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Sample records for boron carbon nitrogen

  1. Prediction of boron carbon nitrogen phase diagram

    NASA Astrophysics Data System (ADS)

    Yao, Sanxi; Zhang, Hantao; Widom, Michael

    We studied the phase diagram of boron, carbon and nitrogen, including the boron-carbon and boron-nitrogen binaries and the boron-carbon-nitrogen ternary. Based on the idea of electron counting and using a technique of mixing similar primitive cells, we constructed many ''electron precise'' structures. First principles calculation is performed on these structures, with either zero or high pressures. For the BN binary, our calculation confirms that a rhmobohedral phase can be stablized at high pressure, consistent with some experimental results. For the BCN ternary, a new ground state structure is discovered and an Ising-like phase transition is suggested. Moreover, we modeled BCN ternary phase diagram and show continuous solubility from boron carbide to the boron subnitride phase.

  2. Efficient boron-carbon-nitrogen nanotube formation via combined laser-gas flow levitation

    DOEpatents

    Whitney, R Roy; Jordan, Kevin; Smith, Michael W

    2015-03-24

    A process for producing boron nitride nanotubes and/or boron-carbon-nitrogen nanotubes of the general formula B.sub.xC.sub.yN.sub.z. The process utilizes a combination of laser light and nitrogen gas flow to support a boron ball target during heating of the boron ball target and production of a boron vapor plume which reacts with nitrogen or nitrogen and carbon to produce boron nitride nanotubes and/or boron-carbon-nitrogen nanotubes of the general formula B.sub.xC.sub.yN.sub.z.

  3. Efficient Boron-Carbon-Nitrogen Nanotube Formation Via Combined Laser-Gas Flow Levitation

    NASA Technical Reports Server (NTRS)

    Whitney, R. Roy (Inventor); Jordan, Kevin (Inventor); Smith, Michael W. (Inventor)

    2015-01-01

    A process for producing boron nitride nanotubes and/or boron-carbon-nitrogen nanotubes of the general formula BxCyNz. The process utilizes a combination of laser light and nitrogen gas flow to support a boron ball target during heating of the boron ball target and production of a boron vapor plume which reacts with nitrogen or nitrogen and carbon to produce boron nitride nanotubes and/or boron-carbon-nitrogen nanotubes of the general formula BxCyNz.

  4. Predicted phase diagram of boron-carbon-nitrogen

    NASA Astrophysics Data System (ADS)

    Zhang, Hantao; Yao, Sanxi; Widom, Michael

    2016-04-01

    Noting the structural relationships between phases of carbon and boron carbide with phases of boron nitride and boron subnitride, we investigate their mutual solubilities using a combination of first-principles total energies supplemented with statistical mechanics to address finite temperatures. Thus we predict the solid-state phase diagram of boron-carbon-nitrogen (B-C-N). Owing to the large energy costs of substitution, we find that the mutual solubilities of the ultrahard materials diamond and cubic boron nitride are negligible, and the same for the quasi-two-dimensional materials graphite and hexagonal boron nitride. In contrast, we find a continuous range of solubility connecting boron carbide to boron subnitride at elevated temperatures. An electron-precise ternary compound B13CN consisting of B12 icosahedra with NBC chains is found to be stable at all temperatures up to melting. It exhibits an order-disorder transition in the orientation of NBC chains at approximately T =500 K. We also propose that the recently discovered binary B13N2 actually has composition B12.67N2 .

  5. Boron/Carbon/Silicon/Nitrogen Ceramics And Precursors

    NASA Technical Reports Server (NTRS)

    Riccitiello, Salvatore; Hsu, Ming TA; Chen, Timothy S.

    1996-01-01

    Ceramics containing various amounts of boron, carbon, silicon, and nitrogen made from variety of polymeric precursors. Synthesized in high yield from readily available and relatively inexpensive starting materials. Stable at room temperature; when polymerized, converted to ceramics in high yield. Ceramics resist oxidation and other forms of degradation at high temperatures; used in bulk to form objects or to infiltrate other ceramics to obtain composites having greater resistance to oxidation and high temperatures.

  6. Direct chemical conversion of graphene to boron- and nitrogen- and carbon-containing atomic layers

    NASA Astrophysics Data System (ADS)

    Gong, Yongji; Shi, Gang; Zhang, Zhuhua; Zhou, Wu; Jung, Jeil; Gao, Weilu; Ma, Lulu; Yang, Yang; Yang, Shubin; You, Ge; Vajtai, Robert; Xu, Qianfan; MacDonald, Allan H.; Yakobson, Boris I.; Lou, Jun; Liu, Zheng; Ajayan, Pulickel M.

    2014-01-01

    Graphene and hexagonal boron nitride are typical conductor and insulator, respectively, while their hybrids hexagonal boron carbonitride are promising as a semiconductor. Here we demonstrate a direct chemical conversion reaction, which systematically converts the hexagonal carbon lattice of graphene to boron nitride, making it possible to produce uniform boron nitride and boron carbonitride structures without disrupting the structural integrity of the original graphene templates. We synthesize high-quality atomic layer films with boron-, nitrogen- and carbon-containing atomic layers with full range of compositions. Using this approach, the electrical resistance, carrier mobilities and bandgaps of these atomic layers can be tuned from conductor to semiconductor to insulator. Combining this technique with lithography, local conversion could be realized at the nanometre scale, enabling the fabrication of in-plane atomic layer structures consisting of graphene, boron nitride and boron carbonitride. This is a step towards scalable synthesis of atomically thin two-dimensional integrated circuits.

  7. Boron nitride converted carbon fiber

    DOEpatents

    Rousseas, Michael; Mickelson, William; Zettl, Alexander K.

    2016-04-05

    This disclosure provides systems, methods, and apparatus related to boron nitride converted carbon fiber. In one aspect, a method may include the operations of providing boron oxide and carbon fiber, heating the boron oxide to melt the boron oxide and heating the carbon fiber, mixing a nitrogen-containing gas with boron oxide vapor from molten boron oxide, and converting at least a portion of the carbon fiber to boron nitride.

  8. Fabrication of particular structures of hexagonal boron nitride and boron-carbon-nitrogen layers by anisotropic etching

    NASA Astrophysics Data System (ADS)

    Vishwakarma, Riteshkumar; Sharma, Subash; Shinde, Sachin M.; Sharma, Kamal P.; Thangaraja, Amutha; Kalita, Golap; Tanemura, Masaki

    2016-05-01

    Anisotropic etching of hexagonal boron nitride (h-BN) and boron-carbon-nitrogen (BCN) basal plane can be an exciting platform to develop well-defined structures with interesting properties. Here, we developed an etching process of atomically thin h-BN and BCN layers to fabricate nanoribbons (NRs) and other distinct structures by annealing in H2 and Ar gas mixture. BCN and h-BN films are grown on Cu foil by chemical vapor deposition (CVD) using solid camphor and ammonia borane as carbon, nitrogen and boron source, respectively. Formation of micron size well-defined etched holes and NRs are obtained in both h-BN and BCN layers by the post growth annealing process. The etching process of h-BN and BCN basal plane to fabricate NRs and other structures with pronounced edges can open up new possibilities in 2D hybrid materials.

  9. Chirality-dependent boron-mediated growth of nitrogen-doped single-walled carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Wiltshire, Joseph G.; Li, Lain-Jong; Herz, Laura M.; Nicholas, Robin J.; Glerup, Marianne; Sauvajol, Jean-Louis; Khlobystov, Andrei N.

    2005-11-01

    A change in the relative abundance of single-walled carbon nanotubes, due to the presence of both nitrogen and boron during synthesis, has been identified through Raman and absorption spectroscopy. Raman spectroscopy shows that for two specific branches boron mediates the growth of smaller-diameter zigzag or near-zigzag nanotubes. We combine our experimental results with an improved Kataura model to identify two of the preferentially grown species as (16,0) and (14,1).

  10. Synthesis of boron, nitrogen co-doped porous carbon from asphaltene for high-performance supercapacitors

    NASA Astrophysics Data System (ADS)

    Zhou, Ying; Wang, Dao-Long; Wang, Chun-Lei; Jin, Xin-Xin; Qiu, Jie-Shan

    2014-08-01

    Oxidized asphaltene (OA), a thermosetting material with plenty of functional groups, is synthesized from asphaltene (A) using HNO3/H2SO4 as the oxidizing agent. Boron, nitrogen co-doped porous carbon (BNC—OA) is prepared by carbonization of the mixture of boric acid and OA at 1173 K in an argon atmosphere. X-ray photoelectron spectroscopy (XPS) characterization reveals that the BNC—OA has a nitrogen content of 3.26 at.% and a boron content of 1.31 at.%, while its oxidation-free counterpart (BNC—SA) has a nitrogen content of 1.61 at.% and a boron content of 3.02 at.%. The specific surface area and total pore volume of BNC—OA are 1103 m2·g-1 and 0.921 cm3·g-1, respectively. At a current density of 0.1 A·g-1, the specific capacitance of BNC-OA is 335 F·g-1 and the capacitance retention can still reach 83% at 1 A·g-1. The analysis shows that the superior electrochemical performance of the BNC—OA is attributed to the pseudocapacitance behavior of surface heteroatom functional groups and an abundant pore-structure. Boron, nitrogen co-doped porous carbon is a promising electrode material for supercapacitors.

  11. Isolated boron and nitrogen sites on porous graphitic carbon synthesized from nitrogen-containing chitosan for supercapacitors.

    PubMed

    Sun, Li; Fu, Yu; Tian, Chungui; Yang, Ying; Wang, Lei; Yin, Jie; Ma, Jing; Wang, Ruihong; Fu, Honggang

    2014-06-01

    Separated boron and nitrogen porous graphitic carbon (BNGC) is fabricated by a facile hydrothermal coordination/ZnCl2-activation process from renewable and inexpensive nitrogen-containing chitosan. In this synthetic pathway, chitosan, which has a high nitrogen content, first coordinates with Fe(3+) ions to form chitosan-Fe that subsequently reacts with boric acid (boron source) to generate the BNGC precursor. After simultaneous carbonization and ZnCl2 activation followed by removal of the Fe catalyst, BNGC, containing isolated boron and nitrogen centers and having a high surface area of 1567 m(2)  g(-1) and good conductivity, can be obtained. Results indicate that use of chitosan as a nitrogen-containing carbon source effectively prevents nitrogen atoms from direct combination with boron atoms. In addition, the incorporation of Fe(3+) ions not only endows BNGC with high graphitization, but also favors for nitrogen fixation. Remarkably, the unique microstructure of BNGC enables its use as an advanced electrode material for energy storage. As electrode material for supercapacitors, BNGC shows a high capacitance of 313 F g(-1) at 1 A g(-1), and also long-term durability and coulombic efficiency of >99.5 % after 5000 cycles. Notably, in organic electrolytes, the energy density could be up to 50.1 Wh kg(-1) at a power density of 10.5 kW kg(-1). The strategy developed herein opens a new avenue to prepare BNGC without inactive BN bonds from commercially available chitosan for high-performance supercapacitors. PMID:24692324

  12. Elementary reactions of nitrogen and oxygen with boron and carbon at high pressures and temperatures

    SciTech Connect

    Yoo, C.S.; Cynn, H.; Nicol, M.F.

    1997-08-01

    The direct elementary reactions among the first and second row elements often yield novel super hard, high energy density, and wide band-gap optical materials. The reactions of oxygen and nitrogen with boron and carbon have been investigated at high pressures and temperatures by using an integrated technique of diamond-anvil cell, laser-heating, x-ray diffraction, Raman spectroscopy. A wide range of products has been synthesized and characterized in-situ at high pressures, including {alpha}-CO{sub 2}, B{sub 2}0{sub 3}-I,B{sub 2}0{sub 3}-II, c-BN, h-BN, h{sup `}-B, amorphous carbon nitrides. The elementary reactions occur exothermically and result in highly polycrystallized products with an exception in carbon-nitrogen reactions. The implication of the elementary reactions to energetic materials applications is discussed.

  13. Isotope shifts in beryllium-, boron-, carbon-, and nitrogen-like ions from relativistic configuration interaction calculations

    SciTech Connect

    Nazé, C.; Verdebout, S.; Godefroid, M.

    2014-09-15

    Energy levels, normal and specific mass shift parameters as well as electronic densities at the nucleus are reported for numerous states along the beryllium, boron, carbon, and nitrogen isoelectronic sequences. Combined with nuclear data, these electronic parameters can be used to determine values of level and transition isotope shifts. The calculation of the electronic parameters is done using first-order perturbation theory with relativistic configuration interaction wavefunctions that account for valence, core–valence, and core–core correlation effects as zero-order functions. Results are compared with experimental and other theoretical values, when available.

  14. Bias in bonding behavior among boron, carbon, and nitrogen atoms in ion implanted a-BN, a-BC, and diamond like carbon films

    SciTech Connect

    Genisel, Mustafa Fatih; Uddin, Md. Nizam; Say, Zafer; Bengu, Erman; Kulakci, Mustafa; Turan, Rasit; Gulseren, Oguz

    2011-10-01

    In this study, we implanted N{sup +} and N{sub 2}{sup +} ions into sputter deposited amorphous boron carbide (a-BC) and diamond like carbon (DLC) thin films in an effort to understand the chemical bonding involved and investigate possible phase separation routes in boron carbon nitride (BCN) films. In addition, we investigated the effect of implanted C{sup +} ions in sputter deposited amorphous boron nitride (a-BN) films. Implanted ion energies for all ion species were set at 40 KeV. Implanted films were then analyzed using x-ray photoelectron spectroscopy (XPS). The changes in the chemical composition and bonding chemistry due to ion-implantation were examined at different depths of the films using sequential ion-beam etching and high resolution XPS analysis cycles. A comparative analysis has been made with the results from sputter deposited BCN films suggesting that implanted nitrogen and carbon atoms behaved very similar to nitrogen and carbon atoms in sputter deposited BCN films. We found that implanted nitrogen atoms would prefer bonding to carbon atoms in the films only if there is no boron atom in the vicinity or after all available boron atoms have been saturated with nitrogen. Implanted carbon atoms also preferred to either bond with available boron atoms or, more likely bonded with other implanted carbon atoms. These results were also supported by ab-initio density functional theory calculations which indicated that carbon-carbon bonds were energetically preferable to carbon-boron and carbon-nitrogen bonds.

  15. Blending materials composed of boron, nitrogen and carbon to transform approaches to liquid hydrogen stores.

    PubMed

    Whittemore, Sean M; Bowden, Mark; Karkamkar, Abhijeet; Parab, Kshitij; Neiner, Doinita; Autrey, Tom; Ishibashi, Jacob S A; Chen, Gang; Liu, Shih-Yuan; Dixon, David A

    2016-04-14

    Mixtures of hydrogen storage materials containing the elements of boron, nitrogen, carbon, i.e., isomers of BN cyclopentanes are examined to find a 'fuel blend' that remains a liquid phase throughout hydrogen release, maximizes hydrogen storage density, minimizes impurities and remains thermally stable at ambient temperatures. We find that the mixture of ammonia borane dissolved in 3-methyl-1,2-dihydro-1,2-azaborolidine (compound B) provide a balance of these properties and provides ca. 5.6 wt% hydrogen. The two hydrogen storage materials decompose at a faster rate than either individually and products formed are a mixture of molecular trimers. Digestion of the product mixture formed from the decomposition of the AB + B fuel blend with methanol leads to the two corresponding methanol adducts of the starting material and not a complex mixture of adducts. The work shows the utility of using blends of materials to reduce volatile impurities and preserve liquid phase. PMID:26629961

  16. Boron/nitrogen co-doped helically unzipped multiwalled carbon nanotubes as efficient electrocatalyst for oxygen reduction.

    PubMed

    Zehtab Yazdi, Alireza; Fei, Huilong; Ye, Ruquan; Wang, Gunuk; Tour, James; Sundararaj, Uttandaraman

    2015-04-15

    Bamboo structured nitrogen doped multiwalled carbon nanotubes have been helically unzipped, and nitrogen doped graphene oxide nanoribbons (CNx-GONRs) with a multifaceted microstructure have been obtained. CNx-GONRs have then been codoped with nitrogen and boron by simultaneous thermal annealing in ammonia and boron oxide atmospheres, respectively. The effects of the codoping time and temperature on the concentration of the dopants and their functional groups have been extensively investigated. X-ray photoelectron spectroscopy results indicate that pyridinic and BC3 are the main nitrogen and boron functional groups, respectively, in the codoped samples. The oxygen reduction reaction (ORR) properties of the samples have been measured in an alkaline electrolyte and compared with the state-of-the-art Pt/C (20%) electrocatalyst. The results show that the nitrogen/boron codoped graphene nanoribbons with helically unzipped structures (CNx/CBx-GNRs) can compete with the Pt/C (20%) electrocatalyst in all of the key ORR properties: onset potential, exchange current density, four electron pathway selectivity, kinetic current density, and stability. The development of such graphene nanoribbon-based electrocatalyst could be a harbinger of precious metal-free carbon-based nanomaterials for ORR applications. PMID:25793636

  17. Boron and nitrogen co-doped porous carbon and its enhanced properties as supercapacitor

    NASA Astrophysics Data System (ADS)

    Guo, Hongliang; Gao, Qiuming

    Boron and nitrogen co-doped porous carbons (BNCs) were prepared through a facile procedure using citric acid, boric acid and nitrogen as C, B and N precursors, respectively. The BNC samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and nitrogen sorption at 77 K. Cyclic voltammetry and galvanostatic charge/discharge experiments were adopted to investigate their electrochemical behaviors. The BNC-9 and BNC-15 samples with high specific surface areas of 894 and 726 m 2 g -1 showed the large specific capacitance up to 268 and 173 F g -1, respectively, with the current of 0.1 A g -1. When the current was set as 1 A g -1, the energy densities were 3.8 and 3.0 Wh kg -1 and the power densities were 165 and 201 W kg -1 for BNC-9 and BNC-15, respectively. Thus, BNC-15 is more suitable to apply in high-power-demanded occasion, while BNC-9 tends to store more energy.

  18. Transition from amorphous boron carbide to hexagonal boron carbon nitride thin films induced by nitrogen ion assistance

    NASA Astrophysics Data System (ADS)

    Gago, R.; Jiménez, I.; Agulló-Rueda, F.; Albella, J. M.; Czigány, Zs.; Hultman, L.

    2002-11-01

    Boron carbon nitride films (BCN) were grown by B4C evaporation under concurrent N2 ion beam assistance. The films were characterized by x-ray absorption near-edge spectroscopy, infrared and Raman spectroscopies, and high-resolution transmission electron microscopy. The bonding structure and film composition correlate with the momentum transfer per incoming atom during deposition. As the momentum transfer is increased, the film structure evolves from an amorphous boron carbide network towards a hexagonal ternary compound (h-BCN) with standing basal planes. The growth of h-BCN takes place for momentum transfer in the window between 80 and 250 (eV×amu)1/2. The characteristic vibrational features of the h-BCN compounds have also been studied. Finally, the solubility limit of carbon in the hexagonal BN structure, under the working conditions of this article, is found to be ˜15 at. %.

  19. Nitrogen- and boron-co-doped core-shell carbon nanoparticles as efficient metal-free catalysts for oxygen reduction reactions in microbial fuel cells

    NASA Astrophysics Data System (ADS)

    Zhong, Shengkui; Zhou, Lihua; Wu, Ling; Tang, Lianfeng; He, Qiyi; Ahmed, Jalal

    2014-12-01

    The most severe bottleneck hindering the widespread application of fuel cell technologies is the difficulty in obtaining an inexpensive and abundant oxygen reduction reaction (ORR) catalyst. The concept of a heteroatom-doped carbon-based metal-free catalyst has recently attracted interest. In this study, a metal-free carbon nanoparticles-based catalyst hybridized with dual nitrogen and boron components was synthesized to catalyze the ORR in microbial fuel cells (MFCs). Multiple physical and chemical characterizations confirmed that the synthetic method enabled the incorporation of both nitrogen and boron dopants. The electrochemical measurements indicated that the co-existence of nitrogen and boron could enhance the ORR kinetics by reducing the overpotential and increasing the current density. The results from the kinetic studies indicated that the nitrogen and boron induced an oxygen adsorption mechanism and a four-electron-dominated reaction pathway for the as-prepared catalyst that was very similar to those induced by Pt/C. The MFC results showed that a maximum power density of ∼642 mW m-2 was obtained using the as-prepared catalyst, which is comparable to that obtained using expensive Pt catalyst. The prepared nitrogen- and boron-co-doped carbon nanoparticles might be an alternative cathode catalyst for MFC applications if large-scale applications and price are considered.

  20. Adsorption properties of nitrogen dioxide on hybrid carbon and boron-nitride nanotubes.

    PubMed

    Liu, Haining; Turner, C Heath

    2014-11-01

    The properties of pristine carbon nanotubes (CNTs) can be modified in a number of different ways: covalent attachments, substitutional doping, induced defects, and non-covalent interactions with ligands. One unconventional approach is to combine CNTs with boron-nitride nanotubes (BNNTs) to form hybrid carbon and boron-nitride nanotube (CBNNT) materials. In this work, we perform a first-principles density functional theory study on the adsorption properties of NO2 on CBNNT heterostructures. It is found that the adsorption of NO2 is significantly increased on both zigzag CBNNT(8,0) and armchair CBNNT(6,6), as compared to either a pristine CNT or BNNT. For example, the chemisorption of NO2 on CNT(8,0) is found to be endothermic, while the chemisorption of NO2 on CBNNT(8,0) is an exothermic process with a very large binding energy of -27.74 kcal mol(-1). Furthermore, the binding of NO2 on both CBNNT(8,0) and CBNNT(6,6) induces an increase in the conductivity of the nanotube. These characteristics indicate that the CBNNT heterostructures may have significant potential as an NO2 sensor or as a catalyst for NO2 decomposition reactions. Our calculations provide critical information for further evaluation, such as molecular-level adsorption simulations and microkinetic studies. PMID:25242148

  1. A balloon measurement of the isotopic composition of galactic cosmic ray boron, carbon and nitrogen. Ph.D. Thesis

    NASA Technical Reports Server (NTRS)

    Zumberge, J. F.

    1981-01-01

    The isotopic compositions of galactic cosmic ray boron, carbon, and nitrogen were measured at energies near 300 MeV amu, using a balloon-borne instrument at an atmospheric depth of approximately 5 g/sq cm. The calibrations of the detectors comprising the instrument are described. The saturation properties of the cesium iodide scintillators used for measurement of particle energy are studied in the context of analyzing the data for mass. The achieved rms mass resolution varies from approximately 0.3 amu at boron to approximately 0.5 amu at nitrogen, consistent with a theoretical analysis of the contributing factors. Corrected for detector interactions and the effects of the residual atmosphere the results are B-10/B=0.33 (+0.17, -0.11), C-13/C=0.06 (+0.13, -0.11), and N-15/N=0.42 (+0.19, -0.17). A model of galactic propagation and solar modulation is described. Assuming a cosmic ray source composition of solar-like isotopic abundances, the model predicts abundances near Earth consistent with the measurements.

  2. Synthesis of thin films in boron-carbon-nitrogen ternary system by microwave plasma enhanced chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Kukreja, Ratandeep Singh

    The Boron Carbon Nitorgen (B-C-N) ternary system includes materials with exceptional properties such as wide band gap, excellent thermal conductivity, high bulk modulus, extreme hardness and transparency in the optical and UV range that find application in most fields ranging from micro-electronics, bio-sensors, and cutting tools to materials for space age technology. Interesting materials that belong to the B-C-N ternary system include Carbon nano-tubes, Boron Carbide, Boron Carbon Nitride (B-CN), hexagonal Boron Nitride ( h-BN), cubic Boron Nitride (c-BN), Diamond and beta Carbon Nitride (beta-C3N4). Synthesis of these materials requires precisely controlled and energetically favorable conditions. Chemical vapor deposition is widely used technique for deposition of thin films of ceramics, metals and metal-organic compounds. Microwave plasma enhanced chemical vapor deposition (MPECVD) is especially interesting because of its ability to deposit materials that are meta-stable under the deposition conditions, for e.g. diamond. In the present study, attempt has been made to synthesize beta-carbon nitride (beta-C3N4) and cubic-Boron Nitride (c-BN) thin films by MPECVD. Also included is the investigation of dependence of residual stress and thermal conductivity of the diamond thin films, deposited by MPECVD, on substrate pre-treatment and deposition temperature. Si incorporated CNx thin films are synthesized and characterized while attempting to deposit beta-C3N4 thin films on Si substrates using Methane (CH4), Nitrogen (N2), and Hydrogen (H2). It is shown that the composition and morphology of Si incorporated CNx thin film can be tailored by controlling the sequence of introduction of the precursor gases in the plasma chamber. Greater than 100mum size hexagonal crystals of N-Si-C are deposited when Nitrogen precursor is introduced first while agglomerates of nano-meter range graphitic needles of C-Si-N are deposited when Carbon precursor is introduced first in the

  3. Transport Properties of p-n Junctions Formed in Boron/Nitrogen Doped Carbon Nanotubes and Graphene Nanoribbons

    NASA Astrophysics Data System (ADS)

    Hammouri, Mahmoud; Vasiliev, Igor

    2014-03-01

    We apply ab initio computational methods based on density functional theory to study the transport properties of p-n junctions made of single-walled carbon nanotubes and graphene nanoribbons. The p-n junctions are formed by doping the opposite ends of carbon nanostructures with boron and nitrogen atoms. Our calculations are carried out using the SIESTA electronic structure code combined with the generalized gradient approximation for the exchange-correlation functional. The transport properties are calculated using a self-consistent nonequilibrium Green's function method implemented in the TranSIESTA package. The modeled nanoscale p-n junctions exhibit linear I-V characteristics in the forward bias and nonlinear I-V characteristics with a negative differential resistance in the reverse bias. The computed transmission spectra and the I-V characteristics of the p-n junctions are compared to the results of other theoretical studies and to the available experimental data. Supported by NMSU GREG Award and by NSF CHE-1112388.

  4. Hyperfine structures and Landé gJ-factors for n=2 states in beryllium-, boron-, carbon-, and nitrogen-like ions from relativistic configuration interaction calculations

    NASA Astrophysics Data System (ADS)

    Verdebout, S.; Nazé, C.; Jönsson, P.; Rynkun, P.; Godefroid, M.; Gaigalas, G.

    2014-09-01

    Energy levels, hyperfine interaction constants, and Landé gJ-factors are reported for n=2 states in beryllium-, boron-, carbon-, and nitrogen-like ions from relativistic configuration interaction calculations. Valence, core-valence, and core-core correlation effects are taken into account through single and double-excitations from multireference expansions to increasing sets of active orbitals. A systematic comparison of the calculated hyperfine interaction constants is made with values from the available literature.

  5. Oxidative synthesis of highly fluorescent boron/nitrogen co-doped carbon nanodots enabling detection of photosensitizer and carcinogenic dye.

    PubMed

    Jahan, Shanaz; Mansoor, Farrukh; Naz, Shagufta; Lei, Jianping; Kanwal, Shamsa

    2013-11-01

    Current research efforts have demonstrated the facile hydrothermal oxidative synthetic route to develop highly fluorescent boron/nitrogen co-doped carbon nanodots (CNDs). During this process, N-(4-hydroxyphenyl)glycine served as a source of N doping and a carbon precursor as well, while boric acid H3BO3 is used as an oxidizing agent in the N2 environment. Surface passivation through ultrasonic treatment of CNDs was performed to induce modifications by using various surface passivating agents. Polyethyleneimine (PEI) remarkably enhanced the fluorescence performance and monodispersity of polymerized carbon nanodots (P-CNDs) in aqueous phase with an enhanced quantum yield of 23.71%, along with an increase in size from ~3 nm to ~200 nm. For characterization of CNDs and P-CNDs, UV, infrared, photoluminescence, transmission electron microscopy, x-ray photoelectron spectra, and atomic force microscopy techniques were utilized. Application potentials of synthesized P-CNDs were developed via introduction of protoporphyrin (PPD, a photosensitizer) which has great doping affinity with polymer PEI to switch-off the fluorescence of P-CNDs, leading to the production of dye-doped nanoprobes. Fluorescence resonance energy transfer (FRET) was also observed during dye-doping, and PPD was detected with a limit of detection (LOD, 3σ) of 15 pM. The fluorescence recovery of this switched-off nanoprobe was made possible by using Sudan red III (carcinogenic dye), which was oxidized by PPD doped in P-CNDs. Sudan red III was detected in the concentration range of 9.9 pM-0.37 nM. Meanwhile, it was also confirmed that the dye-doped nanoprobe is highly selective and exceptionally sensitive to detect this carcinogenic agent in commercial products with a LOD (3σ) of 90 fM. PMID:24083490

  6. Isotopic composition of cosmic-ray boron and nitrogen

    NASA Technical Reports Server (NTRS)

    Krombel, K. E.; Wiedenbeck, M. E.

    1988-01-01

    New measurements of the cosmic-ray boron and nitrogen isotopes at earth and of the elemental abundances of boron, carbon, nitrogen, and oxygen are presented. A region of mutually allowed values for the cosmic-ray nitrogen source ratios is determined, and the cosmic-ray escape mean free path is determined as a function of energy using a leaky box model for cosmic-ray propagation in the Galaxy. Relative to O-16, a N-15 source abundance consistent with solar system composition and a N-14 source abundance which is a factor of about three underabundant relative to the solar value are found.

  7. Tensile properties of a boron/nitrogen-doped carbon nanotube–graphene hybrid structure

    PubMed Central

    Xia, Kang; Zhan, Haifei; Wei, Ye

    2014-01-01

    Summary Doping is an effective approach that allows for the intrinsic modification of the electrical and chemical properties of nanomaterials. Recently, a graphene and carbon nanotube hybrid structure (GNHS) has been reported, which extends the excellent properties of carbon-based materials to three dimensions. In this paper, we carried out a first-time investigation on the tensile properties of the hybrid structures with different dopants. It is found that with the presence of dopants, the hybrid structures usually exhibit lower yield strength, Young’s modulus, and earlier yielding compared to that of a pristine hybrid structure. For dopant concentrations below 2.5% no significant reduction of Young’s modulus or yield strength could be observed. For all considered samples, the failure is found to initiate at the region where the nanotubes and graphene sheets are connected. After failure, monatomic chains are normally observed around the failure region. Dangling graphene layers without the separation of a residual CNT wall are found to adhere to each other after failure with a distance of about 3.4 Å. This study provides a fundamental understanding of the tensile properties of the doped graphene–nanotube hybrid structures, which will benefit the design and also the applications of graphene-based hybrid materials. PMID:24778956

  8. The stability and electronic structure of lithium adsorbed in triplet form of (5.0) carbon nanotubes and (5.0) boron nitrogen nanotubes: Density functional theory studies

    NASA Astrophysics Data System (ADS)

    Li, Ke Jing; Shao, Qing Yi; Zhang, Juan; Yao, Xin Hua

    2016-07-01

    Using density functional theory (DFT), we have investigated the stability and electronic structure of lithium (Li) adsorbed in triplet form of (5.0) carbon nanotubes (CNTs) and (5.0) boron nitrogen nanotubes (BNNTs). We have mainly found that three (5.0) tubes are covalently connected. The triplet form is an energetically stable semiconductor. Li atom can be chemically adsorbed in the triplet form of nanotubes (NTs). Meanwhile, upon the adsorption of Li, the triplet form convert into metal. Hence, the triplet form can improve reactivity and sensitivity of NTs to Li significantly.

  9. Two-dimensional boron-nitrogen-carbon monolayers with tunable direct band gaps.

    PubMed

    Zhang, Miao; Gao, Guoying; Kutana, Alex; Wang, Yanchao; Zou, Xiaolong; Tse, John S; Yakobson, Boris I; Li, Hongdong; Liu, Hanyu; Ma, Yanming

    2015-07-28

    The search for new candidate semiconductors with direct band gaps of ∼1.4 eV has attracted significant attention, especially among the two-dimensional (2D) materials, which have become potential candidates for next-generation optoelectronics. Herein, we systematically studied 2D B(x)/2N(x/2)C(1-x) (0 < x < 1) compounds in particular focus on the four stoichiometric B(x)/2N(x/2)C(1-x) (x = 2/3, 1/2, 2/5 and 1/3) using a recently developed global optimization method (CALYPSO) in conjunction with density functional theory. Furthermore, we examine more stoichiometries by the cluster expansion technique based on a hexagonal lattice. The results reveal that all monolayer B(x)/2N(x/2)C(1-x) stoichiometries adopt a planar honeycomb character and are dynamically stable. Remarkably, electronic structural calculations show that most of B(x)/2N(x/2)C(1-x) phases possess direct band gaps within the optical range, thereby they can potentially be used in high-efficiency conversion of solar energy to electric power, as well as in p-n junction photovoltaic modules. The present results also show that the band gaps of B(x)/2N(x/2)C(1-x) can be widely tuned within the optical range by changing the concentration of carbon, thus allowing the fast development of band gap engineered materials in optoelectronics. These new findings may enable new approaches to the design of microelectronic devices. PMID:26111661

  10. Boron and Nitrogen Codoped Carbon Layers of LiFePO4 Improve the High-Rate Electrochemical Performance for Lithium Ion Batteries.

    PubMed

    Zhang, Jinli; Nie, Ning; Liu, Yuanyuan; Wang, Jiao; Yu, Feng; Gu, Junjie; Li, Wei

    2015-09-16

    An evolutionary composite of LiFePO4 with nitrogen and boron codoped carbon layers was prepared by processing hydrothermal-synthesized LiFePO4. This novel codoping method is successfully applied to LiFePO4 for commercial use, and it achieved excellent electrochemical performance. The electrochemical performance can be improved through single nitrogen doping (LiFePO4/C-N) or boron doping (LiFePO4/C-B). When modifying the LiFePO4/C-B with nitrogen (to synthesis LiFePO4/C-B+N) the undesired nonconducting N-B configurations (190.1 and 397.9 eV) are generated. This decreases the electronic conductivity from 2.56×10(-2) to 1.30×10(-2) S cm(-1) resulting in weak electrochemical performance. Nevertheless, using the opposite order to decorate LiFePO4/C-N with boron (to obtain LiFePO4/C-N+B) not only eliminates the nonconducting N-B impurity, but also promotes the conductive C-N (398.3, 400.3, and 401.1 eV) and C-B (189.5 eV) configurations-this markedly improves the electronic conductivity to 1.36×10(-1) S cm(-1). Meanwhile the positive doping strategy leads to synergistic electrochemical activity distinctly compared with single N- or B-doped materials (even much better than their sum capacity at 20 C). Moreover, due to the electron and hole-type carriers donated by nitrogen and boron atoms, the N+B codoped carbon coating tremendously enhances the electrochemical property: at the rate of 20 C, the codoped sample can elevate the discharge capacity of LFP/C from 101.1 mAh g(-1) to 121.6 mAh g(-1), and the codoped product based on commercial LiFePO4/C shows a discharge capacity of 78.4 mAh g(-1) rather than 48.1 mAh g(-1). Nevertheless, the B+N codoped sample decreases the discharge capacity of LFP/C from 101.1 mAh g(-1) to 95.4 mAh g(-1), while the commercial LFP/C changes from 48.1 mAh g(-1) to 40.6 mAh g(-1). PMID:26305802

  11. Boron and nitrogen impurities in SiC nanoribbons: an ab initio investigation

    NASA Astrophysics Data System (ADS)

    Costa, C. D.; Morbec, J. M.

    2011-05-01

    Using ab initio calculations based on density-functional theory we have performed a theoretical investigation of substitutional boron and nitrogen impurities in silicon carbide (SiC) nanoribbons. We have considered hydrogen terminated SiC ribbons with zigzag and armchair edges. In both systems we verify that the boron and nitrogen atoms energetically prefer to be localized at the edges of the nanoribbons. However, while boron preferentially substitutes a silicon atom, nitrogen prefers to occupy a carbon site. In addition, our electronic-structure calculations indicate that (i) substitutional boron and nitrogen impurities do not affect the semiconducting character of the armchair SiC nanoribbons, and (ii) the half-metallic behavior of the zigzag nanoribbons is maintained in the presence of substitutional boron impurities. In contrast, nitrogen atoms occupying edge carbon sites transform half-metallic zigzag nanoribbons into metallic systems.

  12. Boron and nitrogen impurities in SiC nanoribbons: an ab initio investigation.

    PubMed

    Costa, C D; Morbec, J M

    2011-05-25

    Using ab initio calculations based on density-functional theory we have performed a theoretical investigation of substitutional boron and nitrogen impurities in silicon carbide (SiC) nanoribbons. We have considered hydrogen terminated SiC ribbons with zigzag and armchair edges. In both systems we verify that the boron and nitrogen atoms energetically prefer to be localized at the edges of the nanoribbons. However, while boron preferentially substitutes a silicon atom, nitrogen prefers to occupy a carbon site. In addition, our electronic-structure calculations indicate that (i) substitutional boron and nitrogen impurities do not affect the semiconducting character of the armchair SiC nanoribbons, and (ii) the half-metallic behavior of the zigzag nanoribbons is maintained in the presence of substitutional boron impurities. In contrast, nitrogen atoms occupying edge carbon sites transform half-metallic zigzag nanoribbons into metallic systems. PMID:21540516

  13. In situ fabrication of three-dimensional nitrogen and boron co-doped porous carbon nanofibers for high performance lithium-ion batteries

    NASA Astrophysics Data System (ADS)

    Zhang, Lijun; Xia, Guanglin; Guo, Zaiping; Sun, Dalin; Li, Xingguo; Yu, Xuebin

    2016-08-01

    This paper reports the fabrication of three-dimensional porous carbon nanofibers network with high doping level of nitrogen (N, 5.17 at.%) and boron (B, 6.87 at.%) through a general electrospinning strategy followed by a calcination process. The employed ammonia borane (NH3BH3, denote as AB) not only functions as a porogen reagent to generate porous structures but also as the heteroatoms source to induce N and B co-doping. Such highly unique nanoarchitectures offer remarkably improved Li storage performance including high reversible capacity (∼910 mAh g-1 at a current density of 100 mA g-1) with good cycling and rate performances.

  14. Hyperfine structures and Landé g{sub J}-factors for n=2 states in beryllium-, boron-, carbon-, and nitrogen-like ions from relativistic configuration interaction calculations

    SciTech Connect

    Verdebout, S.; Nazé, C.; Rynkun, P.; Godefroid, M.

    2014-09-15

    Energy levels, hyperfine interaction constants, and Landé g{sub J}-factors are reported for n=2 states in beryllium-, boron-, carbon-, and nitrogen-like ions from relativistic configuration interaction calculations. Valence, core–valence, and core–core correlation effects are taken into account through single and double-excitations from multireference expansions to increasing sets of active orbitals. A systematic comparison of the calculated hyperfine interaction constants is made with values from the available literature.

  15. Phenylene bridged boron-nitrogen containing dendrimers.

    PubMed

    Proń, Agnieszka; Baumgarten, Martin; Müllen, Klaus

    2010-10-01

    The synthesis and characterization of novel phenylene bridged boron-nitrogen containing π-conjugated dendrimers N3B6 and N3B3, with peripheral boron atoms and 1,3,5-triaminobenzene moiety as a core, are presented. UV-vis absorption and emission measurements reveal that the optical properties of the resulting compounds can be controlled by changing the donor/acceptor ratio: a 1:1 ratio results in a more efficient charge transfer than the 1:2 ratio. This was proven by the red shift of the emission maxima and the stronger solvatochromic effect in N3B3 compared to N3B6. PMID:20822169

  16. Zinc Oxide-Containing Porous Boron-Carbon-Nitrogen Sheets from Glycine-Nitrate Combustion: Synthesis, Self-Cleaning, and Sunlight-Driven Photocatalytic Activity.

    PubMed

    Bharathidasan, T; Mandalam, Aditya; Balasubramanian, M; Dhandapani, P; Sathiyanarayanan, S; Mayavan, Sundar

    2015-08-26

    We developed a single-step thermal method that enables successful inclusion of ZnO components in the porous boron-carbon-nitrogen (BCN) framework to form a new class of functional hybrid. ZnO-containing BCN hybrids were prepared by treating a mixture of B2O3, glycine, and zinc nitrate at 500 °C. Glycine-nitrate decomposition along with B2O3 acts as a source for ZnO-BCN formation. The incorporation of ZnO onto BCN has extended the photoresponse of ZnO in the visible region, which makes ZnO-BCN a preferable photocatalyst relative to ZnO upon sunlight exposure. It is interesting to note that as-prepared 2D ZnO-BCN sheets dispersed in PDMS form a stable coating over aluminum alloys. The surface exhibited a water contact angle (CA) of 157.6° with 66.6 wt % ZnO-BCN in polydimethylsiloxane (PDMS) and a water droplet (7 μL) roll-off angle of <6° and also demonstrates oil fouling resistant superhydrophobicity. In brief, the present study focuses on the gram scale synthesis of a new class of sunlight-driven photocatalyst and also its application toward the development of superhydrophobic and oleophobic coating. PMID:26252873

  17. Producing carbon stripper foils containing boron

    SciTech Connect

    Stoner, J. O. Jr.

    2012-12-19

    Parameters being actively tested by the accelerator community for the purpose of extending carbon stripper foil lifetimes in fast ion beams include methods of deposition, parting agents, mounting techniques, support (fork) materials, and inclusion of alloying elements, particularly boron. Specialized production apparatus is required for either sequential deposition or co-deposition of boron in carbon foils. A dual-use vacuum evaporator for arc evaporation of carbon and electron-beam evaporation of boron and other materials has been built for such development. Production of both carbon and boron foils has begun and improvements are in progress.

  18. Binary and ternary doping of nitrogen, boron, and phosphorus into carbon for enhancing electrochemical oxygen reduction activity.

    PubMed

    Choi, Chang Hyuck; Park, Sung Hyeon; Woo, Seong Ihl

    2012-08-28

    N-doped carbon, a promising alternative to Pt catalyst for oxygen reduction reactions (ORRs) in acidic media, is modified in order to increase its catalytic activity through the additional doping of B and P at the carbon growth step. This additional doping alters the electrical, physical, and morphological properties of the carbon. The B-doping reinforces the sp(2)-structure of graphite and increases the portion of pyridinic-N sites in the carbon lattice, whereas P-doping enhances the charge delocalization of the carbon atoms and produces carbon structures with many edge sites. These electrical and physical alternations of the N-doped carbon are more favorable for the reduction of the oxygen on the carbon surface. Compared with N-doped carbon, B,N-doped or P,N-doped carbon shows 1.2 or 2.1 times higher ORR activity at 0.6 V (vs RHE) in acidic media. The most active catalyst in the reaction is the ternary-doped carbon (B,P,N-doped carbon), which records -6.0 mA/mg of mass activity at 0.6 V (vs RHE), and it is 2.3 times higher than that of the N-doped carbon. These results imply that the binary or ternary doping of B and P with N into carbon induces remarkable performance enhancements, and the charge delocalization of the carbon atoms or number of edge sites of the carbon is a significant factor in deciding the oxygen reduction activity in carbon-based catalysts. PMID:22769428

  19. Boron and nitrogen doping in graphene antidot lattices

    NASA Astrophysics Data System (ADS)

    Brun, Søren J.; Pereira, Vitor M.; Pedersen, Thomas G.

    2016-06-01

    Bottom-up fabrication of graphene antidot lattices (GALs) has previously yielded atomically precise structures with subnanometer periodicity. Focusing on this type of experimentally realized GAL, we perform density functional theory calculations on the pristine structure as well as GALs with edge carbon atoms substituted with boron or nitrogen. We show that p - and n -type doping levels emerge with activation energies that depend on the level of hydrogenation at the impurity. Furthermore, a tight-binding parametrization together with a Green's function method are used to describe more dilute doping. Finally, random configurations of impurities in moderately doped systems are considered to show that the doping properties are robust against disorder.

  20. Methods of forming boron nitride

    SciTech Connect

    Trowbridge, Tammy L; Wertsching, Alan K; Pinhero, Patrick J; Crandall, David L

    2015-03-03

    A method of forming a boron nitride. The method comprises contacting a metal article with a monomeric boron-nitrogen compound and converting the monomeric boron-nitrogen compound to a boron nitride. The boron nitride is formed on the same or a different metal article. The monomeric boron-nitrogen compound is borazine, cycloborazane, trimethylcycloborazane, polyborazylene, B-vinylborazine, poly(B-vinylborazine), or combinations thereof. The monomeric boron-nitrogen compound is polymerized to form the boron nitride by exposure to a temperature greater than approximately 100.degree. C. The boron nitride is amorphous boron nitride, hexagonal boron nitride, rhombohedral boron nitride, turbostratic boron nitride, wurzite boron nitride, combinations thereof, or boron nitride and carbon. A method of conditioning a ballistic weapon and a metal article coated with the monomeric boron-nitrogen compound are also disclosed.

  1. Iron encapsulated in boron and nitrogen codoped carbon nanotubes as synergistic catalysts for Fenton-like reaction.

    PubMed

    Yao, Yunjin; Chen, Hao; Qin, Jiacheng; Wu, Guodong; Lian, Chao; Zhang, Jie; Wang, Shaobin

    2016-09-15

    Iron nanoparticles (NPs) encapsulated in B, N-codoped carbon nanotubes (Fe@C-BN) as heterogeneous Fenton-like catalysts were obtained by a simple and scalable pyrolysis method, and their performances were examined in the oxidative degradation of various organics in the presence of the different oxidants. The results showed that organic dyes can be effectively degraded by Fe@C-BN in the presence of peroxymonosulfate. Calcination temperature and mass of iron salt significantly affected the structures and performances of the catalysts. The effects of several reaction conditions, such as initial dye concentration, oxidant type (peroxymonosulfate, peroxydisulfate, and H2O2) and dosage, initial pH, inorganic anions, reaction temperature and dye types on oxidation as well as the stability of the composite were extensively evaluated in view of the practical applications. Through the investigation of reaction processes, HO(·) and SO4(·-) radicals were identified using quenching experiments. Owing to the synergistic effects between the iron NPs and B, N-doped carbon, Fe@C-BN catalysts intrinsically display an excellent catalytic activity for Fenton-like reaction. This study gives new insights into the design and preparation of iron NPs encapsulated in B, N-codoped carbon nanotubes as an effective strategy to enhance the overall catalytic activity. PMID:27267476

  2. Boron-Filled Hybrid Carbon Nanotubes

    PubMed Central

    Patel, Rajen B.; Chou, Tsengming; Kanwal, Alokik; Apigo, David J.; Lefebvre, Joseph; Owens, Frank; Iqbal, Zafar

    2016-01-01

    A unique nanoheterostructure, a boron-filled hybrid carbon nanotube (BHCNT), has been synthesized using a one-step chemical vapor deposition process. The BHCNTs can be considered to be a novel form of boron carbide consisting of boron doped, distorted multiwalled carbon nanotubes (MWCNTs) encapsulating boron nanowires. These MWCNTs were found to be insulating in spite of their graphitic layered outer structures. While conventional MWCNTs have great axial strength, they have weak radial compressive strength, and do not bond well to one another or to other materials. In contrast, BHCNTs are shown to be up to 31% stiffer and 233% stronger than conventional MWCNTs in radial compression and have excellent mechanical properties at elevated temperatures. The corrugated surface of BHCNTs enables them to bond easily to themselves and other materials, in contrast to carbon nanotubes (CNTs). BHCNTs can, therefore, be used to make nanocomposites, nanopaper sheets, and bundles that are stronger than those made with CNTs. PMID:27460526

  3. Boron-Filled Hybrid Carbon Nanotubes

    NASA Astrophysics Data System (ADS)

    Patel, Rajen B.; Chou, Tsengming; Kanwal, Alokik; Apigo, David J.; Lefebvre, Joseph; Owens, Frank; Iqbal, Zafar

    2016-07-01

    A unique nanoheterostructure, a boron-filled hybrid carbon nanotube (BHCNT), has been synthesized using a one-step chemical vapor deposition process. The BHCNTs can be considered to be a novel form of boron carbide consisting of boron doped, distorted multiwalled carbon nanotubes (MWCNTs) encapsulating boron nanowires. These MWCNTs were found to be insulating in spite of their graphitic layered outer structures. While conventional MWCNTs have great axial strength, they have weak radial compressive strength, and do not bond well to one another or to other materials. In contrast, BHCNTs are shown to be up to 31% stiffer and 233% stronger than conventional MWCNTs in radial compression and have excellent mechanical properties at elevated temperatures. The corrugated surface of BHCNTs enables them to bond easily to themselves and other materials, in contrast to carbon nanotubes (CNTs). BHCNTs can, therefore, be used to make nanocomposites, nanopaper sheets, and bundles that are stronger than those made with CNTs.

  4. Boron-Filled Hybrid Carbon Nanotubes.

    PubMed

    Patel, Rajen B; Chou, Tsengming; Kanwal, Alokik; Apigo, David J; Lefebvre, Joseph; Owens, Frank; Iqbal, Zafar

    2016-01-01

    A unique nanoheterostructure, a boron-filled hybrid carbon nanotube (BHCNT), has been synthesized using a one-step chemical vapor deposition process. The BHCNTs can be considered to be a novel form of boron carbide consisting of boron doped, distorted multiwalled carbon nanotubes (MWCNTs) encapsulating boron nanowires. These MWCNTs were found to be insulating in spite of their graphitic layered outer structures. While conventional MWCNTs have great axial strength, they have weak radial compressive strength, and do not bond well to one another or to other materials. In contrast, BHCNTs are shown to be up to 31% stiffer and 233% stronger than conventional MWCNTs in radial compression and have excellent mechanical properties at elevated temperatures. The corrugated surface of BHCNTs enables them to bond easily to themselves and other materials, in contrast to carbon nanotubes (CNTs). BHCNTs can, therefore, be used to make nanocomposites, nanopaper sheets, and bundles that are stronger than those made with CNTs. PMID:27460526

  5. Chemical and photoluminescence analyses of new carbon-based boron oxynitride phosphors

    SciTech Connect

    Wang, Wei-Ning; Kaihatsu, Yutaka; Iskandar, Ferry; Okuyama, Kikuo

    2009-11-15

    Analyses of newly developed carbon-based boron oxynitride phosphors using an electron energy-loss spectrometer and a spectroflurophotometer were carried out. The results showed that the prepared phosphor powder has covalently bonded boron, nitrogen, and oxygen atoms with a soft carbon framework. Photoluminescence characterization revealed that the resultant phosphor has a direct bandgap transition with defect broadened band edges, resulting in a high quantum efficiency, because the atomic distances of the phosphor are smaller than those of conventional carbon-based boron nitride compounds, which have an indirect bandgap transition and a low quantum efficiency. The atomic distances of the phosphor are smaller owing to the presence of oxygen atoms, which have a higher electron affinity and a smaller covalent bond radius compared with boron, carbon and nitrogen.

  6. Amorphous Carbon-Boron Nitride Nanotube Hybrids

    NASA Technical Reports Server (NTRS)

    Kim, Jae Woo (Inventor); Siochi, Emilie J. (Inventor); Wise, Kristopher E. (Inventor); Lin, Yi (Inventor); Connell, John (Inventor)

    2016-01-01

    A method for joining or repairing boron nitride nanotubes (BNNTs). In joining BNNTs, the nanotube structure is modified with amorphous carbon deposited by controlled electron beam irradiation to form well bonded hybrid a-C/BNNT structures. In repairing BNNTs, the damaged site of the nanotube structure is modified with amorphous carbon deposited by controlled electron beam irradiation to form well bonded hybrid a-C/BNNT structures at the damage site.

  7. Nitrogen implantation effects on the chemical bonding and hardness of boron and boron nitride coatings

    SciTech Connect

    Anders, S; Felter, T; Hayes, J; Jankowski, A F; Patterson, R; Poker, D; Stamler, T

    1999-02-08

    Boron nitride (BN) coatings are deposited by the reactive sputtering of fully dense, boron (B) targets utilizing an argon-nitrogen (Ar-N{sub 2}) reactive gas mixture. Near-edge x-ray absorption fine structure analysis reveals features of chemical bonding in the B 1s photoabsorption spectrum. Hardness is measured at the film surface using nanoindentation. The BN coatings prepared at low, sputter gas pressure with substrate heating are found to have bonding characteristic of a defected hexagonal phase. The coatings are subjected to post-deposition nitrogen (N{sup +} and N{sub 2}{sup +}) implantation at different energies and current densities. The changes in film hardness attributed to the implantation can be correlated to changes observed in the B 1s NEXAFS spectra.

  8. Graphitic electrodes modified with boron and nitrogen for electrochemical energy storage enhancement

    NASA Astrophysics Data System (ADS)

    Xiong, Guoping; Paul, Rajib; Reifenberger, Ron; Fisher, Timothy

    2013-03-01

    Electrodes based on carbon nanomaterials (carbon nanotubes or graphitic nanopetals) have been modified with boron (B) and nitrogen (N) through a facile microwave heating cycle. During the microwave heating, the electrodes are immersed in a precursor solution consisting of urea and boric acid dissolved in either water or methanol. After microwave heating and overnight vacuum drying, the electrodes are again heated in nitrogen to remove unreacted chemicals and to form CxBN. Hydrogen plasma was then used to remove any residual boron oxide from the surface of the electrodes. Carbon nanotubes modified with B and N exhibited higher lithium storage capacity as compared to pure carbon nanotube electrodes. We note that the modification appears to produce a highly unexpected and substantial cycle-to-cycle improvement in battery capacity as the electrode cycles through hundreds of charge-discharge iterations. This process can be applied to other carbon-based electrodes, which themselves are recognized for their high performance, to add further improvements. AFOSR MURI No. 105800

  9. Fabrication and characterization of carbon and boron carbide nanostructured materials

    NASA Astrophysics Data System (ADS)

    Reynaud, Sara

    , nanostructured BC compounds are fabricated by arc discharge technique using graphite or boron carbide electrodes submerged in liquid nitrogen, de-ionised water, or argon gas. Microscopic and spectroscopic investigation of the synthesized material confirms formation of various BC and carbon nanostructures. Specifically, arc discharge initiated in inert environment by applying low current leads to the formation of nanostructured BC without contaminants.

  10. Ceramic silicon-boron-carbon fibers from organic silicon-boron-polymers

    NASA Technical Reports Server (NTRS)

    Riccitiello, Salvatore R. (Inventor); Hsu, Ming-Ta S. (Inventor); Chen, Timothy S. (Inventor)

    1993-01-01

    Novel high strength ceramic fibers derived from boron, silicon, and carbon organic precursor polymers are discussed. The ceramic fibers are thermally stable up to and beyond 1200 C in air. The method of preparation of the boron-silicon-carbon fibers from a low oxygen content organosilicon boron precursor polymer of the general formula Si(R2)BR(sup 1) includes melt-spinning, crosslinking, and pyrolysis. Specifically, the crosslinked (or cured) precursor organic polymer fibers do not melt or deform during pyrolysis to form the silicon-boron-carbon ceramic fiber. These novel silicon-boron-carbon ceramic fibers are useful in high temperature applications because they retain tensile and other properties up to 1200 C, from 1200 to 1300 C, and in some cases higher than 1300 C.

  11. Carbon or boron modified titanium silicide

    DOEpatents

    Thom, Andrew J.; Akinc, Mufit

    1997-12-02

    A titanium silicide material based on Ti.sub.5 Si.sub.3 intermetallic compound exhibits substantially improved oxidative stability at elevated temperatures. In particular, carbon is added to a Ti.sub.5 Si.sub.3 base material in an amount (e.g. about 0.3 to about 3.6 weight % C) effective to impart substantially improved oxidative stability at elevated temperatures, such as about 1000.degree. C. Boron is added to a Ti.sub.5 Si.sub.3 base material in an amount (e.g. about 0.3 to about 3.3 weight % B) to this same end.

  12. Carbon or boron modified titanium silicide

    DOEpatents

    Thom, A.J.; Akinc, M.

    1996-12-03

    A titanium silicide material based on Ti{sub 5}Si{sub 3} intermetallic compound exhibits substantially improved oxidative stability at elevated temperatures. In particular, carbon is added to a Ti{sub 5}Si{sub 3} base material in an amount (e.g. about 0.3 to about 3.6 weight % C) effective to impart substantially improved oxidative stability at elevated temperatures, such as about 1000 C. Boron is added to a Ti{sub 5}Si{sub 3} base material in an amount (e.g. about 0.3 to about 3.3 weight % B) to this same end. 3 figs.

  13. Carbon or boron modified titanium silicide

    DOEpatents

    Thom, Andrew J.; Akinc, Mufit

    1996-12-03

    A titanium silicide material based on Ti.sub.5 Si.sub.3 intermetallic compound exhibits substantially improved oxidative stability at elevated temperatures. In particular, carbon is added to a Ti.sub.5 Si.sub.3 base material in an amount (e.g. about 0.3 to about 3.6 weight % C) effective to impart substantially improved oxidative stability at elevated temperatures, such as about 1000.degree. C. Boron is added to a Ti.sub.5 Si.sub.3 base material in an amount (e.g. about 0.3 to about 3.3 weight % B) to this same end.

  14. Carbon or boron modified titanium silicide

    DOEpatents

    Thom, A.J.; Akinc, M.

    1998-07-14

    A titanium silicide material based on Ti{sub 5}Si{sub 3} intermetallic compound exhibits substantially improved oxidative stability at elevated temperatures. In particular, carbon is added to a Ti{sub 5}Si{sub 3} base material in an amount (e.g. about 0.3 to about 3.6 weight % C) effective to impart substantially improved oxidative stability at elevated temperatures, such as about 1000 C. Boron is added to a Ti{sub 5}Si{sub 3} base material in an amount (e.g. about 0.3 to about 3.3 weight % B) to this same end. 3 figs.

  15. Carbon or boron modified titanium silicide

    DOEpatents

    Thom, Andrew J.; Akinc, Mufit

    1998-07-14

    A titanium silicide material based on Ti.sub.5 Si.sub.3 intermetallic compound exhibits substantially improved oxidative stability at elevated temperatures. In particular, carbon is added to a Ti.sub.5 Si.sub.3 base material in an amount (e.g. about 0.3 to about 3.6 weight % C) effective to impart substantially improved oxidative stability at elevated temperatures, such as about 1000.degree. C. Boron is added to a Ti.sub.5 Si.sub.3 base material in an amount (e.g. about 0.3 to about 3.3 weight % B) to this same end.

  16. Carbon or boron modified titanium silicide

    DOEpatents

    Thom, A.J.; Akinc, M.

    1997-12-02

    A titanium silicide material based on Ti{sub 5}Si{sub 3} intermetallic compound exhibits substantially improved oxidative stability at elevated temperatures. In particular, carbon is added to a Ti{sub 5}Si{sub 3} base material in an amount (e.g. about 0.3 to about 3.6 weight % C) effective to impart substantially improved oxidative stability at elevated temperatures, such as about 1000 C. Boron is added to a Ti{sub 5}Si{sub 3} base material in an amount (e.g. about 0.3 to about 3.3 weight % B) to this same end. 3 figs.

  17. Photoelectron spectra and electronic structure of nitrogen analogues of boron β-diketonates

    NASA Astrophysics Data System (ADS)

    Tikhonov, Sergey A.; Vovna, Vitaliy I.; Borisenko, Aleksandr V.

    2016-07-01

    The electronic structure of the valence levels of seven nitrogen-containing boron complexes was investigated using methods of ultraviolet photoelectron spectroscopy and density functional theory. The ionization energies of π- and σ-levels were obtained from photoelectron spectra. The electronic structure of nitrogen-containing compounds was compared with the electronic structure of β-diketonates. It was shown the influence of various substituents on carbon and nitrogen atoms of six-membered ring on the electronic structure of complexes. The changes in the electronic structure after the substitution of atoms in condensed cycles have been identified. In order to compare the experimental vertical ionization energies IEi with Kohn-Sham orbital energies εi we used the analogue of Koopmans theorem and average amendment to the orbital energy of the electrons (δbari). For 26 electronic levels of seven studied complexes, the calculated values are in good accordance with experimental energy intervals between electron levels.

  18. Role of boron nutrient in nodules growth and nitrogen fixation rates in soybean genotypes under water stress conditions

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Although boron has a stimulatory effect on nodule growth and nitrogen fixation, mechanisms of how boron affects nodules growth and nitrogen fixation, especially under water stress, are still unknown. The stimulatory effect of boron (B) on nodules and nitrogen fixation (NF) is influenced by biotic (s...

  19. Reactivity of boron- and nitrogen-doped carbon nanotubes functionalized by (Pt, Eu) atoms toward O2 and CO: A density functional study

    NASA Astrophysics Data System (ADS)

    Abdel Aal, S.

    2016-01-01

    The adsorption behavior and electronic properties of CO and O2 molecules at the supported Pt and Eu atoms on (5,5) armchair SWCNT have been systematically investigated within density functional theory (DFT). Fundamental aspects such as adsorption energy, natural bond orbital (NBO), charge transfer, frontier orbitals and the projected density of states (PDOS) are elucidated to analyze the adsorption properties of CO and O2 molecules. The results reveal that B- and N-doping CNTs can enhance the binding strength and catalytic activity of Pt (Eu) anchored on the doped-CNT, where boron-doping is more effective. The electronic structures of supported metal are strongly influenced by the presence of gases. After adsorption of CO and O2, the changes in binding energy, charge transfer and conductance may lead to the different response in the metal-doped CNT-based sensors. It is expected that these results could provide helpful information for the design and fabrication of the CO and O2 sensing devices. The high catalytic activity of Pt supported at doped-CNT toward the interaction with CO and O2 may be attributed to the electronic resonance particularly among Pt-5d, CO-2π* and O2-2π* antibonding orbitals. In contrast to the supported Eu at doped-CNT, the Eu atom becomes more positively charged, which leads to weaken the CO adsorption and promote the O2 adsorption, consequently enhancing the activity for CO oxidation and alleviating the CO poisoning of the europium catalysts. A notable orbital hybridization and electrostatic interaction between these two species in adsorption process being an evidence of strong interaction. The electronic structure of O2 adsorbed on Eu-doped CNT resembles that of O2‑, therefore the transferred charge weakens the O-O bonds and facilitates the dissociation process, which is the precondition for the oxygen reduction reaction (ORR).

  20. Boron Substitution in Disordered Graphene-like Carbon

    NASA Astrophysics Data System (ADS)

    Schaeperkoetter, Joe; Gillespie, Andrew; Wexler, Carlos; Pfeifer, Peter; Materials Research Institute-Missouri S&T Collaboration; Paul Rulis Collaboration

    2015-03-01

    X-ray photoelectron spectroscopy was used to determine both the elemental composition of boron doped carbons as well as gain insight into the arrangement of atoms in the material. The hypothesized arrangement of atoms is a direct substitution of boron for carbon into a graphene like sheet, maintaining the hexagonal honeycomb lattice of sp2 sigma bonds. Such a boron atom would have an electronic configuration of 1s2(sp2)3 . With a graphitic carbon atom, the pz orbitals are maintained and participate in mobile pi bonds with neighboring carbon atoms, as understood in the aromatic model. Boron, however, would require a charge donation to fill its pz orbital. Thus, three possible models are proposed for the out of plane electron density: (1) the orbital remains unoccupied and the boron is a free radical, (2) charge is donated from a neighboring atom and the boron atom is ionic, (3) the delocalization of charge in the aromatic system results in a partial charge transfer with an effective charge somewhere between neutral and anionic. Our results suggest that boron is not in an anionic state, and, by doing a quantitative and simultaneous analysis from multiple elemental spectra, we conclude that no more than 2 wt% of boron is being substitutionally doped into the system.

  1. Efficient Boron Nitride Nanotube Formation via Combined Laser-Gas Flow Levitation

    NASA Technical Reports Server (NTRS)

    Whitney, R. Roy (Inventor); Jordan, Kevin (Inventor); Smith, Michael W. (Inventor)

    2014-01-01

    A process for producing boron nitride nanotubes and/or boron-carbon-nitrogen nanotubes of the general formula B(sub x)C(sub y)N(sub z) The process utilizes a combination of laser light and nitrogen gas flow to support a boron ball target during heating of the boron ball target and production of a boron vapor plume which reacts with nitrogen or nitrogen and carbon to produce boron nitride nanotubes and/or boron-carbon-nitrogen nanotubes of the general formula B(sub x)C(sub y)N(sub z).

  2. Efficient boron nitride nanotube formation via combined laser-gas flow levitation

    DOEpatents

    Whitney, R. Roy; Jordan, Kevin; Smith, Michael

    2014-03-18

    A process for producing boron nitride nanotubes and/or boron-carbon-nitrogen nanotubes of the general formula B.sub.xC.sub.yN.sub.z. The process utilizes a combination of laser light and nitrogen gas flow to support a boron ball target during heating of the boron ball target and production of a boron vapor plume which reacts with nitrogen or nitrogen and carbon to produce boron nitride nanotubes and/or boron-carbon-nitrogen nanotubes of the general formula B.sub.xC.sub.yN.sub.z.

  3. Band gap opening and semiconductor-metal phase transition in (n, n) single-walled carbon nanotubes with distinctive boron-nitrogen line defect.

    PubMed

    Qiu, Ming; Xie, Yuanyuan; Gao, Xianfeng; Li, Jianyang; Deng, Yelin; Guan, Dongsheng; Ma, Lulu; Yuan, Chris

    2016-02-14

    Band gap opening and modulating are critical in dictating the functionalities of single walled carbon nanotubes (SWCNTs) in a broad array of nano-devices. Using first-principles density functional theory calculations, a class of semiconducting armchair SWCNTs with a distinctive BN line defect are studied, showing a super capacity to open the band gap of (4, 4) SWCNT to as large as 0.86 eV, while the opened band gap are found decreasing with the increasing diameters of SWCNTs. The opened band gap of SWCNTs can also be successfully modulated through both mechanical and electrical approaches by applying compressive uniaxial strain and electric field. This study provides novel insights into the large band gap opening and modulating of SWCNTs and could be useful in facilitating future applications of SWCNTs in electronic, optical and thermoelectric devices. PMID:26794602

  4. Measured Enthalpies of Adsorption of Boron-Doped Activated Carbons

    NASA Astrophysics Data System (ADS)

    Beckner, M.; Romanos, J.; Dohnke, E.; Singh, A.; Schaeperkoetter, J.; Stalla, D.; Burress, J.; Jalisatgi, S.; Suppes, G.; Hawthorne, M. F.; Yu, P.; Wexler, C.; Pfeifer, P.

    2012-02-01

    There is significant interest in the properties of boron-doped activated carbons for their potential to improve hydrogen storage.ootnotetextMultiply Surface-Functionalized Nanoporous Carbon for Vehicular Hydrogen Storage, P. Pfeifer et al. DOE Hydrogen Program 2011 Annual Progress Report, IV.C.3, 444-449 (2011). Boron-doped activated carbons have been produced using a process involving the pyrolysis of decaborane (B10H14) and subsequent high-temperature annealing. In this talk, we will present a systematic study of the effect of different boron doping processes on the samples' structure, hydrogen sorption, and surface chemistry. Initial room temperature experiments show a 20% increase in the hydrogen excess adsorption per surface area compared to the undoped material. Experimental enthalpies of adsorption will be presented for comparison to theoretical predictions for boron-doped carbon materials. Additionally, results from a modified version of the doping process will be presented.

  5. New Carbonate Standard Reference Materials for Boron Isotope Geochemistry

    NASA Astrophysics Data System (ADS)

    Stewart, J.; Christopher, S. J.; Day, R. D.

    2015-12-01

    The isotopic composition of boron (δ11B) in marine carbonates is well established as a proxy for past ocean pH. Yet, before palaeoceanographic interpretation can be made, rigorous assessment of analytical uncertainty of δ11B data is required; particularly in light of recent interlaboratory comparison studies that reported significant measurement disagreement between laboratories [1]. Well characterised boron standard reference materials (SRMs) in a carbonate matrix are needed to assess the accuracy and precision of carbonate δ11B measurements throughout the entire procedural chemistry; from sample cleaning, to ionic separation of boron from the carbonate matrix, and final δ11B measurement by multi-collector inductively coupled plasma mass spectrometry. To date only two carbonate reference materials exist that have been value-assigned by the boron isotope measurement community [2]; JCp-1 (porites coral) and JCt-1 (Giant Clam) [3]. The National Institute of Standards and Technology (NIST) will supplement these existing standards with new solution based inorganic carbonate boron SRMs that replicate typical foraminiferal and coral B/Ca ratios and δ11B values. These new SRMs will not only ensure quality control of full procedural chemistry between laboratories, but have the added benefits of being both in abundant supply and free from any restrictions associated with shipment of biogenic samples derived from protected species. Here we present in-house δ11B measurements of these new boron carbonate SRM solutions. These preliminary data will feed into an interlaboratory comparison study to establish certified values for these new NIST SRMs. 1. Foster, G.L., et al., Chemical Geology, 2013. 358(0): p. 1-14. 2. Gutjahr, M., et al., Boron Isotope Intercomparison Project (BIIP): Development of a new carbonate standard for stable isotopic analyses. Geophysical Research Abstracts, EGU General Assembly 2014, 2014. 16(EGU2014-5028-1). 3. Inoue, M., et al., Geostandards and

  6. The boron-carbon-nitrogen heterocyclic rings

    NASA Astrophysics Data System (ADS)

    Srivastava, Ambrish Kumar; Misra, Neeraj

    2015-04-01

    The heterocyclic rings containing B, C and N atoms, also known as azaborines, are systematically studied. The electronic properties of these BCN rings are explored by using second order perturbation theory and their aromaticity is discussed by the nucleus independent chemical shifts. These heterocyclic rings are found to be chemically more reactive than benzene and borazine, due to smaller HOMO-LUMO gap and non-zero dipole moment. However, the aromaticity of these BCN rings is less than benzene but two or three times that of borazine.

  7. Structure, Mechanics and Synthesis of Nanoscale Carbon and Boron Nitride

    NASA Astrophysics Data System (ADS)

    Rinaldo, Steven G.

    This thesis is divided into two parts. In Part I, we examine the properties of thin sheets of carbon and boron nitride. We begin with an introduction to the theory of elastic sheets, where the stretching and bending modes are considered in detail. The coupling between stretching and bending modes is thought to play a crucial role in the thermodynamic stability of atomically-thin 2D sheets such as graphene. In Chapter 2, we begin by looking at the fabrication of suspended, atomically thin sheets of graphene. We then study their mechanical resonances which are read via an optical transduction technique. The frequency of the resonators was found to depend on their temperature, as was their quality factor. We conclude by offering some interpretations of the data in terms of the stretching and bending modes of graphene. In Chapter 3, we look briefly at the fabrication of thin sheets of carbon and boron nitride nanotubes. We examine the structure of the sheets using transmission and scanning electron microscopy (TEM and SEM, respectively). We then show a technique by which one can make sheets suspended over a trench with adjustable supports. Finally, DC measurements of the resistivity of the sheets in the temperature range 600 -- 1400 C are presented. In Chapter 4, we study the folding of few-layer graphene oxide, graphene and boron nitride into 3D aerogel monoliths. The properties of graphene oxide are first considered, after which the structure of graphene and boron nitride aerogels is examined using TEM and SEM. Some models for their structure are proposed. In Part II, we look at synthesis techniques for boron nitride (BN). In Chapter 5, we study the conversion of carbon structures of boron nitride via the application of carbothermal reduction of boron oxide followed by nitridation. We apply the conversion to a wide variety of morphologies, including aerogels, carbon fibers and nanotubes, and highly oriented pyrolytic graphite. In the latter chapters, we look at the

  8. Structural Modification in Carbon Nanotubes by Boron Incorporation.

    PubMed

    Handuja, Sangeeta; Srivastava, P; Vankar, V D

    2009-01-01

    We have synthesized boron-incorporated carbon nanotubes (CNTs) by decomposition of ferrocene and xylene in a thermal chemical vapor deposition set up using boric acid as the boron source. Scanning and transmission electron microscopy studies of the synthesized CNT samples showed that there was deterioration in crystallinity and improvement in alignment of the CNTs as the boron content in precursor solution increased from 0% to 15%. Raman analysis of these samples showed a shift of ~7 cm(-1) in wave number to higher side and broadening of the G band with increasing boron concentration along with an increase in intensity of the G band. Furthermore, there was an increase in the intensity of the D band along with a decrease in its wave number position with increase in boron content. We speculate that these structural modifications in the morphology and microstructure of CNTs might be due to the charge transfer from boron to the graphite matrix, resulting in shortening of the carbon-carbon bonds. PMID:20596333

  9. Structural Modification in Carbon Nanotubes by Boron Incorporation

    NASA Astrophysics Data System (ADS)

    Handuja, Sangeeta; Srivastava, P.; Vankar, V. D.

    2009-08-01

    We have synthesized boron-incorporated carbon nanotubes (CNTs) by decomposition of ferrocene and xylene in a thermal chemical vapor deposition set up using boric acid as the boron source. Scanning and transmission electron microscopy studies of the synthesized CNT samples showed that there was deterioration in crystallinity and improvement in alignment of the CNTs as the boron content in precursor solution increased from 0% to 15%. Raman analysis of these samples showed a shift of ~7 cm-1 in wave number to higher side and broadening of the G band with increasing boron concentration along with an increase in intensity of the G band. Furthermore, there was an increase in the intensity of the D band along with a decrease in its wave number position with increase in boron content. We speculate that these structural modifications in the morphology and microstructure of CNTs might be due to the charge transfer from boron to the graphite matrix, resulting in shortening of the carbon-carbon bonds.

  10. Carbon-rich icosahedral boron carbide designed from first principles

    SciTech Connect

    Jay, Antoine; Vast, Nathalie; Sjakste, Jelena; Duparc, Olivier Hardouin

    2014-07-21

    The carbon-rich boron-carbide (B{sub 11}C)C-C has been designed from first principles within the density functional theory. With respect to the most common boron carbide at 20% carbon concentration B{sub 4}C, the structural modification consists in removing boron atoms from the chains linking (B{sub 11}C) icosahedra. With C-C instead of C-B-C chains, the formation of vacancies is shown to be hindered, leading to enhanced mechanical strength with respect to B{sub 4}C. The phonon frequencies and elastic constants turn out to prove the stability of the carbon-rich phase, and important fingerprints for its characterization have been identified.

