodied in the deployment of baths and dense medium cyclones in the planning stages of a plant.

  12. Dense module enumeration in biological networks

    NASA Astrophysics Data System (ADS)

    Tsuda, Koji; Georgii, Elisabeth

    2009-12-01

    Analysis of large networks is a central topic in various research fields including biology, sociology, and web mining. Detection of dense modules (a.k.a. clusters) is an important step to analyze the networks. Though numerous methods have been proposed to this aim, they often lack mathematical rigorousness. Namely, there is no guarantee that all dense modules are detected. Here, we present a novel reverse-search-based method for enumerating all dense modules. Furthermore, constraints from additional data sources such as gene expression profiles or customer profiles can be integrated, so that we can systematically detect dense modules with interesting profiles. We report successful applications in human protein interaction network analyses.

  13. Oriented graphene nanoribbons embedded in hexagonal boron nitride trenches

    NASA Astrophysics Data System (ADS)

    Chen, Lingxiu; He, Li; Wang, Hui Shan; Wang, Haomin; Tang, Shujie; Cong, Chunxiao; Xie, Hong; Li, Lei; Xia, Hui; Li, Tianxin; Wu, Tianru; Zhang, Daoli; Deng, Lianwen; Yu, Ting; Xie, Xiaoming; Jiang, Mianheng

    2017-03-01

    Graphene nanoribbons (GNRs) are ultra-narrow strips of graphene that have the potential to be used in high-performance graphene-based semiconductor electronics. However, controlled growth of GNRs on dielectric substrates remains a challenge. Here, we report the successful growth of GNRs directly on hexagonal boron nitride substrates with smooth edges and controllable widths using chemical vapour deposition. The approach is based on a type of template growth that allows for the in-plane epitaxy of mono-layered GNRs in nano-trenches on hexagonal boron nitride with edges following a zigzag direction. The embedded GNR channels show excellent electronic properties, even at room temperature. Such in-plane hetero-integration of GNRs, which is compatible with integrated circuit processing, creates a gapped channel with a width of a few benzene rings, enabling the development of digital integrated circuitry based on GNRs.

  14. Chemical and Bandgap Engineering in Monolayer Hexagonal Boron Nitride

    NASA Astrophysics Data System (ADS)

    Ba, Kun; Jiang, Wei; Cheng, Jingxin; Bao, Jingxian; Xuan, Ningning; Sun, Yangye; Liu, Bing; Xie, Aozhen; Wu, Shiwei; Sun, Zhengzong

    2017-04-01

    Monolayer hexagonal boron nitride (h-BN) possesses a wide bandgap of ~6 eV. Trimming down the bandgap is technically attractive, yet poses remarkable challenges in chemistry. One strategy is to topological reform the h-BN’s hexagonal structure, which involves defects or grain boundaries (GBs) engineering in the basal plane. The other way is to invite foreign atoms, such as carbon, to forge bizarre hybrid structures like hetero-junctions or semiconducting h-BNC materials. Here we successfully developed a general chemical method to synthesize these different h-BN derivatives, showcasing how the chemical structure can be manipulated with or without a graphene precursor, and the bandgap be tuned to ~2 eV, only one third of the pristine one’s.

  15. Oriented graphene nanoribbons embedded in hexagonal boron nitride trenches

    PubMed Central

    Chen, Lingxiu; He, Li; Wang, Hui Shan; Wang, Haomin; Tang, Shujie; Cong, Chunxiao; Xie, Hong; Li, Lei; Xia, Hui; Li, Tianxin; Wu, Tianru; Zhang, Daoli; Deng, Lianwen; Yu, Ting; Xie, Xiaoming; Jiang, Mianheng

    2017-01-01

    Graphene nanoribbons (GNRs) are ultra-narrow strips of graphene that have the potential to be used in high-performance graphene-based semiconductor electronics. However, controlled growth of GNRs on dielectric substrates remains a challenge. Here, we report the successful growth of GNRs directly on hexagonal boron nitride substrates with smooth edges and controllable widths using chemical vapour deposition. The approach is based on a type of template growth that allows for the in-plane epitaxy of mono-layered GNRs in nano-trenches on hexagonal boron nitride with edges following a zigzag direction. The embedded GNR channels show excellent electronic properties, even at room temperature. Such in-plane hetero-integration of GNRs, which is compatible with integrated circuit processing, creates a gapped channel with a width of a few benzene rings, enabling the development of digital integrated circuitry based on GNRs. PMID:28276532

  16. Electrically dependent bandgaps in graphene on hexagonal boron nitride

    SciTech Connect

    Kaplan, D. Swaminathan, V.; Recine, G.

    2014-03-31

    We present first-principles calculations on the bandgap of graphene on a layer of hexagonal boron nitride in three different stacking configurations. Relative stability of the configurations is identified and bandgap tunability is demonstrated through the application of an external, perpendicularly applied electric field. We carefully examine the bandgap's sensitivity to both magnitude of the applied field as well as separation between the graphene and hexagonal boron nitride layers. Features of the band structure are examined and configuration-dependent relationships between the field and bandgap are revealed and elucidated through the atom-projected density of states. These findings suggest the potential for opening and modulating a bandgap in graphene as high as several hundred meV.

  17. Dirac semimetal phase in hexagonal LiZnBi

    NASA Astrophysics Data System (ADS)

    Cao, Wendong; Tang, Peizhe; Xu, Yong; Wu, Jian; Gu, Bing-Lin; Duan, Wenhui

    2017-09-01

    Based on first-principles calculations, we find that LiZnBi, a metallic hexagonal A B C compound, has a pair of three-dimensional Dirac nodes and exhibits nontrivial topological properties under proper strain configurations. The nontrivial topological nature of the strained LiZnBi is directly demonstrated by calculating its Z2 index and the surface states. The low-energy states are shown to be sensitive to strain configurations, and we propose that these nontrivial topological properties can be observed under compressive in-plane strain in experiments. The finding of the Dirac semimetal phase in LiZnBi may intrigue further research on the topological properties of hexagonal A B C materials and promote new practical applications.

  18. Calculation of Accurate Hexagonal Discontinuity Factors for PARCS

    SciTech Connect

    Pounders. J., Bandini, B. R. , Xu, Y, and Downar, T. J.

    2007-11-01

    In this study we derive a methodology for calculating discontinuity factors consistent with the Triangle-based Polynomial Expansion Nodal (TPEN) method implemented in PARCS for hexagonal reactor geometries. The accuracy of coarse-mesh nodal methods is greatly enhanced by permitting flux discontinuities at node boundaries, but the practice of calculating discontinuity factors from infinite-medium (zero-current) single bundle calculations may not be sufficiently accurate for more challenging problems in which there is a large amount of internodal neutron streaming. The authors therefore derive a TPEN-based method for calculating discontinuity factors that are exact with respect to generalized equivalence theory. The method is validated by reproducing the reference solution for a small hexagonal core.

  19. Thickness-dependent bending modulus of hexagonal boron nitride nanosheets.

    PubMed

    Li, Chun; Bando, Yoshio; Zhi, Chunyi; Huang, Yang; Golberg, Dmitri

    2009-09-23

    Bending modulus of exfoliation-made single-crystalline hexagonal boron nitride nanosheets (BNNSs) with thicknesses of 25-300 nm and sizes of 1.2-3.0 microm were measured using three-point bending tests in an atomic force microscope. BNNSs suspended on an SiO(2) trench were clamped by a metal film via microfabrication based on electron beam lithography. Calculated by the plate theory of a doubly clamped plate under a concentrated load, the bending modulus of BNNSs was found to increase with the decrease of sheet thickness and approach the theoretical C(33) value of a hexagonal BN single crystal in thinner sheets (thickness<50 nm). The thickness-dependent bending modulus was suggested to be due to the layer distribution of stacking faults which were also thought to be responsible for the layer-by-layer BNNS exfoliation.

  20. Zonal wavefront estimation using an array of hexagonal grating patterns

    SciTech Connect

    Pathak, Biswajit E-mail: brboruah@iitg.ernet.in; Boruah, Bosanta R. E-mail: brboruah@iitg.ernet.in

    2014-10-15

    Accuracy of Shack-Hartmann type wavefront sensors depends on the shape and layout of the lenslet array that samples the incoming wavefront. It has been shown that an array of gratings followed by a focusing lens provide a substitution for the lensslet array. Taking advantage of the computer generated holography technique, any arbitrary diffraction grating aperture shape, size or pattern can be designed with little penalty for complexity. In the present work, such a holographic technique is implemented to design regular hexagonal grating array to have zero dead space between grating patterns, eliminating the possibility of leakage of wavefront during the estimation of the wavefront. Tessellation of regular hexagonal shape, unlike other commonly used shapes, also reduces the estimation error by incorporating more number of neighboring slope values at an equal separation.

  1. Chemical and Bandgap Engineering in Monolayer Hexagonal Boron Nitride.

    PubMed

    Ba, Kun; Jiang, Wei; Cheng, Jingxin; Bao, Jingxian; Xuan, Ningning; Sun, Yangye; Liu, Bing; Xie, Aozhen; Wu, Shiwei; Sun, Zhengzong

    2017-04-03

    Monolayer hexagonal boron nitride (h-BN) possesses a wide bandgap of ~6 eV. Trimming down the bandgap is technically attractive, yet poses remarkable challenges in chemistry. One strategy is to topological reform the h-BN's hexagonal structure, which involves defects or grain boundaries (GBs) engineering in the basal plane. The other way is to invite foreign atoms, such as carbon, to forge bizarre hybrid structures like hetero-junctions or semiconducting h-BNC materials. Here we successfully developed a general chemical method to synthesize these different h-BN derivatives, showcasing how the chemical structure can be manipulated with or without a graphene precursor, and the bandgap be tuned to ~2 eV, only one third of the pristine one's.

  2. Oriented graphene nanoribbons embedded in hexagonal boron nitride trenches.

    PubMed

    Chen, Lingxiu; He, Li; Wang, Hui Shan; Wang, Haomin; Tang, Shujie; Cong, Chunxiao; Xie, Hong; Li, Lei; Xia, Hui; Li, Tianxin; Wu, Tianru; Zhang, Daoli; Deng, Lianwen; Yu, Ting; Xie, Xiaoming; Jiang, Mianheng

    2017-03-09

    Graphene nanoribbons (GNRs) are ultra-narrow strips of graphene that have the potential to be used in high-performance graphene-based semiconductor electronics. However, controlled growth of GNRs on dielectric substrates remains a challenge. Here, we report the successful growth of GNRs directly on hexagonal boron nitride substrates with smooth edges and controllable widths using chemical vapour deposition. The approach is based on a type of template growth that allows for the in-plane epitaxy of mono-layered GNRs in nano-trenches on hexagonal boron nitride with edges following a zigzag direction. The embedded GNR channels show excellent electronic properties, even at room temperature. Such in-plane hetero-integration of GNRs, which is compatible with integrated circuit processing, creates a gapped channel with a width of a few benzene rings, enabling the development of digital integrated circuitry based on GNRs.

  3. Switching behavior and novel stable states of magnetic hexagonal nanorings

    NASA Astrophysics Data System (ADS)

    Yasir Rafique, M.; Pan, Liqing; Guo, Zhengang

    2017-06-01

    Micromagnetic simulations for Cobalt hexagonal shape nanorings show onion (O) and vortex state (V) along with new state named ;tri-domain state;. The tri-domain state is observed in sufficiently large width of ring. The magnetic reversible mechanism and transition of states are explained with help of vector field display. The transitions from one state to other occur by propagation of domain wall. The vertical parts of hexagonal rings play important role in developing the new ;tri-domain; state. The behaviors of switching fields from onion to tri-domain (HO-Tr), tri-domain to vortex state (HTr-V) and vortex to onion state and ;states size; are discussed in term of geometrical parameter of ring.

  4. The Formation and Characterization of GaN Hexagonal Pyramids

    NASA Astrophysics Data System (ADS)

    Zhang, Shi-Ying; Xiu, Xiang-Qian; Lin, Zeng-Qin; Hua, Xue-Mei; Xie, Zi-Li; Zhang, Rong; Zheng, You-Dou

    2013-05-01

    GaN with hexagonal pyramids is fabricated using the photo-assisted electroless chemical etching method. Defective areas of the GaN substrate are selectively etched in a mixed solution of KOH and K2S2O8 under ultraviolet illumination, producing submicron-sized pyramids. Hexagonal pyramids on the etched GaN with well-defined {101¯1¯} facets and very sharp tips are formed. High-resolution x-ray diffraction shows that etched GaN with pyramids has a higher crystal quality, and micro-Raman spectra reveal a tensile stress relaxation in GaN with pyramids compared with normal GaN. The cathodoluminescence intensity of GaN after etching is significantly increased by three times, which is attributed to the reduction in the internal reflection, high-quality GaN with pyramids and the Bragg effect.

  5. Pedestrian simulations in hexagonal cell local field model

    NASA Astrophysics Data System (ADS)

    Leng, Biao; Wang, Jianyuan; Xiong, Zhang

    2015-11-01

    Pedestrian dynamics have caused wide concern over the recent years. This paper presents a local field (LF) model based on regular hexagonal cells to simulate pedestrian dynamics in scenarios such as corridors and bottlenecks. In this model, the simulation scenarios are discretized into regular hexagonal cells. The local field is a small region around pedestrian. Each pedestrian will choose his/her target cell according to the situation in his/her local field. Different walking strategies are considered in the simulation in corridor scenario and the fundamental graphs are used to verify this model. Different shapes of exit are also discussed in the bottleneck scenario. The statistics of push effect show that the smooth bottleneck exit may be more safe.

  6. Thickness-dependent bending modulus of hexagonal boron nitride nanosheets

    NASA Astrophysics Data System (ADS)

    Li, Chun; Bando, Yoshio; Zhi, Chunyi; Huang, Yang; Golberg, Dmitri

    2009-09-01

    Bending modulus of exfoliation-made single-crystalline hexagonal boron nitride nanosheets (BNNSs) with thicknesses of 25-300 nm and sizes of 1.2-3.0 µm were measured using three-point bending tests in an atomic force microscope. BNNSs suspended on an SiO2 trench were clamped by a metal film via microfabrication based on electron beam lithography. Calculated by the plate theory of a doubly clamped plate under a concentrated load, the bending modulus of BNNSs was found to increase with the decrease of sheet thickness and approach the theoretical C33 value of a hexagonal BN single crystal in thinner sheets (thickness<50 nm). The thickness-dependent bending modulus was suggested to be due to the layer distribution of stacking faults which were also thought to be responsible for the layer-by-layer BNNS exfoliation.

  7. Chemical and Bandgap Engineering in Monolayer Hexagonal Boron Nitride

    PubMed Central

    Ba, Kun; Jiang, Wei; Cheng, Jingxin; Bao, Jingxian; Xuan, Ningning; Sun, Yangye; Liu, Bing; Xie, Aozhen; Wu, Shiwei; Sun, Zhengzong

    2017-01-01

    Monolayer hexagonal boron nitride (h-BN) possesses a wide bandgap of ~6 eV. Trimming down the bandgap is technically attractive, yet poses remarkable challenges in chemistry. One strategy is to topological reform the h-BN’s hexagonal structure, which involves defects or grain boundaries (GBs) engineering in the basal plane. The other way is to invite foreign atoms, such as carbon, to forge bizarre hybrid structures like hetero-junctions or semiconducting h-BNC materials. Here we successfully developed a general chemical method to synthesize these different h-BN derivatives, showcasing how the chemical structure can be manipulated with or without a graphene precursor, and the bandgap be tuned to ~2 eV, only one third of the pristine one’s. PMID:28367992

  8. Melting of hexagonal skyrmion states in chiral magnets

    NASA Astrophysics Data System (ADS)

    Ambrose, M. C.; Stamps, R. L.

    2013-05-01

    Skyrmions are spiral structures observed in thin films of certain magnetic materials (Uchida et al 2006 Science 311 359-61). Of the phases allowed by the crystalline symmetries of these materials (Yi et al 2009 Phys. Rev. B 80 054416), only the hexagonally packed phases (SCh) have been observed. Here the melting of the SCh phase is investigated using Monte Carlo simulations. In addition to the usual measure of skyrmion density, chiral charge, a morphological measure is considered. In doing so it is shown that the low-temperature reduction in chiral charge is associated with a change in skyrmion profiles rather than skyrmion destruction. At higher temperatures, the loss of six-fold symmetry is associated with the appearance of elongated skyrmions that disrupt the hexagonal packing.

  9. Hexagonal boron nitride is an indirect bandgap semiconductor

    NASA Astrophysics Data System (ADS)

    Cassabois, G.; Valvin, P.; Gil, B.

    2016-04-01

    Hexagonal boron nitride is a wide bandgap semiconductor with very high thermal and chemical stability that is used in devices operating under extreme conditions. The growth of high-purity crystals has recently revealed the potential of this material for deep ultraviolet emission, with intense emission around 215 nm. In the last few years, hexagonal boron nitride has been attracting even more attention with the emergence of two-dimensional atomic crystals and van der Waals heterostructures, initiated with the discovery of graphene. Despite this growing interest and a seemingly simple structure, the basic questions of the bandgap nature and value are still controversial. Here, we resolve this long-debated issue by demonstrating evidence for an indirect bandgap at 5.955 eV by means of optical spectroscopy. We demonstrate the existence of phonon-assisted optical transitions and we measure an exciton binding energy of about 130 meV by two-photon spectroscopy.

  10. Hexagonal liquid crystal lens array for 3D endoscopy.

    PubMed

    Hassanfiroozi, Amir; Huang, Yi-Pai; Javidi, Bahram; Shieh, Han-Ping D

    2015-01-26

    A liquid crystal lens array with a hexagonal arrangement is investigated experimentally. The uniqueness of this study exists in the fact that using convex-ring electrode provides a smooth and controllable applied potential profile across the aperture to manage the phase profile. We observed considerable differences between flat electrode and convex-ring electrode; in particular the lens focal length is variable in a wider range from 2.5cm to infinity. This study presents several noteworthy characteristics such as low driving voltage; 30 μm cell gap and the lens is electrically switchable between 2D/3D modes. We demonstrate a hexagonal LC-lens array for capturing 3D images by using single sensor using integral imaging.

  11. A new interlayer potential for hexagonal boron nitride

    NASA Astrophysics Data System (ADS)

    Akıner, Tolga; Mason, Jeremy K.; Ertürk, Hakan

    2016-09-01

    A new interlayer potential is developed for interlayer interactions of hexagonal boron nitride sheets, and its performance is compared with other potentials in the literature using molecular dynamics simulations. The proposed potential contains Coulombic and Lennard-Jones 6-12 terms, and is calibrated with recent experimental data including the hexagonal boron nitride interlayer distance and elastic constants. The potentials are evaluated by comparing the experimental and simulated values of interlayer distance, density, elastic constants, and thermal conductivity using non-equilibrium molecular dynamics. The proposed potential is found to be in reasonable agreement with experiments, and improves on earlier potentials in several respects. Simulated thermal conductivity values as a function of the number of layers and of temperature suggest that the proposed LJ 6-12 potential has the ability to predict some phonon behaviour during heat transport in the out-of-plane direction.

  12. Surface plasmon dispersion in hexagonal, honeycomb and kagome plasmonic crystals.

    PubMed

    Tenner, V T; de Dood, M J A; van Exter, M P

    2016-12-26

    We present a systematic experimental study on the optical properties of plasmonic crystals (PlC) with hexagonal symmetry. We compare the dispersion and avoided crossings of surface plasmon modes around the Γ-point of Au-metal hole arrays with a hexagonal, honeycomb and kagome lattice. Symmetry arguments and group theory are used to label the six modes and understand their radiative and dispersive properties. Plasmon-plasmon interaction are accurately described by a coupled mode model, that contains effective scattering amplitudes of surface plasmons on a lattice of air holes under 60°, 120°, and 180°. We determine these rates in the experiment and find that they are dominated by the hole-density and not on the complexity of the unit-cell. Our analysis shows that the observed angle-dependent scattering can be explained by a single-hole model based on electric and magnetic dipoles.

  13. Polynomial expansion nodal transport method in hexagonal geometry

    SciTech Connect

    Cho, Jin Young; Kim, Chang Hyo; Noh, Taewan

    1997-12-01

    Recently, the polynomial expansion nodal (PEN) method was developed as a new nodal diffusion scheme for hexagonal core analyses. Using the direct polynomial expansion for the node flux, the PEN method not only eliminates the complicated transverse integration procedures-especially in hexagonal geometry-which are frequently used in conventional nodal methods, but also provides a number of features such as the convenient energy group expendability and much enhanced accuracy with less computational effort. In this paper, we further develop the PEN method for the transport equation for the cases where the transport effects are important: highly heterogeneous, small (high-leakage), and fast reactors, etc. Here, we take the even-parity form of transport equation. The main reason is that the diffusion-like nature of the even-parity equation is adequate to establish the new nodal transport method (PEN-TR) using the earlier developed PEN method in diffusion theory.

  14. Ideally Hexagonally Ordered TiO2 Nanotube Arrays

    PubMed Central

    Sopha, Hanna; Samoril, Tomas; Palesch, Erik; Hromadko, Ludek; Zazpe, Raul; Skoda, David; Urbanek, Michal; Ng, Siowwoon; Prikryl, Jan

    2017-01-01

    Abstract Ideally hexagonally ordered TiO2 nanotube layers were produced through the optimized anodization of Ti substrates. The Ti substrates were firstly covered with a TiN protecting layer prepared through atomic layer deposition (ALD). Pre‐texturing of the TiN‐protected Ti substrate on an area of 20×20 μm2 was carried out by focused ion beam (FIB) milling, yielding uniform nanoholes with a hexagonal arrangement throughout the TiN layer with three different interpore distances. The subsequent anodic nanotube growth using ethylene‐glycol‐based electrolyte followed the pre‐textured nanoholes, resulting in perfectly ordered nanotube layers (resembling honeycomb porous anodic alumina) without any point defects and with a thickness of approximately 2 μm over the whole area of the pattern. PMID:28794939

  15. Zonal wavefront estimation using an array of hexagonal grating patterns

    NASA Astrophysics Data System (ADS)

    Pathak, Biswajit; Boruah, Bosanta R.

    2014-10-01

    Accuracy of Shack-Hartmann type wavefront sensors depends on the shape and layout of the lenslet array that samples the incoming wavefront. It has been shown that an array of gratings followed by a focusing lens provide a substitution for the lensslet array. Taking advantage of the computer generated holography technique, any arbitrary diffraction grating aperture shape, size or pattern can be designed with little penalty for complexity. In the present work, such a holographic technique is implemented to design regular hexagonal grating array to have zero dead space between grating patterns, eliminating the possibility of leakage of wavefront during the estimation of the wavefront. Tessellation of regular hexagonal shape, unlike other commonly used shapes, also reduces the estimation error by incorporating more number of neighboring slope values at an equal separation.

  16. Energy landscapes for shells assembled from pentagonal and hexagonal pyramids.

    PubMed

    Fejer, Szilard N; James, Tim R; Hernández-Rojas, Javier; Wales, David J

    2009-03-28

    We present new rigid body potentials that should favour efficient self-assembly of pentagonal and hexagonal pyramids into icosahedral shells over a wide range of temperature. By adding an extra repulsive site opposite the existing apex sites of the pyramids considered in a previously published model, frustrated energy landscapes are transformed into systems identified with self-assembling properties. The extra interaction may be considered analogous to a hydrophobic-hydrophilic repulsion, as in micelle formation.

  17. Superstructural planar defects in ordered alloys with hexagonal close packing

    SciTech Connect

    Dmitriev, S.V.; Frolov, A.M.; Golobokova, S.I.; Starostenkov, M.D.

    1995-03-01

    An analysis of superstructural defects in ordered alloys with hexagonal close packing was performed by complementing the packing to form the lattice. An algorithm for determining all energetically equivalent but geometrically different representations of a superstructure is given. The maximum number of super-structural planar defects of the same orientation but different energies is estimated. The method is exemplified on the DO{sub 19} superstructure. 13 refs.

  18. Hexagons, kinks, and disorder in oscillated granular layers

    SciTech Connect

    Melo, F.; Umbanhowar, P.B.; Swinney, H.L.

    1995-11-20

    Experiments on vertically oscillated granular layers in an evacuated container reveal a sequence of well-defined pattern bifurcations as the container acceleration is increased. Period doublings of the layer center of mass motion and a standing wave instability interact to produce hexagons and more complicated patterns composed of distinct spatial domains of different relative phase separated by kinks (phase discontinuities). A simple model displays quantitative agreement with the observed transition sequence. {copyright} {ital 1995} {ital The} {ital American} {ital Physical} {ital Society}.

  19. Covalently functionalized hexagonal boron nitride nanosheets by nitrene addition.

    PubMed

    Sainsbury, Toby; Satti, Amro; May, Peter; O'Neill, Arlene; Nicolosi, Valeria; Gun'ko, Yurii K; Coleman, Jonathan N

    2012-08-27

    The covalent functionalization of exfoliated hexagonal boron nitride (h-BN) nanosheets by nitrene addition is described. Integration of functionalized h-BN nanosheets within a polycarbonate matrix is demonstrated and was found to afford significant increases in mechanical properties. This integration methodology was further extended by the covalent modification of the h-BN nanosheets with polymer chains of a polycarbonate analogue, and the integration of the polymer modified h-BN within the polymer matrix.

  20. Lambda modes of the neutron diffusion equation in hexagonal geometry

    SciTech Connect

    Barrachina, T.; Ginestar, D.; Verdu, G.

    2006-07-01

    A nodal collocation method is proposed to compute the dominant Lambda modes of nuclear reactor core with a hexagonal geometry. This method is based on a triangular mesh and assumes that the neutronic flux can be approximated as a finite expansion in terms of Dubiner's polynomials. The method transforms the initial differential eigenvalue problem into a generalized algebraic one, from which the dominant modes of the reactor can be computed. The performance of the method is tested with two benchmark problems. (authors)

  1. Planar stacking effect on elastic stability of hexagonal boron nitride

    NASA Astrophysics Data System (ADS)

    Qi, Yue; Hector, Louis G.

    2007-02-01

    The elastic stability of five hexagonal boron nitride (h-BN) stacking sequences is investigated with density functional theory. All components of the elasticity tensor are computed and used to evaluate the Born stability criteria. Phonon spectra are computed for one elastically stable and one elastically unstable h-BN structure and the normal modes associated with instability are identified. Charge density difference contour plots provide a qualitative connection between elastic stability and charge transfer.

  2. Acetone sensor based on zinc oxide hexagonal tubes

    SciTech Connect

    Hastir, Anita Singh, Onkar Anand, Kanika Singh, Ravi Chand

    2014-04-24

    In this work hexagonal tubes of zinc oxide have been synthesized by co-precipitation method. For structural, morphological, elemental and optical analysis synthesized powders were characterized by using x-ray diffraction, field emission scanning microscope, EDX, UV-visible and FTIR techniques. For acetone sensing thick films of zinc oxide have been deposited on alumina substrate. The fabricated sensors exhibited maximum sensing response towards acetone vapour at an optimum operating temperature of 400°C.

  3. Raman study of magnetic phase transitions of hexagonal manganites

    NASA Astrophysics Data System (ADS)

    Nam, Ji-Yeon; Hien, Nguyen T. M.; Huyen, Nguyen T.; Han, Kiok; Chen, Xiang-Bai; Cheong, S. W.; Lee, D.; Noh, T. W.; Sung, N. H.; Cho, B. K.; Yang, In-Sang

    2014-03-01

    Results of Raman studies of magnetic phase transitions of hexagonal LuMnO3 single crystal and HoMnO3 thin films are compared directly with the results of magnetic measurements. Our results show that the temperature dependent Raman study of magnon scattering provides a simple and accurate method for investigating magnetic phase transitions, especially in HoMnO3 thin films. In single crystal, our optical method provides results as good as magnetization measurements.

  4. Quantum interference and decoherence in hexagonal antidot lattices

    NASA Astrophysics Data System (ADS)

    Iye, Yasuhiro; Ueki, Masaaki; Endo, Akira; Katsumoto, Shingo

    2003-09-01

    The Altshuler-Aronov-Spivak (AAS) oscillations and the Aharonov-Bohm (AB) type oscillations both at low and high magnetic fields were observed in hexagonal antidot lattices fabricated from a GaAs/AlGaAs two-dimensional electron gas sample. The periodicities in the magnetic field and in the gate bias voltage, of the high field AB oscillation furnish information on the edge states localized around the antidots. The temperature dependences of these quantum oscillations are studied.

  5. Shock waves in polycrystalline iron.

    PubMed

    Kadau, Kai; Germann, Timothy C; Lomdahl, Peter S; Albers, Robert C; Wark, Justin S; Higginbotham, Andrew; Holian, Brad Lee

    2007-03-30

    The propagation of shock waves through polycrystalline iron is explored by large-scale atomistic simulations. For large enough shock strengths the passage of the wave causes the body-centered-cubic phase to transform into a close-packed phase with most structure being isotropic hexagonal-close-packed (hcp) and, depending on shock strength and grain orientation, some fraction of face-centered-cubic (fcc) structure. The simulated shock Hugoniot is compared to experiments. By calculating the extended x-ray absorption fine structure (EXAFS) directly from the atomic configurations, a comparison to experimental EXAFS measurements of nanosecond-laser shocks shows that the experimental data is consistent with such a phase transformation. However, the atomistically simulated EXAFS spectra also show that an experimental distinction between the hcp or fcc phase is not possible based on the spectra alone.

  6. Effects of microbial redox cycling of iron on cast iron pipe corrosion in drinking water distribution systems.

    PubMed

    Wang, Haibo; Hu, Chun; Zhang, Lili; Li, Xiaoxiao; Zhang, Yu; Yang, Min

    2014-11-15

    Bacterial characteristics in corrosion products and their effect on the formation of dense corrosion scales on cast iron coupons were studied in drinking water, with sterile water acting as a reference. The corrosion process and corrosion scales were characterized by electrochemical and physico-chemical measurements. The results indicated that the corrosion was more rapidly inhibited and iron release was lower due to formation of more dense protective corrosion scales in drinking water than in sterile water. The microbial community and denitrifying functional genes were analyzed by pyrosequencing and quantitative polymerase chain reactions (qPCR), respectively. Principal component analysis (PCA) showed that the bacteria in corrosion products played an important role in the corrosion process in drinking water. Nitrate-reducing bacteria (NRB) Acidovorax and Hydrogenophaga enhanced iron corrosion before 6 days. After 20 days, the dominant bacteria became NRB Dechloromonas (40.08%) with the protective corrosion layer formation. The Dechloromonas exhibited the stronger corrosion inhibition by inducing the redox cycling of iron, to enhance the precipitation of iron oxides and formation of Fe3O4. Subsequently, other minor bacteria appeared in the corrosion scales, including iron-respiring bacteria and Rhizobium which captured iron by the produced siderophores, having a weaker corrosion-inhibition effect. Therefore, the microbially-driven redox cycling of iron with associated microbial capture of iron caused more compact corrosion scales formation and lower iron release.

  7. Discovery of Superconductivity in Hard Hexagonal ε-NbN

    PubMed Central

    Zou, Yongtao; Qi, Xintong; Zhang, Cheng; Ma, Shuailing; Zhang, Wei; Li, Ying; Chen, Ting; Wang, Xuebing; Chen, Zhiqiang; Welch, David; Zhu, Pinwen; Liu, Bingbing; Li, Qiang; Cui, Tian; Li, Baosheng

    2016-01-01

    Since the discovery of superconductivity in boron-doped diamond with a critical temperature (TC) near 4 K, great interest has been attracted in hard superconductors such as transition-metal nitrides and carbides. Here we report the new discovery of superconductivity in polycrystalline hexagonal ε-NbN synthesized at high pressure and high temperature. Direct magnetization and electrical resistivity measurements demonstrate that the superconductivity in bulk polycrystalline hexagonal ε-NbN is below ∼11.6 K, which is significantly higher than that for boron-doped diamond. The nature of superconductivity in hexagonal ε-NbN and the physical mechanism for the relatively lower TC have been addressed by the weaker bonding in the Nb-N network, the co-planarity of Nb-N layer as well as its relatively weaker electron-phonon coupling, as compared with the cubic δ-NbN counterpart. Moreover, the newly discovered ε-NbN superconductor remains stable at pressures up to ∼20 GPa and is significantly harder than cubic δ-NbN; it is as hard as sapphire, ultra-incompressible and has a high shear rigidity of 201 GPa to rival hard/superhard material γ-B (∼227 GPa). This exploration opens a new class of highly desirable materials combining the outstanding mechanical/elastic properties with superconductivity, which may be particularly attractive for its technological and engineering applications in extreme environments. PMID:26923318

  8. Discovery of superconductivity in hard hexagonal ε-NbN

    DOE PAGES

    Zou, Yongtao; Li, Qiang; Qi, Xintong; ...

    2016-02-29

    Since the discovery of superconductivity in boron-doped diamond with a critical temperature (TC) near 4 K, great interest has been attracted in hard superconductors such as transition-metal nitrides and carbides. Here we report the new discovery of superconductivity in polycrystalline hexagonal ε-NbN synthesized at high pressure and high temperature. Direct magnetization and electrical resistivity measurements demonstrate that the superconductivity in bulk polycrystalline hexagonal ε-NbN is below ~11.6 K, which is significantly higher than that for boron-doped diamond. The nature of superconductivity in hexagonal ε-NbN and the physical mechanism for the relatively lower TC have been addressed by the weaker bondingmore » in the Nb-N network, the co-planarity of Nb-N layer as well as its relatively weaker electron-phonon coupling, as compared with the cubic δ-NbN counterpart. Moreover, the newly discovered ε-NbN superconductor remains stable at pressures up to ~20 GPa and is significantly harder than cubic δ-NbN; it is as hard as sapphire, ultra-incompressible and has a high shear rigidity of 201 GPa to rival hard/superhard material γ-B (~227 GPa). Furthermore, this exploration opens a new class of highly desirable materials combining the outstanding mechanical/elastic properties with superconductivity, which may be particularly attractive for its technological and engineering applications in extreme environments.« less

  9. Discovery of superconductivity in hard hexagonal ε-NbN

    SciTech Connect

    Zou, Yongtao; Li, Qiang; Qi, Xintong; Zhang, Cheng; Ma, Shuailing; Zhang, Wei; Li, Ying; Chen, Ting; Wang, Xuebing; Chen, Zhiqiang; Welch, David; Pinwen Zhu; Cui, Tian; Li, Bingbing; Li, Baosheng

    2016-02-29

    Since the discovery of superconductivity in boron-doped diamond with a critical temperature (TC) near 4 K, great interest has been attracted in hard superconductors such as transition-metal nitrides and carbides. Here we report the new discovery of superconductivity in polycrystalline hexagonal ε-NbN synthesized at high pressure and high temperature. Direct magnetization and electrical resistivity measurements demonstrate that the superconductivity in bulk polycrystalline hexagonal ε-NbN is below ~11.6 K, which is significantly higher than that for boron-doped diamond. The nature of superconductivity in hexagonal ε-NbN and the physical mechanism for the relatively lower TC have been addressed by the weaker bonding in the Nb-N network, the co-planarity of Nb-N layer as well as its relatively weaker electron-phonon coupling, as compared with the cubic δ-NbN counterpart. Moreover, the newly discovered ε-NbN superconductor remains stable at pressures up to ~20 GPa and is significantly harder than cubic δ-NbN; it is as hard as sapphire, ultra-incompressible and has a high shear rigidity of 201 GPa to rival hard/superhard material γ-B (~227 GPa). Furthermore, this exploration opens a new class of highly desirable materials combining the outstanding mechanical/elastic properties with superconductivity, which may be particularly attractive for its technological and engineering applications in extreme environments.

