27,477 research outputs found
Enhanced flux pinning and formation of Ba4Y2CuMoOy in top-seeded melt growth processed YBa2Cu3O7-d superconductors with Mo additions
No full textThe effect of Mo addition (0-10 wt%) on the superconductivity of top-seeded melt growth (TSMG) processed YBa2Cu3O7-y (Y123) superconductors was studied. The low level Mo addition (<= 1 wt%) led to a small decrease of the superconducting transition temperature (T-c) and increase of the critical current density (J(c)). The J(c) improvement induced by the low level Mo additions appeared as a peak effect at the intermediated magnetic fields and peak position shift to the lower magnetic fields with increasing Mo content. The enhanced flux pinning caused by Mo additions seems to be attributed to the partial Cu substitution by Mo, YBa2(Cu1-xMox)(3)O7-d. The high level Mo additions (2-10 wt%), however, led to a large J(c) decrease and broad superconducting transition due to the formation of low-T-c phases and the increased volume of the non-superconducting Mo-containing phase. The second particle phase formed by the high level Mo additions was identified as Ba4Y2CuMoOy (Mo4211) by x-ray diffraction (XRD) and scanning electron microscopy energy dispersive x-ray (SEM EDX) analysis
The first layered analogue of Sr<sub>2</sub>FeMoO<sub>6</sub>; the structure and electronic properties of Sr<sub>4</sub>FeMoO<sub>8</sub>
No full textThe n = 1 Ruddlesden–Popper phase Sr4FeMoO8 has been synthesised by high temperature ceramic methods under reducing conditions. Rietveld refinements of the structure against X-ray and neutron powder diffraction data shows that this phase adopts the space group I4/mmm (a = 3.92962(5), c = 12.6707(2) Å) and contains a crystallographically disordered arrangement of Fe and Mo on the single octahedral site in the structure. Mössbauer spectroscopy data show that iron is in the trivalent state and that the transition metals are fully disordered at a local scale. SQUID magnetometry measurements and low temperature neutron diffraction experiments have been used to examine the magnetic properties of this material. The magnetic susceptibility shows Curie–Weiss paramagnetism above a magnetic transition at 16(1) K. Below this temperature the sample shows magnetic hysteresis, but the neutron diffraction data show no evidence of the additional Bragg intensity associated with the formation of a magnetically ordered phase. The magnetic transition at 16 K is therefore assigned to the formation of a spin-glass phase. The absence of magnetic order in this material is due to the chemical disorder in the Fe/Mo occupancy of the octahedral site and thus the randomisation of the magnetic exchange interactions
Studies on Bis(imido) molybdenum complexes containing unsaturated hydrocarbon ligands
No full textThis thesis describes the synthesis and characterisation of molybdenum bis(imido) complexes containing unsaturated hydrocarbon ligands. A principal objective of the work was to examine the effect of various imido substituents on the coordination number of the complex and the orientations adopted by olefin and acetylene ligands. Chapter One highlights areas of transition metal chemistry relevant to the thesis, with particular emphasis on the psuedo-isolobal analogy between cyclopentadienyl and imido ligands, A convenient one-pot synthesis of molybdenum bis(imido) complexes of the type Mo(NR)(NR')Cl(_2).DME (R=R'=l-adamantyl, 2-t- BUC(_6)H(_4); R=2,6-i-Pr(_2)C(_6)H(_3), R'=t-Bu) is described in Chapter Two. Mo(N-l- adamantyl)(O)Cl(_2).DME has been synthesised, and its structure determined by single crystal X-ray diffraction.- The preparation of olefin complexes Mo(NR)(NR')(C(_2)H(_4))(PMe(_3))n (R=R'=l-adamantyl, n=l; R=R'=2-t-BuC(_6)H(_4), n=2; R=2,6-i-Pr(_2)C(_6)H(_3), R'=t- Bu, n=l) is outlined in Chapter Three. Structural information derived from NMR data has allowed comparison with metallocene-like olefin adducts. Chapter Four describes the synthesis of complexes containing σ-bound phenyl ligands (Mo(NR)(NR')(σ-C(_6)H(_5))(PMe(_3)) (R=R'=l-adamantyl, 2-t-BuC(_6)H(_4); R=2,6-i-Pr(_2)C(_6)H(_3), R'=t-Bu)) as potential precursors to benzyne complexes. Chapter Five describes the preparation of diphenylacetylene complexes Mo(NR)(NR')(PhC=CPh)(PMe(_3)), structural information derived from NMR data allows comparison with previously known metallocene-like acetylene complexes. Full experimental details for Chapters Two to Five are given in Chapter Six
Electrical, morphological and structural properties of RF magnetron sputtered Mo thin films for application in thin film photovoltaic solar cells