  11. Coprecipitation and isotopic fractionation of boron in modern biogenic carbonates

    SciTech Connect

    Vengosh, A. Hebrew Univ., Jerusalem ); Chivas, A.R.; McCulloch, M.T. ); Kolodny, Y.; Starinsky, A. )

    1991-10-01

    The abundances and isotopic composition of boron in modern, biogenic calcareous skeletons from the Gulf of Elat, Israel, the Great Barrier Reef, Australia, and in deep-sea sediments have been examined by negative thermal-ionization mass spectrometry. The selected species (Foraminifera, Pteropoda, corals, Gastropoda, and Pelecypoda) yield large variations in boron concentration that range from 1 ppm in gastropod shells to 80 ppm in corals. The variations of {delta}{sup 11}B may be controlled by isotopic exchange of boron species in which {sup 10}B is preferentially partitioned into the tetrahedral species, and coprecipitation of different proportions of trigonal and tetrahedral species in the calcium carbonates. The B content and {delta}{sup 11}B values of deep-sea sediments, Foraminifera tests, and corals are used to estimate the global oceanic sink of elemental boron by calcium carbonate deposition. As a result of enrichment of B in corals, a substantially higher biogenic sink of 6.4 {plus minus} 0.9 {times} 10{sup 10} g/yr is calculated for carbonates. This is only slightly lower than the sink for desorbable B in marine sediments (10 {times} 10{sup 10} g/yr) and approximately half that of altered oceanic crust (14 {times} 10{sup 10} g/yr). Thus, carbonates are an important sink for B in the oceans being {approximately}20% of the total sinks. The preferential incorporation of {sup 10}B into calcium carbonate results in oceanic {sup 11}B-enrichment, estimated as 1.2 {plus minus} 0.3 {times} 10{sup 12} per mil {center dot} g/yr. The boron-isotope composition of authigenic, well-preserved carbonate skeletons may provide a useful tool to record secular boron-isotope variations in seawater at various times in the geological record.

  12. Boron isotope fractionation in magma via crustal carbonate dissolution

    PubMed Central

    Deegan, Frances M.; Troll, Valentin R.; Whitehouse, Martin J.; Jolis, Ester M.; Freda, Carmela

    2016-01-01

    Carbon dioxide released by arc volcanoes is widely considered to originate from the mantle and from subducted sediments. Fluids released from upper arc carbonates, however, have recently been proposed to help modulate arc CO2 fluxes. Here we use boron as a tracer, which substitutes for carbon in limestone, to further investigate crustal carbonate degassing in volcanic arcs. We performed laboratory experiments replicating limestone assimilation into magma at crustal pressure-temperature conditions and analysed boron isotope ratios in the resulting experimental glasses. Limestone dissolution and assimilation generates CaO-enriched glass near the reaction site and a CO2-dominated vapour phase. The CaO-rich glasses have extremely low δ11B values down to −41.5‰, reflecting preferential partitioning of 10B into the assimilating melt. Loss of 11B from the reaction site occurs via the CO2 vapour phase generated during carbonate dissolution, which transports 11B away from the reaction site as a boron-rich fluid phase. Our results demonstrate the efficacy of boron isotope fractionation during crustal carbonate assimilation and suggest that low δ11B melt values in arc magmas could flag shallow-level additions to the subduction cycle. PMID:27488228

  13. Boron isotope fractionation in magma via crustal carbonate dissolution.

    PubMed

    Deegan, Frances M; Troll, Valentin R; Whitehouse, Martin J; Jolis, Ester M; Freda, Carmela

    2016-01-01

    Carbon dioxide released by arc volcanoes is widely considered to originate from the mantle and from subducted sediments. Fluids released from upper arc carbonates, however, have recently been proposed to help modulate arc CO2 fluxes. Here we use boron as a tracer, which substitutes for carbon in limestone, to further investigate crustal carbonate degassing in volcanic arcs. We performed laboratory experiments replicating limestone assimilation into magma at crustal pressure-temperature conditions and analysed boron isotope ratios in the resulting experimental glasses. Limestone dissolution and assimilation generates CaO-enriched glass near the reaction site and a CO2-dominated vapour phase. The CaO-rich glasses have extremely low δ(11)B values down to -41.5‰, reflecting preferential partitioning of (10)B into the assimilating melt. Loss of (11)B from the reaction site occurs via the CO2 vapour phase generated during carbonate dissolution, which transports (11)B away from the reaction site as a boron-rich fluid phase. Our results demonstrate the efficacy of boron isotope fractionation during crustal carbonate assimilation and suggest that low δ(11)B melt values in arc magmas could flag shallow-level additions to the subduction cycle. PMID:27488228

  14. Boron isotope fractionation in magma via crustal carbonate dissolution

    NASA Astrophysics Data System (ADS)

    Deegan, Frances M.; Troll, Valentin R.; Whitehouse, Martin J.; Jolis, Ester M.; Freda, Carmela

    2016-08-01

    Carbon dioxide released by arc volcanoes is widely considered to originate from the mantle and from subducted sediments. Fluids released from upper arc carbonates, however, have recently been proposed to help modulate arc CO2 fluxes. Here we use boron as a tracer, which substitutes for carbon in limestone, to further investigate crustal carbonate degassing in volcanic arcs. We performed laboratory experiments replicating limestone assimilation into magma at crustal pressure-temperature conditions and analysed boron isotope ratios in the resulting experimental glasses. Limestone dissolution and assimilation generates CaO-enriched glass near the reaction site and a CO2-dominated vapour phase. The CaO-rich glasses have extremely low δ11B values down to ‑41.5‰, reflecting preferential partitioning of 10B into the assimilating melt. Loss of 11B from the reaction site occurs via the CO2 vapour phase generated during carbonate dissolution, which transports 11B away from the reaction site as a boron-rich fluid phase. Our results demonstrate the efficacy of boron isotope fractionation during crustal carbonate assimilation and suggest that low δ11B melt values in arc magmas could flag shallow-level additions to the subduction cycle.

  15. Effect of nitrogen on the growth of boron doped single crystal diamond

    SciTech Connect

    Karna, Sunil; Vohra, Yogesh

    2013-11-18

    Boron-doped single crystal diamond films were grown homoepitaxially on synthetic (100) Type Ib diamond substrates using microwave plasma assisted chemical vapor deposition. A modification in surface morphology of the film with increasing boron concentration in the plasma has been observed using atomic force microscopy. Use of nitrogen during boron doping has been found to improve the surface morphology and the growth rate of films but it lowers the electrical conductivity of the film. The Raman spectra indicated a zone center optical phonon mode along with a few additional bands at the lower wavenumber regions. The change in the peak profile of the zone center optical phonon mode and its downshift were observed with the increasing boron content in the film. Furthermore, sharpening and upshift of Raman line was observed in the film that was grown in presence of nitrogen along with diborane in process gas.

  16. Effect of nitrogen on the growth of boron doped single crystal diamond

    DOE PAGESBeta

    Karna, Sunil; Vohra, Yogesh

    2013-11-18

    Boron-doped single crystal diamond films were grown homoepitaxially on synthetic (100) Type Ib diamond substrates using microwave plasma assisted chemical vapor deposition. A modification in surface morphology of the film with increasing boron concentration in the plasma has been observed using atomic force microscopy. Use of nitrogen during boron doping has been found to improve the surface morphology and the growth rate of films but it lowers the electrical conductivity of the film. The Raman spectra indicated a zone center optical phonon mode along with a few additional bands at the lower wavenumber regions. The change in the peak profilemore » of the zone center optical phonon mode and its downshift were observed with the increasing boron content in the film. Furthermore, sharpening and upshift of Raman line was observed in the film that was grown in presence of nitrogen along with diborane in process gas.« less

  17. Boron

    MedlinePlus

    Boron is a mineral that is found in food and the environment. People take boron supplements as medicine. Boron is used for building ... to affect the way the body handles other minerals such as magnesium and phosphorus. It also seems ...

  18. Closeout of Advanced Boron and Metal Loaded High Porosity Carbons.

    SciTech Connect

    Peter C. Eklund; T. C. Mike Chung; Henry C. Foley; Vincent H. Crespi

    2011-05-01

    The Penn State effort explored the development of new high-surface-area materials for hydrogen storage, materials that could offer enhancement in the hydrogen binding energy through a direct chemical modification of the framework in high specific-surface-area platforms. The team chemically substituted boron into the hexagonal sp2 carbon framework, dispersed metal atoms bound to the boro-carbon structure, and generated the theory of novel nanoscale geometries that can enhance storage through chemical frustration, sheet curvature, electron deficiency, large local fields and mixed hybridization states. New boro-carbon materials were synthesized by high temperature plasma, pyrolysis of boron-carbon precursor molecules, and post-synthesis modification of carbons. Hydrogen uptake has been assessed, and several promising leads have been identified, with the requirement to simultaneously optimize total surface area while maintaining the enhanced hydrogen binding energies already demonstrated.

  19. Imaging carbon and nitrogen concentrations for narcotics and explosives screening

    SciTech Connect

    Trower, W.P.

    1993-12-31

    The author describes a nuclear technique for imaging carbon and nitrogen concentrations with surface densities characteristics of bulk narcotics and concealed explosives, the Carbon and the Nitrogen Camera. The physics is rooted in the tightly bound carbon-12 nucleus to which its neighboring isobars, nitrogen-12 and boron-12, decay rapidly (11 and 20 ms), mostly to its ground state, by emitting energetic beta particles (E{sub {beta}}{sup max} {approximately} 13 and 17 MeV) all of which produce bremsstrahlung and some yield annihilate radiation. The signal, photons detected in the multiscalar mode, results from the reactions {sup 13}C({gamma},p){sup 12}{Beta} for the bulk narcotics application and {sup 14}N({gamma},2n){sup 12}N and 14N({gamma},2p){sup 12}{Beta} for explosives detection and are initiated by a stepped pulsed electron beam with energy of {approximately} 30 and {approximately} 50 MeV, respectively. Images of 180 {approximately} 5 cm{sup 2} pixels taken in {approximately} 7 seconds will be presented of the carbon in a kilo of cocaine and the nitrogen in 125 grams of SEMTEX.

  20. The atomic and electronic structure of nitrogen- and boron-doped phosphorene.

    PubMed

    Boukhvalov, Danil W

    2015-10-28

    First principles modeling of nitrogen- and boron-doped phosphorene demonstrates the tendency toward the formation of highly ordered structures. Nitrogen doping leads to the formation of -N-P-P-P-N- lines. Further transformation into -P-N-P-N- lines across the chains of phosphorene occurs with increasing band gap and increasing nitrogen concentration, which coincides with the decreasing chemical activity of N-doped phosphorene. In contrast to the case of nitrogen, boron atoms prefer to form -B-B- pairs with the further formation of -P-P-B-B-P-P- patterns along the phosphorene chains. The low concentration of boron dopants converts the phosphorene from a semiconductor into a semimetal with the simultaneous enhancement of its chemical activity. Co-doping of phosphorene by both boron and nitrogen starts from the formation of -B-N- pairs, which provides flat bands and further transformation of these pairs into hexagonal BN lines and ribbons across the phosphorene chains. PMID:26417893

  1. Ambient carbon dioxide capture by boron-rich boron nitride nanotube.

    PubMed

    Choi, Heechol; Park, Young Choon; Kim, Yong-Hyun; Lee, Yoon Sup

    2011-02-23

    Carbon dioxides (CO(2)) emitted from large-scale coal-fired power stations or industrial manufacturing plants have to be properly captured to minimize environmental side effects. From results of ab initio calculations using plane waves [PAW-PBE] and localized atomic orbitals [ONIOM(wB97X-D/6-31G*:AM1)], we report strong CO(2) adsorption on boron antisite (B(N)) in boron-rich boron nitride nanotube (BNNT). We have identified two adsorption states: (1) A linear CO(2) molecule is physically adsorbed on the B(N), showing electron donation from the CO(2) lone-pair states to the B(N) double-acceptor state, and (2) the physisorbed CO(2) undergoes a carboxylate-like structural distortion and C═O π-bond breaking due to electron back-donation from B(N) to CO(2). The CO(2) chemisorption energy on B(N) is almost independent of tube diameter and, more importantly, higher than the standard free energy of gaseous CO(2) at room temperature. This implies that boron-rich BNNT could capture CO(2) effectively at ambient conditions. PMID:21287992

  2. Direct elementary reactions of boron and nitrogen at high pressures and temperatures

    SciTech Connect

    Yoo, C.S.; Akella, J.; Cynn, H.; Nicol, M.

    1997-07-01

    Highly exothermic direct reactions between elements boron and nitrogen at high pressures and temperatures yield technologically important forms of hexagonal and cubic boron nitride (BN). The crystal structures of the reaction products vary with pressure. Below 10 GPa, hexagonal BN is the product; cubic or wurzite BN form at higher pressures. Under nitrogen-rich conditions, another hexagonal allotrope occurs; this seems to be a highly transparent, low density h{sup {prime}}-BN. No direct reactions occur at ambient temperature even at pressures as high as 50 GPa, implying that a large activation barrier limits the kinetics of these exothermic processes. Direct reactions between boron and oxygen are also discussed. {copyright} {ital 1997} {ital The American Physical Society}

  3. Lightweight Ceramic Composition of Carbon Silicon Oxygen and Boron

    NASA Technical Reports Server (NTRS)

    Leiser, Daniel B. (Inventor); Hsu, Ming-Ta (Inventor); Chen, Timothy S. (Inventor)

    1997-01-01

    Lightweight, monolithic ceramics resistant to oxidation in air at high temperatures are made by impregnating a porous carbon preform with a sol which contains a mixture of tetraethoxysilane, dimethyldiethoxysilane and trimethyl borate. The sol is gelled and dried on the carbon preform to form a ceramic precursor. The precursor is pyrolyzed in an inert atmosphere to form the ceramic which is made of carbon, silicon, oxygen and boron. The carbon of the preform reacts with the dried gel during the pyrolysis to form a component of the resulting ceramic. The ceramic is of the same size, shape and form as the carbon precursor. Thus, using a porous, fibrous carbon precursor, such as a carbon felt, results in a porous, fibrous ceramic. Ceramics of the invention are useful as lightweight tiles for a reentry spacecraft.

  4. Nitrogen metabolism and seed composition as influenced by foliar boron application in soybean

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The effect of foliar boron (B) application on nitrogen metabolism and seed composition in soybean was not well investigated, especially under water stress conditions. Nonirrigated field experiment and watered (W) and water-stressed (WS) greenhouse experiments were conducted to investigate the effect...

  5. Carbon- and Nitrogen-Based Organic Frameworks.

    PubMed

    Sakaushi, Ken; Antonietti, Markus

    2015-06-16

    This Account provides an overview of organic, covalent, porous frameworks and solid-state materials mainly composed of the elements carbon and nitrogen. The structures under consideration are rather diverse and cover a wide spectrum. This Account will summarize current works on the synthetic concepts leading toward those systems and cover the application side where emphasis is set on the exploration of those systems as candidates for unusual high-performance catalysis, electrocatalysis, electrochemical energy storage, and artificial photosynthesis. These issues are motivated by the new global energy cycles and the fact that sustainable technologies should not be based on rare and expensive resources. We therefore present the strategic design of functionality in cost-effective, affordable artificial materials starting from a spectrum of simple synthetic options to end up with carbon- and nitrogen-based porous frameworks. Following the synthetic strategies, we demonstrate how the electronic structure of polymeric frameworks can be tuned and how this can modify property profiles in a very unexpected fashion. Covalent triazine-based frameworks (CTFs), for instance, showed both enormously high energy and high power density in lithium and sodium battery systems. Other C,N-based organic frameworks, such as triazine-based graphitic carbon nitride, are suggested to show promising band gaps for many (photo)electrochemical reactions. Nitrogen-rich carbonaceous frameworks, which are developed from C,N-based organic framework strategies, are highlighted in order to address their promising electrocatalytic properties, such as in the hydrogen evolution reaction, oxygen reduction reaction (ORR), and oxygen evolution reaction (OER). With careful design, those materials can be multifunctional catalysts, such as a bifunctional ORR/OER electrocatalyst. Although the majority of new C,N-based materials are still not competitive with the best (usually nonsustainable candidates) for each

  6. Boron

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Boron is an essential micronutrient element required for plant growth. Boron deficiency is wide-spread in crop plants throughout the world especially in coarse-textured soils in humid areas. Boron toxicity can also occur, especially in arid regions under irrigation. Plants respond directly to the...

  7. Methods of Boron-carbon Deposited Film Removal

    NASA Astrophysics Data System (ADS)

    Airapetov, A.; Terentiev, V.; Voituk, A.; Zakharov, A.

    Boron carbide was proposed as a material for in-situ renewable protecting coating for tungsten tiles of the ITER divertor. It is necessary to develop a method of gasification of boron-carbon film which deposits during B4C sputtering. In this paper the results of the first stage investigation of gasification methods of boron-carbon films are presented. Two gasification methods of films are investigated: interaction with the ozone-oxygen mixture and irradiation in plasma with the working gas composed of oxygen, ethanol, and, in some cases, helium. The gasification rate in the ozone-oxygen mixture at 250 °C for B/C films with different B/C ratio and carbon fiber composite (CFC), was measured. For B/C films the gasification rate decreased with increasing B/C ratio (from 45 nm/h at B/C=0.7 to 4 nm/h at B/C=2.1; for CFC - 15 μm/h). Films gasification rates were measured under ion irradiation from ethanol-oxygen-helium plasma at different temperatures, with different ion energies and different gas mixtures. The maximum obtained removal rate was near 230 nm/h in case of ethanol-oxygen plasma and at 150°C of the sample temperature.

  8. Nitrogen, phosphorus, carbon and population.

    PubMed

    Gilland, Bernard

    2015-01-01

    Population growth makes food production increase necessary; economic growth increases demand for animal products and livestock feed. As further increase of the cropland area is ecologically undesirable, it is necessary to increase crop yields; this requires, inter alia, more nitrogen and phosphorus fertiliser despite the environmental problems which this will exacerbate. It is probable that a satisfactory food supply and an environmentally benign agriculture worldwide cannot be achieved without reducing population to approximately three billion. The reduction could be achieved by 2200 if the total fertility rate--currently 2.5--declined to 1.5 as a world average by 2050, and remained at that level until 2200, but the probability of such a global fertility trajectory is close to zero. It will also be necessary to replace fossil energy by nuclear and renewable energy in order to stabilise atmospheric carbon dioxide concentration, but the phase-out cannot be completed until the 22nd century, when the atmospheric concentration will be approximately 50% above the 2015 level of 400 ppm. PMID:26790176

  9. Tuning the Electrochemical Reactivity of Boron- and Nitrogen-Substituted Graphene.

    PubMed

    Wu, Jingjie; Rodrigues, Marco-Tulio F; Vajtai, Robert; Ajayan, Pulickel M

    2016-08-01

    The structural modification of nanomaterials at the atomic level has the potential to generate tailor-made components with enhanced performance for a variety of tasks. The chemical versatility of graphene has been constantly employed to fabricate multi-functional doped 2D materials with applications encompassing energy storage and electrocatalysis. Despite the many reports on boron- and nitrogen-doped graphenes, the possible synergy that arises from combining these electronically complementary elements has yet to be fully understood and explored. The techniques used for the fabrication of these nanomaterials are reviewed, along with the most recent reports on the benefits of B, N singly doping and co-doping in the electrocatalysis for oxygen reduction reactions and for energy storage in supercapacitors and lithium secondary batteries. The investigation of bulk co-doped materials has intrinsic limitations in fully understanding the real role of heteroatoms in the above applications. Ultimately, the design and creation of substituted monolayers with controlled compositions might hold the key for carbon-based energy-related applications. PMID:27028898

  10. Investigating Carbonate System Perturbations across the Cretaceous-Palaeogene Transition using Boron Isotopes in Planktonic Foraminifera.

    NASA Astrophysics Data System (ADS)

    Henehan, M. J.; Hull, P. M.; Planavsky, N. J.; Huber, B. T.; Thomas, E.

    2014-12-01

    The interval spanning the latest Maastrichtian to the early Palaeocene has great potential in helping to elucidate the stabilising mechanisms on the Earth's carbonate system on both long and very short geological timescales, from the geologically-instantaneous production of sulphate-rich aerosols and nitrogen oxides from the K-Pg bolide impact to the relatively more gradual degassing from Deccan volcanism in the latest Maastrichtian. The extent to which ocean pH (and atmospheric CO2 concentrations) changed in response to these contrasting acidification pressures, and the timescales of their recovery, may provide unique insight into the efficiency of the Earth's oceans in buffering greenhouse gas increases (through carbonate dissolution, weathering-derived alkalinity flux, and biological carbon cycling). The boron isotope palaeo-pH proxy in planktic foraminifera is well suited to such investigations, but its application over this interval has been problematic, not least due to a scarcity of sample material and a near-complete turnover of planktonic foraminiferal species across the K-Pg boundary. To attempt to circumvent these issues, we investigate the biological influences on boron isotope signals in Maastrichtian and Danian planktonic foraminifera, with the goal of producing more accurate palaeo-pH reconstructions. With these findings in mind, we present preliminary constraints on ocean pH and carbonate system dynamics across this critical interval of geological time.

  11. Preparation of nitrogen-doped carbon tubes

    SciTech Connect

    Chung, Hoon Taek; Zelenay, Piotr

    2015-12-22

    A method for synthesizing nitrogen-doped carbon tubes involves preparing a solution of cyanamide and a suitable transition metal-containing salt in a solvent, evaporating the solvent to form a solid, and pyrolyzing the solid under an inert atmosphere under conditions suitable for the production of nitrogen-doped carbon tubes from the solid. Pyrolyzing for a shorter period of time followed by rapid cooling resulted in a tubes with a narrower average diameter.

  12. Boron- and Nitrogen-Substituted Graphene Nanoribbons as Efficient Catalysts for Oxygen Reduction Reaction

    DOE PAGESBeta

    Gong, Yongji; Fei, Huilong; Zou, Xiaolong; Zhou, Wu; Yang, Shubin; Ye, Gonglan; Liu, Zheng; Peng, Zhiwei; Lou, Jun; Vajtai, Robert; et al

    2015-02-02

    Here, we show that nanoribbons of boron- and nitrogen-substituted graphene can be used as efficient electrocatalysts for the oxygen reduction reaction (ORR). Optimally doped graphene nanoribbons made into three-dimensional porous constructs exhibit the highest onset and half-wave potentials among the reported metal-free catalysts for this reaction and show superior performance compared to commercial Pt/C catalyst. Moreover, this catalyst possesses high kinetic current density and four-electron transfer pathway with low hydrogen peroxide yield during the reaction. Finally, first-principles calculations suggest that such excellent electrocatalytic properties originate from the abundant edges of boron- and nitrogen-codoped graphene nanoribbons, which significantly reduce the energymore » barriers of the rate-determining steps of the ORR reaction.« less

  13. Boron- and Nitrogen-Substituted Graphene Nanoribbons as Efficient Catalysts for Oxygen Reduction Reaction

    SciTech Connect

    Gong, Yongji; Fei, Huilong; Zou, Xiaolong; Zhou, Wu; Yang, Shubin; Ye, Gonglan; Liu, Zheng; Peng, Zhiwei; Lou, Jun; Vajtai, Robert; Yakobson, Boris I.; Tour, James M.; Ajayan, Pulickel M.

    2015-02-02

    Here, we show that nanoribbons of boron- and nitrogen-substituted graphene can be used as efficient electrocatalysts for the oxygen reduction reaction (ORR). Optimally doped graphene nanoribbons made into three-dimensional porous constructs exhibit the highest onset and half-wave potentials among the reported metal-free catalysts for this reaction and show superior performance compared to commercial Pt/C catalyst. Moreover, this catalyst possesses high kinetic current density and four-electron transfer pathway with low hydrogen peroxide yield during the reaction. Finally, first-principles calculations suggest that such excellent electrocatalytic properties originate from the abundant edges of boron- and nitrogen-codoped graphene nanoribbons, which significantly reduce the energy barriers of the rate-determining steps of the ORR reaction.

  14. Worldwide organic soil carbon and nitrogen data

    SciTech Connect

    Zinke, P.J.; Stangenberger, A.G.; Post, W.M.; Emanuel, W.R.; Olson, J.S.

    1984-05-01

    A compilation of soil carbon and nitrogen storage data for more than 3500 soil profiles from under natural vegetation or relatively undisturbed sites is presented in this report. A summary table of the carbon and nitrogen storage in a pedon of surface cubic meter for each soil profile, as well as location, elevation, climate, parent material, and vegetation information, are presented. The data were used to determine average carbon and nitrogen storage on land surfaces of the world. Calculations were also made of storage related to climatic classifications, ecosystem clasifications, and latitudinal increments from the equator to 75/sup 0/. Carbon (kg.m/sup -3/) varies from 2 in hot dry climates, through 10 in many cold dry or seasonally moist (warm or hot) climates, to more than 30 in wet alpine or subpolar climates. Nitrogen storage, an order of magnitude smaller than carbon storage in soils, shows broad parallels but exceeds 1600 g.m/sup -3/ for subtropical/tropical premontane or lower montane soils, as well as alpine or subpolar wet soils. Such limiting conditions, defined by a balance of income and loss rates for mature soil profiles, also explain much of the variation among major ecosystem complexes whose soils are partly disturbed, incompletely recovered, or imperfectly known regarding their maturity and stability. Classifying profiles into Holdridge life zones and using appropriate life zone areas, we estimate 1309 x 10/sup 15/ g carbon and 92 x 10/sup 15/ g nitrogen in the world's soils. Alternatively, using average organic carbon and nitrogen densities from one degree latitude bands multiplied by the earth's surface area in the respective bands, we arrive at 1728 x 10/sup 15/ g of carbon and 117 x 10/sup 15/ g of nitrogen. Inadequacies that lead to the disparate estimates are discussed. 123 references, 5 figures, 7 tables.

  15. Carbon Cost of Applying Nitrogen Fertilizer

    SciTech Connect

    Izaurralde, R Cesar C. ); Mcgill, William B.; Rosenberg, Norman J.

    2000-05-05

    When the addition of nitrogen (N) fertilizer leads to increased crop biomass, it also augments carbon (C)inputs to the soil and, hence often increases soil organic matter. Consequently, the efficient use of fertilizer N to increase crop production has also been found valuable for sequestering atmospheric carbon in soil.

  16. 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.

  17. Convert Graphene Sheets to Boron Nitride and Boron Nitride-carbon Sheets via a Carbon-substitution Reaction

    SciTech Connect

    W Han; H Yu; Z Liu

    2011-12-31

    Here we discuss our synthesis of highly crystalline pure boron nitride (BN) and BN-carbon (BN-C) sheets by using graphene sheets as templates via a carbon-substitution reaction. Typically, these sheets are several micrometers wide and have a few layers. The composition ratios of BN-C sheets can be controlled by the post-treatment (remove carbon by oxidation) temperature. We also observed pure BN and BN-C nanoribbons. We characterized the BN-C sheets via Raman spectroscopy and density functional theory calculations. The results reveal that BN-C sheets with an armchair C-BN chain, and embedded C2 or C6 units in BN-dominated regions energetically are the most favorable.

  18. Convert Graphene Sheets to Boron Nitride and Boron Nitride-Carbon Sheets via a Carbon-Substitution-Reaction

    SciTech Connect

    Han, W.; Yu, H.-G.; Liu. Z.

    2011-05-16

    Here we discuss our synthesis of highly crystalline pure boron nitride (BN) and BN-carbon (BN-C) sheets by using graphene sheets as templates via a carbon-substitution reaction. Typically, these sheets are several micrometers wide and have a few layers. The composition ratios of BN-C sheets can be controlled by the post-treatment (remove carbon by oxidation) temperature. We also observed pure BN and BN-C nanoribbons. We characterized the BN-C sheets via Raman spectroscopy and density functional theory calculations. The results reveal that BN-C sheets with an armchair C-BN chain, and embedded C{sub 2} or C{sub 6} units in BN-dominated regions energetically are the most favorable.

  19. Wich Parameter of the Carbonate System Influences the Boron Isotopic Composition and the Boron Calcium Ratio in Foraminiferal Tests?

    NASA Astrophysics Data System (ADS)

    Kaczmarek, K.; Nehrke, G.; Horn, I.; Langer, G.; Misra, S.; Bijma, J.

    2013-12-01

    We performed culture experiments with the benthic symbiont bearing foraminifer Amphistegina lessonii in order to determine which parameter of the marine carbonate system influences the boron isotopic composition (δ11B) and the boron calcium ratio (B/Ca) in the test. A. lessonii grew for two months in treatments of culture media with decoupled pH-carbonate chemistry. We measured δ11B and B/Ca simultaneously on single tests using a recently new developed mass spectrometric technique. Our results show a clear pH dependence on δ11B. The B/Ca in the shell show a positive correlation with aqueous B(OH)4-/HCO3-.

  20. Electronic structure of carbon-boron nitride nanotubes

    NASA Astrophysics Data System (ADS)

    Sanginés-Mendoza, Raúl; Martinez, Edgar

    2013-03-01

    Structures of carbon and boron nitride nanotubes (CNTs, BNNTs) are quite similar, conversely, electronic properties are radically different from each other. Carbon nanotubes, whose electronic properties can be either metallic or semiconducting depending on their chiral structure, boron nitride nanotubes are always semiconductors with bandgaps over 4 eV. We have looked to hybrid systems, to predict a new kind of nanostructures with novel electronic properties. In this way, we explore the electronic properties of C-BN nanotubes. In particular, we studied the electronic structure of armchair C-BN nanotubes. The calculations were performed using the pseudopotential LCAO method with a Generalized Gradient Approximation for the exchange-correlation energy functional. The band structure of most of these systems have semiconductor character with an indirect gap smaller than its analogous BNNTs. In addition, the most prominent feature of these systems is the existence of flat bands both at the valence band top and at the conduction band minimum. Such flat bands results in sharp and narrow peaks on the total density of states. The behavior of these flat bands mainly indicates that electrons are largely localized. Thus, a detailed analysis on the electronic band structure shows that hybridization between those orbitals on the interfaces is responsible to exhibit localization effects on the hybrid systems.This research was supported by Conacyt under Grant No. 133022.

  1. Novel molecular sources for dispersing boron in carbon-carbon composites. Final report, 1 Jun-30 Nov 91

    SciTech Connect

    Chen, P.S.; Stevens, W.C.

    1991-12-31

    Improving the oxidation resistance of carbon-carbon composites is key to expanding the use of this material system into higher temperature applications. While boron particles have been added to these materials to seal cracks in protective coatings, oxidation of the carbon matrix neighboring the boron particles seriously affects composite strength. This problem is exacerbate by a natural segregation of the boron particles to fiber rich areas of the composites. Carborane, a robust molecular source of boron, was used as the precursor for atomically dispersed boron in a phenolic derived carbon matrix. Modifications of the chemical structure of carborane were used to improve the solubility in phenolic. Additions of carboranes into the phenolic resins dramatically improved the oxidation resistance of the carbonized char. The char yield of the phenolic resin was also increased significantly.

  2. Resonance of graphene nanoribbons doped with nitrogen and boron: a molecular dynamics study.

    PubMed

    Wei, Ye; Zhan, Haifei; Xia, Kang; Zhang, Wendong; Sang, Shengbo; Gu, Yuantong

    2014-01-01

    Based on its enticing properties, graphene has been envisioned with applications in the area of electronics, photonics, sensors, bio-applications and others. To facilitate various applications, doping has been frequently used to manipulate the properties of graphene. Despite a number of studies conducted on doped graphene regarding its electrical and chemical properties, the impact of doping on the mechanical properties of graphene has been rarely discussed. A systematic study of the vibrational properties of graphene doped with nitrogen and boron is performed by means of a molecular dynamics simulation. The influence from different density or species of dopants has been assessed. It is found that the impacts on the quality factor, Q, resulting from different densities of dopants vary greatly, while the influence on the resonance frequency is insignificant. The reduction of the resonance frequency caused by doping with boron only is larger than the reduction caused by doping with both boron and nitrogen. This study gives a fundamental understanding of the resonance of graphene with different dopants, which may benefit their application as resonators. PMID:24991509

  3. Worldwide organic soil carbon and nitrogen data

    SciTech Connect

    Zinke, P.J.; Stangenberger, A.G.; Post, W.M.; Emanual, W.R.; Olson, J.S.

    1986-09-01

    The objective of the research presented in this package was to identify data that could be used to estimate the size of the soil organic carbon pool under relatively undisturbed soil conditions. A subset of the data can be used to estimate amounts of soil carbon storage at equilibrium with natural soil-forming factors. The magnitude of soil properties so defined is a resulting nonequilibrium values for carbon storage. Variation in these values is due to differences in local and geographic soil-forming factors. Therefore, information is included on location, soil nitrogen content, climate, and vegetation along with carbon density and variation.

  4. Synthesis of boron and nitrogen doped graphene supporting PtRu nanoparticles as catalysts for methanol electrooxidation

    NASA Astrophysics Data System (ADS)

    Lu, Jiming; Zhou, Yingke; Tian, Xiaohui; Xu, Xiao; Zhu, Hongxi; Zhang, Shaowei; Yuan, Tao

    2014-10-01

    In this study, we demonstrate a single-step heat treatment approach to synthesize boron and nitrogen doped graphene supporting PtRu electrocatalysts for methanol electro-oxidation reaction. The reduction of graphene oxide, boron or nitrogen doping of graphene and loading of PtRu nanoparticles happened simultaneously during the reaction process. The morphologies and microstructures of the as-prepared catalysts were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The electrocatalytic methanol oxidation activity and durability of the obtained catalysts were evaluated by the cyclic voltammetry and chronoamperometric techniques. The results reveal that the boron and nitrogen doped graphene supporting PtRu electrocatalysts can be successfully prepared by the single step heat treatment technique, and the introduction of boron or nitrogen containing function groups into the reduced graphene sheets could modulate the particle size and dispersion of the supporting PtRu nanoparticles and improve the electrocatalytic performance of methanol oxidation reaction. The optimal annealing temperature is 800 °C, the preferable heat treatment time is 60 min for the nitrogen-doped catalysts and 90 min for the boron-doped catalysts, and the catalysts prepared under such conditions present superior catalytic activities for methanol oxidation than those prepared under other heat treatment conditions.

  5. Flame retardant finishing of cotton fabric based on synergistic compounds containing boron and nitrogen.

    PubMed

    Xie, Kongliang; Gao, Aiqin; Zhang, Yongsheng

    2013-10-15

    Boric acid and compound containing nitrogen, 2,4,6-tri[(2-hydroxy-3-trimethyl-ammonium)propyl]-1,3,5-triazine chloride (Tri-HTAC) were used to finish cotton fabric. The flame retardant properties of the finished cotton fabrics and the synergetic effects of boron and nitrogen elements were investigated and evaluated by limited oxygen index (LOI) method. The mechanism of cross-linking reaction among cotton fiber, Tri-HTAC, and boric acid was discussed by FTIR and element analysis. The thermal stability and surface morphology of the finished cotton fabrics were investigated by thermogravimetric analysis (TGA) and scanning electron microscope (SEM), respectively. The finishing system of the mixture containing boron and nitrogen showed excellent synergistic flame retardancy for cotton fabric. The cotton fabric finished with mixture system had excellent flame retardancy. The LOI value of the treated cotton fabric increased over 27.5. Tri-HTAC could form covalent bonds with cellulose fiber and boric acid. The flame retardant cotton fabric showed a slight decrease in tensile strength and whiteness. The surface morphology of flame retardant cotton fiber was smooth. PMID:23987402

  6. Soil warming, carbon-nitrogen interactions, and forest carbon budgets.

    PubMed

    Melillo, Jerry M; Butler, Sarah; Johnson, Jennifer; Mohan, Jacqueline; Steudler, Paul; Lux, Heidi; Burrows, Elizabeth; Bowles, Francis; Smith, Rose; Scott, Lindsay; Vario, Chelsea; Hill, Troy; Burton, Andrew; Zhou, Yu-Mei; Tang, Jim

    2011-06-01

    Soil warming has the potential to alter both soil and plant processes that affect carbon storage in forest ecosystems. We have quantified these effects in a large, long-term (7-y) soil-warming study in a deciduous forest in New England. Soil warming has resulted in carbon losses from the soil and stimulated carbon gains in the woody tissue of trees. The warming-enhanced decay of soil organic matter also released enough additional inorganic nitrogen into the soil solution to support the observed increases in plant carbon storage. Although soil warming has resulted in a cumulative net loss of carbon from a New England forest relative to a control area over the 7-y study, the annual net losses generally decreased over time as plant carbon storage increased. In the seventh year, warming-induced soil carbon losses were almost totally compensated for by plant carbon gains in response to warming. We attribute the plant gains primarily to warming-induced increases in nitrogen availability. This study underscores the importance of incorporating carbon-nitrogen interactions in atmosphere-ocean-land earth system models to accurately simulate land feedbacks to the climate system. PMID:21606374

  7. Calculation of residual principal stresses in CVD boron on carbon filaments

    NASA Technical Reports Server (NTRS)

    Behrendt, D. R.

    1980-01-01

    A three-dimensional finite element model of the chemical vapor deposition (CVD) of boron on a carbon substrate (B/C) is developed. The model includes an expansion of the boron after deposition due to atomic rearrangement and includes creep of the boron and carbon. Curves are presented to show how the principal residual stresses and the filament elongation vary as the parameters defining deposition strain and creep are varied. The calculated results are compared with experimental axial residual stress and elongation measurements made on B/C filaments. This comparison requires that for good agreement between calculated and experimental results, the deposited boron must continue to expand after deposition, and that the build-up of residual stresses is limited by significant boron and carbon creep rates.

  8. Calculation of residual principal stresses in CVD boron on carbon filaments

    NASA Technical Reports Server (NTRS)

    Behrendt, D. R.

    1980-01-01

    A three-dimensional finite element model of the chemical vapor deposition of boron on a carbon substrate (B/C) is developed. The model includes an expansion of the boron after deposition due to atomic rearrangement and includes creep of the boron and carbon. Curves are presented showing the variation of the principal residual stresses and the filament elongation with the parameters defining deposition strain and creep. The calculated results are compared with experimental axial residual stress and elongation measurements made on B/C filaments. For good agreement between calculated and experimental results, the deposited boron must continue to expand after deposition, and the build up of residual stresses must be limited by significant boron and carbon creep rates.

  9. Structural stability of nitrogen-doped ultrathin single-walled boron nanotubes: an ab initio study

    NASA Astrophysics Data System (ADS)

    Jain, Sandeep Kumar; Srivastava, Pankaj

    2012-09-01

    Ab initio calculations have been performed for determining structural stabilities of nitrogen-doped ultrathin single-walled boron nanotube. We have considered ultrathin boron nanotubes of diameters <0.5 nm, which include mainly three conformations of BNTs viz. zigzag (5,0), armchair (3,3) and chiral (4,2) with diameters 4.60, 4.78 and 4.87 Å, respectively. It has been investigated that α-BNTs are highly stable, while hexagonal BNTs are found to be least stable. In view of increasing structural stability of hexagonal BNTs, substitutional doping of foreign atoms, i.e. nitrogen is chosen. The nitrogen atoms substitute the host atoms at the middle of the tubes. The substitution doping is made with all the three conformations. The structural stabilities of BNTs have been investigated by using density functional theory (DFT). Subsequently, the cohesive energy is calculated, which directly measures the structural stability. The cohesive energy of BNTs has been calculated for different nitrogen concentrations. We found that the structures get energetically more stable with increasing nitrogen concentration. Moreover, it is also revealed that all the three BNTs are almost equally stable for single-atom doping, while the armchair BNT (3,3) is highly stable followed by zigzag (5,0) and chiral (4,2) BNTs for two- and three-atom doping. The structural stability is an important factor for realization of any physical device. Thus, these BNTs can be used for field emission, semiconducting and highly conducting devices at nanoscale.

  10. Hydrogen storage by boron-nitrogen heterocycles: a simple route for spent fuel regeneration.

    PubMed

    Campbell, Patrick G; Zakharov, Lev N; Grant, Daniel J; Dixon, David A; Liu, Shih-Yuan

    2010-03-17

    We describe a new hydrogen storage platform based on well-defined BN heterocyle materials. Specifically, we demonstrate that regeneration of the spent fuel back to the charged fuel can be accomplished using molecular H(2) and H(-)/H(+) sources. Crystallographic characterization of intermediates along the regeneration pathway confirms our structural assignments and reveals unique bonding changes associated with increasing hydrogen content on boron and nitrogen. Synthetic access to the fully charged BN cyclohexane fuels will now enable investigations of these materials in hydrogen desorption studies. PMID:20214402

  11. Controlling the Bandgap of Boron Nitride Nanotubes with Carbon Doping

    NASA Astrophysics Data System (ADS)

    Mousavi, Hamze; Bagheri, Mehran

    2015-08-01

    This study explores the effects of doping by carbon (C) atoms on electronic properties of (10,10) and (16,0) boron nitride (BN) nanotubes (NTs). We exploit the random tight-binding model with Green's function technique and coherent potential approximation to show that the C dopant causes a decrease in the bandgap of the BN NTs, and their matching Van Hove singularities (VHS) in the density of states (DOS) are broadened. When the impurity concentration is large enough, the form of the DOS of the BN NTs becomes similar to that of metallic (10,10) and semiconducting (16,0) C NTs and their VHS get sharpened. This work might provide opportunities for creating new optoelectronic devices based on BN honeycomb nanosystems.

  12. Irradiation studies on carbon nanotube-reinforced boron carbide

    NASA Astrophysics Data System (ADS)

    Aitkaliyeva, Assel; McCarthy, Michael C.; Jeong, Hae-Kwon; Shao, Lin

    2012-02-01

    Radiation response of carbon nanotube (CNT) reinforced boron carbide composite has been studied for its application as a structural component in nuclear engineering. The composite was bombarded by 140 keV He ions at room temperature to a fluence ranging from 1 × 10 14 to 1 × 10 17 cm -2. Two-dimensional Raman mapping shows inhomogeneous distribution of CNTs, and was used to select regions of interest for damage characterization. For CNTs, the intensities ratio of D-G bands ( ID/ IG) increased with fluence up to a certain value, and decreased at the fluence of 5 × 10 16 cm -2. This fluence also corresponds to a trend break in the plot of FWHM (full width at half maximum) of G band vs. ID/ IG ratio, which indicates amorphization of CNTs. The study shows that Raman spectroscopy is a powerful tool to quantitatively characterize radiation damage in CNT-reinforced composites.

  13. Preparation and study on microwave absorbing materials of boron nitride coated pyrolytic carbon particles

    NASA Astrophysics Data System (ADS)

    Zhou, Wei; Xiao, Peng; Li, Yang

    2012-09-01

    Boron nitride coatings were synthesized on pyrolytic carbon (BN-coated PyC) particles via chemical reaction of boric acid and urea in nitrogen. The results of Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FI-IR) and X-ray photoelectron spectroscopy (XPS) show the formation of boron nitride coating. The TGA curves indicate that the oxidation resistance of the PyC particles is improved by incorporating BN coating on the surface. The mass of the BN-coated PyC particles remains over 60% at 1200 °C whereas the PyC particles are oxidized completely at 920 °C. The investigation of microwave absorbing property reveals that compared with the PyC particles, the BN-coated PyC particles have lower permittivity (ɛ', ɛ″) and better absorbing property. The BN-coated PyC particles show a strong absorbing peak at 10.64 GHz, where the lowest reflectivity -21.72 dB is reached. And the reflectivity less than -10 dB is over the range of 9.6-12 GHz.

  14. New synthesis and physical property of low resistivity boron-doped multi-walled carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Ishii, S.; Watanabe, T.; Ueda, S.; Tsuda, S.; Yamaguchi, T.; Takano, Y.

    2008-09-01

    A novel growth technique of boron-doped multi-walled carbon nanotubes (MWNTs) was developed. Our new technique uses a methanol solution of boric acid as a source material. Resistivity of the boron-doped MWNTs was successfully reduced independently of chirality by our technique. Temperature dependence of resistivity in each individual boron-doped MWNT was measured by using small-sized four-point contacts, which were fabricated by electron beam (EB) lithography technique. Conduction carriers were introduced into the MWNT effectively by boron-doping.

  15. Electron knock-on cross section of carbon and boron nitride nanotubes

    NASA Astrophysics Data System (ADS)

    Zobelli, A.; Gloter, A.; Ewels, C. P.; Seifert, G.; Colliex, C.

    2007-06-01

    We present a theoretical description of electron irradiation of single-walled carbon and boron nitride nanotubes. In a first step, the anisotropy of the atomic emission energy threshold is obtained within extended molecular-dynamics simulations based on the density-functional tight-binding method. In a second step, we numerically derive the total Mott cross section for different emission sites as a function of the incident electron energy. Two regimes are then described: at low irradiation energies (below 300keV ), the atoms are preferentially ejected from the upper and lower parts of the tube, while at high energies (above 300keV ), the atoms are preferentially ejected from the side walls. Typical values from a fraction of barn (at side wall for 150keV electron) up to around 20barn (for 1MeV electrons) are obtained for the total cross section of knock-on processes for both C and BN nanotubes. These values are smaller than those previously reported using isotropic models and the main reasons for the discrepancies are discussed. Finally, in boron nitride nanotubes, we report that the emission energy threshold maps show boron sputtering to be more favorable for low irradiation energies, while nitrogen sputtering is more favorable at high energies. These calculations of the total knock-on cross section for various nanotubes can be used as a guideline for transmission electron microscopy experimentalists using high energy focused beams to shape nanotubes, and also more generally if electron irradiation is to be used to change nanotube properties such as their optical behavior or conductivity.

  16. Electron knock-on cross section of carbon and boron nitride nanotubes

    SciTech Connect

    Zobelli, A.; Gloter, A.; Colliex, C.; Ewels, C. P.; Seifert, G.

    2007-06-15

    We present a theoretical description of electron irradiation of single-walled carbon and boron nitride nanotubes. In a first step, the anisotropy of the atomic emission energy threshold is obtained within extended molecular-dynamics simulations based on the density-functional tight-binding method. In a second step, we numerically derive the total Mott cross section for different emission sites as a function of the incident electron energy. Two regimes are then described: at low irradiation energies (below 300 keV), the atoms are preferentially ejected from the upper and lower parts of the tube, while at high energies (above 300 keV), the atoms are preferentially ejected from the side walls. Typical values from a fraction of barn (at side wall for 150 keV electron) up to around 20 barn (for 1 MeV electrons) are obtained for the total cross section of knock-on processes for both C and BN nanotubes. These values are smaller than those previously reported using isotropic models and the main reasons for the discrepancies are discussed. Finally, in boron nitride nanotubes, we report that the emission energy threshold maps show boron sputtering to be more favorable for low irradiation energies, while nitrogen sputtering is more favorable at high energies. These calculations of the total knock-on cross section for various nanotubes can be used as a guideline for transmission electron microscopy experimentalists using high energy focused beams to shape nanotubes, and also more generally if electron irradiation is to be used to change nanotube properties such as their optical behavior or conductivity.

  17. Synthesis and Raman Characterization of Boron Doped Single Walled Carbon Nanotubes (SWNTs)

    NASA Astrophysics Data System (ADS)

    McGuire, K.; Gothard, N.; Gai, P. L.; Chou, S. G.; Dresselhaus, M. S.; Rao, A. M.

    2003-03-01

    Boron-doped SWNTs were prepared by pulsed laser vaporization of carbon targets containing boron with concentrations ranging between 0.5 - 10 at%. As-prepared samples were characterized using Raman spectroscopy and HRTEM measurements. Above a threshold boron concentration of 3 at%, the growth of SWNT bundles ceases due to the low solubility of boron in carbon at ˜1200 ^oC. Interestingly, a few ˜0.5 nm diameter single walled tubes are found, along with nanographitic material in the soot generated from a target with a boron concentration of ˜7 at%. As expected, the intensity of the ˜1350 cm-1 D-band increases with increasing boron concentration due to boron substitution into the honeycomb lattice. Both the radial breathing mode and tangential G- bands were observed in the Raman spectra in samples with <3 at % boron at ˜186 cm-1 and ˜1591 cm-1, respectively. Implications of boron doping in the nanotube shell will be discussed.

  18. Synthesis and Raman Characterization of Boron Doped Single Walled Carbon Nanotubes (SWNTs)

    NASA Astrophysics Data System (ADS)

    McGuire, K.; Gothard, N.; Gai, P. L.; Chao, S. G.; Dresselhaus, M. S.; Rao, A. M.

    2003-11-01

    Boron-doped SWNTs were prepared by pulsed laser vaporization of carbon targets containing boron with concentrations ranging between 0.5 - 10 at%. As-prepared samples were characterized using Raman spectroscopy and HRTEM measurements. Above a threshold boron concentration of 3 at%, the growth of SWNT bundles ceases due to the low solubility of boron in carbon at ˜1200 ^oC. Interestingly, a few ˜0.5 nm diameter single walled tubes are found, along with nanographitic material in the soot generated from a target with a boron concentration of ˜7 at%. As expected, the intensity of the ˜1350 cm-1 D-band increases with increasing boron concentration due to boron substitution into the honeycomb lattice. Both the radial breathing mode and tangential G- bands were observed in the Raman spectra in samples with <3 at % boron at ˜186 cm-1 and ˜1591 cm-1, respectively. Implications of boron doping in the nanotube shell will be discussed.

  19. Spanning graphene to carbon-nitride: A 2-D semiconductor alloy system of carbon and nitrogen

    NASA Astrophysics Data System (ADS)

    Therrien, Joel; Li, Yancen; Schmidt, Daniel

    2014-03-01

    With the explosion of materials that form 2-D structures in the past few years, there have been a much more diverse ecosystem of combinations of characteristics to explore. Yet with the majority of materials investigated, the properties are fixed according to the composition of the material. Ideally, one wishes to have a tunable system similar to the semiconductor alloy systems, such as AlxGa1-xAs. There have been some theoretical studies of transition metal dichalogenides, none have been reported experimentally as of this writing. The tertianary alloy of BCN has been synthesized, however it was found that the boron had the tendency to cause phase segregation of the material into domains of graphene and boron nitride. Here we will report on the synthesis of non-phase seperated carbon-nitrogen 2D alloys ranging from graphene (Eg = 0 eV) to carbon-nitride, or melon, (Eg = 2.7 eV). We will report on synthesis methods and a summary of relevant electronic and material properties of selected alloys.

  20. Growth of crystals of several boron-carbon compositions by chemical vapor deposition

    NASA Technical Reports Server (NTRS)

    Kevill, D. N.; Rissmann, T. J.; Brewe, D.; Wood, C.

    1986-01-01

    Boron-carbon compounds have been deposited by the flow of carbon tetrachloride and boron trichloride, in the presence of a large excess of hydrogen, over a graphite surface maintained at 1000-1300 C. Deposits were formed on either an RF-heated disc or a tube or insert heated by a resistance furnace. Crystalline materials ranging in composition from B2C to B17C have been obtained.

  1. Gap state related blue light emitting boron-carbon core shell structures

    NASA Astrophysics Data System (ADS)

    Singh, Paviter; Kaur, Manpreet; Singh, Bikramjeet; Kaur, Gurpreet; Singh, Kulwinder; Kumar, Manjeet; Bala, Rajni; Thakur, Anup; Kumar, Akshay

    2016-05-01

    Boron- carbon core shell structures have been synthesized by solvo-thermal synthesis route. The synthesized material is highly pure. X-ray diffraction analysis confirms the reduction of reactants in to boron and carbon. Scanning Electron Microscopy (SEM) analysis showed that the shell is uniform with average thickness of 340 nm. Photo luminescence studies showed that the material is blue light emitting with CIE color coordinates: x=0.16085, y=0.07554.

  2. Suppression of boron-oxygen defects in Czochralski silicon by carbon co-doping

    SciTech Connect

    Wu, Yichao; Yu, Xuegong He, Hang; Chen, Peng; Yang, Deren

    2015-03-09

    We have investigated the influence of carbon co-doping on the formation of boron-oxygen defects in Czochralski silicon. It is found that carbon can effectively suppress the formation of boron-oxygen defects. Based on our experiments and first-principle theoretical calculations, it is believed that this effect is attributed to the formation of more energetically favorable carbon-oxygen complexes. Moreover, the diffusion of oxygen dimers in carbon co-doped silicon also becomes more difficult. All these phenomena should be associated with the tensile stress field induced by carbon doping in silicon.

  3. Radiochemistry of carbon, nitrogen and oxygen

    SciTech Connect

    Sajjad, M.; Lambrecht, R.M.

    1988-01-01

    The present monograph consists of two reviews. The first section deals with radiopharmaceutical and biomedical applications. The second section deals with analysis of carbon, nitrogen and oxygen in different materials by use of nuclear techniques. This monograph is published as part of our continuing effort to update, revise, and expand the previously published monographs to keep them current and relevant. 158 refs., 4 figs., 12 tabs.

  4. Soil Carbon and Nitrogen Cycle Modeling

    NASA Astrophysics Data System (ADS)

    Woo, D.; Chaoka, S.; Kumar, P.; Quijano, J. C.

    2012-12-01

    Second generation bioenergy crops, such as miscanthus (Miscantus × giganteus) and switchgrass (Panicum virgatum), are regarded as clean energy sources, and are an attractive option to mitigate the human-induced climate change. However, the global climate change and the expansion of perennial grass bioenergy crops have the power to alter the biogeochemical cycles in soil, especially, soil carbon storages, over long time scales. In order to develop a predictive understanding, this study develops a coupled hydrological-soil nutrient model to simulate soil carbon responses under different climate scenarios such as: (i) current weather condition, (ii) decreased precipitation by -15%, and (iii) increased temperature up to +3C for four different crops, namely miscanthus, switchgrass, maize, and natural prairie. We use Precision Agricultural Landscape Modeling System (PALMS), version 5.4.0, to capture biophysical and hydrological components coupled with a multilayer carbon and ¬nitrogen cycle model. We apply the model at daily time scale to the Energy Biosciences Institute study site, located in the University of Illinois Research Farms, in Urbana, Illinois. The atmospheric forcing used to run the model was generated stochastically from parameters obtained using available data recorded in Bondville Ameriflux Site. The model simulations are validated with observations of drainage and nitrate and ammonium concentrations recorded in drain tiles during 2011. The results of this study show (1) total soil carbon storage of miscanthus accumulates most noticeably due to the significant amount of aboveground plant carbon, and a relatively high carbon to nitrogen ratio and lignin content, which reduce the litter decomposition rate. Also, (2) the decreased precipitation contributes to the enhancement of total soil carbon storage and soil nitrogen concentration because of the reduced microbial biomass pool. However, (3) an opposite effect on the cycle is introduced by the increased

  5. Effect of water stress and foliar boron application on seed protein oil fatty acids and nitrogen metabolism in soybean

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Effects of water stress and foliar boron (FB) application on soybean (Glycine max (L) Merr.) seed composition and nitrogen metabolism have not been well investigated. Therefore, the objective of this study was to investigate the effects of water stress and FB on seed protein, oil, fatty acids, nitra...

  6. Effect of Glyphosate-boron Application on Seed Composition and Nitrogen Metabolism in Glyphosate-resistant Soybean

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Information is limited on the effect of combined foliar application of glyphosate (Gly) and boron (B) on seed composition and nitrogen metabolism in glyphosate resistant soybean (Glycine max(L.)Merr.). Therefore, the objective of this two-year field study was to evaluate the effects of single foliar...

  7. Resistivity reduction of boron-doped multiwalled carbon nanotubes synthesized from a methanol solution containing boric acid

    NASA Astrophysics Data System (ADS)

    Ishii, Satoshi; Watanabe, Tohru; Ueda, Shinya; Tsuda, Shunsuke; Yamaguchi, Takahide; Takano, Yoshihiko

    2008-05-01

    Boron-doped multiwalled carbon nanotubes (MWNTs) were synthesized using a methanol solution of boric acid as a source material. Accurate measurements of the electrical resistivity of an individual boron-doped MWNT was performed with a four-point contact, which was fabricated using an electron beam lithography technique. The doped boron provides conduction carriers, which reduces the resistivity of the MWNT.

  8. Formation of Boron-Carbon Nanosheets and Bilayers in Boron-Doped Diamond: Origin of Metallicity and Superconductivity.

    PubMed

    Polyakov, S N; Denisov, V N; Mavrin, B N; Kirichenko, A N; Kuznetsov, M S; Martyushov, S Yu; Terentiev, S A; Blank, V D

    2016-12-01

    The insufficient data on a structure of the boron-doped diamond (BDD) has frustrated efforts to fully understand the fascinating electronic properties of this material and how they evolve with doping. We have employed X-ray diffraction and Raman scattering for detailed study of the large-sized BDD single crystals. We demonstrate a formation of boron-carbon (B-C) nanosheets and bilayers in BDD with increasing boron concentration. An incorporation of two boron atoms in the diamond unit cell plays a key role for the B-C nanosheets and bilayer formation. Evidence for these B-C bilayers which are parallel to {111} planes is provided by the observation of high-order, super-lattice reflections in X-ray diffraction and Laue patterns. B-C nanosheets and bilayers minimize the strain energy and affect the electronic structure of BDD. A new shallow acceptor level associated with B-C nanosheets at ~37 meV and the spin-orbit splitting of the valence band of ~6 meV are observed in electronic Raman scattering. We identified that the superconducting transitions occur in the (111) BDD surfaces only. We believe that the origin of Mott and superconducting transitions is associated with the two-dimensional (2D) misfit layer structure of BDD. A model for the BDD crystal structure, based on X-ray and Raman data, is proposed and confirmed by density functional theoretical calculation. PMID:26754937

  9. Formation of Boron-Carbon Nanosheets and Bilayers in Boron-Doped Diamond: Origin of Metallicity and Superconductivity

    NASA Astrophysics Data System (ADS)

    Polyakov, S. N.; Denisov, V. N.; Mavrin, B. N.; Kirichenko, A. N.; Kuznetsov, M. S.; Martyushov, S. Yu; Terentiev, S. A.; Blank, V. D.

    2016-01-01

    The insufficient data on a structure of the boron-doped diamond (BDD) has frustrated efforts to fully understand the fascinating electronic properties of this material and how they evolve with doping. We have employed X-ray diffraction and Raman scattering for detailed study of the large-sized BDD single crystals. We demonstrate a formation of boron-carbon (B-C) nanosheets and bilayers in BDD with increasing boron concentration. An incorporation of two boron atoms in the diamond unit cell plays a key role for the B-C nanosheets and bilayer formation. Evidence for these B-C bilayers which are parallel to {111} planes is provided by the observation of high-order, super-lattice reflections in X-ray diffraction and Laue patterns. B-C nanosheets and bilayers minimize the strain energy and affect the electronic structure of BDD. A new shallow acceptor level associated with B-C nanosheets at 37 meV and the spin-orbit splitting of the valence band of 6 meV are observed in electronic Raman scattering. We identified that the superconducting transitions occur in the (111) BDD surfaces only. We believe that the origin of Mott and superconducting transitions is associated with the two-dimensional (2D) misfit layer structure of BDD. A model for the BDD crystal structure, based on X-ray and Raman data, is proposed and confirmed by density functional theoretical calculation.

  10. Pentagonal monolayer crystals of carbon, boron nitride, and silver azide

    SciTech Connect

    Yagmurcukardes, M. Senger, R. T.; Sahin, H.; Kang, J.; Torun, E.; Peeters, F. M.

    2015-09-14

    In this study, we present a theoretical investigation of structural, electronic, and mechanical properties of pentagonal monolayers of carbon (p-graphene), boron nitride (p-B{sub 2}N{sub 4} and p-B{sub 4}N{sub 2}), and silver azide (p-AgN{sub 3}) by performing state-of-the-art first principles calculations. Our total energy calculations suggest feasible formation of monolayer crystal structures composed entirely of pentagons. In addition, electronic band dispersion calculations indicate that while p-graphene and p-AgN{sub 3} are semiconductors with indirect bandgaps, p-BN structures display metallic behavior. We also investigate the mechanical properties (in-plane stiffness and the Poisson's ratio) of four different pentagonal structures under uniaxial strain. p-graphene is found to have the highest stiffness value and the corresponding Poisson's ratio is found to be negative. Similarly, p-B{sub 2}N{sub 4} and p-B{sub 4}N{sub 2} have negative Poisson's ratio values. On the other hand, the p-AgN{sub 3} has a large and positive Poisson's ratio. In dynamical stability tests based on calculated phonon spectra of these pentagonal monolayers, we find that only p-graphene and p-B{sub 2}N{sub 4} are stable, but p-AgN{sub 3} and p-B{sub 4}N{sub 2} are vulnerable against vibrational excitations.

  11. Mechanical properties of hybrid boron nitride-carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Zhang, Jin; Wang, Chengyuan

    2016-04-01

    Hybrid boron nitride-carbon nanotubes (BN-CNTs) have attracted considerable attention in recent research. In this effort, molecular dynamics simulations were performed to study the fundamentals of BN-CNTs in tensile tests, i.e. Young’s modulus and fracture strength (strain). Particular attention was paid to the influence of the atomic structure, hybrid style, and BN concentration on the tensile properties. The morphological changes were also investigated for the BN-CNTs at the onset of fracture. It is noted that the Young’s modulus of BN-CNTs decreases almost linearly with increasing the BN concentration with a rate of change independent of the hybrid style. In contrast, the sensitivity of the fracture strength and fracture strain to the variation of BN concentration depends strongly on the hybrid style of BN-CNTs. These results are expected to significantly expand the knowledge of the elastic and fracture properties of novel nanostructures and facilitate their applications in bandgap-engineering.

  12. New Pathways and Metrics for Enhanced, Reversible Hydrogen Storage in Boron-Doped Carbon Nanospaces

    SciTech Connect

    Pfeifer, Peter; Wexler, Carlos; Hawthorne, M. Frederick; Lee, Mark W.; Jalistegi, Satish S.

    2014-08-14

    This project, since its start in 2007—entitled “Networks of boron-doped carbon nanopores for low-pressure reversible hydrogen storage” (2007-10) and “New pathways and metrics for enhanced, reversible hydrogen storage in boron-doped carbon nanospaces” (2010-13)—is in support of the DOE's National Hydrogen Storage Project, as part of the DOE Hydrogen and Fuel Cells Program’s comprehensive efforts to enable the widespread commercialization of hydrogen and fuel cell technologies in diverse sectors of the economy. Hydrogen storage is widely recognized as a critical enabling technology for the successful commercialization and market acceptance of hydrogen powered vehicles. Storing sufficient hydrogen on board a wide range of vehicle platforms, at energy densities comparable to gasoline, without compromising passenger or cargo space, remains an outstanding technical challenge. Of the main three thrust areas in 2007—metal hydrides, chemical hydrogen storage, and sorption-based hydrogen storage—sorption-based storage, i.e., storage of molecular hydrogen by adsorption on high-surface-area materials (carbons, metal-organic frameworks, and other porous organic networks), has emerged as the most promising path toward achieving the 2017 DOE storage targets of 0.055 kg H2/kg system (“5.5 wt%”) and 0.040 kg H2/liter system. The objective of the project is to develop high-surface-area carbon materials that are boron-doped by incorporation of boron into the carbon lattice at the outset, i.e., during the synthesis of the material. The rationale for boron-doping is the prediction that boron atoms in carbon will raise the binding energy of hydro- gen from 4-5 kJ/mol on the undoped surface to 10-14 kJ/mol on a doped surface, and accordingly the hydro- gen storage capacity of the material. The mechanism for the increase in binding energy is electron donation from H2 to electron-deficient B atoms, in the form of sp2 boron-carbon bonds. Our team is proud to have

  13. Melting and spheroidization of hexagonal boron nitride in a microwave-powered, atmospheric pressure nitrogen plasma `

    SciTech Connect

    Gleiman, S. S.; Phillips, J.

    2001-01-01

    We have developed a method for producing spherically-shaped, hexagonal phase boron nitride (hBN) particles of controlled diameter in the 10-100 micron size range. Specifically, platelet-shaped hBN particles are passed as an aerosol through a microwave-generated, atmospheric pressure, nitrogen plasma. In the plasma, agglomerates formed by collisions between input hBN particles, melt and forms spheres. We postulate that this unprecedented process takes place in the unique environment of a plasma containing a high N-atom concentration, because in such an environment the decomposition temperature can be raised above the melting temperature. Indeed, given the following relationship [1]: BN{sub (condensed)} {leftrightarrow} B{sub (gas)} + N{sub (gas)}. Standard equilibrium thermodynamics indicate that the decomposition temperature of hBN is increased in the presence of high concentrations of N atoms. We postulate that in our plasma system the N atom concentration is high enough to raise the decomposition temperature above the (undetermined) melting temperature. Keywords Microwave plasma, boron nitride, melting, spherical, thermodynamics, integrated circuit package.

  14. Silicon carbide nanocones: Computational analysis of chemical shieldings for pristine and boron/nitrogen decorated models

    NASA Astrophysics Data System (ADS)

    Mirzaei, Mahmoud

    2012-09-01

    Density functional theory (DFT) calculations were performed to investigate the electronic and structural properties of pristine and boron/nitrogen (B/N) decorated models of a representative silicon carbide nanocone (SiCNC). The atoms of apexes and tips were differently decorated by B/N atoms to make all possible decorations of the investigated SiCNC. The evaluated parameters by the optimization processes and nuclear magnetic resonance (NMR) calculations indicated that the overall and atomic scale properties of the investigated SiCNCs are significantly dependent on the ways of decorations of Si/C atoms by B/N atoms. The Si/C atoms close to the decorated regions also exhibited notable changes in comparison to the pristine model.

  15. The electronic structure of graphene tuned by hexagonal boron nitrogen layers: Semimetal-semiconductor transition

    NASA Astrophysics Data System (ADS)

    Liu, Ming-Yang; Chen, Qing-Yuan; Ma, Tai; He, Yao; Cao, Chao

    2016-05-01

    The electronic structure of graphene and hexagonal boron nitrogen (G/h-BN) systems have been carefully investigated using the pseudo-potential plane-wave within density functional theory (DFT) framework. We find that the stacking geometries and interlayer distances significantly affect the electronic structure of G/h-BN systems. By studying four stacking geometries, we conclude that the monolayer G/h-BN systems should possess metallic electronic properties. The monolayer G/h-BN systems can be transited from metallicity to semiconductor by increasing h-BN layers. It reveals that the alteration of interlayer distances 2.50-3.50 Å can obtain the metal-semiconductor-semimetal variation and a tunable band gap for G/h-BN composite systems. The band dispersion along K-H direction is analogous to the band of rhombohedral graphite when the G/h-BN systems are semiconducting.

  16. Boron nitride nanotubes

    DOEpatents

    Smith, Michael W.; Jordan, Kevin; Park, Cheol

    2012-06-06

    Boron nitride nanotubes are prepared by a process which includes: (a) creating a source of boron vapor; (b) mixing the boron vapor with nitrogen gas so that a mixture of boron vapor and nitrogen gas is present at a nucleation site, which is a surface, the nitrogen gas being provided at a pressure elevated above atmospheric, e.g., from greater than about 2 atmospheres up to about 250 atmospheres; and (c) harvesting boron nitride nanotubes, which are formed at the nucleation site.

  17. Boron Nitride Nanotubes

    NASA Technical Reports Server (NTRS)

    Smith, Michael W. (Inventor); Jordan, Kevin (Inventor); Park, Cheol (Inventor)

    2012-01-01

    Boron nitride nanotubes are prepared by a process which includes: (a) creating a source of boron vapor; (b) mixing the boron vapor with nitrogen gas so that a mixture of boron vapor and nitrogen gas is present at a nucleation site, which is a surface, the nitrogen gas being provided at a pressure elevated above atmospheric, e.g., from greater than about 2 atmospheres up to about 250 atmospheres; and (c) harvesting boron nitride nanotubes, which are formed at the nucleation site.

  18. In Situ Observation of Phase Transformation in Low-Carbon, Boron-Treated Steels

    NASA Astrophysics Data System (ADS)

    Zhang, Di; Shintaku, Yoshiaki; Suzuki, Shuichi; Komizo, Yu-Ichi

    2012-02-01

    It is known that adding the appropriate amount of boron to steels dramatically increases their hardness and toughness as a result of the transition of the microstructure from grain boundary nucleation to intragranular nucleation. In this study, precipitation and phase transformation kinetics in heat-affected zones of low-carbon, boron-treated steels are observed directly by high-temperature laser scanning confocal microscopy. The effects of boron content and austenite grain size on the phase transformation process are investigated systematically by quantifying the transformation product, the transformation start temperature, the average length of the ferrite plates, and the average number of potent nucleation sites. Finally, detailed methods for controlling and optimizing the microstructure in the heat-affected zones of low-carbon, boron-treated steels are discussed.

  19. Nitrogen fertilizer improves boron phytoextraction by Brassica juncea grown in contaminated sediments and alleviates plant stress.

    PubMed

    Giansoldati, Virginia; Tassi, Eliana; Morelli, Elisabetta; Gabellieri, Edi; Pedron, Francesca; Barbafieri, Meri

    2012-06-01

    In this study we evaluated the effect of different fertilizer treatments on Brassica plants grown on boron-contaminated sediments. Experiments were conducted in the laboratory and on the lysimeter scale. At laboratory scale (microcosm), five different fertilizers were tested for a 35-d period. On the lysimeter scale, nitrogen fertilization was tested at three different doses and plants were allowed to grow until the end of the vegetative phase (70 d). Results showed that nitrogen application had effectively increased plant biomass production, while B uptake was not affected. Total B phytoextracted increased three-fold when the highest nitrogen dose was applied. Phytotoxicity on Brassica was evaluated by biochemical parameters. In plants grown in unfertilized B-contaminated sediments, the activity of antioxidant enzymes superoxide dismutase (SOD), ascorbate peroxidase (APX) and pyrogallol peroxidase (PPX) increased, whereas catalase (CAT) decreased with respect to control plants. Addition of N progressively mitigated the alteration of enzymatic activity, thus suggesting that N can aid in alleviating B-induced oxidative stress. SOD activity was restored to control levels just at the lowest N treatment, whereas the CAT inhibition was partially restored only at the highest one. N application also lowered the B-induced increase in APX and PPX activities. Increased glutathione reductase activity indicated the need to restore the oxidative balance of glutathione. Data also suggest a role of glutathione and phytochelatins in B defense mechanisms. Results suggest that the nitrogen fertilizer was effective in improving B phytoextraction by increasing Brassica biomass and by alleviating B-induced oxidative stress. PMID:22382070

  20. Boron incorporation in the foraminifer Amphistegina lessonii under a decoupled carbonate chemistry

    NASA Astrophysics Data System (ADS)

    Kaczmarek, K.; Langer, G.; Nehrke, G.; Horn, I.; Misra, S.; Janse, M.; Bijma, J.

    2014-12-01

    A number of studies have shown that the boron isotopic composition (δ11B) and the B/Ca ratio of biogenic carbonates (mostly foraminifers) can serve as proxies for two parameters of the ocean's carbonate chemistry, rendering it possible to calculate the entire carbonate system. However, the B incorporation mechanism into marine carbonates is still not fully understood and analyses of field samples show species specific and hydrographic effects on the B proxies complicating their application. Identifying the carbonate system parameter influencing boron incorporation is difficult due to the co-variation of pH, CO32-, and B(OH)4-. To shed light on the question which parameter of the carbonate system is related to the boron incorporation, we performed culture experiments with the benthic symbiont-bearing foraminifer Amphistegina lessonii using a decoupled pH-CO32- chemistry. The determination of the boron isotopic composition and B/Ca ratios was performed simultaneously by means of a new in situ technique combining optical emission spectroscopy and laser ablation MC-ICP-MS. The boron isotopic composition in the tests gets heavier with increasing pH and B/Ca increases with increasing BOH4-/HCO3- of the culture media. The latter indicates that boron uptake of A. lessonii features a competition between B(OH)4- and HCO3-. Furthermore, the simultaneous determination of B/Ca and δ11B on single specimens allows for assessing the relative variability of these parameters. Among different treatments the B/Ca shows an increasing variability with increasing boron concentration in the test whereas the variability in the isotope distribution is constant.

  1. Relationship between carbon and nitrogen mineralization in a subtropical soil

    NASA Astrophysics Data System (ADS)

    Li, Qianru; Sun, Yue; Zhang, Xinyu; Xu, Xingliang; Kuzyakov, Yakov

    2014-05-01

    In most soils, more than 90% nitrogen is bonded with carbon in organic forms. This indicates that carbon mineralization should be closely coupled with nitrogen mineralization, showing a positive correlation between carbon and nitrogen mineralization. To test this hypothesis above, we conducted an incubation using a subtropical soil for 10 days at 15 °C and 25 °C. 13C-labeled glucose and 15N-labeled ammonium or nitrate was used to separate CO2 and mineral N released from mineralization of soil organic matter and added glucose or inorganic nitrogen. Phospholipid fatty acid (PLFA) and four exoenzymes (i.e. β-1,4- Glucosaminidase, chitinase, acid phosphatase, β-1,4-N- acetyl glucosamine glycosidase) were also analyzed to detect change in microbial activities during the incubation. Our results showed that CO2 release decreased with increasing nitrogen mineralization rates. Temperature did not change this relationship between carbon and nitrogen mineralization. Although some changes in PLFA and the four exoenzymes were observed, these changes did not contribute to changes in carbon and nitrogen mineralization. These findings indicates that carbon and nitrogen mineralization in soil are more complicated than as previously expected. Future investigation should focus on why carbon and nitrogen mineralization are coupled in a negative correlation not in a positive correlation in many soils for a better understanding of carbon and nitrogen transformation during their mineralization.

  2. Study of Nitrogen Effect on the Boron Diffusion during Heat Treatment in Polycrystalline Silicon/Nitrogen-Doped Silicon Thin Films

    NASA Astrophysics Data System (ADS)

    Saci, Lynda; Mahamdi, Ramdane; Mansour, Farida; Boucher, Jonathan; Collet, Maéva; Bedel Pereira, Eléna; Temple-Boyer, Pierre

    2011-05-01

    The present paper studies the boron (B) diffusion in nitrogen (N) doped amorphous silicon (a-Si) layer in original bi-layer B-doped polycrystalline silicon (poly-Si)/in-situ N-doped Si layers (NIDOS) thin films deposited by low pressure chemical vapor deposition (LPCVD) technique. The B diffusion in the NIDOS layer was investigated by secondary ion mass spectrometry (SIMS) and Fourier transform infrared spectroscopy (FTIR) analysis. A new extended diffusion model is proposed to fit the SIMS profile of the bi-layer films. This model introduces new terms which take into account the effect of N concentration on the complex diffusion phenomena of B atoms in bi-layer films. SIMS results show that B diffusion does not exceed one third of NIDOS layer thickness after annealing. The reduction of the B diffusion in the NIDOS layer is due to the formation of complex B-N as shown by infrared absorption measurements. Electrical measurements using four-probe and Hall effect techniques show the good conductivity of the B-doped poly-Si layer after annealing treatment.

