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Sample records for mg espinhaco range

  1. Divacancies and the hydrogenation of Mg-Ti films with short range chemical order

    SciTech Connect

    Leegwater, H.; Schut, H.; Eijt, S. W. H.; Egger, W.; Baldi, A.; Dam, B.

    2010-03-22

    We obtained evidence for the partial chemical segregation of as-deposited and hydrogenated Mg{sub 1-y}Ti{sub y} films (0<=y<=0.30) into nanoscale Ti and Mg domains using positron Doppler-broadening. We exclusively monitor the hydrogenation of Mg domains, owing to the large difference in positron affinity for Mg and Ti. The electron momentum distribution broadens significantly upon transformation to the MgH{sub 2} phase over the whole compositional range. This reveals the similarity of the metal-insulator transition for rutile and fluorite MgH{sub 2}. Positron lifetime studies show the presence of divacancies in the as-deposited and hydrogenated Mg-Ti metal films. In conjunction with the relatively large local lattice relaxations we deduce to be present in fluorite MgH{sub 2}, these may be responsible for the fast hydrogen sorption kinetics in this MgH{sub 2} phase.

  2. Mg-based multilayers and their thermal stabilities for EUV range

    NASA Astrophysics Data System (ADS)

    Zhu, Jingtao; Zhou, Sika; Li, Haochuan; Huang, Qiushi; Jiang, Li; Wang, Fengli; Zhang, Zhong; Wang, Zhanshan; Zhou, Hongjun; Huo, Tonglin

    2011-09-01

    We have investigated the optical properties and thermal stabilities of a serial of Mg-based multilayers including Mg/SiC, Mg/Co and Mg/Zr in extreme ultraviolet (EUV) range. Mg/X multilayer mirrors were deposited by magnetron sputtering technique onto polished silicon wafers. In order to study their stabilities under heat resistance, annealing experiments were carried out in vacuum environment keeping 1hour at different temperatures from 200°C to 550°C. Their EUV reflectivities were measured by using synchrotron radiation. Grazing incident X-ray and EUV reflection measurements were used to estimate the thermal stability of these multilayer systems. Mg/SiC and Mg/Co are stable up to 200°C and the reflectivity decreases drastically with the increase of temperature, while the reflectivity of Mg/Zr keeps constant during annealing at 300°C and falls slowly as the temperature increases. Up to 550°C, Bragg peaks of Mg/Zr multilayer are still sharp in X-ray reflectivity curve, and EUV reflectivity is 25% at 26.2nm at 30 degree incidence. These measurement results indicate that Mg/Co and Mg/SiC should be used in application requiring no heating above 200°C, while the new material combination Mg/Zr is a promising multilayer for practical application requiring stronger heat resistance in EUV range.

  3. Extension of the Optical Absorption Range in Zn-Doped MgO Powders and Its Effect on Antibacterial Activity

    NASA Astrophysics Data System (ADS)

    Ohira, Toshiaki; Kawamura, Mari; Fukuda, Masayuki; Alvarez, Kelly; Özkal, Burak; Yamamoto, Osamu

    2010-04-01

    In order to produce powder samples of Zn-doped MgO, the precursors, MgO and ZnO, were mixed in a molar ratio higher than 1.86 and subsequently treated at 1200 °C for 5 h in air atmosphere. With increasing Zn content in MgO, the lattice constant increased linearly, and the optical absorption intensity increased in the wavelength ranging from 200 to 400 nm. Antibacterial activity of the obtained powder samples was examined by colony count method using Escherichia coli and Staphylococcus aureus. In the antibacterial tests, it was found that the antibacterial activity enhanced with increasing Zn content in MgO. Antibacterial action toward S. aureus was greater than that toward E. coli, irrespective of the Zn content in MgO. From these results, the enhancement of the antibacterial activity could be related with the optical absorption of Zn-doped MgO.

  4. In-vivo noninvasive glucose monitoring with optical heterodyne polarimetry in a range of 50 mg/dl to 100 mg/dl

    NASA Astrophysics Data System (ADS)

    Wang, Wei-Shing; Han, Chien-Yuan; Tu, Pei-Chin; Chou, Chien

    2000-07-01

    An amplitude sensitive optical heterodyne polarimeter was setup in order to monitor noninvasively the aqueous glucose concentration in rabbit's eye. A range of the blood glucose from 35 mg/dl to 135 mg/dl was measured in vivo by biological glucose assay (BGA), while the optional rotation of the aqueous glucose was measured by a polarimeter simultaneously. The experimental results showed the consistence between these two independent measurements. There was no time delay between the blood glucose and the aqueous glucose when the blood glucose was descending after the insulin was injected. It was in contract to a 10 minutes time delay when the blood glucose was ascending. The detection sensitivity of the polarimeter was 4 mg/dl in the measurement.

  5. Lattice dynamics and dielectric response of Mg-doped SrTiO3 ceramics in a wide frequency range

    NASA Astrophysics Data System (ADS)

    Tkach, A.; Vilarinho, P. M.; Kholkin, A. L.; Pashkin, A.; Samoukhina, P.; Pokorny, J.; Veljko, S.; Petzelt, J.

    2005-02-01

    Atomic substitutions in the SrTiO3 (ST) perovskite lattice are foreseen to modify the lattice vibration modes, which are apparently sensitive to the site at which the substitution occurs. In order to understand the effect of Mg substitution in the ST lattice, the dielectric properties of Sr1-xMgxTiO3 and SrTi1-yMgyO3-δ ceramics were investigated in radio frequency (rf), microwave, terahertz (THz), and infrared (IR) ranges. Micro-Raman spectroscopy and rf tunability measurements were also conducted on these samples. The micro-Raman spectra and the high-frequency dielectric properties of Sr1-xMgxTiO3, including rf tunability, do not differ considerably from the properties of undoped SrTiO3, confirming only slight (if any) incorporation of Mg into the Sr site of ST perovskite lattice. At the same time, Ti-site Mg doping results in significant stiffening of the soft lattice mode observed in IR reflectivity spectra. Dielectric permittivity and dielectric losses decrease in both rf and THz ranges accompanied by the decrease of the tunability, in accordance with the stiffened ferroelectric soft mode. The appearance in the Raman spectra of the forbidden polar modes TO4 at 545cm-1 and TO2 at 174cm-1 at room temperature and their strengthening on cooling, demonstrate the local loss of the inversion center and the breaking of the cubic symmetry by the substitution of Ti4+ by Mg2+ ions. These results confirm more favorable occupation of Mg at the Ti site of the ST lattice and show the possibility of using Ti-site Mg-doped ST as an active material for low-loss microwave waveguides and resonators.

  6. Specific heat and thermodynamic characteristics of the system Bi-Sr-Ca-Mg-Cu-O in the temperature range 4.2 300 K

    NASA Astrophysics Data System (ADS)

    Gololobov, E. M.; Novysh, B. V.; Prytkova, N. A.; Tomilo, Zh. M.; Shimanskaya, N. M.; Abeliov, Ya. A.; Maiornikova, G. V.; Yagina, A. B.

    1991-06-01

    Results are presented from an experimental study of specific heat of the superconductive metal oxide system Bi -Sr-Ca-Mg-Cu-O over the temperature range 4.2 300 K. Temperature-dependent components of entropy and enthalpy are calculated. A correlation is made between Tc and standard entropy and enthalpy values for high temperature superconductors of various classes.

  7. Thermodynamic study of the NiO-MgO system in the temperature range 1,073 to 1,473 K by a galvanic cell technique

    SciTech Connect

    Jakobsson, A.; Sichen, D.; Seetharaman, S.

    1993-12-01

    In the present work, the thermodynamic activities of NiO in NiO-MgO solid solutions were measured by means of the ZrO{sub 2}-CaO solid-electrolyte galvanic cell method in the temperature range 1,073 to 1,473 K. The systems shows a near-ideal behavior, while at lower temperatures, the results are anomalous at a high MgO content. Lattice parameter measurements show that the system conforms to Vegard`s law. The enthalpies estimated from the present results are compared with previous work as well as those estimated from theoretical models. A complete thermodynamic description and a calculation of the phase diagram of the NiO-MgO system are enabled by the application of a two-sublattice model.

  8. Short- and long-range binding of Be with Mg in the X1Σ+ ground state and in the A1Π excited state

    NASA Astrophysics Data System (ADS)

    Kerkines, Ioannis S. K.; Nicolaides, Cleanthes A.

    2012-09-01

    We present results of configuration-interaction (CI) computations of wavefunctions and of properties of the first two singlet states, X1Σ+ and A1Π, of the, as yet unobserved, BeMg polar molecule, for internuclear distances in the range [2.5-1000] Å. The X1Σ+ state is very weakly bound, (De = 469.4 cm-1 at Re = 3.241 Å), whereas the A1Π state, which correlates with the excited dissociation channel [Mg KL3s3p1Po + Be 1s22s2 1S], is bound rather strongly (De = 19 394 cm-1 (55.5 kcal/mol) at Re = 2.385 Å). The X1Σ+ state supports 12 vibrational levels, for which vibrationally averaged dipole moments, ⟨μ⟩υ, were obtained, while 71 vibrational levels were found for A1Π. For the level (X1Σ+), ⟨μ⟩0 = 0.213 D. The υ″ = 7 and 8 X1Σ+ vibrational levels are found to have the highest probability to be reached via emission from the lowest lying vibrational levels of A1Π. The work had a dual outcome: First, it explored consequences of different choices of the state-specific reference "Fermi-sea" space ("active" space), which is required for the construction and execution of the multiconfigurational "complete active space self-consistent field" calculations and the subsequent multi-reference CI calculations. In this context, comparisons with results on the weakly bound ground states of the homonuclear Be2 and Mg2 molecules were made. Second, it produced reliable data for the short- as well as the long-range parts of the potential energy curve (PEC). Such information is relevant to analyses concerning cold and ultra-cold Physics and Chemistry. For example, accurate fits to the X1Σ+ PEC, which was computed to nano-Hartree accuracy, with account for basis-set-superposition error, produced the C6 and C8 dispersion coefficients as 364.3 ± 1.1 a.u. and 28 000 ± 500 a.u., respectively. The result for C6 is in excellent agreement with that of Derevianko et al. [At. Data Nucl. Data Tables 96, 323 (2010), 10.1016/j.adt.2009.12.002], (364 ± 4 a.u.), that was

  9. Influence of long-range cation order on relaxor properties of doped Pb(Mg1/3Nb2/3)O3 ceramics

    NASA Astrophysics Data System (ADS)

    Zhao, X.; Qu, W.; Tan, X.; Bokov, A. A.; Ye, Z.-G.

    2009-04-01

    The 1:1 B -site cation order in Pb(Mg1/3Nb2/3)O3 relaxor ferroelectric ceramics was significantly enhanced by doping of minor amounts of La3+ , Sc3+ , or W6+ (less than 3at.% ) combined with a slow cooling procedure. Transmission electron microscopy examination confirmed the size increase of the cation-ordered regions embedded in a disordered matrix in the samples that were slowly cooled after sintering. The average cation ordering parameter (S) determined from x-ray diffraction data in these partially ordered samples was about 0.3-0.4. The ferroelectric properties and dielectric relaxation were compared in partially ordered and disordered (S=0) samples with the same composition. It was found that typical relaxor behavior was preserved in partially ordered ceramics. Furthermore, the temperature and diffuseness of the characteristic relaxor permittivity peak and the parameters of dielectric relaxation (in particular, the distribution of relaxation times and the Vogel-Fulcher freezing temperature) were practically independent of S . In contrast, the diffuseness of the phase transition from the ferroelectric phase (induced by external electric field) to the ergodic relaxor phase appeared to be much larger in the disordered samples than in the partially ordered ones (this diffuseness was assessed using pyroelectric current and ferroelectric hysteresis loops). These results suggest that cation ordering did not influence the behavior of polar nanoregions which are responsible for the dielectric response in the ergodic relaxor phase but significantly influenced the ferroelectric phase transition. The results are interpreted in terms of different types of polar regions in the disordered matrix and cation-ordered domains.

  10. Cosmic-ray isotopic composition of C, N, O, Ne, Mg, Si nuclei in the energy range 50-200 MeV per nucleon measured by the Voyager spacecraft during the solar minimum period

    NASA Technical Reports Server (NTRS)

    Lukasiak, A.; Ferrando, P.; Mcdonald, F. B.; Webber, W. R.

    1994-01-01

    The isotopic composition of C, N, O, Ne, Mg, Si cosmic ray nuclei has been measured in the energy range 50-200 MeV per nucleon using data collected by the High-Energy Telescope of the cosmic-ray subsystem experiment on the Voyager 1 and 2 spacecraft. These data were collected during the period of minimum solar activity in 1986-1988 at an average distance of 27 AU with an effective solar modulation that was much less than at the Earth. The isotope analysis, based on the energy loss - total energy method, has a mass resolution of 0.2 amu for carbon and 0.4 amu at silicon. We find a (C-13)/(C-12) ratio slightly lower and a (O-18)/(O-16) ratio slightly enhanced over their solar system value. We also observe the previously reported enhancement of the (Ne-22)/(Ne-20) ratio relative to solar at the cosmic-ray source but only a weak, if any, enhancement of the (Mg-25)/(Mg-24), (Mg-26)/(Mg 24), and (Si-30)/(Si-28) ratios.

  11. Merging multireference perturbation and density-functional theories by means of range separation: Potential curves for Be{sub 2}, Mg{sub 2}, and Ca{sub 2}

    SciTech Connect

    Fromager, Emmanuel; Jensen, Hans Joergen Aa.

    2010-02-15

    A rigorous combination of multireference perturbation theory and density functional theory (DFT) is proposed. Based on a range separation of the regular two-electron Coulomb interaction, it combines a short-range density functional with second-order strongly contracted n-electron valence state perturbation theory (sc-NEVPT2). The huge advantage of the sc-NEVPT2 approach is that the density is unchanged through first order due to a generalized-Brillouin-type theorem so that the computationally cumbersome self-consistency contribution of short-range DFT to the second-order energy correction equals zero. The method yields very promising results for the van der Waals systems Be{sub 2}, Mg{sub 2}, and Ca{sub 2}; including the multireference system Be{sub 2}.

  12. Microstructure and Thermal Conductivity of the As-Cast and Annealed Al-Cu-Mg-Si Alloys in the Temperature Range from 25°C to 400° C

    NASA Astrophysics Data System (ADS)

    Zhang, Cong; Du, Yong; Liu, Shuhong; Liu, Shaojun; Jie, Wanqi; Sundman, Bosse

    2015-11-01

    Four Al-based Al-Cu-Mg-Si alloy ingots were prepared by electrical resistance furnace. Microstructures and phase identification of the alloys were investigated by using electron probe microanalysis and X-ray diffraction techniques, respectively. The temperature dependences of thermal diffusivity and thermal conductivity of the as-cast and annealed alloys were investigated within the temperature range from 25°C to 400° C, and the estimated thermal conductivity was correlated with the microstructure and (Al) matrix phase compositions of the alloys. According to the results, the thermal conductivity of Al-Cu-Mg-Si alloys increased with temperature. The formation of precipitates, which consumes solute elements in the (Al) phase, contributes to the improvement in thermal diffusivity and thermal conductivity of annealed Al-Cu-Mg-Si alloys. The complex interconnection precipitates with a lower thermal conductivity than (Al) phase may affect the continuity of the matrix phase in microstructure and decreasing the thermal conductivity of the alloys significantly.

  13. Relaxor-like ferroelectric behaviour favoured by short-range B-site ordering in 10% Ba{sup 2+} substituted MgFe{sub 2}O{sub 4}

    SciTech Connect

    Chithra Lekha, P.; Ramesh, G.; Revathi, V.; Subramanian, V.

    2014-05-01

    Graphical abstract: - Highlights: • Mechanism driving polarization in MgFe{sub 2}O{sub 4} is the Maxwell–Wagner polarization. • But Raman studies confirm the existence of local P4{sub 1}22/P4{sub 3}22 symmetry in MgFe{sub 2}O{sub 4}. • Ba{sup 2+} substitution increases ferroelectric ordering, ΔT{sub m} span, and masks electronic contribution. - Abstract: Using the molten salt method, pristine and Ba{sup 2+} substituted MgFe{sub 2}O{sub 4} are prepared. The relaxor-like behaviour observed in the dielectric dispersion indicates the existence of B-site short-range ordering with the local P4{sub 1}22/P4{sub 3}22 symmetry which is confirmed by the Raman spectroscopy. The paper further analyses the origin of polarization using Maxwell–Wagner fit and Nyquist plot. This work suggests a possible way to increase the relaxor-like ferroelectric ordering, larger span of relaxation temperature (ΔT{sub m}) and the effective masking of electronic contribution by the substitution of Ba{sup 2+} ion.

  14. LiF:Mg,Ti TLD response as a function of photon energy for moderately filtered x-ray spectra in the range of 20-250 kVp relative to 60Co.

    PubMed

    Nunn, A A; Davis, S D; Micka, J A; DeWerd, L A

    2008-05-01

    The response of LiF:Mg,Ti thermoluminescent dosimeters (TLDs) as a function of photon energy was determined using irradiations with moderately filtered x-ray beams in the energy range of 20-250 kVp relative to the response to irradiations with 60Co photons. To determine if the relative light output from LiF:Mg,Ti TLDs per unit air kerma as a function of photon energy can be predicted using calculations such as Monte Carlo (MC) simulations, measurements from the x-ray beam irradiations were compared with MC calculated results, similar to the methodology used by Davis et al. [Radiat. Prot. Dosim. 106, 33-43 (2003)]. TLDs were irradiated in photon beams with well-known air kerma rates using the National Institute of Standards and Technology traceable M-series x-ray beams in the range of 20-250 kVp. For each x-ray beam, several sets of TLDs were irradiated for times corresponding to different air kerma levels to take into account any dose nonlinearity. TLD light output was then compared to that from several sets of TLDs irradiated at similar corresponding air kerma levels using a 60Co irradiator. The MC code MCNP5 was used to account for photon scatter and attenuation in the holder and TLDs and was used to calculate the predicted relative TLD light output per unit air kerma for irradiations with each of the experimentally used photon beams. The measured relative TLD response as a function of photon energy differed by up to 13% from the MC calculations. We conclude that MC calculations do not accurately predict the relative response of TLDs as a function of photon energy, consistent with the conclusions of Davis et al. [Radiat. Prot. Dosim. 106, 33-43 (2003)]. This is likely due to complications in the solid state physics of the thermoluminescence process that are not incorporated into the simulation.

  15. LiF:Mg,Ti TLD response as a function of photon energy for moderately filtered x-ray spectra in the range of 20-250 kVp relative to {sup 60}Co

    SciTech Connect

    Nunn, A. A.; Davis, S. D.; Micka, J. A.; DeWerd, L. A.

    2008-05-15

    The response of LiF:Mg,Ti thermoluminescent dosimeters (TLDs) as a function of photon energy was determined using irradiations with moderately filtered x-ray beams in the energy range of 20-250 kVp relative to the response to irradiations with {sup 60}Co photons. To determine if the relative light output from LiF:Mg,Ti TLDs per unit air kerma as a function of photon energy can be predicted using calculations such as Monte Carlo (MC) simulations, measurements from the x-ray beam irradiations were compared with MC calculated results, similar to the methodology used by Davis et al. [Radiat. Prot. Dosim. 106, 33-43 (2003)]. TLDs were irradiated in photon beams with well-known air kerma rates using the National Institute of Standards and Technology traceable M-series x-ray beams in the range of 20-250 kVp. For each x-ray beam, several sets of TLDs were irradiated for times corresponding to different air kerma levels to take into account any dose nonlinearity. TLD light output was then compared to that from several sets of TLDs irradiated at similar corresponding air kerma levels using a {sup 60}Co irradiator. The MC code MCNP5 was used to account for photon scatter and attenuation in the holder and TLDs and was used to calculate the predicted relative TLD light output per unit air kerma for irradiations with each of the experimentally used photon beams. The measured relative TLD response as a function of photon energy differed by up to 13% from the MC calculations. We conclude that MC calculations do not accurately predict the relative response of TLDs as a function of photon energy, consistent with the conclusions of Davis et al. [Radiat. Prot. Dosim. 106, 33-43 (2003)]. This is likely due to complications in the solid state physics of the thermoluminescence process that are not incorporated into the simulation.

  16. Experimental binding energies for the metal complexes [Mg(CH3OH)n](2+), [Ca(CH3OH)n](2+), and [Sr(CH3OH)n](2+) for n in the range 4-20.

    PubMed

    Bruzzi, E; Stace, A J

    2014-10-01

    A supersonic source of clusters has been used to prepare neutral complexes of methanol in association with an alkaline earth metal atom. From these complexes the following metal-containing dications have been generated through electron ionization: [Mg(CH3OH)n](2+), [Ca(CH3OH)n](2+), and [Sr(CH3OH)n](2+), and for n in the range 4-20, kinetic energy release measurements following the evaporation of a single molecule have been undertaken using a high resolution mass spectrometer. Using finite heat bath theory, these data have been transformed into binding energies for individual methanol molecules attached to each of the three cluster systems. In the larger complexes (n > 6) the results exhibit a consistent trend, whereby the experimental binding energy data for all three metal ions are similar, suggesting that the magnitude of the charge rather than charge density influences the strength of the interaction. From a comparison with data recorded previously for (CH3OH)nH(+) it is found that the 2+ charge on a metal ion has an effect on the binding energy of molecules in complexes containing up to 20 solvent molecules. The results recorded for [Ca(CH3OH)n](2+) show evidence of a very marked transition between n = 6 and 7, which is thought to coincide with the completion of a primary solvation shell and the onset of molecules starting to occupy a second and most probably a third shell.

  17. Phase transformation of Mg-Fe alloys

    SciTech Connect

    Yoneda, Yasuhiro; Abe, Hiroshi; Ohshima, Takeshi; Uchida, Hirohisa

    2010-05-15

    An Mg-Fe alloy system prepared through mechanical alloying (MA) was structurally analyzed. MA can produce single-phase bcc alloys using Mg concentrations up to about 15 mol %. Use of conventional average structure analysis and x-ray pair-distribution function method enabled the long-range and short-range order structures of the Mg-Fe alloys to be bridged. The substituted Mg atoms were randomly arranged in the low-Mg composition but started to have an order structure. The partially ordered Mg-Fe alloy undergoes an austenitic (cubic) to martensitic (orthorhombic) phase change, as increasing Mg composition.

  18. The Arabidopsis Mg Transporter, MRS2-4, is Essential for Mg Homeostasis Under Both Low and High Mg Conditions.

    PubMed

    Oda, Koshiro; Kamiya, Takehiro; Shikanai, Yusuke; Shigenobu, Shuji; Yamaguchi, Katsushi; Fujiwara, Toru

    2016-04-01

    Magnesium (Mg) is an essential macronutrient, functioning as both a cofactor of many enzymes and as a component of Chl. Mg is abundant in plants; however, further investigation of the Mg transporters involved in Mg uptake and distribution is needed. Here, we isolated an Arabidopsis thaliana mutant sensitive to high calcium (Ca) conditions without Mg supplementation. The causal gene of the mutant encodes MRS2-4, an Mg transporter.MRS2-4 single mutants exhibited growth defects under low Mg conditions, whereas an MRS2-4 and MRS2-7 double mutant exhibited growth defects even under normal Mg concentrations. Under normal Mg conditions, the Mg concentration of the MRS2-4 mutant was lower than that of the wild type. The transcriptome profiles of mrs2-4-1 mutants under normal conditions were similar to those of wild-type plants grown under low Mg conditions. In addition, both mrs2-4 and mrs2-7 mutants were sensitive to high levels of Mg. These results indicate that both MRS2-4 and MRS2-7 are essential for Mg homeostasis, even under normal and high Mg conditions. MRS2-4-green fluorescent protein (GFP) was mainly detected in the endoplasmic reticulum. These results indicate that these two MRS2 transporter genes are essential for the ability to adapt to a wide range of environmental Mg concentrations. PMID:26748081

  19. Polymeric gamma-MgCl2 Nanoribbons

    SciTech Connect

    Vittadello,M.; Stallworth, P.; Alamgir, F.; Suarez, S.; Abbrent, S.; Drain, C.; Di Noto, V.; Greenbaum, S.

    2006-01-01

    {delta}-MgCl{sub 2} has relevant applications in the field of electrochemical energy storage and Ziegler-Natta catalysis. Here, we clarify the short-range structural peculiarities that make the disordered phase {delta}-MgCl{sub 2} extremely chemically active relative to the higher lattice energy phases, {alpha}-MgCl{sub 2} and {beta}-MgCl{sub 2}. X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS) and nuclear magnetic resonance (NMR) results are included. These findings, demonstrate the existence of [MgCl{sub 2}]{sub n} nanoribbons and active nanosurfaces in {delta}-MgCl{sub 2} and provide new insight about the nature of the bonding in the allotropic forms of MgCl{sub 2}.

  20. Role of Mg interlayers in Fe/Mg/MgO/Fe and Fe/Mg/MgO/Mg/Fe magnetic tunnel junctions

    SciTech Connect

    Wang, Y.; Zhang, J.; Zhang, Xiaoguang; Cheng, Hai-Ping; Han, Prof. X. F.

    2010-01-01

    -Fe(001)/Mg/MgO/Fe- and -Fe(001)/Mg/MgO/Mg/Fe- magnetic tunnel junctions (MTJs) with Mg interlayers are studied by first-principles calculation. An important role of the Mg interlayer is identified to be preserving the preferential transmission of the majority-spin states with \\Delta_1 symmetry, which dominate the spin-dependent electron transport of MTJs with MgO barrier. One layer of Mg at the electrode/barrier interface does not decrease the tunneling magnetoresistance (TMR) ratio nearly as much as one layer of oxide. At certain Mg thickness case the TMR could be strongly influenced by the resonance tunneling states in minority-spin channel, these states are mainly raised from the quantum-well states formed in the Mg interlayer and coupled with interfacial resonance states which are very sensitive to the interface structures.

  1. The MG Composite

    PubMed Central

    Burns, Ted M.; Conaway, Mark; Sanders, Donald B.

    2010-01-01

    Objective: To study the concurrent and construct validity and test-retest reliability in the practice setting of an outcome measure for myasthenia gravis (MG). Methods: Eleven centers participated in the validation study of the Myasthenia Gravis Composite (MGC) scale. Patients with MG were evaluated at 2 consecutive visits. Concurrent and construct validities of the MGC were assessed by evaluating MGC scores in the context of other MG-specific outcome measures. We used numerous potential indicators of clinical improvement to assess the sensitivity and specificity of the MGC for detecting clinical improvement. Test-retest reliability was performed on patients at the University of Virginia. Results: A total of 175 patients with MG were enrolled at 11 sites from July 1, 2008, to January 31, 2009. A total of 151 patients were seen in follow-up. Total MGC scores showed excellent concurrent validity with other MG-specific scales. Analyses of sensitivities and specificities of the MGC revealed that a 3-point improvement in total MGC score was optimal for signifying clinical improvement. A 3-point improvement in the MGC also appears to represent a meaningful improvement to most patients, as indicated by improved 15-item myasthenia gravis quality of life scale (MG-QOL15) scores. The psychometric properties were no better for an individualized subscore made up of the 2 functional domains that the patient identified as most important to treat. The test-retest reliability coefficient of the MGC was 98%, with a lower 95% confidence interval of 97%, indicating excellent test-retest reliability. Conclusions: The Myasthenia Gravis Composite is a reliable and valid instrument for measuring clinical status of patients with myasthenia gravis in the practice setting and in clinical trials. PMID:20439845

  2. Mg Isotopic Compositions of Modern Marine Carbonates

    NASA Astrophysics Data System (ADS)

    Krogstad, E.; Bizzarro, M.; Hemming, N.

    2003-12-01

    We have used a MC-ICP-MS to measure the isotopic composition of magnesium in a number of samples of modern marine carbonate. Due to the large mass difference between 26Mg and 24Mg (similar to that between 13C and 12C), there is potential for mass fractionation during geologic and biologic processes that may make this isotope system useful for geochemical studies. These samples are from the study of Hemming and Hanson (1992, GCA 56: 537-543). The carbonate minerals analyzed include aragonite, low-Mg calcite, and high-Mg calcite. The samples include corals, echinoderms, ooids, etc., from subtropical to Antarctic settings. Mg purification was accomplished by ion-exchange chromatography, using Bio-Rad AG50W-X12 resin on which greater than 99 percent recovery of Mg is achieved. Samples were introduced into the MC-ICP-MS (VG Axiom) using a Cetac MCN-6000 nebuliser. We use a standard-sample-standard bracketing technique, and samples are analysed at least three times. For lab standards we find that the reproducibility on the 26Mg/24Mg to be about ñ 0.12 permil (2 s.d.). We monitored our separated samples for Na and Ca, as we have found that high Ca/Mg and Na/Mg produce variable magnesium isotopic fractionation during mass spectrometry due to as yet unclear matrix effects. We have normalized our results to our measured values for seawater. We observed a d26Mg(s.w.) range of -1.4 to -2.4 permil in our modern carbonate samples relative to present day seawater. Due to the long residence time of Mg in the oceans (ca. 50 my), this must be due to kinetic or biologic effects. Our d25Mg(s.w.) variations as a function of d26Mg(s.w.) plot along the terrestrial fractionation trend. With an average d26Mg(s.w.) of ca. +0.5 permil in all samples of mantle lithologies and mantle-derived igneous rocks (Bizzarro et al., Goldschmidt abs., 2003), we can assume that the Mg isotopic composition of Earth's river water lies between ca. -2.4 and +0.5 permil (relative to seawater). The actual

  3. Mg Content Dependence of EML-PVD Zn-Mg Coating Adhesion on Steel Strip

    NASA Astrophysics Data System (ADS)

    Jung, Woo Sung; Lee, Chang Wook; Kim, Tae Yeob; De Cooman, Bruno C.

    2016-09-01

    The effect of coating thickness and Mg concentration on the adhesion strength of electromagnetic levitation physical vapor deposited Zn-Mg alloy coatings on steel strip was investigated. The phase fraction of Zn, Mg2Zn11, and MgZn2 was determined for a coating Mg concentration in the 0 to 15 wt pct range. Coatings with a Mg content less than 5 pct consisted of an Zn and Mg2Zn11 phase mixture. The coatings showed good adhesion strength and ductile fracture behavior. Coatings with a higher Mg concentration, which consisted of a Mg2Zn11 and MgZn2 phase mixture, had a poor adhesion strength and a brittle fracture behavior. The adhesion strength of PVD Zn-Mg alloy coatings was found to be related to the pure Zn phase fraction. The effect of coating thickness on adhesion strength was found to be negligible. The microstructure of the interface between steel and Zn-Mg alloy coatings was investigated in detail by electron microscopy, electron diffraction, and atom probe tomography.

  4. Mg Isotopes of USGS Igneous Rock Standards

    NASA Astrophysics Data System (ADS)

    Huang, F.; Glessner, J. J.; Lundstrom, C. C.

    2008-12-01

    Magnesium has three stable isotopes, 24Mg, 25Mg, and 26Mg with abundances of 78.99%, 10.00%, and 11.01%, respectively. It is one of the most abundant elements in the crust and mantle. As advancements of analytical techniques using MC-ICP-MS have dramatically advanced our ability to measure isotope ratios of Mg with greater precision, Mg isotopes can now be applied to study a variety of fundamental geological processes, such as continental crust weathering, chemical diffusion, and chondrule formation. Therefore the need for well characterized Mg isotope ratios for geological materials is increasingly important. Routine measurement of readily-available USGS rock standards is a viable way for inter-lab comparison to show the quality of data. However, the Mg isotope data for USGS standards reported in the literature are limited and inconsistent. USGS standards reported by different MC-ICP-MS labs have a range of Mg isotopic data outside of the normal external error of 0.1‰ (2σ). Mg isotopes of USGS igneous rock standards (dunite, DTS-1; basalts, BCR-1, BCR-2, BHVO-1; and andesite, AGV-1) were measured by a sample-standard bracketing method using a low resolution MC-ICP- MS (Nu-Plasma HR). The method has a large tolerance of matrix bias with Na/Mg and Al/Mg > 100% only changing the δ26Mg by less than 0.1‰. Dilution effects do not cause significant error (< 0.1‰) until the concentration difference between standard and sample is greater than 25%. The isobaric interference of CN+ on 26Mg was avoided by measuring Mg signal on the low mass shoulder. Only purified samples with excellent yields (>99.5%) and acceptable concentrations of matrix (mainly Na, Al, Ca, and Fe) are included in these results. Duplicate analyses of independently processed standards yielded the following results (δ26MgDSM-3 (‰)): BCR-2 (-0.306±0.144, - 0.290±0.116, -0.283±0.048, -0.288±0.057), BCR-1 (-0.399±0.079, -0.346±0.046), AGV-1 (-0.295±0.110, -0.307±0.086, -0.339±0.068), BHVO-1

  5. The effect of the MgO buffer layer thickness on magnetic anisotropy in MgO/Fe/Cr/MgO buffer/MgO(001)

    NASA Astrophysics Data System (ADS)

    Kozioł-Rachwał, Anna; Nozaki, Takayuki; Zayets, Vadym; Kubota, Hitoshi; Fukushima, Akio; Yuasa, Shinji; Suzuki, Yoshishige

    2016-08-01

    The relationship between the magnetic properties and MgO buffer layer thickness d was studied in epitaxial MgO/Fe(t)/Cr/MgO(d) layers grown on MgO(001) substrate in which the Fe thickness t ranged from 0.4 nm to 1.1 nm. For 0.4 nm ≤ t ≤ 0.7 nm, a non-monotonic coercivity dependence on the MgO buffer thickness was shown by perpendicular magneto-optic Kerr effect magnetometry. For thicker Fe films, an increase in the buffer layer thickness resulted in a spin reorientation transition from perpendicular to the in-plane magnetization direction. Possible origins of these unusual behaviors were discussed in terms of the suppression of carbon contamination at the Fe surface and changes in the magnetoelastic anisotropy in the system. These results illustrate a method to control magnetic anisotropy in MgO/Fe/Cr/MgO(d) via an appropriate choice of MgO buffer layer thickness d.

  6. Energy loss straggling data of 28Si, 27Al, 24Mg, 19F, 16O, and 12C heavy ions in thin polymeric Formvar foil over a range of energies 0.1-0.6 MeV/u by time-of-flight spectrometry

    NASA Astrophysics Data System (ADS)

    Guesmia, A.; Ammi, H.; Msimanga, M.; Dib, A.; Mammeri, S.; Pineda-Vargas, C. A.; Hedibel, M.

    2015-02-01

    The energy-loss straggling of 28Si, 27Al, 24Mg, 19F, 16O and 12C partially stripped heavy ions has been determined in Formvar polymeric thin foil over a continuous range of energies 0.1-0.6 MeV/u, by using a powerful method based on the combination of Heavy Ion-Elastic Recoil Detection Analysis (HI-ERDA) technique and Time of Flight (ToF) spectrometer. The obtained energy loss straggling values have been analyzed and compared with the corresponding computed values adopting some widely used energy loss straggling formulations such as, Bohr, Bethe-Livingston and Yang formulas. The aim of such a comparison is to check the reliability and accuracy of the existing energy loss straggling formulations. The experimental results of energy loss straggling of all ions are found to be significantly greater than those predicted by the theories. These differences can be attributed to the charge exchange straggling. This effect has to be taken into account in order to explain the obtained results.

  7. UHV and Ambient Pressure XPS: Potentials for Mg, MgO, and Mg(OH)2 Surface Analysis

    NASA Astrophysics Data System (ADS)

    Head, Ashley R.; Schnadt, Joachim

    2016-10-01

    The surface sensitivity of x-ray photoelectron spectroscopy (XPS) has positioned the technique as a routine analysis tool for chemical and electronic structure information. Samples ranging from ideal model systems to industrial materials can be analyzed. Instrumentational developments in the past two decades have popularized ambient pressure XPS, with pressures in the tens of mbar now commonplace. Here, we briefly review the technique, including a discussion of developments that allow data collection at higher pressures. We illustrate the information XPS can provide by using examples from the literature, including MgO studies. We hope to illustrate the possibilities of ambient pressure XPS to Mg, MgO, and Mg(OH)2 systems, both in fundamental and applied studies.

  8. Diffusion of Ca and Mg in Calcite

    SciTech Connect

    Cygan, R.T.; Fisler, D.K.

    1999-02-10

    The self-diffusion of Ca and the tracer diffusion of Mg in calcite have been experimentally measured using isotopic tracers of {sup 25}Mg and {sup 44}Ca. Natural single crystals of calcite were coated with a thermally-sputtered oxide thin film and then annealed in a CO{sub 2} gas at one atmosphere total pressure and temperatures from 550 to 800 C. Diffusion coefficient values were derived from the depth profiles obtained by ion microprobe analysis. The resultant activation energies for Mg tracer diffusion and Ca self-diffusion are respectively: E{sub a}(Mg) = 284 {+-} 74 kJ/mol and E{sub a}(Ca) = 271 {+-} 80 kJ/mol. For the temperature ranges in these experiments, the diffusion of Mg is faster than Ca. The results are generally consistent in magnitude with divalent cation diffusion rates obtained in previous studies and provide a means of interpreting the thermal histories of carbonate minerals, the mechanism of dolomitization, and other diffusion-controlled processes. The results indicate that cation diffusion in calcite is relatively slow and cations are the rate-limiting diffusing species for the deformation of calcite and carbonate rocks. Application of the calcite-dolomite geothermometer to metamorphic assemblages will be constrained by cation diffusion and cooling rates. The direct measurement of Mg tracer diffusion in calcite indicates that dolomitization is unlikely to be accomplished by Mg diffusion in the solid state but by a recrystallization process.

  9. Mg/Ca of Continental Ostracode Shells

    NASA Astrophysics Data System (ADS)

    Ito, E.; Forester, R. M.; Marco-Barba, J.; Mezquita, F.

    2007-12-01

    Marine ionic chemistry is thought to remain constant. This, together with the belief that marine calcifiers partition Mg/Ca in a systematic manner as functions of temperature (and Mg/Ca) of water forms the basis of the Mg/Ca thermometer. In continental settings both of these assumptions are usually not true. Continental waters contain a wide variety of solutes in absolute and relative ion concentrations. Hence, waters with identical Mg/Ca may have very different concentrations of Mg and Ca and very different anions. Here we use two examples to focus on the effects of ion chemistry on Mg/Ca partitioning in continental ostracode shells and we ignore the complexities of solute evolution, which can change Mg/Ca over timescales of minutes to millennia. Palacios-Fest and Dettman (2001) conducted a monthly study of ,Cypridopsis vidua at El Yeso Lake in Sonora, Mexico. They established a relation between temperature and average shell Mg/Ca using regression analyses on averaged data. When their Mg/Ca-temperature relation is applied to monthly ,C. vidua data from Page Pond near Cleveland, Ohio, water temperatures of -8 to -1°C are obtained. The observed Mg/Ca ranges for El Yeso Lake (0.31 to 0.46) and Page Pond (0.33 to 0.46) are similar, as are their specific conductivities (700 to 850μS for El Yeso Lake; 400 to 600μS for Page Pond). However, [Ca] is 140-260 mg/L for El Yeso, but only 70-90 mg/L for Page Pond. Page Pond data, in fact, shows a good temperature shell Mg/Ca relation for .C. vidua, but the relation is different from that at El Yeso. Hence, shell Mg/Ca is a multi-valued, family of curves function of temperature and Mg/Ca of water that depends on the [Mg] and [Ca] values in water and perhaps other factors. Our second example comes from sites near Valencia, Spain and involves shell data for ,Cyprideis torosa, an estuarine ostracode that is tolerant of a wide range of salinity and can live in continental waters as long as the carbonate alkalinity to Ca ratio is

  10. Porous Mg thin films for Mg-air batteries.

    PubMed

    Xin, Gongbiao; Wang, Xiaojuan; Wang, Chongyun; Zheng, Jie; Li, Xingguo

    2013-12-28

    An alkaline primary Mg-air battery made from a porous Mg thin film displayed superior discharge performances, including a flat discharge plateau, a high open-circuit voltage of 1.41 V and a large discharge capacity of 821 mAh g(-1), suggesting that the electrochemical performances of Mg-air batteries can be improved by controlling the Mg anode morphology. PMID:24158667

  11. Mg isotope fractionation during calcite precipitation: An experimental study

    NASA Astrophysics Data System (ADS)

    Saulnier, Ségolène; Rollion-Bard, Claire; Vigier, Nathalie; Chaussidon, Marc

    2012-08-01

    Experimental precipitations of calcite and other carbonate minerals were performed under various conditions of pH, temperature and solution Mg/Ca to determine the Mg partition coefficient and Mg isotope fractionation. Fifteen experiments were performed at pH ranging from 7.41 ± 0.07 to 8.51 ± 0.39, temperature ranging from 16.2 ± 0.7 to 26.5 ± 0.3 °C and Mg/Casolution ranging from 0.11 to 0.52 mol/mol. The apparent Mg partition coefficient between calcite and solution (DMg) spans a large range of values from 0.018 ± 0.014 to 0.15 ± 0.11 and carbonate Mg isotope fractionation (Δ26Mg) ranges from -2.53 ± 0.25‰ to -1.33 ± 0.14‰ and does not correlate with either pH or temperature. The range in DMg and Δ26Mg suggests non-equilibrium partitioning controlled by the processes of calcite growth, i.e. mixing between calcite grown at equilibrium and fluid inclusions, and entrapment of a surface Mg-rich calcite layer in isotopic equilibrium with the solution. The equilibrium Mg isotope fractionation between inorganic calcite and solution is estimated to be -2.13 ± 0.24‰. Additional Mg elemental and isotopic fractionations are observed to occur during biogenic formation of calcite due to variable removal of Mg by the organisms (high-Mg calcite corals, foraminifera) of seawater Mg from their calcification medium.

  12. Observations of Local Interstellar Mg I and Mg II

    NASA Technical Reports Server (NTRS)

    Bruhweiler, F. C.; Oegerle, W.; Weiler, E.; Stencel, R. E.; Kondo, Y.

    1984-01-01

    Copernicus and IUE observations of 5 stars within 50 pc of the Sun were combined to study the ionization of magnesium in the local interstellar medium (LISM). The high resolution Copernicus spectrometer was used to detect interstellar MG I 2852 in the spectra of alpha Gru, alpha Eri, and alpha Lyr, while placing upper limits on Mg I in the spectra of alpha CMa and alpha PsA. Observations of Mg II 2795, 2802 for these stars were also obtained with IUE and Copernicus. The column densities of Mg I and Mg II are used to place constraints on the temperature of the LISM.

  13. The dependence of Raman scattering on Mg concentration in Mg-doped GaN grown by MBE

    NASA Astrophysics Data System (ADS)

    Flynn, Chris; Lee, William

    2014-04-01

    Magnesium-doped GaN (GaN:Mg) films having Mg concentrations in the range 5 × 1018-5 × 1020 cm-3 were fabricated by molecular beam epitaxy. Raman spectroscopy was employed to study the effects of Mg incorporation on the positions of the E2 and A1(LO) lines identifiable in the Raman spectra. For Mg concentrations in excess of 2 × 1019 cm-3, increases in the Mg concentration shift both lines to higher wave numbers. The shifts of the Raman lines reveal a trend towards compressive stress induced by incorporation of Mg into the GaN films. The observed correlation between the Mg concentration and the Raman line positions establish Raman spectroscopy as a useful tool for optimizing growth of Mg-doped GaN.

  14. Mg Isotopes of the Late Permian Evaporites, New Mexico, USA

    NASA Astrophysics Data System (ADS)

    Feng, C.; Gao, C. H.; Chang, S. C.

    2015-12-01

    Mg isotope holds promise to decipher the evaporative environment of evaporites. High-precision Mg isotope compositions of the late Permian langbeinites have been measured by using MC-ICPMS. The equilibrium Mg isotope fractionation factor between langbeinite and aqueous Mg2+ solutions has been determined using quantum chemistry calculations. All computations are employed at B3LYP/6-311++G(2d,2p) level and solvation effects are treated by solvent model ("water-droplet" approach), mineral structures are constructed using volume variable cluster models (VVCM). The Mg isotope compositions of the langbeinite samples, whose total formation thickness ranges up to 100 meters, are extremely isotopically lighter than that of modern seawater and relatively homogeneous (δ26MgDSM3 is from -4.12±0.03‰ to -3.81±0.07‰ v.s. -0.83‰ of modern seawater). The computed equilibrium Mg isotope fractionation factors between langbeinite and aqueous Mg2+ solutions are -2.73‰, -2.66‰ and -2.53‰ at 25, 30 and 40 ℃, respectively. These significant equilibrium fractionation factors indicate that a huge equilibrium Mg isotope fractionation between langbeinite and its parent brine can happen during langbeinite depositions, and langbeinites are enriched in isotopically light 24Mg comparing to the brine. Using the computed fractionation factors to simulate a Rayleigh fractionation process of langbeinite Mg precipitation, we find that a significant Mg isotope difference between langbeinite and its growing brine (seawater) is indeed present but the Mg isotope composition of langbeinite merely increase monotonically in a closed system. Because of that, the homogenous Mg isotope compositions of such a thick evaporite sequence suggest a disequlibrium effect rather than an equilibrium Mg isotope fractionation behavior during its formation. Combined with its prevailing Mg-bearing character, the homogenous Mg isotope compositions reveal that this the late Permian langbeinite sequence has

  15. Substitution of Mn for Mg in MgB_2*

    NASA Astrophysics Data System (ADS)

    Fitzpatrick, Michael D.; Johnston, David C.; Miller, Lance L.; Hill, Julienne M.

    2002-03-01

    The study of solid solutions in which the Mg in MgB2 is partially replaced by magnetic 3d or 4f atoms can potentially reveal important information on the superconducting state of MgB_2. As an end-member of the hypothetical Mg_1-xMn_xB2 system, MnB2 is isostructural with MgB2 and is an antiferromagnet below TN = 760 K which becomes canted at 157 K. A previous study by Moritomo et al.[1] examined the structure and properties of multi-phase samples with 0.01<= x<= 0.15. We attempted to obtain single-phase samples with x<= 0.25 by reacting the constituent elements in sealed Ta tubes and/or using prereacted MnBx synthesized using an arc furnace. The results of x-ray diffraction and magnetization measurements on those samples will be presented. * Supported by the USDOE under contract no. W-7405-Eng-82. [1] "Mn-substitution effects on MgB2 superconductor", Y.Moritomo et al. J. Phys. Soc. Japan b70, 1889 (2001).; “Effects of transition metal doping in MgB2 superconductor", Y. Moritomo at al. arXiv:cond-mat/0104568.

  16. Coulomb excitation of 31Mg

    NASA Astrophysics Data System (ADS)

    Seidlitz, M.; Mücher, D.; Reiter, P.; Bildstein, V.; Blazhev, A.; Bree, N.; Bruyneel, B.; Cederkäll, J.; Clement, E.; Davinson, T.; Van Duppen, P.; Ekström, A.; Finke, F.; Fraile, L. M.; Geibel, K.; Gernhäuser, R.; Hess, H.; Holler, A.; Huyse, M.; Ivanov, O.; Jolie, J.; Kalkühler, M.; Kotthaus, T.; Krücken, R.; Lutter, R.; Piselli, E.; Scheit, H.; Stefanescu, I.; Van de Walle, J.; Voulot, D.; Warr, N.; Wenander, F.; Wiens, A.

    2011-06-01

    The ground state properties of 31Mg indicate a change of nuclear shape at N = 19 with a deformed Jπ = 1 /2+ intruder state as a ground state, implying that 31Mg is part of the "island of inversion". The collective properties of excited states were the subject of a Coulomb excitation experiment at REX-ISOLDE, CERN, employing a radioactive 31Mg beam. De-excitation γ-rays were detected by the MINIBALL γ-spectrometer in coincidence with scattered particles in a segmented Si-detector. The level scheme of 31Mg was extended. Spin and parity assignment of the 945 keV state yielded 5 /2+ and its de-excitation is dominated by a strong collective M1 transition. Comparison of the transition probabilities of 30,31,32Mg establishes that for the N = 19 magnesium isotope not only the ground state but also excited states are largely dominated by a deformed pf intruder configuration.

  17. Energy band bowing parameter in MgZnO alloys

    SciTech Connect

    Wang, Xu; Saito, Katsuhiko; Tanaka, Tooru; Nishio, Mitsuhiro; Guo, Qixin; Nagaoka, Takashi; Arita, Makoto

    2015-07-13

    We report on bandgap bowing parameters for wurtzite and cubic MgZnO alloys from a study of high quality and single phase films in all Mg content range. The Mg contents in the MgZnO films were accurately determined using the energy dispersive spectrometer and X-ray photoelectron spectroscopy (XPS). The measurement of bandgap energies by examining the onset of inelastic energy loss in core-level atomic spectra from XPS is proved to be valid for determining the bandgap of MgZnO films. The dependence of the energy bandgap on Mg content is found to deviate downwards from linearity. Fitting of the bandgap data resulted in two bowing parameters of 2.01 ± 0.04 eV and 1.48 ± 0.11 eV corresponding to wurtzite and cubic MgZnO films, respectively.

  18. Mg isotopic composition of carbonate: insight from speleothem formation

    NASA Astrophysics Data System (ADS)

    Galy, Albert; Bar-Matthews, Miryam; Halicz, Ludwik; O'Nions, R. Keith

    2002-07-01

    Simultaneous high-precision measurement of 24Mg, 25Mg and 26Mg isotopic compositions were made by multiple collector inductively coupled mass spectrometry (MC-ICP-MS) relative to the international standard SRM980. Data are presented on low-Mg calcite speleothems and their associated host rocks and waters from four caves, one in the French Alps and three in Israel, covering various climate conditions. In addition, data are presented on three dolostones and three limestones from the Himalaya. The overall variation is 4.13‰ and 2.14‰ in δ 26Mg and δ 25Mg, respectively. This is 35 times the uncertainty of the measurements and clearly demonstrates that the terrestrial isotopic composition of Mg is not unique. Each speleothem shows a characteristic range of δ 26Mg values that are attributed to the isotopic composition of the local water. Differences between the isotopic composition of Mg in the water dripping from stalactites and that of the modern speleothem are interpreted as being due to Mg isotopic fractionation during carbonate precipitation in the temperature range of 4-18°C. The low-Mg calcite is enriched in light isotopes by 1.35‰/AMU and the dependence on temperature has been found to be less than 0.02‰/AMU/°C. Despite various geological settings, the δ 26Mg of the studied dolostones is 2.0±1.2‰ higher than the δ 26Mg of the limestones. All together, these results suggest a strong mineralogical control and a weak temperature effect on the Mg isotopic composition of carbonate.

  19. Projectile deformation effects in the breakup of 37Mg

    NASA Astrophysics Data System (ADS)

    Shubhchintak; Chatterjee, R.; Shyam, R.

    2016-05-01

    We study the breakup of 37Mg on Pb at 244MeV/u with the recently developed extended theory of Coulomb breakup within the postform finite range distorted wave Born approximation that includes deformation of the projectile. Comparing our calculated cross section with the available Coulomb breakup data we determine the possible ground state configuration of 37Mg.

  20. Thermodynamic data of Mg-chloritoid

    NASA Astrophysics Data System (ADS)

    Grevel, K.-D.; Navrotsky, A.; Kahl, W.-A.; Majzlan, J.; Lathe, C.

    2003-04-01

    Calorimetric and P-V-T data for synthetic Mg-chloritoid (MgAl2SiO5(OH)2) have been obtained. The enthalpy of drop-solution was measured by high-temperature oxide melt calorimetry in two laboratories (UC Davis, California, and Ruhr-University Bochum, Germany) using lead borate (2 PbO\\cdotB2O3) at T = 700 oC as solvent. The resulting values were used to calculate the enthalpy of formation from the elements; they range from -3552.7 ± 4.9 kJ mol-1 to -3555.4±6.1 kJ mol-1. Some preliminary heat capacity measurements of MgAl2SiO5(OH)2 have shown that a Berman and Brown (1985) type four-term equation based on the Neumann-Kopp rule represents the heat capacity over the entire temperature range to within the experimental uncertainty. The P-V-T behaviour of Mg-chloritoid has been determined under high pressures and high temperatures up to 8.5 GPa and 800 oC using a MAX 80 cubic anvil high-pressure apparatus. The samples were mixed with vaseline to ensure hydrostatic pressure transmitting conditions, NaCl served as an internal standard for pressure calibration. By fitting a Birch-Murnaghan EOS to the data, the bulk modulus was determined as 131.0 ± 2.4 GPa, (K' = 4), VT,0 = 456.58 Å3 exp [int(0.30±0.02) × 10-4 dT], (partialKT/partialT)P = -0.023±0.007 GPa K-1. The thermodynamic data obtained for Mg-chloritoid are consistent with phase equilibrium data reported in the literature. The best agreement was obtained with ΔfH0298 (Mg-chloritoid) = -3557.5 kJ mol-1, and S0298 (Mg-chloritoid) = 131.7 J K-1mol-1.

  1. Solubility of MgO in MgCl{sub 2}-NaCl-NaF melts

    SciTech Connect

    Mediaas, H.; Vinstad, J.E.; Oestvold, T.

    1996-10-01

    The solubility of MgO in MgCl{sub 2}-NaCl-NaF melts has been measured for melts with varying NaF concentration for x{sub MgCl{sub 2}} = 0.10 and 0.63 and for x{sub MgCl{sub 2}}/x{sub NaCl} = 1.70. Melt samples have been analyzed by carbothermal reduction (Leco TC-436) for total oxide content. The oxide content in the binary melt MgCl{sub 2}-NaCl was also analyzed by Iodometric titration. The results indicate two different oxide-containing species, denoted MgOCl and MgOF, in the solidified samples withdrawn from the melt. The latter appears only in fluoride-containing melts, but may, however, also contain chloride ions. The oxide solubility is increasing with increasing concentration of Mg{sup 2+} in both MgCl{sub 2}-NaCl and MgCl{sub 2}-NaCl-NaF melts. The solubility of MgO is always higher in fluoride containing melts at the same Mg{sup 2+} concentration. In the systems concentrated in MgCl{sub 2}, the increase in oxide solubility as function of x{sub NaF} is more pronounced than what is predicted from a simple model calculation. The increase is much smaller in the x{sub NaF} < 0.2 range for small MgCl{sub 2} contents than predicted from the same model calculation. The introduction of 1.7 mol% NaF to an industrial electrolyte does not seem to change the oxide solubility significantly. In such an electrolyte, where x{sub MgCl{sub 2}} {approx_equal} 0.1, the data gives a constant oxide solubility around 10 ppm O up to 5 mol% NaF.

  2. Electron microscopy of Mg/TiO{sub 2} photocatalyst morphology for deep desulfurization of diesel

    SciTech Connect

    Yin, Yee Cia; Kait, Chong Fai Fatimah, Hayyiratul Wilfred, Cecilia

    2015-07-22

    A series of Mg/TiO{sub 2} photocatalysts were prepared and characterized using Field Emission Scanning Electron Microscopy (FESEM) and High-Resolution Transmission Electron Microscopy (HRTEM). The average particle sizes of the photocatalysts were ranging from 25.7 to 35.8 nm. Incorporation of Mg on TiO{sub 2} did not lead to any surface lattice distortion to TiO{sub 2}. HRTEM data indicated the presence of MgO and Mg(OH){sub 2} mixture at low Mg loading while at higher Mg loading, the presence of lamellar Mg-oxyhydroxide intermediates and Mg(OH){sub 2}.

  3. Spin assignments of 22Mg states through a 24Mg(p,t)22Mg measurement

    SciTech Connect

    Chae, K. Y.; Jones, K. L.; Moazen, Brian; Pittman, S. T.; Bardayan, Daniel W; Blackmon, Jeff C; Liang, J Felix; Smith, Michael Scott; Chipps, K.; Hatarik, Robert; O'Malley, Patrick; Pain, Steven D; Kozub, R. L.; Matei, Catalin; Nesaraja, Caroline D

    2009-01-01

    The {sup 18}Ne({alpha},p){sup 21}Na reaction plays a crucial role in the ({alpha},p) process, which leads to the rapid proton capture process in X-ray bursts. The reaction rate depends upon properties of {sup 22}Mg levels above the {alpha} threshold at 8.14 MeV. Despite recent studies of these levels, only the excitation energies are known for most with no constraints on the spins. We have studied the {sup 24}Mg(p,t){sup 22}Mg reaction at the Oak Ridge National Laboratory (ORNL) Holifield Radioactive Ion Beam Facility (HRIBF), and by measuring the angular distributions of outgoing tritons, we provide the first experimental constraints on the spins of astrophysically-important {sup 18}Ne({alpha},p){sup 21}Na resonances.

  4. Interstitial Fe in MgO

    NASA Astrophysics Data System (ADS)

    Mølholt, T. E.; Mantovan, R.; Gunnlaugsson, H. P.; Svane, A.; Masenda, H.; Naidoo, D.; Bharuth-Ram, K.; Fanciulli, M.; Gislason, H. P.; Johnston, K.; Langouche, G.; Ólafsson, S.; Sielemann, R.; Weyer, G.

    2014-01-01

    Isolated 57Fe atoms were studied in MgO single-crystals by emission Mössbauer spectroscopy following implantation of 57Mn decaying to 57Fe. Four Mössbauer spectral components were found corresponding to different Fe lattice positions and/or charge states. Two components represent Fe atoms substituting Mg as Fe2+ and Fe3+, respectively; a third component is due to Fe in a strongly implantation-induced disturbed region. The fourth component, which is the focus of this paper, can be assigned to Fe at an interstitial site. Comparison of its measured isomer shift with ab initio calculations suggests that the interstitial Fe is located on, or close to, the face of the rock-salt MgO structure. To harmonize such an assignment with the measured near-zero quadrupole interaction a local motion process (cage motion) of the Fe has to be stipulated. The relation of such a local motion as a starting point for long range diffusion is discussed.

  5. Interstitial Fe in MgO

    SciTech Connect

    Mølholt, T. E. Gislason, H. P.; Ólafsson, S.; Mantovan, R.; Gunnlaugsson, H. P.; Svane, A.; Weyer, G.; Masenda, H.; Naidoo, D.; Bharuth-Ram, K.; Fanciulli, M.; Johnston, K.; Sielemann, R.

    2014-01-14

    Isolated {sup 57}Fe atoms were studied in MgO single-crystals by emission Mössbauer spectroscopy following implantation of {sup 57}Mn decaying to {sup 57}Fe. Four Mössbauer spectral components were found corresponding to different Fe lattice positions and/or charge states. Two components represent Fe atoms substituting Mg as Fe{sup 2+} and Fe{sup 3+}, respectively; a third component is due to Fe in a strongly implantation-induced disturbed region. The fourth component, which is the focus of this paper, can be assigned to Fe at an interstitial site. Comparison of its measured isomer shift with ab initio calculations suggests that the interstitial Fe is located on, or close to, the face of the rock-salt MgO structure. To harmonize such an assignment with the measured near-zero quadrupole interaction a local motion process (cage motion) of the Fe has to be stipulated. The relation of such a local motion as a starting point for long range diffusion is discussed.

  6. Experimental calibration of Mg isotope fractionation between aragonite and seawater

    NASA Astrophysics Data System (ADS)

    Wang, Zhengrong; Hu, Ping; Gaetani, Glenn; Liu, Chao; Saenger, Casey; Cohen, Anne; Hart, Stanley

    2013-02-01

    The detectable magnesium (Mg) isotope fractionation between biogenic aragonite (including aragonitic corals, bivalves, scaphopod, and sclerosponges) and seawater can potentially be applied to reconstruct sea surface temperature (SST) in the past. To calibrate this thermometer, eight sets of inorganic precipitation experiments ('free-drift') in seawater (Mg/Ca = 5 or 10) have been carried out at 25-55 °C over a range of degassing rate. A cleaning procedure was adopted to remove Mg contamination by sea salt, surface absorbed Mg and silicate dust as nucleation centers. The Mg isotope fractionation between cleaned aragonite and seawater-like aqueous solution varies insignificantly with Mg/Ca ratios and Mg isotope compositions of the initial solution, and the CO2-degassing rate (0-75 cc/min), but decreases noticeably with increasing temperatures having a temperature sensitivity of ˜0.008-0.01‰/°C in the following form: Δ≈1000lnα=1.67(±0.36)-0.82(±0.11)×{1000}/{T} where αaragonite-seawater is the fractionation factor, and T is the absolute temperature in Kelvin. It is consistent with equilibrium fractionation between Mg2+ aquo-complex and magnesite predicted by one theoretical calculation. Qualitative comparison among Mg-bearing carbonates based on Mg-O bond strengths show the relative sequence of 26Mg enrichment is aragonite > dolomite > magnesite > calcite. Thus, the surprising agreement indicates either the calculation overestimated Mg fractionation between magnesite and fluid, or both theoretical calculation and our calibration represent Mg isotope fractionation between MgCO30-H2O cluster and Mg2+ aquo complexes. Comparison of our calibration with the Mg isotope fractionation between biogenic aragonite and seawater suggests Mg and oxygen isotope fractionations of some biogenic aragonites (e.g., Porites sp. corals) agree with our calibration within analytical uncertainty, whereas others deviate significantly, indicating biological and/or kinetic isotope

  7. Interdiffusion and Intrinsic Diffusion in the Mg-Al System

    SciTech Connect

    Brennan, Sarah; Bermudez, Katrina; Sohn, Yong Ho; Kulkarni, Nagraj S

    2012-01-01

    Solid-to-solid diffusion couples were assembled and annealed to examine the diffusion between pure Mg (99.96%) and Al (99.999%). Diffusion anneals were carried out at 300 , 350 , and 400 C for 720, 360, and 240 hours, respectively. Optical and scanning electron microscopes were utilized to identify the formation of the intermetallic phases, -Al12Mg17 and -Al3Mg2 and absence of the -phase in the diffusion couples. Thicknesses of the -Al12Mg17 and -Al3Mg2 phases were measured and the parabolic growth constants were calculated to determine the activation energies for the growth, 165 and 86 KJ/mole, respectively. Concentration profiles were determined with electron microprobe analysis using pure elemental standards. Composition-dependent interdiffusion coefficients in Mg-solid solution, -Al12Mg17 and - Al3Mg2 and Al-solid solutions were calculated based on the Boltzmann-Matano analysis. Average effective interdiffusion coefficients for each phase were also calculated, and the magnitude was the highest for the -Al3Mg2 phase, followed by -Al12Mg17, Al-solid solution and Mg-solid solution. Intrinsic diffusion coefficients based on Huemann s analysis (e.g., marker plane) were determined for the ~38 at.% Mg in the -Al3Mg2 phase. Activation energies and the pre-exponential factors for the inter- and intrinsic diffusion coefficients were calculated for the temperature range examined. The -Al3Mg2 phase was found to have the lowest activation energies for growth and interdiffusion among all four phases studied. At the marker location in the -Al3Mg2 phase, the intrinsic diffusion of Al was found to be faster than that of Mg. Extrapolations of the impurity diffusion coefficients in the terminal solid solutions were made and compared to the available self- and impurity diffusion data from literature. Thermodynamic factor, tracer diffusion coefficients and atomic mobilities at the marker plane composition were approximated using available literature values of Mg activity in the -Al

  8. Scleractinian Fossil Corals as Archives of Seawater δ26Mg

    NASA Astrophysics Data System (ADS)

    Gothmann, A. O.; Higgins, J. A.; Adkins, J. F.; Stolarski, J.; Bender, M. L.

    2014-12-01

    The recovery of environmental signatures from coral skeletons is often made difficult by 'vital effects', which cause skeletal chemistry to deviate from the expected composition of aragonite in equilibrium with seawater. Recent studies show that Mg isotopes in scleractinian corals are subject to vital effects, which appear as a departure of the δ26Mg coral temperature dependence from that of inorganic aragonite [1]. However, different from the case for Mg/Ca or δ44Ca in coral, the magnitude of the observed Mg-isotope vital effect is small (on the order of 0.1 ‰ or less). In addition, measurements of different species of modern coral show similar fractionations, suggesting that coral δ26Mg is not species dependent [2]. Together, these observations indicate that corals should faithfully record the seawater Mg-isotope composition, and that vital effects will not bias reconstructions. We measured Mg isotopes in a set of extremely well-preserved fossil scleractinian corals, ranging in age from Jurassic through Recent, to reconstruct past seawater δ26Mg. Well-preserved fossil corals of similar age show a range in δ26Mg of ~0.2 ‰, pointing to the presence of vital effects. However, our results show little variability in the δ26Mg of fossil corals across different geologic ages, suggesting that seawater δ26Mg has remained relatively constant throughout the Cenozoic and Mesozoic. This pattern has implications for our understanding of the mechanisms driving secular variations in seawater Mg/Ca. In particular, our data imply that dolomitization rates have not changed enough during the Mesozoic and Cenozoic to account for secular variations in seawater Mg/Ca. Our coral δ26Mg record agrees with a Cenozoic record from bulk foraminifera, further supporting the faithfulness of the coral archive. However, both of these records disagree with a third Cenozoic Mg-isotope record, derived from species-specific planktic forams [3]. [1] Saenger, C. et al. (2014) Chem. Geol

  9. Preparation and characterisation of Os doped MgB2

    NASA Astrophysics Data System (ADS)

    Grivel, J.-C.; Namazkar, S.; Alexiou, A.; Holte, O. J.

    2014-12-01

    Polycrystalline samples with Mg1-xOsxB2.04 nominal stoichiometry were made by reacting elemental powders at 800 °C under argon atmosphere. Based on XRD diffraction patterns, EDS analysis and magnetisation measurements, it is found that Os can replace up to about 1 at.% Mg in the MgB2 lattice. Beyond this doping level, unreacted Os and Mg-rich Mg-Os impurity phases are formed. The a-axis parameter contracts upon doping while the superconducting transition temperature decreases at a rate of 2.1 K/at.% Os substitution. At 10 K, Os doping induces an improvement of the normalised critical current density under applied magnetic fields in excess of 0.5 T, indicating a modest enhancement of flux pinning in this range.

  10. Phase stability in the Cd-Mg system

    SciTech Connect

    Asta, M.; McCormack, R.; de Fontaine, D.

    1993-12-31

    This paper reports on results of a theoretical study of solid-state phase equilibria and short-range order in Cd-Mg alloys. Results of first-principles linear muffin-tin orbital method total-energy calculations for seven hcp-based superstructures have been combined with cluster-variation-method calculations of thermodynamic properties in order to compute the Cd-Mg phase diagram. Effect on the calculated phase diagram of contributions to the alloy free energy arising from atomic vibrations and structural relaxations are assessed using available experimental information for ordered and disordered alloys in the Cd-Mg system.

  11. Mg2+ coordinating dynamics in Mg:ATP fueled motor proteins

    NASA Astrophysics Data System (ADS)

    Bojovschi, A.; Liu, Ming S.; Sadus, Richard J.

    2014-03-01

    The coordination of Mg2+ with the triphosphate group of adenosine triphosphate (ATP) in motor proteins is investigated using data mining and molecular dynamics. The possible coordination structures available from crystal data for actin, myosin, RNA polymerase, DNA polymerase, DNA helicase, and F1-ATPase are verified and investigated further by molecular dynamics. Coordination states are evaluated using structural analysis and quantified by radial distribution functions, coordination numbers, and pair interaction energy calculations. The results reveal a diverse range of both transitory and stable coordination arrangements between Mg2+ and ATP. The two most stable coordinating states occur when Mg2+ coordinates two or three oxygens from the triphosphate group of ATP. Evidence for five-site coordination is also reported involving water in addition to the triphosphate group. The stable states correspond to a pair interaction energy of either ˜-2750 kJ/mol or -3500 kJ/mol. The role of water molecules in the hydration shell surrounding Mg2+ is also reported.

  12. Oxidation and growth of Mg thin films on Ru(001)

    NASA Astrophysics Data System (ADS)

    Huang, H. H.; Jiang, X.; Siew, H. L.; Chin, W. S.; Sim, W. S.; Xu, G. Q.

    1999-08-01

    The oxidation and growth of ultra-thin Mg films on a Ru(001) substrate have been studied using X-ray photoelectron spectroscopy (XPS) and thermal desorption spectroscopy (TDS) in the temperature range of 300-1500 K. Our results suggest that the growth of Mg thin films follows a layer-by-layer mode. Upon oxygen adsorption at 300 K, two O 1s peaks were detected on the Mg film. The peak at 532.2-532.6 eV could be attributed to either dioxygen or partially reduced species (O δ-, δ<2), whereas that at 530.1-530.6 eV is due to lattice oxygen in MgO. Annealing of the oxidized film to 800 K causes the conversion of the dioxygen or partially reduced species to the oxide state. Thermal desorption peaks of MgO were directly detected at 1000-1127 and 1350-1380 K, respectively. However, initial evaporation of Mg atoms onto an oxygen pre-adsorbed surface yields a fully oxidized MgO. Further Mg deposition results in the formation of a partially oxidized film with the observation of an O 1s peak at 532.2 eV.

  13. LOW Mg/Si PLANETARY HOST STARS AND THEIR Mg-DEPLETED TERRESTRIAL PLANETS

    SciTech Connect

    Carter-Bond, Jade C.; O'Brien, David P.; Delgado Mena, Elisa; Israelian, Garik; Gonzalez Hernandez, Jonay I.; Santos, Nuno C.

    2012-03-15

    Simulations have shown that a diverse range of extrasolar terrestrial planet bulk compositions are likely to exist based on the observed variations in host star elemental abundances. Based on recent studies, it is expected that a significant proportion of host stars may have Mg/Si ratios below 1. Here we examine this previously neglected group of systems. Planets simulated as forming within these systems are found to be Mg-depleted (compared to Earth), consisting of silicate species such as pyroxene and various feldspars. Planetary carbon abundances also vary in accordance with the host star C/O ratio. The predicted abundances are in keeping with observations of polluted white dwarfs, lending validity to this approach. Further studies are required to determine the full planetary impacts of the bulk compositions predicted here.

  14. Room-temperature perpendicular magnetic anisotropy of MgO/Fe/MgO ultrathin films

    SciTech Connect

    Kozioł-Rachwał, A.; Ślęzak, T.; Przewoźnik, J.; Skowroński, W.; Stobiecki, T.; Wilgocka-Ślęzak, D.; Qin, Q. H.; Dijken, S. van; Korecki, J.

    2013-12-14

    We used the anomalous Hall effect to study the magnetic properties of MgO/Fe(t)/MgO(001) structures in which the Fe thickness t ranged from 4 Å to 14 Å. For the iron deposited at 140 K, we obtained perpendicular magnetization at room temperature below the critical thickness of t{sub c} = (9 ± 1) Å. In the vicinity of t{sub c}, the easy magnetization axis switched from an out-of-plane orientation to an in-plane orientation, and the observed spin-reorientation transition was considered in terms of the competition among different anisotropies. The perpendicular magnetization direction was attributed to magnetoelastic anisotropy. Finally, the temperature-dependent spin-reorientation transition was analyzed for Fe thicknesses close to t{sub c}.

  15. Improved hydrogen storage kinetics of the Li-Mg-N-H system by addition of Mg(BH4)2.

    PubMed

    Pan, Hongge; Shi, Songbo; Liu, Yongfeng; Li, Bo; Yang, Yanjing; Gao, Mingxia

    2013-03-21

    A Mg(BH(4))(2)-added Mg(NH(2))(2)-2LiH system was prepared by ball milling the corresponding chemicals. The hydrogen storage properties of the Mg(NH(2))(2)-2LiH-xMg(BH(4))(2) (x = 0, 0.1, 0.2, 0.3) samples and the role played by Mg(BH(4))(2) were systematically investigated. The results show that the onset and peak temperatures for hydrogen desorption from the Mg(BH(4))(2)-added Mg(NH(2))(2)-2LiH sample shifted to lower temperatures. In particular, the Mg(NH(2))(2)-2LiH-0.1Mg(BH(4))(2) sample could reversibly absorb ~4.5 wt% of hydrogen in the temperature range of 120-150 °C, which is superior to the pristine sample. During ball milling, a metathesis reaction between Mg(BH(4))(2) and LiH readily occurred to form LiBH(4) and MgH(2) and subsequently, the newly formed MgH(2) reacted with Mg(NH(2))(2) to generate MgNH. Upon heating, the presence of LiBH(4) not only decreased the recrystallization temperature of Mg(NH(2))(2) but also reacted with LiNH(2) to form the Li(4)(BH(4))(NH(2))(3) intermediate, which weakens the N-H bonding and enhances the ion conductivity. Meanwhile, MgNH may act as the nucleation center for the dehydrogenation product of Li(2)MgN(2)H(2) due to the structural similarity. Thus, the in situ formed LiBH(4) and MgNH provide a synergetic effect to improve the hydrogen storage performances of the Mg(NH(2))(2)-2LiH system. PMID:23178338

  16. Global Mapping of Mg-Number Derived from Clementine Data.

    NASA Astrophysics Data System (ADS)

    Cahill, J. T.; Lucey, P. G.; Gillis, J. J.; Steutel, D.

    2004-12-01

    environmental space exposure on the optical properties of these minerals. This was accomplished using Clementine ultraviolet and visible (UVVIS) data and a Hapke radiative transfer mixing model. The major features evident in these maps are the strong distinction between mare and highland regions, the former showing low Mg* and the latter generally higher; a large northern highlands unit with low Mg*, and an Mg* high north of South Pole-Aitken basin. Mare units are not universally low, mare Frigoris in particular has elevated Mg* relative to other mare. The strongest variations in the highlands occur in plagioclase rich, low FeO units, that exhibit values ranging near 50 to near 100 in coherent units. The craters Tycho and Aristarchus also exhibit high Mg*; these gabbroic anomalies may indicate more extensive Mg-rich material at depth. Deposits within SPA are unremarkable relative to surroundings, and share the intermediate Mg* of most of the highlands. 1. James, O.B. et al. PLPSC. 1989.; 2.Bersch, M.G., et al., GRL, 1991.; 3. Floss, C., et al., GCA, 1998.; 4. Korotev, R.L., et al., GCA, 2003.

  17. Characterization of Mg2+ Distributions around RNA in Solution

    PubMed Central

    2016-01-01

    Binding of metal ions is an important factor governing the folding and dynamics of RNA. Shielding of charges in the polyanionic backbone allows RNA to adopt a diverse range of folded structures that give rise to their many functions within the cell. Some RNA sequences fold only in the presence of Mg2+, which may be bound via direct interactions or occupy the more diffuse “ion atmosphere” around the RNA. To understand the driving forces for RNA folding, it is important to be able to fully characterize the distribution of metal ions around the RNA. In this work, a combined Grand Canonical Monte Carlo-Molecular Dynamics (GCMC-MD) method is applied to characterize Mg2+ distributions around folded RNA structures. The GCMC-MD approach identifies known inner- and outer-shell Mg2+ coordination, while also predicting new regions occupied by Mg2+ that are not observed in crystal structures but that may be relevant in solution, including the case of the Mg2+ riboswitch, for which alternate Mg2+ binding sites may have implications for its function. This work represents a significant step forward in establishing a structural and thermodynamic description of RNA–Mg2+ interactions and their role in RNA structure and function.

  18. ZnCdMgSe-Based Semiconductors for Intersubband Devices

    SciTech Connect

    Tamargo, Maria C.

    2008-11-13

    This paper presents a review of recent results on the application of ZnCdMgSe-based wide bandgap II-VI compounds to intersubband devices such as quantum cascade lasers and quantum well infrared photodetectors operating in the mid-infrared region. The conduction band offset of ZnCdSe/ZnCdMgSe quantum well structures was determined from contactless electroreflectance measurements to be as high as 1.12 eV. FT-IR was used to measure intersubband absorption in multi-quantum well structures in the mid-IR range. Electroluminescence at 4.8 {mu}m was observed from a quantum cascade emitter structure made from these materials. Preliminary results are also presented on self assembled quantum dots of CdSe on ZnCdMgSe, and novel quantum well structures with metastable binary MgSe barriers.

  19. Telemetry Ranging: Concepts

    NASA Astrophysics Data System (ADS)

    Hamkins, J.; Kinman, P.; Xie, H.; Vilnrotter, V.; Dolinar, S.

    2015-11-01

    Telemetry ranging is a proposed alternative to conventional two-way ranging for determining the two-way time delay between a Deep Space Station (DSS) and a spacecraft. The advantage of telemetry ranging is that the ranging signal on the uplink is not echoed to the downlink, so that telemetry alone modulates the downlink carrier. The timing information needed on the downlink, in order to determine the two-way time delay, is obtained from telemetry frames. This article describes the phase and timing estimates required for telemetry ranging, and how two-way range is calculated from these estimates. It explains why the telemetry ranging architecture does not require the spacecraft transponder to have a high-frequency or high-quality oscillator, and it describes how a telemetry ranging system can be infused in the Deep Space Network.

  20. First-principles study of Mg(0001)/MgO(1-11) interfaces

    NASA Astrophysics Data System (ADS)

    Song, Hong-Quan; Zhao, Ming; Li, Jian-Guo

    2016-06-01

    By means of first-principles density-functional calculations, we studied the surface energy of a nonstoichiometric MgO(1-11) slab, the interfacial energy and interfacial bonding characteristics of Mg-terminated and O-terminated Mg/MgO(1-11) interfaces with three stacking-site (TOP, HCP and FCC sites) models, and the effect of the thickness of Mg films on the O-terminated MgO(1-11) surface. The results indicate that the surface energies of the nonstoichiometric MgO(1-11) slab and interfacial energies of Mg/Mg(1-11) interface depend on Mg chemical potential. We found that the Mg-terminated MgO(1-11) surface is more stable than the O-terminated MgO(1-11) surface at high Mg chemical potential, and Mg/MgO(1-11) with FCC stacking-site model is the most stable configuration in the Mg/MgO(1-11) interfaces. The results of the electronic structure reveals that the interfacial bonding of Mg-terminated interface with FCC site model mainly consists of metallic bond and of the O-terminated interface with FCC site model is mainly ionic with a small degree of σ-type covalent bond. Although the interfacial energy of Mg-terminated Mg/MgO interface with FCC stacking-site model is slightly higher than that of O-terminated Mg/MgO interface, the molten Mg would epitaxially grow on the FCC sites of the Mg-terminated MgO(1-11) surface because of the high evaporation pressure of Mg at high temperature.

