1,944 research outputs found
Corrigendum to “Evaluation of black carbon estimations in global aerosol models” published in Atmos. Chem. Phys., 9, 9001-9026, 2009
Evaluation of black carbon estimations in global aerosol models
We evaluate black carbon (BC) model predictions from the AeroCom model intercomparison project by considering the diversity among year 2000 model simulations and comparing model predictions with available measurements. These model-measurement intercomparisons include BC surface and aircraft concentrations, aerosol absorption optical depth (AAOD) retrievals from AERONET and Ozone Monitoring Instrument (OMI) and BC column estimations based on AERONET. In regions other than Asia, most models are biased high compared to surface concentration measurements. However compared with (column) AAOD or BC burden retreivals, the models are generally biased low. The average ratio of model to retrieved AAOD is less than 0.7 in South American and 0.6 in African biomass burning regions; both of these regions lack surface concentration measurements. In Asia the average model to observed ratio is 0.7 for AAOD and 0.5 for BC surface concentrations. Compared with aircraft measurements over the Americas at latitudes between 0 and 50N, the average model is a factor of 8 larger than observed, and most models exceed the measured BC standard deviation in the mid to upper troposphere. At higher latitudes the average model to aircraft BC ratio is 0.4 and models underestimate the observed BC loading in the lower and middle troposphere associated with springtime Arctic haze. Low model bias for AAOD but overestimation of surface and upper atmospheric BC concentrations at lower latitudes suggests that most models are underestimating BC absorption and should improve estimates for refractive index, particle size, and optical effects of BC coating. Retrieval uncertainties and/or differences with model diagnostic treatment may also contribute to the model-measurement disparity. Largest AeroCom model diversity occurred in northern Eurasia and the remote Arctic, regions influenced by anthropogenic sources. Changing emissions, aging, removal, or optical properties within a single model generated a smaller change in model predictions than the range represented by the full set of AeroCom models. Upper tropospheric concentrations of BC mass from the aircraft measurements are suggested to provide a unique new benchmark to test scavenging and vertical dispersion of BC in global models
Preparation of integrated passive microwave devices through inkjet printing
Barium strontium titanate (BST) is a promising material for passive tunable microwave devices such as phase shifters or tunable matching networks. This publication covers the preparation of BST thick-films for microwave applications through inkjet printing. Two barium strontium titanate (BST) inks were prepared, printed on alumina substrates and sintered at different temperatures. The first ink was prepared with pure BST and sintered between 1100°C and 1200°C. The second ink was prepared with a BST–ZnO–B2O3 composition and was suitable to reduce the sintering temperature down to 800°C. The microstructure of the thick-films reveals the evolution of grain growth with increasing sintering temperature in the thick-films. Furthermore, a reaction with the substrate was observed for both inks at high sintering temperatures. The microwave characterization of the thick-films shows that for the permittivity and the tunability of the films, the effect of grain growth and reaction with the substrate compete against each other. Hence, the optimal microwave properties were achieved at a transition temperature, where first additional phases could already be observed. Even though, the properties are poorer for lower sintering temperatures, the investigations show that the preparation of silver- or gold-based metal–insulator–metal (MIM) structures through inkjet printing is possible with this composition. This allows various new design concepts for partly or fully inkjet printed passive microwave devices. Furthermore, it gives the opportunity for a future integration of passive tunable microwave devices in a low temperature co-fired ceramic (LTCC) fabrication process.</jats:p
The Pomeron In Exclusive Vector Meson Production
An earlier developed model for vector meson photoproduction, based on a
dipole Pomeron exchange, is extended to electroproduction. Universality of the
non linear Pomeron trajectory is tested by fitting the model to ZEUS and H1
data as well as to CDF data on elastic scattering.Comment: 12 pages, 13 figure
Hard-Sphere Fluids in Contact with Curved Substrates
The properties of a hard-sphere fluid in contact with hard spherical and
cylindrical walls are studied. Rosenfeld's density functional theory (DFT) is
applied to determine the density profile and surface tension for wide
ranges of radii of the curved walls and densities of the hard-sphere fluid.
Particular attention is paid to investigate the curvature dependence and the
possible existence of a contribution to that is proportional to the
logarithm of the radius of curvature. Moreover, by treating the curved wall as
a second component at infinite dilution we provide an analytical expression for
the surface tension of a hard-sphere fluid close to arbitrary hard convex
walls. The agreement between the analytical expression and DFT is good. Our
results show no signs for the existence of a logarithmic term in the curvature
dependence of .Comment: 15 pages, 6 figure
Relativistic ponderomotive force, uphill acceleration, and transition to chaos
Starting from a covariant cycle-averaged Lagrangian the relativistic
oscillation center equation of motion of a point charge is deduced and
analytical formulae for the ponderomotive force in a travelling wave of
arbitrary strength are presented. It is further shown that the ponderomotive
forces for transverse and longitudinal waves are different; in the latter,
uphill acceleration can occur. In a standing wave there exists a threshold
intensity above which, owing to transition to chaos, the secular motion can no
longer be described by a regular ponderomotive force.
PACS number(s): 52.20.Dq,05.45.+b,52.35.Mw,52.60.+hComment: 8 pages, RevTeX, 3 figures in PostScript, see also
http://www.physik.th-darmstadt.de/tqe
- …