  3. Localization effects in the Auger spectra of ring nitrogen systems: Pyridine, poly(2-vinyl)pyridine, borazine, and boron nitride

    SciTech Connect

    Rye, R.R.; Kelber, J.A.; Kellogg, G.E.; Nebesny, K.W.; Lichtenberger, D.L.

    1987-04-15

    The N(KVV) Auger spectra of gas phase pyridine (C/sub 5/H/sub 5/N) and borazine (B/sub 3/N/sub 3/H/sub 6/), and of solid phase poly(2-vinyl)pyridine (PVP) and hexagonal boron nitride ((BN)/sub x/) are reported and analyzed. The data indicate two Auger ''fingerprint'' types of nitrogen. Ammonia (NH/sub 3/) is the prototype for the first, where three of the five valence electrons are sigma bonding and the other two are the lone pair. This localized electronic structure gives rise to relatively sharp features in the N(KVV) spectrum. Typical of the second fingerprint type is pyridine, where there are two sigma bonding electrons, a lone pair of electrons, and one electron contributing to the delocalized ..pi.. system. Theoretical nitrogen Auger transition energies and intensities are calculated for pyridine to demonstrate the general origin of the overlapping features in the relatively broad N(KVV) spectrum of this molecule. PVP fits into the second fingerprint type while borazine and boron nitride give nitrogen Auger spectra more like ammonia. Approximate calculations using the equivalent core concept are used to clarify the relationship between the ammonia, borazine, and boron nitride spectra. It is shown that in these systems the initial Auger state (core--hole) largely localizes the bonds and lone pair on the nitrogen. The Auger spectra show that it is the sigma, ..pi.. and nonbonding orbital characters that provide the Auger fingerprint.

  4. Investigation of the sensitivity, selectivity, and reversibility of the chemically-sensitive field-effect transistor (CHEMFET) to detect nitrogen dioxide, dimethyl methylphosphonate, and boron trifluoride. Master's thesis

    SciTech Connect

    Hauschild, N.T.

    1993-09-01

    This study investigated the sensitivity, selectivity, and reversibility of a chemically-sensitive field-effect transistor (CHEMFET) gas microsensor. Various physical operating parameters were tested to determine which produced the most significant sensitivity, selectivity, and reversibility which were computed from response changes generated from electrical conductivity modulations when exposed to challenge gases. The variable operating parameters included: thinfilm material, film thickness, challenge gas specie, challenge gas concentration, and operating temperature. Copper phthalocyanine and lead phthalocyanine were used as thin films to detect the following challenge gases: nitrogen dioxide, dimethyl methylphosphonate, boron trifluoride, methanol, carbon monoxide, vinyl chloride, and trichloroethylene. Tests revealed that copper phthalocyanine was the most sensitive to dimethyl methylphosphonate and boron trifluoride, whereas lead phthalocyanine was the most sensitive to the remaining challenge gases. The CHEMFET was selective to the binary challenge gas combinations. The films were most selective for nitrogen dioxide. The CHEMFET was fully reversibly, and the time duration for full reversibility increased with increasing challenge gas concentrations and increasing time of exposure.

  5. Ab initio studies of vacancies in (8,0) and (8,8) Single-walled carbon and boron nitride nanotubes.

    PubMed

    Mashapa, M G; Chetty, N; Ray, S Sinha

    2012-09-01

    A systematic study of vacancies in single-walled carbon nanotubes and boron nitride nanotubes was carried out. First principles calculations within the framework of density functional theory using the CASTEP code are used to optimize fully the geometries of the systems. The generalized gradient approximation is used for the exchange-correlation functional. We find that the pristine single-walled carbon nanotubes have lower heats of formation compared with the boron nitride nanotubes, consistent with other findings. The zig-zag (8,0) carbon nnaotube has a slightly lower (-3.32 eV) heat of formation compared to the armchair (8,8) configuration (-3.25 eV). Comparison of the heats of formation of the vacancy systems is made and we draw conclusions about the relative stability of these defects. The heats of formation and atomic relaxations of the vacancies are explained as resulting from the tendency of the affected ions to recover the lost electronic coordination. For the boron nitride nanotube, we find that the vacancies on the nitrogen and boron site, namely V(N), and V(B), are respectively the more stable vacancies in the B- and N-rich environments. The electronic structure of the single vacancies also depends on the nanotube chirality. PMID:23035429

  6. Boron and nitrogen co-doped titania with enhanced visible-light photocatalytic activity for hydrogen evolution

    NASA Astrophysics Data System (ADS)

    Li, Yuexiang; Ma, Gangfeng; Peng, Shaoqin; Lu, Gongxuan; Li, Shuben

    2008-08-01

    A visible-light boron and nitrogen co-doped titania (B-N-TiO 2) photocatalyst was prepared by sol-gel method with titanium tetra- n-butyl oxide, urea and boric acid as precursors. The photocatalyst was characterized by Fourier Transform Infrared (FT-IR), UV-vis diffusive reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), BET and electrochemistry method. Photocatalytic activity for hydrogen production over platinized B-N-TiO 2 under visible-light ( λ ≥ 420 nm) irradiation was investigated. In nitrogen doped titania (N-TiO 2) N sbnd Ti sbnd O bond is formed, which extends the absorption edge to the visible-light region. A part of doping boron enters into titania lattice and most of the boron exists at the surface of the catalyst. The crystallite size of B-N-TiO 2 decreases compared to N-TiO 2, while its photocurrent and the surface hydroxyl group increase. Furthermore, doping boron could act as shallow traps for photoinduced electrons to prolong the life of the electrons and holes. Therefore, the visible-light activity of B-N-iO 2 increases greatly compared with that of N-TiO 2.

  7. Boron incorporation in the foraminifer Amphistegina lessonii under a decoupled carbonate chemistry

    NASA Astrophysics Data System (ADS)

    Kaczmarek, K.; Langer, G.; Nehrke, G.; Horn, I.; Misra, S.; Janse, M.; Bijma, J.

    2015-03-01

    A number of studies have shown that the boron isotopic composition (δ11B) and the B / Ca ratio of biogenic carbonates (mostly foraminifers) can serve as proxies for two parameters of the ocean's carbonate chemistry, rendering it possible to calculate the entire carbonate system. However, the B incorporation mechanism into marine carbonates is still not fully understood and analyses of field samples show species-specific and hydrographic effects on the B proxies complicating their application. Identifying the carbonate system parameter influencing boron incorporation is difficult due to the co-variation of pH, CO32- and B(OH)4-. To shed light on the question which parameter of the carbonate system is related to the boron incorporation, we performed culture experiments with the benthic symbiont-bearing foraminifer Amphistegina lessonii using a decoupled pH-CO32- chemistry. The determination of the δ11B and B / Ca ratios was performed simultaneously by means of a new in situ technique combining optical emission spectroscopy and laser ablation MC-ICP-MS. The boron isotopic composition in the tests gets heavier with increasing pH and B / Ca increases with increasing B(OH)4- / HCO3- of the culture media. The latter indicates that boron uptake of A. lessonii features a competition between B(OH)4- and HCO3-. Furthermore, the simultaneous determination of B / Ca and δ11B on single specimens allows for assessing the relative variability of these parameters. Among different treatments the B / Ca shows an increasing variability with increasing boron concentration in the test whereas the variability in the isotope distribution is constant.

  8. Study of the effect of nano-sized precipitates on the mechanical properties of boron-added low-carbon steels by neutron scattering techniques

    PubMed Central

    Seong, B. S.; Cho, Y. R.; Shin, E. J.; Kim, S. I.; Choi, S.-H.; Kim, H. R.; Kim, Y. J.

    2008-01-01

    Small-angle neutron scattering (SANS) and neutron powder diffraction (ND) techniques were used to study quantitatively the effect of nano-sized precipitates and boron addition on the mechanical properties of low-carbon steels. SANS was used to evaluate nano-sized precipitates, smaller than about 600 Å in diameter, and ND was used to determine the weight fraction of the cementite precipitates. Fine core–shell structured spherical precipitates with an average radius of ~50 Å, such as MnS and/or CuS, surrounded by BN layers were observed in the boron-added (BA) low-carbon steels; fine spherical precipitates with an average radius of ~48 Å were mainly observed in the boron-free (BF) low-carbon steels. In the BA steels, the number of boron precipitates, such as BN, Fe3(C,B) and MnS, surrounded by BN layers increased drastically at higher hot-rolling temperatures. The volume fraction of the fine precipitates of the BA steels was higher than that of the BF steels; this difference is related to the rapid growth of the BN layers on the MnS and CuS precipitates. Boron addition to low-carbon steels resulted in a reduction in strength and an improvement in elongation; this behaviour is related to the reduction of the solute carbon and the nitrogen contents in the ferrite matrix caused by the precipitation of BN, as well by the increase in the volume fraction of the cementites. PMID:19461851

  9. Study of the effect of nano-sized precipitates on the mechanical properties of boron-added low-carbon steels by neutron scattering techniques.

    PubMed

    Seong, B S; Cho, Y R; Shin, E J; Kim, S I; Choi, S-H; Kim, H R; Kim, Y J

    2008-10-01

    Small-angle neutron scattering (SANS) and neutron powder diffraction (ND) techniques were used to study quantitatively the effect of nano-sized precipitates and boron addition on the mechanical properties of low-carbon steels. SANS was used to evaluate nano-sized precipitates, smaller than about 600 A in diameter, and ND was used to determine the weight fraction of the cementite precipitates. Fine core-shell structured spherical precipitates with an average radius of ~50 A, such as MnS and/or CuS, surrounded by BN layers were observed in the boron-added (BA) low-carbon steels; fine spherical precipitates with an average radius of ~48 A were mainly observed in the boron-free (BF) low-carbon steels. In the BA steels, the number of boron precipitates, such as BN, Fe(3)(C,B) and MnS, surrounded by BN layers increased drastically at higher hot-rolling temperatures. The volume fraction of the fine precipitates of the BA steels was higher than that of the BF steels; this difference is related to the rapid growth of the BN layers on the MnS and CuS precipitates. Boron addition to low-carbon steels resulted in a reduction in strength and an improvement in elongation; this behaviour is related to the reduction of the solute carbon and the nitrogen contents in the ferrite matrix caused by the precipitation of BN, as well by the increase in the volume fraction of the cementites. PMID:19461851

  10. Preparation of nitrogen-enriched activated carbons from brown coal

    SciTech Connect

    Robert Pietrzak; Helena Wachowska; Piotr Nowicki

    2006-05-15

    Nitrogen-enriched activated carbons were prepared from a Polish brown coal. Nitrogen was introduced from urea at 350{sup o}C in an oxidizing atmosphere both to carbonizates obtained at 500-700{sup o}C and to activated carbons prepared from them. The activation was performed at 800{sup o}C with KOH in argon. It has been observed that the carbonization temperature determines the amount of nitrogen that is incorporated (DC5U, 8.4 wt % N{sup daf}; DC6U, 6.3 wt % N{sup daf}; and DC7U, 5.4 wt % N{sup daf}). X-ray photoelectron spectroscopy (XPS) measurements have shown that nitrogen introduced both at the stage of carbonizates and at the stage of activated carbons occurs mainly as -6, -5, and imine, amine and amide groups. On the other hand, the activation of carbons enriched with nitrogen results in the formation of pyridonic nitrogen and N-Q. The introduction of nitrogen at the activated carbon stage leads to a slight decrease in surface area. It has been proven that the most effective way of preparing microporous activated carbons enriched with nitrogen to a considerable extent and having high surface area ({approximately} 3000 m{sup 2}/g) is the following: carbonization - activation - reaction with urea. 40 refs., 1 fig., 6 tabs.

  11. Interactive effects of nitrogen deposition and insect herbivory on carbon and nitrogen dynamics: Results from CENTURY

    NASA Astrophysics Data System (ADS)

    Throop, H. L.; Holland, E. A.; Parton, W. J.; Ojima, D. S.; Keough, C.

    2002-12-01

    The direct effects of nitrogen deposition on nutrient availability in ecosystems have been well studied, however, little is known about the indirect effects of nitrogen deposition on insect herbivory and subsequent changes to ecosystem processes. Numerous empirical studies have demonstrated that host plant nitrogen concentration can strongly affect individual insect consumption rates and population dynamics. We used the CENTURY ecosystem model to explore how interactions between nitrogen deposition and insect herbivory might affect plant production and the pools and fluxes of carbon and nitrogen in an old field community. We modified the preexisting CENTURY mammalian grazing functions to reflect patterns of insect herbivory. Vegetative tissue loss to herbivores was modeled as a dynamic function based on the carbon to nitrogen ratio of aboveground vegetation. Parameterization of the plant response to nitrogen and herbivory was based on field data collected on Ambrosia artemisiifolia (common ragweed, Asteraceae). The modeled response to nitrogen deposition included a strong increase in plant production, decreased plant C:N ratios, and increased soil organic carbon pools. Insect herbivory alone generally caused depressed aboveground production, decreased soil organic carbon pools, and decreased nitrogen mineralization rates. These relationships broke down, however, under moderate nitrogen deposition loads (over 30 kg N ha-1 yr-1) in simulations where insect herbivory increased in response to declining plant C:N. In these cases, herbivory acted to depress the positive influence of nitrogen deposition on carbon storage in soil and vegetative pools and caused strong increases in nitrogen mineralization rates. The results of these simulations suggest that herbivory may play an increasingly important role in affecting ecosystem processes under conditions of high nitrogen deposition. Including effects of herbivory in ecosystem analyses, particularly in systems where rates

  12. Characteristic Study of Boron Doped Carbon Nanowalls Films Deposited by Microwave Plasma Enhanced Chemical Vapor Deposition.

    PubMed

    Lu, Chunyuan; Dong, Qi; Tulugan, Kelimu; Park, Yeong Min; More, Mahendra A; Kim, Jaeho; Kim, Tae Gyu

    2016-02-01

    In this research, catalyst-free vertically aligned boron doped carbon nanowalls films were fabricated on silicon (100) substrates by MPECVD using feeding gases CH4, H2 and B2H6 (diluted with H2 to 5% vol) as precursors. The substrates were pre-seeded with nanodiamond colloid. The fabricated CNWs films were characterized by Scanning Electron Microscopy (SEM) and Raman Spectroscopy. The data obtained from SEM confirms that the CNWs films have different density and wall thickness. From Raman spectrum, a G peak around 1588 cm(-1) and a D band peak at 1362 cm(-1) were observed, which indicates a successful fabrication of CNWs films. The EDX spectrum of boron doped CNWs film shows the existence of boron and carbon. Furthermore, field emission properties of boron doped carbon nanowalls films were measured and field enhancement factor was calculated using Fowler-Nordheim plot. The result indicates that boron doped CNWs films could be potential electron emitting materials. PMID:27433646

  13. Synthesis and characterization of boron carbon nitride thin films as protective overcoat for hard disk drives

    NASA Astrophysics Data System (ADS)

    Chen, Yanfeng

    The current goal in the magnetic storage industry is to reach the areal density of 1Tbit/in2 in a few years. This requires the head-media spacing (HMS), which includes media overcoat, lubricant layer, air bearing, and head overcoat, not to exceed 5.0 nm. Trade-off between these layers results in requiring the protective overcoat to be 1.0 nm or less. The protective overcoat must be hard, wear-resistant, continuous, thermally stable, and compatible with the magnetic layer and lubricant. This thesis work is mainly to develop protective overcoat for ultra high density hard disk drives (HDD). Amorphous carbon nitride (a-CNx) thin films were synthesized using pulseDC magnetron sputtering. The influence of substrate bias, substrate tilt, and substrate rotation on film growth and properties was studied. X-ray reflectivity (XRR) was used to measure film density, roughness and thickness. Surface roughness and thickness measurements from XRR are comparable to AFM and surface profiler measurements respectively. a-CNx films have good mechanical properties. Auger electron spectroscopy (AES) and high resolution transmission microscope (HRTEM) were used to obtain the film composition and microstructure. HRTEM cross sectioned experiments showed that CN x film is amorphous. Chemical corrosion experiments display drastic decrease of corrosion spots for thin films synthesized under optimum conditions. In pursuit of new materials for hard disk drive protective overcoat, boron carbide (B4C) and boron carbon nitride (BxC yNz) thin films were synthesized by pulse-DC magnetron sputtering. Effects of target power, target pulse frequency, substrate bias and pulse frequency on surface roughness were studied by AFM. Nitrogen incorporation into B4C films, which gives BxCyNz thin films, has a beneficial effect to decrease the film roughness. Auger electron spectroscopy was used to characterize the film composition. High-resolution cross-sectioned TEM studies showed that both films are amorphous

  14. Influence of the boron precursor and drying method on surface properties and electrochemical behavior of boron-doped carbon gels.

    PubMed

    Zapata-Benabihe, Zulamita; Moreno-Castilla, Carlos; Carrasco-Marín, Francisco

    2014-02-18

    Two series of B-doped carbon gels were prepared by the polymerization of resorcinol and formaldehyde in water using either boric acid or phenyl boronic acid as dopants. Both organic hydrogels were dried by four methods: supercritical, freeze, microwave oven, and vacuum oven drying. The effects of the boron precursor and drying method on the surface characteristics were studied by N2 and CO2 adsorption at -196 and 0 °C, respectively, immersion calorimetry into benzene and water, temperature-programmed desorption coupled with mass spectrometry, X-ray photoelectron spectroscopy, and thermogravimetric analysis. Electrochemical characterization was carried out in a three-electrode cell, using Ag/AgCl as a reference electrode and a Pt wire as a counter electrode. The surface area obtained from immersion calorimetry into benzene was more realistic than that yielded by the Brunauer-Emmett-Teller (BET) equation. The hydrophobicity of the samples decreased linearly with a higher oxygen content. In addition, the oxygen content of the B-doped carbon gels increased linearly with a higher B content, and the interfacial or areal capacitance decreased linearly with a larger surface area. The capacitance was increased by B addition because of the pseudocapacitance effects of the higher oxygen content of the samples. The cryogel and vacuum-dried xerogel obtained from the boric acid series, Bc and Bv, respectively, showed the largest gravimetric and volumetric capacitances, around 140 F/g and 95 F/cm(3), respectively. PMID:24460055

  15. Dry Process for Making Polyimide/ Carbon-and-Boron-Fiber Tape

    NASA Technical Reports Server (NTRS)

    Belvin, Harry L.; Cano, Roberto J.; Johnston, Norman J.; Marchello, Joseph M.

    2003-01-01

    A dry process has been invented as an improved means of manufacturing composite prepreg tapes that consist of high-temperature thermoplastic polyimide resin matrices reinforced with carbon and boron fibers. Such tapes are used (especially in the aircraft industry) to fabricate strong, lightweight composite-material structural components. The inclusion of boron fibers results in compression strengths greater than can be achieved by use of carbon fibers alone. The present dry process is intended to enable the manufacture of prepreg tapes (1) that contain little or no solvent; (2) that have the desired dimensions, fiber areal weight, and resin content; and (3) in which all of the fibers are adequately wetted by resin and the boron fibers are fully encapsulated and evenly dispersed. Prepreg tapes must have these properties to be useable in the manufacture of high-quality composites by automated tape placement. The elimination of solvent and the use of automated tape placement would reduce the overall costs of manufacturing.

  16. Electroextraction of boron from boron carbide scrap

    SciTech Connect

    Jain, Ashish; Anthonysamy, S.; Ghosh, C.; Ravindran, T.R.; Divakar, R.; Mohandas, E.

    2013-10-15

    Studies were carried out to extract elemental boron from boron carbide scrap. The physicochemical nature of boron obtained through this process was examined by characterizing its chemical purity, specific surface area, size distribution of particles and X-ray crystallite size. The microstructural characteristics of the extracted boron powder were analyzed by using scanning electron microscopy and transmission electron microscopy. Raman spectroscopic examination of boron powder was also carried out to determine its crystalline form. Oxygen and carbon were found to be the major impurities in boron. Boron powder of purity ∼ 92 wt. % could be produced by the electroextraction process developed in this study. Optimized method could be used for the recovery of enriched boron ({sup 10}B > 20 at. %) from boron carbide scrap generated during the production of boron carbide. - Highlights: • Recovery of {sup 10}B from nuclear grade boron carbide scrap • Development of process flow sheet • Physicochemical characterization of electroextracted boron • Microscopic examination of electroextracted boron.

  17. TiO 2 nanopowders doped with boron and nitrogen for photocatalytic applications

    NASA Astrophysics Data System (ADS)

    Gombac, V.; De Rogatis, L.; Gasparotto, A.; Vicario, G.; Montini, T.; Barreca, D.; Balducci, G.; Fornasiero, P.; Tondello, E.; Graziani, M.

    2007-10-01

    TiO 2-based systems have attracted an increasing interest for their potential use as photocatalysts under visible-light irradiation. In this context, the present work was dedicated to the tailored synthesis of TiO 2 nanopowders doped with boron, nitrogen or both species for the photocatalytic degradation of organic dyes. In particular, the systems were synthesized by a sol-gel route starting from titanium(IV) butoxide as a Ti source and thoroughly characterized by the combined use of N 2 physisorption, X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), UV-Vis reflectance spectroscopy and temperature-programmed oxidation (TPO). Finally, the photocatalytic performances in the decomposition of the azo-dye methyl orange (MO) were investigated. The obtained results suggest that both dopants promote the photocatalytic activity with respect to pure TiO 2 systems. Nevertheless, while our surface N-doping does not appreciably modify the titania structure and texture, B incorporation inhibits the TiO 2 crystallite growth and induces an increase in the surface area. As regards the codoped systems, a remarkable reactivity improvement was observed only when B is present in excess with respect to N. A rational interpretation of the observed behaviour was attempted by calculations based on the density functional theory (DFT). We suggest that the presence of B in molar excess with respect to N generates reactive Ti(III) sites, which, in turn, might induce the formation of reactive superoxide species.

  18. Boosting sensitivity of boron nitride nanotube (BNNT) to nitrogen dioxide by Fe encapsulation.

    PubMed

    Zhang, Yu-qing; Liu, Yue-Jie; Liu, Yan-ling; Zhao, Jing-xiang

    2014-06-01

    The pristine boron nitride nanotube (BNNT) exhibits a poor chemical reactivity to some adsorbates, thus greatly limiting its application for the gas sensor. In the present work, using density functional theory (DFT) methods, we put forward a novel strategy to enhance the sensitivity of BNNT to nitrogen dioxide (NO2) by the encapsulation of a single Fe atom inside its cavity. The results suggest that the NO2 molecule can be only physically adsorbed on the pristine BNNT with a small adsorption energy (-0.10 eV). After the inclusion of the Fe atom inside BNNT (Fe@BNNT), the interaction of NO2 molecules with this tube is significantly enhanced, leading to a transformation from the physisorption of on pristine BNNT to the current chemisorption. Interestingly, up to five NO2 molecules can be adsorbed on this encapsulated BNNT along its circumference with the average adsorption energy of -0.52 eV, corresponding to a short recovery time (6 ms). Moreover, 0.38 electrons are transferred from the Fe@BNNT to the adsorbed NO2 molecules, which is enough to induce the obvious change of its electrical conductance. Thus, we predict that the encapsulation of Fe atom inside BNNT would greatly boosts its sensitivity to NO2 molecules, indicating its potential application as NO2 sensors. PMID:24837498

  19. Structure and electrochemical applications of boron-doped graphitized carbon nanofibers

    NASA Astrophysics Data System (ADS)

    Yeo, Jae-Seong; Jang, Sang-Min; Miyawaki, Jin; An, Bai; Mochida, Isao; Rhee, Choong Kyun; Yoon, Seong-Ho

    2012-08-01

    Boron-doped graphitized carbon nanofibers (CNFs) were prepared by optimizing CNFs preparation, surface treatment, graphitization and boron-added graphitization. The interlayer spacing (d002) of the boron-doped graphitized CNFs reached 3.356 Å, similar to that of single-crystal graphite. Special platelet CNFs (PCNFs), for which d002 is less than 3.400 Å, were selected for further heat treatment. The first heat treatment of PCNFs at 2800 °C yielded a d002 between 3.357 and 3.365 Å. Successive nitric acid treatment and a second heat treatment with boric acid reduced d002 to 3.356 Å. The resulting boron-doped PCNFs exhibited a high discharge capacity of 338 mAh g-1 between 0 and 0.5 V versus Li/Li+ and 368 mAh g-1 between 0 and 1.5 V versus Li/Li+. The first-cycle Coulombic efficiency was also enhanced to 71-80%. Such capacity is comparable to that of natural graphite under the same charge/discharge conditions. The boron-doped PCNFs also exhibited improved rate performance with twice the capacity of boron-doped natural graphite at a discharge rate of 5 C.

  20. Structure and electrochemical applications of boron-doped graphitized carbon nanofibers.

    PubMed

    Yeo, Jae-Seong; Jang, Sang-Min; Miyawaki, Jin; An, Bai; Mochida, Isao; Rhee, Choong Kyun; Yoon, Seong-Ho

    2012-08-10

    Boron-doped graphitized carbon nanofibers (CNFs) were prepared by optimizing CNFs preparation, surface treatment, graphitization and boron-added graphitization. The interlayer spacing (d₀₀₂) of the boron-doped graphitized CNFs reached 3.356 Å, similar to that of single-crystal graphite. Special platelet CNFs (PCNFs), for which d₀₀₂ is less than 3.400 Å, were selected for further heat treatment. The first heat treatment of PCNFs at 2800 °C yielded a d₀₀₂ between 3.357 and 3.365 Å. Successive nitric acid treatment and a second heat treatment with boric acid reduced d₀₀₂ to 3.356 Å. The resulting boron-doped PCNFs exhibited a high discharge capacity of 338 mAh g⁻¹ between 0 and 0.5 V versus Li/Li⁺ and 368 mAh g⁻¹ between 0 and 1.5 V versus Li/Li⁺. The first-cycle Coulombic efficiency was also enhanced to 71-80%. Such capacity is comparable to that of natural graphite under the same charge/discharge conditions. The boron-doped PCNFs also exhibited improved rate performance with twice the capacity of boron-doped natural graphite at a discharge rate of 5 C. PMID:22797214

  1. Water dispersible, highly graphitic and nitrogen-doped carbon nanobubbles.

    PubMed

    Soll, Sebastian; Fellinger, Tim-Patrick; Wang, Xinchen; Zhao, Qiang; Antonietti, Markus; Yuan, Jiayin

    2013-12-20

    Dispersible, highly graphitic, and nitrogen-doped carbon hollow nanospheres (25-90 nm), termed 'nanobubbles', are prepared via confined carbonization through a silica nanocasting technique. Poly(ionic liquid) nanoparticles are employed as easy-to-make and multifunctional templates, which simultaneously act as both the carbon and nitrogen source. The promising potential of the nanobubbles in oxygen reduction reactions for fuel cells is demonstrated. PMID:23847129

  2. Multi-component boron coatings on low carbon steel AISI 1018

    NASA Astrophysics Data System (ADS)

    Suwattananont, Naruemon

    Boronizing and metalizing are thermo-chemical surface hardening treatments in which boron and metal atoms diffuse into the metal substrate forming metallic boride layers, providing complex properties of B-Me-Fe system. To study multi-component boron coatings on low carbon steel AISI 1018, the simultaneous powder pack method of boronizing and metalizing was selected to perform the coatings. One B-Fe system and eight boron-metal (B-Me-Fe) systems from transition metals group IVB (Ti, Zr, HO, group VB (Nb, Ta), and group VIB (Cr, Mo, W) were studied. The system specimens were thereto-chemically treated at 950°C for 4 hours in a crucible containing powder mixture of boron source, transition metal powder, and activator. After the heat treatment process, the multi-component boron coatings were characterized by using optical microscope, microhardness tester, TGA, XRD, and Synchrotron microdiffraction. The coating morphology was observed and the coating thickness was measured as well as the microhardness across the depth of coating. The corrosion resistance of the coatings was evaluated by the continuous weighting method. The high temperature oxidation was also detected by isothermal method at a temperature range of 400-800°C for 24 hours. The Rietveld refinement method was used to examine the quantitative phase analysis, crystalline size, microstrain and lattice parameters of the multi-component boron coatings. The results have shown that adding transition metals into the B-Fe system caused the formation of solid solution of transition-metal borides. The distortion of crystal lattice parameters generated microstrain in the boride phase. The Synchrotron microdiffraction confirmed the presence of about 5-10 microns of transition-metal boride phase at the surface. Moreover, the additional transition metal can provide better corrosion and high temperature oxidation resistance to the B-Fe system, preventing the deboronizing and stabilizing the boride phases.

  3. Fabrication Of Carbon-Boron Reinforced Dry Polymer Matrix Composite Tape

    NASA Technical Reports Server (NTRS)

    Belvin, Harry L.; Cano, Roberto J.; Treasure, Monte; Shahood, Thomas W.

    1999-01-01

    Future generation aerospace vehicles will require specialized hybrid material forms for component structure fabrication. For this reason, high temperature composite prepregs in both dry and wet forms are being developed at NASA Langley Research Center (LaRC). In an attempt to improve compressive properties of carbon fiber reinforced composites, a hybrid carbon-boron tape was developed and used to fabricate composite laminates which were subsequently cut into flexural and compression specimens and tested. The hybrid material, given the designation HYCARB, was fabricated by modifying a previously developed process for the manufacture of dry polymer matrix composite (PMC) tape at LaRC. In this work, boron fibers were processed with IM7/LaRC(TradeMark)IAX poly(amide acid) solution-coated prepreg to form a dry hybrid tape for Automated Tow Placement (ATP). Boron fibers were encapsulated between two (2) layers of reduced volatile, low fiber areal weight poly(amide acid) solution-coated prepreg. The hybrid prepreg was then fully imidized and consolidated into a dry tape suitable for ATP. The fabrication of a hybrid boron material form for tow placement aids in the reduction of the overall manufacturing cost of boron reinforced composites, while realizing the improved compression strengths. Composite specimens were press-molded from the hybrid material and exhibited excellent mechanical properties.

  4. Boron Trifluoride Catalized Ring-Opening Polymerization of Epoxidized Soybean Oil in Liquid Carbon Dioxide

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Boron trifluoride diethyl etherate (BF3.OEt2) catalyzed ring-opening polymerization of epoxidized soybean oil (ESO), in liquid carbon dioxide, was conducted in an effort to develop useful biobased biodegradable polymers. The resulting polymers (RPESO) were characterized by FTIR spectroscopy, differ...

  5. Growth Mechanisms of Vertically-aligned Carbon, Boron Nitride, and Zinc Oxide Nanotubes

    SciTech Connect

    Yap, Yoke Khin

    2009-07-07

    Nanotubes are one-dimensional nanomaterials with all atoms located near the surface. This article provides a brief review on the possible growth mechanisms of a series of inorganic nanotubes, in particular, vertically-aligned (VA) carbon nanotubes (CNTs), boron nitride nanotubes (BNNTs), and ZnO nanotubes (ZnO NTs).

  6. Intercropping enhances soil carbon and nitrogen.

    PubMed

    Cong, Wen-Feng; Hoffland, Ellis; Li, Long; Six, Johan; Sun, Jian-Hao; Bao, Xing-Guo; Zhang, Fu-Suo; Van Der Werf, Wopke

    2015-04-01

    Intercropping, the simultaneous cultivation of multiple crop species in a single field, increases aboveground productivity due to species complementarity. We hypothesized that intercrops may have greater belowground productivity than sole crops, and sequester more soil carbon over time due to greater input of root litter. Here, we demonstrate a divergence in soil organic carbon (C) and nitrogen (N) content over 7 years in a field experiment that compared rotational strip intercrop systems and ordinary crop rotations. Soil organic C content in the top 20 cm was 4% ± 1% greater in intercrops than in sole crops, indicating a difference in C sequestration rate between intercrop and sole crop systems of 184 ± 86 kg C ha(-1) yr(-1). Soil organic N content in the top 20 cm was 11% ± 1% greater in intercrops than in sole crops, indicating a difference in N sequestration rate between intercrop and sole crop systems of 45 ± 10 kg N ha(-1) yr(-1). Total root biomass in intercrops was on average 23% greater than the average root biomass in sole crops, providing a possible mechanism for the observed divergence in soil C sequestration between sole crop and intercrop systems. A lowering of the soil δ(15) N signature suggested that increased biological N fixation and/or reduced gaseous N losses contributed to the increases in soil N in intercrop rotations with faba bean. Increases in soil N in wheat/maize intercrop pointed to contributions from a broader suite of mechanisms for N retention, e.g., complementary N uptake strategies of the intercropped plant species. Our results indicate that soil C sequestration potential of strip intercropping is similar in magnitude to that of currently recommended management practises to conserve organic matter in soil. Intercropping can contribute to multiple agroecosystem services by increased yield, better soil quality and soil C sequestration. PMID:25216023

  7. Report on carbon and nitrogen abundance studies

    NASA Technical Reports Server (NTRS)

    Boehm-Vitense, Erika

    1991-01-01

    The aim of the proposal was to determine the nitrogen to carbon abundance ratios from transition layer lines in stars with different T(sub eff) and luminosities. The equations which give the surface emission line fluxes and the measured ratio of the NV to CIV emission line fluxes are presented and explained. The abundance results are compared with those of photospheric abundance studies for stars in common with the photospheric investigations. The results show that the analyses are at least as accurate as the photospheric determinations. These studies can be extended to F and early G stars for which photospheric abundance determinations for giants are hard to do because molecular bands become too weak. The abundance determination in the context of stellar evolution is addressed. The N/C abundance ratio increases steeply at the point of evolution for which the convection zone reaches deepest. Looking at the evolution of the rotation velocities v sin i, a steep decrease in v sin i is related to the increasing depth of the convection zone. It is concluded that the decrease in v sin i for T(sub eff) less than or approximately = 5800 K is most probably due to the rearrangement of the angular momentum in the stars due to deep convective mixing. It appears that the convection zone is rotating with nearly depth independent angular momentum. Other research results and ongoing projects are discussed.

  8. Method of chemical vapor deposition of boron nitride using polymeric cyanoborane

    DOEpatents

    Maya, L.

    1994-06-14

    Polymeric cyanoborane is volatilized, decomposed by thermal or microwave plasma energy, and deposited on a substrate as an amorphous film containing boron, nitrogen and carbon. Residual carbon present in the film is removed by ammonia treatment at an increased temperature, producing an adherent, essentially stoichiometric boron nitride film. 11 figs.

  9. Method of chemical vapor deposition of boron nitride using polymeric cyanoborane

    DOEpatents

    Maya, Leon

    1994-01-01

    Polymeric cyanoborane is volatilized, decomposed by thermal or microwave plasma energy, and deposited on a substrate as an amorphous film containing boron, nitrogen and carbon. Residual carbon present in the film is removed by ammonia treatment at an increased temperature, producing an adherent, essentially stoichiometric boron nitride film.

  10. Synergic nitrogen source route to inorganic fullerene-like boron nitride with vessel, hollow sphere, onion, and peanut nanostructures.

    PubMed

    Xu, Fen; Xie, Yi; Zhang, Xu; Zhang, Shuyuan; Liu, Xianming; Tian, Xiaobo

    2004-01-26

    In this paper we describe the large-scale synthesis of inorganic fullerene-like (IF-like) hexagonal boron nitride with vessel, hollow sphere, peanut, and onion structures by reacting BBr(3) with the synergic nitrogen sources NaNH(2) and NH(4)Cl at 400-450 degrees C for 6-12 h. The composition of products could be confirmed to be pure boron nitride with hexagonal structures by the XRD patterns and FT-IR, XPS, and EDXA spectra. The representative HRTEM images clearly reveal the layerlike features of the products. Here, the peanut-like structure of the IF-like BN is reported for the first time, and added to the list as one kind of new morphology of BN nanomaterials. The similarity in the structure between h-BN and graphite is responsible for the formation of IF-like BN with nanostructures of vessels, hollow spheres, peanuts, and onions. PMID:14731047

  11. Nitrogen/Sulfur-Codoped Carbon Materials from Chitosan for Supercapacitors

    NASA Astrophysics Data System (ADS)

    Li, Mei; Han, Xianlong; Chang, Xiaoqing; Yin, Wenchao; Ma, Jingyun

    2016-08-01

    d-Methionine and chitosan have been used for fabrication of nitrogen/sulfur-codoped carbon materials by a hydrothermal process followed by carbonization at 750°C for 3 h. The as-prepared carbon materials showed enhanced electrochemical performance, combining electrical double-layer capacitance with pseudocapacitance owing to the doping with sulfur and nitrogen. The specific capacitance of the obtained carbon material reached 135 F g-1 at current density of 1 A g-1, which is much higher than undoped chitosan (67 F g-1). The capacitance retention of the carbon material was almost 97.2% after 5000 cycles at current density of 1 A g-1. With such improved electrochemical performance, the nitrogen/sulfur-codoped carbon material may have promising potential for use in energy-storage electrodes of supercapacitors.

  12. Nitrogen/Sulfur-Codoped Carbon Materials from Chitosan for Supercapacitors

    NASA Astrophysics Data System (ADS)

    Li, Mei; Han, Xianlong; Chang, Xiaoqing; Yin, Wenchao; Ma, Jingyun

    2016-05-01

    uc(d)-Methionine and chitosan have been used for fabrication of nitrogen/sulfur-codoped carbon materials by a hydrothermal process followed by carbonization at 750°C for 3 h. The as-prepared carbon materials showed enhanced electrochemical performance, combining electrical double-layer capacitance with pseudocapacitance owing to the doping with sulfur and nitrogen. The specific capacitance of the obtained carbon material reached 135 F g-1 at current density of 1 A g-1, which is much higher than undoped chitosan (67 F g-1). The capacitance retention of the carbon material was almost 97.2% after 5000 cycles at current density of 1 A g-1. With such improved electrochemical performance, the nitrogen/sulfur-codoped carbon material may have promising potential for use in energy-storage electrodes of supercapacitors.

  13. Properties and electrochemical characteristics of boron-doped multi-walled carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Tsierkezos, Nikos G.; Ritter, Uwe; Nugraha Thaha, Yudi; Krischok, Stefan; Himmerlich, Marcel; Downing, Clive

    2015-10-01

    Boron-doped multi-walled carbon nanotubes were synthesized upon decomposition of ethyl alcohol and boric acid via chemical vapor deposition. The boron-doped nanotubes were treated with hydrochloric acid and were characterized by means of scanning electron and transmission electron microscopy in conjunction with energy-dispersive X-ray spectrometry and X-ray photoelectron spectroscopy. The electrochemistry of ferrocyanide/ferricyanide on boron-doped nanotubes was studied in temperature range of 283.15-303.15 K. The findings exhibit an improvement of films' current response and kinetics of electron transfer with the rise in temperature. The kinetics for electron transfer enhances and the redox process occurs slightly more spontaneously upon acid treatment.

  14. Investigations on the system boron-carbon silicon

    NASA Technical Reports Server (NTRS)

    Kieffer, R.; Gugel, E.; Leimer, G.; Ettmayer, P.

    1983-01-01

    The above elements form with each other binary compounds which are very interesting from the point of view of their structure and their chemistry and which are important for technology. The present investigation is concerned with the three-component system and the behavior of the binary compounds occurring in it. Investigations employing various techniques, such as X-ray, chemical analysis, microscopy and fusion experiments showed that no ternary phase exists within the boundary of the ternary system. There is no compound with a higher abrasion capacity than boron carbide. The probable phase field divisions at two isothermic intersections and the fusion isotherms are indicated.

  15. Electromagnetic properties of phosphate composite materials with boron-containing carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Plyushch, A. O.; Sokol, A. A.; Lapko, K. N.; Kuzhir, P. P.; Fedoseeva, Yu. V.; Romanenko, A. I.; Anikeeva, O. B.; Bulusheva, L. G.; Okotrub, A. V.

    2014-12-01

    The possibility of developing electromagnetic composite materials based on unfired heat-resistant mechanically strong phosphate ceramics has been studied. Boron-containing multiwalled carbon nanotubes and onion-like particles (B-MWCNTs) synthesized by electric-arc evaporation of a graphite rod enriched with boron are used as a functional additive to the phosphate matrix. According to transmission electron microscopy, the average nanoparticle length is ˜100 nm. According to X-ray photoelectron spectroscopy and X-ray absorption spectroscopy, the boron content in B-MWCNT walls is less than 1 at %, and substitution of carbon atoms with boron leads to the formation of acceptor states in the conduction band. An increase in the electromagnetic response of phosphate ceramics by ˜53 and ˜13-15% for 1.5 wt % B-MWCNT additive is detected in quasi-static and gigahertz ranges, respectively. It is assumed that a stronger effect can be achieved using longer B-MWCNTs than those formed under electric arc conditions.

  16. High quality boron carbon nitride/ZnO-nanorods p-n heterojunctions based on magnetron sputtered boron carbon nitride films

    SciTech Connect

    Qian, J. C.; Jha, S. K. E-mail: apwjzh@cityu.edu.hk; Wang, B. Q.; Jelenković, E. V.; Bello, I.; Klemberg-Sapieha, J. E.; Martinu, L.; Zhang, W. J. E-mail: apwjzh@cityu.edu.hk

    2014-11-10

    Boron carbon nitride (BCN) films were synthesized on Si (100) and fused silica substrates by radio-frequency magnetron sputtering from a B{sub 4}C target in an Ar/N{sub 2} gas mixture. The BCN films were amorphous, and they exhibited an optical band gap of ∼1.0 eV and p-type conductivity. The BCN films were over-coated with ZnO nanorod arrays using hydrothermal synthesis to form BCN/ZnO-nanorods p-n heterojunctions, exhibiting a rectification ratio of 1500 at bias voltages of ±5 V.

  17. Applicability of carbon and boron nitride nanotubes as biosensors: Effect of biomolecular adsorption on the transport properties of carbon and boron nitride nanotubes

    NASA Astrophysics Data System (ADS)

    Zhong, Xiaoliang; Mukhopadhyay, Saikat; Gowtham, S.; Pandey, Ravindra; Karna, Shashi P.

    2013-04-01

    The effect of molecular adsorption on the transport properties of single walled carbon and boron nitride nanotubes (CNTs and BNNTs) is investigated using density functional theory and non-equilibrium Green's function methods. The calculated I-V characteristics predict noticeable changes in the conductivity of semiconducting BNNTs due to physisorption of nucleic acid base molecules. Specifically, guanine which binds to the side wall of BNNT significantly enhances its conductivity by introducing conduction channels near the Fermi energy of the bioconjugated system. For metallic CNTs, a large background current masks relatively small changes in current due to the biomolecular adsorption. The results therefore suggest the suitability of BNNTs for biosensing applications.

  18. Isotopic inferences of ancient biochemistries - Carbon, sulfur, hydrogen, and nitrogen

    NASA Technical Reports Server (NTRS)

    Schidlowski, M.; Hayes, J. M.; Kaplan, I. R.

    1983-01-01

    In processes of biological incorporation and subsequent biochemical processing sizable isotope effects occur as a result of both thermodynamic and kinetic fractionations which take place during metabolic and biosynthetic reactions. In this chapter a review is provided of earlier work and recent studies on isotope fractionations in the biogeochemical cycles of carbon, sulfur, hydrogen, and nitrogen. Attention is given to the biochemistry of carbon isotope fractionation, carbon isotope fractionation in extant plants and microorganisms, isotope fractionation in the terrestrial carbon cycle, the effects of diagenesis and metamorphism on the isotopic composition of sedimentary carbon, the isotopic composition of sedimentary carbon through time, implications of the sedimentary carbon isotope record, the biochemistry of sulfur isotope fractionation, pathways of the biogeochemical cycle of nitrogen, and the D/H ratio in naturally occurring materials.

  19. LARGE AREA FILTERED ARC DEPOSITION OF CARBON AND BORON BASED HARD COATINGS

    SciTech Connect

    Bhattacharya, Rabi S.

    2003-12-05

    This document is a final report covering work performed under Contract No. DE-FG02-99ER82911 from the Department of Energy under a SBIR Phase II Program. Wear resistant, hard coatings can play a vital role in many engineering applications. The primary goal of this project was to develop coatings containing boron and carbon with hardness greater than 30 GPa and evaluate these coatings for machining applications. UES has developed a number of carbon and boron containing coatings with hardness in the range of 34 to 65 GPa using a combination of filtered cathodic arc and magnetron sputtering. The boron containing coatings were based on TiB2, TiBN, and TiBCN, while the carbon containing coatings ere TiC+C and hydrogen free diamond-like-carbon. Machining tests were performed with single and multilayer coated tools. The turning and milling tests were run at TechSolve Inc., under a subcontract at Ohio State University. Significant increases in tool lives were realized in end milling of H-13 die steel (8X) and titanium alloy (80%) using the TiBN coating. A multilayer TiBN/TiN performed the best in end-milling of highly abrasive Al-Si alloys. A 40% increase in life over the TiAlN benchmark coating was found. Further evaluations of these coatings with commercialization partners are currently in progress.

  20. Shock induced polymorphic transition in quartz, carbon, and boron nitride

    NASA Technical Reports Server (NTRS)

    Tan, Hua; Ahrens, Thomas J.

    1990-01-01

    The model proposed by Ahrens (1988) to explain the mechanism of the polymorphism in silicates is revised, and the revised model is applied to the quartz/stishovite, graphite/diamond, and graphite-boron nitride (g-BN) phase transformations. In this model, a key assumption is that transformation to a high-density amorphous or possibly liquid phase which rapidly crystallized to the high-pressure phase is triggered by the high temperatures in the shear band and upon crossing the metastable extension of a melting curve. Good agreement between the calcualted results and published data is obtained. The present theory predicts the standard entropy for cubic BN to be 0.4-0.5 J/g K.

  1. CARBON EFFECTS ON NITROGEN RETENTION AND NITROGEN TRANSFORMING MICROBIAL POPULATIONS

    EPA Science Inventory

    Approach: A factorial design with three levels of ammonium chloride (0, 100 and 1000 kg N/ha), and two forms of carbon (glucose and tannic acid), each with three levels (0, 100 and 1000 kg C/ha) has been replicated three times at each of two old-field sites in southeastern Oklah...

  2. Sequestration of Carbon in Mycorrhizal Fungi Under Nitrogen Fertilization

    NASA Astrophysics Data System (ADS)

    Treseder, K. K.; Turner, K. M.

    2005-12-01

    Mycorrhizal fungi are root symbionts that facilitate plant uptake of soil nutrients in exchange for plant carbohydrates. They grow in almost every terrestrial ecosystem on earth, form relationships with about 80% of plant species, and receive 10 to 20% of the carbon fixed by their host plants. As such, they could potentially sequester a significant amount of carbon in ecosystems. We hypothesized that nitrogen fertilization would decrease carbon storage in mycorrhizal fungi, because plants should reduce investment of carbon in mycorrhizal fungi when nitrogen availability is high. We measured the abundance of two major groups of mycorrhizal fungi, arbuscular mycorrhizal (AM) and ectomycorrhizal (ECM) fungi, in control and nitrogen-fertilized plots within three boreal ecosystems of inland Alaska. The ecosystems represented different recovery stages following severe fire, and comprised a young site dominated by AM fungi, an old site dominated by ECM fungi, and an intermediate site co-dominated by both groups. Pools of mycorrhizal carbon included root-associated AM and ECM structures, soil-associated AM hyphae, and soil-associated glomalin. Glomalin is a glycoprotein produced only by AM fungi. It is present in the cell walls of AM hyphae, and then is deposited in the soil as the hyphae senesce. Nitrogen significantly altered total mycorrhizal carbon pools, but its effect varied by site (site * N interaction, P = 0.05). Under nitrogen fertilization, mycorrhizal carbon was reduced from 99 to 50 g C m2 in the youngest site, was increased from 124 to 203 g C m2 in the intermediate-aged site, and remained at 35 g C m2 in the oldest site. The changes in total mycorrhizal carbon stocks were driven mostly by changes in glomalin (site * N interaction, P = 0.05), and glomalin stocks were strongly correlated with AM hyphal abundance (P < 0.01). Nevertheless, it is not clear why AM hyphae responded differently to nitrogen fertilization in the different sites. Carbon stocks within

  3. Shear induced formation of carbon and boron nitride nano-scrolls

    NASA Astrophysics Data System (ADS)

    Chen, Xianjue; Boulos, Ramiz A.; Dobson, John F.; Raston, Colin L.

    2012-12-01

    A `top down' synthesis of carbon and hexagonal boron nitride (h-BN) nano-scrolls has been developed using the shear forces within dynamic thin films of N-methyl-2-pyrrolidone (NMP) generated on a rapidly rotating spinning disc processor (SDP), along with a theoretical understanding of the formation of the scrolls.A `top down' synthesis of carbon and hexagonal boron nitride (h-BN) nano-scrolls has been developed using the shear forces within dynamic thin films of N-methyl-2-pyrrolidone (NMP) generated on a rapidly rotating spinning disc processor (SDP), along with a theoretical understanding of the formation of the scrolls. Electronic supplementary information (ESI) available. See DOI: 10.1039/c2nr33071g

  4. Measurement of boron and carbon fluxes in cosmic rays with the PAMELA experiment

    SciTech Connect

    Adriani, O.; Bongi, M.; Barbarino, G. C.; Bazilevskaya, G. A.; Bellotti, R.; Bruno, A.; Boezio, M.; Bonvicini, V.; Carbone, R.; Bogomolov, E. A.; Bottai, S.; Cafagna, F.; Campana, D.; Carlson, P.; Casolino, M.; De Donato, C.; De Santis, C.; De Simone, N.; Castellini, G.; Danilchenko, I. A.; and others

    2014-08-20

    The propagation of cosmic rays inside our galaxy plays a fundamental role in shaping their injection spectra into those observed at Earth. One of the best tools to investigate this issue is the ratio of fluxes for secondary and primary species. The boron-to-carbon (B/C) ratio, in particular, is a sensitive probe to investigate propagation mechanisms. This paper presents new measurements of the absolute fluxes of boron and carbon nuclei as well as the B/C ratio from the PAMELA space experiment. The results span the range 0.44-129 GeV/n in kinetic energy for data taken in the period 2006 July to 2008 March.

  5. Microstructure development in hot-pressed silicon carbide: Effects of aluminum, boron, and carbon additives

    SciTech Connect

    Zhang, Xiao Feng; Yang, Qing; De Jonghe, Lutgard C.

    2002-12-18

    SiC was hot-pressed with aluminum, boron, and carbon additives. The Al content was modified either to obtain SiC samples containing a continuous Al gradient, or to vary the average Al content. In both cases, dramatic changes in microstructure, phase composition, and grain boundary structure were observed as a result of the Al variation. Similar processing and characterization were done with modified boron and carbon average contents. The systematic experiments allowed identification of the roles of Al, B, and C in developing grain morphology and phase composition. The experiments also clarified the mechanical property responses to microstructural modification. Tailoring of the SiC microstructure to suit different applications would be possible.

  6. Hierarchical carbon nanotube assemblies created by sugar-boric or boronic acid interactions.

    PubMed

    Tamesue, Shingo; Numata, Munenori; Kaneko, Kenji; James, Tony D; Shinkai, Seiji

    2008-10-01

    We previously found that polysaccharide "schizophyllan (SPG)" can entrap as-grown and cut single-walled carbon nanotubes (as-SWNTs and c-SWNTs, respectively): we here reported that the c-SWNT-s-SPG (single stranded SPG) composites thus obtained can be aligned regularly using the covalent bond formation between boric acid or boronic acid derivatives and the 4,6-dihydroxyl group of the glucose side-chain unit. PMID:18802596

  7. Preparation of carbon nanoparticles and carbon nitride from high nitrogen compound

    DOEpatents

    Huynh, My Hang V.; Hiskey, Michael A.

    2009-09-01

    The high-nitrogen compound 3,6-di(azido)-1,2,4,5-tetrazine (DiAT) was synthesized by a relatively simple method and used as a precursor for the preparation of carbon nanospheres and nanopolygons, and nitrogen-rich carbon nitrides.

  8. Effect of boron, nitrogen, and oxygen impurities on the electronic structure and deformation behavior of Ti3SiC2

    NASA Astrophysics Data System (ADS)

    Medvedeva, N. I.

    2013-03-01

    The effect of nitrogen, oxygen, and boron impurities on the lattice parameters, local distortions, stability, and electronic structure of ternary silicon carbide Ti3SiC2 was studied by the ab initio density functional theory method. An axial tension was simulated, and the effect of impurities on the deformation behavior of Ti3SiC2 was predicted. It was shown that nitrogen can favor the strengthening of Ti3SiC2, whereas boron and oxygen should lead to the laminate separation.

  9. Computational Study of Electronic and Transport Properties of Novel Boron and Carbon Nano-Structures

    NASA Astrophysics Data System (ADS)

    Sadrzadeh, Arta

    In the first part of this dissertation, we study mainly novel boron structures and their electronic and mechanical properties, using ab initio calculations. The electronic structure and construction of the boron buckyball B80 , and boron nanotubes as the alpha- sheet wrapped around a cylinder are studied. The alpha-sheet is considered so far to be the most stable structure energetically out of the two dimensional boron assemblies. We will argue however that there are other sheets close in energy, using cluster expansion method. The boron buckyball is shown to have different possible isomers. Characterization of these isomers according to their geometry and electronic structure is studied in detail. Since the B80 structure is made of interwoven double-ring clusters, we also investigate double-rings with various diameters. We investigate the properties of nanotubes obtained from alpha-sheet. Computations confirm their high stability and identify mechanical stiffness parameters. Careful relaxation reveals the curvature-induced buckling of certain atoms off the original plane. This distortion opens up the gap in narrow tubes, rendering them semi-conducting. Wider tubes with the diameter d ≥ 1.7 nm retain original metallic character of the alpha-sheet. We conclude this part by investigation into hydrogen storage capacity of boron-rich compounds, namely the metallacarboranes. In the second part of dissertation, we switch our focus to electronic and transport properties of carbon nano-structures. We study the application of carbon nanotubes as electro-chemical gas sensors. The effect of physisorption of NO2 gas molecules on electron transport properties of semi-conducting carbon nanotubes is studied using ab initio calculations and Green's function formalism. It is shown that upon exposure of nanotube to different concentrations of gas, the common feature is the shift in conductance towards lower energies. This suggests that physisorption of NO2 will result in a

  10. Novel molecular sources for dispersing boron in carbon-carbon composites. Final report, 8 September 1992-7 September 1994

    SciTech Connect

    Chen, P.S.; Stevens, W.C.

    1993-11-07

    Improving the oxidation resistance of carbon-carbon composites is key to extending the applications of this material system into higher temperature regimes. While molecularly dispersed boron, through addition of carborane, helps to provide oxidation protection to phenolic derived carbon, the moisture affinity of the boria seriously affects composite performance. Substitution of furfuryl and pitch as the resin precursors significantly improved the moisture resistance of the carbon matrix material by stabilizing the boron at low temperatures and minimizing premature boria formation. Carborane addition to a commercial furfuryl/pitch blend (Kaiser Code88A) yielded a carbon char with reduced moisture affinity and improved oxidation resistance. Mechanical properties of the Code88A matrix composites were not significantly affected by the addition of carborane. Although sample size limitations in testing detracted from the demonstration of success, data suggests that the oxidation resistance of carbon-carbons can be significantly enhanced via this approach without detriment to the physical attributes and moisture resistance of the composite.

  11. Boron-silicon solid solution: synthesis and crystal structure of a carbon-doped boron-rich SiB{sub n} (n{approx}30) compound

    SciTech Connect

    Roger, Jerome; Babizhetskyy, Volodymyr; Halet, Jean-Francois; Guerin, Roland . E-mail: roland.guerin@univ-rennes1.fr

    2004-11-01

    The carbon-doped SiB{sub 3}{approx}{sub 30} compound was obtained during attempts to synthesize by arc-melting boron-rich binaries belonging to the SiB{sub n} solid solution (13n<32). Its crystal structure was determined from X-ray single-crystal intensity data (R-3m, Z=1, a=11.0152(3)A, and c=23.8625(8)A) and led to the final formula SiB{sub {approx}}{sub 30}C{sub 0.35}. Carbon is incorporated fortuitously in the structure. The boron framework of these phases slightly differs from that encountered in {beta}-boron. The salient characteristic is the partial occupancy of three interstitial boron sites by silicon and one by carbon atoms. This is in contrast with the structurally related compounds such as SiB{sub {approx}}{sub 36}, CrB{sub {approx}}{sub 41}, or FeB{sub {approx}}{sub 40}, in which only two interstitial sites are partially occupied.

  12. Connecting effect on the first hyperpolarizability of armchair carbon-boron-nitride heteronanotubes: pattern versus proportion.

    PubMed

    Zhong, Rong-Lin; Xu, Hong-Liang; Su, Zhong-Min

    2016-05-18

    Carbon-boron-nitride heteronanotubes (BNCNT) have attracted a lot of attention because of their adjustable properties and potential applications in many fields. In this work, a series of CA, PA and HA armchair BNCNT models were designed to explore their nonlinear optical (NLO) properties and provide physical insight into the structure-property relationships; CA, PA and HA represent the models that are obtained by doping the carbon segment into pristine boron nitride nanotube (BNNT) fragments circularly around the tube axis, parallel to the tube axis and helically to the tube axis, respectively. Results show that the first hyperpolarizability (β0) of an armchair BNCNT model is dramatically dependent on the connecting patterns of carbon with the boron nitride fragment. Significantly, the β0 value of PA-6 is 2.00 × 10(4) au, which is almost two orders of magnitude larger than those (6.07 × 10(2) and 1.55 × 10(2) au) of HA-6 and CA-6. In addition, the β0 values of PA and CA models increase with the increase in carbon proportion, whereas those of HA models show a different tendency. Further investigations on transition properties show that the curved charge transfer from N-connecting carbon atoms to B-connecting carbon atoms of PA models is essentially the origin of the big difference among these models. This new knowledge about armchair BNCNTs may provide important information for the design and preparation of advanced NLO nano-materials. PMID:27152376

  13. Eutectic Syntheses of Graphitic Carbon with High Pyrazinic Nitrogen Content.

    PubMed

    Fechler, Nina; Zussblatt, Niels P; Rothe, Regina; Schlögl, Robert; Willinger, Marc-Georg; Chmelka, Bradley F; Antonietti, Markus

    2016-02-10

    Mixtures of phenols/ketones and urea show eutectic behavior upon gentle heating. These mixtures possess liquid-crystalline-like phases that can be processed. The architecture of phenol/ketone acts as structure-donating motif, while urea serves as melting-point reduction agent. Condensation at elevated temperatures results in nitrogen-containing carbons with remarkably high nitrogen content of mainly pyrazinic nature. PMID:26178584

  14. Carbon and nitrogen isotope studies in an arctic ecosystem

    SciTech Connect

    Schell, D.M.

    1989-12-31

    This proposal requests funding for the completion of our current ecological studies at the MS-117 research site at Toolik Lake, Alaska. We have been using a mix of stable and radioisotope techniques to assess the fluxes of carbon and nitrogen within the ecosystem and the implications for long-term carbon storage or loss from the tundra. Several tentative conclusions have emerged from our study including: Tundra in the foothills is no longer accumulating carbon. Surficial radiocarbon abundances show little or no accumulation since 1000--2500 yrs BP. Coastal plain tundra is still accumulating carbon, but the rate of accumulation has dropped in the last few thousand years. Carbon export from watersheds in the Kuparuk and Imnavait Creek drainages are in excess of that expected from estimated primary productivity; and Nitrogen isotope abundances vary between species of plants and along hydrologic gradients.

  15. Carbon and nitrogen isotope studies in an arctic ecosystem

    SciTech Connect

    Schell, D.M.

    1989-01-01

    This proposal requests funding for the completion of our current ecological studies at the MS-117 research site at Toolik Lake, Alaska. We have been using a mix of stable and radioisotope techniques to assess the fluxes of carbon and nitrogen within the ecosystem and the implications for long-term carbon storage or loss from the tundra. Several tentative conclusions have emerged from our study including: Tundra in the foothills is no longer accumulating carbon. Surficial radiocarbon abundances show little or no accumulation since 1000--2500 yrs BP. Coastal plain tundra is still accumulating carbon, but the rate of accumulation has dropped in the last few thousand years. Carbon export from watersheds in the Kuparuk and Imnavait Creek drainages are in excess of that expected from estimated primary productivity; and Nitrogen isotope abundances vary between species of plants and along hydrologic gradients.

  16. Soil warming, carbon–nitrogen interactions, and forest carbon budgets

    PubMed Central

    Melillo, Jerry M.; Butler, Sarah; Johnson, Jennifer; Mohan, Jacqueline; Steudler, Paul; Lux, Heidi; Burrows, Elizabeth; Bowles, Francis; Smith, Rose; Scott, Lindsay; Vario, Chelsea; Hill, Troy; Burton, Andrew; Zhou, Yu-Mei; Tang, Jim

    2011-01-01

    Soil warming has the potential to alter both soil and plant processes that affect carbon storage in forest ecosystems. We have quantified these effects in a large, long-term (7-y) soil-warming study in a deciduous forest in New England. Soil warming has resulted in carbon losses from the soil and stimulated carbon gains in the woody tissue of trees. The warming-enhanced decay of soil organic matter also released enough additional inorganic nitrogen into the soil solution to support the observed increases in plant carbon storage. Although soil warming has resulted in a cumulative net loss of carbon from a New England forest relative to a control area over the 7-y study, the annual net losses generally decreased over time as plant carbon storage increased. In the seventh year, warming-induced soil carbon losses were almost totally compensated for by plant carbon gains in response to warming. We attribute the plant gains primarily to warming-induced increases in nitrogen availability. This study underscores the importance of incorporating carbon–nitrogen interactions in atmosphere–ocean–land earth system models to accurately simulate land feedbacks to the climate system. PMID:21606374

  17. Bioelectrochemical conversion of urea to nitrogen using aminated carbon electrode.

    PubMed

    Watanabe, Hiroaki; Nishi, Hideki; Hamana, Hiroshi; Sekioka, Naoyuki; Wang, Xiuyun; Uchiyama, Shunichi

    2009-01-01

    Urea decomposes to ammonia and carbon dioxide via carbamic acid, and amine groups can be introduced to the glassy carbon electrode surface during the electrode oxidation of carbamic acid. This modified carbon electrode has excellent catalytic activity of the oxidation of carbamic acid, and can be used to electrooxidize urea by combining urease reaction and electrode oxidation. We found that nitrogen gas is finally produced by the carbamic acid produced from urea. The production of nitrogen was confirmed by gas chromatography-mass spectrometry, and fragment pattern of hydrazine was also detected in the electrolyzed solution of urea. We intend to describe new electrochemical conversion system of urea to harmless nitrogen gas. The electrode oxidation current of urea was decreased by addition of radical trapping agent such as DMPO (5,5-dimethyl-1-pyrroline N-oxide), and this fact suggests that carbamic acid radical couples to form nitrogen-nitrogen bond, and this dimer is oxidized to nitrogen. The electrode oxidation current of urea became larger when oxygen was removed. This fact indicates that the intermediate species (probably hydrazine) produced by the electrolysis is oxidized by not only electrode reaction but also oxygen. PMID:25084444

  18. tert-Butanesulfinamides as Nitrogen Nucleophiles in Carbon-Nitrogen Bond Forming Reactions.

    PubMed

    Ramirez Hernandez, Johana; Chemla, Fabrice; Ferreira, Franck; Jackowski, Olivier; Oble, Julie; Perez-Luna, Alejandro; Poli, Giovanni

    2016-01-01

    The use of tert-butanesulfinamides as nitrogen nucleophiles in carbon-nitrogen bond forming reactions is reviewed. This field has grown in the shadow of the general interest in N-tert-butanesulfinyl imines for asymmetric synthesis and occupies now an important place in its own right in the chemistry of the chiral amine reagent tert-butanesulfinamide. This article provides an overview of the area and emphasizes recent contributions wherein the tert-butanesulfinamides act as chiral auxiliaries or perform as nitrogen donors in metal-catalyzed amination reactions. PMID:26931222

  19. Estimation of the upper limit of carbon concentration in boron carbide crystals

    NASA Astrophysics Data System (ADS)

    Konovalikhin, S. V.; Ponomarev, V. I.

    2010-08-01

    The existence of a boron carbide phase with ˜25 at % carbon was proven experimentally. To evaluate the maximum possible concentration of C atoms in boron carbide (B12 - x C x )(BC2) crystals, we performed quantum-chemical calculations of (B12 - x C x )(BH2)6(CH3)6 model compounds ( x = 0-4; the goal of calculations was to determine the upper limiting number of C atoms in the B12 - x C x icosahedron) by the density functional theory method (B3LYP, 6-31G** basis set, full geometry optimization). A comparison of the experimental and calculated data showed that the calculations of the model compounds reproduced the experimental dependences of the structural parameters of the icosahedron (mean bond length and volume) on the number of C atoms in it. The icosahedra were found to be stable at x ≤ 3. According to the results of the quantum-chemical calculations, the maximum carbon concentration in boron carbide was 33 at %, which corresponded to the composition B10C5 and the structural formula (B9C3)(BC2).

  20. Thermal conduction mechanisms in isotope-disordered boron nitride and carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Savic, Ivana; Mingo, Natalio; Stewart, Derek

    2009-03-01

    We present first principles studies which determine dominant effects limiting the heat conduction in isotope-disordered boron nitride and carbon nanotubes [1]. Using an ab initio atomistic Green's function approach, we demonstrate that localization cannot be observed in the thermal conductivity measurements [1], and that diffusive scattering is the dominant mechanism which reduces the thermal conductivity [2]. We also give concrete predictions of the magnitude of the isotope effect on the thermal conductivities of carbon and boron nitride single-walled nanotubes [2]. We furthermore show that intershell scattering is not the main limiting mechanism for the heat flow through multi-walled boron nitride nanotubes [1], and that heat conduction restricted to a few shells leads to the low thermal conductivities experimentally measured [1]. We consequently successfully compare the results of our calculations [3] with the experimental measurements [1]. [1] C. W. Chang, A. M. Fennimore, A. Afanasiev, D. Okawa, T. Ikuno, H. Garcia, D. Li, A. Majumdar, A. Zettl, Phys. Rev. Lett. 2006, 97, 085901. [2] I. Savic, N. Mingo, D. A. Stewart, Phys. Rev. Lett. 2008, 101, 165502. [3] I. Savic, D. A. Stewart, N. Mingo, to be published.

  1. Landscape level differences in soil carbon and nitrogen: implications for soil carbon sequestration

    SciTech Connect

    Garten Jr, Charles T; Ashwood, Tom L

    2002-12-01

    The objective of this research was to understand how land cover and topography act, independently or together, as determinants of soil carbon and nitrogen storage over a complex terrain. Such information could help to direct land management for the purpose of carbon sequestration. Soils were sampled under different land covers and at different topographic positions on the mostly forested 14,000 ha Oak Ridge Reservation in Tennessee, USA. Most of the soil carbon stock, to a 40-cm soil depth, was found to reside in the surface 20 cm of mineral soil. Surface soil carbon and nitrogen stocks were partitioned into particulate ({ge}53 {micro}m) and mineral-associated organic matter (<53 {micro}m). Generally, soils under pasture had greater nitrogen availability, greater carbon and nitrogen stocks, and lower C:N ratios than soils under transitional vegetation and forests. The effects of topography were usually secondary to those of land cover. Because of greater soil carbon stocks, and greater allocation of soil carbon to mineral-associated organic matter (a long-term pool), we conclude that soil carbon sequestration, but not necessarily total ecosystem carbon storage, is greater under pastures than under forests. The implications of landscape-level variation in soil carbon and nitrogen for carbon sequestration are discussed at several different levels: (1) nitrogen limitations to soil carbon storage; (2) controls on soil carbon turnover as a result of litter chemistry and soil carbon partitioning; (3) residual effects of past land use history; and (4) statistical limitations to the quantification of soil carbon stocks.

  2. Application of sodium carbonate-zinc oxide decomposition mixture on ICP-AES determination of boron in tourmaline.

    PubMed

    Lihareva, N; Kosturkova, P; Vakarelska, T

    2000-05-01

    Boron in tourmaline, a high refractory mineral with a high boron content (approximately 3%), can be determined after aqueous leaching of a sodium carbonate-zinc oxide melt. Boron is separated effectively from the major elements of matrix, such as silicon, calcium and magnesium and especially from iron, the main spectral interfering element. Measurements were performed by inductively coupled plasma atomic emission spectrometry. A determination limit of 4 microg/g could be achieved when 200 mg of sample are analyzed with a precision of 5.2% RSD. This method could be applied to the determination of fluorine in the same solution. PMID:11227440

  3. Investigation of nitrogen and carbon co-implantation under room temperature and cryo-condition

    NASA Astrophysics Data System (ADS)

    He, Yonggen; Wu, Bing; Yu, Guobin; Chen, Yong; Liu, Hailong; He, Youfeng; Dai, Haibo; Wu, Jingang; Zhang, David Wei; Lu, Junfeng; Xu, Jingrui; Guo, Baonian

    2012-11-01

    Co-implantation of non-dopant species is widely used in 65nm and beyond Complementary Metal-Oxide-Semiconductor (CMOS) technology node to meet ITRS ultra shallow junction roadmap and device performance requirement. With co-implantation, non-dopant species, such as Carbon (C), Fluorine (F) and Nitrogen (N), can either suppress doping diffusion or modify material property and improve device reliability. Cold implantation with wafer pedestal cooling to near -100°C is another hot topic in CMOS manufacture recently. It has obvious benefits, such as good amorphization performance, less end of range defect, less stress relaxation especially for e-SiGe formation. In the present work, different co-implantations with nitrogen and/or carbon were investigated for advanced NMOS Lightly Doped Drain (LDD) junction formation. The co-implantation was performed under room temperature or -100°C. It was found that C or C plus N co-implantations are very effective to suppress the diffusion of halo-implanted boron. Comparing with room temperature, the cryo-implantation under -100°C can get much better amorphization and less End of Range (EOR) defects, which result in reduced junction leakage and high activation as observed on blanket wafer and device wafers.

  4. Nitrogen-doped, carbon-rich, highly photoluminescent carbon dots from ammonium citrate

    NASA Astrophysics Data System (ADS)

    Yang, Zhi; Xu, Minghan; Liu, Yun; He, Fengjiao; Gao, Feng; Su, Yanjie; Wei, Hao; Zhang, Yafei

    2014-01-01

    The synthesis of water-soluble nitrogen-doped carbon dots has received great attention, due to their wide applications in oxygen reduction reaction, cell imaging, sensors, and drug delivery. Herein, nitrogen-doped, carbon-rich, highly photoluminescent carbon dots have been synthesized for the first time from ammonium citrate under hydrothermal conditions. The obtained nitrogen-doped carbon dots possess bright blue luminescence, short fluorescence lifetime, pH-sensitivity and excellent stability at a high salt concentration. They have potential to be used for pH sensors, cell imaging, solar cells, and photocatalysis.The synthesis of water-soluble nitrogen-doped carbon dots has received great attention, due to their wide applications in oxygen reduction reaction, cell imaging, sensors, and drug delivery. Herein, nitrogen-doped, carbon-rich, highly photoluminescent carbon dots have been synthesized for the first time from ammonium citrate under hydrothermal conditions. The obtained nitrogen-doped carbon dots possess bright blue luminescence, short fluorescence lifetime, pH-sensitivity and excellent stability at a high salt concentration. They have potential to be used for pH sensors, cell imaging, solar cells, and photocatalysis. Electronic supplementary information (ESI) available: The curve of photoluminescence and absorbance of N-doped CDs and quinine sulfate, and the table showing XPS detailed information. See DOI: 10.1039/c3nr05380f

  5. Fabrication of Polyimide-Matrix/Carbon and Boron-Fiber Tape

    NASA Technical Reports Server (NTRS)

    Belvin, Harry L.; Cano, Roberto J.; Treasure, Monte; Shahood, Thomas W.

    2007-01-01

    The term HYCARB denotes a hybrid composite of polyimide matrices reinforced with carbon and boron fibers. HYCARB and an improved process for fabricating dry HYCARB tapes have been invented in a continuing effort to develop lightweight, strong composite materials for aerospace vehicles. Like other composite tapes in this line of development, HYCARB tapes are intended to be used to build up laminated structures having possibly complex shapes by means of automated tow placement (ATP) - a process in which a computer-controlled multiaxis machine lays down prepreg tape or tows. The special significance of the present process for making dry HYCARB for ATP is that it contributes to the reduction of the overall cost of manufacturing boron-reinforced composite-material structures while making it possible to realize increased compression strengths. The present process for making HYCARB tapes incorporates a "wet to dry" process developed previously at Langley Research Center. In the "wet to dry" process, a flattened bundle of carbon fiber tows, pulled along a continuous production line between pairs of rollers, is impregnated with a solution of a poly(amide acid) in N-methyl-2-pyrrolidinone (NMP), then most of the NMP is removed by evaporation in hot air. In the present case, the polyamide acid is, more specifically, that of LaRC. IAX (or equivalent) thermoplastic polyimide, and the fibers are, more specifically, Manganite IM7 (or equivalent) polyacrylonitrile- based carbon filaments that have a diameter of 5.2 m and are supplied in 12,000-filament tows. The present process stands in contrast to a prior process in which HYCARB tape was made by pressing boron fibers into the face of a wet carbon-fiber/ poly(amide acid) prepreg tape . that is, a prepreg tape from which the NMP solvent had not been removed. In the present process, one or more layer(s) of side-by-side boron fibers are pressed between dry prepreg tapes that have been prepared by the aforementioned gwet to dry h

  6. Electron spin-polarization and spin lattices in the boron- and nitrogen-doped organic framework COF-5.

    PubMed

    Liu, Xiaobiao; Tan, Jie; Wang, Aizhu; Zhang, Xiaoming; Zhao, Mingwen

    2014-11-14

    Covalent organic frameworks (COFs) hold great promise in several applications, such as sieves, catalytic supports and gas storage because of their unique structures and electronic properties. However, most of these metal-free COFs are nonmagnetic and cannot be directly used in spintronics. Here, based on first-principles calculations, we predict that substitutional doping of COF-5 with nitrogen and boron atoms can modify the electronic structures, inducing stable electron spin-polarization in the framework. The preferability of the different doping sites is checked. The electronic structures of the doped COF-5 are dependent on the doping sites and doping atoms, which offer high degrees of freedom to tune the electronic properties. Kagome lattices of S = 1/2 spins can be achieved in the COF-5, suggesting a promising candidate for spin-liquid materials. PMID:25255699

  7. Angular distribution of photoelectrons from atomic oxygen, nitrogen, and carbon

    NASA Technical Reports Server (NTRS)

    Manson, S. T.; Kennedy, D. J.; Starace, A. F.; Dill, D.