  1. RADIO RANGING DEVICE

    DOEpatents

    Nieset, R.T.

    1961-05-16

    A radio ranging device is described. It utilizes a super regenerative detector-oscillator in which echoes of transmitted pulses are received in proper phase to reduce noise energy at a selected range and also at multiples of the selected range.

  2. SAR ambiguous range suppression.

    SciTech Connect

    Doerry, Armin Walter

    2006-09-01

    Pulsed Radar systems suffer range ambiguities, that is, echoes from pulses transmitted at different times arrive at the receiver simultaneously. Conventional mitigation techniques are not always adequate. However, pulse modulation schemes exist that allow separation of ambiguous ranges in Doppler space, allowing easy filtering of problematic ambiguous ranges.

  3. Simultaneous desorption behavior of M borohydrides and Mg2FeH6 reactive hydride composites (M = Mg, then Li, Na, K, Ca)

    NASA Astrophysics Data System (ADS)

    Chaudhary, Anna-Lisa; Li, Guanqiao; Matsuo, Motoaki; Orimo, Shin-ichi; Deledda, Stefano; Sørby, Magnus H.; Hauback, Bjørn C.; Pistidda, Claudio; Klassen, Thomas; Dornheim, Martin

    2015-08-01

    Combinations of complex metal borohydrides ball milled with the transition metal complex hydride, Mg2FeH6, are analysed and compared. Initially, the Reactive Hydride Composite (RHC) of Mg2+ cation mixtures of Mg2FeH6 and γ-Mg(BH4)2 is combined in a range of molar ratios and heated to a maximum of 450 °C. For the molar ratio of 6 Mg2FeH6 + Mg(BH4)2, simultaneous desorption of the two hydrides occurred, which resulted in a single event of hydrogen release. This single step desorption occurred at temperatures between those of Mg2FeH6 and γ-Mg(BH4)2. Keeping this anionic ratio constant, the desorption behavior of four other borohydrides, Li-, Na-, K-, and Ca-borohydrides was studied by using materials ball milled with Mg2FeH6 applying the same milling parameters. The mixtures containing Mg-, Li-, and Ca-borohydrides also released hydrogen in a single event. The Mass Spectrometry (MS) results show a double step reaction within a narrow temperature range for both the Na- and K-borohydride mixtures. This phenomenon, observed for the RHC systems at the same anionic ratio with all five light metal borohydride mixtures, can be described as simultaneous hydrogen desorption within a narrow temperature range centered around 300 °C.

  4. Telemetry Ranging: Signal Processing

    NASA Astrophysics Data System (ADS)

    Hamkins, J.; Kinman, P.; Xie, H.; Vilnrotter, V.; Dolinar, S.

    2016-02-01

    This article describes the details of the signal processing used in a telemetry ranging system in which timing information is extracted from the downlink telemetry signal in order to compute spacecraft range. A previous article describes telemetry ranging concepts and architecture, which are a slight variation of a scheme published earlier. As in that earlier work, the telemetry ranging concept eliminates the need for a dedicated downlink ranging signal to communicate the necessary timing information. The present article describes the operation and performance of the major receiver functions on the spacecraft and the ground --- many of which are standard tracking loops already in use in JPL's flight and ground radios --- and how they can be used to provide the relevant information for making a range measurement. It also describes the implementation of these functions in software, and performance of an end-to-end software simulation of the telemetry ranging system.

  5. Highly (100) oriented MgO growth on thin Mg layer in MTJ structure

    NASA Astrophysics Data System (ADS)

    Jimbo, K.; Nakagawa, S.

    2011-01-01

    In order to apply Stress Assisted Magnetization Reversal (SAMR) method to perpendicular magnetoresistive random access memory (p-MRAM) with magnetic tunnel junction (MTJ) using MgO (001) oriented barrier layer, multilayer of Ta/ Terfenol-D/ Mg/ MgO and Ta/ Terfenol-D/ MgO were prepared. While the MgO layer, deposited directly on the Terfenol-D layer, did not show (100) orientatin, very thin metallic Mg layer, deposited prior to the MgO deposition, was effective to attain MgO (100) orientation. The crystalline orientation was very weak without Mg, however, the multilayer with Mg showed very strong MgO(100) peak and the MgO orientation was shifted depending on the Mg thickness.

  6. Telemetry-Based Ranging

    NASA Technical Reports Server (NTRS)

    Hamkins, Jon; Vilnrotter, Victor A.; Andrews, Kenneth S.; Shambayati, Shervin

    2011-01-01

    A telemetry-based ranging scheme was developed in which the downlink ranging signal is eliminated, and the range is computed directly from the downlink telemetry signal. This is the first Deep Space Network (DSN) ranging technology that does not require the spacecraft to transmit a separate ranging signal. By contrast, the evolutionary ranging techniques used over the years by NASA missions, including sequential ranging (transmission of a sequence of sinusoids) and PN-ranging (transmission of a pseudo-noise sequence) whether regenerative (spacecraft acquires, then regenerates and retransmits a noise-free ranging signal) or transparent (spacecraft feeds the noisy demodulated uplink ranging signal into the downlink phase modulator) relied on spacecraft power and bandwidth to transmit an explicit ranging signal. The state of the art in ranging is described in an emerging CCSDS (Consultative Committee for Space Data Systems) standard, in which a pseudo-noise (PN) sequence is transmitted from the ground to the spacecraft, acquired onboard, and the PN sequence is coherently retransmitted back to the ground, where a delay measurement is made between the uplink and downlink signals. In this work, the telemetry signal is aligned with the uplink PN code epoch. The ground station computes the delay between the uplink signal transmission and the received downlink telemetry. Such a computation is feasible because symbol synchronizability is already an integral part of the telemetry design. Under existing technology, the telemetry signal cannot be used for ranging because its arrival-time information is not coherent with any Earth reference signal. By introducing this coherence, and performing joint telemetry detection and arrival-time estimation on the ground, a high-rate telemetry signal can provide all the precision necessary for spacecraft ranging.

  7. Micron Accurate Absolute Ranging System: Range Extension

    NASA Technical Reports Server (NTRS)

    Smalley, Larry L.; Smith, Kely L.

    1999-01-01

    The purpose of this research is to investigate Fresnel diffraction as a means of obtaining absolute distance measurements with micron or greater accuracy. It is believed that such a system would prove useful to the Next Generation Space Telescope (NGST) as a non-intrusive, non-contact measuring system for use with secondary concentrator station-keeping systems. The present research attempts to validate past experiments and develop ways to apply the phenomena of Fresnel diffraction to micron accurate measurement. This report discusses past research on the phenomena, and the basis of the use Fresnel diffraction distance metrology. The apparatus used in the recent investigations, experimental procedures used, preliminary results are discussed in detail. Continued research and equipment requirements on the extension of the effective range of the Fresnel diffraction systems is also described.

  8. Fabrication and superconducting properties of internal Mg diffusion processed MgB2 wires using MgB4 precursors

    NASA Astrophysics Data System (ADS)

    Xu, Da; Wang, Dongliang; Yao, Chao; Zhang, Xianping; Ma, Yanwei; Oguro, Hidetoshi; Awaji, Satoshi; Watanabe, Kazuo

    2016-10-01

    Monofilament MgB2/Nb/Monel wires were fabricated using three different MgB4 precursors by an internal Mg diffusion (IMD) process. The wire geometry and heat-treatment conditions were optimized in order to improve the critical current density (J c) of the MgB2 wire. The influences of the quality of MgB4 powders, such as the particle size and MgO impurity, on the microstructure and superconducting properties of the wires were discussed. Although there were small amounts of voids, unreacted MgB4 particles and MgO impurity existed in the superconducting layers, and the transport layer J c of the wire with the MgB4 precursor reached 3.0 × 104 A cm-2 at 4.2 K and 10 T, which was comparable to that of IMD-processed wires fabricated using boron precursors. Both the non-barrier J c and engineering J c of MgB2 wire made using a MgB4 precursor were enhanced due to the improved grain connectivity and the enlarged fill factor.

  9. The acute effects of amisulpride (50 mg and 200 mg) and haloperidol (2 mg) on cognitive function in healthy elderly volunteers.

    PubMed

    Legangneux, E; McEwen, J; Wesnes, K A; Bergougnan, L; Miget, N; Canal, M; L'Heritier, C; Pinquier, J L; Rosenzweig, P

    2000-06-01

    In this double-blind, placebo controlled, four-way cross-over trial in 16 healthy elderly volunteers, the acute effects of haloperidol 2 mg, amisulpride 50 mg and 200 mg, were assessed on a range of tests of cognitive function. On each study day, cognitive performance was assessed prior to dosing and at 2, 4, 6, 9, 12 and 24 h after dosing with the following tests from the Cognitive Drug Research computerized assessment system: simple reaction time, digit vigilance task, choice reaction time, visual tracking, Critical Flicker Fusion, body sway, numeric working memory, immediate and delayed word recall, word recognition and self-ratings of mood and alertness. Haloperidol showed a general tendency to impair performance, and although this did not reach significance compared to placebo, for two tasks there were significant impairments with haloperidol compared to amisulpride. Amisulpride 50 mg and 200 mg, was not associated with impairment. In fact, there was some suggestion of improvement over placebo on three measures. The timings of assessment were appropriate for the study compounds. Furthermore, in a recent study in which a smaller number of elderly volunteers was tested on the same cognitive assessment system, a clear profile of acute impairments of haloperidol 3 mg, was identified. This indicates that haloperidol 2 mg, is not a sufficient dose to affect cognitive function in the elderly, supporting the general absence of effects with this dose in the young. Thus, the general absence of cognitive impairments with amisulpride at the doses used in this study suggests that this compound does not impair cognitive function in the elderly. PMID:10890311

  10. Atomistically informed solute drag in Al Mg

    NASA Astrophysics Data System (ADS)

    Zhang, F.; Curtin, W. A.

    2008-07-01

    Solute drag in solute-strengthened alloys, caused by diffusion of solute atoms around moving dislocations, controls the stress at deformation rates and temperatures useful for plastic forming processes. In the technologically important Al-Mg alloys, the solute drag stresses predicted by classical theories are much larger than experiments, which is resolved in general by eliminating the singularity of the dislocation core via Peierls-Nabarro-type models. Here, the drag stress versus dislocation velocity is computed numerically using a realistic dislocation core structure obtained from an atomistic model to investigate the role of the core and obtain quantitative stresses for comparison with experiment. The model solves a discrete diffusion equation in a reference frame moving with the dislocation, with input solute enthalpies and diffusion activation barriers in the core computed by or estimated from atomistic studies. At low dislocation velocities, the solute drag stress is controlled by bulk solute diffusion because the core diffusion occurs too quickly. In this regime, the drag stress can be obtained using a Peierls-Nabarro model with a core spreading parameter tuned to best match the atomistic models. At intermediate velocities, both bulk and core diffusion can contribute to the drag, leading to a complex stress-velocity relationship showing two peaks in stress. At high velocities, the drag stress is controlled solely by diffusion within and across the core. Like the continuum models, the drag stress is nearly linear in solute concentration. The Orowan relationship is used to connect dislocation velocity to deformation strain rate. Accounting for the dependence of mobile dislocation density on stress, the simulations are in good agreement with experiments on Al-Mg alloys over a range of concentrations and temperatures.

  11. Automatic range selector

    DOEpatents

    McNeilly, Clyde E.

    1977-01-04

    A device is provided for automatically selecting from a plurality of ranges of a scale of values to which a meter may be made responsive, that range which encompasses the value of an unknown parameter. A meter relay indicates whether the unknown is of greater or lesser value than the range to which the meter is then responsive. The rotatable part of a stepping relay is rotated in one direction or the other in response to the indication from the meter relay. Various positions of the rotatable part are associated with particular scales. Switching means are sensitive to the position of the rotatable part to couple the associated range to the meter.

  12. Inhibition of DNA ejection from bacteriophage by Mg+2 counterions

    NASA Astrophysics Data System (ADS)

    Lee, Sell; Tran, C. V.; Nguyen, T. T.

    2011-03-01

    The problem of inhibiting viral DNA ejection from bacteriophages by multivalent counterions, specifically Mg+2 counterions, is studied. Experimentally, it is known that MgSO4 salt has a strong and nonmonotonic effect on the amount of DNA ejected. There exists an optimal concentration at which the minimum amount of DNA is ejected from the virus. At lower or higher concentrations, more DNA is ejected from the capsid. We propose that this phenomenon is the result of DNA overcharging by Mg+2 multivalent counterions. As Mg+2 concentration increases from zero, the net charge of DNA changes from negative to positive. The optimal inhibition corresponds to the Mg+2 concentration where DNA is neutral. At lower/higher concentrations, DNA genome is charged. It prefers to be in solution to lower its electrostatic self-energy, which consequently leads to an increase in DNA ejection. By fitting our theory to available experimental data, the strength of DNA-DNA short range attraction energies, mediated by Mg+2, is found to be -0.004 kBT per nucleotide base. This and other fitted parameters agree well with known values from other experiments and computer simulations. The parameters are also in agreement qualitatively with values for tri- and tetravalent counterions.

  13. Inhibition of DNA ejection from bacteriophage by Mg^+2 counterions

    NASA Astrophysics Data System (ADS)

    Lee, Seil; Tran, Cathy V.; Nguyen, Toan T.

    2009-03-01

    The problem of inhibiting viral DNA ejection from bacteriophages by multivalent counterions, especially Mg^+2 counterions, is studied. Experimentally, it is known that MgSO4 salt has a strong and non-monotonic effect on the amount of DNA ejected. There exists an optimal concentration at which the least DNA is ejected from the virus. At lower or higher concentrations, more DNA is ejected from the capsid. We propose that this phenomenon is the result of DNA overcharging by Mg^+2 multivalent counterions. As Mg^+2 concentration increases from zero, DNA net charge changes from negative to positive. The optimal inhibition corresponds to the Mg^+2 concentration where DNA is neutral. At lower/higher concentrations, DNA genome is charged. It prefers to be in solution to lower its electrostatic self-energy, which consequently leads to an increase in DNA ejection. Our theory fits experimental data well. The strength of DNA-DNA short range attraction, mediated by Mg^+2, is found to be -0.003 kBT per nucleotide base.

  14. Impact of Mg concentration on energy-band-depth profile of Mg-doped InN epilayers analyzed by hard X-ray photoelectron spectroscopy

    SciTech Connect

    Imura, M.; Tsuda, S.; Nagata, T.; Takeda, H.; Liao, M. Y.; Koide, Y.; Yang, A. L.; Yamashita, Y.; Yoshikawa, H.; Kobayashi, K.; Kaneko, M.; Uematsu, N.; Wang, K.; Araki, T.; Nanishi, Y.

    2013-10-14

    The electronic structures of Mg-doped InN (Mg-InN) epilayers with the Mg concentration, [Mg], ranging from 1 × 10{sup 19} to 5 × 10{sup 19} cm{sup −3} were systematically investigated by soft and hard X-ray photoelectron spectroscopies. The angle-resolved results on the core-level and valence band photoelectron spectra as a function of [Mg] revealed that the energy band of Mg-InN showed downward bending due to the n{sup +} surface electron accumulation and p type layers formed in the bulk. With an increase in [Mg], the energy-band changed from monotonic to two-step n{sup +}p homojunction structures. The oxygen concentration rapidly increased at the middle-bulk region (∼4.5 to ∼7.5 nm) from the surface, which was one of the reasons of the transformation of two-step energy band.

  15. Range Scheduling Aid (RSA)

    NASA Technical Reports Server (NTRS)

    Logan, J. R.; Pulvermacher, M. K.

    1991-01-01

    Range Scheduling Aid (RSA) is presented in the form of the viewgraphs. The following subject areas are covered: satellite control network; current and new approaches to range scheduling; MITRE tasking; RSA features; RSA display; constraint based analytic capability; RSA architecture; and RSA benefits.

  16. A Facile Approach Using MgCl2 to Formulate High Performance Mg2+ Electrolytes for Rechargeable Mg Batteries

    SciTech Connect

    Liu, Tianbiao L.; Shao, Yuyan; Li, Guosheng; Gu, Meng; Hu, Jian Z.; Xu, Suochang; Nie, Zimin; Chen, Xilin; Wang, Chong M.; Liu, Jun

    2014-01-01

    Rechargeable Mg batteries have been regarded as a viable battery technology for grid scale energy storage and transportation applications. However, the limited performance of Mg2+ electrolytes has been a primary technical hurdle to develop high energy density rechargeable Mg batteries. In this study, MgCl2 is demonstrated as a non-nucleophilic and cheap Mg2+ source in combining with Al Lewis acids (AlCl3, AlPh3 and AlEtCl2) to formulate a series of Mg2+ electrolytes characteristic of high oxidation stability (up to 3.4 V vs Mg), sulfur compatibility and electrochemical reversibility (up to 100% coulombic efficiency). Three electrolyte systems (MgCl2-AlCl3, MgCl2-AlPh3, and MgCl2-AlEtCl2) were prepared free of purification and fully characterized by multinuclear NMR (27Al{1H} and 25Mg{1H}) spectroscopies, single crystal X-ray diffraction, and electrochemical analysis. The reaction mechanism of MgCl2 and the Al Lewis acids in THF is discussed to highlight the formation of the electrochemically active [(µ-Cl)3Mg2(THF)6]+ monocation in these electrolytes. We are grateful for the financial support from the Pacific Northwest National Laboratory (PNNL)-Laboratory Directed Research and Development (LDRD) program for developing magnesium battery technology. The XRD and SEM data were collected at the Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the DOE’s Office of Biological and Environmental Research and located at PNNL. PNNL is a multiprogram laboratory operated by Battelle Memorial Institute for the Department of Energy under Contract DE-AC05-76RL01830.

  17. Home range and travels

    USGS Publications Warehouse

    Stickel, L.F.; King, John A.

    1968-01-01

    The concept of home range was expressed by Seton (1909) in the term 'home region,' which Burr (1940, 1943) clarified with a definition of home range and exemplified in a definitive study of Peromyscus in the field. Burt pointed out the ever-changing characteristics of home-range area and the consequent absence of boundaries in the usual sense--a finding verified by investigators thereafter. In the studies summarized in this paper, sizes of home ranges of Peromyscus varied within two magnitudes, approximately from 0.1 acre to ten acres, in 34 studies conducted in a variety of habitats from the seaside dunes of Florida to the Alaskan forests. Variation in sizes of home ranges was correlated with both environmental and physiological factors; with habitat it was conspicuous, both in the same and different regions. Food supply also was related to size of home range, both seasonally and in relation to habitat. Home ranges generally were smallest in winter and largest in spring, at the onset of the breeding season. Activity and size also were affected by changes in weather. Activity was least when temperatures were low and nights were bright. Effects of rainfall were variable. Sizes varied according to sex and age; young mice remained in the parents' range until they approached maturity, when they began to travel more widely. Adult males commonly had larger home ranges than females, although there were a number of exceptions. An inverse relationship between population density and size of home range was shown in several studies and probably is the usual relationship. A basic need for activity and exploration also appeared to influence size of home range. Behavior within the home range was discussed in terms of travel patterns, travels in relation to home sites and refuges, territory, and stability of size of home range. Travels within the home range consisted of repeated use of well-worn trails to sites of food, shelter, and refuge, plus more random exploratory travels

  18. The role of Mg in the crystallization of monohydrocalcite

    NASA Astrophysics Data System (ADS)

    Rodriguez-Blanco, Juan Diego; Shaw, Samuel; Bots, Pieter; Roncal-Herrero, Teresa; Benning, Liane G.

    2014-02-01

    Monohydrocalcite is a member of the carbonate family which forms in Mg-rich environments at a wide range of Mg/Ca ratios Mg2+aq/Ca2+aq≥0.17<65. Although found in modern sedimentary deposits and as a product of biomineralization, there is a lack of information about its formation mechanisms and about the role of Mg during its crystallization. In this work we have quantitatively assessed the mechanism of crystallization of monohydrocalcite through in situ synchrotron-based small and wide angle X-ray scattering (SAXS/WAXS) and off-line spectroscopic, microscopic and wet chemical analyses. Monohydrocalcite crystallizes via a 4-stage process beginning with highly supersaturated solutions from which a Mg-bearing, amorphous calcium carbonate (ACC) precursor precipitates. This precursor crystallizes to monohydrocalcite via a nucleation-controlled reaction in stage two, while in stage three it is further aged through Ostwald-ripening at a rate of 1.8 ± 0.1 nm/h1/2. In stage four, a secondary Ostwald ripening process (66.3 ± 4.3 nm/h1/2) coincides with the release of Mg from the monohydrocalcite structure and the concomitant formation of minor hydromagnesite. Our data reveal that monohydrocalcite can accommodate significant amounts of Mg in its structure (χMgCO3 = 0.26) and that its Mg content and dehydration temperature are directly proportional to the saturation index for monohydrocalcite (SIMHC) immediately after mixing the stock solutions. However, its crystallite and particle size are inversely proportional to these parameters. At high supersaturations (SIMHC = 3.89) nanometer-sized single crystals of monohydrocalcite form, while at low values (SIMHC = 2.43) the process leads to low-angle branching spherulites. Many carbonates produced during biomineralization form at similar conditions to most synthetic monohydrocalcites, and thus we hypothesize that some calcite or aragonite deposits found in the geologic record that have formed at high Mg/Ca ratios could be

  19. Mg isotope constraints on soil pore-fluid chemistry: Evidence from Santa Cruz, California

    NASA Astrophysics Data System (ADS)

    Tipper, Edward T.; Gaillardet, Jérôme; Louvat, Pascale; Capmas, Françoise; White, Art F.

    2010-07-01

    Mg isotope ratios ( 26Mg/ 24Mg) are reported in soil pore-fluids, rain and seawater, grass and smectite from a 90 kyr old soil, developed on an uplifted marine terrace from Santa Cruz, California. Rain water has an invariant 26Mg/ 24Mg ratio (expressed as δ26Mg) at -0.79 ± 0.05‰, identical to seawater δ26Mg. Detrital smectite (from the base of the soil profile, and therefore unweathered) has a δ26Mg value of 0.11‰, potentially enriched in 26Mg by up to 0.3‰ compared to the bulk silicate Earth Mg isotope composition (although within the range of all terrestrial silicates). The soil pore-waters show a continuous profile with depth for δ26Mg, ranging from -0.99‰ near the surface to -0.43‰ at the base of the profile. Shallow pore-waters (<1 m) have δ26Mg values that are similar to, or slightly lower than the rain waters. This implies that the degree of biological cycling of Mg in the pore-waters is relatively small and is quantified as <32%, calculated using the average Mg isotope enrichment factor between grass and rain ( δ26Mg-δ26Mg) of 0.21‰. The deep pore-waters (1-15 m deep) have δ26Mg values that are intermediate between the smectite and rain, ranging from -0.76‰ to -0.43‰, and show a similar trend with depth compared to Sr isotope ratios. The similarity between Sr and Mg isotope ratios confirms that the Mg in the pore-waters can be explained by a mixture between rain and smectite derived Mg, despite the fact that Mg and Sr concentrations may be buffered by the exchangeable reservoir. However, whilst Sr isotope ratios in the pore-waters span almost the complete range between mineral and rain inputs, Mg isotopes compositions are much closer to the rain inputs. If Mg and Sr isotope ratios are controlled uniquely by a mixture, the data can be used to estimate the mineral weathering inputs to the pore-waters, by correcting for the rain inputs. This isotopic correction is compared to the commonly used chloride correction for precipitation

  20. Interstellar fossil Mg-26 and its possible relationship to excess meteoritic Mg-26

    NASA Technical Reports Server (NTRS)

    Clayton, Donald D.

    1986-01-01

    A plausible scenario is advanced for explainig a linear correlation found in some solar system solids between their Mg-26/Mg-24 isotopic ratios and their Al/Mg elemental abundance ratios. This scenario involves three stages: (1) the mechanical aggregation of an average ensemble of Al-bearing dust particles that is postulated to be modestly enriched in the Al/Mg abundance ratio because the aggregated particles themselves are; (2) the extraction, perhaps but not necessarily by hot distillation, of almost all Mg, leaving an aggregate with a large Al/Mg ratio and a large Mg-26 excess; and (3) the uptake of normal ambient Mg by the resulting hot Al-rich solid as it cools in Mg-rich vapor. A linear correlation in solids between their Mg-26/Mg-24 isotopic ratio and their aluminum enrichment may be a fossil correlation inherited from interstellar dust.

  1. Transformation of Mg-bearing amorphous calcium carbonate to Mg-calcite - In situ monitoring

    NASA Astrophysics Data System (ADS)

    Purgstaller, Bettina; Mavromatis, Vasileios; Immenhauser, Adrian; Dietzel, Martin

    2016-02-01

    The formation of Mg-bearing calcite via an amorphous precursor is a poorly understood process that is of relevance for biogenic and abiogenic carbonate precipitation. In order to gain an improved insight on the controls of Mg incorporation in calcite formed via an Mg-rich amorphous calcium carbonate (Mg-ACC) precursor, the precipitation of Mg-ACC and its transformation to Mg-calcite was monitored by in situ Raman spectroscopy. The experiments were performed at 25.0 ± 0.03 °C and pH 8.3 ± 0.1 and revealed two distinct pathways of Mg-calcite formation: (i) At initial aqueous Mg/Ca molar ratios ⩽ 1:6, Mg-calcite formation occurs via direct precipitation from solution. (ii) Conversely, at higher initial Mg/Ca molar ratios, Mg-calcite forms via an intermediate Mg-rich ACC phase. In the latter case, the final product is a calcite with up to 20 mol% Mg. This Mg content is significant higher than that of the Mg-rich ACC precursor phase. Thus, a strong net uptake of Mg ions from the solution into the crystalline precipitate throughout and also subsequent to ACC transformation is postulated. Moreover, the temporal evolution of the geochemical composition of the reactive solution and the Mg-ACC has no significant effect on the obtained "solubility product" of Mg-ACC. The enrichment of Mg in calcite throughout and subsequent to Mg-ACC transformation is likely affected by the high aqueous Mg/Ca ratio and carbonate alkalinity concentrations in the reactive solution. The experimental results have a bearing on the formation mechanism of Mg-rich calcites in marine early diagenetic environments, where high carbonate alkalinity concentrations are the rule rather than the exception, and on the insufficiently investigated inorganic component of biomineralisation pathways in many calcite secreting organisms.

  2. A SIMS Calibration of Benthic Foraminiferal Mg/Ca

    NASA Astrophysics Data System (ADS)

    Curry, W. B.; Marchitto, T. M.

    2005-12-01

    Using a suite of multi-core tops, we have produced a calibration of C. pachyderma Mg/Ca versus temperature spanning the temperature range of 5 to 18 °C. The core tops are located along the Florida margin south of Dry Tortugas (KNR166), along the Bahamas west of Andros Island and Great Bahama Bank (KNR166), and along the southeastern margin of Brazil (KNR159). Water depths range from about 200 to 800 m for the Florida Straits multi-cores and 400 to 800 m for the Brazil margin multi-cores. Five of the KNR166 core tops contain post-1950 bomb radiocarbon with Fmodern> 1; several others have bomb radiocarbon mixed in with pre-bomb sediments to give ages less than 0 BP. Core top ages are generally older for the KNR159 multi-cores, but each is from a location with a well documented Holocene section. Sedimentation rates for KNR166 multi-cores vary from 10 to 100 cm kyr-1; for KNR159 multi-cores, sedimentation rates vary from 5 to 10 cm kyr-1. Elemental ratios were determined by Secondary Ionization Mass Spectrometry (SIMS) using a Cameca IMS 3f ion probe calibrated for Mg/Ca and Sr/Ca using two standards which were independently measured using ICP-MS. Using SIMS, the external precision of the calibration standards averages ±3.5% (1σ RSD) for Mg/Ca and ± 1.7% (1σ RSD) for Sr/Ca. SIMS elemental measurements were performed on one to three individual C. pachyderma tests in each core top; more than 30 tests have been measured from 18 multi-core tops. Mg/Ca variability within C. pachyderma tests averages ± 20% (1σ RSD) with a small but significant trend toward higher variability at higher Mg/Ca. Higher Mg/Ca is observed in warmer waters, but the Mg/Ca values are generally lower (at comparable warm temperatures) than observed in previous calibration studies. At temperatures below 8 °C, C. pachyderma Mg/Ca values are less than 2 mmole/mole. At temperatures warmer than 15 °C, C. pachyderma Mg/Ca values exceed 3 mmole/mole. The slope of Mg/Ca versus temperature (~0.14 mmole

  3. SNOWY RANGE WILDERNESS, WYOMING.

    USGS Publications Warehouse

    Houston, Robert S.; Bigsby, Philip R.

    1984-01-01

    A mineral survey of the Snowy Range Wilderness in Wyoming was undertaken and was followed up with more detailed geologic and geochemical surveys, culminating in diamond drilling of one hole in the Snowy Range Wilderness. No mineral deposits were identified in the Snowy Range Wilderness, but inasmuch as low-grade uranium and associated gold resources were identified in rocks similar to those of the northern Snowy Range Wilderness in an area about 5 mi northeast of the wilderness boundary, the authors conclude that the northern half of the wilderness has a probable-resource potential for uranium and gold. Closely spaced drilling would be required to completely evaluate this mineral potential. The geologic terrane precludes the occurrence of fossil fuels.

  4. Sunspot umbral oscillations in Mg II k

    NASA Technical Reports Server (NTRS)

    Gurman, Joseph B.

    1987-01-01

    Time series observations of the profile of the Mg II k line 2795.52 A have been obtained in five sunspots with the Ultraviolet Spectrometer and Polarimeter on the Solar Maximum Mission. The three sunspots with umbrae larger than the 3 x 3 arcsec pixel size show significant oscillations in integrated line intensity and line centroid, with frequencies in the range 5.29-7.55 mHz (periods of 132-190 s). The frequencies of significant peaks in average umbral power spectra agree well with the frequencies of the three lowest-frequency transmission peaks predicted by a model of resonant transmission of acoustic waves. If radiative delays are unimportant, and the line centroid can be interpreted straightforwardly as a Doppler shift, the measured velocity-intensity phase differences indicate the superposition of upward-propagating and downward-propagating waves in the umbral chromosphere; this is further evidence for the resonant transmission model. A single, quiet sun time series of k core profiles yields power spectra and a phase difference consistent with the existence of a chromospheric p-mode.

  5. Mu-2 ranging

    NASA Technical Reports Server (NTRS)

    Martin, W. L.; Zygielbaum, A. I.

    1977-01-01

    The Mu-II Dual-Channel Sequential Ranging System designed as a model for future Deep Space Network ranging equipment is described. A list of design objectives is followed by a theoretical explanation of the digital demodulation techniques first employed in this machine. Hardware and software implementation are discussed, together with the details relating to the construction of the device. Two appendixes are included relating to the programming and operation of this equipment to yield the maximum scientific data.

  6. Surface segregation of Ba in MgO

    NASA Astrophysics Data System (ADS)

    Cotter, M.; Campbell, S.; Cao, L. L.; Egdell, R. G.; Mackrodt, W. C.

    1989-02-01

    Surface segregation of Ba in doped polycrystalline and single crystal MgO has been studied by XPS. There is little variation in surface coverage of Ba over a range of bulk doping levels from 7 to 7000 ppm in ceramic pellets equilibrated at 1630 K. This remarkable behaviour is shown to be consistent with surface coverage calculated from heats of segregation derived from ionic model simulations of the surface if due account is taken of the strong variation of the segregation energy with coverage. The coverage of Ba on a MgO(001) single crystal surface doped by indiffusion of Ba deposited onto the crystal from a getter source can be made similar to that of the polycrystalline material. The Ba-segregated MgO(001) surface exhibits a complex LEED pattern.

  7. EBSD analysis of MgB2 bulk superconductors

    NASA Astrophysics Data System (ADS)

    Koblischka-Veneva, A.; Koblischka, M. R.; Schmauch, J.; Inoue, K.; Muralidhar, M.; Berger, K.; Noudem, J.

    2016-04-01

    The grain orientation, the texture and the grain boundary misorientations are important parameters for the understanding of the magnetic properties of the bulk MgB2 samples intended for super-magnet applications. Such data can be provided by electron backscatter diffraction (EBSD) analysis. However, as the grain size (GS) of the MgB2 bulks is preferably in the 100-200 nm range, the common EBSD technique working in reflection operates properly only on highly dense samples. In order to achieve a reasonably good Kikuchi pattern quality on all samples, we apply here the newly developed transmission EBSD (t-EBSD) technique to several bulk MgB2 samples. This method requires the preparation of TEM slices by means of focused ion-beam milling, which are then analyzed within the SEM, operating with a specific sample holder. We present several EBSD mappings of samples prepared with different techniques and at various reaction temperatures.

  8. Analysis of the Deformation Behavior of Mg-RE and Mg-Li Alloys using In-situ Energy-dispersive Synchrotron X-ray Diffraction

    SciTech Connect

    Lentz, Martin; Clausen, Bjorn; Reimers, Walter

    2012-08-06

    EPSC-Model is able to predict the complex deformation behavior of Mg-RE and Mg-Li alloys within a wide range of strains. Modification of the texture by RE-elements and the addition of Li increases the activity of slip systems at low strains - Reorientation due to twinning is stretch over a larger range of plastic deformation. Deformation at high strains is realized mainly by the basal and the -pyramidal slip systems.

  9. Antibacterial biodegradable Mg-Ag alloys.

    PubMed

    Tie, D; Feyerabend, F; Müller, W D; Schade, R; Liefeith, K; Kainer, K U; Willumeit, R

    2013-06-16

    The use of magnesium alloys as degradable metals for biomedical applications is a topic of ongoing research and the demand for multifunctional materials is increasing. Hence, binary Mg-Ag alloys were designed as implant materials to combine the favourable properties of magnesium with the well-known antibacterial property of silver. In this study, three Mg-Ag alloys, Mg2Ag, Mg4Ag and Mg6Ag that contain 1.87 %, 3.82 % and 6.00 % silver by weight, respectively, were cast and processed with solution (T4) and aging (T6) heat treatment. The metallurgical analysis and phase identification showed that all alloys contained Mg4Ag as the dominant β phase. After heat treatment, the mechanical properties of all Mg-Ag alloys were significantly improved and the corrosion rate was also significantly reduced, due to presence of silver. Mg(OH)₂ and MgO present the main magnesium corrosion products, while AgCl was found as the corresponding primary silver corrosion product. Immersion tests, under cell culture conditions, demonstrated that the silver content did not significantly shift the pH and magnesium ion release. In vitro tests, with both primary osteoblasts and cell lines (MG63, RAW 264.7), revealed that Mg-Ag alloys show negligible cytotoxicity and sound cytocompatibility. Antibacterial assays, performed in a dynamic bioreactor system, proved that the alloys reduce the viability of two common pathogenic bacteria, Staphylococcus aureus (DSMZ 20231) and Staphylococcus epidermidis (DSMZ 3269), and the results showed that the killing rate of the alloys against tested bacteria exceeded 90%. In summary, biodegradable Mg-Ag alloys are cytocompatible materials with adjustable mechanical and corrosion properties and show promising antibacterial activity, which indicates their potential as antibacterial biodegradable implant materials.

  10. Effect of organic ligands on Mg partitioning and Mg isotope fractionation during low-temperature precipitation of calcite

    NASA Astrophysics Data System (ADS)

    Mavromatis, Vasileios; Immenhauser, Adrian; Buhl, Dieter; Purgstaller, Bettina; Baldermann, Andre; Dietzel, Martin

    2016-04-01

    Calcite growth experiments have been performed at 25 oC and 1 bar pCO2 in the presence of aqueous Mg and six organic ligands in the concentration range from 10‑5 to 10‑3 M. These experiments were performed in order to quantify the effect of distinct organic ligands on the Mg partitioning and Mg stable isotope fractionation during its incorporation in calcite at similar growth rates normalized to total surface area. The organic ligands used in this study comprise of (i) acetate acid, (ii) citrate, (iii) glutamate, (iv) salicylate, (v) glycine and (vi) ethylenediaminetetraacetic acid (EDTA), containing carboxyl- and amino-groups. These fuctional groups are required for bacterial activity and growth as well as related to biotic and abiotic mineralization processes occurring in sedimentary and earliest diagenetic aquatic environments (e.g. soil, cave, lacustrine, marine). The results obtained in this study indicate that the presence of organic ligands promotes an increase in the partition coefficient of Mg in calcite (DMg = (Mg/Ca)calcite (Mg/Ca)fluid). This behaviour can be explained by the temporal formation of aqueous Mg-ligand complexes that are subsequently adsorbed on the calcite surfaces and thereby reducing the active growth sites of calcite. The increase of DMg values as a function of the supersaturation degree of calcite in the fluid phase can be described by the linear equation LogDMg =0.3694 (±0.0329)×SIcalcite - 1.9066 (±0.0147); R2=0.92 In contrast, the presence of organic ligands, with exception of citrate, does not significantly affect the Mg isotope fractionation factor between calcite and reactive fluid (Δ26Mgcalcite‑fluid = -2.5 ±0.1). Citrate likely exhibits larger fractionation between the Mg-ligand complexes and free aqueous Mg2+, compared to the other organic ligands studied in this work, as evidenced by the smaller Δ26Mgcalcite‑fluid values. These results indicate that in Earth's surface calcite precipitating environments that are

  11. Effect of organic ligands on Mg partitioning and Mg isotope fractionation during low-temperature precipitation of calcite

    NASA Astrophysics Data System (ADS)

    Mavromatis, Vasileios; Immenhauser, Adrian; Buhl, Dieter; Purgstaller, Bettina; Baldermann, Andre; Dietzel, Martin

    2016-04-01

    Calcite growth experiments have been performed at 25 oC and 1 bar pCO2 in the presence of aqueous Mg and six organic ligands in the concentration range from 10-5 to 10-3 M. These experiments were performed in order to quantify the effect of distinct organic ligands on the Mg partitioning and Mg stable isotope fractionation during its incorporation in calcite at similar growth rates normalized to total surface area. The organic ligands used in this study comprise of (i) acetate acid, (ii) citrate, (iii) glutamate, (iv) salicylate, (v) glycine and (vi) ethylenediaminetetraacetic acid (EDTA), containing carboxyl- and amino-groups. These fuctional groups are required for bacterial activity and growth as well as related to biotic and abiotic mineralization processes occurring in sedimentary and earliest diagenetic aquatic environments (e.g. soil, cave, lacustrine, marine). The results obtained in this study indicate that the presence of organic ligands promotes an increase in the partition coefficient of Mg in calcite (DMg = (Mg/Ca)calcite (Mg/Ca)fluid). This behaviour can be explained by the temporal formation of aqueous Mg-ligand complexes that are subsequently adsorbed on the calcite surfaces and thereby reducing the active growth sites of calcite. The increase of DMg values as a function of the supersaturation degree of calcite in the fluid phase can be described by the linear equation LogDMg =0.3694 (±0.0329)×SIcalcite - 1.9066 (±0.0147); R2=0.92 In contrast, the presence of organic ligands, with exception of citrate, does not significantly affect the Mg isotope fractionation factor between calcite and reactive fluid (Δ26Mgcalcite-fluid = -2.5 ±0.1). Citrate likely exhibits larger fractionation between the Mg-ligand complexes and free aqueous Mg2+, compared to the other organic ligands studied in this work, as evidenced by the smaller Δ26Mgcalcite-fluid values. These results indicate that in Earth's surface calcite precipitating environments that are

  12. [Fluorescent probes for intracellular Mg2+ measurement].

    PubMed

    Komatsu, Hirokazu; Suzuki, Yoshio; Suzuki, Koji

    2004-08-01

    Recently, fluorescent probes are widely used as tools for dynamical measurement of ion distributions and concentrations in cells. They are highly sensitive, and offer imaging by the use of fluorescent microscopy in easily and less cell damaging way. This paper discusses the selectivity and optical character of the three novel Mg(2+) fluorescent probes. KMG-20AM offers ratiometric quantative measurement of Mg(2+), KMG-104 provides high-sensitive qualitative analysis and 3-D measurement. With those improved Mg(2+) fluorescent probes, the physiological and pathological role of Mg(2+) are going to be more and more clear. PMID:15577092

  13. Laser Ranging Simulation Program

    NASA Technical Reports Server (NTRS)

    Piazolla, Sabino; Hemmati, Hamid; Tratt, David

    2003-01-01

    Laser Ranging Simulation Program (LRSP) is a computer program that predicts selected aspects of the performances of a laser altimeter or other laser ranging or remote-sensing systems and is especially applicable to a laser-based system used to map terrain from a distance of several kilometers. Designed to run in a more recent version (5 or higher) of the MATLAB programming language, LRSP exploits the numerical and graphical capabilities of MATLAB. LRSP generates a graphical user interface that includes a pop-up menu that prompts the user for the input of data that determine the performance of a laser ranging system. Examples of input data include duration and energy of the laser pulse, the laser wavelength, the width of the laser beam, and several parameters that characterize the transmitting and receiving optics, the receiving electronic circuitry, and the optical properties of the atmosphere and the terrain. When the input data have been entered, LRSP computes the signal-to-noise ratio as a function of range, signal and noise currents, and ranging and pointing errors.

  14. Coherent interface structures and intergrain Josephson coupling in dense MgO/Mg2Si/MgB2 nanocomposites

    NASA Astrophysics Data System (ADS)

    Ueno, Katsuya; Nagashima, Yukihito; Seto, Yusuke; Matsumoto, Megumi; Sakurai, Takahiro; Ohta, Hitoshi; Takahashi, Kazuyuki; Uchino, Takashi

    2016-07-01

    Many efforts are under way to control the structure of heterointerfaces in nanostructured composite materials for designing functionality and engineering application. However, the fabrication of high-quality heterointerfaces is challenging because the crystal/crystal interface is usually the most defective part of the nanocomposite materials. In this work, we show that fully dense insulator (MgO)/semiconductor(Mg2Si)/superconductor(MgB2) nanocomposites with atomically smooth and continuous interfaces, including epitaxial-like MgO/Mg2Si interfaces, are obtained by solid phase reaction between metallic magnesium and a borosilicate glass. The resulting nanocomposites exhibit a semiconductor-superconducting transition at 36 K owing to the MgB2 nanograins surrounded by the MgO/Mg2Si matrix. This transition is followed by the intergrain phase-lock transition at ˜24 K due to the construction of Josephson-coupled network, eventually leading to a near-zero resistance state at 17 K. The method not only provides a simple process to fabricate dense nanocomposites with high-quality interfaces, but also enables to investigate the electric and magnetic properties of embedded superconducting nanograins with good intergrain coupling.

  15. Nanoscale order in ZnSe:(Mg, O)

    SciTech Connect

    Elyukhin, Vyacheslav A.

    2014-02-21

    Self-assembling of 1O4Mg identical tetrahedral clusters resulting in the nanoscale order in ZnSe:(Mg, O) is presented. Co-doping transforms ZnSe into Mg{sub x}Zn{sub 1−x}O{sub y}Se{sub 1−y} alloy of MgO, MgSe, ZnO and ZnSe. The decrease of a sum of the enthalpies of the constituent compounds and diminution of the strain energy are the causes of this phenomenon. The self-assembling conditions are obtained from the free energy minimum when magnesium and oxygen are in the dilute and ultra dilute limits, correspondingly. The occurrence of 1O4Mg clusters and completion of self-assembling when all oxygen atoms are in clusters are results of the continuous phase transitions. The self-assembling occurrence temperature does not depend on the oxygen content and it is a function of magnesium concentration. Mg{sub x}Zn{sub 1−x}O{sub y}Se{sub 1−y} with all oxygen atoms in clusters can be obtained in temperature ranges from T = 206 °C (x = 0.001, y = 1×10{sup −4}) to T = 456 °C (x = 0.01, y = 1×10{sup −4}) and from T = 237 °C (x = 0.001, y = 1×10{sup −6}) to T = 462 °C (x = 0.01, y = 1×10{sup −6})

  16. Reconfigurable laser ranging instrument

    NASA Astrophysics Data System (ADS)

    Schneiter, John

    1994-03-01

    This paper describes the design and operation of a fast, flexible, non-contact, eye-safe laser ranging instrument useful in a variety of industrial metrology situations, such as in-process machining control and part inspection. The system has variable computer-controlled standoff and depth of field, and can obtain 3-D images of surfaces within a range of from 1.5 ft to almost 10 ft from the final optical element. The minimum depth of field is about 3.5 in. at 1.5 ft and about 26 in. at the far range. The largest depth of field for which useful data are available is about 41 in. Resolution, with appropriate averaging, is about one part in 4000 of the depth of field, which implies a best case resolution for this prototype of 0.00075 in. System flexibility is achieved by computer controlled relative positioning of optical components.

  17. The range scheduling aid

    NASA Technical Reports Server (NTRS)

    Halbfinger, Eliezer M.; Smith, Barry D.

    1991-01-01

    The Air Force Space Command schedules telemetry, tracking and control activities across the Air Force Satellite Control network. The Range Scheduling Aid (RSA) is a rapid prototype combining a user-friendly, portable, graphical interface with a sophisticated object-oriented database. The RSA has been a rapid prototyping effort whose purpose is to elucidate and define suitable technology for enhancing the performance of the range schedulers. Designing a system to assist schedulers in their task and using their current techniques as well as enhancements enabled by an electronic environment, has created a continuously developing model that will serve as a standard for future range scheduling systems. The RSA system is easy to use, easily ported between platforms, fast, and provides a set of tools for the scheduler that substantially increases his productivity.

  18. Differential Conductance Measurements of MgB2/I/Pb Heterojunctions and all-MgB2 Junctions

    NASA Astrophysics Data System (ADS)

    Cusick, David; Eckhardt, Matthew; Dai, Wenqing; Li, Qi; Chen, Ke; Cunnane, Daniel; Zhuang, C. G.; Xi, X. X.; Naito, Michio; Ramos, Roberto

    2015-03-01

    We present our work characterizing several types of Magnesium Diboride Josephson junctions, including MgB2/I/Pb heterojunctions and all-MgB2 junctions. We will report on the I-V and dI/dV-V data collected at various temperatures using both a cryocooler-based experimental platform between 2 and 20 Kelvin and using a 3He probe platform between 0.3 and 1.0 Kelvin. These were both developed by undergraduates in a liberal arts university. Using high-sampling rates with a 24-bit data acquisition card and access to a broad of range of temperatures, we track and report energy gap distributions and temperature-dependent features of dI/dV peaks of MgB2, comparing these with theoretical predictions. R.C.R. acknowledges support from National Science Foundation Grant # DMR-1206561.

  19. Magnesium isotopic compositions of the Mesoproterozoic dolostones: Implications for Mg isotopic systematics of marine carbonates

    NASA Astrophysics Data System (ADS)

    Huang, Kang-Jun; Shen, Bing; Lang, Xian-Guo; Tang, Wen-Bo; Peng, Yang; Ke, Shan; Kaufman, Alan J.; Ma, Hao-Ran; Li, Fang-Bing

    2015-09-01

    Available Mg isotope data indicate that dolostones of different ages have overlapping range of Mg isotopic composition (δ26Mg) and there is no systematic difference among different types of dolomites. To further explore the Mg isotopic systematics of dolomite formation, we measured Mg isotopic compositions of Mesoproterozoic dolostones from the Wumishan Formation in North China Block, because dolomite formation in Mesoproterozoic might have been fundamentally different from the younger counterparts. Based on petrographic observations, three texturally-different dolomite phases (dolomicrite, subhedral dolomite and anhedral dolomite) are recognized in the Wumishan dolostones. Nevertheless, these three types of dolomites have similar δ26Mg values, ranging from -1.35‰ to -1.72‰, which are indistinguishable from Neoproterozoic and Phanerozoic dolostones. To explain δ26Mg values of dolostones, we simulate the Mg isotopic system during dolomite formation by applying the one-dimensional Diffusion-Advection-Reaction (1D-DAR) model, assuming that the contemporaneous seawater is the Mg source of dolostone. The 1D-DAR modeling results indicate that the degree of dolomitization is controlled by sedimentation rate, seawater Mg concentration, temperature, and reaction rate of dolomite formation, whereas Mg isotopic composition of dolostone is not only dependent on these factors, but also affected by δ26Mg of seawater and isotope fractionation during dolomite formation. Moreover, the 1D-DAR model predicts that dolomite formation within sediments has limited range of variation in δ26Mg with respect to limestones. Furthermore, the modeling results demonstrate that dolostone is always isotopically heavier than Ca-carbonate precipitated from seawater, explaining the systematic isotopic difference between dolostones and limestones. Finally, we can infer from the 1D-DAR model that early-formed dolostone at shallower depth of sediments is always isotopically lighter than that

  20. Western Aeronautical Test Range

    NASA Technical Reports Server (NTRS)

    Sakahara, Robert D.

    2008-01-01

    This viewgraph presentation reviews the work of the Western Aeronautical Test Range (WATR). NASA's Western Aeronautical Test Range is a network of facilities used to support aeronautical research, science missions, exploration system concepts, and space operations. The WATR resides at NASA's Dryden Flight Research Center located at Edwards Air Force Base, California. The WATR is a part of NASA's Corporate Management of Aeronautical Facilities and funded by the Strategic Capability Asset Program (SCAP). Maps show the general location of the WATR area that is used for aeronautical testing and evaluation. The products, services and facilities of WATR are discussed,

  1. Himalayan Mountain Range, India

    NASA Technical Reports Server (NTRS)

    1981-01-01

    Snow is present the year round in most of the high Himalaya Mountain Range (33.0N, 76.5E). In this view taken at the onset of winter, the continuous snow line can be seen for hundreds of miles along the south face of the range in the Indian states of Punjab and Kashmir. The snow line is at about 12,000 ft. altitude but the deep Cenab River gorge is easily delineated as a break along the south edge of the snow covered mountains. '

  2. Satellite Laser Ranging operations

    NASA Technical Reports Server (NTRS)

    Pearlman, Michael R.

    1994-01-01

    Satellite Laser Ranging (SLR) is currently providing precision orbit determination for measurements of: 1) Ocean surface topography from satellite borne radar altimetry, 2) Spatial and temporal variations of the gravity field, 3) Earth and ocean tides, 4) Plate tectonic and regional deformation, 5) Post-glacial uplift and subsidence, 6) Variations in the Earth's center-of-mass, and 7) Variations in Earth rotation. SLR also supports specialized programs in time transfer and classical geodetic positioning, and will soon provide precision ranging to support experiments in relativity.

  3. Satellite laser ranging

    NASA Astrophysics Data System (ADS)

    Osorio, J. P.

    1992-03-01

    Laser ranging to satellites is one of the most precise methods for positio ning on the surface of the Earth. Reference is made to the need for precise posi tioning and to the improvement brought by the use of space techniques. Satellite Laser Ranging system is then described and in view of the high precision of the results derived from its measurements comments are made to some of the more important applications: high precision networks tectonic plate motion polar motion and earth''s rotation. Finally plans for system improvement in the near future are also presented.

  4. On the Incidence and Kinematics of Strong Mg II Absorbers

    NASA Astrophysics Data System (ADS)

    Prochter, Gabriel E.; Prochaska, Jason X.; Burles, Scott M.

    2006-03-01

    We present the results of two complementary investigations into the nature of strong (rest equivalent width, Wr>1.0 Å) Mg II absorption systems at high redshift. The first line of questioning examines the complete Sloan Digital Sky Survey Data Release 3 set of quasar spectra to determine the evolution of the incidence of strong Mg II absorption. This search resulted in 7421 confirmed Mg II systems of Wr>1.0 Å, yielding a >95% complete statistical sample of 4835 absorbers (systems detected in S/N>7 spectral regions) spanning a redshift range 0.35Mg(X), is characterized by a roughly constant value at z>0.8, indicating that the product of the number density and gas cross section of halos hosting strong Mg II is unevolving at these redshifts. In contrast, one observes a decline in lMg(X) at z<0.8, which we interpret as a decrease in the gas cross section to strong Mg II absorption and therefore a decline in the physical processes relevant to strong Mg II absorption. Perhaps uncoincidentally, this evolution roughly tracks the global evolution of the star formation rate density. Dividing the systems in Wr subsamples, the lMg(X) curves show similar shape with lower normalization at higher Wr values and a more pronounced decrease in lMg(X) at z<0.8 for larger Wr systems. We also present the results of a search for strong Mg II absorption in a set of 91 high-resolution quasar spectra collected on the ESI and HIRES spectrographs. These data allow us to investigate the kinematics of such systems at 0.81.0 Å were discovered. These systems are characterized by the presence of numerous components spread over an average velocity width of Δv~200 km s-1. Also, absorption due to more highly ionized species (e.g., Al III, C IV, Si IV) tends to display kinematic profiles similar to the corresponding Mg II and Fe II absorption. We consider all of these

  5. RADIO RANGING DEVICE

    DOEpatents

    Bogle, R.W.

    1960-11-22

    A description is given of a super-regenerative oscillator ranging device provided with radiating and receiving means and being capable of indicating the occurrence of that distance between itself and a reflecting object which so phases the received echo of energy of a preceding emitted oscillation that the intervals between oscillations become uniform.

  6. Agriculture, forest, and range

    NASA Technical Reports Server (NTRS)

    1975-01-01

    The findings and recommendations of the panel for developing a satellite remote-sensing global information system in the next decade are reported. User requirements were identified in five categories: (1) cultivated crops, (2) land resources, (3)water resources, (4)forest management, and (5) range management. The benefits from the applications of satellite data are discussed.

  7. Agriculture, forestry, range resources

    NASA Technical Reports Server (NTRS)

    Crea, W. J.

    1974-01-01

    In the area of crop specie identification, it has been found that temporal data analysis, preliminary stratification, and unequal probability analysis were several of the factors that contributed to high identification accuracies. Single data set accuracies on fields of greater than 80,000 sq m (20 acres) are in the 70- to 90-percent range; however, with the use of temporal data, accuracies of 95 percent have been reported. Identification accuracy drops off significantly on areas of less than 80,000 sq m (20 acres) as does measurement accuracy. Forest stratification into coniferous and deciduous areas has been accomplished to a 90- to 95-percent accuracy level. Using multistage sampling techniques, the timber volume of a national forest district has been estimated to a confidence level and standard deviation acceptable to the Forest Service at a very favorable cost-benefit time ratio. Range specie/plant community vegetation mapping has been accomplished at various levels of success (69- to 90-percent accuracy). However, several investigators have obtained encouraging initial results in range biomass (forage production) estimation and range readiness predictions. Soil association map correction and soil association mapping in new area appear to have been proven feasible on large areas; however, testing in a complex soil area should be undertaken.

  8. Agriculture, forestry, range resources

    NASA Technical Reports Server (NTRS)

    Macdonald, R. B.

    1974-01-01

    The necessary elements to perform global inventories of agriculture, forestry, and range resources are being brought together through the use of satellites, sensors, computers, mathematics, and phenomenology. Results of ERTS-1 applications in these areas, as well as soil mapping, are described.

  9. Institutional Long Range Planning.

    ERIC Educational Resources Information Center

    Caldwell Community Coll. and Technical Inst., Lenoir, NC.

    Long-range institutional planning has been in effect at Caldwell Community College and Technical Institute since 1973. The first step in the process was the identification of planning areas: administration, organization, educational programs, learning resources, student services, faculty, facilities, maintenance/operation, and finances. The major…

  10. STDN ranging equipment

    NASA Technical Reports Server (NTRS)

    Jones, C. E.

    1975-01-01

    Final results of the Spaceflight Tracking and Data Network (STDN) Ranging Equipment program are summarized. Basic design concepts and final design approaches are described. Theoretical analyses which define requirements and support the design approaches are presented. Design verification criteria are delineated and verification test results are specified.

  11. Laser ranging data analysis

    NASA Technical Reports Server (NTRS)

    1992-01-01

    Center for Space Research efforts have focused on the near real-time analysis of Lageos laser ranging data and on the production of predictive ephemerides. The data are analyzed in terms of range bias, time bias, and internal precision, and estimates for the Earth orientation parameters X(sub p), Y(sub p) and UT1 are obtained. The results of these analyses are reported in a variety of formats. In addition several additional stations began sending not only quick-look observations but also normal points created on-site with new software. These normal points are transmitted in a new standard format different from either current quick-look or MERIT-II full-rate formats. Thus new preprocessing software was written and successfully tested on these data. Inspection of the Bendix produced Lageos full-rate normal points continued, with detailed analyses and filtering of all 1991 A and B release normal points for Lageos through the beginning of 1992. A summary of the combined full-rate and quick-look normal point data set created for 1991 is provided. New long-term ephemerides for Lageos satellite, as well as for Etalon-1 and Etalon-2 (the so-called high satellites used for laser ranging) were produced and distributed to the network stations in cooperation with the Crustal Dynamics Project and Eurolas. These predictions are used by essentially every laser ranging site obtaining regular returns from any of these three satellites.

  12. Front Range Branch Officers

    NASA Astrophysics Data System (ADS)

    The Front Range Branch of AGU has installed officers for 1990: Ray Noble, National Center for Atmospheric Research, chair; Sherry Oaks, U.S. Geological Survey, chair-elect; Howard Garcia, NOAA, treasurer; Catharine Skokan, Colorado School of Mines, secretary. JoAnn Joselyn of NOAA is past chair. Members at large are Wallace Campbell, NOAA; William Neff, USGS; and Stephen Schneider, NCAR.

  13. Fact Sheet: Range Complex

    NASA Technical Reports Server (NTRS)

    Cornelson, C.; Fretter, E.

    2004-01-01

    NASA Ames has a long tradition in leadership with the use of ballistic ranges and shock tubes for the purpose of studying the physics and phenomena associated with hypervelocity flight. Cutting-edge areas of research run the gamut from aerodynamics, to impact physics, to flow-field structure and chemistry. This legacy of testing began in the NACA era of the 1940's with the Supersonic Free Flight Tunnel, and evolved dramatically up through the late 1950s with the pioneering work in the Ames Hypersonic Ballistic Range. The tradition continued in the mid-60s with the commissioning of the three newest facilities: the Ames Vertical Gun Range (AVGR) in 1964, the Hypervelocity Free Flight Facility (HFFF) in 1965 and the Electric Arc Shock Tube (EAST) in 1966. Today the Range Complex continues to provide unique and critical testing in support of the Nation's programs for planetary geology and geophysics; exobiology; solar system origins; earth atmospheric entry, planetary entry, and aerobraking vehicles; and various configurations for supersonic and hypersonic aircraft.

  14. Electric vehicles: Driving range

    NASA Astrophysics Data System (ADS)

    Kempton, Willett

    2016-09-01

    For uptake of electric vehicles to increase, consumers' driving-range needs must be fulfilled. Analysis of the driving patterns of personal vehicles in the US now shows that today's electric vehicles can meet all travel needs on almost 90% of days from a single overnight charge.

  15. Mobile satellite ranging

    NASA Technical Reports Server (NTRS)

    Silverberg, E. C.

    1978-01-01

    A brief review of the constraints which have limited satellite ranging hardware and an outline of the steps which are underway to improve the status of the equipment in this area are given. In addition, some suggestions are presented for the utilization of newer instruments and for possible future research and development work in this area.

  16. The puzzle of {sup 32}Mg

    SciTech Connect

    Fortune, H. T.

    2011-08-15

    An analysis of results of the {sup 30}Mg(t,p) {sup 32}Mg reaction demonstrates that the ground state is the normal state and the excited 0{sup +} state is the intruder, contrary to popular belief. Additional experiments are suggested.

  17. Mg acceptors in GaN: Dependence of the /g-anisotropy on the doping concentration

    NASA Astrophysics Data System (ADS)

    Hofmann, Detlev M.; Burkhardt, Wolfgang; Leiter, Frank; Walter von Förster; Alves, Helder; Hofstaetter, Albrecht; Meyer, Bruno K.; Romanov, Nikolai G.; Amano, Hiroshi; Akasaki, Isamu

    1999-12-01

    Mg acceptors in GaN epitaxial layers grown by metal-organic vapour-phase epitaxy were investigated by optically detected magnetic resonance (ODMR) spectroscopy. The magnetic resonances were detected on the magnetic circular dichroism (MCD) of the acceptor bound exciton (Mg0X) in the near bandgap region, and in the infrared spectral range on the MCD of the hole ionisation transition Mg0+hν→Mg-+hVB. The observed g-values of the Mg0 acceptors range for g|| from 2.102 to 2.065 and for g⊥ from 1.94 to 2.00, respectively. These variations depend on the Mg doping concentration.

  18. Twinning-mediated formability in Mg alloys

    PubMed Central

    Suh, Byeong-Chan; Kim, Jae H.; Hwang, Ji Hyun; Shim, Myeong-Shik; Kim, Nack J.

    2016-01-01

    Mg alloys are promising candidates for automotive applications due to their low density and high specific strength. However, their widespread applications have not been realized mainly because of poor formability at room temperature, arising from limited number of active deformation systems and strong basal texture. It has been recently shown that Mg-Zn-Ca alloys have excellent stretch formability, which has been ascribed to their weak basal texture. However, the distribution of basal poles is orthotropic, which might result in anisotropy during deformation and have adverse effect on formability. Here, we show that tension twinning is mainly responsible for enhanced formability of Mg-Zn-Ca alloys. We found that tension twinning is quite active during both uniaxial deformation and biaxial deformation of Mg-Zn-Ca alloy even under the stress conditions unfavourable for the formation of tensile twins. Our results provide new insights into the development of Mg alloys having high formability. PMID:26926655

  19. Preparation and characterization of Mg nanoparticles

    SciTech Connect

    Song Meirong; Chen Miao Zhang Zhijun

    2008-05-15

    In this paper, Mg nanoparticles were prepared in tetrahydrofuran via lithium reduction of the corresponding Mg salt. X-ray diffraction and scanning electron microscope investigations confirm the formation of hexagonal phase Mg particles with an average size of 300 nm. X-ray photoelectron spectrometer analysis indicates that the as-prepared Mg nanoparticles are covered with a protecting layer consisting of residue solvents, naphthalene and Mg(OH){sub 2}, which slows down further oxidation under ambient conditions. Thermal analysis shows that the rapid oxidation and nitridation processes of the particles take place at around 500 deg. C and 553 deg. C, respectively. Furthermore, the addition of a small amount of magnesium nanoparticles remarkably catalyzes the decomposition process of ammonium perchlorate by lowering the decomposition temperature and enhancing its heat output.

  20. Experimental 25Mg and 13C NMR and Computational Modeling Studies of Amorphous Mg-Ca Carbonates

    NASA Astrophysics Data System (ADS)

    Singer, J. W.; Yazaydin, A. O.; Kirkpatrick, R. J.; Saharay, M.; Bowers, G. M.

    2012-12-01

    Nuclear magnetic resonance (NMR) spectroscopy of synthetic Mg-Ca amorphous carbonates (AMC-ACC) provides direct, element specific structural information about these complicated phases. The 13C, 25Mg, and 43Ca resonances are typically broad and span the chemical shift ranges of all the crystalline polymorphs in the Ca-Mg-CO3-H2O system. In a fashion similar to our previous analysis of 43Ca NMR results for ACC,1 here we integrate new experimental 13C and 25Mg spectra obtained at 20T for samples with Mg/(Ca+Mg) ratios from x=0 to x=1 with quantum chemical calculations of the NMR parameters of the crystalline phases using CASTEP calculations, simulations of the spectra using the SIMPSON software, and classical molecular dynamics calculations. XRD and 13C NMR results are in general agreement with the one-phase/two-phase model of ACC-AMC derived from thermochemical work by others.2 13C-NMR spectra of amorphous materials having intermediate compositions can not be completely fit by mechanical mixing of ACC and AMC end members—requiring a degree of Ca/Mg solid solution. Amorphous samples in two-phase region crystallize to assemblages of dolomite-like (x~0.5) and hydromagnesite-like (x~1) defective structures, but we also observe aragonite co-nucleation in the presence of excess water, indicative of a more complex evolution. While 43Ca NMR of X-ray amorphous materials shows featureless, symmetric, Gaussian line shapes, the large quadrupole moment of 25Mg gives rise to superposition of several quadrupolar line shapes representing different local structural environments. Singularities of static Mg spectra are best explained by local environments similar to nequehonite, hydromagnesite, and landsfordite. The spectra can not exclude minor contributions from anhydrous phases dolomite, huntite, and magnesite. Additional sites having very large quadrupolar coupling and/or site asymmetry are not explained by any known reference phases. CITATIONS (1) Singer, J. W.; Yazaydin, A. O

  1. Quantification and Localization of Intracellular Free Mg2+ in Bovine Chromaffin Cells

    PubMed Central

    Montezinho, Liliana P.; Fonseca, Carla P.; Geraldes, Carlos F. G. C.

    2002-01-01

    Magnesium is an essential element for all living systems. The quantification of free intracellular Mg2+ concentration ([Mg2+]i) is of utmost importance since changes in its basal value may be an indication of different pathologies due to abnormalities of Mg2+ metabolism. In this work we used 31P NMR and fluorescence spectroscopy to determine the resting [Mg2+]i in bovine chromaffin cells, a neuron-like cellular model, as well as confocal laser scanning microscopy to study the free Mg2+ spatial distribution in these cells. 31P NMR spectroscopy did not prove to be effective for the determination of [Mg2+]i in this particular case due to some special morphological and physiological properties of this cell type. A basal [Mg2+]i value of 0.551 ± 0.008 mM was found for these cells using fluorescence spectroscopy and the Mg2+-sensitive probe furaptra; this value falls in the concentration range reported in the literature for neurons from different sources. This technique proved to be an accurate and sensitive tool to determine the [Mg2+]i. lntraceilular free Mg2+ seems to be essentially localized in the nucleus and around it, as shown by confocal microscopy with the Mg2+-sensitive probe Magnesium Green. It was not possible to derive any conclusion about free Mg2+ localization inside the chromaffin granules and/or in the cytoplasm due to the lack of sufficient spatial resolution and to probe compartmentalization. PMID:18475427

  2. Light beam range finder

    DOEpatents

    McEwan, T.E.

    1998-06-16

    A ``laser tape measure`` for measuring distance is disclosed which includes a transmitter such as a laser diode which transmits a sequence of electromagnetic pulses in response to a transmit timing signal. A receiver samples reflections from objects within the field of the sequence of visible electromagnetic pulses with controlled timing, in response to a receive timing signal. The receiver generates a sample signal in response to the samples which indicates distance to the object causing the reflections. The timing circuit supplies the transmit timing signal to the transmitter and supplies the receive timing signal to the receiver. The receive timing signal causes the receiver to sample the reflection such that the time between transmission of pulses in the sequence in sampling by the receiver sweeps over a range of delays. The transmit timing signal causes the transmitter to transmit the sequence of electromagnetic pulses at a pulse repetition rate, and the received timing signal sweeps over the range of delays in a sweep cycle such that reflections are sampled at the pulse repetition rate and with different delays in the range of delays, such that the sample signal represents received reflections in equivalent time. The receiver according to one aspect of the invention includes an avalanche photodiode and a sampling gate coupled to the photodiode which is responsive to the received timing signal. The transmitter includes a laser diode which supplies a sequence of visible electromagnetic pulses. A bright spot projected on to the target clearly indicates the point that is being measured, and the user can read the range to that point with precision of better than 0.1%. 7 figs.

  3. Light beam range finder

    DOEpatents

    McEwan, Thomas E.

    1998-01-01

    A "laser tape measure" for measuring distance which includes a transmitter such as a laser diode which transmits a sequence of electromagnetic pulses in response to a transmit timing signal. A receiver samples reflections from objects within the field of the sequence of visible electromagnetic pulses with controlled timing, in response to a receive timing signal. The receiver generates a sample signal in response to the samples which indicates distance to the object causing the reflections. The timing circuit supplies the transmit timing signal to the transmitter and supplies the receive timing signal to the receiver. The receive timing signal causes the receiver to sample the reflection such that the time between transmission of pulses in the sequence in sampling by the receiver sweeps over a range of delays. The transmit timing signal causes the transmitter to transmit the sequence of electromagnetic pulses at a pulse repetition rate, and the received timing signal sweeps over the range of delays in a sweep cycle such that reflections are sampled at the pulse repetition rate and with different delays in the range of delays, such that the sample signal represents received reflections in equivalent time. The receiver according to one aspect of the invention includes an avalanche photodiode and a sampling gate coupled to the photodiode which is responsive to the received timing signal. The transmitter includes a laser diode which supplies a sequence of visible electromagnetic pulses. A bright spot projected on to the target clearly indicates the point that is being measured, and the user can read the range to that point with precision of better than 0.1%.

  4. The role of Mg in the crystallization of monohydrocalcite

    NASA Astrophysics Data System (ADS)

    Rodriguez-Blanco, Juan Diego; Shaw, Samuel; Bots, Pieter; Roncal-Herrero, Teresa; Benning, Liane G.

    2014-02-01

    Monohydrocalcite is a member of the carbonate family which forms in Mg-rich environments at a wide range of Mg/Ca ratios Mg2+aq/Ca2+aq≥0.17<65. Although found in modern sedimentary deposits and as a product of biomineralization, there is a lack of information about its formation mechanisms and about the role of Mg during its crystallization. In this work we have quantitatively assessed the mechanism of crystallization of monohydrocalcite through in situ synchrotron-based small and wide angle X-ray scattering (SAXS/WAXS) and off-line spectroscopic, microscopic and wet chemical analyses. Monohydrocalcite crystallizes via a 4-stage process beginning with highly supersaturated solutions from which a Mg-bearing, amorphous calcium carbonate (ACC) precursor precipitates. This precursor crystallizes to monohydrocalcite via a nucleation-controlled reaction in stage two, while in stage three it is further aged through Ostwald-ripening at a rate of 1.8 ± 0.1 nm/h1/2. In stage four, a secondary Ostwald ripening process (66.3 ± 4.3 nm/h1/2) coincides with the release of Mg from the monohydrocalcite structure and the concomitant formation of minor hydromagnesite. Our data reveal that monohydrocalcite can accommodate significant amounts of Mg in its structure (χMgCO3 = 0.26) and that its Mg content and dehydration temperature are directly proportional to the saturation index for monohydrocalcite (SIMHC) immediately after mixing the stock solutions. However, its crystallite and particle size are inversely proportional to these parameters. At high supersaturations (SIMHC = 3.89) nanometer-sized single crystals of monohydrocalcite form, while at low values (SIMHC = 2.43) the process leads to low-angle branching spherulites. Many carbonates produced during biomineralization form at similar conditions to most synthetic monohydrocalcites, and thus we hypothesize that some calcite or aragonite deposits found in the geologic record that have formed at high Mg/Ca ratios could be

  5. Single-dose rasburicase 6 mg in the management of tumor lysis syndrome in adults.

    PubMed

    McDonnell, Anne M; Lenz, Kristi L; Frei-Lahr, Debra A; Hayslip, John; Hall, Philip D

    2006-06-01

    Rasburicase is currently approved at a dosage of 0.15-0.2 mg/kg once/day for 5 days in pediatric patients with cancer to lower plasma uric acid concentrations and manage tumor lysis syndrome (TLS). Information on rasburicase dosing in adults is limited, with some data on using rasburicase as a single dose instead of multiple daily doses. Therefore, we evaluated the efficacy of a single dose of rasburicase for preventing or managing TLS in adults. We collected retrospective data for 11 adults with hematologic malignancies who received a single 6-mg dose of rasburicase. All patients received intravenous hydration with urinary alkalinization and allopurinol; however, due to adverse reactions, two patients received short courses of allopurinol. Only patients at high risk for TLS (e.g., large tumor burden, increasing uric acid concentration) or those with TLS received rasburicase. The single dose of rasburicase 6 mg resulted in a median 0.0773-mg/kg dose (range 0.0232-0.1361 mg/kg). The single 6-mg dose rapidly lowered uric acid concentrations in 10 of the 11 patients. The median uric acid concentration of 11.7 mg/dl (range 7.4-17.4 mg/dl) declined to 2.0 mg/dl (range 0.5-15.4 mg/dl) within a day after rasburicase administration (p=0.022). In these 10 patients, uric acid concentrations remained low despite subsequent chemotherapy, and none required additional rasburicase doses. The only patient who did not respond to the single 6-mg rasburicase dose was a morbidly obese man (259 kg, body mass index 87 kg/m2) who subsequently responded to an additional dose of rasburicase 12 mg. These results warrant further investigation of a single 6-mg dose of rasburicase in adults with TLS or at high-risk for developing TLS.

  6. Sc(2)MgGa(2) and Y(2)MgGa(2).

    PubMed

    Sahlberg, Martin; Andersson, Yvonne

    2009-03-01

    Scandium magnesium gallide, Sc(2)MgGa(2), and yttrium magnesium gallide, Y(2)MgGa(2), were synthesized from the corresponding elements by heating under an argon atmosphere in an induction furnace. These intermetallic compounds crystallize in the tetragonal Mo(2)FeB(2)-type structure. All three crystallographically unique atoms occupy special positions and the site symmetries of (Sc/Y, Ga) and Mg are m2m and 4/m, respectively. The coordinations around Sc/Y, Mg and Ga are pentagonal (Sc/Y), tetragonal (Mg) and triangular (Ga) prisms, with four (Mg) or three (Ga) additional capping atoms leading to the coordination numbers [10], [8+4] and [6+3], respectively. The crystal structure of Sc(2)MgGa(2 )was determined from single-crystal diffraction intensities and the isostructural Y(2)MgGa(2) was identified from powder diffraction data. PMID:19265212

  7. Sc(2)MgGa(2) and Y(2)MgGa(2).

    PubMed

    Sahlberg, Martin; Andersson, Yvonne

    2009-03-01

    Scandium magnesium gallide, Sc(2)MgGa(2), and yttrium magnesium gallide, Y(2)MgGa(2), were synthesized from the corresponding elements by heating under an argon atmosphere in an induction furnace. These intermetallic compounds crystallize in the tetragonal Mo(2)FeB(2)-type structure. All three crystallographically unique atoms occupy special positions and the site symmetries of (Sc/Y, Ga) and Mg are m2m and 4/m, respectively. The coordinations around Sc/Y, Mg and Ga are pentagonal (Sc/Y), tetragonal (Mg) and triangular (Ga) prisms, with four (Mg) or three (Ga) additional capping atoms leading to the coordination numbers [10], [8+4] and [6+3], respectively. The crystal structure of Sc(2)MgGa(2 )was determined from single-crystal diffraction intensities and the isostructural Y(2)MgGa(2) was identified from powder diffraction data.

  8. Comparative analysis of Mg-dependent and Mg-independent HCO3(-) ATPases.

    PubMed

    Dzneladze, S; Tsakadze, L; Leladze, M; Nozadze, E; Arutinova, N; Shioshvili, L; Chkadua, G

    2015-02-01

    The comparative analysis between two enzymes, Mg-dependent and Mg-independent HCO3(-) ATPases, were studied in synaptosomal and microsomal membrane fractions of albino rat brain, using the method of kinetic analysis of the multi-sited enzyme systems. Therefore, it can be inferred that Mg-dependent HCO3(-) ATPase belongs to the group of "P-type" transporting ATPases. Mg-independent HCO3(-) ATPase with its kinetic properties may be attributed to the group of "Ecto" ATPases.

  9. Gas cooking range

    SciTech Connect

    Narang, R.K.; Narang, K.

    1984-02-14

    An energy-efficient gas cooking range features an oven section with improved heat circulation and air preheat, a compact oven/broiler burner, a smoke-free drip pan, an efficient piloted ignition, flame-containing rangetop burner rings, and a small, portable oven that can be supported on the burner rings. Panels spaced away from the oven walls and circulation fans provide very effective air flow within the oven. A gas shutoff valve automatically controls the discharge of heated gases from the oven so that they are discharged only when combustion is occurring.

  10. In vitro and in vivo comparison of binary Mg alloys and pure Mg.

    PubMed

    Myrissa, Anastasia; Agha, Nezha Ahmad; Lu, Yiyi; Martinelli, Elisabeth; Eichler, Johannes; Szakács, Gábor; Kleinhans, Claudia; Willumeit-Römer, Regine; Schäfer, Ute; Weinberg, Annelie-Martina

    2016-04-01

    Biodegradable materials are under investigation due to their promising properties for biomedical applications as implant material. In the present study, two binary magnesium (Mg) alloys (Mg2Ag and Mg10Gd) and pure Mg (99.99%) were used in order to compare the degradation performance of the materials in in vitro to in vivo conditions. In vitro analysis of cell distribution and viability was performed on discs of pure Mg, Mg2Ag and Mg10Gd. The results verified viable pre-osteoblast cells on all three alloys and no obvious toxic effect within the first two weeks. The degradation rates in in vitro and in vivo conditions (Sprague-Dawley® rats) showed that the degradation rates differ especially in the 1st week of the experiments. While in vitro Mg2Ag displayed the fastest degradation rate, in vivo, Mg10Gd revealed the highest degradation rate. After four weeks of in vitro immersion tests, the degradation rate of Mg2Ag was significantly reduced and approached the values of pure Mg and Mg10Gd. Interestingly, after 4 weeks the estimated in vitro degradation rates approximate in vivo values. Our systematic experiment indicates that a correlation between in vitro and in vivo observations still has some limitations that have to be considered in order to perform representative in vitro experiments that display the in vivo situation.