  10. Discovery of Superconductivity in Hard Hexagonal ε-NbN

    NASA Astrophysics Data System (ADS)

    Zou, Yongtao; Qi, Xintong; Zhang, Cheng; Ma, Shuailing; Zhang, Wei; Li, Ying; Chen, Ting; Wang, Xuebing; Chen, Zhiqiang; Welch, David; Zhu, Pinwen; Liu, Bingbing; Li, Qiang; Cui, Tian; Li, Baosheng

    2016-02-01

    Since the discovery of superconductivity in boron-doped diamond with a critical temperature (TC) near 4 K, great interest has been attracted in hard superconductors such as transition-metal nitrides and carbides. Here we report the new discovery of superconductivity in polycrystalline hexagonal ε-NbN synthesized at high pressure and high temperature. Direct magnetization and electrical resistivity measurements demonstrate that the superconductivity in bulk polycrystalline hexagonal ε-NbN is below ∼11.6 K, which is significantly higher than that for boron-doped diamond. The nature of superconductivity in hexagonal ε-NbN and the physical mechanism for the relatively lower TC have been addressed by the weaker bonding in the Nb-N network, the co-planarity of Nb-N layer as well as its relatively weaker electron-phonon coupling, as compared with the cubic δ-NbN counterpart. Moreover, the newly discovered ε-NbN superconductor remains stable at pressures up to ∼20 GPa and is significantly harder than cubic δ-NbN it is as hard as sapphire, ultra-incompressible and has a high shear rigidity of 201 GPa to rival hard/superhard material γ-B (∼227 GPa). This exploration opens a new class of highly desirable materials combining the outstanding mechanical/elastic properties with superconductivity, which may be particularly attractive for its technological and engineering applications in extreme environments.

  11. Cubic and Hexagonal Liquid Crystals as Drug Delivery Systems

    PubMed Central

    Chen, Yulin; Ma, Ping; Gui, Shuangying

    2014-01-01

    Lipids have been widely used as main constituents in various drug delivery systems, such as liposomes, solid lipid nanoparticles, nanostructured lipid carriers, and lipid-based lyotropic liquid crystals. Among them, lipid-based lyotropic liquid crystals have highly ordered, thermodynamically stable internal nanostructure, thereby offering the potential as a sustained drug release matrix. The intricate nanostructures of the cubic phase and hexagonal phase have been shown to provide diffusion controlled release of active pharmaceutical ingredients with a wide range of molecular weights and polarities. In addition, the biodegradable and biocompatible nature of lipids demonstrates the minimum toxicity and thus they are used for various routes of administration. Therefore, the research on lipid-based lyotropic liquid crystalline phases has attracted a lot of attention in recent years. This review will provide an overview of the lipids used to prepare cubic phase and hexagonal phase at physiological temperature, as well as the influencing factors on the phase transition of liquid crystals. In particular, the most current research progresses on cubic and hexagonal phases as drug delivery systems will be discussed. PMID:24995330

  12. Femtosecond laser direct writing of monocrystalline hexagonal silver prisms

    SciTech Connect

    Vora, Kevin; Kang, SeungYeon; Moebius, Michael; Mazur, Eric

    2014-10-06

    Bottom-up growth methods and top-down patterning techniques are both used to fabricate metal nanostructures, each with a distinct advantage: One creates crystalline structures and the other offers precise positioning. Here, we present a technique that localizes the growth of metal crystals to the focal volume of a laser beam, combining advantages from both approaches. We report the fabrication of silver nanoprisms—hexagonal nanoscale silver crystals—through irradiation with focused femtosecond laser pulses. The growth of these nanoprisms is due to a nonlinear optical interaction between femtosecond laser pulses and a polyvinylpyrrolidone film doped with silver nitrate. The hexagonal nanoprisms have bases hundreds of nanometers in size and the crystal growth occurs over exposure times of less than 1 ms (8 orders of magnitude faster than traditional chemical techniques). Electron backscatter diffraction analysis shows that the hexagonal nanoprisms are monocrystalline. The fabrication method combines advantages from both wet chemistry and femtosecond laser direct-writing to grow silver crystals in targeted locations. The results presented in this letter offer an approach to directly positioning and growing silver crystals on a substrate, which can be used for plasmonic devices.

  13. Discovery of Superconductivity in Hard Hexagonal ε-NbN.

    PubMed

    Zou, Yongtao; Qi, Xintong; Zhang, Cheng; Ma, Shuailing; Zhang, Wei; Li, Ying; Chen, Ting; Wang, Xuebing; Chen, Zhiqiang; Welch, David; Zhu, Pinwen; Liu, Bingbing; Li, Qiang; Cui, Tian; Li, Baosheng

    2016-02-29

    Since the discovery of superconductivity in boron-doped diamond with a critical temperature (TC) near 4 K, great interest has been attracted in hard superconductors such as transition-metal nitrides and carbides. Here we report the new discovery of superconductivity in polycrystalline hexagonal ε-NbN synthesized at high pressure and high temperature. Direct magnetization and electrical resistivity measurements demonstrate that the superconductivity in bulk polycrystalline hexagonal ε-NbN is below ∼11.6 K, which is significantly higher than that for boron-doped diamond. The nature of superconductivity in hexagonal ε-NbN and the physical mechanism for the relatively lower TC have been addressed by the weaker bonding in the Nb-N network, the co-planarity of Nb-N layer as well as its relatively weaker electron-phonon coupling, as compared with the cubic δ-NbN counterpart. Moreover, the newly discovered ε-NbN superconductor remains stable at pressures up to ∼20 GPa and is significantly harder than cubic δ-NbN; it is as hard as sapphire, ultra-incompressible and has a high shear rigidity of 201 GPa to rival hard/superhard material γ-B (∼227 GPa). This exploration opens a new class of highly desirable materials combining the outstanding mechanical/elastic properties with superconductivity, which may be particularly attractive for its technological and engineering applications in extreme environments.

  14. Femtosecond laser direct writing of monocrystalline hexagonal silver prisms

    NASA Astrophysics Data System (ADS)

    Vora, Kevin; Kang, SeungYeon; Moebius, Michael; Mazur, Eric

    2014-10-01

    Bottom-up growth methods and top-down patterning techniques are both used to fabricate metal nanostructures, each with a distinct advantage: One creates crystalline structures and the other offers precise positioning. Here, we present a technique that localizes the growth of metal crystals to the focal volume of a laser beam, combining advantages from both approaches. We report the fabrication of silver nanoprisms—hexagonal nanoscale silver crystals—through irradiation with focused femtosecond laser pulses. The growth of these nanoprisms is due to a nonlinear optical interaction between femtosecond laser pulses and a polyvinylpyrrolidone film doped with silver nitrate. The hexagonal nanoprisms have bases hundreds of nanometers in size and the crystal growth occurs over exposure times of less than 1 ms (8 orders of magnitude faster than traditional chemical techniques). Electron backscatter diffraction analysis shows that the hexagonal nanoprisms are monocrystalline. The fabrication method combines advantages from both wet chemistry and femtosecond laser direct-writing to grow silver crystals in targeted locations. The results presented in this letter offer an approach to directly positioning and growing silver crystals on a substrate, which can be used for plasmonic devices.

  15. Design of a solar concentrator with hexagonal facets

    NASA Astrophysics Data System (ADS)

    Herrera Vázquez, Joel; Vázquez y Montiel, Sergio

    2007-09-01

    In this work we present the optical design of a solar concentrator for an High-Flux solar furnace of a solar laboratory, these concentrator is compound for an aspheric mirror surface sectioned in 121 hexagonal facets to simplify the construction process, its total diameter is 6.6 m and a focal length is 3.68 m, also was developed the corresponding algorithm to determine the correct position and orientation of each hexagonal section that compound the arrangement. We present the results of the focused energy of this configuration and we propose a modification on the original position of the mirrors for optimizing the focusing of energy by the sun furnace. These modifications produces an increment on the energy focused on a small area in a remarkable way similar to used a parabolic mirror. The algorithm before mentioned was programmed in MathCAD and it calculates the modification of the original position of each hexagonal mirror giving us a file that ZEMAX can read. This file contains the information of each 121 mirrors from the arrangement and also the correct form, position and direction, simplifying the traditional input process one by one.

  16. Cubic and hexagonal liquid crystals as drug delivery systems.

    PubMed

    Chen, Yulin; Ma, Ping; Gui, Shuangying

    2014-01-01

    Lipids have been widely used as main constituents in various drug delivery systems, such as liposomes, solid lipid nanoparticles, nanostructured lipid carriers, and lipid-based lyotropic liquid crystals. Among them, lipid-based lyotropic liquid crystals have highly ordered, thermodynamically stable internal nanostructure, thereby offering the potential as a sustained drug release matrix. The intricate nanostructures of the cubic phase and hexagonal phase have been shown to provide diffusion controlled release of active pharmaceutical ingredients with a wide range of molecular weights and polarities. In addition, the biodegradable and biocompatible nature of lipids demonstrates the minimum toxicity and thus they are used for various routes of administration. Therefore, the research on lipid-based lyotropic liquid crystalline phases has attracted a lot of attention in recent years. This review will provide an overview of the lipids used to prepare cubic phase and hexagonal phase at physiological temperature, as well as the influencing factors on the phase transition of liquid crystals. In particular, the most current research progresses on cubic and hexagonal phases as drug delivery systems will be discussed.

  17. Lipolysis and structure controlled drug release from reversed hexagonal mesophase.

    PubMed

    Garti, Nissim; Hoshen, Geut; Aserin, Abraham

    2012-06-01

    The present work investigates a system composed of a ternary reversed hexagonal mesophase (H(II)) loaded with a lipase for modulating drug delivery capabilities of the system. Thermomyces lanuginosa lipase was solubilized into H(II) mesophase for the benefits of continuing lipolysis of the lipids, consequently disordering and decomposing the hexagonal mesophase and thereby enhancing the diffusion of the encapsulated drug. A single transition from the H(II) structure to a random micellar phase was detected during the lipolysis. In the first lipolysis stage the hexagonal system (glycerol monooleate, tricaprylin, and water) preserved its symmetry within ca. 200 min. During this step about 40-60% molar of the lipids were hydrolyzed, and a gradual shrinking of the H(II) cylinders (decrease of 8 Å in lattice parameter) was detected. In the second lipolysis stage, the H(II) mesophase gradually disintegrated (faster rate) and the release of a model drug (sodium diclofenac) was significantly enhanced, which was assumed to be lipolysis rate-controlled. After about 15 h the H(II) mesophase was disintegrated into two dispersed immiscible phases. The release obeyed two-step Higuchi kinetics with two consecutive linear correlations of the drug release. Copyright © 2012 Elsevier B.V. All rights reserved.

  18. sd(2) Graphene: Kagome band in a hexagonal lattice.

    PubMed

    Zhou, Miao; Liu, Zheng; Ming, Wenmei; Wang, Zhengfei; Liu, Feng

    2014-12-05

    Graphene, made of sp^{2} hybridized carbon, is characterized with a Dirac band, representative of its underlying 2D hexagonal lattice. The fundamental understanding of graphene has recently spurred a surge in the search for 2D topological quantum phases in solid-state materials. Here, we propose a new form of 2D material, consisting of sd^{2} hybridized transition metal atoms in hexagonal lattice, called sd^{2} "graphene." The sd^{2} graphene is characterized by bond-centered electronic hopping, which transforms the apparent atomic hexagonal lattice into the physics of a kagome lattice that may exhibit a wide range of topological quantum phases. Based on first-principles calculations, room-temperature quantum anomalous Hall states with an energy gap of ∼0.1  eV are demonstrated for one such lattice made of W, which can be epitaxially grown on a semiconductor surface of 1/3 monolayer Cl-covered Si(111), with high thermodynamic and kinetic stability.

  19. METABOLISM OF IRON STORES

    PubMed Central

    SAITO, HIROSHI

    2014-01-01

    ABSTRACT Remarkable progress was recently achieved in the studies on molecular regulators of iron metabolism. Among the main regulators, storage iron, iron absorption, erythropoiesis and hepcidin interact in keeping iron homeostasis. Diseases with gene-mutations resulting in iron overload, iron deficiency, and local iron deposition have been introduced in relation to the regulators of storage iron metabolism. On the other hand, the research on storage iron metabolism has not advanced since the pioneering research by Shoden in 1953. However, we recently developed a new method for determining ferritin iron and hemosiderin iron by computer-assisted serum ferritin kinetics. Serum ferritin increase or decrease curves were measured in patients with normal storage iron levels (chronic hepatitis C and iron deficiency anemia treated by intravenous iron injection), and iron overload (hereditary hemochromatosis and transfusion dependent anemia). We thereby confirmed the existence of two iron pathways where iron flows followed the numbered order (1) labile iron, (2) ferritin and (3) hemosiderin in iron deposition and mobilization among many previously proposed but mostly unproven routes. We also demonstrated the increasing and decreasing phases of ferritin iron and hemosiderin iron in iron deposition and mobilization. The author first demonstrated here the change in proportion between pre-existing ferritin iron and new ferritin iron synthesized by removing iron from hemosiderin in the course of iron removal. In addition, the author disclosed the cause of underestimation of storage iron turnover rate which had been reported by previous investigators in estimating storage iron turnover rate of normal subjects. PMID:25741033

  20. Optimal probabilistic dense coding schemes

    NASA Astrophysics Data System (ADS)

    Kögler, Roger A.; Neves, Leonardo

    2017-04-01

    Dense coding with non-maximally entangled states has been investigated in many different scenarios. We revisit this problem for protocols adopting the standard encoding scheme. In this case, the set of possible classical messages cannot be perfectly distinguished due to the non-orthogonality of the quantum states carrying them. So far, the decoding process has been approached in two ways: (i) The message is always inferred, but with an associated (minimum) error; (ii) the message is inferred without error, but only sometimes; in case of failure, nothing else is done. Here, we generalize on these approaches and propose novel optimal probabilistic decoding schemes. The first uses quantum-state separation to increase the distinguishability of the messages with an optimal success probability. This scheme is shown to include (i) and (ii) as special cases and continuously interpolate between them, which enables the decoder to trade-off between the level of confidence desired to identify the received messages and the success probability for doing so. The second scheme, called multistage decoding, applies only for qudits ( d-level quantum systems with d>2) and consists of further attempts in the state identification process in case of failure in the first one. We show that this scheme is advantageous over (ii) as it increases the mutual information between the sender and receiver.

  1. Percolation in dense storage arrays

    NASA Astrophysics Data System (ADS)

    Kirkpatrick, Scott; Wilcke, Winfried W.; Garner, Robert B.; Huels, Harald

    2002-11-01

    As computers and their accessories become smaller, cheaper, and faster the providers of news, retail sales, and other services we now take for granted on the Internet have met their increasing computing needs by putting more and more computers, hard disks, power supplies, and the data communications linking them to each other and to the rest of the wired world into ever smaller spaces. This has created a new and quite interesting percolation problem. It is no longer desirable to fix computers, storage or switchgear which fail in such a dense array. Attempts to repair things are all too likely to make problems worse. The alternative approach, letting units “fail in place”, be removed from service and routed around, means that a data communications environment will evolve with an underlying regular structure but a very high density of missing pieces. Some of the properties of this kind of network can be described within the existing paradigm of site or bond percolation on lattices, but other important questions have not been explored. I will discuss 3D arrays of hundreds to thousands of storage servers (something which it is quite feasible to build in the next few years), and show that bandwidth, but not percolation fraction or shortest path lengths, is the critical factor affected by the “fail in place” disorder. Redundancy strategies traditionally employed in storage systems may have to be revised. Novel approaches to routing information among the servers have been developed to minimize the impact.

  2. A new hexagonal carbon nitride synthesized at high pressure and high temperature

    NASA Astrophysics Data System (ADS)

    Sougawa, Masaya; Shima, Yuta; Hirai, Masaaki; Takarabe, Kenichi; Okada, Taku; InstituteSolid State Physics, University of Tokyo Collaboration

    2013-06-01

    A new hexagonal carbon nitride has been synthesized by subjecting the C3N4Hxprecursor to high pressure and high temperature. The XRD pattern of the new hexagonal carbon nitride is indexed as the hexagonal unit cell with the lattice parameters; a = b = 2.83 Å, c = 9.82 Å (V = 68.10 Å3) . The unit cell of this new hexagonal carbon nitride differs from the several hexagonal carbon nitrides reported so far by the theoretical and experimental studies. Hart et al. proposed the hexagonal CN structure with 1:1 stoichiometry is based on the known GaSe layer with the unit cell parameters of the hexagonal unit a = b = 2.37 Å, c = 11.38 Å (V = 55.36 Å3) , respectively, and the space group is P63/mmc. Bojdys et al. synthesized the graphitic-C3N4 (g-C3N4) with the hexagonal unit cell with the lattice parameters; a = b = 8.43 Å, c = 6.72 Å (V = 414.09 Å3) , and the space group is P63cm. These reported hexagonal lattice constants disagree with the new hexagonal carbon nitrides synthesized in this report. We will report the full analysis of the crystal structure of the new hexagonal carbon nitride at the conference.

  3. Hexagonal sampling in the infrared domain: an introduction to array set addressing

    NASA Astrophysics Data System (ADS)

    Rummelt, Nicholas I.; Barrows, Geoffrey L.; Massie, Mark A.

    2011-06-01

    It has been known since the early 1960s that hexagonal sampling is the optimal sampling approach for isotropically band-limited images, providing a 13.4% improvement in sampling efficiency over rectangular sampling. Despite this fact and other significant advantages of hexagonal sampling, rectangular sampling is still used for virtually all modern digital image processing systems. This is arguably due to the lack of an efficient addressing system for hexagonal grids. Array set addressing (ASA) is a recent advance in addressing hexagonal grids that allows image processing techniques to be performed efficiently on hexagonally sampled images. This paper will describe ASA and discuss its advantages. With ASA, a renewed interest in sensors that sample hexagonally is occurring. We will describe a new visible imager that simultaneously samples both hexagonally and rectangularly. This novel research tool has the ability to provide real imagery that can be used to quantitatively compare the performance of an image processing operation on both hexagonally sampled and rectangularly sampled images. We will also describe current efforts and plans for future visible sensors that sample hexagonally. The advantages of hexagonal sampling are not limited to the visible domain and should be equally realizable in the infrared domain. This paper will discuss considerations for developing infrared sensors that sample hexagonally. On-focal plane array (FPA) processing, readout architectures, detector materials, and bump-bonding are among the topics to be discussed.

  4. Transitions induced by solubilized fat into reverse hexagonal mesophases.

    PubMed

    Amar-Yuli, Idit; Garti, Nissim

    2005-06-25

    Lyotropic liquid crystals of glycerol monooleate (GMO) and water binary mixtures have been extensively studied and their resemblance to human membranes has intrigued many scientists. Biological systems as well as food mixtures are composed of lipids and fat components including triacylglycerols (TAGs, triglycerides) that can affect the nature of the assembly of the mesophase. The present study examines the effect of TAGs of different chain lengths (C(2)-C(18)) at various water/GMO compositions, on phase transitions from lamellar or cubic to reverse hexagonal (L(alpha)-H(II) and Q-H(II)). The ability of the triglycerides to promote the formation of an H(II) mesophase is chain length-dependent. It was found that TAG molecules with very short acyl chains (triacetin) can hydrate the head groups of the lipid and do not affect the critical packing parameter (CPP) of the amphiphile; therefore, they do not affect the self-assembly of the GMO in water, and the mesophase remains lamellar or cubic. However, TAGs with medium chain fatty acids will solvate the tails of the lipid, and will affect the CPP of the GMO, and transform the lamellar or cubic phases into hexagonal mesophase. TAGs with long chain fatty acids are very bulky, not very miscible with the GMO, and therefore, kinetically are very slow to solvate the lipid tails of the amphiphile and are difficult to accommodate into the lipophilic parts of the GMO. Their effect on the transitions from a lamellar or cubic phase to hexagonal is detected only after months of equilibration. In order to enhance the effect of the TAG on the phase transitions in the GMO/triglyceride/water systems, temperature and electrolytes effects were examined. In the presence of short and medium chain triglycerides, increasing temperature caused a transition from lamellar or hexagonal to L(2) phase (highest CPP value). However, in the presence of long chain TAGs, increasing temperature to ca. 40 degrees C caused a formation of H(II) mesophase

  5. Unit cell structure of water-filled monoolein into inverted hexagonal (H(II)) mesophase modeled by molecular dynamics.

    PubMed

    Kolev, Vesselin L; Ivanova, Anela N; Madjarova, Galia K; Aserin, Abraham; Garti, Nissim

    2014-05-22

    The study investigates the unit cell structure of inverted hexagonal (H(II)) mesophase composed of monoolein (1-monoolein, GMO) and water using atomistic molecular dynamics methods without imposing any restraints on lipid and water molecules. Statistically meaningful and very contrast images of the radial mass density distribution, scrutinizing also the separate components water, monoolein, the polar headgroups of the lipids, the double bond, and the termini of the hydrocarbon chain (the tail), are obtained. The lipid/water interface structure is analyzed based on the obtained water density distribution, on the estimated number of hydrogen bonds per monoolein headgroup, and on the headgroup-water radial distribution functions. The headgroup mass density distribution demonstrates hexagonal shape of the monoolein/water interface that is well-defined at higher water/monoolein ratios. Water interacts with the headgroups by forming a three-layer diffusive mass density distribution, and each layer's shape is close to hexagonal, which is an indication of long-range structural interactions. It is found that the monoolein headgroups form a constant number of hydrogen bonds leaving an excessive amount of water molecules outside the first lipid coordination sphere. Furthermore, the quantity of water at the monoolein/water interface increases steadily upon extension of the unit cell, so the interface should have a very dynamic structure. Investigation of the hydrocarbon residues reveals high compression and well-expressed structuring of the tails. The tails form a very compressed and constrained structure of defined layers across the unit cell with properties corresponding to a more densely packed nonpolar liquid (oil). Due to the hexagonal shape the 2D packing frustration is constant and does not depend on the water content. All reported structural features are based on averaging of the atomic coordinates over the time-length of the simulation trajectories. That kind of

  6. Containerless Solidification of Hexagonal Metastable Phases from an Undercooled R3Fe5O12 Melt

    NASA Astrophysics Data System (ADS)

    Kumar, Vijaya; Kentei Yu, Yu; Kameko, Masashi; Ishikawa, Takehiko; Kuribayashi, Kazuhiko; Yoda, Shinichi

    Containerless processing is a promising technique to explore the technologically important materials using rapid solidification of an undercooled melt because it provides large undercooling prior to nucleation. In the R-Fe-O system (R=Rare-earth element), rare-earth iron garnet (R3 Fe5 O12 ) can be formed through a peritectic reaction between RFeO3 , which is a primary phase, and a melt, which contains more Fe2 O3 than the R3 Fe5 O12 composition. The iron garnet is know to become unstable with increasing ionic radius of the rare-earth ion from Lu to Sm and does not exist in a stable form in La, Pr, and Nd [1,2]. Recently, we investigated the effect of oxygen partial pressure Po2 on metastable phase formation from an undercooled RFeO3 melt through containerless solidification. On the other hand, Po2 was considered to be one of the most important thermodynamic parameters which control phase constituents during containerless processing. In the R-Fe-O system, multiferroic hexagonal RFeO3 (P63 cm) and Fe2+ -containing ferroelectric phases such as RFe2 O4 (r-R3m) and new hexagonal R3 Fe2 O7 (P63 /mmc) phases were obtained metastably with decreasing Po2 from 105 to 10-1 Pa [3,4]. However, in the R3 Fe5 O12 system, the effect of Po2 during rapid solidification has not been studied yet. The purpose of this study is to elucidate the effect of Po2 on the formation of metastable phases from an undercooled R3 Fe5 O12 melt under controlled Po2 using gas-jet levitation technique. In order to undercool the melt deeply below the melting temperature under a precisely con-trolled oxygen partial pressure, an aerodynamic levitator (ADL) combined with ZrO2 oxygen sensor was designed. A spherical R3 Fe5 O12 sample was levitated by an ADL and completely melted by a CO2 laser in an atmosphere with predetermined Po2 . The surface temperature of the levitated droplet was monitored by a two-color pyrometer. Then, the droplet was cooled by turning off the CO2 laser. Meanwhile, the recalescence

  7. Electronic reconstruction of hexagonal FeS: a view from density functional dynamical mean-field theory

    NASA Astrophysics Data System (ADS)

    Craco, L.; Faria, J. L. B.; Leoni, S.

    2017-03-01

    We present a detailed study of correlation- and pressure-induced electronic reconstruction in hexagonal iron monosulfide, a system which is widely found in meteorites and one of the components of Earth’s core. Based on a perusal of experimental data, we stress the importance of multi-orbital electron-electron interactions in concert with first-principles band structure calculations for a consistent understanding of its intrinsic Mott–Hubbard insulating state. We explain the anomalous nature of pressure-induced insulator-metal-insulator transition seen in experiment, showing that it is driven by dynamical spectral weight transfer in response to changes in the crystal-field splittings under pressure. As a byproduct of this analysis, we confirm that the electronic transitions observed in pristine FeS at moderated pressures are triggered by changes in the spin state which causes orbital-selective Kondo quasiparticle electronic reconstruction at low energies.

  8. Fabrication of dense non-circular nanomagnetic device arrays using self-limiting low-energy glow-discharge processing.

    PubMed

    Zheng, Zhen; Chang, Long; Nekrashevich, Ivan; Ruchhoeft, Paul; Khizroev, Sakhrat; Litvinov, Dmitri

    2013-01-01

    We describe a low-energy glow-discharge process using reactive ion etching system that enables non-circular device patterns, such as squares or hexagons, to be formed from a precursor array of uniform circular openings in polymethyl methacrylate, PMMA, defined by electron beam lithography. This technique is of a particular interest for bit-patterned magnetic recording medium fabrication, where close packed square magnetic bits may improve its recording performance. The process and results of generating close packed square patterns by self-limiting low-energy glow-discharge are investigated. Dense magnetic arrays formed by electrochemical deposition of nickel over self-limiting formed molds are demonstrated.

  9. Total iron binding capacity

    MedlinePlus

    ... iron supplies are low. This can occur with: Iron deficiency anemia Pregnancy (late) Lower-than-normal TIBC may ... Brittenham GM. Disorders of iron homeostasis: iron deficiency and ... Basic Principles and Practice . 6th ed. Philadelphia, PA: ...

  10. Hexagonal organization of Moloney murine leukemia virus capsid proteins.

    PubMed

    Mayo, Keith; McDermott, Jason; Barklis, Eric

    2002-06-20

    To help elucidate the mechanisms by which retrovirus structural proteins associate to form virus particles, we have examined membrane-bound assemblies of Moloney murine leukemia virus (M-MuLV) capsid (CA) proteins. Electron microscopy and image reconstruction techniques showed that CA dimers appear to function as organizational subunits of the cage-like, membrane-bound protein arrays. However, new three-dimensional (3D) data also were consistent with hexagonal (p6) assembly models. The p6 3D reconstructions of membrane-bound M-MuLV CA proteins gave unit cells of a = b = 80.3 A, c = 110 A, gamma = 120 degrees, in which six dimer units formed a cage lattice. Neighbor cage hole-to-hole distances were 45 A, while distances between hexagonal cage holes corresponded to unit cell lengths (80.3 A). The hexagonal model predicts two types of cage holes (trimer and hexamer holes), uses symmetric head-to-head dimer building blocks, and permits the introduction of lattice curvature by conversion of hexamer to pentamer units. The M-MuLV CA lattice is similar to those formed in helical tubes by HIV CA in that hexamer units surround cage holes of 25-30 A, but differs in that M-MuLV hexamer units appear to be CA dimers, whereas HIV CA units appear to be monomers. These results suggest that while general assembly principles apply to different retroviruses, clear assembly distinctions exist between these virus types. (c) 2002 Elsevier Science (USA).

  11. On the dynamical nature of Saturn's North Polar hexagon

    NASA Astrophysics Data System (ADS)

    Rostami, Masoud; Zeitlin, Vladimir; Spiga, Aymeric

    2017-04-01

    An explanation of long-lived Saturn's North Pole hexagonal circumpolar jet in terms of instability of the coupled system polar vortex - circumpolar jet is proposed in the framework of the rotating shallow water model, where scarcely known vertical structure of the Saturn's atmosphere is averaged out. The absence of a hexagonal structure at the Saturn's South Pole is explained along the same lines. By using the latest state-of-the-art observed winds in Saturn's polar regions a detailed linear stability analysis of the circumpolar jet is performed (i) excluding (``jet-only" configuration), and (2) including (``jet+vortex" configuration) the north polar vortex in the system. A domain of parameters: latitude of the circumpolar jet and curvature of its azimuthal velocity profile, where the most unstable mode of the system has azimuthal wavenumber 6, is identified. Fully nonlinear simulations are then performed, initialized either with the most unstable mode of small amplitude, or with the random combination of unstable modes. It is shown that developing barotropic instability of the ``jet+vortex" system produces a long-living structure akin to the observed hexagon, which is not the case of the ``jet-only" system, which was studied in this context in a number of papers in literature. The north polar vortex, thus, plays a decisive dynamical role. The influence of moist convection, which was recently suggested to be at the origin of Saturn's north polar vortex system in the literature, is investigated in the framework of the model and does not alter the conclusions.

  12. Hexagon functions and the three-loop remainder function

    SciTech Connect

    Dixon, Lance J.; Drummond, James M.; von Hippel, Matt; Pennington, Jeffrey

    2013-12-01

    We present the three-loop remainder function, which describes the scattering of six gluons in the maximally-helicity-violating configuration in planar NN = 4 super-Yang-Mills theory, as a function of the three dual conformal cross ratios. The result can be expressed in terms of multiple Goncharov polylogarithms. We also employ a more restricted class of hexagon functions which have the correct branch cuts and certain other restrictions on their symbols. We classify all the hexagon functions through transcendental weight five, using the coproduct for their Hopf algebra iteratively, which amounts to a set of first-order differential equations. The three-loop remainder function is a particular weight-six hexagon function, whose symbol was determined previously. The differential equations can be integrated numerically for generic values of the cross ratios, or analytically in certain kinematic limits, including the near-collinear and multi-Regge limits. These limits allow us to impose constraints from the operator product expansion and multi-Regge factorization directly at the function level, and thereby to fix uniquely a set of Riemann ζ valued constants that could not be fixed at the level of the symbol. The near-collinear limits agree precisely with recent predictions by Basso, Sever and Vieira based on integrability. The multi-Regge limits agree with the factorization formula of Fadin and Lipatov, and determine three constants entering the impact factor at this order. We plot the three-loop remainder function for various slices of the Euclidean region of positive cross ratios, and compare it to the two-loop one. For large ranges of the cross ratios, the ratio of the three-loop to the two-loop remainder function is relatively constant, and close to -7.

  13. Hexagon functions and the three-loop remainder function

    NASA Astrophysics Data System (ADS)

    Dixon, Lance J.; Drummond, James M.; von Hippel, Matt; Pennington, Jeffrey

    2013-12-01

    We present the three-loop remainder function, which describes the scattering of six gluons in the maximally-helicity-violating configuration in planar = 4 super-Yang-Mills theory, as a function of the three dual conformal cross ratios. The result can be expressed in terms of multiple Goncharov polylogarithms. We also employ a more restricted class of hexagon functions which have the correct branch cuts and certain other restrictions on their symbols. We classify all the hexagon functions through transcendental weight five, using the coproduct for their Hopf algebra iteratively, which amounts to a set of first-order differential equations. The three-loop remainder function is a particular weight-six hexagon function, whose symbol was determined previously. The differential equations can be integrated numerically for generic values of the cross ratios, or analytically in certain kinematic limits, including the near-collinear and multi-Regge limits. These limits allow us to impose constraints from the operator product expansion and multi-Regge factorization directly at the function level, and thereby to fix uniquely a set of Riemann ζ valued constants that could not be fixed at the level of the symbol. The near-collinear limits agree precisely with recent predictions by Basso, Sever and Vieira based on integrability. The multi-Regge limits agree with the factorization formula of Fadin and Lipatov, and determine three constants entering the impact factor at this order. We plot the three-loop remainder function for various slices of the Euclidean region of positive cross ratios, and compare it to the two-loop one. For large ranges of the cross ratios, the ratio of the three-loop to the two-loop remainder function is relatively constant, and close to -7.

  14. Iron and alloys of iron. [lunar resources

    NASA Technical Reports Server (NTRS)

    Sastri, Sankar

    1992-01-01

    All lunar soil contains iron in the metallic form, mostly as an iron-nickel alloy in concentrations of a few tenths of 1 percent. Some of this free iron can be easily separated by magnetic means. It is estimated that the magnetic separation of 100,000 tons of lunar soil would yield 150-200 tons of iron. Agglutinates contain metallic iron which could be extracted by melting and made into powder metallurgy products. The characteristics and potential uses of the pure-iron and iron-alloy lunar products are discussed. Processes for working iron that might be used in a nonterrestrial facility are also addressed.

  15. Corrosion resistance of monolayer hexagonal boron nitride on copper

    PubMed Central

    Mahvash, F.; Eissa, S.; Bordjiba, T.; Tavares, A. C.; Szkopek, T.; Siaj, M.