    1974-01-01

    The angular distribution of photoelectrons from atomic oxygen is investigated using Hartree-Fock (HF) wave functions. The correct formulation is used to compare HS and HF results. Agreement between these results is good and the HS calculations have been extended to atomic nitrogen and carbon as well.

  8. Landscape controls on carbon and nitrogen cycling in boreal forests

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Climate change in the boreal forest biome is having a large impact on two of the main controllers of carbon (C) and nitrogen (N) cycling within this region: permafrost and fire. Permafrost, and its effects on soil drainage, controls the inputs and losses of C and N via net primary productivity (NP...

  9. A mobile light source for carbon/nitrogen cameras

    NASA Astrophysics Data System (ADS)

    Trower, W. P.; Karev, A. I.; Melekhin, V. N.; Shvedunov, V. I.; Sobenin, N. P.

    1995-05-01

    The pulsed light source for carbon/nitrogen cameras developed to image concealed narcotics/explosives is described. This race-track microtron will produce 40 mA pulses of 70 MeV electrons, have minimal size and weight, and maximal ruggedness and reliability, so that it can be transported on a truck.

  10. Nitrogen fertilization effects on irrigated no-till corn production and soil carbon and nitrogen

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Converting from conventional tillage (CT) to a no-till (NT) production system can affect N requirements for optimizing corn (Zea mays L.) yields while enhancing soil organic carbon (SOC) and N levels. Nitrogen fertilization impacts on irrigated, NT continuous-corn grain, stalk, cob, and stover yiel...

  11. Spatial heterogeneity of forest soil carbon and nitrogen controls nitrogen transformations and trace gas production

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Small-scale spatial heterogeneity of soil nitrogen (N) and carbon (C) pools and net transformation processes in forested ecosystems are not well understood. Two forests in central Oregon (Black Butte and Santiam Pass) were used to test the hypothesis that spatial distribution of soil nutrients cont...

  12. Covalently bonded three-dimensional carbon nanotube solids via boron induced nanojunctions

    SciTech Connect

    Sumpter, Bobby G; Meunier, Vincent; Terrones Maldonado, Humberto; Terrones Maldonado, Mauricio; Ajayan, Pullikel M; Hashim, Daniel; Romo Herrera, Jose M; Cullen, David; Munoz-Sandoval, Emilio; Smith, David J; Vajtai, Robert; Roy, Ajit K; Ganguli, Sabyasachi; Kelkhoff, Doug; Suttle, Joesph; Lezzi, Peter; Hahm, Gwan; Narayanan, Narayanan

    2012-01-01

    The establishment of covalent junctions between carbon nanotubes (CNTs) and the modification of their straight tubular morphology are two strategies needed to successfully synthesize nanotube-based three-dimensional (3D) frameworks exhibiting superior material properties. Engineering such 3D structures in scalable synthetic processes still remains a challenge. This work pioneers the bulk synthesis of 3D macroscale nanotube elastic solids directly via a boron-doping strategy during chemical vapor deposition, which influences the formation of atomic-scale elbow junctions and nanotube covalent interconnections. Detailed elemental analysis revealed that the elbow junctions are preferred sites for excess boron atoms, indicating the role of boron and curvature in the junction formation mechanism, in agreement with our first principle theoretical calculations. Exploiting this material s ultra-light weight, super-hydrophobicity, high porosity, thermal stability, and mechanical flexibility, the strongly oleophilic sponge-like solids are demonstrated as unique reusable sorbent scaffolds able to efficiently remove oil from contaminated seawater even after repeated use.

  13. Covalently bonded three-dimensional carbon nanotube solids via boron induced nanojunctions

    PubMed Central

    Hashim, Daniel P.; Narayanan, Narayanan T.; Romo-Herrera, Jose M.; Cullen, David A.; Hahm, Myung Gwan; Lezzi, Peter; Suttle, Joseph R.; Kelkhoff, Doug; Muñoz-Sandoval, E.; Ganguli, Sabyasachi; Roy, Ajit K.; Smith, David J.; Vajtai, Robert; Sumpter, Bobby G.; Meunier, Vincent; Terrones, Humberto; Terrones, Mauricio; Ajayan, Pulickel M.

    2012-01-01

    The establishment of covalent junctions between carbon nanotubes (CNTs) and the modification of their straight tubular morphology are two strategies needed to successfully synthesize nanotube-based three-dimensional (3D) frameworks exhibiting superior material properties. Engineering such 3D structures in scalable synthetic processes still remains a challenge. This work pioneers the bulk synthesis of 3D macroscale nanotube elastic solids directly via a boron-doping strategy during chemical vapour deposition, which influences the formation of atomic-scale “elbow” junctions and nanotube covalent interconnections. Detailed elemental analysis revealed that the “elbow” junctions are preferred sites for excess boron atoms, indicating the role of boron and curvature in the junction formation mechanism, in agreement with our first principle theoretical calculations. Exploiting this material’s ultra-light weight, super-hydrophobicity, high porosity, thermal stability, and mechanical flexibility, the strongly oleophilic sponge-like solids are demonstrated as unique reusable sorbent scaffolds able to efficiently remove oil from contaminated seawater even after repeated use. PMID:22509463

  14. Removal of boron from aqueous solution using magnetic carbon nanotube improved with tartaric acid

    PubMed Central

    2014-01-01

    Boron removal capacity of multi-walled carbon nanotubes (MWCNTs) modified with tartaric acid was investigated in this study. Modification of MWCNTs with tartaric acid was confirmed by Boehm surface chemistry method and fourier transform infra-red (FT-IR) spectroscopy. Experiments were performed to determine the adsorption isotherm and adsorption thermodynamic parameters of boron adsorption on tartaric acid modified MWCNTs (TA-MWCNTs). The effect of variables including initial pH, dosage of adsorbent, contact time and temperature was investigated. Analysis of data showed that adsorption equilibrium could be better described by Freundlich isotherm and the maximum adsorption capacities obtained at the pH of 6.0 was 1.97 mg/g. The estimated thermodynamic values of free energy (ΔG°), entropy (ΔS°) and enthalpy (ΔH°) indicated a spontaneous and an endothermic process. Furthermore, the TA-MWCNTs was magnetized for separation of boron-contaminated adsorbent from aqueous solution by applying magnetic field. The results showed that magnetic TA-MWCNTs particles were separated effectively after adsorption from contaminated water. PMID:24393401

  15. Facile synthesis of boronic acid-functionalized magnetic carbon nanotubes for highly specific enrichment of glycopeptides

    NASA Astrophysics Data System (ADS)

    Ma, Rongna; Hu, Junjie; Cai, Zongwei; Ju, Huangxian

    2014-02-01

    A stepwise strategy was developed to synthesize boronic acid functionalized magnetic carbon nanotubes (MCNTs) for highly specific enrichment of glycopeptides. The MCNTs were synthesized by a solvothermal reaction of Fe3+ loaded on the acid-treated CNTs and modified with 1-pyrenebutanoic acid N-hydroxysuccinimidyl ester (PASE) to bind aminophenylboronic acid (APBA) via an amide reaction. The introduction of PASE could bridge the MCNT and APBA, suppress the nonspecific adsorption and reduce the steric hindrance among the bound molecules. Due to the excellent structure of the MCNTs, the functionalization of PASE and then APBA on MCNTs was quite simple, specific and effective. The glycopeptides enrichment and separation with a magnetic field could be achieved by their reversible covalent binding with the boronic group of APBA-MCNTs. The exceptionally large specific surface area and the high density of boronic acid groups of APBA-MCNTs resulted in rapid and highly efficient enrichment of glycopeptides, even in the presence of large amounts of interfering nonglycopeptides. The functional MCNTs possessed high selectivity for enrichment of 21 glycopeptides from the digest of horseradish peroxidase demonstrated by MALDI-TOF mass spectrometric analysis showing more glycopeptides detected than the usual 9 glycopeptides with commercially available APBA-agarose. The proposed system showed better specificity for glycopeptides even in the presence of non-glycopeptides with 50 times higher concentration. The boronic acid functionalized MCNTs provide a promising selective enrichment platform for precise glycoproteomic analysis.A stepwise strategy was developed to synthesize boronic acid functionalized magnetic carbon nanotubes (MCNTs) for highly specific enrichment of glycopeptides. The MCNTs were synthesized by a solvothermal reaction of Fe3+ loaded on the acid-treated CNTs and modified with 1-pyrenebutanoic acid N-hydroxysuccinimidyl ester (PASE) to bind aminophenylboronic acid

  16. Effects of strain on carbon donors and acceptors in hexagonal boron nitride monolayers

    NASA Astrophysics Data System (ADS)

    Fujimoto, Yoshitaka; Saito, Susumu

    2016-01-01

    We present first-principles density functional calculations that clarify the electronic properties of carbon defects in hexagonal boron nitride (h -BN) monolayers under biaxially applied strains. We find that strain can control the ionization energies of both donor and acceptor states. Furthermore, we also find that strain can lead to the dramatic change in conduction channel properties of donor states due to the interchange of the conduction-band-minimum state with the nearly-free-electron state. We also report the simulated scanning tunneling microscopy (STM) images of carbon defects in h -BN monolayers for experimental identification of those defects. We show that the STM images strongly reflect distinctive spatial distributions of local density of states around carbon defects depending on the substitution sites and thereby they could be identified by using STM experiments.

  17. Effect of carbon and boron on the high-temperature oxidation of silicon carbide

    SciTech Connect

    Fergus, J.W.; Worrel, W.L.

    1995-07-01

    Silicon carbide has good oxidation resistance, due to the formation of a protective silica layer. Although amorphous silica is an excellent oxygen barrier, it is very sensitive to impurity elements, which affect its viscosity, oxygen diffusivity,a nd crystallization kinetics. This paper compares the oxidation rates of CVD SiC, sintered {alpha}-SiC, and CVD SiC-coated graphite in 1 atm oxygen at 1,500 C to determine the effects of small additions of boron and carbon. the formation of bubbles in the silica scale formed on sintered {alpha}-Sic in oxygen between 1,230 and 1,550 C is also discussed.

  18. The deposition of boron nitride and carbon films on silica glass fibers

    SciTech Connect

    Smith, W.L.; Michalske, T.A.; Rye, R.R.

    1993-11-01

    A chemical vapor deposition technique is used to produce amorphous boron nitride and carbon thin films on high strength silica glass fibers. In this method, the fiber is drawn under ultra high vacuum conditions and low pressure process gases, in the presence of a hot tungsten filament, are used to grow films at low substrate temperatures. Films deposited with this technique do not degrade the intrinsic pristine strength of the silica fibers under dry conditions and, when stressed in chemically aggressive environments, act as effective barrier coatings.

  19. Thermal properties of carbon-boron-titanium compounds as plasma facing materials

    NASA Astrophysics Data System (ADS)

    Tanabe, T.; Baba, T.; Ono, A.; Fujitsuka, M.; Shikama, T.; Shinno, H.

    1992-09-01

    The carbon-boron-titanium compounds were synthesized by hot press and subsequent HIP (high temperature isostatic press) treatment. The thermal diffusivity of the compounds was measured by the advanced laser-flash technique, and the heat-load shock resistance was evaluated with a low energy and high current electron beam. The obtained results were analyzed as a function of chemical composition of the compounds. The so-called gradient material was formed to attempt to improve the heat-load shock resistance.

  20. Coaxial nanocable: silicon carbide and silicon oxide sheathed with boron nitride and carbon

    PubMed

    Zhang; Suenaga; Colliex; Iijima

    1998-08-14

    Multielement nanotubes comprising multiple phases, with diameters of a few tens of nanometers and lengths up to 50 micrometers, were successfully synthesized by means of reactive laser ablation. The experimentally determined structure consists of a beta-phase silicon carbide core, an amorphous silicon oxide intermediate layer, and graphitic outer shells made of boron nitride and carbon layers separated in the radial direction. The structure resembles a coaxial nanocable with a semiconductor-insulator-metal (or semiconductor-insulator-semiconductor) geometry and suggests applications in nanoscale electronic devices that take advantage of this self-organization mechanism for multielement nanotube formation. PMID:9703508

  1. Long-term natural attenuation of carbon and nitrogen within a groundwater plume after removal of the treated wastewater source

    USGS Publications Warehouse

    Repert, D.A.; Barber, L.B.; Hess, K.M.; Keefe, S.H.; Kent, D.B.; LeBlanc, D.R.; Smith, R.L.

    2006-01-01

    Disposal of treated wastewater for more than 60 years onto infiltration beds on Cape Cod, Massachusetts produced a groundwater contaminant plume greater than 6 km long in a surficial sand and gravel aquifer. In December 1995 the wastewater disposal ceased. A long-term, continuous study was conducted to characterize the post-cessation attenuation of the plume from the source to 0.6 km downgradient. Concentrations and total pools of mobile constituents, such as boron and nitrate, steadily decreased within 1-4 years along the transect. Dissolved organic carbon loads also decreased, but to a lesser extent, particularly downgradient of the infiltration beds. After 4 years, concentrations and pools of carbon and nitrogen in groundwater were relatively constant with time and distance, but substantially elevated above background. The contaminant plume core remained anoxic for the entire 10-year study period; temporal patterns of integrated oxygen deficit decreased slowly at all sites. In 2004, substantial amounts of total dissolved carbon (7 mol C m-2) and fixed (dissolved plus sorbed) inorganic nitrogen (0.5 mol N m-2) were still present in a 28-m vertical interval at the disposal site. Sorbed constituents have contributed substantially to the dissolved carbon and nitrogen pools and are responsible for the long-term persistence of the contaminant plume. Natural aquifer restoration at the discharge location will take at least several decades, even though groundwater flow rates and the potential for contaminant flushing are relatively high.

  2. Boron nitride: Composition, optical properties and mechanical behavior

    NASA Technical Reports Server (NTRS)

    Pouch, John J.; Alterovitz, Samuel A.; Miyoshi, Kazuhisa; Warner, Joseph D.

    1987-01-01

    A low energy ion beam deposition technique was used to grow boron nitride films on quartz, germanium, silicon, gallium arsenide, and indium phosphate. The film structure was amorphous with evidence of a hexagonal phase. The peak boron concentration was 82 at %. The carbon and oxygen impurities were in the 5 to 8 at % range. Boron-nitrogen and boron-boron bonds were revealed by X-ray photoelectron spectroscopy. The index of refraction varied from 1.65 to 1.67 for films deposited on III-V compound semiconductors. The coefficient of friction for boron nitride in sliding contact with diamond was less than 0.1. The substrate was silicon.

  3. Carbon and nitrogen cycling in thermally heated sediments

    NASA Astrophysics Data System (ADS)

    Meyer-Dombard, D. R.; Burton, M.; Vennelakanti, S.; Havig, J. R.; Shock, E.

    2009-12-01

    Hydrothermally heated sediment environments, such as are found in abundance throughout Yellowstone National Park, host fully functional microbial ecosystems. As with any ecosystem, both sources and sinks of carbon, nitrogen, and a myriad of other nutrients and energy-driving factors must be supplied. While we know microbial communities in hydrothermal environments can be surprisingly diverse, we know little about basic ecological functions such as carbon and nitrogen cycling. Previous work has shown that carbon cycling in one hot spring in Yellowstone National Park [“Bison Pool”] and its associated runoff channel functions as a complex system. Analysis of carbon and nitrogen isotopes in sediments and biofilms across a temperature and chemical gradient at this location revealed that the four best studied carbon fixation pathways [Calvin, reverse tricarboxylic acid, acetyl-CoA, 3-hydroxypropionate cycles] may all be functioning in this system, and nitrogen fixation varies across the chemosynthetic/photosynthetic ecotone [1]. Microcosm experiments using biofilms from this hot spring as inoculae with 13C labeled carbon substrates indicate heterotrophic growth [2]. In addition, metagenomic analysis of environmental DNA has indicated the presence of genes involved in carbon fixation [both phototrophic and autotrophic], and heterotrophy, as well as nitrogen fixation [3]. Studies from other Yellowstone locations have also found genetic evidence for carbon and nitrogen fixation [4, 5]. Of particular interest is the role of individuals in carbon and nitrogen cycling as environmental conditions suitable for chemosynthetic and photosynthetic growth vary. This study explores the diversity of cbbM/cbbL [Calvin cycle], aclB/oor/porA [rTCA cycle], nifH [nitrogen fixation], nirK [nitrite reduction] and amoA [ammonia oxidation] genes across a variety of Yellowstone environments. The transition of genetic diversity within sediments and biofilms is focused on the chemosynthetic

  4. Methods of detection and identificationoc carbon- and nitrogen-containing materials

    DOEpatents

    Karev, Alexander Ivanovich; Raevsky, Valery Georgievich; Dzhalivyan, Leonid Zavenovich; Brothers, Louis Joseph; Wilhide, Larry K

    2013-11-12

    Methods for detecting and identifying carbon- and/or nitrogen-containing materials are disclosed. The methods may comprise detection of photo-nuclear reaction products of nitrogen and carbon to detect and identify the carbon- and/or nitrogen-containing materials.

  5. Boron isotope evidence for oceanic carbon dioxide leakage during the last deglaciation.

    PubMed

    Martínez-Botí, M A; Marino, G; Foster, G L; Ziveri, P; Henehan, M J; Rae, J W B; Mortyn, P G; Vance, D

    2015-02-12

    Atmospheric CO2 fluctuations over glacial-interglacial cycles remain a major challenge to our understanding of the carbon cycle and the climate system. Leading hypotheses put forward to explain glacial-interglacial atmospheric CO2 variations invoke changes in deep-ocean carbon storage, probably modulated by processes in the Southern Ocean, where much of the deep ocean is ventilated. A central aspect of such models is that, during deglaciations, an isolated glacial deep-ocean carbon reservoir is reconnected with the atmosphere, driving the atmospheric CO2 rise observed in ice-core records. However, direct documentation of changes in surface ocean carbon content and the associated transfer of carbon to the atmosphere during deglaciations has been hindered by the lack of proxy reconstructions that unambiguously reflect the oceanic carbonate system. Radiocarbon activity tracks changes in ocean ventilation, but not in ocean carbon content, whereas proxies that record increased deglacial upwelling do not constrain the proportion of upwelled carbon that is degassed relative to that which is taken up by the biological pump. Here we apply the boron isotope pH proxy in planktic foraminifera to two sediment cores from the sub-Antarctic Atlantic and the eastern equatorial Pacific as a more direct tracer of oceanic CO2 outgassing. We show that surface waters at both locations, which partly derive from deep water upwelled in the Southern Ocean, became a significant source of carbon to the atmosphere during the last deglaciation, when the concentration of atmospheric CO2 was increasing. This oceanic CO2 outgassing supports the view that the ventilation of a deep-ocean carbon reservoir in the Southern Ocean had a key role in the deglacial CO2 rise, although our results allow for the possibility that processes operating in other regions may also have been important for the glacial-interglacial ocean-atmosphere exchange of carbon. PMID:25673416

  6. Carbon and Nitrogen Chemistry of Lodranites: Relationship to Acapulco?

    NASA Astrophysics Data System (ADS)

    Grady, M. M.; Franchi, I. A.; Pillinger, C. T.

    1993-07-01

    Recent studies on the mineralogy, petrology, and oxygen isotopic composition of lodranites and acapulcoites indicate that these meteorites are probably derived from a common parent body, but experienced different degrees of partial melting [1,2]. Ar-Ar chronometry implies that lodranites were heated ca. 100 degrees C higher than acapulcoites, and cooled more slowly [3], however measurement of nitrogen and xenon in Acapulco [4,5] shows that volatiles are not equilibrated between different phases within the meteorite, hence its thermal history has been complex. The aim of this study is to determine the carbon and nitrogen chemistry of lodranites, for comparison with Acapulco, to indicate the effect that differing thermal histories might have had on the volatile inventories of these meteorites. The carbon chemistry of Acapulco has been described previously [6]. The meteorite contains ca. 400 ppm indigenous carbon, distributed between two major phases: graphite and carbides. Graphite has been identified petrographically in Acapulco [7], where it is intimately associated with metal. In contrast, both Lodran and MAC 88177 contain much lower quantities of indigenous carbon: approximately 100 ppm and 38 ppm respectively, released in decreasing amounts up to 1200 degrees C. In Lodran, delta^13C rises almost monotonically, from -25 per mil at 600 degrees C to -12 per mil at 1200 degrees C; total delta^13C is ca. -23 per mil. Neither meteorite shows evidence for the occurrence of graphite. Nitrogen released by pyrolysis of Acapulco totals ca. 2.8 ppm [4,5], and is resolvable into two components, with delta^15N ca. +10 per mil and -120 per mil [8]. The first component is, as yet, unidentified, but the second is believed to be associated with the metal fraction [8]. The procedure used herein, of several combustion steps below 500 degrees C to remove contaminants, followed by high resolution combustion up to 1200 degrees C, would also resolve discrete nitrogen-bearing components

  7. Boron Isotope Intercomparison Project (BIIP): Development of a new carbonate standard for stable isotopic analyses

    NASA Astrophysics Data System (ADS)

    Gutjahr, Marcus; Bordier, Louise; Douville, Eric; Farmer, Jesse; Foster, Gavin L.; Hathorne, Ed; Hönisch, Bärbel; Lemarchand, Damien; Louvat, Pascale; McCulloch, Malcolm; Noireaux, Johanna; Pallavicini, Nicola; Rodushkin, Ilia; Roux, Philippe; Stewart, Joseph; Thil, François; You, Chen-Feng

    2014-05-01

    Boron consists of only of two isotopes with a relatively large mass difference (~10 %). It is also volatile in acidic media and prone to contamination during analytical treatment. Nevertheless, an increasing number of isotope laboratories are successfully using boron isotope compositions (expressed in δ11B) in marine biogenic carbonates to reconstruct seawater pH. Recent interlaboratory comparison efforts [1] highlighted the existence of a relatively high level of disagreement between laboratories when measuring such material, so in order to further strengthen the validity of this carbonate system proxy, appropriate reference materials need to be urgently characterised. We describe here the latest results of the Boron Isotope Intercomparison Project (BIIP) where we aim to characterise the boron isotopic composition of two marine carbonates: Japanese Geological Survey carbonate standard materials JCp-1 (coral porites) [2] and JCt-1 (Giant Clam) [3]. This boron isotope interlaboratory comparison study has two aims: (i) to assess to what extent chemical pre-treatment, aimed at removing organic material, can influence the resulting carbonate δ11B; (ii) to determine the isotopic composition of the two reference materials with a number of analytical techniques to provide the community with reference δ11B values for JCp-1 and JCt-1 and to further explore any differences related to analytical technique. In total eight isotope laboratories participated, of which one determined δ11B via negative thermal ionisation mass spectrometry (NTIMS) and seven used multi collector inductively coupled plasma mass spectrometry (MC-ICPMS). For the latter several different introduction systems and chemical purification methods were used. Overall the results are strikingly consistent between the participating labs. The oxidation of organic material slightly lowered the median δ11B by ~0.1 ‰ for both JCp-1 and JCt-1, while the mean δ11B of all labs for both standards was lowered by 0

  8. Controlled release of alendronate from nitrogen-doped mesoporous carbon

    DOE PAGESBeta

    Saha, Dipendu; Spurri, Amanda; Chen, Jihua; Hensley, Dale K.

    2016-04-13

    With this study, we have synthesized a nitrogen doped mesoporous carbon with the BET surface area of 1066 m2/g, total pore volume 0.6 cm3/g and nitrogen content of 0.5%. Total alendronate adsorption in this carbon was ~5%. The release experiments were designed in four different media with sequential pH values of 1.2, 4.5, 6.8 and 7.4 for 3, 1, 3 and 5 h, respectively and at 37 °C to imitate the physiological conditions of stomach, duodenum, small intestine and colon, respectively. Release of the drug demonstrated a controlled fashion; only 20% of the drug was released in the media withmore » pH = 1.2, whereas 64% of the drug was released in pH = 7.4. This is in contrary to pure alendronate that was completely dissolved within 30 min in the first release media (pH = 1.2) only. The relatively larger uptake of alendronate in this carbon and its sustained fashion of release can be attributed to the hydrogen bonding between the drug and the nitrogen functionalities on carbon surface. Based on this result, it can be inferred that this formulation may lower the side effects of oral delivery of alendronate.« less

  9. Simultaneous tracing of carbon and nitrogen isotopes in human cells.

    PubMed

    Nilsson, Roland; Jain, Mohit

    2016-05-24

    Stable isotope tracing is a powerful method for interrogating metabolic enzyme activities across the metabolic network of living cells. However, most studies of mammalian cells have used (13)C-labeled tracers only and focused on reactions in central carbon metabolism. Cellular metabolism, however, involves other biologically important elements, including nitrogen, hydrogen, oxygen, phosphate and sulfur. Tracing stable isotopes of such elements may help shed light on poorly understood metabolic pathways. Here, we demonstrate the use of high-resolution mass spectrometry to simultaneously trace carbon and nitrogen metabolism in human cells cultured with (13)C- and (15)N-labeled glucose and glutamine. To facilitate interpretation of the complex isotopomer data generated, we extend current methods for metabolic flux analysis to handle multivariate mass isotopomer distributions (MMIDs). We find that observed MMIDs are broadly consistent with known biochemical pathways. Whereas measured (13)C MIDs were informative for central carbon metabolism, (15)N isotopes provided evidence for nitrogen-carrying reactions in amino acid and nucleotide metabolism. This computational and experimental methodology expands the scope of metabolic flux analysis beyond carbon metabolism, and may prove important to understanding metabolic phenotypes in health and disease. PMID:27098229

  10. Integrating the nitrogen cycle in carbon and GHG observation systems

    NASA Astrophysics Data System (ADS)

    Kutsch, W. L.; Brummer, C.

    2013-12-01

    Nitrogen is an important factor for the regulation of carbon and GHG fluxes within ecosystems and between ecosystems and the atmosphere. Nitrogen fertilization is important for high agricultural yields but also increases N2O emissions. In Germany, e.g., N2O emissions from agriculture comprise about 6 % of the total GHG inventory. Nitrogen deposition may enhance productivity of ecosystems (e.g. forests, natural grasslands or wetlands) but may also change community structure - in particular in ecosystems that are adapted to low nitrogen availability. It also can lead to increased N2O emissions. Global nitrogen fluxes due to the trade of agricultural products may concentrate nitrogen in specific areas (e.g. in areas with high animal stock). In these areas increased N2O emissions are to be expected. The Thünen Institute of Climate-Smart Agriculture drives parts of the German ICOS consortium with a special focus on agricultural sites or indirect effects of agriculture on GHG emissions. We propose a concept to integrate nitrogen into research infrastructures for GHG monitoring. A conceptual frame will identify the most important parameters of the N cycle. Data from the CarboEurope and NitroEurope core site Gebesee (crop) will be presented to show first integrative results.Finally, first experiences with new technologies will be presented, comprising quantum cascade laser measurements of N2O and ammonia used with eddy covariance (EC) and chambers and EC measurements of total reactive nitrogen with the TRANC methodology (Marx et al. 2012).

  11. Oxygen adsorption characteristics on hybrid carbon and boron-nitride nanotubes.

    PubMed

    Liu, Haining; Turner, C Heath

    2014-05-30

    In this work, first-principles density functional theory (DFT) is used to predict oxygen adsorption on two types of hybrid carbon and boron-nitride nanotubes (CBNNTs), zigzag (8,0), and armchair (6,6). Although the chemisorption of O2 on CBNNT(6,6) is calculated to be a thermodynamically unfavorable process, the binding of O2 on CBNNT(8,0) is found to be an exothermic process and can form both chemisorbed and physisorbed complexes. The CBNNT(8,0) has very different O2 adsorption properties compared with pristine carbon nanotubes (CNTs) and boron-nitride nanotube (BNNTs). For example, O2 chemisorption is significantly enhanced on CBNNTs, and O2 physisorption complexes also show stronger binding, as compared to pristine CNTs or BNNTs. Furthermore, it is found that the O2 adsorption is able to increase the conductivity of CBNNTs. Overall, these properties suggest that the CBNNT hybrid nanotubes may be useful as a gas sensor or as a catalyst for the oxygen reduction reaction. PMID:24659221

  12. Electrochemical behavior of triflusal, aspirin and their metabolites at glassy carbon and boron doped diamond electrodes.

    PubMed

    Enache, Teodor Adrian; Fatibello-Filho, Orlando; Oliveira-Brett, Ana Maria

    2010-08-01

    The electrochemical behavior of triflusal (TRF) and aspirin (ASA), before and after hydrolysis in water and in alkaline medium using two different electrode surfaces, glassy carbon and boron doped diamond, was study by differential pulse voltammetry over a wide pH range. The hydrolysis products are 2-(hydroxyl)-4-(trifluoromethyl)-benzoic acid (HTB) for triflusal and salicylic acid (SA) for aspirin, which in vivo represent their main metabolites. The hydrolysis processes were also followed by spectrophotometry. The UV results showed complete hydrolysis after one hour for TRF and after two hours for ASA in alkaline solution. The glassy carbon electrode enables only indirect determination of TRF and ASA through the electrochemical detection of their hydrolysis products HTB and SA, respectively. The oxidation processes of HTB and SA are pH dependent and involve different numbers of electrons and protons. Moreover, the difference between the oxidation peak potential of SA and HTB was equal to 100 mV in the studied pH range from 1 to 8 due to the CF3 of the aromatic ring of HTB molecule. Due to its wider oxidation potential range, the boron doped diamond electrode was used to study the direct oxidation of TRF and ASA, as well as of their respective metabolites HTB and SA. PMID:20402644

  13. Engineering radial deformations in single-walled carbon and boron nitride nanotubes using ultrathin nanomembranes.

    PubMed

    Zheng, Meng; Zou, Lian-Feng; Wang, Howard; Park, Cheol; Ke, Changhong

    2012-02-28

    Radial deformations of carbon and boron-nitride nanotubes are of great importance to their respective electronic properties and applications. In this paper, we present a simple and practical approach of engineering radial deformations in single-walled carbon and boron-nitride nanotubes (SWCNTs and SW-BNNTs) through covering individual nanotubes lying on flat substrates with subnanometer-thick monolayer graphene oxide (GO) nanomembranes. The GO membrane conforms to and transversely compresses the underlying nanotube as a result of its adhesion binding interaction with the substrate. Our atomic force microscopy (AFM) imaging measurements reveal that the engineered net radial deformations of both types of tubes increase with the tube diameter and are more for SW-BNNTs compared with SWCNTs of the same tube diameter. Our results capture the net cross-section height reductions of up to 44.1% for SW-BNNTs and up to 29.7% for SWCNTs. Our work clearly demonstrates the effectiveness of our proposed approach for engineering and controlling the radial deformation in one-dimensional tubular nanostructures and opens a promising route for mechanical tuning of their electronic properties for novel nanoelectronics applications. PMID:22280493

  14. In Situ Mechanical Property Measurements of Amorphous Carbon-Boron Nitride Nanotube Nanostructures

    NASA Technical Reports Server (NTRS)

    Kim, Jae-Woo; Lin, Yi; Nunez, Jennifer Carpena; Siochi, Emilie J.; Wise, Kristopher E.; Connell, John W.; Smith, Michael W.

    2011-01-01

    To understand the mechanical properties of amorphous carbon (a-C)/boron nitride nanotube (BNNT) nanostructures, in situ mechanical tests are conducted inside a transmission electron microscope equipped with an integrated atomic force microscope system. The nanotube structure is modified with amorphous carbon deposited by controlled electron beam irradiation. We demonstrate multiple in situ tensile, compressive, and lap shear tests with a-C/BNNT hybrid nanostructures. The tensile strength of the a-C/BNNT hybrid nanostructure is 5.29 GPa with about 90 vol% of a-C. The tensile strength and strain of the end-to-end joint structure with a-C welding is 0.8 GPa and 5.2% whereas the lap shear strength of the side-by-side joint structure with a-C is 0.25 GPa.

  15. In situ mechanical property measurements of amorphous carbon-boron nitride nanotube nanostructures

    NASA Astrophysics Data System (ADS)

    Kim, Jae-Woo; Carpena Núñez, Jennifer; Siochi, Emilie J.; Wise, Kristopher E.; Lin, Yi; Connell, John W.; Smith, Michael W.

    2012-01-01

    To understand the mechanical properties of amorphous carbon (a-C)/boron nitride nanotube (BNNT) nanostructures, in situ mechanical tests are conducted inside a transmission electron microscope equipped with an integrated atomic force microscope system. The nanotube structure is modified with amorphous carbon deposited by controlled electron beam irradiation. We demonstrate multiple in situ tensile, compressive, and lap shear tests with a-C/BNNT hybrid nanostructures. The tensile strength of the a-C/BNNT hybrid nanostructure is 5.29 GPa with about 90 vol% of a-C. The tensile strength and strain of the end-to-end joint structure with a-C welding is 0.8 GPa and 5.2% whereas the lap shear strength of the side-by-side joint structure with a-C is 0.25 GPa.

  16. Effect of carbon monoxide and nitrogen dioxide on ICR mice

    NASA Technical Reports Server (NTRS)

    Hilado, C. J.; Cumming, H. J.

    1977-01-01

    Times to incapacitation and death and LC(50) values were determined for male ICR mice exposed to different concentration of carbon monoxide for 30 min and of nitrogen dioxide for 10 min in a 4.2 liter hemispherical chamber. The data indicate that ICR mice are more resistant to these two toxicants than Swiss albino mice. The carbon monoxide LC(50) for a 30-min exposure was about 8,000 ppm for ICR mice compared to 3,570 ppm for Swiss albino mice. The nitrogen dioxide LC(50) for a 10-min exposure was above 2,000 ppm for ICR mice compared to about 1,000 ppm for Swiss albino mice.

  17. Effect of reaction conditions on methyl red degradation mediated by boron and nitrogen doped TiO2

    NASA Astrophysics Data System (ADS)

    Galenda, A.; Crociani, L.; Habra, N. El; Favaro, M.; Natile, M. M.; Rossetto, G.

    2014-09-01

    Nowadays the employment of renewable and sustainable energy sources, and solar light as main option, becomes an urgent need. Photocatalytic processes received great attention in wastewater treatment due to their cheapness, environmental compatibility and optimal performances. Despite the general low selectivity of the photocatalysts, an accurate optimisation of the operational parameters needs to be carried out in order to maximise the process yield. Because of this reason, the present contribution aims to deepen either the knowledge in boron and/or nitrogen doped TiO2-based systems and their employment in methyl red removal from aqueous solutions. The samples were obtained by coprecipitation and characterised by XRD, SEM, BET specific surface area, UV-vis and XPS techniques. The catalytic activity was for the first time carefully evaluated with respect to methyl red photodegradation in different conditions as a function of working pH, counter-ions and pre-adsorption time. An ad-hoc study was performed on the importance of the pre-adsorption of the dye, suggesting that an extended adsorption is useless for the catalyst photoactivity, while a partial coverage is preferable. The photocatalytic tests demonstrate the positive influence of boron doping in photo-activated reactions and the great importance of the operational parameters with respect to the simple methyl red bleaching rather than the overall pollutant mineralisation. It is proved, indeed, that different working pH, acidifying means and substrate pre-adsorption time can enhance or limit the catalyst performances with respect to the complete pollutant degradation rather than its partial breakage.

  18. Vacancy Mediated Mechanism of Nitrogen Substitution in Carbon Nanotubes

    NASA Technical Reports Server (NTRS)

    Srivastava, Deepak; Menon, Madhu; Sadanadan, Bindu; Rao, Apparao M.

    2003-01-01

    Nitrogen substitution reaction in a graphene sheet and carbon nanotubes of different diameter are investigated using the generalized tight-binding molecular dynamics method. The formation of a vacancy in curved graphene sheet or a carbon nanotube is found to cause a curvature dependent local reconstruction of the surface. Our simulations and analysis show that vacancy mediated N substitution (rather than N chemisorption) is favored on the surface of nanotubes with diameter larger than 8 nm. This predicted value of the critical minimum diameter for N incorporation is confirmed by experimental results presented.

  19. Autophagy controls carbon, nitrogen, and redox homeostasis in plants.

    PubMed

    Masclaux-Daubresse, C

    2016-05-01

    During leaf senescence, autophagy is essential for nutrient recycling and remobilization, and for plant productivity. Metabolome and transcriptome studies performed on autophagy mutants revealed major disorders in nitrogen, carbon, and redox metabolisms. Analysis showed that autophagy mutants are depleted of antioxidant anthocyanin molecules. Transcriptome analysis revealed that the depletion of anthocyanin is due to the downregulation of the master genes encoding the enzymes and regulatory proteins involved in the flavonoid pathway. The hyperaccumulation of salicylic acid and the depletion of anthocyanin in autophagy mutants might result from the rerouting of carbon resources in the phenylpropanoid pathway and amplify oxidative stress in autophagy mutants. PMID:25484096

  20. Glacial-interglacial Changes in Ocean Carbon Chemistry constrained by Boron Isotopes, Trace Elements, and Modelling

    NASA Astrophysics Data System (ADS)

    Rae, J. W. B.; Adkins, J. F.; Foreman, A. D.; Charles, C.

    2014-12-01

    Deep ocean carbon storage and release is commonly invoked to explain glacial-interglacial CO2 cycles, but records of the carbonate chemistry of the glacial ocean have, until recently, been scarce. Here we present new boron isotope (δ11B) and trace metal data from benthic foraminifera from a suite of 15 cores from the South Atlantic from depths ranging from 1500 to 4000 m. These records show distinct changes in the water column depth structure of these tracers between the last glacial maximum (LGM) and late Holocene. Comparison of these paired trace element and isotope ratios reveals new insights to the shared and individual controls on tracers including Li/Ca, Sr/Ca, U/Ca, Mg/Li and δ11B. We further examine these data using a recently developed tracer fields modelling approach (Lund et al. 2011). This has previously been applied to δ18O data to investigate changes in circulation at the LGM. Here we extend this method to non-conservative isotopic and trace elemental tracers, allowing us to constrain the roles of circulation, the biological pump of organic carbon and CaCO3, and carbonate compensation, in setting deep ocean carbon storage at the LGM. Lund, D. C., J. F. Adkins, and R. Ferrari (2011), Abyssal Atlantic circulation during the Last Glacial Maximum: Constraining the ratio between transport and vertical mixing, Paleoceanography, 26, PA1213, doi:10.1029/2010PA001938.

  1. Can trans-polyacetylene be formed on single-walled carbon-doped boron nitride nanotubes?

    PubMed

    Chen, Ying; Wang, Hong-xia; Zhao, Jing-xiang; Cai, Qing-hai; Wang, Xiao-guang; Wang, Xuan-zhang

    2012-07-01

    Recently, the grafting of polymer chains onto nanotubes has attracted increasing attention as it can potentially be used to enhance the solubility of nanotubes and in the development of novel nanotube-based devices. In this article, based on density functional theory (DFT) calculations, we report the formation of trans-polyacetylene on single-walled carbon-doped boron nitride nanotubes (BNNTs) through their adsorption of a series of C(2)H(2) molecules. The results show that, rather than through [2 + 2] cycloaddition, an individualmolecule would preferentially attach to a carbon-doped BNNT via "carbon attack" (i.e., a carbon in the C(2)H(2) attacks a site on the BNNT). The adsorption energy gradually decreases with increasing tube diameter. The free radical of the carbon-doped BNNT is almost completely transferred to the carbon atom at the end of the adsorbed C(2)H(2) molecule. When another C(2)H(2) molecule approaches the carbon-doped BNNT, it is most energetically favorable for this C(2)H(2) molecule to be adsorbed at the end of the previously adsorbed C(2)H(2) molecule, and so on with extra C(2)H(2) molecules, leading to the formation of polyacetylene on the nanotube. The spin of the whole system is always localized at the tip of the polyacetylene formed, which initiates the adsorption of the incoming species. The present results imply that carbon-doped BNNT is an effective "metal-free" initiator for the formation of polyacetylene. PMID:22271098

  2. Synthesis and electronic properties of nitrogen-bridged dimers of boron subphthalocyanines.

    PubMed

    Guilleme, J; González-Rodríguez, D; Torres, T

    2016-07-28

    The synthesis of new symmetric and unsymmetric axial nitrogen-bridged dimers of subphthalocyanines (μ-azo dimers) has been carried out via activated triflate intermediates. Their spectroscopic and electrochemical properties have been studied and compared to their μ-oxo analogues. PMID:27416999

  3. Electrical and Electrochemical Properties of Nitrogen-Containing Tetrahedral Amorphous Carbon (ta-C) Thin Films

    NASA Astrophysics Data System (ADS)

    Yang, Xingyi

    Tetrahedral amorphous carbon (ta-C) is a diamond-like carbon (DLC) material comprised of a mixture of sp2 (˜40%) and sp3-bonded (˜60%) carbon domains. The physicochemical structure and electrochemical properties depend strongly on the sp2/sp3 bonding ratio as well as the incorporation of impurities, such as hydrogen or nitrogen. The ability to grow ta-C films at lower temperatures (25-100 °C) on a wider variety of substrates is a potential advantage of these materials as compared with diamond films. In this project, the basic structural and electrochemical properties of nitrogen-incorporated ta-C thin films will be discussed. The major goal of this work was to determine if the ta-C:N films exhibit electrochemical properties more closely aligned with those of boron-doped diamond (sp 3 carbon) or glassy carbon (amorphous sp2 carbon). Much like diamond, ta-C:N thin-film electrodes are characterized by a low background voltammetric current, a wide working potential window, relatively rapid electron-transfer kinetics for aqueous redox systems, such as Fe(CN) 6-3/-4 and Ru(NH3)6+3/+2 , and weak adsorption of polar molecules from solution. For example, negligible adsorption of methylene blue was found on the ta-C:N films in contrast to glassy carbon; a surface on which this molecule strongly adsorbs. The film microstructure was studied with x-ray photoelectron microscopy (XPS), visible Raman spectroscopy and electron-energy loss spectroscopy (EELS); all of which revealed the sp2-bonded carbon content increased with increasing nitrogen. The electrical properties of ta-C:N films were studied by four-point probe resistance measurement and conductive-probe AFM (CP-AFM). The incorporation of nitrogen into ta-C films increased the electrical conductivity primarily by increasing the sp2-bonded carbon content. CP-AFM showed the distribution of the conductive sp2-carbon on the film surface was not uniform. These films have potential to be used in field emission area. The

  4. Improving low-energy boron/nitrogen ion implantation in graphene by ion bombardment at oblique angles

    NASA Astrophysics Data System (ADS)

    Bai, Zhitong; Zhang, Lin; Liu, Ling

    2016-04-01

    Ion implantation is a widely adopted approach to structurally modify graphene and tune its electrical properties for a variety of applications. Further development of the approach requires a fundamental understanding of the mechanisms that govern the ion bombardment process as well as establishment of key relationships between the controlling parameters and the dominant physics. Here, using molecular dynamics simulations with adaptive bond order calculations, we demonstrate that boron and nitrogen ion bombardment at oblique angles (particularly at 70°) can improve both the productivity and quality of perfect substitution by over 25%. We accomplished this by systematically analyzing the effects of the incident angle and ion energy in determining the probabilities of six distinct types of physics that may occur in an ion bombardment event, including reflection, absorption, substitution, single vacancy, double vacancy, and transmission. By analyzing the atomic trajectories from 576 000 simulations, we identified three single vacancy creation mechanisms and four double vacancy creation mechanisms, and quantified their probability distributions in the angle-energy space. These findings further open the door for improved control of ion implantation towards a wide range of applications of graphene.Ion implantation is a widely adopted approach to structurally modify graphene and tune its electrical properties for a variety of applications. Further development of the approach requires a fundamental understanding of the mechanisms that govern the ion bombardment process as well as establishment of key relationships between the controlling parameters and the dominant physics. Here, using molecular dynamics simulations with adaptive bond order calculations, we demonstrate that boron and nitrogen ion bombardment at oblique angles (particularly at 70°) can improve both the productivity and quality of perfect substitution by over 25%. We accomplished this by systematically

  5. Carbon and Nitrogen Accumulation Rates in Salt Marshes in Oregon, USA

    EPA Science Inventory

    Two important ecosystem services of wetlands are carbon sequestration and filtration of nutrients and particulates. We quantified the carbon and nitrogen accumulation rates in salt marshes at 135 plots distributed across eight estuaries located in Oregon, USA. Net carbon and ...

  6. Elastic properties of B-C-N films grown by N{sub 2}-reactive sputtering from boron carbide targets

    SciTech Connect

    Salas, E.; Jiménez Riobóo, R. J.; Jiménez-Villacorta, F.; Prieto, C.; Sánchez-Marcos, J.; Muñoz-Martín, A.; Prieto, J. E.; Joco, V.

    2013-12-07

    Boron-carbon-nitrogen films were grown by RF reactive sputtering from a B{sub 4}C target and N{sub 2} as reactive gas. The films present phase segregation and are mechanically softer than boron carbide films (a factor of more than 2 in Young's modulus). This fact can turn out as an advantage in order to select buffer layers to better anchor boron carbide films on substrates eliminating thermally induced mechanical tensions.

  7. Theoretical uncertainties in extracting cosmic-ray diffusion parameters: the boron-to-carbon ratio

    NASA Astrophysics Data System (ADS)

    Genolini, Yoann

    2016-05-01

    PAMELA and, more recently, AMS-02, are ushering us into a new era of greatly reduced statistical uncertainties in experimental measurements of cosmic ray fluxes. In particular, new determinations of traditional diagnostic tools such as the boron to carbon ratio (B/C) are expected to significantly reduce errors on cosmic-ray diffusion parameters, with important implications for astroparticle physics, ranging from inferring primary source spectra to indirect dark matter searches. It is timely to stress, however, that the conclusions inferred crucially depend on the framework in which the data are interpreted as well as on some nuclear input parameters. We aim at assessing the theoretical uncertainties affecting the outcome, with models as simple as possible while still retaining the key dependences. We compare different semi-analytical, two-zone model descriptions of cosmic ray transport in the Galaxy: infinite slab(lD), cylindrical symmetry (2D) with homogeneous sources, cylindrical symmetry (2D) with inhomogeneous source distribution. We tested for the effect of a primary source contamination in the boron flux by parametrically altering its flux. We also tested for nuclear cross-section uncertainties.

  8. Dielectric response of carbon and boron nitride nanotubes from first-principles calculations

    NASA Astrophysics Data System (ADS)

    Kozinsky, Boris; Marzari, Nicola

    2007-03-01

    We present a complete characterization of the dielectric response of isolated single- and multi-wall carbon (CNT) and boron-nitride nanotubes (BNNT) using first-principles calculations and density-functional theory. The longitudinal polarizability of a nanotube is sensitive to the band gap and its radius, and in multi-wall nanotubes and bundles it is trivially given by the sum of the polarizabilities of the constituent tubes. The transverse polarizability of both types of nanotubes is insensitive to band gap and chirality and depends only on the radius. However, the transverse response and screening properties of BNNTs are qualitatively different from those of metallic and semiconducting CNTs. The fundamental differences in electronic properties of the two materials are inherited from the corresponding two-dimensional sheets - graphene and boron-nitride. The screening of the external field in CNTs is stronger than in BNNTs and has a different radius dependence. The transverse response in BNNTs is found to be that of an insulator, while in CNTs it is intermediate between metallic and semiconducting. Our results have practical implications for selective growth of different types of nanotubes using aligning electric fields and for Raman characterization of nanotubes.

  9. Fabrication and characterization of thermomechanically processed sulfur and boron doped amorphous carbon films

    NASA Astrophysics Data System (ADS)

    Carlson, Lonnie

    Small scale, high power density, reliable, and long-life power supplies would be useful or even critical for space missions or the growing number of microdetectors, microsensors, and miniature vehicles. Alpha or beta particle voltaic devices could satisfy these requirements but have been shown to degrade quickly due to radiation damage. Amorphous carbon (a-C) PN junctions or PIN devices could provide radiation hardness and sufficiently high efficiency. As the range of alpha and beta particles in a-C is ˜20-120microm, much thicker films than are typical are needed to maximize collection of the particle energy. In this work, the fabrication of thermomechanically processed p- and n-type doped a-C films were investigated as a first step in the future development of radiation hard voltaic devices. Boron carbide (B4C) powder was mixed with a-C nanopowders as a possible p-type dopant with sulfur powder utilized as a possible n-type dopant. Doping levels of 2.5at%, 5.0at%, and 10.0at% were investigated for both dopants with films pressed at 109°C over a pressure range of 0.3-5.0GPa. Initial attempts to fabricate rectifying PN junctions and PIN devices was unsuccessful. Bonding properties were characterized using Raman spectroscopy with electronic properties primarily assessed using the van der Pauw method. Undoped a-C and boron-doped films were found to be slightly p-type with sulfur-doped films converting to n-type. All films were found to consist almost entirely of nano-graphitic sp2 rings with only slight changes in disorder at different pressures. Sulfur doped films were less brittle which is indicative of crosslinking. Boron doping did not significantly change the film electronic properties and is not an effective dopant at these temperatures and pressures. Sulfur doping had a greater effect and could likely be utilized as basis for an n-type material in a device. Initial irradiation studies using alpha particles showed that boron and undoped films became more p

  10. Boron dipyrromethene (BODIPY) functionalized carbon nano-onions for high resolution cellular imaging

    NASA Astrophysics Data System (ADS)

    Bartelmess, Juergen; de Luca, Elisa; Signorelli, Angelo; Baldrighi, Michele; Becce, Michele; Brescia, Rosaria; Nardone, Valentina; Parisini, Emilio; Echegoyen, Luis; Pompa, Pier Paolo; Giordani, Silvia

    2014-10-01

    Carbon nano-onions (CNOs) are an exciting class of carbon nanomaterials, which have recently demonstrated a facile cell-penetration capability. In the present work, highly fluorescent boron dipyrromethene (BODIPY) dyes were covalently attached to the surface of CNOs. The introduction of this new carbon nanomaterial-based imaging platform, made of CNOs and BODIPY fluorophores, allows for the exploration of synergetic effects between the two building blocks and for the elucidation of its performance in biological applications. The high fluorescence intensity exhibited by the functionalized CNOs translates into an excellent in vitro probe for the high resolution imaging of MCF-7 human breast cancer cells. It was also found that the CNOs, internalized by the cells by endocytosis, localized in the lysosomes and did not show any cytotoxic effects. The presented results highlight CNOs as excellent platforms for biological and biomedical studies due to their low toxicity, efficient cellular uptake and low fluorescence quenching of attached probes.Carbon nano-onions (CNOs) are an exciting class of carbon nanomaterials, which have recently demonstrated a facile cell-penetration capability. In the present work, highly fluorescent boron dipyrromethene (BODIPY) dyes were covalently attached to the surface of CNOs. The introduction of this new carbon nanomaterial-based imaging platform, made of CNOs and BODIPY fluorophores, allows for the exploration of synergetic effects between the two building blocks and for the elucidation of its performance in biological applications. The high fluorescence intensity exhibited by the functionalized CNOs translates into an excellent in vitro probe for the high resolution imaging of MCF-7 human breast cancer cells. It was also found that the CNOs, internalized by the cells by endocytosis, localized in the lysosomes and did not show any cytotoxic effects. The presented results highlight CNOs as excellent platforms for biological and biomedical

  11. Dual Catalysis Using Boronic Acid and Chiral Amine: Acyclic Quaternary Carbons via Enantioselective Alkylation of Branched Aldehydes with Allylic Alcohols.

    PubMed

    Mo, Xiaobin; Hall, Dennis G

    2016-08-31

    A ferrocenium boronic acid salt activates allylic alcohols to generate transient carbocations that react with in situ-generated chiral enamines from branched aldehydes. The optimized conditions afford the desired acyclic products embedding a methyl-aryl quaternary carbon center with up to 90% yield and 97:3 enantiomeric ratio, with only water as the byproduct. This noble-metal-free method complements alternative methods that are incompatible with carbon-halogen bonds and other sensitive functional groups. PMID:27518200

  12. Effect of a nitrogen-carbon interaction on terrestrial carbon fluxes estimated by biosphere model

    NASA Astrophysics Data System (ADS)

    Sasai, T.; Yamaguchi, Y.

    2007-12-01

    It is important for the global warming to accurately understand the terrestrial carbon fluxes at global scale. Estimating spatial and temporal patterns in the carbon fluxes, recently, many global biosphere models were proposed and developed. However, since the model analyses have always some uncertainties. One of the major uncertainties is an effect of nitrogen cycle on the carbon cycle, as nitrogen largely controls carbon dynamics as plant and soil microbe nutrients. A goal of this study is to investigate the effect of terrestrial carbon-nitrogen interaction on NPP using new biosphere model. Firstly, a new nitrogen cycle model was constructed including twelve main nitrogen flows (nitrogen fixation, deposition, nitrifications, volatilization, nitrate leaching, plant uptake, allocation, translocation, retranslocation, soil organic and inorganic nitrogen dynamics), and fourteen pools (three biomass, four litter fall, five soil organic, and two inorganic). Secondly, the nitrogen model was integrated to the existing biosphere model, BEAMS (Biosphere model integrating Eco-physiological And Mechanistic approaches using Satellite data) [Sasai et al., 2005, 2007]. The new biosphere model was run for 20 years (1982-2001) at a global scale. The inputs datasets used were NCEP/NCAR re-analysis and fPAR/LAI based on NOAA/AVHRR produced by Boston University. The two-dimensional distributions of monthly GPP and NPP were calculated. And, the GPP estimates by the original and new BEAMS were compared with ground measurements at flux-tower sites. We compared seasonal changes in GPP between the new model and eddy covariance measurements at flux sites. As a result, the GPP estimates had good agreement with the GPP measurements (r2 = 0.91). In view of a comparison in GPP between the measurements and the original BEAMS (r2 = 0.84), the new model is better than the original BEAMS. Especially, we could observe an indisputable improvement of the new model on a seasonal change in the growing

  13. Carbon and nitrogen abundances determined from transition layer lines

    NASA Technical Reports Server (NTRS)

    Boehm-Vitense, Erika; Mena-Werth, Jose

    1992-01-01

    The possibility of determining relative carbon, nitrogen, and silicon abundances from the emission-line fluxes in the lower transition layers between stellar chromospheres and coronae is explored. Observations for main-sequence and luminosity class IV stars with presumably solar element abundances show that for the lower transition layers Em = BT sup -gamma. For a given carbon abundance the constants gamma and B in this relation can be determined from the C II and C IV emission-line fluxes. From the N V and S IV lines, the abundances of these elements relative to carbon can be determined from their surface emission-line fluxes. Ratios of N/C abundances determined in this way for some giants and supergiants agree within the limits of errors with those determined from molecular bands. For giants, an increase in the ratio of N/C at B-V of about 0.8 is found, as expected theoretically.

  14. Carbon and nitrogen isotope studies in an arctic aquatic ecosystem

    SciTech Connect

    Schell, D.M.

    1989-01-01

    The Phase II studies of the R4D Program on stream and watershed ecology reflect the accomplishments and accumulation of baseline information obtained during the past studies. Although our rough estimates indicate that nitrogen inputs to the watershed ba lance losses, the carbon fluxes suggest that they are not in equilibrium and that there is a net loss of carbon from the tundra ecosystem through respiration and transport out of the watershed via the stream system. Radiocarbon profiles of soil sections coupled with mass transport calculations revealed that peat accumulation has essentially ceased in the R4D watershed and appears to be in ablative loss. Thus the carbon flux measurements provide validation tests for the PLANTGRO and GAS-HYDRO models of the PHASE II studies. These findings are also important in the context of global CO[sub 2] increases from positive feedback mechanisms in peatlands associated with climatic warming in the subarctic regions.

  15. Carbon and nitrogen isotope studies in an arctic aquatic ecosystem

    SciTech Connect

    Schell, D.M.

    1989-12-31

    The Phase II studies of the R4D Program on stream and watershed ecology reflect the accomplishments and accumulation of baseline information obtained during the past studies. Although our rough estimates indicate that nitrogen inputs to the watershed ba lance losses, the carbon fluxes suggest that they are not in equilibrium and that there is a net loss of carbon from the tundra ecosystem through respiration and transport out of the watershed via the stream system. Radiocarbon profiles of soil sections coupled with mass transport calculations revealed that peat accumulation has essentially ceased in the R4D watershed and appears to be in ablative loss. Thus the carbon flux measurements provide validation tests for the PLANTGRO and GAS-HYDRO models of the PHASE II studies. These findings are also important in the context of global CO{sub 2} increases from positive feedback mechanisms in peatlands associated with climatic warming in the subarctic regions.

  16. Oxidative unzipping of stacked nitrogen-doped carbon nanotube cups.

    PubMed

    Dong, Haifeng; Zhao, Yong; Tang, Yifan; Burkert, Seth C; Star, Alexander

    2015-05-27

    We demonstrate a facile synthesis of different nanostructures by oxidative unzipping of stacked nitrogen-doped carbon nanotube cups (NCNCs). Depending on the initial number of stacked-cup segments, this method can yield graphene nanosheets (GNSs) or hybrid nanostructures comprised of graphene nanoribbons partially unzipped from a central nanotube core. Due to the stacked-cup structure of as-synthesized NCNCs, preventing complete exposure of graphitic planes, the unzipping mechanism is hindered, resulting in incomplete unzipping; however, individual, separated NCNCs are completely unzipped, yielding individual nitrogen-doped GNSs. Graphene-based materials have been employed as electrocatalysts for many important chemical reactions, and it has been proposed that increasing the reactive edges results in more efficient electrocatalysis. In this paper, we apply these graphene conjugates as electrocatalysts for the oxygen reduction reaction (ORR) to determine how the increase in reactive edges affects the electrocatalytic activity. This investigation introduces a new method for the improvement of ORR electrocatalysts by using nitrogen dopants more effectively, allowing for enhanced ORR performance with lower overall nitrogen content. Additionally, the GNSs were functionalized with gold nanoparticles (GNPs), resulting in a GNS/GNP hybrid, which shows efficient surface-enhanced Raman scattering and expands the scope of its application in advanced device fabrication and biosensing. PMID:25946723

  17. Proton induced gamma-ray production cross sections and thick-target yields for boron, nitrogen and silicon

    NASA Astrophysics Data System (ADS)

    Marchand, Benoît; Mizohata, Kenichiro; Räisänen, Jyrki

    2016-07-01

    The excitation functions for the reactions 14N(p,p‧γ)14N, 28Si(p,p‧γ)28Si and 29Si(p,p‧γ)29Si were measured at an angle of 55° by bombarding a thin Si3N4 target with protons in the energy range of 3.6-6.9 MeV. The deduced γ-ray production cross section data is compared with available literature data relevant for ion beam analytical work. Thick-target γ-ray yields for boron, nitrogen and silicon were measured at 4.0, 4.5, 5.0, 5.5, 6.0 and 6.5 MeV proton energies utilizing thick BN and Si3N4 targets. The measured yield values are put together with available yield data found in the literature. The experimental yield data has been used to cross-check the γ-ray production cross section values by comparing them with calculated thick-target yields deduced from the present and literature experimental excitation curves. All values were found to be in reasonable agreement taking into account the experimental uncertainties.

  18. Complex Boron Redistribution in P+ Doped-polysilicon / Nitrogen Doped Silicon Bi-layers during Activation Annealing

    NASA Astrophysics Data System (ADS)

    Abadli, S.; Mansour, F.; Perrera, E. Bedel

    We have investigated and modeled the complex phenomenon of boron (B) redistribution process in strongly doped silicon bilayers structure. A one-dimensional two stream transfer model well adapted to the particular structure of bi- layers and to the effects of strong-concentrations has been developed. This model takes into account the instantaneous kinetics of B transfer, trapping, clustering and segregation during the thermal B activation annealing. The used silicon bi-layers have been obtained by low pressure chemical vapor deposition (LPCVD) method, using in-situ nitrogen- doped-silicon (NiDoS) layer and strongly B doped polycrystalline-silicon (P+) layer. To avoid long redistributions, thermal annealing was carried out at relatively lowtemperatures (600 °C and 700 °C) for various times ranging between 30 minutes and 2 hours. The good adjustment of the simulated profiles with the experimental secondary ion mass spectroscopy (SIMS) profiles allowed a fundamental understanding about the instantaneous physical phenomena giving and disturbing the complex B redistribution profiles-shoulders kinetics.

  19. Role of defects in the process of graphene growth on hexagonal boron nitride from atomic carbon

    SciTech Connect

    Dabrowski, J. Lippert, G.; Schroeder, T.; Lupina, G.

    2014-11-10

    Hexagonal boron nitride (h-BN) is an attractive substrate for graphene, as the interaction between these materials is weak enough for high carrier mobility to be retained in graphene but strong enough to allow for some epitaxial relationship. We deposited graphene on exfoliated h-BN by molecular beam epitaxy (MBE), we analyzed the atomistic details of the process by ab initio density functional theory (DFT), and we linked the DFT and MBE results by random walk theory. Graphene appears to nucleate around defects in virgin h-BN. The DFT analysis reveals that sticking of carbon to perfect h-BN is strongly reduced by desorption, so that pre-existing seeds are needed for the nucleation. The dominant nucleation seeds are C{sub N}C{sub B} and O{sub N}C{sub N} pairs and B{sub 2}O{sub 3} inclusions in the virgin substrate.

  20. Heteroepitaxial Growth of Single-Walled Carbon Nanotubes from Boron Nitride

    PubMed Central

    Tang, Dai-Ming; Zhang, Li-Li; Liu, Chang; Yin, Li-Chang; Hou, Peng-Xiang; Jiang, Hua; Zhu, Zhen; Li, Feng; Liu, Bilu; Kauppinen, Esko I.; Cheng, Hui-Ming

    2012-01-01

    The growth of single-walled carbon nanotubes (SWCNTs) with predefined structure is of great importance for both fundamental research and their practical applications. Traditionally, SWCNTs are grown from a metal catalyst with a vapor-liquid-solid mechanism, where the catalyst is in liquid state with fluctuating structures, and it is intrinsically unfavorable for the structure control of SWCNTs. Here we report the heteroepitaxial growth of SWCNTs from a platelet boron nitride nanofiber (BNNF), which is composed of stacked (002) planes and is stable at high temperatures. SWCNTs are found to grow epitaxially from the open (002) edges of the BNNFs, and the diameters of the SWCNTs are multiples of the BN (002) interplanar distance. In situ transmission electron microscopy observations coupled with first principles calculations reveal that the growth of SWCNTs from the BNNFs follows a vapor-solid-solid mechanism. Our work opens opportunities for the control over the structure of SWCNTs by hetero-crystallographic epitaxy. PMID:23240076

  1. Influence of oxygen impurity on electronic properties of carbon and boron nitride nanotubes: A comparative study

    SciTech Connect

    Singh, Ram Sevak

    2015-11-15

    Influence of oxygen impurity on electronic properties of carbon and boron nitride nanotubes (CNTs and BNNTs) is systematically studied using first principle calculations based on density functional theory. Energy band structures and density of states of optimized zigzag (5, 0), armchair (3, 3), and chiral (4, 2) structures of CNT and BNNT are calculated. Oxygen doping in zigzag CNT exhibits a reduction in metallicity with opening of band gap in near-infrared region while metallicity is enhanced in armchair and chiral CNTs. Unlike oxygen-doped CNTs, energy bands are drastically modulated in oxygen-doped zigzag and armchair BNNTs, showing the nanotubes to have metallic behaviour. Furthermore, oxygen impurity in chiral BNNT induces narrowing of band gap, indicating a gradual modification of electronic band structure. This study underscores the understanding of different electronic properties induced in CNTs and BNNTs under oxygen doping, and has potential in fabrication of various nanoelectronic devices.

  2. Preparation and properties of dysprosium nanocapsules coated with boron, carbon, and dysprosium oxide

    SciTech Connect

    Si, P.Z.; Brueck, E.; Zhang, Z.D.; Skorvanek, I.; Kovac, J.; Zhang, M

    2004-06-08

    Boron-coated dysprosium/dysprosium oxide, carbon-coated dysprosium/DyC{sub 2}, and dysprosium oxide-coated dysprosium nanocapsules were prepared using an arc discharge method in diborane, methane, and argon, respectively. The magnetization of these nanocapsules has been measured at temperatures between 4 and 290 K, in applied fields up to 6 T. The transition temperature of nanocrystalline Dy from the helical phase to the ferromagnetic phase is much lower than that of bulk Dy. The linear temperature dependence of the inverse susceptibility of these nanocapsules, being a mixture of superparamagnetic Dy and paramagnetic dysprosium oxide or carbide, can be explained within the molecular field theory with magnetic moments with the total angular momentum J=15/2 and the Lande factor g=4/3. We discuss the relations between the structure and the magnetization of these nanocapsules.

  3. Boron Nitride Coated Carbon Nanotube Arrays with Enhanced Compressive Mechanical Property

    NASA Astrophysics Data System (ADS)

    Jing, Lin; Tay, Roland Yingjie; Li, Hongling; Tsang, Siu Hon; Tan, Dunlin; Zhang, Bowei; Tok, Alfred Iing Yoong; Teo, Edwin Hang Tong

    Vertically aligned carbon nanotube (CNT) array is one of the most promising energy dissipating materials due to its excellent temperature invariant mechanical property. However, the CNT arrays with desirable recoverability after compression is still a challenge. Here, we report on the mechanical enhancement of the CNT arrays reinforced by coating with boron nitride (BN) layers. These BN coated CNT (BN/CNT) arrays exhibit excellent compressive strength and recoverability as compared to those of the as-prepared CNT arrays which totally collapsed after compression. In addition, the BN coating also provides better resistance to oxidation due to its intrinsic thermal stability. This work presented here opens a new pathway towards tuning mechanical behavior of any arbitrary CNT arrays for promising potential such as damper, vibration isolator and shock absorber applications.

  4. Nitrogen-Doped Carbon Nanocoil Array Integrated on Carbon Nanofiber Paper for Supercapacitor Electrodes.

    PubMed

    Choi, Won Ho; Choi, Mi Jin; Bang, Jin Ho

    2015-09-01

    Integrating a nanostructured carbon array on a conductive substrate remains a challenging task that presently relies primarily on high-vacuum deposition technology. To overcome the problems associated with current vacuum techniques, we demonstrate the formation of an N-doped carbon array by pyrolysis of a polymer array that was electrochemically grown on carbon fiber paper. The resulting carbon array was investigated for use as a supercapacitor electrode. In-depth surface characterization results revealed that the microtextural properties, surface functionalities, and degree of nitrogen incorporated into the N-doped carbon array can be delicately controlled by manipulating carbonization temperatures. Furthermore, electrochemical measurements showed that subtle changes in these physical properties resulted in significant changes in the capacitive behavior of the N-doped carbon array. Pore structures and nitrogen/oxygen functional groups, which are favorable for charge storage, were formed at low carbonization temperatures. This result showed the importance of having a comprehensive understanding of how the surface characteristics of carbon affect its capacitive performance. When utilized as a substrate in a pseudocapacitive electrode material, the N-doped carbon array maximizes capacitive performance by simultaneously achieving high gravimetric and areal capacitances due to its large surface area and high electrical conductivity. PMID:26264641

  5. Functional diversity of leaf nitrogen concentrations drives grassland carbon fluxes.

    PubMed

    Milcu, Alexandru; Roscher, Christiane; Gessler, Arthur; Bachmann, Dörte; Gockele, Annette; Guderle, Markus; Landais, Damien; Piel, Clément; Escape, Christophe; Devidal, Sebastien; Ravel, Olivier; Buchmann, Nina; Gleixner, Gerd; Hildebrandt, Anke; Roy, Jacques

    2014-04-01

    Little is known about the role of plant functional diversity for ecosystem-level carbon (C) fluxes. To fill this knowledge gap, we translocated monoliths hosting communities with four and 16 sown species from a long-term grassland biodiversity experiment ('The Jena Experiment') into a controlled environment facility for ecosystem research (Ecotron). This allowed quantifying the effects of plant diversity on ecosystem C fluxes as well as three parameters of C uptake efficiency (water and nitrogen use efficiencies and apparent quantum yield). By combining data on ecosystem C fluxes with vegetation structure and functional trait-based predictors, we found that increasing plant species and functional diversity led to higher gross and net ecosystem C uptake rates. Path analyses and light response curves unravelled the diversity of leaf nitrogen concentration in the canopy as a key functional predictor of C fluxes, either directly or indirectly via LAI and aboveground biomass. PMID:24393400

  6. High-concentration nitrogen-doped carbon nanotube arrays

    NASA Astrophysics Data System (ADS)

    Cao, L. M.; Zhang, X. Y.; Gao, C. X.; Wang, W. K.; Zhang, Z. L.; Zhang, Z.

    2003-08-01

    Large arrays of aligned CNx nanotubes were synthesized by radiofrequency magnetron sputtering of a mixture of nanometre-sized graphite and nickel powders in a nitrogen atmosphere. The CNx nanotubes produced assembled into bundle-like arrays standing perpendicularly on the silicon substrates. The nickel nanoparticles located in the tips suggest that a 'tip-growth' mechanism governs their growth process. Transmission electron microscopy and electron energy-loss spectroscopy studies reveal that the nanotubes possess a bamboo-like structure and nitrogen to carbon atomic ratios in the range of 0.22-0.32, commensurate with C3Nx (x < 1) stoichiometries. Our results illustrate the potential of the magnetron sputtering method for the creation of a large number of ordered nanostructures.

  7. Permafrost carbon-climate feedback is sensitive to deep soil carbon decomposability but not deep soil nitrogen dynamics.

    PubMed

    Koven, Charles D; Lawrence, David M; Riley, William J

    2015-03-24

    Permafrost soils contain enormous amounts of organic carbon whose stability is contingent on remaining frozen. With future warming, these soils may release carbon to the atmosphere and act as a positive feedback to climate change. Significant uncertainty remains on the postthaw carbon dynamics of permafrost-affected ecosystems, in particular since most of the carbon resides at depth where decomposition dynamics may differ from surface soils, and since nitrogen mineralized by decomposition may enhance plant growth. Here we show, using a carbon-nitrogen model that includes permafrost processes forced in an unmitigated warming scenario, that the future carbon balance of the permafrost region is highly sensitive to the decomposability of deeper carbon, with the net balance ranging from 21 Pg C to 164 Pg C losses by 2300. Increased soil nitrogen mineralization reduces nutrient limitations, but the impact of deep nitrogen on the carbon budget is small due to enhanced nitrogen availability from warming surface soils and seasonal asynchrony between deeper nitrogen availability and plant nitrogen demands. Although nitrogen dynamics are highly uncertain, the future carbon balance of this region is projected to hinge more on the rate and extent of permafrost thaw and soil decomposition than on enhanced nitrogen availability for vegetation growth resulting from permafrost thaw. PMID:25775603

  8. Permafrost carbon-climate feedback is sensitive to deep soil carbon decomposability but not deep soil nitrogen dynamics

    NASA Astrophysics Data System (ADS)

    Koven, Charles D.; Lawrence, David M.; Riley, William J.

    2015-03-01

    Permafrost soils contain enormous amounts of organic carbon whose stability is contingent on remaining frozen. With future warming, these soils may release carbon to the atmosphere and act as a positive feedback to climate change. Significant uncertainty remains on the postthaw carbon dynamics of permafrost-affected ecosystems, in particular since most of the carbon resides at depth where decomposition dynamics may differ from surface soils, and since nitrogen mineralized by decomposition may enhance plant growth. Here we show, using a carbon-nitrogen model that includes permafrost processes forced in an unmitigated warming scenario, that the future carbon balance of the permafrost region is highly sensitive to the decomposability of deeper carbon, with the net balance ranging from 21 Pg C to 164 Pg C losses by 2300. Increased soil nitrogen mineralization reduces nutrient limitations, but the impact of deep nitrogen on the carbon budget is small due to enhanced nitrogen availability from warming surface soils and seasonal asynchrony between deeper nitrogen availability and plant nitrogen demands. Although nitrogen dynamics are highly uncertain, the future carbon balance of this region is projected to hinge more on the rate and extent of permafrost thaw and soil decomposition than on enhanced nitrogen availability for vegetation growth resulting from permafrost thaw.

  9. Leaf nitrogen dioxide uptake coupling apoplastic chemistry, carbon/sulfur assimilation, and plant nitrogen status.

    PubMed

    Hu, Yanbo; Sun, Guangyu

    2010-10-01

    Emission and plant uptake of atmospheric nitrogen oxides (NO + NO(2)) significantly influence regional climate change by regulating the oxidative chemistry of the lower atmosphere, species composition and the recycling of carbon and nutrients, etc. Plant uptake of nitrogen dioxide (NO(2)) is concentration-dependent and species-specific, and covaries with environmental factors. An important factor determining NO(2) influx into leaves is the replenishment of the substomatal cavity. The apoplastic chemistry of the substomatal cavity plays crucial roles in NO(2) deposition rates and the tolerance to NO(2), involving the reactions between NO(2) and apoplastic antioxidants, NO(2)-responsive germin-like proteins, apoplastic acidification, and nitrite-dependent NO synthesis, etc. Moreover, leaf apoplast is a favorable site for the colonization by microbes, which disturbs nitrogen metabolism of host plants. For most plant species, NO(2) assimilation in a leaf primarily depends on the nitrate (NO(3) (-)) assimilation pathway. NO(2)-N assimilation is coupled with carbon and sulfur (sulfate and SO(2)) assimilation as indicated by the mutual needs for metabolic intermediates (or metabolites) and the NO(2)-caused changes of key metabolic enzymes such as phosphoenolpyruvate carboxylase (PEPc) and adenosine 5'-phosphosulfate sulfotransferase, organic acids, and photorespiration. Moreover, arbuscular mycorrhizal (AM) colonization improves the tolerance of host plants to NO(2) by enhancing the efficiency of nutrient absorption and translocation and influencing foliar chemistry. Further progress is proposed to gain a better understanding of the coordination between NO(2)-N, S and C assimilation, especially the investigation of metabolic checkpoints, and the effects of photorespiratory nitrogen cycle, diverse PEPc and the metabolites such as cysteine, O-acetylserine (OAS) and glutathione. PMID:20628880

  10. Boron-doped, carbon-coated SnO2/graphene nanosheets for enhanced lithium storage.

    PubMed

    Liu, Yuxin; Liu, Ping; Wu, Dongqing; Huang, Yanshan; Tang, Yanping; Su, Yuezeng; Zhang, Fan; Feng, Xinliang

    2015-03-27

    Heteroatom doping is an effective method to adjust the electrochemical behavior of carbonaceous materials. In this work, boron-doped, carbon-coated SnO2 /graphene hybrids (BCTGs) were fabricated by hydrothermal carbonization of sucrose in the presence of SnO2/graphene nanosheets and phenylboronic acid or boric acid as dopant source and subsequent thermal treatment. Owing to their unique 2D core-shell architecture and B-doped carbon shells, BCTGs have enhanced conductivity and extra active sites for lithium storage. With phenylboronic acid as B source, the resulting hybrid shows outstanding electrochemical performance as the anode in lithium-ion batteries with a highly stable capacity of 1165 mA h g(-1) at 0.1 A g(-1) after 360 cycles and an excellent rate capability of 600 mA h g(-1) at 3.2 A g(-1), and thus outperforms most of the previously reported SnO2-based anode materials. PMID:25694249

  11. Boron containing multilayer coatings and method of fabrication

    DOEpatents

    Makowiecki, Daniel M.; Jankowski, Alan F.