  11. Narrowband filters for the FUV range

    NASA Astrophysics Data System (ADS)

    Rodríguez-de Marcos, Luis; Larruquert, Juan I.; Méndez, José A.; Aznárez, José A.; Fu, Liping

    2015-05-01

    We address the design, fabrication, and characterization of transmittance filters for the Ionosphere Photometer instrument (IP), developed by the Center for Space Science and Applied Research (CSSAR). IP, a payload of Feng-Yun 3D meteorological satellite, to be launched on 2016, is aimed to perform photometry measurements of Earth's ionosphere by the analysis of the OI (135.6 nm) spectral line and N2 Lyman-Birge-Hopfield (LBH, 140-180 nm) band, both of them in the far ultraviolet (FUV) range. The most convenient procedure to isolate a spectral band is the use of tunable transmittance filters. In many applications the intensity of the ultraviolet, visible and infrared background is higher than the intensity of the target FUV lines; therefore one of the most important requirements for transmittance filters is to reject (by reflecting and/or by absorbing) as efficiently as possible the visible and close ranges. In the FUV range, (Al/MgF2)n transmittance filters are the most common, and they are suitable to reject the visible and adjacent ranges. These materials present unique properties in this range: MgF2 is transparent down to ˜115 nm and Al has a very low refractive index in the FUV that contrasts well with MgF2. Narrowband tunable filters with very low transmittance at long wavelengths are achievable. The main data on the preparation and characterization of IP filters by Grupo de Óptica de Láminas Delgadas (GOLD) is detailed. In this proceeding we present (Al/MgF2)3 filters peaked at either 135.6 nm or at the center of the LBH band (˜160 nm). Filters were characterized in the 125-800 nm range (143-800 nm range for the LBH filter). After some storage in a desiccator, both coatings kept a transmittance of ~0.14 at their target wavelengths, with visible-to-peak transmittance ratios of 1.2·10-4 (OI filter) and 1.3·10-4 (LBH filter). One filter tuned at each target wavelength was exposed to ~300 Gy 60Co gamma dose, with no significant transmittance change.

  12. Is Mg-stabilized amorphous calcium carbonate a homogeneous mixture of amorphous magnesium carbonate and amorphous calcium carbonate?

    PubMed

    Yang, Sheng-Yu; Chang, Hsun-Hui; Lin, Cang-Jie; Huang, Shing-Jong; Chan, Jerry C C

    2016-10-01

    We find two types of carbonate ions in Mg stabilized amorphous calcium carbonate (Mg-ACC), whose short-range orders are identical to those of ACC and amorphous magnesium carbonate (AMC). Mg-ACC comprises a homogeneous mixture of the nano-clusters of ACC and AMC. Their relative amount varies systematically at different pH. PMID:27524162

  13. Western Aeronautical Test Range

    NASA Technical Reports Server (NTRS)

    Sakahara, Robert D.

    2008-01-01

    NASA's Western Aeronautical Test Range (WATR) is a network of facilities used to support aeronautical research, science missions, exploration system concepts, and space operations. The WATR resides at NASA's Dryden Flight Research Center located at Edwards Air Force Base, California. The WATR is a part of NASA's Corporate Management of Aeronautical Facilities and funded by the Strategic Capability Asset Program (SCAP). It is managed by the Aeronautics Test Program (ATP) of the Aeronautics Research Mission Directorate (ARMD) to provide the right facility at the right time. NASA is a tenant on Edwards Air Force Base and has an agreement with the Air Force Flight Test Center to use the land and airspace controlled by the Department of Defense (DoD). The topics include: 1) The WATR supports a variety of vehicles; 2) Dryden shares airspace with the AFFTC; 3) Restricted airspace, corridors, and special use areas are available for experimental aircraft; 4) WATR Products and Services; 5) WATR Support Configuration; 6) Telemetry Tracking; 7) Time Space Positioning; 8) Video; 9) Voice Communication; 10) Mobile Operations Facilities; 11) Data Processing; 12) Mission Control Center; 13) Real-Time Data Analysis; and 14) Range Safety.

  14. Monocular visual ranging

    NASA Astrophysics Data System (ADS)

    Witus, Gary; Hunt, Shawn

    2008-04-01

    The vision system of a mobile robot for checkpoint and perimeter security inspection performs multiple functions: providing surveillance video, providing high resolution still images, and providing video for semi-autonomous visual navigation. Mid-priced commercial digital cameras support the primary inspection functions. Semi-autonomous visual navigation is a tertiary function whose purpose is to reduce the burden of teleoperation and free the security personnel for their primary functions. Approaches to robot visual navigation require some form of depth perception for speed control to prevent the robot from colliding with objects. In this paper present the initial results of an exploration of the capabilities and limitations of using a single monocular commercial digital camera for depth perception. Our approach combines complementary methods in alternating stationary and moving behaviors. When the platform is stationary, it computes a range image from differential blur in the image stack collected at multiple focus settings. When the robot is moving, it extracts an estimate of range from the camera auto-focus function, and combines this with an estimate derived from angular expansion of a constellation of visual tracking points.

  15. Range Process Simulation Tool

    NASA Technical Reports Server (NTRS)

    Phillips, Dave; Haas, William; Barth, Tim; Benjamin, Perakath; Graul, Michael; Bagatourova, Olga

    2005-01-01

    Range Process Simulation Tool (RPST) is a computer program that assists managers in rapidly predicting and quantitatively assessing the operational effects of proposed technological additions to, and/or upgrades of, complex facilities and engineering systems such as the Eastern Test Range. Originally designed for application to space transportation systems, RPST is also suitable for assessing effects of proposed changes in industrial facilities and large organizations. RPST follows a model-based approach that includes finite-capacity schedule analysis and discrete-event process simulation. A component-based, scalable, open architecture makes RPST easily and rapidly tailorable for diverse applications. Specific RPST functions include: (1) definition of analysis objectives and performance metrics; (2) selection of process templates from a processtemplate library; (3) configuration of process models for detailed simulation and schedule analysis; (4) design of operations- analysis experiments; (5) schedule and simulation-based process analysis; and (6) optimization of performance by use of genetic algorithms and simulated annealing. The main benefits afforded by RPST are provision of information that can be used to reduce costs of operation and maintenance, and the capability for affordable, accurate, and reliable prediction and exploration of the consequences of many alternative proposed decisions.

  16. The Mg impurity in nitride alloys

    SciTech Connect

    Zvanut, M. E.; Willoughby, W. R.; Sunay, U. R.; Koleske, D. D.; Allerman, A. A.; Wang, Ke; Araki, Tsutomu; Nanishi, Yasushi

    2014-02-21

    Although several magnetic resonance studies address the Mg acceptor in GaN, there are few reports on Mg doping in the alloys, where hole production depends strongly on the Al or In content. Our electron paramagnetic resonance (EPR) measurements of the p-type alloys suggest that the Mg impurity retains the axial symmetry, characteristic of a p-type dopant in both alloys; however, In and Al produce additional, different characteristics of the acceptor. In InGaN, the behavior is consistent with a lowering of the acceptor level and increasing hole density as In concentration increases. For AlGaN, the amount of neutral Mg decreases with increasing Al content, which is attributed to different kinetics of hydrogen diffusion thought to occur in samples with higher Al mole fraction.

  17. Formation of Mg{sub 2}Ni with enhanced kinetics: Using MgH{sub 2} instead of Mg as a starting material

    SciTech Connect

    Zhao Bin; Fang Fang; Sun Dalin; Zhang Qingan; Wei Shiqiang; Cao Fenglei; Sun Huai; Ouyang Liuzhang; Zhu Min

    2012-08-15

    At a temperature over the decomposition point (375 Degree-Sign C) of MgH{sub 2}, the formation of Mg{sub 2}Ni is greatly enhanced from the 2MgH{sub 2}+Ni system, as compared to the 2Mg+Ni system. In support of this finding, in-situ observation of X-ray absorption fine structure of the two systems indicates that Mg---Ni bonds form faster in the 2MgH{sub 2}+Ni system than in the 2Mg+Ni system. Furthermore, theoretical modeling also shows that Mg atoms are readily released from MgH{sub 2} using much less energy and thus are more available to react with Ni once the dehydrogenation of MgH{sub 2} occurs, as compared to normal Mg. - Graphical Abstract: The formation of Mg{sub 2}Ni is greatly enhanced by using MgH{sub 2} instead of Mg at a temperature higher than the MgH{sub 2} decomposition point. Highlights: Black-Right-Pointing-Pointer A new and efficient synthesis of Mg-based compounds at a reduced temperature. Black-Right-Pointing-Pointer Mg{sub 2}Ni formation is enhanced by using MgH{sub 2} instead of Mg as a starting material. Black-Right-Pointing-Pointer XAFS results show that Mg---Ni bonds are formed faster in 4MgH{sub 2}+Ni than in 4Mg+Ni. Black-Right-Pointing-Pointer DFT calculations show that Mg atoms are released from MgH{sub 2} more readily than from Mg. Black-Right-Pointing-Pointer Mg formed by MgH{sub 2} dehydrogenation is more available to react with Ni than normal Mg.

  18. High pressure phase diagram of MgO

    NASA Astrophysics Data System (ADS)

    French, Martin; Cebulla, Daniel; Redmer, Ronald

    2015-06-01

    In order to improve the understanding of the interior of super-Earths (planets in the range of 1-10 Earth masses) and other exoplanets, ab inito calculations for the planetary materials and the equation of state (EOS) and phase diagram of planetary materials are needed. A typical representative is MgO, which is an abundant material in the Earth's mantle and is also expected to be important for the mantle of exoplanets as well as for the rocky cores of gas giants such as Jupiter. Using ab initio molecular dynamic simulations, we have determined the phase diagram for MgO up to 20000 K and 1.5 TPa. In particular, the transition from the solid to the molten salt has been studied using diffusion analyses and pair distribution functions. The transition from the B1 to the B2 structure in solid MgO is determined by calculating the respective free enthalpies. The phase diagram of MgO is constructed based on accurate EOS data. We compare with results from (decaying) shock and ramp compression experiments and theoretical calculations for the B1-B2 and the liquid-solid transition line.

  19. Mg-isotopic fractionation in the manila clam (Ruditapes philippinarum): New insights into Mg incorporation pathway and calcification process of bivalves

    NASA Astrophysics Data System (ADS)

    Planchon, Frédéric; Poulain, Céline; Langlet, Denis; Paulet, Yves-Marie; André, Luc

    2013-11-01

    We estimate the magnesium stable isotopic composition (δ26Mg) of the major compartments involved in the biomineralisation process of euryhaline bivalve, the manila clam Ruditapes philippinarum. Our aim is to identify the fractionation processes associated with Mg uptake and its cycling/transport in the bivalve organism, in order to better assess the controlling factors of the Mg isotopic records in bivalve shells. δ26Mg were determined in seawater, in hemolymph, extrapallial fluid (EPF), soft tissues and aragonitic shell of adult clams collected along the Auray River estuary (Gulf of Morbihan, France) at two sites showing contrasted salinity regimes. The large overall δ26Mg variations (4.16‰) demonstrate that significant mass-dependent Mg isotopic fractionations occur during Mg transfer from seawater to the aragonitic shell. Soft tissues span a range of fractionation factors relative to seawater (Δ26Mgsoft tissue-seawater) of 0.42 ± 0.12‰ to 0.76 ± 0.12‰, and show evidence for biological isotopic fractionation of Mg. Hemolymph and EPF are on average isotopically close to seawater (Δ26Mghemolymph-seawater = -0.20 ± 0.27‰; 2 sd; n = 5 and Δ26MgEPF-seawater = -0.23 ± 0.25‰; 2 sd; n = 5) indicating (1) a predominant seawater origin for Mg in the intercellular medium and (2) a relatively passive transfer route through the bivalve organism into the calcifying fluid. The lightest isotopic composition is found in shell, with δ26Mg ranging from -1.89 ± 0.07‰ to -4.22 ± 0.06‰. This range is the largest in the dataset and is proposed to result from a combination of abiotic and biologically-driven fractionation processes. Abiotic control includes fractionation during precipitation of aragonite and accounts for Δ26Mgaragonite-seawater ≈ 1000 ln αaragonite-seawater = -1.13 ± 0.28‰ at 20 °C based on literature data. Deviations from inorganic precipitate (expressed as Δ26MgPhysiol) appear particularly variable in the clam shell, ranging from 0

  20. Investigating the behaviour of Mg isotopes during the formation of clay minerals

    NASA Astrophysics Data System (ADS)

    Wimpenny, Joshua; Colla, Christopher A.; Yin, Qing-Zhu; Rustad, James R.; Casey, William H.

    2014-03-01

    We present elemental and isotopic data detailing how the Mg isotope system behaves in natural and experimentally synthesized clay minerals. We show that the bulk Mg isotopic composition (δ26Mg) of a set of natural illite, montmorillonite and kaolinite spans a 2‰ range, and that their isotopic composition depends strongly on a balance between the relative proportions of structural and exchangeable Mg. After acid leaching, these natural clays become relatively enriched in isotopically heavy Mg by between 0.2‰ and 1.6‰. Results of exchange experiments indicate that the Mg that has adsorbed to interlayer spaces and surface charged sites is relatively enriched in isotopically light Mg compared to the residual clay. The isotopic composition of this exchangeable Mg (-1.49‰ to -2.03‰) is characteristic of the isotopic composition of Mg found in many natural waters. Further experiments with an isotopically characterized MgCl2 solution shows that the clay minerals adsorb this exchangeable Mg with little or no isotopic fractionation, although we cannot discount the possibility that the uptake of exchangeable Mg does so with a slight preference for 24Mg. To characterize the behaviour of Mg isotopes during clay mineral formation we synthesized brucite (Mg(OH)2), which we consider to be a good analogue for the incorporation of Mg into the octahedral sheet of Mg-rich clay minerals or into the brucitic layer of clays such as chlorite. In our experiment the brucite mineral becomes enriched in the heavy isotopes of Mg while the corresponding solution is always relatively enriched in isotopically light Mg. The system reaches a steady state after 10 days with a final fractionation factor (αsolid-solution) of 1.0005 at near-neutral pH. This result is consistent with the general consensus that secondary clay minerals preferentially take up isotopically heavy Mg during their formation. However our results also show that exchangeable Mg is an important component within bulk

  1. Reactive wetting of amorphous silica by molten Al-Mg alloys and their interfacial structures

    NASA Astrophysics Data System (ADS)

    Shi, Laixin; Shen, Ping; Zhang, Dan; Jiang, Qichuan

    2016-07-01

    The reactive wetting of amorphous silica substrates by molten Al-Mg alloys over a wide composition range was studied using a dispensed sessile drop method in a flowing Ar atmosphere. The effects of the nominal Mg concentration and temperature on the wetting and interfacial microstructures were discussed. The initial contact angle for pure Al on the SiO2 surface was 115° while that for pure Mg was 35° at 1073 K. For the Al-Mg alloy drop, it decreased with increasing nominal Mg concentration. The reaction zone was characterized by layered structures, whose formation was primarily controlled by the variation in the alloy concentration due to the evaporation of Mg and the interfacial reaction from the viewpoint of thermodynamics as well as by the penetration or diffusion of Mg, Al and Si from the viewpoint of kinetics. In addition, the effects of the reaction and the evaporation of Mg on the movement of the triple line were examined. The spreading of the Al-Mg alloy on the SiO2 surface was mainly attributed to the formation of Mg2Si at the interface and the recession of the triple line to the diminishing Mg concentration in the alloy.

  2. Range imaging laser radar

    DOEpatents

    Scott, M.W.

    1990-06-19

    A laser source is operated continuously and modulated periodically (typically sinusoidally). A receiver imposes another periodic modulation on the received optical signal, the modulated signal being detected by an array of detectors of the integrating type. Range to the target determined by measuring the phase shift of the intensity modulation on the received optical beam relative to a reference. The receiver comprises a photoemitter for converting the reflected, periodically modulated, return beam to an accordingly modulated electron stream. The electron stream is modulated by a local demodulation signal source and subsequently converted back to a photon stream by a detector. A charge coupled device (CCD) array then averages and samples the photon stream to provide an electrical signal in accordance with the photon stream. 2 figs.

  3. Range imaging laser radar

    DOEpatents

    Scott, Marion W.

    1990-01-01

    A laser source is operated continuously and modulated periodically (typicy sinusoidally). A receiver imposes another periodic modulation on the received optical signal, the modulated signal being detected by an array of detectors of the integrating type. Range to the target determined by measuring the phase shift of the intensity modulation on the received optical beam relative to a reference. The receiver comprises a photoemitter for converting the reflected, periodically modulated, return beam to an accordingly modulated electron stream. The electron stream is modulated by a local demodulation signal source and subsequently converted back to a photon stream by a detector. A charge coupled device (CCD) array then averages and samples the photon stream to provide an electrical signal in accordance with the photon stream.

  4. Long-range connectomics.

    PubMed

    Jbabdi, Saad; Behrens, Timothy E

    2013-12-01

    Decoding neural algorithms is one of the major goals of neuroscience. It is generally accepted that brain computations rely on the orchestration of neural activity at local scales, as well as across the brain through long-range connections. Understanding the relationship between brain activity and connectivity is therefore a prerequisite to cracking the neural code. In the past few decades, tremendous technological advances have been achieved in connectivity measurement techniques. We now possess a battery of tools to measure brain activity and connections at all available scales. A great source of excitement are the new in vivo tools that allow us to measure structural and functional connections noninvasively. Here, we discuss how these new technologies may contribute to deciphering the neural code.

  5. Diffusion behavior and distribution regulation of MgO in MgO-bearing pellets

    NASA Astrophysics Data System (ADS)

    Gao, Qiang-jian; Shen, Yan-song; Wei, Guo; Jiang, Xin; Shen, Feng-man

    2016-09-01

    In this paper, the diffusion behavior between MgO and Fe2O3 (the main iron oxide in pellets) is investigated using a diffusion couple method. In addition, the distribution regulation of MgO in MgO-bearing pellets is analyzed via pelletizing experiments. The results illustrate that MgO is prone to diffuse into Fe2O3 in the form of solid solution; the diffusion rate considered here is 13.64 µm·min-1. Most MgO content distributes in the iron phase instead of the slag phase. The MF phase {(Mg1-x Fex)O·Fe2O3, x ≤ 1} is generated in the MgO-bearing pellets. However, the distribution of MgO in the radial direction of the pellets is inconsistent. The solid solution portion of MgO in the MF phase is larger in the outer layer of the pellets than in the inner layer. In this work, the approximate chemical composition of the MF phase in the outer layer of the pellets is {(Mg0.35-0.77·Fe0.65-0.23) O·Fe2O3} and in the inner layer is {(Mg0.13-0.45·Fe0.87-0.55) O·Fe2O3}.

  6. Spontaneously intermixed Al-Mg barriers enable corrosion-resistant Mg/SiC multilayer coatings

    SciTech Connect

    Soufli, Regina; Fernandez-Perea, Monica; Baker, Sherry L.; Robinson, Jeff C.; Alameda, Jennifer; Walton, Christopher C.

    2012-07-24

    Magnesium/silicon carbide (Mg/SiC) has the potential to be the best-performing reflective multilayercoating in the 25–80 nm wavelength region but suffers from Mg-related corrosion, an insidious problem which completely degrades reflectance. We have elucidated the origins and mechanisms of corrosion propagation within Mg/SiC multilayers. Based on our findings, we have demonstrated an efficient and simple-to-implement corrosion barrier for Mg/SiC multilayers. In conclusion, the barrier consists of nanometer-scale Mg and Al layers that intermix spontaneously to form a partially amorphous Al-Mg layer and is shown to prevent atmospheric corrosion while maintaining the unique combination of favorable Mg/SiC reflective properties.

  7. Mg deficiency affects leaf Mg remobilization and the proteome in Brassica napus.

    PubMed

    Billard, Vincent; Maillard, Anne; Coquet, Laurent; Jouenne, Thierry; Cruz, Florence; Garcia-Mina, José-Maria; Yvin, Jean-Claude; Ourry, Alain; Etienne, Philippe

    2016-10-01

    In order to cope with variable mineral nutrient availability, higher plants have developed numerous strategies including the remobilization of nutrients from source to sink tissues. However, such processes remain relatively unknown for magnesium (Mg), which is the third most important cation in plant tissues. Using Mg depletion of Brassica napus, we have demonstrated that Mg is remobilized from old leaves to young shoot tissues. Moreover, this study showed that Mg depletion induces modification of nutrient uptake, especially Zn and Mn. Finally, comparative proteomic analysis of old leaves (source of Mg) revealed amongst other results that some proteins requiring Mg for their functionality (isocitrate dehydrogenase for example) were up-regulated. Moreover, down-regulation of proteases suggested that mobilization of Mg from old leaves was not associated with senescence. PMID:27362297

  8. Fourier transform infrared emission spectra of MgH and MgD

    NASA Astrophysics Data System (ADS)

    Shayesteh, A.; Appadoo, D. R. T.; Gordon, I.; Le Roy, R. J.; Bernath, P. F.

    2004-06-01

    High resolution Fourier transform infrared emission spectra of MgH and MgD have been recorded. The molecules were generated in an emission source that combines an electrical discharge with a high temperature furnace. Several vibration-rotation bands were observed for all six isotopomers in the X 2Σ+ ground electronic state: v=1→0 to 4→3 for 24MgH, v=1→0 to 3→2 for 25MgH and 26MgH, v=1→0 to 5→4 for 24MgD, v=1→0 to 4→3 for 25MgD and 26MgD. The new data were combined with the previous ground state data, obtained from diode laser vibration-rotation measurements and pure rotation spectra, and spectroscopic constants were determined for the v=0 to 4 levels of 24MgH and the v=0 to 5 levels of 24MgD. In addition, Dunham constants and Born-Oppenheimer breakdown correction parameters were obtained in a combined fit of the six isotopomers. The equilibrium vibrational constants (ωe) for 24MgH and 24MgD were found to be 1492.776(7) cm-1 and 1077.298(5) cm-1, respectively, while the equilibrium rotational constants (Be) are 5.825 523(8) cm-1 and 3.034 344(4) cm-1. The associated equilibrium bond distances (re) were determined to be 1.729 721(1) Å for 24MgH and 1.729 157(1) Å for 24MgD.

  9. AB Initio Characterization of MgCCH, MgCCH(+), and MgC2, and Pathways to their Formation in the Interstellar Medium

    NASA Technical Reports Server (NTRS)

    Woon, David E.

    1996-01-01

    A study of Mg-bearing compounds has been performed in order to determine molecular properties which are critical for planning new astronomical searches and laboratory studies. The primary focus of the work is on MgCCH, MgCCH(+), and the isomers of MgC2. Only MgCCH has been identified in laboratory studies. Additional calculations have been carried out on MgH, MgNC, MgCN, and their cations in an effort to evaluate pathways to the formation of MgCCH and MgCCH(+) in the InterStellar Medium (ISM) or in circumstellar envelopes. Correlated ab initio methods and correlation-consistent basis sets have been employed. Properties including structures, rotational constants, dipole moments, and harmonic frequencies are reported. A transition state between linear MgCC and cyclic MgC2 has been characterized and was found to yield a minimal barrier (approx. 0.5 kcal/mole), indicating easy interconversion to the cyclic form. Direct reactions in the ISM between Mg or Mg(+) and HCCH are precluded by energetic considerations, but a number of ion- molecule or neutral-neutral exchange reactions between CCH and various Mg-containing species offer plausible pathways to MgCCH or MgCCH(+). Weakly bound MgH may react with CCH to form MgCCH, but MgH has not been detected. Both MgNC and MgCN have been observed, but reactions with CCH are slightly endothermic by 1-3 kcal/mole. Although MgH(+), MgNC(+), and MgCN(+) have not been detected, their reactions with CCH to form MgCCH(+) are all exothermic. With only a small barrier separating linear MgCC and cyclic MgC2, the dissociative recombination of MgCCH(+) with an electron is expected to yield cyclic MgC2, and regenerate Mg and CCH. New astronomical searches for MgCCH, MgCCH(+), cyclic MgC2, MgNC(+), and MgCN(+) will provide further insight into organo-magnesium astrochemistry.

  10. Effect of secular variation in oceanic Mg/Ca on calcareous biomineralization

    NASA Astrophysics Data System (ADS)

    Ries, J. B.; Stanley, S. M.

    2006-12-01

    The polymorph mineralogy of simple, hypercalcifying marine organisms has generally varied in synchroneity with the polymorph mineralogy of abiotic CaCO3 precipitates (ooids, marine cements) throughout the Phanerozoic Eon. This synchroneity is caused by secular variation in the Mg/Ca ratio of seawater (SW; mMg/Ca > 2 = aragonite + high-Mg calcite; mMg/Ca < 2 = calcite), determined primarily by the mixing rate of mid-ocean-ridge/large-igneous-province hydrothermal brines and river water, driven by the global rate of ocean crust production. Here, we present experiments evaluating the effect of seawater Mg/Ca on the biomineralization and growth of extant representatives of hypercalcifying taxa that have been subjected to fluctuations in oceanic Mg/Ca in the past. Codiacean algae (arag), scleractinian corals (arag), coccolithophores (low-high Mg-calc), coralline algae (high Mg-calc), various reef-dwelling animals (echinoids, crabs, shrimp, calcareous serpulid worms; high Mg- calc), and calcifying microbial mats (arag + high-Mg calc) were grown in artificial SW formulated over the range of mMg/Ca (1.0 to 5.2) that occurred throughout each taxon's history. Codiacean algae and scleractinian corals exhibited higher rates of calcification and growth in artificial SW favoring their aragonite mineralogy and, significantly, produced a portion of their CaCO3 as calcite in the artificial calcite SW. Coccolithophores (low-high Mg calc.) showed higher calcification and growth rates and produced low-Mg calcite in the calcite SW. Likewise, coralline algae and the reef-dwelling animals (high-Mg calc) varied skeletal Mg/Ca with seawater Mg/Ca. The calcifying microbial mats grew equally well in the calcite and aragonite SW and varied their mineral polymorph commensurate with the SW (mMg/Ca<2 = low- Mg calc; mMg/Ca>2 = arag + high-Mg calc), suggesting a nearly abiotic mode of calcification. The precipitation of low-Mg calcite + aragonite by codiacean algae and scleractinian corals (arag

  11. Neutron range spectrometer

    DOEpatents

    Manglos, Stephen H.

    1989-06-06

    A neutron range spectrometer and method for determining the neutron energy spectrum of a neutron emitting source are disclosed. Neutrons from the source are collimnated along a collimation axis and a position sensitive neutron counter is disposed in the path of the collimated neutron beam. The counter determines positions along the collimation axis of interactions between the neutrons in the neutron beam and a neutron-absorbing material in the counter. From the interaction positions, a computer analyzes the data and determines the neutron energy spectrum of the neutron beam. The counter is preferably shielded and a suitable neutron-absorbing material is He-3. The computer solves the following equation in the analysis: ##EQU1## where: N(x).DELTA.x=the number of neutron interactions measured between a position x and x+.DELTA.x, A.sub.i (E.sub.i).DELTA.E.sub.i =the number of incident neutrons with energy between E.sub.i and E.sub.i +.DELTA.E.sub.i, and C=C(E.sub.i)=N .sigma.(E.sub.i) where N=the number density of absorbing atoms in the position sensitive counter means and .sigma. (E.sub.i)=the average cross section of the absorbing interaction between E.sub.i and E.sub.i +.DELTA.E.sub.i.

  12. Accuracy, standardization, and interlaboratory calibration standards for foraminiferal Mg/Ca thermometry

    NASA Astrophysics Data System (ADS)

    Greaves, Mervyn; Barker, Stephen; Daunt, Caroline; Elderfield, Henry

    2005-02-01

    The use of liquid and solid standards for foraminiferal Mg/Ca and Sr/Ca determinations and interlaboratory calibration has been investigated. Preparation of single element standard solutions from primary solid standard material enables the preparation of mixed standard solutions with Mg/Ca and Sr/Ca ratios of known accuracy to better than 0.1%. We also investigated commercial reference materials to determine whether existing carbonate standards could be used as reference material for Mg/Ca determinations in foraminiferal calcite. We propose that, in the absence of a pure calcium carbonate standard certified for Mg/Ca, ECRM 752-1, a limestone CRM containing Mg/Ca within the range of typical foraminifera, is a suitable solid standard for interlaboratory calibration. Replicate Mg/Ca determinations showed that, provided silicate phases are removed by centrifugation, this material is homogenous within the precision of daily instrumental Mg/Ca determinations over a range of sample weights from 10 to 1000 mg, taken from two separate bottles of ECRM 752-1. Results gave an average value of Mg/Ca = 3.75 mmol/mol (0.015 s.d., 0.41% r.s.d.) on 118 determinations from the two bottles.

  13. Temperature dependence of resistance in epitaxial Fe/MgO/Fe magnetic tunnel junctions

    SciTech Connect

    Ma, Q. L.; Wang, Shouguo; Wang, Y.; Zhang, J.; Ward, R. C. C.; Kohn, A.; Zhang, Xiaoguang; Han, Prof. X. F.

    2009-01-01

    The temperature dependence of resistance in parallel P and antiparallel AP configurations RP,AP has been investigated in epitaxial Fe/MgO/Fe junctions with varying MgO barrier thicknesses tMgO. RAP exhibits a substantial decrease with increasing temperature for samples with tMgO ranging from 3.0 to 1.5 nm. In contrast, RP is approximately temperature independent when tMgO =3.0 nm and increases with temperature when tMgO=2.1 and 1.5 nm. Possible origins of this temperature dependence of resistance, which include taking into account a spin independent term and consideration of spin-flip scattering, are discussed. We attribute the temperature dependence of RP,AP to the misalignment of magnetic moments in the electrodes due to thermal excitations and its effect on the spin dependent tunneling.

  14. Thermoluminescence responses of photon- and electron-irradiated lithium potassium borate co-doped with Cu+Mg or Ti+Mg.

    PubMed

    Alajerami, Y S M; Hashim, S; Ramli, A T; Saleh, M A; Saripan, M I; Alzimami, K; Min Ung, Ngie

    2013-08-01

    New glasses Li2CO3-K2CO3-H3BO3 (LKB) co-doped with CuO and MgO, or with TiO2 and MgO, were synthesized by the chemical quenching technique. The thermoluminescence (TL) responses of LKB:Cu,Mg and LKB:Ti,Mg irradiated with 6 MV photons or 6 MeV electrons were compared in the dose range 0.5-4.0 Gy. The standard commercial dosimeter LiF:Mg,Ti (TLD-100) was used to calibrate the TL reader and as a reference in comparison of the TL properties of the new materials. The dependence of the responses of the new materials on (60)Co dose is linear in the range of 1-1000 Gy. The TL yields of both of the co-doped glasses and TLD-100 are greater for electron irradiation than for photon irradiation. The TL sensitivity of LKB:Ti,Mg is 1.3 times higher than the sensitivity of LKB:Cu,Mg and 12 times less than the sensitivity of TLD-100. The new TL dosimetric materials have low effective atomic numbers, good linearity of the dose responses, excellent signal reproducibility, and a simple glow curve structure. This combination of properties makes them suitable for radiation dosimetry.

  15. Interlaboratory comparison study of calibration standards for foraminiferal Mg/Ca thermometry

    NASA Astrophysics Data System (ADS)

    Greaves, M.; Caillon, N.; Rebaubier, H.; Bartoli, G.; Bohaty, S.; Cacho, I.; Clarke, L.; Cooper, M.; Daunt, C.; Delaney, M.; Demenocal, P.; Dutton, A.; Eggins, S.; Elderfield, H.; Garbe-Schoenberg, D.; Goddard, E.; Green, D.; Groeneveld, J.; Hastings, D.; Hathorne, E.; Kimoto, K.; Klinkhammer, G.; Labeyrie, L.; Lea, D. W.; Marchitto, T.; MartíNez-Botí, M. A.; Mortyn, P. G.; Ni, Y.; Nuernberg, D.; Paradis, G.; Pena, L.; Quinn, T.; Rosenthal, Y.; Russell, A.; Sagawa, T.; Sosdian, S.; Stott, L.; Tachikawa, K.; Tappa, E.; Thunell, R.; Wilson, P. A.

    2008-08-01

    An interlaboratory study of Mg/Ca and Sr/Ca ratios in three commercially available carbonate reference materials (BAM RS3, CMSI 1767, and ECRM 752-1) was performed with the participation of 25 laboratories that determine foraminiferal Mg/Ca ratios worldwide. These reference materials containing Mg/Ca in the range of foraminiferal calcite (0.8 mmol/mol to 6 mmol/mol) were circulated with a dissolution protocol for analysis. Participants were asked to make replicate dissolutions of the powdered samples and to analyze them using the instruments and calibration standards routinely used in their laboratories. Statistical analysis was performed in accordance with the International Standardization Organization standard 5725, which is based on the analysis of variance (ANOVA) technique. Repeatability (RSDr%), an indicator of intralaboratory precision, for Mg/Ca determinations in solutions after centrifuging increased with decreasing Mg/Ca, ranging from 0.78% at Mg/Ca = 5.56 mmol/mol to 1.15% at Mg/Ca = 0.79 mmol/mol. Reproducibility (RSDR%), an indicator of the interlaboratory method precision, for Mg/Ca determinations in centrifuged solutions was noticeably worse than repeatability, ranging from 4.5% at Mg/Ca = 5.56 mmol/mol to 8.7% at Mg/Ca = 0.79 mmol/mol. Results of this study show that interlaboratory variability is dominated by inconsistencies among instrument calibrations and highlight the need to improve interlaboratory compatibility. Additionally, the study confirmed the suitability of these solid standards as reference materials for foraminiferal Mg/Ca (and Sr/Ca) determinations, provided that appropriate procedures are adopted to minimize and to monitor possible contamination from silicate mineral phases.

  16. High Spin States in ^24Mg

    NASA Astrophysics Data System (ADS)

    Schwartz, J.; Lister, C. J.; Wuosmaa, A.; Betts, R. R.; Blumenthal, D.; Carpenter, M. P.; Davids, C. N.; Fischer, S. M.; Hackman, G.; Janssens, R. V. F.

    1996-05-01

    The ^12C(^16O,α)^24Mg reaction was used at 51.5MeV to populate high angular momentum states in ^24Mg. Gamma-rays de-exciting high spin states were detected in a 20 detector spectrometer (the AYE-ball) triggered by the ANL Fragment Mass Analyser (FMA). Channel selection, through detection of ^24Mg nuclei with the appropriate time of flight, was excellent. All the known decays from high spin states were seen in a few hours, with the exception of the 5.04 MeV γ-decay of the J^π=9^- state at 16.904 MeV footnote A.E.Smith et al., Phys. Lett. \\underlineB176, (1986)292. which could not be confirmed. The potential of the technique for studying the radiative decay of states with very high spin in light nuclei will be discussed.

  17. "Safe" Coulomb excitation of 30Mg.

    PubMed

    Niedermaier, O; Scheit, H; Bildstein, V; Boie, H; Fitting, J; von Hahn, R; Köck, F; Lauer, M; Pal, U K; Podlech, H; Repnow, R; Schwalm, D; Alvarez, C; Ames, F; Bollen, G; Emhofer, S; Habs, D; Kester, O; Lutter, R; Rudolph, K; Pasini, M; Thirolf, P G; Wolf, B H; Eberth, J; Gersch, G; Hess, H; Reiter, P; Thelen, O; Warr, N; Weisshaar, D; Aksouh, F; Van den Bergh, P; Van Duppen, P; Huyse, M; Ivanov, O; Mayet, P; Van de Walle, J; Aystö, J; Butler, P A; Cederkäll, J; Delahaye, P; Fynbo, H O U; Fraile, L M; Forstner, O; Franchoo, S; Köster, U; Nilsson, T; Oinonen, M; Sieber, T; Wenander, F; Pantea, M; Richter, A; Schrieder, G; Simon, H; Behrens, T; Gernhäuser, R; Kröll, T; Krücken, R; Münch, M; Davinson, T; Gerl, J; Huber, G; Hurst, A; Iwanicki, J; Jonson, B; Lieb, P; Liljeby, L; Schempp, A; Scherillo, A; Schmidt, P; Walter, G

    2005-05-01

    We report on the first radioactive beam experiment performed at the recently commissioned REX-ISOLDE facility at CERN in conjunction with the highly efficient gamma spectrometer MINIBALL. Using 30Mg ions accelerated to an energy of 2.25 MeV/u together with a thin (nat)Ni target, Coulomb excitation of the first excited 2+ states of the projectile and target nuclei well below the Coulomb barrier was observed. From the measured relative deexcitation gamma-ray yields the B(E2;0(+)gs-->2(+)1) value of 30Mg was determined to be 241(31)e2 fm4. Our result is lower than values obtained at projectile fragmentation facilities using the intermediate-energy Coulomb excitation method, and confirms the theoretical conjecture that the neutron-rich magnesium isotope 30Mg resides outside the "island of inversion."

  18. Unraveling the role of Mg(++) in osteoarthritis.

    PubMed

    Li, Yaqiang; Yue, Jiaji; Yang, Chunxi

    2016-02-15

    Mg(++) is widely involved in human physiological processes that may play key roles in the generation and progression of diseases. Osteoarthritis (OA) is a complex joint disorder characterized by articular cartilage degradation, abnormal mineralization and inflammation. Magnesium deficiency is considered to be a major risk factor for OA development and progression. Magnesium deficiency is active in several pathways that have been implicated in OA, including increased inflammatory mediators, cartilage damage, defective chondrocyte biosynthesis, aberrant calcification and a weakened effect of analgesics. Abundant in vitro and in vivo evidence in animal models now suggests that the nutritional supplementation or local infiltration of Mg(++) represent effective therapies for OA. The goal of this review is to summarize the current understanding of the role of Mg(++) in OA with particular emphasis on the related molecular mechanisms involved in OA progression. PMID:26800786

  19. Mg2(Si,Sn)-based thermoelectric materials and devices

    NASA Astrophysics Data System (ADS)

    Gao, Peng

    Thermoelectric effects are phenomena found in materials that can achieve direct conversion between heat flow and electricity. One important application of thermoelectric effects is thermoelectric generators, which can generate electricity when a temperature gradient is applied. Thermoelectric generators make use of various sources of heat and it is considered a promising solution for waste heat recovery. The conversion efficiency of thermoelectric generators depends on the materials used in the devices. Significant improvement in the performance of thermoelectric materials has been made in the past few decades. However, most of the good thermoelectric materials being investigated have limitations, such as the high materials cost, high materials density and toxicity of the constituent elements. The Mg2(Si,Sn)-based materials studied in this work are promising candidates for thermoelectric generators in the mid-temperature range and have drawn increasing research interest in recent years because these materials are high performance thermoelectrics that are low cost, low-density and non-toxic. In this work, systematic studies were performed on the Mg2(Si,Sn) thermoelectric materials. Thermal phase stability was studied for different compositions of Mg2Si1-xSnx and Mg2Si0.4Sn 0.6 was used as base material for further optimization. Both n-type and p-type samples were obtained by doping the materials with different elements. Peak ZT ˜ 1.5 for the n-type and ZT ˜ 0.7 for the p-type materials were obtained, both of which are among the best reported results so far. Experimental work was also done to study the techniques to develop the Mg2Si 0.4Sn0.6 materials into working devices. Different electrode materials were tested in bonding experiment for this compound, and copper was found to be the best electrode material for Mg2Si 0.4Sn0.6. Preliminary work was done to demonstrate the possibility of fabricating a Mg2Si0.4Sn0.6-based thermoelectric generator and the result is

  20. Efficient hydrogen storage with the combination of lightweight Mg/MgH2 and nanostructures.

    PubMed

    Cheng, Fangyi; Tao, Zhanliang; Liang, Jing; Chen, Jun

    2012-07-28

    Efficient hydrogen storage plays a key role in realizing the incoming hydrogen economy. However, it still remains a great challenge to develop hydrogen storage media with high capacity, favourable thermodynamics, fast kinetics, controllable reversibility, long cycle life, low cost and high safety. To achieve this goal, the combination of lightweight materials and nanostructures should offer great opportunities. In this article, we review recent advances in the field of chemical hydrogen storage that couples lightweight materials and nanostructures, focusing on Mg/MgH(2)-based systems. Selective theoretical and experimental studies on Mg/MgH(2) nanostructures are overviewed, with the emphasis on illustrating the influences of nanostructures on the hydrogenation/dehydrogenation mechanisms and hydrogen storage properties such as capacity, thermodynamics and kinetics. In particular, theoretical studies have shown that the thermodynamics of Mg/MgH(2) clusters below 2 nm change more prominently as particle size decreases. PMID:22715459

  1. The millimeter-wave spectrum of the MgH and MgD radicals

    NASA Technical Reports Server (NTRS)

    Ziurys, L. M.; Barclay, W. L., Jr.; Anderson, M. A.

    1993-01-01

    The pure rotational spectrum of MgH radical (X 2 Sigma (+)) in its ground state v = 0 and v = 1 vibrational modes has been observed in the laboratory using millimeter/submillimeter direct absorption spectroscopy. The rotational spectra of two isotopically substituted species, MgD and (Mg-26)H, have been detected as well. All six hyperfine components of the N = 0 -1 transition of MgH in its v = 0 and v = 1 states have been directly measured to an accuracy of +/-50 kHz, and the five components have been observed for (Mg-26)H. The N = 0 +/-1 and N = 1 -2 transitions of MgD have also been detected. Rotational, fine structure, and hyperfine constants were determined for all species from a nonlinear least-squared fit to the data using a 2 Sigma Hamiltonian.

  2. Interdiffusion in the Mg-Al system and Intrinsic Diffusion in (Al3Mg2) Phase

    SciTech Connect

    Brennan, Sarah; Bermudez, Katrina; Kulkarni, Nagraj S; Sohn, Yong Ho

    2011-01-01

    Increasing use and development of lightweight Mg-alloys have led to the desire for more fundamental research in and understanding of Mg-based systems. As a strengthening component, Al is one of the most important and common alloying elements for Mg-alloys. In this study, solid-to-solid diffusion couple techniques were employed to examine the interdiffusion between pure Mg and Al. Diffusion anneals were carried out at 300 , 350 , and 400 C for 720, 360, and 240 hours, respectively. Optical and scanning electron microscopies (SEM) were employed to observe the formation of the intermetallics -Al12Mg17 and -Al3Mg2, but not -phase. Concentration profiles were determined using X-ray energy dispersive spectroscopy (XEDS). The growth constants and activation energies were determined for each intermetallic phase.

  3. Superconductivity in MgPtSi: An orthorhombic variant of MgB2

    NASA Astrophysics Data System (ADS)

    Kudo, Kazutaka; Fujimura, Kazunori; Onari, Seiichiro; Ota, Hiromi; Nohara, Minoru

    2015-05-01

    A ternary compound, MgPtSi, was synthesized by solid-state reaction. An examination of the compound by powder x-ray diffraction revealed that it crystallizes in the orthorhombic TiNiSi-type structure with the P n m a space group. The structure comprises alternately stacked layers of Mg and PtSi honeycomb network, which is reminiscent of MgB2, and the buckling of the honeycomb network causes orthorhombic distortion. Electrical and magnetic studies revealed that MgPtSi exhibited superconductivity with a transition temperature of 2.5 K. However, its isostructural compounds, namely, MgRhSi and MgIrSi, were not found to exhibit superconductivity.

  4. Controls of carbonate mineralogy and solid-solution of Mg in calcite: evidence from spelean systems

    SciTech Connect

    Gonzalez, L.A.; Lohmann, K.C.

    1985-01-01

    Precipitation of carbonate minerals in spelean systems occurs under a wide range of fluid chemistry, Mg-Ca ratios, alkalinities, pH and temperatures; thus, spelean systems provide ideal settings to determine factors controlling the mineralogy of precipitated carbonates and solid-solution of Mg in calcite. Cave waters and actively-precipitating carbonate speleothems were collected from Carlsbad Caverns National Park, New Mexico and the Mammoth-Flint Cave System, Kentucky. Carbonate mineralogy of precipitated phases was determined by x-ray diffraction, and major and minor element composition of waters and accompanying minerals were determined by Atomic Absorption Spectrophotometry. Results demonstrate that at a constant CO3 concentration the precipitation threshold for calcite to aragonite is controlled dominantly by the Mg/Ca ratio of the ambient fluid. Aragonite precipitation is favored by high Mg/Ca ratios. Conversely, with increasing CO3 concentration at constant fluid Mg/Ca ratios, calcite is preferentially precipitated. Solid-solution of Mg in calcite is positively correlated with both increased Mg/Ca ratios and CO3 concentrations. These data suggest that Mg contents of calcite can not be defined solely in terms of a homogeneous distribution coefficient. Rather, Mg concentrations can be also be affected by the CO3 concentration and degree of calcite saturation, suggesting that the rate of crystal growth also plays and important role in Mg solid-solution in calcites.

  5. Excited intruder states in {sup 32}Mg

    SciTech Connect

    Tripathi, Vandana; Tabor, S. L.; Bender, P.; Hoffman, C. R.; Lee, Sangjin; Pepper, K.; Perry, M.; Utsuno, Y.; Otsuka, T.; Mantica, P. F.; Pinter, J. S.; Stoker, J. B.; Cook, J. M.; Pereira, J.; Weisshaar, D.

    2008-03-15

    The low energy level structure of N=20 {sup 32}Mg obtained via {beta}-delayed {gamma} spectroscopy is reported. The level structure of {sup 32}Mg is found to be completely dominated by intruders. An inversion between the 1p-1h and 3p-3h states is observed for the negative parity states, similar to the 0p-0h and 2p-2h inversion for the positive parity states in these N{approx}20 nuclei. The intruder excited states, both positive and negative parity, are reasonably explained by Monte Carlo shell model calculations, which suggest a shrinking N=20 shell gap with decreasing Z.

  6. Biocompatibility Assessment of Novel Bioresorbable Alloys Mg-Zn-Se and Mg-Zn-Cu for Endovascular Applications: In- Vitro Studies

    PubMed Central

    Budiansky, Noah; McGoron, Anthony J.

    2013-01-01

    Previous studies have shown that using biodegradable magnesium alloys such as Mg-Zn and Mg-Zn-Al possess the appropriate mechanical properties and biocompatibility to serve in a multitude of biological applications ranging from endovascular to orthopedic and fixation devices. The objective of this study was to evaluate the biocompatibility of novel as-cast magnesium alloys Mg-1Zn-1Cu wt.% and Mg-1Zn-1Se wt.% as potential implantable biomedical materials, and compare their biologically effective properties to a binary Mg-Zn alloy. The cytotoxicity of these experimental alloys was evaluated using a tetrazolium based- MTS (3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium) assay and a lactate dehydrogenase membrane integrity assay (LDH). The MTS assay was performed on extract solutions obtained from a 30-day period of alloy immersion and agitation in simulated body fluid to evaluate the major degradation products eluted from the alloy materials. Human foreskin fibroblast cell growth on the experimental magnesium alloys was evaluated for a 72 hour period, and cell death was quantified by measuring lactate dehydrogenase concentrations. Both Mg-Zn-Se and Mg-Zn-Cu alloys exhibit low cytotoxicity levels which are suitable for biomaterial applications. The Mg-Zn-Cu alloy was found to completely degrade within 72 hours, resulting in lower human foreskin fibroblast cell viability. The Mg-Zn-Se alloy was shown to be less cytotoxic than both the Mg-Zn-Cu and Mg-Zn alloys. PMID:24058329

  7. Role of MgATP and MgADP in the cross-bridge kinetics in chemically skinned rabbit psoas fibers. Study of a fast exponential process (C)

    PubMed Central

    Kawai, M; Halvorson, H R

    1989-01-01

    The role of the substrate (MgATP) and product (MgADP) molecules in cross-bridge kinetics is investigated by small amplitude length oscillations (peak to peak: 3 nm/cross-bridge) and by following amplitude change and phase shift in tension time courses. The range of discrete frequencies used for this investigation is 0.25-250 Hz, which corresponds to 0.6-600 ms in time domain. This report investigates the identity of the high frequency exponential advance (process C), which is equivalent to "phase 2" of step analysis. The experiments are performed in maximally activated (pCa 4.5-5.0) single fibers from chemically skinned rabbit psoas fibers at 20 degrees C and at the ionic strength 195 mM. The rate constant 2 pi c deduced from process (C) increases and saturates hyperbolically with an increase in MgATP concentration, whereas the same rate constant decreases monotonically with an increase in MgADP concentration. The effects of MgATP and MgADP are opposite in all respects we have studied. These observations are consistent with a cross-bridge scheme in which MgATP and MgADP are in rapid equilibria with rigorlike cross-bridges, and they compete for the substrate site on myosin heads. From our measurements, the association constants are found to be 1.4 mM-1 for MgATP and 2.8 mM-1 for MgADP. We further deduced that the composite second order rate constant of MgATP binding to cross-bridges and subsequent isomerization/dissociation reaction to be 0.57 x 10(6)M-1s-1. PMID:2785822

  8. The Electrochemical Co-reduction of Mg-Al-Y Alloys in the LiCl-NaCl-MgCl2-AlF3-YCl3 Melts

    NASA Astrophysics Data System (ADS)

    Li, Mei; Liu, Yaochen; Han, Wei; Wang, Shanshan; Zhang, Milin; Yan, Yongde; Shi, Weiqun

    2015-04-01

    The electrochemical formation of Mg-Al-Y alloys was studied in the LiCl-NaCl-MgCl2 melts by the addition of AlF3 and YCl3 on a molybdenum electrode at 973 K (700 °C). In order to reduce the volatilization of salt solvent in the electrolysis process, the volatile loss of LiCl-NaCl-MgCl2 and LiCl-KCl-MgCl2 melts was first measured in the temperature range from 873 K to 1023 K (600 °C to 750 °C). Then, the electrochemical behaviors of Mg(II), Al(III), Y(III) ions and alloy formation processes were investigated by cyclic voltammetry, chronopotentiometry, and open circuit chronopotentiometry. The cyclic voltammograms indicate that the under-potential deposition of magnesium and yttrium on pre-deposited Al leads to formation of Mg-Al and Al-Y intermetallic compounds. The Mg-Al-Y alloys were prepared by galvanostatic electrolysis in the LiCl-NaCl-MgCl2-AlF3-YCl3 melts and characterized by X-ray diffraction and scanning electron microscopy with energy dispersive spectrometry. Composition of the alloys was analyzed by inductively coupled plasma-atomic emission spectrometer, and current efficiency was also determined by the alloy composition.

  9. Effect of Mg diffusion on photoluminescence spectra of MgZnO/ZnO bi-layers annealed at different temperatures

    NASA Astrophysics Data System (ADS)

    Das, Amit K.; Misra, P.; Ajimsha, R. S.; Bose, A.; Joshi, S. C.; Porwal, S.; Sharma, T. K.; Oak, S. M.; Kukreja, L. M.

    2013-11-01

    MgZnO/ZnO bilayers (Mg concentration of ˜30%) have been grown and subsequently annealed at different temperatures in the range of 600-900 °C with the specific interest of studying the effect of inter-diffusion of Mg on the photoluminescence (PL) properties of the bilayers. The influence of Mg diffusion and material homogenization is evaluated through absorption, PL, and secondary ion mass spectrometry (SIMS) measurements. No appreciable change in the spectral positions is seen either in PL or absorption up to an annealing temperature of 700 °C, which is also supported by SIMS. However at higher annealing temperatures, diffusion of Mg into the ZnO layer is clearly evident in SIMS profile, which results in the red-shift (blue-shift) of spectral positions of MgZnO (ZnO) layer, respectively. Finally, for the sample annealed at 900 °C, the two layers are completely merged providing a single peak at ˜3.60 eV in PL/absorption corresponding to a completely homogenized MgZnO layer. Spectroscopic results are corroborated by the numerical simulations based on a simple theoretical model, which correlates the observed PL spectra of the heterostructures with the experimental Mg diffusion profiles across the heterointerface, as measured by SIMS.

  10. Recovery of SO2 and MgO from By-Products of MgO Wet Flue Gas Desulfurization.

    PubMed

    Yan, Liyun; Lu, Xiaofeng; Wang, Quanhai; Guo, Qiang

    2014-11-01

    An industrial demonstration unit using natural gas as a heat source was built to calcine the by-products of MgO wet flue gas desulfurization from power plants; influencing factors on the SO2 content in calciner gas were comprehensively analyzed; and an advantageous recycling condition of MgO and SO2 from by-products was summarized. Results showed that the SO2 content in the calciner gas was increased by more than 10 times under a lower excess air coefficient, a higher feed rate, a lower crystal water in by-products, and a higher feed port position. For the tests conducted under the excess air coefficient above and below one, the effect of the furnace temperature on the SO2 content in the calciner gas was reversed. Results of activity analysis indicate that particles of MgO generated under the calcination temperature of 900-1,000°C had a high activity. In contrast, due to the slight sintering, MgO generated under the calcination temperature of 1,100°C had a low activity. To recycle SO2 as well as MgO, a temperature range of 900-927°C for TE103 is proposed. These studies will prompt the desulfurization market diversification, reduce the sulfur's dependence on imports for making sulfuric acid, be meaningful to balance the usage of the natural resource in China, and be regarded as a reference for the development of this technology for other similar developing countries.

  11. Recovery of SO2 and MgO from By-Products of MgO Wet Flue Gas Desulfurization

    PubMed Central

    Yan, Liyun; Lu, Xiaofeng; Wang, Quanhai; Guo, Qiang

    2014-01-01

    Abstract An industrial demonstration unit using natural gas as a heat source was built to calcine the by-products of MgO wet flue gas desulfurization from power plants; influencing factors on the SO2 content in calciner gas were comprehensively analyzed; and an advantageous recycling condition of MgO and SO2 from by-products was summarized. Results showed that the SO2 content in the calciner gas was increased by more than 10 times under a lower excess air coefficient, a higher feed rate, a lower crystal water in by-products, and a higher feed port position. For the tests conducted under the excess air coefficient above and below one, the effect of the furnace temperature on the SO2 content in the calciner gas was reversed. Results of activity analysis indicate that particles of MgO generated under the calcination temperature of 900–1,000°C had a high activity. In contrast, due to the slight sintering, MgO generated under the calcination temperature of 1,100°C had a low activity. To recycle SO2 as well as MgO, a temperature range of 900–927°C for TE103 is proposed. These studies will prompt the desulfurization market diversification, reduce the sulfur's dependence on imports for making sulfuric acid, be meaningful to balance the usage of the natural resource in China, and be regarded as a reference for the development of this technology for other similar developing countries. PMID:25371652

  12. The Interplay of Al and Mg Speciation in Advanced Mg Battery Electrolyte Solutions.

    PubMed

    See, Kimberly A; Chapman, Karena W; Zhu, Lingyang; Wiaderek, Kamila M; Borkiewicz, Olaf J; Barile, Christopher J; Chupas, Peter J; Gewirth, Andrew A

    2016-01-13

    Mg batteries are an attractive alternative to Li-based energy storage due to the possibility of higher volumetric capacities with the added advantage of using sustainable materials. A promising emerging electrolyte for Mg batteries is the magnesium aluminum chloride complex (MACC) which shows high Mg electrodeposition and stripping efficiencies and relatively high anodic stabilities. As prepared, MACC is inactive with respect to Mg deposition; however, efficient Mg electrodeposition can be achieved following an electrolytic conditioning process. Through the use of Raman spectroscopy, surface enhanced Raman spectroscopy, (27)Al and (35)Cl nuclear magnetic resonance spectroscopy, and pair distribution function analysis, we explore the active vs inactive complexes in the MACC electrolyte and demonstrate the codependence of Al and Mg speciation. These techniques report on significant changes occurring in the bulk speciation of the conditioned electrolyte relative to the as-prepared solution. Analysis shows that the active Mg complex in conditioned MACC is very likely the [Mg2(μ-Cl)3·6THF](+) complex that is observed in the solid state structure. Additionally, conditioning creates free Cl(-) in the electrolyte solution, and we suggest the free Cl(-) adsorbs at the electrode surface to enhance Mg electrodeposition.

  13. A MgB2 superferric racetrack magnet

    NASA Astrophysics Data System (ADS)

    Musenich, R.; Sorbi, M.; Tavilla, G.; Volpini, G.; Marabotto, R.; Modica, M.; Nardelli, D.

    2008-10-01

    A magnesium diboride, cryogen-free, H-dipole magnet with cold iron yoke was constructed and tested. The racetrack coil, 48 cm long, was wound with 350 m of nickel-clad, copper-MgB2 tape. The iron yoke forms a 2.6 cm gap. The magnet was connected to a cryocooler and tested at different temperatures ranging between 8.5 and 24 K. The maximum current, 263 A, was reached, without training, at 8.5 K. The corresponding field in the gap was 2.35 T.

  14. Measurement of lifetimes in 23Mg

    NASA Astrophysics Data System (ADS)

    Kirsebom, O. S.; Bender, P.; Cheeseman, A.; Christian, G.; Churchman, R.; Cross, D. S.; Davids, B.; Evitts, L. J.; Fallis, J.; Galinski, N.; Garnsworthy, A. B.; Hackman, G.; Lighthall, J.; Ketelhut, S.; Machule, P.; Miller, D.; Nielsen, S. T.; Nobs, C. R.; Pearson, C. J.; Rajabali, M. M.; Radich, A. J.; Rojas, A.; Ruiz, C.; Sanetullaev, A.; Unsworth, C. D.; Wrede, C.

    2016-02-01

    Several lifetimes in 23Mg have been determined for the first time using the Doppler-shift attenuation method. A Monte Carlo simulation code has been written to model the γ -ray line shape. An upper limit of τ <12 fs at the 95% C.L. has been obtained for the astrophysically important 7787 keV state.

  15. Optical properties of MgO irradiated by fast neutrons

    NASA Astrophysics Data System (ADS)

    Okada, M.; Seiyama, T.; Ichihara, C.; Nakagawa, M.

    1985-08-01

    Optical properties of color centers in MgO single crystals irradiated by fission neutrons (Kyoto University Reactor, KUR) and by 14 MeV neutrons (RTNS-II, at Lawrence Livermore National Laboratory, LLNL) have been investigated. The absorption spectra of MgO crystals irradiated by neutrons from the two different sources are similar; exhibited principal bands are 250 nm band consisting of F and F + bands, 352 (F 2 center), 570 and 975 (F 2 center) nm bands. In the samples irradiated by fission neutrons, the absorption intensity of the 570 nm band does not reach a maximum by neutron fluence through which the F and F 2 type bands reach a maximum. These phenomena are remarkable in the impurity-doped samples. A linear increase of the intensity of the 570 nm band with a dose of fast neutrons does not change with impurity contents, and exists in the extensive range examined of fast neutron dose (10 15-10 19 n/cm 2). This fact suggests that the crystalline MgO can be applied as a fluence monitor for fast neutrons with extensive energy.

  16. Preliminary study of the characteristics of a high Mg containing Al-Mg-Si alloy

    NASA Astrophysics Data System (ADS)

    Yan, F.; McKay, B. J.; Fan, Z.; Chen, M. F.

    2012-01-01

    An Al-20Mg-4Si high Mg containing alloy has been produced and its characteristics investigated. The as-cast alloy revealed primary Mg2Si particles evenly distributed throughout an α-Al matrix with a β-Al3Mg2 fully divorced eutectic phase observed in interdendritic regions. The Mg2Si particles displayed octahedral, truncated octahedral, and hopper morphologies. Additions of Sb, Ti and Zr had a refining influence reducing the size of the Mg2Si from 52 ± 4 μm to 25 ± 0.1 μm, 35 ± 1 μm and 34 ± 1 μm respectively. HPDC tensile test samples could be produced with a 0.6 wt.% Mn addition which prevented die soldering. Solution heating for 1 hr was found to dissolve the majority of the Al3Mg2 eutectic phase with no evidence of any effect on the primary Mg2Si. Preliminary results indicate that the heat treatment has a beneficial effect on the elongation and the UTS.

  17. Thermoelectric properties of n-Type Mg2Si-Mg2Sn solid solutions with different grain sizes

    NASA Astrophysics Data System (ADS)

    Samunin, A. Yu.; Zaitsev, V. K.; Pshenay-Severin, D. A.; Konstantinov, P. P.; Isachenko, G. N.; Fedorov, M. I.; Novikov, S. V.

    2016-08-01

    Influence of the grain sizes on thermoelectric parameters of pressurized solid solutions of the composition Mg2Si0.8Sn0.2 was studied. The Seebeck coefficient, electric conductivity, thermal conductivity, and Hall coefficient were determined. Decreasing the grain size to the nanoscale was found to decrease the mobility at low temperatures and resulted in a peculiar temperature dependence of the electric conductivity, but did not lead to a decrease in the thermo EMF. It was found that the grain size had no effect on the thermoelectric efficiency of the investigated solid solution in the operating temperature range.

  18. What is the Right Temperature Sensitivity for Foraminiferal Mg/ca Paleothermometry in Ancient Oceans?

    NASA Astrophysics Data System (ADS)

    Eggins, S.; Holland, K.; Hoenisch, B.; Spero, H. J.; Allen, K. A.

    2013-12-01

    Mg/Ca seawater thermometry has become a cornerstone of modern paleoceanography. Laboratory experiments, seafloor core-top samples, plankton trap and tow collected materials all indicate consistent temperature sensitivity (9-10% increase in Mg/Ca per °C) for a full range of modern planktic foraminifer species. While these results demonstrate the overall robustness of Mg/Ca paleothermometry for the modern ocean, it is an empirical tool for which there is limited understanding of its bio-physio-chemical basis and its applicability to ancient oceans. We have undertaken experimental cultures of Orbulina universa, Globigerinoides sacculifer and Globigerinoides ruber (pink) across a range of seawater compositions (temperature, carbonate chemistry and Mg/Casw) that encompass modern and ancient Paleogene and Cretaceous ocean compositions (Mg/Casw 0.25x to 2x modern and pCO2 = 200 to 1500 ppmv). Our results reveal that the sensitivity of the Mg/Ca-thermometer for planktic foraminifers reduces significantly with Mg/Casw, rather than remaining constant as has been widely assumed or, increasing at lower Mg/Casw as proposed recently by Evans and Müller (2012). These results indicate that the modern sensitivity of 9-10% increase in Mg/Ca per °C cannot yet be applied to obtain reliable relative temperature change estimates to ancient oceans. These results further suggest that variations in foraminiferal Mg/Ca compositions in ancient oceans with lower Mg/Casw may correspond to larger temperature variations than in the modern ocean. Evans D. and Müller W., Paleoceanography, vol. 27, PA4205, doi:10.1029/2012PA002315, 2012

  19. Photodissociation spectroscopy of the complexes of Mg+ with di- and tri-ethylamine

    NASA Astrophysics Data System (ADS)

    Guo, Wenyue; Liu, Haichuan; Yang, Shihe

    2002-02-01

    We present the photodissociation spectroscopy of the complexes of Mg+ with di- and tri-ethylamine in the spectral range of 230-440 nm. Mass spectrometry of the two parent complexes exhibits the persistent product Mg+ from nonreactive quenching throughout the whole wavelength range. As for the reactive channels, C3H7•-elimination products are dominant when the complexes are excited to 3Px,y. Furthermore, photoexcitation of Mg+-NH(C2H5)2 to 3Px,y yields a minor MgH-elimination fragment. On the other hand, photodissociation of Mg+-N(C2H5)3 produces charge-transfer fragments N+(C2H5)3 and (C2H5)2N+CH2. The action spectra of the two complexes consist of two pronounced peaks on the red and blue side of the Mg+ 3 2P←3 2S atomic transition. The calculated absorption spectra of the two complexes using the optimized structures of their ground states agree nicely with the observed action spectra. Photofragment branching fractions of the products are shown to be nearly independent of the photon energy for the 3Px,y excitation, indicating the importance of exit channel effects. A photoreaction mechanism is proposed for C3H7•-elimination, which entails Mg+ insertion into one C-N bond, followed by a nonadiabatic transition to the ground-state surface through a conical intersection. However, for the MgH-elimination channel in the photodissociation of Mg+-NH(C2H5)2, Mg+ rather inserts into the α-C-H bond. Finally, photoexcitation of Mg+-N(C2H5)3 leads to a prominent charge-transfer product [N+(C2H5)3]*, which dissociates further to (C2H5)2N+CH2 by a loss of CH3•.

  20. Biocompatibility and biodegradability of Mg-Sr alloys: the formation of Sr-substituted hydroxyapatite.

    PubMed

    Bornapour, M; Muja, N; Shum-Tim, D; Cerruti, M; Pekguleryuz, M

    2013-02-01

    Magnesium is an attractive material for use in biodegradable implants due to its low density, non-toxicity and mechanical properties similar to those of human tissue such as bone. Its biocompatibility makes it amenable for use in a wide range of applications from bone to cardiovascular implants. Here we investigated the corrosion rate in simulated body fluid (SBF) of a series of Mg-Sr alloys, with Sr in the range of 0.3-2.5%, and found that the Mg-0.5 Sr alloy showed the slowest corrosion rate. The degradation rate from this alloy indicated that the daily Sr intake from a typical stent would be 0.01-0.02 mg day⁻¹, which is well below the maximum daily Sr intake levels of 4 mg day⁻¹. Indirect cytotoxicity assays using human umbilical vascular endothelial cells indicated that Mg-0.5 Sr extraction medium did not cause any toxicity or detrimental effect on the viability of the cells. Finally, a tubular Mg-0.5 Sr stent sample, along with a WE43 control stent, was implanted into the right and left dog femoral artery. No thrombosis effect was observed in the Mg-0.5 Sr stent after 3 weeks of implantation while the WE43 stent thrombosed. X-ray diffraction demonstrated the formation of hydroxyapatite and Mg(OH)₂ as a result of the degradation of Mg-0.5 Sr alloy after 3 days in SBF. X-ray photoelectron spectroscopy further showed the possibility of the formation of a hydroxyapatite Sr-substituted layer that presents as a thin layer at the interface between the Mg-0.5 Sr alloy and the corrosion products. We believe that this interfacial layer stabilizes the surface of the Mg-0.5 Sr alloy, and slows down its degradation rate over time. PMID:22871640

  1. Zinc Binding to MG53 Protein Facilitates Repair of Injury to Cell Membranes*

    PubMed Central

    Cai, Chuanxi; Lin, Peihui; Zhu, Hua; Ko, Jae-Kyun; Hwang, Moonsun; Tan, Tao; Pan, Zui; Korichneva, Irina; Ma, Jianjie

    2015-01-01

    Zinc is an essential trace element that participates in a wide range of biological functions, including wound healing. Although Zn2+ deficiency has been linked to compromised wound healing and tissue repair in human diseases, the molecular mechanisms underlying Zn2+-mediated tissue repair remain unknown. Our previous studies established that MG53, a TRIM (tripartite motif) family protein, is an essential component of the cell membrane repair machinery. Domain homology analysis revealed that MG53 contains two Zn2+-binding motifs. Here, we show that Zn2+ binding to MG53 is indispensable to assembly of the cell membrane repair machinery. Live cell imaging illustrated that Zn2+ entry from extracellular space is essential for translocation of MG53-containing vesicles to the acute membrane injury sites for formation of a repair patch. The effect of Zn2+ on membrane repair is abolished in mg53−/− muscle fibers, suggesting that MG53 functions as a potential target for Zn2+ during membrane repair. Mutagenesis studies suggested that both RING and B-box motifs of MG53 constitute Zn2+-binding domains that contribute to MG53-mediated membrane repair. Overall, this study establishes a base for Zn2+ interaction with MG53 in protection against injury to the cell membrane. PMID:25869134

  2. Space-Based Range Safety and Future Space Range Applications

    NASA Technical Reports Server (NTRS)

    Whiteman, Donald E.; Valencia, Lisa M.; Simpson, James C.

    2005-01-01

    The National Aeronautics and Space Administration (NASA) Space-Based Telemetry and Range Safety (STARS) study is a multiphase project to demonstrate the performance, flexibility and cost savings that can be realized by using space-based assets for the Range Safety [global positioning system (GPS) metric tracking data, flight termination command and range safety data relay] and Range User (telemetry) functions during vehicle launches and landings. Phase 1 included flight testing S-band Range Safety and Range User hardware in 2003 onboard a high-dynamic aircraft platform at Dryden Flight Research Center (Edwards, California, USA) using the NASA Tracking and Data Relay Satellite System (TDRSS) as the communications link. The current effort, Phase 2, includes hardware and packaging upgrades to the S-band Range Safety system and development of a high data rate Ku-band Range User system. The enhanced Phase 2 Range Safety Unit (RSU) provided real-time video for three days during the historic Global Flyer (Scaled Composites, Mojave, California, USA) flight in March, 2005. Additional Phase 2 testing will include a sounding rocket test of the Range Safety system and aircraft flight testing of both systems. Future testing will include a flight test on a launch vehicle platform. This paper discusses both Range Safety and Range User developments and testing with emphasis on the Range Safety system. The operational concept of a future space-based range is also discussed.

  3. Space-Based Range Safety and Future Space Range Applications

    NASA Technical Reports Server (NTRS)

    Whiteman, Donald E.; Valencia, Lisa M.; Simpson, James C.

    2005-01-01

    The National Aeronautics and Space Administration Space-Based Telemetry and Range Safety study is a multiphase project to demonstrate the performance, flexibility and cost savings that can be realized by using space-based assets for the Range Safety (global positioning system metric tracking data, flight termination command and range safety data relay) and Range User (telemetry) functions during vehicle launches and landings. Phase 1 included flight testing S-band Range Safety and Range User hardware in 2003 onboard a high-dynamic aircraft platform at Dryden Flight Research Center (Edwards, California) using the NASA Tracking and Data Relay Satellite System as the communications link. The current effort, Phase 2, includes hardware and packaging upgrades to the S-band Range Safety system and development of a high data rate Ku-band Range User system. The enhanced Phase 2 Range Safety Unit provided real-time video for three days during the historic GlobalFlyer (Scaled Composites, Mojave, California) flight in March, 2005. Additional Phase 2 testing will include a sounding rocket test of the Range Safety system and aircraft flight testing of both systems. Future testing will include a flight test on a launch vehicle platform. This report discusses both Range Safety and Range User developments and testing with emphasis on the Range Safety system. The operational concept of a future space-based range is also discussed.

  4. Dust in MG II Absorption Systems

    NASA Astrophysics Data System (ADS)

    Malhotra, S.

    The dust absorption feature at 2175 AA is detected in a composite spectrum of Mg II absorbers. The composite absorber spectrum is obtained by taking the geometric mean of 92 quasar spectra after aligning them in the rest-frame of 96 absorbers. By aligning the spectra according to absorber redshifts we reinforce the spectral features of the absorbers, and smooth over possible bumps and wiggles in the emission spectra. The width of the observed absorption feature is 200-300 AA (FWHM), or 0.4-0.6 microns^{-1} and the central wavelength is 2240 AA. The Galactic dust feature has a central wavelength of 2176 AA and FWHM = 0.8-1.25 microns^{-1}. Simulations show that this discrepancy between the properties of the 2175 AA feature in Mg II absorbers and Galactic ISM can be mostly explained by the different methods used to measure them (cf. Malhotra 1997).

  5. Multilayer MgB2 superconducting quantum interference filter magnetometers

    NASA Astrophysics Data System (ADS)

    Galan, Elias; Melbourne, Thomas; Davidson, Bruce A.; Xi, X. X.; Chen, Ke

    2016-04-01

    We report two types of all-MgB2 superconductive quantum interference filter (SQIF) magnetometers that can measure absolute magnetic fields with high sensitivity. In one configuration, the SQIFs were made of 20 multilayer nonplanar all-MgB2 superconducting quantum interference devices (SQUIDs) connected in parallel with loop areas ranging in size from 0.4 to 3.6 μm2. These devices are sensitive to magnetic fields parallel to the substrate and show a single antipeak from 3 to 16 K with a maximum transfer function of ˜16 V/T at 3 K and a field noise of ˜110 pT/Hz1/2 above 100 Hz at 10 K. In a second configuration, the SQIFs were made with 16 planar SQUIDs connected in parallel with loop areas ranging in size from 4 μm2 to 25 μm2 and are sensitive to the magnetic fields perpendicular to the substrate. The planar SQIF shows a single antipeak from 10 to 22 K with a maximum transfer function of 7800 V/T at 10 K and a field noise of ˜70 pT/Hz1/2 above 100 Hz at 20 K.

  6. Effects of atorvastatin 20 mg, rosuvastatin 10 mg, and atorvastatin/ezetimibe 5 mg/5 mg on lipoproteins and glucose metabolism.

    PubMed

    Her, Ae-Young; Kim, Jong-Youn; Kang, Seok-Min; Choi, Donghoon; Jang, Yangsoo; Chung, Namsik; Manabe, Ichiro; Lee, Sang-Hak

    2010-06-01

    The aim of this study was to compare the effects of 3 different statin regimens that have equivalent low-density lipoprotein cholesterol (LDL-C) lowering efficacy on the apolipoprotein B/A1 ratio and glucose metabolism. After a 4-week dietary lead-in, 90 hypercholeserolemic patients were randomly assigned to 1 of 3 treatment groups for 8 weeks: atorvastatin 20 mg, rosuvastatin 10 mg, or atorvastatin/ezetimibe 5 mg/5 mg. At drug treatment week 8, we compared the percentage changes in lipid parameters, apolipoprotein B/A1 ratio, hemoglobin A1c, and homeostasis model assessment-insulin resistance (HOMA-IR) from baseline. Seventy-six patients completed the study and the percentage changes in LDL-C were comparable among the groups. However, the percentage reduction in the apolipoprotein B/A1 ratio was significantly greater in the rosuvastatin group (-47% +/- 14%, P = .04) and the combination group (-46% +/- 8%, P = .05) than in the atorvastatin group (-39% +/- 11%). The percentage increase in hemoglobin A1c was small but significantly greater in the atorvastatin group compared to the combination group (3.0% +/- 5.2% and -0.4% +/- 4.0%, P = .03). The effect of rosuvastatin on hemoglobin A1c was not different from those of the other 2 regimens. The effects of 3 statin regimens were similar on HOMA-IR. In conclusion, 3 statin regimens have differential effect on apolipoprotein B/A1 and glycemic control after comparable LDL-C reduction.

  7. Enhancement of Be and Mg incorporation in wurtzite quaternary BeMgZnO alloys with up to 5.1 eV optical bandgap

    NASA Astrophysics Data System (ADS)

    Toporkov, M.; Avrutin, V.; Okur, S.; Izyumskaya, N.; Demchenko, D.; Volk, J.; Smith, D. J.; Morkoç, H.; Özgür, Ü.

    2014-09-01

    A wide range of optical bandgap modulation up to 5.1 eV was achieved for quaternary BeMgZnO thin films prepared using plasma assisted molecular beam epitaxy, enabling development of UV emitters and solar-blind photodetectors. The significantly improved structural quality and bandgap widening in BeMgZnO layers as compared to those of BeZnO and MgZnO ternaries indicate enhanced incorporation of both Be and Mg on Zn sites in the wurtzite lattice. Correlation of lattice parameters with optical bandgaps reveals that co-alloying MgO and BeO with ZnO helps overcome the impediment of limited bandgap extension offered by the corresponding ternary compounds due to phase separation and allows lattice-matched or nearly lattice-matched BeMgZnO/ZnO heterostructures. Optimization of growth conditions at higher Mg and/or Be fluxes is expected to provide bandgaps beyond 5.1 eV.

  8. Thermodynamic calculations of Fe–Mg interdiffusion in (Mg,Fe){sub 2}SiO{sub 4} polymorphs and perovskite

    SciTech Connect

    Zhang, Baohua Shan, Shuangming

    2015-02-07

    In this study, we show that the temperature and pressure dependence of Fe–Mg interdiffusion in (Fe,Mg){sub 2}SiO{sub 4} polymorphs (olivine, wadsleyite, and ringwoodite) and perovskite can be successfully reproduced in terms of bulk elastic and expansivity data through a thermodynamic model (so-called cBΩ model) that interconnects point defect parameters with bulk properties. Under dry and wet conditions, our calculated Fe–Mg interdiffusion coefficients D{sub calc}{sup Fe-Mg} (particularly for anisotropic diffusivity in olivine), activation enthalpy h{sup act}, and activation volume υ{sup act} over a wide range of geologically relevant temperatures (1000–2400 K) and pressures (0–100 GPa) are consistent with the experimental ones when the uncertainties are considered.

  9. Highly Reversible Mg Insertion in Nanostructured Bi for Mg Ion Batteries

    SciTech Connect

    Shao, Yuyan; Gu, Meng; Li, Xiaolin; Nie, Zimin; Zuo, Pengjian; Li, Guosheng; Liu, Tianbiao L.; Xiao, Jie; Cheng, Yingwen; Wang, Chong M.; Zhang, Jiguang; Liu, Jun

    2014-01-08

    Rechargeable magnesium batteries have attracted wide attention for energy storage. Currently, most studies focus on Mg metal as the anode, but this approach is still limited by the properties of the electrolyte and poor control of the Mg plating/stripping processes.1,2 Here we report the synthesis and application of Bi nanotubes as a high performance anode material for rechargeable Mg ion batteries. The nanostructured Bi anode delivers a high reversible specific capacity (350 mAh/gBi, or 3430 mAh/cm3 Bi), excellent stability, and high columbic efficiency (95 % initial and very close to 100% afterwards). The good performance is attributed to the unique properties of in-situ formed, interconnected nanoporous bismuth. Such nanostructures can effectively accommodate the large volume change without losing electric contact and significantly reduce diffusion length for Mg2+. Significantly, the nanostructured Bi anode can be used with conventional electrolytes which will open new opportunities to study Mg ion battery chemistry and further improve the properties. The performance and the stability of a full cell Mg ion battery have been demonstrated with conventional electrolytes. This work suggests that other high energy density alloy compounds may also be considered for Mg-ion chemistry for high capacity electrode materials.