    2017-01-01

    Hexagonal boron nitride (hBN) is a layered material with high thermal and chemical stability ideal for ultrathin corrosion resistant coatings. Here, we report the corrosion resistance of Cu with hBN grown by chemical vapor deposition (CVD). Cyclic voltammetry measurements reveal that hBN layers inhibit Cu corrosion and oxygen reduction. We find that CVD grown hBN reduces the Cu corrosion rate by one order of magnitude compared to bare Cu, suggesting that this ultrathin layer can be employed as an atomically thin corrosion-inhibition coating. PMID:28191822

  16. Hexagon POPE: effective particles and tree level resummation

    NASA Astrophysics Data System (ADS)

    Córdova, Lucía

    2017-01-01

    We present the resummation of the full Pentagon Operator Product Expansion series of the hexagon Wilson loop in planar N=4 SYM at tree level. We do so by considering the one effective particle states formed by a fundamental flux tube excitation and an arbitrary number of the so called small fermions which are then integrated out. We derive the one effective particle measures at finite coupling. By evaluating these measures at tree level and summing over all one effective particle states we reproduce the full 6 point tree level amplitude.

  17. Inter-layer potential for hexagonal boron nitride

    NASA Astrophysics Data System (ADS)

    Leven, Itai; Azuri, Ido; Kronik, Leeor; Hod, Oded

    2014-03-01

    A new interlayer force-field for layered hexagonal boron nitride (h-BN) based structures is presented. The force-field contains three terms representing the interlayer attraction due to dispersive interactions, repulsion due to anisotropic overlaps of electron clouds, and monopolar electrostatic interactions. With appropriate parameterization, the potential is able to simultaneously capture well the binding and lateral sliding energies of planar h-BN based dimer systems as well as the interlayer telescoping and rotation of double walled boron-nitride nanotubes of different crystallographic orientations. The new potential thus allows for the accurate and efficient modeling and simulation of large-scale h-BN based layered structures.

  18. Mysterious hexagonal pyramids on the surface of Pyrobaculum cells.

    PubMed

    Rensen, Elena; Krupovic, Mart; Prangishvili, David

    2015-11-01

    In attempts to induce putative temperate viruses, we UV-irradiated cells of the hyperthermophilic archaeon Pyrobaculum oguniense. Virus replication could not be detected; however, we observed the development of pyramidal structures with 6-fold symmetry on the cell surface. The hexagonal basis of the pyramids was continuous with the cellular cytoplasmic membrane and apparently grew via the gradual expansion of the 6 triangular lateral faces, ultimately protruding through the S-layer. When the base of these isosceles triangles reached approximately 200 nm in length, the pyramids opened like flower petals. The origin and function of these mysterious nanostructures remain unknown.

  19. Corrosion resistance of monolayer hexagonal boron nitride on copper.

    PubMed

    Mahvash, F; Eissa, S; Bordjiba, T; Tavares, A C; Szkopek, T; Siaj, M

    2017-02-13

    Hexagonal boron nitride (hBN) is a layered material with high thermal and chemical stability ideal for ultrathin corrosion resistant coatings. Here, we report the corrosion resistance of Cu with hBN grown by chemical vapor deposition (CVD). Cyclic voltammetry measurements reveal that hBN layers inhibit Cu corrosion and oxygen reduction. We find that CVD grown hBN reduces the Cu corrosion rate by one order of magnitude compared to bare Cu, suggesting that this ultrathin layer can be employed as an atomically thin corrosion-inhibition coating.

  20. Inter-layer potential for hexagonal boron nitride

    SciTech Connect

    Leven, Itai; Hod, Oded; Azuri, Ido; Kronik, Leeor

    2014-03-14

    A new interlayer force-field for layered hexagonal boron nitride (h-BN) based structures is presented. The force-field contains three terms representing the interlayer attraction due to dispersive interactions, repulsion due to anisotropic overlaps of electron clouds, and monopolar electrostatic interactions. With appropriate parameterization, the potential is able to simultaneously capture well the binding and lateral sliding energies of planar h-BN based dimer systems as well as the interlayer telescoping and rotation of double walled boron-nitride nanotubes of different crystallographic orientations. The new potential thus allows for the accurate and efficient modeling and simulation of large-scale h-BN based layered structures.

  1. Structural performance of two aerobrake hexagonal heat shield panel concepts

    NASA Technical Reports Server (NTRS)

    Dorsey, John T.; Dyess, James W.

    1992-01-01

    Structural sizing and performance are presented for two structural concepts for an aerobrake hexagonal heat shield panel. One concept features a sandwich construction with an aluminum honeycomb core and thin quasi-isotropic graphite-epoxy face sheets. The other concept features a skin-rib isogrid construction with thin quasi-isotropic graphite-epoxy skins and graphite-epoxy ribs oriented at 0, +60, and -60 degs along the panel. Linear static, linear bifurcation buckling, and nonlinear static analyses were performed to compare the structural performance of the two panel concepts and assess their feasibility for a lunar transfer vehicle aerobrake application.

  2. Effective mechanical properties of hexagonal boron nitride nanosheets.

    PubMed

    Boldrin, L; Scarpa, F; Chowdhury, R; Adhikari, S

    2011-12-16

    We propose an analytical formulation to extract from energy equivalence principles the equivalent thickness and in-plane mechanical properties (tensile and shear rigidity, and Poisson's ratio) of hexagonal boron nitride (h-BN) nanosheets. The model developed provides not only very good agreement with existing data available in the open literature from experimental, density functional theory (DFT) and molecular dynamics (MD) simulations, but also highlights the specific deformation mechanisms existing in boron nitride sheets, and their difference with carbon-based graphitic systems.

  3. Quantum simulation of collective proton tunneling in hexagonal ice crystals.

    PubMed

    Drechsel-Grau, Christof; Marx, Dominik

    2014-04-11

    The effect of proton tunneling on many-body correlated proton transfer in hexagonal ice is investigated by quantum simulation. Classical single-particle hopping along individual hydrogen bonds leads to charge defects at high temperature, whereas six protons in ringlike topologies can move concertedly as a delocalized quasiparticle via collective tunneling at low temperature, thus preventing the creation of high-energy topological defects. Our findings rationalize many-body quantum tunneling in hydrogen-bonded networks and suggest that this phenomenon might be more widespread than previously thought.

  4. Stable three-dimensional metallic carbon with interlocking hexagons

    PubMed Central

    Zhang, Shunhong; Wang, Qian; Chen, Xiaoshuang; Jena, Puru

    2013-01-01

    Design and synthesis of 3D metallic carbon that is stable under ambient conditions has been a long-standing dream. We predict the existence of such phases, T6- and T14-carbon, consisting of interlocking hexagons. Their dynamic, mechanical, and thermal stabilities are confirmed by carrying out a variety of state-of-the-art theoretical calculations. Unlike the previously studied K4 and the simple cubic high pressure metallic phases, the structures predicted in this work are stable under ambient conditions. Equally important, they may be synthesized chemically by using benzene or polyacenes molecules. PMID:24191020

  5. Optical Design of Segmented Hexagon Array Solar Mirror

    NASA Technical Reports Server (NTRS)

    Huegele, Vince

    2000-01-01

    A segmented array of mirrors was designed for a solar concentrator test stand at MSFC for firing solar thermal propulsion engines. The 144 mirrors each have a spherical surface to approximate a parabolic concentrator when combined into the entire 18-foot diameter array. The mirror segments are aluminum hexagons that had the surface diamond turned and quartz coated. The array focuses sunlight reflected from a heliostat to a 4 inch diameter spot containing 10 kw of power at the 15-foot focal point. The derivation of the surface figure for the respective mirror elements is shown. The alignment process of the array is discussed and test results of the system's performance is given.

  6. Colorings of odd or even chirality on hexagonal lattices

    NASA Astrophysics Data System (ADS)

    Cépas, O.

    2017-02-01

    We define two classes of colorings that have odd or even chirality on hexagonal lattices. This parity is an invariant in the dynamics of all loops, and explains why standard Monte Carlo algorithms are nonergodic. We argue that adding the motion of "stranded" loops allows for parity changes. By implementing this algorithm, we show that the even and odd classes have the same entropy. In general, they do not have the same number of states, except for the special geometry of long strips, where a Z2 symmetry between even and odd states occurs in the thermodynamic limit.

  7. Carbon nanotube quantum dots on hexagonal boron nitride

    SciTech Connect

    Baumgartner, A. Abulizi, G.; Gramich, J.; Schönenberger, C.; Watanabe, K.; Taniguchi, T.

    2014-07-14

    We report the fabrication details and low-temperature characteristics of carbon nanotube (CNT) quantum dots on flakes of hexagonal boron nitride (hBN) as substrate. We demonstrate that CNTs can be grown on hBN by standard chemical vapor deposition and that standard scanning electron microscopy imaging and lithography can be employed to fabricate nanoelectronic structures when using optimized parameters. This proof of concept paves the way to more complex devices on hBN, with more predictable and reproducible characteristics and electronic stability.

  8. Honeybee combs: how the circular cells transform into rounded hexagons

    PubMed Central

    Karihaloo, B. L.; Zhang, K.; Wang, J.

    2013-01-01

    We report that the cells in a natural honeybee comb have a circular shape at ‘birth’ but quickly transform into the familiar rounded hexagonal shape, while the comb is being built. The mechanism for this transformation is the flow of molten visco-elastic wax near the triple junction between the neighbouring circular cells. The flow may be unconstrained or constrained by the unmolten wax away from the junction. The heat for melting the wax is provided by the ‘hot’ worker bees. PMID:23864500

  9. Corrosion resistance of monolayer hexagonal boron nitride on copper

    NASA Astrophysics Data System (ADS)

    Mahvash, F.; Eissa, S.; Bordjiba, T.; Tavares, A. C.; Szkopek, T.; Siaj, M.

    2017-02-01

    Hexagonal boron nitride (hBN) is a layered material with high thermal and chemical stability ideal for ultrathin corrosion resistant coatings. Here, we report the corrosion resistance of Cu with hBN grown by chemical vapor deposition (CVD). Cyclic voltammetry measurements reveal that hBN layers inhibit Cu corrosion and oxygen reduction. We find that CVD grown hBN reduces the Cu corrosion rate by one order of magnitude compared to bare Cu, suggesting that this ultrathin layer can be employed as an atomically thin corrosion-inhibition coating.

  10. Manipulation of ferroelectric vortex domains in hexagonal manganites

    NASA Astrophysics Data System (ADS)

    Lilienblum, M.; Soergel, E.; Fiebig, M.

    2011-09-01

    The modification of ferroelectric vortex domain patterns in hexagonal manganites (here exemplified by YMnO3 and HoMnO3) owing to chemical treatment, thermal annealing, and local electric-field poling is investigated by piezoresponse force microscopy. Chemical treatment transfers the domain pattern into a topographical pattern by domain selective etching. Thermal annealing alters the domain pattern without any sign of temperature memory effects. Local electric fields affect the domain structure with possible signs of electric memory effects. These observations are important for future investigations of the microscopic mechanisms and macroscopic parameters defining the formation of ferroelectric domains in this unusual multiferroic.

  11. Tunable magnetic states in hexagonal boron nitride sheets

    NASA Astrophysics Data System (ADS)

    Machado-Charry, Eduardo; Boulanger, Paul; Genovese, Luigi; Mousseau, Normand; Pochet, Pascal

    2012-09-01

    Magnetism in two dimensional atomic sheets has attracted considerable interest as its existence could allow the development of electronic and spintronic devices. The existence of magnetism is not sufficient for devices, however, as states must be addressable and modifiable through the application of an external drive. We show that defects in hexagonal boron nitride present a strong interplay between the N-N distance in the edge and the magnetic moments of the defects. By stress-induced geometry modifications, we change the ground state magnetic moment of the defects. This control is made possible by the triangular shape of the defects as well as the strong spin localisation in the magnetic state.

  12. Strong coupling of ferroelectricity and magnetism in the hexagonal ferrites

    NASA Astrophysics Data System (ADS)

    Das, Hena

    2013-03-01

    During the last decade one of the most extensively studied class of multiferroics has been the hexagonal rare-earth manganites RMnO3 where R=Dy-Lu, Y, Sc. These compounds exhibit antiferromagnetic (AFM) order with a Néel temperature TN ~ 100 K . In addition, they are improper ferroelectrics (TC > 1200 K) driven a by zone-tripling structural distortion associated with a buckling of the R-planes and a rotation of the oxygen trigonal bipyramids. The improper nature of the transition is responsible for the fascinating, topologically protected trimer-domains. Even though magnetism and ferroelectricity in these materials are not intrinsically coupled, there is a non-trivial interaction between the structural and magnetic domain walls. In contrast to the manganites, the ground state structure of the rare-earth ferrites RFeO3 is the orthorhombic perovskite. Recently, however, thin films of RFeO3 have been epitaxially stabilized in the hexagonal rare-earth manganite structure. This development has triggered several new studies of these hexagonal ferrite systems. Similar to manganites, ferrites exhibit ferroelectricity above room temperature and crystallize in P63cm polar structure but conflicting results have been reported as to the origin of ferroelectricity in these materials. Unlike the manganites, recent neutron diffraction measurements suggest a considerably high AFM ordering temperature, TN = 440 K. Additionally there is an indication of a second temperature, TwFM ~ 100 K , at which weak ferromagnetism has been observed. In this work my collaborators (Alex Wysocki and Craig J. Fennie) and I address the nature of ferroelectricity and magnetic order in the RFeO3 systems from first-principles. We elucidate the origin of ferroelectricity in the rare-earth ferrites and provide many useful insights into their magnetic behavior, which we will show is fundamentally different than that observed in the manganites. Combining first-principles calculations with a detailed

  13. Hippocampal Spike-Timing Correlations Lead to Hexagonal Grid Fields

    NASA Astrophysics Data System (ADS)

    Monsalve-Mercado, Mauro M.; Leibold, Christian

    2017-07-01

    Space is represented in the mammalian brain by the activity of hippocampal place cells, as well as in their spike-timing correlations. Here, we propose a theory for how this temporal code is transformed to spatial firing rate patterns via spike-timing-dependent synaptic plasticity. The resulting dynamics of synaptic weights resembles well-known pattern formation models in which a lateral inhibition mechanism gives rise to a Turing instability. We identify parameter regimes in which hexagonal firing patterns develop as they have been found in medial entorhinal cortex.

  14. Optical design of SHASM: segmented hexagon array solar mirror

    NASA Astrophysics Data System (ADS)

    Huegele, Vinson B.

    2000-10-01

    A segmented array of mirrors was designed for a solar concentrator test stand at MSFC for firing solar thermal propulsion engines. The 144 mirrors each have s spherical surface to approximate a parabolic concentrator when combined into the entire 17-foot diameter array. The mirror segments are aluminum hexagons that had the surface diamond turned and quartz coated. The array focuses sunlight reflected from a heliostat to a 4 inch diameter spot containing 8 kilowatts of power at the 15 foot focal point. The derivation of the surface figure for the respective mirror elements is shown. The alignment process of the array is discussed and test results of the system's performance are given.

  15. Self-assembled GaN hexagonal micropyramid and microdisk

    SciTech Connect

    Lo Ikai; Hsieh, C.-H.; Hsu, Y.-C.; Pang, W.-Y.; Chou, M.-C.

    2009-02-09

    The self-assembled GaN hexagonal micropyramid and microdisk were grown on LiAlO{sub 2} by plasma-assisted molecular-beam epitaxy. It was found that the (0001) disk was established with the capture of N atoms by most-outside Ga atoms as the (1x1) surface was constructing, while the pyramid was obtained due to the missing of most-outside N atoms. The intensity of cathode luminescence excited from the microdisk was one order of amplitude greater than that from M-plane GaN.

  16. Field emission characteristics from graphene on hexagonal boron nitride

    SciTech Connect

    Yamada, Takatoshi; Masuzawa, Tomoaki; Ebisudani, Taishi; Okano, Ken; Taniguchi, Takashi

    2014-06-02

    An attempt has been made to utilize uniquely high electron mobility of graphene on hexagonal boron nitride (h-BN) to electron emitter. The field emission property of graphene/h-BN/Si structure has shown enhanced threshold voltage and emission current, both of which are key to develop novel vacuum nanoelectronics devices. The field emission property was discussed along with the electronic structure of graphene investigated by Fowler-Nordheim plot and ultraviolet photoelectron spectroscopy. The result suggested that transferring graphene on h-BN modified its work function, which changed field emission mechanism. Our report opens up a possibility of graphene-based vacuum nanoelectronics devices with tuned work function.

  17. Propagation Of Dense Plasma Jets

    NASA Astrophysics Data System (ADS)

    Turchi, Peter J.; Davis, John F.

    1988-05-01

    A variety of schemes have been proposed over the last two decades for delivering lethal amounts of energy and/or momentum to targets such as missiles and high speed aircraft. Techniques have ranged from high energy lasers and high voltage charged-particle accelerators to less exotic but still challenging devices such as electromagnetic railguns. One class of technology involves the use of high speed plasmas. The primary attraction of such technology is the possibility of utilizing relatively compact accelerators and electrical power systems that could allow highly mobile and agile operation from rocket or aircraft platforms, or in special ordnance. Three years ago, R & D Associates examined the possibility of plasma propagation for military applications and concluded that the only viable approach consisted of long dense plasma jets, contained in radial equilibrium by the atmosphere, while propagating at speeds of about 10 km/s. Without atmospheric confinement the plasma density would diminish too rapidly for adequate range and lethality. Propagation of atmospherically-confined jets at speeds much greater than 10 km/s required significant increases in power levels and/or operating altitudes to achieve useful ranges. The present research effort has been developing the experimental conditions necessary to achieve reasonable comparison with theoretical predictions for plasma jet propagation in the atmosphere. Time-resolved measurements have been made of high speed argon plasma jets penetrating a helium background (simulating xenon jets propagating into air). Basic radial confinement of the jet has been observed by photography and spectroscopy and structures in the flow field resemble those predicted by numerical calculations. Results from our successful initial experiments have been used to design improved diagnostic procedures and arcjet source characteristics for further experiments. In experiments with a modified arcjet source, radial confinement of the jet is again

  18. Genetics Home Reference: iron-refractory iron deficiency anemia

    MedlinePlus

    ... Conditions iron-refractory iron deficiency anemia iron-refractory iron deficiency anemia Printable PDF Open All Close All Enable ... view the expand/collapse boxes. Description Iron-refractory iron deficiency anemia is one of many types of anemia , ...

  19. Ultrastructural aspects of iron storage, transport and metabolism.

    PubMed

    Iancu, Theodore C

    2011-03-01

    The iron storage proteins, ferritin and hemosiderin, enable electron microscopic visualization thanks to their electron-dense iron content, which is not present in other compounds involved in transport or metabolism of iron such as transferrin, lactoferrin, or hemoglobin. It is this electron density which contributed to the unraveling of stages in absorption, transport, deposition, storage, and release of iron. In recent years, additional methods of investigation have further supported the information achieved by the ultrastructural studies. Even while using new analytical methods, the seminal morphological observations remain valid for understanding the role of iron in health and disease. In this review, we will illustrate a few basic findings of electron microscopy in humans, experimental animals, and cell cultures. The importance of H chain ferritin as a transporter across the blood-brain barrier is just an example of a new role revealed for an "old" storage protein, explaining some controversial observations on the presence of iron in the brain.

  20. Iron and iron derived radicals

    SciTech Connect

    Borg, D.C.; Schaich, K.M.

    1987-04-01

    We have discussed some reactions of iron and iron-derived oxygen radicals that may be important in the production or treatment of tissue injury. Our conclusions challenge, to some extent, the usual lines of thought in this field of research. Insofar as they are born out by subsequent developments, the lessons they teach are two: Think fastexclamation Think smallexclamation In other words, think of the many fast reactions that can rapidly alter the production and fate of highly reactive intermediates, and when considering the impact of competitive reactions on such species, think how they affect the microenvironment (on the molecular scale) ''seen'' by each reactive molecule. 21 refs., 3 figs., 1 tab.

  1. Dense Plasma Heating and Radiation Generation.

    DTIC Science & Technology

    The investigations under this grant consist of three parts: CO2 laser heating of dense preformed plasmas, interaction of a dense hot plasma with a...small solid pellet, and pulsed power systems and technology. The laser plasma heating experiment has demonstrated both beam guiding by the plasma and...plasma heating by the beam. These results will be useful in heating plasmas for radiation generation. Experiments have shown that the pellet-plasma

  2. Magnetic Phases in Dense Quark Matter

    SciTech Connect

    Incera, Vivian de la

    2007-10-26

    In this paper I discuss the magnetic phases of the three-flavor color superconductor. These phases can take place at different field strengths in a highly dense quark system. Given that the best natural candidates for the realization of color superconductivity are the extremely dense cores of neutron stars, which typically have very large magnetic fields, the magnetic phases here discussed could have implications for the physics of these compact objects.

  3. Dynamical theory of dense groups of galaxies

    NASA Technical Reports Server (NTRS)

    Mamon, Gary A.

    1990-01-01

    It is well known that galaxies associate in groups and clusters. Perhaps 40% of all galaxies are found in groups of 4 to 20 galaxies (e.g., Tully 1987). Although most groups appear to be so loose that the galaxy interactions within them ought to be insignificant, the apparently densest groups, known as compact groups appear so dense when seen in projection onto the plane of the sky that their members often overlap. These groups thus appear as dense as the cores of rich clusters. The most popular catalog of compact groups, compiled by Hickson (1982), includes isolation among its selection critera. Therefore, in comparison with the cores of rich clusters, Hickson's compact groups (HCGs) appear to be the densest isolated regions in the Universe (in galaxies per unit volume), and thus provide in principle a clean laboratory for studying the competition of very strong gravitational interactions. The $64,000 question here is then: Are compact groups really bound systems as dense as they appear? If dense groups indeed exist, then one expects that each of the dynamical processes leading to the interaction of their member galaxies should be greatly enhanced. This leads us to the questions: How stable are dense groups? How do they form? And the related question, fascinating to any theorist: What dynamical processes predominate in dense groups of galaxies? If HCGs are not bound dense systems, but instead 1D change alignments (Mamon 1986, 1987; Walke & Mamon 1989) or 3D transient cores (Rose 1979) within larger looser systems of galaxies, then the relevant question is: How frequent are chance configurations within loose groups? Here, the author answers these last four questions after comparing in some detail the methods used and the results obtained in the different studies of dense groups.

  4. Dissociation energy of molecules in dense gases

    NASA Technical Reports Server (NTRS)

    Kunc, J. A.

    1992-01-01

    A general approach is presented for calculating the reduction of the dissociation energy of diatomic molecules immersed in a dense (n = less than 10 exp 22/cu cm) gas of molecules and atoms. The dissociation energy of a molecule in a dense gas differs from that of the molecule in vacuum because the intermolecular forces change the intramolecular dynamics of the molecule, and, consequently, the energy of the molecular bond.

  5. Dissociation energy of molecules in dense gases

    NASA Technical Reports Server (NTRS)

    Kunc, J. A.

    1992-01-01

    A general approach is presented for calculating the reduction of the dissociation energy of diatomic molecules immersed in a dense (n = less than 10 exp 22/cu cm) gas of molecules and atoms. The dissociation energy of a molecule in a dense gas differs from that of the molecule in vacuum because the intermolecular forces change the intramolecular dynamics of the molecule, and, consequently, the energy of the molecular bond.

  6. Properties of iron under core conditions

    NASA Astrophysics Data System (ADS)

    Brown, J. M.

    2003-04-01

    Underlying an understanding of the geodynamo and evolution of the core is knowledge of the physical and chemical properties of iron and iron mixtures under high pressure and temperature conditions. Key properties include the viscosity of the fluid outer core, thermal diffusivity, equations-of-state, elastic properties of solid phases, and phase equilibria for iron and iron-dominated mixtures. As is expected for work that continues to tax technological and intellectual limits, controversy has followed both experimental and theoretical progress in this field. However, estimates for the melting temperature of the inner core show convergence and the equation-of-state for iron as determined in independent experiments and theories are in remarkable accord. Furthermore, although the structure and elastic properties of the solid inner-core phase remains uncertain, theoretical and experimental underpinnings are better understood and substantial progress is likely in the near future. This talk will focus on an identification of properties that are reasonably well known and those that merit further detailed study. In particular, both theoretical and experimental (static and shock wave) determinations of the density of iron under extreme conditions are in agreement at the 1% or better level. The behavior of the Gruneisen parameter (which determines the geothermal gradient and controls much of the outer core heat flux) is constrained by experiment and theory under core conditions for both solid and liquid phases. Recent experiments and theory are suggestive of structure or structures other than the high-pressure hexagonal close-packed (HCP) phase. Various theories and experiments for the elasticity of HCP iron remain in poor accord. Uncontroversial constraints on core chemistry will likely never be possible. However, reasonable bounds are possible on the basis of seismic profiles, geochemical arguments, and determinations of sound velocities and densities at high pressure and

  7. The Dense Gas in M82

    NASA Astrophysics Data System (ADS)

    Salas, P.; Galaz, G.; Salter, D.; Bolatto, A.; Herrera-Camus, R.

    2014-10-01

    Galactic winds are responsible of carrying energy and matter from the inner regions of galaxies to the outer regions, even reaching the intergalactic medium. This process removes gas from the inner regions, the available material to form stars. How and in which amount these winds remove gas from galaxies plays an important role in galaxy evolution. To study this effect we have obtained 3 mm maps of dense gas (n_{{crit}}>10^{4} cm^{-3}) in the central region of the starburst galaxy M82. We detect line emission from the dense molecular gas tracers HCN, HCO^{+}, HNC, CS, HC_{3}N and C_{6}H. Our maps reveal a considerable amount of HCO^{+} emission extending above and bellow the central star-forming disk, indicating that the dense gas is entangled in the outflow. The mass of molecular Hydrogen outside the central starburst is M_{{out}}≍ 3 ± 1× 10^{6} M_{odot}, while in the central starburst is M_{{disk}}≍ 8 ± 2× 10^{6} M_{odot}. These maps also show variations of the amount of dense gas over the starburst disk, revealing that the gas is more concentrated towards the center of the starburst and less towards the edges. It is the average amount of dense gas what drives the observed star formation law between dense gas and star formation rate on galactic scales.

  8. METHOD OF PRODUCING DENSE CONSOLIDATED METALLIC REGULUS

    DOEpatents

    Magel, T.T.

    1959-08-11

    A methcd is presented for reducing dense metal compositions while simultaneously separating impurities from the reduced dense metal and casting the reduced parified dense metal, such as uranium, into well consolidated metal ingots. The reduction is accomplished by heating the dense metallic salt in the presence of a reducing agent, such as an alkali metal or alkaline earth metal in a bomb type reacting chamber, while applying centrifugal force on the reacting materials. Separation of the metal from the impurities is accomplished essentially by the incorporation of a constricted passageway at the vertex of a conical reacting chamber which is in direct communication with a collecting chamber. When a centrifugal force is applled to the molten metal and slag from the reduction in a direction collinear with the axis of the constricted passage, the dense molten metal is forced therethrough while the less dense slag is retained within the reaction chamber, resulting in a simultaneous separation of the reduced molten metal from the slag and a compacting of the reduced metal in a homogeneous mass.

  9. FAINT LUMINESCENT RING OVER SATURN’S POLAR HEXAGON

    SciTech Connect

    Adriani, Alberto; D’Aversa, Emiliano; Oliva, Fabrizio; Filacchione, Gianrico; Moriconi, Maria Luisa

    2015-07-20

    Springtime insolation is presently advancing across Saturn's north polar region. Early solar radiation scattered through the gaseous giant's atmosphere gives a unique opportunity to sound the atmospheric structure at its upper troposphere/lower stratosphere at high latitudes. Here, we report the detection of a tenuous bright structure in Saturn's northern polar cap corresponding to the hexagon equatorward boundary, observed by Cassini Visual and Infrared Mapping Spectrometer on 2013 June. The structure is spectrally characterized by an anomalously enhanced intensity in the 3610–3730 nm wavelength range and near 2500 nm, pertaining to relatively low opacity windows between strong methane absorption bands. Our first results suggest that a strong forward scattering by tropospheric clouds, higher in respect to the surrounding cloud deck, can be responsible for the enhanced intensity of the feature. This can be consistent with the atmospheric dynamics associated with the jet stream embedded in the polar hexagon. Further investigations at higher spectral resolution are needed to better assess the vertical distribution and microphysics of the clouds in this interesting region.

  10. Vertical transport in graphene-hexagonal boron nitride heterostructure devices

    NASA Astrophysics Data System (ADS)

    Bruzzone, Samantha; Logoteta, Demetrio; Fiori, Gianluca; Iannaccone, Giuseppe

    2015-09-01

    Research in graphene-based electronics is recently focusing on devices based on vertical heterostructures of two-dimensional materials. Here we use density functional theory and multiscale simulations to investigate the tunneling properties of single- and double-barrier structures with graphene and few-layer hexagonal boron nitride (h-BN) or hexagonal boron carbon nitride (h-BC2N). We find that tunneling through a single barrier exhibit a weak dependence on energy. We also show that in double barriers separated by a graphene layer we do not observe resonant tunneling, but a significant increase of the tunneling probability with respect to a single barrier of thickness equal to the sum of the two barriers. This is due to the fact that the graphene layer acts as an effective phase randomizer, suppressing resonant tunneling and effectively letting a double-barrier structure behave as two single-barriers in series. Finally, we use multiscale simulations to reproduce a current-voltage characteristics resembling that of a resonant tunneling diode, that has been experimentally observed in single barrier structure. The peak current is obtained when there is perfect matching between the densities of states of the cathode and anode graphene regions.

  11. Vertical transport in graphene-hexagonal boron nitride heterostructure devices.

    PubMed

    Bruzzone, Samantha; Logoteta, Demetrio; Fiori, Gianluca; Iannaccone, Giuseppe

    2015-09-29

    Research in graphene-based electronics is recently focusing on devices based on vertical heterostructures of two-dimensional materials. Here we use density functional theory and multiscale simulations to investigate the tunneling properties of single- and double-barrier structures with graphene and few-layer hexagonal boron nitride (h-BN) or hexagonal boron carbon nitride (h-BC2N). We find that tunneling through a single barrier exhibit a weak dependence on energy. We also show that in double barriers separated by a graphene layer we do not observe resonant tunneling, but a significant increase of the tunneling probability with respect to a single barrier of thickness equal to the sum of the two barriers. This is due to the fact that the graphene layer acts as an effective phase randomizer, suppressing resonant tunneling and effectively letting a double-barrier structure behave as two single-barriers in series. Finally, we use multiscale simulations to reproduce a current-voltage characteristics resembling that of a resonant tunneling diode, that has been experimentally observed in single barrier structure. The peak current is obtained when there is perfect matching between the densities of states of the cathode and anode graphene regions.

  12. Vertical transport in graphene-hexagonal boron nitride heterostructure devices

    PubMed Central

    Bruzzone, Samantha; Logoteta, Demetrio; Fiori, Gianluca; Iannaccone, Giuseppe

    2015-01-01

    Research in graphene-based electronics is recently focusing on devices based on vertical heterostructures of two-dimensional materials. Here we use density functional theory and multiscale simulations to investigate the tunneling properties of single- and double-barrier structures with graphene and few-layer hexagonal boron nitride (h-BN) or hexagonal boron carbon nitride (h-BC2N). We find that tunneling through a single barrier exhibit a weak dependence on energy. We also show that in double barriers separated by a graphene layer we do not observe resonant tunneling, but a significant increase of the tunneling probability with respect to a single barrier of thickness equal to the sum of the two barriers. This is due to the fact that the graphene layer acts as an effective phase randomizer, suppressing resonant tunneling and effectively letting a double-barrier structure behave as two single-barriers in series. Finally, we use multiscale simulations to reproduce a current-voltage characteristics resembling that of a resonant tunneling diode, that has been experimentally observed in single barrier structure. The peak current is obtained when there is perfect matching between the densities of states of the cathode and anode graphene regions. PMID:26415656

  13. Spin-orbit coupling in a hexagonal ring of pendula

    NASA Astrophysics Data System (ADS)

    Salerno, Grazia; Berardo, Alice; Ozawa, Tomoki; Price, Hannah M.; Taxis, Ludovic; Pugno, Nicola M.; Carusotto, Iacopo

    2017-05-01

    We consider the mechanical motion of a system of six macroscopic pendula which are connected with springs and arranged in a hexagonal geometry. When the springs are pre-tensioned, the coupling between neighbouring pendula along the longitudinal (L) and the transverse (T) directions are different: identifying the motion along the L and T directions as the two components of a spin-like degree of freedom, we theoretically and experimentally verify that the pre-tensioned springs result in a tunable spin-orbit coupling. We elucidate the structure of such a spin-orbit coupling in the extended two-dimensional honeycomb lattice, making connections to physics of graphene. The experimental frequencies and the oscillation patterns of the eigenmodes for the hexagonal ring of pendula are extracted from a spectral analysis of the motion of the pendula in response to an external excitation and are found to be in good agreement with our theoretical predictions. We anticipate that extending this classical analogue of quantum mechanical spin-orbit coupling to two-dimensional lattices will lead to exciting new topological phenomena in classical mechanics.

  14. Band gap effects of hexagonal boron nitride using oxygen plasma

    SciTech Connect

    Sevak Singh, Ram; Leong Chow, Wai; Yingjie Tay, Roland; Hon Tsang, Siu; Mallick, Govind; Tong Teo, Edwin Hang

    2014-04-21

    Tuning of band gap of hexagonal boron nitride (h-BN) has been a challenging problem due to its inherent chemical stability and inertness. In this work, we report the changes in band gaps in a few layers of chemical vapor deposition processed as-grown h-BN using a simple oxygen plasma treatment. Optical absorption spectra show a trend of band gap narrowing monotonically from 6 eV of pristine h-BN to 4.31 eV when exposed to oxygen plasma for 12 s. The narrowing of band gap causes the reduction in electrical resistance by ∼100 fold. The x-ray photoelectron spectroscopy results of plasma treated hexagonal boron nitride surface show the predominant doping of oxygen for the nitrogen vacancy. Energy sub-band formations inside the band gap of h-BN, due to the incorporation of oxygen dopants, cause a red shift in absorption edge corresponding to the band gap narrowing.