    1997-01-01

    Hard coatings are fabricated from multilayer boron/boron carbide, boron carbide/cubic boron nitride, and boron/boron nitride/boron carbide, and the fabrication thereof involves magnetron sputtering in a selected atmosphere. These hard coatings may be applied to tools and engine and other parts, as well to reduce wear on tribological surfaces and electronic devices. These boron coatings contain no morphological growth features. For example, the boron and boron carbide used in forming the multilayers are formed in an inert (e.g. argon) atmosphere, while the cubic boron nitride is formed in a reactive (e.g. nitrogen) atmosphere. The multilayer boron/boron carbide, and boron carbide/cubic boron nitride is produced by depositing alternate layers of boron, cubic boron nitride or boron carbide, with the alternate layers having a thickness of 1 nanometer to 1 micrometer, and at least the interfaces of the layers may be of a discrete or a blended or graded composition.

  12. Nitrogen Application Rate and Carbon Asssimilation in Potato: What can this tell us about nitrogen demand and uptake?

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The interaction between nitrogen application rate and carbon assimilation in potato strongly affects growth and developmental rates. Two consecutive experiments were carried out in the summer of 2005 in six sunlit, controlled environment plant growth chambers with six nitrogen application rates and ...

  13. Gas and aerosol fluxes. [emphasizing sulfur, nitrogen, and carbon

    NASA Technical Reports Server (NTRS)

    Martens, C. S.

    1980-01-01

    The development of remote sensing techniques to address the global need for accurate distribution and flux determinations of both man made and natural materials which affect the chemical composition of the atmosphere, the heat budget of the Earth, and the depletion, of stratospheric ozone is considered. Specifically, trace gas fluxes, sea salt aerosol production, and the effect of sea surface microlayer on gas and aerosol fluxes are examined. Volatile sulfur, carbon, nitrogen, and halocarbon compounds are discussed including a statement of the problem associated with each compound or group of compounds, a brief summary of current understanding, and suggestions for needed research.

  14. Preparation of a new sorbent based on boronate affinity monolith and evaluation of its extraction performance for nitrogen-containing pollutants.

    PubMed

    Hu, Hongyou; Zhang, Yu; Zhang, Yong; Huang, Xiaojia; Yuan, Dongxing

    2014-05-16

    In this study, a new boronate affinity sorbent based on poly(4-vinylphenylboronic acid-divinylbenzene) monolith (VPB-DB) was prepared and used as extractive medium of stir cake sorptive extraction (SCSE). The effect of the preparation parameters in the polymerization mixture on extraction performance was investigated thoroughly. The sorbent was characterized by infrared spectroscopy, elemental analysis, scanning electron microscopy and mercury intrusion porosimetry. The determination of 8 sulfonamides in environmental water samples with the combination of SCSE and high performance liquid chromatography tandem mass spectrometry detection was selected as a paradigm for the evaluation of extraction performance of poly(VPB-DB) monolith for nitrogen-containing pollutants. Under the optimal extraction conditions, the limits of detection (S/N=3) and limits of quantification (S/N=10) for the target analytes were 0.0012-0.010 and 0.0040-0.033μg/L, respectively. The method also showed good linearity, repeatability, recoveries and high feasibility. At the same time, aromatic amines, nitrophenols, amide herbicides and sudan dyes were also used to evaluate the extractive performance of the sorbent for nitrogen-containing compounds. Results well indicate that the interaction of boron-nitrogen coordination between sorbent and analytes plays a key role in the extraction of nitrogen-containing compounds. PMID:24713423

  15. Nano-solenoid: helicoid carbon-boron nitride hetero-nanotube

    NASA Astrophysics Data System (ADS)

    Zhang, Zi-Yue; Miao, Chunyang; Guo, Wanlin

    2013-11-01

    As a fundamental element of a nanoscale passive circuit, a nano-inductor is proposed based on a hetero-nanotube consisting of a spiral carbon strip and a spiral boron nitride strip. It is shown by density functional theory associated with nonequilibrium Green function calculations that the nanotube exhibits attractive transport properties tunable by tube chirality, diameter, component proportion and connection manner between the two strips, with excellent `OFF' state performance and high current on the order of 10-100 μA. All the hetero-nanotubes show negative differential resistance. The transmission peaks of current are absolutely derived from the helicoid carbon strips or C-BN boundaries, giving rise to a spiral current analogous with an energized nano-solenoid. According to Ampere's Law, the energized nano-solenoid can generate a uniform and tremendous magnetic field of more than 1 tesla, closing to that generated by the main magnet of medical nuclear magnetic resonance. Moreover, the magnitude of magnetic field can be easily modulated by bias voltage, providing great promise for a nano-inductor to realize electromagnetic conversion at the nanoscale.As a fundamental element of a nanoscale passive circuit, a nano-inductor is proposed based on a hetero-nanotube consisting of a spiral carbon strip and a spiral boron nitride strip. It is shown by density functional theory associated with nonequilibrium Green function calculations that the nanotube exhibits attractive transport properties tunable by tube chirality, diameter, component proportion and connection manner between the two strips, with excellent `OFF' state performance and high current on the order of 10-100 μA. All the hetero-nanotubes show negative differential resistance. The transmission peaks of current are absolutely derived from the helicoid carbon strips or C-BN boundaries, giving rise to a spiral current analogous with an energized nano-solenoid. According to Ampere's Law, the energized nano

  16. Hyperspectral Analysis of Soil Nitrogen, Carbon, Carbonate, and Organic Matter Using Regression Trees

    PubMed Central

    Gmur, Stephan; Vogt, Daniel; Zabowski, Darlene; Moskal, L. Monika

    2012-01-01

    The characterization of soil attributes using hyperspectral sensors has revealed patterns in soil spectra that are known to respond to mineral composition, organic matter, soil moisture and particle size distribution. Soil samples from different soil horizons of replicated soil series from sites located within Washington and Oregon were analyzed with the FieldSpec Spectroradiometer to measure their spectral signatures across the electromagnetic range of 400 to 1,000 nm. Similarity rankings of individual soil samples reveal differences between replicate series as well as samples within the same replicate series. Using classification and regression tree statistical methods, regression trees were fitted to each spectral response using concentrations of nitrogen, carbon, carbonate and organic matter as the response variables. Statistics resulting from fitted trees were: nitrogen R2 0.91 (p < 0.01) at 403, 470, 687, and 846 nm spectral band widths, carbonate R2 0.95 (p < 0.01) at 531 and 898 nm band widths, total carbon R2 0.93 (p < 0.01) at 400, 409, 441 and 907 nm band widths, and organic matter R2 0.98 (p < 0.01) at 300, 400, 441, 832 and 907 nm band widths. Use of the 400 to 1,000 nm electromagnetic range utilizing regression trees provided a powerful, rapid and inexpensive method for assessing nitrogen, carbon, carbonate and organic matter for upper soil horizons in a nondestructive method. PMID:23112620

  17. Hyperspectral analysis of soil nitrogen, carbon, carbonate, and organic matter using regression trees.

    PubMed

    Gmur, Stephan; Vogt, Daniel; Zabowski, Darlene; Moskal, L Monika

    2012-01-01

    The characterization of soil attributes using hyperspectral sensors has revealed patterns in soil spectra that are known to respond to mineral composition, organic matter, soil moisture and particle size distribution. Soil samples from different soil horizons of replicated soil series from sites located within Washington and Oregon were analyzed with the FieldSpec Spectroradiometer to measure their spectral signatures across the electromagnetic range of 400 to 1,000 nm. Similarity rankings of individual soil samples reveal differences between replicate series as well as samples within the same replicate series. Using classification and regression tree statistical methods, regression trees were fitted to each spectral response using concentrations of nitrogen, carbon, carbonate and organic matter as the response variables. Statistics resulting from fitted trees were: nitrogen R(2) 0.91 (p < 0.01) at 403, 470, 687, and 846 nm spectral band widths, carbonate R(2) 0.95 (p < 0.01) at 531 and 898 nm band widths, total carbon R(2) 0.93 (p < 0.01) at 400, 409, 441 and 907 nm band widths, and organic matter R(2) 0.98 (p < 0.01) at 300, 400, 441, 832 and 907 nm band widths. Use of the 400 to 1,000 nm electromagnetic range utilizing regression trees provided a powerful, rapid and inexpensive method for assessing nitrogen, carbon, carbonate and organic matter for upper soil horizons in a nondestructive method. PMID:23112620

  18. Ab initio theoretical study of hydrogen and its interaction with boron acceptors and nitrogen donors in single-wall silicon carbide nanotubes

    NASA Astrophysics Data System (ADS)

    Gali, A.

    2007-02-01

    Silicon carbide nanotubes have a great potential for biological applications. It is of interest to explore the electronic properties of these nanotubes, and how those are modified in the presence of impurities. Hydrogen is a common impurity that can appear during the growth of silicon carbide nanotubes or in the environment. In this paper we studied the properties of one and two hydrogen atoms in armchair and zigzag silicon carbide nanotubes by ab initio supercell calculations beyond the standard density functional theory. We found that a single hydrogen atom is an amphoteric defect: it can act as a donor as well as an acceptor, depending on the adsorption site. However, both sites are nearly equally stable; therefore these defects compensate each other in SiC nanotube semiconductors. We found that hydrogen can absorb onto SiC nanotubes when atomic hydrogen is present in the environment. In addition, we investigated the incorporation of hydrogen by applying BH and NH molecules in the environment of SiC nanotubes. The simulations predict that boron dissolves into SiC nanotubes together with hydrogen; thus boron can be used to raise the concentration of hydrogen in SiC nanotubes. Nitrogen is also incorporated with hydrogen. We predict that the shallow boron acceptor and the nitrogen donor may be activated in these processes.

  19. Synthesis, Characterization, and Tribological Evaluation of TiO2-Reinforced Boron and Nitrogen co-Doped Reduced Graphene Oxide Based Hybrid Nanomaterials as Efficient Antiwear Lubricant Additives.

    PubMed

    Jaiswal, Vinay; Kalyani; Umrao, Sima; Rastogi, Rashmi B; Kumar, Rajesh; Srivastava, Anchal

    2016-05-11

    The microwave-synthesized reduced graphene oxide (MRG), boron-doped reduced graphene oxide (B-MRG), nitrogen-doped reduced graphene oxide (N-MRG), boron-nitrogen-co-doped reduced graphene oxide (B-N-MRG), and TiO2-reinforced B-N-MRG (TiO2-B-N-MRG) nanomaterials have been synthesized and characterized by various state-of-the-art techniques, like Raman spectroscopy, powder X-ray diffraction, scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy, high-resolution transmission electron microscopy, and X-ray photoelectron spectroscopy. Furthermore, the tribological properties of prepared nanomaterials as antiwear additives in neutral paraffin oil have been evaluated using a four-ball machine at an optimized additive concentration (0.15% w/v). The tribological parameters, like mean wear scar diameter, coefficient of friction, and wear rates, revealed that these nanomaterials have potential to be developed as environmentally friendly sulfated-ash-, phosphorus-, and sulfur-free antiwear lubricant additives. The friction- and wear-reducing behavior of MRG increased upon successive doping of nitrogen, boron, and both nitrogen and boron. Among these additives, B-N-co-doped MRG shows superior tribological behavior in paraffin base oil. Besides this, the load-carrying properties of B-N-co-doped MRG have significantly improved after its reinforcement with TiO2 nanoparticles. A comparative study of the surface morphology of a lubricated track in the presence of various additives has been assessed by SEM and contact-mode atomic force microscopy. The X-ray photoelectron spectroscopy studies have proved that the excellent lubrication properties of TiO2-B-N-MRG are due to the in situ formation of a tribofilm composed of boron nitride, adsorbed graphene layers, and tribosintered TiO2 nanoparticles during the tribocontact. Being sulfur-, halogen-, and phosphorus-free, these graphene-based nanomaterials act as green antiwear additives, protecting interacting

  20. Mineralizable phosphorus, nitrogen, and carbon relationships in dairy manure at various carbon-to-phosphorus ratios

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Animal manure contains all major elements required for plant and microorganisms’ uptake and assimilation for growth, namely, phosphorus (P), nitrogen, and carbon. Information about interactions between transformations of nutrients and the turnover of P forms in dairy manure, is essential to accurat...

  1. Nitrogen controlled iron catalyst phase during carbon nanotube growth

    SciTech Connect

    Bayer, Bernhard C.; Baehtz, Carsten; Kidambi, Piran R.; Weatherup, Robert S.; Caneva, Sabina; Cabrero-Vilatela, Andrea; Hofmann, Stephan; Mangler, Clemens; Kotakoski, Jani; Meyer, Jannik C.; Goddard, Caroline J. L.

    2014-10-06

    Close control over the active catalyst phase and hence carbon nanotube structure remains challenging in catalytic chemical vapor deposition since multiple competing active catalyst phases typically co-exist under realistic synthesis conditions. Here, using in-situ X-ray diffractometry, we show that the phase of supported iron catalyst particles can be reliably controlled via the addition of NH{sub 3} during nanotube synthesis. Unlike polydisperse catalyst phase mixtures during H{sub 2} diluted nanotube growth, nitrogen addition controllably leads to phase-pure γ-Fe during pre-treatment and to phase-pure Fe{sub 3}C during growth. We rationalize these findings in the context of ternary Fe-C-N phase diagram calculations and, thus, highlight the use of pre-treatment- and add-gases as a key parameter towards controlled carbon nanotube growth.

  2. Implantation of nitrogen, carbon, and phosphorus ions into metals

    SciTech Connect

    Guseva, M.I.; Gordeeva, G.V.

    1987-01-01

    The application of ion implantation for alloying offers a unique opportunity to modify the chemical composition, phase constitution, and microstructure of the surface layers of metals. The authors studied ion implantation of nitrogen and carbon into the surface layers of metallic targets. The phase composition of the implanted layers obtained on the Kh18N10T stainless steel, the refractory molybdenum alloy TsM-6, niobium, and nickel was determined according to the conventional method of recording the x-ray diffraction pattern of the specimens using monochromatic FeK/sub alpha/-radiation on a DRON-2,0 diffractometer. The targets were bombarded at room temperature in an ILU-3 ion accelerator. The implantation of metalloid ions was also conducted with the targets being bombarded with 100-keV phosphorus ions and 40-keV carbon ions.

  3. Hydraulic studies of drilling microbores with supercritical steam, nitrogen and carbon dioxide

    DOE Data Explorer

    Ken Oglesby

    2010-01-01

    Hydraulic studies of drilling microbores at various depths and with various hole sizes, tubing, fluids and rates showed theoretical feasibility. WELLFLO SIMULATIONS REPORT STEP 4: DRILLING 10,000 FT WELLS WITH SUPERCRITICAL STEAM, NITROGEN AND CARBON DIOXIDE STEP 5: DRILLING 20,000 FT WELLS WITH SUPERCRITICAL STEAM, NITROGEN AND CARBON DIOXIDE STEP 6: DRILLING 30,000 FT WELLS WITH SUPERCRITICAL STEAM, NITROGEN AND CARBON DIOXIDE Mehmet Karaaslan, MSI

  4. Process for microwave sintering boron carbide

    DOEpatents

    Holcombe, Cressie E.; Morrow, Marvin S.

    1993-01-01

    A method of microwave sintering boron carbide comprises leaching boron carbide powder with an aqueous solution of nitric acid to form a leached boron carbide powder. The leached boron carbide powder is coated with a glassy carbon precursor to form a coated boron carbide powder. The coated boron carbide powder is consolidated in an enclosure of boron nitride particles coated with a layer of glassy carbon within a container for microwave heating to form an enclosed coated boron carbide powder. The enclosed coated boron carbide powder is sintered within the container for microwave heating with microwave energy.

  5. Process for microwave sintering boron carbide

    DOEpatents

    Holcombe, C.E.; Morrow, M.S.

    1993-10-12

    A method of microwave sintering boron carbide comprises leaching boron carbide powder with an aqueous solution of nitric acid to form a leached boron carbide powder. The leached boron carbide powder is coated with a glassy carbon precursor to form a coated boron carbide powder. The coated boron carbide powder is consolidated in an enclosure of boron nitride particles coated with a layer of glassy carbon within a container for microwave heating to form an enclosed coated boron carbide powder. The enclosed coated boron carbide powder is sintered within the container for microwave heating with microwave energy.

  6. Carbon, nitrogen, and phosphorus transport by world rivers

    SciTech Connect

    Meybeck, M.

    1982-04-01

    The various forms (dissolved and particulate, organic and inorganic) of carbon, nitrogen, and phosphorus in world rivers are reviewed from literature data. Natural levels are based mainly on major rivers for the subarctic and tropical zones which are still unpolluted and on smaller streams for the temperate zone. Atmospheric fallout is also reviewed. Natural contents of dissolved organic carbon (DOC) are mainly dependent on environmental conditions: DOC varies from 1 mg 1/sup -1/ in the mountainous alpine environments to 20 mg 1/sup -1/ in some taiga rivers. The world DOC average is 5.75 mg l/sup -1/. Nitrogen forms include dissolved organic nitrogen (DON), dissolved inorganic nitrogen (DIN = N - NH/sub 4//sup +/ + N - NO/sub 3//sup -/ + N - NO/sub 2//sup -/), and particulate organic nitrogen (PON). Natural levels are very low: DIN = 120 ..mu..g 1/sup -1/ of which only 15 percent is present as ammonia, and 1 percent as nitrite. Phosphorus is naturally present in very low amounts: around 10 ..mu..g 1/sup -1/ for P-PO/sub 4//sup 3/ and 25 ..mu..g 1/sup -1/ for total dissolved phosphorus (TDP which includes the organic form). The average nutrient content of rains has been estimated with a set of unpolluted stations: P - PO/sub 4/ = 5 ..mu..g 1/sup -1/, TDP = 10, N - NO/sub 2/ = 5, N - NH/sub 4/ = 225, DON = 225, and N - NO/sub 3/ = 175 ..mu..g 1/sup -1/. TOC levels are probably around several mg 1/sup -1/. These contents are very similar to those found in unpolluted rivers. Man's influence on surface waters has now greatly increased natural nutrient levels. Total dissolved P and N have globally increased by a factor of two and locally (Western Europe, North America) by factors of 10 to 50. These increases were found to be directly proportional to the watershed population and to its energy consumption.

  7. Carbon- and crack-free growth of hexagonal boron nitride nanosheets and their uncommon stacking order.

    PubMed

    Khan, Majharul Haque; Casillas, Gilberto; Mitchell, David R G; Liu, Hua Kun; Jiang, Lei; Huang, Zhenguo

    2016-09-21

    The quality of hexagonal boron nitride nanosheets (h-BNNS) is often associated with the most visible aspects such as lateral size and thickness. Less obvious factors such as sheet stacking order could also have a dramatic impact on the properties of BNNS and therefore its applications. The stacking order can be affected by contamination, cracks, and growth temperatures. In view of the significance of chemical-vapour-decomposition (CVD) assisted growth of BNNS, this paper reports on strategies to grow carbon- and crack-free BNNS by CVD and describes the stacking order of the resultant BNNS. Pretreatment of the most commonly used precursor, ammonia borane, is necessary to remove carbon contamination caused by residual hydrocarbons. Flattening the Cu and W substrates prior to growth and slow cooling around the Cu melting point effectively facilitate the uniform growth of h-BNNS, as a result of a minimal temperature gradient across the Cu substrate. Confining the growth inside alumina boats effectively minimizes etching of the nanosheet by silica nanoparticles originating from the commonly used quartz reactor tube. h-BNNS grown on solid Cu surfaces using this method adopt AB, ABA, AC', and AC'B stacking orders, which are known to have higher energies than the most stable AA' configuration. These findings identify a pathway for the fabrication of high-quality h-BNNS via CVD and should spur studies on stacking order-dependent properties of h-BNNS. PMID:27455464

  8. Pure and carbon-doped boron phosphide (6,0) zigzag nanotube: A computational NMR study

    NASA Astrophysics Data System (ADS)

    Arshadi, S.; Bekhradnia, A. R.; Alipour, F.; Abedini, S.

    2015-11-01

    Calculations were performed for investigation of the properties of the electronic structure of Carbon- Doped Boron Phosphide Nanotube (CDBPNT). Pristine and three models of C-doped structures of (6,0) zigzag BPNT were studied at density functional theory (DFT) in combination with 6-311G* basis set using Gaussian package of program. The calculated parameters reveal that various 11B and 31P nuclei are divided into some layers with equivalent electrostatic properties. The electronic structure properties are highly influenced by replacement of 11B and 31P atoms by 12C atoms in pristine model. Furthermore, the HOMO-LUMO gap energy for suggested doped models (I), (II) and (III) were lower than pure BPNT pristine systems. The dipole moment values of models (II) and (III) were decreased to 1.788 and 1.789, respectively while the dipole moments of model (I) were enhanced to 4.373, in compare to pure pristine one (2.586). The magnitude of changes in Chemical Shielding (CS) tensor parameters revealed that the electron density at the site of 31P was higher than that at the site of 11B due to carbon doping.

  9. Coaxial carbon@boron nitride nanotube arrays with enhanced thermal stability and compressive mechanical properties.

    PubMed

    Jing, Lin; Tay, Roland Yingjie; Li, Hongling; Tsang, Siu Hon; Huang, Jingfeng; Tan, Dunlin; Zhang, Bowei; Teo, Edwin Hang Tong; Tok, Alfred Iing Yoong

    2016-06-01

    Vertically aligned carbon nanotube (CNT) arrays have aroused considerable interest because of their remarkable mechanical properties. However, the mechanical behaviour of as-synthesized CNT arrays could vary drastically at a macro-scale depending on their morphologies, dimensions and array density, which are determined by the synthesis method. Here, we demonstrate a coaxial carbon@boron nitride nanotube (C@BNNT) array with enhanced compressive strength and shape recoverability. CNT arrays are grown using a commercially available thermal chemical vapor deposition (TCVD) technique and an outer BNNT with a wall thickness up to 1.37 nm is introduced by a post-growth TCVD treatment. Importantly, compared to the as-grown CNT arrays which deform almost plastically upon compression, the coaxial C@BNNT arrays exhibit an impressive ∼4-fold increase in compressive strength with nearly full recovery after the first compression cycle at a 50% strain (76% recovery maintained after 10 cycles), as well as a significantly high and persistent energy dissipation ratio (∼60% at a 50% strain after 100 cycles), attributed to the synergistic effect between the CNT and outer BNNT. Additionally, the as-prepared C@BNNT arrays show an improved structural stability in air at elevated temperatures, attributing to the outstanding thermal stability of the outer BNNT. This work provides new insights into tailoring the mechanical and thermal behaviours of arbitrary CNT arrays which enables a broader range of applications. PMID:27227818

  10. [XPS and Raman spectral analysis of nitrogenated tetrahedral amorphous carbon (ta-C : N) films with different nitrogen content].

    PubMed

    Chen, Wang-Shou; Zhu, Jia-Qi; Han, Jie-Cai; Tian, Gui; Tan, Man-Lin

    2009-01-01

    Nitrogenated tetrahedral amorphous carbon (ta-C : N) films were prepared on the polished C--Si substrates by introducing highly pure nitrogen gas into the cathode region and the depositing chamber synchronously using filtered cathodic vacuum arc (FCVA) technology. The nitrogen content in the films was controlled by changing the flow rate of nitrogen gas. The configuration of ta-C : N films was investigated by means of X-ray photoelectron spectroscopy (XPS) and visible Raman spectroscopy. It was shown that the nitrogen content in the films increased from 0.84 at% to 5.37 at% monotonously when the nitrogen flow rate was varied from 2 seem to 20 sccm. The peak position of C (1s) core level moved towards higher binding energy with the increase in nitrogen content. The shift of C (1s) peak position could be ascribed to the chemical bonding between carbon and nitrogen atoms even though more three-fold coordinated sp2 configuration as in graphite was formed when the films were doped with more nitrogen atoms. Additionally, the half width of C(1s) peak gradually was also broadened with increasing nitrogen content. In order to discover clearly the changing regularities of the microstructure of the films, the XPS C(1s) spectra and Raman spectra were deconvoluted using a Gaussian-Lorentzian mixed lineshape. It was shown that the tetrahedral hybridization component was still dominant even though the ratio of sp2/sp3 obtained from C(1s) spectra rose with the increase in nitrogen content. The Raman measurements demonstrated that the G peak position shifted towards higher frequency from 1,561 to 1,578 cm(-1) and the ratio of ID/IG also rose with the increase in nitrogen content. Both results indicated that the graphitizing tendency could occur with the increase in nitrogen content in the films. PMID:19385255

  11. A Computational Investigation of the Nitrogen-Boron Interaction in o-(N,N-Dialkylaminomethyl)arylboronate Systems

    PubMed Central

    Larkin, Joseph D.; Fossey, John S.; James, Tony D.; Brooks, Bernard R.; Bock, Charles W.

    2014-01-01

    o-(N,N-Dialkylaminomethyl)arylboronate systems are an important class of compounds in diol-sensor development. We report results from a computational investigation of fourteen o-(N,N-dialkylaminomethyl)arylboronates using second-order Møller-Plesset (MP2) perturbation theory. Geometry optimizations were performed at the MP2/cc-pVDZ level and followed by single-point calculations at the MP2/aug-cc-pVDZ(cc-pVTZ) levels. These results are compared to those from density functional theory (DFT) at the PBE1PBE(PBE1PBE-D)/6-311++G(d,p)(aug-cc-pVDZ) levels, as well as to experiment. Results from continuum PCM and CPCM solvation models were employed to assess the effects of a bulk aqueous environment. Although the behaviour of o-(N,N-dialkylaminomethyl) free acid and ester proved to be complicated, we were able to extract some important trends from our calculations: 1) for the free acids the intramolecular hydrogen-bonded B-O-H⋯N seven-membered ring conformers 12 and 16 are found to be slightly lower in energy than the dative-bonded N→B five-membered ring conformers 10 and 14 while conformers 13 and 17, with no direct boron-nitrogen interaction, are significantly higher in energy than 12 and 16; 2) for the esters where no intramolecular B-O-H⋯N bonded form is possible, the N→B conformers 18 and 21 are significantly lower in energy than the no-interaction forms 20 and 23; 3) H2O insertion reactions into the N→B structures 10, 14, 18, and 21 leading to the seven-membered intermolecular hydrogen-bonded B⋯OH2⋯N ring structures 11, 15, 19, and 22 are all energetically favorable. PMID:21050022

  12. Encapsulation of cisplatin as an anti-cancer drug into boron-nitride and carbon nanotubes: Molecular simulation and free energy calculation.

    PubMed

    Roosta, Sara; Hashemianzadeh, Seyed Majid; Ketabi, Sepideh

    2016-10-01

    Encapsulation of cisplatin anticancer drug into the single walled (10, 0) carbon nanotube and (10, 0) boron-nitride nanotube was investigated by quantum mechanical calculations and Monte Carlo Simulation in aqueous solution. Solvation free energies and complexation free energies of the cisplatin@ carbon nanotube and cisplatin@ boron-nitride nanotube complexes was determined as well as radial distribution functions of entitled compounds. Solvation free energies of cisplatin@ carbon nanotube and cisplatin@ boron-nitride nanotube were -4.128kcalmol(-1) and -2457.124kcalmol(-1) respectively. The results showed that cisplatin@ boron-nitride nanotube was more soluble species in water. In addition electrostatic contribution of the interaction of boron- nitride nanotube complex and solvent was -281.937kcalmol(-1) which really more than Van der Waals and so the electrostatic interactions play a distinctive role in the solvation free energies of boron- nitride nanotube compounds. On the other hand electrostatic part of the interaction of carbon nanotube complex and solvent were almost the same as Van der Waals contribution. Complexation free energies were also computed to study the stability of related structures and the free energies were negative (-374.082 and -245.766kcalmol(-1)) which confirmed encapsulation of drug into abovementioned nanotubes. However, boron-nitride nanotubes were more appropriate for encapsulation due to their larger solubility in aqueous solution. PMID:27287103

  13. Methods of producing continuous boron carbide fibers

    SciTech Connect

    Garnier, John E.; Griffith, George W.

    2015-12-01

    Methods of producing continuous boron carbide fibers. The method comprises reacting a continuous carbon fiber material and a boron oxide gas within a temperature range of from approximately 1400.degree. C. to approximately 2200.degree. C. Continuous boron carbide fibers, continuous fibers comprising boron carbide, and articles including at least a boron carbide coating are also disclosed.

  14. Nitrogen-Containing Carbon Nanotube Synthesized from Polymelem and Activated Carbon Derived from Polymer Blend

    NASA Astrophysics Data System (ADS)

    Qin, Nan

    Polymelem possesses a polymeric structure of heptazine (C6N 7) rings connected by amine bridges and our study has demonstrated that it is a promising precursor for the synthesis of nitrogen-containing carbon materials. Nitrogen-containing carbon nanotube (NCNT) was produced by pyrolyzing polymelem as a dual source of carbon and nitrogen with Raney nickel in a high pressure stainless steel cell. Activated carbon was produced from poly(ether ether ketone)/poly(ether imide) (PEEK/PEI blend) and incorporated with polymelem to enhance the hydrogen adsorption. Polymelem was successfully synthesized by pyrolyzing melamine at 450--650 °C and its structure was elucidated by 13C solid state NMR, FTIR, and XRD. The molecular weight determined by a novel LDI MS equipped with a LIFT mode illuminated that polymelem has both linear and cyclic connectivity with a degree of polymerization of 2--5 depending on the synthesis temperature. The decomposition products of polymelem were determined to be cyanoamide, dicyanoamide, and tricyanoamine. Tricyanoamine is the smallest carbon nitride molecule and has been experimentally confirmed for the first time in this study. When polymelem was decomposed in the presence of Raney nickel, homogenous NCNT with nitrogen content of ˜ 4--19 atom% was produced. A mechanism based on a detail analysis of the TEM images at different growth stages proposed that the NCNT propagated via a tip-growth mechanism originating at the nano-domains within the Raney nickel, and was accompanied with the aggregation of the nickel catalysts. Such NCNT exhibited a cup-stack wall structure paired with a compartmental feature. The nitrogen content, tube diameter and wall thickness greatly depended on synthesis conditions. The activated carbon derived from PEEK/PEI blend demonstrated a surface area up to ˜3000 m2/g, and average pore size of < 20 A. Such activated carbon exhibited a hydrogen storage capacity of up to 6.47 wt% at 40 bar, 77 K. The activated carbon has

  15. Theoretical uncertainties in extracting cosmic-ray diffusion parameters: the boron-to-carbon ratio

    NASA Astrophysics Data System (ADS)

    Genolini, Y.; Putze, A.; Salati, P.; Serpico, P. D.

    2015-08-01

    Context. PAMELA and, more recently, AMS-02, are ushering us into a new era of greatly reduced statistical uncertainties in experimental measurements of cosmic-ray fluxes. In particular, new determinations of traditional diagnostic tools such as the boron-to-carbon ratio (B/C) are expected to significantly reduce errors on cosmic-ray diffusion parameters, with important implications for astroparticle physics, ranging from inferring primary source spectra to indirect dark matter searches. Aims: It is timely to stress, however, that the conclusions obtained crucially depend on the framework in which the data are interpreted as well as on some nuclear input parameters. We aim at assessing the theoretical uncertainties affecting the outcome, with models as simple as possible while still retaining the key dependencies. Methods: We compared different semi-analytical, two-zone model descriptions of cosmic-ray transport in the Galaxy: infinite slab(1D), cylindrical symmetry (2D) with homogeneous sources, cylindrical symmetry (2D) with inhomogeneous source distribution. We tested for the effect of a primary source contamination in the boron flux by parametrically altering its flux. We also tested for nuclear cross-section uncertainties. All hypotheses were compared by χ2 minimisation techniques to preliminary results from AMS-02. Results: We find that the main theoretical bias on the determination of the diffusion coefficient index δ (up to a factor two) is represented by the assumption that no injection of boron takes place at the source. The next most important uncertainty is represented by cross-section uncertainties, which reach ± 20% in δ. As a comparison, nuclear uncertainties are more important than the shift in the best-fit when introducing a convective wind of velocity ≲30 km s-1, with respect to a pure diffusive baseline model. Perhaps surprisingly, homogeneous 1D vs. 2D performances are similar in determining diffusion parameters. An inhomogeneous source

  16. Chemical Analysis of Impurity Boron Atoms in Diamond Using Soft X-ray Emission Spectroscopy

    SciTech Connect

    Muramatsu, Yasuji; Iihara, Junji; Takebe, Toshihiko; Denlinger, Jonathan D.

    2008-03-29

    To analyze the local structure and/or chemical states of boron atoms in boron-doped diamond, which can be synthesized by the microwave plasma-assisted chemical vapor deposition method (CVD-B-diamond) and the temperature gradient method at high pressure and high temperature (HPT-B-diamond), we measured the soft X-ray emission spectra in the CK and BK regions of B-diamonds using synchrotron radiation at the Advanced Light Source (ALS). X-ray spectral analyses using the fingerprint method and molecular orbital calculations confirm that boron atoms in CVD-B-diamond substitute for carbon atoms in the diamond lattice to form covalent B-C bonds, while boron atoms in HPT-B-diamond react with the impurity nitrogen atoms to form hexagonal boron nitride. This suggests that the high purity diamond without nitrogen impurities is necessary to synthesize p-type B-diamond semiconductors.

  17. Fluorescently tuned nitrogen-doped carbon dots from carbon source with different content of carboxyl groups

    SciTech Connect

    Wang, Hao; Wang, Yun; Dai, Xiao; Zou, Guifu E-mail: zouguifu@suda.edu.cn; Gao, Peng; Zhang, Ke-Qin E-mail: zouguifu@suda.edu.cn; Du, Dezhuang; Guo, Jun

    2015-08-01

    In this study, fluorescent nitrogen-doped carbon dots (NCDs) were tuned via varying the sources with different number of carboxyl groups. Owing to the interaction between amino and carboxyl, more amino groups conjugate the surface of the NCDs by the source with more carboxyl groups. Fluorescent NCDs were tuned via varying the sources with different content of carboxyl groups. Correspondingly, the nitrogen content, fluorescence quantum yields and lifetime of NCDs increases with the content of carboxyl groups from the source. Furthermore, cytotoxicity assay and cell imaging test indicate that the resultant NCDs possess low cytotoxicity and excellent biocompatibility.

  18. Liquid Phase Sintering of Boron-Containing Powder Metallurgy Steel with Chromium and Carbon

    NASA Astrophysics Data System (ADS)

    Wu, Ming-Wei; Fan, Yu-Chi; Huang, Her-Yueh; Cai, Wen-Zhang

    2015-11-01

    Liquid phase sintering is an effective method to improve the densification of powder metallurgy materials. Boron is an excellent alloying element for liquid phase sintering of Fe-based materials. However, the roles of chromium and carbon, and particularly that of the former, on liquid phase sintering are still undetermined. This study demonstrated the effects of chromium and carbon on the microstructure, elemental distribution, boride structure, liquid formation, and densification of Fe-B-Cr and Fe-B-Cr-C steels during liquid phase sintering. The results showed that steels with 0.5 wt pct C densify faster than those without 0.5 wt pct C. Moreover, although only one liquid phase forms in Fe-B-Cr steel, adding 0.5 wt pct C reduces the formation temperature of the liquid phase by about 50 K (°C) and facilitates the formation of an additional liquid, resulting in better densification at 1473 K (1200 °C). In both Fe-B-Cr and Fe-B-Cr-C steels, increasing the chromium content from 1.5 to 3 wt pct raises the temperature of liquid formation by about 10 K (°C). Thermodynamic simulations and experimental results demonstrated that carbon atoms dissolved in austenite facilitate the eutectic reaction and reduce the formation temperature of the liquid phase. In contrast, both chromium and molybdenum atoms dissolved in austenite delay the eutectic reaction. Furthermore, the 3Cr-0.5Mo additive in the Fe-0.4B steel does not change the typical boride structure of M2B. With the addition of 0.5 wt pct C, the crystal structure is completely transformed from M2B boride to M3(B,C) boro-carbide.

  19. Bayesian Nitrate Source Apportionment to Individual Groundwater Wells in the Central Valley by use of Nitrogen, Oxygen, and Boron Isotopic Tracers

    NASA Astrophysics Data System (ADS)

    Lockhart, K.; Harter, T.; Grote, M.; Young, M. B.; Eppich, G.; Deinhart, A.; Wimpenny, J.; Yin, Q. Z.

    2014-12-01

    Groundwater quality is a concern in alluvial aquifers underlying agricultural areas worldwide, an example of which is the San Joaquin Valley, California. Nitrate from land applied fertilizers or from animal waste can leach to groundwater and contaminate drinking water resources. Dairy manure and synthetic fertilizers are the major sources of nitrate in groundwater in the San Joaquin Valley, however, septic waste can be a major source in some areas. As in other such regions around the world, the rural population in the San Joaquin Valley relies almost exclusively on shallow domestic wells (≤150 m deep), of which many have been affected by nitrate. Consumption of water containing nitrate above the drinking water limit has been linked to major health effects including low blood oxygen in infants and certain cancers. Knowledge of the proportion of each of the three main nitrate sources (manure, synthetic fertilizer, and septic waste) contributing to individual well nitrate can aid future regulatory decisions. Nitrogen, oxygen, and boron isotopes can be used as tracers to differentiate between the three main nitrate sources. Mixing models quantify the proportional contributions of sources to a mixture by using the concentration of conservative tracers within each source as a source signature. Deterministic mixing models are common, but do not allow for variability in the tracer source concentration or overlap of tracer concentrations between sources. Bayesian statistics used in conjunction with mixing models can incorporate variability in the source signature. We developed a Bayesian mixing model on a pilot network of 32 private domestic wells in the San Joaquin Valley for which nitrate as well as nitrogen, oxygen, and boron isotopes were measured. Probability distributions for nitrogen, oxygen, and boron isotope source signatures for manure, fertilizer, and septic waste were compiled from the literature and from a previous groundwater monitoring project on several

  20. Soil nitrogen and carbon impacts of raising chickens on pasture

    NASA Astrophysics Data System (ADS)

    Ryals, R.; Leach, A.; Tang, J.; Hastings, M. G.; Galloway, J. N.

    2014-12-01

    Chicken is the most consumed meat in the US, and production continues to intensify rapidly around the world. Chicken manure from confined feeding operations is typically applied in its raw form to nearby croplands, resulting in hotspots of soil nitrous oxide (N2O) emissions. Pasture-raised chicken is an alternative to industrial production and is growing in popularity with rising consumer demand for more humanely raised protein sources. In this agricultural model, manure is deposited directly onto grassland soils where it is thought to increase pools of soil carbon and nitrogen. The fate of manure nitrogen from pasture-raised chicken production remains poorly understood. We conducted a controlled, replicated experiment on a permaculture farm in Charlottesville, Virginia (Timbercreek Organics) in which small chicken coops (10 ft x 12 ft) were moved daily in a pasture. We measured manure deposition rates, soil inorganic nitrogen pools, soil moisture, and soil N2O and CO2 emissions. Measurements were made for the 28-day pasture life of three separate flocks of chickens in the spring, summer, and fall. Each flock consisted of approximately 200-300 chickens occupying three to five coops (~65 chickens/coop). Measurements were also made in paired ungrazed control plots. Manure deposition rates were similar across flocks and averaged 1.5 kgdrywt ha-1 during the spring grazing event and 4.0 kgdrywt ha-1 during the summer and fall grazing events. Manure deposition was relatively constant over the four weeks pasture-lifetime of the chickens. Compared to control plots, grazed areas exhibited higher soil N2O and CO2 fluxes. The magnitude of these fluxes diminished significantly over the four-week span. Soil gas fluxes significantly increased following rainfall events. For a given rainfall event, higher fluxes were observed from transects that were grazed more recently. Soil gaseous reactive nitrogen losses were less in this pasture system compared to cultivated field amended

  1. Increased forest ecosystem carbon and nitrogen storage from nitrogen rich bedrock.

    PubMed

    Morford, Scott L; Houlton, Benjamin Z; Dahlgren, Randy A

    2011-09-01

    Nitrogen (N) limits the productivity of many ecosystems worldwide, thereby restricting the ability of terrestrial ecosystems to offset the effects of rising atmospheric CO(2) emissions naturally. Understanding input pathways of bioavailable N is therefore paramount for predicting carbon (C) storage on land, particularly in temperate and boreal forests. Paradigms of nutrient cycling and limitation posit that new N enters terrestrial ecosystems solely from the atmosphere. Here we show that bedrock comprises a hitherto overlooked source of ecologically available N to forests. We report that the N content of soils and forest foliage on N-rich metasedimentary rocks (350-950 mg N kg(-1)) is elevated by more than 50% compared with similar temperate forest sites underlain by N-poor igneous parent material (30-70 mg N kg(-1)). Natural abundance N isotopes attribute this difference to rock-derived N: (15)N/(14)N values for rock, soils and plants are indistinguishable in sites underlain by N-rich lithology, in marked contrast to sites on N-poor substrates. Furthermore, forests associated with N-rich parent material contain on average 42% more carbon in above-ground tree biomass and 60% more carbon in the upper 30 cm of the soil than similar sites underlain by N-poor rocks. Our results raise the possibility that bedrock N input may represent an important and overlooked component of ecosystem N and C cycling elsewhere. PMID:21886160

  2. Increased tree carbon storage in response to nitrogen deposition in the US

    NASA Astrophysics Data System (ADS)

    Quinn Thomas, R.; Canham, Charles D.; Weathers, Kathleen C.; Goodale, Christine L.

    2010-01-01

    Human activities have greatly accelerated emissions of both carbon dioxide and biologically reactive nitrogen to the atmosphere. As nitrogen availability often limits forest productivity, it has long been expected that anthropogenic nitrogen deposition could stimulate carbon sequestration in forests. However, spatially extensive evidence for deposition-induced stimulation of forest growth has been lacking, and quantitative estimates from models and plot-level studies are controversial. Here, we use forest inventory data to examine the impact of nitrogen deposition on tree growth, survival and carbon storage across the northeastern and north-central USA during the 1980s and 1990s. We show a range of growth and mortality responses to nitrogen deposition among the region's 24 most common tree species. Nitrogen deposition (which ranged from 3 to 11kgha-1yr-1) enhanced the growth of 11 species and decreased the growth of 3 species. Nitrogen deposition enhanced growth of all tree species with arbuscular mycorrhizal fungi associations. In the absence of disturbances that reduced carbon stocks by more than 50%, above-ground biomass increment increased by 61kg of carbon per kg of nitrogen deposited, amounting to a 40% enhancement over pre-industrial conditions. Extrapolating to the globe, we estimate that nitrogen deposition could increase tree carbon storage by 0.31Pg carbon yr-1.

  3. Local atomic and electronic structure of boron chemical doping in monolayer graphene.

    PubMed

    Zhao, Liuyan; Levendorf, Mark; Goncher, Scott; Schiros, Theanne; Pálová, Lucia; Zabet-Khosousi, Amir; Rim, Kwang Taeg; Gutiérrez, Christopher; Nordlund, Dennis; Jaye, Cherno; Hybertsen, Mark; Reichman, David; Flynn, George W; Park, Jiwoong; Pasupathy, Abhay N

    2013-10-01

    We use scanning tunneling microscopy and X-ray spectroscopy to characterize the atomic and electronic structure of boron-doped and nitrogen-doped graphene created by chemical vapor deposition on copper substrates. Microscopic measurements show that boron, like nitrogen, incorporates into the carbon lattice primarily in the graphitic form and contributes ~0.5 carriers into the graphene sheet per dopant. Density functional theory calculations indicate that boron dopants interact strongly with the underlying copper substrate while nitrogen dopants do not. The local bonding differences between graphitic boron and nitrogen dopants lead to large scale differences in dopant distribution. The distribution of dopants is observed to be completely random in the case of boron, while nitrogen displays strong sublattice clustering. Structurally, nitrogen-doped graphene is relatively defect-free while boron-doped graphene films show a large number of Stone-Wales defects. These defects create local electronic resonances and cause electronic scattering, but do not electronically dope the graphene film. PMID:24032458

  4. Sub-ambient carbon dioxide adsorption properties of nitrogen doped graphene

    SciTech Connect

    Tamilarasan, P.; Ramaprabhu, Sundara

    2015-04-14

    Carbon dioxide adsorption on carbon surface can be enhanced by doping the surface with heterogeneous atoms, which can increase local surface affinity. This study presents the carbon dioxide adsorption properties of nitrogen doped graphene at low pressures (<100 kPa). Graphene was exposed to nitrogen plasma, which dopes nitrogen atoms into carbon hexagonal lattice, mainly in pyridinic and pyrrolic forms. It is found that nitrogen doping significantly improves the CO{sub 2} adsorption capacity at all temperatures, due to the enrichment of local Lewis basic sites. In general, isotherm and thermodynamic parameters suggest that doped nitrogen sites have nearly same adsorption energy of surface defects and residual functional groups. The isosteric heat of adsorption remains in physisorption range, which falls with surface coverage, suggesting the distribution of magnitude of adsorption energy. The absolute values of isosteric heat and entropy of adsorption are slightly increased upon nitrogen doping.

  5. Nitrogen and carbon oxides chemistry in the HRS retorting process

    SciTech Connect

    Reynolds, J.G.

    1993-11-12

    The HRS Oil Shale Retort process consists of a pyrolysis section which converts kerogen of the shale to liquid and gaseous products, and a combustion section which burns residual carbon on the shale to heat the process. Average gas concentrations of selected gas phase species were determined from data measured at several placed on the combustion system of the Lawrence Livermore National Laboratory Hot-Recycled-Solids Retort Pilot Plant for representative rich and lean shale runs. The data was measured on-line and in real time by on-line meters (CO{sub 2}, CO, O{sub 2}), mass spectrometry (CO{sub 2}, O{sub 2}, H{sub 2}O, NO, CH{sub 4}, SO{sub 2}, N{sub 2} and Ar), and Fourier transform infrared spectroscopy (CO{sub 2}, CO, H{sub 2}O, NO, N{sub 2}O, NO{sub 2}, CH{sub 4}, SO{sub 2}, NH{sub 3}, and HCN). For both the rich and leans shale runs, the Lift-Pipe Combustor (LFT) exhibited gas concentrations (sampled at the exit of the LFT) indicative of incomplete combustion and oxidation; the Delayed-Fall Combustor (DFC) exhibited gas concentrations (sampled at the annulus and the exit of the DFC) indicative of much more complete combustion and oxidation. The Fluidized-Bed Combustor exhibited gas concentrations which were controlled to a large extent by the injection atmosphere of the FBC. High levels of nitrogen oxides and low levels of CO were detected when full air injection was used, while high levels of CO and low levels of nitrogen-oxides were detected with partial N{sub 2} injection. Sequential sampling limitations and nitrogen balances are also discussed.

  6. Does canopy nitrogen uptake enhance carbon sequestration by trees?

    PubMed

    Nair, Richard K F; Perks, Micheal P; Weatherall, Andrew; Baggs, Elizabeth M; Mencuccini, Maurizio

    2016-02-01

    Temperate forest (15) N isotope trace experiments find nitrogen (N) addition-driven carbon (C) uptake is modest as little additional N is acquired by trees; however, several correlations of ambient N deposition against forest productivity imply a greater effect of atmospheric nitrogen deposition than these studies. We asked whether N deposition experiments adequately represent all processes found in ambient conditions. In particular, experiments typically apply (15) N to directly to forest floors, assuming uptake of nitrogen intercepted by canopies (CNU) is minimal. Additionally, conventional (15) N additions typically trace mineral (15) N additions rather than litter N recycling and may increase total N inputs above ambient levels. To test the importance of CNU and recycled N to tree nutrition, we conducted a mesocosm experiment, applying 54 g N/(15) N ha(-1)  yr(-1) to Sitka spruce saplings. We compared tree and soil (15) N recovery among treatments where enrichment was due to either (1) a (15) N-enriched litter layer, or mineral (15) N additions to (2) the soil or (3) the canopy. We found that 60% of (15) N applied to the canopy was recovered above ground (in needles, stem and branches) while only 21% of (15) N applied to the soil was found in these pools. (15) N recovery from litter was low and highly variable. (15) N partitioning among biomass pools and age classes also differed among treatments, with twice as much (15) N found in woody biomass when deposited on the canopy than soil. Stoichiometrically calculated N effect on C uptake from (15) N applied to the soil, scaled to real-world conditions, was 43 kg C kg N(-1) , similar to manipulation studies. The effect from the canopy treatment was 114 kg C kg N(-1) . Canopy treatments may be critical to accurately represent N deposition in the field and may address the discrepancy between manipulative and correlative studies. PMID:26391113

  7. Device for detection and identification of carbon- and nitrogen-containing materials

    DOEpatents

    Karev, Alexander Ivanovich; Raevsky, Valery Georgievich; Dzhilavyan, Leonid Zavenovich; Laptev, Valery Dmitrievich; Pakhomov, Nikolay Ivanovich; Shvedunov, Vasily Ivanovich; Rykalin, Vladimir Ivanovich; Brothers, Louis Joseph; Wilhide, Larry K

    2014-03-25

    A device for detection and identification of carbon- and nitrogen-containing materials is described. In particular, the device performs the detection and identification of carbon- and nitrogen-containing materials by photo-nuclear detection. The device may comprise a race-track microtron, a breaking target, and a water-filled Cherenkov radiation counter.

  8. Development and evaluation of the carbon-nitrogen cycle module for the GPFARM-Range model

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Rangelands cover approximately 50% of the terrestrial surface of the earth. The soil carbon and nitrogen storage and turnover in rangeland systems are becoming increasingly important for sustainable grazing management and adaptations to climate change. In this study, a carbon-nitrogen (C-N) cycle m...

  9. Carbon and nitrogen provisions alter the metabolic flux in developing soybean embryos

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Soybeans store approximately 40% of their biomass in the form of protein. Protein concentrations reflect the carbon and nitrogen levels received by the developing embryo. The relationship between carbon and nitrogen supply and seed composition during filling was examined through a series of embryo c...

  10. Carbon Accumulation and Nitrogen Pool Recovery during Transitions from Savanna to Forest in Central Brazil

    NASA Astrophysics Data System (ADS)

    Pellegrini, A.; Hoffmann, W. A.; Franco, A. C.

    2014-12-01

    The expansion of tropical forest into savanna may potentially be a large carbon sink, but little is known about the patterns of carbon sequestration during transitional forest formation. Moreover, it is unclear how nutrient limitation, due to extended exposure to firedriven nutrient losses, may constrain carbon accumulation. Here, we sampled plots that spanned a woody biomass gradient from savanna to transitional forest in response to differential fire protection in central Brazil. These plots were used to investigate how the process of transitional forest formation affects the size and distribution of carbon (C) and nitrogen (N) pools. This was paired with a detailed analysis of the nitrogen cycle to explore possible connections between carbon accumulation and nitrogen limitation. An analysis of carbon pools in the vegetation, upper soil, and litter shows that the transition from savanna to transitional forest can result in a fourfold increase in total carbon (from 43 to 179 Mg C/ha) with a doubling of carbon stocks in the litter and soil layers. Total nitrogen in the litter and soil layers increased with forest development in both the bulk (+68%) and plant-available (+150%) pools, with the most pronounced changes occurring in the upper layers. However, the analyses of nitrate concentrations, nitrate : ammonium ratios, plant stoichiometry of carbon and nitrogen, and soil and foliar nitrogen isotope ratios suggest that a conservative nitrogen cycle persists throughout forest development, indicating that nitrogen remains in low supply relative to demand. Furthermore, the lack of variation in underlying soil type (>20 cm depth) suggests that the biogeochemical trends across the gradient are driven by vegetation. Our results provide evidence for high carbon sequestration potential with forest encroachment on savanna, but nitrogen limitation may play a large and persistent role in governing carbon sequestration in savannas or other equally fire-disturbed tropical

  11. Low Carbon Costs of Nitrogen Fixation in Tropical Dry Forests

    NASA Astrophysics Data System (ADS)

    Gei, M. G.; Powers, J. S.

    2015-12-01

    Legume tree species with the ability to fix nitrogen (N) are highly diverse and widespread across tropical forests but in particular in the dry tropics. Their ecological success in lower latitudes has been called a "paradox": soil N in the tropics is thought to be high, while acquiring N through fixation incurs high energetic costs. However, the long held assumptions that N fixation is limited by photosynthate and that N fixation penalizes plant productivity have rarely been tested, particularly in legume tree species. We show results from three different experiments where we grew eleven species of tropical dry forest legumes. We quantified plant biomass and N fixation using nodulation and the 15N natural isotope abundance (Ndfa or nitrogen derived from fixation). These data show little evidence for costs of N fixation in seedlings grown under different soil fertility, light regimes, and with different microbial communities. Seedling productivity did not incur major costs because of N fixation: indeed, the average slope between Ndfa and biomass was positive (range in slopes: -0.03 to 0.3). Moreover, foliar N, which varied among species, was tightly constrained and not correlated with Ndfa. This finding implies that legume species have a target N that does not change depending on N acquisition strategies. The process of N fixation in tropical legumes may be more carbon efficient than previously thought. This view is more consistent with the hyperabundance of members of this family in tropical ecosystems.

  12. Theory of nitrogen doping of carbon nanoribbons: Edge effects

    SciTech Connect

    Jiang, Jie; Turnbull, Joseph; Lu, Wenchang; Boguslawski, Piotr; Bernholc, J.

    2012-01-01

    Nitrogen doping of a carbon nanoribbon is profoundly affected by its one-dimensional character, symmetry, and interaction with edge states. Using state-of-the-art ab initio calculations, including hybrid exact-exchange density functional theory, we find that, for N-doped zigzag ribbons, the electronic properties are strongly dependent upon sublattice effects due to the non-equivalence of the two sublattices. For armchair ribbons, N-doping effects are different depending upon the ribbon family: for families 2 and 0, the N-induced levels are in the conduction band, while for family 1 the N levels are in the gap. In zigzag nanoribbons, nitrogen close to the edge is a deep center, while in armchair nanoribbons its behavior is close to an effective-mass-like donor with the ionization energy dependent on the value of the band gap. In chiral nanoribbons, we find strong dependence of the impurity level and formation energy upon the edge position of the dopant, while such site-specificity is not manifested in the magnitude of the magnetization.

  13. Theory of nitrogen doping of carbon nanoribbons: Edge effects

    DOE PAGESBeta

    Jiang, Jie; Turnbull, Joseph; Lu, Wenchang; Oak Ridge National Lab.; Boguslawski, Piotr; Univ. of Warsaw; Bernholc, J.; Oak Ridge National Lab.

    2012-01-01

    Nitrogen doping of a carbon nanoribbon is profoundly affected by its one-dimensional character, symmetry, and interaction with edge states. Using state-of-the-art ab initio calculations, including hybrid exact-exchange density functional theory, we find that, for N-doped zigzag ribbons, the electronic properties are strongly dependent upon sublattice effects due to the non-equivalence of the two sublattices. For armchair ribbons, N-doping effects are different depending upon the ribbon family: for families 2 and 0, the N-induced levels are in the conduction band, while for family 1 the N levels are in the gap. In zigzag nanoribbons, nitrogen close to the edge is amore » deep center, while in armchair nanoribbons its behavior is close to an effective-mass-like donor with the ionization energy dependent on the value of the band gap. In chiral nanoribbons, we find strong dependence of the impurity level and formation energy upon the edge position of the dopant, while such site-specificity is not manifested in the magnitude of the magnetization.« less

  14. Novel Tool for Simultaneous Carbon and Nitrogen Stable Isotope Analyses in Aqueous Samples

    NASA Astrophysics Data System (ADS)

    Federherr, E.; Schmidt, T. C.; Cerli, C.; Kalbitz, K.; Kupka, H. J.; Lange, L.; Dunsbach, R.; Panetta, R. J.; Kasson, A.

    2014-12-01

    Investigation of transformation and transport processes of carbon and nitrogen in ecosystems plays an important role to understand and predict their dynamics and role in biogeochemistry. Consequently, suitable and accurate methods for concentration as well as stable isotopic composition analysis of carbon and nitrogen in waters and aqueous solutions play a significant role. Traditionally dissolved carbon and nitrogen stable isotope analysis (SIA) is performed using either offline sample preparation followed by elemental analysis isotope ratio mass spectrometry (EA/IRMS) or modified wet chemical oxidation based device coupled to IRMS. Recently we presented a high temperature combustion system (HTC), which significantly improves upon these methods for dissolved organic carbon (DOC) SIA. The analysis of δ15N of dissolved nitrogen still has large limitations. Its low concentration makes EA/IRMS laborious, time and sample consuming. Systems based on wet chemical oxidation-IRMS bare the risk of sensitivity loss as well as of fractionation due to incomplete mineralization. In addition, the high solubility of molecular nitrogen in water remains a technical challenge, as it requires additional separation steps to distinguish between physically dissolved nitrogen and bound nitrogen. Further development of our HTC system lead to the implementation of the δ15N determination which now coupled, into a novel total organic carbon (TOC) analyzing system, especially designed for SIA of both, carbon and nitrogen. Integrated, innovative purge and trap technique (peak focusing) for nitrogen with aluminosilicate adsorber and peltier element based cooling system, in combination with high injection volume (up to 3 mL) as well as favorable carrier gas flow significantly improves sensitivity. Down to 1ppm and less total nitrogen can be measured with precision of ≤ 0.5‰. To lower the background caused by physically dissolved nitrogen new, membrane-vacuum based, degasser was designed

  15. Role of nitrogen in pore development in activated carbon prepared by potassium carbonate activation of lignin

    NASA Astrophysics Data System (ADS)

    Tsubouchi, Naoto; Nishio, Megumi; Mochizuki, Yuuki

    2016-05-01

    The present work focuses on the role of nitrogen in the development of pores in activated carbon produced from lignin by K2CO3 activation, employing a fixed bed reactor under a high-purity He stream at temperatures of 500-900 °C. The specific surface area and pore volume obtained by activation of lignin alone are 230 m2/g and 0.13 cm3/g at 800 °C, and 540 m2/g and 0.31 cm3/g at 900 °C, respectively. Activation of a mixture of lignin and urea provides a significant increase in the surface area and volume, respectively reaching 3300-3400 m2/g and 2.0-2.3 cm3/g after holding at 800-900 °C for 1 h. Heating a lignin/urea/K2CO3 mixture leads to a significant decrease in the yield of released N-containing gases compared to the results for urea alone and a lignin/urea mixture, and most of the nitrogen in the urea is retained in the solid phase. X-ray photoelectron spectroscopy and X-ray diffraction analyses clearly show that part of the remaining nitrogen is present in heterocyclic structures (for example, pyridinic and pyrrolic nitrogen), and the rest is contained as KOCN at ≤600 °C and as KCN at ≥700 °C, such that the latter two compounds can be almost completely removed by water washing. The fate of nitrogen during heating of lignin/urea/K2CO3 and role of nitrogen in pore development in activated carbon are discussed on the basis of the results mentioned above.

  16. Particulate organic carbon and nitrogen export from major Arctic rivers

    NASA Astrophysics Data System (ADS)

    McClelland, J. W.; Holmes, R. M.; Peterson, B. J.; Raymond, P. A.; Striegl, R. G.; Zhulidov, A. V.; Zimov, S. A.; Zimov, N.; Tank, S. E.; Spencer, R. G. M.; Staples, R.; Gurtovaya, T. Y.; Griffin, C. G.

    2016-05-01

    Northern rivers connect a land area of approximately 20.5 million km2 to the Arctic Ocean and surrounding seas. These rivers account for ~10% of global river discharge and transport massive quantities of dissolved and particulate materials that reflect watershed sources and impact biogeochemical cycling in the ocean. In this paper, multiyear data sets from a coordinated sampling program are used to characterize particulate organic carbon (POC) and particulate nitrogen (PN) export from the six largest rivers within the pan-Arctic watershed (Yenisey, Lena, Ob', Mackenzie, Yukon, Kolyma). Together, these rivers export an average of 3055 × 109 g of POC and 368 × 109 g of PN each year. Scaled up to the pan-Arctic watershed as a whole, fluvial export estimates increase to 5767 × 109 g and 695 × 109 g of POC and PN per year, respectively. POC export is substantially lower than dissolved organic carbon export by these rivers, whereas PN export is roughly equal to dissolved nitrogen export. Seasonal patterns in concentrations and source/composition indicators (C:N, δ13C, Δ14C, δ15N) are broadly similar among rivers, but distinct regional differences are also evident. For example, average radiocarbon ages of POC range from ~2000 (Ob') to ~5500 (Mackenzie) years before present. Rapid changes within the Arctic system as a consequence of global warming make it challenging to establish a contemporary baseline of fluvial export, but the results presented in this paper capture variability and quantify average conditions for nearly a decade at the beginning of the 21st century.

  17. Gas uptake and thermal stability analysis of boron nitride and carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Guan, Mengyu

    Carbon nanotubes (CNTs) exist in many forms and can have critical pore diameters on the angstrom length scale, making them suitable for molecular capture. By combining the porous structure of CNTs with the chemical stability of carbide and/or nitride materials, one can create a more robust, nanoporous material for gas capture in high temperature conditions. Boron nitride nanotubes (BNNTs) are more chemically and thermally robust than pure CNTs, and were synthesized using CNTs as a structural precursor. However, this reaction mechanism was found to be unfavorable to produce high-yield and purity BNNTs. Adsorption tests using gases of interest (N2, He) were performed on commercial CNTs and BNNTs to determine their porosity and gas uptake abilities. Their thermal stability and oxidation resistance when heated up to 1773 K in air was also studied using differential scanning calorimetry and thermogravimetric analysis. While the CNTs began to oxidize between 450 °C and 750 °C, depending on the nanotube diameter, the BNNTs remained stable up until 1000 °C.

  18. Theoretical investigation of methane adsorption onto boron nitride and carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Darvish Ganji, Masoud; Mirnejad, Amir; Najafi, Ali

    2010-08-01

    Methane adsorption onto single-wall boron nitride nanotubes (BNNTs) and carbon nanotubes (CNTs) was studied using the density functional theory within the generalized gradient approximation. The structural optimization of several bonding configurations for a CH4 molecule approaching the outer surface of the (8,0) BNNT and (8,0) CNT shows that the CH4 molecule is preferentially adsorbed onto the CNT with a binding energy of -2.84 kcal mol-1. A comparative study of nanotubes with different diameters (curvatures) reveals that the methane adsorptive capability for the exterior surface increases for wider CNTs and decreases for wider BNNTs. The introduction of defects in the BNNT significantly enhances methane adsorption. We also examined the possibility of binding a bilayer or a single layer of methane molecules and found that methane molecules preferentially adsorb as a single layer onto either BNNTs or CNTs. However, bilayer adsorption is feasible for CNTs and defective BNNTs and requires binding energies of -3.00 and -1.44 kcal mol-1 per adsorbed CH4 molecule, respectively. Our first-principles findings indicate that BNNTs might be an unsuitable material for natural gas storage.

  19. Carbon doping induced peculiar transport properties of boron nitride nanoribbons p-n junctions

    SciTech Connect

    Liu, N.; Gao, G. Y.; Zhu, S. C.; Ni, Y.; Wang, S. L.; Yao, K. L.; Liu, J. B.

    2014-07-14

    By applying nonequilibrium Green's function combined with density functional theory, we investigate the electronic transport properties of carbon-doped p-n nanojunction based on hexagonal boron nitride armchair nanoribbons. The calculated I-V curves show that both the center and edge doping systems present obvious negative differential resistance (NDR) behavior and excellent rectifying effect. At low positive bias, the edge doping systems possess better NDR performance with larger peak-to-valley ratio (∼10{sup 5}), while at negative bias, the obtained peak-to-valley ratio for both of the edge and center doping systems can reach the order of 10{sup 7}. Meanwhile, center doping systems present better rectifying performance than the edge doping ones, and giant rectification ratio up to 10{sup 6} can be obtained in a wide bias range. These outstanding transport properties are explained by the evolution of the transmission spectra and band structures with applied bias, together with molecular projected self-consistent Hamiltonian eigenvalues and eigenstates.

  20. Semiconducting polymers with nanocrystallites interconnected via boron-doped carbon nanotubes.

    PubMed

    Yu, Kilho; Lee, Ju Min; Kim, Junghwan; Kim, Geunjin; Kang, Hongkyu; Park, Byoungwook; Ho Kahng, Yung; Kwon, Sooncheol; Lee, Sangchul; Lee, Byoung Hun; Kim, Jehan; Park, Hyung Il; Kim, Sang Ouk; Lee, Kwanghee

    2014-12-10

    Organic semiconductors are key building blocks for future electronic devices that require unprecedented properties of low-weight, flexibility, and portability. However, the low charge-carrier mobility and undesirable processing conditions limit their compatibility with low-cost, flexible, and printable electronics. Here, we present significantly enhanced field-effect mobility (μ(FET)) in semiconducting polymers mixed with boron-doped carbon nanotubes (B-CNTs). In contrast to undoped CNTs, which tend to form undesired aggregates, the B-CNTs exhibit an excellent dispersion in conjugated polymer matrices and improve the charge transport between polymer chains. Consequently, the B-CNT-mixed semiconducting polymers enable the fabrication of high-performance FETs on plastic substrates via a solution process; the μFET of the resulting FETs reaches 7.2 cm(2) V(-1) s(-1), which is the highest value reported for a flexible FET based on a semiconducting polymer. Our approach is applicable to various semiconducting polymers without any additional undesirable processing treatments, indicating its versatility, universality, and potential for high-performance printable electronics. PMID:25372930

  1. Dibenzothiophene adsorption at boron doped carbon nanoribbons studied within density functional theory

    SciTech Connect

    López-Albarrán, P.; Navarro-Santos, P.; Garcia-Ramirez, M. A.; Ricardo-Chávez, J. L.

    2015-06-21

    The adsorption of dibenzothiophene (DBT) on bare and boron-doped armchair carbon nanoribbons (ACNRs) is being investigated in the framework of the density functional theory by implementing periodic boundary conditions that include corrections from dispersion interactions. The reactivity of the ACNRs is characterized by using the Fukui functions as well as the electrostatic potential as local descriptors. Non-covalent adsorption mechanism is found when using the local Perdew-Becke-Ernzerhof functional, regardless of the DBT orientation and adsorption location. The dispersion interactions addition is a milestone to describe the adsorption process. The charge defects introduced in small number (i.e., by doping with B atoms), within the ACNRs increases the selectivity towards sulfur mainly due to the charge depletion at B sites. The DBT magnitude in the adsorption energy shows non-covalent interactions. As a consequence, the configurations where the DBT is adsorbed on a BC{sub 3} island increase the adsorption energy compared to random B arrangements. The stability of these configurations can be explained satisfactorily in terms of dipole interactions. Nevertheless, from the charge-density difference analysis and the weak Bader charge-distribution interactions cannot be ruled out completely. This is why the electronic properties of the ribbons are analyzed in order to elucidate the key role played by the B and DBT states in the adsorbed configurations.

  2. Fabrication of boron articles

    DOEpatents

    Benton, Samuel T.

    1976-01-01

    This invention is directed to the fabrication of boron articles by a powder metallurgical method wherein the articles are of a density close to the theoretical density of boron and are essentially crackfree. The method comprises the steps of admixing 1 to 10 weight percent carbon powder with amorphous boron powder, cold pressing the mixture and then hot pressing the cold pressed compact into the desired article. The addition of the carbon to the mixture provides a pressing aid for inhibiting the cracking of the hot pressed article and is of a concentration less than that which would cause the articles to possess significant concentrations of boron carbide.

  3. Intermolecular carbon-carbon, nitrogen-nitrogen and oxygen-oxygen non-covalent bonding in dipolar molecules.

    PubMed

    Remya, Karunakaran; Suresh, Cherumuttathu H

    2015-07-28

    Clear evidence for the existence of intermolecular carbon-carbon (C···C), nitrogen-nitrogen (N···N) and oxygen-oxygen (O···O) interactions between atoms in similar chemical environments in homogeneous dimers of organic dipolar molecules has been obtained from molecular orbital (MO), natural bond orbital (NBO) and atoms-in-molecule (AIM) electron density analyses at the M06L/6-311++G(d,p) level of density functional theory (DFT). These X···X type interactions are mainly the result of local polarization effects, causing segregation of electron-rich and electron-deficient regions in the X atoms, leading to complementary electrostatic interactions. NBO analysis provides evidence of charge transfer between the two X atoms. Even in symmetrical molecules such as acetylene, induced dipoles in the dimer create C···C bonding interactions. The strength of this type of interaction increases with increase in the dipole moment of the molecule. Energy decomposition analysis (EDA) shows that the electrostatic component of the interaction energy (Eint) is very high, up to 95.86%. The C···C interactions between similar carbon atoms are located for several crystal structures obtained from the literature. In addition, MO, AIM and electrostatic potential analyses support interactions between similar oxygen (O···O) and nitrogen (N···N) atoms in a variety of molecular dimers. Good prediction of Eint is achieved in terms of the total gain in electron density at non-covalently interacting intermolecular bonds (∑ρ) and the monomer dipole moment (μ). A rigorously tested QSAR equation has been derived to predict Eint for all dimer systems: Eint (kcal mol(-1)) = -138.395∑ρ(au) - 0.551μ (Debye). This equation suggests that the polarization-induced bonding interaction between atoms in a similar chemical environment could well be a general chemical phenomenon. The results have been further validated by different density functional methods and also by G3MP2 method

  4. Coaxial carbon@boron nitride nanotube arrays with enhanced thermal stability and compressive mechanical properties

    NASA Astrophysics Data System (ADS)

    Jing, Lin; Tay, Roland Yingjie; Li, Hongling; Tsang, Siu Hon; Huang, Jingfeng; Tan, Dunlin; Zhang, Bowei; Teo, Edwin Hang Tong; Tok, Alfred Iing Yoong

    2016-05-01

    Vertically aligned carbon nanotube (CNT) arrays have aroused considerable interest because of their remarkable mechanical properties. However, the mechanical behaviour of as-synthesized CNT arrays could vary drastically at a macro-scale depending on their morphologies, dimensions and array density, which are determined by the synthesis method. Here, we demonstrate a coaxial carbon@boron nitride nanotube (C@BNNT) array with enhanced compressive strength and shape recoverability. CNT arrays are grown using a commercially available thermal chemical vapor deposition (TCVD) technique and an outer BNNT with a wall thickness up to 1.37 nm is introduced by a post-growth TCVD treatment. Importantly, compared to the as-grown CNT arrays which deform almost plastically upon compression, the coaxial C@BNNT arrays exhibit an impressive ~4-fold increase in compressive strength with nearly full recovery after the first compression cycle at a 50% strain (76% recovery maintained after 10 cycles), as well as a significantly high and persistent energy dissipation ratio (~60% at a 50% strain after 100 cycles), attributed to the synergistic effect between the CNT and outer BNNT. Additionally, the as-prepared C@BNNT arrays show an improved structural stability in air at elevated temperatures, attributing to the outstanding thermal stability of the outer BNNT. This work provides new insights into tailoring the mechanical and thermal behaviours of arbitrary CNT arrays which enables a broader range of applications.Vertically aligned carbon nanotube (CNT) arrays have aroused considerable interest because of their remarkable mechanical properties. However, the mechanical behaviour of as-synthesized CNT arrays could vary drastically at a macro-scale depending on their morphologies, dimensions and array density, which are determined by the synthesis method. Here, we demonstrate a coaxial carbon@boron nitride nanotube (C@BNNT) array with enhanced compressive strength and shape recoverability

  5. Impacts of Land Use Change, Nitrogen Deposition and Nitrogen Fertilizers on Carbon and Nitrogen Stocks of Plants and Soils

    NASA Astrophysics Data System (ADS)

    Jain, A. K.; Yang, X.; Liang, M.; Barman, R.; Meiyappan, P.

    2010-12-01

    Changes in Earth’s vegetation cover have a potential to alter regional and global climate through changes in the biophysical and biogeochemical characteristics of the Earth’s surface. Historically, land-use change (LUC) activities have generally released carbon (C) to the atmosphere through the conversion of forests to croplands and pastures, but in recent decades C stocks in forest ecosystems have increased through reforestation, afforestation and forest regrowth on abandoned land. The accumulation of C stocks can be constrained if the LUCs occur in nitrogen (N) limited regions. However, soil N supply through N fertilizer application and N deposition could reduce, or even remove the N limitation on C uptake. These additional sources of N in soils are a major source of nitrous oxide (N2O) through nitrification and denitrification processes. Therefore, the terrestrial ecosystem responses to LUCs have a potential to change the concentrations of CO2 and N2O, two important greenhouse gases, and climate. In this study, an existing terrestrial coupled C-N cycle model, the Integrated Science Assessment Model (ISAM), is used to examine the response of terrestrial C and N stocks to historical LUC and the interactions with atmospheric CO2, climate, N deposition and N fertilizer. The ISAM biogeochemical cycles consist of fully prognostic C and N dynamics associated with changes in LUCs, vegetation, litter decomposition, and soil organic matter. The ISAM biophysical model accounts for water and energy processes in the vegetation and soil column. By quantifying the spatial distribution of C and N sources and sinks, this study will help us more accurately determine how much carbon is being stored or released. This is particularly important in the context of the Kyoto protocol, which allows a country to apply the carbon stored in its forests and other ecosystems toward its budgeted reduction in CO2 and other greenhouse gases.