  10. The significance of Mg in prebiotic geochemistry

    PubMed Central

    Holm, N G

    2012-01-01

    Magnesium plays a special role in biochemistry because of its ability to coordinate six oxygen atoms efficiently in its first coordination shell. Such oxygen atoms may be part of one or two charged oxyanions, which means that Mg2+ can, for instance, tie together two different phosphate groups that are located at distance from each other in a macromolecule, and in this way be responsible for the folding of molecules like RNA. This property of Mg2+ also helps the stabilization of diphosphate and triphosphate groups of nucleotides, as well as promoting the condensation of orthophosphate to oligophosphates, like pyrophosphate and trimetaphosphate. Borates, on the other hand, are known to promote the formation of nucleobases and carbohydrates, ribose in particular, which is yet another constituent of nucleotides. The oldest borate minerals that we find on Earth today are magnesium borates. Dissolved borate stabilizes pentose sugars by forming complexes with cis-hydroxyl groups. In the furanose form of ribose, the preferential binding occurs to the 2 and 3 carbon, leaving the 5 carbon free for phosphorylation. The central role of Mg2+ in the function of ribozymes and its ‘archaic’ position in ribosomes, and the fact that magnesium generally has coordination properties different from other cations, suggests that the inorganic chemistry of magnesium had a key position in the first chemical processes leading to the origin and early evolution of life. PMID:22429303

  11. Isopiestic Investigation of the Osmotic and Activity Coefficients of {yMgCl2 + (1 - y)MgSO4}(aq) and the Osmotic Coefficients of Na2SO4.MgSO4(aq) at 298.15 K

    SciTech Connect

    Miladinovic, J; Ninkovic, R; Todorovic, M; Rard, J A

    2007-06-06

    Isopiestic vapor pressure measurements were made for {l_brace}yMgCl{sub 2} + (1-y)MgSO{sub 4}{r_brace}(aq) solutions with MgCl{sub 2} ionic strength fractions of y = 0, 0.1997, 0.3989, 0.5992, 0.8008, and (1) at the temperature 298.15 K, using KCl(aq) as the reference standard. These measurements for the mixtures cover the ionic strength range I = 0.9794 to 9.4318 mol {center_dot} kg{sup -1}. In addition, isopiestic measurements were made with NaCl(aq) as reference standard for mixtures of {l_brace}xNa{sub 2}SO{sub 4} + (1-x)MgSO{sub 4}{r_brace}(aq) with the molality fraction x = 0.50000 that correspond to solutions of the evaporite mineral bloedite (astrakanite), Na{sub 2}Mg(SO{sub 4}){sub 2} {center_dot} 4H{sub 2}O(cr). The total molalities, m{sub T} = m(Na{sub 2}SO{sub 4}) + m(MgSO{sub 4}), range from m{sub T} = 1.4479 to 4.4312 mol {center_dot} kg{sup -1} (I = 5.0677 to 15.509 mol {center_dot} kg{sup -1}), where the uppermost concentration is the highest oversaturation molality that could be achieved by isothermal evaporation of the solvent at 298.15 K. The parameters of an extended ion-interaction (Pitzer) model for MgCl2(aq) at 298.15 K, which were required for an analysis of the {l_brace}yMgCl{sub 2} + (1-y)MgSO{sub 4}{r_brace}(aq) mixture results, were evaluated up to I = 12.025 mol {center_dot} kg{sup -1} from published isopiestic data together with the six new osmotic coefficients obtained in this study. Osmotic coefficients of {l_brace}yMgCl{sub 2} + (1-y)MgSO{sub 4}{r_brace}(aq) solutions from the present study, along with critically-assessed values from previous studies, were used to evaluate the mixing parameters of the extended ion-interaction model.

  12. Optical properties of Mg-doped VO2: Absorption measurements and hybrid functional calculations

    NASA Astrophysics Data System (ADS)

    Hu, Shuanglin; Li, S.-Y.; Ahuja, R.; Granqvist, C. G.; Hermansson, K.; Niklasson, G. A.; Scheicher, R. H.

    2012-11-01

    Mg-doped VO2 thin films with thermochromic properties were made by reactive DC magnetron co-sputtering onto heated substrates, and spectral absorption was recorded at room temperature in the 0.5 < ħω < 3.5 eV energy range. Clear evidence was found for a widening of the main band gap from 1.67 to 2.32 eV as the Mg/(V + Mg) atomic ratio went from zero to 0.19, thereby significantly lowering the luminous absorption. This technologically important effect could be reconciled with spin-polarized density functional theory calculations using the Heyd-Scuseria-Ernzerhof [Heyd et al., J. Chem. Phys. 118, 8207 (2003); ibid. 124, 219906 (2006)] hybrid functional. Specifically, the calculated luminous absorptance decreased when the Mg/(V + Mg) ratio was increased from 0.125 to 0.250.

  13. Optical properties of Mg-doped VO{sub 2}: Absorption measurements and hybrid functional calculations

    SciTech Connect

    Hu Shuanglin; Li, S.-Y.; Granqvist, C. G.; Niklasson, G. A.; Ahuja, R.; Scheicher, R. H.; Hermansson, K.

    2012-11-12

    Mg-doped VO{sub 2} thin films with thermochromic properties were made by reactive DC magnetron co-sputtering onto heated substrates, and spectral absorption was recorded at room temperature in the 0.5 < h{omega} < 3.5 eV energy range. Clear evidence was found for a widening of the main band gap from 1.67 to 2.32 eV as the Mg/(V + Mg) atomic ratio went from zero to 0.19, thereby significantly lowering the luminous absorption. This technologically important effect could be reconciled with spin-polarized density functional theory calculations using the Heyd-Scuseria-Ernzerhof [Heyd et al., J. Chem. Phys. 118, 8207 (2003); ibid. 124, 219906 (2006)] hybrid functional. Specifically, the calculated luminous absorptance decreased when the Mg/(V + Mg) ratio was increased from 0.125 to 0.250.

  14. Study of the microwave electrodynamic response of MgB 2 thin films

    NASA Astrophysics Data System (ADS)

    Andreone, A.; Cassinese, A.; Cantoni, C.; Di Gennaro, E.; Lamura, G.; Maglione, M. G.; Paranthaman, M.; Salluzzo, M.; Vaglio, R.

    2002-08-01

    We present a study on the power dependence of the microwave surface impedance in thin films of the novel superconductor MgB 2. 500 nm thick samples exhibiting critical temperatures ranging between 26 and 38 K are synthesized by an ex situ post-anneal of e-beam evaporated boron in the presence of an Mg vapor at 900 °C. Preliminary results on films grown in situ by a high rate magnetron sputtering technique from stoichiometric MgB 2 and Mg targets are also reported. Microwave measurements have been carried out employing a dielectrically loaded niobium superconducting cavity operating at 19.8 GHz and 4 K. The study shows that the electrodynamic response of MgB 2 films is presently dominated by extrinsic sources of dissipation, appearing already at low microwave power, likely to be ascribed to the presence of grain boundaries and normal inclusions in the samples.

  15. Influence of Mg component and pressure on magnetic ordering of (Mg,Fe)O

    NASA Astrophysics Data System (ADS)

    Fujii, A.; Kondo, T.; Taniguchi, T.

    2012-12-01

    (Mg,Fe)O is the second most abundant phase in the Earth's lower mantle. Knowing the fundamental properties of (Mg,Fe)O is important to understand the Earth's materials. The relation between rhombohedral distortion and antiferromagnetic ordering in FeO have been discussed, as an end member of (Mg,Fe)O. However, it does not fully understand for (Mg,Fe)O yet because its structural transition pressure is influenced by Mg component and stress condition [e.g. Zhuravlev et al., 2007]. We should also account compositional dependence on Néel temperature [Woods and Fine, 1969; Fujii et al., 2011] and spin glass-like behavior [Abbas and Hicks, 1990; Jing et al., 1993]. In this study, we investigated the compositional dependence of magnetic ordering at ambient pressure, and pressure dependence of Néel temperature up to 1.27 GPa. Superconducting Quantum Interference Device (SQUID, MPMS-7, Quantum design) was used for all magnetic measurements. We measured the temperature dependence of susceptibilities cooling with in zero field (ZFC) and in a field (FC) at ambient pressure and observed splitting between susceptibility of ZFC and FC. We confirmed that the smaller compositional dependence on Néel temperature in (Mg1-XFeX)O (X ≤ 0.60) [Fujii et al., 2011] may be explained by spin-glass transition. The transition temperature of (Mg0.40Fe0.60)O is 82 K and is close to 76 K that observed in (Mg0.23Fe0.77)0.92O [Abbas and Hicks, 1990]. The spin-glass like behavior does not affect on the Néel temperature of (Mg1-XFeX)O (X ≥ 0.70) suggested by previous work [Fujii et al., 2011] because spin-glass transition temperature would not exceed 82 K. We also measured the pressure dependence of Néel temperature of (Mg0.30Fe0.70)O, (Mg0.25Fe0.75)O and (Mg0.20Fe0.80)O using a piston cylinder type pressure cell. We calibrated pressure by superconducting transition of tin. Néel temperature of (Mg,Fe)O were increased with increasing pressure except for some measurements under non

  16. Impact of Mg content on native point defects in Mg{sub x}Zn{sub 1−x}O (0 ≤ x ≤ 0.56)

    SciTech Connect

    Perkins, J.; Foster, G. M.; Myer, M.; Mehra, S.; Chauveau, J. M.; Hierro, A.; Windl, W.; Brillson, L. J.

    2015-06-01

    We used depth-resolved cathodoluminescence spectroscopy and surface photovoltage spectroscopy to measure the densities, energy levels, and spatial distributions of zinc/magnesium cation and oxygen vacancies in isostructural, single-phase, non-polar Mg{sub x}Zn{sub 1−x}O alloys over a wide (0 ≤ x ≤ 0.56) range. Within this wide range, both defect types exhibit strong Mg content-dependent surface segregation and pronounced bulk density minima corresponding to unit cell volume minima, which can inhibit defect formation due to electrostatic repulsion. Mg in ZnO significantly reduces native defect densities and their non-polar surface segregation, both major factors in carrier transport and doping of these oxide semiconductors.

  17. Intracellular Mg2+ and magnesium depletion in isolated renal thick ascending limb cells.

    PubMed Central

    Dai, L J; Quamme, G A

    1991-01-01

    Magnesium reabsorption and regulation within the kidney occur principally within the cortical thick ascending limb (cTAL) cells of the loop of Henle. Fluorometry with the dye, mag-fura-2, was used to characterize intracellular Mg2+ concentration ([Mg2+]i) in single cTAL cells. Primary cell cultures were prepared from porcine kidneys using a double antibody technique (goat anti-human Tamm-Horsfall and rabbit anti-goat IgG antibodies). Basal [Mg2+]i was 0.52 +/- 0.02 mM, which was approximately 2% of the total cellular Mg. Cells cultured (16 h) in high magnesium media (5 mM) maintained basal [Mg2+]i, 0.48 +/- 0.02, in the normal range. However, cells cultured in nominally magnesium-free media possessed [Mg2+]i, 0.27 +/- 0.01 mM, which was associated with a significant increase in net Mg transport, (control, 0.19 +/- 0.03 and low Mg, 0.35 +/- 0.01 nmol.mg-1 protein.min-1) as assessed by 28Mg uptake. Mg(2+)-depleted cells were subsequently placed in high Mg solution (5 mM) and the Mg2+ refill rate was assessed by fluorescence. [Mg2+]i returned to normal basal levels, 0.53 +/- 0.03 mM, with a refill rate of 257 +/- 37 nM/s. Mg2+ entry was not changed by 5.0 mM Ca2+ or 2 mM Sr2+, Cd2+, Co2+, nor Ba2+ but was inhibited by Mn2+ approximately La3+ approximately Gd3+ approximately Zn2+ approximately Be2+ at 2 mM. Intracellular Ca2+ and 45Ca uptake was not altered by Mg depletion or Mg2+ refill, indicating that the entry is relatively specific to Mg2+. Mg2+ uptake was inhibited by nifedipine (117 +/- 20 nM/s), verapamil (165 +/- 34 nM/s), and diltiazem (194 +/- 19 nM/s) but enhanced by the dihydropyridine analogue, Bay K 8644 (366 +/- 71 nM/s). These antagonists and agonists were reversible with removal and [Mg2+]i subsequently returned to normal basal levels. Mg2+ entry rate was concentration and voltage dependent and maximally stimulated after 4 h in magnesium-free media. Cellular magnesium depletion results in increases in a Mg2+ refill rate which is dependent, in part, on

  18. The dependence of RNA tertiary structure stability on Mg2+ concentration: interpretation of the Hill equation and coefficient†

    PubMed Central

    Leipply, Desirae; Draper, David E.

    2010-01-01

    The Mg2+-induced folding of RNA tertiary structures is readily observed via titrations of RNA with MgCl2. Such titrations are commonly analyzed using a site-binding formalism that includes a parameter, the Hill coefficient n, which is sometimes deemed the number of Mg2+ ions bound by the native RNA at specific sites. However, the long-range nature of electrostatic interactions allows ions some distance from the RNA to stabilize an RNA structure. A complete description of all interactions taking place between Mg2+ and an RNA uses a preferential interaction coefficient, Γ2+, which represents the 'excess' Mg2+ neutralizing the RNA charge. The difference between Γ2+ for the native and unfolded RNA forms (ΔΓ2+) is the number of Mg2+ ions ‘taken up’ by an RNA upon folding. Here we ask under what conditions the Hill coefficient n can be equated to the ion uptake ΔΓ2+, and find that two approximations are necessary: (i) the Mg2+ activity coefficient is independent of concentration during a titration, and (ii) the dependence of ΔΓ2+ on Mg2+ concentration is weak. Titration experiments with a Mg2+-binding dye and an adenine-binding riboswitch were designed to test these approximations. Inclusion of a 30-fold excess of KCl over MgCl2 was sufficient to maintain a constant Mg2+ activity coefficient. We also observed that Mg2+ uptake by the RNA varied from near zero to ~2.6 as the Mg2+ concentration increases over ~100-fold range. It is possible to determine ΔΓ2+ from Mg2+ - RNA titrations, but the values are only applicable to a limited range of solution conditions. PMID:20112919

  19. Dependence of RNA tertiary structural stability on Mg2+ concentration: interpretation of the Hill equation and coefficient.

    PubMed

    Leipply, Desirae; Draper, David E

    2010-03-01

    The Mg(2+)-induced folding of RNA tertiary structures is readily observed via titrations of RNA with MgCl(2). Such titrations are commonly analyzed using a site binding formalism that includes a parameter, the Hill coefficient n, which is sometimes deemed the number of Mg(2+) ions bound by the native RNA at specific sites. However, the long-range nature of electrostatic interactions allows ions some distance from the RNA to stabilize an RNA structure. A complete description of all interactions taking place between Mg(2+) and an RNA uses a preferential interaction coefficient, Gamma(2+), which represents the "excess" Mg(2+) neutralizing the RNA charge. The difference between Gamma(2+) for the native and unfolded RNA forms (DeltaGamma(2+)) is the number of Mg(2+) ions "taken up" by an RNA upon folding. Here we determine the conditions under which the Hill coefficient n can be equated to the ion uptake DeltaGamma(2+) and find that two approximations are necessary: (i) the Mg(2+) activity coefficient is independent of concentration during a titration, and (ii) the dependence of DeltaGamma(2+) on Mg(2+) concentration is weak. Titration experiments with a Mg(2+)-binding dye and an adenine-binding riboswitch were designed to test these approximations. Inclusion of a 30-fold excess of KCl over MgCl(2) was sufficient to maintain a constant Mg(2+) activity coefficient. We also observed that Mg(2+) uptake by the RNA varied from near zero to approximately 2.6 as the Mg(2+) concentration increases over an approximately 100-fold range. It is possible to determine DeltaGamma(2+) from Mg(2+)-RNA titrations, but the values are only applicable to a limited range of solution conditions.

  20. Multiparticle-multihole states in 31Mg and 33Mg: A critical evaluation

    NASA Astrophysics Data System (ADS)

    Neyens, Gerda

    2011-12-01

    The experiments that provide information about the level structure of the “island of inversion” isotopes 31Mg and 33Mg are reviewed. Since the model-independent measurement of their ground-state spins was done, much experimental data can be reinterpreted, and spins and parities can be assigned to their excited states. Both experimental level schemes are found in very good agreement with calculations based on antisymmetrized molecular dynamics combined with the generator coordinate method. These calculations predict that both ground states are dominated by 2ℏω neutron excitations (more than 85% of the wave function). In the case of 33Mg, the energy of the 1ℏω and 3ℏω levels are calculated about 400 keV too high with respect to the ground state, while in 31Mg the 1ℏω levels are calculated only 200 keV too high. New key experiments are suggested.

  1. Mg intercalation in layered and spinel host crystal structures for Mg batteries.

    PubMed

    Emly, Alexandra; Van der Ven, Anton

    2015-05-01

    We investigate electrochemical properties of Mg in layered and spinel intercalation compounds from first-principles using TiS2 as a model system. Our calculations predict that Mg(x)TiS2 in both the layered and spinel crystal structures exhibits sloping voltage profiles with steps at stoichiometric compositions due to Mg-vacancy ordering. Mg ions are predicted to occupy the octahedral sites in both layered and spinel TiS2 with diffusion mediated by hops between octahedral sites that pass through adjacent tetrahedral sites. Predicted migration barriers are substantially higher than typical Li-migration barriers in intercalation compounds. The migration barriers are shown to be very sensitive to lattice parameters of the host crystal structure. We also discuss the possible role of rehybridization between the transition metal and the anion in affecting migration barriers.

  2. Terahertz surface impedance of epitaxial MgB2 thin film

    NASA Astrophysics Data System (ADS)

    Jin, B. B.; Kuzel, P.; Kadlec, F.; Dahm, T.; Redwing, J. M.; Pogrebnyakov, A. V.; Xi, X. X.; Klein, N.

    2005-08-01

    We report on terahertz (THz) surface impedance measurement of an epitaxial MgB2 thin film using time domain THz spectroscopy. We show that the surface resistance of the MgB2 film is much lower than that of YBa2Cu3O7-δ and copper in the THz range. A linear dependence of the surface reactance on frequency is observed, yielding a penetration depth of about 100nm at low temperatures. The measurements agree qualitatively with calculations based on impurity scattering in the Born limit. Our results clearly indicate that MgB2 thin films have a great potential for THz electronic applications.

  3. Laser cooling of MgCl and MgBr in theoretical approach

    SciTech Connect

    Wan, Mingjie; Shao, Juxiang; Huang, Duohui; Yang, Junsheng; Cao, Qilong; Jin, Chengguo; Wang, Fanhou; Gao, Yufeng

    2015-07-14

    Ab initio calculations for three low-lying electronic states (X{sup 2}Σ{sup +}, A{sup 2}Π, and 2{sup 2}Π) of MgCl and MgBr molecules, including spin-orbit coupling, are performed using multi-reference configuration interaction plus Davidson correction method. The calculations involve all-electronic basis sets and Douglas–Kroll scalar relativistic correction. Spectroscopic parameters well agree with available theoretical and experimental data. Highly diagonally distributed Franck-Condon factors f{sub 00} for A{sup 2}Π{sub 3/2,1/2} (υ′ = 0) → X{sup 2}Σ{sup +}{sub 1/2} (υ″ = 0) are determined for both MgCl and MgBr molecules. Suitable radiative lifetimes τ of A{sup 2}Π{sub 3/2,1/2} (υ′ = 0) states for rapid laser cooling are also obtained. The proposed laser drives A{sup 2}Π{sub 3/2} (υ′ = 0) → X{sup 2}Σ{sup +}{sub 1/2} (υ″ = 0) transition by using three wavelengths (main pump laser λ{sub 00}; two repumping lasers λ{sub 10} and λ{sub 21}). These results indicate the probability of laser cooling MgCl and MgBr molecules.

  4. Laser cooling of MgCl and MgBr in theoretical approach

    NASA Astrophysics Data System (ADS)

    Wan, Mingjie; Shao, Juxiang; Gao, Yufeng; Huang, Duohui; Yang, Junsheng; Cao, Qilong; Jin, Chengguo; Wang, Fanhou

    2015-07-01

    Ab initio calculations for three low-lying electronic states (X2Σ+, A2Π, and 22Π) of MgCl and MgBr molecules, including spin-orbit coupling, are performed using multi-reference configuration interaction plus Davidson correction method. The calculations involve all-electronic basis sets and Douglas-Kroll scalar relativistic correction. Spectroscopic parameters well agree with available theoretical and experimental data. Highly diagonally distributed Franck-Condon factors f00 for A2Π3/2,1/2 (υ' = 0) → X2Σ+1/2 (υ″ = 0) are determined for both MgCl and MgBr molecules. Suitable radiative lifetimes τ of A2Π3/2,1/2 (υ' = 0) states for rapid laser cooling are also obtained. The proposed laser drives A2Π3/2 (υ' = 0) → X2Σ+1/2 (υ″ = 0) transition by using three wavelengths (main pump laser λ00; two repumping lasers λ10 and λ21). These results indicate the probability of laser cooling MgCl and MgBr molecules.

  5. Significant enhancement of the superconducting properties of MgB2 by polyvinyl alcohol additives

    NASA Astrophysics Data System (ADS)

    Zeng, R.; Lu, L.; Dou, S. X.

    2008-08-01

    We report a systematic study of the effects of polymer addition on the lattice parameters, microstructure and superconducting properties of MgB2. Polyvinyl alcohol [-C2H4O-]n (PVA) as a typical polymer was used as an additive to MgB2. It was found that PVA additions have the following features: (1) the polymer can have a very low oxygen (O) content or even none at all, and PVA has a low O content (C:O = 2:1), which reduces the impurities brought into MgB2 from the doping, and (2) PVA decomposes at a temperature of 400-650 °C, which means that the reaction occurs in the same temperature range as MgB2 formation, providing highly reactive C, which homogeneously substitutes for B at this low-temperature range. The above considerations significantly enhance the critical current, Jc, the irreversibility field, Hirr, and the upper critical field, Hc2, of MgB2 compared to un-doped samples or those doped with other carbon sources. In this work, suitable PVA doping levels improved both the connectivity and flux pinning, so that the Jc of PVA-doped MgB2 was improved over the whole field range.

  6. Interdiffusion and impurity diffusion in polycrystalline Mg solid solution with Al or Zn

    SciTech Connect

    Kammerer, Catherine; Kulkarni, Nagraj S; Warmack, Robert J Bruce; Sohn, Yong Ho

    2014-01-01

    Interdiffusion and impurity diffusion in Mg binary solid solutions, Mg(Al) and Mg(Zn) were investigated at temperatures ranging from 623 to 723 K. Interdiffusion coef cients were determined via the Boltzmann Matano Method using solid-to-solid diffusion couples assembled with polycrystalline Mg and Mg(Al) or Mg(Zn) solid solutions. In addition, the Hall method was employed to extrapolate the impurity diffusion coef cients of Al and Zn in pure polycrystalline Mg. For all diffusion couples, electron micro-probe analysis was utilized for the measurement of concentration pro les. The interdiffusion coef cient in Mg(Zn) was higher than that of Mg(Al) by an order of magnitude. Additionally, the interdiffusion coef cient increased signi cantly as a function of Al content in Mg(Al) solid solution, but very little with Zn content in Mg(Zn) solid solution. The activation energy and pre-exponential factor for the average effective interdiffusion coef cient in Mg(Al) solid solution were determined to be 186.8 ( 0.9) kJ/mol and 7.69 x 10-1 ( 1.80 x 10-1) m2/s, respectively, while those determined for Mg(Zn) solid solution were 139.5 ( 4.0) kJ/mol and 1.48 x 10-3 ( 1.13 x 10-3) m2/s. In Mg, the Zn impurity diffusion coef cient was an order of magnitude higher than the Al impurity diffusion coef cient. The activation energy and pre-exponential factor for diffusion of Al impurity in Mg were determined to be 139.3 ( 14.8) kJ/mol and 6.25 x 10-5 ( 5.37 x 10-4) m2/s, respectively, while those for diffusion of Zn impurity in Mg were determined to be 118.6 ( 6.3) kJ/mol and 2.90 x 10-5 ( 4.41 x 10-5) m2/s.

  7. On the dissociation energy of Mg2

    NASA Technical Reports Server (NTRS)

    Partridge, Harry; Bauschlicher, Charles W., Jr.; Pettersson, Lars G. M.; Mclean, A. D.; Liu, Bowen

    1990-01-01

    The bonding in the X 1Sigma(+)g state of Mg2 is investigated using near-complete valence one-particle Slater and Gaussian basis sets containing up to h functions. It is shown that the four-electron complete CI limit can be approached using a sequence of either second-order CI (SOCI) or interacting correlated fragment (ICF) calculations. At the valence level, the best estimate of the dissociation energy D(e) was 464/cm. This is a lower limit and is probably within 5/cm of the complete basis value.

  8. -MgO Melt by Super Gravity

    NASA Astrophysics Data System (ADS)

    Li, Juncheng; Guo, Zhancheng; Gao, Jintao; Li, Jingwei

    2014-08-01

    Perovskite phase was successfully separated from CaO-TiO2-SiO2-Al2O3-MgO melt by super gravity. Under the hypothesis that the titanium exists in the slag in terms of TiO2, with the gravity coefficient G = 600, time t = 5 minutes, and temperature T = 1563 K (1290 °C), the mass fraction of TiO2 in the concentrate is up to 52.94 pct, while that of the tailing is just 5.88 pct. The recovery ratio of Ti in the concentrate is up to 81.28 pct by centrifugal separation.

  9. Measurement of matrix free Mg2+ concentration in rat heart mitochondria by using entrapped fluorescent probes.

    PubMed Central

    Rutter, G A; Osbaldeston, N J; McCormack, J G; Denton, R M

    1990-01-01

    1. The concentration of free Mg2+ ([Mg2+]m) within the matrix of isolated rat heart mitochondria was measured after loading of the mitochondria with the fluorescent Mg2+ indicators mag-indo-1 and mag-fura-2. No detectable change in total mitochondrial magnesium content occurred during loading with the indicators. Apparent Kd values for Mg2+ of 3.7 mM and 2.3 mM were obtained for mag-indo-1 and mag-fura-2 respectively within mitochondria permeabilized to bivalent cations with ionomycin and the uncoupler carbonyl cyanide p-trifluoromethoxyphenylhydrazone. These values are 2.7- and 1.8-fold greater respectively than those obtained for the free acid forms of the dyes in incubation medium. 2. Based on the above Kd values, mitochondrial matrix Mg2+ concentrations were found to lie in the range 0.8-1.5 mM in the absence, or immediately after the addition, of a respiratory substrate. 3. Incubation of mitochondria in the presence of respiratory substrate, but in the absence of external Mg2+, led to a time-dependent decline in [Mg2+]m to about half the initial values after 5 min. This was accompanied by a fall in the total mitochondrial magnesium content from 12.7 to 7.0 nmol/mg of protein. 4. ADP (0.5 mM), ATP (0.5 mM) or 10 mM-NaCl had no significant effect on the fall in [Mg2+], whereas 1 microM-nigericin blocked, and 0.3 microM-valinomycin accelerated, the fall. 5. External Mg2+ concentrations above 1 mM progressively inhibited and reversed the decline in free and total mitochondrial Mg2+. PMID:2244870

  10. MagFRET: The First Genetically Encoded Fluorescent Mg2+ Sensor

    PubMed Central

    Oortwijn, Jorn; Aper, Stijn J. A.; Merkx, Maarten

    2013-01-01

    Magnesium has important structural, catalytic and signaling roles in cells, yet few tools exist to image this metal ion in real time and at subcellular resolution. Here we report the first genetically encoded sensor for Mg2+, MagFRET-1. This sensor is based on the high-affinity Mg2+ binding domain of human centrin 3 (HsCen3), which undergoes a transition from a molten-globular apo form to a compactly-folded Mg2+-bound state. Fusion of Cerulean and Citrine fluorescent domains to the ends of HsCen3, yielded MagFRET-1, which combines a physiologically relevant Mg2+ affinity (Kd = 148 µM) with a 50% increase in emission ratio upon Mg2+ binding due to a change in FRET efficiency between Cerulean and Citrine. Mutations in the metal binding sites yielded MagFRET variants whose Mg2+ affinities were attenuated 2- to 100-fold relative to MagFRET-1, thus covering a broad range of Mg2+ concentrations. In situ experiments in HEK293 cells showed that MagFRET-1 can be targeted to the cytosol and the nucleus. Clear responses to changes in extracellular Mg2+ concentration were observed for MagFRET-1-expressing HEK293 cells when they were permeabilized with digitonin, whereas similar changes were not observed for intact cells. Although MagFRET-1 is also sensitive to Ca2+, this affinity is sufficiently attenuated (Kd of 10 µM) to make the sensor insensitive to known Ca2+ stimuli in HEK293 cells. While the potential and limitations of the MagFRET sensors for intracellular Mg2+ imaging need to be further established, we expect that these genetically encoded and ratiometric fluorescent Mg2+ sensors could prove very useful in understanding intracellular Mg2+ homeostasis and signaling. PMID:24312622

  11. [Effect of glycine and strychnine on Cl(-)-activated Mg2+-ATPase from bream brain microsomes (Abamis brama L.)].

    PubMed

    Menzikov, S A; Menzikova, O V

    2001-01-01

    The effect of glycine and strychnine on Mg2+-ATPase from the microsomal fraction of the bream (Abramis brama L.) brain was studied. The glycine in the concentration range 10(-7)-10(-4) M activates the enzyme. The effect of glycine on Mg2+-ATPase is obviated by 100 microM strychnine. The strychnine in the concentration range 5-90 microM activates the basal Mg2+-ATPase but decreases the effect of the enzyme activation by 10(-4) M glycine. The effect of Cl- on Mg2+-ATPase depends on the substrate concentration (Mg2+-ATP) and is not observed in the presence of 100 microM strychnine. A receptor-dependent pathway of glycine and strychnine action on Cl(-)-activated Mg2+-ATPase from bream brain microsomes is proposed.

  12. Sr, Mg cosubstituted HA porous macro-granules: potentialities as resorbable bone filler with antiosteoporotic functions.

    PubMed

    Landi, Elena; Uggeri, Jacopo; Medri, Valentina; Guizzardi, Stefano

    2013-09-01

    Porous macro-granules of nanostructured apatite with Ca ions partially cosubstituted with Mg and Sr ions in different ratios (SrMgHAs), were synthesized at 37°C and compared with Mg and/or Sr free apatites (MgHAs and HA). Strontium improved the Mg substitution extent in the apatite and the chemical-physical and thermal stability of the resulting cosubstituted apatite. Porous macro-granules of 400-600 micron with selected composition were tested for the ionic release in synthetic body fluid and the data were related with the results of preliminary cell investigation in vitro. As compared to the corresponding Sr-free granulate, the SrMgHA could be exploited to prolong the beneficial Mg release during the bone regeneration process. In addition the contemporary in situ supply of Sr, an antiosteoporotic and anticarie ion, could influence the quality of new hard tissues. The ionic multirelease created a more favorable environment for human osteoblasts, demonstrated by a proliferative effect for each dose tested in the range 0.1-10 mg/mL. PMID:23348958

  13. Magnesium absorption in human subjects from leafy vegetables, intrinsically labeled with stable /sup 26/Mg

    SciTech Connect

    Schwartz, R.; Spencer, H.; Welsh, J.J.

    1984-04-01

    Collards, turnip greens, leaf lettuce, and spinach, grown in nutrient solution so that their Mg content was 80 to 90% /sup 26/Mg, were tested in ambulant male volunteers stabilized on a constant metabolic diet. The freeze-dried vegetables were incorporated in bran muffins in which the vegetables replaced part of the bran. Bran muffins without vegetables were consumed for breakfast each day. They were also used as a standard test meal to which the vegetable muffins were compared. All subjects participated in three consecutive isotope absorption tests: one of the standard test meal and two of the vegetables. The standard test was carried out after at least 30 days on the controlled diet. Subsequent tests of vegetables followed at 4-wk intervals. Each test meal contained 30 microCi /sup 28/MgCl2 and 50 mg stable /sup 26/Mg, the latter either as the intrinsic label of a test vegetable or as /sup 26/MgCl/sub 2/ in solution taken with the standard bran muffins. Net absorption of both isotopes was measured to establish exchangeability and to determine relative Mg absorption from the vegetables. Exchangeability was 90% or higher from all meals tested. Relative Mg absorption was highest from collards and least from the standard test meal. Net absorption values ranged from 40 to 60%.

  14. Variable Stars from the MG-1 Catalog

    NASA Astrophysics Data System (ADS)

    Flurchick, K. M.; Griego, Ben; Culver, Roger B.

    2014-06-01

    This work describes the recent efforts at North Carolina A&T(NCAT) mining the MG catalogs for variable stars. NCAT is a node in both the GNAT network and the SKYNET collaboration which forms the basis of the collaboration including access to instruments. The initial data analysis to obtain the light curves (LC) for MG-1 has been performed and a number of candidate variable stars have been identified including brown dwarf stars, eclipsing binaries and long period variable stars.Many of the identified candidate variable stars are now the subject of coordinated multi-site follow-on observations to elucidate the details of the variability. The coordinated observing includes researchers in Australia, Arizona, Colorado and North Carolina. As a node in both the GNAT network and the SKYNET collaboration NCAT has access to a number of instruments. Much of the observational work is performed using the SKYNET node in Chile.For the North Carolina work reported here, the observational work and initial LC generation is performed using telescopes and applications from the SKYNET program. In this work the instrumentation, the LC analysis and status of the coordinated follow-on observations arepresented.

  15. Sequential ranging: How it works

    NASA Technical Reports Server (NTRS)

    Baugh, Harold W.

    1993-01-01

    This publication is directed to the users of data from the Sequential Ranging Assembly (SRA), and to others who have a general interest in range measurements. It covers the hardware, the software, and the processes used in acquiring range data; it does not cover analytical aspects such as the theory of modulation, detection, noise spectral density, and other highly technical subjects. In other words, it covers how ranging is done, but not the details of why it works. The publication also includes an appendix that gives a brief discussion of PN ranging, a capability now under development.

  16. Multistage growth of Fe-Mg-carpholite and Fe-Mg-chloritoid, from field evidence to thermodynamic modelling

    NASA Astrophysics Data System (ADS)

    Pourteau, Amaury; Bousquet, Romain; Vidal, Olivier; Plunder, Alexis; Duesterhoeft, Erik; Candan, Osman; Oberhänsli, Roland

    2015-04-01

    We provide new insights into the prograde evolution of HP/LT meta-sedimentary rocks on the basis of detailed petrologic examination, element-partitioning analysis, and thermodynamic modelling of well-preserved Fe-Mg-carpholite- and chloritoid-bearing rocks from the Afyon zone (Anatolia). Study samples, stemming from three different areas of the metamorphic belt, include typical quartz-carpholite veins as well as quartz-free and quartz-bearing phyllites. All samples exhibit multiple stages of carpholite, whereas zoning was until now rarely documented in this type of rocks. We document continuous, and discontinuous compositional (ferro-magnesian substitution) zoning of carpholite (overall XMg = 0.27-0.73) and chloritoid (overall XMg = 0.07-0.30), as well as clear equilibrium, and disequilibrium (i.e. reaction-related) textures involving carpholite and chloritoid, which consistently account for the consistent enrichment in Mg of both minerals through time, and the progressive replacement of carpholite by chloritoid. Mg/Fe distribution coefficients calculated between carpholite and chloritoid vary widely within samples (2.2-20.0). Among this range, only values of 7-11 correlate with equilibrium textures, in agreement with data from the literature. Equilibrium phase diagrams for (NaK)FMASH rock compositions are calculated using a newly modified thermodynamic dataset, including most recent data for carpholite, chloritoid, chlorite, and white mica, as well as further refinements for Fe-carpholite, and both chloritoid end-members, as required to reproduce accurately petrologic observations (phase relations, experimental constraints, Mg/Fe partitioning). Modelling reveals that Mg/Fe partitioning between carpholite and chloritoid is greatly sensitive to temperature, and calls for a future evaluation of possible use as a thermometer, valid for blueschist-facies conditions, which has so far been missing. In addition, calculations show significant effective bulk composition

  17. The magnesium isotope (δ26Mg) signature of dolomites

    NASA Astrophysics Data System (ADS)

    Geske, A.; Goldstein, R. H.; Mavromatis, V.; Richter, D. K.; Buhl, D.; Kluge, T.; John, C. M.; Immenhauser, A.

    2015-01-01

    Dolomite precipitation models and kinetics are debated and complicated due to the complex and temporally fluctuating fluid chemistry and different diagenetic environments. Using well-established isotope systems (δ18O, δ13C, 87Sr/86Sr), fluid inclusions and elemental data, as well as a detailed sedimentological and petrographic data set, we established the precipitation environment and subsequent diagenetic pathways of a series of Proterozoic to Pleistocene syn-depositional marine evaporative (sabkha) dolomites, syn-depositional non-marine evaporative (lacustrine and palustrine) dolomites, altered marine ("mixing zone") dolomites and late diagenetic hydrothermal dolomites. These data form the prerequisite for a systematic investigation of dolomite magnesium isotope ratios (δ26Mgdol). Dolomite δ26Mg ratios documented here range, from -2.49‰ to -0.45‰ (δ26Mgmean = -1.75 ± 1.08‰, n = 42). The isotopically most depleted end member is represented by earliest diagenetic marine evaporative sabkha dolomites (-2.11 ± 0.54‰ 2σ, n = 14). In comparing ancient compositions to modern ones, some of the variation is probably due to alteration. Altered marine (-1.41 ± 0.64‰ 2σ, n = 4), and earliest diagenetic lacustrine and palustrine dolomites (-1.25 ± 0.86‰ 2σ, n = 14) are less negative than sabkha dolomites but not distinct in composition. Various hydrothermal dolomites are characterized by a comparatively wide range of δ26Mg ratios, with values of -1.44 ± 1.33‰ (2σ, n = 10). By using fluid inclusion data and clumped isotope thermometry (Δ47) to represent temperature of precipitation for hydrothermal dolomites, there is no correlation between fluid temperature (∼100 to 180 °C) and dolomite Mg isotope signature (R2 = 0.14); nor is there a correlation between δ26Mgdol and δ18Odol. Magnesium-isotope values of different dolomite types are affected by a complex array of different Mg sources and sinks, dissolution/precipitation and non

  18. Laser Ranging Experiment on Lunar Reconnaissance Orbiter: Clocks and Ranges

    NASA Astrophysics Data System (ADS)

    Mao, D.; Rowlands, D. D.; McGarry, J.; Zuber, M. T.; Smith, D. E.; Torrence, M. H.; Neumann, G. A.; Mazarico, E.; Sun, X.; Zagwodzki, T. W.; Cavanaugh, J. F.; Ramos-Izquierdo, L.

    2010-12-01

    Accurate ranges from Earth to the Lunar Reconnaissance Orbiter (LRO) spacecraft Laser Ranging (LR) system supplement the precision orbit determination (POD) of LRO. LRO is tracked by ten LR stations from the International Laser Ranging Service (ILRS), using H-maser, GPS steered Rb, and Cs standard oscillators as reference clocks. The LR system routinely makes one-way range measurements via laser time-of-flight from Earth to LRO. Uplink photons are received by a telescope mounted on the high-gain antenna on LRO , transferred through a fiber optic cable to the Lunar Orbiter Laser Altimeter (LOLA), and timed-tagged by the spacecraft clock. The range from the LR Earth station to LRO is derived from paired outgoing and received times. Accurate ranges can only be obtained after solving for both the spacecraft and ground station clock errors. The drift rate and aging rate of the LRO clock are calculated from data provided by the primary LR station, NASA's Next Generation Satellite Laser Ranging System (NGSLR) in Greenbelt, Maryland. The results confirm the LRO clock oscillator mid to long term stability measured during ground testing. These rates also agree well with those determined through POD. Simultaneous and near-simultaneous ranging to LRO from multiple LR stations in America, Europe, and Australia has been successfully achieved within a 10 hour window. Data analysis of these ranging experiments allows for precision modeling of the clock behaviors of each LR ground station and characterization of the station ground fire times.

  19. Global Investigation of the Mg Atom and ion Layers using SCIAMACHY/Envisat Observations between 70 km and 150 km Altitude and WACCM-MG Model Results

    NASA Technical Reports Server (NTRS)

    Langowski, M.; vonSavigny, C.; Burrows, J. P.; Feng, W.; Plane, J. M. C.; Marsh, D. R.; Janches, Diego; Sinnhuber, M.; Aikin, A. C.

    2014-01-01

    Mg and Mg+ concentration fields in the upper mesosphere/lower thermosphere (UMLT) region are retrieved from SCIAMACHY/Envisat limb measurements of Mg and Mg+ dayglow emissions using a 2-D tomographic retrieval approach. The time series of monthly means of Mg and Mg+ for number density as well as vertical column density in different latitudinal regions are shown. Data from the limb mesosphere-thermosphere mode of SCIAMACHY/Envisat are used, which covers the 50 km to 150 km altitude region with a vertical sampling of 3.3 km and a highest latitude of 82 deg. The high latitudes are not covered in the winter months, because there is no dayglow emission during polar night. The measurements were performed every 14 days from mid-2008 until April 2012. Mg profiles show a peak at around 90 km altitude with a density between 750 cm(exp-3) and 2000 cm(exp-3). Mg does not show strong seasonal variation at mid-latitudes. The Mg+ peak occurs 5-15 km above the neutral Mg peak at 95-105 km. Furthermore, the ions show a significant seasonal cycle with a summer maximum in both hemispheres at mid- and high-latitudes. The strongest seasonal variations of the ions are observed at mid-latitudes between 20-40 deg and densities at the peak altitude range from 500 cm(exp-3) to 6000 cm(exp-3). The peak altitude of the ions shows a latitudinal dependence with a maximum at mid-latitudes that is up to 10 km higher than the peak altitude at the equator. The SCIAMACHY measurements are compared to other measurements and WACCM model results. In contrast to the SCIAMACHY results, the WACCM results show a strong seasonal variability for Mg with a winter maximum, which is not observable by SCIAMACHY, and globally higher peak densities. Although the peak densities do not agree the vertical column densities agree, since SCIAMACHY results show a wider vertical profile. The agreement of SCIAMACHY and WACCM results is much better for Mg+, showing the same seasonality and similar peak densities. However

  20. Inter-species and Seasonal Variability in Mg / Ca in Larger Benthic Foraminifera: Implications for Paleo-proxy

    NASA Astrophysics Data System (ADS)

    Singh, A.; Saraswati, P. K.; Pande, K.; Sanyal, P.

    2015-12-01

    The reports of inter-species variability to intra-test heterogeneity in Mg/Ca in several species of foraminifera have raised question about its use in estimation of seawater temperatures and necessitate field and culture studies to verify it for species from different habitats. In this study, we attempt to investigate if Mg/Ca in larger benthic foraminifera (LBF) could be a potential proxy of seawater temperatures for shallow marine carbonates. The samples were collected in different seasons from coral reef at Akajima (Okinawa, Japan). The Ca and Mg of 13 species of LBF and small benthic foraminifera from the same season were determined to examine variation in Mg/Ca among the species calcified under presumably the same temperature and salinity conditions. We also analyzed Amphistegina lessoni from different seasons for Ca, Mg and δ18O to determine variation in Mg/Ca with temperature and see how the two proxies of temperatures, Mg/Ca and δ18O, correlate in the same species. The species cluster about two distinctly separated Mg/Ca values. The first group comprising species of Amphistegina, Gypsina, Ammonia and Elphidium have relatively lower Mg/Ca, varying from 30 to 45 mmol/mol. The second group, having average Mg/Ca ranging from ~110 to 170 mmol/mol, includes species of Schlumbergerella, Baculogypsinoides, Baculogypsina, Heterostegina, Operculina, Calcarina, Amphisorus, Alveolinella and Poroeponides. The result suggests large interspecies variability implying vital effect in foraminiferal Mg/Ca. There is no distinct difference in Mg/Ca values between porcelaneous and hyaline types or symbiont-bearing and symbiont-free types. In Amphistegina lessoni the variation in Mg/Ca between individuals of the same season is as large as variation across the seasons. There is no correlation between Mg/Ca and seawater temperature. Lack of correlation between Mg/Ca and δ18O further suggests that Mg/Ca in the species is not primarily controlled by temperature.

  1. Thermoluminescence studies of γ-irradiated ZnO:Mg2+ nanoparticles

    NASA Astrophysics Data System (ADS)

    Pushpa, N.; Kokila, M. K.; Nagabhushana, K. R.

    2016-07-01

    Pure and Mg2+ doped ZnO nanoparticles are synthesized by solution combustion method. X-ray diffraction studies of the samples confirm hexagonal phase. Crystallite size is calculated using Scherer formula and found to be ∼30 nm for undoped ZnO and 34-38 nm for Mg2+ doped ZnO. A broad PL emission in the range 400-600 nm with peaks at 400, 450, 468, 483, 492, 517, 553 nm are observed in both pure and Mg2+ doped nanoparticles. Near band edge emission of ZnO is observed at 400 nm. The broad band emissions are due to surface defects. PL emission intensity is found to increase with Mg2+ concentration up to 1.5 mol% and then decreases due to concentration quenching. Samples are irradiated with γ-rays in a dose range 0.05-8 kGy. Gamma irradiation doesn't affect PL properties. Undoped samples exhibit unstructured low intense TL glow with peak at 720 K. Whereas Mg2+ doped samples exhibit well structured TL glow curves with peak at ∼618 K. TL glow peak intensity of Mg2+ doped samples increases with Mg2+ concentration up to 2 mol%, thereafter decreases. TL curves of Mg2+ (2 mol%) doped ZnO exhibit two glows, a high intense peak at 618 K and a weak one with peak at ∼485 K. TL intensity of Mg2+ (2 mol%) doped ZnO samples increases with gamma dose up to 1 kGy and then decreases. Kinetic parameters of TL glows are calculated by deconvolution technique. Activation energy and frequency factor are found to be 1.5 eV and 3.38 × 1011 s-1 respectively.

  2. Toward Understanding the Roaming Mechanism in H + MgH → Mg + HH Reaction.

    PubMed

    Mauguière, Frédéric A L; Collins, Peter; Stamatiadis, Stamatis; Li, Anyang; Ezra, Gregory S; Farantos, Stavros C; Kramer, Zeb C; Carpenter, Barry K; Wiggins, Stephen; Guo, Hua

    2016-07-14

    The roaming mechanism in the reaction H + MgH →Mg + HH is investigated by classical and quantum dynamics employing an accurate ab initio three-dimensional ground electronic state potential energy surface. The reaction dynamics are explored by running trajectories initialized on a four-dimensional dividing surface anchored on three-dimensional normally hyperbolic invariant manifold associated with a family of unstable orbiting periodic orbits in the entrance channel of the reaction (H + MgH). By locating periodic orbits localized in the HMgH well or involving H orbiting around the MgH diatom, and following their continuation with the total energy, regions in phase space where reactive or nonreactive trajectories may be trapped are found. In this way roaming reaction pathways are deduced in phase space. Patterns similar to periodic orbits projected into configuration space are found for the quantum bound and resonance eigenstates. Roaming is attributed to the capture of the trajectories in the neighborhood of certain periodic orbits. The complex forming trajectories in the HMgH well can either return to the radical channel or "roam" to the MgHH minimum from where the molecule may react. PMID:26918375

  3. Refinements in an Mg/MgH2/H2O-Based Hydrogen Generator

    NASA Technical Reports Server (NTRS)

    Kindler, Andrew; Huang, Yuhong

    2010-01-01

    Some refinements have been conceived for a proposed apparatus that would generate hydrogen (for use in a fuel cell) by means of chemical reactions among magnesium, magnesium hydride, and steam. The refinements lie in tailoring spatial and temporal distributions of steam and liquid water so as to obtain greater overall energy-storage or energy-generation efficiency than would otherwise be possible. A description of the prior art is prerequisite to a meaningful description of the present refinements. The hydrogen-generating apparatus in question is one of two versions of what was called the "advanced hydrogen generator" in "Fuel-Cell Power Systems Incorporating Mg-Based H2 Generators" (NPO-43554), NASA Tech Briefs, Vol. 33, No. 1 (January 2009), page 52. To recapitulate: The apparatus would include a reactor vessel that would be initially charged with magnesium hydride. The apparatus would exploit two reactions: The endothermic decomposition reaction MgH2-->Mg + H2, which occurs at a temperature greater than or equal to 300 C, and The exothermic oxidation reaction MgH2 + H2O MgO + 2H2, which occurs at a temperature greater than or equal to 330 C.

  4. Kwajalein missile range, Kwajalein, Marshall Islands range reference atmosphere 0-70 km altitude

    SciTech Connect

    Not Available

    1982-01-01

    Atmospheric parameters are essential to the research and development of missiles and aerospace vehicles. The need for realistic atmospheric models derived in a consistent manner for each of the several major test ranges was recognized in the early 1960's. An atmospheric model which is derived from statistical data for a particular geographical location is referred to as a reference atmosphere. This committee, Task MG-1, establishes RRAs Range Reference Atmospheres for the several ranges as provided by the RCC Range Commander's Council. An RRA is a model of the Earth's atmosphere over a geographical location of interest for use by DOD and other U.S. Government range users. The RRA is used to provide planning data for evaluating environmental constraints for the particular configurations of environment-sensitive systems and components being developed or undergoing tests. Using the best available upper atmosphere data base to include rawinsonde, rocketsonde and possibly other high-altitude data sources for the range location, the task is to establish a model of certain statistics for wind and thermodynamic quantities derived in a uniform manner and published in a standardized format.

  5. Vortex-flux anomalies in MgB 2 polycrystals

    NASA Astrophysics Data System (ADS)

    Goeckner, H. P.; Claus, H.; Kouvel, J. S.

    2005-02-01

    For two MgB 2 polycrystalline samples prepared differently, magnetic hysteresis loops at 4.2 K revealed some striking magnetization ( M) anomalies at low magnetic fields ( H). In one sample, M drops abruptly by an amount that diminishes to zero as the maximum M, reached just before the drop, is reduced below a critical value (by reducing the slowly cycled H). The remanent magnetization ( Mrem), measured as the temperature ( T) was slowly raised from 4.2 K to Tc (39 K), was seen to decrease very rapidly just above 4.2 K and then remain constant up to ∼20 K, where it starts to descend gradually to zero at Tc. A similar set of anomalies was observed with the second sample, but where the hysteretic drop of M is rapid but not abrupt. However, both samples showed that the vortex-flux component of M remains nearly constant over a range of H just before the rapid drop of M, indicating that the vortices in the sample stay fairly constant in number before many of them exit the sample rapidly. For both MgB 2 samples, this whole set of anomalous properties disappears at temperatures above 5 K, where the slow steady descent of Mrem as T increases to Tc indicates that the size distribution of vortex pinning forces extends up to very high values.

  6. Novel Co:MgF2 lidar for aerosol profiler

    NASA Technical Reports Server (NTRS)

    Acharekar, M. A.

    1993-01-01

    Lidars are of great interest because of their unique capabilities in remote sensing applications in sounding of the atmosphere, meteorology, and climatology. In this small business innovative research (SBIR) phase II program, laser sources including Co:MgF2, CTH:YAG, CTH:YSGG, CT:YAG, and Er:Glass were evaluated. Modulator of fused silica and TeO2 materials with Brewster's angle end faces were used with these lasers as acousto-optical (AO) Q-switches. A higher hold-off energy and hence a higher Q-switched energy was obtained by using a high power RF driver. The report provides performance characteristics of these lasers. The tunable (1.75-2.50 microns) Co:MgF2 laser damaged the TeO2 Q-switch cell. However, the CTH:YAG laser operating at 2.09 microns provided output energy of over 300 mJ/p in 50 ns pulse width using the fused silica Q-switch. This Q-switched CTH:YAG laser was used in a breadboard vertical aerosol profiler. A 40 cm diameter telescope, InSb and InGaAs detectors were used in the receiver. The data obtained using this lidar is provided in the report. The data shows that the eye safe lidar using CTH:YAG laser for the vertical aerosol density and range measurements is the viable approach.

  7. Ranging Behaviour of Commercial Free-Range Laying Hens.

    PubMed

    Chielo, Leonard Ikenna; Pike, Tom; Cooper, Jonathan

    2016-01-01

    In this study, the range use and behaviour of laying hens in commercial free-range flocks was explored. Six flocks were each visited on four separate days and data collected from their outdoor area (divided into zones based on distance from shed and available resources). These were: apron (0-10 m from shed normally without cover or other enrichments); enriched belt (10-50 m from shed where resources such as manmade cover, saplings and dust baths were provided); and outer range (beyond 50 m from shed with no cover and mainly grass pasture). Data collection consisted of counting the number of hens in each zone and recording behaviour, feather condition and nearest neighbour distance (NND) of 20 birds per zone on each visit day. In addition, we used techniques derived from ecological surveys to establish four transects perpendicular to the shed, running through the apron, enriched belt and outer range. Number of hens in each 10 m × 10 m quadrat was recorded four times per day as was the temperature and relative humidity of the outer range. On average, 12.5% of hens were found outside. Of these, 5.4% were found in the apron; 4.3% in the enriched zone; and 2.8% were in the outer range. This pattern was supported by data from quadrats, where the density of hens sharply dropped with increasing distance from shed. Consequently, NND was greatest in the outer range, least in the apron and intermediate in the enriched belt. Hens sampled in outer range and enriched belts had better feather condition than those from the apron. Standing, ground pecking, walking and foraging were the most commonly recorded activities with standing and pecking most likely to occur in the apron, and walking and foraging more common in the outer range. Use of the outer range declined with lower temperatures and increasing relative humidity, though use of apron and enriched belt was not affected by variation in these measures. These data support previous findings that outer range areas tend to be

  8. Is the Low-Temperature Isotope Geochemistry of Mg Driven by Biology?

    NASA Astrophysics Data System (ADS)

    Galy, A.; Tipper, E. T.; Carder, E. A.; Dessert, C.

    2008-12-01

    In the last decade, the development of a new field of isotope geochemistry sometime referred as non traditional stable isotope geochemistry together with a renewed interest for the origin of life has raised one of the key question in biogeochemistry: how can we fingerprint life beyond the conventional use of C-based molecules? A general idea has been to recognise that biomediated chemical reactions are rarely at thermodynamic equilibrium and strongly affected by kinetics with an associated isotopic fractionation much greater than the isotopic fractionation characteristic of the equilibrium reaction. This approach led to the false idea that stable isotope of heavy elements (mass greater than 40) can only be fractionated by biological reaction and divalent cations and among them Magnesium (Mg) are no exception. Differences in the relative abundances of Mg three stable isotopes, 24Mg (78.99%), 25Mg (10.00%), and 26Mg (11.01%), could be expected because of the large relative mass differences between 26Mg and 24Mg. However, Mg-bonds are dominantly ionic (a weak bond) and while kinetic processes affect all type of physico-chemical reactions, the scale of the isotopic effect of thermodynamic equilibrium is strongly related to the strength of chemical bonds. This view is supported by the lack of Mg isotopic fractionation during magmatic differentiation (Teng et al., doi:10.1016/j.epsl.2007.06.004) and the very small isotopic differences (less than 0.1‰ in δ26Mg) among igneous rock, when their analysis are immune of analytical artefact (Tipper et al., ). Therefore, the range of almost 5‰ for aqueous solution and associated precipitated material (e.g. Young and Galy, Tipper et al., doi:10.1016/j.epsl.2006.07.037) could be interpreted as widespread kinetic isotopic fractionation by Mg mobilisation at the surface of the Earth. Indeed, large isotopic fractionations are generated by biomineralisations and the largest is associated with the precipitation of low-Mg calcite by

  9. Role of dopants in LiF:Mg,Cu, LiF:Mg,P and LiF:Mg,Cu,P detectors

    SciTech Connect

    Mohammadi, Kh. Moussavi Zarandi, A.; Afarideh, H.; Shahmaleki, S.

    2013-06-15

    In this study, electronic structure of LiF crystal doped with Mg,Cu,P impurities was studied with WIEN2k code on the basis of FPLAPW+lo method. Results show that in Mg-doped LiF composition, an electronic trap was created with impurity concentration of 1.56% and 3.125%. In this condition, the electronic trap with increasing the percentage of the impurities up to 4.687% is annihilated. It was found, that by doping of Mg and Cu or P simultaneously, a hole-trap is created in valence band. It was realized that in LiF:Mg,Cu, LiF:Mg,P and LiF:Mg,Cu,P, Cu impurity and Li atom, have a key role in creation of levels which lead to create electronic and hole traps. Mg impurity and F atom, only have a role in creation of electronic traps. In addition, P impurity has a main role in creation of the electronic and hole traps in LiF:Mg,Cu,P. The activation energy of electronic and hole trap in LiF:Mg,Cu, LiF:Mg,P and LiF:Mg,Cu,P crystalline lattice were obtained as 0.3 and 5.5 eV, 0.92 and 3.4 eV and 0.75 and 3.1 eV, respectively. - Graphical abstract: Figure (a) and (b) shows changes in electronic structure and band gap energy of LiF crystal due to presence of Mg and Cu, Mg and P ions respectively. - Highlights: • Electronic structure of LiF, LiF:Mg,Cu, LiF:Mg,P and LiF:Mg,Cu,P materials were studied with WIEN2K code. • In LiF:Mg,Cu and LiF:Mg,Cu,P, Li atom and Cu impurity have a key role in creation of levels. • F atom and Mg impurity only have a role in creation of electronic traps. • In LiF:Mg,Cu,P, P impurity has a main role in creation of electronic and hole traps.

  10. Phase transition and optoelectronic properties of MgH2

    NASA Astrophysics Data System (ADS)

    Nayak, Vikas; Verma, U. P.

    2016-05-01

    In this article, structural and electronic properties of MgH2 have been studied. The aim behind this study was to find out the ground state crystal structure of MgH2. For the purpose, density functional theory (DFT)-based full-potential linearized augmented plane wave (FP-LAPW) calculations have been performed in three different space groups: P42/mnm (α-MgH2), Pa3 (β-MgH2) and Pbcn (γ-MgH2). It has been found that the ground state structure of MgH2 is α-MgH2. The present study shows that α-MgH2 transforms into γ-MgH2 at a pressure of 0.41 GPa. After further increase in pressure, γ-MgH2 transforms into β-MgH2 at a pressure of 3.67 GPa. The obtained results are in good agreement with previously reported experimental data. In all the studied phases, the behavior of MgH2 is insulating and its optical conductivity is around 6.0 eV. The α-MgH2 and γ-MgH2 are anisotropic materials while β-MgH2 is isotropic in nature.

  11. Results from d(30Mg, p)31Mg at Rex-Isolde

    NASA Astrophysics Data System (ADS)

    Bildstein, V.

    2013-03-01

    In this proceedings the preliminary results of a d(30Mg, p)31Mg experiment at REXISOLDE are presented. The experiment was performed using the new T-REX setup for transfer reactions in inverse kinematics. The angular distribution of protons was measured for the second excited state at 221 keV in coincidence with de-excitation γ-rays. The comparison of the angular distribution with DWBA calculations for different transferred orbital momenta, identifies the state for the first time as an l = 1 state.

  12. Porous composite materials ZrO2(MgO)-MgO for osteoimplantology

    NASA Astrophysics Data System (ADS)

    Buyakov, Ales; Litvinova, Larisa; Shupletsova, Valeria; Kulbakin, Denis; Kulkov, Sergey

    2016-08-01

    The pore structure and phase composition of ceramic composite material ZrO2(Mg)-MgO at different sintering temperatures were studied. The main mechanical characteristics of the material were determined and it was shown that they are close to the characteristics of natural bone tissues. It was shown that material structure has a positive effect on the pre-osteoblast cells proliferation. In-vitro studies of pre-osteoblast cells, cultivation on material surface showed a good cell adhesion, proliferation and differentiation of MMSC by osteogenic type.

  13. Can Mg isotopes be used to trace cyanobacteria-mediated magnesium carbonate precipitation in alkaline lakes?

    NASA Astrophysics Data System (ADS)

    Shirokova, L. S.; Mavromatis, V.; Bundeleva, I.; Pokrovsky, O. S.; Bénézeth, P.; Pearce, C.; Gérard, E.; Balor, S.; Oelkers, E. H.

    2011-07-01

    The fractionation of Mg isotopes was determined during the cyanobacterial mediated precipitation of hydrous magnesium carbonate precipitation in both natural environments and in the laboratory. Natural samples were obtained from Lake Salda (SE Turkey), one of the few modern environments on the Earth's surface where hydrous Mg-carbonates are the dominant precipitating minerals. This precipitation was associated with cyanobacterial stromatolites which were abundant in this aquatic ecosystem. Mg isotope analyses were performed on samples of incoming streams, groundwaters, lake waters, stromatolites, and hydromagnesite-rich sediments. Laboratory Mg carbonate precipitation experiments were conducted in the presence of purified Synechococcus sp cyanobacteria that were isolated from the lake water and stromatolites. The hydrous magnesium carbonates nesquehonite (MgCO3·3H2O) and dypingite (Mg5(CO3)4(OH)25(H2O)) were precipitated in these batch reactor experiments from aqueous solutions containing either synthetic NaHCO3/MgCl2 mixtures or natural Lake Salda water, in the presence and absence of live photosynthesizing Synechococcus sp. Bulk precipitation rates were not to affected by the presence of bacteria when air was bubbled through the system. In the stirred non-bubbled reactors, conditions similar to natural settings, bacterial photosynthesis provoked nesquehonite precipitation, whilst no precipitation occurred in bacteria-free systems in the absence of air bubbling, despite the fluids achieving a similar or higher degree of supersaturation. The extent of Mg isotope fractionation (Δ26Mgsolid-solution) between the mineral and solution in the abiotic experiments was found to be identical, within uncertainty, to that measured in cyanobacteria-bearing experiments, and ranges from -1.4 to -0.7 ‰. This similarity refutes the use of Mg isotopes to validate microbial mediated precipitation of hydrous Mg carbonates.

  14. Low-temperature atomic layer deposition of MgO thin films on Si

    NASA Astrophysics Data System (ADS)

    Vangelista, S.; Mantovan, R.; Lamperti, A.; Tallarida, G.; Kutrzeba-Kotowska, B.; Spiga, S.; Fanciulli, M.

    2013-12-01

    Magnesium oxide (MgO) films have been grown by atomic layer deposition in the wide deposition temperature window of 80-350 °C by using bis(cyclopentadienyl)magnesium and H2O precursors. MgO thin films are deposited on both HF-last Si(1 0 0) and SiO2/Si substrates at a constant growth rate of ˜0.12 nm cycle-1. The structural, morphological and chemical properties of the synthesized MgO thin films are investigated by x-ray reflectivity, grazing incidence x-ray diffraction, time-of-flight secondary ion mass spectrometry and atomic force microscopy measurements. MgO layers are characterized by sharp interface with the substrate and limited surface roughness, besides good chemical uniformity and polycrystalline structure for thickness above 7 nm. C-V measurements performed on Al/MgO/Si MOS capacitors, with MgO in the 4.6-11 nm thickness range, allow determining a dielectric constant (κ) ˜ 11. Co layers are grown by chemical vapour deposition in direct contact with MgO without vacuum-break (base pressure 10-5-10-6 Pa). The as-grown Co/MgO stacks show sharp interfaces and no elements interdiffusion among layers. C-V and I-V measurements have been conducted on Co/MgO/Si MOS capacitors. The dielectric properties of MgO are not influenced by the further process of Co deposition.

  15. Ranging Behaviour of Commercial Free-Range Laying Hens

    PubMed Central

    Chielo, Leonard Ikenna; Pike, Tom; Cooper, Jonathan

    2016-01-01

    Simple Summary Commercial free-range production has become a significant sector of the fresh egg market due to legislation banning conventional cages and consumer preference for products perceived as welfare friendly, as access to outdoor range can lead to welfare benefits such as greater freedom of movement and enhanced behavioural opportunities. This study investigated dispersal patterns, feather condition and activity of laying hens in three distinct zones of the range area; the apron area near shed; enriched zone 10–50 m from shed; and outer range beyond 50 m, in six flocks of laying hens under commercial free-range conditions varying in size between 4000 and 24,000 hens. Each flock was visited for four days to record number of hens in each zone, their behaviour, feather condition and nearest neighbour distances (NND), as well as record temperature and relative humidity during the visit. Temperature and relative humidity varied across the study period in line with seasonal variations and influenced the use of range with fewer hens out of shed as temperature fell or relative humidity rose. On average, 12.5% of the hens were observed on the range and most of these hens were recorded in the apron zone as hen density decreased rapidly with increasing distance from the shed. Larger flocks appeared to have a lower proportion of hens on range. The hens used the range more in the early morning followed by a progressive decrease through to early afternoon. The NND was greatest in the outer range and decreased towards the shed. Feather condition was generally good and hens observed in the outer range had the best overall feather condition. Standing, pecking, walking and foraging were the most commonly recorded behaviours and of these, standing occurred most in the apron whereas walking and foraging behaviours were recorded most in the outer range. This study supported the findings of previous studies that reported few hens in the range and greater use of areas closer

  16. Effect of inorganic and organic ligands on the sorption/desorption of arsenate on/from Al-Mg and Fe-Mg layered double hydroxides

    NASA Astrophysics Data System (ADS)

    Caporale, A. G.; Pigna, M.; Dynes, J. J.; Cozzolino, V.; Zhu, J.; Violante, A.

    2012-04-01

    ligand concentration and was greater on Al-Mg-LDH than on Fe-Mg-LDH, evidently because arsenate anions have a stronger affinity for Fe than Al and for the presence in Fe-Mg-LDH of short-range-ordered materials on which arsenate forms very strong inner-sphere complexes not easily desorbable by competing ligands. The longer the arsenate residence time on the LDH surfaces the less effective the competing ligands were in desorbing arsenate from sorbents. The effect of increasing residence time on desorbing arsenate was similar for all ligands. However, for Al-Mg-LDH systems with phosphate, tartrate and oxalate, more arsenate was desorbed compared to Fe-Mg-LDH systems, at the same residence time. The amounts of arsenate desorbed by phosphate from LDHs increased with time, being characterized by an initially very fast desorption reaction followed by a much slower desorption reaction until a plateau was reached. A greater percentage of arsenate was removed by phosphate from Al-Mg-LDH than from Fe-Mg-LDH, suggesting that the main difference between two LDHs was in the amount of more easily desorbable arsenate. The implementation of decontamination systems of As-contaminated sources by providing for LDHs use would be able to combine the lower costs of remediation and effective removal of As from them.

  17. The influence of MgH2 on the assessment of electrochemical data to predict the degradation rate of Mg and Mg alloys.

    PubMed

    Mueller, Wolf-Dieter; Hornberger, Helga

    2014-06-26

    Mg and Mg alloys are becoming more and more of interest for several applications. In the case of biomaterial applications, a special interest exists due to the fact that a predictable degradation should be given. Various investigations were made to characterize and predict the corrosion behavior in vitro and in vivo. Mostly, the simple oxidation of Mg to Mg2+ ions connected with adequate hydrogen development is assumed, and the negative difference effect (NDE) is attributed to various mechanisms and electrochemical results. The aim of this paper is to compare the different views on the corrosion pathway of Mg or Mg alloys and to present a neglected pathway based on thermodynamic data as a guideline for possible reactions combined with experimental observations of a delay of visible hydrogen evolution during cyclic voltammetry. Various reaction pathways are considered and discussed to explain these results, like the stability of the Mg+ intermediate state, the stability of MgH2 and the role of hydrogen overpotential. Finally, the impact of MgH2 formation is shown as an appropriate base for the prediction of the degradation behavior and calculation of the corrosion rate of Mg and Mg alloys.

  18. The Influence of MgH2 on the Assessment of Electrochemical Data to Predict the Degradation Rate of Mg and Mg Alloys

    PubMed Central

    Mueller, Wolf-Dieter; Hornberger, Helga

    2014-01-01

    Mg and Mg alloys are becoming more and more of interest for several applications. In the case of biomaterial applications, a special interest exists due to the fact that a predictable degradation should be given. Various investigations were made to characterize and predict the corrosion behavior in vitro and in vivo. Mostly, the simple oxidation of Mg to Mg2+ ions connected with adequate hydrogen development is assumed, and the negative difference effect (NDE) is attributed to various mechanisms and electrochemical results. The aim of this paper is to compare the different views on the corrosion pathway of Mg or Mg alloys and to present a neglected pathway based on thermodynamic data as a guideline for possible reactions combined with experimental observations of a delay of visible hydrogen evolution during cyclic voltammetry. Various reaction pathways are considered and discussed to explain these results, like the stability of the Mg+ intermediate state, the stability of MgH2 and the role of hydrogen overpotential. Finally, the impact of MgH2 formation is shown as an appropriate base for the prediction of the degradation behavior and calculation of the corrosion rate of Mg and Mg alloys. PMID:24972140

  19. Photo-induced reactions in the ion-molecule complex Mg+-OCNC2H5

    NASA Astrophysics Data System (ADS)

    Sun, Ju-Long; Liu, Haichuan; Han, Ke-Li; Yang, Shihe

    2003-06-01

    Ion-molecule complexes of magnesium cation with ethyl isocyanate were produced in a laser-ablation supersonic expansion nozzle source. Photo-induced reactions in the 1:1 complexes have been studied in the spectral range of 230-410 nm. Photodissociation mass spectrometry revealed the persistent product Mg+ from nonreactive quenching throughout the entire wavelength range. As for the reactive channels, the photoproducts, Mg+OCN and C2H5+, were produced only in the blue absorption band of the complex with low yields. The action spectrum of Mg+(OCNC2H5) consists of two pronounced peaks on the red and blue sides of the Mg+ 32P←32S atomic transition. The ground state geometry of Mg+-OCNC2H5 was fully optimized at B3LYP/6-31+G** level by using GAUSSIAN 98 package. The calculated absorption spectrum of the complex using the optimized structure of its ground state agrees well with the observed action spectrum. Photofragment branching fractions of the products are almost independent of the photolysis photon energy for the 3Px,y,z excitations. The very low branching ratio of reactive products to nonreactive fragment suggests that evaporation is the main relaxation pathway in the photo-induced reactions of Mg+(OCNC2H5).

  20. PN ranging/telemetry transmission

    NASA Technical Reports Server (NTRS)

    Deerkoski, L. F.

    1977-01-01

    System can transmit range-indicating pseudonoise (PN) codes and simultaneously transmit auxiliary information as binary data at a rate at least on order of pseudonoise chipping rate. PN code is modulated by data stream with relatively low bit rate. Data stream with high bit rate can be transmitted in same frequency band as PN ranging code.

  1. Extended range chemical sensing apparatus

    DOEpatents

    Hughes, Robert C.; Schubert, W. Kent

    1994-01-01

    An apparatus for sensing chemicals over extended range of concentrations. In particular, first and second sensors each having separate, but overlapping ranges for sensing concentrations of hydrogen are provided. Preferably, the first sensor is a MOS solid state device wherein the metal electrode or gate is a nickel alloy. The second sensor is a chemiresistor comprising a nickel alloy.

  2. Institutional Long-Range Planning.

    ERIC Educational Resources Information Center

    Bolin, John G.

    This booklet presents a general outline for conducting a long-range planning study that can be adapted for use by any institution of higher education. The basic components of an effective long-range plan should include: (1) purposes of the plan, which define the scope of the study and provide the setting in which it will be initiated; (2) a set of…

  3. Elastic and Thermodynamic Properties of Complex Mg-Al Intermetallic Compounds via Orbital-Free Density Functional Theory

    NASA Astrophysics Data System (ADS)

    Zhuang, Houlong; Chen, Mohan; Carter, Emily A.

    2016-06-01

    Magnesium-aluminum (Mg-Al) alloys are important metal alloys with a wide range of engineering applications. We investigate the elastic and thermodynamic properties of Mg, Al, and four stoichiometric Mg-Al compounds including Mg17Al12 , Mg13Al14 , and Mg23Al30 , and MgAl2 with orbital-free density-functional theory (OFDFT). We first calculate the lattice constants, zero-temperature formation energy, and independent elastic constants of these six materials and compare the results to those computed via Kohn-Sham DFT (KSDFT) benchmarks. We obtain excellent agreement between these two methods. Our calculated elastic constants of hexagonal close-packed Mg and face-centered-cubic Al are also consistent with available experimental data. We next compute their phonon spectra using the force constants extracted from the very fast OFDFT calculations, because such calculations are computationally challenging using KSDFT. This is especially the case for the Mg23Al30 compound, whose 3 ×3 ×3 supercell consists of 1431 atoms. We finally employ the quasiharmonic approximation to investigate temperature-dependent thermodynamic properties, including formation energies, heat capacities, and thermal expansion of the four Mg-Al intermetallic compounds. The calculated heat capacity and thermal expansion of both Mg and Al agree well with experimental data. We additionally find that Mg13Al14 and MgAl2 are both unstable, consistent with their absence from the equilibrium Mg-Al phase diagram. Our work demonstrates that OFDFT is an efficient and accurate quantum-mechanical computational tool for predicting elastic and thermodynamic properties of complicated Mg-Al alloys and also should be applicable to many other engineering alloys.

  4. Thermal Parameters and Microstructural Development in Directionally Solidified Zn-Rich Zn-Mg Alloys

    NASA Astrophysics Data System (ADS)

    Vida, Talita A.; Freitas, Emmanuelle S.; Brito, Crystopher; Cheung, Noé; Arenas, Maria A.; Conde, Ana; De Damborenea, Juan; Garcia, Amauri

    2016-06-01

    Transient directional solidification experiments have been carried out with Zn-Mg hypoeutectic alloys under an extensive range of cooling rates with a view to analyzing the evolution of microstructure. It is shown that the microstructure is formed by a Zn-rich matrix of different morphologies and competitive eutectic mixtures (Zn-Zn11Mg2 and Zn-Zn2Mg). For 0.3 wt-pct Mg and 0.5 wt-pct Mg alloys, the Zn-rich matrix is shown to be characterized by high-cooling rates plate-like cells (cooling rates >9.5 and 24 K/s, respectively), followed by a granular-dendritic morphological transition for lower cooling rates. In contrast, a directionally solidified Zn1.2 wt-pct Mg alloy casting is shown to have the Zn-rich matrix formed only by dendritic equiaxed grains. Experimental growth laws are proposed relating the plate-like cellular interphase, the secondary dendritic arm spacing, and the eutectic interphase spacings to solidification thermal parameters, i.e., cooling rate and growth rate. The experimental law for the growth of secondary dendritic spacings under unsteady-state solidifications is also shown to encompass results of hypoeutectic Zn-Mg alloys subjected to steady-state Bridgman growth.

  5. Comparison between Mg II k and Ca II H images recorded by SUNRISE/SuFI

    SciTech Connect

    Danilovic, S.; Hirzberger, J.; Riethmüller, T. L.; Solanki, S. K.; Barthol, P.; Gandorfer, A.; Gizon, L.; Berkefeld, T.; Schmidt, W.; Knölker, M.; Rodríguez, J. Blanco; Iniesta, J. C. Del Toro

    2014-03-20

    We present a comparison of high-resolution images of the solar surface taken in the Mg II k and Ca II H channels of the Filter Imager on the balloon-borne solar observatory SUNRISE. The Mg and Ca lines are sampled with 0.48 nm and 0.11 nm wide filters, respectively. The two channels show remarkable qualitative and quantitative similarities in the quiet Sun, in an active region plage and during a small flare. However, the Mg filtergrams display 1.4-1.7 times higher intensity contrast and appear more smeared and smoothed in the quiet Sun. In addition, the fibrils in a plage are wider. Although the exposure time is 100 times longer for Mg images, the evidence suggests that these differences cannot be explained only with instrumental effects or the evolution of the solar scene. The differences at least partially arise because of different line-formation heights, the stronger response of Mg k emission peaks to the higher temperatures, and the larger height range sampled by the broad Mg filter used here. This is evidently manifested during the flare when a surge in Mg evolves differently than in Ca.

  6. Oxide solubilities and phase relations in the system Mg-Nd-O-Cl

    SciTech Connect

    Kipouros, G.; Mediaas, H.; Vindstad, J.E.; Oestvold, T.; Tkatcheva, O.

    1996-10-01

    Freezing point depression measurements have been performed for the CaCl{sub 2}-NdOCl, Cs{sub 2}MgCl{sub 4}-NdOCl and MgCl{sub 2}-NdOCl liquid binaries with small additions of NdOCl. Very low NdOCl solubilities are observed in all the three binaries. Calculated solubility products of NdOCl at 1,073 K in CaCl{sub 2} and Cs{sub 2}MgCl{sub 4} are in the range 10{sup {minus}6}--10{sup {minus}8} confirming the experimental data.The MgCl{sub 2}-NdOCl system is more complicated. In the very dilute region NdOCl dissolves by forming two foreign ions probably Mg{sub 2}OCl{sub 5}{sup 3{minus}} and Nd{sup 3+} or NdO{sup +} and Mg{sub n}Cl{sub m}{sup (2n-m)-} depending on which cation Mg{sup 2+} or Nd{sup 3+} will bond the O{sup 2{minus}} ion most strongly.

  7. Ostracode Mg/Ca Ratios from Quaternary Sediments of the Arctic Ocean

    NASA Astrophysics Data System (ADS)

    Dwyer, G. S.; Caverly, E. K.; Cronin, T. M.; Polyak, L. V.; DeNinno, L.; Rodriguez-Lazaro, J.

    2013-12-01

    We analyzed magnesium/calcium (Mg/Ca) ratios from adult, calcitic shells of the deep-sea ostracode Krithe from the Northwind and Mendeleev Ridges, Arctic Ocean, to reconstruct orbital-scale Quaternary bottom-water temperature history. Results show an early Pleistocene (~1.5 Ma to 500 ka) Mg/CaKrithe pattern with low-amplitude, possibly orbitally controlled, oscillations between 10.5 and 12.5 mmol/mol followed by a progressive trend towards higher ratios (> 17 mmol/mol) during the last 500 ka. This shift coincides with the mid-Pleistocene Transition and mid-Brunhes Event (~ 300-500 ka) recognized in microfaunal proxy records in the Arctic Ocean. Analyses of Mg/CaKrithe from intervals representing marine isotope stage 11 (MIS 11) in 5 cores from water depths from 700 to 1470 m show Mg/Ca ratios ranging from 10.5 to 14 mmol/mol. A 2 mmol/mol excursion in Mg/CaKrithe within MIS 11 seen in all cores likely corresponds to a brief stadial event recognized also in planktic and benthic microfaunas. We will discuss the implications of Mg/Ca paleothermometry for deep Arctic Ocean circulation and the evolution of Arctic sea ice during major Quaternary climatic transitions as well as possible factors other than water temperature that may influence Mg/Ca ratios in Krithe shells from Quaternary sediments from the Arctic Ocean.