  15. Carbon-assisted chemical vapor deposition of hexagonal boron nitride

    NASA Astrophysics Data System (ADS)

    Ismach, Ariel; Chou, Harry; Mende, Patrick; Dolocan, Andrei; Addou, Rafik; Aloni, Shaul; Wallace, Robert; Feenstra, Randall; Ruoff, Rodney S.; Colombo, Luigi

    2017-06-01

    We show that in a low-pressure chemical vapor deposition (CVD) system, the residual oxygen and/or air play a crucial role in the mechanism of the growth of hexagonal boron nitride (h-BN) films on Ni foil ‘enclosures’. Hexagonal-BN films grow on the Ni foil surface via the formation of an intermediate boric-oxide (BO x ) phase followed by a thermal reduction of the BO x by a carbon source (either amorphous carbon powder or methane), leading to the formation of single- and bi-layer h-BN. Low energy electron microscopy (LEEM) and diffraction (LEED) were used to map the number of layers over large areas; Raman spectroscopy, time-of-flight secondary ion mass spectrometry (ToF-SIMS), x-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM) were used to characterize the structure and physical quality of the ultra-thin h-BN film. The growth procedure reported here leads to a better understanding and control of the synthesis of ultra-thin h-BN films.

  16. Spatial anisotropy of topological domain structure in hexagonal manganites

    NASA Astrophysics Data System (ADS)

    Yang, K. L.; Zhang, Y.; Zheng, S. H.; Lin, L.; Yan, Z. B.; Liu, J.-M.; Cheong, S.-W.

    2017-01-01

    The domain structure of hexagonal manganites is simulated based on the phenomenological Ginzburg-Landau theory, and special attention is paid to the evolution of a topological vortex-antivortex pattern with the varying out-of-plane anisotropies of two stiffness parameters for the in-plane (x y -plane) trimerization amplitude Q and out-of-plane (z -axis) polarization P . It is revealed that the topological domain structure can be remarkably modulated by the stiffness anisotropies. A larger stiffness for Q along the z axis causes the trajectory lines of the vortex nodes and antivortex nodes to be seriously stretched along the z axis, eventually leading to the topological stripelike domain pattern. The larger stiffness for either Q or P along the z axis makes the domain walls perpendicular to the z axis wider, while the domain walls parallel to the z axis remain less affected. The present work suggests that the topological domain structure may be controlled by some approaches (e.g., lattice strain) which can change the trimerization stiffness and polarization stiffness in hexagonal manganites.

  17. DNA-Cationic Lipid Complexes: Lamellar and Inverted Hexagonal Phases

    NASA Astrophysics Data System (ADS)

    Koltover, I.; Salditt, T.; Raedler, J.; Safinya, C.

    1998-03-01

    Cationic lipid-DNA (CL-DNA) complexes can be efficient non-viral vectors for gene therapy. However, it is not known why transfection rates vary widely for complexes with different lipid compositions. We have discovered a transition between two distinct liquid crystalline (LC) structures of the complex by varying the lipid composition: a lamellar structure ( J. Raedler, I. Koltover, T. Salditt, C. Safinya, Science 275, 810 (1997)) and a novel LC phase with DNA double-strands surrounded by lipid monolayers arranged on a regular hexagonal lattice. The CL-DNA complexes with the two structures interact differently with giant negatively charged liposomes, which represent the simplest model of cellular membranes. We demonstrate the generality of the lamellar-hexagonal transformation by observing it in complexes of cationic lipid with two other negatively charged biopolymers - polyglutamic acid (PGA), a model polypeptide and poly-thymine (polyT), a model single-stranded oligo-nucleotide. We identify the interactions leading to the transformations between the two complex phases for the three different polyelectrolytes. Supported by NSF DMR-9624091 and a Los Alamos CULAR grant No.STB/UC:95-146.

  18. Silicene-type Surface Reconstruction on C40 Hexagonal Silicides

    NASA Astrophysics Data System (ADS)

    Volders, Cameron; Reinke, Petra

    Silicene has emerged as the next two-dimensional material possessing a Dirac type electronic structure making it a prime candidate for integration in electronic devices. The study of silicene is relatively new and many aspects have yet to be fully understood. Here we present a scanning tunneling microscopy (STM) study of a Silicene-type surface reconstruction observed on nanometer scale hexagonal-MoSi2 crystallites. This surface reconstruction is specific to the C40 structure of h-MoSi2 and can initially be defined as a geometric silicene while the coupling between the silicene surface and the silicide bulk is under investigation. The lateral dimensions correspond to a superstructure where the silicene hexagons are slightly buckled and two of the six Si atoms are visible in the STM images creating a honeycomb pattern. The local electronic structure of the silicene is currently being studied with ST spectroscopy and the impact of confinement will be addressed. These results open an alternative route to Silicene growth by using surface reconstructions on metallic and semiconducting C40 silicide structures, which is promising for direct device integration on Si-platforms.

  19. Application of genetic algorithm to hexagon-based motion estimation.

    PubMed

    Kung, Chih-Ming; Cheng, Wan-Shu; Jeng, Jyh-Horng

    2014-01-01

    With the improvement of science and technology, the development of the network, and the exploitation of the HDTV, the demands of audio and video become more and more important. Depending on the video coding technology would be the solution for achieving these requirements. Motion estimation, which removes the redundancy in video frames, plays an important role in the video coding. Therefore, many experts devote themselves to the issues. The existing fast algorithms rely on the assumption that the matching error decreases monotonically as the searched point moves closer to the global optimum. However, genetic algorithm is not fundamentally limited to this restriction. The character would help the proposed scheme to search the mean square error closer to the algorithm of full search than those fast algorithms. The aim of this paper is to propose a new technique which focuses on combing the hexagon-based search algorithm, which is faster than diamond search, and genetic algorithm. Experiments are performed to demonstrate the encoding speed and accuracy of hexagon-based search pattern method and proposed method.

  20. Proposal for generating synthetic magnetic fields in hexagonal optical lattices

    NASA Astrophysics Data System (ADS)

    Tian, Binbin; Endres, Manuel; Pekker, David

    2015-05-01

    We propose a new approach to generating synthetic magnetic fields in ultra cold atom systems that does not rely on either Raman transitions nor periodic drive. Instead, we consider a hexagonal optical lattice produced by the intersection of three laser beams at 120 degree angles, where the intensity of one or more of the beams is spatially non-uniform. The resulting optical lattice remains hexagonal, but has spatially varying hopping matrix elements. For atoms near the Dirac points, these spatial variations appear as a gauge field, similar to the fictitious gauge field that is induced for for electrons in strained graphene. We suggest that a robust way to generate a gauge field that corresponds to a uniform flux is to aligning three gaussian beams to intersect in an equilateral triangle. Using realistic experimental parameters, we show how the proposed setup can be used to observe cyclotron motion of an atom cloud - the conventional Hall effect and distinct Landau levels - the integer quantum Hall effect.

  1. Excitation of intense acoustic waves in hexagonal crystals

    SciTech Connect

    Alshits, V. I. Bessonov, D. A.; Lyubimov, V. N.

    2013-11-15

    Resonant excitation of an intense elastic wave using reflection of a pump wave from a free surface of hexagonal crystal is described. A resonance arises in the case of specially chosen propagation geometry where the reflecting boundary slightly deviates from symmetric orientation and the propagation direction of an intense reflected wave is close to that of an exceptional bulk wave, which satisfies the free boundary condition in unperturbed symmetric orientation. It is shown that, in crystals with elastic moduli c{sub 44}>c{sub 66}, a resonance arises when the initial boundary is chosen parallel to the hexagonal axis 6, whereas in crystals characterized by the relation c{sub 44}

  2. Tellurite microstructure fibers with small hexagonal core for supercontinuum generation.

    PubMed

    Liao, Meisong; Chaudhari, Chitrarekha; Qin, Guanshi; Yan, Xin; Suzuki, Takenobu; Ohishi, Yasutake

    2009-07-06

    Tellurite glass microstructure fibers with a 1 microm hexagonal core were fabricated successfully by accurately controlling the temperature field in the fiber-drawing process. The diameter ratio of holey region to core (DRHC) for the fiber can be adjusted freely in the range of 1-20 by pumping a positive pressure into the holes when drawing fiber, which provides much freedom in engineering the chromatic dispersion. With the increase of DRHC from 3.5 to 20, the zero dispersion wavelengths were shifted several hundred nanometers, the cutoff wavelength due to confinement loss was increased from 1600 nm to 3800 nm, and the nonlinear coefficient gamma was increased from 3.9 to 5.7 W(-1)/m. Efficient visible emissions due to third harmonic generation were found for fibers with a DRHC of 10 and 20 under the 1557 nm pump of a femtosecond fiber laser. One octave flattened supercontinuum spectrum was generated from fibers with a DRHC of 3.5, 10 and 20 by the 1064 nm pump of a picosecond fiber laser. To the best of our knowledge, we have for the first time fabricated a hexagonal core fiber by soft glass with such a small core size, and have demonstrated a large influence of the holey region on the dispersion, nonlinear coefficient and supercontinuum generation for such fiber.

  3. Unveiling subsurface hydrogen-bond structure of hexagonal water ice

    NASA Astrophysics Data System (ADS)

    Otsuki, Yuji; Sugimoto, Toshiki; Ishiyama, Tatsuya; Morita, Akihiro; Watanabe, Kazuya; Matsumoto, Yoshiyasu

    2017-09-01

    The phase-resolved sum-frequency-generation (SFG) spectrum for the basal face of hexagonal ice is reported and is interpreted by molecular dynamics simulations combined with ab initio quantum calculations. Here, we demonstrate that the line shape of the SFG spectra of isotope-diluted OH chromophores is a sensitive indicator of structural rumpling uniquely emerging at the subsurface of hexagonal ice. In the outermost subsurface between the first (B1) and second (B2) bilayer, the hydrogen bond of OB 1-H ⋯OB 2 is weaker than that of OB 1⋯H -OB 2 . This implies that subsurface O-O distance is laterally altered, depending on the direction of O-H bond along the surface normal: H-up or H-down, which is in stark contrast to bulk hydrogen bonds. This new finding uncovers how water molecules undercoordinated at the topmost surface influence on the subsurface structural rumpling associated with orientational frustration inherent in water ice.

  4. Application of Genetic Algorithm to Hexagon-Based Motion Estimation

    PubMed Central

    Cheng, Wan-Shu

    2014-01-01

    With the improvement of science and technology, the development of the network, and the exploitation of the HDTV, the demands of audio and video become more and more important. Depending on the video coding technology would be the solution for achieving these requirements. Motion estimation, which removes the redundancy in video frames, plays an important role in the video coding. Therefore, many experts devote themselves to the issues. The existing fast algorithms rely on the assumption that the matching error decreases monotonically as the searched point moves closer to the global optimum. However, genetic algorithm is not fundamentally limited to this restriction. The character would help the proposed scheme to search the mean square error closer to the algorithm of full search than those fast algorithms. The aim of this paper is to propose a new technique which focuses on combing the hexagon-based search algorithm, which is faster than diamond search, and genetic algorithm. Experiments are performed to demonstrate the encoding speed and accuracy of hexagon-based search pattern method and proposed method. PMID:24592178

  5. Asymptotic Analysis of Fiber-Reinforced Composites of Hexagonal Structure

    NASA Astrophysics Data System (ADS)

    Kalamkarov, Alexander L.; Andrianov, Igor V.; Pacheco, Pedro M. C. L.; Savi, Marcelo A.; Starushenko, Galina A.

    2016-08-01

    The fiber-reinforced composite materials with periodic cylindrical inclusions of a circular cross-section arranged in a hexagonal array are analyzed. The governing analytical relations of the thermal conductivity problem for such composites are obtained using the asymptotic homogenization method. The lubrication theory is applied for the asymptotic solution of the unit cell problems in the cases of inclusions of large and close to limit diameters, and for inclusions with high conductivity. The lubrication method is further generalized to the cases of finite values of the physical properties of inclusions, as well as for the cases of medium-sized inclusions. The analytical formulas for the effective coefficient of thermal conductivity of the fiber-reinforced composite materials of a hexagonal structure are derived in the cases of small conductivity of inclusions, as well as in the cases of extremely low conductivity of inclusions. The three-phase composite model (TPhM) is applied for solving the unit cell problems in the cases of the inclusions with small diameters, and the asymptotic analysis of the obtained solutions is performed for inclusions of small sizes. The obtained results are analyzed and illustrated graphically, and the limits of their applicability are evaluated. They are compared with the known numerical and asymptotic data in some particular cases, and very good agreement is demonstrated.

  6. Interplay between cubic and hexagonal phases in block copolymer solutions.

    PubMed

    Park, Moon Jeong; Char, Kookheon; Bang, Joona; Lodge, Timothy P

    2005-02-15

    The phase behavior of a symmetric styrene-isoprene (SI) diblock copolymer in a styrene-selective solvent, diethylphthalate, was investigated by in situ small-angle X-ray scattering on isotropic and shear-oriented solutions and by rheology and birefringence. A remarkable new feature in this phase diagram is the coexistence of both body-centered cubic (bcc) and hexagonally close-packed (hcp) sphere phases, in a region between close-packed spheres (cps) and hexagonally packed cylinders (hex) over the concentration range phi approximately 0.33-0.45. By focusing on the transitions among these various ordered phases during heating and cooling cycles, we observed a strong hysteresis: supercooled cylinders persisted upon cooling. The stability of these supercooled cylinders is quite dependent on concentration, and for phi > or = 0.40, the supercooled cylinders do not revert to spheres even after quiescent annealing for 1 month. The spontaneous formation of spheres due to the dissociation of cylinders is kinetically hindered in this case, and the system is apparently not amenable to any pretransitional fluctuations of cylinders prior to the cylinder-to-sphere transition. This contrasts with the case of cylinders transforming to spheres upon heating in the melt. The application of large amplitude shear to the supercooled cylinders is effective in restoring the equilibrium sphere phases.

  7. Strain-induced incommensurate phases in hexagonal manganites

    NASA Astrophysics Data System (ADS)

    Xue, Fei; Wang, Xueyun; Shi, Yin; Cheong, Sang-Wook; Chen, Long-Qing

    2017-09-01

    An incommensurate phase refers to a solid state in which the period of a superstructure is incommensurable with its primitive unit cell. It was recently shown that an incommensurate phase, which displays a single chiral modulation of six domain variants, could be induced by applying an in-plane strain to a hexagonal manganite. Here we combine Landau theory description of thermodynamics and the phase-field method to investigate and understand the formation of the incommensurate phase in hexagonal manganites. It is shown that the equilibrium wavelength of the incommensurate phase is determined by both the temperature and the magnitude of the applied strain, and a temperature-strain phase diagram is constructed for graphically displaying the temperature and strain conditions for the stability of the incommensurate phase. Temporal evolution of domain structures reveals that the applied strain not only produces the force pulling the vortices and antivortices in opposite directions, but also results in the creation and annihilation of vortex-antivortex pairs.

  8. Thermal stability of hexagonal OsB{sub 2}

    SciTech Connect

    Xie, Zhilin; Blair, Richard G.; Orlovskaya, Nina; Cullen, David A.; Andrew Payzant, E.

    2014-11-15

    The synthesis of novel hexagonal ReB{sub 2}-type OsB{sub 2} ceramic powder was performed by high energy ball milling of elemental Os and B powders. Two different sources of B powder have been used for this mechanochemical synthesis. One B powder consisted of a mixture of amorphous and crystalline phases and a mixture of {sup 10}B and {sup 11}B isotopes with a fine particle size, while another B powder was a purely crystalline (rhombohedral) material consisting of enriched {sup 11}B isotope with coarse particle size. The same Os powder was used for the synthesis in both cases. It was established that, in the first case, the hexagonal OsB{sub 2} phase was the main product of synthesis with a small quantity of Os{sub 2}B{sub 3} phase present after synthesis as an intermediate product. In the second case, where coarse crystalline {sup 11}B powder was used as a raw material, only Os{sub 2}B{sub 3} boride was synthesized mechanochemically. The thermal stability of hexagonal OsB{sub 2} powder was studied by heating under argon up to 876 °C and cooling in vacuo down to −225 °C. During the heating, the sacrificial reaction 2OsB{sub 2}+3O{sub 2}→2Os+2B{sub 2}O{sub 3} took place due to presence of O{sub 2}/water vapor molecules in the heating chamber, resulting in the oxidation of B atoms and formation of B{sub 2}O{sub 3} and precipitation of Os metal out of the OsB{sub 2} lattice. As a result of such phase changes during heating, the lattice parameters of hexagonal OsB{sub 2} changed significantly. The shrinkage of the a lattice parameter was recorded in 276–426 °C temperature range upon heating, which was attributed to the removal of B atoms from the OsB{sub 2} lattice due to oxidation followed by the precipitation of Os atoms and formation of Os metal. While significant structural changes occurred upon heating due to presence of O{sub 2}, the hexagonal OsB{sub 2} ceramic demonstrated good phase stability upon cooling in vacuo with linear shrinkage of the lattice

  9. High-pressure chemistry of hydrogen in metals: in situ study of iron hydride.

    PubMed

    Badding, J V; Hemley, R J; Mao, H K

    1991-07-26

    Optical observations and x-ray diffraction measurements of the reaction between iron and hydrogen at high pressure to form iron hydride are described. The reaction is associated with a sudden pressure-induced expansion at 3.5 gigapascals of iron samples immersed in fluid hydrogen. Synchrotron x-ray diffraction measurements carried out to 62 gigapascals demonstrate that iron hydride has a double hexagonal close-packed structure, a cell volume up to 17% larger than pure iron, and a stoichiometry close to FeH. These results greatly extend the pressure range over which the technologically important iron-hydrogen phase diagram has been characterized and have implications for problems ranging from hydrogen degradation and embrittlement of ferrous metals to the presence of hydrogen in Earth's metallic core.

  10. Modeling of hydrogen-assisted cracking in iron crystal using a quasi-Newton method.

    PubMed

    Telitchev, Igor Ye; Vinogradov, Oleg

    2008-07-01

    A Quasi-Newton method was applied in the context of a molecular statics approach to simulate the phenomenon of hydrogen embrittlement of an iron lattice. The atomic system is treated as a truss-type structure. The interatomic forces between the hydrogen-iron and the iron-iron atoms are defined by Morse and modified Morse potential functions, respectively. Two-dimensional hexagonal and 3D bcc crystal structures were subjected to tensile numerical tests. It was shown that the Inverse Broyden's Algorithm-a quasi-Newton method-provides a computationally efficient technique for modeling of the hydrogen-assisted cracking in iron crystal. Simulation results demonstrate that atoms of hydrogen placed near the crack tip produce a strong deformation and crack propagation effect in iron lattice, leading to a decrease in the residual strength of numerically tested samples.

  11. Evolution of Dense Gas with Starburst Age: When Star Formation Versus Dense Gas Relations Break Down

    NASA Astrophysics Data System (ADS)

    Meier, David S.; Turner, J. L.; Schinnerer, E.

    2011-05-01

    Dense gas correlates well with star formation on kpc scales. On smaller scales, motions of individual clouds become comparable to the 100 Myr ages of starbursts. One then expects the star formation rate vs. dense gas relations to break down on giant molecular cloud scales. We exploit this to study the evolutionary history of nuclear starburst in the nearby spiral, IC 342. Maps of the J=5-4 and 16-15 transitions of dense gas tracer HC3N at 20 pc resolution made with the VLA and the Plateau de Bure interferometer are presented. The 5-4 line of HC3N traces very dense gas in the cold phase, while the 16-15 transition traces warm, dense gas. These reveal changes in dense cloud structure on scales of 30 pc among clouds with star formation histories differing by only a few Myrs. HC3N emission does not correlate well with young star formation at these high spatial resolutions, but gas excitation does. The cold, dense gas extends well beyond the starburst region implying large amounts of dense quiescent gas not yet actively forming stars. Close to the starburst the high excitation combined with faint emission indicates that the immediate (30 pc) vicinity of the starburst lacks large masses of very dense gas and has high dense gas star formation efficiencies. The dense gas appears to be in pressure equilibrium with the starburst. We propose a scenario where the starburst is being caught in the act of dispersing or destroying the dense gas in the presence of the expanding HII region. This work is supported by the NSF through NRAO and grant AST-1009620.

  12. Dynamics of the shock-induced transition from graphite to warm dense diamond and liquid carbon

    NASA Astrophysics Data System (ADS)

    Kraus, D.; Barbrel, B.; Frydrych, S.; Helfrich, J.; Schaumann, G.; Vorberger, J.; Gericke, D. O.; Fletcher, L. B.; Gauthier, M.; Goede, S.; Granados, E.; Lee, H. J.; Nagler, B.; Gamboa, E.; Ravasio, A.; Schumaker, W.; Doeppner, T.; Bachmann, B.; Neumayer, P.; Gregori, G.; Roth, M.; Glenzer, S. H.; Falcone, R. W.

    2015-03-01

    We present novel experimental observations of the ion structure in warm dense carbon at pressures from 20 to 220 GPa and temperatures of several thousand Kelvins. Our experiments employ x-ray sources at kilo-joule class laser facilities and at the Linac Coherent Light Source to perform spectrally and angularly resolved x-ray scattering from shock-compressed graphite samples. Using different types of graphite and varying drive laser intensity, we were able to probe conditions below and above the melting line, resolving the shock-induced graphite-to-diamond and graphite-to-liquid transitions on nanosecond time scale. Moreover, we have observed the dynamic formation of hexagonal diamond by shock-compression of highly oriented graphite samples. This work was supported SSAA program Contract No. DEFG52- 06NA26212.

  13. Iron-refractory iron deficiency anemia (IRIDA).

    PubMed

    Heeney, Matthew M; Finberg, Karin E

    2014-08-01

    Iron deficiency anemia is a common global problem whose etiology is typically attributed to acquired inadequate dietary intake and/or chronic blood loss. However, in several kindreds multiple family members are affected with iron deficiency anemia that is unresponsive to oral iron supplementation and only partially responsive to parenteral iron therapy. The discovery that many of these cases harbor mutations in the TMPRSS6 gene led to the recognition that they represent a single clinical entity: iron-refractory iron deficiency anemia (IRIDA). This article reviews clinical features of IRIDA, recent genetic studies, and insights this disorder provides into the regulation of systemic iron homeostasis.

  14. EXAFS measurement of iron bcc-to-hcp phase transformation in nanosecond-laser shocks.

    PubMed

    Yaakobi, B; Boehly, T R; Meyerhofer, D D; Collins, T J B; Remington, B A; Allen, P G; Pollaine, S M; Lorenzana, H E; Eggert, J H

    2005-08-12

    Extended x-ray absorption fine structure (EXAFS) measurements have demonstrated the phase transformation from body-centered-cubic (bcc) to hexagonal-close-packed (hcp) iron due to nanosecond, laser-generated shocks. The EXAFS spectra are also used to determine the compression and temperature in the shocked iron, which are consistent with hydrodynamic simulations and with the compression inferred from velocity interferometry. This is a direct, atomic-level, and in situ proof of shock-induced transformation in iron, as opposed to the previous indirect proof based on shock-wave splitting.

  15. Preparation of hexagonal WO{sub 3} from hexagonal ammonium tungsten bronze for sensing NH{sub 3}

    SciTech Connect

    Szilagyi, Imre Miklos Wang Lisheng; Gouma, Pelagia-Irene; Balazsi, Csaba; Madarasz, Janos; Pokol, Gyoergy

    2009-03-05

    Hexagonal tungsten oxide (h-WO{sub 3}) was prepared by annealing hexagonal ammonium tungsten bronze, (NH{sub 4}){sub 0.07}(NH{sub 3}){sub 0.04}(H{sub 2}O){sub 0.09}WO{sub 2.95}. The structure, composition and morphology of h-WO{sub 3} were studied by XRD, XPS, Raman, {sup 1}H MAS (magic angle spinning) NMR, scanning electron microscopy (SEM), and BET-N{sub 2} specific surface area measurement, while its thermal stability was investigated by in situ XRD. The h-WO{sub 3} sample was built up by 50-100 nm particles, had an average specific surface area of 8.3 m{sup 2}/g and was thermally stable up to 450 deg. C. Gas sensing tests showed that h-WO{sub 3} was sensitive to various levels (10-50 ppm) of NH{sub 3}, with the shortest response and recovery times (1.3 and 3.8 min, respectively) to 50 ppm NH{sub 3}. To this NH{sub 3} concentration, the sensor had significantly higher sensitivity than h-WO{sub 3} samples prepared by wet chemical methods.

  16. Defect properties of cobalt-doped hexagonal barium titanate ceramics

    NASA Astrophysics Data System (ADS)

    Langhammer, H. T.; Böttcher, R.; Müller, T.; Walther, T.; Ebbinghaus, S. G.

    2015-07-01

    X-ray diffraction (XRD) patterns, electron paramagnetic resonance (EPR) powder spectra (9 and 34 GHz) and the magnetic susceptibility of BaTiO3 + 0.04 BaO + x/2 Co2O3 (0.001 ⩽ x ⩽ 0.02) ceramics were studied to investigate the incorporation of Co ions in the BaTiO3 lattice and their valence states as well as the development of the hexagonal phase (6H modification) in dependence on doping level x and sintering temperature Ts. At Ts = 1400 °C the 6H modification begins to occur at a nominal Co concentration x of about 0.001 and for x > 0.005 the samples are completely hexagonal at room temperature. Two different EPR spectra were observed in the 6H modification of BaTiO3, which were both assigned to paramagnetic Co2+ ions located at the two crystallographically non-equivalent Ti sites in 6H-BaTiO3. The EPR g tensor values as well as the molar paramagnetic susceptibility, measured in the temperature range 5 K-300 K at a magnetic field of 9 T, were analyzed in the framework of the ligand field theory using the program CONCORD. The combination of EPR and magnetic measurements reveals that in air-sintered 6H BaTiO3, the incorporated Co occurs as a mixture of paramagnetic Co2+ and diamagnetic Co3+ ions, whereas in samples annealed in reducing atmosphere the majority of Co is in the divalent state. The occurrence of Co4+ can be excluded for all investigated samples. The sample color caused by Co2+ and Co3+ ions is beige/light yellow and dark grey/black, respectively. The majority of the Co2+ ions substitutes Ti in the exclusively corner-sharing oxygen octahedra possessing nearly cubic symmetry. The corresponding ligand field parameter B04(3) amounts to about -28 000 cm-1 (Wybourne notation, 10Dq ≈ 20 000 cm-1). In the reduced samples nearly 5% of the detected Co2+ ions occupy the Ti site in the face-sharing oxygen octahedra, which are significantly trigonally distorted. The negative sign of the obtained ligand field parameter B02 ≈ -7300 cm-1

  17. HEXPANDO Expanding Head for Fastener-Retention Hexagonal Wrench

    NASA Technical Reports Server (NTRS)

    Bishop, John

    2011-01-01

    The HEXPANDO is an expanding-head hexagonal wrench designed to retain fasteners and keep them from being dislodged from the tool. The tool is intended to remove or install socket-head cap screws (SHCSs) in remote, hard-to-reach locations or in circumstances when a dropped fastener could cause damage to delicate or sensitive hardware. It is not intended for application of torque. This tool is made of two assembled portions. The first portion of the tool comprises tubing, or a hollow shaft, at a length that gives the user adequate reach to the intended location. At one end of the tubing is the expanding hexagonal head fitting with six radial slits cut into it (one at each of the points of the hexagonal shape), and a small hole drilled axially through the center and the end opposite the hex is internally and externally threaded. This fitting is threaded into the shaft (via external threads) and staked or bonded so that it will not loosen. At the other end of the tubing is a knurled collar with a through hole into which the tubing is threaded. This knob is secured in place by a stop nut. The second assembled portion of the tool comprises a length of all thread or solid rod that is slightly longer than the steel tubing. One end has a slightly larger knurled collar affixed while the other end is tapered/pointed and threaded. When the two portions are assembled, the all thread/rod portion feeds through the tubing and is threaded into the expanding hex head fitting. The tapered point allows it to be driven into the through hole of the hex fitting. While holding the smaller collar on the shaft, the user turns the larger collar, and as the threads feed into the fitting, the hex head expands and grips the SHCS, thus providing a safe way to install and remove fasteners. The clamping force retaining the SHCS varies depending on how far the tapered end is inserted into the tool head. Initial tests of the prototype tool, designed for a 5 mm or # 10SHCS have resulted in up to 8 lb

  18. Iron and Fe-Ni alloy coatings containing ɛ-Fe produced by non-stationary deposition method

    NASA Astrophysics Data System (ADS)

    Smirnova, Natalya; Zhikhareva, Irina; Schmidt, Vadim; Vorobyev, Oleg

    2016-09-01

    A novel material, an electrolytic coating of iron and Fe-Ni alloy containing ɛ-Fe hexagonal close-packed phase (HCP) was obtained using the method of high-frequency alternating current at atmospheric pressure. This transition occurs according to the orientational mechanism by removing weak extreme iron atoms in the crystal lattice of α-Fe due to anodic dissolution and action of the electromagnetic waves loosening the valence bonds.

  19. Strong 3D and 1D magnetism in hexagonal Fe-chalcogenides FeS and FeSe vs. weak magnetism in hexagonal FeTe.

    PubMed

    Parker, David S

    2017-06-13

    We present a comparative theoretical study of the hexagonal forms of the Fe-chalcogenides FeS, FeSe and FeTe with their better known tetragonal forms. While the tetragonal forms exhibit only an incipient antiferromagnetism and experimentally show superconductivity when doped, the hexagonal forms of FeS and FeSe display a robust magnetism. We show that this strong magnetism arises from a van Hove singularity associated with the direct Fe-Fe c-axis chains in the generally more three-dimensional NiAs structure. We also find that hexagonal FeTe is much less magnetic than the other two hexagonal materials, so that unconventional magnetically-mediated superconductivity is possible, although a large T c value is unlikely.

  20. Strong 3D and 1D magnetism in hexagonal Fe-chalcogenides FeS and FeSe vs. weak magnetism in hexagonal FeTe

    DOE PAGES

    Parker, David S.

    2017-06-13

    We present a comparative theoretical study of the hexagonal forms of the Fe-chalcogenides FeS, FeSe and FeTe with their better known tetragonal forms. While the tetragonal forms exhibit only an incipient antiferromagnetism and experimentally show superconductivity when doped, the hexagonal forms of FeS and FeSe display a robust magnetism. We show that this strong magnetism arises from a van Hove singularity associated with the direct Fe-Fe c-axis chains in the generally more three-dimensional NiAs structure. We also find that hexagonal FeTe is much less magnetic than the other two hexagonal materials, so that unconventional magnetically-mediated superconductivity is possible, although amore » large Tc value is unlikely.« less

  1. Metallurgy Beyond Iron

    NASA Astrophysics Data System (ADS)

    Gallino, Isabella; Busch, Ralf

    2009-08-01

    Metallurgy is one of the oldest sciences. Its history can be traced back to 6000 BCE with the discovery of Gold, and each new discovery - Copper, Silver, Lead, Tin, Iron and Mercury - marked the beginning of a new era of civilization. Currently there are 86 known metals, but until the end of the 17th century, only 12 of these were known. Steel (Fe-C alloy) was discovered in the 11th century BCE; however, it took until 1709 CE before we mastered the smelting of pig-iron by using coke instead of charcoal and started the industrial revolution. The metallurgy of nowadays is mainly about discovering better materials with superior properties to fulfil the increasing demand of the global market. Promising are the Glassy Metals or Bulk Metallic Glasses (BMGs) - discovered at first in the late 50s at the California Institute of Technology - which are several times stronger than the best industrial steels and 10-times springier. The unusual structure that lacks crystalline grains makes BMGs so promising. They have a liquid-like structure that means they melt at lower temperatures, can be moulded nearly as easily as plastics, and can be shaped into features just 10 nm across. The best BMG formers are based on Zr, Pd, Pt, Ca, Au and, recently discovered, also Fe. They have typically three to five components with large atomic size mismatch and a composition close to a deep eutectic. Packing in such liquids is very dense, with a low content of free volume, resulting in viscosities that are several orders of magnitude higher than in pure metal melts.

  2. Transdermal iron replenishment therapy.

    PubMed

    Modepalli, Naresh; Shivakumar, H N; Kanni, K L Paranjothy; Murthy, S Narasimha

    2015-01-01

    Iron deficiency anemia is one of the major nutritional deficiency disorders. Iron deficiency anemia occurs due to decreased absorption of iron from diet, chronic blood loss and other associated diseases. The importance of iron and deleterious effects of iron deficiency anemia are discussed briefly in this review followed by the transdermal approaches to deliver iron. Transdermal delivery of iron would be able to overcome the side effects associated with conventional oral and parenteral iron therapy and improves the patient compliance. During preliminary investigations, ferric pyrophosphate and iron dextran were selected as iron sources for transdermal delivery. Different biophysical techniques were explored to assess their efficiency in delivering iron across the skin, and in vivo studies were carried out using anemic rat model. Transdermal iron delivery is a promising approach that could make a huge positive impact on patients suffering with iron deficiency.

  3. [Iron dysregulation and anemias].

    PubMed

    Ikuta, Katsuya

    2015-10-01

    Most iron in the body is utilized as a component of hemoglobin that delivers oxygen to the entire body. Under normal conditions, the iron balance is tightly regulated. However, iron dysregulation does occasionally occur; total iron content reductions cause iron deficiency anemia and overexpression of the iron regulatory peptide hepcidin disturbs iron utilization resulting in anemia of chronic disease. Conversely, the presence of anemia may ultimately lead to iron overload; for example, thalassemia, a common hereditary anemia worldwide, often requires transfusion, but long-term transfusions cause iron accumulation that leads to organ damage and other poor outcomes. On the other hand, there is a possibility that iron overload itself can cause anemia; iron chelation therapy for the post-transfusion iron overload observed in myelodysplastic syndrome or aplastic anemia improves dependency on transfusions in some cases. These observations reflect the extremely close relationship between anemias and iron metabolism.

  4. Pharmacology of Iron Transport

    PubMed Central

    Byrne, Shaina L.; Krishnamurthy, Divya; Wessling-Resnick, Marianne

    2013-01-01

    Elucidating the molecular basis for the regulation of iron uptake, storage, and distribution is necessary to understand iron homeostasis. Pharmacological tools are emerging to identify and distinguish among different iron transport pathways. Stimulatory or inhibitory small molecules with effects on iron uptake can help characterize the mechanistic elements of iron transport and the roles of the transporters involved in these processes. In particular, iron chelators can serve as potential pharmacological tools to alleviate diseases of iron overload. This review focuses on the pharmacology of iron transport, introducing iron transport membrane proteins and known inhibitors. PMID:23020294

  5. Pharmacology of iron transport.

    PubMed

    Byrne, Shaina L; Krishnamurthy, Divya; Wessling-Resnick, Marianne

    2013-01-01

    Elucidating the molecular basis for the regulation of iron uptake, storage, and distribution is necessary to understand iron homeostasis. Pharmacological tools are emerging to identify and distinguish among different iron transport pathways. Stimulatory or inhibitory small molecules with effects on iron uptake can help characterize the mechanistic elements of iron transport and the roles of the transporters involved in these processes. In particular, iron chelators can serve as potential pharmacological tools to alleviate diseases of iron overload. This review focuses on the pharmacology of iron transport, introducing iron transport membrane proteins and known inhibitors.