No full textMolybdenum (Mo) thin films were deposited using radio frequency magnetron sputtering, for application as a metal back contact material in ‘‘substrate configuration’’ thin film solar cells. The variations of the electrical, morphological, and structural properties of the deposited films with sputtering pressure, sputtering power and post-deposition annealing were determined. The electrical conductivity of the Mo films was found to increase with decreasing sputtering pressure and increasing sputtering power. X-ray diffraction data showed that all the films had a (110) preferred orientation that became less pronounced at higher sputtering power while being relatively insensitive to process pressure. The lattice stress within the films changed from tensile to compressive with increasing sputtering power and the tensile stress increased with increasing sputtering pressure. The surface morphology of the films changed from pyramids to cigar-shaped grains for a sputtering power between 100 and 200 W, remaining largely unchanged at higher power. These grains were also observed to decrease in size with increasing sputtering pressure. Annealing the films was found to affect the resistivity and stress of the films. The resistivity increased due to the presence of residual oxygen and the stress changed from tensile to compressive. The annealing step was not found to affect the crystallisation and grain growth of the Mo films
Nuevos aceros sinterizados de baja aleación Al Cr-Mo : sinterabilidad, comportamiento mecánico y tribológico, tratamientos térmicos y termoquímicos
No full textEn esta Tesis Doctoral se estudia con profundidad el desarrollo de aceros sinterizados de baja aleación aleados con Cr, Mo y Mn, siendo su principal objetivo la optimización del comportamiento mecánico y tribológico de aceros basados en el polvo prealeado Fe 3Cr-0,5Mo, mediante actuaciones en el proceso de conformado y los tratamientos térmicos y termoquímicos.
En metalurgia de polvos existen dos posibles vías que conducen a la mejora del nivel de las propiedades mecánicas y tribológicas de un material: 1) actuar sobre la densidad y, 2) modificar el sistema de aleación, introduciendo nuevos elementos que propicien mejoras por
endurecimiento por solución sólida o bien a través de los tratamientos térmicos.
En esta Tesis Doctoral se ha actuado en los dos sentidos. Por un lado se ha mejorado la densidad: mediante compactación de polvos precalentados (“warm compaction”), sinterizando a
temperaturas elevadas (1250°C) o modificando el proceso de sinterización introduciendo fases líquidas transitorias. Y también se ha utilizado la segunda vía, utilizándose la adición de Mn como posible camino de mejora de las propiedades.
Todos los materiales desarrollados, han sido optimizados mediante un completo estudio de sinterabilidad, apoyado en técnicas de análisis térmico (dilatometría, y análisis térmico
diferencial con análisis termogravimétrico simultáneo, “STA”), y caracterizados desde el punto de vista mecánico y tribológico, tanto
en estado sinterizado como tratado térmica y termoquímicamente.
Aunque el cromo sea un elemento al uso en los aceros de colada, en los aceros pulvimetallúrgicos, debido a su gran afinidad
por el oxígeno, su implantación se ha visto limitada por el desarrollo tecnológico de hornos y control de atmósferas. Su utilización, al
igual que el manganeso, cayó en desuso a partir de los 80. La década de los 90 y el final de los 80 han estado marcadas por la aceptación de los polvos, bien aleados por difusión o bien prealeados, con contenidos en níquel, molibdeno y cobre fundamentalmente. Solucionar esas limitaciones técnicas, y encontrar la forma para optimizar la sinterización de aceros con contenidos en cromo, es otro de los objetivos de esta investigación.
_________________________________________________The development of this Thesis comprises a deeply study of low prealloyed sintered steels with Cr, Mo and Mn. Its main objective is optimise the mechanical and wear behaviour of sintered steel based
on a prealloyed powder Fe-3Cr-0,5Mo, through improvements on
processing parameters, either on compactation and sintering or on
secondary treatments as heat and thermo chemical treatments.
In powder metallurgy there is two possible ways to lead an
increase of mechanical properties and wear resistance level: 1) it is
possible to act on the density, 2) to modify the alloy system by
adding new alloying elements that promote by solid solution
improvements, or through heat treatments.
Both senses have been taken into account in this Thesis.
Density has been enhanced by warm compaction and high sintering
temperature (1250°C), or by modifying the sintering process
introducing transient liquid phases. Mn additions are the answer
when solid solution effect or heat treatments improvements want to
be achieved.