  8. Pathway and molecular mechanisms for malachite green biodegradation in Exiguobacterium sp. MG2.

    PubMed

    Wang, Ji'ai; Gao, Feng; Liu, Zhongzhong; Qiao, Min; Niu, Xuemei; Zhang, Ke-Qin; Huang, Xiaowei

    2012-01-01

    Malachite green (MG), N-methylated diaminotriphenylmethane, is one of the most common dyes in textile industry and has also been used as an effective antifungal agent. However, due to its negative impact on the environment and carcinogenic effects to mammalian cells, there is a significant interest in developing microbial agents to degrade this type of recalcitrant molecules. Here, an Exiguobacterium sp. MG2 was isolated from a river in Yunnan Province of China as one of the best malachite green degraders. This strain had a high decolorization capability even at the concentration of 2500 mg/l and maintained its stable activity within the pH range from 5.0 to 9.0. High-pressure liquid chromatography, liquid chromatography-mass spectrometry and gas chromatography-mass spectrometry were employed to detect the catabolic pathway of MG. Six intermediate products were identified and a potential biodegradation pathway was proposed. This pathway involves a series of reactions of N-demethylation, reduction, benzene ring-removal, and oxidation, which eventually converted N-methylated diaminotriphenylmethane into N, N-dimethylaniline that is the key precursor to MG. Furthermore, our molecular biology experiments suggested that both triphenylmethane reductase gene tmr and cytochrome P450 participated in MG degradation, consistent with their roles in the proposed pathway. Collectively, our investigation is the first report on a biodegradation pathway of triphenylmethane dye MG in bacteria.

  9. A search for Mg-poor stars using LAMOST survey data

    NASA Astrophysics Data System (ADS)

    Xing, Qian-Fan; Zhao, Gang; Zhang, Yong; Hou, Yong-Hui; Wang, Yue-Fei; Wu, Yue

    2015-08-01

    Most Galactic metal-poor stars exhibit enhanced α-abundances (e.g. [Mg/Fe] ˜ +0.4) according to previous studies of stellar chemical compositions. However, a handful of metal-poor stars with large deficiencies in Mg (e.g. [Mg/Fe] ˜ -0.2) show severe departures from this α-enhancement trend. The sub-solar [Mg/Fe] ratios of these anomalous stars indicate that they possess different chemical enrichment histories than the majority of Galactic metal-poor stars. In previous work, we presented a method to select Mg-poor metal-poor stars from low-resolution SDSS spectra based on a spectral matching technique. In this paper, a similar method is applied to low-resolution (R ˜ 1800) LAMOST spectra. Stellar [Mg/Fe] abundances are determined by using stellar parameters delivered by the LAMOST Data Release 2 catalog. From a sample of ˜ 60 000 stars with atmospheric parameters in the range Teff = [5500, 6500] K and [Fe/H] = [-2.4, +0.5], we select 15 candidate Mg-poor metal-poor stars.

  10. Effect of scandium on the microstructure and ageing behaviour of cast Al-6Mg alloy

    SciTech Connect

    Kaiser, M.S.; Datta, S.; Roychowdhury, A. Banerjee, M.K.

    2008-11-15

    Microstructural modification and grain refinement due to addition of scandium in Al-6Mg alloy has been studied. Transmission electron microscopy is used to understand the microstructure and precipitation behaviour in Al-6Mg alloy doped with scandium. It is seen from the microstructure that the dendrites of the cast Al-6Mg alloy have been refined significantly due to addition of scandium. Increasing amount of scandium leads to a greater dendrite refinement. The age hardening effect in scandium added Al-6Mg alloys has been studied by subjecting the alloys containing varying amount of scandium ranging from 0.2 wt.% to 0.6 wt.% to isochronal and isothermal ageing at various temperatures for different times. It is observed that significant hardening takes place in the aged alloys due to the precipitation of scandium aluminides.

  11. Combustion synthesis of MgO nanoparticles using plant extract: Structural characterization and photoluminescence studies

    SciTech Connect

    Kumar, Danith; Chikkahanumantharayappa; Yadav, L. S. Reddy; Nagaraju, G.; Lingaraju, K.; Naika, H. Raja; Manjunath, K.; Suresh, D.; Prasad, Daruka; Nagabhushana, H.; Sharma, S. C.

    2015-06-24

    Magnesium oxide nanoparticles (MgO Nps) have been successfully synthesized via solution combustion method using Parthenium plant extract as fuel for the first time. Powder X-ray diffraction (PXRD) pattern reveal that product belongs to the cubic phase (Periclase). FTIR spectrum shows the band at 822 cm{sup −1} indicates the formation of cubic periclase MgO. The optical band gap of MgO Nps estimated from UV –Vis spectrum was found to be in the range 5.40–5.45 eV. SEM images showed that, the product is agglomerated and particle in nature. Photoluminescence (PL) studies shows violet emission at 390 nm, blue emission at 470 nm and green emission at 550 nm. MgO Nps shows good photocatalytic activity for the degradation of methylene blue (MB) dye under UV/Sun light irradiation.

  12. Combustion synthesis of MgO nanoparticles using plant extract: Structural characterization and photoluminescence studies

    NASA Astrophysics Data System (ADS)

    Kumar, Danith; Yadav, L. S. Reddy; Lingaraju, K.; Manjunath, K.; Suresh, D.; Prasad, Daruka; Nagabhushana, H.; Sharma, S. C.; Naika, H. Raja; Chikkahanumantharayappa, Nagaraju, G.

    2015-06-01

    Magnesium oxide nanoparticles (MgO Nps) have been successfully synthesized via solution combustion method using Parthenium plant extract as fuel for the first time. Powder X-ray diffraction (PXRD) pattern reveal that product belongs to the cubic phase (Periclase). FTIR spectrum shows the band at 822 cm-1 indicates the formation of cubic periclase MgO. The optical band gap of MgO Nps estimated from UV -Vis spectrum was found to be in the range 5.40-5.45 eV. SEM images showed that, the product is agglomerated and particle in nature. Photoluminescence (PL) studies shows violet emission at 390 nm, blue emission at 470 nm and green emission at 550 nm. MgO Nps shows good photocatalytic activity for the degradation of methylene blue (MB) dye under UV/Sun light irradiation.

  13. Fabrication and Spark Plasma Sintering of Magnetic alpha-Fe/MgO Nanocomposite by Mechanical Alloying.

    PubMed

    Lee, Chung-Hyo

    2016-02-01

    Solid-state reduction has occurred during mechanical alloying of a mixture of Fe2O3 and Mg powders at room temperature. It is found that magnetic nanocomposite in which MgO is dispersed in alpha-Fe matrix with nano-sized grains is obtained by mechanical alloying of Fe2O3 with Mg for 30 min. Consolidation of the ball-milled powders was performed in a spark plasma sintering (SPS) machine up to 800-1000 degrees C. X-ray diffraction result shows that the average grain size of alpha-Fe in a-Fe/MgO nanocomposite sintered at 800 degrees C is in the range of 110 nm. It can be also seen that the coercivity of SPS sample sintered at 800 degrees C is still high value of 88 Oe, suggesting that the grain growth of magnetic alpha-Fe phase during SPS process tends to be suppressed. PMID:27433621

  14. Direct determination of the band alignment at the (Zn,Mg)O/CISSe interface

    SciTech Connect

    Erfurth, F.; Reinert, F.; Weinhardt, L.; Grimm, A.; Palm, J.; Niesen, T. P.; Umbach, E.

    2011-04-04

    The electronic and chemical properties of the (Zn{sub 1-x},Mg{sub x})O/CuIn(S,Se){sub 2} interface, prepared by sputtering of thin (Zn,Mg)O layers, were investigated with direct and inverse photoelectron spectroscopy on in situ prepared samples. With the combination of both techniques we have determined the band alignment at this interface as a function of Mg-content in the range 0{<=}x{<=}0.30. We find that the band alignment at the interface can be tailored between a ''cliff'' (downward step) in the conduction band for pure ZnO and a 'spike' (upward step) for high Mg-contents. A direct influence of the band alignment modifications on the solar cell parameters is found.

  15. Directional Solidification and Thermoelectric Properties of Undoped Mg2Sn Crystal

    NASA Astrophysics Data System (ADS)

    Li, Xin; Li, Shuang-ming; Feng, Song-ke; Zhong, Hong; Fu, Heng-zhi

    2016-06-01

    Single-phase Mg2Sn crystal has been successfully directionally solidified from the melt with a high temperature gradient of 185 K cm-1. The solidified distance for the growth of single-phase Mg2Sn crystal was predicted theoretically and agreed well with the experimental result. The grown Mg2Sn crystals exhibit better thermoelectric performance and high thermoelectric figure of merit along the growth direction. In the temperature range from 300 K to 700 K, the maximum Seebeck coefficient S and electrical conductivity σ reached -261 μV K-1 and 525 Ω-1 m-1, respectively. The minimum thermal conductivity κ was measured to be 4.3 W m-1 K-1, and the lattice thermal conductivity approximated 90% of the bulk thermal conductivity of the crystal. The method developed in this work provides a methodological reference for preparation of Mg2BIV and its doped and solid-solution compounds.

  16. Two-color Laser Desorption of Nanostructured MgO Thin Films

    SciTech Connect

    Beck, Kenneth M.; Joly, Alan G.; Hess, Wayne P.

    2009-09-30

    Neutral magnesium atom emission from nanostructured MgO thin films is induced using two-color nanosecond laser excitation. We find that combined visible/UV excitation, for single-color pulse energies below the desorption threshold, induces neutral Mg-atom emission with hyperthermal kinetic energies in the range of 0.1- 0.2 eV. The observed metal atom emission is consistent with a mechanism involving rapid electron transfer to 3-coordinated Mg surface sites. The two-color Mg-atom signal is significant only for parallel laser polarizations and temporally overlapped laser pulses indicating that intermediate excited states are short-lived compared to the 5 nanosecond laser pulse duration.

  17. Mg doped InN and confirmation of free holes in InN

    SciTech Connect

    Wang, K.; Yamaguchi, T.; Miller, N.; Mayer, M. A.; Haller, E. E.; Iwamoto, R.; Araki, T.; Nanishi, Y.; Yu, K. M.; Walukiewicz, W.; Ager, J. W. III

    2011-01-24

    We report a systematic investigation on Mg doped InN epilayers grown by radio-frequency plasma-assisted molecular beam epitaxy. Electrolyte capacitance voltage (ECV) combined with thermopower measurements find p-type conduction over an Mg concentration range. For InN:Mg in this p-type 'window' the Seebeck coefficients dramatically change their signs from negative to positive when the thickness of undoped InN interlayer decreases to zero. This notable sign change of Seebeck coefficient explains the previous inconsistency between ECV and thermopower results and confirms the existence of mobile holes in the InN:Mg. Taking into account the undoped InN interlayer, the hole density and mobility are extracted.

  18. Nanocomposite formation in haematite-Mg, Ti system induced by high-energy ball milling.

    PubMed

    Lee, Chung-Hyo

    2013-06-01

    Reactant materials of haematite and Mg, Ti powders have been milled, where pure metals are used as reducing agent. It is found that nanocomposite powders in which MgO and TiO2 are dispersed in alpha-Fe matrix with nano-sized grains are obtained by MA of Fe2O3 with Mg and Ti for 30 min and 5 hours, respectively. It is suggested that the shorter MA time for the nanocomposite formation in Fe2O3-Mg is due to a larger negative heat associated with the chemical reduction of reactant materials. X-ray diffraction results show that the average grain size of alpha-Fe in alpha-Fe/TiO2 nanocomposite powders is in the range of 40 nm. From magnetic measurement, we can also obtain indirect information about the details of the solid-state reduction process during MA.

  19. Thermoelectric properties of Zintl compound Ca1-xNaxMg2Bi1.98

    NASA Astrophysics Data System (ADS)

    Shuai, Jing; Kim, Hee Seok; Liu, Zihang; He, Ran; Sui, Jiehe; Ren, Zhifeng

    2016-05-01

    Motivated by good thermoelectric performance of Bi-based Zintl compounds Ca1-xYbxMg2Biy, we further studied the thermoelectric properties of Zintl compound CaMg2Bi1.98 by doping Na into Ca as Ca1-xNaxMg2Bi1.98 via mechanical alloying and hot pressing. We found that the electrical conductivity, Seebeck coefficient, power factor, and carrier concentration can be effectively adjusted by tuning the Na concentration. Transport measurement and calculations revealed that an optimal doping of 0.5 at. % Na achieved better average ZT and efficiency. The enhancement in thermoelectric performance is attributed to the increased carrier concentration and power factor. The low cost and nontoxicity of Ca1-xNaxMg2Bi1.98 makes it a potentially promising thermoelectric material for power generation in the mid-temperature range.

  20. Ranging Behaviour of Commercial Free-Range Laying Hens

    PubMed Central

    Chielo, Leonard Ikenna; Pike, Tom; Cooper, Jonathan

    2016-01-01

    Simple Summary Commercial free-range production has become a significant sector of the fresh egg market due to legislation banning conventional cages and consumer preference for products perceived as welfare friendly, as access to outdoor range can lead to welfare benefits such as greater freedom of movement and enhanced behavioural opportunities. This study investigated dispersal patterns, feather condition and activity of laying hens in three distinct zones of the range area; the apron area near shed; enriched zone 10–50 m from shed; and outer range beyond 50 m, in six flocks of laying hens under commercial free-range conditions varying in size between 4000 and 24,000 hens. Each flock was visited for four days to record number of hens in each zone, their behaviour, feather condition and nearest neighbour distances (NND), as well as record temperature and relative humidity during the visit. Temperature and relative humidity varied across the study period in line with seasonal variations and influenced the use of range with fewer hens out of shed as temperature fell or relative humidity rose. On average, 12.5% of the hens were observed on the range and most of these hens were recorded in the apron zone as hen density decreased rapidly with increasing distance from the shed. Larger flocks appeared to have a lower proportion of hens on range. The hens used the range more in the early morning followed by a progressive decrease through to early afternoon. The NND was greatest in the outer range and decreased towards the shed. Feather condition was generally good and hens observed in the outer range had the best overall feather condition. Standing, pecking, walking and foraging were the most commonly recorded behaviours and of these, standing occurred most in the apron whereas walking and foraging behaviours were recorded most in the outer range. This study supported the findings of previous studies that reported few hens in the range and greater use of areas closer

  1. ZnO/(ZnMg)O single quantum wells with high Mg content graded barriers

    SciTech Connect

    Laumer, Bernhard; Schuster, Fabian; Wassner, Thomas A.; Stutzmann, Martin; Rohnke, Marcus; Schoermann, Joerg; Eickhoff, Martin

    2012-06-01

    ZnO/Zn{sub 1-x}Mg{sub x}O single quantum wells (SQWs) were grown by plasma-assisted molecular beam epitaxy on c-plane sapphire substrates. Compositional grading allows the application of optimized growth conditions for the fabrication of Zn{sub 1-x}Mg{sub x}O barriers with high crystalline quality and a maximum Mg content of x = 0.23. High resolution x-ray diffraction reveals partial relaxation of the graded barriers. Due to exciton localization, the SQW emission is found to consist of contributions from donor-bound and free excitons. While for narrow SQWs with well width d{sub W}{<=}2.5nm, the observed increase of the exciton binding energy is caused by quantum confinement, the drop of the photoluminescence emission below the ZnO bulk value found for wide SQWs is attributed to the quantum-confined Stark effect. For a Mg content of x = 0.23, a built-in electric field of 630 kV/cm is extracted, giving rise to a decrease of the exciton binding energy and rapid thermal quenching of the SQW emission characterized by an activation energy of (24 {+-} 4) meV for d{sub W} = 8.3 nm.

  2. Rupatadine 20 mg and 40 mg are Effective in Reducing the Symptoms of Chronic Cold Urticaria.

    PubMed

    Abajian, Marina; Curto-Barredo, Laia; Krause, Karoline; Santamaria, Eva; Izquierdo, Iñaki; Church, Martin K; Maurer, Marcus; Giménez-Arnau, Ana

    2016-01-01

    Chronic cold urticaria (ColdU) is a rare disease characterized by mast cell-mediated wheals and angioedema following cold exposure. Second-generation H1-antihistamines, such as rupatadine, are the recommended first-line therapy. As of yet, the effects of rupatadine up-dosing on development of ColdU symptom have only been partially characterized. Two-centre, randomized, double-blind, 3-way crossover, placebo-controlled study in patients with a confirmed ColdU was designed to assess the effects of up-dosing of rupatadine. A total of 23 patients were randomized to receive placebo, rupatadine 20 mg/day, and rupatadine 40 mg/day for 1 week. The primary outcome was change in critical temperature thresholds and critical stimulation time thresholds after treatment. Secondary endpoints included assessment of safety and tolerability of rupatadine. Both 20 and 40 mg rupatadine were highly effective in reducing critical temperature thresholds (p < 0.001) and critical stimulation time thresholds (p < 0.001). In conclusion, rupatadine 20 and 40 mg significantly reduced the development of chronic cold urticaria symptom without an increase in adverse effects.

  3. Range indices of geomagnetic activity

    USGS Publications Warehouse

    Stuart, W.F.; Green, A.W.

    1988-01-01

    The simplest index of geomagnetic activity is the range in nT from maximum to minimum value of the field in a given time interval. The hourly range R was recommended by IAGA for use at observatories at latitudes greater than 65??, but was superceded by AE. The most used geomagnetic index K is based on the range of activity in a 3 h interval corrected for the regular daily variation. In order to take advantage of real time data processing, now available at many observatories, it is proposed to introduce a 1 h range index and also a 3 h range index. Both will be computed hourly, i.e. each will have a series of 24 per day, the 3 h values overlapping. The new data will be available as the range (R) of activity in nT and also as a logarithmic index (I) of the range. The exponent relating index to range in nT is based closely on the scale used for computing K values. The new ranges and range indices are available, from June 1987, to users in real time and can be accessed by telephone connection or computer network. Their first year of production is regarded as a trial period during which their value to the scientific and commercial communities will be assessed, together with their potential as indicators of regional and global disturbances' and in which trials will be conducted into ways of eliminating excessive bias at quiet times due to the rate of change of the daily variation field. ?? 1988.

  4. Foraging optimally for home ranges

    USGS Publications Warehouse

    Mitchell, Michael S.; Powell, Roger A.

    2012-01-01

    Economic models predict behavior of animals based on the presumption that natural selection has shaped behaviors important to an animal's fitness to maximize benefits over costs. Economic analyses have shown that territories of animals are structured by trade-offs between benefits gained from resources and costs of defending them. Intuitively, home ranges should be similarly structured, but trade-offs are difficult to assess because there are no costs of defense, thus economic models of home-range behavior are rare. We present economic models that predict how home ranges can be efficient with respect to spatially distributed resources, discounted for travel costs, under 2 strategies of optimization, resource maximization and area minimization. We show how constraints such as competitors can influence structure of homes ranges through resource depression, ultimately structuring density of animals within a population and their distribution on a landscape. We present simulations based on these models to show how they can be generally predictive of home-range behavior and the mechanisms that structure the spatial distribution of animals. We also show how contiguous home ranges estimated statistically from location data can be misleading for animals that optimize home ranges on landscapes with patchily distributed resources. We conclude with a summary of how we applied our models to nonterritorial black bears (Ursus americanus) living in the mountains of North Carolina, where we found their home ranges were best predicted by an area-minimization strategy constrained by intraspecific competition within a social hierarchy. Economic models can provide strong inference about home-range behavior and the resources that structure home ranges by offering falsifiable, a priori hypotheses that can be tested with field observations.

  5. Microstructural formation in a hypereutectic Mg-Si alloy

    SciTech Connect

    Pan Yichuan . E-mail: riverpan@mail.sdu.edu.cn; Liu Xiangfa; Yang Hua

    2005-09-15

    In the present work, the microstructure of an ingot metallurgy hypereutectic Mg-8 wt.% Si alloy was studied using electron probe microanalysis (EPMA) and the solidification process was discussed. The components of the alloy are Mg{sub 2}Si and Mg. The solidified microstructure of the alloy contains three constituents: Mg{sub 2}Si primary dendrites that are surrounded by Mg sub-primary particles and the Mg-Mg{sub 2}Si eutectic. The primary Mg{sub 2}Si dendrites have a secondary dendrite arm spacing d {sub 2} of approximately 17 {mu}m or show polygonal morphologies with a mean size of 30 {mu}m. An Mg phase appearing as halos surround the Mg{sub 2}Si constituents. The Mg-Mg{sub 2}Si eutectic has a regular morphology of rod-like Mg{sub 2}Si distributed in a continuous matrix of Mg having an interphase spacing r of approximately 0.8 {mu}m.

  6. Home range analysis using a mechanistic home range model

    SciTech Connect

    Moorcroft, P.R. . Dept. of Ecology and Evolutionary Biology); Lewis, M.A. . Dept. of Mathematics) Crabtree, R.L. . Dept. of Fish and Wildlife Resources)

    1999-07-01

    The traditional models used to characterize animal home ranges have no mechanistic basis underlying their descriptions of space use, and as a result, the analysis of animal home ranges has primarily been a descriptive endeavor. In this paper, the authors characterize coyote (Canis latrans) home range patterns using partial differential equations for expected space use that are formally derived from underlying descriptions of individual movement behavior. To the authors' knowledge, this is the first time that mechanistic models have been used to characterize animal home ranges. The results provide empirical support for a model formulation of movement response to scent marks, and suggest that having relocation data for individuals in adjacent groups is necessary to capture the spatial arrangement of home range boundaries. The authors then show how the model fits can be used to obtain predictions for individual movement and scent marking behavior and to predict changes in home range patterns. More generally, the findings illustrate how mechanistic models permit the development of a predictive theory for the relationship between movement behavior and animal spatial distribution.

  7. Thermoelectric properties of Mg2Si-based compounds synthesized partially using magnesium alloy

    NASA Astrophysics Data System (ADS)

    Itoh, Takashi; Hagio, Kento

    2012-06-01

    Mg2Si compounds are promising eco-friendly thermoelectric materials because both constituent elements of Mg and Si have no toxicity and exist richly in earth crust. We have a plan to use the compounds in the applications that convert waste heat in the temperature range (600-900 K) into electric power. However, the thermoelectric performance of the compounds has not yet reached to the practical use level. In addition, the compounds don't have durability in the thermoelectric performance under atmospheric circumstances in the temperature range of 750-900 K. These issues have to be solved for the practical use. In our previous work, we obtained knowledge that Al doping in Mg2Si lower the electrical resistivity and improved the thermoelectric performance. We newly attempted to use a magnesium alloy (AZ61) that includes the main three elements of aluminum (5.8-7.2 wt%), zinc (0.4-1.5 wt%) and manganese (0.15-0.35 wt%) in order to synthesize the Mg2Si-based compounds. The Mg2Si-based compound powders were synthesized from the mixture of silicon powder, AZ61 chips and Mg powder by the liquid-solid phase reaction method. The compound powders were sintered by the pulse discharge sintering method. The influence of mixing ratio of two metals of AZ61 and pure Mg on the thermoelectric properties was investigated. Addition of AZ61 greatly decreased the electrical resistivity as well as Al-doped Mg2Si and the thermoelectric performance had improved most in the 50wt%AZ61 sample.

  8. Mg/Ca composition of benthic foraminifera Miliolacea as a new tool of paleoceanography

    NASA Astrophysics Data System (ADS)

    Sadekov, Aleksey Yu.; Bush, Flora; Kerr, Joanna; Ganeshram, Raja; Elderfield, Henry

    2014-10-01

    The Mg/Ca compositions of benthic foraminifera from the superfamily Miliolacea have been studied to explore the use of these high-Mg foraminifera as a proxy for deep ocean conditions. Taxonomic analyses, relative abundance, and depth distributions of different Miliolacea species were carried out on a collection of core top samples, covering a depth range of 131 m to 2530 m, along the Australian coast of the Timor Sea. Pyrgo sp., composed of Pyrgo sarsi and Pyrgo murrhina, was found to be the most suitable for proxy studies. Mg/Ca values of this group of foraminifera show a strong correlation with bottom water temperatures and carbonate ion saturation described by the linear relationship: Mg/Ca = 2.53(±0.22) × BWT + 0.129(±0.023) × Δ[CO32-] + 4.63(±0.53), within the -1°C to 8°C temperature range. Absolute Mg/Ca values of Pyrgo sp. calcite and their temperature sensitivity are similar to those observed for inorganic calcite, suggesting that Mg composition of Pyrgo sp. calcite is mainly controlled by inorganic processes. The Mg/Ca composition of Pyrgo sp. calcite provides a new tool for reconstructing both water temperature and carbonate ion saturation when combined with other proxies for one of these parameters. A down core record from the Eastern Equatorial Pacific has been generated to illustrate how Mg/Ca values can be used for paleoclimate studies. This down core record shows large changes in Pacific bottom waters [CO32-] across glacial-interglacial transition, implying an increase in [CO32-] during the glacial period.

  9. IMPACT OF A REVISED {sup 25}Mg(p, {gamma}){sup 26}Al REACTION RATE ON THE OPERATION OF THE Mg-Al CYCLE

    SciTech Connect

    Straniero, O.; Cristallo, S.; Imbriani, G.; DiLeva, A.; Limata, B.; Strieder, F.; Bemmerer, D.; Broggini, C.; Caciolli, A.; Corvisiero, P.; Costantini, H.; Lemut, A.; Formicola, A.; Gustavino, C.; Junker, M.; Elekes, Z.; Fueloep, Zs.; Gyuerky, Gy.; Gervino, G.; Guglielmetti, A.; and others

    2013-02-15

    Proton captures on Mg isotopes play an important role in the Mg-Al cycle active in stellar H-burning regions. In particular, low-energy nuclear resonances in the {sup 25}Mg(p, {gamma}){sup 26}Al reaction affect the production of radioactive {sup 26}Al{sup gs} as well as the resulting Mg/Al abundance ratio. Reliable estimations of these quantities require precise measurements of the strengths of low-energy resonances. Based on a new experimental study performed at the Laboratory for Underground Nuclear Astrophysics, we provide revised rates of the {sup 25}Mg(p, {gamma}){sup 26}Al{sup gs} and the {sup 25}Mg(p, {gamma}){sup 26}Al {sup m} reactions with corresponding uncertainties. In the temperature range 50-150 MK, the new recommended rate of {sup 26}Al {sup m} production is up to five times higher than previously assumed. In addition, at T = 100 MK, the revised total reaction rate is a factor of two higher. Note that this is the range of temperature at which the Mg-Al cycle operates in a H-burning zone. The effects of this revision are discussed. Due to the significantly larger {sup 25}Mg(p, {gamma}){sup 26}Al {sup m} rate, the estimated production of {sup 26}Al{sup gs} in H-burning regions is less efficient than previously obtained. As a result, the new rates should imply a smaller contribution from Wolf-Rayet stars to the galactic {sup 26}Al budget. Similarly, we show that the asymptotic giant branch (AGB) extra-mixing scenario does not appear able to explain the most extreme values of {sup 26}Al/{sup 27}Al, i.e., >10{sup -2}, found in some O-rich presolar grains. Finally, the substantial increase of the total reaction rate makes the hypothesis of self-pollution by massive AGBs a more robust explanation for the Mg-Al anticorrelation observed in globular-cluster stars.

  10. Revealing the Properties of Mg II Absorbing Galaxies at z > 1 with HST WFC3/IR

    NASA Astrophysics Data System (ADS)

    Lundgren, Britt; Brammer, Gabriel, , Dr.; York, Donald G.; Chisholm, John P.; Erb, Dawn; Kulkarni, Varsha P.; Straka, Lorrie; Tremonti, Christina A.; Van Dokkum, Pieter G.; Wake, David

    2015-01-01

    Intervening absorption from Mg II in the spectra of distant quasars is understood to trace the tidal stripping, accretion and outflows of cold, enriched gas in the circumgalactic medium of galaxies, independent of luminosity, to high redshift. Tens of thousands of Mg II absorbers in the range 0.3 < z < 2.2 have been extracted to date from the SDSS spectroscopic quasar sample, but their utility in aiding our understanding of the gaseous processes driving galaxy evolution has been hindered by the observational difficulties of detecting their host galaxies at intermediate and high redshifts and at small angular separations from brighter background quasars. We present first results from an 18-orbit HST Cycle 21 WFC3/IR program, which has obtained direct imaging and grism observations of galaxies in the fields surrounding the 9 quasar sight lines in the SDSS with the highest frequency of uncorrelated foreground Mg II absorption in the range 0.7< z < 2.2. These highly efficient observations include 56 Mg II absorbers, most all of which are matched unambiguously to galaxies in the grism data, thereby doubling the number of spectroscopically confirmed Mg II absorbing galaxies at z > 1. The data further enable precise measurements of the impact parameters, morphologies, inclination angles, star formation rates, and star formation rate surface densities of typical Mg II-selected galaxies, as a function of Mg II absorption strength, which are complete for a large range in projected separations (7-450 kpc) and to low star formation rates (~1.3 Msun/yr).

  11. The eclipse of species ranges.

    PubMed

    Hemerik, Lia; Hengeveld, Rob; Lippe, Ernst

    2006-01-01

    This paper distinguishes four recognisably different geographical processes in principle causing species to die out. One of these processes, the one we dub "range eclipse", holds that one range expands at the expense of another one, thereby usurping it. Channell and Lomolino (2000a, Journal of Biogeography 27: 169-179; 2000b, Nature 403: 84-87; see also Lomolino and Channell, 1995, Journal of Mammalogy 76: 335-347) measured the course of this process in terms of the proportion of the total range remaining in its original centre, thereby essentially assuming a homogeneous distribution of animals over the range. However, part of their measure seems mistaken. By giving a general, analytical formulation of eclipsing ranges, we estimate the exact course of this process. Also, our formulation does not partition a range into two spatially equal parts, its core and its edge, but it assumes continuity. For applying this model to data on the time evolution of species, individual time series should be available for each of them. For practical purposes we give an alternative way of plotting and interpreting such time series. Our approach, being more sensitive than Channell and Lomolino's, gives a less optimistic indication of range eclipses than theirs once these have started. PMID:17318329

  12. Mg intercalation into Ti2C building block

    NASA Astrophysics Data System (ADS)

    Yu, Xue-fang; Cheng, Jianbo; Liu, Zhenbo; Li, Qingzhong; Li, Wenzuo; Yang, Xin; Xiao, Bo

    2015-06-01

    Generally, intercalation occurs when foreign atoms intercalate into multi-layer structures, while adsorption occurs when foreign atoms interact with monolayer structures or surfaces. We performed an investigation on the Mg intercalation into Ti2C building block (MXene) from first-principles simulation. We found that Mg can favorably intercalate into MXene, forming the stable compound Ti2MgC, which corresponds to the stage I in the Li intercalation into graphite. Based on the evaluation of the average cell potential and the energy barrier of Mg diffusion for the most energetically stable structure, our results suggest that Ti2MgC is a potential anode for Mg ion batteries.

  13. Anisotropy of superconducting MgB2 as seen in electron spin resonance and magnetization data.

    PubMed

    Simon, F; Jánossy, A; Fehér, T; Murányi, F; Garaj, S; Forró, L; Petrovic, C; Bud'ko, S L; Lapertot, G; Kogan, V G; Canfield, P C

    2001-07-23

    We observed the conduction electron spin resonance (CESR) in fine powders of MgB2 both in the superconducting and normal states. The Pauli susceptibility is chi(s) = 2.0 x 10(-5) emu/mole in the temperature range of 450 to 600 K. The spin relaxation rate has an anomalous temperature dependence. The CESR measured below T(c) at several frequencies suggests that MgB2 is a strongly anisotropic superconductor with the upper critical field, H(c2), ranging between 2 and 16 T. The high-field reversible magnetization data of a randomly oriented powder sample are well described assuming that MgB2 is an anisotropic superconductor with H(ab)(c2)/H(c)(c2) approximately 6-9.

  14. Alternative wavelengths for laser ranging

    NASA Technical Reports Server (NTRS)

    Hamal, Karel

    1993-01-01

    The following are considered to be necessary to accomplish multicolor laser ranging: the nature of the atmospheric dispersion and absorption, the satellite/lunar/ground retro-array characteristics, and ground/satellite ranging machine performance. The energy balance and jitter budget have to be considered as well. It is concluded that the existing satellite/laser retroreflectors seem inadequate for future experiments. The Raman Stokes/Anti-Stokes (0.68/0.43 micron) plus solid state detector appear to be promising instrumentation that satisfy the ground/satellite and satellite/ground ranging machine requirements on the precision, compactness, and data processing.

  15. GPS test range mission planning

    NASA Astrophysics Data System (ADS)

    Roberts, Iris P.; Hancock, Thomas P.

    The principal features of the Test Range User Mission Planner (TRUMP), a PC-resident tool designed to aid in deploying and utilizing GPS-based test range assets, are reviewed. TRUMP features time history plots of time-space-position information (TSPI); performance based on a dynamic GPS/inertial system simulation; time history plots of TSPI data link connectivity; digital terrain elevation data maps with user-defined cultural features; and two-dimensional coverage plots of ground-based test range assets. Some functions to be added during the next development phase are discussed.

  16. Structural and electronic properties of Mg and Mg-Nb co-doped TiO2 (101) anatase surface

    NASA Astrophysics Data System (ADS)

    Sasani, Alireza; Baktash, Ardeshir; Mirabbaszadeh, Kavoos; Khoshnevisan, Bahram

    2016-10-01

    In this paper, by using density functional theory, Mg and Nb-Mg co-doping of TiO2 anatase (101) surfaces are studied. By studying the formation energy of the defects and the bond length distribution of the surface, it is shown that Mg defects tend to stay as far as possible to induce least possible lattice distortion while Nb and Mg defects stay close to each other to cause less stress to the surface. By investigating band structure of the surface and changes stemmed from the defects, potential effects of Mg and Mg-Nb co-doping of TiO2 surface on dye-sensitized solar cells are investigated. In this study, it is shown that the Nb-Mg co-doping could increase JSC of the surface while slightly decreasing VOC compared to Mg doped surface, which might result in an increase in efficiency of the DSSCs compared to Nb or Mg doped surfaces.

  17. The effect of Mg location on Co-Mg-Ru/γ-Al2O3 Fischer–Tropsch catalysts

    PubMed Central

    Combes, Gary B.; Ozkaya, Don; Enache, Dan I.; Ellis, Peter R.; Kelly, Gordon; Rosseinsky, Matthew J.

    2016-01-01

    The effectiveness of Mg as a promoter of Co-Ru/γ-Al2O3 Fischer–Tropsch catalysts depends on how and when the Mg is added. When the Mg is impregnated into the support before the Co and Ru addition, some Mg is incorporated into the support in the form of MgxAl2O3+x if the material is calcined at 550°C or 800°C after the impregnation, while the remainder is present as amorphous MgO/MgCO3 phases. After subsequent Co-Ru impregnation MgxCo3−xO4 is formed which decomposes on reduction, leading to Co(0) particles intimately mixed with Mg, as shown by high-resolution transmission electron microscopy. The process of impregnating Co into an Mg-modified support results in dissolution of the amorphous Mg, and it is this Mg which is then incorporated into MgxCo3−xO4. Acid washing or higher temperature calcination after Mg impregnation can remove most of this amorphous Mg, resulting in lower values of x in MgxCo3−xO4. Catalytic testing of these materials reveals that Mg incorporation into the Co oxide phase is severely detrimental to the site-time yield, while Mg incorporation into the support may provide some enhancement of activity at high temperature. PMID:26755760

  18. A fundamental study on the [(μ-Cl)3 Mg2 (THF)6 ]+ dimer electrolytes for rechargeable Mg batteries

    DOE PAGESBeta

    Liu, Tianbiao; Cox, Jonathan T.; Hu, Dehong; Deng, Xuchu; Hu, Jianzhi; Hu, Mary Y.; Xiao, Jie; Shao, Yuyan; Tang, Keqi; Liu, Jun

    2015-01-05

    We present a fundamental study on [(μ-Cl)3 Mg2 (THF)6 ]+ dimer electrolytes using various physical methods including Subambient Pressure Ionization with Nanoelectrospray Mass spectrometry (SPIN-MS), Raman spectroscopy, 25Mg{1H} NMR, 27Al{1H} NMR and electrochemical analysis. For the first time, long time sought THF solvated [MgCl]+ species was experimentally characterized by SPIN mass spectrometry in the solution of the Mgdimer containing electrolyte, confirming the mono-Cl- abstraction reaction between MgCl2 and an Al Lewis acid. Solvated MgCl2 in the electrolyte was confirmed by Raman spectroscopy. The experimental results establish the previously proposed dimerization equilibrium of solvated [MgCl]+ and MgCl2 with [(μ-Cl)3Mg2(THF)6]+.more » 25Mg{1H} NMR, 27Al{1H} NMR and electrochemical analysis on chloration reaction of [(μ-Cl)3Mg2(THF)6]AlPh3Cl with external Cl- led to further insights on the coordination chemistry of the dimer electrolyte. Finally, a comprehensive mechanism is proposed for the reversible electrochemical Mg deposition and stripping and Mg2+ and Cl- ion transports of the Mg dimer electrolytes in rechargeable Mg batteries.« less

  19. Alterations of ionized Mg2+ in human blood after exercise.

    PubMed

    Mooren, Frank C; Golf, S W; Lechtermann, A; Völker, K

    2005-07-29

    Magnesium (Mg) is the second most abundant intracellular cation with modulating properties in a number of metabolic processes, e.g. in glycolysis, and intracellular signalling processes, e.g. regulation of ion channels and transporters. There are conflicting data available about the regulation of Mg in blood cells during exercise. Moreover, there are no data available about changes of the metabolic important fraction of ionized Mg(2+) both in blood and in blood cells during exercise. The present study investigated the changes of ionized Mg(2+) and total Mg concentration in different compartments after a stepwise treadmill ergometer test. Intracellular ionized Mg(2+) of thrombocytes and erythrocytes was determined by the magnesium sensitive fluorescent dyes mag-fura-2 and Mag-Green using fluorescence spectroscopy and flow cytometry, respectively. Ionized Mg(2+) in blood/serum was measured by an ion-sensitive microelectrode. Total cellular and serum Mg concentration were investigated using atomic absorbance spectroscopy and photometry, respectively. The present results shown that at the end of the ergometer test, ionized Mg(2+) in both blood and serum and total serum Mg decreased. In contrast, intracellular concentration of ionized Mg increased in both thrombocytes and erythrocytes. Total intracellular Mg was unchanged making a Mg(2+) shift between the intra- and extracellular compartment unlikely. The present study therefore demonstrated opposite changes of the ratio [ionized Mg(2+)]/[total Mg] in the intracellular and the extracellular compartment after anaerobic exercise. In in vitro experiments, similar changes of ionized Mg(2+) in both compartments could be mimicked by application of weak acids like propionic and lactic acid. It is concluded changes in the fraction of ionized Mg(2+) should be high enough to influence intracellular signalling and metabolic processes.

  20. Photodissociation spectroscopy of the Mg{sup +}-acetic acid complex

    SciTech Connect

    Abate, Yohannes; Kleiber, P. D.

    2006-11-14

    We have studied the structure and photodissociation of Mg{sup +}-acetic acid clusters. Ab initio calculations suggest four relatively strongly bound ground state isomers for the [MgC{sub 2}H{sub 4}O{sub 2}]{sup +} complex. These isomers include the cis and trans forms of the Mg{sup +}-acetic acid association complex with Mg{sup +} bonded to the carbonyl O atom of acetic acid, the Mg{sup +}-acetic acid association complex with Mg{sup +} bonded to the hydroxyl O atom of acetic acid, or to a Mg{sup +}-ethenediol association complex. Photodissociation through the Mg{sup +}-based 3p<-3s absorption bands in the near UV leads to direct (nonreactive) and reactive dissociation products: Mg{sup +}, MgOH{sup +}, Mg(H{sub 2}O){sup +}, CH{sub 3}CO{sup +}, and MgCH{sub 3}{sup +}. At low energies the dominant reactive quenching pathway is through dehydration to Mg(H{sub 2}O){sup +}, but additional reaction channels involving C-H and C-C bond activation are also open at higher energies.

  1. Transition probabilities and radiative lifetimes of Mg III

    NASA Astrophysics Data System (ADS)

    Alonso-Medina, A.; Colón, C.; Moreno-Díaz, C.

    2015-03-01

    There have been calculated transition probabilities for 365 lines arising from 2p5 n s(n = 3 , 4 , 5) , 2p5 n p(n = 3 , 4) , 2p5 n d(n = 3 , 4) , 2p5 n f(n = 4 , 5) and 2p5 5g configurations of Mg III and radiative lifetimes corresponding to 89 levels. These values were obtained in intermediate coupling (IC) by using ab initio relativistic Hartree-Fock (HFR) calculations. Later, we use the standard method of least square fitting of experimental energy levels for the IC calculations by means of Cowan's computer codes. The vast majority of the calculated transition probabilities correspond to lines lying in the ultraviolet range (UV) which are of high interest in astrophysics. Our results are compared to those previously reported in the literature. Furthermore, the values of transition probabilities of configuration levels 2p5 4d, 2p5 n f(n = 4 , 5) and 2p5 5g are presented for the first time. In light of these findings, it is possible to extend the range of wavelengths which allows us to estimate the temperature in plasma diagnostic. In addition, our results for radiative lifetimes have been compared to the available experimental values.

  2. Effect of Melt-to-Solid Insert Volume Ratio on Mg/Al Dissimilar Metals Bonding

    NASA Astrophysics Data System (ADS)

    Emami, S. M.; Divandari, M.; Arabi, H.; Hajjari, E.

    2013-01-01

    Compound casting is used as a process to join various similar and dissimilar metallic couples. The ratio of melt-to-solid volume is one of the main factors that can affect the contact time between melt and the solid insert. In this investigation, magnesium and aluminum metals (magnesium as the cast metal and aluminum as the solid insert) having melt-to-solid volume ratios ( V m/ V s) of 1.25, 3, and 5.25 were successfully bonded via compound casting. Results demonstrated that by increasing the ratio of V m/ V s from 1.25 to 5.25, the thickness of the reaction interface between Al and Mg varies within the range of 200 to 1800 μm. X-ray diffraction, scanning electron microscopy, and Vickers microhardness study of the bonding of these two metals showed that the interface consisted of three separate sub-layers within reaction layer. These sub-layers had higher hardness than those of the Al and Mg bulk metals. In all specimens, composition of the sub-layer adjacent to Al (layer I) was Al3Mg2 and that adjacent to Mg (layer III) was Al12Mg17/(Mg) eutectic structure. The intermediate layer composition (layer II) in specimens with volume ratio of 1.25 and 3 was a single-phase Al12Mg17, while for the case of volume ratio 5.25 this sub-layer consisted of Al12Mg17/(Mg) eutectic dispersed in Al12Mg17 intermetallic. The results of this research showed that in low melt/solid volume ratios, diffusion-reaction was the dominant mechanism for formation of Al-Mg intermetallic. However, when V m/ V s and the melt/solid insert contact time increased, the dominant mechanism of Al-Mg intermetallics changed to fusion-solidification due to increase in surface melting of the solid insert. Also the results of push-out tests showed that shear strengths of the interface decrease from 27.1 to 15.1 and 8.3 MPa for the Al/Mg couples prepared at 1.25, 3, and 5.25 V m/ V s respectively.

  3. Airborne 2 color ranging experiment

    NASA Technical Reports Server (NTRS)

    Millar, Pamela S.; Abshire, James B.; Mcgarry, Jan F.; Zagwodzki, Thomas W.; Pacini, Linda K.

    1993-01-01

    Horizontal variations in the atmospheric refractivity are a limiting error source for many precise laser and radio space geodetic techniques. This experiment was designed to directly measure horizontal variations in atmospheric refractivity, for the first time, by using 2 color laser ranging measurements to an aircraft. The 2 color laser system at the Goddard Optical Research Facility (GORF) ranged to a cooperative laser target package on a T-39 aircraft. Circular patterns which extended from the southern edge of the Washington D.C. Beltway to the southern edge of Baltimore, MD were flown counter clockwise around Greenbelt, MD. Successful acquisition, tracking, and ranging for 21 circular paths were achieved on three flights in August 1992, resulting in over 20,000 two color ranging measurements.

  4. Phosphate Capacities of CaF2-MgO and CaF2-CaO-MgO Slags

    NASA Astrophysics Data System (ADS)

    Akbari, F.; Pickles, C. A.

    2015-02-01

    Previously published sulphide capacity data and thermodynamic arguments have been employed to calculate the phosphate capacities and the phosphorus partition ratios between a molten carbon saturated iron alloy and binary CaF2-MgO slags and also ternary CaF2 -CaO-MgO slags at 1450 °C. For the CaF2-MgO binary system, a linear relationship was found between the phosphate and the sulphide capacities as follows: log ? = 1.2 log Cs + 25.2. For the ternary CaF2-CaO-MgO system at 1450 °C, the logarithm of the calculated phosphate capacities ranged from 19.47 to 20.15. With the addition of CaO, the phosphate capacities initially increased, reached a maximum and then decreased slightly. The addition of MgO to the CaF2-CaO system resulted in a decrease in the phosphate capacity. The calculated phosphorus partition ratios increased slightly with increasing mole fraction of CaO in the ternary system.

  5. Texture and microstructure in co-sputtered Mg-M-O (M = Mg, Al, Cr, Ti, Zr, and Y) films

    NASA Astrophysics Data System (ADS)

    Saraiva, M.; Depla, D.

    2012-05-01

    Mg-M-O solid solution films (M = Mg, Al, Cr, Ti, Zr, and Y) with various M contents are grown employing reactive co-sputtering by varying the target-to-substrate distance. It is shown that all films are biaxially aligned. When the two cathodes are equipped with the same target material (Mg), the in-plane alignment is determined by the cathode closest to the substrate, i.e., by the largest material flux. In the case of nearly equal material fluxes from the two cathodes, double in-plane orientation is observed. This is also the case for the Mg-Al-O and Mg-Cr-O films, while the Mg-Ti-O, Mg-Zr-O and Mg-Y-O films exhibit single in-plane orientation. Pole figures indicate that the grains in Mg-M-O (M different than Mg) are titled; in the Mg-Al-O, Mg-Cr-O, and Mg-Ti-O films, the grains tilt towards the Al, Cr, and Ti metal flux, respectively, while the grain tilt of the Mg-Zr-O and Mg-Y-O films is found to be towards the Mg metal flux. Furthermore, SEM cross-sectional images of the Mg-M-O films reveal columnar microstructure with columns tilted to the same direction as the grains. A mechanism which is based on the cation radius change upon the incorporation of an M atom in the MgO lattice is proposed to explain the tilting.

  6. Interface and thickness dependent domain switching and stability in Mg doped lithium niobate

    SciTech Connect

    Neumayer, Sabine M.; Rodriguez, Brian J. E-mail: brian.rodriguez@ucd.ie; Ivanov, Ilia N.; Manzo, Michele; Gallo, Katia E-mail: brian.rodriguez@ucd.ie; Kholkin, Andrei L.

    2015-12-14

    Controlling ferroelectric switching in Mg doped lithium niobate (Mg:LN) is of fundamental importance for optical device and domain wall electronics applications that require precise domain patterns. Stable ferroelectric switching has been previously observed in undoped LN layers above proton exchanged (PE) phases that exhibit reduced polarization, whereas PE layers have been found to inhibit lateral domain growth. Here, Mg doping, which is known to significantly alter ferroelectric switching properties including coercive field and switching currents, is shown to inhibit domain nucleation and stability in Mg:LN above buried PE phases that allow for precise ferroelectric patterning via domain growth control. Furthermore, piezoresponse force microscopy (PFM) and switching spectroscopy PFM reveal that the voltage at which polarization switches from the “up” to the “down” state increases with increasing thickness in pure Mg:LN, whereas the voltage required for stable back switching to the original “up” state does not exhibit this thickness dependence. This behavior is consistent with the presence of an internal frozen defect field. The inhibition of domain nucleation above PE interfaces, observed in this study, is a phenomenon that occurs in Mg:LN but not in undoped samples and is mainly ascribed to a remaining frozen polarization in the PE phase that opposes polarization reversal. This reduced frozen depolarization field in the PE phase also influences the depolarization field of the Mg:LN layer above due to the presence of uncompensated polarization charge at the PE-Mg:LN boundary. These alterations in internal electric fields within the sample cause long-range lattice distortions in Mg:LN via electromechanical coupling, which were corroborated with complimentary Raman measurements.

  7. Testing the cation-hydration effect on the crystallization of Ca-Mg-CO3 systems.

    PubMed

    Xu, Jie; Yan, Chao; Zhang, Fangfu; Konishi, Hiromi; Xu, Huifang; Teng, H Henry

    2013-10-29

    Dolomite and magnesite are simple anhydrous calcium and/or magnesium carbonate minerals occurring mostly at Earth surfaces. However, laboratory synthesis of neither species at ambient temperature and pressure conditions has been proven practically possible, and the lack of success was assumed to be related to the strong solvation shells of magnesium ions in aqueous media. Here, we report the synthesis of MgCO3 and MgxCa(1-x)CO3 (0 < x < 1) solid phases at ambient conditions in the absence of water. Experiments were carried out in dry organic solvent, and the results showed that, although anhydrous phases were readily precipitated in the water-free environment, the precipitates' crystallinity was highly dependent on the Mg molar percentage content in the solution. In specific, magnesian calcite dominated in low [Mg(2+)]/[Ca(2+)] solutions but gave way to exclusive formation of amorphous MgxCa(1-x)CO3 and MgCO3 in high-[Mg(2+)]/[Ca(2+)] and pure-Mg solutions. At conditions of [Mg(2+)]/[Ca(2+)] = 1, both nanocrystals of Ca-rich protodolomite and amorphous phase of Mg-rich MgxCa(1-x)CO3 were formed. These findings exposed a previously unrecognized intrinsic barrier for Mg(2+) and CO3(2-) to develop long-range orders at ambient conditions and suggested that the long-held belief of cation-hydration inhibition on dolomite and magnesite mineralization needed to be reevaluated. Our study provides significant insight into the long-standing "dolomite problem" in geochemistry and mineralogy and may promote a better understanding of the fundamental chemistry in biomineralization and mineral-carbonation processes.

  8. The role of starch doping on the superconducting properties of MgB2

    NASA Astrophysics Data System (ADS)

    Tripathi, D.; Moharana, S. S.; Dey, T. K.

    2014-09-01

    The effect of different amount of starch addition on structural and superconducting properties of superconducting MgB2 has been discussed. The samples are synthesized by conventional solid reaction method. XRD analysis confirms that carbon, which is produced during synthesis due to decomposition of starch, is substituted in the B sites. High resolution transmission electron microscope (HRTEM) picture infers the presence of large number of nanosized precipitates (size ∼10-20 nm) in starch doped MgB2 pellets. Superconducting transition temperature (Tc0) of MgB2 (∼38 K) decreases due to the addition of starch. The critical current density (Jc) of starch added MgB2 samples, however, shows significant improvement in whole field range, especially at high magnetic fields. MgB2 added with 2 wt.% of starch gives the best performance amongst the investigated samples and at 20 K displays ∼42 times enhancement in Jc under 4 T field compared to that for pure MgB2. The field dependence of the critical current density (Jc) of starch added MgB2 is explained fairly well in terms of collective pinning theory. An excellent scaling of the reduced critical current density, Jn(=Jc/Jc(0)) and the reduced field hn (=H/H0) is observed for both pure and starch added MgB2 polycrystalline pellets at different temperatures, where Jc(0) and H0 are the fitting parameters obtained from collective pinning model. However, the normalized pinning force density (FP/Fp(max)) of starch added samples does not display any scaling, but shows an excellent correspondence with modified Dew-Hughes expression. The presence of anisotropy and grain orientation is thought to be responsible for the absence of scaling of normalized pinning force density in starch added MgB2 pellets.

  9. Estimating the Mg II Index from 1961 Through 1981 Using Ca II K Images from the MtWilson Observatory

    NASA Astrophysics Data System (ADS)

    McMullin, D.; Morrill, J. S.; Floyd, L. E.; Weaver, S. J.; Ulrich, R. K.

    2011-12-01

    An empirical model of solar UV spectral irradiance has been developed that is based on observed spectral radiance measurements and full disk Ca II K images. The Mg II index is then calculated from the estimated spectra in a narrow wavelength range (180 Å) near theMg II doublet at 2800 Å. Our long term goal is to expand this wavelength range from 10 to 4000 Å in continuing studies based on spectral data covering this wavelength range (e.g. Skylab, UARS/SUSIM, TIMED/SEE, etc.). Our previous modeling effort produced spectra in this 180 Å range and the resulting Mg II index values for the period from 1991 through 1995 and we have used observations during this time period to validate the model results. The current paper presents results from this model based on a 21-year portion of the recently digitized Ca II K images from the Mt Wilson Observatory (MWO) film archive. Here we present details of the model, the required model modifications, and the resulting Mg II index from 1961 through 1981. Since the NOAA Mg II index did not begin until 1978, the present model results are compared to a Mg II index estimated from the F10.7 radio flux over this 21-year period. The NOAA Mg II index, which is derived from measured UV spectra, is also included for comparison from late 1978 through 1981.

  10. Optical and electrical properties of Mg-doped AlN nanowires grown by molecular beam epitaxy

    SciTech Connect

    Connie, Ashfiqua Tahseen; Zhao, Songrui; Sadaf, Sharif Md.; Shih, Ishiang; Mi, Zetian; Du, Xiaozhang; Lin, Jingyu; Jiang, Hongxing

    2015-05-25

    In this paper, the optical and electrical properties of Mg-doped AlN nanowires are discussed. At room temperature, with the increase of Mg-doping concentration, the Mg-acceptor energy level related optical transition can be clearly measured, which is separated about 0.6 eV from the band-edge transition, consistent with the Mg activation energy in AlN. The electrical conduction measurements indicate an activation energy of 23 meV at 300 K–450 K temperature range, which is significantly smaller than the Mg-ionization energy in AlN, suggesting the p-type conduction being mostly related to hopping conduction. The free hole concentration of AlN:Mg nanowires is estimated to be on the order of 10{sup 16 }cm{sup −3}, or higher.

  11. The possibility of forming a sacrificial anode coating for Mg

    SciTech Connect

    Dudney, Nancy J; Li, Juchuan; Sacci, Robert L; Thomson, Jeffery K

    2014-01-01

    Mg is the most active engineering metal, and is often used as a sacrificial anode/coating to protect other engineering metals from corrosion attack. So far no sacrificial anode coating has been developed or considered for Mg. This study explores the possibility of forming a sacrificial coating for Mg. A lithiated carbon coating and a metaphosphated coating are applied on the Mg surface, respectively, and their open-circuit-potentials are measured in saturated Mg(OH)2 solution. They exhibit more negative potentials than bare Mg. SEM reveals that the metaphosphated coating offers more effective and uniform protection for Mg than the lithiated carbon coating. These preliminary results indicate that development of a sacrificial anode coating for Mg is indeed possible.

  12. Microsolvation of the Mg2SO42+ Cation: Cryogenic Vibrational Spectroscopy of (Mg2+)2SO42-(H2O)n=4-11

    NASA Astrophysics Data System (ADS)

    Kelleher, Patrick J.; DePalma, Joseph W.; Johnson, Christopher J.; Fournier, Joseph; Johnson, Mark

    2015-06-01

    Cryogenic ion vibrational predissociation (CIVP) spectroscopy was used to examine the onset of solvation upon the incremental addition of water molecules to the Mg2SO42+(H2O)n cation (n = 4 - 11). D2 predissociation spectra are reported for each cluster over the range 1000-3800 cm-1. Initially, the Mg2+ atoms each interact with two oxygen atoms on the sulfate anion in a bifurcated arrangement. The breaking of this motif occurs upon addition of the eighth water molecule as evidenced by splitting of the water bend, and broad absorption in the 3000-3400 cm-1 range indicative of hydrogen bonding between the water molecules and sulfate ion.

  13. Electron-Impact Ionization of Mg

    NASA Technical Reports Server (NTRS)

    Boivin, R. F.; Srivastava, S. K.

    1997-01-01

    A pulsed crossed beam technique is used to measure inonization cross-sections of metallic atoms. Relative values of cross-sections of single, double and triple inonization of magnesium have been successfully measured with good accuracy over the o-700 eV range. Absolute values of cross sections have been obtained by normalization to a theoretical value at high electron energy. Results are compared to previously published values and, for single inonization in particular, a comparison with theoretical cross-extions is perfomed.

  14. Impact of Mg Content on (Mg,Zn)O Native Point Defects

    NASA Astrophysics Data System (ADS)

    Ball, Molly; Restrepo, Oscar; Brillson, Leonard; Windl, Wolfgang; Department of Material Science; Engineering Collaboration; Department of Physics Collaboration

    2015-03-01

    The two most thermodynamically stable defects in ZnO are oxygen vacancies (VO) and zinc vacancies (VZn) . These native point defects are electrically charged and can contribute to free carrier densities. Experiment shows that Mg addition to ZnO significantly changes native defect densities. To better understand this dramatic decrease in VZn and VO-related defects with increasing Mg content up to x =0.44 and the subsequent increase, we performed density functional theory (DFT) calculations using PAW potentials within PBE using VASP. The results showed to be very sensitive to DFT method used and chemical-potential calculation. For the latter, the literature shows that one can assume that the oxygen chemical potential equals that of the atoms in the oxygen molecules at a given surrounding partial oxygen pressure. However, one can also postulate that the total defect concentrations conserve the stoichiometry, or limiting potentials from elemental equilibrium phases can be used. The experimentally observed dependence helped identify the correct way to reproduce the experimental dependence of formation energy on Mg concentration, which will be discussed in detail in this presentation.

  15. Enhancing phosphate adsorption by Mg/Al layered double hydroxide functionalized biochar with different Mg/Al ratios.

    PubMed

    Li, Ronghua; Wang, Jim J; Zhou, Baoyue; Awasthi, Mukesh Kumar; Ali, Amjad; Zhang, Zengqiang; Gaston, Lewis A; Lahori, Altaf Hussain; Mahar, Amanullah

    2016-07-15

    Mg/Al ratio plays a significant role for anion adsorption by Mg/Al-layered double hydroxides (Mg/Al-LDHs) modified biochar. In this study, Mg/Al-LDHs biochar with different Mg/Al ratios (2, 3, 4) were prepared by co-precipitation for phosphate removal from aqueous solution. Factors on phosphate adsorption including Mg/Al ratio, pH, and the presence of other inorganic anions were investigated through batch experiments. Increasing Mg/Al ratio in the Mg/Al-LDHs biochar composites generally enhanced phosphate adsorption with Langmuir adsorption maximum calculated at 81.83mg phosphorous (P) per gram of 4:1Mg/Al-LDHs biochar at pH3.0. The adsorption process was best described by the pseudo-second-order kinetic model. Solution pH had greater effects on the phosphate adsorption by Mg/Al LDHs biochar composites with lower Mg/Al ratios. The presence of other inorganic anions decreased the phosphate adsorption efficiency in the order of F(-) > SO4(2-) > NO2(-) >Cl(-). Phosphate adsorption mechanism involves ion exchange, electrostatic attraction and surface inner-sphere complex formation. Overall, Mg/Al-LDHs biochar composites offer a potential alternative of carbon-based adsorbent for phosphate removal from aqueous solution. PMID:27058131

  16. Optical range and range rate estimation for teleoperator systems

    NASA Technical Reports Server (NTRS)

    Shields, N. L., Jr.; Kirkpatrick, M., III; Malone, T. B.; Huggins, C. T.

    1974-01-01

    Range and range rate are crucial parameters which must be available to the operator during remote controlled orbital docking operations. A method was developed for the estimation of both these parameters using an aided television system. An experiment was performed to determine the human operator's capability to measure displayed image size using a fixed reticle or movable cursor as the television aid. The movable cursor was found to yield mean image size estimation errors on the order of 2.3 per cent of the correct value. This error rate was significantly lower than that for the fixed reticle. Performance using the movable cursor was found to be less sensitive to signal-to-noise ratio variation than was that for the fixed reticle. The mean image size estimation errors for the movable cursor correspond to an error of approximately 2.25 per cent in range suggesting that the system has some merit. Determining the accuracy of range rate estimation using a rate controlled cursor will require further experimentation.

  17. Dehydrogenation kinetics of air-exposed MgH2/Mg2Cu and MgH2/MgCu2 studied with in situ X-ray powder diffraction

    NASA Astrophysics Data System (ADS)

    Andreasen, A.; Sørensen, M. B.; Burkarl, R.; Møller, B.; Molenbroek, A. M.; Pedersen, A. S.; Vegge, T.; Jensen, T. R.

    2006-02-01

    The dehydrogenation kinetics of air exposed samples of MgH2/Mg2Cu and MgH2/MgCu2 have been studied with in situ time resolved X-ray powder diffraction. The X-ray setup enabled the recording of full diffraction patterns within 150 s, thereby allowing the study of structural changes combined with simultaneous extraction of kinetic parameters. Phase fractions as a function of time and temperature were derived from series of consecutive diffraction patterns by numerical integration of selected diffraction peaks. The apparent activation energy for the dehydrogenation of the MgH2/Mg2Cu, and MgH2/MgCu2 sample was found to be 108 kJ/mol and 160 kJ/mol, respectively. Furthermore, substantially improved dehydrogenation kinetics of MgH2 and resistance towards oxidation of Mg due to the presence of Mg2Cu/MgCu2 are discussed in relation to previous work.

  18. Geographic range limits: achieving synthesis

    PubMed Central

    Gaston, Kevin J.

    2009-01-01

    Understanding of the determinants of species' geographic range limits remains poorly integrated. In part, this is because of the diversity of perspectives on the issue, and because empirical studies have lagged substantially behind developments in theory. Here, I provide a broad overview, drawing together many of the disparate threads, considering, in turn, how influences on the terms of a simple single-population equation can determine range limits. There is theoretical and empirical evidence for systematic changes towards range limits under some circumstances in each of the demographic parameters. However, under other circumstances, no such changes may take place in particular parameters, or they may occur in a different direction, with limitation still occurring. This suggests that (i) little about range limitation can categorically be inferred from many empirical studies, which document change in only one demographic parameter, (ii) there is a need for studies that document variation in all of the parameters, and (iii) in agreement with theoretical evidence that range limits can be formed in the presence or absence of hard boundaries, environmental gradients or biotic interactions, there may be few general patterns as to the determinants of these limits, with most claimed generalities at least having many exceptions. PMID:19324809

  19. Thermodynamic data of the high-pressure phase Mg5Al5Si6O21(OH)7 (Mg-sursassite)

    NASA Astrophysics Data System (ADS)

    Grevel, K.-D.; Navrotsky, A.; Kahl, W. A.; Fasshauer, D. W.; Majzlan, J.

    Calorimetric and P-V-T data for the high-pressure phase Mg5Al5Si6O21(OH)7 (Mg-sursassite) have been obtained. The enthalpy of drop solution of three different samples was measured by high-temperature oxide melt calorimetry in two laboratories (UC Davis, California, and Ruhr University Bochum, Germany) using lead borate (2PbO.B2O3) at T=700∘C as solvent. The resulting values were used to calculate the enthalpy of formation from different thermodynamic datasets; they range from -221.1 to -259.4kJmol-1 (formation from the oxides) respectively -13892.2 to -13927.9kJmol-1 (formation from the elements). The heat capacity of Mg5Al5Si6O21(OH)7 has been measured from T=50 ∘C to T=500 ∘C by differential scanning calorimetry in step-scanning mode. A Berman and Brown (1985)-type four-term equation represents the heat capacity over the entire temperature range to within the experimental uncertainty: CP (Mg-sursassite) =(1571.104 -10560.89×T-0.5-26217890.0 ×T-2+1798861000.0×T-3) J K-1 mol-1 (T in K). The PVT behaviour of Mg-sursassite has been determined under high pressures and high temperatures up to 8GPa and 800∘C using a MAX 80 cubic anvil high-pressure apparatus. The samples were mixed with Vaseline to ensure hydrostatic pressure-transmitting conditions, NaCl served as an internal standard for pressure calibration. By fitting a Birch-Murnaghan EOS to the data, the bulk modulus was determined as 116.0+/-1.3GPa, (K'=4), VT,0=446.49 3 exp[∫(0.33+/-0.05) × 10-4 + (0.65+/-0.85)×10-8T dT], (KT/T)P=-0.011+/- 0.004GPaK-1. The thermodynamic data obtained for Mg-sursassite are consistent with phase equilibrium data reported recently (Fockenberg 1998); the best agreement was obtained with ΔfH0298 (Mg-sursassite)= -13901.33kJmol-1, and S0298 (Mg-sursassite)= 614.61JK-1mol-1.

  20. Melting relations in the system FeCO3-MgCO3 and thermodynamic modelling of Fe-Mg carbonate melts

    NASA Astrophysics Data System (ADS)

    Kang, Nathan; Schmidt, Max W.; Poli, Stefano; Connolly, James A. D.; Franzolin, Ettore

    2016-09-01

    To constrain the thermodynamics and melting relations of the siderite-magnesite (FeCO3-MgCO3) system, 27 piston cylinder experiments were conducted at 3.5 GPa and 1170-1575 °C. Fe-rich compositions were also investigated with 13 multi-anvil experiments at 10, 13.6 and 20 GPa, 1500-1890 °C. At 3.5 GPa, the solid solution siderite-magnesite coexists with melt over a compositional range of X Mg (=Mg/(Mg + Fetot)) = 0.38-1.0, while at ≥10 GPa solid solution appears to be complete. At 3.5 GPa, the system is pseudo-binary because of the limited stability of siderite or liquid FeCO3, Fe-rich carbonates decomposing at subsolidus conditions to magnetite-magnesioferrite solid solution, graphite and CO2. Similar reactions also occur with liquid FeCO3 resulting in melt species with ferric iron components, but the decomposition of the liquid decreases in importance with pressure. At 3.5 GPa, the metastable melting temperature of pure siderite is located at 1264 °C, whereas pure magnesite melts at 1629 °C. The melting loop is non-ideal on the Fe side where the dissociation reaction resulting in Fe3+ in the melt depresses melting temperatures and causes a minimum. Over the pressure range of 3.5-20 GPa, this minimum is 20-35 °C lower than the (metastable) siderite melting temperature. By merging all present and previous experimental data, standard state (298.15 K, 1 bar) thermodynamic properties of the magnesite melt (MgCO3L) end member are calculated and the properties of (Fe,Mg)CO3 melt fit by a regular solution model with an interaction parameter of -7600 J/mol. The solution model reproduces the asymmetric melting loop and predicts the thermal minimum at 1240 °C near the siderite side at X Mg = 0.2 (3.5 GPa). The solution model is applicable to pressures reaching to the bottom of the upper mantle and allows calculation of phase relations in the FeO-MgO-O2-C system.

  1. Thermodynamics of MgO shocked to 250 GPa and 9000 K

    NASA Astrophysics Data System (ADS)

    Fat'yanov, O. V.; Asimow, P. D.; Ahrens, T. J.

    2011-06-01

    Plate impact experiments in the 200-250 GPa pressure range were done on <100 > single-crystal MgO preheated before compression to 1850 K. Hot Mo(driver)-MgO targets were impacted with Ta flyers launched by the Caltech two-stage light-gas gun up to 7.5 km/s. Radiative temperatures and shock velocities were measured with 3-5% and 1-2% respective uncertainty by a 6-channel pyrometer with 3 ns time resolution, over 500-900 nm spectral range. MgO shock front reflectivity was determined in additional experiments at 220 and 250 GPa using 50/50 high-temperature sapphire beamsplitters. Shock temperatures and preheated MgO Hugoniot data reported here are in good agreement with the corresponding values calculated using Mie-Grüneisen equation of state with γ0 = 1.4 and constant γ / V . Our experiments showed no evidence of MgO melting up to 250 GPa and 9.2 kK. The highest shock temperatures exceed the extrapolated melting curve of Zerr & Boehler by >3000 K at 250 GPa, which seems too much for any realistic superheating.

  2. Mg and Ca isotope signatures of authigenic dolomite in siliceous deep-sea sediments

    NASA Astrophysics Data System (ADS)

    Blättler, Clara L.; Miller, Nathaniel R.; Higgins, John A.

    2015-06-01

    Authigenic carbonates in marine sediments frequently have carbon isotope ratios that reflect local organic carbon processing rather than the δ13C of the global DIC (dissolved inorganic carbon) reservoir, but their contributions to ancient sedimentary sections are difficult to assess. In this study of authigenic dolomite from the Miocene-age Monterey Formation of offshore California, Mg and Ca isotopes are shown to vary with stratigraphic depth as a result of early diagenetic processes. The dolomite is a pre-compaction authigenic phase that occurs as beds and nodules with δ13C ranging from -16 to + 9 ‰. Light δ13C values were likely acquired from the sedimentary zone of microbial sulfate reduction, while heavy δ13C values were acquired from the zone of methanogenesis. Mg and Ca isotopes are roughly anti-correlated, with intervals of negative δ13C associated with low δ26Mg and higher δ 44/40Ca values. The variability is observed over a wide range of length-scales, from 10-2 meters within individual authigenic beds/nodules, to 102 meters over the entire stratigraphic column, and can be understood as the consequence of dolomite precipitation in pore fluids where Mg supply is limited by diffusive transport. The relationship of δ26Mg and δ 44/40Ca to the more common stable isotope measurements of δ13C and δ18O represents a new, diagenetically robust, geochemical fingerprint for identifying synsedimentary authigenic carbonates in the geological record.

  3. APOLLO: millimeter lunar laser ranging

    NASA Astrophysics Data System (ADS)

    Murphy, T. W., Jr.; Adelberger, E. G.; Battat, J. B. R.; Hoyle, C. D.; Johnson, N. H.; McMillan, R. J.; Stubbs, C. W.; Swanson, H. E.

    2012-09-01

    Lunar laser ranging (LLR) has for decades stood at the forefront of tests of gravitational physics, including tests of the equivalence principle (EP). Current LLR results on the EP achieve a sensitivity of Δa/a ≈ 10-13 based on few-centimeter data/model fidelity. A recent push in LLR, called APOLLO (the Apache Point Observatory Lunar Laser-ranging Operation) produces millimeter-quality data. This paper demonstrates the few-millimeter range precision achieved by APOLLO, leading to an expectation that LLR will be able to extend EP sensitivity by an order-of-magnitude to Δa/a ˜ 10-14, once modeling efforts improve to this level.

  4. Solid Solution Effects on the MgAl2O4-MgGa2O4 System

    SciTech Connect

    O'Hara, Kelley; Smith, Jeffrey D; Hemrick, James Gordon

    2009-01-01

    Phase relations between two spinel compounds (MgAl2O4 and MgGa2O4) were studied. Stoichiometric MgAl2O4 was formed in the laboratory through a coprecipitation method. Complete solid solution formation int eh MgAl2O4-MgGa2O4 systems was confirmed through X-ray diffraction analysis. Solid solution between MgAl2O4-MgGa2O4 decreases thermal conductivity at all temperatures up to 900oC. At 200oC with 10 mol% additoin of MgGa2O4 thermal conductivity decreases approximately 25%, and at 900oC there was still an 8% decrease. Additionally, preliminary studies show that porosity between 5% and 10% does not have an appreciable effect on the thermal conductivity in this study.

  5. Improving magnetic properties of MgB2 bulk superconductors by synthetic engine oil treatment

    NASA Astrophysics Data System (ADS)

    Taylan Koparan, E.; Savaskan, B.; Yanmaz, E.

    2016-08-01

    The present study focuses on the effects of standby time of the MgB2 samples immersed in synthetic engine oil on the critical current density (Jc(H)), magnetic field dependence of the pinning force density fp(b) and Tc performances of MgB2 bulk superconductors. Synthetic engine oil was used as a product which is cheap and a rich carbon source. Manufactured MgB2 pellet samples were immersed at different standby time of 30 min, 120 min, 300 min and 1440 min in synthetic engine oil after the first heating process. Finally, MgB2 samples immersed in synthetic engine oil were sintered at 1000 °C and kept for 15 min in Ar atmosphere. The critical current density of all of MgB2 samples immersed at different standby time in engine oil in whole field range was better than that of the pure MgB2 sample because of the number of the pinning centers. The MgB2 sample immersed at 300 min standby time in synthetic engine oil has the best performance compared to other samples. The Jc value for the pure sample is 2.0 × 103 A/cm2, whereas for the MgB2 sample immersed at 300 min standby time in engine oil the Jc is enhanced to 4.8 × 103A/cm2 at 5 K and 3 T. The superconducting transition temperature (Tc) did not change with the increasing standby time of the samples in synthetic engine oil at all. The best diamagnetic property was obtained from the sample which kept in synthetic engine oil for 300 min. Synthetic engine oil treatment results in remarkable improvement of the critical current density and pinning force performances of MgB2 superconductors. It was found that all MgB2 samples have a different pinning property at different measuring temperatures. Using synthetic engine oil as a product which is cheap and a rich carbon source in MgB2 bulk superconductors makes MgB2 samples immersed in synthetic engine oil a good candidate for industrial applications.

  6. RANGE INCREASER FOR PNEUMATIC GAUGES

    DOEpatents

    Fowler, A.H.; Seaborn, G.B. Jr.

    1960-09-27

    An improved pneumatic gage is offered in which the linear range has been increased without excessive air consumption. This has been accomplished by providing an expansible antechamber connected to the nozzle of the gage so that the position of the nozzle with respect to the workpiece is varied automatically by variation in pressure within the antechamber. This arrangement ensures that the nozzle-to-workpiece clearance is maintained within certain limits, thus obtaining a linear relation of air flow to nozzle-to-workpiece clearance over a wider range.

  7. Nanostructured Mg-Al hydrotalcite as catalyst for fine chemical synthesis.

    PubMed

    Basahel, Sulaiman N; Al-Thabaiti, Shaeel A; Narasimharao, Katabathini; Ahmed, Nesreen S; Mokhtar, Mohamed

    2014-02-01

    This paper reviews the recent research of nanostructured Mg-Al hydrotalcite (Mg-Al HT) and its application as an efficient solid base catalyst for the synthesis of fine chemicals. Mg-Al HT has many beneficial features, such as low cost, selectivity, catalytic properties, and wide range of preparation and modification methods. They hold promise for providing sought-after, environmentally friendly technologies for the 21st century. Replacement of currently used homogeneous alkaline bases for the synthesis of fine chemicals by a solid catalyst can result in catalyst re-use and waste stream reduction. We introduce briefly the structure, properties and characterization of the nanostructured Mg-Al HT. The efficacy and benign applications of Mg-Al HT as an alternative solid base to homogenous catalysts in the synthesis of fine chemicals are then reviewed. The challenges for the future applications of Mg-Al HT in the synthesis of fine chemicals in terms of green protocol processes are discussed. PMID:24749466

  8. Influence of layer microstructure on the double nucleation process in Cu/Mg multilayers

    SciTech Connect

    Gonzalez-Silveira, M.; Rodriguez-Viejo, J.; Garcia, G.; Pi, F.; Ager, F. J.; Labar, J. L.; Barna, A.; Menyhard, M.; Kotis, L.

    2006-12-01

    We have investigated by differential scanning calorimetry the thermal evolution of Cu/Mg multilayers with different modulation lengths, ranging from 7/28 to 30/120 nm. The Cu and Mg layers were grown by sequential evaporation in an electron beam deposition system. The phase identification and layer microstructure were determined by cross-section transmission electron microscopy, Rutherford backscattering, and scanning electron microscopy with focused ion beam for sample preparation. Upon heating, the intermetallic CuMg{sub 2} forms at the interfaces until coalescence is reached and thickens through a diffusion-limited process. Cross-section transmission electron microscopy observations show a distinct microstructure at the top and bottom of the as-prepared Mg layers, while no significant differences were seen in the Cu layers. We show that this effect is responsible for the observed asymmetry in the nucleation process between the Cu on Mg and the Mg on Cu interfaces. By modeling the calorimetric data we determine the role of both interfaces in the nucleation and lateral growth stages. We also show that vertical growth proceeds by grain development of the product phase, increasing significantly the roughness of the interfaces.

  9. High-pressure synthesis of pure and doped superconducting MgB2 compounds

    NASA Astrophysics Data System (ADS)

    Toulemonde, P.; Musolino, N.; Flükiger, R.

    2003-02-01

    Superconducting properties of bulk, dense, pure MgB2 and doped (Mg1-xAx)B2 samples with A = Na, Ca, Cu, Ag, Zn and Al were studied for compositional ranges 0 < x leq 0.20. The effects on pinning properties and critical current were investigated, particularly for A = aluminium. The samples were sintered and/or synthesized at high pressure-high temperature in a cubic multi-anvil press (typically 3.5-6 GPa, 900-1000 °C). They were characterized by x-ray diffraction, scanning electron microscopy and their superconducting properties were investigated by ac susceptibility, magnetization (VSM and SQUID) and transport measurements under a magnetic field. Only Al really substitutes on the Mg site. The other elements form secondary phases with B or Mg which do not act as pinning centres. No positive effect is observed on the superconducting properties of the bulk MgB2 samples with these doping elements added: Tc, critical current jc, Hirr and Hc2. For Al, the effect on Hc2 remains small, and the irreversibility line does not move, thus not improving the critical current of the Al-doped MgB2 samples.

  10. Sol-Gel Derived Hydroxyapatite Coating on Mg-3Zn Alloy for Orthopedic Application

    NASA Astrophysics Data System (ADS)

    Singh, Sanjay; Manoj Kumar, R.; Kuntal, Kishor Kumar; Gupta, Pallavi; Das, Snehashish; Jayaganthan, R.; Roy, Partha; Lahiri, Debrupa

    2015-04-01

    In recent years, magnesium and its alloys have gained a lot of interest as orthopedic implant constituents because their biodegradability and mechanical properties are closer to that of human bone. However, one major concern with Mg in orthopedics is its high corrosion rate that results in the reduction of mechanical integrity before healing the bone tissue. The current study evaluates the sol-gel-derived hydroxyapatite (HA) coating on a selected Mg alloy (Mg-3Zn) for decreasing the corrosion rate and increasing the bioactivity of the Mg surface. The mechanical integrity of the coating is established as a function of the surface roughness of the substrate and the sintering temperature of the coating. Coating on a substrate roughness of 15-20 nm and sintering at 400°C shows the mechanical properties in similar range of bone, thus making it suitable to avoid the stress-shielding effect. The hydroxyapatite coating on the Mg alloy surface also increases corrosion resistance very significantly by 40 times. Bone cells are also found proliferating better in the HA-coated surface. All these benefits together establish the candidature of sol-gel HA-coated Mg-3Zn alloy in orthopedic application.