  6. High-entropy alloys in hexagonal close-packed structure

    DOE PAGES

    Gao, Michael C.; Zhang, B.; Guo, S. M.; ...

    2015-08-28

    The microstructures and properties of high-entropy alloys (HEAs) based on the face-centered cubic and body-centered cubic structures have been studied extensively in the literature, but reports on HEAs in the hexagonal close-packed (HCP) structure are very limited. Using an efficient strategy in combining phase diagram inspection, CALPHAD modeling, and ab initio molecular dynamics simulations, a variety of new compositions are suggested that may hold great potentials in forming single-phase HCP HEAs that comprise rare earth elements and transition metals, respectively. Lastly, experimental verification was carried out on CoFeReRu and CoReRuV using X-ray diffraction, scanning electron microscopy, and energy dispersion spectroscopy.

  7. Hydroxyapatite: Vibrational spectra and monoclinic to hexagonal phase transition

    NASA Astrophysics Data System (ADS)

    Slepko, Alexander; Demkov, Alexander A.

    2015-02-01

    Fundamental studies of biomaterials are necessary to deepen our understanding of their degradation and to develop cure for related illnesses. Biomineral hydroxyapatite Ca10(PO4)6(OH)2 is the main mineral constituent of mammal bone, and its synthetic analogues are used in biomedical applications. The mineral can be found in either hexagonal or monoclinic form. The transformation between these two phases is poorly understood, but knowing its mechanism may be critical to reversing processes in bone related to aging. Using density functional theory, we investigate the mechanisms of the phase transformation and estimate the transition temperature to be 680 K in fair agreement with the experimental temperature of 470 K. We also report the heat capacity of hydroxyapatite and a peculiarity in its phonon dispersion that might allow for non-destructive measurements of the crystal composition with applications in preventive medical screening for bone mineral loss.

  8. Hexagonal photonic crystal waveguide based on barium titanate thin films

    NASA Astrophysics Data System (ADS)

    Li, Jianheng; Liu, Zhifu; Wessels, Bruce W.; Tu, Yongming; Ho, Seng-Tiong; Joshi-Imre, Alexandra; Ocola, Leonidas E.

    2011-03-01

    The simulation, fabrication and measurement of nonlinear photonic crystals (PhCs) with hexagonal symmetry in epitaxial BaTiO3 were investigated. The optical transmission properties of a PhC were simulated by a 2-D finite-difference time domain (FDTD) method. A complete bandgap exists for both the TE and TM optical modes. The fabricated PhC has a well-defined stop band over the spectral region of 1525 to 1575 nm. A microcavity structure was also fabricated by incorporation of a line defect in the PhC. Transmission of the microcavity structure over the spectral region from 1456 to 1584nm shows a well-defined 5 nm wide window at 1495nm. Simulations indicate that the phase velocity matched PhC microcavity device of 0.5 mm long can potentially serve as modulator with a 3 dB bandwidth of 4 THz.

  9. Atomic scale modelling of hexagonal structured metallic fission product alloys

    PubMed Central

    Middleburgh, S. C.; King, D. M.; Lumpkin, G. R.

    2015-01-01

    Noble metal particles in the Mo-Pd-Rh-Ru-Tc system have been simulated on the atomic scale using density functional theory techniques for the first time. The composition and behaviour of the epsilon phases are consistent with high-entropy alloys (or multi-principal component alloys)—making the epsilon phase the only hexagonally close packed high-entropy alloy currently described. Configurational entropy effects were considered to predict the stability of the alloys with increasing temperatures. The variation of Mo content was modelled to understand the change in alloy structure and behaviour with fuel burnup (Mo molar content decreases in these alloys as burnup increases). The predicted structures compare extremely well with experimentally ascertained values. Vacancy formation energies and the behaviour of extrinsic defects (including iodine and xenon) in the epsilon phase were also investigated to further understand the impact that the metallic precipitates have on fuel performance. PMID:26064629

  10. Atomic scale modelling of hexagonal structured metallic fission product alloys.

    PubMed

    Middleburgh, S C; King, D M; Lumpkin, G R

    2015-04-01

    Noble metal particles in the Mo-Pd-Rh-Ru-Tc system have been simulated on the atomic scale using density functional theory techniques for the first time. The composition and behaviour of the epsilon phases are consistent with high-entropy alloys (or multi-principal component alloys)-making the epsilon phase the only hexagonally close packed high-entropy alloy currently described. Configurational entropy effects were considered to predict the stability of the alloys with increasing temperatures. The variation of Mo content was modelled to understand the change in alloy structure and behaviour with fuel burnup (Mo molar content decreases in these alloys as burnup increases). The predicted structures compare extremely well with experimentally ascertained values. Vacancy formation energies and the behaviour of extrinsic defects (including iodine and xenon) in the epsilon phase were also investigated to further understand the impact that the metallic precipitates have on fuel performance.

  11. Understanding thermal transport in asymmetric layer hexagonal boron nitride heterostructure

    NASA Astrophysics Data System (ADS)

    Zhang, Jingchao; Wang, Xinyu; Hong, Yang; Xiong, Qingang; Jiang, Jin; Yue, Yanan

    2017-01-01

    In this work, thermal transport at the junction of an asymmetric layer hexagonal boron-nitride (h-BN) heterostructure is explored using a non-equilibrium molecular dynamics method. A thermal contact resistance of 3.6 × 10-11 K · m2 W-1 is characterized at a temperature of 300 K with heat flux from the trilayer to monolayer regions. The mismatch in the flexural phonon modes revealed by power spectra analysis provides the driving force for the calculated thermal resistance. A high thermal rectification efficiency of 360% is calculated at the layer junction surpassing that of graphene. Several modulators, i.e. the system temperature, contact pressure and lateral dimensions, are applied to manipulate the thermal conductance and rectification across the interfaces. The predicted thermal rectification sustains positive correlations with temperature and phonon propagation lengths with little change to the coupling strength.

  12. Functionalised hexagonal-domain graphene for position-sensitive photodetectors

    NASA Astrophysics Data System (ADS)

    De Sanctis, Adolfo; Barnes, Matthew D.; Amit, Iddo; Craciun, Monica F.; Russo, Saverio

    2017-03-01

    Graphene’s unique photoresponse has been largely used in a multitude of optoelectronics applications ranging from broadband photodetectors to wave-guide modulators. In this work we extend the range of applications to position-sensitive photodetectors (PSDs) using FeCl3-intercalated hexagonal domains of graphene grown by atmospheric pressure chemical vapour deposition (APCVD). The FeCl3-based chemical functionalisation of APCVD graphene crystals is affected by the presence of wrinkles and results in a non-uniform doping of the graphene layers. This doping profile creates multiple p-p+ photoactive junctions which show a linear and bipolar photoresponse with respect to the position of a focused light spot, which is ideal for the realization of a PSD. Our study paves the way towards the fabrication of flexible and transparent PSDs that could be embedded in smart textile and wearable electronics.

  13. Functionalised hexagonal-domain graphene for position-sensitive photodetectors.

    PubMed

    De Sanctis, Adolfo; Barnes, Matthew D; Amit, Iddo; Craciun, Monica F; Russo, Saverio

    2017-03-24

    Graphene's unique photoresponse has been largely used in a multitude of optoelectronics applications ranging from broadband photodetectors to wave-guide modulators. In this work we extend the range of applications to position-sensitive photodetectors (PSDs) using FeCl3-intercalated hexagonal domains of graphene grown by atmospheric pressure chemical vapour deposition (APCVD). The FeCl3-based chemical functionalisation of APCVD graphene crystals is affected by the presence of wrinkles and results in a non-uniform doping of the graphene layers. This doping profile creates multiple p-p(+) photoactive junctions which show a linear and bipolar photoresponse with respect to the position of a focused light spot, which is ideal for the realization of a PSD. Our study paves the way towards the fabrication of flexible and transparent PSDs that could be embedded in smart textile and wearable electronics.

  14. Activated chemoreceptor arrays remain intact and hexagonally packed

    PubMed Central

    Briegel, Ariane; Beeby, Morgan; Thanbichler, Martin; Jensen, Grant J.

    2013-01-01

    Summary Bacterial chemoreceptors cluster into exquisitively sensitive, tunable, highly ordered, polar arrays. While these arrays serve as paradigms of cell signalling in general, it remains unclear what conformational changes transduce signals from the periplasmic tips, where attractants and repellents bind, to the cytoplasmic signalling domains. Conflicting reports support and contest the hypothesis that activation causes large changes in the packing arrangement of the arrays, up to and including their complete disassembly. Using electron cryotomography, here we show that in Caulobacter crescentus, chemoreceptor arrays in cells grown in different media and immediately after exposure to the attractant galactose all exhibit the same 12 nm hexagonal packing arrangement, array size and other structural parameters. ΔcheB and ΔcheR mutants mimicking attractant- or repellent-bound states prior to adaptation also show the same lattice structure. We conclude that signal transduction and amplification must be accomplished through only small, nanoscale conformational changes. PMID:21992450

  15. Columnar epitaxy of hexagonal and orthorhombic silicides on Si(111)

    NASA Technical Reports Server (NTRS)

    Fathauer, R. W.; Nieh, C. W.; Xiao, Q. F.; Hashimoto, Shin

    1990-01-01

    Columnar grains of PtSi and CrSi2 surrounded by high-quality epitaxial silicon are obtained by ultrahigh vacuum codeposition of Si and metal in an approximately 10:1 ratio on Si(111) substrates heated to 610-840 C. This result is similar to that found previously for CoSi2 (a nearly-lattice-matched cubic-fluorite crystal) on Si(111), in spite of the respective orthorhombic and hexagonal structures of PtSi and CrSi2. The PtSi grains are epitaxial and have one of three variants of the relation defined by PtSi(010)/Si(111), with PtSi 001 line/Si 110 line type.

  16. Dislocation dynamics in hexagonal close-packed crystals

    DOE PAGES

    Aubry, S.; Rhee, M.; Hommes, G.; ...

    2016-04-14

    Extensions of the dislocation dynamics methodology necessary to enable accurate simulations of crystal plasticity in hexagonal close-packed (HCP) metals are presented. They concern the introduction of dislocation motion in HCP crystals through linear and non-linear mobility laws, as well as the treatment of composite dislocation physics. Formation, stability and dissociation of and other dislocations with large Burgers vectors defined as composite dislocations are examined and a new topological operation is proposed to enable their dissociation. Furthermore, the results of our simulations suggest that composite dislocations are omnipresent and may play important roles both in specific dislocation mechanisms and in bulkmore » crystal plasticity in HCP materials. While fully microscopic, our bulk DD simulations provide wealth of data that can be used to develop and parameterize constitutive models of crystal plasticity at the mesoscale.« less

  17. Hexagonal boron nitride epitaxial layers as neutron detector materials

    NASA Astrophysics Data System (ADS)

    Li, J.; Dahal, R.; Majety, S.; Lin, J. Y.; Jiang, H. X.

    2011-10-01

    Micro-strip metal-semiconductor-metal detectors for thermal neutron sensing were fabricated from hexagonal boron nitride (hBN) epilayers synthesized by metal organic chemical vapor deposition. Experimental measurements indicated that the thermal neutron absorption coefficient and length of natural hBN epilayers are about 0.00361 μm -1 and 277 μm, respectively. A continuous irradiation with a thermal neutron beam generated an appreciable current response in hBN detectors, corresponding to an effective conversion efficiency approaching ˜80% for absorbed neutrons. Our results indicate that hBN semiconductors would enable the development of essentially ideal solid-state thermal neutron detectors in which both neutron capture and carrier collection are accomplished in the same hBN semiconductor. These solid-state detectors have the potential to replace 3He gas detectors, which faces the very serious issue of 3He gas shortage.

  18. Modelling heat conduction in polycrystalline hexagonal boron-nitride films.

    PubMed

    Mortazavi, Bohayra; Pereira, Luiz Felipe C; Jiang, Jin-Wu; Rabczuk, Timon

    2015-08-19

    We conducted extensive molecular dynamics simulations to investigate the thermal conductivity of polycrystalline hexagonal boron-nitride (h-BN) films. To this aim, we constructed large atomistic models of polycrystalline h-BN sheets with random and uniform grain configuration. By performing equilibrium molecular dynamics (EMD) simulations, we investigated the influence of the average grain size on the thermal conductivity of polycrystalline h-BN films at various temperatures. Using the EMD results, we constructed finite element models of polycrystalline h-BN sheets to probe the thermal conductivity of samples with larger grain sizes. Our multiscale investigations not only provide a general viewpoint regarding the heat conduction in h-BN films but also propose that polycrystalline h-BN sheets present high thermal conductivity comparable to monocrystalline sheets.

  19. Modelling heat conduction in polycrystalline hexagonal boron-nitride films

    PubMed Central

    Mortazavi, Bohayra; Pereira, Luiz Felipe C.; Jiang, Jin-Wu; Rabczuk, Timon

    2015-01-01

    We conducted extensive molecular dynamics simulations to investigate the thermal conductivity of polycrystalline hexagonal boron-nitride (h-BN) films. To this aim, we constructed large atomistic models of polycrystalline h-BN sheets with random and uniform grain configuration. By performing equilibrium molecular dynamics (EMD) simulations, we investigated the influence of the average grain size on the thermal conductivity of polycrystalline h-BN films at various temperatures. Using the EMD results, we constructed finite element models of polycrystalline h-BN sheets to probe the thermal conductivity of samples with larger grain sizes. Our multiscale investigations not only provide a general viewpoint regarding the heat conduction in h-BN films but also propose that polycrystalline h-BN sheets present high thermal conductivity comparable to monocrystalline sheets. PMID:26286820

  20. High-Entropy Alloys in Hexagonal Close-Packed Structure

    NASA Astrophysics Data System (ADS)

    Gao, M. C.; Zhang, B.; Guo, S. M.; Qiao, J. W.; Hawk, J. A.

    2016-07-01

    The microstructures and properties of high-entropy alloys (HEAs) based on the face-centered cubic and body-centered cubic structures have been studied extensively in the literature, but reports on HEAs in the hexagonal close-packed (HCP) structure are very limited. Using an efficient strategy in combining phase diagram inspection, CALPHAD modeling, and ab initio molecular dynamics simulations, a variety of new compositions are suggested that may hold great potentials in forming single-phase HCP HEAs that comprise rare earth elements and transition metals, respectively. Experimental verification was carried out on CoFeReRu and CoReRuV using X-ray diffraction, scanning electron microscopy, and energy dispersion spectroscopy.

  1. Dislocation dynamics in hexagonal close-packed crystals

    SciTech Connect

    Aubry, S.; Rhee, M.; Hommes, G.; Bulatov, V. V.; Arsenlis, A.

    2016-04-14

    Extensions of the dislocation dynamics methodology necessary to enable accurate simulations of crystal plasticity in hexagonal close-packed (HCP) metals are presented. They concern the introduction of dislocation motion in HCP crystals through linear and non-linear mobility laws, as well as the treatment of composite dislocation physics. Formation, stability and dissociation of and other dislocations with large Burgers vectors defined as composite dislocations are examined and a new topological operation is proposed to enable their dissociation. Furthermore, the results of our simulations suggest that composite dislocations are omnipresent and may play important roles both in specific dislocation mechanisms and in bulk crystal plasticity in HCP materials. While fully microscopic, our bulk DD simulations provide wealth of data that can be used to develop and parameterize constitutive models of crystal plasticity at the mesoscale.

  2. Light scattering by absorbing hexagonal ice crystals in cirrus clouds.

    PubMed

    Zhang, J; Xu, L

    1995-09-01

    An improved ray-optics theory for single scattering and polarization of hexagonal columns and plates randomly oriented in space has been developed by considering absorption and by using the Chebyshev solution for diffraction integrals. The vector-tracing method and statistics technique of random sampling are employed. The equivalent forms of Snell's law and Fresnel formulas for absorbing ice crystals are derived, and two equivalent optical constants, m' and m″, are obtained. Comparison is made of the computed results of our model and the Takano and Liou model for asymmetry factors, single-scattering albedos, and scattering phase matrix elements. Some characteristics of our model are discussed, and these analyses demonstrate that our ray-optics model is practical and much improved.

  3. Vibration characteristics of hexagonal radial rib and hoop platforms

    NASA Technical Reports Server (NTRS)

    Belvin, W. K.

    1983-01-01

    Experiment and analysis have been used to characterize the modes of vibration of planar radial rib and hoop hexagonal platforms. Finite element analysis correlated very well with experimental results. The sensitivity of mode shapes and frequencies to cable stiffness and initial tension is presented. Threshold values have been identified, above which changes in cable stiffness do not affect the first few platform vibration modes. Primary vibration modes of the radial rib platform involve beam bending. Vibration modes of the hoop platform exhibit both beam bending and frame bending and torsion. Results indicate for low order polygonal structures, the radial rib concept produced a higher fundamental frequency. For high order polygonal structures, the hoop concept has the potential to achieve a higher fundamental frequency than the radial rib concept.

  4. Columnar epitaxy of hexagonal and orthorhombic silicides on Si(111)

    NASA Technical Reports Server (NTRS)

    Fathauer, R. W.; Nieh, C. W.; Xiao, Q. F.; Hashimoto, Shin

    1990-01-01

    Columnar grains of PtSi and CrSi2 surrounded by high-quality epitaxial silicon are obtained by ultrahigh vacuum codeposition of Si and metal in an approximately 10:1 ratio on Si(111) substrates heated to 610-840 C. This result is similar to that found previously for CoSi2 (a nearly-lattice-matched cubic-fluorite crystal) on Si(111), in spite of the respective orthorhombic and hexagonal structures of PtSi and CrSi2. The PtSi grains are epitaxial and have one of three variants of the relation defined by PtSi(010)/Si(111), with PtSi 001 line/Si 110 line type.

  5. Huge excitonic effects in layered hexagonal boron nitride.

    PubMed

    Arnaud, B; Lebègue, S; Rabiller, P; Alouani, M

    2006-01-20

    The all-electron GW approximation energy band gap of bulk hexagonal boron nitride is shown to be of indirect type. The resulting computed in-plane polarized optical spectrum, obtained by solving the Bethe-Salpeter equation for the electron-hole two-particle Green function, is in excellent agreement with experiment and has a strong anisotropy compared to out-of-plane polarized spectrum. A detailed analysis of the excitonic structures within the band gap shows that the low-lying excitons belong to the Frenkel class and are tightly confined within the layers. The calculated exciton binding energy is much larger than that obtained by Watanabe et al. [Nat. Mater. 3, 404 (2004).] based on a Wannier model assuming h-BN to be a direct-band-gap semiconductor.

  6. Chemical synthesis of hexagonal indium nitride nanocrystallines at low temperature

    NASA Astrophysics Data System (ADS)

    Wang, Liangbiao; Shen, Qianli; Zhao, Dejian; Lu, Juanjuan; Liu, Weiqiao; Zhang, Junhao; Bao, Keyan; Zhou, Quanfa

    2017-08-01

    In this study, hexagonal indium nitride nanocystallines with high crystallinity have been prepared by the reaction of InCl3·4H2O, sulfur and NaNH2 in an autoclave at 160 °C. The crystal structures and morphologies of the obtained InN sample are characterized by X-ray diffraction and scanning electron microscope. As InCl3·4H2O is substituted by In(NO3)3·4.5H2O, InN nanocrystallines could also be obtained by using the similar method. The photoluminescence spectrum shows that the InN emits a broad peak positioned at 2.3 eV.

  7. Electronic structure of interfaces between hexagonal and rhombohedral graphite

    NASA Astrophysics Data System (ADS)

    Taut, M.; Koepernik, K.

    2016-07-01

    An analysis of the electronic structure of interfaces between hexagonal (A B ) and rhombohedral (A B C ) graphite based on density functional theory is presented. Both of the two simplest interface structures host (localized) interface bands, which are located around the K point in the Brillouin zone, and which give rise to strong peaks in the density of states at the Fermi level. All interface bands near the Fermi energy are localized at monomers (single atoms with dangling pz orbitals), whereas those around 0.5 eV belong to pz-bonded trimers, which are introduced by the interface and which are not found in the two adjacent bulk substances. There is also an interface band at the (A B ) side of the interface which resembles one of the interface states near a stacking fault in (A B ) graphite.

  8. Magnetic tunnel junctions with monolayer hexagonal boron nitride tunnel barriers

    SciTech Connect

    Piquemal-Banci, M.; Galceran, R.; Bouzehouane, K.; Anane, A.; Petroff, F.; Fert, A.; Dlubak, B.; Seneor, P.; Caneva, S.; Martin, M.-B.; Weatherup, R. S.; Kidambi, P. R.; Robertson, J.; Hofmann, S.; Xavier, S.

    2016-03-07

    We report on the integration of atomically thin 2D insulating hexagonal boron nitride (h-BN) tunnel barriers into Co/h-BN/Fe magnetic tunnel junctions (MTJs). The h-BN monolayer is directly grown by chemical vapor deposition on Fe. The Conductive Tip Atomic Force Microscopy (CT-AFM) measurements reveal the homogeneity of the tunnel behavior of our h-BN layers. As expected for tunneling, the resistance depends exponentially on the number of h-BN layers. The h-BN monolayer properties are also characterized through integration into complete MTJ devices. A Tunnel Magnetoresistance of up to 6% is observed for a MTJ based on a single atomically thin h-BN layer.

  9. Functionalized hexagonal boron nitride nanomaterials: emerging properties and applications.

    PubMed

    Weng, Qunhong; Wang, Xuebin; Wang, Xi; Bando, Yoshio; Golberg, Dmitri

    2016-07-11

    Functionalization is an important way to breed new properties and applications for a material. This review presents an overview of the progresses in functionalized hexagonal boron nitride (h-BN) nanomaterials. It begins with an introduction of h-BN structural features, physical and chemical properties, followed by an emphasis on the developments of BN functionalization strategies and its emerging properties/applications, and ends with the research perspectives. Different functionalization methods, including physical and chemical routes, are comprehensively described toward fabrication of various BN derivatives, hetero- and porous structures, etc. Novel properties of functionalized BN materials, such as high water solubility, excellent biocompatibility, tunable surface affinities, good processibility, adjustable band gaps, etc., have guaranteed wide applications in biomedical, electronic, composite, environmental and "green" energy-related fields.

  10. Importance of the hexagonal lipid phase in biological membrane organization

    PubMed Central

    Jouhet, Juliette

    2013-01-01

    Domains are present in every natural membrane. They are characterized by a distinctive protein and/or lipid composition. Their size is highly variable from the nano- to the micrometer scale. The domains confer specific properties to the membrane leading to original structure and function. The determinants leading to domain organization are therefore important but remain obscure. This review presents how the ability of lipids to organize into hexagonal II or lamellar phases can promote particular local structures within membranes. Since biological membranes are composed of a mixture of lipids, each with distinctive biophysical properties, lateral and transversal sorting of lipids can promote creation of domains inside the membrane through local modulation of the lipid phase. Lipid biophysical properties have been characterized for long based on in vitro analyses using non-natural lipid molecules; their re-examinations using natural lipids might open interesting perspectives on membrane architecture occurring in vivo in various cellular and physiological contexts. PMID:24348497

  11. Connected hexagonal photonic crystals with largest full band gap.

    PubMed

    Fu, H; Chen, Y; Chern, R; Chang, Chien

    2005-10-03

    A two-dimensional photonic crystal with a large full band gap has been designed, fabricated, and characterized. The photonic crystal design was based on a calculation using inverse iteration with multigrid acceleration. The fabrication of the photonic crystal on silicon was realized by the processes of electron-beam lithography and inductively coupled plasma reactive ion etching. It was found that the hexagonal array of circular columns and rods has an optimal full photonic band gap. In addition, we show that a larger extraction of light from our designed photonic crystal can be obtained when compared with the frequently used photonic crystals reported previously. Our designed PC structure therefore should be very useful for creating highly efficient optoelectronic devices.

  12. Origin of band gaps in graphene on hexagonal boron nitride

    PubMed Central

    Jung, Jeil; DaSilva, Ashley M.; MacDonald, Allan H.; Adam, Shaffique

    2015-01-01

    Recent progress in preparing well-controlled two-dimensional van der Waals heterojunctions has opened up a new frontier in materials physics. Here we address the intriguing energy gaps that are sometimes observed when a graphene sheet is placed on a hexagonal boron nitride substrate, demonstrating that they are produced by an interesting interplay between structural and electronic properties, including electronic many-body exchange interactions. Our theory is able to explain the observed gap behaviour by accounting first for the structural relaxation of graphene’s carbon atoms when placed on a boron nitride substrate, and then for the influence of the substrate on low-energy π-electrons located at relaxed carbon atom sites. The methods we employ can be applied to many other van der Waals heterojunctions. PMID:25695638

  13. Synthesis of hexagonal close-packed gold nanostructures.

    PubMed

    Huang, Xiao; Li, Shaozhou; Huang, Yizhong; Wu, Shixin; Zhou, Xiaozhu; Li, Shuzhou; Gan, Chee Lip; Boey, Freddy; Mirkin, Chad A; Zhang, Hua

    2011-01-01

    Solid gold is usually most stable as a face-centred cubic (fcc) structure. To date, no one has synthesized a colloidal form of Au that is exclusively hexagonal close-packed (hcp) and stable under ambient conditions. Here we report the first in situ synthesis of dispersible hcp Au square sheets on graphene oxide sheets, which exhibit an edge length of 200-500 nm and a thickness of ~ 2.4 nm (~ 16 Au atomic layers). Interestingly, the Au square sheet transforms from hcp to a fcc structure on exposure to an electron beam during transmission electron microscopy analysis. In addition, as the square sheet grows thicker (from ~ 2.4 to 6 nm), fcc segments begin to appear. A detailed experimental analysis of these structures shows that for structures with ultrasmall dimensions (for example, <~ 6 nm thickness for the square sheets), the previously unobserved pure hcp structure becomes stable and isolable.

  14. Electron knock-on damage in hexagonal boron nitride monolayers

    SciTech Connect

    Kotakoski, J.; Lehtinen, O.; Jin, C. H.; Suenaga, K.; Krasheninnikov, A. V.

    2010-09-15

    We combine first-principles molecular-dynamics simulations with high-resolution transmission electron microscopy experiments to draw a detailed microscopic picture of irradiation effects in hexagonal boron nitride (h-BN) monolayers. We determine the displacement threshold energies for boron and nitrogen atoms in h-BN, which differ significantly from the tight-binding estimates found in the literature and remove ambiguity from the interpretation of the experimental results. We further develop a kinetic Monte Carlo model which allows to extend the simulations to macroscopic time scales and make a direct comparison between theory and experiments. Our results provide a comprehensive picture of the response of h-BN nanostructures to electron irradiation.

  15. Electronic structure of spontaneously strained graphene on hexagonal boron nitride

    NASA Astrophysics Data System (ADS)

    San-Jose, Pablo; Gutiérrez-Rubio, A.; Sturla, Mauricio; Guinea, Francisco

    2014-09-01

    Hexagonal boron nitride substrates have been shown to dramatically improve the electric properties of graphene. Recently, it has been observed that when the two honeycomb crystals are close to perfect alignment, strong lattice distortions develop in graphene due to the moiré adhesion landscape. Simultaneously, a gap opens at the Dirac point. Here, we derive a simple low-energy electronic model for graphene aligned with the substrate, taking into account spontaneous strains at equilibrium and pseudogauge fields. We carry out a detailed characterization of the modified band structure, gap, local and global density of states, and band topology in terms of physical parameters. We show that the overall electronic structure is strongly modified by the spontaneous strains.

  16. High-entropy alloys in hexagonal close-packed structure

    SciTech Connect

    Gao, Michael C.; Zhang, B.; Guo, S. M.; Qiao, J. W.; Hawk, J. A.

    2015-08-28

    The microstructures and properties of high-entropy alloys (HEAs) based on the face-centered cubic and body-centered cubic structures have been studied extensively in the literature, but reports on HEAs in the hexagonal close-packed (HCP) structure are very limited. Using an efficient strategy in combining phase diagram inspection, CALPHAD modeling, and ab initio molecular dynamics simulations, a variety of new compositions are suggested that may hold great potentials in forming single-phase HCP HEAs that comprise rare earth elements and transition metals, respectively. Lastly, experimental verification was carried out on CoFeReRu and CoReRuV using X-ray diffraction, scanning electron microscopy, and energy dispersion spectroscopy.

  17. Hexagonal shaped ice spicules in frozen antifreeze protein solutions.

    PubMed

    Wilson, P W; Gould, M; DeVries, A L

    2002-06-01

    In the presence of antifreeze proteins from both Antarctic and Arctic fishes, water freezes in the form of long c-axis spikes or spicular-like crystals. Transmission electron microscopy of the Pt/C replicas of the freeze fractured spicular ice in a small capillary revealed the presence of many hexagonally shaped structures whose cross-sectional dimensions were between 0.5 and 10 microm. Well-defined parallel faces were associated with most fractured and etched spicules. When fracture planes occurred near the tip of a spicule, well-defined pyramidal faces were apparent. Steps were sometimes associated with these pyramidal spicular crystal faces. On some of the replicas obvious roughening of certain crystal faces of the spicule was observed, suggesting that the antifreeze proteins may have adsorbed to those faces.

  18. Classical Heisenberg spins on a hexagonal lattice with Kitaev couplings.

    PubMed

    Chandra, Samarth; Ramola, Kabir; Dhar, Deepak

    2010-09-01

    We analyze the low temperature properties of a system of classical Heisenberg spins on a hexagonal lattice with Kitaev couplings. For a lattice of 2N sites with periodic boundary conditions, the ground states form an (N+1) dimensional manifold. We show that the ensemble of ground states is equivalent to that of a solid-on-solid model with continuously variable heights and nearest neighbor interactions, at a finite temperature. For temperature T tending to zero, all ground states have equal weight, and there is no order by disorder in this model. We argue that the bond-energy bond-energy correlations at distance R decay as 1/R2 at zero temperature. This is verified by Monte Carlo simulations. We also discuss the relation to the quantum spin- S Kitaev model for large S, and obtain lower and upper bounds on the ground-state energy of the quantum model.

  19. Thermal conductance of graphene/hexagonal boron nitride heterostructures

    NASA Astrophysics Data System (ADS)

    Lu, Simon; McGaughey, Alan J. H.

    2017-03-01

    The lattice-based scattering boundary method is applied to compute the phonon mode-resolved transmission coefficients and thermal conductances of in-plane heterostructures built from graphene and hexagonal boron nitride (hBN). The thermal conductance of all structures is dominated by acoustic phonon modes near the Brillouin zone center that have high group velocity, population, and transmission coefficient. Out-of-plane modes make their most significant contributions at low frequencies, whereas in-plane modes contribute across the frequency spectrum. Finite-length superlattice junctions between graphene and hBN leads have a lower thermal conductance than comparable junctions between two graphene leads due to lack of transmission in the hBN phonon bandgap. The thermal conductances of bilayer systems differ by less than 10% from their single-layer counterparts on a per area basis, in contrast to the strong thermal conductivity reduction when moving from single- to multi-layer graphene.

  20. Half metal in two-dimensional hexagonal organometallic framework.

    PubMed

    Hu, Hao; Wang, Zhengfei; Liu, Feng

    2014-12-01

    Two-dimensional (2D) hexagonal organometallic framework (HOMF) made of triphenyl-metal molecules bridged by metal atoms has been recently shown to exhibit exotic electronic properties, such as half-metallic and topological insulating states. Here, using first-principles calculations, we investigate systematically the structural, electronic, and magnetic properties of such HOMFs containing 3d transition metal (TM) series (Sc to Cu). Two types of structures are found for these HOMFs: a buckled structure for those made of TMs with less half-filled 3d band and a twisted structure otherwise. The HOMFs show both ferromagnetic and antiferromagnetic properties, as well as nonmagnetic properties, due to the electronic configuration of the TM atoms. The V, Mn, and Fe lattices are ferromagnetic half metals with a large band gap of more than 1.5 eV in the insulating spin channel, making them potential 2D materials for spintronics application.

  1. Protein folding in HP model on hexagonal lattices with diagonals

    PubMed Central

    2014-01-01

    Three dimensional structure prediction of a protein from its amino acid sequence, known as protein folding, is one of the most studied computational problem in bioinformatics and computational biology. Since, this is a hard problem, a number of simplified models have been proposed in literature to capture the essential properties of this problem. In this paper we introduce the hexagonal lattices with diagonals to handle the protein folding problem considering the well researched HP model. We give two approximation algorithms for protein folding on this lattice. Our first algorithm is a 53-approximation algorithm, which is based on the strategy of partitioning the entire protein sequence into two pieces. Our next algorithm is also based on partitioning approaches and improves upon the first algorithm. PMID:24564789

  2. Etched graphene quantum dots on hexagonal boron nitride

    NASA Astrophysics Data System (ADS)

    Engels, S.; Epping, A.; Volk, C.; Korte, S.; Voigtländer, B.; Watanabe, K.; Taniguchi, T.; Trellenkamp, S.; Stampfer, C.

    2013-08-01

    We report on the fabrication and characterization of etched graphene quantum dots (QDs) on hexagonal boron nitride (hBN) and SiO2 with different island diameters. We perform a statistical analysis of Coulomb peak spacings over a wide energy range. For graphene QDs on hBN, the standard deviation of the normalized peak spacing distribution decreases with increasing QD diameter, whereas for QDs on SiO2 no diameter dependency is observed. In addition, QDs on hBN are more stable under the influence of perpendicular magnetic fields up to 9 T. Both results indicate a substantially reduced substrate induced disorder potential in graphene QDs on hBN.