  6. Synthesis, Characterization and Applications of New Nonmetallic Photocatalysts -- Resorcinol Formaldehyde Resin and Boron Carbon Oxynitride

    NASA Astrophysics Data System (ADS)

    Gu, Ting

    This thesis describes the synthesis, characterization and applications of two kinds of nonmetallic photocatalysts: resorcinol formaldehyde (RF) resin and boron carbon oxynitride (BCNO). Part I: Catalyst-free hydrothermal method was developed to synthesize RF resin. It started with a solution containing only resorcinol and formaldehyde. The products were characterized by transmission electron microscopy (TEM), Solid state 13C nuclear magnetic resonance (13C-NMR) spectrometer and UV-Visible absorption spectroscopy. The particle size (diameter: 100nm-4microm) of RF the spheres was controlled by changing the concentration of the reactants. With increasing particle size, visible light absorption of the product was also increased. These RF spheres could degrade Rhodamine B and generate OH radicals under visible light irradiation. Besides, highly concentrated starting reactants would form large macroporous gel instead of individual particles. This kind of gel could be easily shaped to dishes and tubes, which could be used in filtration and degradation of air pollutants. Part II: The BCNO was prepared by heating a mixture of boric acid, melamine and PEG in atmosphere. The optical properties of the products were measured by UV-Visible absorption spectroscopy with integrating sphere. The X-ray powder diffraction (XRD) patterns indicated that all BCNO compounds had the turbostratic boron nitride (t-BN) structure. Meanwhile, X-ray photoelectron spectroscopy (XPS) and electron energy loss spectrum (EELS) were used to determine the chemical composition of the catalyst. The BCNO could be identified as t-BN with N atoms partly substituted by O and C atoms. The degree of substitution affected its photocatalytic properties. Perdew--Burke--Ernzerhof (PBE) exchange model was introduced to simulate the density of state (DOS) of BCNO using these supercells. Simulation results indicated that C and O substitution induced occupied impurity states in the gap region which modified the band

  7. Synthesis and characterization of wear-resistant boron-carbon-nitride thin films

    NASA Astrophysics Data System (ADS)

    Guruz, Murat Unal

    2001-12-01

    In this thesis research, synthesis and characterization of a number of technologically and scientifically interesting B-C-N thin films was investigated. These solids, owing to their short and strong covalent bonds, have the potential to be very hard. Magnetron sputtering was utilized for film deposition and the films were characterization by a wide variety of techniques to obtain information on hardness, microstructure, composition, surface morphology, corrosion performance, and wear rate. Ultrathin carbon nitride coatings were grown for use as protective overcoats in computer hard drives. In order to obtain an areal storage density of 100 Gbits/in2, the overcoat thickness is required to be within 2 nm, and the coating needs to be wear-resistant, smooth and defect-free. These requirements were satisfied for films grown under an optimum substrate bias where the energy distribution of the incoming ions was minimized and the substrate and target power supplies were pulsed at high frequency. Synthesis of cubic boron nitride coatings was possible in films grown under intense ion bombardment, where the ion flux was controlled by an externally applied magnetic field. These films were prone to rapid delamination, especially in humid environments. Films grown under mild bombardment had the hexagonal structure, did not exhibit any tendency for delamination, and were relatively hard, with smooth surface morphology and were highly resistive. In order to obtain thick and adherent c-BN films, deposition of multilayer BN coatings was proposed. This was accomplished by varying the substrate bias as well as the incoming ion flux, however, no significant improvement in film adhesion was observed. As an alternative to c-BN growth, deposition of boron carbide films was investigated. Such films exhibited high hardness, low surface roughness, along with high elasticity, and high wear resistance and did not show any signs of delamination under optimum growth conditions. The required

  8. Abrasive wear of nitrogen-implanted boron-coated Ti-6Al-4V and temperature effect on microhardness and sliding friction coefficient

    NASA Astrophysics Data System (ADS)

    Baazi, Tandjaoui; Knystautas, Emile J.; Fiset, Michel

    1993-02-01

    Boron was electron-gun evaporated onto manually polished surfaces of Ti-6Al-4V and bombarded with 100 keV nitrogen ions for different doses. The highest increase in Knoop microhardness was observed for the highest dose considered in this work, i.e., 10 17ions cm -2, which was maintained for subsequent abrasive wear investigation by optical and scanning electron microscopies. Relative changes of Knoop microhardness and sliding friction coefficient as a function of implantation temperature (room temperature, 150, 300, 450 and 600°C) were measured. The optimal improvements obtained for the 450°C implantation correlate with the higher nitrogen retention as evidenced by XPS depth-concentration analysis.

  9. Method 440.0 Determination of Carbon and Nitrogen in Sediments and Particulatesof Estuarine/Coastal Waters Using Elemental Analysis

    EPA Science Inventory

    Elemental analysis is used to determine particulate carbon (PC) and particulate nitrogen (PN) in estuarine and coastal waters and sediment. The method measures the total carbon and nitrogen irrespective of source (inorganic or organic).

  10. Importance of Nitrogen Availability on Land Carbon Sequestration in Northern Eurasia during the 21st Century

    NASA Astrophysics Data System (ADS)

    Kicklighter, D. W.; Melillo, J. M.; Monier, E.; Sokolov, A. P.; Lu, X.; Zhuang, Q.

    2015-12-01

    Atmospheric nitrogen deposition, nitrogen fixation, and the application of nitrogen fertilizers provide subsidies to land ecosystems that can increase nitrogen availability for vegetation production and thereby influence land carbon dynamics. In addition, enhanced decomposition of soil organic matter (SOM) from warming soils and permafrost degradation may also increase nitrogen availability in Northern Eurasia. Here, we examine how changes in nitrogen availability may influence land carbon dynamics in Northern Eurasia during the 21st century by comparing results for a "business as usual" scenario (the IPCC Representative Concentration Pathways or RCP 8.5) and a stabilization scenario (RCP 4.5) between a version of the Terrestrial Ecosystem Model that does not consider the effects of atmospheric nitrogen deposition, nitrogen fixation and soil thermal dynamics on land carbon dynamics (TEM 4.4) and a version that does consider these dynamics (TEM 6.0). In these simulations, atmospheric nitrogen deposition, nitrogen fixation, and fertilizer applications provide an additional 3.3 Pg N (RCP 4.5) to 3.9 Pg N (RCP 8.5) to Northern Eurasian ecosystems over the 21st century. Land ecosystems retain about 38% (RCP4.5) to 48% (RCP 8.5) of this nitrogen subsidy. Net nitrogen mineralization estimated by TEM 6.0 provide an additional 1.0 Pg N to vegetation than estimated by TEM 4.4 over the 21st century from enhanced decomposition of SOM including SOM formerly protected by permafrost. The enhanced nitrogen availability in TEM 6.0 allows Northern Eurasian ecosystems to sequester 1.8x (RCP 8.5) to 2.4x (RCP 4.5) more carbon over the 21st century than estimated by TEM 4.4. Our results indicate that consideration of nitrogen subsidies and soil thermal dynamics have a large influence on how simulated land carbon dynamics in Northern Eurasia will respond to future changes in climate, atmospheric chemistry, and disturbances.

  11. Carbon and nitrogen fluxes between beech and their ectomycorrhizal assemblage.

    PubMed

    Valtanen, Kerttu; Eissfeller, Verena; Beyer, Friderike; Hertel, Dietrich; Scheu, Stefan; Polle, Andrea

    2014-11-01

    To determine the exchange of nitrogen and carbon between ectomycorrhiza and host plant, young beech (Fagus sylvatica) trees from natural regeneration in intact soil cores were labelled for one growing season in a greenhouse with (13)CO2 and (15)NO3 (15)NH4. The specific enrichments of (15)N and (13)C were higher in ectomycorrhizas (EMs) than in any other tissue. The enrichments of (13)C and (15)N were also higher in the fine-root segments directly connected with the EM (mainly second-order roots) than that in bulk fine or coarse roots. A strict, positive correlation was found between the specific (15)N enrichment in EM and the attached second-order roots. This finding indicates that strong N accumulators provide more N to their host than low N accumulators. A significant correlation was also found for the specific (13)C enrichment in EM and the attached second-order roots. However, the specific enrichments for (15)N and (13)C in EM were unrelated showing that under long-term conditions, C and N exchange between host and EMs are uncoupled. These findings suggest that EM-mediated N flux to the plant is not the main control on carbon flux to the fungus, probably because EMs provide many different services to their hosts in addition to N provision in their natural assemblages. PMID:24756632

  12. Nitrogen-doped mesoporous carbons for high performance supercapacitors

    NASA Astrophysics Data System (ADS)

    Wu, Kai; Liu, Qiming

    2016-08-01

    The mesoporous carbons have been synthesized by using α-D(+)-Glucose, D-Glucosamine hydrochloride or their mixture as carbon precursors and mesoporous silicas (SBA-15 or MCF) as hard templates. The as-prepared products show a large pore volume (0.59-0.97 cm3 g-1), high surface areas (352.72-1152.67 m2 g-1) and rational nitrogen content (ca. 2.5-3.9 wt.%). The results of electrochemical tests demonstrate that both heteroatom doping and suitable pore structure play a decisive role in the performance of supercapacitors. The representative sample of SBA-15 replica obtained using D-Glucosamine hydrochloride only exhibits high specific capacitance (212.8 F g-1 at 0.5 A g-1) and good cycle durability (86.1% of the initial capacitance after 2000 cycles) in 6 M KOH aqueous electrolyte, which is attributed to the contribution of double layer capacitance and pseudo-capacitance. The excellent electrochemical performance makes it a promising electrode material for supercapacitors.

  13. Nitrogen feedbacks increase future terrestrial ecosystem carbon uptake in an individual-based dynamic vegetation model

    NASA Astrophysics Data System (ADS)

    Wårlind, D.; Smith, B.; Hickler, T.; Arneth, A.

    2014-11-01

    Recently a considerable amount of effort has been put into quantifying how interactions of the carbon and nitrogen cycle affect future terrestrial carbon sinks. Dynamic vegetation models, representing the nitrogen cycle with varying degree of complexity, have shown diverging constraints of nitrogen dynamics on future carbon sequestration. In this study, we use LPJ-GUESS, a dynamic vegetation model employing a detailed individual- and patch-based representation of vegetation dynamics, to evaluate how population dynamics and resource competition between plant functional types, combined with nitrogen dynamics, have influenced the terrestrial carbon storage in the past and to investigate how terrestrial carbon and nitrogen dynamics might change in the future (1850 to 2100; one representative "business-as-usual" climate scenario). Single-factor model experiments of CO2 fertilisation and climate change show generally similar directions of the responses of C-N interactions, compared to the C-only version of the model as documented in previous studies using other global models. Under an RCP 8.5 scenario, nitrogen limitation suppresses potential CO2 fertilisation, reducing the cumulative net ecosystem carbon uptake between 1850 and 2100 by 61%, and soil warming-induced increase in nitrogen mineralisation reduces terrestrial carbon loss by 31%. When environmental changes are considered conjointly, carbon sequestration is limited by nitrogen dynamics up to the present. However, during the 21st century, nitrogen dynamics induce a net increase in carbon sequestration, resulting in an overall larger carbon uptake of 17% over the full period. This contrasts with previous results with other global models that have shown an 8 to 37% decrease in carbon uptake relative to modern baseline conditions. Implications for the plausibility of earlier projections of future terrestrial C dynamics based on C-only models are discussed.

  14. Nitrogen-Doped Carbon Dots for "green" Quantum Dot Solar Cells.

    PubMed

    Wang, Hao; Sun, Pengfei; Cong, Shan; Wu, Jiang; Gao, Lijun; Wang, Yun; Dai, Xiao; Yi, Qinghua; Zou, Guifu

    2016-12-01

    Considering the environment protection, "green" materials are increasingly explored for photovoltaics. Here, we developed a kind of quantum dots solar cell based on nitrogen-doped carbon dots. The nitrogen-doped carbon dots were prepared by direct pyrolysis of citric acid and ammonia. The nitrogen-doped carbon dots' excitonic absorption depends on the N-doping content in the carbon dots. The N-doping can be readily modified by the mass ratio of reactants. The constructed "green" nitrogen-doped carbon dots solar cell achieves the best power conversion efficiency of 0.79 % under AM 1.5 G one full sun illumination, which is the highest efficiency for carbon dot-based solar cells. PMID:26781285

  15. Nitrogen-Doped Carbon Dots for "green" Quantum Dot Solar Cells

    NASA Astrophysics Data System (ADS)

    Wang, Hao; Sun, Pengfei; Cong, Shan; Wu, Jiang; Gao, Lijun; Wang, Yun; Dai, Xiao; Yi, Qinghua; Zou, Guifu

    2016-01-01

    Considering the environment protection, "green" materials are increasingly explored for photovoltaics. Here, we developed a kind of quantum dots solar cell based on nitrogen-doped carbon dots. The nitrogen-doped carbon dots were prepared by direct pyrolysis of citric acid and ammonia. The nitrogen-doped carbon dots' excitonic absorption depends on the N-doping content in the carbon dots. The N-doping can be readily modified by the mass ratio of reactants. The constructed "green" nitrogen-doped carbon dots solar cell achieves the best power conversion efficiency of 0.79 % under AM 1.5 G one full sun illumination, which is the highest efficiency for carbon dot-based solar cells.

  16. Nitrogen-doped carbon nanotube as a potential metal-free catalyst for CO oxidation.

    PubMed

    Lin, I-Hsiang; Lu, Yu-Huan; Chen, Hsin-Tsung

    2016-04-28

    We elucidate the possibility of nitrogen-doped carbon nanotube as a robust catalyst for CO oxidation. We have performed first-principles calculations considering the spin-polarization effect to demonstrate the reaction of CO oxidation catalyzed by the nitrogen-doped carbon nanotube. The calculations show that O2 species can be partially reduced with charge transfer from the nitrogen-doped carbon nanotube and directly chemisorbed on the C-N sites of the nitrogen-doped carbon nanotube. The partially reduced O2 species at the C-N sites can further directly react with a CO molecule via the Eley-Rideal mechanism with the barriers of 0.45-0.58 eV for the different diameter of nanotube. Ab initio molecular dynamics (AIMD) simulations were performed and showed that the oxidation of CO occurs by the Eley-Rideal mechanism. The relationship between the curvature and reactivity of the nitrogen doped carbon nanotube was also unraveled. It appears that the barrier height of the rate-limiting step depends on the curvature of the nitrogen-doped carbon nanotube in the trend of (3,3)-NCNT < (4,4)-NCNT < (5,5)-NCNT (decreases with increased curvature). Using this relationship, we can predict the barriers for other N-doped carbon nanotubes with different tube diameters. Our results reveal that the nitrogen doped carbon nanomaterials can be a good, low-cost, and metal-free catalyst for CO oxidation. PMID:27074831

  17. Mechanisms controlling soil carbon sequestration under atmospheric nitrogen deposition

    SciTech Connect

    R.L. Sinsabaugh; D.R. Zak; D.L. Moorhead

    2008-02-19

    Increased atmospheric nitrogen (N) deposition can alter the processing and storage of organic carbon in soils. In 2000, we began studying the effects of simulated atmospheric N deposition on soil carbon dynamics in three types of northern temperate forest that occur across a wide geographic range in the Upper Great Lakes region. These ecosystems range from 100% oak in the overstory (black oak-white oak ecosystem; BOWO) to 0% overstory oak (sugar maple-basswood; SMBW) and include the sugar maple-red oak ecosystem (SMRO) that has intermediate oak abundance. The leaf litter biochemistry of these ecosystems range from highly lignified litter (BOWO) to litter of low lignin content (SMBW). We selected three replicate stands of each ecosystem type and established three plots in each stand. Each plot was randomly assigned one of three levels of N deposition (0, 30 & 80 kg N ha-1 y-1) imposed by adding NaNO3 in six equal increments applied over the growing season. Through experiments ranging from the molecular to the ecosystem scales, we produced a conceptual framework that describes the biogeochemistry of soil carbon storage in N-saturated ecosystems as the product of interactions between the composition of plant litter, the composition of the soil microbial community and the expression of extracellular enzyme activities. A key finding is that atmospheric N deposition can increase or decrease the soil C storage by modifying the expression of extracellular enzymes by soil microbial communities. The critical interactions within this conceptual framework have been incorporated into a new class of simulations called guild decomposition models.

  18. Revealing the Origin of Activity in Nitrogen-Doped Nanocarbons towards Electrocatalytic Reduction of Carbon Dioxide.

    PubMed

    Xu, Junyuan; Kan, Yuhe; Huang, Rui; Zhang, Bingsen; Wang, Bolun; Wu, Kuang-Hsu; Lin, Yangming; Sun, Xiaoyan; Li, Qingfeng; Centi, Gabriele; Su, Dangsheng

    2016-05-23

    Carbon nanotubes (CNTs) are functionalized with nitrogen atoms for reduction of carbon dioxide (CO2 ). The investigation explores the origin of the catalyst's activity and the role of nitrogen chemical states therein. The catalysts show excellent performances, with about 90 % current efficiency for CO formation and stability over 60 hours. The Tafel analyses and density functional theory calculations suggest that the reduction of CO2 proceeds through an initial rate-determining transfer of one electron to CO2 , which leads to the formation of carbon dioxide radical anion (CO2 (.-) ). The initial reduction barrier is too high on pristine CNTs, resulting in a very high overpotentials at which the hydrogen evolution reaction dominates over CO2 reduction. The doped nitrogen atoms stabilize the radical anion, thereby lowering the initial reduction barrier and improving the intrinsic activity. The most efficient nitrogen chemical state for this reaction is quaternary nitrogen, followed by pyridinic and pyrrolic nitrogen. PMID:27100272

  19. Nitrogen-15 NMR spectroscopy of the catalytic-triad histidine of a serine protease in peptide boronic acid inhibitor complexes

    SciTech Connect

    Bachovchin, W.W.; Wong, W.Y.L.; Farr-Jones, S. ); Shenvi, A.B.; Kettner, C.A. )

    1988-10-04

    {sup 15}N NMR spectroscopy was used to examine the active-site histidyl residue of {alpha}-lytic protease in peptide boronic acid inhibitor complexes. Two distinct types of complexes were observed: (1) Boronic acids that are analogues of substrates form complexes in which the active-site imidazole ring is protonated and both imidazole N-H protons are strongly hydrogen bonded. (2) Boronic acids that are not substrate analogues form complexes in which N{sup {epsilon}2} of the active-site histidine is covalently bonded to the boron atom of the inhibitor. The proton bound to N{sup {delta}1} of the histidine in these histidine-boronate adducts remains strongly hydrogen bonded, presumably to the active-site aspartate. In both types of complexes the N-H protons of His-57 exchange unusually slowly as evidenced by the room temperature visibility of the low-field {sup 1}H resonances and the {sup 15}N-H spin couplings. These results indicate that occupancy of the specificity subsites may be required to fully form the transition-state binding site. The significance of these findings for understanding inhibitor binding and the catalytic mechanism of serine proteases is discussed.

  20. Oxygen and carbon requirements for biological nitrogen removal processes accomplishing nitrification, nitritation, and anammox.

    PubMed

    Daigger, Glen T

    2014-03-01

    The oxygen and carbon savings associated with novel nitrogen removal processes for the treatment of high ammonia, low biodegradable organic matter waste streams such as the recycle streams from the dewatering of anaerobically digested sludges are well documented.This understanding may lead some to think that similar oxygen savings are possible if novel processes such as nitritation/ denitritation and partial nitritation-deammonification are incorporated into main liquid stream processes where influent biodegradable organic matter is used to denitrify residual oxidized nitrogen (nitrite and nitrate). It is demonstrated that the net oxygen required for nitrogen removal is 1.71 mg O2/mg ammonia-nitrogen converted to nitrogen gas as long as influent biodegradable organic matter is used to denitrify residual oxidized nitrogen. Less oxygen is required to produce oxidized nitrogen with these novel processes, but less biodegradable organic matter is also required for oxidized nitrogen reduction to nitrogen gas, resulting in reduced oxygen savings for the oxidation of biodegradable organic matter. The net oxygen requirement is the same since the net electron transfer for the conversion of ammonia-nitrogen to nitrogen gas is the same. The biodegradable organic matter required to reduce the oxidized nitrogen to nitrogen gas is estimated for these processes based on standard biological process calculations. It is estimated to be in the range of 3.5 to 4.0 mg biodegradable COD/mg ammonia-nitrogen reduced to nitrogen gas for nitrification-denitrification, 2.0 to 2.5 for nitritation-denitritation, and 0.5 for partial nitritation-deammonification. The resulting limiting influent wastewater carbon-to-nitrogen ratios are estimated and can be used to guide the appropriate selection of biological nitrogen removal process given knowledge of the biological process influent wastewater carbon-to-nitrogen ratio. Energy savings possible for mainstream processes incorporating these novel

  1. Carbon and nitrogen abundance variations in globular cluster red giants

    NASA Astrophysics Data System (ADS)

    Martell, Sarah L.

    2008-06-01

    This dissertation describes investigations into two of the persistent questions of elemental abundances in Galactic globular clusters: the phenomenon of deep mixing, observed through the progressive depletion of surface carbon abundance as stars evolve along the red giant branch, and abundance bimodality, a phenomenon observed only in globular clusters, in which a subset of stars in a given globular cluster have a distinctive pattern of elemental enhancements and depletions relative to the Solar pattern. The first chapter gives an introduction to the history of globular cluster abundance studies, with particular focus on low-resolution spectroscopy. For both deep mixing and abundance bimodality, the leading theoretical models and the data which support and challenge them are laid out. Each section ends with a description of presently-unanswered questions; these are the motivation for the various projects contained in this dissertation. The second chapter describes the use of molecular handstrengths for determining elemental abundances from low-resolution spectra, and introduces a new CH bandstrength index that is designed to be sensitive to carbon abundance and insensitive to nitrogen abundance in Pop. II red giants over a wide range of metallicity. Various CH indices defined elsewhere in the literature are also discussed, and are shown to have comparable accuracy to the new index only over a limited range of stellar properties. Carbon abundances determined using the new CH index are compared to literature abundances for a few stars, and general concordance with published abundances is found. The third chapter contains a large-scale application of the new CH index: a survey of present-day carbon abundances and calculated carbon depletion rates in bright red giants belonging to eleven Galactic globular clusters spanning the full metallicity range of halo globular clusters. Targets were selected with similar evolutionary states, were observed with one instrument on

  2. Nitrogen-15 NMR spectroscopy of the catalytic-triad histidine of a serine protease in peptide boronic acid inhibitor complexes.

    PubMed

    Bachovchin, W W; Wong, W Y; Farr-Jones, S; Shenvi, A B; Kettner, C A

    1988-10-01

    15N NMR spectroscopy was used to examine the active-site histidyl residue of alpha-lytic protease in peptide boronic acid inhibitor complexes. Two distinct types of complexes were observed: (1) Boronic acids that are analogues of substrates form complexes in which the active-site imidazole ring is protonated and both imidazole N-H protons are strongly hydrogen bonded. With the better inhibitors of the class this arrangement is stable over the pH range 4.0-10.5. The results are consistent with a putative tetrahedral intermediate like complex involving a negatively charged, tetrahedral boron atom covalently bonded to O gamma of the active-site serine. (2) Boronic acids that are not substrate analogues form complexes in which N epsilon 2 of the active-site histidine is covalently bonded to the boron atom of the inhibitor. The proton bound to N delta 1 of the histidine in these histidine-boronate adducts remains strongly hydrogen bonded, presumably to the active-site aspartate. Benzeneboronic acid, which falls in this category, forms an adduct with histidine. In both types of complexes the N-H protons of His-57 exchange unusually slowly as evidenced by the room temperature visibility of the low-field 1H resonances and the 15N-H spin couplings. These results, coupled with the kinetic data of the preceding paper [Kettner, C. A., Bone, R., Agard, D. A., & Bachovchin, W. W. (1988) Biochemistry (preceding paper in this issue)], indicate that occupancy of the specificity subsites may be required to fully form the transition-state binding site. The significance of these findings for understanding inhibitor binding and the catalytic mechanism of serine proteases is discussed. PMID:3207700

  3. Compressible elastomeric aerogels of hexagonal boron nitride and single-walled carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Joo Jeong, Yeon; Islam, Mohammad F.

    2015-07-01

    Lightweight porous ceramic materials that can recover their shapes after mechanical deformation have numerous applications. However, these types of materials tend to be highly fragile and often crack when compressed. Here, we report on the fabrication and characterization of highly porous, freestanding composites of hexagonal boron nitride (h-BN) and single-walled carbon nanotubes (SWCNTs) of density 13-15 mg mL-1, which corresponds to a volume fraction of 0.009, that were mechanically robust and recovered their original shape even after uniaxially compressing them by more than 50%. We made these porous elastomeric composites using a solution based assembly process that involved first shaping SWCNTs into porous networks of density ~7 mg mL-1 (volume fraction ~0.005) followed by coatings of SWCNT networks with 6-8 mg mL-1 of h-BN (volume fraction ~0.003-0.004). The h-BN coating strengthened the underlying SWCNT networks, likely via reinforcement of the nodes between the SWCNTs, resulting in an increase in Young's modulus by ~100% compared to that of SWCNT networks alone. Surprisingly, SWCNT networks, which were initially highly fragile, became elastomeric after h-BN coating, even though porous structures solely from h-BN are very brittle. Our fabrication approach preserves the morphology of the underlying networks, allowing for fabrication of various shapes and sizes of porous composites of h-BN and SWCNTs. Finally, our fabrication scheme is robust and facile for the preparation of porous composites of diverse ceramic materials and SWCNTs using the appropriate ceramic-precursor.Lightweight porous ceramic materials that can recover their shapes after mechanical deformation have numerous applications. However, these types of materials tend to be highly fragile and often crack when compressed. Here, we report on the fabrication and characterization of highly porous, freestanding composites of hexagonal boron nitride (h-BN) and single-walled carbon nanotubes (SWCNTs) of

  4. Ionicities of Boron-Boron Bonds in B12 Icosahedra

    NASA Astrophysics Data System (ADS)

    He, Julong; Wu, Erdong; Wang, Huitian; Liu, Riping; Tian, Yongjun

    2005-01-01

    First-principles calculations are used to investigate ionicities of boron-boron bonds in B12 icosahedra. It is observed that the geometrical symmetry breaking of B12 icosahedra results in the spatial asymmetry of charge density on each boron-boron bond, and further in the ionicity of B12 icosahedra. The results calculated by a new ionicity scale, a population ionicity scale, indicate that the maximum ionicity among those boron-boron bonds is larger than that of boron-nitrogen bonds in the III-V compound cubic BN. It is of great importance that such an ionicity concept can be extended to boron-rich solids and identical atom clusters.

  5. Carbon and nitrogen dynamics in a soil profile: Model development

    NASA Astrophysics Data System (ADS)

    Batlle-Aguilar, Jordi; Brovelli, Alessandro; Barry, D. Andrew

    2010-05-01

    In order to meet demands for crops, pasture and firewood, the rate of land use change from forested to agricultural uses has steadily increased over several decades, resulting in an increased release of nutrients towards groundwater and surface water bodies. In parallel, the degradation of riparian zones has diminished their capacity to provide critical ecosystem functions, such as the ability to control and buffer nutrient cycles. In recent years, however, the key environmental importance of natural, healthy ecosystems has been progressively recognized and restoration of degraded lands towards their former natural state has become an area of active research worldwide. Land use changes and restoration practices are known to affect both soil nutrient dynamics and their transport to neighbouring areas. To this end, in order to interpret field experiments and elucidate the different mechanisms taking place, numerical tools are beneficial. Microbiological transformations of the soil organic matter, including decomposition and nutrient turnover are controlled to a large extent by soil water content, influenced in turn by climatic and environmental conditions such as precipitation and evapotranspiration. The work presented here is part of the Swiss RECORD project (http://www.cces.ethz.ch/projects/nature/Record), a large collaborative research effort undertaken to monitor the changes in ecosystem functioning in riparian areas undergoing restoration. In this context we have developed a numerical model to simulate carbon and nitrogen transport and turnover in a one-dimensional variably saturated soil profile. The model is based on the zero-dimensional mechanistic batch model of Porporato et al. (Adv. Water Res., 26: 45-58, 2003), but extends its capabilities to simulate (i) the transport of the mobile components towards deeper horizons, and (ii) the vertical evolution of the profile and the subsequent distribution of the organic matter. The soil is divided in four

  6. Compressible elastomeric aerogels of hexagonal boron nitride and single-walled carbon nanotubes.

    PubMed

    Jeong, Yeon Joo; Islam, Mohammad F

    2015-08-14

    Lightweight porous ceramic materials that can recover their shapes after mechanical deformation have numerous applications. However, these types of materials tend to be highly fragile and often crack when compressed. Here, we report on the fabrication and characterization of highly porous, freestanding composites of hexagonal boron nitride (h-BN) and single-walled carbon nanotubes (SWCNTs) of density 13-15 mg mL(-1), which corresponds to a volume fraction of 0.009, that were mechanically robust and recovered their original shape even after uniaxially compressing them by more than 50%. We made these porous elastomeric composites using a solution based assembly process that involved first shaping SWCNTs into porous networks of density ∼7 mg mL(-1) (volume fraction ∼0.005) followed by coatings of SWCNT networks with 6-8 mg mL(-1) of h-BN (volume fraction ∼0.003-0.004). The h-BN coating strengthened the underlying SWCNT networks, likely via reinforcement of the nodes between the SWCNTs, resulting in an increase in Young's modulus by ∼100% compared to that of SWCNT networks alone. Surprisingly, SWCNT networks, which were initially highly fragile, became elastomeric after h-BN coating, even though porous structures solely from h-BN are very brittle. Our fabrication approach preserves the morphology of the underlying networks, allowing for fabrication of various shapes and sizes of porous composites of h-BN and SWCNTs. Finally, our fabrication scheme is robust and facile for the preparation of porous composites of diverse ceramic materials and SWCNTs using the appropriate ceramic-precursor. PMID:26161911

  7. A facile approach towards increasing the nitrogen-content in nitrogen-doped carbon nanotubes via halogenated catalysts

    NASA Astrophysics Data System (ADS)

    Ombaka, L. M.; Ndungu, P. G.; Omondi, B.; McGettrick, J. D.; Davies, M. L.; Nyamori, V. O.

    2016-03-01

    Nitrogen-doped carbon nanotubes (N-CNTs) have been synthesized at 850 °C via a CVD deposition technique by use of three ferrocenyl derivative catalysts, i.e. para-CN, -CF3 and -Cl substituted-phenyl rings. The synthesized catalysts have been characterized by NMR, IR, HR-MS and XRD. The XRD analysis of the para-CF3 catalyst indicates that steric factors influence the X-ray structure of 1,1‧-ferrocenylphenyldiacrylonitriles. Acetonitrile or pyridine was used as carbon and nitrogen sources to yield mixtures of N-CNTs and carbon spheres (CS). The N-CNTs obtained from the para-CF3 catalysts, in pyridine, have the highest nitrogen-doping level, show a helical morphology and are less thermally stable compared with those synthesized by use of the para-CN and -Cl as catalyst. This suggests that fluorine heteroatoms enhance nitrogen-doping in N-CNTs and formation of helical-N-CNTs (H-N-CNTs). The para-CF3 and para-Cl catalysts in acetonitrile yielded iron-filled N-CNTs, indicating that halogens promote encapsulation of iron into the cavity of N-CNT. The use of acetonitrile, as carbon and nitrogen source, with the para-CN and -Cl as catalysts also yielded a mixture of N-CNTs and carbon nanofibres (CNFs), with less abundance of CNFs in the products obtained using para-Cl catalysts. However, para-CF3 catalyst in acetonitrile gave N-CNTs as the only shaped carbon nanomaterials.

  8. Nitrogen deposition, land cover conversion, and contemporary carbon balance of Europe

    NASA Astrophysics Data System (ADS)

    Churkina, G.; Zaehle, S.; Hughes, J.; Viovy, N.; Jung, M.; Chen, Y.; Heimann, M.; Roedenbeck, C.; Jones, C.

    2009-04-01

    In Europe, atmospheric nitrogen deposition has more than doubled, forest cover was steadily increasing, and agricultural area was declining over the last 50 years. What effect have these changes had on the European carbon balance? In this study we estimate responses of the European land ecosystems to nitrogen deposition, land cover conversion and climate. We use results from four ecosystem process models such as BIOME-BGC, JULES, ORCHIDEE, and ORCHIDEE-CN to address this question. We discuss to which degree carbon balance of Europe has been altered by nitrogen deposition in comparison to other drivers and identify areas which carbon balance has been most effected by anthropogenic changes.

  9. An analytical study of nitrogen oxides and carbon monoxide emissions in hydrocarbon combustion with added nitrogen, preliminary results

    NASA Technical Reports Server (NTRS)

    Bittker, D. A.

    1979-01-01

    The effect of combustor operating conditions on the conversion of fuel-bound nitrogen (FBN) to nitrogen oxides NO sub x was analytically determined. The effect of FBN and of operating conditions on carbon monoxide (CO) formation was also studied. For these computations, the combustor was assumed to be a two stage, adiabatic, perfectly-stirred reactor. Propane-air was used as the combustible mixture and fuel-bound nitrogen was simulated by adding nitrogen atoms to the mixture. The oxidation of propane and formation of NO sub x and CO were modeled by a fifty-seven reaction chemical mechanism. The results for NO sub x and CO formation are given as functions of primary and secondary stage equivalence ratios and residence times.

  10. Carbon: nitrogen stoichiometry following afforestation: a global synthesis

    PubMed Central

    Xu, Xia; Li, Dejun; Cheng, Xiaoli; Ruan, Honghua; Luo, Yiqi

    2016-01-01

    Though carbon (C): nitrogen (N) stoichiometry has been widely studied in terrestrial ecosystems, little is known about its variation following afforestation. By synthesizing the results of 53 studies, we examined temporal and spatial variation in C: N ratios and in N-C scaling relationships of both the organic and the mineral soil horizons. Results showed that C: N ratios remained constant in the mineral horizon but significantly decreased in the organic horizon over the age sequence following afforestation. Among different climate zones, C: N ratios of the organic and the mineral horizons increased and decreased, respectively, with increasing mean annual temperature (MAT) (decreasing latitude). Pasture exhibited higher C: N ratios than cropland in the organic horizon while C: N of the mineral horizon did not change much among different land use types. For both the organic and the mineral horizons, hardwoods exhibited lower C: N ratios than pine and softwoods. Additionally, N and C in general scaled isometrically in both the organic and the mineral horizons over the age sequence and among different climate zones, land use types, and plantation species following afforestation. Our results suggest that C and N may remain coupled following afforestation. PMID:26743490

  11. Carbon: nitrogen stoichiometry following afforestation: a global synthesis.

    PubMed

    Xu, Xia; Li, Dejun; Cheng, Xiaoli; Ruan, Honghua; Luo, Yiqi

    2016-01-01

    Though carbon (C): nitrogen (N) stoichiometry has been widely studied in terrestrial ecosystems, little is known about its variation following afforestation. By synthesizing the results of 53 studies, we examined temporal and spatial variation in C: N ratios and in N-C scaling relationships of both the organic and the mineral soil horizons. Results showed that C: N ratios remained constant in the mineral horizon but significantly decreased in the organic horizon over the age sequence following afforestation. Among different climate zones, C: N ratios of the organic and the mineral horizons increased and decreased, respectively, with increasing mean annual temperature (MAT) (decreasing latitude). Pasture exhibited higher C: N ratios than cropland in the organic horizon while C: N of the mineral horizon did not change much among different land use types. For both the organic and the mineral horizons, hardwoods exhibited lower C: N ratios than pine and softwoods. Additionally, N and C in general scaled isometrically in both the organic and the mineral horizons over the age sequence and among different climate zones, land use types, and plantation species following afforestation. Our results suggest that C and N may remain coupled following afforestation. PMID:26743490

  12. Modelling soil nitrogen: the MAGIC model with nitrogen retention linked to carbon turnover using decomposer dynamics.

    PubMed

    Oulehle, F; Cosby, B J; Wright, R F; Hruška, J; Kopáček, J; Krám, P; Evans, C D; Moldan, F

    2012-06-01

    We present a new formulation of the acidification model MAGIC that uses decomposer dynamics to link nitrogen (N) cycling to carbon (C) turnover in soils. The new model is evaluated by application to 15-30 years of water chemistry data at three coniferous-forested sites in the Czech Republic where deposition of sulphur (S) and N have decreased by >80% and 40%, respectively. Sulphate concentrations in waters have declined commensurately with S deposition, but nitrate concentrations have shown much larger decreases relative to N deposition. This behaviour is inconsistent with most conceptual models of N saturation, and with earlier versions of MAGIC which assume N retention to be a first-order function of N deposition and/or controlled by the soil C/N ratio. In comparison with earlier versions, the new formulation more correctly simulates observed short-term changes in nitrate leaching, as well as long-term retention of N in soils. The model suggests that, despite recent deposition reductions and recovery, progressive N saturation will lead to increased future nitrate leaching, ecosystem eutrophication and re-acidification. PMID:22459669

  13. Warming and nitrogen deposition lessen microbial residue contribution to soil carbon pool.

    PubMed

    Liang, Chao; Balser, Teri C

    2012-01-01

    Microorganisms have a role as gatekeepers for terrestrial carbon fluxes, either causing its release to the atmosphere through their decomposition activities or preventing its release by stabilizing the carbon in a form that cannot be easily decomposed. Although research has focused on microbial sources of greenhouse gas production, somewhat limited attention has been paid to the microbial role in carbon sequestration. However, increasing numbers of reports indicate the importance of incorporating microbial-derived carbon into soil stable carbon pools. Here we investigate microbial residues in a California annual grassland after a continuous 9-year manipulation of three environmental factors (elevated CO(2), warming and nitrogen deposition), singly and in combination. Our results indicate that warming and nitrogen deposition can both alter the fraction of carbon derived from microbes in soils, though for two very different reasons. A reduction in microbial carbon contribution to stable carbon pools may have implications for our predictions of global change impacts on soil stored carbon. PMID:23187622

  14. Method of fabricating boron containing coatings

    DOEpatents

    Makowiecki, Daniel M.; Jankowski, Alan F.

    1999-01-01

    Hard coatings are fabricated from boron nitride, cubic boron nitride, and multilayer boron/cubic boron nitride, and the fabrication thereof involves magnetron sputtering in a selected atmosphere. These hard coatings may be applied to tools and engine and other parts, as well to reduce wear on tribological surfaces and electronic devices. These boron coatings contain no morphological growth features. For example, the boron is formed in an inert (e.g. argon) atmosphere, while the cubic boron nitride is formed in a reactive (e.g. nitrogen) atmosphere. The multilayer boron/cubic boron nitride, is produced by depositing alternate layers of boron and cubic boron nitride, with the alternate layers having a thickness of 1 nanometer to 1 micrometer, and at least the interfaces of the layers may be discrete or of a blended or graded composition.

  15. Method of fabricating boron containing coatings

    DOEpatents

    Makowiecki, D.M.; Jankowski, A.F.

    1999-04-27

    Hard coatings are fabricated from boron nitride, cubic boron nitride, and multilayer boron/cubic boron nitride, and the fabrication thereof involves magnetron sputtering in a selected atmosphere. These hard coatings may be applied to tools and engine and other parts, as well to reduce wear on tribological surfaces and electronic devices. These boron coatings contain no morphological growth features. For example, the boron is formed in an inert (e.g. argon) atmosphere, while the cubic boron nitride is formed in a reactive (e.g. nitrogen) atmosphere. The multilayer boron/cubic boron nitride, is produced by depositing alternate layers of boron and cubic boron nitride, with the alternate layers having a thickness of 1 nanometer to 1 micrometer, and at least the interfaces of the layers may be discrete or of a blended or graded composition. 3 figs.

  16. Novel nanometer-level uniform amorphous carbon coating for boron powders by direct pyrolysis of coronene without solvent.

    PubMed

    Ye, ShuJun; Song, MingHui; Kumakura, Hiroaki

    2015-01-30

    A 3 nm coronene coating and a 4 nm amorphous carbon coating with a uniform shell-core encapsulation structure for nanosized boron (B) powders are formed by a simple process in which coronene is directly mixed with boron particles without a solvent and heated at 520 °C for 1 h or at 630 °C for 3 h in a vacuum-sealed silica tube. Coronene has a melting point lower than its decomposition temperature, which enables liquid coronene to cover B particles by liquid diffusion and penetration without the need for a solvent. The diffusion and penetration of coronene can extend to the boundaries of particles and to inside the agglomerated nanoparticles to form a complete shell-core encapsulated structure. As the temperature is increased, thermal decomposition of coronene on the B particles results in the formation of a uniform amorphous carbon coating layer. This novel and simple nanometer-level uniform amorphous carbon coating method can possibly be applied to many other powders; thus, it has potential applications in many fields at low cost. PMID:25556855

  17. Boron Isotopes Analyses of Carbonates, Phosphates and Silicates by Laser Ablation MC-ICP-MS: the Influence of Sample Matrix

    NASA Astrophysics Data System (ADS)

    Gerdes, A.

    2013-12-01

    Methods for in-situ analyses of boron isotopes by laser ablation MC-ICP-MS, although presented by 3 labs over the last years, are still not routinely applied despite of the growing interest in B isotopes, e.g. in palaeoclimate research. This study evaluates the ability to analyse boron isotopes by laser ablation at levels down to 0.2 ppm in biogenic carbonates as well as in various minerals (e.g., calcit, garnet, cpx, apatite, hematite, quartz, diamond ...) and natural and synthetic glass (NIST, USGS, and MPI-DING). Mounted and polished samples were ablated in a two-volume Helix cell using a RESOlution 193nm Excimer laser coupled to a Thermo-Finnigan Neptune (No. 1, build in 2000). Due to high sensitivity isotope signals were detected using Faraday collectors (1011 Ohm resistors). Analyses were performed as static spots over 25s with diameters of 235 to 7 μm depending on boron concentration, which yield typical 11B signals of about 0.04 (≤ 1ppm; e.g., cherts) to >0.6 V (3wt.%; tourmaline). Therefore, sample amount consumed during analyses range from 1 nanogram to 10 microgram with total analysed B content in the range of 5 to 1000 picogram. For correction of drift and mass fractionation soda-lime glass NIST-612 or NIST-610 were analysed every 30min. The applied method yields for various materials a typical analytical precision and reproducibility (1σ) of the 11B/10B of about 0.5‰ or better at boron concentration of more than 2 ppm. The effect of various parameters such as gas background, surface contamination, cross contamination, spot size, laser energy, and depth drilling will be discussed briefly. However, crucial for in-situ analyse is the evaluation of the accuracy and the influence of the sample matrix on it. Approaches to test this are still hampered by the lack of well-characterized low-B (e.g. <20ppm) reference materiel of different sample matrix. Nevertheless, in contrast to previous studies an effect of sample matrix on the boron isotope ratio was

  18. Spontaneous Boron-doping of Graphene at Room Temperature

    NASA Astrophysics Data System (ADS)

    Pan, Lida; Que, Yande; Du, Shixuan; Gao, Hongjun; Pantelides, Sokrates T.

    2015-03-01

    Doping graphene with boron or nitrogen is an effective way to modify its electronic properties. However, the reaction barrier for introducing these impurities is quite high, making the doping process difficult. In this work, we propose a low-energy reaction route derived from first-principles calculations and subsequently validated by experiments. The calculations show that, when graphene is placed on a ruthenium substrate and exposed to atomic boron, boron atoms can incorporate substitutionally into the graphene sheet with an energy barrier about 0.1 eV, displacing carbon atoms below the graphene sheet where they migrates away. This result suggests that spontaneous doping by boron can take place at room temperature. Following the prediction, we grew high-quality graphene on the Ru(0001) surface and then expose it to B2H6 which decomposes into atomic boron. XPS and STM results indicate that boron dopes graphene substantially without disturbing the graphene lattice, confirming the theoretical predictions. Doping by nitrogen and co-doping by B and N will also be discussed.

  19. Spin-polarized electron current from carbon-doped open armchair boron nitride nanotubes: Implication for nano-spintronic devices

    NASA Astrophysics Data System (ADS)

    Zhou, Gang; Duan, Wenhui

    2007-03-01

    Spin-polarized density functional calculations show that the substitutional doping of carbon (C) atom at the mouth changes the atomic and spin configurations of open armchair boron nitride nanotubes (BNNTs). The occupied/unoccupied deep gap states are observed with the significant spin-splitting. The structures and spin-polarized properties are basically stable under the considerable electric field, which is important for practical applications. The magnetization mechanism is attributed to the interactions of s, p states between the C and its neighboring B or N atoms. Ultimately, advantageous geometrical and electronic effects mean that C-doped open armchair BNNTs would have promising applications in nano-spintronic devices.

  20. Carbon and Nitrogen cycling in a permafrost soil profile

    NASA Astrophysics Data System (ADS)

    Salmon, V. G.; Schaedel, C.; Mack, M. C.; Schuur, E.

    2015-12-01

    In high latitude ecosystems, active layer soils thaw during the growing season and are situated on top of perennially frozen soils (permafrost). Permafrost affected soil profiles currently store a globally important pool of carbon (1330-1580 PgC) due to cold temperatures constraining the decomposition of soil organic matter. With global warming, however, seasonal thaw is expected to increase in speed and extend to deeper portions of the soil profile. As permafrost soils become part of the active layer, carbon (C) and nitrogen (N) previously stored in soil organic matter will be released via decomposition. In this experiment, the dynamic relationship between N mineralization, C mineralization, and C quality was investigated in moist acidic tundra soils. Soils from the active layer surface down through the permafrost (80cm) were incubated aerobically at 15°C for 225 days. Carbon dioxide fluxes were fit with a two pool exponential decay model so that the size and turnover of both the quickly decomposing C pool (Cfast) and the slowly decomposing C pool (Cslow) could be assessed. Soil extractions with 2M KCl were performed at six time points throughout the incubation so that dissolve inorganic N (DIN) and dissolved organic C (DOC) could be measured. DIN was readily extractable from deep permafrost soils throughout the incubation (0.05 mgN/g dry soil) but in active layer soils DIN was only produced after Cfast had been depleted. In contrast, active layer soils had high levels of DOC (0.65 mgC/g dry soil) throughout the incubation but in permafrost soils, DOC became depleted as Cfast reduced in size. The strong contrasts between the C and N cycling in active layer soils versus permafrost soils suggest that the deeper thaw will dramatically increase N availability in these soil profiles. Plants and soil microbes in the tundra are currently N limited so our findings imply that deepening thaw will 1) provide N necessary for increased plant growth and 2) stimulate losses of

  1. Modeling the above and below ground carbon and nitrogen stocks in northern high latitude terrestrial ecosystems

    NASA Astrophysics Data System (ADS)

    ElMasri, B.; Jain, A. K.

    2012-12-01

    Climate change is expected to cause warming in the northern high latitudes, but it is still uncertain what the respond of the northern high latitudes ecosystem will be to such warming. One of the biggest scientific questions is to determine whether northern high latitude ecosystem are or will act as a terrestrial carbon sink or source. Therefore, it is essential to understand and quantify the biogeochemical cycle of the northern high latitude ecosystems in order to predict their respond to climate change. Using a land surface model, the Integrated Science Assessment Model (ISAM) with its coupled carbon-nitrogen cycle, we provide a detail quantification of the carbon and nitrogen in the vegetation pools and the soil carbon for the northern high latitude ecosystems. We focus on soil carbon and vegetation carbon and nitrogen, though we provide results for gross primary production (GPP), autotrophic respiration (Ra), net primary production (NPP), net ecosystem exchange (NEE), and heterotrophic respiration (Rh). In addition, we examine the effect of nitrogen limitation on the carbon fluxes and soil carbon. We present the results for several flux tower sites representative of the tundra and the boreal ecosystems as well as for the northern high latitude region. Our results provide a comprehensive assessment of below and above ground carbon and nitrogen pools in the northern high latitude and the model calibrated parameters can be used to improve the results of other land surface models.

  2. α-ketoglutarate coordinates carbon and nitrogen utilization via Enzyme I inhibition

    PubMed Central

    Doucette, Christopher D; Schwab, David J; Wingreen, Ned S; Rabinowitz, Joshua D

    2011-01-01

    Microbes survive in a variety of nutrient environments by modulating their intracellular metabolism. Balanced growth requires coordinated uptake of carbon and nitrogen, the primary substrates for biomass production. The mechanisms that balance carbon and nitrogen uptake are, however, poorly understood. We find in Escherichia coli that a sudden increase in nitrogen availability results in an almost immediate increase in glucose uptake. The concentrations of known glycolytic intermediates and regulators, however, remain homeostatic. Instead, we find that α-ketoglutarate, which accumulates in nitrogen limitation, directly blocks glucose uptake by inhibiting Enzyme I, the first step of the phosphotransferase system (PTS). This enables rapid modulation of glycolytic flux without marked concentration changes in glycolytic intermediates by simultaneously accelerating glucose import and consumption of the terminal glycolytic intermediate phosphoenolpyruvate. Quantitative modeling shows that this previously unidentified regulatory connection is in principle sufficient to coordinate carbon and nitrogen utilization. PMID:22002719

  3. Effects of Carbon and Nitrogen on the Microstructure and Mechanical Properties of Carbonitrided Low-Carbon Steel

    NASA Astrophysics Data System (ADS)

    Taweejun, Nipon; Kanchanomai, Chaosuan

    2015-12-01

    Various carbonitriding processes have been applied to low-carbon steel. The carbon and nitrogen contents in the case of carbonitrided low-carbon steels have been evaluated, and their influences on microstructure, distortion, hardness, and strength have been investigated. The factor limiting the ferrite and pearlite formations with increasing nitrogen content was a mechanism that resulted in more retained austenite in the case of low-carbon steel treated using a high flow rate of ammonia. The high-nitrogen content and high amount of retained austenite in the case of carbonitrided low-carbon steel slightly reduced the hardness, case depth, and strength. However, the elongation was improved, and the distortion was reduced. In the case zones, fractures occurred along the grain boundaries, i.e., intergranular fractures, whereas the fracture surfaces in the core regions were typical ductile fractures, i.e., dimples were observed.

  4. Pore size analysis of activated carbons from argon and nitrogen porosimetry using density functional theory

    SciTech Connect

    Dombrowski, R.J.; Hyduke, D.R.; Lastoskie, C.M.

    2000-05-30

    The authors present isotherms calculated from density functional theory for the adsorption of argon in model slit-shaped carbon pores at 77 K. The model isotherms are used to interpret experimental argon uptake measurements and to obtain the pore size distributions of several porous carbons. A similar set of density measurements and to obtain the pore size distributions of several porous carbons. A similar set of density functional theory isotherms, previously reported for nitrogen adsorption on carbon slit pores at 77 K, are used to determine pore size distributions for the same set of carbons. The pore size distribution maxima, mean pore widths, and specific pore volumes measured using the two different probe gases are all found to agree to within approximately 8% on average. Some of the differences in the pore size distributions obtained from argon and nitrogen porosimetry may be attributable to quadrupolar interactions of the nitrogen molecules with functional groups on the carbon surface.

  5. STABLE ISOTOPIC EVIDENCE OF CARBON AND NITROGEN USE IN CULTURED ECTOMYCORRHIZAL AND SAPROTROPHIC FUNGI

    EPA Science Inventory

    Stable isotopes in sporocarps have proven useful for inferring ectomycorrhizal or saprotrophic status and understanding carbon (C) and nitrogen (N) utilization. However, greater understanding of processes producing isotopic concentrations is needed. We measured natural abundanc...

  6. Biological cycling of carbon and nitrogen to reduce agricultural pollution by nutrients

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Carbon and nitrogen are two key elements of global significance, playing large roles in the production of food, feed, fiber, and fuel for human existence, as well as providing numerous other ecosystem services. Although nitrogen is often a limiting element in natural systems, it can become a pollut...

  7. An analytical study of nitrogen oxides and carbon monoxide emissions in hydrocarbon combustion with added nitrogen - Preliminary results

    NASA Technical Reports Server (NTRS)

    Bittker, D. A.

    1980-01-01

    The influence of ground-based gas turbine combustor operating conditions and fuel-bound nitrogen (FBN) found in coal-derived liquid fuels on the formation of nitrogen oxides and carbon monoxide is investigated. Analytical predictions of NOx and CO concentrations are obtained for a two-stage, adiabatic, perfectly-stirred reactor operating on a propane-air mixture, with primary equivalence ratios from 0.5 to 1.7, secondary equivalence ratios of 0.5 or 0.7, primary stage residence times from 12 to 20 msec, secondary stage residence times of 1, 2 and 3 msec and fuel nitrogen contents of 0.5, 1.0 and 2.0 wt %. Minimum nitrogen oxide but maximum carbon monoxide formation is obtained at primary zone equivalence ratios between 1.4 and 1.5, with percentage conversion of FBN to NOx decreasing with increased fuel nitrogen content. Additional secondary dilution is observed to reduce final pollutant concentrations, with NOx concentration independent of secondary residence time and CO decreasing with secondary residence time; primary zone residence time is not observed to affect final NOx and CO concentrations significantly. Finally, comparison of computed results with experimental values shows a good semiquantitative agreement.

  8. Impact of transition metal on nitrogen retention and activity of iron-nitrogen-carbon oxygen reduction catalysts.

    PubMed

    Ganesan, Selvarani; Leonard, Nathaniel; Barton, Scott Calabrese

    2014-03-14

    Iron based nitrogen doped carbon (FeNC) catalysts are synthesized by high-pressure pyrolysis of carbon and melamine with varying amounts of iron acetate in a closed, constant-volume reactor. The optimum nominal amount of Fe (1.2 wt%) in FeNC catalysts is established through oxygen reduction reaction (ORR) polarization. Since the quantity of iron used in FeNCs is very small, the amount of Fe retained in FeNC catalysts after leaching is determined by UV-VIS spectroscopy. As nitrogen is considered to be a component of active sites, the amount of bulk and surface nitrogen retention in FeNC catalysts are measured using elemental analysis and X-ray photoelectron spectroscopy, respectively. It is found that increasing nominal Fe content in FeNC catalysts leads to a decreased level of nitrogen retention. Thermogravimetric analysis demonstrates that increasing nominal Fe content leads to increased weight loss during pyrolysis, particularly at high temperatures. Catalysts are also prepared in the absence of iron source, and with iron removed by washing with hot aqua regia post-pyrolysis. FeNC catalysts prepared with no Fe show high retained nitrogen content but poor ORR activity, and aqua regia washed catalysts demonstrate similar activity to Fe-free catalysts, indicating that Fe is an active site component. PMID:24457909

  9. Graphitic and pyridinic nitrogen in carbon nanotubes: energetic and polarization aspects

    NASA Astrophysics Data System (ADS)

    Sedelnikova, Olga V.; Bulusheva, Lyubov G.; Okotrub, Alexander V.

    2016-03-01

    The incorporation of nitrogen atoms into carbon nanotube (CNT) walls occurs mainly via bonding with three or two carbon atoms, and the obtained configurations are referred to as graphitic and pyridinic nitrogen forms. Here, we evaluate the energy of formation of these nitrogen defects in an armchair (6,6) CNT and the static polarizability of the obtained nitrogen-containing carbon (CNx) nanotubes using a dispersion-corrected hybrid functional. The calculations showed that the graphitic nitrogen atoms prefer to be in the pentagonal rings located at a nanotube cap. The CNx nanotubes with such nitrogen impurities have enhanced polarizability as compared to their nondoped counterparts. The formation of the pyridinic nitrogen defect requires ˜7.1 eV however, if the CNT already contains a vacancy, this energy reduces to ˜0.2 eV. The presence of pyridinic nitrogen atoms in CNx nanotubes should not increase the polarization response. Our results suggest that the electromagnetic properties of CNx nanotubes can be tuned by interconverting between graphitic and pyridinic nitrogen forms.

  10. Microbial stoichiometry overrides biomass as a regulator of soil carbon and nitrogen cycling.

    PubMed

    Buchkowski, Robert W; Schmitz, Oswald J; Bradford, Mark A

    2015-04-01

    Understanding the role of soil microbial communities in coupled carbon and nitrogen cycles has become an area of great interest as we strive to understand how global change will influence ecosystem function. In this endeavor, microbially explicit decomposition models are being adopted because they include microbial stoichiometry- and biomass-mediated mechanisms that may be important in shaping ecosystem response to environmental change. Yet there has been a dearth of empirical tests to verify the predictions of these models and hence identify potential improvements. We measured the response of soil microbes to multiple rates of carbon and nitrogen amendment in experimental microcosms, and used the respiration and nitrogen mineralization responses to assess a well-established, single-pool, microbial decomposition model. The model generally predicted the empirical trends in carbon and nitrogen fluxes, but failed to predict the empirical trends in microbial biomass. Further examination of this discontinuity indicated that the model successfully predicted carbon and nitrogen cycling because stoichiometry overrode microbial biomass as a regulator of cycling rates. Stoichiometric control meant that the addition of carbon generally increased respiration and decreased nitrogen mineralization, whereas nitrogen had the opposite effects. Biomass only assumed importance as a control on cycling rates when stoichiometric ratios of resource inputs were a close match to those of the microbial biomass. Our work highlights the need to advance our understanding of the stoichiometric demands of microbial biomass in order to better understand biogeochemical cycles in the face of changing organic- and inorganic-matter inputs to terrestrial ecosystems. PMID:26230033

  11. Boron Nitride Nanotube: Synthesis and Applications

    NASA Technical Reports Server (NTRS)

    Tiano, Amanda L.; Park, Cheol; Lee, Joseph W.; Luong, Hoa H.; Gibbons, Luke J.; Chu, Sang-Hyon; Applin, Samantha I.; Gnoffo, Peter; Lowther, Sharon; Kim, Hyun Jung; Danehy, Paul M.; Inman, Jennifer A.; Jones, Stephen B.; Kang, Jin Ho; Sauti, Godfrey; Thibeault, Sheila A.; Yamakov, Vesselin; Wise, Kristopher E.; Su, Ji; Fay, Catharine C.

    2014-01-01

    Scientists have predicted that carbon's immediate neighbors on the periodic chart, boron and nitrogen, may also form perfect nanotubes, since the advent of carbon nanotubes (CNTs) in 1991. First proposed then synthesized by researchers at UC Berkeley in the mid 1990's, the boron nitride nanotube (BNNT) has proven very difficult to make until now. Herein we provide an update on a catalyst-free method for synthesizing highly crystalline, small diameter BNNTs with a high aspect ratio using a high power laser under a high pressure and high temperature environment first discovered jointly by NASA/NIA JSA. Progress in purification methods, dispersion studies, BNNT mat and composite formation, and modeling and diagnostics will also be presented. The white BNNTs offer extraordinary properties including neutron radiation shielding, piezoelectricity, thermal oxidative stability (> 800 C in air), mechanical strength, and toughness. The characteristics of the novel BNNTs and BNNT polymer composites and their potential applications are discussed.

  12. Simultaneous inhibition of carbon and nitrogen mineralization in a forest soil by simulated acid precipitation

    SciTech Connect

    Klein, T.M.; Novick, N.J.; Kreitinger, J.P.; Alexander, M.

    1984-06-01

    One method to simulate the long-term exposure of soil to acid rain involves the addition of single doses of concentrated acid. The inhibition of carbon mineralization accompanied by a stimulation of nitrogen mineralization may result from this severe, unnatural treatment. The present study was designed to determine whether the inhibition of carbon mineralization and the accompanying enhanced nitrogen mineralization would occur when soils are treated with more dilute acid for long periods of time, as takes place in nature.

  13. Infrared spectrum of the complex of formaldehyde with carbon dioxide in argon and nitrogen matrices

    NASA Technical Reports Server (NTRS)

    Van Der Zwet, G. P.; Allamandola, Louis J.; Baas, F.; Greenberg, J. M.

    1989-01-01

    The complex of formaldehyde with carbon dioxide has been studied by infrared spectroscopy in argon and nitrogen matrices. The shifts relative to the free species show that the complex is weak and similar in argon and nitrogen. The results give evidence for T-shaped complexes, which are isolated in several configurations. Some evidence is also presented which indicates that, in addition to the two well-known sites in argon, carbon dioxide can be trapped in a third site.

  14. Structure and Electroanalytical Application of Nitrogen-doped Carbon Thin Film Electrode with Lower Nitrogen Concentration.

    PubMed

    Kamata, Tomoyuki; Kato, Dai; Umemura, Shigeru; Niwa, Osamu

    2015-01-01

    We studied a nitrogen-doped nanocarbon film electrode with a nitrogen concentration of lower than 10.9 at% formed by the unbalanced magnetron (UBM) sputtering method. The sp(3) content in the nitrogen-doped UBM sputtering nanocarbon film (N-UBM film) slightly increases with increasing nitrogen concentration. The nitrogen-containing graphite-like bonding decreases and pyridine-like bonding increases with increasing nitrogen concentration. The N-UBM film has a very smooth surface with an average roughness of 0.1 to 0.3 nm, which is almost independent of nitrogen concentration. The N-UBM film electrode shows a wider potential window (4.1 V) than a pure-UBM film electrode (3.9 V) due to its slight increase in the sp(3) content. The electrocatalytic activity increased with increasing nitrogen concentration, suggesting that the electroactivity is maximum when the nitrogen concentration is around 10.9 at%, which is confirmed by the peak separation of Fe(CN)6(4-). The hydrogen peroxide (H2O2) reduction potentials at the N-UBM film electrode shifted about 0.1 V, and the peak current of H2O2 increased about 4 times. PMID:26165287

  15. Overexpression of Arabidopsis NLP7 improves plant growth under both nitrogen-limiting and -sufficient conditions by enhancing nitrogen and carbon assimilation.

    PubMed

    Yu, Lin-Hui; Wu, Jie; Tang, Hui; Yuan, Yang; Wang, Shi-Mei; Wang, Yu-Ping; Zhu, Qi-Sheng; Li, Shi-Gui; Xiang, Cheng-Bin

    2016-01-01

    Nitrogen is essential for plant survival and growth. Excessive application of nitrogenous fertilizer has generated serious environment pollution and increased production cost in agriculture. To deal with this problem, tremendous efforts have been invested worldwide to increase the nitrogen use ability of crops. However, only limited success has been achieved to date. Here we report that NLP7 (NIN-LIKE PROTEIN 7) is a potential candidate to improve plant nitrogen use ability. When overexpressed in Arabidopsis, NLP7 increases plant biomass under both nitrogen-poor and -rich conditions with better-developed root system and reduced shoot/root ratio. NLP7-overexpressing plants show a significant increase in key nitrogen metabolites, nitrogen uptake, total nitrogen content, and expression levels of genes involved in nitrogen assimilation and signalling. More importantly, overexpression of NLP7 also enhances photosynthesis rate and carbon assimilation, whereas knockout of NLP7 impaired both nitrogen and carbon assimilation. In addition, NLP7 improves plant growth and nitrogen use in transgenic tobacco (Nicotiana tabacum). Our results demonstrate that NLP7 significantly improves plant growth under both nitrogen-poor and -rich conditions by coordinately enhancing nitrogen and carbon assimilation and sheds light on crop improvement. PMID:27293103

  16. Overexpression of Arabidopsis NLP7 improves plant growth under both nitrogen-limiting and -sufficient conditions by enhancing nitrogen and carbon assimilation

    PubMed Central

    Yu, Lin-Hui; Wu, Jie; Tang, Hui; Yuan, Yang; Wang, Shi-Mei; Wang, Yu-Ping; Zhu, Qi-Sheng; Li, Shi-Gui; Xiang, Cheng-Bin

    2016-01-01

    Nitrogen is essential for plant survival and growth. Excessive application of nitrogenous fertilizer has generated serious environment pollution and increased production cost in agriculture. To deal with this problem, tremendous efforts have been invested worldwide to increase the nitrogen use ability of crops. However, only limited success has been achieved to date. Here we report that NLP7 (NIN-LIKE PROTEIN 7) is a potential candidate to improve plant nitrogen use ability. When overexpressed in Arabidopsis, NLP7 increases plant biomass under both nitrogen-poor and -rich conditions with better-developed root system and reduced shoot/root ratio. NLP7–overexpressing plants show a significant increase in key nitrogen metabolites, nitrogen uptake, total nitrogen content, and expression levels of genes involved in nitrogen assimilation and signalling. More importantly, overexpression of NLP7 also enhances photosynthesis rate and carbon assimilation, whereas knockout of NLP7 impaired both nitrogen and carbon assimilation. In addition, NLP7 improves plant growth and nitrogen use in transgenic tobacco (Nicotiana tabacum). Our results demonstrate that NLP7 significantly improves plant growth under both nitrogen-poor and -rich conditions by coordinately enhancing nitrogen and carbon assimilation and sheds light on crop improvement. PMID:27293103

  17. Direct assessment of the mechanical modulus of graphene co-doped with low concentrations of boron-nitrogen by a non-contact approach

    NASA Astrophysics Data System (ADS)

    Pan, Shun-Hsien; Medina, Henry; Wang, Sheng-Bo; Chou, Li-Jen; Wang, Zhiming M.; Chen, Kuei-Hsien; Chen, Li-Chyong; Chueh, Yu-Lun

    2014-07-01

    Boron and nitrogen co-doping has been shown to be an effective way to induce a band gap in graphene for electrical applications but only a few theoretical studies have been done to understand the elastic and mechanical properties of the modified graphene. Until now, no experimental assessment of the mechanical modulus of boron-nitrogen-doped graphene (BNG) has been reported in the literature. Here, we demonstrate a novel non-contact approach to determine the in-plane stiffness of BNG at low BN concentrations. The in-plane stiffness of BNG with 2 at% BN concentration was estimated to be about 309 N m-1, which is lower than that of pristine graphene, in good agreement with some theoretical studies. Moreover, we correlated the conductivity of BNG with induced strain and found the BNG to be more sensitive than pristine graphene in response to externally applied strain. This result indicates that BNG is a more suitable material than graphene for strain sensor applications.Boron and nitrogen co-doping has been shown to be an effective way to induce a band gap in graphene for electrical applications but only a few theoretical studies have been done to understand the elastic and mechanical properties of the modified graphene. Until now, no experimental assessment of the mechanical modulus of boron-nitrogen-doped graphene (BNG) has been reported in the literature. Here, we demonstrate a novel non-contact approach to determine the in-plane stiffness of BNG at low BN concentrations. The in-plane stiffness of BNG with 2 at% BN concentration was estimated to be about 309 N m-1, which is lower than that of pristine graphene, in good agreement with some theoretical studies. Moreover, we correlated the conductivity of BNG with induced strain and found the BNG to be more sensitive than pristine graphene in response to externally applied strain. This result indicates that BNG is a more suitable material than graphene for strain sensor applications. Electronic supplementary

  18. Textural properties of raw carbon nanotubes by nitrogen adsorption and mercury porosimetry

    NASA Astrophysics Data System (ADS)

    Bossuot, Ch.; Bister, G.; Fonseca, A.; Nagy, J. B.; Pirard, J.-P.

    2001-11-01

    A sample of raw material made by catalytic decomposition of methane and containing a fraction of single-wall carbon nanotubes (SWNTs) was studied. Interpretation of mercury porosimetry and nitrogen adsorption-desorption isotherms was difficult because the purity of carbon nanotubes, thermogravimetry revealed, was rather poor. Indeed, the raw material was made up by carbon soot, graphitic disordered carbon, damaged nanotubes, SWNTs and catalyst residues. The raw material was mainly microporous with some mesopores.

  19. Hetero-junctions of Boron Nitride and Carbon Nanotubes: Synthesis and Characterization

    SciTech Connect

    Yap, Yoke Khin

    2013-03-14

    Hetero-junctions of boron nitride nanotubes (BNNTs) and carbon nanotubes (CNTs) are expected to have appealing new properties that are not available from pure BNNTs and CNTs. Theoretical studies indicate that BNNT/CNT junctions could be multifunctional and applicable as memory, spintronic, electronic, and photonics devices with tunable band structures. This will lead to energy and material efficient multifunctional devices that will be beneficial to the society. However, experimental realization of BNNT/CNT junctions was hindered by the absent of a common growth technique for BNNTs and CNTs. In fact, the synthesis of BNNTs was very challenging and may involve high temperatures (up to 3000 degree Celsius by laser ablation) and explosive chemicals. During the award period, we have successfully developed a simple chemical vapor deposition (CVD) technique to grow BNNTs at 1100-1200 degree Celsius without using dangerous chemicals. A series of common catalyst have then been identified for the synthesis of BNNTs and CNTs. Both of these breakthroughs have led to our preliminary success in growing two types of BNNT/CNT junctions and two additional new nanostructures: 1) branching BNNT/CNT junctions and 2) co-axial BNNT/CNT junctions, 3) quantum dots functionalized BNNTs (QDs-BNNTs), 4) BNNT/graphene junctions. We have started to understand their structural, compositional, and electronic properties. Latest results indicate that the branching BNNT/CNT junctions and QDs-BNNTs are functional as room-temperature tunneling devices. We have submitted the application of a renewal grant to continue the study of these new energy efficient materials. Finally, this project has also strengthened our collaborations with multiple Department of Energy's Nanoscale Science Research Centers (NSRCs), including the Center for Nanophase Materials Sciences (CNMS) at Oak Ridge National Laboratory, and the Center for Integrated Nanotechnologies (CINTs) at Sandia National Laboratories and Los

  20. Land Cover Differences in Soil Carbon and Nitrogen at Fort Benning, Georgia

    SciTech Connect

    Garten Jr., C.T.

    2004-02-09

    Land cover characterization might help land managers assess the impacts of management practices and land cover change on attributes linked to the maintenance and/or recovery of soil quality. However, connections between land cover and measures of soil quality are not well established. The objective of this limited investigation was to examine differences in soil carbon and nitrogen among various land cover types at Fort Benning, Georgia. Forty-one sampling sites were classified into five major land cover types: deciduous forest, mixed forest, evergreen forest or plantation, transitional herbaceous vegetation, and barren land. Key measures of soil quality (including mineral soil density, nitrogen availability, soil carbon and nitrogen stocks, as well as properties and chemistry of the O-horizon) were significantly different among the five land covers. In general, barren land had the poorest soil quality. Barren land, created through disturbance by tracked vehicles and/or erosion, had significantly greater soil density and a substantial loss of carbon and nitrogen relative to soils at less disturbed sites. We estimate that recovery of soil carbon under barren land at Fort Benning to current day levels under transitional vegetation or forests would require about 60 years following reestablishment of vegetation. Maps of soil carbon and nitrogen were produced for Fort Benning based on a 1999 land cover map and field measurements of soil carbon and nitrogen stocks under different land cover categories.

  1. Impacts of Invasive Pests on Forest Carbon and Nitrogen Dynamics

    NASA Astrophysics Data System (ADS)

    Lovett, G. M.; Crowley, K. F.

    2014-12-01

    Forests of the U.S. have been subject to repeated invasions of destructive insects and diseases imported from other continents. Like other disturbances, these pests can produce short-term ecosystem effects due to tree mortality, but unlike other disturbances, they often target individual species and therefore can cause long-term species change in the forest. Because tree species vary in their influence on carbon (C) and nitrogen (N) cycles, pest-induced species change can radically alter the biogeochemistry of a forest. In this paper we use both data and modeling to examine how pest-induced species change may alter the C and N cycling in forests of the eastern U.S. We describe a new forest ecosystem model that distinguishes individual tree species and allows species composition to shift over the course of the model run. Results indicate that the mortality of eastern hemlock (Tsuga canadensis) by hemlock woolly adelgid and its replacement by faster-growing species such as black birch (Betula lenta) will reduce forest floor C stocks but increase productivity as the birch become established. Decline of American beech (Fagus grandifolia) from beech bark disease and its replacement by sugar maple (Acer saccharum) is likely to decrease soil C storage and increase N leaching from the ecosystem. Responses to other invasive pests will also be discussed. The magnitude of these species-specific effects on C and N cycling is in many cases larger than direct effects expected from changes in climate and atmospheric N deposition, indicating that species change should be included in models that predict forest ecosystem function under future environmental conditions.