  11. First-principle study of thermoelectric properties of impurity-doped magnesium silicide Mg2Si

    NASA Astrophysics Data System (ADS)

    Funashima, Hiroki

    2014-03-01

    The electronic structure and the thermoelectric properties of Mg2Si doped with several dopants, Al, Bi, Sb, and Zn, are theoretically examined using a first-principles calculation method. Mg2Si is a promising thermoelectric material that is functional in the temperature range from 500 to 800 K. Therefore, it is expected to be useful for recovering waste heat from exhaust gas in automotive applications, incinerators, and boilers. Moreover, this material has several desirable attributes with respect to cost and environmental protection: it is cheap, nontoxic, and composed of elements abundant on Earth. These advantages are important for practical usage in thermoelectric applications. Impurity doping is a well-established way to improve the thermoelectric performance of Mg2Si. Undoped Mg2Si crystals have n-type conductivity, but they can be doped with both n- and p-type impurities. A fundamental understanding of the relationship between impurity doping and the thermoelectric properties of Mg2Si will allow us to provide theoretical guidelines for further development of this material. As an effort toward this goal, we present here the band structure of Mg2Si using the full-potential linearized augmented plane-wave (FLAPW) method based on LDA/DFT and the conductivity.

  12. Intergrain connectivity of MgB{sub 2} ceramics studied by impedance analysis

    SciTech Connect

    Wang, C. C.; Wang, C.; Zeng, R.; Dou, S. X.

    2010-07-15

    First, by using of the conventional Rowell analysis, we demonstrated that the addition of nano BN particles can effectively eliminate MgO and pores in MgB{sub 2} resulting in a very high density and good connectivity of BN-doped MgB{sub 2}. Then, another method--low-frequency dielectric impedance analysis--was introduced to characterize the properties of the grain boundaries of MgB{sub 2}. A comparative impedance study was performed in the frequency range from 100 Hz to 100 MHz on pure and nano BN-doped MgB{sub 2}. The study revealed some following interesting results: (1) a dielectric resonance around frequency of 10{sup 8} in both samples was observed, which was argued to be related to an inductance-capacitance and (2) the pure sample has two dielectric relaxations originating from intergrains, while the doped sample has only one intergranular contribution. This convinces that the electric connectivity of the doped sample is really improved by the addition of nano BN particles. Our results indicate that dielectric technique may be a useful tool to characterize the grain boundary properties and grain boundary-related properties of MgB{sub 2}.

  13. On the cosmic evolution of Fe/Mg in QSO absorption line systems

    NASA Astrophysics Data System (ADS)

    Dey, Arjun; Torrey, Paul; Rubin, Kate H. R.; Zhu, Guangtun Ben; Suresh, Joshua

    2015-08-01

    We investigate the variation of the ratio of the equivalent widths of the Fe II λ2600 line to the Mg II λλ2796, 2803 doublet as a function of redshift in a large sample of absorption lines drawn from the Johns Hopkins University - Sloan Digital Sky Survey Absorption Line Catalog. We find that despite large scatter, the observed ratio shows a trend where the equivalent width ratio R≡ W_{Fe II}/W_{Mg II} decreases monotonically with increasing redshift z over the range 0.55 ≤ z ≤ 1.90. Selecting the subset of absorbers where the signal-to-noise ratio of the Mg II equivalent width W_{Mg II} is ≥ 3 and modelling the equivalent width ratio distribution as a Gaussian, we find that the mean of the Gaussian distribution varies as R∝ (-0.045± 0.005)z. We discuss various possible reasons for the trend. A monotonic trend in the Fe/Mg abundance ratio is predicted by a simple model where the abundances of Mg and Fe in the absorbing clouds are assumed to be the result of supernova (SN) ejecta and where the cosmic evolution in the SNIa and core-collapse SN rates is related to the cosmic star formation rate. If the trend in R reflects the evolution in the abundances, then it is consistent with the predictions of the simple model.

  14. Nutraceutically inspired pectin-Mg(OH)₂ nanocomposites for bioactive packaging applications.

    PubMed

    Moreira, Francys K V; De Camargo, Lais A; Marconcini, José M; Mattoso, Luiz H C

    2013-07-24

    This paper reports on the development of bioactive edible films based on pectin as a dietary matrix and magnesium hydroxide (Mg(OH)2) nanoplates as a reinforcing filler. Nanocomposites of high-methoxyl (HM) and low-methoxyl (LM) pectins were prepared using the casting method at concentrations of Mg(OH)2 ranging from 0.5 to 5 wt %. Atomic force microscopy and FTIR spectroscopy were employed to characterize the nanocomposite structure. The tensile properties and thermal stability of the nanocomposites were also examined to ascertain the effect of Mg(OH)2 inclusion and degree of methoxylation. The results provided evidence that the Mg(OH)2 nanoplates were uniformly dispersed and interacted strongly with the film matrix. The mechanical and thermal properties were significantly improved in the nanocomposite films compared to the control. Mg(OH)2 nanoplates were more effective in improving properties of LM pectin. Preliminary migration studies using arugula leaves confirmed that pectin-Mg(OH)2 nanocomposites can release magnesium hydroxide by contact, demonstrating their potential for magnesium supplementation in bioactive packaging.

  15. Evolution of nanostructure and specific surface area during thermally driven dehydration of Mg(OH)2

    NASA Astrophysics Data System (ADS)

    Pimminger, H.; Habler, G.; Freiberger, N.; Abart, R.

    2016-01-01

    The thermally induced dehydration of micrometer-sized particles of Mg(OH)2 was investigated experimentally at ambient pressure and temperatures ranging from 350 to 1300 °C. Reaction progress is correlated with the evolution of the specific surface area and of the particle internal nanostructure. The maximum specific surface area of about 320 m2/g corresponding to a 70-fold increase relative to the starting material is obtained after heat treatment at 350 °C for about 2 h. This is due to the formation of a highly porous, particle-internal nanostructure comprised of newly crystallized strictly aligned, cube-shaped and nanometer-sized crystals of MgO and about 50 vol% porosity. Associated with the dehydration, intensive fracturing and defoliation occurs parallel to the (0001) plane of the original Mg(OH)2 or (111) of the topotaxially grown MgO. After heat treatment at increasingly higher temperatures, enhanced coarsening and sintering of the MgO crystals and healing of cracks leads to a successive decrease of the specific surface area. After heat treatment at 1300 °C for 2.5 h, the specific surface area has decreased to 5 m2/g close to the value typical for the original Mg(OH)2.

  16. Inter-mineral Mg isotope fractionation during hydrothermal ultramafic rock alteration - Implications for the global Mg-cycle

    NASA Astrophysics Data System (ADS)

    Beinlich, Andreas; Mavromatis, Vasileios; Austrheim, Håkon; Oelkers, Eric H.

    2014-04-01

    Both riverine and ocean waters are enriched in 24Mg compared to the homogeneous chondritic Mg isotopic composition of the Earth's mantle requiring a fractionation step that is generally attributed to low temperature continental crust weathering. Here we present new observations that indicate that this 24Mg enrichment of surface waters may originate from Mg isotope fractionation during the hydrothermal alteration of primary silicate minerals. Mineral separates of hydrothermally altered ultramafic rocks were collected from three different localities in Norway. Coexisting olivine and serpentine exhibit invariant Mg isotope ratios suggesting that serpentinization does not fractionate Mg isotopes. In contrast, carbonation results in significant inter-mineral Mg isotope fractionation between the antigorite, magnesite, and talc. The carbonation of the natural samples is constrained by O isotope thermometry at ∼275 °C and hence closes the temperature gap between previous investigations of the natural distribution of Mg isotopes during surface weathering and magmatic processes. The precursor antigorite has an isotopic composition of δ26Mg (DSM-3)=-0.11±0.05‰, whereas the talc is enriched in 26Mg with mean δMg26=0.17±0.08‰ and the magnesite is depleted in 26Mg with mean δMg26=-0.95±0.15‰. As carbonate minerals dissolve faster than silicate minerals, the chemical weathering of carbonated ultramafic and by analogy mafic rocks on the continents will yield isotopically lighter Mg to natural surface waters consistent with field observations. Moreover, the Mg fractionation observed in this study suggests that sub-seafloor hydrothermal carbonation may be a significant contribution to the Mg isotopic composition of ocean water.

  17. Study of some Mg-based ferrites as humidity sensors

    NASA Astrophysics Data System (ADS)

    Rezlescu, N.; Rezlescu, E.; Doroftei, C.; Popa, P. D.

    2005-01-01

    The micostructure and humidity sensitivity of MgFe2O4 + CaO, Mg0.5Cu0.5Fe1.8Ga0.2O4, Mg0.5Zn0.5Fe2O4 + KCl and MgMn0.2Fe1.8O4 ferrites were investigated. We have found that the humidity sensitivity largely depends on composition, crystallite size, surface area and porosity. The best results concerning humidity sensitivity were obtained for MgMn0.2Fe1.8O4 ferrite.

  18. Effect of MgO spacer and annealing on interface and magnetic properties of ion beam sputtered NiFe/Mg/MgO/CoFe layer structures

    SciTech Connect

    Bhusan Singh, Braj; Chaudhary, Sujeet

    2012-09-15

    The effect of variation in the thickness of ion assisted ion beam sputtered MgO spacer layer deposited at oxygen ion assisted energy of 50 eV on the extent of magnetic coupling of NiFe and CoFe layers in Si/NiFe(10 nm)/Mg(1 nm)/MgO(2,4,6 nm)/CoFe(10 nm) sandwich structure is investigated. At MgO spacer layer thickness of 4 nm, the separate reversal of magnetizations of the two ferromagnetic layers is observed in the hystresis loop recorded along easy direction. This results in a 3.5 Oe wide plateau like region during magnetization reversal, which became 4.5 Oe at 6 nm thin MgO. At 2 nm thin MgO, the absence of plateau during magnetization reversal region revealed ferromagnetic coupling between the two ferromagnetic layers, which is understood to arise due to the growth of very thin and low density (1.22 gm/cc) MgO spacer layer, indicating the presence of pinholes as revealed by x-ray reflectometry. After vaccum annealing (200 Degree-Sign C/1 h), the plateau region for 4 and 6 nm thin MgO case decreased to 1.5 Oe and 2.0 Oe, respectively, due to enhanced interface roughness/mixing. In addition, an enhancement of the in-plane magnetic anisotropy is also observed.

  19. Atmospheric effects and ultimate ranging accuracy for lunar laser ranging

    NASA Astrophysics Data System (ADS)

    Currie, Douglas G.; Prochazka, Ivan

    2014-10-01

    The deployment of next generation lunar laser retroreflectors is planned in the near future. With proper robotic deployment, these will support single shot single photo-electron ranging accuracy at the 100 micron level or better. There are available technologies for the support at this accuracy by advanced ground stations, however, the major question is the ultimate limit imposed on the ranging accuracy due to the changing timing delays due to turbulence and horizontal gradients in the earth's atmosphere. In particular, there are questions of the delay and temporal broadening of a very narrow laser pulse. Theoretical and experimental results will be discussed that address estimates of the magnitudes of these effects and the issue of precision vs. accuracy.

  20. A Computational Investigation of Precipitates in Mg-RE Alloys With Applications To Mg-X Systems

    NASA Astrophysics Data System (ADS)

    Issa, Ahmed

    Increasing fuel efficiency in transportation vehicles is a major policy goal for both government and auto and aerospace manufacturers. Lightweight structural materials, such as magnesium alloys, hold great promise in enabling such fuel efficiency gains. Understanding the controlling factors in Mg alloy strengthening is crucial for the rational design of structurally strong and inexpensive Mg alloys. In this work, we seek to understand the energetic underpinnings giving rise to a class of remarkably strong Mg alloys: Mg-RE systems. We use first-principles methods to efficiently explore seventeen Mg-RE systems, drawing out broad patterns and distilling our knowledge into simple design rules for Mg alloys. We begin by investigating the controlling factors for the Mg-strengthening prismatic plate precipitates in Mg-RE systems, discovering the critical role of strain in such systems. We then proceed to investigate the surprising role of interfacial energies in determining the course of the Mg-RE precipitation reactions. Using strain and interfacial energies, we construct a phase-field model which accurately depicts the precipitate morphology as a function of time and size in a Mg-Nd system. Finally, we combine our gained insights to implement a computational alloy design scheme on a large portion of the periodic table where we seek Mg-strengthening solutes. Our work advances the understanding of strengthening in Mg alloys and lays the groundwork for full scale computational alloy design.

  1. Diffusion Couple Investigation of the Mg-Zn System

    SciTech Connect

    Brennan, Sarah; Bermudez, Katrina; Sohn, Yong Ho; Kulkarni, Nagraj S

    2012-01-01

    Phase layer growth and interdiffusion in the binary Mg-Zn system was investigated utilizing solid-to-solid diffusion couples annealed at 295 , 315 and 325 C for 21, 7 and 5 days, respectively. The diffusion microstructure was examined by scanning electron microscopy and concentration profiles were determined using X-ray energy dispersive spectroscopy and electron microprobe analysis. The Mg solid solution, Mg2Zn11, MgZn2 and Mg2Zn3 in all three couples were observed in addition to the high temperature, Mg51Zn20 phase at 325 C. The MgZn2 phase was observed to grow the thickest layer, followed by the Mg2Zn3 and the Mg2Zn11 phases. Activation energies for the parabolic growth were calculated to be 105 kJ/mol and 207 kJ/mol for the Mg2Zn3 and MgZn2, respectively. Relevant interdiffusion coefficients were calculated for the phases present by analyses of concentration profiles. This study was sponsored by the US Department of Energy, Office of Energy Efficiency and Renewable Energy, Vehicle Technologies Program (DE-AC05-00OR22725).

  2. Anatomy of a Mountain Range.

    ERIC Educational Resources Information Center

    Chew, Berkeley

    1993-01-01

    Provides written tour of Colorado Rockies along San Juan Skyway in which the geological features and formation of the mountain range is explored. Discusses evidence of geologic forces and products such as plate tectonic movement and the Ancestral Rockies; subduction and the Laramide Orogeny; volcanism and calderas; erosion, faulting, land…

  3. Back Home on the Range.

    ERIC Educational Resources Information Center

    Breining, Greg

    1992-01-01

    Presents the history of the buffalo's demise and reemergence in the United States and Canada. Discusses the problems facing herds today caused by a small genetic pool, disease, range concerns, lack of predation, and culling. Points out the benefits of buffalo raising as compared to cattle raising, including the marketing advantages. (MCO)

  4. Physiological characterization of Mg deficiency in Arabidopsis thaliana.

    PubMed

    Hermans, Christian; Verbruggen, Nathalie

    2005-08-01

    Although the symptoms of magnesium deficiency are well documented in plants, the primary physiological effects of low Mg availability remain largely unknown. This paper describes the physiological responses of Mg starvation in Arabidopsis thaliana. Growth characteristics, Mg and sugar concentration, and photochemical performance were measured at regular intervals during the induction of Mg deficiency. These data show that Mg deficiency increased the sugar concentration and altered sucrose export from young source leaves before any noticeable effect on photosynthetic activity was seen. The decline in photosynthetic activity might be elicited by increased leaf sugar concentrations. Transcript levels of Cab2 (encoding a chlorophyll a/b protein) were lower in Mg-deficient plants before any obvious decrease in the chlorophyll concentration. These transcriptional data suggest that the reduction of chlorophyll is a response to sugar levels, rather than a lack of Mg atoms for chelating chlorophyll. PMID:15983014

  5. Mechanical Properties of High Strength Al-Mg Alloy Sheet

    NASA Astrophysics Data System (ADS)

    Choi, Bong-Jae; Hong, Kyung-Eui; Kim, Young-Jig

    The aim of this research is to develop the high strength Al alloy sheet for the automotive body. For the fabrication Al-Mg alloy sheet, the composition of alloying elements was designed by the properties database and CALPHAD (Calculation Phase Diagram) approach which can predict the phases during solidification using thermodynamic database. Al-Mg alloys were designed using CALPHAD approach according to the high content of Mg with minor alloying elements. After phase predictions by CALPHAD, designed Al-Mg alloys were manufactured. Addition of Mg in Al melts were protected by dry air/Sulphur hexafluoride (SF6) mixture gas which can control the severe Mg ignition and oxidation. After rolling procedure of manufactured Al-Mg alloys, mechanical properties were examined with the variation of the heat treatment conditions.

  6. Phase Equilibria, Crystal Structure and Hydriding/Dehydriding Mechanism of Nd4Mg80Ni8 Compound

    NASA Astrophysics Data System (ADS)

    Luo, Qun; Gu, Qin-Fen; Zhang, Jie-Yu; Chen, Shuang-Lin; Chou, Kuo-Chih; Li, Qian

    2015-10-01

    In order to find out the optimal composition of novel Nd-Mg-Ni alloys for hydrogen storage, the isothermal section of Nd-Mg-Ni system at 400 °C is established by examining the equilibrated alloys. A new ternary compound Nd4Mg80Ni8 is discovered in the Mg-rich corner. It has the crystal structure of space group I41/amd with lattice parameters of a = b = 11.2743(1) Å and c = 15.9170(2) Å, characterized by the synchrotron powder X-ray diffraction (SR-PXRD). High-resolution transmission electron microscopy (HR-TEM) is used to investigate the microstructure of Nd4Mg80Ni8 and its hydrogen-induced microstructure evolution. The hydrogenation leads to Nd4Mg80Ni8 decomposing into NdH2.61-MgH2-Mg2NiH0.3 nanocomposites, where the high density phase boundaries provide a great deal of hydrogen atoms diffusion channels and nucleation sites of hydrides, which greatly enhances the hydriding/dehydriding (H/D) properties. The Nd4Mg80Ni8 exhibits a good cycle ability. The kinetic mechanisms of H/D reactions are studied by Real Physical Picture (RPP) model. The rate controlling steps are diffusion for hydriding reaction in the temperature range of 100 ~ 350 °C and surface penetration for dehydriding reaction at 291 ~ 347 °C. In-situ SR-PXRD results reveal the phase transformations of Mg to MgH2 and Mg2Ni to Mg2NiH4 as functions of hydrogen pressure and hydriding time.

  7. Phase Equilibria, Crystal Structure and Hydriding/Dehydriding Mechanism of Nd4Mg80Ni8 Compound

    PubMed Central

    Luo, Qun; Gu, Qin-Fen; Zhang, Jie-Yu; Chen, Shuang-Lin; Chou, Kuo-Chih; Li, Qian

    2015-01-01

    In order to find out the optimal composition of novel Nd-Mg-Ni alloys for hydrogen storage, the isothermal section of Nd-Mg-Ni system at 400 °C is established by examining the equilibrated alloys. A new ternary compound Nd4Mg80Ni8 is discovered in the Mg-rich corner. It has the crystal structure of space group I41/amd with lattice parameters of a = b = 11.2743(1) Å and c = 15.9170(2) Å, characterized by the synchrotron powder X-ray diffraction (SR-PXRD). High-resolution transmission electron microscopy (HR-TEM) is used to investigate the microstructure of Nd4Mg80Ni8 and its hydrogen-induced microstructure evolution. The hydrogenation leads to Nd4Mg80Ni8 decomposing into NdH2.61-MgH2-Mg2NiH0.3 nanocomposites, where the high density phase boundaries provide a great deal of hydrogen atoms diffusion channels and nucleation sites of hydrides, which greatly enhances the hydriding/dehydriding (H/D) properties. The Nd4Mg80Ni8 exhibits a good cycle ability. The kinetic mechanisms of H/D reactions are studied by Real Physical Picture (RPP) model. The rate controlling steps are diffusion for hydriding reaction in the temperature range of 100 ~ 350 °C and surface penetration for dehydriding reaction at 291 ~ 347 °C. In-situ SR-PXRD results reveal the phase transformations of Mg to MgH2 and Mg2Ni to Mg2NiH4 as functions of hydrogen pressure and hydriding time. PMID:26471964

  8. Relativity in Satellite Laser Ranging

    NASA Astrophysics Data System (ADS)

    Ries, John C.

    2009-05-01

    Satellite laser ranging (SLR) is the measurement of the round-trip light time of ultra-short laser pulses to satellites deploying specifically designed retroreflectors. The ranging data are used to determine cm-precision satellite orbits, temporal variations in the Earth's gravity field, mm/yr accuracy determinations of station motion on a global scale, and fundamental physical constants. The SLR stations form an important part of the international network of space geodetic observatories that define and maintain the International Terrestrial Reference System. Starting in 1964, the precision of satellite laser ranging has improved from a few meters to a few mm for the better stations. With a measurement accuracy better than the part-per-billion level, the effects General Relativity must be considered. These include additional perturbations to the orbit dynamics, corrections to the round-trip light-time computation, and fundamental aspects of space-time in the definition of the geocentric reference frame. While these effects are significant, they are generally not large enough to provide useful tests of General Relativity. An important exception, however, is the relativistic prediction of the Lense-Thirring orbit precession, i.e the effect of `frame-dragging’ on the satellite orbit due to the spinning Earth's mass. While the signal is large enough to be easily observed with satellite laser ranging, the Lense-Thirring measurement uncertainty is limited by the knowledge of the even zonal harmonics of the Earth's gravity field that also produce Newtonian secular orbit precessions. However, this problem has been overcome with the dramatically improved models resulting from the joint NASA-DLR Gravity Recovery and Climate Experiment (GRACE) mission. Using laser ranging to the LAGEOS satellites, it is possible to confirm the General Relativity prediction of the Lense-Thirring precession with an uncertainty better than 15%. This research was supported by the National

  9. The calcite → aragonite transformation in low-Mg marble: Equilibrium relations, transformations mechanisms, and rates

    USGS Publications Warehouse

    Hacker, Bradley R.; Rubie, David C.; Kirby, Stephen H.; Bohlen, Steven R.

    2005-01-01

    Experimental transformation of a rather pure natural calcite marble to aragonite marble did not proceed via the expected straightforward polymorphic replacement. Instead, the small amount of Mg in the starting material (0.36 wt %) was excluded from the growing aragonite and diffused preferentially into the remaining calcite grains, producing Mg-rich calcite rods that persisted as relicts. Nucleation of aragonite occurred exclusively on grain boundaries, with aragonite [001] oriented subparallel to calcite [0001]. The aragonite crystals preferentially consumed the calcite crystal on which they nucleated, and the reaction fronts developed preferentially along the {010} and {110} planes of aragonite. Each aragonite neoblast that grew was nearly free of Mg (typically <0.1 wt %). The excess Mg was taken up by the calcite grains in between, stabilizing them and causing a few volume percent rodlike relicts of Mg-enriched calcite (up to 10 wt % MgO) to be left behind by the advancing reaction front. The aragonite growth rates are approximately linear and range from ∼3 × 10−11 m s−1 at 600°C to ∼9 × 10−9 m s−1 at 850°C, with an apparent activation enthalpy of 166 ± 91 kJ mol−1. This reaction mechanism and the resultant texture are akin to cellular precipitation reactions in metals. Similar transformation textures have been reported from high-Mg marbles in Japan and China that disproportionated to low-Mg calcite and dolomite.

  10. Effect of MgO Additive on Volumetric Expansion of Self-Degradable Cements

    SciTech Connect

    Sugama T.; Warren, J.; Butcher, T.

    2011-09-30

    We identified hard-burned magnesium oxide (MgO) as a suitable expansive additive for improving the plugging performance of self-degradable, temporary sodium silicate-activated slag/Class C fly ash (SSASC) blend cement sealers into rock fractures in Enhanced Geothermal Systems (EGSs). MgO extended the volumetric expansion of sealers during their exposure to a hydrothermal environment at 200 C under pressures, ranging from 300 to 1500 psi. A great expansion ratc of 19.3% was observed by adding 3.0 wt% MgO under 300 psi pressure, thus promising to plug thoroughly inner fracture. When the pressure was increased from 300 psi to 1500 psi, the expansion rate of cement markedly reduced, corresponding to the formaLion of crack-free specimens and the improvement of compressive strength. However, with 3.0 wt% MgO, the specimens still engendered the generation of numerous visual cracks, although they were prepared under a high pressure of 1500 psi. The effective content of MgO in minimizing and eliminating the generation of cracks was 2.0 wt%, which provided a moderate expansion of {ge} 0.5%. The compressive strength of 2.0 wt% MgO specimens made under a pressure of 300 psi rose {approx} 1.7-fold to 4816 psi with an increasing pressure to 1500 psi. The in-situ growth of brucite crystal formed by the hydrothermal hydration of MgO was responsive for such an expansion of the SSASC cement; meanwhile. two crystalline hydrothermal reaction products, 1.1 nm tobermorite and calcium silicate hydrated, contributed to the development of the sealer's compressive strength. Thus, the increasing pressure seems to suppress and control a growth rate of brucite crystal in response to a lower extension of expansion. Furthermore, all MgO-conlaining SSASC sealers possessed the water-catalyzed self-degradable properties.

  11. Reduced enthalpy of metal hydride formation for Mg-Ti nanocomposites produced by spark discharge generation.

    PubMed

    Anastasopol, Anca; Pfeiffer, Tobias V; Middelkoop, Joost; Lafont, Ugo; Canales-Perez, Roger J; Schmidt-Ott, Andreas; Mulder, Fokko M; Eijt, Stephan W H

    2013-05-29

    Spark discharge generation was used to synthesize Mg-Ti nanocomposites consisting primarily of a metastable body-centered-cubic (bcc) alloy of Mg and Ti. The bcc Mg-Ti alloy transformed upon hydrogenation into the face-centered-cubic fluorite Mg1-yTiyHx phase with favorable hydrogen storage properties. Both metal and metal hydride nanocomposites showed a fractal-like porous morphology, with a primary particle size of 10-20 nm. The metal content of 70 atom % (at %) Mg and 30 at % Ti, consistently determined by XRD, TEM-EDS, and ICP-OES, was distributed uniformly across the as-prepared sample. Pressure-composition isotherms for the Mg-Ti-H nanocomposites revealed large differences in the thermodynamics relative to bulk MgH2, with a much less negative enthalpy of formation of the hydride as small as -45 ± 3 kJ/molH2 as deduced from van't Hoff plots. The plateau pressures of hydrogenation were substantially higher than those for bulk MgH2 in the low temperature range from 150 to 250 °C. The reaction entropy was simultaneously reduced to values down to 84 ± 5 J/K mol H2, following a linear relationship between the enthalpy and entropy. Plausible mechanisms for the modified thermodynamics are discussed, including the effect of lattice strains, the presence of interfaces and hydrogen vacancies, and the formation of excess free volume due to local deformations. These mechanisms all rely on the finely interdispersed nanocomposite character of the samples which is maintained by grain refinement.

  12. Phenomenological two-gap model for the specific heat of MgB2

    SciTech Connect

    Bouquet, F.; Wang, Y.; Fisher, R.A.; Hinks, D.G.; Jorgensen, J.D.; Junod, A.; Phillips, N.E.

    2001-06-22

    The authors show that the specific heat of the superconductor MgB{sub 2} in zero field, for which significant non-BCS features have been reported, can be fitted, essentially within experimental error, over the entire range of temperature to T{sub c} by a phenomenological two-gap model. The resulting gap parameters agree with previous determinations from band-structure calculations, and from various spectroscopic experiments. The determination from specific heat, a bulk property, shows that the presence of two superconducting gaps in MgB{sub 2} is a volume effect.

  13. Experimental hybrid power transmission line with liquid hydrogen and MgB2-based superconducting cable

    NASA Astrophysics Data System (ADS)

    Kostyuk, V. V.; Antyukhov, I. V.; Blagov, E. V.; Vysotsky, V. S.; Katorgin, B. I.; Nosov, A. A.; Fetisov, S. S.; Firsov, V. P.

    2012-03-01

    Results of developing and testing an experimental hybrid power transmission line with liquid hydrogen and superconducting power (SCP) cable based on magnesium diboride (MgB2) are presented. Critical currents of the MgB2 based prototype SCP cable have been determined for the first time at the forced flow of liquid hydrogen in a temperature interval of 20-26 K. Various regimes of SCP cable cryostatting with both subcooled saturated liquid hydrogen have been tested in a broad range of supply rates (7-220 g/s) and pressures (0.15-0.4 MPa).

  14. The preliminary study of the quench protection of an MgB2

    NASA Astrophysics Data System (ADS)

    Juster, F. P.; Berriaud, C.; Bonelli, A.; Pasquet, R.; Przybilski, H.; Schild, T.; Scola, L.

    2014-01-01

    In the framework of general studies currently carried out at CEA/Saclay in collaboration with Sigmaphi Company on dry MgB2 magnet operating at 10 K and medium range field, 1 T up to 4 T., we plan to build a prototype-coil with a commercial MgB2 wire. This coil, the nominal axial magnetic field of which is 1 tesla, will be placed in a 3 teslas background field generated by a classical NbTi coil. This paper deals with the preliminary quench protection studies including stability and quench propagation modeling.

  15. Optically stimulated luminescence in NaMgF{sub 3}:Eu{sup 2+}

    SciTech Connect

    Dotzler, C.; Williams, G. V. M.; Rieser, U.; Edgar, A.

    2007-09-17

    Optically stimulated luminescence (OSL) and thermoluminescence (TL) measurements were performed on polycrystalline NaMgF{sub 3}:Eu{sup 2+} as well as sintered and quenched NaMgF{sub 3}:Eu{sup 2+} after exposure to ionizing radiation. The authors find a range of TL traps and the sintering and quenching process reduces the concentration of shallow traps. The resultant time integrated OSL intensity is linear from microgray dose levels to approximately 100 Gy, and hence this material is suitable for a personal and environmental dosimetry, where low dose levels are encountered and high sensitivity is required.

  16. Transformation of echinoid Mg calcite skeletons by heating

    NASA Astrophysics Data System (ADS)

    Dickson, J. A. D.

    2001-02-01

    Interambularcral plates of echinoid Heterocentrotus trigonarius, composed of Mg calcite 1 (≈14 mol% MgCO 3), were heated in three timed series of experiments at 300°C. Dried plate fragments and fragments with added water were heated separately in pressurized bombs. X-ray powder diffractometry, unit cell dimensions, and phase compositions are used to monitor reaction progress. After 10 h heating in the bombs dolomite (43.5 mol% MgCO 3) and Mg calcite appear (4-7 mol% MgCO 3); by 20 h all Mg calcite 1 is consumed, and at 120 h dolomite composition has evolved to ≈47 mol% MgCO 3 and calcite to ≈2 mol% MgCO 3. Whole plates heated at 300°C in an open muffle furnace develop dolomite (≈42 mol% MgCO 3) and Mg calcite 2 (≈6 mol% MgCO 3) after 10 h and remain compositionally invariant throughout subsequent heating to 620 h. Limited skeletal water catalyzes the early reaction but escapes from the open furnace and consequently reaction ceases after ≈10 h. The experimentally produced dolomite has relative Mg-Ca ordering of 75% to 79%. The stabilization of echinoid Mg calcite by heating at 300°C to a mixture of dolomite and calcite occurs through a dissolution/precipitation reaction. The alteration fabric produced within the stereom consists of irregularly shaped, branched dolomite crystals > 5 μm homoaxially set in a calcite 2 (bomb) or Mg calcite 2 (furnace) matrix. Round and tubular pores 1 to 5 μm are randomly distributed throughout this fabric. The stereom pore system remains intact during furnace heating but is destroyed during heating in bombs. The texture of experimentally stabilized echinoid skeletons is different from that of fossil echinoderms that are composed of microrhomic dolomite homoaxially set in a single calcite crystal.

  17. The Effects of Temperature and Salinity on Mg Incorporation in Planktonic Foraminifera Globigerinoides ruber (white): Results from a Global Sediment Trap Mg/Ca Database

    NASA Astrophysics Data System (ADS)

    Gray, W. R.; Weldeab, S.; Lea, D. W.

    2015-12-01

    Mg/Ca in Globigerinoides ruber is arguably the most important proxy for sea surface temperature (SST) in tropical and sub tropical regions, and as such guides our understanding of past climatic change in these regions. However, the sensitivity of Mg/Ca to salinity is debated; while analysis of foraminifera grown in cultures generally indicates a sensitivity of 3 - 6% per salinity unit, core-top studies have suggested a much higher sensitivity of between 15 - 27% per salinity unit, bringing the utility of Mg/Ca as a SST proxy into dispute. Sediment traps circumvent the issues of dissolution and post-depositional calcite precipitation that hamper core-top calibration studies, whilst allowing the analysis of foraminifera that have calcified under natural conditions within a well constrained period of time. We collated previously published sediment trap/plankton tow G. ruber (white) Mg/Ca data, and generated new Mg/Ca data from a sediment trap located in the highly-saline tropical North Atlantic, close to West Africa. Calcification temperature and salinity were calculated for the time interval represented by each trap/tow sample using World Ocean Atlas 2013 data. The resulting dataset comprises >240 Mg/Ca measurements (in the size fraction 150 - 350 µm), that span a temperature range of 18 - 28 °C and 33.6 - 36.7 PSU. Multiple regression of the dataset reveals a temperature sensitivity of 7 ± 0.4% per °C (p < 2.2*10-16) and a salinity sensitivity of 4 ± 1% per salinity unit (p = 2*10-5). Application of this calibration has significant implications for both the magnitude and timing of glacial-interglacial temperature changes when variations in salinity are accounted for.

  18. Deep traps and photo-electric properties of p-Si/MgO/n-Zn{sub 1−x}Mg{sub x}O heterojunction

    SciTech Connect

    Placzek-Popko, E. Paradowska, K. M.; Gumienny, Z.; Biegański, P.; Pietrzyk, M. A.; Kozanecki, A.

    2015-08-21

    In the paper, the photoluminescence (PL) measurements, current–voltage–temperature (I-V-T) measurements, space charge techniques (C-V and deep level transient spectroscopy (DLTS)), and photocurrent spectral characteristics have been applied to investigate defects in p-Si/MgO/ n-Zn{sub 1−x}Mg{sub x}O heterojunction (HJ). The HJ structure was grown on p-type Si (111) substrate with resistivity equal to 0.1 Ω cm by the plasma-assisted molecular beam epitaxy technique. A radio-frequency cell was used for the generation of oxygen plasma. PL spectrum let us determine the Mg content ∼10%. Besides the excitonic Zn{sub 0.9}Mg{sub 0.1}O line, the PL spectrum also contains green and yellow emission bands indicating the presence of defect states in the investigated structures. I-V measurements reveal the rectifying properties of the HJ and the current thermally activated with a trap with the activation energy equal to 0.42 eV. DLTS studies yield the majority trap of the activation energy 0.42 eV, confirming the result obtained from the I-V measurements. It was found that the defects related to this trap have a point like behaviour. A spectral characteristic of the photocurrent shows that the p-Si/MgO/n-Zn{sub 1−x}Mg{sub x}O HJ may be applied as a photodiode operating within the wavelength range of 300 nm-1100 nm. The dark current transport and photocurrent spectrum were explained using the Anderson model of a HJ.

  19. Tuning the Mg/Ca Paleothermometer for High-Latitude Species and Insights into Intraspecific and Intrashell Variability

    NASA Astrophysics Data System (ADS)

    Davis, C. V.; Fehrenbacher, J. S.; Russell, A. D.; Spero, H. J.; Hill, T. M.

    2015-12-01

    The Mg/Ca of planktic foraminifera shells has become a widely used paleothermometer. However, culture-based calibrations have been confined primarily to low-latitude species with limited data from species growing below 12°C. Some core-top calibrations on high-latitude Neogloboquadrinids raise questions about the influence of [CO3-2] and low Mg/Ca "crusts" on shell geochemistry (e.g. 1). This study seeks to extend the low temperature range of culture-based calibrations to temperatures relevant in high-latitudes and active upwelling areas, taking into account the wide range of [CO3-2] observed in these environments. We further examine whether intrashell geochemical variability in the form of "crusting" poses a limitation to Mg/Ca paleothermometry of crust-forming species. Here we present the results of laboratory experiments with living Neogloboquadrina incompta and Neogloboquadrina pachyderma collected and cultured at UC Davis Bodega Marine Laboratory at temperatures between 6° and 12°C and a range of [CO3-2]. We use a combination of Laser Ablation Inductively Coupled Mass Spectrometry and Electron Microprobe mapping, to analyze both intraspecific and intrashell variability in Mg/Ca. We extend existing culture-based temperature calibrations to 6°C, while accounting for the effect of environmental [CO3-2]. Single-shell analyses reveal a high degree of intraspecific variability in the Mg/Ca of calcite grown under stable laboratory conditions. Intrashell analyses identify characteristic low Mg/Ca "crusts" in N. incomptagrown at constant temperature, which record chamber average Mg/Ca within the range of uncrusted conspecifics grown at the same temperature. 1. R. Kozdon et al., Reassessing Mg/Ca temperature calibrations of Neogloboquadrina pachyderma (sinistral) using paired δ44/40Ca and Mg/Ca measurements. Geochem Geophys. 10, Q03005 (2009).

  20. Incidence of strong Mg II absorbers towards different types of quasars

    NASA Astrophysics Data System (ADS)

    Joshi, Ravi; Chand, Hum; Gopal-Krishna

    2013-10-01

    We report the first comparative study of strong Mg II absorbers (Wr ≥ 1.0 Å) seen towards radio-loud quasars of core-dominated (CDQ) and lobe-dominated (LDQ) types and normal quasars (QSOs). The CDQ and LDQ samples were derived from the Sloan Digital Sky Survey Data Release 7 after excluding known `broad-absorption-line' quasars and blazars. The Mg II associated absorption systems having a velocity offset v < 5000 km s-1 from the systemic velocity of the background quasar were also excluded. Existing spectroscopic data for redshift-matched sightlines of 3975 CDQs and 1583 LDQs, covering an emission redshift range 0.39-4.87, were analysed and 864 strong Mg II absorbers were found, covering the redshift range 0.45-2.17. The conclusions reached using this well-defined large data set of strong Mg II absorbers are (i) the number density, dN/dz, towards CDQs shows a small, marginally significant excess (˜9 per cent at 1.5σ significance) over the estimate available for QSOs; (ii) in the redshift space, this difference is reflected in terms of a 1.6σ excess of dN/dz over the QSOs, within the narrow redshift interval 1.2-1.8; (iii) the dN/dβ distribution (with β = v/c) for CDQs shows a significant excess (at 3.75σ level) over the distribution found for a redshift- and luminosity-matched sample of QSOs, at β in the range 0.05-0.1. This leads us to infer that a significant fraction of strong Mg II absorption systems seen in this offset velocity range are probably associated with the CDQs and might be accelerated into the line of sight by their powerful jets and/or due to the accretion-disc outflows close to our direction. Support to this scenario comes from a consistency check in which we consider only the spectral range corresponding to β > 0.2. The computed redshift distribution for strong Mg II absorbers towards CDQs now shows excellent agreement with that known for QSOs, as indeed is expected for purely intervening absorption systems. Thus, it appears that for

  1. Mg isotopes in biocarbonates: new insight into vital effects associated to echinoderms and bivalves calcification

    NASA Astrophysics Data System (ADS)

    Planchon, F.; Hermans, J.; Borremans, C.; Dubois, P.; Poulain, C.; Paulet, Y.; Andre, L.

    2007-12-01

    specific control of isotopic exchange by ACC. For bivalves, we considered one clam species (Ruditapes Philippinarum) from two different sampling sites in the gulf of Morbihan (Brittany, France). One site (Locmariaquer, Loc) is coastal and marine while the other (Le bono, BO) located upstream in the Auray river. For each site and specimen, we considered all reservoirs involved in the shell build-up: seawater, internal fluids with hemolymph (H) and extrapaleal fluid (EPF), soft tissues with mantle, muscle and remaining part (R) and finally aragonitic shells. Water d26Mg are -0.82 at Loc and -0.79 at BO and appear to be highly similar to internal fluids values (EPF and H), -0.6 for Loc and -0.8 for BO. The soft tissues with mean values of -2.7 (Mantle), -2.1 (Muscle), -2.8 (R) at both sites, show pronounced enrichments in the light isotopic fraction of Mg. The shells display the widest range of Mg isotopic signatures with -1.9 at Loc and -4.2 at BO suggesting that different routes of fractionation are acting. The shell signature at Loc similar to aragonitic coral (-1.9) suggests that moderate biological effects have influenced the shell composition at this site. In contrast, at BO, the very light signature of the shell suggests that a significant fraction of Mg has been internally recycled by the clam and used for the building of the shell.

  2. Structural organization, micro-phase separation and polyamorphism of liquid MgSiO3 under compression

    NASA Astrophysics Data System (ADS)

    San, Luyen Thi; Van Hong, Nguyen; Iitaka, Toshiaki; Hung, Pham Khac

    2016-03-01

    The structure, structural change and micro-phase separation in liquid MgSiO3 under pressure are studied by molecular dynamics simulation with pair-wise potentials. Models consisting of 5000 atoms are constructed at 3500 K in the 0-30 GPa pressure range. The structural organization and structural phase transition under compression as well as network topology of liquid MgSiO3 are clarified through analysis and visualization of molecular dynamics simulation data. The short-range structure, intermediate-range structure and the degree of polymerization as well as structural, compositional and dynamical heterogeneities are also discussed in detail.

  3. Cascade Mountain Range in Oregon

    USGS Publications Warehouse

    Sherrod, David R.

    2016-01-01

    Along its Oregon segment, the Cascade Range is almost entirely volcanic in origin. The volcanoes and their eroded remnants are the visible magmatic expression of the Cascadia subduction zone, where the offshore Juan de Fuca tectonic plate is subducted beneath North America. Subduction occurs as two lithospheric plates collide, and an underthrusted oceanic plate is commonly dragged into the mantle by the pull of gravity, carrying ocean-bottom rock and sediment down to where heat and pressure expel water. As this water rises, it lowers the melting temperature in the overlying hot mantle rocks, thereby promoting melting. The molten rock supplies the volcanic arcs with heat and magma. Cascade Range volcanoes are part of the Ring of Fire, a popular term for the numerous volcanic arcs that encircle the Pacific Ocean.

  4. Long range handheld thermal imager

    NASA Astrophysics Data System (ADS)

    Seibel, Edward; Struckhoff, Andrew; McDaniel, Robert; Shamai, Shlomo

    2006-05-01

    Today's warfighter requires a lightweight, high performance thermal imager for use in night and reduced visibility conditions. To fill this need, the United States Marine Corps issued requirements for a Thermal Binocular System (TBS) Long Range Thermal Imager (LRTI). The requirements dictated that the system be lightweight, but still have significant range capabilities and extended operating time on a single battery load. Kollsman, Inc. with our partner Electro-Optics Industries, Ltd. (ElOp) responded to this need with the CORAL - a third-generation, Military Off-the-Shelf (MOTS) product that required very little modification to fully meet the LRTI specification. This paper will discuss the LRTI, a successful result of size, weight and power (SWaP) tradeoffs made to ensure a lightweight, but high performance thermal imager.

  5. Contrails reduce daily temperature range.

    PubMed

    Travis, David J; Carleton, Andrew M; Lauritsen, Ryan G

    2002-08-01

    The potential of condensation trails (contrails) from jet aircraft to affect regional-scale surface temperatures has been debated for years, but was difficult to verify until an opportunity arose as a result of the three-day grounding of all commercial aircraft in the United States in the aftermath of the terrorist attacks on 11 September 2001. Here we show that there was an anomalous increase in the average diurnal temperature range (that is, the difference between the daytime maximum and night-time minimum temperatures) for the period 11-14 September 2001. Because persisting contrails can reduce the transfer of both incoming solar and outgoing infrared radiation and so reduce the daily temperature range, we attribute at least a portion of this anomaly to the absence of contrails over this period. PMID:12167846

  6. Contrails reduce daily temperature range.

    PubMed

    Travis, David J; Carleton, Andrew M; Lauritsen, Ryan G

    2002-08-01

    The potential of condensation trails (contrails) from jet aircraft to affect regional-scale surface temperatures has been debated for years, but was difficult to verify until an opportunity arose as a result of the three-day grounding of all commercial aircraft in the United States in the aftermath of the terrorist attacks on 11 September 2001. Here we show that there was an anomalous increase in the average diurnal temperature range (that is, the difference between the daytime maximum and night-time minimum temperatures) for the period 11-14 September 2001. Because persisting contrails can reduce the transfer of both incoming solar and outgoing infrared radiation and so reduce the daily temperature range, we attribute at least a portion of this anomaly to the absence of contrails over this period.

  7. Dual-color ultraviolet photodetector based on mixed-phase-MgZnO/i-MgO/p-Si double heterojunction

    NASA Astrophysics Data System (ADS)

    Xie, X. H.; Zhang, Z. Z.; Shan, C. X.; Chen, H. Y.; Shen, D. Z.

    2012-08-01

    We report a dual-color ultraviolet (UV) photodetector based on mixed-phase-MgZnO/i-MgO/p-Si double heterojunction. The device exhibits distinct dominant responses at solar blind (250 nm) and visible blind (around 330 nm) UV regions under different reverse biases. By using the energy band diagram of the structure, it is found that the bias-tunable two-color detection is originated from different valence band offset between cubic MgZnO/MgO and hexagonal MgZnO/MgO. Meanwhile, due to the large conduction band offset at the Si/MgO interface, the visible-light photoresponse from Si substrate is suppressed.

  8. Hammersley Range, northern Western Australia

    NASA Technical Reports Server (NTRS)

    1990-01-01

    The oval shaped basin of the sedimentary rocks of the Hammersley Range, northern Western Australia (23.0S, 119.0E) dominates the center of this near nadir view. The Fortescue River is the remarkably straight, fault controlled feature bordering the Hammersley on the north. Sand dunes are the main surface features in the northeast and southwest. Many dry lakebeds can be seen to the east as light grey colored patches along the watercourses.

  9. Propagator for finite range potentials

    SciTech Connect

    Cacciari, Ilaria; Moretti, Paolo

    2006-12-15

    The Schroedinger equation in integral form is applied to the one-dimensional scattering problem in the case of a general finite range, nonsingular potential. A simple expression for the Laplace transform of the transmission propagator is obtained in terms of the associated Fredholm determinant, by means of matrix methods; the particular form of the kernel and the peculiar aspects of the transmission problem play an important role. The application to an array of delta potentials is shown.

  10. Range determination for scannerless imaging

    DOEpatents

    Muguira, Maritza Rosa; Sackos, John Theodore; Bradley, Bart Davis; Nellums, Robert

    2000-01-01

    A new method of operating a scannerless range imaging system (e.g., a scannerless laser radar) has been developed. This method is designed to compensate for nonlinear effects which appear in many real-world components. The system operates by determining the phase shift of the laser modulation, which is a physical quantity related physically to the path length between the laser source and the detector, for each pixel of an image.

  11. Range expansion of heterogeneous populations.

    PubMed

    Reiter, Matthias; Rulands, Steffen; Frey, Erwin

    2014-04-11

    Risk spreading in bacterial populations is generally regarded as a strategy to maximize survival. Here, we study its role during range expansion of a genetically diverse population where growth and motility are two alternative traits. We find that during the initial expansion phase fast-growing cells do have a selective advantage. By contrast, asymptotically, generalists balancing motility and reproduction are evolutionarily most successful. These findings are rationalized by a set of coupled Fisher equations complemented by stochastic simulations. PMID:24766021

  12. Range Expansion of Heterogeneous Populations

    NASA Astrophysics Data System (ADS)

    Reiter, Matthias; Rulands, Steffen; Frey, Erwin

    2014-04-01

    Risk spreading in bacterial populations is generally regarded as a strategy to maximize survival. Here, we study its role during range expansion of a genetically diverse population where growth and motility are two alternative traits. We find that during the initial expansion phase fast-growing cells do have a selective advantage. By contrast, asymptotically, generalists balancing motility and reproduction are evolutionarily most successful. These findings are rationalized by a set of coupled Fisher equations complemented by stochastic simulations.

  13. Short-range communication system

    NASA Technical Reports Server (NTRS)

    Alhorn, Dean C. (Inventor); Howard, David E. (Inventor); Smith, Dennis A. (Inventor)

    2012-01-01

    A short-range communication system includes an antenna, a transmitter, and a receiver. The antenna is an electrical conductor formed as a planar coil with rings thereof being uniformly spaced. The transmitter is spaced apart from the plane of the coil by a gap. An amplitude-modulated and asynchronous signal indicative of a data stream of known peak amplitude is transmitted into the gap. The receiver detects the coil's resonance and decodes same to recover the data stream.

  14. The International Laser Ranging Service

    NASA Astrophysics Data System (ADS)

    Pearlman, M. R.; Degnan, J. J.; Bosworth, J. M.

    2002-07-01

    The International Laser Ranging Service (ILRS) was established in September 1998 to support programs in geodetic, geophysical, and lunar research activities and to provide the International Earth Rotation Service (IERS) with products important to the maintenance of an accurate International Terrestrial Reference Frame (ITRF). Now in operation for nearly two years, the ILRS develops (1) the standards and specifications necessary for product consistency, and (2) the priorities and tracking strategies required to maximize network efficiency. The Service collects, merges, analyzes, archives and distributes satellite and lunar laser ranging data to satisfy a variety of scientific, engineering, and operational needs and encourages the application of new technologies to enhance the quality, quantity, and cost effectiveness of its data products. The ILRS works with (1) new satellite missions in the design and building of retroreflector targets to maximize data quality and quantity, and (2) science programs to optimize scientific data yield. The ILRS is organized into permanent components: (1) a Governing Board, (2) a Central Bureau, (3) Tracking Stations and Subnetworks, (4) Operations Centers, (5) Global and Regional Data Centers, and (6) Analysis, Lunar Analysis, and Associate Analysis Centers. The Governing Board, with broad representation from the international Satellite Laser Ranging (SLR) and Lunar Laser Ranging (LLR) community, provides overall guidance and defines service policies, while the Central Bureau oversees and coordinates the daily service activities, maintains scientific and technological data bases, and facilitates communications. Active Working Groups in (1) Missions, (2) Networks and Engineering, (3) Data Formats and Procedures, (4) Analysis, and (5) Signal Processing provide key operational and technical expertise to better exploit current capabilities and to challenge the ILRS participants to keep pace with evolving user needs. The ILRS currently

  15. Magnesium and cadmium containing Heusler phases REPd2Mg, REPd2Cd, REAg2Mg, REAu2Mg and REAu2Cd

    NASA Astrophysics Data System (ADS)

    Johnscher, Michael; Stein, Sebastian; Niehaus, Oliver; Benndorf, Christopher; Heletta, Lukas; Kersting, Marcel; Höting, Christoph; Eckert, Hellmut; Pöttgen, Rainer

    2016-02-01

    Twenty-eight new Heusler phases REPd2Mg, REPd2Cd, REAg2Mg, REAu2Mg and REAu2Cd with different rare earth elements were synthesized from the elements in sealed niobium ampoules in a water-cooled sample chamber of an induction furnace. The samples were characterized by powder X-ray diffraction. The cell volumes show the expected lanthanide contraction. The structures of YPd2Cd, GdPd2Cd, GdAu2Cd, Y1.12Ag2Mg0.88 and GdAg2Mg were refined based on single crystal diffractometer data. The magnetic properties were determined for fifteen phase pure samples. LuAu2Mg is a weak Pauli paramagnet with a susceptibility of 1.0(2) × 10-5 emu mol-1 at room temperature. The remaining samples show stable trivalent rare earth ions and most of them order magnetically at low temperatures. The ferromagnet GdAg2Mg shows the highest ordering temperature of TC = 98.3 K. 113Cd and 89Y MAS NMR spectra of YAu2Cd and YPd2Cd confirm the presence of unique crystallographic sites. The resonances are characterized by large Knight shifts, whose magnitude can be correlated with electronegativity trends.

  16. Clustering effects in 48Cr composite nuclei produced via the 24Mg+24Mg reaction

    NASA Astrophysics Data System (ADS)

    Di Nitto, A.; Vardaci, E.; Brondi, A.; La Rana, G.; Cinausero, M.; Gelli, N.; Moro, R.; Nadtochy, P. N.; Prete, G.; Vanzanella, A.

    2016-04-01

    The nuclear properties of 48Cr composite α -like nuclei produced at 60 MeV of excitation energy via the 24Mg+24Mg reaction were investigated. This excitation energy corresponds to a resonance with a narrow width (170 keV) observed in the elastic and inelastic channels, which was interpreted as a highly deformed state. To gain insight on the deformation of this state exclusive measurements of light charged particles were carried out with 8 π LP apparatus at Laboratori Nazionali di Legnaro and compared to statistical model predictions. The measured of α -particle energy spectra, α -evaporation residues, α -α , and α -α -α correlations indicate the limitation of the rotating liquid drop model in describing the nuclear shape of the compound nucleus along the decay cascade. To reproduce the full set of experimental data very elongated nuclear shapes had to be considered, with an axis ratio 3 :1 at the resonance angular momentum. This large deformation is consistent with previous findings for α -like nuclei and with the predictions of the cranked cluster model.

  17. Mg isotope fractionation during microbe-mineral interactions

    NASA Astrophysics Data System (ADS)

    Kim, Insu; Ryu, Jong-sik; Lee, Kwang-sik; Lee, Dongho

    2014-05-01

    Magnesium is involved in various biogeochemical processes important to the global climate change over geological time-scale. Mg isotopes allow us to directly trace the Mg cycle in the Earth's surface but the factors controlling Mg isotopic compositions have not fully understood yet. Here, we conducted a batch experiment using two bacterial species (Shewanella putrefaciens and Burkholderia fungorum) and three major Mg-bearing minerals (biotite, dolomite and hornblende). All elemental concentrations increased by 336 h and then reached to steady-state values, of which Mg concentrations varied depending on minerals and bacterial species. This result indicates that the mineral dissolution is affect by the presence of microbes, which either provide organic acids or attach onto mineral surface. The Mg isotopic compositions of initial minerals biotite, dolomite and hornblende are -0.35o of biotite, -0.99o of dolomite, and -0.24o of hornblende, in δ26Mg. Similarly, δ26Mg values increased by 336 h and reached to steady-state values, which also varied with minerals and microbes. During dissolution of three minerals, the light isotope of Mg is preferentially incorporated into the dissolved phases and then the dissolved δ26Mg values become consistent with those of minerals with the time.

  18. Ion beam assisted deposition of MgO barriers for magnetic tunnel junctions

    SciTech Connect

    Cardoso, S.; Macedo, R. J.; Ferreira, R.; Augusto, A.; Wisniowski, P.; Freitas, P. P.

    2008-04-01

    This work reports for the first time results on MgO tunnel junctions prepared by ion beam. The MgO barrier was deposited from a ceramic MgO target using an assisted beam, following the deposition and assisted beam phase diagram which relate the beam profile with the current and energy. The deposition rate for MgO is calculated with and without assisted beam, and compared with the experimental values. The MgO film growth on Ta/CoFeB/MgO simple stacks was optimized aiming at a (002) preferred orientation for the MgO growth, measured by x-ray diffraction. The optimum assist beam energy was tuned for each deposition beam condition (+800,+1000,+1200 V), using assist beams of 40 mA ({approx}130 {mu}A/cm{sup 2}) with 0 to +600 V. Without assist beam, no texture is observed for the MgO, while the (002) orientation appears for assisted deposition. The optimum range of assist voltages is large, being limited by the onset of etching at high voltages, reducing the deposition rate. Magnetic tunnel junctions were deposited with the structure Ta 50 A/Ru 200 A/Ta 50 A/Mn{sub 78}Ir{sub 22} 150 A/Co{sub 90}Fe{sub 10} 30 A/Ru 8 A/Co{sub 56}Fe{sub 24}B{sub 20} 40 A/MgO t/Co{sub 56}Fe{sub 24}B{sub 20} 30 A/Ru 30 A/Ta 50 A, with the MgO barrier deposited with the conditions optimized by x rays. The effect of the assist beam energy on the junction properties (magnetoresistance and magnetization) are discussed. Tunnel magnetoresistance values up to 110%, with RA products of 100-400 {omega} {mu}m{sup 2}, for 11 A thick MgO barriers are obtained using assisted deposition with a +100 V assist beam, which is a major improvement of the {approx}30% of TMR, if no beam is used.

  19. Dual range infinitely variable transmission

    SciTech Connect

    Eichenberger, P.

    1989-10-31

    This patent describes in a transaxle assembly comprising an infinitely variably belt and sheave assembly driving sheave portions and driven sheave portions, a housing assembly enclosing the sheave portions. It includes a torque input shaft coaxially disposed with respect to the driving sheave portions, means for drivably connecting the driving sheave portions and the input shaft; a secondary shaft having an axis in spaced parallel relationship with respect to the torque input shaft. The driven sheave portions being mounted for rotation on the axis of the secondary shaft; a flexible drive member driveable connected to the input sheave portions and the output sheave portions. The flexible drive member engaging the input and output sheave portions at an effective pitch diameter for each sheave portion; fluid pressure servo means for adjustable positioning the sheave portions to effect variations in the effective pitch diameters of the driving sheave portions and the driven sheave portions; a countershaft mounted in spaced parallel dispositions with respect to the secondary shaft, a bearing assembly means for journalling the countershaft in the housing assembly, a high speed range gear train connecting the secondary shaft with the countershaft; fluid pressure operated clutch means for activating and deactivating selectively the high speed range gear train and the low speed range gear train; and planetary forward and reverse means disposed concentrically with respect to the countershaft including clutch means.

  20. Range gated strip proximity sensor

    DOEpatents

    McEwan, Thomas E.

    1996-01-01

    A range gated strip proximity sensor uses one set of sensor electronics and a distributed antenna or strip which extends along the perimeter to be sensed. A micro-power RF transmitter is coupled to the first end of the strip and transmits a sequence of RF pulses on the strip to produce a sensor field along the strip. A receiver is coupled to the second end of the strip, and generates a field reference signal in response to the sequence of pulse on the line combined with received electromagnetic energy from reflections in the field. The sensor signals comprise pulses of radio frequency signals having a duration of less than 10 nanoseconds, and a pulse repetition rate on the order of 1 to 10 MegaHertz or less. The duration of the radio frequency pulses is adjusted to control the range of the sensor. An RF detector feeds a filter capacitor in response to received pulses on the strip line to produce a field reference signal representing the average amplitude of the received pulses. When a received pulse is mixed with a received echo, the mixing causes a fluctuation in the amplitude of the field reference signal, providing a range-limited Doppler type signature of a field disturbance.

  1. Range gated strip proximity sensor

    DOEpatents

    McEwan, T.E.

    1996-12-03

    A range gated strip proximity sensor uses one set of sensor electronics and a distributed antenna or strip which extends along the perimeter to be sensed. A micro-power RF transmitter is coupled to the first end of the strip and transmits a sequence of RF pulses on the strip to produce a sensor field along the strip. A receiver is coupled to the second end of the strip, and generates a field reference signal in response to the sequence of pulse on the line combined with received electromagnetic energy from reflections in the field. The sensor signals comprise pulses of radio frequency signals having a duration of less than 10 nanoseconds, and a pulse repetition rate on the order of 1 to 10 MegaHertz or less. The duration of the radio frequency pulses is adjusted to control the range of the sensor. An RF detector feeds a filter capacitor in response to received pulses on the strip line to produce a field reference signal representing the average amplitude of the received pulses. When a received pulse is mixed with a received echo, the mixing causes a fluctuation in the amplitude of the field reference signal, providing a range-limited Doppler type signature of a field disturbance. 6 figs.

  2. White-light luminescence properties of Mg and Sn doped ZnO prepared by thermal oxidation

    SciTech Connect

    Zeng, Jun; Fan, Huiqing; Xue, Jun; Wang, Yangli

    2014-02-01

    Graphical abstract: The PL spectrum of MgSnZnO was measured at room temperature through multi-peak Gaussian fitting, it is found that the broad emission is composed of six peaks. - Highlights: • Mg and Sn doped ZnO are synthesized by thermal oxidation of MgSnZn alloys. • The structure is characterized by XRD and micro-Raman scattering technology. • The optical properties are characterized by photoluminescence spectrum. • The resulting Mg and Sn doped ZnO shows white photoluminescence. - Abstract: This work reports that Mg and Sn doped ZnO (MgSnZnO) are synthesized by thermal oxidation of MgSnZn alloys. The structure and optical properties are characterized by X-ray diffraction (XRD), micro-Raman scattering technology and photoluminescence spectrum. Interestingly, the resulting MgSnZnO shows white photoluminescence. Additionally, the photoluminescence spectrum of MgSnZnO shows two broad emission bands ranging from 360 to 420 nm and 420 to 630 nm, respectively. Through multi-peak Gaussian fitting, it is found that the broad emission is composed of six Gaussian peaks. The six Gaussian peaks are centrered at 383 nm, 397 nm, 455 nm, 516 nm, 560 nm and 614 nm.

  3. The A1Σu+ system of Mg2

    NASA Astrophysics Data System (ADS)

    Knöckel, Horst; Rühmann, Steffen; Tiemann, Eberhard

    2014-10-01

    The A1Σu+-X1Σg+ UV spectrum of Mg2 has been investigated with high resolution employing Fourier-transform spectroscopy and laser excitation. Computer simulation and fit of line positions to the overlapping structures in the spectra yield precise transition frequencies. Starting with the well characterized ground state X1Σg+ from former work, we derived excited energy levels and report on the evaluation of the A1Σu+ excited state, which is found to interact with another electronic state, which we identify as the lower part of the (1)1Πu state. A coupled channels fit to the level energies of the upper state yields a reliable potential energy curve for the A1Σu+ state for the range of vibrational levels 1 ≤ v' ≤ 46. A potential energy curve for the (1)1Πu state is proposed, but the (1)1Πu state is only characterized by its coupling to the A state, and no direct transition to a level of the (1)1Πu state could be uniquely identified due to the overlapping spectral structures. Supplementary material in the form of one dat file available from the Journal web page at http://dx.doi.org/10.1140/epjd/e2014-50289-9

  4. Solubility and release of fenbufen intercalated in Mg, Al and Mg, Al, Fe layered double hydroxides (LDH): The effect of Eudragit S 100 covering

    SciTech Connect

    Arco, M. del; Fernandez, A.; Martin, C.; Rives, V.

    2010-12-15

    Following different preparation routes, fenbufen has been intercalated in the interlayer space of layered double hydroxides with Mg{sup 2+} and Al{sup 3+} or Mg{sup 2+}, Al{sup 3+} and Fe{sup 3+} in the layers. Well crystallized samples were obtained in most of the cases (intercalation was not observed by reconstruction of the MgAlFe matrix), with layer heights ranging between 16.1 and 18.8 A. The presence of the LDH increases the solubility of fenbufen, especially when used as a matrix. The dissolution rate of the drug decreases when the drug is intercalated, and is even lower in those systems containing iron; release takes place through ionic exchange with phosphate anions from the solution. Preparation of microspheres with Eudragit S 100 leads to solids with an homogeneous, smooth surface with efficient covering of the LDH surface, as drug release was not observed at pH lower than 7. - Graphical abstract: LDHs containing Mg, Al, Fe increase fenbufen solubility, release takes place through ionic exchange with phosphate anions from the medium. Spherical solids with homogeneous, smooth surface are formed when using Eudragit S 100, efficiently covering the LDH surface. Display Omitted

  5. Cardiovascular effect of dental anesthesia with articaine (40 mg with epinefrine 0,5 mg % and 40 mg with epinefrine 1 mg%) versus mepivacaine (30mg and 20 mg with epinefrine 1 mg%) in medically compromised cardiac patients: A cross-over, randomized, single blinded study

    PubMed Central

    Torres-Lagares, Daniel; Serrera-Figallo, María Á.; Corcuera-Flores, José R.; Machuca-Portillo, Carmen; Castillo-Oyagüe, Raquel; Gutiérrez-Pérez, José L.

    2012-01-01

    Objectives: The aim of the present study is to compare cardiovascular safety profiles of two dental anesthetics: articaine versus two standard mepivacaine solutions used during etiological periodontal treatment in cardiovascular patients. Study Design: Using a cross-over study design, ten cardiovascular patients were randomly assigned to dental treatment with 1.8mL of a local anesthetic injected on each quadrant of the mouth: Articaine (40mg with Epinephrine 0.5mg % and 40mg with Epinephrine 1mg %) or Mepivacaine (30mg and 20mg with Epinephrine 1mg %). A computer programme enabled continuous longitudinal data collection: O2 saturation, blood pressure (BP) and heart rate (HR). Results: No severe clinical side effects were observed. During the treatment period, we observed statistically significant differences as regards HR between injections with and without adrenalin (p< 0.039) and as regards systolic (p< 0.046) and diastolic (p < 0.046) blood pressure during the stabilization period. In both cases, the parameters under study increase. Age, gender, jaw treated, treatment duration and the rest of cardiovascular variables did not affect the results. None of the patients underwent ischemic alterations or any other complication derived from the treatment or the anesthesia. Conclusions: According to the results of our study, dental anesthetics with standard concentrations of Epinephrine seem to alter HR and BP. Although no cardiac ischemic alterations or any other cardiovascular complications have been observed, we must be cautious with the administration of anesthetics containing vasoconstrictors in patients with cardiovascular diseases. Key words:Dental anesthesia, cardiovascular diseases, chronic periodontitis, drug toxicity. PMID:22322521

  6. First principle investigation of the electronic and thermoelectric properties of Mg2C

    NASA Astrophysics Data System (ADS)

    Kulwinder, Kaur; Ranjan, Kumar

    2016-02-01

    In this paper, electronic and thermoelectric properties of Mg2C are investigated by using first principle pseudo potential method based on density functional theory and Boltzmann transport equations. We calculate the lattice parameters, bulk modulus, band gap and thermoelectric properties (Seebeck coefficient, electrical conductivity, and thermal conductivity) of this material at different temperatures and compare them with available experimental and other theoretical data. The calculations show that Mg2C is indirect band semiconductor with a band gap of 0.75 eV. The negative value of Seebeck coefficient shows that the conduction is due to electrons. The electrical conductivity decreases with temperature and Power factor (PF) increases with temperature. The thermoelectric properties of Mg2C have been calculated in a temperature range of 100 K-1200 K. Kulwinder Kaur thanks Council of Scientific & Industrial Research (CSIR), India for providing fellowship.

  7. 24Mg( p, α)21Na reaction study for spectroscopy of 21Na

    NASA Astrophysics Data System (ADS)

    Cha, S. M.; Chae, K. Y.; Kim, A.; Lee, E. J.; Ahn, S.; Bardayan, D. W.; Chipps, K. A.; Cizewski, J. A.; Howard, M. E.; Manning, B.; O'Malley, P. D.; Ratkiewicz, A.; Strauss, S.; Kozub, R. L.; Matos, M.; Pain, S. D.; Pittman, S. T.; Smith, M. S.; Peters, W. A.

    2015-10-01

    The 24Mg( p, α)21Na reaction was measured at the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory in order to better constrain the spins and parities of the energy levels in 21Na for the astrophysically important 17F( α, p)20Ne reaction rate calculation. 31-MeV proton beams from the 25-MV tandem accelerator and enriched 24Mg solid targets were used. Recoiling 4He particles from the 24Mg( p, α)21Na reaction were detected by a highly segmented silicon detector array which measured the yields of 4He particles over a range of angles simultaneously. A new level at 6661 ± 5 keV was observed in the present work. The extracted angular distributions for the first four levels of 21Na and the results from distorted wave Born approximation (DWBA) calculations were compared to verify and extract the angular momentum transfer.

  8. The millimeter and submillimeter rotational spectrum of the MgCN radical (X (sup 2) Sigma(+))

    NASA Technical Reports Server (NTRS)

    Anderson, M. A.; Steimle, T. C.; Ziurys, L. M.

    1994-01-01

    The pure rotational spectrum of the MgCN radical has been recorded in the laboratory using millimeter/submillimeter direct absorption spectroscopy. Twenty-seven rotational transitions of the species were observed in the range 101-376 GHz and indicate that the molecule is linear with a (sup 2)Sigma(+) ground electronic state, as predicted by theory. Spin rotation interactions were resolved in the spectra, but no hyperfine splittings were observed, which would originate with the nitrogen nuclear spin. The rotational and fine-structure constants were determined for this radical from a nonlinear least-squares fit to the data using a (sup 2)Sigma Hamiltonian. MgCN is of astrophysical interest because it is the metastable isomer of MgNC, which recently has been detected toward IRC +10216

  9. Deep-sea ostracode shell chemistry (Mg:Ca ratios) and late Quaternary Arctic Ocean history

    USGS Publications Warehouse

    Cronin, T. M.; Dwyer, G.S.; Baker, P.A.; Rodriguez-Lazaro, J.; Briggs, W.M., Jr.

    1996-01-01

    The magnesium:calcium (Mg:Ca) and strontium:calcium (Sr:Ca) ratios were investigated in shells of the benthic ostracode genus Krithe obtained from 64 core-tops from water depths of 73 to 4411 m in the Arctic Ocean and Nordic seas to determine the potential of ostracode shell chemistry for paleoceanographic study. Shells from the abyssal plain and ridges of the Nansen, Amundsen and Makarov basins and the Norwegian and Greenland seas had a wide scatter of Mg:Ca ratios ranging from 0.007 to 0.012 that may signify post-mortem chemical alteration of the shells from Arctic deep-sea environments below about 1000 m water depth. There is a positive correlation (r2=0.59) between Mg:Ca ratios and bottom-water temperature in Krithe shells from water depths <900 m.

  10. Magnetization and electric transport properties of single-crystal MgB2 nanowires.

    PubMed

    Wu, Cen-Shawn; Chang, Yu-Cheng; Chen, Weimeng; Chen, Chinping; Feng, Qingrong

    2012-11-23

    High quality single-crystal magnesium diboride (MgB(2)) nanowires with lengths exceeding 10 μm were successfully synthesized by hybrid physical chemical vapor deposition. The magnetization and electrical transport properties of single-crystal MgB(2) nanowires (NWs) were measured. The superconducting transition temperature of the NWs was 37 K, as confirmed by magnetization measurements. The disordered behavior of the nanowires was observed by four-terminal current-voltage characteristic measurements of an individual NW from T = 10 to 300 K. The temperature-dependent resistivity curves for seven NWs collapsed into a universal curve described by the variable range hopping model, showing intrinsic nonmetallic transport properties. This implies that the granular superconducting defect states are critical to the superconductivity of the individual MgB(2) NWs.

  11. Removal of perchlorate in water by calcined MgAl-CO3 layered double hydroxides.

    PubMed

    Yang, Yiqiong; Gao, Naiyun; Deng, Yang; Yu, Guoping

    2013-04-01

    Perchlorate is widely known as an inorganic endocrine disruptor. In this study, MgAl-CO3 layered double hydroxides with different Mg/Al molar ratios were prepared using a coprecipitation method and followed by a calcination process at a temperature range of 300 to 700 degrees C. Results showed that the best synthesis conditions were a calcination temperature of 550 degrees C and Mg/Al molar ratio of 3. Further, the adsorbent and its adsorption product were characterized by x-ray diffraction, Fourier transform-infrared spectroscopy, and thermogravimetric-differential thermal analysis. The layered double hydroxides structures in the adsorbent were lost during calcination at 550 degrees C but were reconstructed subsequent to adsorption of perchlorate, indicating that the "memory effect" appeared to play an important role in perchlorate adsorption. The perchlorate adsorption pattern was best described by the pseudo-second-order kinetics model, while the Freundlich isotherms appropriately explained perchlorate adsorption data.

  12. The roles of Zr and Mn in processing and superplasticity of Al-Mg alloys

    NASA Technical Reports Server (NTRS)

    Mcnelley, Terry R.; Hales, S. J.

    1990-01-01

    Processing studies have been conducted on two alloys, of nominal compositions Al-10Mg-0.1Zr or Al-10Mg-0.5Mn, in order to clarify the role of the dispersoid forming Zr or Mn additions. Mechanical property data reveal that the Mn-containing alloy has a lower maximum elongation but exhibits superplastic response over a broader range of temperature. Microstructural investigations and texture analyses were utilized to assess the effect of the presence of Al8Mg5 precipitates in combination with either Al3Zr or Al6Mn dispersoid particles during isothermal rolling at 300 C and subsequent tensile deformation at temperatures from 200-425 C.

  13. Microstructure-property relationships in Al-Cu-Li-Ag-Mg Weldalite (tm) alloys, part 2

    NASA Technical Reports Server (NTRS)

    Langan, T. J.; Pickens, J. R.

    1991-01-01

    The microstructure and mechanical properties of the ultrahigh strength Al-Cu-Li-Ag-Mg alloy, Weldalite (tm) 049, were studied. Specifically, the microstructural features along with tensile strength, weldability, Young's modulus and fracture toughness were studied for Weldalite (tm) 049 type alloys with Li contents ranging from 1.3 to 1.9 wt. pct. The tensile properties of Weldalite 049 and Weldalite 049 reinforced with TiB2 particles fabricated using the XD (tm) process were also evaluated at cryogenic, room, and elevated temperatures. In addition, an experimental alloy, similar in composition to Weldalite 049 but without the Ag+Mg, was fabricated. The microstructure of this alloy was compared with that of Weldalite 049 in the T6 condition to assess the effect of Ag+Mg on nucleation of strengthening phases in the absence of cold work.

  14. Preparation and characterisation of Ru doped MgB2

    NASA Astrophysics Data System (ADS)

    Grivel, J.-C.; Holte, O. J.

    2013-12-01

    Samples with Mg1-xRuxB2 nominal stoichiometry were prepared by sintering at 800 °C. The critical transition temperature decreases up to a substitution level of x ≈ 0.015. A maximum solubility limit slightly in excess of 1 at.% Ru for Mg is confirmed by energy dispersive spectroscopy measurements. From and beyond this limit, an unidentified phase appears in the X-ray diffraction patterns. Interestingly, the lattice parameters of the MgB2 phase are constant up to x = 0.015, but start to decrease for higher Ru contents. This feature could be related to the fact that a Mg-Ru impurity phase results in a Mg-deficient (Mg,Ru)B2 matrix.

  15. Order-Disorder Transition and Phase Separation in the MgB2 Metallic Sublattice Induced by Al Doping.

    PubMed

    Brutti, S; Gigli, G

    2009-07-14

    MgB2 is a superconductor constituted by alternating Mg and B planar layers: doping of both the sublattices has been observed experimentally to destroy the outstanding superconductive properties of this simple material. In this study we present the investigation by first principles methods at atomistic scale of the phase separation induced by aluminum doping in the MgB2 lattice. The calculations were performed by Density Functional Theory in generalized gradient approximation and pseudopotentials. Orthorhombic oP36 supercells derived by the primitive hR3 MgB2 cell were built in order to simulate the aluminum-magnesium substitution in the 0-50% composition range. The computational results explained the occurrence of a phase separation in the Mg1-xAlxB2 system. The miscibility gap is predicted to be induced by an order-disorder transition in the metallic sublattice at high Al concentration. Indeed at 1000 K aluminum substitution takes place on random Mg sites for concentration up to 17% of the total metallic sites, whereas at Al content larger than 31% the substitution is energetically more favorable on alternated metallic layers (Mg undoped planes alternate with Mg-Al layers). The formation of this Al-rich phase lead at 50% doping to the formation of the double omega Mg1/2Al1/2B2 ordered lattice. From 17 to 31% the two phases, the disordered Mg1-xAlxB2 (x < 0.17) and the ordered Mg1/2+yAl1/2-yB2 (y < 0.19) lattices, coexist. This phase separation is driven by the balance of the enthalpy and entropy contributions to the Gibbs energy. Present DFT-GGA calculations indicate that this thermodynamically predicted suppression of the Al doping disorder in the metallic sublattice of MgB2 occurs in parallel with the collapse of the superconductive properties of the material.

  16. Mg/Ca-temperature and seawater-test chemistry relationships in the shallow-dwelling large benthic foraminifera Operculina ammonoides

    NASA Astrophysics Data System (ADS)

    Evans, David; Erez, Jonathan; Oron, Shai; Müller, Wolfgang

    2015-01-01

    The foraminifera Mg/Ca palaeothermometer contributes significantly to our understanding of palaeoceanic temperature variation. However, since seawater Mg/Ca has undergone large secular variation and the relationship between seawater and test Mg/Ca has not been calibrated in detail for any species with a substantial fossil record, it is only possible to assess relative temperature changes in pre-Pleistocene fossil samples. In order to establish the basis of accurate quantitative Mg/Ca-derived deep-time temperature reconstructions, we have calibrated the relationship between test Mg/Ca, seawater chemistry and temperature in laboratory cultures of the shallow-dwelling large benthic species Operculina ammonoides. Operculina has a fossil range extending back to the early Paleogene and is the nearest living relative of the abundant genus Nummulites. We find a temperature sensitivity of 1.7% °C-1 and a linear relationship between the Mg distribution coefficient and seawater Mg/Ca (Mg /Casw) with m = -1.9 × 10-3 , within error of the equivalent slope for inorganic calcite. The higher test Mg/Ca of O. ammonoides compared to inorganic calcite may be explained by an elevated pH of the calcifying fluid, implying that these foraminifera do not modify the Mg/Ca ratio of the seawater from which they calcify, differentiating them in this respect from most other perforate foraminifera. Applying these calibrations to previously published fossil data results in palaeo-Mg /Casw reconstruction consistent with independent proxy evidence. Furthermore, our data enable accurate absolute palaeotemperature reconstructions if Mg /Casw is constrained by another technique (e.g. ridge flank vein carbonate; fluid inclusions). Finally, we examine Li, Na, Sr and Ba incorporation into the test of O. ammonoides and discuss the control exerted by temperature, seawater chemistry, saturation state and growth rate on these emerging proxies.

  17. Magnesium isotopes constraints on the origin of Mg-rich olivines from the Allende chondrite: Nebular versus planetary?