Ah materials have been optimised through a complete sintered
study, based on thermal analysis (STA and dilatometries). They have
been characterised from the point of view of their mechanical and
wear behaviour, comparing in every case ah the possible finished
states that the material could has.
Although chromium was a common used alloy element on ingot
steels, in powder metallurgy, due to its high oxygen affinity, its
introduction has been imitated for the technical resources as wehl as
for the improper atmosphere control. Its use, with manganese
element, falls down in 80’s. The 90’s decade and also the lasts 80’s
have been marked for the favourable reception of prealloyed steels
with Nickel, Molybdenum and Copper. To solve technical limitations
and to find the appropriate sintering process of chromium-alloyed
steels are also objectives of this research
Measurement of J/Ψ production in pp collisions at √s=7 TeV
No full textThe production of J/psi mesons in proton-proton collisions at root s = 7 TeV is studied with the LHCb detector at the LHC. The differential cross-section for prompt J/psi production is measured as a function of the J/psi transverse momentum p(T) and rapidity y in the fiducial region p(T) is an element of [0; 14] GeV/c and y is an element of [2.0; 4.5]. The differential cross-section and fraction of J/psi from b-hadron decays are also measured in the same p(T) and y ranges. The analysis is based on a data sample corresponding to an integrated luminosity of 5.2 pb(-1). The measured cross-sections integrated over the fiducial region are 10.52 +/- 0.04 +/- 1.40(-2.20)(+1.64) mu b for prompt J/psi production and 1.14 +/- 0.01 +/- 0.16 mu b for J/psi from b-hadron decays, where the first uncertainty is statistical and the second systematic. The prompt J/psi production cross-section is obtained assuming no J/psi polarisation and the third error indicates the acceptance uncertainty due to this assumption
sj-docx-1-jdr-10.1177_00220345221084200 – Supplemental material for Identification of Periosteal Osteogenic Progenitors in Jawbone
No full textSupplemental material, sj-docx-1-jdr-10.1177_00220345221084200 for Identification of Periosteal Osteogenic Progenitors in Jawbone by Y. Ding, C. Mo, J. Geng, J. Li and Y. Sun in Journal of Dental Research</p
Evidence for the decay B0→J/ψω and measurement of the relative branching fractions of meson decays to J/ψη and J/ψη′
No full textFirst evidence of the B 0 → J / ψ ω decay is found and the B s 0 → J / ψ η and B s 0 → J / ψ η ′ decays are studied using a dataset corresponding to an integrated luminosity of 1.0 fb -1 collected by the LHCb experiment in proton-proton collisions at a centre-of-mass energy of sqrt(s) = 7 TeV. The branching fractions of these decays are measured relative to that of the B 0 → J / ψ ρ 0 decay:frac(B (B 0 → J / ψ ω), B (B 0 → J / ψ ρ 0)) = 0.89 ± 0.19 (stat) - 0.13 + 0.07 (syst),frac(B (B s 0 → J / ψ η), B (B 0 → J / ψ ρ 0)) = 14.0 ± 1.2 (stat) - 1.5 + 1.1 (syst) - 1.0 + 1.1 (frac(f d, f s)),frac(B (B s 0 → J / ψ η ′), B (B 0 → J / ψ ρ 0)) = 12.7 ± 1.1 (stat) - 1.3 + 0.5 (syst) - 0.9 + 1.0 (frac(f d, f s)), where the last uncertainty is due to the knowledge of f d / f s, the ratio of b-quark hadronization factors that accounts for the different production rate of B 0 and B s 0 mesons. The ratio of the branching fractions of B s 0 → J / ψ η ′ and B s 0 → J / ψ η decays is measured to befrac(B (B s 0 → J / ψ η ′), B (B s 0 → J / ψ η)) = 0.90 ± 0.09 (stat) - 0.02 + 0.06 (syst)
Measurement of the ratio of prompt χ c to J / ψ production in pp collisions at √s = 7 TeV
No full textThe prompt production of charmonium χ c and J / ψ states is studied in proton-proton collisions at a centre-of-mass energy of √s = 7 TeV at the Large Hadron Collider. The χ c and J / ψ mesons are identified through their decays χ c → J / ψ γ and J / ψ → μ + μ - using 36 pb - 1 of data collected by the LHCb detector in 2010. The ratio of the prompt production cross-sections for χ c and J / ψ, σ (χ c → J / ψ γ) / σ (J / ψ), is determined as a function of the J / ψ transverse momentum in the range 2 < p T J / ψ < 15 GeV / c. The results are in excellent agreement with next-to-leading order non-relativistic expectations and show a significant discrepancy compared with the colour singlet model prediction at leading order, especially in the low p T J / ψ region
- …