  2. Anthropogenic nitrogen deposition enhances carbon sequestration in boreal soils.

    PubMed

    Maaroufi, Nadia I; Nordin, Annika; Hasselquist, Niles J; Bach, Lisbet H; Palmqvist, Kristin; Gundale, Michael J

    2015-08-01

    It is proposed that carbon (C) sequestration in response to reactive nitrogen (Nr ) deposition in boreal forests accounts for a large portion of the terrestrial sink for anthropogenic CO2 emissions. While studies have helped clarify the magnitude by which Nr deposition enhances C sequestration by forest vegetation, there remains a paucity of long-term experimental studies evaluating how soil C pools respond. We conducted a long-term experiment, maintained since 1996, consisting of three N addition levels (0, 12.5, and 50 kg N ha(-1) yr(-1) ) in the boreal zone of northern Sweden to understand how atmospheric Nr deposition affects soil C accumulation, soil microbial communities, and soil respiration. We hypothesized that soil C sequestration will increase, and soil microbial biomass and soil respiration will decrease, with disproportionately large changes expected compared to low levels of N addition. Our data showed that the low N addition treatment caused a non-significant increase in the organic horizon C pool of ~15% and a significant increase of ~30% in response to the high N treatment relative to the control. The relationship between C sequestration and N addition in the organic horizon was linear, with a slope of 10 kg C kg(-1) N. We also found a concomitant decrease in total microbial and fungal biomasses and a ~11% reduction in soil respiration in response to the high N treatment. Our data complement previous data from the same study system describing aboveground C sequestration, indicating a total ecosystem sequestration rate of 26 kg C kg(-1) N. These estimates are far lower than suggested by some previous modeling studies, and thus will help improve and validate current modeling efforts aimed at separating the effect of multiple global change factors on the C balance of the boreal region. PMID:25711504

  3. Nitrogen Deposition Enhances Carbon Sequestration by Plantations in Northern China

    PubMed Central

    Du, Zhihong; Wang, Wei; Zeng, Wenjing; Zeng, Hui

    2014-01-01

    Nitrogen (N) deposition and its ecological effects on forest ecosystems have received global attention. Plantations play an important role in mitigating climate change through assimilating atmospheric CO2. However, the mechanisms by which increasing N additions affect net ecosystem production (NEP) of plantations remain poorly understood. A field experiment was initialized in May 2009, which incorporated additions of four rates of N (control (no N addition), low-N (5 g N m−2 yr−1), medium-N (10 g N m−2 yr−1), and high-N (15 g N m−2 yr−1)) at the Saihanba Forestry Center, Hebei Province, northern China, a locality that contains the largest area of plantations in China. Net primary production (NPP), soil respiration, and its autotrophic and heterotrophic components were measured. Plant tissue carbon (C) and N concentrations (including foliage, litter, and fine roots), microbial biomass, microbial community composition, extracellular enzyme activities, and soil pH were also measured. N addition significantly increased NPP, which was associated with increased litter N concentrations. Autotrophic respiration (AR) increased but heterotrophic respiration (HR) decreased in the high N compared with the medium N plots, although the HR in high and medium N plots did not significantly differ from that in the control. The increased AR may derive from mycorrhizal respiration and rhizospheric microbial respiration, not live root respiration, because fine root biomass and N concentrations showed no significant differences. Although the HR was significantly suppressed in the high-N plots, soil microbial biomass, composition, or activity of extracellular enzymes were not significantly changed. Reduced pH with fertilization also could not explain the pattern of HR. The reduction of HR may be related to altered microbial C use efficiency. NEP was significantly enhanced by N addition, from 149 to 426.6 g C m−2 yr−1. Short-term N addition may significantly enhance the

  4. Nitrogen attenuation of terrestrial carbon cycle response to global environmental factors

    NASA Astrophysics Data System (ADS)

    Jain, Atul; Yang, Xiaojuan; Kheshgi, Haroon; McGuire, A. David; Post, Wilfred; Kicklighter, David

    2009-12-01

    Nitrogen cycle dynamics have the capacity to attenuate the magnitude of global terrestrial carbon sinks and sources driven by CO2 fertilization and changes in climate. In this study, two versions of the terrestrial carbon and nitrogen cycle components of the Integrated Science Assessment Model (ISAM) are used to evaluate how variation in nitrogen availability influences terrestrial carbon sinks and sources in response to changes over the 20th century in global environmental factors including atmospheric CO2 concentration, nitrogen inputs, temperature, precipitation and land use. The two versions of ISAM vary in their treatment of nitrogen availability: ISAM-NC has a terrestrial carbon cycle model coupled to a fully dynamic nitrogen cycle while ISAM-C has an identical carbon cycle model but nitrogen availability is always in sufficient supply. Overall, the two versions of the model estimate approximately the same amount of global mean carbon uptake over the 20th century. However, comparisons of results of ISAM-NC relative to ISAM-C reveal that nitrogen dynamics: (1) reduced the 1990s carbon sink associated with increasing atmospheric CO2 by 0.53 PgC yr-1 (1 Pg = 1015g), (2) reduced the 1990s carbon source associated with changes in temperature and precipitation of 0.34 PgC yr-1 in the 1990s, (3) an enhanced sink associated with nitrogen inputs by 0.26 PgC yr-1, and (4) enhanced the 1990s carbon source associated with changes in land use by 0.08 PgC yr-1 in the 1990s. These effects of nitrogen limitation influenced the spatial distribution of the estimated exchange of CO2 with greater sink activity in high latitudes associated with climate effects and a smaller sink of CO2 in the southeastern United States caused by N limitation associated with both CO2 fertilization and forest regrowth. These results indicate that the dynamics of nitrogen availability are important to consider in assessing the spatial distribution and temporal dynamics of terrestrial carbon sources

  5. Nitrogen attenuation of terrestrial carbon cycle response to global environmental factors

    USGS Publications Warehouse

    Jain, A.A.; Yang, Xiaojuan; Kheshgi, H.; McGuire, Anthony; Post, W.; Kicklighter, David W.

    2009-01-01

    Nitrogen cycle dynamics have the capacity to attenuate the magnitude of global terrestrial carbon sinks and sources driven by CO2 fertilization and changes in climate. In this study, two versions of the terrestrial carbon and nitrogen cycle components of the Integrated Science Assessment Model (ISAM) are used to evaluate how variation in nitrogen availability influences terrestrial carbon sinks and sources in response to changes over the 20th century in global environmental factors including atmospheric CO2 concentration, nitrogen inputs, temperature, precipitation and land use. The two versions of ISAM vary in their treatment of nitrogen availability: ISAM-NC has a terrestrial carbon cycle model coupled to a fully dynamic nitrogen cycle while ISAM-C has an identical carbon cycle model but nitrogen availability is always in sufficient supply. Overall, the two versions of the model estimate approximately the same amount of global mean carbon uptake over the 20th century. However, comparisons of results of ISAM-NC relative to ISAM-C reveal that nitrogen dynamics: (1) reduced the 1990s carbon sink associated with increasing atmospheric CO2 by 0.53 PgC yr−1 (1 Pg = 1015g), (2) reduced the 1990s carbon source associated with changes in temperature and precipitation of 0.34 PgC yr−1 in the 1990s, (3) an enhanced sink associated with nitrogen inputs by 0.26 PgC yr−1, and (4) enhanced the 1990s carbon source associated with changes in land use by 0.08 PgC yr−1 in the 1990s. These effects of nitrogen limitation influenced the spatial distribution of the estimated exchange of CO2 with greater sink activity in high latitudes associated with climate effects and a smaller sink of CO2 in the southeastern United States caused by N limitation associated with both CO2 fertilization and forest regrowth. These results indicate that the dynamics of nitrogen availability are important to consider in assessing the spatial distribution and temporal dynamics of terrestrial carbon

  6. Nitrogen attenuation of terrestrial carbon cycle response to global environmental factors

    SciTech Connect

    Jain, Atul; Yang, Xiaojuan; Kheshgi, Haroon; Mcguire, David; Post, Wilfred M

    2009-01-01

    Nitrogen cycle dynamics have the capacity to attenuate the magnitude of global terrestrial carbon sinks and sources driven by CO2 fertilization and changes in climate. In this study, two versions of the terrestrial carbon and nitrogen cycle components of the Integrated Science Assessment Model (ISAM) are used to evaluate how variation in nitrogen availability influences terrestrial carbon sinks and sources in response to changes over the 20th century in global environmental factors including atmospheric CO2 concentration, nitrogen inputs, temperature, precipitation and land use. The two versions of ISAM vary in their treatment of nitrogen availability: ISAM-NC has a terrestrial carbon cycle model coupled to a fully dynamic nitrogen cycle while ISAM-C has an identical carbon cycle model but nitrogen availability is always in sufficient supply. Overall, the two versions of the model estimate approximately the same amount of global mean carbon uptake over the 20th century. However, comparisons of results of ISAM-NC relative to ISAM-C reveal that nitrogen dynamics: (1) reduced the 1990s carbon sink associated with increasing atmospheric CO2 by 0.53 PgC yr1 (1 Pg = 1015g), (2) reduced the 1990s carbon source associated with changes in temperature and precipitation of 0.34 PgC yr1 in the 1990s, (3) an enhanced sink associated with nitrogen inputs by 0.26 PgC yr1, and (4) enhanced the 1990s carbon source associated with changes in land use by 0.08 PgC yr1 in the 1990s. These effects of nitrogen limitation influenced the spatial distribution of the estimated exchange of CO2 with greater sink activity in high latitudes associated with climate effects and a smaller sink of CO2 in the southeastern United States caused by N limitation associated with both CO2 fertilization and forest regrowth. These results indicate that the dynamics of nitrogen availability are important to consider in assessing the spatial distribution and temporal dynamics of terrestrial carbon sources and

  7. Boron doped diamond and glassy carbon electrodes comparative study of the oxidation behaviour of cysteine and methionine.

    PubMed

    Enache, T A; Oliveira-Brett, A M

    2011-04-01

    The electrochemical oxidation behaviour at boron doped diamond and glassy carbon electrodes of the sulphur-containing amino acids cysteine and methionine, using cyclic and differential pulse voltammetry over a wide pH range, was compared. The oxidation reactions of these amino acids are irreversible, diffusion-controlled pH dependent processes, and occur in a complex cascade mechanism. The amino acid cysteine undergoes similar three consecutive oxidation reactions at both electrodes. The first step involves the oxidation of the sulfhydryl group with radical formation, that undergoes nucleophilic attack by water to give an intermediate species that is oxidized in the second step to cysteic acid. The oxidation of the sulfhydryl group leads to a disulfide bridge between two similar cysteine moieties forming cysteine. The subsequent oxidation of cystine occurs at a higher potential, due to the strong disulfide bridge covalent bond. The electro-oxidation of methionine at a glassy carbon electrode occurs in two steps, corresponding to the formation of sulfoxide and sulfone, involving the adsorption and protonation/deprotonation of the thiol group, followed by electrochemical oxidation. Methionine undergoes a one-step oxidation reaction at boron doped diamond electrodes due to the negligible adsorption, and the oxidation also leads to the formation of methionine sulfone. PMID:21377428

  8. Boron isotope systematics during magma-carbonate interaction: an experimental study from Merapi (Indonesia) and Vesuvius (Italy)

    NASA Astrophysics Data System (ADS)

    Deegan, F. M.; Jolis, E. M.; Troll, V. R.; Freda, C.; Whitehouse, M.

    2011-12-01

    Carbonate assimilation is increasingly recognized as an important process affecting the compositional evolution of magma and its inherent ability to erupt explosively due to release of carbonate-derived CO2 [e.g., 1, 2, 3]. In order to gain insights into this process, we performed short time-scale carbonate dissolution experiments in silicate melt using natural starting materials from Merapi and Vesuvius volcanoes at magmatic pressure and temperature [2, 4]. The experiments enable us to resolve in detail the timescales, textures and chemical features of carbonate assimilation. Three compositionally distinct glass domains have been defined: i) Ca-normal glass, similar in composition to the starting material; ii) Ca-rich, contaminated glass; and iii) a diffusional glass interface between the Ca-normal and Ca-rich glass, characterized by steady interchange between SiO2 and CaO. Here we present new boron isotope data for the experimental products obtained by SIMS. The glasses show distinct and systematic variation in their δ11B (%) values. The contaminated glasses generally show extremely negative δ11B values (down to -41 %) relative to both the uncontaminated experimental glass and fresh arc volcanics (-7 to +7 % [5]). Considering that carbonates have δ11B values of +9 to +26 [6], the data cannot be explained by simple mixing processes between the end-members alone. This implies that the δ11B of the original contaminant was drastically modified before being incorporated into the melt, which can be explained by B isotope fractionation during breakdown and degassing of the carbonate. Our data represents the first B isotope analyses of experimental products of carbonate assimilation. They provide novel and well constrained insights into the behavior of boron upon degassing of carbonate. This, in turn, has implications for both i) late stage contamination and volatile addition to hazardous volcanic systems located over carbonate basement (cf. [7]) and ii) studies of

  9. Influence of cubic boron nitride grinding on the fatigue strengths of carbon steels and a nickel-base superalloy

    SciTech Connect

    Kawagoishi, N.; Chen, Q.; Kondo, E.; Goto, M.; Nisitani, H.

    1999-04-01

    The influence of cubic boron nitride (CBN) grinding on fatigue strength was investigated on an annealed carbon steel, a quenched and tempered carbon steel at room temperature, and a nickel-base superalloy, Inconel 718, at room temperature and 500 C. The results were discussed from several viewpoints, including surface roughness, residual stress, and work hardening or softening due to CBN grinding. The fatigue strength increased upon CBN grinding at room temperature, primarily because of the generation of compressive residual stress in the surface region. However, in the case of Inconel 718, this marked increase in the fatigue strength tended to disappear at the elevated temperature due to the release of compressive residual stress and the decrease of crack growth resistance at an elevated temperature.

  10. Carbon-nitrogen interactions regulate climate-carbon cycle feedbacks: results from an atmosphere-ocean general circulation model

    SciTech Connect

    Thornton, Peter E; Doney, Scott C.; Lindsay, Keith; Moore, Jefferson Keith; Mahowald, Natalie; Randerson, James T; Fung, Inez; Lamarque, Jean-Francois H; Feddema, Johan J.

    2009-01-01

    Inclusion of fundamental ecological interactions between carbon and nitrogen cycles in the land component of an atmosphere-ocean general circulation model (AOGCM) leads to decreased carbon uptake associated with CO{sub 2} fertilization, and increased carbon uptake associated with warming of the climate system. The balance of these two opposing effects is to reduce the fraction of anthropogenic CO{sub 2} predicted to be sequestered in land ecosystems. The primary mechanism responsible for increased land carbon storage under radiatively forced climate change is shown to be fertilization of plant growth by increased mineralization of nitrogen directly associated with increased decomposition of soil organic matter under a warming climate, which in this particular model results in a negative gain for the climate-carbon feedback. Estimates for the land and ocean sink fractions of recent anthropogenic emissions are individually within the range of observational estimates, but the combined land plus ocean sink fractions produce an airborne fraction which is too high compared to observations. This bias is likely due in part to an underestimation of the ocean sink fraction. Our results show a significant growth in the airborne fraction of anthropogenic CO{sub 2} emissions over the coming century, attributable in part to a steady decline in the ocean sink fraction. Comparison to experimental studies on the fate of radio-labeled nitrogen tracers in temperate forests indicates that the model representation of competition between plants and microbes for new mineral nitrogen resources is reasonable. Our results suggest a weaker dependence of net land carbon flux on soil moisture changes in tropical regions, and a stronger positive growth response to warming in those regions, than predicted by a similar AOGCM implemented without land carbon-nitrogen interactions. We expect that the between-model uncertainty in predictions of future atmospheric CO{sub 2} concentration and

  11. Synthesis of ultra dispersed graphite-like structures doped with nitrogen in supersonic carbon plasma flow

    NASA Astrophysics Data System (ADS)

    Sivkov, A.; Pak, A.; Shanenkov, I.; Kolganova, J.; Shatrova, K.

    2014-10-01

    In this paper the synthesis of ultra dispersed graphite-like structures doped with nitrogen by using a magneto plasma accelerator is shown. The synthesis of such structures is realized during supersonic carbon plasma jet flowing into the chamber filled with the nitrogen atmosphere. Plasma jet is generated by coaxial magneto plasma accelerator (CMPA) based on graphite electrode system. The CMPA is supplied from the pulsed capacitive energy storage with the maximum value of stored energy of 360 kJ. Electrical and energy parameters of plasma flow are recorded during experiment. According to X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM) methods obtained particles with well seen triangle sectors are graphite-like carbon structures doped with nitrogen atoms. This is confirmed by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy analyses in which carbon- nitrogen bonding configurations have been identified.

  12. Contribution of cryptogamic covers to the global cycles of carbon and nitrogen

    NASA Astrophysics Data System (ADS)

    Elbert, Wolfgang; Weber, Bettina; Burrows, Susannah; Steinkamp, Jörg; Büdel, Burkhard; Andreae, Meinrat O.; Pöschl, Ulrich

    2012-07-01

    Many terrestrial surfaces, including soils, rocks and plants, are covered by photoautotrophic communities, capable of synthesizing their own food from inorganic substances using sunlight as an energy source. These communities, known as cryptogamic covers, comprise variable proportions of cyanobacteria, algae, fungi, lichens and bryophytes, and are able to fix carbon dioxide and nitrogen from the atmosphere. However, their influence on global and regional biogeochemical cycling of carbon and nitrogen has not yet been assessed. Here, we analyse previously published data on the spatial coverage of cryptogamic communities, and the associated fluxes of carbon and nitrogen, in different types of ecosystem across the globe. We estimate that globally, cryptogamic covers take up around 3.9 Pg carbon per year, corresponding to around 7% of net primary production by terrestrial vegetation. We derive a nitrogen uptake by cryptogamic covers of around 49 Tg per year, suggesting that cryptogamic covers account for nearly half of the biological nitrogen fixation on land. We suggest that nitrogen fixation by cryptogamic covers may be crucial for carbon sequestration by plants.

  13. Nitrogen management and the future of food: Lessons from the management of energy and carbon

    PubMed Central

    Socolow, Robert H.

    1999-01-01

    The food system dominates anthropogenic disruption of the nitrogen cycle by generating excess fixed nitrogen. Excess fixed nitrogen, in various guises, augments the greenhouse effect, diminishes stratospheric ozone, promotes smog, contaminates drinking water, acidifies rain, eutrophies bays and estuaries, and stresses ecosystems. Yet, to date, regulatory efforts to limit these disruptions largely ignore the food system. There are many parallels between food and energy. Food is to nitrogen as energy is to carbon. Nitrogen fertilizer is analogous to fossil fuel. Organic agriculture and agricultural biotechnology play roles analogous to renewable energy and nuclear power in political discourse. Nutrition research resembles energy end-use analysis. Meat is the electricity of food. As the agriculture and food system evolves to contain its impacts on the nitrogen cycle, several lessons can be extracted from energy and carbon: (i) set the goal of ecosystem stabilization; (ii) search the entire production and consumption system (grain, livestock, food distribution, and diet) for opportunities to improve efficiency; (iii) implement cap-and-trade systems for fixed nitrogen; (iv) expand research at the intersection of agriculture and ecology, and (v) focus on the food choices of the prosperous. There are important nitrogen-carbon links. The global increase in fixed nitrogen may be fertilizing the Earth, transferring significant amounts of carbon from the atmosphere to the biosphere, and mitigating global warming. A modern biofuels industry someday may produce biofuels from crop residues or dedicated energy crops, reducing the rate of fossil fuel use, while losses of nitrogen and other nutrients are minimized. PMID:10339531

  14. Nitrogen management and the future of food: lessons from the management of energy and carbon.

    PubMed

    Socolow, R H

    1999-05-25

    The food system dominates anthropogenic disruption of the nitrogen cycle by generating excess fixed nitrogen. Excess fixed nitrogen, in various guises, augments the greenhouse effect, diminishes stratospheric ozone, promotes smog, contaminates drinking water, acidifies rain, eutrophies bays and estuaries, and stresses ecosystems. Yet, to date, regulatory efforts to limit these disruptions largely ignore the food system. There are many parallels between food and energy. Food is to nitrogen as energy is to carbon. Nitrogen fertilizer is analogous to fossil fuel. Organic agriculture and agricultural biotechnology play roles analogous to renewable energy and nuclear power in political discourse. Nutrition research resembles energy end-use analysis. Meat is the electricity of food. As the agriculture and food system evolves to contain its impacts on the nitrogen cycle, several lessons can be extracted from energy and carbon: (i) set the goal of ecosystem stabilization; (ii) search the entire production and consumption system (grain, livestock, food distribution, and diet) for opportunities to improve efficiency; (iii) implement cap-and-trade systems for fixed nitrogen; (iv) expand research at the intersection of agriculture and ecology, and (v) focus on the food choices of the prosperous. There are important nitrogen-carbon links. The global increase in fixed nitrogen may be fertilizing the Earth, transferring significant amounts of carbon from the atmosphere to the biosphere, and mitigating global warming. A modern biofuels industry someday may produce biofuels from crop residues or dedicated energy crops, reducing the rate of fossil fuel use, while losses of nitrogen and other nutrients are minimized. PMID:10339531

  15. Carbon and nitrogen balance of leaf-eating sesarmid crabs ( Neoepisesarma versicolor) offered different food sources

    NASA Astrophysics Data System (ADS)

    Thongtham, Nalinee; Kristensen, Erik

    2005-10-01

    Carbon and nitrogen budgets for the leaf-eating crab, Neoepisesarma versicolor, were established for individuals living on pure leaf diets. Crabs were fed fresh (green), senescent (yellow) and partly degraded (brown) leaves of the mangrove tree Rhizophora apiculata. Ingestion, egestion and metabolic loss of carbon and nitrogen were determined from laboratory experiments. In addition, bacterial abundance in various compartments of the crabs' digestive tract was enumerated after dissection of live individuals. Ingestion and egestion rates (in terms of dry weight) were highest, while the assimilation efficiency was poorest for crabs fed on brown leaves. The low assimilation efficiency was more than counteracted by the high ingestion rate providing more carbon for growth than for crabs fed green and yellow leaves. In any case, the results show that all types of leaves can provide adequate carbon while nitrogen was insufficient to support both maintenance (yellow leaves) and growth (green, yellow and brown leaves). Leaf-eating crabs must therefore obtain supplementary nitrogen by other means in order to meet their nitrogen requirement. Three hypotheses were evaluated: (1) crabs supplement their diet with bacteria and benthic microalgae by ingesting own faeces and/or selective grazing at the sediment surface; (2) assimilation of symbiotic nitrogen-fixing bacteria in the crabs' own intestinal system; and (3) nitrogen storage following occasional feeding on animal tissues (e.g. meiofauna and carcasses). It appears that hypothesis 1 is of limited importance for N. versicolor since faeces and sediment can only supply a minor fraction of the missing nitrogen due to physical constraints on the amount of material the crabs can consume. Hypothesis 2 can be ruled out because tests showed no nitrogen fixation activity in the intestinal system of N. versicolor. It is therefore likely that leaf-eating crabs provide most of their nitrogen requirement from intracellular deposits

  16. Contributions of secondary forest and nitrogen dynamics to terrestrial carbon uptake

    NASA Astrophysics Data System (ADS)

    Yang, X.; Richardson, T. K.; Jain, A. K.

    2010-04-01

    We use a terrestrial carbon-nitrogen cycle component of the Integrated Science Assessment Model (ISAM) to investigate the impacts of nitrogen dynamics on regrowing secondary forests over the 20th century. We further examine what the impacts of nitrogen deposition and land use change history are on terrestrial carbon uptake since preindustrial time. Our results suggest that global total net land use emissions for the 1990s associated with changes in cropland, pastureland, and wood harvest are 1.22 GtC/yr. Without considering the secondary forest regrowth, the estimated net global total land use emissions are 1.58 GtC/yr or about 0.36 GtC/yr higher than if secondary forest regrowth is considered. Results also show that without considering the nitrogen dynamics and deposition, the estimated global total secondary forest sink for the 1990s is 0.90 GtC/yr or about 0.54 GtC/yr higher than estimates that include the impacts of nitrogen dynamics and deposition. Nitrogen deposition alone is responsible for about 0.13 GtC/yr of the total secondary forest sink. While nitrogen is not a limiting nutrient in the intact primary forests in tropical regions, our study suggests that nitrogen becomes a limiting nutrient for regrowing secondary forests of the tropical regions, in particular Latin America and Tropical Africa. This is because land use change activities, especially wood harvest, removes large amounts of nitrogen from the system when slash is burnt or wood is removed for harvest. However, our model results show that carbon uptake is enhanced in the tropical secondary forests of the Indian region. We argue that this may be due to enhanced nitrogen mineralization and increased nitrogen availability following land use change in the Indian tropical forest ecosystems. Results also demonstrate that there is a significant amount of carbon accumulating in the Northern Hemisphere where most land use changes and forest regrowth has occurred in recent decades. This study indicates

  17. Contributions of secondary forest and nitrogen dynamics to terrestrial carbon uptake

    NASA Astrophysics Data System (ADS)

    Yang, X.; Richardson, T. K.; Jain, A. K.

    2010-10-01

    We use a terrestrial carbon-nitrogen cycle component of the Integrated Science Assessment Model (ISAM) to investigate the impacts of nitrogen dynamics on regrowing secondary forests over the 20th century. We further examine what the impacts of nitrogen deposition and land use change history are on terrestrial carbon uptake since preindustrial time. Our results suggest that global total net land use emissions for the 1990s associated with changes in cropland, pastureland, and wood harvest are 1.22 GtC/yr. Without considering the secondary forest regrowth, the estimated net global total land use emissions are 1.58 GtC/yr or about 0.36 GtC/yr higher than if secondary forest regrowth is considered. Results also show that without considering the nitrogen dynamics and deposition, the estimated global total secondary forest sink for the 1990s is 0.90 GtC/yr or about 0.54 GtC/yr higher than estimates that include the impacts of nitrogen dynamics and deposition. Nitrogen deposition alone is responsible for about 0.13 GtC/yr of the total secondary forest sink. While nitrogen is not a limiting nutrient in the intact primary forests in tropical regions, our study suggests that nitrogen becomes a limiting nutrient for regrowing secondary forests of the tropical regions, in particular Latin America and Tropical Africa. This is because land use change activities, especially wood harvest, removes large amounts of nitrogen from the system when slash is burnt or wood is removed for harvest. However, our model results show that carbon uptake is enhanced in the tropical secondary forests of the Indian region. We argue that this may be due to enhanced nitrogen mineralization and increased nitrogen availability following land use change in the Indian tropical forest ecosystems. Results also demonstrate that there is a significant amount of carbon accumulating in the Northern Hemisphere where most land use changes and forest regrowth has occurred in recent decades. This study indicates

  18. Coupling of Carbon Monoxide with Nitrogen Monoxide at a Frustrated Lewis Pair Template.

    PubMed

    Ye, Ke-Yin; Kehr, Gerald; Daniliuc, Constantin G; Liu, Lei; Grimme, Stefan; Erker, Gerhard

    2016-08-01

    Coupling of carbon monoxide with nitrogen monoxide was achieved at a frustrated Lewis pair template. This unique reaction uses hydride as an auxiliary, which reductively activates carbon monoxide at the frustrated Lewis pair. The CO/NO coupling reaction then takes place through a pathway involving a radical reaction in which the hydrogen atom auxiliary is eventually removed again. PMID:27328914

  19. Modeling of carbon and nitrogen gaseous emissions from cattle manure compost windrows

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Windrow composting of cattle manure is a significant source of gaseous emissions, which include ammonia (NH3) and the greenhouse gases (GHGs) of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). A manure compost model was developed to simulate carbon (C) and nitrogen (N) processes includ...

  20. Carbon availability for the fungus triggers nitrogen uptake and transport in the arbuscular mycorrhizal symbiosis

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The arbuscular mycorrhizal (AM) symbiosis is characterized by a transfer of nutrients in exchange for carbon. We tested the effect of the carbon availability for the AM fungus Glomus intraradices on nitrogen (N) uptake and transport in the symbiosis. We followed the uptake and transport of 15N and ...

  1. Nitrogen and carbon interactions in controlling terrestrial greenhouse gas fluxes

    NASA Astrophysics Data System (ADS)

    Ineson, Phil; Toet, Sylvia; Christiansen, Jesper

    2016-04-01

    The increased input of N to terrestrial systems may have profound impacts on net greenhouse gas (GHGs) fluxes and, consequently, our future climate; however, fully capturing and quantifying these interactions under field conditions urgently requires new, more efficient, measurement approaches. We have recently developed and deployed a novel system for the automation of terrestrial GHG flux measurements at the chamber and plot scales, using the approach of 'flying' a single measurement chamber to multiple points in an experimental field arena. As an example of the value of this approach, we shall describe the results from a field experiment investigating the interactions between increasing inorganic nitrogen (N) and carbon (C) additions on net ecosystem exchanges of N2O, CH4 and CO2, enabling the simultaneous application of 25 treatments, replicated five times in a fully replicated block field design. We will describe how the ability to deliver automated GHG flux measurements, highly replicated in space and time, has revealed hitherto unreported findings on N and C interactions in field soil. In our experiments we found insignificant N2O fluxes from bare field soil, even at very high inorganic N addition rates, but the interactive addition of even small amounts of available C resulted in very large and rapid N2O fluxes. The SkyGas experimental system enabled investigation of the underlying interacting response surfaces on the fluxes of the major soil-derived GHGs (CO2, CH4 and N2O) to increasing N and C inputs, and revealed unexpected interactions. In addition to these results we will also discuss some of the technical problems which have been overcome in developing these 'flying' systems and the potential of the systems for automatically screening the impacts of large numbers of treatments on GHG fluxes, and other ecosystem responses, under field conditions. We describe here technological advances that can facilitate the development of more robust GHG mitigation

  2. Microbes mediate carbon and nitrogen retention in shallow photic sediments

    NASA Astrophysics Data System (ADS)

    Hardison, A.; Anderson, I.; Canuel, E. A.; Tobias, C.; Veuger, B.

    2009-12-01

    Sediments in shallow coastal bays are sites of intense biogeochemical cycling facilitated by a complex microbial consortium. Unlike deeper coastal environments, much of the benthos is illuminated by sunlight in these bays. As a result, benthic autotrophs such as benthic microalgae (BMA) and macroalgae play an integral role in nutrient cycling. Investigating pathways of carbon (C) and nitrogen (N) flow through individual compartments within the sediment microbial community has previously proved challenging due to methodological difficulties. However, it is now possible using stable isotopes and microbial biomarkers such as fatty acids and amino acids to track C and N flow through individual microbial pools. We investigated the uptake and retention of C and N by bacteria and BMA in a shallow subtidal system. Using bulk and compound specific isotopic analysis, we traced the pathways of dissolved inorganic 13C and 15N under various treatments: 1) in ambient light or dark, 2) from porewater or water column sources, and 3) in the presence or absence of bloom forming nuisance macroalgae. Excess 13C and 15N in THAAs and excess 13C in total PLFAs showed a strong dependence on light. Enrichment of these pools represents uptake by the microbial community, which can include both autotrophic and heterotrophic components. Higher excess 13C in benthic microalgal fatty acids (C20, C22 PUFAs) provides evidence that benthic microalgae were fixing 13C. Aditionally, the ratio of excess 13C in branched fatty acids to microbial fatty acids (BAR) and excess 13C and 15N in D-Ala to L-Ala (D/L-Ala) were low, suggesting dominance by benthic microalgae over bacteria to total label incorporation. Our results support uptake and retention of C and N by the sediment microbial community and indicate a tight coupling between BMA and bacteria in shallow illuminated systems. This uptake is diminished in the presence of macroalgae, likely due to shading and/or nutrient competition. Therefore

  3. Nitrogen, Carbon, and Sulfur Metabolism in Natural Thioploca Samples

    PubMed Central

    Otte, Sandra; Kuenen, J. Gijs; Nielsen, Lars P.; Paerl, Hans W.; Zopfi, Jakob; Schulz, Heide N.; Teske, Andreas; Strotmann, Bettina; Gallardo, Victor A.; Jørgensen, Bo B.

    1999-01-01

    Filamentous sulfur bacteria of the genus Thioploca occur as dense mats on the continental shelf off the coast of Chile and Peru. Since little is known about their nitrogen, sulfur, and carbon metabolism, this study was undertaken to investigate their (eco)physiology. Thioploca is able to store internally high concentrations of sulfur globules and nitrate. It has been previously hypothesized that these large vacuolated bacteria can oxidize sulfide by reducing their internally stored nitrate. We examined this nitrate reduction by incubation experiments of washed Thioploca sheaths with trichomes in combination with 15N compounds and mass spectrometry and found that these Thioploca samples produce ammonium at a rate of 1 nmol min−1 mg of protein−1. Controls showed no significant activity. Sulfate was shown to be the end product of sulfide oxidation and was observed at a rate of 2 to 3 nmol min−1 mg of protein−1. The ammonium and sulfate production rates were not influenced by the addition of sulfide, suggesting that sulfide is first oxidized to elemental sulfur, and in a second independent step elemental sulfur is oxidized to sulfate. The average sulfide oxidation rate measured was 5 nmol min−1 mg of protein−1 and could be increased to 10.7 nmol min−1 mg of protein−1 after the trichomes were starved for 45 h. Incorporation of 14CO2 was at a rate of 0.4 to 0.8 nmol min−1 mg of protein−1, which is half the rate calculated from sulfide oxidation. [2-14C]acetate incorporation was 0.4 nmol min−1 mg of protein−1, which is equal to the CO2 fixation rate, and no 14CO2 production was detected. These results suggest that Thioploca species are facultative chemolithoautotrophs capable of mixotrophic growth. Microautoradiography confirmed that Thioploca cells assimilated the majority of the radiocarbon from [2-14C]acetate, with only a minor contribution by epibiontic bacteria present in the samples. PMID:10388716

  4. From roots to globe: How the terrestrial nitrogen cycle alters the global carbon cycle?

    NASA Astrophysics Data System (ADS)

    Shi, M.; Fisher, J. B.; Brzostek, E. R.; Phillips, R.

    2014-12-01

    Plants typically expend a significant portion of their available carbon for nitrogen (N) acquisition, especially through root exudation in N-limited soils; this is the amount of carbon that would otherwise go to growth in the presence of ample N. Most global terrestrial biogeochemistry models (TBMs) do not consider the carbon cost for N acquisition. In order to evaluate the carbon-nitrogen trade process and improve the carbon­-nitrogen dynamics in TBMs, this study integrates a cutting-edge global plant nitrogen model—Fixation and Uptake of Nitrogen (FUN) version 2.0 (FUN2.0) into the Community Land Model 4.0. The coupled model (i.e., CLM4CN-FUN2.0) is tested at local and global scales. Generally, plant N acquisition is dynamically simulated, and the carbon cost for N acquisition is estimated by the coupled model. Sensitivity tests indicate that the low soil N uptakes of the coupled model are associated with the low soil mineral N amount represented by CLM4CN. According to the observational evidence, the retranslocated N pool in CLM4CN needs to be combined with other non-structural N pools. These deficiencies in the model open new possibilities for improving TBMs, which is widely used in global climate change studies.

  5. How can carbon favor planar multi-coordination in boron-based clusters? Global structures of CB(x)E(y)(2-) (E = Al, Ga, x + y = 4).

    PubMed

    Cui, Zhong-hua; Sui, Jing-jing; Ding, Yi-hong

    2015-12-21

    With the high preference in forming multi-center bonding, boron has been a miracle ligand in constructing diverse planar multi-coordinate (pM) (tetra/hyper) species. Unfortunately, the boron ligand usually dislikes encompassing a pM carbon (pMC) due to the high competition with pM boron (pMB), which makes the realization of boron-based pMC very difficult and quite challenging. Herein, we propose a strategy that by means of cooperative doping and charge-compensation, we can successfully improve and tune the stability of pMC relative to pMB for CB4(2-). In the free CBxEy(2-) (E = Al/Ga) species, ptC is thermodynamically less stable than the global ptB in mono- and di-substituted systems, in agreement with the results of Boldyrev and Wang. However, the thermodynamic preference of pMC increases along with the Al/Ga-doping. The pMC species can be further stabilized by the introduction of the alkaline-earth counterion (Mg(2+)). CB2E2Mg (E = Al, Ga) designed in the present study represents the first successful design of a boron-based planar penta-coordinate carbon (ppC) structures as the global minima. The strategy proposed in this study should be useful in the manipulation of competition between exotic pMC and pMB in B-based systems. PMID:26574884

  6. Oxygen, carbon, hydrogen and nitrogen in crystalline silicon

    SciTech Connect

    Mikkelsen, J.C.; Pearton, S.J.; Corbett, J.W.; Pennycook, S.J

    1986-01-01

    These proceedings collect papers on interstitial material in silicon. Topics include: hydrogen in crystalline silicon, low energy hydrogen ion bombarded silicon, oxygen in silicon, oxygen thermal donor formation, thermal donor generation and annihilation effects on oxygen precipitation oxygen effects on plastic flow during growth of dendrixic web silicon, nitrogen in silicon, off-center nitrogen and oxygen in silicon, and thermal donor hierarchies in silicon and germanium.

  7. Superior critical current density obtained in MgB2 bulks via employing carbon-coated boron and minor Cu addition

    NASA Astrophysics Data System (ADS)

    Peng, Junming; Liu, Yongchang; Ma, Zongqing; Shahriar Al Hossain, M.; Xin, Ying; Jin, Jianxun

    2016-09-01

    High performance Cu doped MgB2 bulks were prepared by an in-situ method with carbon-coated amorphous boron as precursor. It was found that the usage of carbon-coated boron in present work leads to the formation of uniformly refined MgB2 grains, as well as a high level of homogeneous carbon doping in the MgB2 samples, which significantly enhance the Jc in both Cu doped and undoped bulks compared to MgB2 bulks with normal amorphous boron precursor. Moreover, minor Cu can service as activator, and thus facilitates the growth of MgB2 grains and improves crystallinity and grain connectivity, which can bring about the excellent critical current density (Jc) at self fields and low fields (the best values are 7 × 105 A/cm2 at self fields, and 1 × 105 A/cm2 at 2 T, 20 K, respectively). Simultaneously, minor Cu addition can reduce the amount of MgO impurity significantly, also contributing to the improvement of Jc at low fields. Our work suggests that Cu-activated sintering combined with employment of carbon-coated amorphous boron as precursor could be a promising technique to produce practical MgB2 bulks or wires with excellent Jc on an industrial scale.

  8. Nitrogen deposition, land cover conversion, climate, and contemporary carbon balance of Europe (Invited)

    NASA Astrophysics Data System (ADS)

    Churkina, G.; Zahle, S.; Hughes, J.; Viovy, N.; Chen, Y.; Jung, M.; Ramankutty, N.; Roedenbeck, C.; Heimann, M.; Jones, C.

    2009-12-01

    In Europe, atmospheric nitrogen deposition has more than doubled, air temperature was rising, forest cover was steadily increasing, while agricultural area was declining over the last 50 years. What effect have these changes had on the European carbon balance? In this study we estimate responses of the European land ecosystems to nitrogen deposition, rising CO2, land cover conversion and climate change. We use results from three ecosystem process models such as BIOME-BGC, JULES, and ORCHIDEE (-CN) to address this question. We discuss to which degree carbon balance of Europe has been altered by nitrogen deposition in comparison to other drivers and identify areas which carbon balance has been affected by anthropogenic changes the most. We also analyze ecosystems carbon pools which were affected by the abovementioned environmental changes.

  9. Dry Process for Manufacturing Hybridized Boron Fiber/Carbon Fiber Thermoplastic Composite Materials from a Solution Coated Precursor

    NASA Technical Reports Server (NTRS)

    Belvin, Harry L. (Inventor); Cano, Roberto J. (Inventor)

    2003-01-01

    An apparatus for producing a hybrid boron reinforced polymer matrix composite from precursor tape and a linear array of boron fibers. The boron fibers are applied onto the precursor tapes and the precursor tape processed within a processing component having an impregnation bar assembly. After passing through variable-dimension forming nip-rollers, the precursor tape with the boron fibers becomes a hybrid boron reinforced polymer matrix composite. A driving mechanism is used to pulled the precursor tape through the method and a take-up spool is used to collect the formed hybrid boron reinforced polymer matrix composite.

  10. Graphitic Carbon Nitride/Nitrogen-Rich Carbon Nanofibers: Highly Efficient Photocatalytic Hydrogen Evolution without Cocatalysts.

    PubMed

    Han, Qing; Wang, Bing; Gao, Jian; Qu, Liangti

    2016-08-26

    An interconnected framework of mesoporous graphitic-C3 N4 nanofibers merged with in situ incorporated nitrogen-rich carbon has been prepared. The unique composition and structure of the nanofibers as well as strong coupling between the components endow them with efficient light-harvesting properties, improved charged separation, and a multidimensional electron transport path that enhance the performance of hydrogen production. The as-obtained catalyst exhibits an extremely high hydrogen-evolution rate of 16885 μmol h(-1)  g(-1) , and a remarkable apparent quantum efficiency of 14.3 % at 420 nm without any cocatalysts, which is much higher than most reported g-C3 N4 -based photocatalysts even in the presence of Pt-based cocatalysts. PMID:27467255

  11. Alterations in internal partitioning of carbon in soybean plants in response to nitrogen stress

    NASA Technical Reports Server (NTRS)

    Rufty, T. W. Jr; Raper, C. D. Jr; Huber, S. C.

    1984-01-01

    Alterations in internal partitioning of carbon were evaluated in plants exposed to limited nitrogen supply. Vegetative, nonnodulated soybean plants (Glycine max (L.) Merrill, 'Ransom') were grown for 21 days with 1.0 mM NO3- and then exposed to solutions containing 1.0, 0.1, or 0.0 mM NO3- for a 25-day treatment period. In nitrogen-limited plants, there were decreases in emergence of new leaves and in the expansion rate and final area at full expansion of individual leaves. As indicated by alterations in accumulation of dry weight, a larger proportion of available carbon in the plant was partitioned to the roots with decreased availability of nitrogen. Partitioning of reduced nitrogen to the root also was increased and, in plants devoid of an external supply, considerable redistribution of reduced nitrogen from leaves to the root occurred. The general decrease in growth potential and sink strength for nutrients in leaves of nitrogen-limited plants suggested that factors other than simply availability of nitrogen likely were involved in the restriction of growth in the leaf canopy and the associated increase in carbon allocation to the roots.

  12. Nitrogen restrictions buffer modeled interactions of water with the carbon cycle

    NASA Astrophysics Data System (ADS)

    Huang, Yuanyuan; Gerber, Stefan

    2016-01-01

    Terrestrial carbon and water cycles are coupled at multiple spatiotemporal scales and are crucial to carbon sequestration. Water related climate extremes, such as drought and intense precipitation, can substantially affect the carbon cycle. Meanwhile, nitrogen is a limiting resource to plant and has therefore the potential to alter the coupling of water and carbon cycles on land. Here we assess the effect of nitrogen limitation on the response of the terrestrial carbon cycle to moisture anomalies using Geophysical Fluid Dynamics Laboratory's land surface model LM3V-N. We analyzed the response of three central carbon fluxes: net primary productivity (NPP), heterotrophic respiration (Rh), and net ecosystem productivity (NEP, the difference between NPP and Rh) and how these fluxes were altered under anomalies of the standardized precipitation and evapotranspiration index (SPEI). We found that globally, the correlations between each of the carbon flux and SPEI depended on the timescale and a strong legacy effect of SPEI anomalies on Rh. Consideration of nitrogen constraints reduced anomalies in carbon fluxes in response to extreme dry/wet events. This nitrogen-induced buffer constrained the growth of plants under wet extremes and allowed for enhanced growth during droughts. Extra gain of soil moisture from the downregulation of canopy transpiration by nitrogen limitation and shifts in the relative importance of water and nitrogen limitation during dry/wet extreme events are possible mechanisms contributing to the buffering of modeled NPP and NEP. Responses of Rh to moisture anomalies were much weaker compared to NPP, and N buffering effects were less evident.

  13. [Spatial distribution characteristics and ecological effects of carbon and nitrogen of soil in Huolin River catchment wetland].

    PubMed

    Bai, Junhong; Deng, Wei; Zhu, Yanming; Luan, Zhaoqing; Zhang, Yuxia

    2003-09-01

    This paper studied the spatial distribution characteristics and ecological effects of organic carbon and nitrogen in soils of Huolin River catchment wetland in horizontal and vertical levels. The results showed that the differences of horizontal and vertical distribution of organic carbon and nitrogen were very obvious, and of all the factors such as the period of wetting and drying cycles, leaching, plant and flood etc., the period of wetting and drying cycles was contents the critical one, which caused the differences. Soil organic carbon was significantly correlated with soil nitrogen (r = 0.977). The ratio of carbon and nitrogen (C/N) changed along with the humidity gradient, and soil pH values obviously influenced the concentration of organic carbon and nitrogen. The correlation of C/N values and organic carbon and nitrogen contents in wetland soil and in grassland soil were remarkably different, and the ecological effects mainly included production effect and clarification effect. PMID:14733006

  14. Nitrogen-Containing Analog of Dibenzoylmethanate of Boron Difluoride: Luminescence, Structure, Quantum Chemical Modeling, and Delay Fluorescence.

    PubMed

    Fedorenko, Elena V; Тretyakova, Galina O; Mirochnik, Anatolii G; Beloliptsev, Anton Yu; Svistunova, Irina V; Sazhnikov, Viacheslav A; Atabekyan, Levon S

    2016-09-01

    Boron difluoride of 3-amino-1,3-diphenyl-2-propene-1-onate (1) has been synthesized and its crystal structure has been determined. The comparative studies of 1 and its oxygen analog 1,3-diphenyl-1,3-dionate (dibenzoylmethanate) of boron difluoride (2) have been performed using the methods of stationary and time-resolved spectroscopy and quantum chemical modeling. It was established that at the transition from solutions to crystals, a bathochromic shift of the spectra and a significant increase of luminescence intensity of 1 take place. The luminescent properties of solutions of 1 and 2 are similar. The peculiarities of crystal packings of 1 and 2 are responsible for differences in crystals luminescent properties. For crystals of 2, one observes the luminescence of J-aggregates and excimers, while for 1, in which a dimer is an elementary structural fragment, only the excimer luminescence is registered. A delayed excimer fluorescence of the P-type was observed for crystals of 1 and 2 at room temperature. The intensity of the delayed fluorescence of 1 is 300-fold higher than that of 2. Graphical Abstract Luminescence of J-aggregates and the formation of excimers in crystals of 1 and 2. PMID:27422696

  15. MIL-100 derived nitrogen-embodied carbon shells embedded with iron nanoparticles

    NASA Astrophysics Data System (ADS)

    Mao, Chengyu; Kong, Aiguo; Wang, Yuan; Bu, Xianhui; Feng, Pingyun

    2015-06-01

    The use of metal-organic frameworks (MOFs) as templates and precursors to synthesize new carbon materials with controllable morphology and pre-selected heteroatom doping holds promise for applications as efficient non-precious metal catalysts. Here, we report a facile pyrolysis pathway to convert MIL-100 into nitrogen-doped carbon shells encapsulating Fe nanoparticles in a comparative study involving multiple selected nitrogen sources. The hierarchical porous architecture, embedded Fe nanoparticles, and nitrogen decoration endow this composite with a superior oxygen reduction activity. Furthermore, the excellent durability and high methanol tolerance even outperform the commercial Pt-C catalyst.The use of metal-organic frameworks (MOFs) as templates and precursors to synthesize new carbon materials with controllable morphology and pre-selected heteroatom doping holds promise for applications as efficient non-precious metal catalysts. Here, we report a facile pyrolysis pathway to convert MIL-100 into nitrogen-doped carbon shells encapsulating Fe nanoparticles in a comparative study involving multiple selected nitrogen sources. The hierarchical porous architecture, embedded Fe nanoparticles, and nitrogen decoration endow this composite with a superior oxygen reduction activity. Furthermore, the excellent durability and high methanol tolerance even outperform the commercial Pt-C catalyst. Electronic supplementary information (ESI) available: Material synthesis and elemental analysis, electrochemistry measurements, and additional figures. See DOI: 10.1039/c5nr02346g

  16. [Effects of different fertilizer species on carbon and nitrogen leaching in a reddish paddy soil].

    PubMed

    Liu, Xi-Yu; Zou, Jing-Dong; Xu, Li-Li; Zhang, Xin-Yu; Yang, Feng-Ting; Dai, Xiao-Qin; Wang, Zhong-Qiang; Sun, Xiao-Min

    2014-08-01

    Enhanced fertilization could decrease nitrogen utilization rate and increase carbon and nitrogen leaching, leading to water pollution in agricultural ecosystem. A long-term field experiment had been established on a reddish paddy soil of Qianyanzhou Ecological Experimental Station (114 degrees 53'E, 26 degrees 48'N) in Jiangxi Province in 1998. Soil solution samples were collected by clay tube and vacuum pump. Four fertilizer species treatments were selected: control with no fertilizer (CK), straw return (ST), nitrogen, phosphorus and potassium mineral fertilizers (NPK) and pig manure (OM), aiming to evaluate the effects of different species of fertilizer on carbon and nitrogen leaching in a double rice cropping system. The results showed that: (1) ammonium nitrogen (NH4(+) -N) was the major type of N in soil leachate in reddish paddy soil. The application of NPK could significantly increase the ammonium nitrogen concentration (1.2 mg x L(-1) +/- 0.1 mg x L(-1)) compared with the CK, ST and OM treatments, and the application of OM could significantly increase the dissolved organic carbon (DOC) concentration (27.3 mg x L(-1) +/- 1.6 mg x L(-1)) in soil leachate. The carbon and nitrogen leaching were more notable in the vegetative growth stage than the reproductive growth stage of rice (P < 0.05); (2) the long-term application of NPK and OM increased the NH4(+) -N, DOC, soil organic carbon (SOC) and total nitrogen (TN) contents. The NPK was best beneficial to improve TN contents and OM to improve SOC contents. (3) The DOC contents in soil leachate and SOC in paddy soil had a positive correlation (P < 0.01), while NH4(+) -N contents in soil leachate and TN contents in paddy soil had a positive correlation (P < 0.01). PMID:25338383

  17. [Release and supplement of carbon, nitrogen and phosphorus from jellyfish (Nemopilema nomurai) decomposition in seawater].

    PubMed

    Qu, Chang-feng; Song, Jin-ming; Li, Ning; Li, Xue-gang; Yuan, Hua-mao; Duan, Li-qin

    2016-01-01

    Abstract: Jellyfish bloom has been increasing in Chinese seas and decomposition after jellyfish bloom has great influences on marine ecological environment. We conducted the incubation of Nemopilema nomurai decomposing to evaluate its effect on carbon, nitrogen and phosphorus recycling of water column by simulated experiments. The results showed that the processes of jellyfish decomposing represented a fast release of biogenic elements, and the release of carbon, nitrogen and phosphorus reached the maximum at the beginning of jellyfish decomposing. The release of biogenic elements from jellyfish decomposition was dominated by dissolved matter, which had a much higher level than particulate matter. The highest net release rates of dissolved organic carbon and particulate organic carbon reached (103.77 ± 12.60) and (1.52 ± 0.37) mg · kg⁻¹ · h⁻¹, respectively. The dissolved nitrogen was dominated by NH₄⁺-N during the whole incubation time, accounting for 69.6%-91.6% of total dissolved nitrogen, whereas the dissolved phosphorus was dominated by dissolved organic phosphorus during the initial stage of decomposition, being 63.9%-86.7% of total dissolved phosphorus and dominated by PO₄³⁻-P during the late stage of decomposition, being 50.4%-60.2%. On the contrary, the particulate nitrogen was mainly in particulate organic nitrogen, accounting for (88.6 ± 6.9) % of total particulate nitrogen, whereas the particulate phosphorus was mainly in particulate. inorganic phosphorus, accounting for (73.9 ±10.5) % of total particulate phosphorus. In addition, jellyfish decomposition decreased the C/N and increased the N/P of water column. These indicated that jellyfish decomposition could result in relative high carbon and nitrogen loads. PMID:27228622

  18. [Effects of nitrogen and carbon addition and arbuscular mycorrhiza on alien invasive plant Ambrosia artemisiifolia].

    PubMed

    Huang, Dong; Sang, Wei-guo; Zhu, Li; Song, Ying-ying; Wang, Jin-ping

    2010-12-01

    A greenhouse control experiment was conducted to explore the effects of nitrogen and carbon addition and arbuscular mycorrhiza (AM) on the growth of alien invasive plant Ambrosia artemisiifolia (common ragweed). Nitrogen addition had no significant effects on the morphological indices, biomass and its allocation, and absolute growth rate of A. artemisiifolia, but increased the nitrogen content in the aboveground and underground parts of the plant significantly. Carbon addition increased the content of soil available nitrogen. In this case, the biomass allocation in root system for nutrient (nitrogen) absorption promoted, resulting in a remarkable decrease of branch number, total leaf area, specific leaf area (SLA), and leaf mass ratio. As a result, the total biomass decreased significantly. The symbiosis of A. artemisiifolia and AM fungi had great influence on the common ragweed's soil nitrogen acclimation, which enhanced its resource-capture by the increase of SLA, and this effect was more significant when the soil nitrogen content was low. AM fungi played an important role in the growth of A. artemisiifolia in low-nitrogen environment. PMID:21442989

  19. Boron Clusters Come of Age

    ERIC Educational Resources Information Center

    Grimes, Russell N.

    2004-01-01

    Boron is the only element other than carbon that can build molecules of unlimited size by covalently boding to itself, a property known as catenation. In contrast to the chains and rings favored by carbon, boron arguably adopts a cluster motif that is reflected in the various forms of the pure element and in the huge area of polyhedral borane…

  20. Nitrogen-incorporated ultrananocrystalline diamond and multi-layer-graphene-like hybrid carbon films.

    PubMed

    Tzeng, Yonhua; Yeh, Shoupu; Fang, Wei Cheng; Chu, Yuehchieh

    2014-01-01

    Nitrogen-incorporated ultrananocrystalline diamond (N-UNCD) and multi-layer-graphene-like hybrid carbon films have been synthesized by microwave plasma enhanced chemical vapor deposition (MPECVD) on oxidized silicon which is pre-seeded with diamond nanoparticles. MPECVD of N-UNCD on nanodiamond seeds produces a base layer, from which carbon structures nucleate and grow perpendicularly to form standing carbon platelets. High-resolution transmission electron microscopy and Raman scattering measurements reveal that these carbon platelets are comprised of ultrananocrystalline diamond embedded in multilayer-graphene-like carbon structures. The hybrid carbon films are of low electrical resistivity. UNCD grains in the N-UNCD base layer and the hybrid carbon platelets serve as high-density diamond nuclei for the deposition of an electrically insulating UNCD film on it. Biocompatible carbon-based heaters made of low-resistivity hybrid carbon heaters encapsulated by insulating UNCD for possible electrosurgical applications have been demonstrated. PMID:24681781

  1. Nitrogen-incorporated ultrananocrystalline diamond and multi-layer-graphene-like hybrid carbon films

    PubMed Central

    Tzeng, Yonhua; Yeh, Shoupu; Fang, Wei Cheng; Chu, Yuehchieh

    2014-01-01

    Nitrogen-incorporated ultrananocrystalline diamond (N-UNCD) and multi-layer-graphene-like hybrid carbon films have been synthesized by microwave plasma enhanced chemical vapor deposition (MPECVD) on oxidized silicon which is pre-seeded with diamond nanoparticles. MPECVD of N-UNCD on nanodiamond seeds produces a base layer, from which carbon structures nucleate and grow perpendicularly to form standing carbon platelets. High-resolution transmission electron microscopy and Raman scattering measurements reveal that these carbon platelets are comprised of ultrananocrystalline diamond embedded in multilayer-graphene-like carbon structures. The hybrid carbon films are of low electrical resistivity. UNCD grains in the N-UNCD base layer and the hybrid carbon platelets serve as high-density diamond nuclei for the deposition of an electrically insulating UNCD film on it. Biocompatible carbon-based heaters made of low-resistivity hybrid carbon heaters encapsulated by insulating UNCD for possible electrosurgical applications have been demonstrated. PMID:24681781

  2. Biophysical Controls over Carbon and Nitrogen Stocks in Desert Playa Wetlands

    NASA Astrophysics Data System (ADS)

    McKenna, O. P.; Sala, O. E.

    2014-12-01

    Playas are ephemeral desert wetlands situated at the bottom of closed catchments. Desert playas in the Southwestern US have not been intensively studied despite their potential importance for the functioning of desert ecosystems. We want to know which geomorphic and ecological variables control of the stock size of soil organic carbon, and soil total nitrogen in playas. We hypothesize that the magnitude of carbon and nitrogen stocks depends on: (a) catchment size, (b) catchment slope, (d) catchment vegetation cover, (e) bare-ground patch size, and (f) catchment soil texture. We chose thirty playas from across the Jornada Basin (Las Cruces, NM) ranging from 0.5-60ha in area and with varying catchment characteristics. We used the available 5m digital elevation map (DEM) to calculate the catchment size and catchment slope for these thirty playas. We measured percent cover, and patch size using the point-intercept method with three 10m transects in each catchment. We used the Bouyoucos-hydrometer soil particle analysis to determine catchment soil texture. Stocks of organic carbon and nitrogen were measured from soil samples at four depths (0-10 cm, 10-30 cm, 30-60 cm, 60-100 cm) using C/N combustion analysis. In terms of nitrogen and organic carbon storage, we found soil nitrogen values in the top 10cm ranging from 41.963-214.365 gN/m2, and soil organic carbon values in the top 10cm ranging from 594.339-2375.326 gC/m2. The results of a multiple regression analysis show a positive relationship between catchment slope and both organic carbon and nitrogen stock size (nitrogen: y= 56.801 +47.053, R2=0.621; organic carbon: y= 683.200 + 499.290x, R2= 0.536). These data support our hypothesis that catchment slope is one of factors controlling carbon and nitrogen stock in desert playas. We also applied our model to the 69 other playas of the Jornada Basin and estimated stock sizes (0-10cm) between 415.07-447.97 Mg for total soil nitrogen and 4627.99-5043.51 Mg for soil organic

  3. Palladium on Nitrogen-Doped Mesoporous Carbon: A Bifunctional Catalyst for Formate-Based, Carbon-Neutral Hydrogen Storage.

    PubMed

    Wang, Fanan; Xu, Jinming; Shao, Xianzhao; Su, Xiong; Huang, Yanqiang; Zhang, Tao

    2016-02-01

    The lack of safe, efficient, and economical hydrogen storage technologies is a hindrance to the realization of the hydrogen economy. Reported herein is a reversible formate-based carbon-neutral hydrogen storage system that is established over a novel catalyst comprising palladium nanoparticles supported on nitrogen-doped mesoporous carbon. The support was fabricated by a hard template method and nitridated under a flow of ammonia. Detailed analyses demonstrate that this bicarbonate/formate redox equilibrium is promoted by the cooperative role of the doped nitrogen functionalities and the well-dispersed, electron-enriched palladium nanoparticles. PMID:26763714

  4. Nitrogen-Doped Carbon Dots as A New Substrate for Sensitive Glucose Determination

    PubMed Central

    Ji, Hanxu; Zhou, Feng; Gu, Jiangjiang; Shu, Chen; Xi, Kai; Jia, Xudong

    2016-01-01

    Nitrogen-doped carbon dots are introduced as a novel substrate suitable for enzyme immobilization in electrochemical detection metods. Nitrogen-doped carbon dots are easily synthesised from polyacrylamide in just one step. With the help of the amino group on chitosan, glucose oxidase is immobilized on nitrogen-doped carbon dots-modified carbon glassy electrodes by amino-carboxyl reactions. The nitrogen-induced charge delocalization at nitrogen-doped carbon dots can enhance the electrocatalytic activity toward the reduction of O2. The specific amino-carboxyl reaction provides strong and stable immobilization of GOx on electrodes. The developed biosensor responds efficiently to the presence of glucose in serum samples over the concentration range from 1 to 12 mM with a detection limit of 0.25 mM. This novel biosensor has good reproducibility and stability, and is highly selective for glucose determination under physiological conditions. These results indicate that N-doped quantum dots represent a novel candidate material for the construction of electrochemical biosensors. PMID:27153071

  5. Nitrogen-Doped Carbon Dots as A New Substrate for Sensitive Glucose Determination.

    PubMed

    Ji, Hanxu; Zhou, Feng; Gu, Jiangjiang; Shu, Chen; Xi, Kai; Jia, Xudong

    2016-01-01

    Nitrogen-doped carbon dots are introduced as a novel substrate suitable for enzyme immobilization in electrochemical detection metods. Nitrogen-doped carbon dots are easily synthesised from polyacrylamide in just one step. With the help of the amino group on chitosan, glucose oxidase is immobilized on nitrogen-doped carbon dots-modified carbon glassy electrodes by amino-carboxyl reactions. The nitrogen-induced charge delocalization at nitrogen-doped carbon dots can enhance the electrocatalytic activity toward the reduction of O₂. The specific amino-carboxyl reaction provides strong and stable immobilization of GOx on electrodes. The developed biosensor responds efficiently to the presence of glucose in serum samples over the concentration range from 1 to 12 mM with a detection limit of 0.25 mM. This novel biosensor has good reproducibility and stability, and is highly selective for glucose determination under physiological conditions. These results indicate that N-doped quantum dots represent a novel candidate material for the construction of electrochemical biosensors. PMID:27153071

  6. Remote Sensing of Vegetation Nitrogen Content for Spatially Explicit Carbon and Water Cycle Estimation

    NASA Astrophysics Data System (ADS)

    Zhang, Y. L.; Miller, J. R.; Chen, J. M.

    2009-05-01

    Foliage nitrogen concentration is a determinant of photosynthetic capacity of leaves, thereby an important input to ecological models for estimating terrestrial carbon and water budgets. Recently, spectrally continuous airborne hyperspectral remote sensing imagery has proven to be useful for retrieving an important related parameter, total chlorophyll content at both leaf and canopy scales. Thus remote sensing of vegetation biochemical parameters has promising potential for improving the prediction of global carbon and water balance patterns. In this research, we explored the feasibility of estimating leaf nitrogen content using hyperspectral remote sensing data for spatially explicit estimation of carbon and water budgets. Multi-year measurements of leaf biochemical contents of seven major boreal forest species were carried out in northeastern Ontario, Canada. The variation of leaf chlorophyll and nitrogen content in response to various growth conditions, and the relationship between them,were investigated. Despite differences in plant type (deciduous and evergreen), leaf age, stand growth conditions and developmental stages, leaf nitrogen content was strongly correlated with leaf chlorophyll content on a mass basis during the active growing season (r2=0.78). With this general correlation, leaf nitrogen content was estimated from leaf chlorophyll content at an accuracy of RMSE=2.2 mg/g, equivalent to 20.5% of the average measured leaf nitrogen content. Based on this correlation and a hyperspectral remote sensing algorithm for leaf chlorophyll content retrieval, the spatial variation of leaf nitrogen content was inferred from the airborne hyperspectral remote sensing imagery acquired by Compact Airborne Spectrographic Imager (CASI). A process-based ecological model Boreal Ecosystem Productivity Simulator (BEPS) was used for estimating terrestrial carbon and water budgets. In contrast to the scenario with leaf nitrogen content assigned as a constant value without

  7. Preparation of diamond-like carbon and boron nitirde films by high-intensity pulsed ion beam deposition

    SciTech Connect

    Rej, D.J.; Davis, H.A.; Remnev, G.E.

    1995-05-01

    Intense ion beams (300-keV C{sup +}, O{sup +}, and H{sup +}, 20--30 kA, 50 to 400-ns pulsewidth, up to 0.3-Hz repetition rate) were used to prepare diamond-like carbon (DLC) and boron nitride (BN) films. Deposition rates of up to 25{plus_minus}5 nm/pulse were obtained with instantaneous rates exceeding 1 mm/s. Most films were uniform, light brown, translucent, and nonporous with some micron-size particulates. Raman and parallel electron energy loss spectroscopy indicated the presence of DLC. The films possessed favorable electron field-emission characteristics desirable for cold-cathode displays. Transmission electron microscopy (TEM) and transmission electron diffraction (TED) revealed that the C films contained diamond crystals with 25 to 125-nm grain size. BN films were composed of hexagonal, cubic and wurtzite phases.

  8. B and N isolate-doped graphitic carbon nanosheets from nitrogen-containing ion-exchanged resins for enhanced oxygen reduction

    NASA Astrophysics Data System (ADS)

    Wang, Lei; Yu, Peng; Zhao, Lu; Tian, Chungui; Zhao, Dongdong; Zhou, Wei; Yin, Jie; Wang, Ruihong; Fu, Honggang

    2014-06-01

    B,N-codoped carbon nanostructures (BNCS) can serve as alternative low-cost metal-free electrocatalysts for oxygen reduction reactions (ORR). However, the compensation effect between the p- (B atoms) and n-type (N atoms) dopants would make the covalent boron-nitride (BN) easily formed during the synthesis of BNCS, leading to a unsatisfactory ORR activity. Therefore, it has been challenging to develop facile and rapid synthetic strategies for highly active BNCS without forming the direct covalent BN. Here, a facile method is developed to prepare B and N isolate-doped graphitic nanosheets (BNGS) by using iron species for saving N element and simultaneous doping the B element from nitrogen-containing ion-exchanged resins (NR). The resulting BNGS exhibits much more onset potential (Eonset) compared with the B-doped graphitic carbon nanosheets (BGS), N-doped graphitic carbon nanosheets (NGS), as well as B,N-codoped disorder carbon (BNC). Moreover, the BNGS shows well methanol tolerance propery and excellent stability (a minimal loss of activity after 5,000 potential cycles) compared to that of commercial Pt/C catalyst. The goog performance for BNGS towards ORR is attributed to the synergistic effect between B and N, and the well electrons transport property of graphitic carbon in BNGS.

  9. B and N isolate-doped graphitic carbon nanosheets from nitrogen-containing ion-exchanged resins for enhanced oxygen reduction

    PubMed Central

    Wang, Lei; Yu, Peng; Zhao, Lu; Tian, Chungui; Zhao, Dongdong; Zhou, Wei; Yin, Jie; Wang, Ruihong; Fu, Honggang

    2014-01-01

    B,N-codoped carbon nanostructures (BNCS) can serve as alternative low-cost metal-free electrocatalysts for oxygen reduction reactions (ORR). However, the compensation effect between the p- (B atoms) and n-type (N atoms) dopants would make the covalent boron-nitride (BN) easily formed during the synthesis of BNCS, leading to a unsatisfactory ORR activity. Therefore, it has been challenging to develop facile and rapid synthetic strategies for highly active BNCS without forming the direct covalent BN. Here, a facile method is developed to prepare B and N isolate-doped graphitic nanosheets (BNGS) by using iron species for saving N element and simultaneous doping the B element from nitrogen-containing ion-exchanged resins (NR). The resulting BNGS exhibits much more onset potential (Eonset) compared with the B-doped graphitic carbon nanosheets (BGS), N-doped graphitic carbon nanosheets (NGS), as well as B,N-codoped disorder carbon (BNC). Moreover, the BNGS shows well methanol tolerance propery and excellent stability (a minimal loss of activity after 5,000 potential cycles) compared to that of commercial Pt/C catalyst. The goog performance for BNGS towards ORR is attributed to the synergistic effect between B and N, and the well electrons transport property of graphitic carbon in BNGS. PMID:24898033

  10. Carbon and nitrogen mineralization are decoupled in organo-mineral fractions

    NASA Astrophysics Data System (ADS)

    Bimüller, Carolin; Mueller, Carsten W.; von Lützow, Margit; Kreyling, Olivia; Kölbl, Angelika; Haug, Stephan; Schloter, Michael; Kögel-Knabner, Ingrid

    2015-04-01

    To improve our comprehension how carbon and nitrogen mineralization are linked in soils, we used a controlled laboratory mineralization approach and compared carbon and nitrogen dynamics in the bulk soil and in soil fractions. Topsoil of a Rendzic Leptosol from a beech forest site near Tuttlingen, Germany, was fractionated into three particle size classes: sand (2000 to 20 µm), silt (20 to 2 µm), and clay (< 2 µm). Bulk soil and particle size fractions were incubated for 40 weeks allowing periodic destructive sampling. We monitored carbon and nitrogen mineralization dynamics, and assessed carbon respiration as well as nitrogen mineralization and microbial biomass carbon and nitrogen contents. Soil organic matter in the incubated fractions was considered by a subsequent density fractionation. The chemical composition of selected samples was qualitatively evaluated by 13C-NMR spectroscopy. When summing up the mineralization rates of the single fractions, the values for respired carbon equaled the bulk soil, whereas the mathematical recombination of mineral nitrogen in all fractions was significantly less than in bulk soil. Hence, carbon mineralization was not affected by the damage of the aggregated soil structure via fractionation, whereas nitrogen mineralization was reduced. Fractionation increased the surface area providing accessory mineral surfaces, which allowed new binding of especially nitrogen-rich compounds, besides ammonium fixation via cation exchange. Density fractionation revealed that organic matter in the sand fraction contained mainly particulate organic matter present as light material comprising partly decomposed plant remnants. The organic matter in the clay fraction was mostly adsorbed on mineral surfaces. Organic matter in the sand and in the clay fraction was dominated by O/N-alkyl C indicating low recalcitrance, but the C/N ratio of organic matter narrowed with decreasing particle size. These results also imply that the C/N ratio as well as

  11. Photoluminescence properties of thermographic phosphors YAG:Dy and YAG:Dy, Er doped with boron and nitrogen

    NASA Astrophysics Data System (ADS)

    Chepyga, Liudmyla M.; Jovicic, Gordana; Vetter, Andreas; Osvet, Andres; Brabec, Christoph J.; Batentschuk, Miroslaw

    2016-08-01

    This paper investigates Dy3+-doped and Dy3+, Er3+-co-doped yttrium aluminum garnets (YAG) with the admixture of boron nitride with the aim of using them as efficient thermographic phosphors at high temperatures. The phosphors were synthesized using a conventional high-temperature solid-state method. The influence of two fluxes, B2O3 and LiF/NH4F, and the effect of activator and coactivator concentrations were investigated. Additionally, the effect of B3+ and N3- substituting for Al3+ and O2- ions, respectively, in the YAG:Dy3+ co-doped with Er3+ was studied for the first time. The changes in the host lattice led to a much stronger photoluminescence compared with the samples without B3+ and N3- substitution. The admixture of BN also improves the thermal sensitivity of the YAG:Dy and YAG:Dy, Er thermographic phosphors.

  12. Whole-ecosystem exposure to elevated carbon dioxide increases total ecosystem carbon and nitrogen in the Mojave Desert

    NASA Astrophysics Data System (ADS)

    Evans, R. D.; Koyama, A.; Sonderegger, D.; Charlet, D.; Newingham, B. A.; Fenstermaker, L.; Ogle, K.; Smith, S. D.; Nowak, R.

    2011-12-01

    Arid ecosystems are predicted to be among the most responsive to global change and their response is globally significant considering their extensive spatial coverage. Although carbon cycling in arid lands is an important component of the global carbon budget, there is substantial uncertainty about the potential impacts of global change drivers, such as elevated CO2, on arid land carbon budgets. Studies suggest that productivity may be stimulated by elevated CO2 directly due to enhanced plant water-use efficiency. The indirect impacts of elevated CO2 on ecosystem productivity may also be constrained by available nitrogen, but little is known about how the importance of the nitrogen constraint or how the nitrogen cycle may be affected by global change drivers. Here we present the carbon and nitrogen mass budgets of a Mojave Desert ecosystem after ten years of exposure to elevated CO2. The Nevada Desert Free-Air Carbon Enrichment Facility (FACE) was established in 1997 to evaluate the response of an intact Mojave Desert ecosystem to elevated CO2. The CO2 concentration of the atmosphere in the elevated treatment was maintained at 513 uL/L until harvest in 2007. At harvest time, all aboveground biomass for 2/3 of each plot was harvested and soils and roots were removed down to 1 m depth and analyzed for total carbon and nitrogen. We observed significantly greater carbon (10,800 versus 9,200 kg C/ha, P=0.004) and nitrogen (1,400 versus 1,100 kg N/ha, P=0.002) in elevated compared to ambient CO2 treatments. Differences between treatments were due solely to greater C and N in soils across all cover types, and no differences were observed in above and belowground plant biomass. Companion research shows that increased soil C was from increased root exudation, microbial residues, and episodic increased litter input under elevated CO2, and these increased C inputs in turn stimulated production of inorganic nitrogen. Results from the Nevada Desert FACE Facility demonstrate

  13. Nitrogen-doped mesoporous carbon of extraordinary capacitance for electrochemical energy storage

    NASA Astrophysics Data System (ADS)

    Lin, Tianquan; Chen, I.-Wei; Liu, Fengxin; Yang, Chongyin; Bi, Hui; Xu, Fangfang; Huang, Fuqiang

    2015-12-01

    Carbon-based supercapacitors can provide high electrical power, but they do not have sufficient energy density to directly compete with batteries. We found that a nitrogen-doped ordered mesoporous few-layer carbon has a capacitance of 855 farads per gram in aqueous electrolytes and can be bipolarly charged or discharged at a fast, carbon-like speed. The improvement mostly stems from robust redox reactions at nitrogen-associated defects that transform inert graphene-like layered carbon into an electrochemically active substance without affecting its electric conductivity. These bipolar aqueous-electrolyte electrochemical cells offer power densities and lifetimes similar to those of carbon-based supercapacitors and can store a specific energy of 41 watt-hours per kilogram (19.5 watt-hours per liter).

  14. Effect of fluence on carbon nanostructures produced by laser ablation in liquid nitrogen

    NASA Astrophysics Data System (ADS)

    Tabatabaie, Nushin; Dorranian, Davoud

    2016-05-01

    Effects of laser fluence on the properties of carbon nanostructures produced by laser ablation method in liquid nitrogen have been studied experimentally. The beam of a Q-switched Nd:YAG laser of 1064-nm wavelength at 7 ns pulse width and different fluences is employed to irradiate the graphite target in liquid nitrogen. Properties of carbon nanostructures were studied using their UV-Vis-NIR spectrum, TEM images, and Raman scattering spectrum. Two categories of graphene nanosheets and carbon nanoparticles were observed due to variation of laser fluence. Results show that in our experimental condition there is a threshold fluence for producing carbon nanoparticles. With increasing the laser fluence from the threshold, the amount of carbon nanoparticles in suspensions was increased, while the amount of graphene nanosheets was decreased.

  15. Nitrogen-doped mesoporous carbon of extraordinary capacitance for electrochemical energy storage.

    PubMed

    Lin, Tianquan; Chen, I-Wei; Liu, Fengxin; Yang, Chongyin; Bi, Hui; Xu, Fangfang; Huang, Fuqiang

    2015-12-18

    Carbon-based supercapacitors can provide high electrical power, but they do not have sufficient energy density to directly compete with batteries. We found that a nitrogen-doped ordered mesoporous few-layer carbon has a capacitance of 855 farads per gram in aqueous electrolytes and can be bipolarly charged or discharged at a fast, carbon-like speed. The improvement mostly stems from robust redox reactions at nitrogen-associated defects that transform inert graphene-like layered carbon into an electrochemically active substance without affecting its electric conductivity. These bipolar aqueous-electrolyte electrochemical cells offer power densities and lifetimes similar to those of carbon-based supercapacitors and can store a specific energy of 41 watt-hours per kilogram (19.5 watt-hours per liter). PMID:26680194

  16. Carbon availability triggers the decomposition of plant litter and assimilation of nitrogen by an ectomycorrhizal fungus

    PubMed Central

    Rineau, F; Shah, F; Smits, M M; Persson, P; Johansson, T; Carleer, R; Troein, C; Tunlid, A

    2013-01-01

    The majority of nitrogen in forest soils is found in organic matter–protein complexes. Ectomycorrhizal fungi (EMF) are thought to have a key role in decomposing and mobilizing nitrogen from such complexes. However, little is known about the mechanisms governing these processes, how they are regulated by the carbon in the host plant and the availability of more easily available forms of nitrogen sources. Here we used spectroscopic analyses and transcriptome profiling to examine how the presence or absence of glucose and/or ammonium regulates decomposition of litter material and nitrogen mobilization by the ectomycorrhizal fungus Paxillus involutus. We found that the assimilation of nitrogen and the decomposition of the litter material are triggered by the addition of glucose. Glucose addition also resulted in upregulation of the expression of genes encoding enzymes involved in oxidative degradation of polysaccharides and polyphenols, peptidases, nitrogen transporters and enzymes in pathways of the nitrogen and carbon metabolism. In contrast, the addition of ammonium to organic matter had relatively minor effects on the expression of transcripts and the decomposition of litter material, occurring only when glucose was present. On the basis of spectroscopic analyses, three major types of chemical modifications of the litter material were observed, each correlated with the expression of specific sets of genes encoding extracellular enzymes. Our data suggest that the expression of the decomposition and nitrogen assimilation processes of EMF can be tightly regulated by the host carbon supply and that the availability of inorganic nitrogen as such has limited effects on saprotrophic activities. PMID:23788332

  17. Thermodynamics and Kinetics of Boron Removal from Metallurgical Grade Silicon by Addition of High Basic Potassium Carbonate to Calcium Silicate Slag

    NASA Astrophysics Data System (ADS)

    Wu, Jijun; Wang, Fanmao; Ma, Wenhui; Lei, Yun; Yang, Bin

    2016-06-01

    In this study, we investigated the thermodynamics and kinetics of boron removal from metallurgical grade silicon (MG-Si) using a calcium silicate slag containing a high basic potassium carbonate. The distribution of boron between slag and silicon was theoretically derived and the distribution coefficients ( L B) of boron with different compositions of CaO, SiO2, and K2CO3 in slag reagents were determined. The maximal value of L B reached 2.08 with a high basicity slag of 40 pctCaO-40 pctSiO2-20 pctK2CO3 (Λ = 0.73). The boron removal rates from MG-Si using CaO-SiO2 and CaO-SiO2-K2CO3 slags at 1823 K (1550 °C) were investigated in an electromagnetic induction furnace. The results showed that the boron concentration in MG-Si can be reduced from 22 to 1.8 ppmw at 1823 K (1550 °C) with 20 pct K2CO3 addition to calcium silicate slag, where the removal efficiency of boron reached 91.8 pct. The mass transfer coefficient ( β S) of boron in binary 50 pctCaO-50 pctSiO2 slag was 3.16 × 10-6 m s-1 at 1823 K (1550 °C) and was 2.43 × 10-5 m s-1 in ternary 40 pctCaO-40 pctSiO2-20 pctK2CO3 slag.