    NASA Astrophysics Data System (ADS)

    Villeneuve, Johan; Chaussidon, Marc; Libourel, Guy

    2011-01-01

    High precision Mg isotope measurements by multi-collector ion microprobe show that refractory olivines from the Allende chondrite, either olivines isolated in the matrix (2 samples studied) or olivines in type I chondrules (6 samples studied), have variable δ26Mg* enrichments and deficits (calculated in permil as the 26Mg deviation from the instrumental mass fractionation line) relative to the Earth. Most average δ26Mg* (noted δ26Mg*av) values (between 10 and 20 analyses per chondrule) are negative but the total range is from -0.029 (± 0.010) ‰ (2 sigma errors) to + 0.011 (± 0.011) ‰ with an exception of one olivine at + 0.043 (± 0.023) ‰. These variations in δ26Mg*av reflect the formation of the olivines from reservoirs enriched in various amounts of 26Mg by the decay of short-lived 26Al (T1/2 = 0.73 Ma). Similarly, 30 analyses of olivines from the Eagle Station pallasite show a δ26Mg*av value of -0.033 ± 0.008‰, as negative as some olivines from Allende chondrules and the Solar system initial δ26Mg* value of -0.038 ± 0.004‰ (defined at the time of formation of type B Ca-Al-rich inclusions - CAIs - when 26Al/27Al = 5.23 × 10-5, Jacobsen et al., 2008). Because olivines are Al-poor and because their Mg isotopic compositions are not reset during the chondrule forming events, their δ26Mg*av can be used to calculate model crystallization ages relative to various theoretical Mg isotope growth curves. The two end-member scenarios considered are (i) a “nebular” growth in which the Al/Mg ratio remains chondritic and (ii) a “planetary” growth in which a significant increase of the Al/Mg ratio can be due to, for instance, olivine magmatic fractionation. The low δ26Mg*av value of olivines from the Eagle Station pallasite demonstrate that metal-silicate differentiation occurred as early as ~ 0. 15- 0. 23+ 0. 29 Ma after CAIs in either of the growth scenarios. Similarly the variable δ26Mg*av values of refractory olivines can be understood if

  18. Ca and Mg Incorporation in Siderite at Low Temperatures (< 50° C): Results from Laboratory Experiments

    NASA Astrophysics Data System (ADS)

    Sanchez-Roman, M.; Romanek, C. S.; Xu, H.; Coleman, M.

    2008-12-01

    Siderite (FeCO3) is a common mineral found in modern environments and in ancient rocks produce usually by microbia mediation [1,2]. It usually forms concretions with strongly varying chemical compositions which are governed by both pore-water origin and by microbial influence. In addition, siderite has also been identified in extraterrestrial material such as meteorites and dust particles [3,4]. The geochemical information stored in siderite provides valuable insights into the environmental conditions of mineral formation and the processes by which it is modified over time [5]. To unerstand the inorganic constraints on precipitation relative to natural compositions we undertook free drift experiments under anaerobic conditions at 25, 35 and 45°C with variable concentrations of Fe, Ca and Mg in solution. Samples of solution and solid were withdrawn at different time intervals (15, 21 and 30 days) during time course experiments to determine the composition of the solution and mineral precipitates, and the morphology and mineralogy of the precipitates. After 15 days of incubation a metastable phase was formed, whereas after 21 and 30 days of incubation siderite, Ca-siderite, Mg-siderite Ca-Mg siderite and/or Fe-pokrovskite (a hydrated magnesium hydroxy carbonate) were formed depending on the aqueous Fe, Ca and Mg concentrations in the solution. The Mg and Ca contents in the siderite increased with increasing Mg and Ca concentrations in the medium and with increasing temperature. Siderite precipitates ranged from 1.5 to 50.81 mol percent CaCO3 and from 0.54 to 41.38 mol percent MgCO3. Pokrovskite precipitates ranged from 48.8 to 57.7 mol percent MgCO3 and from 42.34 to 51.17 mol percent FeCO3. The Fe content in the pokrovskite increased with increasing temperature. These inorganic experiments will help to understand the mechanism of Ca-Mg-Fe carbonate formation in natural systems and they are of fundamental importance not only for understanding modern and

  19. P-type InGaN across the entire alloy composition range

    SciTech Connect

    Wang, K.; Araki, T.; Katsuki, T.; Yu, K. M.; Mayer, M. A.; Ager, J. W. III; Walukiewicz, W.; Alarcon-Llado, E.; Nanishi, Y.

    2013-03-11

    A systematic investigation on Mg doped and undoped InGaN epilayers grown by plasma-assisted molecular beam epitaxy has been conducted. Single phase InGaN alloys across the entire composition range were synthesized and Mg was doped into In{sub x}Ga{sub 1-x}N (0.1 {<=} x {<=} 0.88) epilayers up to {approx}10{sup 20}/cm{sup 3}. Hall effect, thermopower, and electrochemical capacitance voltage experimental results demonstrate the realization of p-type InGaN across the entire alloy composition range for properly Mg doped InGaN. Hole densities have been measured or estimated to be in the lower {approx}10{sup 18}/cm{sup 3} range when the net acceptor concentrations are in the lower {approx}10{sup 19}/cm{sup 3} range across the composition range.

  20. A novel Drosophila mitochondrial carrier protein acts as a Mg(2+) exporter in fine-tuning mitochondrial Mg(2+) homeostasis.

    PubMed

    Cui, Yixian; Zhao, Shanke; Wang, Xudong; Zhou, Bing

    2016-01-01

    The homeostasis of magnesium (Mg(2+)), an abundant divalent cation indispensable for many biological processes including mitochondrial functions, is underexplored. In yeast, the mitochondrial Mg(2+) homeostasis is accurately controlled through the combined effects of importers, Mrs2 and Lpe10, and an exporter, Mme1. However, little is known about this Mg(2+) homeostatic process in multicellular organisms. Here, we identified the first mitochondrial Mg(2+) transporter in Drosophila, the orthologue of yeast Mme1, dMme1, by homologous comparison and functional complementation. dMme1 can mediate the exportation of mitochondrial Mg(2+) when heterologously expressed in yeast. Altering the expression of dMme1, although only resulting in about a 10% change in mitochondrial Mg(2+) levels in either direction, led to a significant survival reduction in Drosophila. Furthermore, the reduced survival resulting from dMme1 expression changes could be completely rescued by feeding the dMME1-RNAi flies Mg(2+)-restricted food or the dMME1-over-expressing flies the Mg(2+)-supplemented diet. Our studies therefore identified the first Drosophila mitochondrial Mg(2+) exporter, which is involved in the precise control of mitochondrial Mg(2+) homeostasis to ensure an optimal state for survival.

  1. High Precision Laser Range Sensor

    NASA Technical Reports Server (NTRS)

    Dubovitsky, Serge (Inventor); Lay, Oliver P. (Inventor)

    2003-01-01

    The present invention is an improved distance measuring interferometer that includes high speed phase modulators and additional phase meters to generate and analyze multiple heterodyne signal pairs with distinct frequencies. Modulation sidebands with large frequency separation are generated by the high speed electro-optic phase modulators, requiring only a single frequency stable laser source and eliminating the need for a fist laser to be tuned or stabilized relative to a second laser. The combination of signals produced by the modulated sidebands is separated and processed to give the target distance. The resulting metrology apparatus enables a sensor with submicron accuracy or better over a multi- kilometer ambiguity range.

  2. Long range planning at NASA

    NASA Technical Reports Server (NTRS)

    Bekey, Ivan

    1987-01-01

    NASA's current plans for the U.S. space program are described. Consideration is given to the debate between manned or unmanned exploration of space, missions to the moon versus missions to Mars, and the exploration of space applications or science. NASA has created the Office of Policy and Planning and the Office of Exploration in order to improve the planning of future space activities. Long-range trends such as second-generation Shuttles, cargo launch vehicles with large capacity systems, an advanced Space Station, the use of robotics, closed cycle life support, health maintenance techniques, and the processing of extraterrestrial materials are considered.

  3. Extended-range tiltable micromirror

    DOEpatents

    Allen, James J.; Wiens, Gloria J.; Bronson, Jessica R.

    2009-05-05

    A tiltable micromirror device is disclosed in which a micromirror is suspended by a progressive linkage with an electrostatic actuator (e.g. a vertical comb actuator or a capacitive plate electrostatic actuator) being located beneath the micromirror. The progressive linkage includes a pair of torsion springs which are connected together to operate similar to a four-bar linkage with spring joints. The progressive linkage provides a non-linear spring constant which can allow the micromirror to be tilted at any angle within its range substantially free from any electrostatic instability or hysteretic behavior.

  4. Wide-range CCD spectrometer

    NASA Astrophysics Data System (ADS)

    Sokolova, Elena A.; Reyes Cortes, Santiago D.

    1996-08-01

    The utilization of wide range spectrometers is a very important feature for the design of optical diagnostics. This paper describes an innovative approach, based on charged coupled device, which allows to analyze different spectral intervals with the same diffraction grating. The spectral interval is varied by changing the position of the entrance slit when the grating is stationary. The optical system can also include a spherical mirror. In this case the geometric position of the mirror is calculated aiming at compensating the first order astigmatism and the meridional coma of the grating. This device is planned to be used in Thomson scattering diagnostic of the TOKAMAK of Instituto Superior Tecnico, Lisbon (ISTTOK).

  5. BENTON RANGE ROADLESS AREA, CALIFORNIA.

    USGS Publications Warehouse

    McKee, Edwin H.; Rains, Richard L.

    1984-01-01

    On the basis of a mineral survey, two parts of the Benton Range Roadless Area, California are considered to have mineral-resource potential. The central and southern part of the roadless area, near several nonoperating mines, has a probable potential for tungsten and gold-silver mineralization in tactite zones. The central part of the area has a substantiated resource potential for gold and silver in quartz veins. Detailed mapping and geochemical sampling for tungsten, gold, and silver in the central and southern part of the roadless area might indicate targets for shallow drilling exploration.

  6. Wide-ranging sensor applications

    NASA Astrophysics Data System (ADS)

    Showstack, Randy

    The next time you sip a glass of wine from California's Napa Valley, you may want to offer a toast to NASA and the U.S. Department of Agriculture (USDA). A new partnership between the two agencies could help to improve the management of vineyards there. The partnership, which will apply remote-sensing data from satellites to 13 initial research issues, also could improve scientists' understanding of wildfires, range management, floodplain drainage, and other resources.The goal of the research, according to NASA, is to accelerate the movement of remote sensing research results and data into the operational arena.

  7. Distribution of calcium (Ca) and magnesium (Mg) in the leaves of Brassica rapa under varying exogenous Ca and Mg supply

    PubMed Central

    Rios, Juan Jose; Ó Lochlainn, Seosamh; Devonshire, Jean; Graham, Neil S.; Hammond, John P.; King, Graham J.; White, Philip J.; Kurup, Smita; Broadley, Martin R.

    2012-01-01

    Background and Aims Leafy vegetable Brassica crops are an important source of dietary calcium (Ca) and magnesium (Mg) and represent potential targets for increasing leaf Ca and Mg concentrations through agronomy or breeding. Although the internal distribution of Ca and Mg within leaves affects the accumulation of these elements, such data are not available for Brassica. The aim of this study was to characterize the internal distribution of Ca and Mg in the leaves of a vegetable Brassica and to determine the effects of altered exogenous Ca and Mg supply on this distribution. Methods Brassica rapa ssp. trilocularis ‘R-o-18’ was grown at four different Ca:Mg treatments for 21 d in a controlled environment. Concentrations of Ca and Mg were determined in fully expanded leaves using inductively coupled plasma-mass spectrometry (ICP-MS). Internal distributions of Ca and Mg were determined in transverse leaf sections at the base and apex of leaves using energy-dispersive X-ray spectroscopy (EDS) with cryo-scanning electron microscopy (cryo-SEM). Key Results Leaf Ca and Mg concentrations were greatest in palisade and spongy mesophyll cells, respectively, although this was dependent on exogenous supply. Calcium accumulation in palisade mesophyll cells was enhanced slightly under high Mg supply; in contrast, Mg accumulation in spongy mesophyll cells was not affected by Ca supply. Conclusions The results are consistent with Arabidopsis thaliana and other Brassicaceae, providing phenotypic evidence that conserved mechanisms regulate leaf Ca and Mg distribution at a cellular scale. The future study of Arabidopsis gene orthologues in mutants of this reference B. rapa genotype will improve our understanding of Ca and Mg homeostasis in plants and may provide a model-to-crop translation pathway for targeted breeding. PMID:22362665

  8. Phase Transfer-Catalyzed Fast CO2 Absorption by MgO-Based Absorbents with High Cycling Capacity

    SciTech Connect

    Zhang, Keling; Li, Xiaohong S.; Li, Weizhen; Rohatgi, Aashish; Duan, Yuhua; Singh, Prabhakar; Li, Liyu; King, David L.

    2014-06-01

    CO2 capture from pre-combustion syngas in the temperature range of 250-400°C is highly desirable from an energy efficiency perspective. Thermodynamically, MgO is a promising material for CO2 capture, but the gas-solid reaction to produce MgCO3 is kinetically slow due to high lattice energy. We report here fast CO2 absorption over a solid MgO-molten nitrate/nitrite aggregate through phase transfer catalysis, in which the molten phase serves as both a catalyst and reaction medium. Reaction with CO2 at the gas-solid-liquid triple phase boundary results in formation of MgCO3 with significant reaction rate and a high conversion of MgO. This methodology is also applicable to other alkaline earth oxides, inspiring the design of absorbents which require activation of the bulk material.

  9. Mechanical properties of particulate composites based on a body-centered-cubic Mg-Li alloy containing boron

    NASA Technical Reports Server (NTRS)

    Whalen, R. T.; Gonzalez-Doncel, G.; Robinson, S. L.; Sherby, O. D.

    1989-01-01

    The effect of substituting the Mg metal in Mg-B composites by a Mg-14 wt pct Li solid solution on the ductility of the resulting composite was investigated using elastic modulus measurements on the P/M composite material prepared with a dispersion of B particles (in a vol pct range of 0-30) in a matrix of Mg-14 wt pct Li-1.5 wt pct Al. It was found that the elastic modulus of the composites increased rapidly with increasing boron, with specific stiffness values reaching about two times that of most structural materials. The values of the compression and tensile strengths increased significantly with boron additions. Good tensile ductility was achieved at the level of 10 vol pct B. However, at 20 vol pct B, the Mg-Li composite exhibited only limited tensile ductility (about 2 percent total elongation).

  10. Thermoelectric and magnetic properties of Yb2MgSi2 prepared by spark plasma sintering method

    NASA Astrophysics Data System (ADS)

    Kubouchi, M.; Hayashi, K.; Miyazaki, Y.

    2016-08-01

    An intermediate-valence compound, Yb2MgSi2, has been prepared using a spark plasma sintering method. The magnetic susceptibility and thermoelectric properties of Yb2MgSi2 are measured in the temperature range from 5 to 300 K. From the magnetic susceptibility results, Yb valence of the Yb2MgSi2 is evaluated. As compared with YbAl3, which is one of the promising thermoelectric materials that can be used at low temperatures, Yb2MgSi2 exhibits a lower absolute value of Seebeck coefficient, higher electrical resistivity, and lower thermal conductivity over the measured temperature range. A maximum dimensionless figure of merit, ZT, of 0.0018 is achieved at around 200 K.

  11. Magnetic lenses using different MgB2 bulk superconductors

    NASA Astrophysics Data System (ADS)

    Zhang, Z. Y.; Choi, S.; Matsumoto, S.; Teranishi, R.; Giunchi, G.; Figini Albisetti, A.; Kiyoshi, T.

    2012-02-01

    A magnetic lens allows the concentration of magnetic fields using the diamagnetism of superconductors. The important features of the magnetic lens are a tapered inner diameter from which the magnetic flux is extruded and a slit to suppress the circumference current that shields the magnetic flux. This concept was experimentally confirmed through the use of GdBaCuO bulks and a stack of NbTi/Nb/Cu sheets. We refer to this arrangement as a magnetic lens. The Mg-reactive liquid infiltration (Mg-RLI) process developed by Edison SpA is suitable for the production of large and high-density MgB2 bulks. Three MgB2 bulk magnetic lenses, each with a different microstructure, were fabricated following the Mg-RLI process. The properties of the MgB2 magnetic lenses were measured in a cryocooler system as well as in liquid helium. The results confirmed that the MgB2 bulk magnetic lenses could concentrate a magnetic field and that their field concentration properties were greatly affected by the temperature and the external field. In addition, the microstructure of the MgB2 bulk also had an influence on the magnetic properties at different external fields. The results indicated that the MgB2 lens might be utilized as a field amplifier in intermediate fields.

  12. A determination of Mg(+)-ligand binding energies

    NASA Technical Reports Server (NTRS)

    Bauschlicher, Charles W., Jr.; Partridge, Harry

    1991-01-01

    Theoretical calculations employing large basis sets and including correlation are carried out for Mg(+) with methanol, water, and formaldehyde. For Mg(+) with ethanol and acetaldehyde, the trends in the binding energies are studied at the self-consistent-field level. The predictions for the binding energy of Mg(+) to methanol and water of 41 + or - 5 and 36 + or - 5 kcal/mol, respectively, are much less than the experimental upper bounds, of 61 + or - 5 and 60 + or - 5 kcal mol, determined by using photodissociation techniques. The theoretical results are inconsistent with the onset of Mg(+) production observed in the photodissociation experiments, as the smallest absorptions are calculated at about 80 kcal/mol for both Mg(+)-CH3OH and Mg(+)-H2O, and these transitions are to bound excited states. The binding energy for Mg(+) with formaldehyde is predicted to be similar to Mg(+)-H2O. The relative binding energies are in reasonable agreement with experiment. The binding energy of a second water molecule to Mg(+) is predicted to be similar to the first. This suggests that the reduced reaction rate observed for the second ligand is not a consequence of a significantly smaller binding energy, at least for the smaller ligards such as those considered in this work.

  13. Boron isotope effect in superconducting MgB2.

    PubMed

    Bud'ko, S L; Lapertot, G; Petrovic, C; Cunningham, C E; Anderson, N; Canfield, P C

    2001-02-26

    We report the preparation method of and boron isotope effect for MgB2, a new binary intermetallic superconductor with a remarkably high superconducting transition temperature T(c)(10B) = 40.2 K. Measurements of both temperature dependent magnetization and specific heat reveal a 1.0 K shift in T(c) between Mg11B2 and Mg10B2. Whereas such a high transition temperature might imply exotic coupling mechanisms, the boron isotope effect in MgB2 is consistent with the material being a phonon-mediated BCS superconductor.

  14. Synthesis of MgB 2 film by electrochemical process

    NASA Astrophysics Data System (ADS)

    Sakurai, Hiroshi; Kuramochi, Takashi; Furuya, Yudai; Oike, Hiromi; Kato, Tadashi; Hoshi, Kazushi

    2008-07-01

    In order to synthesize MgB2 films, electrolysis is performed in an electrolyte comprising a fused mixture of B2O3, KCl and MgCl2 in a molar ratio of B2O3:KCl:MgCl2 = x:3.5:5. The results of the Meissner effects and X-ray diffraction measurements indicate the formation of MgB2 films on graphite and Si substrates. The superconducting critical temperature depends on both the synthesis temperature of the electrolysis and the amount of B2O3 in the electrolyte.

  15. Mg-Zr-Sr alloys as biodegradable implant materials.

    PubMed

    Li, Yuncang; Wen, Cuie; Mushahary, Dolly; Sravanthi, Ragamouni; Harishankar, Nemani; Pande, Gopal; Hodgson, Peter

    2012-08-01

    Novel Mg-Zr-Sr alloys have recently been developed for use as biodegradable implant materials. The Mg-Zr-Sr alloys were prepared by diluting Mg-Zr and Mg-Sr master alloys with pure Mg. The impact of Zr and Sr on the mechanical and biological properties has been thoroughly examined. The microstructures and mechanical properties of the alloys were characterized using optical microscopy, X-ray diffraction and compressive tests. The corrosion resistance was evaluated by electrochemical analysis and hydrogen evolution measurement. The in vitro biocompatibility was assessed using osteoblast-like SaOS2 cells and MTS and haemolysis tests. In vivo bone formation and biodegradability were studied in a rabbit model. The results indicated that both Zr and Sr are excellent candidates for Mg alloying elements in manufacturing biodegradable Mg alloy implants. Zr addition refined the grain size, improved the ductility, smoothed the grain boundaries and enhanced the corrosion resistance of Mg alloys. Sr addition led to an increase in compressive strength, better in vitro biocompatibility, and significantly higher bone formation in vivo. This study demonstrated that Mg-xZr-ySr alloys with x and y ≤5 wt.% would make excellent biodegradable implant materials for load-bearing applications.

  16. Mg and Mg alloys: how comparable are in vitro and in vivo corrosion rates? A review.

    PubMed

    Martinez Sanchez, Adela Helvia; Luthringer, Bérengère J C; Feyerabend, Frank; Willumeit, Regine

    2015-02-01

    Due to their biodegradability, magnesium and magnesium-based alloys could represent the third generation of biomaterials. However, their mechanical properties and time of degradation have to match the needs of applications. Several approaches, such as choice of alloying elements or tailored microstructure, are employed to tailor corrosion behaviour. Due to the high electrochemical activity of Mg, numerous environmental factors (e.g. temperature and surrounding ion composition) influence its corrosion behaviour, making it unpredictable. Nevertheless, the need of reliable in vitro model(s) to predict in vivo implant degradation is increasing. In an attempt to find a correlation between in vitro and vivo corrosion rates, this review presents a systematic literature survey, as well as an attempt to correlate the different results.

  17. The Ames Vertical Gun Range

    NASA Technical Reports Server (NTRS)

    Karcz, J. S.; Bowling, D.; Cornelison, C.; Parrish, A.; Perez, A.; Raiche, G.; Wiens, J.-P.

    2016-01-01

    The Ames Vertical Gun Range (AVGR) is a national facility for conducting laboratory- scale investigations of high-speed impact processes. It provides a set of light-gas, powder, and compressed gas guns capable of accelerating projectiles to speeds up to 7 km s(exp -1). The AVGR has a unique capability to vary the angle between the projectile-launch and gravity vectors between 0 and 90 deg. The target resides in a large chamber (diameter approximately 2.5 m) that can be held at vacuum or filled with an experiment-specific atmosphere. The chamber provides a number of viewing ports and feed-throughs for data, power, and fluids. Impacts are observed via high-speed digital cameras along with investigation-specific instrumentation, such as spectrometers. Use of the range is available via grant proposals through any Planetary Science Research Program element of the NASA Research Opportunities in Space and Earth Sciences (ROSES) calls. Exploratory experiments (one to two days) are additionally possible in order to develop a new proposal.

  18. Range-Measuring Video Sensors

    NASA Technical Reports Server (NTRS)

    Howard, Richard T.; Briscoe, Jeri M.; Corder, Eric L.; Broderick, David

    2006-01-01

    Optoelectronic sensors of a proposed type would perform the functions of both electronic cameras and triangulation- type laser range finders. That is to say, these sensors would both (1) generate ordinary video or snapshot digital images and (2) measure the distances to selected spots in the images. These sensors would be well suited to use on robots that are required to measure distances to targets in their work spaces. In addition, these sensors could be used for all the purposes for which electronic cameras have been used heretofore. The simplest sensor of this type, illustrated schematically in the upper part of the figure, would include a laser, an electronic camera (either video or snapshot), a frame-grabber/image-capturing circuit, an image-data-storage memory circuit, and an image-data processor. There would be no moving parts. The laser would be positioned at a lateral distance d to one side of the camera and would be aimed parallel to the optical axis of the camera. When the range of a target in the field of view of the camera was required, the laser would be turned on and an image of the target would be stored and preprocessed to locate the angle (a) between the optical axis and the line of sight to the centroid of the laser spot.

  19. Live Fire Range Environmental Assessment

    SciTech Connect

    1993-08-01

    The Central Training Academy (CTA) is a DOE Headquarters Organization located in Albuquerque, New Mexico, with the mission to effectively and efficiently educate and train personnel involved in the protection of vital national security interests of DOE. The CTA Live Fire Range (LFR), where most of the firearms and tactical training occurs, is a complex separate from the main campus. The purpose of the proposed action is to expand the LFR to allow more options of implementing required training. The Department of Energy has prepared this Environmental Assessment (EA) for the proposed construction and operation of an expanded Live Fire Range Facility at the Central Training Academy in Albuquerque, New Mexico. Based on the analysis in the EA, DOE has determined that the proposed action is not a major Federal action significantly affecting the quality of the human environment, within the meaning of the National Environmental Policy Act (NEPA) of 1969. Therefore, the preparation of an environmental impact statement is not required and DOE is issuing this Finding of No Significant Impact (FONSI).

  20. Range Imaging without Moving Parts

    NASA Technical Reports Server (NTRS)

    Blair, J. Bryan; Scott, V. Stanley, III; Ramos-Izquierdo, Luis

    2008-01-01

    Range-imaging instruments of a type now under development are intended to generate the equivalent of three-dimensional images from measurements of the round-trip times of flight of laser pulses along known directions. These instruments could also provide information on characteristics of targets, including roughnesses and reflectivities of surfaces and optical densities of such semi-solid objects as trees and clouds. Unlike in prior range-imaging instruments based on times of flight along known directions, there would be no moving parts; aiming of the laser beams along the known directions would not be accomplished by mechanical scanning of mirrors, prisms, or other optical components. Instead, aiming would be accomplished by using solid-state devices to switch input and output beams along different fiber-optic paths. Because of the lack of moving parts, these instruments could be extraordinarily reliable, rugged, and long-lasting. An instrument of this type would include an optical transmitter that would send out a laser pulse along a chosen direction to a target. An optical receiver coaligned with the transmitter would measure the temporally varying intensity of laser light reflected from the target to determine the distance and surface characteristics of the target. The transmitter would be a combination of devices for generating precise directional laser illumination. It would include a pulsed laser, the output of which would be coupled into a fiber-optic cable with a fan-out and solid-state optical switches that would enable switching of the laser beam onto one or more optical fibers terminated at known locations in an array on a face at the focal plane of a telescope. The array would be imaged by the telescope onto the target space. The receiver optical system could share the aforementioned telescope with the transmitter or could include a separate telescope aimed in the same direction as that of the transmitting telescope. In either case, light reflected

  1. Oxygen isotopic constraints on the origin of Mg-rich olivines from chondritic meteorites

    NASA Astrophysics Data System (ADS)

    Libourel, Guy; Chaussidon, Marc

    2011-01-01

    Chondrules are the major high temperature components of chondritic meteorites which accreted a few millions years after the oldest solids of the solar system, the calcium-aluminum-rich inclusions, were condensed from the nebula gas. Chondrules formed during brief heating events by incomplete melting of solid dust precursors in the protoplanetary disk. Petrographic, compositional and isotopic arguments allowed the identification of metal-bearing Mg-rich olivine aggregates among the precursors of magnesian type I chondrules. Two very different settings can be considered for the formation of these Mg-rich olivines: either a nebular setting corresponding mostly to condensation-evaporation processes in the nebular gas or a planetary setting corresponding mostly to differentiation processes in a planetesimal. An ion microprobe survey of Mg-rich olivines of a set of type I chondrules and isolated olivines from unequilibrated ordinary chondrites and carbonaceous chondrites revealed the existence of several modes in the distribution of the ∆17O values and the presence of a large range of mass fractionation (several ‰) within each mode. The chemistry and the oxygen isotopic compositions indicate that Mg-rich olivines are unlikely to be of nebular origin (i.e., solar nebula condensates) but are more likely debris of broken differentiated planetesimals (each of them being characterized by a given ∆17O). Mg-rich olivines could have crystallized from magma ocean-like environments on partially molten planetesimals undergoing metal-silicate differentiation processes. Considering the very old age of chondrules, Mg-rich olivine grains or aggregates might be considered as millimeter-sized fragments from disrupted first-generation differentiated planetesimals. Finally, the finding of only a small number of discrete ∆17O modes for Mg-rich olivines grains or aggregates in a given chondrite suggests that these shattered fragments have not been efficiently mixed in the disk and

  2. Assessment of liquid hydrogen cooled MgB2 conductors for magnetically confined fusion

    NASA Astrophysics Data System (ADS)

    Glowacki, B. A.; Nuttall, W. J.

    2008-02-01

    Importantly environmental factors are not the only policy-driver for the hydrogen economy. Over the timescale of the development of fusion energy systems, energy security issues are likely to motivate a shift towards both hydrogen production and fusion as an energy source. These technologies combine local control of the system with the collaborative research interests of the major energy users in the global economy. A concept Fusion Island Reactor that might be used to generate H2 (rather than electricity) is presented. Exploitation of produced hydrogen as a coolant and as a fuel is proposed in conjunction with MgB2 conductors for the tokomak magnets windings, and electrotechnical devices for Fusion Island's infrastructure. The benefits of using MgB2 over the Nb-based conductors during construction, operation and decommissioning of the Fusion Island Reactor are presented. The comparison of Nb3Sn strands for ITER fusion magnet with newly developed high field composite MgB2 PIT conductors has shown that at 14 Tesla MgB2 possesses better properties than any of the Nb3Sn conductors produced. In this paper the potential of MgB2 conductors is examined for tokamaks of both the conventional ITER type and a Spherical Tokamak geometry. In each case MgB2 is considered as a conductor for a range of field coil applications and the potential for operation at both liquid helium and liquid hydrogen temperatures is considered. Further research plans concerning the application of MgB2 conductors for Fusion Island are also considered.

  3. Mg-Doped Hydroxyapatite/Chitosan Composite Coated 316L Stainless Steel Implants for Biomedical Applications.

    PubMed

    Sutha, S; Dhineshbabu, N R; Prabhu, M; Rajendran, V

    2015-06-01

    In this investigation, ultrasonication process was used for the synthesis of magnesium doped nano-hydroxyapatite (MH) (0, 1, 2, and 3 mol% of Mg concentration) particles with controlled size and surface morphology. The size of the prepared MH particles was in the range of 20-100 nm with narrow distribution. Increase in the concentration of Mg reduced the particle size distribution from 60 to 40 nm. On incorporation of Mg in HAp lattice, an increase of 20-66 nm in specific surface area was observed in microporous HAp particles. XRF and XRD patterns reveal that the particles possess stoichiometric composition with reduced crystallinity with respect to the Mg concentration. Surface morphology of MH/chitosan (CTS) coated implant was found to be uniform without any defects. The corrosion rate of the implant decreased with increase in Mg concentration. The in vitro formation of bonelike apatite layer on the surface of the MH/CTS coated implant was observed from simulated body fluid studies. The antimicrobial activity of the MH/CTS composites against gram-positive and gram-negative bacterial strains indicated that increasing Mg concentration enhanced antimicrobial properties. Nanoindentation analysis of apatite coated implant surface reveals that the mechanical property depends on the concentration of magnesium in HAp. From the cytotoxicity analysis against NIH 3T3 fibroblast, it was observed that the Mg incorporated HAp/CTS composite was less toxic than the MHO/CTS composite. From this result, it was concluded that the MH/CTS nanocomposites coated implant is the excellent material for implants.

  4. Ca-Mg kutnahorite and struvite production by Idiomarina strains at modern seawater salinities.

    PubMed

    González-Muñoz, María Teresa; De Linares, Concepción; Martínez-Ruiz, Francisca; Morcillo, Fernando; Martín-Ramos, Daniel; Arias, José María

    2008-06-01

    The production of Mg-rich carbonates by Idiomarina bacteria at modern seawater salinities has been investigated. With this objective, four strains: Idiomarina abyssalis (strain ATCC BAA-312), Idiomarina baltica (strain DSM 15154), Idiomarina loihiensis (strains DSM 15497 and MAH1) were used. The strain I. loihiensis MAH1 is a new isolate, identified in the scope of this work. The four moderately halophilic strains precipitated struvite (NH4MgPO4 x 6H2O) crystals that appear encased by small Ca-Mg kutnahorite [CaMg(CO3)2] spheres and dumbbells, which are also regularly distributed in the bacterial colonies. The proportion of Ca-Mg kutnahorite produced by the bacteria assayed ranged from 50% to 20%, and I. abyssalis also produced monohydrocalcite. All precipitated minerals appeared to be related to the bacterial metabolism and, consequently, can be considered biologically induced. Amino acid metabolism resulted in a release of ammonia and CO2 that increase the pH and CO(3)(2-) concentration of the culture medium, creating an alkaline environment that favoured carbonate and struvite precipitation. This precipitation may be also related to heterogeneous nucleation on negatively charged points of biological structures. Because the nature of the organic matrix determines which ion is preferentially adsorbed and, consequently, which mineral phase is formed, the uniquely high content in odd-iso-branched fatty acids of the Idiomarina suggests that their particular membrane characteristics could induce Ca-Mg kutnahorite production. The Ca-Mg kutnahorite, a mineral with a dolomite-ordered structure, production at seawater salinities is noticeable. To date, such precipitation in laboratory cultures, has only been described in hypersaline conditions. It has also been the first time that biomineralization processes have been related to Idiomarina bacteria. PMID:18355891

  5. Functional characterization of osmotically inducible protein C (MG_427) from Mycoplasma genitalium.

    PubMed

    Zhang, Wenbo; Baseman, Joel B

    2014-03-01

    Mycoplasma genitalium is the smallest self-replicating bacterium and an important human pathogen responsible for a range of urogenital infections and pathologies. Due to its limited genome size, many genes conserved in other bacteria are missing in M. genitalium. Genes encoding catalase and superoxide dismutase are absent, and how this pathogen overcomes oxidative stress remains poorly understood. In this study, we characterized MG_427, a homolog of the conserved osmC, which encodes hydroperoxide peroxidase, shown to protect bacteria against oxidative stress. We found that recombinant MG_427 protein reduced organic and inorganic peroxide substrates. Also, we showed that a deletion mutant of MG_427 was highly sensitive to killing by tert-butyl hydroperoxide and H2O2 compared to the sensitivity of the wild type. Further, the fully complemented mutant strain reversed its oxidative sensitivity. Examination of the expression pattern of MG_427 during osmotic shock, oxidative stress, and other stress conditions revealed its lack of induction, distinguishing MG_427 from other previously characterized osmC genes. PMID:24363346

  6. Synthesis and Characterization of Al-Doped Mg2Si Thermoelectric Materials

    NASA Astrophysics Data System (ADS)

    Battiston, S.; Fiameni, S.; Saleemi, M.; Boldrini, S.; Famengo, A.; Agresti, F.; Stingaciu, M.; Toprak, M. S.; Fabrizio, M.; Barison, S.

    2013-07-01

    Magnesium silicide (Mg2Si)-based alloys are promising candidates for thermoelectric (TE) energy conversion for the middle to high range of temperature. These materials are very attractive for TE research because of the abundance of their constituent elements in the Earth's crust. Mg2Si could replace lead-based TE materials, due to its low cost, nontoxicity, and low density. In this work, the role of aluminum doping (Mg2Si:Al = 1: x for x = 0.005, 0.01, 0.02, and 0.04 molar ratio) in dense Mg2Si materials was investigated. The synthesis process was performed by planetary milling under inert atmosphere starting from commercial Mg2Si pieces and Al powder. After ball milling, the samples were sintered by means of spark plasma sintering to density >95%. The morphology, composition, and crystal structure of the samples were characterized by field-emission scanning electron microscopy, energy-dispersive spectroscopy, and x-ray diffraction analyses. Moreover, Seebeck coefficient analyses, as well as electrical and thermal conductivity measurements were performed for all samples up to 600°C. The resultant estimated ZT values are comparable to those reported in the literature for these materials. In particular, the maximum ZT achieved was 0.50 for the x = 0.01 Al-doped sample at 600°C.

  7. Structural and Thermoelectric Properties of Polycrystalline p-Type Mg2- x Li x Si

    NASA Astrophysics Data System (ADS)

    Nieroda, P.; Kolezynski, A.; Oszajca, M.; Milczarek, J.; Wojciechowski, K. T.

    2016-07-01

    The aim of this study was to determine the location of Li atoms in Mg2Si structure, and verify the influence of Li dopant on the transport properties of obtained thermoelectric materials. The results of theoretical studies of the electronic band structure (full potential linearized augmented plane wave method) in Li-doped Mg2Si are presented. Theoretical calculations indicate that only in the case when Li is located in the Mg position, the samples will have p-type conduction. To confirm the theoretical predictions, a series of samples with nominal composition Mg2- x Li x Si ( x = 0-0.5) were prepared using the spark plasma sintering (SPS) method. Structural and phase composition analyses were carried out by x-ray and neutron powder diffraction, as well as scanning electron microscopy. Neutron diffraction studies confirmed that the lithium atoms substitute magnesium in the Mg2Si structure. The investigations of the influence of Li dopant on the transport properties, i.e. electrical conductivity, the Seebeck coefficient and the thermal conductivity, were carried out in a temperature range from 340 K to 720 K. Carrier concentration was measured with Hall method. The positive values of the Seebeck coefficient and Hall coefficient indicate that all examined samples show p-type conductivity. On the basis of the experimental data, the temperature dependencies of the thermoelectric figure of merit ZT were calculated.

  8. Effect of Solute Impurity of Mg on the Microstructure of Calcite

    NASA Astrophysics Data System (ADS)

    Xu, L.; Evans, B. J.; Renner, J.

    2006-12-01

    We produced synthetic marbles by hot isostatic pressing (HIPing) mixtures of calcite and dolomite powders for different intervals (2 to 30 hrs) at 850°C and 300 MPa confining pressure. The HIP treatment resulted in macroscopically homogeneous calcite aggregates with Mg content ranging from 0.5 to 17 mol%. We performed creep tests on samples after HIP at differential stresses from ~ 20 to 170 MPa using constant strain rate and stress-stepping method. Microstructure of both HIPed and deformed samples were studied using both scanning electron microscope (SEM) and transmitted electron microscope (TEM). Both back- scattered electron images and chemical analysis using ion probe suggested that the dolomite phase is completely dissolved, and that the Mg distribution is homogeneous throughout the samples at a scale of a few microns. Grain sizes increase with HIP time and decrease with increasing Mg content (> 3.0 mol%). The growth exponent varies from 2.7 to 3.5 for samples containing 0.3 to 17.0 mol% Mg. Some HIPed samples have intragranular spherical pores, but the shape of the grain boundaries indicates pore drag. At stresses above 80 MPa, the stress sensitivity of strain, n, is greater than 3, indicating an increasing contribution of dislocation creep. The strength of calcite increases with the Mg content in the dislocation creep regime, but not when the rocks deform by diffusion creep. In some deformed samples (ɛ ~ 0.25), a bimodal distribution of large protoblasts and small recrystallized neoblasts coexisted..

  9. ZnO and MgZnO Nanocrystalline Flexible Films: Optical and Material Properties

    DOE PAGESBeta

    Huso, Jesse; Morrison, John L.; Che, Hui; Sundararajan, Jency P.; Yeh, Wei Jiang; McIlroy, David; Williams, Thomas J.; Bergman, Leah

    2011-01-01

    An emore » merging material for flexible UV applications is Mg x Zn 1 − x O which is capable of tunable bandgap and luminescence in the UV range of ~3.4 eV–7.4 eV depending on the composition x . Studies on the optical and material characteristics of ZnO and Mg 0.3 Zn 0.7 O nanocrystalline flexible films are presented. The analysis indicates that the ZnO and Mg 0.3 Zn 0.7 O have bandgaps of 3.34 eV and 4.02 eV, respectively. The photoluminescence (PL) of the ZnO film was found to exhibit a structural defect-related emission at ~3.316 eV inherent to the nanocrystalline morphology. The PL of the Mg 0.3 Zn 0.7 O film exhibits two broad peaks at 3.38 eV and at 3.95 eV that are discussed in terms of the solubility limit of the ZnO-MgO alloy system. Additionally, external deformation of the film did not have a significant impact on its properties as indicated by the Raman LO-mode behavior, making these films attractive for UV flexible applications.« less

  10. Fabrication of stable, wide-bandgap thin films of Mg, Zn and O

    DOEpatents

    Katiyar, Ram S.; Bhattacharya, Pijush; Das, Rasmi R.

    2006-07-25

    A stable, wide-bandgap (approximately 6 eV) ZnO/MgO multilayer thin film is fabricated using pulsed-laser deposition on c-plane Al2O3 substrates. Layers of ZnO alternate with layers of MgO. The thickness of MgO is a constant of approximately 1 nm; the thicknesses of ZnO layers vary from approximately 0.75 to 2.5 nm. Abrupt structural transitions from hexagonal to cubic phase follow a decrease in the thickness of ZnO sublayers within this range. The band gap of the thin films is also influenced by the crystalline structure of multilayer stacks. Thin films with hexagonal and cubic structure have band-gap values of 3.5 and 6 eV, respectively. In the hexagonal phase, Mg content of the films is approximately 40%; in the cubic phase Mg content is approximately 60%. The thin films are stable and their structural and optical properties are unaffected by annealing at 750.degree. C.

  11. Spin crossover in liquid (Mg,Fe)O at extreme conditions

    NASA Astrophysics Data System (ADS)

    Holmström, E.; Stixrude, L.

    2016-05-01

    We use first-principles free-energy calculations to predict a pressure-induced spin crossover in the liquid planetary material (Mg,Fe)O, whereby the magnetic moments of Fe ions vanish gradually over a range of hundreds of GPa. Because electronic entropy strongly favors the nonmagnetic low-spin state of Fe, the crossover has a negative effective Clapeyron slope, in stark contrast to the crystalline counterpart of this transition-metal oxide. Diffusivity of liquid (Mg,Fe)O is similar to that of MgO, displaying a weak dependence on element and spin state. Fe-O and Mg-O coordination increases from approximately 4 to 7 as pressure goes from 0 to 200 GPa. We find partitioning of Fe to induce a density inversion between the crystal and melt, implying separation of a basal magma ocean from a surficial one in the early Earth. The spin crossover induces an anomaly into the density contrast, and the oppositely signed Clapeyron slopes for the crossover in the liquid and crystalline phases imply that the solid-liquid transition induces a spin transition in (Mg,Fe)O.

  12. THE JHU-SDSS METAL ABSORPTION LINE CATALOG: REDSHIFT EVOLUTION AND PROPERTIES OF Mg II ABSORBERS

    SciTech Connect

    Zhu Guangtun; Menard, Brice

    2013-06-20

    We present a generic and fully automatic method aimed at detecting absorption lines in the spectra of astronomical objects. The algorithm estimates the source continuum flux using a dimensionality reduction technique and nonnegative matrix factorization, and then detects and identifies metal absorption lines. We apply it to a sample of {approx}10{sup 5} quasar spectra from the Sloan Digital Sky Survey and compile a sample of {approx}40,000 Mg II- and Fe II-absorber systems, spanning the redshift range 0.4 < z < 2.3. The corresponding catalog is publicly available. We study the statistical properties of these absorber systems and find that the rest equivalent width distribution of strong Mg II absorbers follows an exponential distribution at all redshifts, confirming previous studies. Combining our results with recent near-infrared observations of Mg II absorbers, we introduce a new parameterization that fully describes the incidence rate of these systems up to z {approx} 5. We find the redshift evolution of strong Mg II absorbers to be remarkably similar to the cosmic star formation history over 0.4 < z < 5.5 (the entire redshift range covered by observations), suggesting a physical link between these two quantities.

  13. Formation of three types of quasi-crystals in Al-Pd-Mg system

    NASA Astrophysics Data System (ADS)

    Koshikawa, Naokiyo; Edagawa, Keiichi; Honda, Yuko; Takeuchi, Shin

    1993-04-01

    In the Al-Pd-Mg system, a Mackay-Icosahedron (MI) type Icosahedral (I) phase with the F-type superlattice order and a Decagonal (D) phase were found to form in a melt-quenched state, in addition to the Frank-Kasper (FK) type stable I-phase reported previously. This is the first example in which the three types of quasi-crystalline phases are formed in the same alloy system. The formation range of the FK-type I-phase in melt-quenched state is rather wide: 5 - 20 at percent Pd and 20 - 45 at percent Mg. In contrast, the MI-type, I-phase and D-phase are formed in small composition ranges around Al52Pd31Mg17 and Al74Pd21Mg5, respectively. Electron diffraction studies showed that the period along the tenfold axis of the D-phase is about 1.6 nm. The formation and stability of the MI-type and FK-type I-phases were discussed in terms of a Hume-Rothery rule.

  14. Influence of peculiarities of electronic excitation relaxation on luminescent properties of MgWO4

    NASA Astrophysics Data System (ADS)

    Krutyak, N. R.; Spassky, D. A.; Tupitsyna, I. A.; Dubovik, A. M.

    2016-07-01

    Luminescent properties of magnesium tungstate monocrystals grown by two different methods are studied. Only the exciton luminescence of these crystals themselves is observed. Temperature dependence of the low-energy range in the luminescence excitation spectra is described by the Urbach rule. Slope coefficient σ0 = 0.74 obtained from this dependence implies autolocalization of the excitons in MgWO4. The processes of electronic excitations relaxation are considered depending on the structure of valence band in MgWO4 and in other wolframites, ZnWO4 and CdWO4. In contrast to ZnWO4 and CdWO4, the d-states of the cation do not participate in formation of the MgWO4 valence band. Using the excitation spectra measured in the range of the fundamental absorption (4-20 eV), it is shown that this difference manifests itself in relaxation of electronic excitations and may be the cause of the relatively low light yield of MgWO4.

  15. The Mg 2 lines as diagnostic of PMS nature in Herbig Ae/Be stars

    NASA Technical Reports Server (NTRS)

    1994-01-01

    The main objective of this program was to observe some newly discovered and previously unobserved Herbig Ae/Be (HAeBe) stars with IUE. A previous archival study suggested that there was a full range of profiles in the Mg II lines for these objects; ranging from the double peak emission to the narrow absorption lines. It has been found that by studying the IUE data of main sequence B and classical Be stars that the P Cygni profiles in the Mg II lines in HAeBe stars are truly unique and are the signature of accelerating winds in their extended circumstellar material. The arguement, for the purposes of this proposal, that the structure of the Mg II lines was a superior diagnostic of the dynamical activity and ultimately the PMS nature of these objects. This program was a follow up study of several interesting intermediate-mass stars with the goal of classifying these objects based on the shape of their MG II lines. A list of publications resulting from this research is included.

  16. Quantum chemistry insight into Mg-substitution in chlorophyll by toxic heavy metals: Cd, Hg and Pb

    NASA Astrophysics Data System (ADS)

    Bechaieb, Rim; Ben Akacha, Azaiez; Gérard, Hélène

    2016-10-01

    In this paper, we examined the structural, electronic and energetic data associated to the Mg-substitution in chlorophyll by three major toxic pollutants: Cd2+, Hg2+ and Pb2+. We evidenced a highly versatile bonding of the cations with the pheophytin ligand, with a strong out-of-plane distortion for Hg and Pb. The binding energies ranged from slightly stronger than Mg2+ in the case of Hg2+ to much smaller for Pb2+. Nevertheless, our various approaches of free cations solvation allowed us to evidence that Mg-substitution should be possible for all title elements.

  17. Wind dynamic range video camera

    NASA Technical Reports Server (NTRS)

    Craig, G. D. (Inventor)

    1985-01-01

    A television camera apparatus is disclosed in which bright objects are attenuated to fit within the dynamic range of the system, while dim objects are not. The apparatus receives linearly polarized light from an object scene, the light being passed by a beam splitter and focused on the output plane of a liquid crystal light valve. The light valve is oriented such that, with no excitation from the cathode ray tube, all light is rotated 90 deg and focused on the input plane of the video sensor. The light is then converted to an electrical signal, which is amplified and used to excite the CRT. The resulting image is collected and focused by a lens onto the light valve which rotates the polarization vector of the light to an extent proportional to the light intensity from the CRT. The overall effect is to selectively attenuate the image pattern focused on the sensor.

  18. Explosives characterization in terahertz range

    NASA Astrophysics Data System (ADS)

    Maestrojuán, I.; Palacios, I.; Etayo, D.; Iriarte, J. C.; Teniente, J.; Ederra, I.; Gonzalo, R.

    2011-11-01

    A Thz spectral characterization of the behaviour of different explosives is presented in this paper. This characterization will be done in the frequency range from 20 GHz to 4 THz using a Teraview Spectra 3000. This system has a capacity of measuring from 20 GHz to 4 THz fed by a laser source. With the Teraview Spectra 3000 equipment will be possible to calculate the refractive index, the absorbance and other important parameters of the explosive samples. With this study it will be possible to characterize some of the most common used explosives, i.e., gun explosive, gunpowder mine, pent, TNT, RDX, etc, and it will allow to determine their electromagnetic peculiarities in order to design a future imaging system that allow detecting them in security and defense sectors.

  19. Extended range tankless water heater

    SciTech Connect

    Harris, J.A.

    1993-04-18

    In this research program, a laboratory test facility was built for the purpose of testing a gas-fired water heating appliance. This test facility can be used to examine the important performance characteristics of efficiency, dynamic response, and quality of combustion. An innovative design for a tankless water heater was built and then tested to determine its performance characteristics. This unit was tested over a 5:1 range in input (20,000 to 100,000 btuh heat input). The unit was then configured as a circulating hot water boiler, and a specially designed heat exchanger was used with it to generate domestic hot water. This unit was also tested, and was found to offer performance advantages with regard to low flow and temperature stability.

  20. Wide Range SET Pulse Measurement

    NASA Technical Reports Server (NTRS)

    Shuler, Robert L.; Chen, Li

    2012-01-01

    A method for measuring a wide range of SET pulses is demonstrated. Use of dynamic logic, faster than ordinary CMOS, allows capture of short pulses. A weighted binning of SET lengths allows measurement of a wide range of pulse lengths with compact circuitry. A pulse-length-conservative pulse combiner tree routes SETs from combinational logic to the measurement circuit, allowing SET measurements in circuits that cannot easily be arranged in long chains. The method is applied to add-multiplex combinational logic, and to an array of NFET routing switches, at .35 micron. Pulses are captured in a chain of Domino Logic AND gates. Propagation through the chain is frozen on the trailing edge by dropping low the second "enable" input to the AND gates. Capacitive loading is increased in the latter stages to create an approximately logarithmic weighted binning, so that a broad range of pulse lengths can be captured with a 10 stage capture chain. Simulations show pulses can be captured which are 1/5th the length of those typically captured with leading edge triggered latch methods, and less than the length of those captured with a trailing edge latch method. After capture, the pulse pattern is transferred to an SEU protected shift register for readout. 64 instances of each of two types of logic are used as targets. One is a full adder with a 4 to 1 mux on its inputs. The other is a 4 x 4 NFET routing matrix. The outputs are passed through buffered XNOR comparators to identify pulses, which are merged in a buffered not-nand (OR) tree designed to avoid pulse absorption as much as possible. The output from each of the two test circuits are input into separate pulse measurement circuits. Test inputs were provided so that the circuit could be bench tested and calibrated. A third SET measurement circuit with no inputs was used to judge the contribution from direct hits on the measurement circuit. Heavy ions were used with an LET range from 12 to 176. At LET of 21 and below, the very

  1. Space - The long range future

    NASA Technical Reports Server (NTRS)

    Von Puttkamer, J.

    1985-01-01

    Space exploration goals for NASA in the year 2000 time frame are examined. A lunar base would offer the opportunity for continuous earth viewing, further cosmogeochemical exploration and rudimentary steps at self-sufficiency in space. The latter two factors are also compelling reasons to plan a manned Mars base. Furthermore, competition and cooperation in a Mars mission and further interplanetary exploration is an attractive substitute for war. The hardware requirements for various configurations of Mars missions are briefly addressed, along with other, unmanned missions to the asteroid belt, Mercury, Venus, Jupiter and the moons of Jupiter and Saturn. Finally, long-range technological requirements for providing adequate living/working facilities for larger human populations in Space Station environments are summarized.

  2. X-ray Raman scattering study of MgSiO₃ glass at high pressure: Implication for triclustered MgSiO₃ melt in Earth's mantle

    SciTech Connect

    Lee, Sung Keun; Lin, Jung-Fu; Cai, Yong Q; Hiraoka, Nozomu; Eng, Peter J; Okuchi, Takuo; Mao, Ho-kwang; Meng, Yue; Hu, Michael Y; Chow, Paul; Shu, Jinfu; Li, Baosheng; Fukui, Hiroshi; Lee, Bum Han; Kim, Hyun Na; Yoo, Choong-Shik

    2008-06-13

    Silicate melts at the top of the transition zone and the core-mantle boundary have significant influences on the dynamics and properties of Earth's interior. MgSiO{sub 3}-rich silicate melts were among the primary components of the magma ocean and thus played essential roles in the chemical differentiation of the early Earth. Diverse macroscopic properties of silicate melts in Earth's interior, such as density, viscosity, and crystal-melt partitioning, depend on their electronic and short-range local structures at high pressures and temperatures. Despite essential roles of silicate melts in many geophysical and geodynamic problems, little is known about their nature under the conditions of Earth's interior, including the densification mechanisms and the atomistic origins of the macroscopic properties at high pressures. Here, we have probed local electronic structures of MgSiO{sub 3} glass (as a precursor to Mg-silicate melts), using high-pressure x-ray Raman spectroscopy up to 39 GPa, in which high-pressure oxygen K-edge features suggest the formation of tricluster oxygens (oxygen coordinated with three Si frameworks; {sup [3]}O) between 12 and 20 GPa. Our results indicate that the densification in MgSiO{sub 3} melt is thus likely to be accompanied with the formation of triculster, in addition to a reduction in nonbridging oxygens. The pressure-induced increase in the fraction of oxygen triclusters >20 GPa would result in enhanced density, viscosity, and crystal-melt partitioning, and reduced element diffusivity in the MgSiO{sub 3} melt toward deeper part of the Earth's lower mantle.

  3. X-ray Raman scattering study of MgSiO3 glass at high pressure: implication for triclustered MgSiO3 melt in Earth's mantle.

    PubMed

    Lee, Sung Keun; Lin, Jung-Fu; Cai, Yong Q; Hiraoka, Nozomu; Eng, Peter J; Okuchi, Takuo; Mao, Ho-Kwang; Meng, Yue; Hu, Michael Y; Chow, Paul; Shu, Jinfu; Li, Baosheng; Fukui, Hiroshi; Lee, Bum Han; Kim, Hyun Na; Yoo, Choong-Shik

    2008-06-10

    Silicate melts at the top of the transition zone and the core-mantle boundary have significant influences on the dynamics and properties of Earth's interior. MgSiO3-rich silicate melts were among the primary components of the magma ocean and thus played essential roles in the chemical differentiation of the early Earth. Diverse macroscopic properties of silicate melts in Earth's interior, such as density, viscosity, and crystal-melt partitioning, depend on their electronic and short-range local structures at high pressures and temperatures. Despite essential roles of silicate melts in many geophysical and geodynamic problems, little is known about their nature under the conditions of Earth's interior, including the densification mechanisms and the atomistic origins of the macroscopic properties at high pressures. Here, we have probed local electronic structures of MgSiO3 glass (as a precursor to Mg-silicate melts), using high-pressure x-ray Raman spectroscopy up to 39 GPa, in which high-pressure oxygen K-edge features suggest the formation of tricluster oxygens (oxygen coordinated with three Si frameworks; 3O) between 12 and 20 GPa. Our results indicate that the densification in MgSiO3 melt is thus likely to be accompanied with the formation of triculster, in addition to a reduction in nonbridging oxygens. The pressure-induced increase in the fraction of oxygen triclusters >20 GPa would result in enhanced density, viscosity, and crystal-melt partitioning, and reduced element diffusivity in the MgSiO3 melt toward deeper part of the Earth's lower mantle. PMID:18535140

  4. X-ray Raman scattering study of MgSiO3 glass at high pressure: implication for triclustered MgSiO3 melt in Earth's mantle.

    PubMed

    Lee, Sung Keun; Lin, Jung-Fu; Cai, Yong Q; Hiraoka, Nozomu; Eng, Peter J; Okuchi, Takuo; Mao, Ho-Kwang; Meng, Yue; Hu, Michael Y; Chow, Paul; Shu, Jinfu; Li, Baosheng; Fukui, Hiroshi; Lee, Bum Han; Kim, Hyun Na; Yoo, Choong-Shik

    2008-06-10

    Silicate melts at the top of the transition zone and the core-mantle boundary have significant influences on the dynamics and properties of Earth's interior. MgSiO3-rich silicate melts were among the primary components of the magma ocean and thus played essential roles in the chemical differentiation of the early Earth. Diverse macroscopic properties of silicate melts in Earth's interior, such as density, viscosity, and crystal-melt partitioning, depend on their electronic and short-range local structures at high pressures and temperatures. Despite essential roles of silicate melts in many geophysical and geodynamic problems, little is known about their nature under the conditions of Earth's interior, including the densification mechanisms and the atomistic origins of the macroscopic properties at high pressures. Here, we have probed local electronic structures of MgSiO3 glass (as a precursor to Mg-silicate melts), using high-pressure x-ray Raman spectroscopy up to 39 GPa, in which high-pressure oxygen K-edge features suggest the formation of tricluster oxygens (oxygen coordinated with three Si frameworks; 3O) between 12 and 20 GPa. Our results indicate that the densification in MgSiO3 melt is thus likely to be accompanied with the formation of triculster, in addition to a reduction in nonbridging oxygens. The pressure-induced increase in the fraction of oxygen triclusters >20 GPa would result in enhanced density, viscosity, and crystal-melt partitioning, and reduced element diffusivity in the MgSiO3 melt toward deeper part of the Earth's lower mantle.

  5. X-ray Raman scattering study of MgSiO₃ glass at high pressure: Implication for triclustered MgSiO₃ melt in Earth's mantle

    SciTech Connect

    Lee, Sung Keun; Lin, Jung-Fu; Cai, Yong Q.; Hiraoka, Nozomu; Eng, Peter J.; Okuchi, Takuo; Mao, Ho-kwang; Meng, Yue; Hu, Michael Y.; Chow, Paul; Shu, Jinfu; Li, Baosheng; Fukui, Hiroshi; Lee, Bum Han; Kim, Hyun Na; Yoo, Choong-Shik

    2015-02-09

    Silicate melts at the top of the transition zone and the core-mantle boundary have significant influences on the dynamics and properties of Earth's interior. MgSiO3-rich silicate melts were among the primary components of the magma ocean and thus played essential roles in the chemical differentiation of the early Earth. Diverse macroscopic properties of silicate melts in Earth's interior, such as density, viscosity, and crystal-melt partitioning, depend on their electronic and short-range local structures at high pressures and temperatures. Despite essential roles of silicate melts in many geophysical and geodynamic problems, little is known about their nature under the conditions of Earth's interior, including the densification mechanisms and the atomistic origins of the macroscopic properties at high pressures. Here, we have probed local electronic structures of MgSiO3 glass (as a precursor to Mg-silicate melts), using high-pressure x-ray Raman spectroscopy up to 39 GPa, in which high-pressure oxygen K-edge features suggest the formation of tricluster oxygens (oxygen coordinated with three Si frameworks; [3]O) between 12 and 20 GPa. Our results indicate that the densification in MgSiO3 melt is thus likely to be accompanied with the formation of triculster, in addition to a reduction in nonbridging oxygens. The pressure-induced increase in the fraction of oxygen triclusters >20 GPa would result in enhanced density, viscosity, and crystal-melt partitioning, and reduced element diffusivity in the MgSiO3 melt toward deeper part of the Earth's lower mantle.

  6. Understanding synthesis imaging dynamic range

    NASA Astrophysics Data System (ADS)

    Braun, R.

    2013-03-01

    We develop a general framework for quantifying the many different contributions to the noise budget of an image made with an array of dishes or aperture array stations. Each noise contribution to the visibility data is associated with a relevant correlation timescale and frequency bandwidth so that the net impact on a complete observation can be assessed when a particular effect is not captured in the instrumental calibration. All quantities are parameterised as function of observing frequency and the visibility baseline length. We apply the resulting noise budget analysis to a wide range of existing and planned telescope systems that will operate between about 100 MHz and 5 GHz to ascertain the magnitude of the calibration challenges that they must overcome to achieve thermal noise limited performance. We conclude that calibration challenges are increased in several respects by small dimensions of the dishes or aperture array stations. It will be more challenging to achieve thermal noise limited performance using 15 m class dishes rather than the 25 m dishes of current arrays. Some of the performance risks are mitigated by the deployment of phased array feeds and more with the choice of an (alt,az,pol) mount, although a larger dish diameter offers the best prospects for risk mitigation. Many improvements to imaging performance can be anticipated at the expense of greater complexity in calibration algorithms. However, a fundamental limitation is ultimately imposed by an insufficient number of data constraints relative to calibration variables. The upcoming aperture array systems will be operating in a regime that has never previously been addressed, where a wide range of effects are expected to exceed the thermal noise by two to three orders of magnitude. Achieving routine thermal noise limited imaging performance with these systems presents an extreme challenge. The magnitude of that challenge is inversely related to the aperture array station diameter.

  7. Wide speed range turboshaft study

    NASA Technical Reports Server (NTRS)

    Dangelo, Martin

    1995-01-01

    NASA-Lewis and NASA-Ames have sponsored a series of studies over the last few years to identify key high speed rotorcraft propulsion and airframe technologies. NASA concluded from these studies that for near term aircraft with cruise speeds up to 450 kt, tilting rotor rotorcraft concepts are the most economical and technologically viable. The propulsion issues critical to tilting rotor rotorcraft are: (1) high speed cruise propulsion system efficiency and (2) adequate power to hover safely with one engine inoperative. High speed cruise propeller efficiency can be dramatically improved by reducing rotor speed, yet high rotor speed is critical for good hover performance. With a conventional turboshaft, this wide range of power turbine operating speeds would result in poor engine performance at one or more of these critical operating conditions. This study identifies several wide speed range turboshaft concepts, and analyzes their potential to improve performance at the diverse cruise and hover operating conditions. Many unique concepts were examined, and the selected concepts are simple, low cost, relatively low risk, and entirely contained within the power turbine. These power turbine concepts contain unique, incidence tolerant airfoil designs that allow the engine to cruise efficiently at 51 percent of the hover rotor speed. Overall propulsion system efficiency in cruise is improved as much as 14 percent, with similar improvements in engine weight and cost. The study is composed of a propulsion requirement survey, a concept screening study, a preliminary definition and evaluation of selected concepts, and identification of key technologies and development needs. In addition, a civil transport tilting rotor rotorcraft mission analysis was performed to show the benefit of these concepts versus a conventional turboshaft. Other potential applications for this technology are discussed.

  8. Expansion-based passive ranging

    NASA Technical Reports Server (NTRS)

    Barniv, Yair

    1993-01-01

    This paper describes a new technique of passive ranging which is based on utilizing the image-plane expansion experienced by every object as its distance from the sensor decreases. This technique belongs in the feature/object-based family. The motion and shape of a small window, assumed to be fully contained inside the boundaries of some object, is approximated by an affine transformation. The parameters of the transformation matrix are derived by initially comparing successive images, and progressively increasing the image time separation so as to achieve much larger triangulation baseline than currently possible. Depth is directly derived from the expansion part of the transformation. To a first approximation, image-plane expansion is independent of image-plane location with respect to the focus of expansion (FOE) and of platform maneuvers. Thus, an expansion-based method has the potential of providing a reliable range in the difficult image area around the FOE. In areas far from the FOE the shift parameters of the affine transformation can provide more accurate depth information than the expansion alone, and can thus be used similarly to the way they have been used in conjunction with the Inertial Navigation Unit (INU) and Kalman filtering. However, the performance of a shift-based algorithm, when the shifts are derived from the affine transformation, would be much improved compared to current algorithms because the shifts--as well as the other parameters--can be obtained between widely separated images. Thus, the main advantage of this new approach is that, allowing the tracked window to expand and rotate, in addition to moving laterally, enables one to correlate images over a very long time span which, in turn, translates into a large spatial baseline resulting in a proportionately higher depth accuracy.

  9. Expansion-based passive ranging

    NASA Technical Reports Server (NTRS)

    Barniv, Yair

    1993-01-01

    A new technique of passive ranging which is based on utilizing the image-plane expansion experienced by every object as its distance from the sensor decreases is described. This technique belongs in the feature/object-based family. The motion and shape of a small window, assumed to be fully contained inside the boundaries of some object, is approximated by an affine transformation. The parameters of the transformation matrix are derived by initially comparing successive images, and progressively increasing the image time separation so as to achieve much larger triangulation baseline than currently possible. Depth is directly derived from the expansion part of the transformation. To a first approximation, image-plane expansion is independent of image-plane location with respect to the focus of expansion (FOE) and of platform maneuvers. Thus, an expansion-based method has the potential of providing a reliable range in the difficult image area around the FOE. In areas far from the FOE the shift parameters of the affine transformation can provide more accurate depth information than the expansion alone, and can thus be used similarly to the way they were used in conjunction with the Inertial Navigation Unit (INU) and Kalman filtering. However, the performance of a shift-based algorithm, when the shifts are derived from the affine transformation, would be much improved compared to current algorithms because the shifts - as well as the other parameters - can be obtained between widely separated images. Thus, the main advantage of this new approach is that, allowing the tracked window to expand and rotate, in addition to moving laterally, enables one to correlate images over a very long time span which, in turn, translates into a large spatial baseline - resulting in a proportionately higher depth accuracy.

  10. Melting and decomposition of MgCO3 at pressures up to 84 GPa

    NASA Astrophysics Data System (ADS)

    Solopova, N. A.; Dubrovinsky, L.; Spivak, A. V.; Litvin, Yu. A.; Dubrovinskaia, N.

    2015-01-01

    Magnesium carbonate MgCO3 (magnesite) was experimentally studied at pressures of 12-84 GPa and temperatures between 1,600 and 3,300 K. We applied the high-pressure technique using a multianvil press and a diamond anvil cell with laser heating. The phase relations and melting of magnesite were investigated by means of Raman and time-resolved multi-wavelength spectroscopy. Magnesite is found to melt congruently within the entire studied pressure range at temperatures of 2,100-2,650 K. At temperatures above 2,700 K, we observed decomposition of magnesite with formation of MgO and a carbon phase (diamond). Our results demonstrate that at high pressures, the magnesium carbonate melt can exist at a wide range of thermodynamic conditions.

  11. Friction Stir Welding of a Thick Al-Zn-Mg Alloy Plate

    NASA Astrophysics Data System (ADS)

    Buchibabu, V.; Reddy, G. M.; Kulkarni, D.; De, A.

    2016-03-01

    Al-Zn-Mg alloys are widely used as structural materials due to high strength-to-weight ratio and impact toughness. As fusion welds in these alloys commonly face hot cracking and macro porosity, friction stir welding is increasingly becoming the preferred recourse. We report here a detailed experimental study on friction stir welding of a specific Al-Zn-Mg alloy with its chemical compositions close to AA7039. The effect of tool rotational speed and welding speed on the weld profile, joint microstructure, and mechanical properties is studied extensively. The results show sound weld profiles and joint properties within the selected range of process conditions. Within the selected range of welding conditions, the welds made at a tool rotational speed of 350 rpm and welding speed of 3 mm/s have showed joint structure, tensile, and impact toughness properties fairly close to that of the base material.

  12. Paramagnetism in the kagome compounds (Zn ,Mg ,Cd ) Cu3(OH) 6Cl2

    NASA Astrophysics Data System (ADS)

    Iqbal, Yasir; Jeschke, Harald O.; Reuther, Johannes; Valentí, Roser; Mazin, I. I.; Greiter, Martin; Thomale, Ronny

    2015-12-01

    Frustrated magnetism on the kagome lattice has been a fertile ground for rich and fascinating physics, ranging from experimental evidence of a spin liquid to theoretical predictions of exotic superconductivity. Among experimentally realized spin-1/2 kagome magnets, herbertsmithite, kapellasite, and haydeeite [(Zn ,Mg ) Cu3(OH) 6Cl2] are all well described by a three-parameter Heisenberg model, but they exhibit distinctly different physics. We address the problem using a pseudofermion functional renormalization-group approach and analyze the low-energy physics in the experimentally accessible parameter range. Our analysis places kapellasite and haydeeite near the boundaries between magnetically ordered and disordered phases, implying that slight modifications could dramatically affect their magnetic properties. Inspired by this, we perform ab initio density functional theory calculations of (Zn,Mg,Cd ) Cu3 (OH) 6Cl2 at various pressures. Our results suggest that by varying pressure and composition one can traverse a paramagnetic regime between different magnetically ordered phases.

  13. HIV suppression with stavudine 30 mg versus 40 mg in adults over 60 kg on antiretroviral therapy in South Africa.

    PubMed

    Hoffmann, Christopher J; Charalambous, Salome; Fielding, Katherine L; Innes, Craig; Chaisson, Richard E; Grant, Alison D; Churchyard, Gavin J

    2009-08-24

    In 2007, the WHO recommended a maximum stavudine dose of 30 mg. We compared virologic suppression among patients weighing more than 60 kg and receiving stavudine 30 mg (n = 110) versus 40 mg (n = 508) in community HIV clinics in South Africa, before and after guidelines changed. At 6 months, HIV RNA less than 400 copies/ml was achieved in 79% and 81% receiving 30 and 40 mg stavudine, respectively (chi2, P = 0.6). In regression modeling, including baseline HIV RNA and nonnucleoside reverse transcriptase inhibitor agent, stavudine dose remained unassociated with suppression.

  14. Spin and charge transport in double-junction Fe/MgO/GaAs/MgO/Fe heterostructures

    SciTech Connect

    Wolski, S. Szczepański, T.; Dugaev, V. K.; Barnaś, J.; Landgraf, B.; Slobodskyy, T.; Hansen, W.

    2015-01-28

    We present theoretical and experimental results on tunneling current in single Fe/MgO/GaAs and double Fe/MgO/GaAs/MgO/Fe tunnel junctions. The charge and spin currents are calculated as a function of external voltage for different sets of parameters characterizing the semiconducting GaAs layer. Transport characteristics of a single Fe/MgO/GaAs junction reveal typical diode as well as spin diode features. The results of numerical calculations are compared with current-voltage characteristics measured experimentally for double tunnel junction structures, and a satisfactory agreement of the theoretical and experimental results has been achieved.

  15. The in vitro biocompatibility and macrophage phagocytosis of Mg17Al12 phase in Mg-Al-Zn alloys.

    PubMed

    Liu, Chen; He, Peng; Wan, Peng; Li, Mei; Wang, Kehong; Tan, Lili; Zhang, Yu; Yang, Ke

    2015-07-01

    Mg alloys are gaining interest for applications as biodegradable medical implant, including Mg-Al-Zn series alloys with good combination of mechanical properties and reasonable corrosion resistance. However, whether the existence of second phase particles in the alloys exerts influence on the biocompatibility is still not clear. A deeper understanding of how the particles regulate specific biological responses is becoming a crucial requirement for their subsequent biomedical application. In this work, the in vitro biocompatibility of Mg17Al12 as a common second phase in biodegradable Mg-Al-Zn alloys was investigated via hemolysis, cytotoxicity, cell proliferation, and cell adhesion tests. Moreover, osteogenic differentiation was evaluated by the extracellular matrix mineralization assay. The Mg17Al12 particles were also prepared to simulate the real situation of second phase in the in vivo environment in order to estimate the cellular response in macrophages to the Mg17Al12 particles. The experimental results indicated that no hemolysis was found and an excellent cytocompatibility was also proved for the Mg17Al12 second phase when co-cultured with L929 cells, MC3T3-E1 cells and BMSCs. Macrophage phagocytosis co-culture test revealed that Mg17Al12 particles exerted no harmful effect on RAW264.7 macrophages and could be phagocytized by the RAW264.7 cells. Furthermore, the possible inflammatory reaction and metabolic way for Mg17Al12 phase were also discussed in detail.

  16. Masses of 17,18,19,20Mg

    NASA Astrophysics Data System (ADS)

    Fortune, H. T.

    2016-10-01

    A previous simple parametrization of mirror energy differences in pairs of nuclei consisting of a p -shell core plus two s d -shell nucleons is applied to a series of mirrors that contain s d -shell nucleons in the core. Results for Mg,2019 agree with experiment and with a potential model. Predictions are made for 2 p separation energies of Mg,1817.

  17. Mg-based compounds for hydrogen and energy storage

    NASA Astrophysics Data System (ADS)

    Crivello, J.-C.; Denys, R. V.; Dornheim, M.; Felderhoff, M.; Grant, D. M.; Huot, J.; Jensen, T. R.; de Jongh, P.; Latroche, M.; Walker, G. S.; Webb, C. J.; Yartys, V. A.

    2016-02-01

    Magnesium-based alloys attract significant interest as cost-efficient hydrogen storage materials allowing the combination of high gravimetric storage capacity of hydrogen with fast rates of hydrogen uptake and release and pronounced destabilization of the metal-hydrogen bonding in comparison with binary Mg-H systems. In this review, various groups of magnesium compounds are considered, including (1) RE-Mg-Ni hydrides (RE = La, Pr, Nd); (2) Mg alloys with p-elements (X = Si, Ge, Sn, and Al); and (3) magnesium alloys with d-elements (Ti, Fe, Co, Ni, Cu, Zn, Pd). The hydrogenation-disproportionation-desorption-recombination process in the Mg-based alloys (LaMg12, LaMg11Ni) and unusually high-pressure hydrides synthesized at pressures exceeding 100 MPa (MgNi2H3) and stabilized by Ni-H bonding are also discussed. The paper reviews interrelations between the properties of the Mg-based hydrides and p- T conditions of the metal-hydrogen interactions, chemical composition of the initial alloys, their crystal structures, and microstructural state.

  18. Titania doping effect on superconducting properties of MgB2 bulk samples

    NASA Astrophysics Data System (ADS)

    Serrano, G.; Bridoux, G.; Serquis, A.

    2009-05-01

    In this work we study the microstructural and superconducting properties of doped and undoped bulk MgB2 samples prepared by solid-state reaction, with 0 and 2.5 %at. nominal TiO2 nanotubes contents, annealed at different temperatures in the 750-900°C range. We discuss the Tc, Jc and Hc2 performance and their correlation with the different synthesis parameters.

  19. Randomized clinical trial of dexketoprofen/tramadol 25 mg/75 mg in moderate-to-severe pain after total hip arthroplasty

    PubMed Central

    McQuay, H. J.; Moore, R. A.; Berta, A.; Gainutdinovs, O.; Fülesdi, B.; Porvaneckas, N.; Petronis, S.; Mitkovic, M.; Bucsi, L.; Samson, L.; Zegunis, V.; Ankin, M. L.; Bertolotti, M.; Pizà-Vallespir, B.; Cuadripani, S.; Contini, M. P.; Nizzardo, A.

    2016-01-01

    Background. The aim was to evaluate the analgesic efficacy and safety of the dexketoprofen/tramadol 25 mg/75 mg fixed-dose combination vs dexketoprofen (25 mg) and tramadol (100 mg) in moderate-to-severe acute pain after total hip arthroplasty. Methods. This was a randomized, double-blind, parallel-group study in patients experiencing pain of at least moderate intensity on the day after surgery, compared with placebo at first administration to validate the pain model. The study drug was administered orally every 8 h throughout a 5 day period. Rescue medication, metamizole 500 mg, was available during the treatment period. The evaluation of efficacy was based on patient assessments of pain intensity and pain relief. The primary end point was the mean sum of the pain intensity difference values throughout the first 8 h (SPID8). Results. Overall, 641 patients, mean age 62 (range 29–80) yr, were analysed; mean (sd) values of SPID8 were 247 (157) for dexketoprofen/tramadol, 209 (155) for dexketoprofen, 205 (146) for tramadol, and 151 (159) for placebo. The primary analysis confirmed the superiority of the combination over dexketoprofen 25 mg (P=0.019; 95% confidence interval 6.4–73) and tramadol 100 mg (P=0.012; 95% confidence interval 9.5–76). The single components were superior to placebo (P<0.05), confirming model sensitivity. Most secondary analyses supported the superiority of the combination. The incidence of adverse drug reactions was low and similar among active treatment groups. Conclusion. The efficacy results confirmed the superiority of dexketoprofen/tramadol over its single components, even at higher doses (tramadol), with a safety profile fully in line with that previously known for these agents in monotherapy. Clinical trial registration. EudraCT 2012-004548-31 (https://www.clinicaltrialsregister.eu/ctr-search/search?query=eudract_number:2012-004548-31); ClinicalTrials.gov NCT01902134 (https://www.clinicaltrials.gov/ct2/show/NCT01902134?term

  20. Magnetic properties of epitaxial discontinuous Fe/MgO multilayers.

    PubMed

    García-García, A; Pardo, J A; Strichovanec, P; Magén, C; Vovk, A; De Teresa, J M; Kakazei, G N; Pogorelov, Yu G; Golub, V; Salyuk, O; Morellón, L; Algarabel, P A; Ibarra, M R

    2012-09-01

    We report magnetic, dynamic and transport properties of discontinuous metal-insulator multilayers Fe/MgO grown on amorphous Corning glass and single-crystalline MgO (001) substrates. The films of structure Substrate/MgO (3 nm)/[Fe (0.6 nm)/MgO (3.0 nm)] x 10 were prepared in ultra-high vacuum conditions using Pulsed Laser Deposition. It was shown that conditions of epitaxial growth are favorable for MgO substrates. As a result a substantial increase of tunneling magnetoresistance caused by spin-filtering effect was observed and reasonably theoretically explained. The value of TMR - 9.2% at room temperature in 18 kOe magnetic field is three times higher comparing to that for the samples grown on Corning glass substrates. PMID:23035505

  1. Defect complexes in Li-doped MgO

    NASA Astrophysics Data System (ADS)

    Richter, N. A.; Stavale, F.; Levchenko, S. V.; Nilius, N.; Freund, H.-J.; Scheffler, M.

    2015-05-01

    Magnesium oxide (MgO) is used in a variety of industrial applications due to its low cost and structural stability. In heterogeneous catalysis, MgO and Li-doped MgO have been studied as catalysts for the oxidative coupling of methane. In this work, we analyze the structure and stability of defect complexes comprising Li dopants and oxygen vacancies in MgO, combining scanning tunneling microscopy, photon-emission experiments, and density-functional theory computations. The experimental results strongly indicate that after annealing Li-doped MgO to temperatures of 600 K and higher, Li evaporates from the surface, but Li defects, such as substitutional defects, interstitials, or defect complexes comprising Li remain in the bulk. Our calculations show that bulk defect complexes containing F2 + color centers, that have donated their two electrons to two adjacent Li defects, are the most stable configurations at realistic pressure and temperature conditions.

  2. The anodic surface film and hydrogen evolution on Mg

    SciTech Connect

    Song, Guang -Ling; Unocic, Kinga A.

