Testing the meson cloud in the nucleon in Drell-Yan processes

We discuss the present status of the \bar u-\bar d asymmetry in the nucleon and analize the quantities which are best suited to verify the asymmetry. We find that the Drell-Yan asymmetry is the quantity insensitive to the valence quark distributions and very sensitive to the flavour asymmetry of the sea. We compare the prediction of the meson cloud model with different experimental data including the Fermilab E772 data and recent data of the NA51 Collaboration at CERN and make predictions for the planned Drell-Yan experiments.Comment: written in ReVTeX, 26 pages + 10 PS-figure

\bar u - \bar d asymmetry - a few remarks

We make a few remarks on possible sources of uncertainties of the $\bar d - \bar u$ asymmetry obtained by different methods and comment on its possible verification in the future. In addition we comment on its present understanding.Comment: 3 pages, a talk at the 7th International Workshop on Deep Inelastic Scattering and QCD (DIS99), Zeuthen, April 199

Polarized rho mesons and the asymmetry between Delta d^bar(x) and Delta u^bar(x) in the sea of the nucleon

We present a calculation of the polarized rho meson cloud in a nucleon using time-ordered perturbation theory in two different variants advocated in the literature. We calculate the induced difference between the distributions Delta d^bar(x) and Delta u^bar(x). We use a recent lattice calculation to motivate an ansatz for the polarized valence quark distribution of the rho meson. Our calculations show that the two theoretical approaches give vastly different results. We conclude that Delta d^bar(x) - Delta u^bar(x) can be of relevant size with important consequences for the combined fits of polarized distribution functions.Comment: 14 pages LaTeX, 8 figures; v3: some minor changes; this preprint supports the version to appear in Phys. Lett. B with an additional appendi

Reggeon and pion contributions in semi-exclusive diffractive processes at HERA

A detailed analysis of semi-exclusive diffractive processes in e-p DIS at HERA, with the diffractive final states in the forward direction is presented. The contributions of the subleading f_2, \omega, a_2, \rho reggeons and the pion exchanges to the diffractive structure function with the forward proton or neutron are estimated. It is found that the (a_2,\rho) reggeons are entirely responsible for the forward neutron production at x_P < 10^{-3}. The \pi N production in the forward region is estimated using the Deck mechanism. The significance of this reaction for the processes measured at HERA, especially with the leading neutron, is discussed.Comment: Strongly revised version accepted for publication in Phys.Rev.D. Latex, 14 pages with 5 eps figures include

Pion Content of the Nucleon as seen in the NA51 Drell-Yan experiment

In a recent CERN Drell-Yan experiment the NA51 group found a strong asymmetry of $\bar u$ and $\bar d$ densities in the proton at $x\simeq0.18$. We interpret this result as a decisive confirmation of the pion-induced sea in the nucleon.Comment: 10 pages + 3 figures, Preprint KFA-IKP(TH)-1994-14 .tex file. After \enddocument a uu-encodeded Postscript file comprising the figures is appende

Mass Transport Limitations in Microbial Fuel Cells:Impact of Flow Configurations

The performance of microbial fuel cells (MFCs) is limited by a number of factors, including metabolic activity of electroactive microorganisms and electrochemical systematic constraints, such as overpotentials at the electrodes or IR losses. Heterogeneities of substrate distribution (availability) can also strongly limit current in MFCs. In this work we investigate how mass transport can be enhanced by changing the flow configurations in MFCs, e.g. by directing the flow through a porous anode or by applying inserts and channels to anodes. Experimental results using a perpendicular flow through the anode were compared to a parallel flow setup, showing increased current output. Finite element method (FEM) simulations were used to simulate the flow profiles and substrate distribution in each setup. The simulations revealed higher average substrate concentrations for the perpendicular flow through a porous carbon fabric anode vs. a parallel flow in the bulk phase of the MFC, related to the enhancement of transport via convection in perpendicular flow. The simulated substrate distributions found for the different inlet setups could be correlated to the experimentally obtained current flow, power output and biofilm distribution. It can be concluded that the increased current output can be explained by the flow profile in the system resulting in an increased substrate distribution in the biofilm on the electrode and a hindered oxygen transport from the cathode