  18. Thermodynamics and Kinetics of Boron Removal from Metallurgical Grade Silicon by Addition of High Basic Potassium Carbonate to Calcium Silicate Slag

    NASA Astrophysics Data System (ADS)

    Wu, Jijun; Wang, Fanmao; Ma, Wenhui; Lei, Yun; Yang, Bin

    2016-02-01

    In this study, we investigated the thermodynamics and kinetics of boron removal from metallurgical grade silicon (MG-Si) using a calcium silicate slag containing a high basic potassium carbonate. The distribution of boron between slag and silicon was theoretically derived and the distribution coefficients (L B) of boron with different compositions of CaO, SiO2, and K2CO3 in slag reagents were determined. The maximal value of L B reached 2.08 with a high basicity slag of 40 pctCaO-40 pctSiO2-20 pctK2CO3 (Λ = 0.73). The boron removal rates from MG-Si using CaO-SiO2 and CaO-SiO2-K2CO3 slags at 1823 K (1550 °C) were investigated in an electromagnetic induction furnace. The results showed that the boron concentration in MG-Si can be reduced from 22 to 1.8 ppmw at 1823 K (1550 °C) with 20 pct K2CO3 addition to calcium silicate slag, where the removal efficiency of boron reached 91.8 pct. The mass transfer coefficient (β S) of boron in binary 50 pctCaO-50 pctSiO2 slag was 3.16 × 10-6 m s-1 at 1823 K (1550 °C) and was 2.43 × 10-5 m s-1 in ternary 40 pctCaO-40 pctSiO2-20 pctK2CO3 slag.

  19. Nitrogen fertilizer effects on irrigated conventional tillage corn yields and soil carbon and nitrogen pools

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Conventional plow tillage (CT) is a common soil management practice under irrigated continuous corn (Zea mays L.) in the semiarid central Great Plains that requires a relatively high nitrogen (N) fertilizer rate to optimize grain yield and economic returns. This study investigated how four rates of ...

  20. The reactivity of lattice carbon and nitrogen species in molybdenum (oxy)carbonitrides prepared by single-source routes

    SciTech Connect

    AlShalwi, M.; Hargreaves, J.S.J.; Liggat, J.J.; Todd, D.

    2012-05-15

    Highlights: Black-Right-Pointing-Pointer Molybdenum (oxy)carbonitrides have been prepared from single source routes. Black-Right-Pointing-Pointer Nitrogen species are more reactive than carbon species within the carbonitrides. Black-Right-Pointing-Pointer The reactivity of nitrogen species is a function of carbonitride composition. -- Abstract: Molybdenum (oxy)carbonitrides of different compositions have been prepared from hexamethylenetetramine molybdate and ethylenediamine molybdate precursors and the reactivity of the lattice carbon and nitrogen species within them has been determined by temperature programmed reduction and thermal volatilisation studies. Nitrogen is found to be much more reactive than carbon and the nature of its reactivity is influenced by composition with the presence of carbon enhancing the reactivity of nitrogen. The difference in reactivity observed indicates that molybdenum carbonitrides are not suitable candidates as reagents for which the simultaneous loss of nitrogen and carbon from the lattice would be desirable.

  1. Effect of surface phosphorus functionalities of activated carbons containing oxygen and nitrogen on electrochemical capacitance

    PubMed Central

    Hulicova-Jurcakova, Denisa; Seredych, Mykola; Lu, Gao Qing; Kodiweera, N.K.A.C.; Stallworth, Phillip E.; Greenbaum, Steven; Bandosz, Teresa J.

    2009-01-01

    Micro/mesoporous activated carbons containing oxygen and phosphorus heteroatoms were modified by incorporation of nitrogen using melamine and urea precursors. The surface chemistry was analyzed by the means of elemental analysis, XPS, and 31P MAS NMR. The results indicate that upon the incorporation of nitrogen at high temperatures not only new species involving carbon/nitrogen/oxygen are formed but also the phosphorous environment is significantly altered. Both urea and melamine precursors have similar effects on formation of P–N and P–C bonds. These compounds, although present in small but measurable quantities seem to affect the performance of carbons in electrochemical capacitors. With an increase in the heterogeneity of phosphorus containing species and with a decrease in the content pyrophosphates the capacitance increases and the retention ratio of the capacitor is improved. PMID:20354586

  2. Nitrogen-doped porous carbon with an ultrahigh specific surface area for superior performance supercapacitors

    NASA Astrophysics Data System (ADS)

    Long, Chao; Zhuang, Jianle; Xiao, Yong; Zheng, Mingtao; Hu, Hang; Dong, Hanwu; Lei, Bingfu; Zhang, Haoran; Liu, Yingliang

    2016-04-01

    Owing to its abundant nitrogen content, silk cocoon is a promising precursor for the synthesis of Nitrogen-doped porous carbon (N-PC). Using a simple staged KOH activation, the prepared sample displays particular nanostructure with ultrahigh specific surface area (3841 m2 g-1) and appropriate pore size, providing favorable pathways for transportation and penetration of electrolyte ions. Additionally, the doped nitrogen atoms ensure the samples with pseudocapacitive behavior. Those special characteristics endow N-PCs with high capacity, low resistance, and long-term stability, indicating a wonderful potential for application in energy-storage devices.

  3. [Effects of land use type on soil organic carbon, total nitrogen, and microbial biomass carbon and nitrogen contents in Karst region of South China].

    PubMed

    Li, Xinai; Xiao, Heai; Wu, Jinshui; Su, Yirong; Huang, Daoyou; Huang, Min; Liu, Shoulong; Peng, Hongcui

    2006-10-01

    A total of 721 surface (0-20 cm) soil samples were collected from the paddy field, upland, and woodland in the Karst region of Dacai, Huanjiang County, Guangxi Province, and the contents of their organic carbon (Oc ), total nitrogen (TN), microbial biomass carbon (Bc) , and microbial biomass nitrogen (BN) were determined. The results showed that the Oc and BN contents and soil pH value showed the trend of paddy field = woodland > upland, while TN and Bc contents had the trend of woodland > paddy field > upland. There was a significant positive correlation between Bc and Oc, and between B5 and TN. Soil microbial biomass C and N had rapid responses to the changes of land use type, which could be used as the sensitive biological indicators in evaluating soil quality and fertility in Karst region. PMID:17209378

  4. Permafrost carbon−climate feedback is sensitive to deep soil carbon decomposability but not deep soil nitrogen dynamics

    PubMed Central

    Koven, Charles D.; Lawrence, David M.; Riley, William J.

    2015-01-01

    Permafrost soils contain enormous amounts of organic carbon whose stability is contingent on remaining frozen. With future warming, these soils may release carbon to the atmosphere and act as a positive feedback to climate change. Significant uncertainty remains on the postthaw carbon dynamics of permafrost-affected ecosystems, in particular since most of the carbon resides at depth where decomposition dynamics may differ from surface soils, and since nitrogen mineralized by decomposition may enhance plant growth. Here we show, using a carbon−nitrogen model that includes permafrost processes forced in an unmitigated warming scenario, that the future carbon balance of the permafrost region is highly sensitive to the decomposability of deeper carbon, with the net balance ranging from 21 Pg C to 164 Pg C losses by 2300. Increased soil nitrogen mineralization reduces nutrient limitations, but the impact of deep nitrogen on the carbon budget is small due to enhanced nitrogen availability from warming surface soils and seasonal asynchrony between deeper nitrogen availability and plant nitrogen demands. Although nitrogen dynamics are highly uncertain, the future carbon balance of this region is projected to hinge more on the rate and extent of permafrost thaw and soil decomposition than on enhanced nitrogen availability for vegetation growth resulting from permafrost thaw. PMID:25775603

  5. Soil carbon and nitrogen turnover in a pine forest under elevated CO2

    NASA Astrophysics Data System (ADS)

    Lichter, J.; Reblin, J.; Kaubris, A.; Austin, R.; Anderson, J.; Wong, N.; Wu, S.

    2010-12-01

    During twelve years of atmospheric CO2 fumigation at the Duke Forest Free-air Enrichment (FACE) experiment, annual net primary productivity increased approximately 25% under the elevated CO2 treatment. A corresponding increase in litterfall resulted in accumulation of approximately 300 g m-2 more carbon under elevated CO2 than under ambient CO2 concentration in the organic soil horizon of this loblolly pine forest. The net accumulation of carbon in the organic horizon under the elevated CO2 treatment occurred entirely during the first six years of the experiment with little change thereafter. However, while carbon accumulated in the organic horizon under elevated CO2, there were no detectable changes in the carbon or nitrogen contents of the bulk mineral soil. To further examine soil carbon and nitrogen content and turnover in soil organic matter pools of different turnover rates, samples of the upper mineral soil (0-5 cm depth) were separated by density, particle size fractionation, and acid digestion. Although no changes in soil carbon and nitrogen content attributable to the elevated CO2 treatment were detected in any of the SOM fractions, change in the 13C content of soil fractions under elevated CO2 indicated incorporation of new organic matter into all SOM fractions at comparable rates. This result suggests that soil microbial community composition and decomposition have been altered by the increased nitrogen demand associated with the CO2-induced growth enhancement, allowing species that are competitive under conditions of intense nitrogen limitation to mine “recalcitrant” SOM pools for the additional nitrogen required to meet the enhanced demand.

  6. Photovoltaic devices based on high density boron-doped single-walled carbon nanotube/n-Si heterojunctions

    SciTech Connect

    Saini, Viney; Li, Zhongrui; Bourdo, Shawn; Kunets, Vasyl P.; Trigwell, Steven; Couraud, Arthur; Rioux, Julien; Boyer, Cyril; Nteziyaremye, Valens; Dervishi, Enkeleda; Biris, Alexandru R.; Salamo, Gregory J.; Viswanathan, Tito; Biris, Alexandru S.

    2011-01-13

    A simple and easily processible photovoltaic device has been developed based on borondoped single-walled carbon nanotubes (B-SWNTs) and n-type silicon (n-Si) heterojunctions. The single-walled carbon nanotubes (SWNTs) were substitutionally doped with boron atoms by thermal annealing, in the presence of B2O3. The samples used for these studies were characterized by Raman spectroscopy, thermal gravimetric analysis (TGA), transmission electron microscopy (TEM), and x-ray photoelectron spectroscopy (XPS). The fully functional solar cell devices were fabricated by airbrush deposition that generated uniform B-SWNT films on top of the n-Si substrates. The carbon nanotube films acted as exciton-generation sites, charge collection and transportation, while the heterojunctions formed between B-SWNTs and n-Si acted as charge dissociation centers. The current-voltage characteristics in the absence of light and under illumination, as well as optical transmittance spectrum are reported here. It should be noted that the device fabrication process can be made amenable to scalability by depositing direct and uniform films using airbrushing, inkjet printing, or spin-coating techniques.

  7. Photovoltaic devices based on high density boron-doped single-walled carbon nanotube/n-Si heterojunctions

    DOE PAGESBeta

    Saini, Viney; Li, Zhongrui; Bourdo, Shawn; Kunets, Vasyl P.; Trigwell, Steven; Couraud, Arthur; Rioux, Julien; Boyer, Cyril; Nteziyaremye, Valens; Dervishi, Enkeleda; et al

    2011-01-13

    A simple and easily processible photovoltaic device has been developed based on borondoped single-walled carbon nanotubes (B-SWNTs) and n-type silicon (n-Si) heterojunctions. The single-walled carbon nanotubes (SWNTs) were substitutionally doped with boron atoms by thermal annealing, in the presence of B2O3. The samples used for these studies were characterized by Raman spectroscopy, thermal gravimetric analysis (TGA), transmission electron microscopy (TEM), and x-ray photoelectron spectroscopy (XPS). The fully functional solar cell devices were fabricated by airbrush deposition that generated uniform B-SWNT films on top of the n-Si substrates. The carbon nanotube films acted as exciton-generation sites, charge collection and transportation, whilemore » the heterojunctions formed between B-SWNTs and n-Si acted as charge dissociation centers. The current-voltage characteristics in the absence of light and under illumination, as well as optical transmittance spectrum are reported here. It should be noted that the device fabrication process can be made amenable to scalability by depositing direct and uniform films using airbrushing, inkjet printing, or spin-coating techniques.« less

  8. Effect of nitrogen-containing groups on enhanced capacitive behaviors of multi-walled carbon nanotubes

    SciTech Connect

    Kim, Ji-Il; Park, Soo-Jin

    2011-08-15

    In this work, electrochemical properties of surface treated multi-walled carbon nanotubes (MWNTs) are studied in supercapacitors. Nitrogen and oxygen functional groups containing MWNTs are prepared by urea and acidic treatments, respectively. The surface properties of the MWNTs are confirmed by X-ray photoelectron spectroscopy (XPS) and zeta-potential measurements. The textural properties are characterized by N{sub 2} adsorption/desorption isotherm at 77 K using the BET eqaution, BJH method, and HK method. The electrochemical properties of the MWNTs are accumulated by cyclic voltammetry, impedance spectra, and charge-discharge cycling performance in 1 M H{sub 2}SO{sub 4} at room temperature. As a result, the functionalized MWNTs lead to an increase in capacitance as compared with pristine MWNTs. It suggests that the pyridinic and pyridinic-N-oxides nitrogen species have effects on the specific capacitance due to the positive charge, and thus an improved electron transfer at high current loads results, the most important functional groups affecting capacitive behaviors. - Graphical Abstract: The N{sub 1s} spectra of nitrogen functionalized multi-walled carbon nanotubes are measured by X-ray photoelectron spectroscopy. Highlights: > Facile method of increasing elemental composition of nitrogen functional groups on carbon materials. > Increased specific capacitance multi-walled carbon nanotubes (MWNTs) for electrode materials as high as general chemical activation process. > Enhanced capacitive behaviors via introducing pyridinic and pyridinic-N-oxides nitrogen species onto the MWNTs. > Improvement of electron transfer at high current loads.

  9. Effect of carbon dioxide and nitrogen on the diffusivity of methane confined in nano-porous carbon aerogel

    SciTech Connect

    Mavila Chathoth, Suresh; He, Lilin; Mamontov, Eugene; Melnichenko, Yuri B

    2012-01-01

    The microscopic diffusivity of methane (CH{sub 4}) confined in nano-porous carbon aerogel was investigated as a function of added carbon dioxide (CO{sub 2}) and nitrogen (N{sub 2}) pressure using quasi-elastic neutron scattering (QENS). In the range of the external pressure of 1-2.5 MPa, the self-diffusivity of methane was found to increase with CO{sub 2} pressure and remain practically unchanged in the N{sub 2} environment. Increasing mobility of methane with CO{sub 2} pressure suggests that the adsorbed CH4 molecules become gradually replaced by CO{sub 2} on the surface of carbon aerogel pores, whereas the presence of N{sub 2} does not induce the replacement. The molecular mobility of the methane, with or without added carbon dioxide and nitrogen, is described by the unrestricted diffusion model, which is characteristic of methane compressed in small pores. On the other hand, both nitrogen and carbon dioxide molecules in carbon aerogel, when studied alone, with no methane present, follow a jump diffusion process, characteristic of the molecular mobility in the densified adsorbed layers on the surface of the aerogel pores.

  10. Benthic biogeochemical cycling, nutrient stoichiometry, and carbon and nitrogen mass balances in a eutrophic freshwater bay

    USGS Publications Warehouse

    Klump, J.V.; Fitzgerald, S.A.; Waplesa, J.T.

    2009-01-01

    Green Bay, while representing only ,7% of the surface area and ??1.4% of the volume of Lake Michigan, contains one-third of the watershed of the lake, and receives approximately one-third of the total nutrient loading to the Lake Michigan basin, largely from the Fox River at the southern end of the bay. With a history of eutrophic conditions dating back nearly a century, the southern portion of the bay behaves as an efficient nutrient and sediment trap, sequestering much of the annual carbon and nitrogen input within sediments accumulating at up to 1 cm per year. Depositional fluxes of organic matter varied from ??0.1 mol C m-2 yr-1 to >10 mol C m-2 yr-1 and were both fairly uniform in stoichiometric composition and relatively labile. Estimates of benthic recycling derived from pore-water concentration gradients, whole-sediment incubation experiments, and deposition-burial models of early diagenesis yielded an estimated 40% of the carbon and 50% of the nitrogen recycled back into the overlying water. Remineralization was relatively rapid with ??50% of the carbon remineralized within <15 yr of deposition, and a mean residence time for metabolizable carbon and nitrogen in the sediments of 20 yr. On average, organic carbon regeneration occurred as 75% CO2, 15% CH4, and 10% dissolved organic carbon (DOC). Carbon and nitrogen budgets for the southern bay were based upon direct measurements of inputs and burial and upon estimates of export and production derived stoichiometrically from a coupled phosphorus budget. Loadings of organic carbon from rivers were ??3.7 mol m-2 yr-1, 80% in the form of DOC and 20% as particulate organic carbon. These inputs were lost through export to northern Green Bay and Lake Michigan (39%), through sediment burial (26%), and net CO2 release to the atmosphere (35%). Total carbon input, including new production, was 4.54 mol m-2 C yr-1, equivalent to ??10% of the gross annual primary production. Nitrogen budget terms were less well quantified

  11. Angular distribution of photoelectrons from atomic oxygen, nitrogen and carbon. [in upper atmosphere

    NASA Technical Reports Server (NTRS)

    Manson, S. J.; Kennedy, D. J.; Starace, A. F.; Dill, D.

    1974-01-01

    The angular distributions of photoelectrons from atomic oxygen, nitrogen, and carbon are calculated. Both Hartree-Fock and Hartree-Slater (Herman-Skillman) wave functions are used for oxygen, and the agreement is excellent; thus only Hartree-Slater functions are used for carbon and nitrogen. The pitch-angle distribution of photoelectrons is discussed, and it is shown that previous approximations of energy-independent isotropic or sin squared theta distributions are at odds with the authors' results, which vary with energy. This variation with energy is discussed, as is the reliability of these calculations.

  12. Performance and recent improvement in microbial fuel cells for simultaneous carbon and nitrogen removal: A review.

    PubMed

    Sun, Haishu; Xu, Shengjun; Zhuang, Guoqiang; Zhuang, Xuliang

    2016-01-01

    Microbial fuel cells (MFCs) have become a promising technology for wastewater treatment accompanying electricity generation. Carbon and nitrogen removal can be achieved by utilizing the electron transfer between the anode and cathode in an MFC. However, large-scale power production and high removal efficiency must be achieved at a low cost to make MFCs practical and economically competitive in the future. This article reviews the principles, feasibility and bottlenecks of MFCs for simultaneous carbon and nitrogen removal, the recent advances and prospective strategies for performance improvement, as well as the involved microbes and electron transfer mechanisms. PMID:26899662

  13. The Modification of Polyurethane Foams Using New Boroorganic Polyols (II) Polyurethane Foams from Boron-Modified Hydroxypropyl Urea Derivatives

    PubMed Central

    2014-01-01

    The work focuses on research related to determination of application possibility of new, ecofriendly boroorganic polyols in rigid polyurethane foams production. Polyols were obtained from hydroxypropyl urea derivatives esterified with boric acid and propylene carbonate. The influence of esterification type on properties of polyols and next on polyurethane foams properties was determined. Nitrogen and boron impacts on the foams' properties were discussed, for instance, on their physical, mechanical, and electric properties. Boron presence causes improvement of dimensional stability and thermal stability of polyurethane foams. They can be applied even at temperature 150°C. Unfortunately, introducing boron in polyurethanes foams affects deterioration of their water absorption, which increases as compared to the foams that do not contain boron. However, presence of both boron and nitrogen determines the decrease of the foams combustibility. Main impact on the decrease combustibility of the obtained foams has nitrogen presence, but in case of proper boron and nitrogen ratio their synergic activity on the combustibility decrease can be easily seen. PMID:24587721

  14. The modification of polyurethane foams using new boroorganic polyols (II) polyurethane foams from boron-modified hydroxypropyl urea derivatives.

    PubMed

    Zarzyka, Iwona

    2014-01-01

    The work focuses on research related to determination of application possibility of new, ecofriendly boroorganic polyols in rigid polyurethane foams production. Polyols were obtained from hydroxypropyl urea derivatives esterified with boric acid and propylene carbonate. The influence of esterification type on properties of polyols and next on polyurethane foams properties was determined. Nitrogen and boron impacts on the foams' properties were discussed, for instance, on their physical, mechanical, and electric properties. Boron presence causes improvement of dimensional stability and thermal stability of polyurethane foams. They can be applied even at temperature 150 °C. Unfortunately, introducing boron in polyurethanes foams affects deterioration of their water absorption, which increases as compared to the foams that do not contain boron. However, presence of both boron and nitrogen determines the decrease of the foams combustibility. Main impact on the decrease combustibility of the obtained foams has nitrogen presence, but in case of proper boron and nitrogen ratio their synergic activity on the combustibility decrease can be easily seen. PMID:24587721

  15. Stocks of carbon and nitrogen and partitioning between above- and belowground pools in the Brazilian coastal Atlantic Forest elevation range

    PubMed Central

    Vieira, Simone A; Alves, Luciana F; Duarte-Neto, Paulo J; Martins, Susian C; Veiga, Larissa G; Scaranello, Marcos A; Picollo, Marisa C; Camargo, Plinio B; do Carmo, Janaina B; Neto, Eráclito Sousa; Santos, Flavio A M; Joly, Carlos A; Martinelli, Luiz A

    2011-01-01

    We estimated carbon and nitrogen stocks in aboveground biomass (AGB) and belowground biomass (BGB) along an elevation range in forest sites located on the steep slopes of the Serra do Mar on the north coast of the State of São Paulo, southeast Brazil. In elevations of 100 m (lowland), 400 m (submontane), and 1000 m (montane) four 1-ha plots were established, and above- (live and dead) and belowground (live and dead) biomass were determined. Carbon and nitrogen concentrations in each compartment were determined and used to convert biomass into carbon and nitrogen stocks. The carbon aboveground stock (CAGB) varied along the elevation range from approximately 110 to 150 Mg·ha−1, and nitrogen aboveground stock (NAGB), varied from approximately 1.0 to 1.9 Mg·ha−1. The carbon belowground stock (CBGB) and the nitrogen belowground stock (NBGB) were significantly higher than the AGB and varied along the elevation range from approximately 200–300 Mg·ha−1, and from 14 to 20 Mg·ha−1, respectively. Finally, the total carbon stock (CTOTAL) varied from approximately 320 to 460 Mg·ha−1, and the nitrogen total stock (NTOTAL) from approximately 15 to 22 Mg·ha−1. Most of the carbon and nitrogen stocks were found belowground and not aboveground as normally found in lowland tropical forests. The above- and belowground stocks, and consequently, the total stocks of carbon and nitrogen increased significantly with elevation. As the soil and air temperature also decreased significantly with elevation, we found a significantly inverse relationship between carbon and nitrogen stocks and temperature. Using this inverse relationship, we made a first approach estimate that an increase of 1°C in soil temperature would decrease the carbon and nitrogen stocks in approximately 17 Mg·ha−1 and 1 Mg·ha−1 of carbon and nitrogen, respectively. PMID:22393511

  16. Synthesis of nitrogen-containing carbon by solution plasma in aniline with high-repetition frequency discharges

    NASA Astrophysics Data System (ADS)

    Hyun, Koangyong; Ueno, Tomonaga; Saito, Nagahiro

    2016-01-01

    Nitrogen-containing carbon nanoparticles were synthesized in aniline by solution plasma with high-repetition frequency discharges. We developed a bipolar pulsed power supply that can apply high-repetition frequencies ranging from 25 to 200 kHz. By utilizing high-repetition frequencies, conductive carbons were directly synthesized. The crystallinity was increased and H/C ratio of carbon was decreased. Furthermore, nitrogen atoms were simultaneously embedded in the carbon matrix. Due to the presence of nitrogen atoms, the conductivity and electrocatalytic activity of the samples were remarkably improved compared to that of a pure carbon matrix synthesized from a benzene precursor.

  17. Nitrogen removal from coal gasification wastewater by activated carbon technologies combined with short-cut nitrogen removal process.

    PubMed

    Zhao, Qian; Han, Hongjun; Hou, Baolin; Zhuang, Haifeng; Jia, Shengyong; Fang, Fang

    2014-11-01

    A system combining granular activated carbon and powdered activated carbon technologies along with shortcut biological nitrogen removal (GAC-PACT-SBNR) was developed to enhance total nitrogen (TN) removal for anaerobically treated coal gasification wastewater with less need for external carbon resources. The TN removal efficiency in SBNR was significantly improved by introducing the effluent from the GAC process into SBNR during the anoxic stage, with removal percentage increasing from 43.8%-49.6% to 68.8%-75.8%. However, the TN removal rate decreased with the progressive deterioration of GAC adsorption. After adding activated sludge to the GAC compartment, the granular carbon had a longer service-life and the demand for external carbon resources became lower. Eventually, the TN removal rate in SBNR was almost constant at approx. 43.3%, as compared to approx. 20.0% before seeding with sludge. In addition, the production of some alkalinity during the denitrification resulted in a net savings in alkalinity requirements for the nitrification reaction and refractory chemical oxygen demand (COD) degradation by autotrophic bacteria in SBNR under oxic conditions. PACT showed excellent resilience to increasing organic loadings. The microbial community analysis revealed that the PACT had a greater variety of bacterial taxons and the dominant species associated with the three compartments were in good agreement with the removal of typical pollutants. The study demonstrated that pre-adsorption by the GAC-sludge process could be a technically and economically feasible method to enhance TN removal in coal gasification wastewater (CGW). PMID:25458677

  18. Tungsten nitride nanocrystals on nitrogen-doped carbon black as efficient electrocatalysts for oxygen reduction reactions.

    PubMed

    Dong, Youzhen; Li, Jinghong

    2015-01-11

    The direct synthesis of tungsten nitride (WN) nanoparticles on nitrogen-doped carbon black (N-carbon black) was achieved through facile nucleation and growth of WN nanoparticles on simultaneously generated N-carbon black under ammonia annealing. As a noble-metal-free catalyst, the WN/N-carbon black hybrid exhibited excellent performance in ORR, coupled with superior methanol tolerance and long-term stability in comparison to commercial Pt/C catalysts, through an efficient four-electron-dominant ORR process. PMID:25413157

  19. The Role of Hyporheic Zones in Cycling of Carbon and Nitrogen

    NASA Astrophysics Data System (ADS)

    Dwivedi, D.; Steefel, C. I.; Arora, B.; Bisht, G.; Williams, K. H.

    2015-12-01

    Hyporheic zones impact the biogeochemical cycling of carbon and nitrogen, both organic and inorganic. To investigate and develop a predictive understanding of the coupled carbon and nitrogen cycling in the subsurface, we integrated a genome inspired complex reaction network with a high-resolution, three-dimensional, reactive flow and transport code - PFLOTRAN. Three-dimensional reactive flow and transport simulations were performed, making use of the high performance computing platform provided by PFLOTRAN, to describe the biogeochemical zonation developed because of the organic carbon rich sediments and a gradient of dissolved oxygen and pH within the hyporheic zone. We conducted this study in the lower East River, a high elevation catchment in southwestern Colorado. The lower East River site displays a rolling-to-mountainous topography with multiple river meanders that extend over a distance of 11 km. We carried out simulations within two stream meanders to examine (1) the impact of hyporheic exchanges on the biogeochemical zonation of variables and (2) how carbon and nitrogen fluxes at the meander scale influence coupled carbon and nitrogen cycling at the river scale. Three-dimensional model domain - 330 m (X) by 400 m (Y) by 48 m (Z) - was uniformly discretized with 10 m horizontal (X and Y) and 0.25 m vertical (Z) resolutions using structured grids in PFLOTRAN. Simulation results show that the intra-meander hyporheic flow paths and biogeochemical reactions result in the lateral redox zonation, which considerably impact the carbon and nitrogen fluxes into the stream system. The meander-driven hyporheic flow paths enhance the denitrification because of relatively longer residence times in the organic carbon-rich sediments.

  20. Isotopic composition of carbon and nitrogen in ureilitic fragments of the Almahata Sitta meteorite

    NASA Astrophysics Data System (ADS)

    Downes, H.; Abernethy, F. A. J.; Smith, C. L.; Ross, A. J.; Verchovsky, A. B.; Grady, M. M.; Jenniskens, P.; Shaddad, M. H.

    2015-02-01

    This study characterizes carbon and nitrogen abundances and isotopic compositions in ureilitic fragments of Almahata Sitta. Ureilites are carbon-rich (containing up to 7 wt% C) and were formed early in solar system history, thus the origin of carbon in ureilites has significance for the origin of solar system carbon. These samples were collected soon after they fell, so they are among the freshest ureilite samples available and were analyzed using stepped combustion mass spectrometry. They contained 1.2-2.3 wt% carbon; most showed the major carbon release at temperatures of 600-700 °C with peak values of δ13C from -7.3 to +0.4‰, similar to literature values for unbrecciated ("monomict") ureilites. They also contained a minor low temperature (≤500 °C) component (δ13C = ca -25‰). Bulk nitrogen contents (9.4-27 ppm) resemble those of unbrecciated ureilites, with major releases mostly occurring at 600-750 °C. A significant lower temperature release of nitrogen occurred in all samples. Main release δ15N values of -53 to -94‰ fall within the range reported for diamond separates and acid residues from ureilites, and identify an isotopically primordial nitrogen component. However, they differ from common polymict ureilites which are more nitrogen-rich and isotopically heavier. Thus, although the parent asteroid 2008TC3 was undoubtedly a polymict ureilite breccia, this cannot be deduced from an isotopic study of individual ureilite fragments. The combined main release δ13C and δ15N values do not overlap the fields for carbonaceous or enstatite chondrites, suggesting that carbon in ureilites was not derived from these sources.

  1. ZIF-Derived Nitrogen-Doped Porous Carbons for Xe Adsorption and Separation

    PubMed Central

    Zhong, Shan; Wang, Qian; Cao, Dapeng

    2016-01-01

    Currently, finding high capacity adsorbents with large selectivity to capture Xe is still a great challenge. In this work, nitrogen-doped porous carbons were prepared by programmable temperature carbonization of zeolitic imidazolate framework-8 (ZIF-8) and ZIF-8/xylitol composite precursors and the resultant samples are marked as Carbon-Z and Carbon-ZX, respectively. Further adsorption measurements indicate that ZIF-derived nitrogen-doped Carbon-ZX exhibits extremely high Xe capacity of 4.42 mmol g−1 at 298 K and 1 bar, which is higher than almost all other pristine MOFs such as CuBTC, Ni/DOBDC, MOF-5 and Al-MIL-53, and even more than three times of the matrix ZIF-8 at similar conditions. Moreover, Carbon-ZX also shows the highest Xe/N2 selectivity about ~120, which is much larger than all other reported MOFs. These remarkable features illustrate that ZIF-derived nitrogen-doped porous carbon is an excellent adsorbent for Xe adsorption and separation at room temperature. PMID:26883471

  2. Nanostructured nitrogen-doped mesoporous carbon derived from polyacrylonitrile for advanced lithium sulfur batteries

    NASA Astrophysics Data System (ADS)

    Liu, Ying; Zhao, Xiaohui; Chauhan, Ghanshyam S.; Ahn, Jou-Hyeon

    2016-09-01

    Nitrogen doping in carbon matrix can effectively improve the wettability of electrolyte and increase electric conductivity of carbon by ensuring fast transfer of ions. We synthesized a series of nitrogen-doped mesoporous carbons (CPANs) via in situ polymerization of polyacrylonitrile (PAN) in SBA-15 template followed by carbonization at different temperatures. Carbonization results in the formation of ladder structure which enhances the stability of the matrix. In this study, CPAN-800, carbon matrix synthesized by the carbonization at 800 °C, was found to possess many desirable properties such as high specific surface area and pore volume, moderate nitrogen content, and highly ordered mesoporous structure. Therefore, it was used to prepare S/CPAN-800 composite as cathode material in lithium sulfur (Li-S) batteries. The S/CPAN-800 composite was proved to be an excellent material for Li-S cells which delivered a high initial discharge capacity of 1585 mAh g-1 and enhanced capacity retention of 862 mAh g-1 at 0.1 C after 100 cycles.

  3. ZIF-Derived Nitrogen-Doped Porous Carbons for Xe Adsorption and Separation.

    PubMed

    Zhong, Shan; Wang, Qian; Cao, Dapeng

    2016-01-01

    Currently, finding high capacity adsorbents with large selectivity to capture Xe is still a great challenge. In this work, nitrogen-doped porous carbons were prepared by programmable temperature carbonization of zeolitic imidazolate framework-8 (ZIF-8) and ZIF-8/xylitol composite precursors and the resultant samples are marked as Carbon-Z and Carbon-ZX, respectively. Further adsorption measurements indicate that ZIF-derived nitrogen-doped Carbon-ZX exhibits extremely high Xe capacity of 4.42 mmol g(-1) at 298 K and 1 bar, which is higher than almost all other pristine MOFs such as CuBTC, Ni/DOBDC, MOF-5 and Al-MIL-53, and even more than three times of the matrix ZIF-8 at similar conditions. Moreover, Carbon-ZX also shows the highest Xe/N2 selectivity about ~120, which is much larger than all other reported MOFs. These remarkable features illustrate that ZIF-derived nitrogen-doped porous carbon is an excellent adsorbent for Xe adsorption and separation at room temperature. PMID:26883471

  4. ZIF-Derived Nitrogen-Doped Porous Carbons for Xe Adsorption and Separation

    NASA Astrophysics Data System (ADS)

    Zhong, Shan; Wang, Qian; Cao, Dapeng

    2016-02-01

    Currently, finding high capacity adsorbents with large selectivity to capture Xe is still a great challenge. In this work, nitrogen-doped porous carbons were prepared by programmable temperature carbonization of zeolitic imidazolate framework-8 (ZIF-8) and ZIF-8/xylitol composite precursors and the resultant samples are marked as Carbon-Z and Carbon-ZX, respectively. Further adsorption measurements indicate that ZIF-derived nitrogen-doped Carbon-ZX exhibits extremely high Xe capacity of 4.42 mmol g-1 at 298 K and 1 bar, which is higher than almost all other pristine MOFs such as CuBTC, Ni/DOBDC, MOF-5 and Al-MIL-53, and even more than three times of the matrix ZIF-8 at similar conditions. Moreover, Carbon-ZX also shows the highest Xe/N2 selectivity about ~120, which is much larger than all other reported MOFs. These remarkable features illustrate that ZIF-derived nitrogen-doped porous carbon is an excellent adsorbent for Xe adsorption and separation at room temperature.

  5. Concentrations and isotope ratios of carbon, nitrogen and sulfur in ocean-floor basalts

    USGS Publications Warehouse

    Sakai, H.; Marais, D.J.D.; Ueda, A.; Moore, J.G.

    1984-01-01

    Fresh submarine basalt glasses from Galapagos Ridge, FAMOUS area, Cayman Trough and Kilauea east rift contain 22 to 160 ppm carbon and 0.3 to 2.8 ppm nitrogen, respectively, as the sums of dissolved species and vesicle-filling gases (CO2 and N2). The large range of variation in carbon content is due to combined effect of depth-dependency of the solubility of carbon in basalt melt and varying extents of vapour loss during magma emplacement as well as in sample crushing. The isotopic ratios of indigenous carbon and nitrogen are in very narrow ranges,-6.2 ?? 0.2% relative to PDB and +0.2 ?? 0.6 %. relative to atmospheric nitrogen, respectively. In basalt samples from Juan de Fuca Ridge, however, isotopically light carbon (??13C = around -24%.) predominates over the indigenous carbon; no indigenous heavy carbon was found. Except for Galapagos Ridge samples, these ocean-floor basalts contain 670 to 1100 ppm sulfur, averaging 810 ppm, in the form of both sulfide and sulfate, whereas basalts from Galapagos Ridge are higher in both sulfur (1490 and 1570 ppm) and iron (11.08% total iron as FeO). The ??34S values average +0.3 ?? 0.5%. with average fractionation factor between sulfate and sulfide of +7.4 ?? 1.6%.. The sulfate/sulfide ratios tend to increase with increasing water content of basalt, probably because the oxygen fugacity increases with increasing water content in basalt melt. ?? 1984.

  6. Physiology and gene expression profiles of Dekkera bruxellensis in response to carbon and nitrogen availability.

    PubMed

    de Barros Pita, Will; Silva, Denise Castro; Simões, Diogo Ardaillon; Passoth, Volkmar; de Morais, Marcos Antonio

    2013-11-01

    The assimilation of nitrate, a nitrogenous compound, was previously described as an important factor favoring Dekkera bruxellensis in the competition with Saccharomyces cerevisiae for the industrial sugarcane substrate. In this substrate, nitrogen sources are limited and diverse, and a recent report showed that amino acids enable D. bruxellensis to grow anaerobically. Thus, understanding the regulation of nitrogen metabolism is one fundamental aspect to comprehend the competiveness of D. bruxellensis in the fermentation environment. In the present study, we evaluated the physiological and transcriptional profiles of D. bruxellensis in response to different carbon and nitrogen supplies to determine their influence on growth, sugar consumption, and ethanol production. Besides, the expression of genes coding for nitrogen permeases and enzymes involved in the biosynthesis of glutamate and energetic metabolism were investigated under these conditions. Our data revealed that genes related to nitrogen uptake in D. bruxellensis are under the control of nitrogen catabolite repression. Moreover, we provide indications that glutamate dehydrogenase and glutamate synthase may switch roles as the major pathway for glutamate biosynthesis in D. bruxellensis. Finally, our data showed that in nonoptimal growth conditions, D. bruxellensis leans toward the respiratory metabolism. The results presented herein show that D. bruxellensis and S. cerevisiae share similar regulation of GDH–GOGAT pathway, while D. bruxellensis converts less glucose to ethanol than S. cerevisiae do when nitrogen is limited. The consequence of this particularity to the industrial process is discussed. PMID:23959165

  7. Utilization of recovered nitrogen from hydrothermal carbonization process by Arthrospira platensis.

    PubMed

    Yao, Changhong; Pan, Yanfei; Lu, Hongbin; Wu, Peichun; Meng, Yingying; Cao, Xupeng; Xue, Song

    2016-07-01

    In the context of sustainable cultivation of microalgae, the present study focused on the use of nitrogen from the hot-water extracted biomass residue of Arthrospira platensis by hydrothermal carbonization (HTC) and the sequential cultivation of the same alga with the HTC aqueous phase (AP). Nearly 90% of the nitrogen recovered from HTC into AP was in the organic form. Under nitrogen-limited condition with HTCAP as nitrogen source the yield and content of carbohydrate were enhanced by 21% and 15% respectively compared with that under the same nitrogen level provided by NaNO3, which entitled HTCAP for the substitution of conventional nitrate. In the same way pilot-scale cultivation of A. platensis in raceway ponds outdoors demonstrated that carbohydrate content of 43.8% DW and productivity of 10.3g/m(2)/d was achieved. Notably 54% of organic nitrogen in the HTCAP could be recycled by cultivation of pre-nitrogen starved A. platensis as seeds under nitrogen limitation. PMID:27070286

  8. A Natural Light/Dark Cycle Regulation of Carbon-Nitrogen Metabolism and Gene Expression in Rice Shoots.

    PubMed

    Li, Haixing; Liang, Zhijun; Ding, Guangda; Shi, Lei; Xu, Fangsen; Cai, Hongmei

    2016-01-01

    Light and temperature are two particularly important environmental cues for plant survival. Carbon and nitrogen are two essential macronutrients required for plant growth and development, and cellular carbon and nitrogen metabolism must be tightly coordinated. In order to understand how the natural light/dark cycle regulates carbon and nitrogen metabolism in rice plants, we analyzed the photosynthesis, key carbon-nitrogen metabolites, and enzyme activities, and differentially expressed genes and miRNAs involved in the carbon and nitrogen metabolic pathway in rice shoots at the following times: 2:00, 6:00, 10:00, 14:00, 18:00, and 22:00. Our results indicated that more CO2 was fixed into carbohydrates by a high net photosynthetic rate, respiratory rate, and stomatal conductance in the daytime. Although high levels of the nitrate reductase activity, free ammonium and carbohydrates were exhibited in the daytime, the protein synthesis was not significantly facilitated by the light and temperature. In mRNA sequencing, the carbon and nitrogen metabolism-related differentially expressed genes were obtained, which could be divided into eight groups: photosynthesis, TCA cycle, sugar transport, sugar metabolism, nitrogen transport, nitrogen reduction, amino acid metabolism, and nitrogen regulation. Additionally, a total of 78,306 alternative splicing events have been identified, which primarily belong to alternative 5' donor sites, alternative 3' acceptor sites, intron retention, and exon skipping. In sRNA sequencing, four carbon and nitrogen metabolism-related miRNAs (osa-miR1440b, osa-miR2876-5p, osa-miR1877 and osa-miR5799) were determined to be regulated by natural light/dark cycle. The expression level analysis showed that the four carbon and nitrogen metabolism-related miRNAs negatively regulated their target genes. These results may provide a good strategy to study how natural light/dark cycle regulates carbon and nitrogen metabolism to ensure plant growth and

  9. Carbon sequestration and Jerusalem artichoke biomass under nitrogen applications in coastal saline zone in the northern region of Jiangsu, China.

    PubMed

    Niu, Li; Manxia, Chen; Xiumei, Gao; Xiaohua, Long; Hongbo, Shao; Zhaopu, Liu; Zed, Rengel

    2016-10-15

    Agriculture is an important source of greenhouse gases, but can also be a significant sink. Nitrogen fertilization is effective in increasing agricultural production and carbon storage. We explored the effects of different rates of nitrogen fertilization on biomass, carbon density, and carbon sequestration in fields under the cultivation of Jerusalem artichoke as well as in soil in a coastal saline zone for two years. Five nitrogen fertilization rates were tested (in guream(-2)): 4 (N1), 8 (N2), 12 (N3), 16 (N4), and 0 (control, CK). The biomass of different organs of Jerusalem artichoke during the growth cycle was significantly higher in N2 than the other treatments. Under different nitrogen treatments, carbon density in organs of Jerusalem artichoke ranged from 336 to 419gCkg(-1). Carbon sequestration in Jerusalem artichoke was higher in treatments with nitrogen fertilization compared to the CK treatment. The highest carbon sequestration was found in the N2 treatment. Soil carbon content was higher in the 0-10cm than 10-20cm layer, with nitrogen fertilization increasing carbon content in both soil layers. The highest soil carbon sequestration was measured in the N2 treatment. Carbon sequestration in both soil and Jerusalem artichoke residue was increased by nitrogen fertilization depending on the rates in the coastal saline zone studied. PMID:27317133

  10. Nitrogen-boron coordination versus OH∙∙∙N hydrogen bonding in pyridoxaboroles - aza analogues of benzoxaboroles.

    PubMed

    Steciuk, I; Durka, K; Gontarczyk, K; Dąbrowski, M; Luliński, S; Woźniak, K

    2015-10-01

    Pyridoxaboroles - fused heterocyclic systems composed of pyridine and five-membered oxaborole rings - have been obtained for the first time from simple halopyridines. Thus, 6-butyl-2-(3'-bromo-4'-pyridyl)-(N-B)-1,3,6,2-dioxazaborocan obtained from 3-bromopyridine was converted into a lithio derivative by Br/Li exchange using nBuLi/THF at -85 °C. This intermediate was trapped with benzaldehydes to give the corresponding pyridoxaboroles after hydrolysis. The use of chlorodiphenylsilane as an electrophile gave rise to a related pyridosiloxaborole. The fluorinated pyridoxaborole was obtained by deprotonation of α-(2-methoxyphenyl)-2-fluoro-4-iodopyridylmethanol with NaH and consecutive iodine-lithium exchange/boronation followed by hydrolysis. Single-crystal X-ray analysis of pyridino[4,3-c]-1,3-dihydro-1-hydroxy-3-mesityl[2,1]oxaborole revealed the formation of a unique 1D coordination polymer based on N-B dative bonds between monomeric molecules. In contrast, the crystal structure of 2-fluoropyridino[4,3-c]-1,3-dihydro-1-hydroxy-3-(2'-methoxyphenyl)[2,1]oxaborole features an infinite H-bonded chain as the main structural motif. The presented considerations are quantified in terms of various computational methods (single molecule and dimer energy calculations, electron density topology, NBO analyses) providing a comprehensive picture of the structural properties of pyridoxaboroles. PMID:26328873

  11. Boron- and Nitrogen-Doped Phenalenyls: Unexpected 2e/ and 4e/all-sites pi-pi Covalency and Genuine Pancake Double Bonding

    DOE PAGESBeta

    Tian, Yong-Hui; Huang, Jingsong; Sumpter, Bobby G

    2015-01-01

    Phenalenyl is an important neutral pi-radical due to its capability to form unconventional pancake pi-pi bonding interactions, whereas its analogues with graphitic boron (B) or nitrogen (N)-doping have been regarded as closed-shell systems and therefore received much less attention. By using high-level quantum chemistry calculations, we show that the B- and N-doped closed-shell phenalenyls unexpectedly form open-shell singlet pi-dimers with diradicaloid character featuring 2e/all-sites double pi-pi bonding. Moreover, by proper substitutions, the doped phenalenyl derivatives can be made open-shell species that form closed shell singlet pi-dimers bound by stronger 4e/all-sites double pi-pi bonding. The covalent pi-pi bonding overlap is distributedmore » on all of the atomic sites giving robust and genuine pancake-shaped pi-dimers which, depending on the number of electrons available in the bonding interactions, are equally or more stable than the pi-dimers of the pristine phenalenyl.« less

  12. Isomers and Conformers of H(NH₂BH₂)(n)H Oligomers: Understanding the Geometries and Electronic Structure of Boron-Nitrogen-Hydrogen Compounds as Potential Hydrogen Storage Materials

    SciTech Connect

    Li, Jun; Kathmann, Shawn M.; Schenter, Gregory K.; Gutowski, Maciej S.

    2007-02-07

    Boron-nitrogen-hydrogen (BNHx) materials are polar analogs of hydrocarbons with potential applications as media for hydrogen storage. As H(NH₂BH₂)nH oligomers result from dehydrogenation of NH₃BH₃ and NH₄BH₄ materials, understanding the geometries, stabilities, and electronic structure of these oligomers is essential for developing chemical methods of hydrogen release and regeneration of the BNHx-based hydrogen storage materials. In this work we have performed computational modeling on the H(NH₂BH₂)nH (n = 1 – 6) oligomers using density functional theory (DFT). We have investigated linear chain structures and the stabilizing effects of coiling, biradicalization, and branching through Car-Parrinello molecular dynamics simulations and geometry optimizations. We find that the zig-zag linear oligomers are unstable with respect to the coiled, square-wave chain, and branched structures, with the coiled structures being the most stable. Dihydrogen bonding in oligomers, where protic Hδ⁺(N) hydrogens interact with hydridic Hδ⁻(B) hydrogens, plays a crucial role in stabilizing different isomers and conformers. The results are consistent with structures of products that are seen in experimental NMR studies of dehydrogenated ammonia borane.

  13. Pancake π–π Bonding Goes Double: Unexpected 4e/All-Sites Bonding in Boron- and Nitrogen-Doped Phenalenyls

    SciTech Connect

    Tian, Yong-Hui; Sumpter, Bobby G.; Du, Shiyu; Huang, Jingsong

    2015-06-03

    Phenalenyl is an important neutral pi-radical due to its capability to form unconventional pancake pi-pi bonding interactions, whereas its analogues with graphitic boron (B) or nitrogen (N)-doping have been regarded as closed-shell systems and therefore received much less attention. By using high-level quantum chemistry calculations, we also show that the B- and N-doped closed-shell phenalenyls unexpectedly form open-shell singlet pi-dimers with diradicaloid character featuring 2e/all-sites double pi-pi bonding. Moreover, by proper substitutions, the doped phenalenyl derivatives can be made open-shell species that form closed shell singlet pi-dimers bound by stronger 4e/all-sites double pi-pi bonding. Moreover, covalent pi-pi bonding overlap is distributed on all of the atomic sites giving robust and genuine pancake-shaped pi-dimers which, depending on the number of electrons available in the bonding interactions, are equally or more stable than the pi-dimers of the pristine phenalenyl.

  14. Pancake π–π Bonding Goes Double: Unexpected 4e/All-Sites Bonding in Boron- and Nitrogen-Doped Phenalenyls

    DOE PAGESBeta

    Tian, Yong-Hui; Sumpter, Bobby G.; Du, Shiyu; Huang, Jingsong

    2015-06-03

    Phenalenyl is an important neutral pi-radical due to its capability to form unconventional pancake pi-pi bonding interactions, whereas its analogues with graphitic boron (B) or nitrogen (N)-doping have been regarded as closed-shell systems and therefore received much less attention. By using high-level quantum chemistry calculations, we also show that the B- and N-doped closed-shell phenalenyls unexpectedly form open-shell singlet pi-dimers with diradicaloid character featuring 2e/all-sites double pi-pi bonding. Moreover, by proper substitutions, the doped phenalenyl derivatives can be made open-shell species that form closed shell singlet pi-dimers bound by stronger 4e/all-sites double pi-pi bonding. Moreover, covalent pi-pi bonding overlap ismore » distributed on all of the atomic sites giving robust and genuine pancake-shaped pi-dimers which, depending on the number of electrons available in the bonding interactions, are equally or more stable than the pi-dimers of the pristine phenalenyl.« less

  15. Adsorption of carbon monoxide on boroxol-ring-doped zigzag boron nitride nanotube: Electronic study via DFT

    NASA Astrophysics Data System (ADS)

    Zahedi, Ehsan; Yari, Maryam; Bahmanpour, Hooman

    2016-04-01

    Previous works have already demonstrated that reactivity and sensitivity of boron nitride nanotubes (BNNTs) toward gas molecules can be modified by impurity. In this work, three nitrogen atoms of BNNT (7,0) are replaced with oxygen to study the adsorption of CO molecule through the surface of boroxol ring with different adsorption patterns, including side-on and end-on. All calculations have been done using the DFT-B3LYP/6-31G * level of theory, and their electronic energies are corrected by gCP and D3 correction terms. The calculated binding energies are large, which indicates that CO molecule undergoes chemical adsorption. NBO results showed that the charge transfer occurs from the tube to the gas molecule, which can slightly change the electronic properties of the tube. Density of state (DOS) and partial DOS (PDOS) analysis revealed that adsorption of CO molecule on the boroxol ring position is covalent in nature. The Laplacian of electron density, Lagrangian kinetic energy density, Hamiltonian kinetic energy density, and potential energy density at bond critical points between the tube and CO indicate that the interaction between the tube and CO molecule is covalent in nature. Topological analysis of the electron localization function shows that electrons in the new formed bonds are approximately localized, meaning that the nature of the adsorption process is chemical covalent.

  16. 40 CFR 60.45Da - Alternative standards for combined nitrogen oxides (NOX) and carbon monoxide (CO).

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... nitrogen oxides (NOX) and carbon monoxide (CO). 60.45Da Section 60.45Da Protection of Environment... SOURCES Standards of Performance for Electric Utility Steam Generating Units § 60.45Da Alternative standards for combined nitrogen oxides (NOX) and carbon monoxide (CO). (a) The owner or operator of...

  17. 40 CFR 60.45Da - Alternative standards for combined nitrogen oxides (NOX) and carbon monoxide (CO).

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... nitrogen oxides (NOX) and carbon monoxide (CO). 60.45Da Section 60.45Da Protection of Environment... SOURCES Standards of Performance for Electric Utility Steam Generating Units § 60.45Da Alternative standards for combined nitrogen oxides (NOX) and carbon monoxide (CO). (a) The owner or operator of...

  18. 40 CFR 60.45Da - Alternative standards for combined nitrogen oxides (NOX) and carbon monoxide (CO).

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... nitrogen oxides (NOX) and carbon monoxide (CO). 60.45Da Section 60.45Da Protection of Environment... SOURCES Standards of Performance for Electric Utility Steam Generating Units § 60.45Da Alternative standards for combined nitrogen oxides (NOX) and carbon monoxide (CO). (a) The owner or operator of...

  19. Permafrost carbon—climate feedback is sensitive to deep soil carbon decomposability but not deep soil nitrogen dynamics

    SciTech Connect

    Koven, Charles D.; Lawrence, David M.; Riley, William J.

    2015-03-09

    Permafrost soils contain enormous amounts of organic carbon whose stability is contingent on remaining frozen. With future warming, these soils may release carbon to the atmosphere and act as a positive feedback to climate change. Significant uncertainty remains on the postthaw carbon dynamics of permafrost-affected ecosystems, in particular since most of the carbon resides at depth where decomposition dynamics may differ from surface soils, and since nitrogen mineralized by decomposition may enhance plant growth. Here we show, using a carbon–nitrogen model that includes permafrost processes forced in an unmitigated warming scenario, that the future carbon balance of the permafrost region is highly sensitive to the decomposability of deeper carbon, with the net balance ranging from 21 Pg C to 164 Pg C losses by 2300. Increased soil nitrogen mineralization reduces nutrient limitations, but the impact of deep nitrogen on the carbon budget is small due to enhanced nitrogen availability from warming surface soils and seasonal asynchrony between deeper nitrogen availability and plant nitrogen demands. The future carbon balance of this region is projected to hinge more on the rate and extent of permafrost thaw and soil decomposition than on enhanced nitrogen availability for vegetation growth resulting from permafrost thaw.

  20. Native plant restoration combats environmental change: development of carbon and nitrogen sequestration capacity using small cordgrass in European salt marshes

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Restoration of salt marshes is critical in the context of climate change and eutrophication of coastal waters, because their vegetation and sediments may act as carbon and nitrogen sinks. Our primary objectives were to quantify carbon (C) and nitrogen (N) stocks and sequestration rates in restored m...

  1. Conductive surface modification of LiFePO4 with nitrogen doped carbon layers for lithium-ion batteries

    SciTech Connect

    Yoon, Sukeun; Liao, Chen; Sun, Xiao-Guang; Bridges, Craig A; Unocic, Raymond R; Nanda, Jagjit; Dai, Sheng; Paranthaman, Mariappan Parans

    2012-01-01

    The LiFePO4 rod surface modified with nitrogen doped carbon layer has been prepared using hydrothermal processing followed by post-annealing in the presence of an ionic liquid. The coated LiFePO4 rod exhibits good capacity retention and high rate capability as the nitrogen doped carbon improves conductivity and prevents aggregation of the rod during cycling.

  2. Permafrost carbon—climate feedback is sensitive to deep soil carbon decomposability but not deep soil nitrogen dynamics

    DOE PAGESBeta

    Koven, Charles D.; Lawrence, David M.; Riley, William J.

    2015-03-09

    Permafrost soils contain enormous amounts of organic carbon whose stability is contingent on remaining frozen. With future warming, these soils may release carbon to the atmosphere and act as a positive feedback to climate change. Significant uncertainty remains on the postthaw carbon dynamics of permafrost-affected ecosystems, in particular since most of the carbon resides at depth where decomposition dynamics may differ from surface soils, and since nitrogen mineralized by decomposition may enhance plant growth. Here we show, using a carbon–nitrogen model that includes permafrost processes forced in an unmitigated warming scenario, that the future carbon balance of the permafrost regionmore » is highly sensitive to the decomposability of deeper carbon, with the net balance ranging from 21 Pg C to 164 Pg C losses by 2300. Increased soil nitrogen mineralization reduces nutrient limitations, but the impact of deep nitrogen on the carbon budget is small due to enhanced nitrogen availability from warming surface soils and seasonal asynchrony between deeper nitrogen availability and plant nitrogen demands. The future carbon balance of this region is projected to hinge more on the rate and extent of permafrost thaw and soil decomposition than on enhanced nitrogen availability for vegetation growth resulting from permafrost thaw.« less

  3. The influence of root assimilated inorganic carbon on nitrogen acquisition/assimilation and carbon partitioning.

    PubMed

    Viktor, A; Cramer, M D

    2005-01-01

    Understanding of the influences of root-zone CO2 concentration on nitrogen (N) metabolism is limited. The influences of root-zone CO2 concentration on growth, N uptake, N metabolism and the partitioning of root assimilated 14C were determined in tomato (Lycopersicon esculentum). Root, but not leaf, nitrate reductase activity was increased in plants supplied with increased root-zone CO2. Root phosphoenolpyruvate carboxylase activity was lower with NO3(-)- than with NH4(+)-nutrition, and in the latter, was also suppressed by increased root-zone CO2. Increased growth rate in NO3(-)-fed plants with elevated root-zone CO2 concentrations was associated with transfer of root-derived organic acids to the shoot and conversion to carbohydrates. With NH4(+)-fed plants, growth and total N were not altered by elevated root-zone CO2 concentrations, although 14C partitioning to amino acid synthesis was increased. Effects of root-zone CO2 concentration on N uptake and metabolism over longer periods (> 1 d) were probably limited by feedback inhibition. Root-derived organic acids contributed to the carbon budget of the leaves through decarboxylation of the organic acids and photosynthetic refixation of released CO2. PMID:15720630

  4. Amino acid diagenesis, organic carbon and nitrogen mineralization in surface sediments from the inner Oslofjord, Norway

    SciTech Connect

    Haugen, J.E. ); Lichtentaler, R. )

    1991-06-01

    Total hydrolyzed amino acids (THAA), total organic carbon (TOC), and total nitrogen (TN) have been measured in an oxic and anoxic surface sediment from the inner Oslofjord. Downcore variations of these parameters are ascribed to both diagenesis and changes in organic matter supply, the latter being most important. These changes are most prominent in the anoxic sediment, which reflects the eutrophication history of the innermost part of the fjord. Downcore, THAA content decreased from 3.8 to 2.0 mg/g (salt-free dry weight) in the oxic sediment and from 22.3 to 3.8 mg/g in the anoxic sediment. Total amino acid nitrogen varied between 17 and 34% of total nitrogen in the oxic, and 25 and 54% in the anoxic, sediment. Organic carbon and organic nitrogen accumulation rates and depth integrated mineralization rates are about three times higher in the anoxic sediment than in the oxic sediment. Recycling of amino acids accounted for 4 to 12% of the total organic carbon and 13 to 40% of the total organic nitrogen regenerated in these sediments.

  5. Nitrogen

    USGS Publications Warehouse

    Kramer, D.A.

    2006-01-01

    In 2005, ammonia was produced by 15 companies at 26 plants in 16 states in the United States. Of the total ammonia production capacity, 55% was centered in Louisiana, Oklahoma and Texas because of their large reserves of natural gas. US producers operated at 66% of their rated capacity. In descending order, Koch Nitrogen, Terra Industries, CF Industries, Agrium and PCS Nitrogen accounted for 81% of the US ammonia production capacity.

  6. Synthesis of Low-Density, Carbon-Doped, Porous Hexagonal Boron Nitride Solids.

    PubMed

    Gautam, Chandkiram; Tiwary, Chandra Sekhar; Jose, Sujin; Brunetto, Gustavo; Ozden, Sehmus; Vinod, Soumya; Raghavan, Prasanth; Biradar, Santoshkumar; Galvao, Douglas Soares; Ajayan, Pulickel M

    2015-12-22

    Here, we report the scalable synthesis and characterization of low-density, porous, three-dimensional (3D) solids consisting of two-dimensional (2D) hexagonal boron nitride (h-BN) sheets. The structures are synthesized using bottom-up, low-temperature (∼300 °C), solid-state reaction of melamine and boric acid giving rise to porous and mechanically stable interconnected h-BN layers. A layered 3D structure forms due to the formation of h-BN, and significant improvements in the mechanical properties were observed over a range of temperatures, compared to graphene oxide or reduced graphene oxide foams. A theoretical model based on Density Functional Theory (DFT) is proposed for the formation of h-BN architectures. The material shows excellent, recyclable absorption capacity for oils and organic solvents. PMID:26580810

  7. Li2S encapsulated by nitrogen-doped carbon for lithium sulfur batteries

    DOE PAGESBeta

    Chen, Lin; Liu, Yuzi; Ashuri, Maziar; Liu, Caihong; Shaw, Leon L.

    2014-09-26

    Using high-energy ball milling of the Li2S plus carbon black mixture followed by carbonization of pyrrole, we have established a facile approach to synthesize Li2S-plus-C composite particles of average size 400 nm, encapsulated by a nitrogen-doped carbon shell. Such an engineered core–shell structure exhibits an ultrahigh initial discharge specific capacity (1029 mAh/g), reaching 88% of the theoretical capacity (1,166 mAh/g of Li2S) and thus offering the highest utilization of Li2S in the cathode among all of the reported works for the encapsulated Li2S cathodes. This Li2S/C composite core with a nitrogen-doped carbon shell can still retain 652 mAh/g after prolongedmore » 100 cycles. These superior properties are attributed to the nitrogen-doped carbon shell that can improve the conductivity to enhance the utilization of Li2S in the cathode. As a result, fine particle sizes and the presence of carbon black within the Li2S core may also play a role in high utilization of Li2S in the cathode.« less

  8. Simulating impacts of Woody Biomass Harvesting on North Temperate Forest Carbon and Nitrogen Cycling and Storage

    NASA Astrophysics Data System (ADS)

    Hua, D.; Desai, A. R.; Bolstad, P.; Cook, B. D.; Scheller, R.

    2012-12-01

    Woody biomass harvesting is a common feature of forest management given its importance to society for acquisition of pulp and paper, lumber, and wood-based biofuel. Harvest affects many aspects of the forest environment such as biodiversity, soil nutrient quality, physical properties of soil, water quality, wildlife habitat, and climate feedbacks. In this study, we applied a modified CENTURY model to the Willow Creek, Wisconsin Ameriflux site for simulation of the impacts of woody biomass removal on forest carbon and nitrogen storage. Woody biomass harvesting scenarios with different harvesting types, interval, tree species, and soil properties were designed and tested in the model to explore the impact of harvesting on forest productivity, soil and biomass carbon and nitrogen storage, and net carbon exchange between terrestrial ecosystem and the atmosphere. Comparisons of the impacts among harvesting scenarios indicate that woody biomass harvesting significantly alters long-term net soil carbon and nitrogen storage as well as carbon exchange between terrestrial ecosystem and the atmosphere. The simulation results also provide a framework for incorporating carbon management into sustainable forest management practices.

  9. Preferred orientation in carbon and boron nitride: Does a thermodynamic theory of elastic strain energy get it right. [C; BN

    SciTech Connect

    McCarty, K.F. )

    1999-09-01

    We address whether the elastic strain-energy theory (minimizing the Gibbs energy of a stressed crystal) of McKenzie and co-workers [D. R. McKenzie and M. M. M. Bilek, J. Vac. Sci. Technol. A [bold 16], 2733 (1998)] adequately explains the preferred orientation observed in carbon and BN films. In the formalism, the Gibbs energy of the cubic materials diamond and cubic boron includes the strain that occurs when the phases form, through specific structural transformations, from graphitic precursors. This treatment violates the requirement of thermodynamics that the Gibbs energy be a path-independent, state function. If the cubic phases are treated using the same (path-independent) formalism applied to the graphitic materials, the crystallographic orientation of lowest Gibbs energy is not that observed experimentally. For graphitic (hexagonal) carbon and BN, an elastic strain approach seems inappropriate because the compressive stresses in energetically deposited films are orders of magnitude higher than the elastic limit of the materials. Furthermore, using the known elastic constants of either ordered or disordered graphitic materials, the theory does not predict the orientation observed by experiment. [copyright] [ital 1999 American Vacuum Society.

  10. Comparison of physicochemical properties of nitrogen-enriched activated carbons prepared by physical and chemical activation of brown coal

    SciTech Connect

    Piotr Nowicki; Robert Pietrzak; Helena Wachowska

    2008-11-15

    Nitrogen-enriched active carbon has been obtained from Polish brown coal from the 'Konin' colliery. The process of ammoxidation by a mixture of ammonia and air at the ratio of 1:3 has been performed at two temperatures (300 and 350{degree}C) at different stages of the production, that is, at that of precursor, char, and active carbon. It has been shown that the stage at which the process of ammoxidation is conducted has profound effect on the amount of nitrogen introduced into the carbon structure. The carbonization and activation (by steam or KOH) of nitrogen-enriched samples leads to significant reduction of the nitrogen content. The final products were microporous active carbons of well-developed surface area varying from 604 to 3181 m{sup 2}/g and having nitrogen content from 0.4 to 6.5 wt%, showing different acid-base character of the surface. 28 refs., 7 tabs.

  11. Nitrogen and sulfur co-doped carbon dots with strong blue luminescence

    NASA Astrophysics Data System (ADS)

    Ding, Hui; Wei, Ji-Shi; Xiong, Huan-Ming

    2014-10-01

    Sulfur-doped carbon dots (S-CDs) with a quantum yield (QY) of 5.5% and nitrogen, sulfur co-doped carbon dots (N,S-CDs) with a QY of 54.4% were synthesized, respectively, via the same hydrothermal route using α-lipoic acid as the carbon source. The obtained S-CDs and N,S-CDs had similar sizes but different optical features. The QY of N,S-CDs was gradually enhanced when extending the reaction time to increase the nitrogen content. After careful characterization of these CDs, the doped nitrogen element was believed to be in the form of C&z.dbd;N and C-N bonds which enhanced the fluorescence efficiency significantly. Meanwhile, the co-doped sulfur element was found to be synergistic for nitrogen doping in N,S-CDs. The optimal N,S-CDs were successfully employed as good multicolor cell imaging probes due to their fine dispersion in water, excitation-dependent emission, excellent fluorescence stability and low toxicity. Besides, such N,S-CDs showed a wide detection range and excellent accuracy as fluorescent sensors for Fe3+ ions.Sulfur-doped carbon dots (S-CDs) with a quantum yield (QY) of 5.5% and nitrogen, sulfur co-doped carbon dots (N,S-CDs) with a QY of 54.4% were synthesized, respectively, via the same hydrothermal route using α-lipoic acid as the carbon source. The obtained S-CDs and N,S-CDs had similar sizes but different optical features. The QY of N,S-CDs was gradually enhanced when extending the reaction time to increase the nitrogen content. After careful characterization of these CDs, the doped nitrogen element was believed to be in the form of C&z.dbd;N and C-N bonds which enhanced the fluorescence efficiency significantly. Meanwhile, the co-doped sulfur element was found to be synergistic for nitrogen doping in N,S-CDs. The optimal N,S-CDs were successfully employed as good multicolor cell imaging probes due to their fine dispersion in water, excitation-dependent emission, excellent fluorescence stability and low toxicity. Besides, such N,S-CDs showed a

  12. Examining the coupling of carbon and nitrogen cycles in Southern Appalachian streams: Understanding the role of dissolved organic nitrogen

    SciTech Connect

    Lutz, Brian D; Bernhardt, Emily; Roberts, Brian; Mulholland, Patrick J

    2011-01-01

    Although regional and global models of nitrogen (N) cycling typically focus on nitrate, dissolved organic nitrogen (DON) is the dominant form of nitrogen export from many watersheds and thus the dominant form of dissolved N in many streams. Our understanding of the processes controlling DON export from temperate forests is poor. In pristine systems, where biological N limitation is common, N contained in recalcitrant organic matter (OM) can dominate watershed N losses. This recalcitrant OM often has moderately constrained carbon:nitrogen (C:N) molar ratios ({approx}25-55) and therefore, greater DON losses should be observed in sites where there is greater total dissolved organic carbon (DOC) loss. In regions where anthropogenic N pollution is high, it has been suggested that increased inorganic N availability can reduce biological demand for organic N and therefore increase watershed DON losses. This would result in a positive correlation between inorganic and organic N concentrations across sites with varying N availability. In four repeated synoptic surveys of stream water chemistry from forested watersheds along an N loading gradient in the southern Appalachians, we found surprisingly little correlation between DON and DOC concentrations. Further, we found that DON concentrations were always significantly correlated with watershed N loading and stream water [NO{sub 3}{sup -}] but that the direction of this relationship was negative in three of the four surveys. The C:N molar ratio of dissolved organic matter (DOM) in streams draining watersheds with high N deposition was very high relative to other freshwaters. This finding, together with results from bioavailability assays in which we directly manipulated C and N availabilities, suggests that heterotrophic demand for labile C can increase as a result of dissolved inorganic N (DIN) loading, and that heterotrophs can preferentially remove N-rich molecules from DOM. These results are inconsistent with the two

  13. Nitrogen-doped carbon nanotubes under electron irradiation simulated with a tight-binding model

    NASA Astrophysics Data System (ADS)

    Loponen, T.; Krasheninnikov, A. V.; Kaukonen, M.; Nieminen, R. M.

    2006-08-01

    Experiments show that nitrogen-doped carbon nanotubes subjected to the electron beam in a transmission electron microscope can easily lose dopant atoms and that overall they are less stable under electron irradiation than the pristine tubes. To understand the lower stability of nitrogen-doped nanotubes we use a density-functional-theory-based tight-binding model and simulate impacts of energetic electrons onto the nanotubes. We show that the dopant atom displacement energy and thus the electron threshold energy is lower for nanotubes with smaller diameter and that, independent of the nanotube diameter, the dopant nitrogen atoms can be displaced more easily than the host carbon atoms. Our results set a limit on the threshold electron energy for damage production in N-doped tubes and indicate that spatially localized electron irradiation of doped nanotubes can be used for local atomic and band structure engineering.

  14. Characteristics of nitrogen-doped carbon nanotubes synthesized by using PECVD and Thermal CVD

    NASA Astrophysics Data System (ADS)

    Kim, Jae-Bum; Kong, So-Jeo; Lee, Sung-Youp; Kim, Je-Han; Lee, Hyeong-Rag; Kim, Chang-Duk; Min, Bong-Ki

    2012-04-01

    Nitrogen-doped carbon nanotubes (N-CNTs) are synthesizd by using plasma-enhanced chemical vapor deposition (PECVD) and thermal chemical vapor deposition (TCVD) because PECVD and TCVD are attractive methods for producing N-CNTs. In this paper, we report the experimental observation of nitrogen incorporation in multiwalled carbon nanotubes grown by using these methods. XPS analysis indicates a shift and broadening of the C 1s spectra peak with increasing disorder induced by nitrogen doping. The N 1s XPS spectra of N-CNTs grown by using PECVD show various structures such as graphitic, pyridinic and N-gaseous forms, while N-CNTs grown by using TCVD have only a graphitic form. Each structure affects the electronic properties of N-CNTs in a different way. TCVD provides a more profitable synthesis method for n-type CNTs while PECVD supports the synthesis of activated N-CNTs with no post-treatment.

  15. SOIL-PROFILE ORGANIC CARBON AND TOTAL NITROGEN UNDER BERMUDAGRASS MANAGEMENT IN THE SOUTHERN PIEDMONT USA

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Estimates of potential carbon (C) and nitrogen (N) sequestration at depths below the traditional plow layer (0-30 cm) are limited, but are needed to improve our understanding of management influences on greenhouse gas emissions and nutrient cycling. Soil samples were collected under `Coastal' bermud...

  16. Effects of harvest on carbon and nitrogen dynamics in a Pacific Northwest forest catchment

    EPA Science Inventory

    We used a new ecohydrological model, Visualizing Ecosystems for Land Management Assessments (VELMA), to analyze the effects of forest harvest on catchment carbon and nitrogen dynamics. We applied the model to a 10 ha headwater catchment in the western Oregon Cascade Range where t...

  17. MODELING NITROGEN-CARBON CYCLING AND OXYGEN CONSUMPTION IN BOTTOM SEDIMENTS

    EPA Science Inventory

    A model framework is presented for simulating nitrogen and carbon cycling at the sediment–water interface, and predicting oxygen consumption by oxidation reactions inside the sediments. Based on conservation of mass and invoking simplifying assumptions, a coupled system of diffus...

  18. The effect of elevated CO2 on carbon and nitrogen metabolism in soybean under FACE

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Crops have the potential to exploit the predicted increase in atmospheric carbon dioxide concentration ([CO2]). Growth is typically stimulated at elevated [CO2], but a sustained and maximal exploitation of rising [CO2] is dependent on an adequate supply of nutrients, principally nitrogen, and suffi...

  19. Long-term changes in soil organic carbon and nitrogen under semiarid tillage and cropping practices

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Understanding long-term changes in soil organic carbon (SOC) and total soil nitrogen (TSN) is important for evaluating C fluxes and optimizing N management. We evaluated long-term SOC and TSN changes under dryland rotations for historical stubble-mulch (HSM) and graded terrace (GT) plots on a clay l...

  20. Mean lives of some astrophysically important excited levels in carbon, nitrogen and oxygen

    NASA Technical Reports Server (NTRS)

    Chang, M. W.; Bickel, W. S.

    1976-01-01

    A number of astrophysically important mean lives of levels in carbon, nitrogen and oxygen were measured with the beam-foil technique. New values are reported and compared with earlier theoretical and experimental values. Direct references to astrophysical applications are listed.