  3. Pattern Coarsening in a Two Dimensional Hexagonal System

    NASA Astrophysics Data System (ADS)

    Chaikin, Paul

    2008-03-01

    We have been studying the ordering, annealing, coarsening and alignment of two dimensional periodically ordered structures in thin films of diblock copolymers*. Coarsening by dislocation and disclination annihilation is clearly observed in AFM studies of monolayer films of cylindrical patterns with a time dependence given by t^α, with α about 1/4. However in hexagonal structures the mechanism is less well defined and appears to involve the collapse of small grains entrained in the grain boundaries of larger domains. Remarkably the exponent of α about 1/4 remains. We also report on shear aligned samples and samples quenched in a gradient after alignment. * Harrison C, Angelescu DE, Trawick M, Cheng ZD, Huse DA, Chaikin PM, Vega DA, Sebastian JM, Register RA, Adamson DH, EUROPHYSICS LETTERS 67 800-806 (2004)

  4. Structural and Oxygen Storage Properties of Hexagonal Manganites

    NASA Astrophysics Data System (ADS)

    Abughayada, Castro; Dabrowski, Bogdan; Kolesnik, Stan; Chmaissem, Omar; NIU Team

    2013-03-01

    Complex oxides exhibiting superior reversible oxygen absorption/release capacities have been generating a great deal of interest due to their critical role in the development of energy related technologies, such as oxy-fuel and chemical looping combustion. Based on our previous studies of tolerance factor, we have successfully synthesized hexagonal (P63cm) RMnO3+δ manganites (R =Dy, Ho, Y) for which we discovered a large reversible oxygen storage/release capacities (within the range of oxygen content 3.0 - 3.4) at unusually low temperatures near 300 °C which make them excellent candidates for air separation and production of high purity oxygen. Resistivity, structural, magnetic, and thermal expansion properties are correlated with the oxygen content 3 + δ for these compounds. Work supported by NIU Great Journey Assistantship.

  5. Superior thermal conductivity in suspended bilayer hexagonal boron nitride

    PubMed Central

    Wang, Chengru; Guo, Jie; Dong, Lan; Aiyiti, Adili; Xu, Xiangfan; Li, Baowen

    2016-01-01

    We reported the basal-plane thermal conductivity in exfoliated bilayer hexagonal boron nitride h-BN that was measured using suspended prepatterned microstructures. The h-BN sample suitable for thermal measurements was fabricated by dry-transfer method, whose sample quality, due to less polymer residues on surfaces, is believed to be superior to that of PMMA-mediated samples. The measured room temperature thermal conductivity is around 484 Wm−1K−1(+141 Wm−1K−1/ −24 Wm−1K−1) which exceeds that in bulk h-BN, providing experimental observation of the thickness-dependent thermal conductivity in suspended few-layer h-BN. PMID:27142571

  6. Dislocation dynamics in hexagonal close-packed crystals

    SciTech Connect

    Aubry, S.; Rhee, M.; Hommes, G.; Bulatov, V. V.; Arsenlis, A.

    2016-04-14

    Extensions of the dislocation dynamics methodology necessary to enable accurate simulations of crystal plasticity in hexagonal close-packed (HCP) metals are presented. They concern the introduction of dislocation motion in HCP crystals through linear and non-linear mobility laws, as well as the treatment of composite dislocation physics. Formation, stability and dissociation of and other dislocations with large Burgers vectors defined as composite dislocations are examined and a new topological operation is proposed to enable their dissociation. Furthermore, the results of our simulations suggest that composite dislocations are omnipresent and may play important roles both in specific dislocation mechanisms and in bulk crystal plasticity in HCP materials. While fully microscopic, our bulk DD simulations provide wealth of data that can be used to develop and parameterize constitutive models of crystal plasticity at the mesoscale.

  7. A Computational Study of the Growth of Hexagonal Ice

    NASA Astrophysics Data System (ADS)

    Fulford, Maxwell; Salvalaglio, Matteo; Parrinello, Michele; Molteni, Carla

    Hexagonal ice (Ih) has two distinct crystallographic surfaces; a basal and prism surface. At low vapour pressures, Ih forms thin plates and elongated prisms, depending on the temperature. The macroscopic shape depends on the relative rate of growth of the basal and prism surfaces. The aim of our research is to estimate the relative rate of growth of the two surfaces for a range of temperatures and ultimately predict the shape of Ih, using computer simulations. Our simulations show the well-know phenomenon that the surface of ice lowers its interfacial free energy by forming a stable quasi-liquid layer (QLL). The QLL mediates crystal growth and has a thickness which varies with temperature and crystallographic surface. We use a combination of Molecular Dynamics and Metadynamics to study how the interfacial structure at the ice/quasi-liquid and quasi-liquid/vapour interfaces influence the adsorption potential, surface transport properties and growth shape..

  8. Discrete solitons and vortices in anisotropic hexagonal and honeycomb lattices

    SciTech Connect

    Hoq, Q. E.; Kevrekidis, P. G.; Bishop, A. R.

    2016-01-14

    We consider the self-focusing discrete nonlinear Schrödinger equation on hexagonal and honeycomb lattice geometries. Our emphasis is on the study of the effects of anisotropy, motivated by the tunability afforded in recent optical and atomic physics experiments. We find that multi-soliton and discrete vortex states undergo destabilizing bifurcations as the relevant anisotropy control parameter is varied. Furthermore, we quantify these bifurcations by means of explicit analytical calculations of the solutions, as well as of their spectral linearization eigenvalues. Finally, we corroborate the relevant stability picture through direct numerical computations. In the latter, we observe the prototypical manifestation of these instabilities to be the spontaneous rearrangement of the solution, for larger values of the coupling, into localized waveforms typically centered over fewer sites than the original unstable structure. In weak coupling, the instability appears to result in a robust breathing of the relevant waveforms.

  9. Discrete solitons and vortices in anisotropic hexagonal and honeycomb lattices

    DOE PAGES

    Hoq, Q. E.; Kevrekidis, P. G.; Bishop, A. R.

    2016-01-14

    We consider the self-focusing discrete nonlinear Schrödinger equation on hexagonal and honeycomb lattice geometries. Our emphasis is on the study of the effects of anisotropy, motivated by the tunability afforded in recent optical and atomic physics experiments. We find that multi-soliton and discrete vortex states undergo destabilizing bifurcations as the relevant anisotropy control parameter is varied. Furthermore, we quantify these bifurcations by means of explicit analytical calculations of the solutions, as well as of their spectral linearization eigenvalues. Finally, we corroborate the relevant stability picture through direct numerical computations. In the latter, we observe the prototypical manifestation of these instabilitiesmore » to be the spontaneous rearrangement of the solution, for larger values of the coupling, into localized waveforms typically centered over fewer sites than the original unstable structure. In weak coupling, the instability appears to result in a robust breathing of the relevant waveforms.« less

  10. Comparison of hexagonal crystal structures between fluorapatite and polytetrafluoroethylene.

    PubMed

    Okazaki, Masayuki

    2017-01-01

    The crystallographic properties of fluorapatite (FAp) and polytetrafluoroethylene (PTFE) as biomedical materials were compared. Both materials contain fluorine and casually belong to the hexagonal crystal system. It is interesting that FAp is an inorganic ionic crystal, while PTFE is an organic covalent-bond crystal. Generally, fluorine contributes to the physicochemical stability and in some cases to the biocompatibility. The crystal structure of FAp was initially analyzed in 1930 by Náray-Szabó, although the analysis of hydroxyapatite (HAp) was markedly delayed until 1964. The computer graphics display demonstrated that fluoride ions serve to stabilize the hydroxyapatite crystals and prevent dental caries. On the other hand, PTFE crystal analysis was reported in 1954 by Bunn and Howells. The PTFE temperature-pressure phase diagram accepted for over 60 years is very complicated and insufficient. PTFE delicately changes its phase near room temperature, although at a glance it appears to have a simple form compared with DNA.

  11. Carbon-rich hexagonal (BN)C alloys

    SciTech Connect

    Uddin, M. R.; Li, J.; Lin, J. Y.; Jiang, H. X.

    2015-06-07

    Thin films of hexagonal boron nitride carbon, h-(BN){sub 1−x}(C{sub 2}){sub x}, alloys in the C-rich side have been synthesized by metal-organic chemical vapor deposition (MOCVD) on c-plane sapphire substrates. X-ray diffraction measurements confirmed single hexagonal phase of h-(BN){sub 1−x}(C{sub 2}){sub x} epilayers. Electrical transport and Raman spectroscopy measurements results revealed evidences that homogenous h-(BN){sub 1−x}(C{sub 2}){sub x} alloys with x ≥ 95% can be synthesized by MOCVD at a growth temperature of 1300 °C. The variable temperature Hall-effect measurements suggested that a bandgap opening of about 93 meV with respect to graphite has been obtained for h-(BN){sub 1−x}(C{sub 2}){sub x} with x = 0.95, which is consistent with the expected value deduced from the alloy dependence of the energy gap of homogenous h-(BN){sub 1−x}(C{sub 2}){sub x} alloys. Atomic composition results obtained from x-ray photoelectron spectroscopy measurements revealed that the carrier type in C-rich h-(BN){sub 1−x}(C{sub 2}){sub x} alloys is controlled by the stoichiometry ratio between the B and N via changing the V/III ratio during the growth. The demonstration of bandgap opening and conductivity control in C-rich h-(BN){sub 1−x}(C{sub 2}){sub x} alloys provide feasibilities for realizing technologically significant devices including infrared (IR) emitters and detectors active from near to far IR and multi-spectral IR emitters and detectors.

  12. Self-assembly of well-defined ferrocene triblock copolymers and their template synthesis of ordered iron oxide nanoparticles.

    PubMed

    Hardy, Christopher G; Ren, Lixia; Ma, Shuguo; Tang, Chuanbing

    2013-05-14

    Well-defined ferrocene-containing triblock copolymers were synthesized by atom transfer radical polymerization and self-assembled into highly ordered hexagonal arrays of cylinders via solvent annealing. The thin films were further used as a template and converted into highly ordered iron oxide nanoparticles (α-Fe2O3) by UV/ozonolysis and thermal pyrolysis.

  13. Pressure in electronically excited warm dense metals

    NASA Astrophysics Data System (ADS)

    Stegailov, Vladimir; Zhilyaev, Petr

    2015-06-01

    Non-equilibrium two-temperature warm dense metals consist of the ion subsystem that is subjected to structural transitions and involved in the mass transfer, and the electron subsystem that in various pulsed experiments absorbs energy and then evolves together with ions to equilibrium. Definition of pressure in such non-equilibrium systems causes certain controversy. In this work we make an attempt to clarify this definition that is vital for proper description of the whole relaxation process. Using the density functional theory we analyze on examples of Al and Au electronic pressure components in warm dense metals. Appealing to the Fermi gas model we elucidate a way to find a number of free delocalized electrons in warm dense metals. First results has been published in. This work is supported by the Russian Science Foundation grant No. 14-19-01487.

  14. Coalescence preference in densely packed microbubbles

    SciTech Connect

    Kim, Yeseul; Lim, Su Jin; Gim, Bopil; Weon, Byung Mook

    2015-01-13

    A bubble merged from two parent bubbles with different size tends to be placed closer to the larger parent. This phenomenon is known as the coalescence preference. Here we demonstrate that the coalescence preference can be blocked inside a densely packed cluster of bubbles. We utilized high-speed high-resolution X-ray microscopy to clearly visualize individual coalescence events inside densely packed microbubbles with a local packing fraction of ~40%. Thus, the surface energy release theory predicts an exponent of 5 in a relation between the relative coalescence position and the parent size ratio, whereas our observation for coalescence in densely packed microbubbles shows a different exponent of 2. We believe that this result would be important to understand the reality of coalescence dynamics in a variety of packing situations of soft matter.

  15. Coalescence preference in densely packed microbubbles

    DOE PAGES

    Kim, Yeseul; Lim, Su Jin; Gim, Bopil; ...

    2015-01-13

    A bubble merged from two parent bubbles with different size tends to be placed closer to the larger parent. This phenomenon is known as the coalescence preference. Here we demonstrate that the coalescence preference can be blocked inside a densely packed cluster of bubbles. We utilized high-speed high-resolution X-ray microscopy to clearly visualize individual coalescence events inside densely packed microbubbles with a local packing fraction of ~40%. Thus, the surface energy release theory predicts an exponent of 5 in a relation between the relative coalescence position and the parent size ratio, whereas our observation for coalescence in densely packed microbubblesmore » shows a different exponent of 2. We believe that this result would be important to understand the reality of coalescence dynamics in a variety of packing situations of soft matter.« less

  16. Dynamic structure factor in warm dense beryllium

    NASA Astrophysics Data System (ADS)

    Plagemann, K.-U.; Sperling, P.; Thiele, R.; Desjarlais, M. P.; Fortmann, C.; Döppner, T.; Lee, H. J.; Glenzer, S. H.; Redmer, R.

    2012-05-01

    We calculate the dynamic structure factor (DSF) in warm dense beryllium by means of ab initio molecular dynamics simulations. The dynamic conductivity is derived from the Kubo-Greenwood formula, and a Drude-like behaviour is observed. The corresponding dielectric function is used to determine the DSF. Since the ab initio approach is so far only applicable for wavenumbers k = 0, the k-dependence of the dielectric function is modelled via the Mermin ansatz. We present the results for the dielectric function and DSF of warm dense beryllium and compare these with perturbative treatments such as the Born-Mermin approximation. We found considerable differences between the results of these approaches; this underlines the need for a first-principles determination of the DSF of warm dense matter.

  17. Eddy Viscosity in Dense Granular Flows

    NASA Astrophysics Data System (ADS)

    Miller, T.; Rognon, P.; Metzger, B.; Einav, I.

    2013-08-01

    We present a seminal set of experiments on dense granular flows in the stadium shear geometry. The advantage of this geometry is that it produces steady shear flow over large deformations, in which the shear stress is constant. The striking result is that the velocity profiles exhibit an S shape, and are not linear as local constitutive laws would predict. We propose a model that suggests this is a result of wall perturbations which span through the system due to the nonlocal behavior of the material. The model is analogous to that of eddy viscosity in turbulent boundary layers, in which the distance to the wall is introduced to predict velocity profiles. Our findings appear pivotal in a number of experimental and practical situations involving dense granular flows next to a boundary. They could further be adapted to other similar materials such as dense suspensions, foams, or emulsions.

  18. Photoelectrochemical water oxidation on photoanodes fabricated with hexagonal nanoflower and nanoblock WO3.

    PubMed

    Wang, Nan; Wang, Donge; Li, Mingrun; Shi, Jingying; Li, Can

    2014-02-21

    Hexagonal nanoflower WO3 arrays have been prepared by using RCOO(-) as the structure directing agent in the microwave-assisted hydrothermal synthesis process. The photoelectrochemical performance of the synthesized hexagonal flower-like WO3 electrode was enhanced compared with the block-like WO3 film.

  19. Facile synthesis of concave gold nanoplates in hexagonal liquid crystal made of SDS/water system.

    PubMed

    Wang, Luyan; Wu, Xinzhou; Li, Xiaonan; Wang, Li; Pei, Meishan; Tao, Xutang

    2010-11-28

    Concave gold nanoplates are obtained in hexagonal liquid crystal (LLC) made of SDS (sodium dodecyl sulfate)/glycine/HAuCl(4) aqueous solution system where glycine plays the key role. All plates are single-crystals, characterized by {111} facets, with concave centers of regular hexagonal or triangular shapes, and with better electrocatalytic activity than gold nanoplates.

  20. IR Spectroscopy of PAHs in Dense Clouds

    NASA Astrophysics Data System (ADS)

    Allamandola, Louis; Bernstein, Max; Mattioda, Andrew; Sandford, Scott

    2007-05-01

    Interstellar PAHs are likely to be a component of the ice mantles that form on dust grains in dense molecular clouds. PAHs frozen in grain mantles will produce IR absorption bands, not IR emission features. A couple of very weak absorption features in ground based spectra of a few objects embedded in dense clouds may be due to PAHs. Additionally spaceborne observations in the 5 to 8 ?m region, the region in which PAH spectroscopy is rich, reveal unidentified new bands and significant variation from object to object. It has not been possible to properly evaluate the contribution of PAH bands to these IR observations because the laboratory absorption spectra of PAHs condensed in realistic interstellar mixed-molecular ice analogs is lacking. This experimental data is necessary to interpret observations because, in ice mantles, the interaction of PAHs with the surrounding molecules effects PAH IR band positions, widths, profiles, and intrinsic strengths. Furthermore, PAHs are readily ionized in pure H2O ice, further altering the PAH spectrum. This laboratory proposal aims to remedy the situation by studying the IR spectroscopy of PAHs frozen in laboratory ice analogs that realistically reflect the composition of the interstellar ices observed in dense clouds. The purpose is to provide laboratory spectra which can be used to interpret IR observations. We will measure the spectra of these mixed molecular ices containing PAHs before and after ionization and determine the intrinsic band strengths of neutral and ionized PAHs in these ice analogs. This will enable a quantitative assessment of the role that PAHs can play in determining the 5-8 ?m spectrum of dense clouds and will directly address the following two fundamental questions associated with dense cloud spectroscopy and chemistry: 1- Can PAHs be detected in dense clouds? 2- Are PAH ions components of interstellar ice?

  1. Superfluid vortices in dense quark matter

    NASA Astrophysics Data System (ADS)

    Mallavarapu, S. Kumar; Alford, Mark; Windisch, Andreas; Vachaspati, Tanmay

    2016-03-01

    Superfluid vortices in the color-flavor-locked (CFL) phase of dense quark matter are known to be energetically disfavored as compared to well-separated triplets of ``semi-superfluid'' color flux tubes. In this talk we will provide results which will identify regions in parameter space where the superfluid vortex spontaneously decays. We will also discuss the nature of the mode that is responsible for the decay of a superfluid vortex in dense quark matter. We will conclude by mentioning the implications of our results to neutron stars.

  2. Controlled Dense Coding with the W State

    NASA Astrophysics Data System (ADS)

    Yang, Xue; Bai, Ming-qiang; Mo, Zhi-wen

    2017-09-01

    The average amount of information is an important factor in implementing dense coding. Based on this, we propose two schemes for controlled dense coding by using the three-qubit entangled W state as the quantum channel in this paper. In these schemes, the controller (Charlie) can adjust the local measurement angle 𝜃 to modulate the entanglement, and consequently the average amount of information transmitted from the sender (Alice) to the receiver (Bob). Although the results for the average amounts of information are the same from the different two schemes, the second scheme has advantage over the first scheme.

  3. Fast temperature relaxation model in dense plasmas

    NASA Astrophysics Data System (ADS)

    Faussurier, Gérald; Blancard, Christophe

    2017-01-01

    We present a fast model to calculate the temperature-relaxation rates in dense plasmas. The electron-ion interaction-potential is calculated by combining a Yukawa approach and a finite-temperature Thomas-Fermi model. We include the internal energy as well as the excess energy of ions using the QEOS model. Comparisons with molecular dynamics simulations and calculations based on an average-atom model are presented. This approach allows the study of the temperature relaxation in a two-temperature electron-ion system in warm and hot dense matter.

  4. Dense gas flow in minimum length nozzles

    SciTech Connect

    Aldo, A.C.; Argrow, B.M.

    1995-06-01

    Recently, dense gases have been investigated for many engineering applications such as for turbomachinery and wind tunnels. Supersonic nozzle design can be complicated by nonclassical dense-gas behavior in the transonic flow regime. In this paper, a method of characteristics (MOC) is developed for two-dimensional (planar) and axisymmetric flow of a van der Waals gas. A minimum length nozzle design code is developed that employs the MOC procedure to generate an inviscid wall contour. The van der Waals results are compared to perfect gas results to show the real-gas effects on the flow properties and inviscid wall contours.

  5. Demagnetization effects in dense nanoparticle assemblies

    NASA Astrophysics Data System (ADS)

    Normile, P. S.; Andersson, M. S.; Mathieu, R.; Lee, S. S.; Singh, G.; De Toro, J. A.

    2016-10-01

    We highlight the relevance of demagnetizing-field corrections in the characterization of dense magnetic nanoparticle assemblies. By an analysis that employs in-plane and out-of-plane magnetometry on cylindrical assemblies, we demonstrate the suitability of a simple analytical formula-based correction method. This allows us to identify artifacts of the demagnetizing field in temperature-dependent susceptibility curves (e.g., shoulder peaks in curves from a disordered assembly of essentially bare magnetic nanoparticles). The same analysis approach is shown to be a straightforward procedure for determining the magnetic nanoparticle packing fraction in dense, disordered assemblies.

  6. Ultrathin high-temperature oxidation-resistant coatings of hexagonal boron nitride.

    PubMed

    Liu, Zheng; Gong, Yongji; Zhou, Wu; Ma, Lulu; Yu, Jingjiang; Idrobo, Juan Carlos; Jung, Jeil; MacDonald, Allan H; Vajtai, Robert; Lou, Jun; Ajayan, Pulickel M

    2013-01-01

    Hexagonal boron nitride is a two-dimensional layered material that can be stable at 1,500 °C in air and will not react with most chemicals. Here we demonstrate large-scale, ultrathin, oxidation-resistant coatings of high-quality hexagonal boron nitride layers with controlled thicknesses from double layers to bulk. We show that such ultrathin hexagonal boron nitride films are impervious to oxygen diffusion even at high temperatures and can serve as high-performance oxidation-resistant coatings for nickel up to 1,100 °C in oxidizing atmospheres. Furthermore, graphene layers coated with a few hexagonal boron nitride layers are also protected at similarly high temperatures. These hexagonal boron nitride atomic layer coatings, which can be synthesized via scalable chemical vapour deposition method down to only two layers, could be the thinnest coating ever shown to withstand such extreme environments and find applications as chemically stable high-temperature coatings.

  7. Magnetic self-orientation of lyotropic hexagonal phases based on long chain alkanoic (fatty) acids.

    PubMed

    Douliez, Jean-Paul

    2010-07-06

    It is presently shown that long chain (C14, C16, and C18) alkanoic (saturated fatty) acids can form magnetically oriented hexagonal phases in aqueous concentrated solutions in mixtures with tetrabutylammonium (TBAOH) as the counterion. The hexagonal phase occurred for a molar ratio, alkanoic acid/TBAOH, higher than 1, i.e., for an excess of fatty acid. The hexagonal phase melted to an isotropic phase (micelles) upon heating at a given temperature depending on the alkyl chain length. The self-orientation of the hexagonal phase occurred upon cooling from the "high-temperature" isotropic phase within the magnetic field. The long axis of the hexagonal phase was shown to self-orient parallel to the magnetic field as evidenced by deuterium solid-state NMR. This finding is expected to be of interest in the field of structural biology and materials chemistry for the synthesis of oriented materials.

  8. Influence of Mineralogical Characteristics of Iron Ore on Formation and Flow of Liquid Phase

    NASA Astrophysics Data System (ADS)

    Su, Bo; Wu, Sheng-li; Zhang, Guo-liang

    The mineralogical characteristics of iron ores can influence their high temperature sintering performance. In this study, eight iron ore samples from Brazil, Australia, and South Africa were characterized by their chemical composition, mineral types, particle morphology, and gangue dispersity. Meanwhile the influence rules between the mineralogical characteristics and the high temperature characteristics were evaluated and analyzed. The results showed that the effect of SiO2 on assimilation characteristic of iron ores was relatively complex, Al2O3 and LOI of iron ores had negative correlation with assimilation temperature of iron ores, the dense slab-flaky mineral granule restrained to the assimilation characteristics of iron ores; liquid phase of iron ores with high SiO2 content and low Al2O3 content had high fluidity, and the higher dispersity of gangue minerals in iron ores was good to the fluidity of liquid phase.

  9. Rapid Pattern Recognition of Three Dimensional Objects Using Parallel Processing Within a Hierarchy of Hexagonal Grids

    NASA Astrophysics Data System (ADS)

    Tang, Haojun

    1995-01-01

    This thesis describes using parallel processing within a hierarchy of hexagonal grids to achieve rapid recognition of patterns. A seven-pixel basic hexagonal neighborhood, a sixty-one-pixel superneighborhood and pyramids of a 2-to-4 area ratio are employed. The hexagonal network achieves improved accuracy over the square network for object boundaries. The hexagonal grid with less directional sensitivity is a better approximation of the human vision grid, is more suited to natural scenes than the square grid and avoids the 4-neighbor/8-neighbor problem. Parallel processing in image analysis saves considerable time versus the traditional line-by-line method. Hexagonal parallel processing combines the optimum hexagonal geometry with the parallel structure. Our work has surveyed behavior and internal properties to construct the image on the different level of hexagonal pixel grids in a parallel computation scheme. A computer code has been developed to detect edges of digital images of real objects taken with a CCD camera within a hexagonal grid at any level. The algorithm uses the differences of the local gray level and those of its six neighbors, and is able to determine the boundary of a digital image in parallel. Also a series of algorithms and techniques have been built up to manage edge linking, feature extraction, etc. The digital images obtained from the improved CRS digital image processing system are a good approximation to the images which would be obtained with a real physical hexagonal grid. We envision that our work done within this little-known area will have some important applications in real-time machine vision. A parallel two-layer hexagonal-array retina has been designed to do pattern recognition using simple operations such as differencing, rationing, thresholding, etc. which may occur in the human retina and other biological vision systems.

  10. Iron and Your Child

    MedlinePlus

    ... get iron by eating foods like meat and dark green leafy vegetables. Iron is also added to ... tofu dried beans and peas dried fruits leafy dark green vegetables iron-fortified breakfast cereals, breads, and ...

  11. Iron metabolism and toxicity

    SciTech Connect

    Papanikolaou, G.; Pantopoulos, K. . E-mail: kostas.pantopoulos@mcgill.ca

    2005-01-15

    Iron is an essential nutrient with limited bioavailability. When present in excess, iron poses a threat to cells and tissues, and therefore iron homeostasis has to be tightly controlled. Iron's toxicity is largely based on its ability to catalyze the generation of radicals, which attack and damage cellular macromolecules and promote cell death and tissue injury. This is lucidly illustrated in diseases of iron overload, such as hereditary hemochromatosis or transfusional siderosis, where excessive iron accumulation results in tissue damage and organ failure. Pathological iron accumulation in the liver has also been linked to the development of hepatocellular cancer. Here we provide a background on the biology and toxicity of iron and the basic concepts of iron homeostasis at the cellular and systemic level. In addition, we provide an overview of the various disorders of iron overload, which are directly linked to iron's toxicity. Finally, we discuss the potential role of iron in malignant transformation and cancer.

  12. DENSE NONAQUEOUS PHASE LIQUIDS -- A WORKSHOP SUMMARY

    EPA Science Inventory

    site characterization, and, therefore, DNAPL remediation, can be expected. Dense nonaqueous phase liquids (DNAPLs) in the subsurface are long-term sources of ground-water contamination, and may persist for centuries before dissolving completely in adjacent ground water. In respo...

  13. Coalescence preference in dense packing of bubbles

    NASA Astrophysics Data System (ADS)

    Kim, Yeseul; Gim, Bopil; Gim, Bopil; Weon, Byung Mook

    2015-11-01

    Coalescence preference is the tendency that a merged bubble from the contact of two original bubbles (parent) tends to be near to the bigger parent. Here, we show that the coalescence preference can be blocked by densely packing of neighbor bubbles. We use high-speed high-resolution X-ray microscopy to clearly visualize individual coalescence phenomenon which occurs in micro scale seconds and inside dense packing of microbubbles with a local packing fraction of ~40%. Previous theory and experimental evidence predict a power of -5 between the relative coalescence position and the parent size. However, our new observation for coalescence preference in densely packed microbubbles shows a different power of -2. We believe that this result may be important to understand coalescence dynamics in dense packing of soft matter. This work (NRF-2013R1A22A04008115) was supported by Mid-career Researcher Program through NRF grant funded by the MEST and also was supported by Ministry of Science, ICT and Future Planning (2009-0082580) and by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry and Education, Science and Technology (NRF-2012R1A6A3A04039257).

  14. Dense peripheral corneal clouding in Scheie syndrome.

    PubMed

    Summers, C G; Whitley, C B; Holland, E J; Purple, R L; Krivit, W

    1994-05-01

    A 28-year-old woman with Scheie syndrome (MPS I-S) presented with the unusual feature of extremely dense peripheral corneal clouding, allowing maintenance of good central visual acuity. Characteristic systemic features, an abnormal electroretinogram result, and absent alpha-L-iduronidase activity confirmed the diagnosis despite the unusual corneal pattern of clouding.

  15. Dense matter at RAON: Challenges and possibilities

    NASA Astrophysics Data System (ADS)

    Lee, Yujeong; Lee, Chang-Hwan; Gaitanos, T.; Kim, Youngman

    2016-11-01

    Dense nuclear matter is ubiquitous in modern nuclear physics because it is related to many interesting microscopic and macroscopic phenomena such as heavy ion collisions, nuclear structure, and neutron stars. The on-going rare isotope science project in Korea will build up a rare isotope accelerator complex called RAON. One of the main goals of RAON is to investigate rare isotope physics including dense nuclear matter. Using the relativistic Boltzmann-Uehling-Uhlenbeck (RBUU) transport code, we estimate the properties of nuclear matter that can be created from low-energy heavyion collisions at RAON.We give predictions for the maximum baryon density, the isospin asymmetry and the temperature of nuclear matter that would be formed during 197Au+197Au and 132Sn+64Ni reactions. With a large isospin asymmetry, various theoretical studies indicate that the critical densities or temperatures of phase transitions to exotic states decrease. Because a large isospin asymmetry is expected in the dense matter created at RAON, we discuss possibilities of observing exotic states of dense nuclear matter at RAON for large isospin asymmetry.

  16. Preparation of a dense, polycrystalline ceramic structure

    SciTech Connect

    Cooley, Jason; Chen, Ching-Fong; Alexander, David

    2010-12-07

    Ceramic nanopowder was sealed inside a metal container under a vacuum. The sealed evacuated container was forced through a severe deformation channel at an elevated temperature below the melting point of the ceramic nanopowder. The result was a dense nanocrystalline ceramic structure inside the metal container.

  17. Dense high temperature ceramic oxide superconductors

    DOEpatents

    Landingham, R.L.

    1993-10-12

    Dense superconducting ceramic oxide articles of manufacture and methods for producing these articles are described. Generally these articles are produced by first processing these superconducting oxides by ceramic processing techniques to optimize materials properties, followed by reestablishing the superconducting state in a desired portion of the ceramic oxide composite.

  18. Dense high temperature ceramic oxide superconductors

    DOEpatents

    Landingham, Richard L.

    1993-01-01

    Dense superconducting ceramic oxide articles of manufacture and methods for producing these articles are described. Generally these articles are produced by first processing these superconducting oxides by ceramic processing techniques to optimize materials properties, followed by reestablishing the superconducting state in a desired portion of the ceramic oxide composite.

  19. Improvements in accuracy of dense OPC models

    NASA Astrophysics Data System (ADS)

    Kallingal, Chidam; Oberschmidt, James; Viswanathan, Ramya; Abdo, Amr; Park, OSeo

    2008-10-01

    Performing model-based optical proximity correction (MBOPC) on layouts has become an integral part of patterning advanced integrated circuits. Earlier technologies used sparse OPC, the run times of which explode when the density of layouts increases. With the move to 45 nm technology node, this increase in run time has resulted in a shift to dense simulation OPC, which is pixel-based. The dense approach becomes more efficient at 45nm technology node and beyond. New OPC model forms can be used with the dense simulation OPC engine, providing the greater accuracy required by smaller technology nodes. Parameters in the optical model have to be optimized to achieve the required accuracy. Dense OPC uses a resist model with a different set of parameters than sparse OPC. The default search ranges used in the optimization of these resist parameters do not always result in the best accuracy. However, it is possible to improve the accuracy of the resist models by understanding the restrictions placed on the search ranges of the physical parameters during optimization. This paper will present results showing the correlation between accuracy of the models and some of these optical and resist parameters. The results will show that better optimization can improve the model fitness of features in both the calibration and verification set.

  20. DNS of turbulent flows of dense gases

    NASA Astrophysics Data System (ADS)

    Sciacovelli, L.; Cinnella, P.; Gloerfelt, X.; Grasso, F.

    2017-03-01

    The influence of dense gas effects on compressible turbulence is investigated by means of numerical simulations of the decay of compressible homogeneous isotropic turbulence (CHIT) and of supersonic turbulent flows through a plane channel (TCF). For both configurations, a parametric study on the Mach and Reynolds numbers is carried out. The dense gas considered in these parametric studies is PP11, a heavy fluorocarbon. The results are systematically compared to those obtained for a diatomic perfect gas (air). In our computations, the thermodynamic behaviour of the dense gases is modelled by means of the Martin-Hou equation of state. For CHIT cases, initial turbulent Mach numbers up to 1 are analyzed using mesh resolutions up to 5123. For TCF, bulk Mach numbers up to 3 and bulk Reynolds numbers up to 12000 are investigated. Average profiles of the thermodynamic quantities exhibit significant differences with respect to perfect-gas solutions for both of the configurations. For high-Mach CHIT, compressible structures are modified with respect to air, with weaker eddy shocklets and stronger expansions. In TCF, the velocity profiles of dense gas flows are much less sensitive to the Mach number and collapse reasonably well in the logarithmic region without any special need for compressible scalings, unlike the case of air, and the overall flow behaviour is midway between that of a variable-property liquid and that of a gas.

  1. DENSE NONAQUEOUS PHASE LIQUIDS -- A WORKSHOP SUMMARY

    EPA Science Inventory

    site characterization, and, therefore, DNAPL remediation, can be expected. Dense nonaqueous phase liquids (DNAPLs) in the subsurface are long-term sources of ground-water contamination, and may persist for centuries before dissolving completely in adjacent ground water. In respo...

  2. Burning Of Dense Clusters Of Fuel Drops

    NASA Technical Reports Server (NTRS)

    Bellan, Josette; Harstad, Kenneth G.

    1992-01-01

    Report presents theoretical study of evaporation, ignition, and combustion of rich and relatively dense clusters of drops of liquid fuel. Focus on interactions between heterogenous liquid/gas mixture in cluster and flame surrounding it. Theoretical model of evaporation, ignition, and combustion presented.

  3. Parenteral iron therapy options.

    PubMed

    Silverstein, Scott B; Rodgers, George M

    2004-05-01

    Parenteral iron therapy is occasionally necessary for patients intolerant or unresponsive to oral iron therapy, for receiving recombinant erythropoietin therapy, or for use in treating functional iron deficiency. There are now three parenteral iron products available: iron dextran, ferric gluconate, and iron sucrose. We summarize the advantages and disadvantages of each product, including risk of anaphylaxis and hypersensitivity, dosage regimens, and costs. The increased availability of multiple parenteral iron preparations should decrease the need to use red cell transfusions in patients with iron-deficiency anemia.