    2015-06-04

    This paper clarifies that the inner and outer layers of the anodic film consist of a nano/micro-porous MgO+Mg(OH)2 mixture. The film becomes thicker and more porous with increasing potential. It can rupture when potential is too positive in a non-corrosive Mg(OH)2 solution. Hydrogen evolution becomes more intensive as polarization potential increases, particularly when the potential at the film-covered Mg surface is close to or more positive than the hydrogen equilibrium potential, suggesting that an “anodic hydrogen evolution” (AHE) reaction occurs on the substrate Mg in film pores, and the significantly intensified AHE causes film rupture at high potential.

  3. Model for nonprotective oxidation of Al-Mg alloys

    SciTech Connect

    Zayan, M.H. )

    1990-12-01

    The oxidation of Al-5Mg alloy has been studied at 550 C in dry air. Morphological details of the MgO layers which develop on this alloy during high-temperature oxidation have been studied by scanning electron microscopy (SEM). A localized detachment of the protective, adherent MgO layer was found, which is caused by voids formed by vacancy condensation at the metal-oxide interface. The source of these vacancies was the outward diffusion of Mg though the oxide layer. Continuing growth of these voids was responsible for cracking of oxide ridges and nodules, as well as the growth of new MgO having a cauliflower morphology. A model describing the process of the outward diffusion is given.

  4. The anodic surface film and hydrogen evolution on Mg

    DOE PAGESBeta

    Song, Guang -Ling; Unocic, Kinga A.

    2015-06-04

    This paper clarifies that the inner and outer layers of the anodic film consist of a nano/micro-porous MgO+Mg(OH)2 mixture. The film becomes thicker and more porous with increasing potential. It can rupture when potential is too positive in a non-corrosive Mg(OH)2 solution. Hydrogen evolution becomes more intensive as polarization potential increases, particularly when the potential at the film-covered Mg surface is close to or more positive than the hydrogen equilibrium potential, suggesting that an “anodic hydrogen evolution” (AHE) reaction occurs on the substrate Mg in film pores, and the significantly intensified AHE causes film rupture at high potential.

  5. The Mg isotopic systematics of granitoids in continental arcs and implications for the role of chemical weathering in crust formation.

    PubMed

    Shen, Bing; Jacobsen, Benjamin; Lee, Cin-Ty A; Yin, Qing-Zhu; Morton, Douglas M

    2009-12-01

    Continental crust is too Si-rich and Mg-poor to derive directly from mantle melting, which generates basaltic rather than felsic magmas. Converting basalt to more felsic compositions requires a second step involving Mg loss, which is thought to be dominated by internal igneous differentiation. However, igneous differentiation alone may not be able to generate granites, the most silicic endmember making up the upper continental crust. Here, we show that granites from the eastern Peninsular Ranges Batholith (PRB) in southern California are isotopically heavy in Mg compared with PRB granodiorites and canonical mantle. Specifically, Mg isotopes correlate positively with Si content and O, Sr, and Pb isotopes and negatively with Mg content. The elevated Sr and Pb isotopes require that a component in the source of the granitic magmas to be ancient preexisting crust making up the prebatholithic crustal basement, but the accompanying O and Mg isotope fractionations suggest that this prebatholithic crust preserved a signature of low-temperature alteration. The protolith of this basement rock may have been the residue of chemical weathering, which progressively leached Mg from the residue, leaving the remaining Mg highly fractionated in terms of its isotopic signature. Our observations indicate that ancient continental crust preserves the isotopic signature of compositional modification by chemical weathering.

  6. Significant improvement of critical current density in MgB2 doped with ferromagnetic Fe3O4 nanoparticles

    NASA Astrophysics Data System (ADS)

    Qu, B.; Sun, X. D.; Li, J.-G.; Xiu, Z. M.; Liu, S. H.; Xue, C. P.

    2009-01-01

    Ferromagnetic Fe3O4-doped MgB2 bulks were first fabricated in this work by the hot pressing method. It was found that Fe3O4 does not react with Mg or B during the fabrication process. Peak Jc values of the 5 wt% Fe3O4-doped MgB2 are higher than 106 A cm-2 in the temperature range 5-30 K. Especially at 30 K, the peak Jc is 1.02 × 106 A cm-2 for the 5 wt% Fe3O4-doped MgB2, the highest values at 30 K found in the literature, and about seven times that of the 5 wt% SiC-doped MgB2 sample. The drop in Jc with increasing field for the Fe3O4-doped MgB2 is significantly slower than that of the SiC-doped MgB2 at 30 K. These results indicate that the Fe3O4-doped MgB2 is a potential superconductor to be used at temperatures greater than 25 K which is a critical temperature for large-scale practical applications.

  7. The Mg isotopic systematics of granitoids in continental arcs and implications for the role of chemical weathering in crust formation

    PubMed Central

    Shen, Bing; Jacobsen, Benjamin; Lee, Cin-Ty A.; Yin, Qing-Zhu; Morton, Douglas M.

    2009-01-01

    Continental crust is too Si-rich and Mg-poor to derive directly from mantle melting, which generates basaltic rather than felsic magmas. Converting basalt to more felsic compositions requires a second step involving Mg loss, which is thought to be dominated by internal igneous differentiation. However, igneous differentiation alone may not be able to generate granites, the most silicic endmember making up the upper continental crust. Here, we show that granites from the eastern Peninsular Ranges Batholith (PRB) in southern California are isotopically heavy in Mg compared with PRB granodiorites and canonical mantle. Specifically, Mg isotopes correlate positively with Si content and O, Sr, and Pb isotopes and negatively with Mg content. The elevated Sr and Pb isotopes require that a component in the source of the granitic magmas to be ancient preexisting crust making up the prebatholithic crustal basement, but the accompanying O and Mg isotope fractionations suggest that this prebatholithic crust preserved a signature of low-temperature alteration. The protolith of this basement rock may have been the residue of chemical weathering, which progressively leached Mg from the residue, leaving the remaining Mg highly fractionated in terms of its isotopic signature. Our observations indicate that ancient continental crust preserves the isotopic signature of compositional modification by chemical weathering. PMID:19920171

  8. Mg Isotope Fractionation Between E. coli and Growth Medium

    NASA Astrophysics Data System (ADS)

    Basset, R.; Lemelle, L.; Albalat, E.; Telouk, P.; Albarède, F.

    2008-12-01

    Magnesium is a major element in both microbial cells and minerals, immune to redox conditions and atmospheric interactions. In organic cells, Mg can be associated with membranes, with cytoplasm (either as an isolated ion or bound to proteins). Its isotope composition can be used to constrain the contribution of organic material to carbonate fluxes and the overall cycle of this element in the exogenous environment [1, 2]. Cells of DH5α E. coli strain were grown in Luria Broth medium and the Mg isotope fractionation between the cells and their growth medium determined after calcination in Pt crucibles, chemical purification by cation exchange chemistry in HCl medium [3] and isotopic analysis on a Nu HR MC-ICPMS. The yield is better than 96%. The Mg contents of 2.19 ± 0.08 mg per g DW in cells and 0.117 ± 0.001 mg per g DW in Luria Broth medium are consistent with literature data [4]. About half of the Mg initially present in the LB medium is taken up by the growing cells. At high cellular concentrations (OD600 = 3.5), cells are enriched in 26Mg by 0.97 ± 0.14 ‰ with respect to the culture medium. Although E. coli may not be a good proxy for oceanic plankton, such a substantial fractionation of Mg isotopes suggests that incorporation of even a few percent organic matter into oceanic oozes depletes oceanic Mg in its heavy isotopes and therefore accounts for the isotopic difference between riverine and marine Mg. [1] Drever, The Sea 5 (1974) 337-357 [2] Tipper et al., EPSL 250 (2006) 241-253 [3] Chang et al., JAAS 18 (2003) 296-301 [4] Outten et al., Science 292 (2001), 2488-2492

  9. In vitro degradation and electrochemical corrosion evaluations of microarc oxidized pure Mg, Mg-Ca and Mg-Ca-Zn alloys for biomedical applications.

    PubMed

    Pan, Yaokun; He, Siyu; Wang, Diangang; Huang, Danlan; Zheng, Tingting; Wang, Siqi; Dong, Pan; Chen, Chuanzhong

    2015-02-01

    Calcium phosphate (CaP) ceramic coatings were fabricated on pure magnesium (Mg) and self-designed Mg-0.6Ca, Mg-0.55Ca-1.74Zn alloys by microarc oxidation (MAO). The coating formation, growth and biomineralization mechanisms were discussed. The coating degradability and bioactivity were evaluated by immersion tests in trishydroxymethyl-aminomethane hydrochloric acid (Tris-HCl) buffer and simulated body fluid (SBF) solutions, respectively. The coatings and corrosion products were characterized by scanning electron microscope (SEM), X-ray diffractometer (XRD), X-ray photoelectron spectrometer (XPS) and fourier transform infrared spectrometer (FT-IR). The electrochemical workstation was used to investigate the electrochemical corrosion behaviors of substrates and coatings. Results showed that Mg-0.55Ca-1.74Zn alloy exhibits the highest mechanical strength and electrochemical corrosion resistance among the three alloys. The MAO-coated Mg-0.55Ca-1.74Zn alloy has the potential to be served as a biodegradable implant.

  10. Wide-range voltage modulation

    SciTech Connect

    Rust, K.R.; Wilson, J.M.

    1992-06-01

    The Superconducting Super Collider`s Medium Energy Booster Abort (MEBA) kicker modulator will supply a current pulse to the abort magnets which deflect the proton beam from the MEB ring into a designated beam stop. The abort kicker will be used extensively during testing of the Low Energy Booster (LEB) and the MEB rings. When the Collider is in full operation, the MEBA kicker modulator will abort the MEB beam in the event of a malfunction during the filling process. The modulator must generate a 14-{mu}s wide pulse with a rise time of less than 1 {mu}s, including the delay and jitter times. It must also be able to deliver a current pulse to the magnet proportional to the beam energy at any time during ramp-up of the accelerator. Tracking the beam energy, which increases from 12 GeV at injection to 200 GeV at extraction, requires the modulator to operate over a wide range of voltages (4 kV to 80 kV). A vacuum spark gap and a thyratron have been chosen for test and evaluation as candidate switches for the abort modulator. Modulator design, switching time delay, jitter and pre-fire data are presented.

  11. Structural and Electronic Properties of a Wide-Gap Quaternary Solid Solution: \\(Zn, Mg\\) \\(S, Se\\)

    NASA Astrophysics Data System (ADS)

    Saitta, A. M.; de Gironcoli, S.; Baroni, S.

    1998-06-01

    The structural properties of the (Zn, Mg) (S, Se) solid solutions are determined by a combination of the computational alchemy and the cluster expansion methods with Monte Carlo simulations. We determine the phase diagram of the alloy and show that the homogeneous phase is characterized by a large amount of short-range order occurring among first-nearest neighbors. Electronic-structure calculations performed using the special quasirandom structure approach indicate that the energy gap of the alloy is rather sensitive to this short-range order.

  12. Calcium-magnesium carbonate solid solutions from Holocene conglomerate cements and travertines in the Coast Range of California

    USGS Publications Warehouse

    Barnes, I.; O'Neil, J.R.

    1971-01-01

    Two calcium-magnesium carbonate solid solutions form Holocene travertines and conglomerate cements in fresh water stream channels of the Coast Range of California. Calcite does not yield the {015} diffraction maximum. The {006} diffraction maximum is lacking over most of the range of composition of calcite. Calcite has compositions from CaCO3 to Ca0.5Mg0.5CO3. Dolomite yields both the {006} and {015} diffraction maxima over its entire composition range, Ca0.6Mg0.4CO3 to Ca0.5Mg0.5CO3. The Ca-Mg carbonates form in isotopic equilibrium and thermodynamic disequilibrium from dispersion of Ca2+-rich water into CO32--rich water within the alluvium. The stable isotope data suggest that all the Mg-rich carbonates are primary precipitates and not a result of Mg-substitution in precursor CaCO3. There is a correlation between ??C13 and Mg content of the carbonates which predicts a 5%. fractionation of C13 between dolomite and calcite at sedimentary temperatures. C14 is incorporated in Ca-Mg carbonates forming from C13-poor meteoric waters and C13-rich waters from Cretaceous sediments. C14 ages of the Ca-Mg carbonates are apparent, and cannot be corrected to absolute values. Solution rates of calcite decrease with increasing MgCO3 content; dolomite dissolves slower than any calcite. ?? 1971.

  13. Toward accurate thermochemistry of the {sup 24}MgH, {sup 25}MgH, and {sup 26}MgH molecules at elevated temperatures: Corrections due to unbound states

    SciTech Connect

    Szidarovszky, Tamás; Császár, Attila G.

    2015-01-07

    The total partition functions Q(T) and their first two moments Q{sup ′}(T) and Q{sup ″}(T), together with the isobaric heat capacities C{sub p}(T), are computed a priori for three major MgH isotopologues on the temperature range of T = 100–3000 K using the recent highly accurate potential energy curve, spin-rotation, and non-adiabatic correction functions of Henderson et al. [J. Phys. Chem. A 117, 13373 (2013)]. Nuclear motion computations are carried out on the ground electronic state to determine the (ro)vibrational energy levels and the scattering phase shifts. The effect of resonance states is found to be significant above about 1000 K and it increases with temperature. Even very short-lived states, due to their relatively large number, have significant contributions to Q(T) at elevated temperatures. The contribution of scattering states is around one fourth of that of resonance states but opposite in sign. Uncertainty estimates are given for the possible error sources, suggesting that all computed thermochemical properties have an accuracy better than 0.005% up to 1200 K. Between 1200 and 2500 K, the uncertainties can rise to around 0.1%, while between 2500 K and 3000 K, a further increase to 0.5% might be observed for Q{sup ″}(T) and C{sub p}(T), principally due to the neglect of excited electronic states. The accurate thermochemical data determined are presented in the supplementary material for the three isotopologues of {sup 24}MgH, {sup 25}MgH, and {sup 26}MgH at 1 K increments. These data, which differ significantly from older standard data, should prove useful for astronomical models incorporating thermodynamic properties of these species.

  14. Comparison of the effects of combination atorvastatin (40 mg) + ezetimibe (10 mg) versus atorvastatin (40 mg) alone on secretory phospholipase A2 activity in patients with stable coronary artery disease or coronary artery disease equivalent.

    PubMed

    Azar, Mireille; Valentin, Emmanuel; Badaoui, Georges; Kassab, Roland; Sarkis, Antoine; Azar, Rabih R

    2011-06-01

    Secretory phospholipase A2 (sPLA2) is an enzyme that plays an important role in the pathogenesis of atherosclerosis and of adverse cardiovascular events. It is currently the target of emerging therapeutic agents. Our study was designed to investigate the effect of aggressive lowering of low-density lipoprotein (LDL) cholesterol with ezetimibe and atorvastatin on sPLA2 activity. We randomized 100 patients with stable coronary artery disease (CAD) or CAD equivalent (diabetes, stroke, or peripheral vascular disease) to receive ezetimibe 10 mg/day in association with atorvastatin 40 mg/day (combination therapy group) versus atorvastatin 40 mg/day and placebo (monotherapy group). Patients on statin therapy before inclusion were allowed to enter the study as long as the potency of the statin was lower than atorvastatin 40 mg/day. Lipid profile, high-sensitivity C-reactive protein (hs-CRP), and sPLA activity were measured at baseline and after 8 weeks of therapy. The decrease in LDL cholesterol was more significant in the combination therapy group, but the decrease in hs-CRP was similar. sPLA2 activity significantly decreased in the ezetimibe/atorvastatin group from 29 U/ml (interquartile range 23 to 35) to 26 U/ml (23 to 29, p = 0.001) but remained similar in the placebo/atorvastatin group (23 U/ml, 19 to 32, vs 22 U/ml, 19 to 28, p = NS). In a multivariate stepwise linear regression model, change in sPLA2 correlated with change in hs-CRP (p <0.001), baseline LDL cholesterol level (p = 0.001), body mass index (p = 0.003), diabetes mellitus (p = 0.04) and combination therapy with ezetimibe/atorvastatin (p = 0.05). In conclusion, this study demonstrates that coadministration of ezetimibe and atorvastatin decreases sPLA2 activity.

  15. A master switch couples Mg²⁺-assisted catalysis to domain motion in B. stearothermophilus tryptophanyl-tRNA Synthetase.

    PubMed

    Weinreb, Violetta; Li, Li; Carter, Charles W

    2012-01-11

    We demonstrate how tryptophanyl-tRNA synthetase uses conformation-dependent Mg(2+) activation to couple catalysis of tryptophan activation to specific, functional domain movements. Rate acceleration by Mg(2+) requires ∼-6.0 kcal/mol in protein⋅Mg(2+) interaction energy, none of which arises from the active site. A highly cooperative interaction between Mg(2+) and four residues from a remote, conserved motif that mediates the shear of domain movement (1) destabilizes the pretransition state conformation, thereby (2) inducing the Mg(2+) to stabilize the transition state for k(cat) by ∼-5.0 kcal/mol. Cooperative, long-range conformational effects on the metal therefore convert an inactive Mg(2+) coordination into one that can stabilize the transition state if, and only if, domain motion occurs. Transient, conformation-dependent Mg(2+) activation, analogous to the escapement in mechanical clocks, explains vectorial coupling. PMID:22244762

  16. Effect of Mg content on the bioactivity and biocompatibility of Mg-substituted fluorapatite nanopowders fabricated via mechanical activation.

    PubMed

    Kheradmandfard, M; Fathi, M H; Ansari, F; Ahmadi, T

    2016-11-01

    The aim of this work was preparation, characterization, bioactivity and biocompatibility evaluation of Mg-substituted fluorapatite (Mg-FA) nanopowders. Mg-FA nanopowders with a chemical composition of Ca10-xMgx(PO4)6F2, with x=0, 0.5, 1, and 2 were prepared by mechanically activated method. The in vitro bioactivity was investigated by soaking the powders in simulated body fluid (SBF) for various time periods to analyze the nucleation and growth of bone-like apatite on the surface of the samples. Cell viability and cell attachment were studied by MTT assay. Results indicated that the bioactivity of all of samples with different Mg content was improved compared with the pure FA. However, the mechanism of bioactivity is different and depends on the amount of Mg substitution. Finally, cell culture suggested that the addition of Mg(2+) has no adverse effect and Mg-FA samples have good biocompatibility. The Mg-FA material shows potential in satisfying the requirements of biomedical applications. PMID:27524005

  17. Reactions of Mg and Mg2 with SO2 in low-temperature matrices: association or insertion?

    PubMed

    Liu, Xing; Xing, Xiaopeng; Zhao, Jie; Wang, Xuefeng

    2015-01-29

    Laser-ablated magnesium species were codeposited with SO2 in excess argon or neon on the substrate at 4 K. The reactions mainly produced Mg(η(2)-O2S), Mg(η(2)-O2S)2, Mg2(η(2)-O2S), OMg2(η(2)-SO), and Mg(η(2)-SO) complexes, which were identified by isotopic substitutions and density functional frequency calculations (B3LYP and BPW91). In addition, the collected infrared spectra suggest that the single Mg atoms could react with SO2 to form the Mg(η(2)-O2S) complex on annealing, which further reacts with SO2 to produce the Mg(η(2)-O2S)2 complex on irradiation. In contrast, the reactions of magnesium dimers lead to cleavage of the S═O bond in SO2 on irradiating. Structural and bonding characteristics of these generated complexes, which shed light on the different performances of single Mg atom and its dimer in their reactions with small molecules, are discussed.

  18. Laser cladding of a Mg based Mg-Gd-Y-Zr alloy with Al-Si powders

    NASA Astrophysics Data System (ADS)

    Chen, Erlei; Zhang, Kemin; Zou, Jianxin

    2016-03-01

    In the present work, a Mg based Mg-Gd-Y-Zr alloy was subjected to laser cladding with Al-Si powders at different laser scanning speeds in order to improve its surface properties. It is observed that the laser clad layer mainly contains Mg2Si, Mg17Al12 and Al2(Gd,Y) phases distributed in the Mg matrix. The depth of the laser clad layer increases with decreasing the scanning speed. The clad layer has graded microstructures and compositions. Both the volume fraction and size of Mg2Si, Mg17Al12 and Al2(Gd,Y) phases decreases with the increasing depth. Due to the formation of these hardening phases, the hardness of clad layer reached a maximum value of HV440 when the laser scanning speed is 2 mm/s, more than 5 times of the substrate (HV75). Besides, the corrosion properties of the untreated and laser treated samples were all measured in a NaCl (3.5 wt.%) aqueous solution. The corrosion potential was increased from -1.77 V for the untreated alloy to -1.13 V for the laser clad alloy with scanning rate of 2 mm/s, while the corrosion current density was reduced from 2.10 × 10-5 A cm-2 to 1.64 × 10-6 A cm-2. The results show that laser cladding is an efficient method to improve surface properties of Mg-Rare earth alloys.

  19. Demixing Instability in Dense Molten MgSiO3 and the Phase Diagram of MgO

    NASA Astrophysics Data System (ADS)

    Boates, Brian; Bonev, Stanimir A.

    2013-03-01

    The phase diagrams of MgSiO3 and MgO are studied from first-principles theory for pressures and temperatures up to 600 GPa and 20 000 K. Through the evaluation of finite-temperature Gibbs free energies, using density-functional theory within the generalized gradient approximation as well as with hybrid exchange-correlation functionals, we find evidence for a vast pressure-temperature regime where molten MgSiO3 decomposes into liquid SiO2 and solid MgO, with a volume change of approximately 1.2%. The demixing transition is driven by the crystallization of MgO—the reaction only occurs below the high-pressure MgO melting curve. The predicted transition pressure at 10 000 K is in close proximity to an anomaly reported in recent laser-driven shock experiments of MgSiO3. We also present new results for the high-pressure melting curve of MgO and its B1-B2 solid phase transition, with a triple point at 364 GPa and 12 000 K.

  20. Simulating GTP:Mg and GDP:Mg with a simple force field: a structural and thermodynamic analysis.

    PubMed

    Simonson, Thomas; Satpati, Priyadarshi

    2013-04-01

    Di- and tri-phosphate nucleotides are essential cofactors for many proteins, usually in an Mg(2+) -bound form. Proteins like GTPases often detect the difference between NDP and NTP and respond by changing conformations. To study such complexes, simple, fixed charge force fields have been used, which allow long simulations and precise free energy calculations. The preference for NTP or NDP binding depends on many factors, including ligand structure and Mg(2+) coordination and the changes they undergo upon binding. Here, we use a simple force field to examine two Mg(2+) coordination modes for the unbound GDP and GTP: direct, or "Inner Sphere" (IS) coordination by one or more phosphate oxygens and indirect, "Outer Sphere" (OS) coordination involving one or more bridging waters. We compare GTP: and GDP:Mg binding with OS and IS coordination; combining the results with experimental data then indicates that GTP prefers the latter. We also examine different kinds of IS coordination and their sensitivity to a key force field parameter: the optimal Mg:oxygen van der Waals distance Rmin . Increasing Rmin improves the Mg:oxygen distances, the GTP: and GDP:Mg binding affinities, and the fraction of GTP:Mg with β + γ phosphate coordination, but does not improve or change the GTP/GDP affinity difference, which remains much larger than experiment. It has no effect on the free energy of GDP binding to a GTPase.

  1. Reactions of Mg and Mg2 with SO2 in low-temperature matrices: association or insertion?

    PubMed

    Liu, Xing; Xing, Xiaopeng; Zhao, Jie; Wang, Xuefeng

    2015-01-29

    Laser-ablated magnesium species were codeposited with SO2 in excess argon or neon on the substrate at 4 K. The reactions mainly produced Mg(η(2)-O2S), Mg(η(2)-O2S)2, Mg2(η(2)-O2S), OMg2(η(2)-SO), and Mg(η(2)-SO) complexes, which were identified by isotopic substitutions and density functional frequency calculations (B3LYP and BPW91). In addition, the collected infrared spectra suggest that the single Mg atoms could react with SO2 to form the Mg(η(2)-O2S) complex on annealing, which further reacts with SO2 to produce the Mg(η(2)-O2S)2 complex on irradiation. In contrast, the reactions of magnesium dimers lead to cleavage of the S═O bond in SO2 on irradiating. Structural and bonding characteristics of these generated complexes, which shed light on the different performances of single Mg atom and its dimer in their reactions with small molecules, are discussed. PMID:25521504

  2. The formation of MgH(2) nanowires during the hydrogenation of Ti-doped Mg film.

    PubMed

    He, Yuping; Liu, Yongjun; Zhao, Yiping

    2008-11-19

    A unique diffusion barrier structure, consisting of layers of a Ti nanorod array and Ti film, has been fabricated on Si substrate for a subsequent 2 at.% Ti-doped Mg film deposition using a combinational technique of multilayer growth, co-deposition and dynamic shadowing growth. The hydrogenation of the Ti-doped Mg film on such a barrier structure shows that the barrier can prevent direct Mg-Si contact and suppress the formation of Mg(2)Si alloy in a high-temperature process. When this film has been hydrogenated at temperatures T≤300 °C for approximately 150 h, tetragonal single-crystal MgH(2) nanowires are formed on the surface of the Ti-doped Mg film. The hydrogenation time and temperature are the two main factors for the nanowire formation. The doping of Ti also plays a significant role. This result reveals that complicated dynamic processes could occur during the hydrogenation of Ti-doped Mg film when Mg(2)Si formation can be eliminated by an effective diffusion barrier layer.

  3. Structural, electronic and bonding properties of antifluorite crystals of Be2C, BeMgC and Mg2C

    NASA Astrophysics Data System (ADS)

    Joshi, K. B.; Trivedi, D. K.; Paliwal, U.; Galav, K. L.

    2016-05-01

    Structure prediction methods are coupled with the first-principles linear combination of atomic orbitals method to propose the crystal parameters and bulk modulus of antifluorite BeMgC. The binary antifluorite methanides Be2C, Mg2C are also studied. Electronic structure calculations and Mulliken population analyses (MPA) are performed to unravel bands dispersion and bonding properties. The values of the indirect band gap Γ → X for Be2C, Mg2C and BeMgC, in order, are 2.90, 2.05 and 1.86 eV. The calculated energies of a few occupied bands in Be2C are in very good agreement with the available experimental data. The application of pressure causes change in the band gap of three carbides. The Γ-Γ, Γ-X and Γ-K band gaps exhibit different trends with pressure. Effective charges on the basis of MPA in the three compounds are {(B{e}+1.095)}2{C}-2.19, {(M{g}+1.615)}2{C}-3.23 and B{e}+1.12M{g}+1.682{C}-2.802. It signifies covalent bonding in Be2C, ionic in Mg2C, and intermediate in the BeMgC.

  4. Homoepitaxy of ZnO and MgZnO Films at 90 °C

    SciTech Connect

    Ehrentraut, Dirk; Goh, Gregory K.L.; Fujii, Katsushi; Ooi, Chin Chun; Quang, Le Hong; Fukuda, Tsuguo; Kano, Masataka; Zhang, Yuantao; Matsuoka, Takashi

    2014-06-01

    The aqueous synthesis of uniform single crystalline homoepitaxial zinc oxide, ZnO, and magnesium zinc oxide, Mg{sub x}Zn{sub 1−x}O, films under very low temperature conditions at T=90 °C and ambient pressure has been explored. A maximum Mg content of 1 mol% was recorded by energy dispersive spectroscopy. The growth on the polar (0 0 0 1) and (0 0 0 1¯) faces resulted in films that are strongly different in their structural and optical quality as evidenced by high-resolution X-ray diffraction, secondary electron microscopy, and photoluminescence. This is a result of the chemistry and temperature of the solution dictating the stability range of growth-governing metastable species. The use of trisodium citrate, Na{sub 3}C{sub 6}H{sub 5}O{sub 7}, yielded coalesced, mirror-like homoepitaxial films whereas adding magnesium nitrate hexahydrate, Mg(NO{sub 3}){sub 2}·6H{sub 2}O, favors the growth of films with pronounced faceting. - Graphical abstract: Homoepitaxial ZnO films grown from aqueous solution below boiling point of water on a ZnO substrate with off-orientation reveal parallel grooves that are characterized by (1 0 1{sup ¯} 1) facets. Adding trisodium citrate yields closed, single-crystalline ZnO films, which can further be functionalized. Alloying with MgO yields MgZnO films with low Mg content only. - Highlights: • A simple method to synthesize uniform single crystalline homoepitaxial ZnO and MgZnO films. • ZnO growth on (0 0 0 1) and (0 0 0 1{sup ¯}) face resulted in films that are strongly different in their structural and optical quality. • Single crystalline MgZnO film was fabricated under mild conditions (90 °C and ambient pressure). • Mg incorporation of nearly 1 mol% was obtained while maintaining single phase wurtzite structure.

  5. Magnetic characterization of CoFeB /MgO and CoFe /MgO interfaces

    NASA Astrophysics Data System (ADS)

    Negusse, Ezana; Lussier, A.; Dvorak, J.; Idzerda, Y. U.; Shinde, S. R.; Nagamine, Y.; Furukawa, S.; Tsunekawa, K.; Djayaprawira, D. D.

    2007-02-01

    The use of CoFeB ferromagnetic electrodes in place of CoFe has been shown to significantly increase the tunneling magnetoresistance (TMR) of MgO based magnetic tunnel junctions (MTJs). By using soft x-ray scattering techniques, we show that the behavior of the magnetic moments located at the CoFe-MgO interface are drastically different from the rest of the CoFe film, whereas the magnetic response of the CoFeB-MgO interfacial moments is coherent with the film's bulk. Our results support the view that the high TMR values observed in MgO based MTJs with CoFeB electrodes are due to the uniform magnetic response of the entire CoFeB electrode including the MgO interfacial moments.

  6. Strengthening of Al and Al-Mg alloy wires by melt inoculation with Al/MgB2 nanocomposite

    NASA Astrophysics Data System (ADS)

    Florián-Algarín, David; Marrero, Raúl; Padilla, Alexandra; Suárez, Oscar Marcelo

    2015-12-01

    This study hinges on the feasibility of strengthening Al and Al-Mg wires by adding Al nanocomposite pellets containing MgB2 nanoparticles into the melt upon fabrication. These MgB2 nanoparticles were obtained by fragmentation using a high-energy ball mill, and were, afterward, mechanically alloyed with pure aluminum. The resulting MgB2/Al nanocomposite pellets were sintered at 260°C to be subsequently added into molten aluminum and an Al-Mg alloy melt. Cold rolling intercalated with stepwise annealing allowed the fabrication of 1 mm diameter wires with a final area reduction of 96%. Mechanical and physical properties of the treated wire specimens were compared to those of similarly processed pure aluminum wire. The ultimate tensile strength of the treated wires increased approximately double fold with respect to untreated wires at the expense of some loss in electrical conductivity.

  7. Orthopyroxene as a recorder of lunar crust evolution: An ion microprobe investigations of Mg-suite norites. [Abstract only

    NASA Technical Reports Server (NTRS)

    Papike, J. J.; Fowler, G. W.; Shearer, C. K.

    1994-01-01

    The lunar Mg suite, which includes dunites, troctolites, and norites, could make up 20-30% of the Moon's crust down to a depth of 60 km. The remainder is largely anorthositic. This report focuses on norites because we have found that the chemical characteristics of orthopyroxene are effective recorders of their parental melt compositions. Many of the samples representing the Mg suite are small and unrepresentative. In addition, they are cumulates and thus are difficult to study by whole-rock techniques. Therefore, we decided to study these rocks by SIMS techniques to analyze a suite of trace elements in orthopyroxene. The 12 norite samples were selected from a recent compilation by Warren who attempted to select the best candidate samples from the standpoint of their pristine character. Our present database includes greater than 300 superior Electromagnetic Pulse (EMP) analyses and greater than 50 scanning ion mass spectroscopy (SIMS) analyses for 8 Rare Earth Elements (REE), Zr, Y, and Sr. The Mg#s for the parental melts calculated from Mg#s in orthopyroxene show that most melts have Mg#s in the range of 0.36-0.60. This compares with a range of Mg#s for lunar volcanic picritic glass beads of 0.4-0.68. Therefore, although the cumulate whole-rock compositions of the Mg suite can be extremely magnesian, the calculated parental melts are not anomalously high in Mg. A chemical characteristic of the Mg-suite norites that is more difficult to explain is the high KREEP content of the calculated parental melts. The REE contents for the calculated norite parental melts have REE that match or exceed the high-K KREEP component of Warren. Therefore, mixing of a KREEP component and a picritic melt cannot, by itself, explain the high estimated REE contents of the melts parental to norites. Advanced crystallization following KREEP incorporation, especially of plagiclase, may also be required.

  8. H2O2: a Ca(2+) or Mg(2+)-sensing function in statin passive diffusion.

    PubMed

    Guillaume, Yves Claude; Lethier, Lydie; André, Claire

    2015-09-01

    In a previous paper Guillaume's group demonstrated that magnesium (Mg(2+) concentration range 0.00-2.60 mm) increased the passive diffusion of statins and thus played a role in their potential toxicity. In order to confirm an increase in this passive diffusion by divalent salt cations, the role of calcium chloride (CaCl2) on the statin-immobilized artificial membrane (IAM) association was studied. It was demonstrated that calcium supplementation (Ca(2+) concentration range 0.00-3.25 mm) increases the statin passive diffusion. In addition, it was shown that the Ca(2+) effect on the statin-IAM association is higher than that of Mg(2+). These results show that Ca(2+) enhances the passive diffusion of drugs into biological membranes and thus their potential toxicity. Also, addition of H2O2 to the medium showed a hyperbolic response for the statin passive diffusion and this effect was enhanced for the highest Ca(2+) or Mg(2+) concentrations in the medium. H2O2 is likely to interact with the polar head groups of the IAM through dipole-dipole interactions. The conformational changes in H2O2-IAM result in a higher degree of exposure of hydrophobic areas, thus explaining why the binding of pravastatin, which showed the lowest logP value, was less affected by H2O2. This result shows the significant contribution of H2O2 and thus the oxidative stress on the statin passive diffusion. Much of the sensitivity derives from the action of Ca(2+) or Mg(2+), in turn supported the idea that H2O2 may serve a Ca(2+) or Mg(2+) sensing function in statin passive diffusion.

  9. Phonon dynamics and Urbach energy studies of MgZnO alloys

    SciTech Connect

    Huso, Jesse Che, Hui; Thapa, Dinesh; Canul, Amrah; Bergman, Leah; McCluskey, M. D.

    2015-03-28

    The Mg{sub x}Zn{sub 1−x}O alloy system is emerging as an environmentally friendly choice in ultraviolet lighting and sensor technologies. Knowledge of defects which impact their optical and material properties is a key issue for utilization of these alloys in various technologies. The impact of phase segregation, structural imperfections, and alloy inhomogeneities on the phonon dynamics and electronic states of Mg{sub x}Zn{sub 1−x}O thin films were studied via selective resonant Raman scattering (SRRS) and Urbach analyses, respectively. A series of samples with Mg composition from 0–68% were grown using a sputtering technique, and the optical gaps were found to span a wide UV range of 3.2–5.8 eV. The extent of the inherent phase segregation was determined via SRRS using two UV-laser lines to achieve resonance with the differing optical gaps of the embedded cubic and wurtzite structural domains. The occurrence of Raman scattering from cubic structures is discussed in terms of relaxation of the selection rules due to symmetry breaking by atomic substitutions. The Raman linewidth and Urbach energy behavior indicate the phase segregation region occurs in the range of 47–66% Mg. Below the phase segregation, the longitudinal optical phonons are found to follow the model of one-mode behavior. The phonon decay model of Balkanski et al. indicates that the major contributor to Raman linewidth arises from the temperature-independent term attributed to structural defects and alloy inhomogeneity, while the contribution from anharmonic decay is relatively small. Moreover, a good correlation between Urbach energy and Raman linewidth was found, implying that the underlying crystal dynamics affecting the phonons also affect the electronic states. Furthermore, for alloys with low Mg composition structural defects are dominant in determining the alloy properties, while at higher compositions alloy inhomogeneity cannot be neglected.

  10. Comparison of serum Concentration of Se, Pb, Mg, Cu, Zn, between MS patients and healthy controls

    PubMed Central

    Alizadeh, Anahita; Mehrpour, Omid; Nikkhah, Karim; Bayat, Golnaz; Espandani, Mahsa; Golzari, Alireza; Jarahi, Lida; Foroughipour, Mohsen

    2016-01-01

    Introduction Multiple Sclerosis (MS) is defined as one of the inflammatory autoimmune disorders and is common. Its exact etiology is unclear. There are some evidences on the role of environmental factors in susceptible genetics. The aim of this study is to evaluate the possible role of Selenium, Zinc, Copper, Lead and Magnesium metals in Multiple Sclerosis patients. Methods In the present analytical cross-sectional study, 56 individuals including 26 patients and 30 healthy controls were enrolled in the evaluation. The serum level of Se, Zn, Cu, Pb were quantified in graphite furnace conditions and flame conditions by utilizing an atomic absorption Perkin Elmer spectrophotometer 3030. The serum levels of Mg were measured by auto analyzer 1500 BT. The mean level of minerals (Zn, Pb, Cu, Mg, Se) in serum samples were compared in both cases and controls. The mean level of minerals (Zn, Pb, Cu, Mg, Se) in serum samples were compared in both cases and controls by using independent-samples t-test for normal distribution and Mann-Whitney U test as a non-parametric test. All statistical analyses were carried out using SPSS 11.0. Results As well as the Zn, Cu, and Se, there was no significant difference between MS patients and healthy individuals in Pb concentrations (p-value = 0.11, 0.14, 0.32, 0.20 respectively) but the level of Mg was significantly different (p= 0.001). Conclusion All serum concentrations of Zn, Pb, Se, Cu in both groups were in normal ranges and there was no difference in MS patients compared with the healthy group who were matched in genetics. Blood level of Mg was significantly lower in MS patients. But it should be noted that even with the low level of serum magnesium in MS patients, this value is still in the normal range. PMID:27757186

  11. The Role of Ca and Mg in Controlling the Skeletal Composition of Scleractinian Corals

    NASA Astrophysics Data System (ADS)

    Swart, Peter; Giri, Sharmila; Devlin, Quinn; Adkins, Jess

    2015-04-01

    The concentrations of many trace and minor elements in aragonitic coral skeletons are widely used within the annual banding structure to provide information on a wide range of environmental factors. Such ratios are measured not only in recent corals, but also in well preserved corals collected from rocks as old as the Triassic where they have been interpreted as reflecting changes in the minor element and calcium concentrations of the oceans. In particular the changing Mg/Ca ratio of seawater throughout geological time. Most of these trace elements are believed to substitute for Ca within the skeleton and therefore a principal tenant of this approach is that the ratio of an element being measured relative to Ca responds directly the same ratio in seawater. In order to test the fundamental assumption in corals we have grown specimens of the coral Pocillopora damicornis in seawater spiked with combinations of elevated Ca and Mg for periods of ~ 10 weeks and measured the concentrations of a number of elements in the new skeletal growth. These elements include Ca, Sr, Mg, Ba, Mn, S, P, B, Li, and Fe. These experiments provide evidence that the minor and trace element incorporation is much more complicated than previously believed. For example, while the Sr/Ca ratio of coral skeletons is directly related to the same ratio in seawater over a wide range, is also influenced by the Mg content of the seawater. Hence raising the Mg content lowers the distribution coefficient for Sr in corals. The incorporation of other elements such as Ba, B, S, and P in the skeleton are influenced in other unexpected ways.

  12. Superconductivity in dense MgB2 wires.

    PubMed

    Canfield, P C; Finnemore, D K; Bud'ko, S L; Ostenson, J E; Lapertot, G; Cunningham, C E; Petrovic, C

    2001-03-12

    MgB2 becomes superconducting just below 40 K. Whereas porous polycrystalline samples of MgB2 can be synthesized from boron powders, in this Letter we demonstrate that dense wires of MgB2 can be prepared by exposing boron filaments to Mg vapor. The resulting wires have a diameter of 160 microm, are better than 80% dense, and manifest the full chi = -1/4pi shielding in the superconducting state. Temperature-dependent resistivity measurements indicate that MgB2 is a highly conducting metal in the normal state with rho(40 K) = 0.38 microOmega cm. By using this value, an electronic mean-free path, l approximately 600 A can be estimated, indicating that MgB2 wires are well within the clean limit. Tc, Hc2(T), and Jc data indicate that MgB2 manifests comparable or better superconducting properties in dense wire form than it manifests as a sintered pellet.

  13. Na(7)Mg(13)Nd(PO(4))(12).

    PubMed

    Jerbi, Hasna; Hidouri, Mourad; Mongi, Ben Amara

    2012-06-01

    Investigations of the quasi-ternary system Na(3)PO(4)-Mg(3)(PO(4))(2)-NdPO(4) allowed us to obtain the new phosphate hepta-sodium trideca-magnesium neodymium dodeca-kis-phosphate, Na(7)Mg(13)Nd(PO(4))(12), by applying a flux method. The crystal structure is isotypic with that of the previously reported Na(7)Mg(13)Ln(PO(4))(12) (Ln = Eu, La) compounds. It consists of a complex three-dimensional framework built up from an NdO(8) polyhedron (m symmetry), an MO(6) octa-hedron statistically occupied by M = Mg and Na, and eight MgO(x) (x = 5, 6) polyhedra (four with site symmetry m), linked either directely by sharing corners, edges and faces, or by one of the eight unique PO(4) tetra-hedra through common corners. Two of the PO(4) tetra-hedra are statisticaly disordered over a mirror plane. The whole structure can be described as resutling from an assembly of two types of structural units, viz [Mg(4)MP(4)O(22)](∞) (2) layers extending parallel to (100) and stacked along [100], and [Mg(4)NdP(4)O(36)](∞) (1) undulating chains running along the [010] direction. The six different Na(+) cations (five with site symmetry m and one with 0.5 occupancy) are situated in six distinct cavities delimited by the framework. The structure was refined from data of a racemic twin.

  14. Elemental maps in human allantochorial placental vessels cells: 2. MgCl2 and MgSO4 effects.

    PubMed

    Michelet-Habchi, Claire; Barberet, Philippe; Dutta, Raj Kumar; Moretto, Philippe; Guiet-Bara, Andrée; Bara, Michel

    2003-09-01

    Extracellular magnesium salts are known to interfere with ionic channels in the cellular membranes. The membrane potential, a regulator of vascular tone, is a function of the physiological activities of ionic channels (particularly, K+ and Ca2+ channels in these cells). These channels regulate the ionic distribution into these cells. Micro-Particule Induced X-ray Emission (PIXE) analysis was applied to determine the ionic composition of vascular smooth muscle cells (VSMC) and of vascular endothelial cells (VEC) in the placental human allantochorial vessels in a physiological medium (Hanks' solution) modified by the addition of 2 mM MgCl2 or 2 mM MgSO4 which block the calcium-sensitive K+ channels (K(Ca)), the ATP-sensitive K+ channels (K(ATP)) and the voltage-sensitive K+ (K(df)) and Ca2+ channels. In VSMC (media layer), the addition of MgCl2 induced no modification of the K, Cl, P, S and Ca concentrations but increased the Na and Mg concentrations and the addition of MgSO4 only significantly increased the Mg concentration, the other ion concentrations remaining constant. In endothelium (VEC), MgCl2 or MgSO4 addition implicated the same observations as in VSMC. These results confirmed the blockage of K(df), K(Ca), K(ATP) and Ca channels in VSMC and VEC by magnesium salts, the relationship between Mg2+ ions and internal Na and demonstrated the possible intervention of a Na+/Mg2+ exchanger.

  15. A Redetermination of the Dissociation Energy of MgO(+)

    NASA Technical Reports Server (NTRS)

    Bauschlicher, Charles W., Jr.; Langhoff, Stephen R.; Partridge, Harry

    1994-01-01

    In 1986, we reported a dissociation energy (D(sub 0) of 2.31 eV for the X(sup 2)Pi ground state of MgO(+). This value was determined by computing the dissociation energy to the Mg(2+) + O(-) limit and adjusting the value to the Mg(+) + O limit using the experimental Ionization Potential (IP) of Mg(+) and the Electron Affinity (EA) of O. The success of this method relies on the assumption that there is little covalent contribution to the bonding. The very small (0.04 eV) correlation contribution to the binding energy was taken as corroboration for the validity of this approach. Our earlier theoretical value was estimated to be accurate to at least 0.2 eV. It is in excellent agreement with the subsequent value of 2.30 +/- 0.13 eV determined by Freiser and co-workers from photodissociation experiments. It is also consistent with the upper (less than 3.1 eV) and lower (greater than 1.1 eV) bounds determined by Rowe obtained by studying the reactions of Mg(+) with 03 and NO2. However, it is inconsistent with an upper bound of 1.7 eV reported by Kappes and Staley based on their failure to observe MgO(+) in the reaction of Mg(+) with N2O. The picture became somewhat clouded, however, by the recent guided-ion beam mass spectrometric studies of Dalleska and Armentrout. Their initial analysis of the reaction data for Mg(+) + O2 lead to a bond dissociation energy of 2.92 +/- 0.25 eV, which is considerably larger than the value of 2.47 +/- 0.06 eV deduced from their studies of the Mg(+)+NO2 reaction.

  16. Study on photorefractive property of Mg:Fe:LiNbO3 crystal

    NASA Astrophysics Data System (ADS)

    Xu, Zhaopeng; Xu, Shiwen; Xu, Yuheng; Wang, Rui

    2005-02-01

    The congruent Fe (0.03%wt):LiNbO3 crystals doped with different concentration of MgO (0, 2, 4, 6 mol%) were grown by Czochralski method in air atmosphere. The ultraviolet-visible absorption spectra, infrared absorption spectra of the crystals were measured in order to analyze their structure. The absorption edge of the Mg: Fe: LiNbO3 crystals shifted to the ultraviolet band compared with that of Fe: LiNbO3. The OH- absorption peaks of I and II crystals located at about 3483cm-1, while those of III and IV crystals shifted to 3536cm-1. The mechanism of OH- absorption peak shifting was studied. The light scattering ability resistance of Mg: Fe: LiNbO3 crystal was observed by straightly observing transmission facula distortion method. It indicated that light scattering ability resistance of III crystals was three orders of magnitude higher than that of Fe: LiNbO3 crystals. The exponential gain coefficient, diffraction efficiency and respond time of Mg: Fe: LiNbO3 crystals were measured by two-wave-coupling technology. The results indicate that exponential gain coefficient of Mg: Fe: LiNbO3 crystal was almost four times as that of iron-doped LiNbO3 and the response time exhibited four times shorter than that of iron-doped LiNbO3. Furthermore, the dynamic range was also calculated by the expression: M # = (τe ∠√η)/τω. The results indicated that Mg (4 mol%): Fe:LiNbO3 was the most proper holographic recording media material among four crystals in the paper.

  17. Suppression of superconductivity in epitaxial MgB2 ultrathin films

    NASA Astrophysics Data System (ADS)

    Zhang, Chen; Wang, Yue; Wang, Da; Zhang, Yan; Liu, Zheng-Hao; Feng, Qing-Rong; Gan, Zi-Zhao

    2013-07-01

    MgB2 ultrathin films have potential to make sensitive superconducting devices such as superconducting single-photon detectors working at relatively high temperatures. We have grown epitaxial MgB2 films in thicknesses ranging from about 40 nm to 6 nm by using the hybrid physical-chemical vapor deposition method and performed electrical transport measurements to study the thickness dependence of the superconducting critical temperature Tc. With reducing film thickness d, although a weak depression of the Tc has been observed, which could be attributed to an increase of disorder (interband impurity scattering) in the film, the Tc retains close to the bulk value of MgB2 (39 K), being about 35 K in the film of 6 nm thick. We show that this result, beneficial to the application of MgB2 ultrathin films and in accordance with recent theoretical calculations, is in contrast to previous findings in MgB2 films prepared by other methods such as co-evaporation and molecular-beam epitaxy, where a severe Tc suppression has been observed with Tc about one third of the bulk value in films of ˜5 nm thick. We discuss this apparent discrepancy in experiments and suggest that, towards the ultrathin limit, the different degrees of Tc suppression displayed in currently obtained MgB2 films by various techniques may arise from the different levels of disorder present in the film or different extents of proximity effect at the film surface or film-substrate interface.

  18. Exposure–response analyses of liraglutide 3.0 mg for weight management

    PubMed Central

    Overgaard, R. V.; Jacobsen, L. V.; Jensen, C. B.; le Roux, C. W.

    2016-01-01

    Aims Liraglutide 3.0 mg, an acylated GLP‐1 analogue approved for weight management, lowers body weight through decreased energy intake. We conducted exposure‐response analyses to provide important information on individual responses to given drug doses, reflecting inter‐individual variations in drug metabolism, absorption and excretion. Methods We report efficacy and safety responses across a wide range of exposure levels, using data from one phase II (liraglutide doses 1.2, 1.8, 2.4 and 3.0 mg), and two phase IIIa [SCALE Obesity and Prediabetes (3.0 mg); SCALE Diabetes (1.8; 3.0 mg)] randomized, placebo‐controlled trials (n = 4372). Results There was a clear exposure–weight loss response. Weight loss increased with greater exposure and appeared to level off at the highest exposures associated with liraglutide 3.0 mg in most individuals, but did not fully plateau in men. In individuals with overweight/obesity and comorbid type 2 diabetes, there was a clear exposure–glycated haemoglobin (HbA1c) relationship. HbA1c reduction increased with higher plasma liraglutide concentration (plateauing at ∼21 nM); however, for individuals with baseline HbA1c >8.5%, HbA1c reduction did not fully plateau. No exposure–response relationship was identified for any safety outcome, with the exception of gastrointestinal adverse events (AEs). Individuals with gallbladder AEs, acute pancreatitis or malignant/breast/benign colorectal neoplasms did not have higher liraglutide exposure compared with the overall population. Conclusions These analyses support the use of liraglutide 3.0 mg for weight management in all subgroups investigated; weight loss increased with higher drug exposure, with no concomitant deterioration in safety/tolerability besides previously known gastrointestinal side effects. PMID:26833744

  19. Selected classes of minimised hammerhead ribozyme have very high cleavage rates at low Mg2+ concentration.

    PubMed Central

    Conaty, J; Hendry, P; Lockett, T

    1999-01-01

    In vitro selection was used to enrich for highly efficient RNA phosphodiesterases within a size-constrained (18 nt) ribonucleotide domain. The starting population (g0) was directed in trans against an RNA oligonucleotide substrate immobilised to an avidin-magnetic phase. Four rounds of selection were conducted using 20 mM Mg2+to fractionate the population on the basis of divalent metal ion-dependent phosphodiesterase activity. The resulting generation 4 (g4) RNA was then directed through a further two rounds of selection using low concentrations of Mg2+. Generation 6 (g6) was composed of sets of active, trans cleaving minimised ribozymes, containing recognised hammerhead motifs in the conserved nucleotides, but with highly variable linker domains (loop II-L.1-L.4). Cleavage rate constants in the g6 population ranged from 0.004 to 1.3 min-1at 1 mM Mg2+(pH 8.0, 37 degrees C). Selection was further used to define conserved positions between G(10.1) and C(11.1) required for high cleavage activity at low Mg2+concentration. At 10 mM MgCl2the kinetic phenotype of these molecules was comparable to a hammerhead ribozyme with 4 bp in helix II. At low Mg2+concentration, the disparity in cleavage rate constants increases in favour of the minimised ribozymes. Favourable kinetic traits appeared to be a general property for specific selected linker sequences, as the high rates of catalysis were transferable to a different substrate system. PMID:10325431

  20. Microfluidic gradient PCR (MG-PCR): a new method for microfluidic DNA amplification.

    PubMed

    Zhang, Chunsun; Xing, Da

    2010-02-01

    This study develops a new microfluidic DNA amplification strategy for executing parallel DNA amplification in the microfluidic gradient polymerase chain reaction (MG-PCR) device. The developed temperature gradient microfluidic system is generated by using an innovative fin design. The device mainly consists of modular thermally conductive copper flake which is attached onto a finned aluminum heat sink with a small fan. In our microfluidic temperature gradient prototype, a non-linear temperature gradient is produced along the gradient direction. On the copper flake of length 45 mm, width 40 mm and thickness 4 mm, the temperature gradient easily spans the range from 97 to 52 degrees Celsius. By making full use of the hot (90-97 degrees Celsius) and cold (60-70 degrees Celsius) regions on the temperature gradient device, the parallel, two-temperature MG-PCR amplification is feasible. As a demonstration, the MG-PCR from three parallel reactions of 112-bp Escherichia coli DNA fragment is performed in a continuous-flow format, in which the flow of the PCR reagent in the closed loop is induced by the buoyancy-driven nature convection. Although the prototype is not optimized, the MG-PCR amplification can be completed in less than 45 min. However, the MG-PCR thermocycler presented herein can be further scaled-down, and thus the amplification times and reagent consumption can be further reduced. In addition, the currently developed temperature gradient technology can be applied onto other continuous-flow MG-PCR systems or used for other analytical purposes such as parallel and combination measurements, and fluorescent melting curve analysis.

  1. Isothermal compression behavior of (Mg,Fe)O using neon as a pressure medium

    SciTech Connect

    Zhuravlev, Kirill K.; Jackson, J.M.; Wolf, A.S.; Wicks, J.K.; Yan, J.; Clark, S.M.

    2012-04-30

    We present isothermal volume compression behavior of two polycrystalline (Mg,Fe)O samples with FeO = 39 and 78 mol% up to {approx}90 GPa at 300 K using synchrotron X-ray diffraction and neon as a pressure-transmitting medium. For the iron-rich (Mg{sub 0.22}Fe{sub 0.78})O sample, a structural transition from the B1 structure to a rhombohedral structure was observed at 41.6 GPa, with no further indication of changes in structural or compression behavior changes up to 93 GPa. In contrast, a change in the compression behavior of (Mg{sub 0.61}Fe{sub 0.39})O was observed during compression at P {ge} 71 GPa and is indicative of a spin crossover occurring in the Fe{sup 2+} component of (Mg{sub 0.61}Fe{sub 0.39})O. The low-spin state exhibited a volume collapse of {approx}3.5%, which is a larger value than what was observed for a similar composition in a laser-heated NaCl medium. Upon decompression, the volume of the high-spin state was recovered at approximately 65 GPa. We therefore bracket the spin crossover at 65 {le} P (GPa) {le} 77 at 300 K (Mg{sub 0.61}Fe{sub 0.39})O. We observed no deviation from the B1 structure in (Mg{sub 0.61}Fe{sub 0.39})O throughout the pressure range investigated.

  2. The oxidation of rolled and heat treated Al-Mg alloys

    NASA Astrophysics Data System (ADS)

    Lea, C.; Ball, J.

    The formation of oxide films on two production grade Al-Mg alloys (0.8wt% and 2.5 wt% Mg) during heat treatment after cold rolling, in the range 350-600°C, in either dry or moist flowing air has been studied. Quantitative Auger electron spectroscopy, in conjunction with argon ion sputtering, has been used to obtain composition-depth profiles through the oxide layers, with concomitant weight gain measurements. The effects on the kinetics and thermodynamics of the oxidation process by changing the bulk magnesium content, the heat treatment and the humidity of the environment have been ascertained. The measurements are consistent with the following oxide growth mechanism. In the cold rolled state a very thin self-healing amorphous film of A1 2O 3 exists. During heat treatment oxide crystallites nucleate and the thickness increases by grain boundary diffusion of aluminium and magnesium to the free surface. The difference in diffusivity of the species ensures that the surface becomes magnesium-rich. An island MgO film forms on the surface while Al 2O 3 in the film is reduced by the outwardly diffusing magnesium to form the spinel MgAl 2O 4. Eventually free aluminium can exist within the oxide. The MgO islands join to form an aluminium-free surface. The kinetics of oxidation and the morphology and composition of the oxide can be controlled by the humidity during heat treatment, probably because of the incorporation of hydroxyl ions. During dry storage at 60°C no significant changes occur in the oxide film but samples stored in moist conditions exhibit a marked reduction in the magnesium atom fraction of the surface, and magnesium-free surfaces can be produced. The implications of the surface layer composition of Al-Mg alloys to joining technology are discussed.

  3. The Physical Nature of Weak MgII Quasar Absorption Line Systems.

    NASA Astrophysics Data System (ADS)

    Narayanan, Anand

    2007-12-01

    In a span of four decades, quasar absorption line spectroscopy has emerged as one of the most efficient methods for probing HI gas and associated metals in a wide range of environments, from redshifts corresponding to the most distant quasars up to the present. The connection between strong MgII quasar absorption systems and the disks/halos of galaxies of various morphologies is fairly well established. In contrast, the physical nature of weak MgII absorbers is not sufficiently understood. In this talk, I will present results from my dissertation work, which is a study of weak MgII quasar absorption line systems at 0MgII clouds, identified at high redshift (z >1), could be gas clouds in the extended halos of galaxies, analogous to the Milky Way high velocity clouds. The gas might correspond to material expelled from rapidly star-forming galaxies in correlated supernova events. Some fraction of the population of weak MgII clouds can also arise along sight lines that intercept tidally stripped interstellar gas, residing in circumgalactic environments. The `iron-rich’ weak MgII clouds, which are prevalent at lower redshifts (z<1), must be tracing Type Ia enriched gas in sites that have been previously enriched by star formation, most likely in dwarf galaxies. These scenarios will be reviewed in my presentation. This work is supported by NSF. I thankfully acknowledge the Zaccheus Daniel Foundation and Sigma Xi for providing generous travel support.

  4. Polyamine/Nucleotide Coacervates Provide Strong Compartmentalization of Mg²⁺, Nucleotides, and RNA.

    PubMed

    Frankel, Erica A; Bevilacqua, Philip C; Keating, Christine D

    2016-03-01

    Phase separation of aqueous solutions containing polyelectrolytes can lead to formation of dense, solute-rich liquid droplets referred to as coacervates, surrounded by a dilute continuous phase of much larger volume. This type of liquid-liquid phase separation is thought to help explain the appearance of polyelectrolyte-rich intracellular droplets in the cytoplasm and nucleoplasm of extant biological cells and may be relevant to protocellular compartmentalization of nucleic acids on the early Earth. Here we describe complex coacervates formed upon mixing the polycation poly(allylamine) (PAH, 15 kDa) with the anionic nucleotides adenosine 5'-mono-, di-, and triphosphate (AMP, ADP, and ATP). Droplet formation was observed over a wide range of pH and MgCl2 concentrations. The nucleotides themselves as well as Mg(2+) and RNA oligonucleotides were all extremely concentrated within the coacervates. Nucleotides present at just 2.5 mM in bulk solution had concentrations greater than 1 M inside the coacervate droplets. A solution with a total Mg(2+) concentration of 10 mM had 1-5 M Mg(2+) in the coacervates, and RNA random sequence (N54) partitioned ∼10,000-fold into the coacervates. Coacervate droplets are thus rich in nucleotides, Mg(2+), and RNA, providing a medium favorable for generating functional RNAs. Compartmentalization of nucleotides at high concentrations could have facilitated their polymerization to form oligonucleotides, which preferentially accumulate in the droplets. Locally high Mg(2+) concentrations could have aided folding and catalysis in an RNA world, making coacervate droplets an appealing platform for exploring protocellular environments. PMID:26844692

  5. Magnetic anisotropy and order structure of L10-FePt(001) single-crystal films grown epitaxially on (001) planes of MgO, SrTiO3, and MgAl2O4 substrates

    NASA Astrophysics Data System (ADS)

    Hotta, A.; Ono, T.; Hatayama, M.; Tsumura, K.; Kikuchi, N.; Okamoto, S.; Kitakami, O.; Shimatsu, T.

    2014-05-01

    L10-FePt(001) single-crystal films were grown epitaxially on SrTiO3(001), MgAl2O4(001), and MgO(001) substrates. Their uniaxial magnetic anisotropy Ku and the order structure were examined for the film thickness t range of 2-14 nm. All series of films show large Ku of 4 × 107 erg/cm3 in the thickness range higher than 10 nm, with order parameter S of 0.8 and saturation magnetization Ms of 1120 emu/cm3. Ku decreased gradually as t decreased. The Ku reduction was considerable when t decreased from 4 nm to 2 nm. No marked difference in the thickness dependence of Ku was found in any series of films, although the lattice mismatch between FePt and the substrates was markedly different. Ku reduction showed good agreement with the reduction of S for the films on MgAl2O4 and MgO. The Ku ˜ S2 plot showed an almost linear relation, which is in good agreement with theoretical predictions. Transmission electron microscopy images for a FePt film on MgO substrate revealed that the lattice mismatch between FePt(001) and MgO(001) was relaxed in the initial 1 or 2 layers of FePt(001) lattices, which is likely to be true also for two other series of films.

  6. Superconductivity of Metallic Boron in MgB2

    NASA Astrophysics Data System (ADS)

    Kortus, J.; Mazin, I. I.; Belashchenko, K. D.; Antropov, V. P.; Boyer, L. L.

    2001-05-01

    Boron in MgB2 forms stacks of honeycomb layers with magnesium as a space filler. Band structure calculations indicate that Mg is substantially ionized, and the bands at the Fermi level derive mainly from B orbitals. Strong bonding with an ionic component and considerable metallic density of states yield a sizable electron-phonon coupling. Together with high phonon frequencies, which we estimate via zone-center frozen phonon calculations to be between 300 and 700 cm-1, this produces a high critical temperature, consistent with recent experiments. Thus MgB2 can be viewed as an analog of the long sought, but still hypothetical, superconducting metallic hydrogen.

  7. Matter radii of {sup 32-35}Mg

    SciTech Connect

    Kanungo, R.; Perro, C.; Prochazka, A.; Farinon, F.; Knoebel, R.; Horiuchi, W.; Nociforo, C.; Aumann, T.; Geissel, H.; Gerl, J.; Kindler, B.; Lommel, B.; Mahata, K.; Scheidenberger, C.; Weick, H.; Winkler, M.; Boutin, D.; Lenske, H.; Cortina-Gil, D.; Davids, B.

    2011-02-15

    The interaction cross sections of {sup 32-35}Mg at 900A MeV have been measured using the fragment separator at GSI. The deviation from the r{sub 0}A{sup 1/3} trend is slightly larger for {sup 35}Mg, signaling the possible formation of a longer tail in the neutron distribution for {sup 35}Mg. The radii extracted from a Glauber model analysis with Fermi densities are consistent with models predicting the development of neutron skins.

  8. Mg II 2800 A emission in late type stars

    NASA Technical Reports Server (NTRS)

    Doherty, L. R.

    1972-01-01

    The largest body of data on ultraviolet spectra of late-type stars now available is the series of scans made with the long wavelength spectrometer onboard OAO-2. Some features of selected scans from this series and estimates of Mg II emission fluxes were reported earlier. Since that time, the effects of sky background, scattered light and variable instrumental sensitivity have become better understood. Additional stars are used to define more clearly the transition from Mg II 2800 A absorption to emission with advancing spectral type, and additional scans of alpha Sco provide a better estimate of Mg II emission strength for this supergiant in OAO observations.

  9. Superconductivity of metallic boron in MgB2.

    PubMed

    Kortus, J; Mazin, I I; Belashchenko, K D; Antropov, V P; Boyer, L L

    2001-05-14

    Boron in MgB2 forms stacks of honeycomb layers with magnesium as a space filler. Band structure calculations indicate that Mg is substantially ionized, and the bands at the Fermi level derive mainly from B orbitals. Strong bonding with an ionic component and considerable metallic density of states yield a sizable electron-phonon coupling. Together with high phonon frequencies, which we estimate via zone-center frozen phonon calculations to be between 300 and 700 cm(-1), this produces a high critical temperature, consistent with recent experiments. Thus MgB2 can be viewed as an analog of the long sought, but still hypothetical, superconducting metallic hydrogen.

  10. PROPERTIES OF DEFECTS AND IMPLANTS IN Mg+ IMPLANTED SILICON CARBIDE

    SciTech Connect

    Jiang, Weilin; Zhu, Zihua; Varga, Tamas; Bowden, Mark E.; Manandhar, Sandeep; Roosendaal, Timothy J.; Hu, Shenyang Y.; Henager, Charles H.; Kurtz, Richard J.; Wang, Yongqiang

    2013-09-25

    As a candidate material for fusion reactor designs, silicon carbide (SiC) under high-energy neutron irradiation undergoes atomic displacement damage and transmutation reactions that create magnesium as one of the major metallic products. The presence of Mg and lattice disorder in SiC is expected to affect structural stability and degrade thermo-mechanical properties that could limit SiC lifetime for service. We have initiated a combined experimental and computational study that uses Mg+ ion implantation and multiscale modeling to investigate the structural and chemical effects in Mg implanted SiC and explore possible property degradation mechanisms.

  11. Electronic structure of Mg: From monolayers to bulk

    SciTech Connect

    Schiller, F.; Laubschat, C.; Heber, M.; Servedio, V.D.P.

    2004-09-15

    The structure of thin Mg films epitaxially grown onto a W(110) crystal was analyzed by low energy electron and Auger electron diffraction verifying a growth of bulk Mg. Normal-emission angle-resolved photoemission spectra of the growing films reveal quantum well states on both sides of a surface state. These states result from electron confinement in the Mg layer and are used to derive the electronic structure perpendicular to the surface. Off-normal, the electronic structure is dominated by the parabolic dispersion of surface states forming circles around the {gamma}-points and ellipses around the M-points in the Fermi surface cuts.

  12. Calculation of Mg(+)-ligand relative binding energies

    NASA Technical Reports Server (NTRS)

    Partridge, Harry; Bauschlicher, Charles W., Jr.

    1992-01-01

    The calculated relative binding energies of 16 organic molecules to Mg(+) are compared with experimental results where available. The geometries of the ligands and the Mg(+)-ligand complexes arc optimized at the self-consistent field level using a 6-31G* basis set. The Mg(+) binding energies are evaluated using second-order perturbation theory and basis sets of triple-sigma quality augmented with two sets of polarization functions. This level of theory is calibrated against higher levels of theory for selected systems. The computed binding energies are accurate to about 2 kcal/mol.

  13. Mg isotope fractionation between inorganic aragonite and aqueous solution

    NASA Astrophysics Data System (ADS)

    Wang, Z.; Zhang, S.; Hu, P.

    2012-12-01

    Recent studies showed δ26Mg values of some species of Scleractinian corals, and aragonitic sponges and Scaphopod are inconsistent with the Mg isotope fractionation calibrated previously between inorganic aragonite and seawater. In this study, we explored Mg isotope fractionation between aragonite and aqueous solution under various experimental conditions, including salinity (mostly in fresh water), Mg/Ca ratio (3-5 in molar), Ca concentration (400-1500 ppm), temperature (25-55oC) and duration of experiments (3-21 days). Precipitation experiments were conducted using 'free-drift' method. The starting solution was made by mixing an appropriate amount of reagent-grade NaHCO3, CaCl2 and MgCl2 in deionized water, flushed with CO2 gas. The mixed solution was filtered after these reagents completely dissolved before any experiment, and then passively-degassed in a water bath kept at a constant temperature. Over the course of the experiments, pH and alkalinity of the aqueous solution were closely monitored. At the end of the experiment, the precipitates were cleaned, characterized by SEM and checked by XRD. The solution and precipitates were treated by acid. The supernatant was passed through two chromatographic columns to extract pure Mg, and measured for their δ26Mg values. In each case, a leaching procedure is employed to clean aragonite before their isotopic compositions were measured. Our preliminary results show that the Mg isotope fractionation between aragonite and solution varies with Ca concentration at a given Mg/Ca ratio, i.e., aragonite are strongly depleted in 26Mg in solution with high and low Ca concentration (e.g., Ca = 400ppm and 2000 ppm), but less depleted in solutions with intermediate Ca concentration (e.g., Ca= 1000 ppm). At a given Ca and Mg/Ca, the fractionation factor is temperature-dependent, defining linear relationship with 1/T (T is temperature in Kelvin) with temperature sensitivity of ~ 0.01‰/oC. These results seem to suggest a kinetic

  14. 26Al- 26Mg deficit dating ultramafic meteorites and silicate planetesimal differentiation in the early Solar System?

    NASA Astrophysics Data System (ADS)

    Baker, Joel A.; Schiller, Martin; Bizzarro, Martin

    2012-01-01

    Meteorites with significantly sub-chondritic Al/Mg that formed in the first 2 million years of the Solar System should be characterised by deficits in the abundance of 26Mg (δ26Mg∗) due to the absence of in-growth of 26Mg from the decay of short-lived 26Al (t1/2 = 0.73 Myr). However, these 26Mg deficits will be small (δ26Mg∗ >-0.037‰) even for material that formed at the same time as the Solar System’s oldest solids - calcium-aluminium-rich inclusions - and thus measurement of these deficits is analytically challenging. Here, we report on a search for 26Mg deficits in three types of ultramafic meteorites (pallasites, ureilites and aubrites) by multiple-collector inductively coupled plasma mass spectrometry. A range of analytical tests were carried out including analysis of: (1) a range of synthetic Mg solution standards; (2) Mg gravimetrically doped with a high purity 26Mg spike; (3) Mg cuts collected sequentially from cation exchange separation columns with fractionated stable Mg isotope compositions; (4) Mg separated from samples that was bracketed by analyses of both DSM-3 and Mg separated from a natural olivine sample subjected to the same chemical processing as the samples. These tests confirm it is possible to resolve differences in δ26Mg∗ from the terrestrial materials that are ⩽0.005‰. However, if Mg yields from chemical separation are low or an inappropriate equilibrium-isotopically fractionated standard is used this will generate analytical artefacts on δ26Mg∗ when this is calculated with the kinetic/exponential mass fractionation law as is the case when correcting for instrumental mass bias during mass spectrometric analysis. Olivine from four different main group pallasites and four bulk ureilites have small deficits in the abundance of 26Mg with δ26MgDSM-3∗=-0.0120±0.0018‰ and δ26MgDSM-3∗=-0.0062±0.0023‰, respectively, relative to terrestrial olivine (δ26MgDSM-3∗=+0.0029±0.0028‰). Six aubrites have δ26MgDSM-3

  15. Control of carbonate alkalinity on Mg incorporation in calcite: Insights on the occurrence of high Mg calcites in diagenetic environments

    NASA Astrophysics Data System (ADS)

    Purgstaller, Bettina; Mavromatis, Vasileios; Dietzel, Martin

    2015-04-01

    High Mg calcites (HMC), with up to 25 mol % of Mg, are common features in early diagenetic environments and are frequently associated with bio-induced anaerobic oxidation of methane (AOM). Such archives hold valuable information about the biogeochemical processes occurring in sedimentary environments in the geological past. Despite the frequency AOM-induced HMC observed in marine diagenetic settings and their potential role in dolomitization, only a minor number of experimental studies has been devoted on deciphering their formation conditions. Thus, in order to improve our understanding on the formation mechanism of HMC induced by elevated carbonate ion concentrations, we precipitated HMC by computer controlled titration of a (Mg,Ca)Cl2 solution at different Mg/Ca ratios into a NaHCO3 solution under precisely defined physicochemical conditions (T = 25.00 ±0.03°C; pH = 8.3 ±0.1). The formation of carbonates was monitored at a high temporal resolution using in situ Raman spectroscopy as well as by continuous sampling and analyzing of precipitates and reactive solutions. We identified two distinct mechanisms of HMC formation. In solutions with molar Mg/Ca ratios ≤ 1/8 calcium carbonate was precipitated as crystalline phases directly from homogeneous solution. In contrast, higher Mg/Ca ratios induced the formation of Mg-rich ACC (up to 10 mol % of Mg), which was subsequently transformed to HMC with up 20 mol % of Mg. Our experimental results highlight that the finally formed HMC has a higher Mg content than the ACC precursor phase. Considering experimental data for Mg containing ACC transformation to crystalline calcium carbonate from literature, the continuous enrichment of Mg in the precipitate throughout transformation of amorphous to crystalline CaCO3 most likely occurs due to the high carbonate alkalinity (DIC about 0.1 M) of our reactive solutions. The Mg incorporation into calcite lattice seems to be favored by intensive supply of carbonate ions as

  16. Evaluation of foraminiferal trace element cleaning methods on the Mg/Ca of marine ostracoda Krithe

    NASA Astrophysics Data System (ADS)

    Gray, W. R.; Holmes, J. A.; Shevenell, A.

    2012-12-01

    microscopy reveals etching of the calcite surface layer following reductive cleaning, suggesting that lower Mg concentrations result from the partial dissolution of the valve's calcite surface. However, both adults and juveniles display the lowest analytical error (7% and 4%, respectively) after reductive cleaning, equivalent to an error of ±0.8oC in adults and ±0.5oC in juveniles suggesting that reductive cleaning may remove high-Mg calcite overgrowths. Finally, we find that valve height explains a greater amount of the Mg/Ca variance than Fe, Al and Mn concentrations, implying that much of the analytical error associated with Krithe Mg/Ca relates to biological variability. Taken together, our results indicate that sonication in methanol is a critical step in the preparation of marine ostracods for accurate and precise primary Mg/Ca analyses, and that identification of an optimal valve height range is required.

  17. The studying of washing of arsenic and sulfur from coals having different ranges of arsenic contents

    USGS Publications Warehouse

    Wang, M.; Song, D.; Zheng, B.; Finkelman, R.B.; ,

    2008-01-01

    To study the effectiveness of washing in removal of arsenic and sulfur from coals with different ranges of arsenic concentration, coal was divided into three groups on the basis of arsenic content: 0-5.5 mg/kg, 5.5 mg/kg-8.00 mg/kg, and over 8.00 mg/kg. The result shows that the arsenic in coals with higher arsenic content occurs mainly in an inorganic state and can be relatively easily removed. Arsenic removal is very difficult and less complete when the arsenic content is lower than 5.5 mg/kg because most of this arsenic is in an organic state. There is no relationship between washing rate of total sulfur and arsenic content, but the relationship between the washing rate of total sulfur and percent of organic sulfur is very strong. ?? 2008 New York Academy of Sciences.

  18. The studying of washing of arsenic and sulfur from coals having different ranges of arsenic contents

    SciTech Connect

    Mingshi Wang; Dangyu Song; Baoshan Zheng; R.B. Finkelman

    2008-10-15

    To study the effectiveness of washing in removal of arsenic and sulfur from coals with different ranges of arsenic concentration, coal was divided into three groups on the basis of arsenic content: 0-5.5 mg/kg, 5.5 mg/kg-8.00 mg/kg, and over 8.00 mg/kg. The result shows that the arsenic in coals with higher arsenic content occurs mainly in an inorganic state and can be relatively easily removed. Arsenic removal is very difficult and less complete when the arsenic content is lower than 5.5 mg/kg because most of this arsenic is in an organic state. There is no relationship between washing rate of total sulfur and arsenic content, but the relationship between the washing rate of total sulfur and percent of organic sulfur is very strong.

  19. The effects of diagenesis and dolomitization on Ca and Mg isotopes in marine platform carbonates: Implications for the geochemical cycles of Ca and Mg

    NASA Astrophysics Data System (ADS)

    Fantle, Matthew S.; Higgins, John

    2014-10-01

    The Ca, Mg, O, and C isotopic and trace elemental compositions of marine limestones and dolostones from ODP Site 1196A, which range in depth (∼58 to 627 mbsf) and in depositional age (∼5 and 23 Ma), are presented. The objectives of the study are to explore the potential for non-traditional isotope systems to fingerprint diagenesis, to quantify the extent to which geochemical proxies are altered during diagenesis, and to investigate the importance of diagenesis within the global Ca and Mg geochemical cycles. The data suggest that Ca, which has a relatively high solid to fluid mass ratio, can be isotopically altered during diagenesis. In addition, the alteration of Ca correlates with the alteration of Mg in such a way that both can serve as useful tools for deciphering diagenesis in ancient rocks. Bulk carbonate δ44Ca values vary between 0.60 and 1.31‰ (SRM-915a scale); the average limestone δ44Ca is 0.97 ± 0.24‰ (1SD), identical within error to the average dolostone (1.03 ± 0.15 1SD ‰). Magnesium isotopic compositions (δ26Mg, DSM-3 scale) range between -2.59‰ and -3.91‰, and limestones (-3.60 ± 0.25‰) and dolostones (-2.68 ± 0.07‰) are isotopically distinct. Carbon isotopic compositions (δ13C, PDB scale) vary between 0.86‰ and 2.47‰, with average limestone (1.96 ± 0.31‰) marginally offset relative to average dolostone (1.68 ± 0.57‰). The oxygen isotopic compositions (δ18O, PDB scale) of limestones (-1.22 ± 0.94‰) are substantially lower than the dolostones measured (2.72 ± 1.07‰). The isotopic data from 1196A suggest distinct and coherent trends in isotopic and elemental compositions that are interpreted in terms of diagenetic trajectories. Numerical modeling supports the contention that such trends can be interpreted as diagenetic, and suggests that the appropriate distribution coefficient (KMg) associated with limestone diagenesis is ∼1 to 5 × 10-3, distinctly lower than those values (>0.015) reported in laboratory

  20. Mechanical properties and phase composition of potential biodegradable Mg-Zn-Mn-base alloys with addition of rare earth elements

    SciTech Connect

    Stulikova, Ivana; Smola, Bohumil

    2010-10-15

    Mechanical properties and creep resistance of the MgY4Zn1Mn1 alloy in the as cast as well as in the T5 condition were compared to those of the MgCe4Zn1Mn1 alloy in the same conditions. Yield tensile stress and ultimate tensile strength of the MgY4Zn1Mn1 alloy are slightly better in the temperature range 20 deg. C-400 deg. C than these of the MgCe4Zn1Mn1 alloy. Better thermal stability of ultimate tensile strength was observed in the T5 treated MgCe4Zn1Mn1 alloy than in this material in the as cast condition. An outstanding creep resistance at 225 deg. C-350 deg. C found in the MgY4Zn1Mn1 alloy is due to the existence of the 18R long period stacking structure persisting in this alloy even a long heat treatment of 500 deg. C/32 h. No similar stacking effects happen when Ce substitutes Y in approximately the same concentration. The creep resistance deteriorates considerably in the MgCe4Zn1Mn1 alloy. Rectangular particles of the equilibrium Mg{sub 12}Ce phase dominate in the microstructure of as cast as well as of high temperature heat-treated MgCe4Zn1Mn1 alloy. A population of small oval particles containing Mg and Zn develops additionally during annealing of this alloy. These particles pin effectively dislocations and can be responsible for the better thermal stability of the T5 treated material.