312 research outputs found
The effect of Nb2O5 and ZrO2 additions on the behaviour of Li/MgO and Li/Na/MgO catalysts for the oxidative coupling of methane
Incorporation of Nb2O5 or ZrO2 into both Li/MgO and Li/Na/MgO systems produced ternary and quaternary catalysts, respectively, capable of attaining optimal C2 yields and selectivities at lower temperatures relative to the unpromoted materials. The degree of enhancement effected by these metal oxide additives was compared to that produced by Li/MgO and Li/Na/MgO catalysts promoted with SnO2 or Co3O4. At reaction temperatures < 700°C, the Li/Co/MgO ternary system showed marked differences in behaviour compared to the other ternary catalysts tested. This was particularly evident in the variation in C2 selectivity with time on stream during ageing studies of (i) untreated materials, (ii) materials pretreated in CO2, and (iii) materials dosed periodically with CHCI3
TAP reactor investigation of methane coupling over samarium oxide catalysts
The adsorption and reaction characteristics of a Ba/Sr/Sm2O3 catalyst for methane coupling has been investigated using the TAP (Temporal Analysis of Products) reactor system. Pulsed adsorption experiments using methane, oxygen and krypton at temperatures ranging from 17°C to 800°C show that the transient response of methane is similar to that of Kr and is either not adsorbed, or weakly adsorbed on the catalyst. By contrast, oxygen is strongly adsorbed at temperatures above 500°C which suggests incorporation into the lattice with possible formation of surface anions. Pump-probe experiments in which methane and oxygen are introduced over the catalyst were also performed to investigate the effect of lifetimes of suspected surface intermediates on the relative yields of ethane and ethene. It is shown that the relative yields of both species increase with increasing values of the pulse valve time delay between introduction of the oxygen and methane. An explanation of these results using current knowledge and reasonable speculation of the mechanism is provided
Dynamics of electrostatically-driven granular media. Effects of Humidity
We performed experimental studies of the effect of humidity on the dynamics
of electrostatically-driven granular materials. Both conducting and dielectric
particles undergo a phase transition from an immobile state (granular solid) to
a fluidized state (granular gas) with increasing applied field. Spontaneous
precipitation of solid clusters from the gas phase occurs as the external
driving is decreased. The clustering dynamics in conducting particles is
primarily controlled by screening of the electric field but is aided by
cohesion due to humidity. It is shown that humidity effects dominate the
clustering process with dielectric particles.Comment: 4 pages, 4 fig
Simulation of Flow of Mixtures Through Anisotropic Porous Media using a Lattice Boltzmann Model
We propose a description for transient penetration simulations of miscible
and immiscible fluid mixtures into anisotropic porous media, using the lattice
Boltzmann (LB) method. Our model incorporates hydrodynamic flow, diffusion,
surface tension, and the possibility for global and local viscosity variations
to consider various types of hardening fluids. The miscible mixture consists of
two fluids, one governed by the hydrodynamic equations and one by diffusion
equations. We validate our model on standard problems like Poiseuille flow, the
collision of a drop with an impermeable, hydrophobic interface and the
deformation of the fluid due to surface tension forces. To demonstrate the
applicability to complex geometries, we simulate the invasion process of
mixtures into wood spruce samples.Comment: Submitted to EPJ
Higgs Decay into Gluons up to O(\alpha_s^3 G_F m_t^2)
The decay of the Standard Model Higgs boson in the intermediate-mass range
into gluons is considered where special emphasis is put on the influence of the
leading electroweak corrections proportional to G_F m_t^2. An effective
Lagrangian approach is used where the top quark is integrated out. The
evaluation of the coefficient function is performed using two different
methods. The first one is concerned with the direct evaluation of the vertex
diagrams and the second method is based on a low-energy theorem. In a first
step the tools needed for the computation are provided namely the
renormalization constants of the QCD Lagrangian are computed up to O(\alpha_s^2
G_F m_t^2). Also the decoupling constants for the strong coupling constant
\alpha_s and the light quark masses relating the quantities of the full theory
to the corresponding quantities of the effective one are evaluated up to order
\alpha_s^2 G_F m_t^2.Comment: 20 pages (revtex), 3 figure
Metabolic, productive and reproductive responses to postpartum short-term supplementation in primiparous beef cows
Limit on oscillation using a jet charge method
A lower limit is set on the B_{s}^{0} meson oscillation parameter \Delta m_{s} using data collected from 1991 to 1994 by the ALEPH detector. Events with a high transverse momentum lepton and a reconstructed secondary vertex are used. The high transverse momentum leptons are produced mainly by b hadron decays, and the sign of the lepton indicates the particle/antiparticle final state in decays of neutral B mesons. The initial state is determined by a jet charge technique using both sides of the event. A maximum likelihood method is used to set a lower limit of \, \Delta m_{s}. The 95\% confidence level lower limit on \Delta m_s ranges between 5.2 and 6.5(\hbar/c^{2})~ps^{-1} when the fraction of b quarks from Z^0 decays that form B_{s}^{0} mesons is varied from 8\% to 16\%. Assuming that the B_{s}^{0} fraction is 12\%, the lower limit would be \Delta m_{s} 6.1(\hbar/c^{2})~ps^{-1} at 95\% confidence level. For x_s = \Delta m_s \, \tau_{B_s}, this limit also gives x_s 8.8 using the B_{s}^{0} lifetime of \tau_{B_s} = 1.55 \pm 0.11~ps and shifting the central value of \tau_{B_s} down by 1\sigma
Measurement of the B lifetime and production rate with D combinations in Z decays
The lifetime of the \bs meson is measured in approximately 3 million hadronic Z decays accumulated using the ALEPH detector at LEP from 1991 to 1994. Seven different \ds decay modes were reconstructed and combined with an opposite sign lepton as evidence of semileptonic \bs decays. Two hundred and eight \dsl candidates satisfy selection criteria designed to ensure precise proper time reconstruction and yield a measured \bs lifetime of \mbox{\result .} Using a larger, less constrained sample of events, the product branching ratio is measured to be \mbox{\pbrresult
- âŠ