  4. Iron and vegetarian diets.

    PubMed

    Saunders, Angela V; Craig, Winston J; Baines, Surinder K; Posen, Jennifer S

    2013-08-19

    Vegetarians who eat a varied and well balanced diet are not at any greater risk of iron deficiency anaemia than non-vegetarians. A diet rich in wholegrains, legumes, nuts, seeds, dried fruits, iron-fortified cereals and green leafy vegetables provides an adequate iron intake. Vitamin C and other organic acids enhance non-haem iron absorption, a process that is carefully regulated by the gut. People with low iron stores or higher physiological need for iron will tend to absorb more iron and excrete less. Research to date on iron absorption has not been designed to accurately measure absorption rates in typical Western vegetarians with low ferritin levels.

  5. Flexure modelling at seamounts with dense cores

    NASA Astrophysics Data System (ADS)

    Kim, Seung-Sep; Wessel, Paul

    2010-08-01

    The lithospheric response to seamounts and ocean islands has been successfully described by deformation of an elastic plate induced by a given volcanic load. If the shape and mass of a seamount are known, the lithospheric flexure due to the seamount is determined by the thickness of an elastic plate, Te, which depends on the load density and the age of the plate at the time of seamount construction. We can thus infer important thermomechanical properties of the lithosphere from Te estimates at seamounts and their correlation with other geophysical inferences, such as cooling of the plate. Whereas the bathymetry (i.e. shape) of a seamount is directly observable, the total mass often requires an assumption of the internal seamount structure. The conventional approach considers the seamount to have a uniform density (e.g. density of the crust). This choice, however, tends to bias the total mass acting on an elastic plate. In this study, we will explore a simple approximation to the seamount's internal structure that considers a dense core and a less dense outer edifice. Although the existence of a core is supported by various gravity and seismic studies, the role of such volcanic cores in flexure modelling has not been fully addressed. Here, we present new analytic solutions for plate flexure due to axisymmetric dense core loads, and use them to examine the effects of dense cores in flexure calculations for a variety of synthetic cases. Comparing analytic solutions with and without a core indicates that the flexure model with uniform density underestimates Te by at least 25 per cent. This bias increases when the uniform density is taken to be equal to the crustal density. We also propose a practical application of the dense core model by constructing a uniform density load of same mass as the dense core load. This approximation allows us to compute the flexural deflection and gravity anomaly of a seamount in the wavenumber domain and minimize the limitations

  6. Manufacturability of dense hole arrays with directed self-assembly using the CHIPS flow

    NASA Astrophysics Data System (ADS)

    Singh, Arjun; Nam, Jaewoo; Lee, Jongsu; Chan, Boon Teik; Wu, Hengpeng; Yin, Jian; Cao, Yi; Gronheid, Roel

    2016-03-01

    Directed self-assembly (DSA) of block copolymers (BCP) has attracted significant interest as a patterning technique over the past few years. We have previously reported the development of a new process flow, the CHIPS flow (Chemo-epitaxy Induced by Pillar Structures), where we use ArFi lithography and plasma etch to print guiding pillar patterns for the DSA of cylindrical phase BCPs into dense hexagonal hole arrays of 22.5 nm half-pitch and 15 nm half-pitch [1]. The ability of this DSA process to generate dense regular patterns makes it an excellent candidate for patterning memory devices. Thus, in this paper we study the applicability of the CHIPS flow to patterning for DRAM storage layers. We report the impact of various process conditions on defect density, defect types and pattern variability. We also perform detailed analysis of the DSA patterns, quantify pattern placement accuracy and demonstrate a route towards excellent LCDU after pattern transfer into a hard mask layer.

  7. Superfluidity and vortices in dense quark matter

    NASA Astrophysics Data System (ADS)

    Mallavarapu, Satyanarayana Kumar

    This dissertation will elucidate specific features of superfluid behavior in dense quark matter, It will start with issues regarding spontaneous decay of superfluid vortices in dense quark matter. This will be followed by topics that explain superfluid phenomena from field theoretical viewpoint. In particular the first part of the dissertation will talk about superfluid vortices in the color-flavor-locked (CFL) phase of dense quark matter which are known to be energetically disfavored as compared to well-separated triplets of "semi-superfluid" color flux tubes. In this talk we will provide results which will identify regions in parameter space where the superfluid vortex spontaneously decays. We will also discuss the nature of the mode that is responsible for the decay of a superfluid vortex in dense quark matter. We will conclude by mentioning the implications of our results to neutron stars. In the field theoretic formulation of a zero-temperature superfluid one connects the superfluid four-velocity which is a macroscopic observable with a microscopic field variable namely the gradient of the phase of a Bose-Condensed scalar field. On the other hand, a superfluid at nonzero temperatures is usually described in terms of a two-fluid model: the superfluid and the normal fluid. In the later part of the dissertation we offer a deeper understanding of the two-fluid model by deriving it from an underlying microscopic field theory. In particular, we shall obtain the macroscopic properties of a uniform, dissipationless superfluid at low temperatures and weak coupling within the framework of a ϕ 4 model. Though our study is very general, it may also be viewed as a step towards understanding the superfluid properties of various phases of dense nuclear and quark matter in the interior of compact star.

  8. Chemical Dense Gas Modeling in Cities

    NASA Astrophysics Data System (ADS)

    Brown, M. J.; Williams, M. D.; Nelson, M. A.; Streit, G. E.

    2007-12-01

    Many industrial facilities have on-site storage of chemicals and are within a few kilometers of residential population. Chemicals are transported around the country via trains and trucks and often go through populated areas on their journey. Many of the chemicals, like chlorine and phosgene, are toxic and when released into the air are heavier-than-air dense gases that hug the ground and result in high airborne concentrations at breathing level. There is considerable concern about the vulnerability of these stored and transported chemicals to terrorist attack and the impact a release could have on highly-populated urban areas. There is the possibility that the impacts of a dense gas release within a city would be exacerbated since the buildings might act to trap the toxic cloud at street level and channel it over a large area down side streets. However, no one is quite sure what will happen for a release in cities since there is a dearth of experimental data. There are a number of fast-running dense gas models used in the air pollution and emergency response community, but there are none that account for the complex flow fields and turbulence generated by buildings. As part of this presentation, we will discuss current knowledge regarding dense gas releases around buildings and other obstacles. We will present information from wind tunnel and field experiments, as well as computational fluid dynamics modeling. We will also discuss new fast response modeling efforts which are trying to account for dense gas transport and dispersion in cities.

  9. Surface complexation of Pb(II) by hexagonal birnessite nanoparticles

    SciTech Connect

    Kwon, K.; Refson, K.; Sposito, G.

    2010-10-15

    Natural hexagonal birnessite is a poorly-crystalline layer type Mn(IV) oxide precipitated by bacteria and fungi which has a particularly high adsorption affinity for Pb(II). X-ray spectroscopic studies have shown that Pb(II) forms strong inner-sphere surface complexes mainly at two sites on hexagonal birnessite nanoparticles: triple corner-sharing (TCS) complexes on Mn(IV) vacancies in the interlayers and double edge-sharing (DES) complexes on lateral edge surfaces. Although the TCS surface complex has been well characterized by spectroscopy, some important questions remain about the structure and stability of the complexes occurring on the edge surfaces. First-principles simulation techniques such as density functional theory (DFT) offer a useful way to address these questions by providing complementary information that is difficult to obtain by spectroscopy. Following this computational approach, we used spin-polarized DFT to perform total-energy-minimization geometry optimizations of several possible Pb(II) surface complexes on model birnessite nanoparticles similar to those that have been studied experimentally. We first validated our DFT calculations by geometry optimizations of (1) the Pb-Mn oxyhydroxide mineral, quenselite (PbMnO{sub 2}OH), and (2) the TCS surface complex, finding good agreement with experimental structural data while uncovering new information about bonding and stability. Our geometry optimizations of several protonated variants of the DES surface complex led us to conclude that the observed edge-surface species is very likely to be this complex if the singly-coordinated terminal O that binds to Pb(II) is protonated. Our geometry optimizations also revealed that an unhydrated double corner-sharing (DCS) species that has been proposed as an alternative to the DES complex is intrinsically unstable on nanoparticle edge surfaces, but could become stabilized if the local coordination environment is well-hydrated. A significant similarity exists

  10. Surface complexation of Pb(II) by hexagonal birnessite nanoparticles

    NASA Astrophysics Data System (ADS)

    Kwon, Kideok D.; Refson, Keith; Sposito, Garrison

    2010-12-01

    Natural hexagonal birnessite is a poorly crystalline layer type Mn(IV) oxide precipitated by bacteria and fungi which has a particularly high adsorption affinity for Pb(II). X-ray spectroscopic studies have shown that Pb(II) forms strong inner-sphere surface complexes mainly at two sites on hexagonal birnessite nanoparticles: triple corner-sharing (TCS) complexes on Mn(IV) vacancies in the interlayers and double edge-sharing (DES) complexes on lateral edge surfaces. Although the TCS surface complex has been well characterized by spectroscopy, some important questions remain about the structure and stability of the complexes occurring on the edge surfaces. First-principles simulation techniques such as density functional theory (DFT) offer a useful way to address these questions by providing complementary information that is difficult to obtain by spectroscopy. Following this computational approach, we used spin-polarized DFT to perform total-energy-minimization geometry optimizations of several possible Pb(II) surface complexes on model birnessite nanoparticles similar to those that have been studied experimentally. We first validated our DFT calculations by geometry optimizations of (1) the Pb-Mn oxyhydroxide mineral, quenselite (PbMnO 2OH), and (2) the TCS surface complex, finding good agreement with experimental structural data while uncovering new information about bonding and stability. Our geometry optimizations of several protonated variants of the DES surface complex led us to conclude that the observed edge-surface species is very likely to be this complex if the singly coordinated terminal O that binds to Pb(II) is protonated. Our geometry optimizations also revealed that an unhydrated double corner-sharing (DCS) species that has been proposed as an alternative to the DES complex is intrinsically unstable on nanoparticle edge surfaces, but could become stabilized if the local coordination environment is well-hydrated. A significant similarity exists in

  11. Iron-Refractory Iron Deficiency Anemia

    PubMed Central

    Yılmaz Keskin, Ebru; Yenicesu, İdil

    2015-01-01

    Iron is essential for life because it is indispensable for several biological reactions, such as oxygen transport, DNA synthesis, and cell proliferation. Over the past few years, our understanding of iron metabolism and its regulation has changed dramatically. New disorders of iron metabolism have emerged, and the role of iron as a cofactor in other disorders has begun to be recognized. The study of genetic conditions such as hemochromatosis and iron-refractory iron deficiency anemia (IRIDA) has provided crucial insights into the molecular mechanisms controlling iron homeostasis. In the future, these advances may be exploited to improve treatment of both genetic and acquired iron disorders. IRIDA is caused by mutations in TMPRSS6, the gene encoding matriptase-2, which downregulates hepcidin expression under conditions of iron deficiency. The typical features of this disorder are hypochromic, microcytic anemia with a very low mean corpuscular volume of erythrocytes, low transferrin saturation, no (or inadequate) response to oral iron, and only a partial response to parenteral iron. In contrast to classic iron deficiency anemia, serum ferritin levels are usually low-normal, and serum or urinary hepcidin levels are inappropriately high for the degree of anemia. Although the number of cases reported thus far in the literature does not exceed 100, this disorder is considered the most common of the “atypical” microcytic anemias. The aim of this review is to share the current knowledge on IRIDA and increase awareness in this field. PMID:25805669

  12. Iron-refractory iron deficiency anemia.

    PubMed

    Yılmaz Keskin, Ebru; Yenicesu, İdil

    2015-03-05

    Iron is essential for life because it is indispensable for several biological reactions, such as oxygen transport, DNA synthesis, and cell proliferation. Over the past few years, our understanding of iron metabolism and its regulation has changed dramatically. New disorders of iron metabolism have emerged, and the role of iron as a cofactor in other disorders has begun to be recognized. The study of genetic conditions such as hemochromatosis and iron-refractory iron deficiency anemia (IRIDA) has provided crucial insights into the molecular mechanisms controlling iron homeostasis. In the future, these advances may be exploited to improve treatment of both genetic and acquired iron disorders. IRIDA is caused by mutations in TMPRSS6, the gene encoding matriptase-2, which downregulates hepcidin expression under conditions of iron deficiency. The typical features of this disorder are hypochromic, microcytic anemia with a very low mean corpuscular volume of erythrocytes, low transferrin saturation, no (or inadequate) response to oral iron, and only a partial response to parenteral iron. In contrast to classic iron deficiency anemia, serum ferritin levels are usually low-normal, and serum or urinary hepcidin levels are inappropriately high for the degree of anemia. Although the number of cases reported thus far in the literature does not exceed 100, this disorder is considered the most common of the "atypical" microcytic anemias. The aim of this review is to share the current knowledge on IRIDA and increase awareness in this field.

  13. Electronic Structure of Graphene and Germanene Based on Double Hexagonal Structure

    NASA Astrophysics Data System (ADS)

    Naji, S.; Belhaj, A.; Labrim, H.; Benyoussef, A.; El Kenz, A.

    2013-11-01

    In this paper, we study the electronic structure of monolayer materials based on a double hexagonal geometry with (1×1) and (√ 3 × √ 3)R30o superstructures. Inspired from the two-dimensional root system of an exceptional Lie algebra called G2, this hexagonal atomic configuration involves two hexagons of unequal side length at angle 30°. The principal unit hexagonal cell contains twelve atoms instead of the usual configuration involving only six ones relying only on the (1×1) superstructure. Using ab initio calculations based on FPLO9.00-34 code, we investigate numerically the graphene and the germanene with the double hexagonal geometry. In particular, we find that the usual electronic properties and the lattice parameters of such materials are modified. More precisely, the lattice parameters are increased. It has been shown that, in the single hexagonal geometry, the grapheme and the germanene behave as a gapless semiconductor and a semi-metallic, respectively. In double hexagonal geometry however, both materials becomes metallic.

  14. Survival and failure modes: platform-switching for internal and external hexagon cemented fixed dental prostheses.

    PubMed

    Anchieta, Rodolfo B; Machado, Lucas S; Hirata, Ronaldo; Coelho, Paulo G; Bonfante, Estevam A

    2016-10-01

    This study evaluated the probability of survival (reliability) of platform-switched fixed dental prostheses (FDPs) cemented on different implant-abutment connection designs. Eighty-four-three-unit FDPs (molar pontic) were cemented on abutments connected to two implants of external or internal hexagon connection. Four groups (n = 21 each) were established: external hexagon connection and regular platform (ERC); external hexagon connection and switched platform (ESC); internal hexagon and regular platform (IRC); and internal hexagon and switched platform (ISC). Prostheses were subjected to step-stress accelerated life testing in water. Weibull curves and probability of survival for a mission of 100,000 cycles at 400 N (two-sided 90% CI) were calculated. The beta values of 0.22, 0.48, 0.50, and 1.25 for groups ERC, ESC, IRC, and ISC, respectively, indicated a limited role of fatigue in damage accumulation, except for group ISC. Survival decreased for both platform-switched groups (ESC: 74%, and ISC: 59%) compared with the regular matching platform counterparts (ERC: 95%, and IRC: 98%). Characteristic strength was higher only for ERC compared with ESC, but not different between internal connections. Failures chiefly involved the abutment screw. Platform switching decreased the probability of survival of FDPs on both external and internal connections. The absence in loss of characteristic strength observed in internal hexagon connections favor their use compared with platform-switched external hexagon connections. © 2016 Eur J Oral Sci.

  15. Prevention of iron deficiency.

    PubMed

    Hallberg, L

    1994-12-01

    This chapter discusses different methods to prevent iron deficiency--to reduce iron losses (e.g. reducing menstrual iron losses by using a contraceptive pill or combating of hookworm infestation) or to increase iron absorption. Iron absorption can be increased (1) by modifying the composition of meals--increasing the content of dietary factors enhancing iron absorption (e.g. meat and ascorbic acid) or reducing the content of factors inhibiting iron absorption such as phytate and iron-binding phenolic compounds, (2) by increasing the iron content of the diet by fortification with iron, or by (3) supplementation with iron tablets. Several factors to consider in the choice of strategy are discussed such as the importance of the bioavailability of the diet for the efficacy of iron fortification, the choice of vehicle for iron fortification that is compatible with the iron compound used, the feasibility to increase the bioavailability of the dietary iron by modification of the composition of the diet and the short time available in pregnancy to ensure a sufficient supply of the extra iron needed limiting the effective measures available to supplementation with iron tablets.

  16. Whispering Gallery Modes in Hexagonal Zinc Oxide Micro- and Nanocrystals

    NASA Astrophysics Data System (ADS)

    Nobis, Thomas; Kaidashev, Evgeni M.; Rahm, Andreas; Lorenz, Michael; Grundmann, Marius

    The resonator properties of zinc oxide (ZnO) micro- and nanocrystals grown by a novel high pressure pulsed laser deposition process have been investigated at room temperature by cathodoluminescence (CL), spatially resolved CL-imaging and polarization resolved micro-photoluminescence (μ-PL) within the visible spectral range. The spectra exhibit a series of comparatively sharp and almost equidistant resonance lines. Using a simple plane wave interference model and taking into account the spectral characteristic n(ω) of the refractive index of ZnO, we can unambiguously attribute those lines to whispering gallery modes (WGMs) of a two dimensional hexagonal resonator. The predicted resonator diameters agree well with the measured crystal sizes. Tapered, high aspect ratio ZnO nanoneedles furthermore allow systematic investigations of the WGMs as a function of cavity diameter D down to zero. Hence, the transition from a multi-mode to a single mode cavity is directly observed. μ-PL experiments demonstrate that the WGMs are mainly TM polarized.

  17. Superconductivity in the Hexagonal Ternary Phosphide ScIrP

    NASA Astrophysics Data System (ADS)

    Okamoto, Yoshihiko; Inohara, Takumi; Yamakawa, Youichi; Yamakage, Ai; Takenaka, Koshi

    2016-01-01

    We report the discovery of a bulk superconducting transition at 3.4 K in the ternary phosphide, ScIrP, which crystallizes in a hexagonal ZrNiAl-type structure without spatial inversion symmetry. On the basis of heat capacity data in a zero magnetic field, ScIrP is suggested to be a weakly-coupled Bardeen-Cooper-Schrieffer superconductor. Alternatively, experimental results under magnetic fields indicate that this material is a type-II superconductor with an upper critical field Hc2 at magnetic fields above 5 T at zero temperature. This moderately high Hc2 does not violate the Pauli limit, but it does imply that there is a significant effect from the strong spin-orbit interaction of Ir 5d electrons in the noncentrosymmetric crystal structure. Electronic structure calculations show an interesting feature of ScIrP, where both the Sc 3d and Ir 5d orbitals contribute to the electronic density of states at the Fermi level.

  18. Hexagonal tungsten oxide nanoflowers as enzymatic mimetics and electrocatalysts

    NASA Astrophysics Data System (ADS)

    Park, Chan Yeong; Seo, Ji Min; Jo, Hongil; Park, Juhyun; Ok, Kang Min; Park, Tae Jung

    2017-01-01

    Tungsten oxide (WOx) has been widely studied for versatile applications based on its photocatalytic, intrinsic catalytic, and electrocatalytic properties. Among the several nanostructures, we focused on the flower-like structures to increase the catalytic efficiency on the interface with both increased substrate interaction capacities due to their large surface area and efficient electron transportation. Therefore, improved WOx nanoflowers (WONFs) with large surface areas were developed through a simple hydrothermal method using sodium tungstate and hydrogen chloride solution at low temperature, without any additional surfactant, capping agent, or reducing agent. Structural determination and electrochemical analyses revealed that the WONFs have hexagonal Na0.17WO3.085·0.17H2O structure and exhibit peroxidase-like activity, turning from colorless to blue by catalyzing the oxidation of a peroxidase substrate, such as 3,3‧,5,5‧-tetramethylbenzidine, in the presence of H2O2. Additionally, a WONF-modified glassy carbon electrode was adopted to monitor the electrocatalytic reduction of H2O2. To verify the catalytic efficiency enhancement by the unique shape and structure of the WONFs, they were compared with calcinated WONFs, cesium WOx nanoparticles, and other peroxidase-like nanomaterials. The results indicated that the WONFs showed a low Michaelis-Menten constant (km), high maximal reaction velocity (vmax), and large surface area.

  19. Internal structure of hexagonal skyrmion lattices in cubic helimagnets

    NASA Astrophysics Data System (ADS)

    McGrouther, D.; Lamb, R. J.; Krajnak, M.; McFadzean, S.; McVitie, S.; Stamps, R. L.; Leonov, A. O.; Bogdanov, A. N.; Togawa, Y.

    2016-09-01

    We report the most precise observations to date concerning the spin structure of magnetic skyrmions in a nanowedge specimen of cubic B20 structured FeGe. Enabled by our development of advanced differential phase contrast (DPC) imaging (in a scanning transmission electron microscope (STEM)) we have obtained high spatial resolution quantitative measurements of skyrmion internal spin profile. For hexagonal skyrmion lattice cells, stabilised by an out-plane applied magnetic field, mapping of the in-plane component of magnetic induction has revealed precise spin profiles and that the internal structure possesses intrinsic six-fold symmetry. With increasing field strength, the diameter of skyrmion cores was measured to decrease and accompanied by a nonlinear variation of the lattice periodicity. Variations in structure for individual skyrmions across an area of the lattice were also studied utilising a new increased sensitivity DPC detection scheme and a variety of symmetry lowering distortions were observed. To provide insight into fundamental energetics we have constructed a phenomenological model, with which our experimental observations of spin profiles and field induced core diameter variation are in good agreement with predicted structure in the middle of the nanowedge crystal. In the vicinity of the crystal surfaces, our model predicts the existence of in-plane twisting distortions which our current experimental observations were not sensitive to. As an alternative to the requirement for as yet unidentified sources of magnetic anisotropy, we demonstrate that surface states could provide the energetic stabilisation needed for predomination over the conical magnetic phase.

  20. On plastic flow in notched hexagonal close packed single crystals

    NASA Astrophysics Data System (ADS)

    Selvarajou, Balaji; Kondori, Babak; Benzerga, A. Amine; Joshi, Shailendra P.

    2016-09-01

    The micromechanics of anisotropic plastic flow by combined slip and twinning is investigated computationally in single crystal notched specimens. Constitutive relations for hexagonal close packed materials are used which take into account elastic anisotropy, thirty potential deformation systems, various hardening mechanisms and rate-sensitivity. The specimens are loaded perpendicular to the c-axis but the presence of a notch generates three-dimensional triaxial stress states. The study is motivated by recent experiments on a polycrystalline magnesium alloy. To enable comparisons with these where appropriate, three sets of activation thresholds for the various deformation systems are used. For the conditions that most closely mimic the alloy material, attention is focused on the relative roles of pyramidal < c + a > and prismatic < a > slip, as well as on the emergence of {1012bar}[101bar1] extension twinning at sufficiently high triaxiality. In all cases, the spatial variations of stress triaxiality and plastic strain, inclusive of various system activities, are quantified along with their evolution upon straining. The implications of these findings in fundamental understanding of ductile failure of HCP alloys in general and Mg alloys in particular are discussed.

  1. Exfoliation of Hexagonal Boron Nitride via Ferric Chloride Intercalation

    NASA Technical Reports Server (NTRS)

    Hung, Ching-cheh; Hurst, Janet; Santiago, Diana; Rogers, Richard B.

    2014-01-01

    Sodium fluoride (NaF) was used as an activation agent to successfully intercalate ferric chloride (FeCl3) into hexagonal boron nitride (hBN). This reaction caused the hBN mass to increase by approx.100 percent, the lattice parameter c to decrease from 6.6585 to between 6.6565 and 6.6569 ?, the x-ray diffraction (XRD) (002) peak to widen from 0.01deg to 0.05deg of the full width half maximum value, the Fourier transform infrared (FTIR) spectrum's broad band (1277/cm peak) to change shape, and new FTIR bands to emerge at 3700 to 2700 and 1600/cm. This indicates hBN's structural and chemical properties are significantly changed. The intercalated product was hygroscopic and interacted with moisture in the air to cause further structural and chemical changes (from XRD and FTIR). During a 24-h hold at room temperature in air with 100 percent relative humidity, the mass increased another 141 percent. The intercalated product, hydrated or not, can be heated to 750 C in air to cause exfoliation. Exfoliation becomes significant after two intercalation-air heating cycles, when 20-nm nanosheets are commonly found. Structural and chemical changes indicated by XRD and FTIR data were nearly reversed after the product was placed in hydrochloric acid (HCl), resulting in purified, exfoliated, thin hBN products.

  2. Realization of highly efficient hexagonal boron nitride neutron detectors

    SciTech Connect

    Maity, A.; Doan, T. C.; Li, J.; Lin, J. Y.; Jiang, H. X.

    2016-08-16

    Here, we report the achievement of highly efficient 10B enriched hexagonal boron nitride (h- 10BN) direct conversion neutron detectors. These detectors were realized from freestanding 4-in. diameter h- 10BN wafers 43 μm in thickness obtained from epitaxy growth and subsequent mechanical separation from sapphire substrates. Both sides of the film were subjected to ohmic contact deposition to form a simple vertical “photoconductor-type” detector. Transport measurements revealed excellent vertical transport properties including high electrical resistivity (>1013 Ω cm) and mobility-lifetime (μτ) products. A much larger μτ product for holes compared to that of electrons along the c-axis of h- BN was observed, implying that holes (electrons) behave like majority (minority) carriers in undoped h- BN. Exposure to thermal neutrons from a californium-252 (252Cf) source moderated by a high density polyethylene moderator reveals that 43 μm h- 10BN detectors possess 51.4% detection efficiency at a bias voltage of 400 V, which is the highest reported efficiency for any semiconductor-based neutron detector. The results point to the possibility of obtaining highly efficient, compact solid-state neutron detectors with high gamma rejection and low manufacturing and maintenance costs.

  3. Realization of highly efficient hexagonal boron nitride neutron detectors

    DOE PAGES

    Maity, A.; Doan, T. C.; Li, J.; ...

    2016-08-16

    Here, we report the achievement of highly efficient 10B enriched hexagonal boron nitride (h- 10BN) direct conversion neutron detectors. These detectors were realized from freestanding 4-in. diameter h- 10BN wafers 43 μm in thickness obtained from epitaxy growth and subsequent mechanical separation from sapphire substrates. Both sides of the film were subjected to ohmic contact deposition to form a simple vertical “photoconductor-type” detector. Transport measurements revealed excellent vertical transport properties including high electrical resistivity (>1013 Ω cm) and mobility-lifetime (μτ) products. A much larger μτ product for holes compared to that of electrons along the c-axis of h- BN wasmore » observed, implying that holes (electrons) behave like majority (minority) carriers in undoped h- BN. Exposure to thermal neutrons from a californium-252 (252Cf) source moderated by a high density polyethylene moderator reveals that 43 μm h- 10BN detectors possess 51.4% detection efficiency at a bias voltage of 400 V, which is the highest reported efficiency for any semiconductor-based neutron detector. The results point to the possibility of obtaining highly efficient, compact solid-state neutron detectors with high gamma rejection and low manufacturing and maintenance costs.« less

  4. Spin transport in fully hexagonal boron nitride encapsulated graphene

    NASA Astrophysics Data System (ADS)

    Gurram, M.; Omar, S.; Zihlmann, S.; Makk, P.; Schönenberger, C.; van Wees, B. J.

    2016-03-01

    We study fully hexagonal boron nitride (hBN) encapsulated graphene spin valve devices at room temperature. The device consists of a graphene channel encapsulated between two crystalline hBN flakes: thick-hBN flake as a bottom gate dielectric substrate which masks the charge impurities from SiO2/Si substrate and single-layer thin-hBN flake as a tunnel barrier. Full encapsulation prevents the graphene from coming in contact with any polymer/chemical during the lithography and thus gives homogeneous charge and spin transport properties across different regions of the encapsulated graphene. Further, even with the multiple electrodes in-between the injection and the detection electrodes which are in conductivity mismatch regime, we observe spin transport over 12.5 -μ m -long distance under the thin-hBN encapsulated graphene channel, demonstrating the clean interface and the pinhole-free nature of the thin hBN as an efficient tunnel barrier.

  5. Realization of highly efficient hexagonal boron nitride neutron detectors

    NASA Astrophysics Data System (ADS)

    Maity, A.; Doan, T. C.; Li, J.; Lin, J. Y.; Jiang, H. X.

    2016-08-01

    We report the achievement of highly efficient 10B enriched hexagonal boron nitride (h-10BN) direct conversion neutron detectors. These detectors were realized from freestanding 4-in. diameter h-10BN wafers 43 μm in thickness obtained from epitaxy growth and subsequent mechanical separation from sapphire substrates. Both sides of the film were subjected to ohmic contact deposition to form a simple vertical "photoconductor-type" detector. Transport measurements revealed excellent vertical transport properties including high electrical resistivity (>1013 Ω cm) and mobility-lifetime (μτ) products. A much larger μτ product for holes compared to that of electrons along the c-axis of h-BN was observed, implying that holes (electrons) behave like majority (minority) carriers in undoped h-BN. Exposure to thermal neutrons from a californium-252 (252Cf) source moderated by a high density polyethylene moderator reveals that 43 μm h-10BN detectors possess 51.4% detection efficiency at a bias voltage of 400 V, which is the highest reported efficiency for any semiconductor-based neutron detector. The results point to the possibility of obtaining highly efficient, compact solid-state neutron detectors with high gamma rejection and low manufacturing and maintenance costs.

  6. Step flow versus mosaic film growth in hexagonal boron nitride.

    PubMed

    Lu, Jiong; Yeo, Pei Shan Emmeline; Zheng, Yi; Xu, Hai; Gan, Chee Kwan; Sullivan, Michael B; Castro Neto, A H; Loh, Kian Ping

    2013-02-13

    Many emerging applications of hexagonal boron nitride (h-BN) in graphene-based nanoelectronics require high-quality monolayers as the ultrathin dielectric. Here, the nucleation and growth of h-BN monolayer on Ru(0001) surface are investigated using scanning tunneling microscopy with a view toward understanding the process of defect formation on a strongly interacted interface. In contrast to homoelemental bonding in graphene, the heteroelemental nature of h-BN gives rise to growth fronts with elemental polarity. This can have consequences in the different stages of film growth, from the nucleation of h-BN magic clusters and their sintering to form compact triangular islands to the growth of patchwork mosaic monolayer with a high density of misfit boundaries. The parallel alignment of triangular islands on the same terrace produces translational fault lines when growth fronts merge, while antiparallel alignment of islands on adjacent terraces produces non-bonded fault lines between domains terminated by like atoms. With these insights into the generation of void defects and fault lines at grain boundaries, we demonstrate a strategy to obtain high-quality h-BN monolayer film based on step flow growth.

  7. DNA Translocation through Hydrophilic Nanopore in Hexagonal Boron Nitride

    PubMed Central

    Zhou, Zhi; Hu, Ying; Wang, Hao; Xu, Zhi; Wang, Wenlong; Bai, Xuedong; Shan, Xinyan; Lu, Xinghua

    2013-01-01

    Ultra-thin solid-state nanopore with good wetting property is strongly desired to achieve high spatial resolution for DNA sequencing applications. Atomic thick hexagonal boron nitride (h-BN) layer provides a promising two-dimensional material for fabricating solid-state nanopores. Due to its good oxidation resistance, the hydrophilicity of h-BN nanopore device can be significantly improved by UV-Ozone treatment. The contact angle of a KCl-TE droplet on h-BN layer can be reduced from 57° to 26° after the treatment. Abundant DNA translocation events have been observed in such devices, and strong DNA-nanopore interaction has been revealed in pores smaller than 10 nm in diameter. The 1/f noise level is closely related to the area of suspended h-BN layer, and it is significantly reduced in smaller supporting window. The demonstrated performance in h-BN nanopore paves the way towards base discrimination in a single DNA molecule. PMID:24256703

  8. Layer-by-layer dielectric breakdown of hexagonal boron nitride.

    PubMed

    Hattori, Yoshiaki; Taniguchi, Takashi; Watanabe, Kenji; Nagashio, Kosuke

    2015-01-27

    Hexagonal boron nitride (BN) is widely used as a substrate and gate insulator for two-dimensional (2D) electronic devices. The studies on insulating properties and electrical reliability of BN itself, however, are quite limited. Here, we report a systematic investigation of the dielectric breakdown characteristics of BN using conductive atomic force microscopy. The electric field strength was found to be ∼ 12 MV/cm, which is comparable to that of conventional SiO2 oxides because of the covalent bonding nature of BN. After the hard dielectric breakdown, the BN fractured like a flower into equilateral triangle fragments. However, when the applied voltage was terminated precisely in the middle of the dielectric breakdown, the formation of a hole that did not penetrate to the bottom metal electrode was clearly observed. Subsequent I-V measurements of the hole indicated that the BN layer remaining in the hole was still electrically inactive. On the basis of these observations, layer-by-layer breakdown was confirmed for BN with regard to both physical fracture and electrical breakdown. Moreover, statistical analysis of the breakdown voltages using a Weibull plot suggested the anisotropic formation of defects. These results are unique to layered materials and unlike the behavior observed for conventional 3D amorphous oxides.

  9. Tilted hexagonal post arrays: DNA electrophoresis in anisotropic media.

    PubMed

    Chen, Zhen; Dorfman, Kevin D

    2014-02-01

    Using Brownian dynamics simulations, we show that DNA electrophoresis in a hexagonal array of micron-sized posts changes qualitatively when the applied electric field vector is not coincident with the lattice vectors of the array. DNA electrophoresis in such "tilted" post arrays is superior to the standard "un-tilted" approach; while the time required to achieve a resolution of unity in a tilted post array is similar to an un-tilted array at a low-electric field strengths, this time (i) decreases exponentially with electric field strength in a tilted array and (ii) increases exponentially with electric field strength in an un-tilted array. Although the DNA dynamics in a post array are complicated, the electrophoretic mobility results indicate that the "free path," i.e. the average distance of ballistic trajectories of point-sized particles launched from random positions in the unit cell until they intersect the next post, is a useful proxy for the detailed DNA trajectories. The analysis of the free path reveals a fundamental connection between anisotropy of the medium and DNA transport therein that goes beyond simply improving the separation device.

