Light propagation in statistically homogeneous and isotropic universes with general matter content

We derive the relationship of the redshift and the angular diameter distance to the average expansion rate for universes which are statistically homogeneous and isotropic and where the distribution evolves slowly, but which have otherwise arbitrary geometry and matter content. The relevant average expansion rate is selected by the observable redshift and the assumed symmetry properties of the spacetime. We show why light deflection and shear remain small. We write down the evolution equations for the average expansion rate and discuss the validity of the dust approximation.Comment: 42 pages, no figures. v2: Corrected one detail about the angular diameter distance and two typos. No change in result

Measurement of the W+W- Production Cross Section in ppbar Collisions at sqrt(s)=1.96 TeV using Dilepton Events

We present a measurement of the W+W- production cross section using 184/pb of ppbar collisions at a center-of-mass energy of 1.96 TeV collected with the Collider Detector at Fermilab. Using the dilepton decay channel W+W- -> l+l-vvbar, where the charged leptons can be either electrons or muons, we find 17 candidate events compared to an expected background of 5.0+2.2-0.8 events. The resulting W+W- production cross section measurement of sigma(ppbar -> W+W-) = 14.6 +5.8 -5.1 (stat) +1.8 -3.0 (syst) +-0.9 (lum) pb agrees well with the Standard Model expectation.Comment: 8 pages, 2 figures, 2 tables. To be submitted to Physical Review Letter

Electrochemical oxidation of sour natural gas over La0.4Ce0.6O1.8 - La0.4Sr0.6TiO3±d anode in SOFC: A mechanism study of H2S effects

For solid oxide fuel cell with La0.4Ce0.6O1.8–La0.4Sr0.6TiO3±δ (LDC-L4ST) impregnated anodes, the electrochemical oxidation rates of H2 and CH4 were significantly improved when H2S (0.5%) was present in the feeds as evidenced by the substantially decreased polarization resistance and the improved power density of the cell although H2S did not predominantly function as a fuel. Conductivity measurements of various anode component materials implied that the addition of H2S into the feeds increased their conductivities. More importantly, from the mass spectroscopic analysis of the anode gas effluents and the thermodynamic calculations, direct evidences of H2S caused SOFC performance improvement have been confirmed, three distinct regions for the electrochemical oxidation pathways of 0.5% H2S–CH4 vs. overpotential (η) were proposed to explain the effect. The chemisorbed S species, together with LDC-L4ST, behaved as an effective catalyst promoting CH4 oxidations via COS and CS2 intermediates. The addition of LDC in the anode enhanced this synergic effect and further increased CH4 electrochemical conversion as well as coking resistance in comparison of the L4ST anode

Static and Dynamic Aerocharacteristics Testing of Strake-Wing Aerial Vehicle in Water Tunnel

This paper focuses on flow visualization, normal force and pitch moment testing of the NASA TP-1803 strake-wing model at high attack angles. The dynamic aerocharacteristics for pitching with various reduced frequencies and two sideslip angles beta = 0 degrees and 10 degrees in the water tunnel are compared with those for static case. For alpha = 20 degrees-50 degrees, the strake/wing vortices breakdown positions occur later for beta = 10 degrees than for = 0. The value of the normal force coefficient under sideslip angle beta = 10 degrees is greater than beta = 0 degrees at high attack angles. In the pitch-down process, the aerodynamic center creates a nose-up pitching moment and the model becomes unstable compared to the static condition. As the pitch reduced frequency increases, the wing vortices sustain longer flow lines and provide more normal force during pitch-up motion. In addition, the hysteresis loop of the normal force curve is larger for higher reduced frequencies

Impregnation of La0.4Ce0.6O1.8-La0.4Sr0.6TiO3 as solid oxide fuel cell anode in H2S-containing fuels

Active anodes were fabricated via wet chemical impregnation of optimized amount of La0.4Sr0.6TiO3 (L4ST) into La0.4Ce0.6O1.8 (LDC) pre-infiltrated porous yttria-stabilized zirconia (YSZ) matrix. Impregnations of 10 wt% LDC with 16 wt% L4ST significantly improved the performance of the fuel cell from 48 mW cm 122 for pure L4ST to 161 mW cm 122 for LDC\u2013L4ST at 900 \ub0C in H2. The contribution of the pre-loaded LDC to this improvement was investigated using electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM) as well as transmission electron microscopy (TEM). The measurement results indicated that pre-infiltrated LDC increased the activity of the anode more effectively by decreasing the total polarization resistance of the cell from 3.3 \u3a9 cm2 to 1.0 \u3a9 cm2 in humidified H2 at 900 \ub0C. More importantly, the LDC nano-deposits (<20 nm) behaved as an effective \u201cadhesive\u201d that substantially enhanced the wettability of L4ST on YSZ matrix, resulting in finer and more uniform structure of L4ST infiltrates. The LDC\u2013L4ST cells also demonstrated significantly improved performances in 0.5% H2S\u2013H2 and 0.5% H2S\u2013CH4 with higher stability than cells with pure L4ST anode.Peer reviewed: YesNRC publication: Ye