  10. The ARIANNA Hexagonal Radio Array - performance and prospects

    NASA Astrophysics Data System (ADS)

    Hallgren, Allan

    2016-04-01

    The origin of the highest energy cosmic rays at ˜1020 eV is still unknown. Ultra-high energy neutrinos from the GZK process should provide information on the sources and their properties. A promising and cost effective method for observing GZK-neutrinos is based on detection of Askaryan radio pulses with antennas installed in ice. The ARIANNA project aims at instrumenting a 36*36 km2 large area on the Ross Ice Shelf with an array of radio detection stations. The deployment of a test system for ARIANNA, the Hexagonal Radio Array (HRA), was completed in December 2014. The three first stations were installed in 2012. Solar panels are used to drive the < 10 W stations. The system hibernated at sunset in April and all stations returned to operation in September. The site is essentially free of anthropogenic noise. Simple cuts eliminate background and provides for efficient selection of neutrino events. Prospects for the sensitivity of the full ARIANNA array to the flux of GZK neutrinos are shown.

  11. DNA Translocation through Hydrophilic Nanopore in Hexagonal Boron Nitride

    NASA Astrophysics Data System (ADS)

    Zhou, Zhi; Hu, Ying; Wang, Hao; Xu, Zhi; Wang, Wenlong; Bai, Xuedong; Shan, Xinyan; Lu, Xinghua

    2013-11-01

    Ultra-thin solid-state nanopore with good wetting property is strongly desired to achieve high spatial resolution for DNA sequencing applications. Atomic thick hexagonal boron nitride (h-BN) layer provides a promising two-dimensional material for fabricating solid-state nanopores. Due to its good oxidation resistance, the hydrophilicity of h-BN nanopore device can be significantly improved by UV-Ozone treatment. The contact angle of a KCl-TE droplet on h-BN layer can be reduced from 57° to 26° after the treatment. Abundant DNA translocation events have been observed in such devices, and strong DNA-nanopore interaction has been revealed in pores smaller than 10 nm in diameter. The 1/f noise level is closely related to the area of suspended h-BN layer, and it is significantly reduced in smaller supporting window. The demonstrated performance in h-BN nanopore paves the way towards base discrimination in a single DNA molecule.

  12. DNA Sequencing by Hexagonal Boron Nitride Nanopore: A Computational Study

    PubMed Central

    Zhang, Liuyang; Wang, Xianqiao

    2016-01-01

    The single molecule detection associated with DNA sequencing has motivated intensive efforts to identify single DNA bases. However, little research has been reported utilizing single-layer hexagonal boron nitride (hBN) for DNA sequencing. Here we employ molecular dynamics simulations to explore pathways for single-strand DNA (ssDNA) sequencing by nanopore on the hBN sheet. We first investigate the adhesive strength between nucleobases and the hBN sheet, which provides the foundation for the hBN-base interaction and nanopore sequencing mechanism. Simulation results show that the purine base has a more remarkable energy profile and affinity than the pyrimidine base on the hBN sheet. The threading of ssDNA through the hBN nanopore can be clearly identified due to their different energy profiles and conformations with circular nanopores on the hBN sheet. The sequencing process is orientation dependent when the shape of the hBN nanopore deviates from the circle. Our results open up a promising avenue to explore the capability of DNA sequencing by hBN nanopore.

  13. Transport properties of ultrathin black phosphorus on hexagonal boron nitride

    SciTech Connect

    Doganov, Rostislav A.; Özyilmaz, Barbaros; Koenig, Steven P.; Yeo, Yuting; Watanabe, Kenji; Taniguchi, Takashi

    2015-02-23

    Ultrathin black phosphorus, or phosphorene, is a two-dimensional material that allows both high carrier mobility and large on/off ratios. Similar to other atomic crystals, like graphene or layered transition metal dichalcogenides, the transport behavior of few-layer black phosphorus is expected to be affected by the underlying substrate. The properties of black phosphorus have so far been studied on the widely utilized SiO{sub 2} substrate. Here, we characterize few-layer black phosphorus field effect transistors on hexagonal boron nitride—an atomically smooth and charge trap-free substrate. We measure the temperature dependence of the field effect mobility for both holes and electrons and explain the observed behavior in terms of charged impurity limited transport. We find that in-situ vacuum annealing at 400 K removes the p-doping of few-layer black phosphorus on both boron nitride and SiO{sub 2} substrates and reduces the hysteresis at room temperature.

  14. Exciton energy-momentum map of hexagonal boron nitride

    NASA Astrophysics Data System (ADS)

    Fugallo, Giorgia; Aramini, Matteo; Koskelo, Jaakko; Watanabe, Kenji; Taniguchi, Takashi; Hakala, Mikko; Huotari, Simo; Gatti, Matteo; Sottile, Francesco

    2015-10-01

    Understanding and controlling the way excitons propagate in solids is a key for tailoring materials with improved optoelectronic properties. A fundamental step in this direction is the determination of the exciton energy-momentum dispersion. Here, thanks to the solution of the parameter-free Bethe-Salpeter equation (BSE), we draw and explain the exciton energy-momentum map of hexagonal boron nitride (h-BN) in the first three Brillouin zones. We show that h-BN displays strong excitonic effects not only in the optical spectra at vanishing momentum q , as previously reported, but also at large q . We validate our theoretical predictions by assessing the calculated exciton map by means of an inelastic x-ray scattering (IXS) experiment. Moreover, we solve the discrepancies between previous experimental data and calculations, proving then that the BSE is highly accurate through the whole momentum range. Therefore, these results put forward the combination BSE and IXS as the tool of choice for addressing the exciton dynamics in complex materials.

  15. Realization of highly efficient hexagonal boron nitride neutron detectors

    SciTech Connect

    Maity, A.; Doan, T. C.; Li, J.; Lin, J. Y.; Jiang, H. X.

    2016-08-16

    Here, we report the achievement of highly efficient 10B enriched hexagonal boron nitride (h- 10BN) direct conversion neutron detectors. These detectors were realized from freestanding 4-in. diameter h- 10BN wafers 43 μm in thickness obtained from epitaxy growth and subsequent mechanical separation from sapphire substrates. Both sides of the film were subjected to ohmic contact deposition to form a simple vertical “photoconductor-type” detector. Transport measurements revealed excellent vertical transport properties including high electrical resistivity (>1013 Ω cm) and mobility-lifetime (μτ) products. A much larger μτ product for holes compared to that of electrons along the c-axis of h- BN was observed, implying that holes (electrons) behave like majority (minority) carriers in undoped h- BN. Exposure to thermal neutrons from a californium-252 (252Cf) source moderated by a high density polyethylene moderator reveals that 43 μm h- 10BN detectors possess 51.4% detection efficiency at a bias voltage of 400 V, which is the highest reported efficiency for any semiconductor-based neutron detector. The results point to the possibility of obtaining highly efficient, compact solid-state neutron detectors with high gamma rejection and low manufacturing and maintenance costs.

  16. Optical Signatures of Quantum Emitters in Suspended Hexagonal Boron Nitride.

    PubMed

    Exarhos, Annemarie L; Hopper, David A; Grote, Richard R; Alkauskas, Audrius; Bassett, Lee C

    2017-03-28

    Hexagonal boron nitride (h-BN) is rapidly emerging as an attractive material for solid-state quantum engineering. Analogously to three-dimensional wide-band-gap semiconductors such as diamond, h-BN hosts isolated defects exhibiting visible fluorescence at room temperature, and the ability to position such quantum emitters within a two-dimensional material promises breakthrough advances in quantum sensing, photonics, and other quantum technologies. Critical to such applications is an understanding of the physics underlying h-BN's quantum emission. We report the creation and characterization of visible single-photon sources in suspended, single-crystal, h-BN films. With substrate interactions eliminated, we study the spectral, temporal, and spatial characteristics of the defects' optical emission. Theoretical analysis of the defects' spectra reveals similarities in vibronic coupling to h-BN phonon modes despite widely varying fluorescence wavelengths, and a statistical analysis of the polarized emission from many emitters throughout the same single-crystal flake uncovers a weak correlation between the optical dipole orientations of some defects and h-BN's primitive crystallographic axes, despite a clear misalignment for other dipoles. These measurements constrain possible defect models and, moreover, suggest that several classes of emitters can exist simultaneously throughout free-standing h-BN, whether they be different defects, different charge states of the same defect, or the result of strong local perturbations.

  17. Thermal transport across graphene and single layer hexagonal boron nitride

    SciTech Connect

    Zhang, Jingchao E-mail: yyue@whu.edu.cn; Hong, Yang; Yue, Yanan E-mail: yyue@whu.edu.cn

    2015-04-07

    As the dimensions of nanocircuits and nanoelectronics shrink, thermal energies are being generated in more confined spaces, making it extremely important and urgent to explore for efficient heat dissipation pathways. In this work, the phonon energy transport across graphene and hexagonal boron-nitride (h-BN) interface is studied using classic molecular dynamics simulations. Effects of temperature, interatomic bond strength, heat flux direction, and functionalization on interfacial thermal transport are investigated. It is found out that by hydrogenating graphene in the hybrid structure, the interfacial thermal resistance (R) between graphene and h-BN can be reduced by 76.3%, indicating an effective approach to manipulate the interfacial thermal transport. Improved in-plane/out-of-plane phonon couplings and broadened phonon channels are observed in the hydrogenated graphene system by analyzing its phonon power spectra. The reported R results monotonically decrease with temperature and interatomic bond strengths. No thermal rectification phenomenon is observed in this interfacial thermal transport. Results reported in this work give the fundamental knowledge on graphene and h-BN thermal transport and provide rational guidelines for next generation thermal interface material designs.

  18. Nature of exciton transitions in hexagonal boron nitride

    SciTech Connect

    Li, J.; Cao, X. K.; Lin, J. Y.; Jiang, H. X.; Hoffman, T. B.; Edgar, J. H.

    2016-03-21

    In contrast to other III-nitride semiconductors GaN and AlN, the intrinsic (or free) exciton transition in hexagonal boron nitride (h-BN) consists of rather complex fine spectral features (resolved into six sharp emission peaks) and the origin of which is still unclear. Here, the free exciton transition (FX) in h-BN bulk crystals synthesized by a solution method at atmospheric pressure has been probed by deep UV time-resolved photoluminescence (PL) spectroscopy. Based on the separations between the energy peak positions of the FX emission lines, the identical PL decay kinetics among different FX emission lines, and the known phonon modes in h-BN, we suggest that there is only one principal emission line corresponding to the direct intrinsic FX transition in h-BN, whereas all other fine features are a result of phonon-assisted transitions. The identified phonon modes are all associated with the center of the Brillouin zone. Our results offer a simple picture for the understanding of the fundamental exciton transitions in h-BN.

  19. Strontium adsorption on tantalum-doped hexagonal tungsten oxide.

    PubMed

    Li, Xingliang; Mu, Wanjun; Xie, Xiang; Liu, Bijun; Tang, Hui; Zhou, Guanhong; Wei, Hongyuan; Jian, Yuan; Luo, Shunzhong

    2014-01-15

    Hexagonal tungsten oxide (hex-WO3) has the potential to separate (137)Cs and (90)Sr from nuclear power plant or fission (99)Mo production waste. This study aims to increase the capacity of hex-WO3 to adsorb Sr(2+). Ta-doped hex-WO3 was synthesized by the hydrothermal treatment of sodium tungstate dihydrate and tantalum chloride in concentrated HCl, in the presence of ammonium sulfate. Incorporating Ta into the WO3 framework caused the interlayer spacing to expand, and the band gap to shift to higher energy. The Sr(2+) adsorption capacity of Ta-doped hex-WO3 was significantly higher than that of hex-WO3. Sr(2+) adsorption reached equilibrium within 2h in acidic solution. Maximum Sr(2+) removal occurred at pH 4. Sr(2+) uptake by hex-WO3 was described better by the Freundlich model than by the Langmuir model. Sr(2+) adsorption on hex-WO3 was spontaneous under the studied conditions.

  20. Visualizing weak ferromagnetic domains in multiferroic hexagonal ferrite thin film

    NASA Astrophysics Data System (ADS)

    Wang, Wenbo; Mundy, Julia A.; Brooks, Charles M.; Moyer, Jarrett A.; Holtz, Megan E.; Muller, David A.; Schlom, Darrell G.; Wu, Weida

    2017-04-01

    We report cryogenic magnetic force microscopy (MFM) studies of a 200-nm-thick hexagonal (h ) LuFeO3 film grown by molecular-beam epitaxy on a (111)-oriented yttria-stabilized cubic-zirconia substrate. Labyrinthlike domains ˜1.8 μ m in size were observed after zero-field cooling below the Néel temperature, TN≈147 K, where weak ferromagnetic order (P 63 cm) with a canted moment of MS≈0.02 μB/f .u . exists. At 6 K, MFM images of the magnetization reversal process reveal a typical domain behavior of a pinning-dominated hard magnet. The pinning strength is substantially reduced at elevated temperature. The temperature dependence of the domain contrast demonstrates that our MFM is able to detect the domain contrast of magnets with tiny magnetic moments (˜0.002 μB/f .u . ). An upper limit of the linear magnetoelectric coefficient of h -LuFeO3 (αz z<6 ps /m ) is estimated by magnetoelectric force microscopy measurements.

  1. A challenging interpretation of a hexagonally layered protein structure

    SciTech Connect

    Thompson, Michael C.; Yeates, Todd O.

    2014-01-01

    The authors describe the structure determination of a hexagonally layered protein structure that suffered from a complicated combination of translational non-crystallographic symmetry and hemihedral twinning. This case serves as a reminder that broken crystallographic symmetry resulting from doubling of a unit-cell axis often requires a new choice of origin. The carboxysome is a giant protein complex that acts as a metabolic organelle in cyanobacteria and some chemoautotrophs. Its outer structure is formed by the assembly of thousands of copies of hexameric shell protein subunits into a molecular layer. The structure determination of a CcmK1 shell protein mutant (L11K) from the β-carboxysome of the cyanobacterium Synechocystis PCC6803 led to challenges in structure determination. Twinning, noncrystallographic symmetry and packing of hexameric units in a special arrangement led to initial difficulties in space-group assignment. The correct space group was clarified after initial model refinement revealed additional symmetry. This study provides an instructive example in which broken symmetry requires a new choice of unit-cell origin in order to identify the highest symmetry space group. An additional observation related to the packing arrangement of molecules in this crystal suggests that these hexameric shell proteins might have lower internal symmetry than previously believed.

  2. Study of Decay Characteristics of Hexagonal and Square Supersonic Jet

    NASA Astrophysics Data System (ADS)

    Mohanta, Prasanta Kumar; Sridhar, B. T. N.

    2017-05-01

    Experiments were carried on nozzles with different exit geometry to study their impact on supersonic core length. Circular, hexagonal, and square exit geometries were considered for the study. Numerical simulations and schlieren image study were performed. The supersonic core decay was found to be of different length for different exit geometries, though the throat to exit area ratio was kept constant. The impact of nozzle exit geometry is to enhance the mixing of primary flow with ambient air, without requiring tab, wire or secondary method to increase the mixing characteristics. The non-circular mixing is faster comparative to circular geometry, which leads to reduction in supersonic core length. The results depict that shorter the hydraulic diameter, the jet mixing is faster. To avoid the losses in divergent section, the cross section of throat was maintained at same geometry as the exit geometry. Investigation shows that the supersonic core region is dependent on the hydraulic diameter and the diagonal. In addition, it has been observed that number of shock cells remain the same irrespective of exit geometry shape for the given nozzle pressure ratio.

  3. Facile synthesis and structure characterization of hexagonal tungsten bronzes crystals

    NASA Astrophysics Data System (ADS)

    Lee, Jiann-Shing; Liu, Hao-Chuan; Peng, Gao-De; Tseng, Yawteng

    2017-05-01

    A facile molten-salt route was used to synthesize hexagonal Cs0.33WO3, Rb0.33WO3 and K0.30WO3 crystals. The three isostructural compounds were successfully prepared from the reaction of MxWO3 powders (M = Cs, Rb, K) in the CsCl/NaCl, RbCl/NaCl and KCl/NaCl fluxes, respectively. The structure determination and refinement, based on single-crystal X-ray diffraction data, are in agreement with previous works, possessing space group P63/mcm. The a and c parameters vary non-linearly with increasing radii of the M+ cations (rM) that is coordinated to twelve oxygen atoms. Both the volumes of unit-cell and WO6 octahedra vary linearly with rM, which become smaller from Cs0.33WO3 to K0.30WO3. The distortion of WO6 octahedra as well as isotropic displacement parameters increases from Cs0.33WO3 to K0.30WO3. The geometry of the WO6 octahedron becomes more regular with increasing rM. These structural trends arise from the effective size of the M+ cation.

  4. The COMET method in 3-D hexagonal geometry

    SciTech Connect

    Connolly, K. J.; Rahnema, F.

    2012-07-01

    The hybrid stochastic-deterministic coarse mesh radiation transport (COMET) method developed at Georgia Tech now solves reactor core problems in 3-D hexagonal geometry. In this paper, the method is used to solve three preliminary test problems designed to challenge the method with steep flux gradients, high leakage, and strong asymmetry and heterogeneity in the core. The test problems are composed of blocks taken from a high temperature test reactor benchmark problem. As the method is still in development, these problems and their results are strictly preliminary. Results are compared to whole core Monte Carlo reference solutions in order to verify the method. Relative errors are on the order of 50 pcm in core eigenvalue, and mean relative error in pin fission density calculations is less than 1% in these difficult test cores. The method requires the one-time pre-computation of a response expansion coefficient library, which may be compiled in a comparable amount of time to a single whole core Monte Carlo calculation. After the library has been computed, COMET may solve any number of core configurations on the order of an hour, representing a significant gain in efficiency over other methods for whole core transport calculations. (authors)

  5. Consolidation of cubic and hexagonal boron nitride composites

    SciTech Connect

    Du Frane, W. L.; Cervantes, O.; Ellsworth, G. F.; Kuntz, J. D.

    2015-12-08

    When we Consolidate cubic boron nitride (cBN) it typically requires either a matrix of metal bearing materials that are undesirable for certain applications, or very high pressures within the cBN phase stability field that are prohibitive to manufacturing size and cost. We present new methodology for consolidating high stiffness cBN composites within a hexagonal boron nitride (hBN) matrix (15–25 vol%) with the aid of a binder phase (0–6 vol%) at moderate pressures (0.5–1.0 GPa) and temperatures (900–1300 °C). The composites are demonstrated to be highly tailorable with a range of compositions and resulting physical/mechanical properties. Ultrasonic measurements indicate that in some cases these composites have elastic mechanical properties that exceed those of the highest strength steel alloys. Moreover, two methods were identified to prevent phase transformation of the metastable cBN phase into hBN during consolidation: 1. removal of hydrocarbons, and 2. increased cBN particle size. Lithium tetraborate worked better as a binder than boron oxide, aiding consolidation without enhancing cBN to hBN phase transformation kinetics. These powder mixtures consolidated within error of their full theoretical mass densities at 1 GPa, and had only slightly lower densities at 0.5 GPa. This shows potential for consolidation of these composites into larger parts, in a variety of shapes, at even lower pressures using more conventional manufacturing methods, such as hot-pressing.

  6. Hexagonal tungsten oxide nanoflowers as enzymatic mimetics and electrocatalysts

    PubMed Central

    Park, Chan Yeong; Seo, Ji Min; Jo, Hongil; Park, Juhyun; Ok, Kang Min; Park, Tae Jung

    2017-01-01

    Tungsten oxide (WOx) has been widely studied for versatile applications based on its photocatalytic, intrinsic catalytic, and electrocatalytic properties. Among the several nanostructures, we focused on the flower-like structures to increase the catalytic efficiency on the interface with both increased substrate interaction capacities due to their large surface area and efficient electron transportation. Therefore, improved WOx nanoflowers (WONFs) with large surface areas were developed through a simple hydrothermal method using sodium tungstate and hydrogen chloride solution at low temperature, without any additional surfactant, capping agent, or reducing agent. Structural determination and electrochemical analyses revealed that the WONFs have hexagonal Na0.17WO3.085·0.17H2O structure and exhibit peroxidase-like activity, turning from colorless to blue by catalyzing the oxidation of a peroxidase substrate, such as 3,3′,5,5′-tetramethylbenzidine, in the presence of H2O2. Additionally, a WONF-modified glassy carbon electrode was adopted to monitor the electrocatalytic reduction of H2O2. To verify the catalytic efficiency enhancement by the unique shape and structure of the WONFs, they were compared with calcinated WONFs, cesium WOx nanoparticles, and other peroxidase-like nanomaterials. The results indicated that the WONFs showed a low Michaelis-Menten constant (km), high maximal reaction velocity (vmax), and large surface area. PMID:28128306

  7. Lightweight Hexagonal Boron Nitride Foam for CO2 Absorption.

    PubMed

    Owuor, Peter Samora; Park, Ok-Kyung; Woellner, Cristiano F; Jalilov, Almaz S; Susarla, Sandhya; Joyner, Jarin; Ozden, Sehmus; Duy, LuongXuan; Villegas Salvatierra, Rodrigo; Vajtai, Robert; Tour, James M; Lou, Jun; Galvão, Douglas Soares; Tiwary, Chandra Sekhar; Ajayan, Pulickel M

    2017-09-26

    Weak van der Waals forces between inert hexagonal boron nitride (h-BN) nanosheets make it easy for them to slide over each other, resulting in an unstable structure in macroscopic dimensions. Creating interconnections between these inert nanosheets can remarkably enhance their mechanical properties. However, controlled design of such interconnections remains a fundamental problem for many applications of h-BN foams. In this work, a scalable in situ freeze-drying synthesis of low-density, lightweight 3D macroscopic structures made of h-BN nanosheets chemically connected by poly(vinyl alcohol) (PVA) molecules via chemical cross-link is demonstrated. Unlike pristine h-BN foam which disintegrates upon handling after freeze-drying, h-BN/PVA foams exhibit stable mechanical integrity in addition to high porosity and large surface area. Fully atomistic simulations are used to understand the interactions between h-BN nanosheets and PVA molecules. In addition, the h-BN/PVA foam is investigated as a possible CO2 absorption and as laser irradiation protection material.

  8. Nature of exciton transitions in hexagonal boron nitride

    NASA Astrophysics Data System (ADS)

    Li, J.; Cao, X. K.; Hoffman, T. B.; Edgar, J. H.; Lin, J. Y.; Jiang, H. X.

    2016-03-01

    In contrast to other III-nitride semiconductors GaN and AlN, the intrinsic (or free) exciton transition in hexagonal boron nitride (h-BN) consists of rather complex fine spectral features (resolved into six sharp emission peaks) and the origin of which is still unclear. Here, the free exciton transition (FX) in h-BN bulk crystals synthesized by a solution method at atmospheric pressure has been probed by deep UV time-resolved photoluminescence (PL) spectroscopy. Based on the separations between the energy peak positions of the FX emission lines, the identical PL decay kinetics among different FX emission lines, and the known phonon modes in h-BN, we suggest that there is only one principal emission line corresponding to the direct intrinsic FX transition in h-BN, whereas all other fine features are a result of phonon-assisted transitions. The identified phonon modes are all associated with the center of the Brillouin zone. Our results offer a simple picture for the understanding of the fundamental exciton transitions in h-BN.

  9. Hyperbolic phonon polaritons in hexagonal boron nitride (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Dai, Siyuan; Ma, Qiong; Fei, Zhe; Liu, Mengkun; Goldflam, Michael D.; Andersen, Trond; Garnett, William; Regan, Will; Wagner, Martin; McLeod, Alexander S.; Rodin, Alexandr; Zhu, Shou-En; Watanabe, Kenji; Taniguchi, T.; Dominguez, Gerado; Thiemens, Mark; Castro Neto, Antonio H.; Janssen, Guido C. A. M.; Zettl, Alex; Keilmann, Fritz; Jarillo-Herrero, Pablo; Fogler, Michael M.; Basov, Dmitri N.

    2016-09-01

    Uniaxial materials whose axial and tangential permittivities have opposite signs are referred to as indefinite or hyperbolic media. While hyperbolic responses are normally achieved with metamaterials, hexagonal boron nitride (hBN) naturally possesses this property due to the anisotropic phonons in the mid-infrared. Using scattering-type scanning near-field optical microscopy, we studied polaritonic phenomena in hBN. We performed infrared nano-imaging of highly confined and low-loss hyperbolic phonon polaritons in hBN. The polariton wavelength was shown to be governed by the hBN thickness according to a linear law persisting down to few atomic layers [1]. Additionally, we carried out the modification of hyperbolic response in meta-structures comprised of a mononlayer graphene deposited on hBN [2]. Electrostatic gating of the top graphene layer allows for the modification of wavelength and intensity of hyperbolic phonon polaritons in bulk hBN. The physics of the modification originates from the plasmon-phonon coupling in the hyperbolic medium. Furthermore, we demonstrated the "hyperlens" for subdiffractional focusing and imaging using a slab of hBN [3]. References [1] S. Dai et al., Science, 343, 1125 (2014). [2] S. Dai et al., Nature Nanotechnology, 10, 682 (2015). [3] S. Dai et al., Nature Communications, 6, 6963 (2015).

  10. Strength of iron at core pressures and evidence for a weak Earth’s inner core

    SciTech Connect

    Gleason, A. E.; Mao, W. L.

    2013-05-12

    The strength of iron at extreme conditions is crucial information for interpreting geophysical observations of the Earth’s core and understanding how the solid inner core deforms. However, the strength of iron, on which deformation depends, is challenging to measure and accurately predict at high pressure. Here we present shear strength measurements of iron up to pressures experienced in the Earth’s core. Hydrostatic X-ray spectroscopy and non-hydrostatic radial X-ray diffraction measurements of the deviatoric strain in hexagonally close-packed iron uniquely determine its shear strength to pressures above 200 GPa at room temperature. Applying numerical modelling of the rheologic behaviour of iron under pressure, we extrapolate our experimental results to inner-core pressures and temperatures, and find that the bulk shear strength of hexagonally close-packed iron is only ~ 1 GPa at the conditions of the Earth’s centre, 364 GPa and 5,500 K. This suggests that the inner core is rheologically weak, which supports dislocation creep as the dominant creep mechanism influencing deformation.

  11. Comparison between SVPWM two level in internal and external circle of hexagon

    NASA Astrophysics Data System (ADS)

    Giyantara, Andhika; Rameli, Mochammad

    2017-01-01

    This study presents a space vector pulse width modulation (SVPWM) method. Switching time for SVPWM two level is used to generate a sinusoidal waveform from the inverter. This waveform using as input for the induction motor. Usually, we use the internal circle to generate sinusoidal method. However, from the calculation, we can get two different equations, for the internal circle in hexagon and external circle for the hexagon. Comparison between voltage vector in the internal and external circle of hexagon using THD (Total Harmonic Distortion) value for each circle.

  12. Pressure Dependence of Structure Stability of Multiferroic Hexagonal-RMnO3

    NASA Astrophysics Data System (ADS)

    Chen, Zhiqiang; Gao, Peng; Tyson, Trevor. A.; Liu, Zhenxian; Hu, Jinzhu; Zhang, Chenglin; Kim, Sung-Baek; Cheong, Sang-Wook

    2009-03-01

    We present high pressure IR and X-ray diffraction measurements of the hexagonal multiferroic systems HoMnO3, YMnO3 and LuMnO3. Measurements were conducted over the pressure range ambient to ˜20 GPa. No phase changes were observed over this broad range of hydrostatic pressures. These suggest that the hexagonal structure is stable at higher pressures. The thermal treatment is necessary to overcome the barrier (breaking and reconnection of bonds) to achieve the hexagonal to orthorhombic phase change. A discussion of the effect of hydrostatic pressure on the ferroelectric properties of these systems will be given based on comparisons with density functional calculations.

  13. Epitaxial stabilization of artificial hexagonal GdMnO3 thin films and their magnetic properties

    NASA Astrophysics Data System (ADS)

    Lee, D.; Lee, J.-H.; Murugavel, P.; Jang, S. Y.; Noh, T. W.; Jo, Y.; Jung, M.-H.; Ko, Y.-D.; Chung, J.-S.

    2007-04-01

    The authors investigated the role of oxygen partial pressure on the epitaxial growth of an artificial hexagonal GdMnO3 phase, which should exist in an orthorhombic structure in bulk. The hexagonal GdMnO3 film showed diverse, but obvious, magnetic phase transitions with highly enhanced ferromagnetic properties. Its remnant magnetization at 4.2K is higher than those of other hexagonal RMnO3 (R =Ho, Er, and Yb) compounds, and the Curie temperature increases by around 25K. The results demonstrate that the epitaxial stabilization technique is a promising method for fabricating an artificial material with enhanced magnetic properties.

  14. Controllable morphologies of ZnO nanocrystals: nanowire attracted nanosheets, nanocartridges and hexagonal nanotowers

    NASA Astrophysics Data System (ADS)

    Hu, P. A.; Liu, Y. Q.; Fu, L.; Wang, X. B.; Zhu, D. B.

    2005-01-01

    ZnO nanowire attracted nanosheets, nanocartridges and hexagonal nanotowers are fabricated by evaporation of ZnS in the presence of trace oxygen under controlled conditions. The nanosheet has an irregular structure, and nanowires sprout from the flange of the nanosheet. The nanocartridge has one row of prismatic nanorods grown on the (0001) surface of the ZnO nanobelts. The hexagonal nanotower, which grows along the c axis, shows an interesting layer structure and seems to form by piling up hexagonal ZnO nanocrystals layer on layer. These nanomaterials might have potential applications in optoelectronics.

  15. Thermal performance analysis of optimized hexagonal finned heat sinks in impinging air jet

    SciTech Connect

    Yakut, Kenan; Yeşildal, Faruk; Karabey, Altuğ; Yakut, Rıdvan

    2016-04-18

    In this study, thermal performance analysis of hexagonal finned heat sinks which optimized according to the experimental design and optimization method of Taguchi were investigated. Experiments of air jet impingement on heated hexagonal finned heat sinks were carried out adhering to the L{sub 18}(2{sup 1*}3{sup 6}) orthogonal array test plan. Optimum geometries were determined and named OH-1, OH-2. Enhancement efficiency with the first law of thermodynamics was analyzed for optimized heat sinks with 100, 150, 200 mm heights of hexagonal fin. Nusselt correlations were found out and variations of enhancement efficiency with Reynolds number presented in η–Re graphics.

  16. Experimental static aerodynamics of a regular hexagonal prism in a low density hypervelocity flow

    NASA Technical Reports Server (NTRS)

    Guy, R. W.; Mueller, J. N.; Lee, L. P.

    1972-01-01

    A regular hexagonal prism, having a fineness ratio of 1.67, has been tested in a wind tunnel to determine its static aerodynamic characteristics in a low-density hypervelocity flow. The prism tested was a 1/4-scale model of the graphite heat shield which houses the radioactive fuel for the Viking spacecraft auxiliary power supply. The basic hexagonal prism was also modified to simulate a prism on which ablation of one of the six side flats had occurred. This modified hexagonal prism was tested to determine the effects on the aerodynamic characteristics of a shape change caused by ablation during a possible side-on stable reentry.

  17. Tunneling characteristics in chemical vapor deposited graphene–hexagonal boron nitride–graphene junctions

    SciTech Connect

    Roy, T.; Hesabi, Z. R.; Joiner, C. A.; Vogel, E. M.; Liu, L.; Gu, G.; Barrera, S. de la; Feenstra, R. M.; Chakrabarti, B.

    2014-03-24

    Large area chemical vapor deposited graphene and hexagonal boron nitride was used to fabricate graphene–hexagonal boron nitride–graphene symmetric field effect transistors. Gate control of the tunneling characteristics is observed similar to previously reported results for exfoliated graphene–hexagonal boron nitride–graphene devices. Density-of-states features are observed in the tunneling characteristics of the devices, although without large resonant peaks that would arise from lateral momentum conservation. The lack of distinct resonant behavior is attributed to disorder in the devices, and a possible source of the disorder is discussed.

  18. Hexagonal superlattice pattern consisting of colliding filament pairs in a dielectric barrier discharge

    SciTech Connect

    Dong Lifang; Li Ben; Lu Ning; Li Xinchun; Shen Zhongkai

    2012-05-15

    Colliding-pairs hexagonal superlattice pattern (CPHSP) is studied in a dielectric barrier discharge system. The evolution of CPHSP bifurcating from a hexagonal pattern to chaos is shown. The phase diagrams of CPHSP as a function of discharge parameters are given. From a series of pictures taken by a high speed video camera, collisions between two spots are observed and the superposition of many collisions results in each big spot presenting four small spots on long time scales. Measurements of the correlation between filaments indicate that the pattern is an interleaving of four different transient hexagonal sublattices. Depending on the discharging sequence, the forces exerted on one colliding spot are discussed briefly.

  19. WARM EXTENDED DENSE GAS AT THE HEART OF A COLD COLLAPSING DENSE CORE

    SciTech Connect

    Shinnaga, Hiroko; Phillips, Thomas G.; Furuya, Ray S.; Kitamura, Yoshimi E-mail: tgp@submm.caltech.ed E-mail: kitamura@isas.jaxa.j

    2009-12-01

    In order to investigate when and how the birth of a protostellar core occurs, we made survey observations of four well-studied dense cores in the Taurus molecular cloud using CO transitions in submillimeter bands. We report here the detection of unexpectedly warm (approx30-70 K), extended (radius of approx2400 AU), dense (a few times 10{sup 5} cm{sup -3}) gas at the heart of one of the dense cores, L1521F (MC27), within the cold dynamically collapsing components. We argue that the detected warm, extended, dense gas may originate from shock regions caused by collisions between the dynamically collapsing components and outflowing/rotating components within the dense core. We propose a new stage of star formation, 'warm-in-cold core stage (WICCS)', i.e., the cold collapsing envelope encases the warm extended dense gas at the center due to the formation of a protostellar core. WICCS would constitute a missing link in evolution between a cold quiescent starless core and a young protostar in class 0 stage that has a large-scale bipolar outflow.

  20. Frontier of the physics of dense plasmas and planetary interiors: experiments, theory, applications

    SciTech Connect

    Saumon, Didier; Fortney, Jonathan J; Glenzer, Siegfried H; Koenig, Michel; Brambrink, E; Militzer, Burkhard; Valencia, Diana

    2008-01-01

    Recent developments of dynamic x-ray characterization experiments of dense matter are reviewed, with particular emphasis on conditions relevant to interiors of terrestrial and gas giant planets. These studies include characterization of compressed states of matter in light elements by x-ray scattering and imaging of shocked iron by radiography. Several applications of this work are examined. These include the structure of massive 'super-Earth' terrestrial planets around other stars, the 40 known extrasolar gas giants with measured masses and radii, and Jupiter itself, which serves as the benchmark for giant planets.