Experimental and theoretical investigations concerning a frequency filter behavior of the human retina regarding electric pulse currents

Investigation involving patients with injuries in the visual nervous system are discussed. This led to the identification of the epithelial ganglion of the retina as a frequency filter. Threshold curves of the injured visual organs were compared with threshold curves obtained with a control group as a basis for identification. A model which considers the epithelial ganglion as a homogeneous cell layer in which adjacent neurons interact is discussed. It is shown the behavior of the cells against alternating exciting currents can be explained

The requirement of matrix ATP for the import of precursor proteins into the mitochondrial matrix and intermembrane space

The role of ATP in the matrix for the import of precursor proteins into the various mitochondrial subcompartments was investigated by studying protein translocation at experimentally defined ATP levels. Proteins targeted to the matrix were neither imported or processed when matrix ATP was depleted. Import and processing of precytochrome b2, (pb2), a precursor carrying a bipartite presequence, into the intermembrane space was also strongly dependent on matrix ATP. Preproteins, consisting of 220 or more residues of pb2 fused to dihydrofolate reductase, showed the same requirement for matrix ATP, whereas the import of shorter fusion proteins (up to 167 residues of pb2) was largely independent of matrix ATP. For those intermembrane-space-targeted proteins that did need matrix ATP, the dependence could be relieved either by unfolding these proteins prior to import or by introducing a deletion into the mature portion of the protein thereby impairing the tight folding of the cytochrome b5 domain. These results suggest the following: (a) The import of matrix-targeted preproteins, in addition to a membrane potential ΔΨ, requires matrix ATP [most likely to facilitate reversible binding of mitochondrial heat-shock protein 70 (mt-Hsp70) to incoming precursors], for two steps, securing the presequence on the matrix side of the inner membrane and for the completion of translocation; (b) in the case of intermembrane-space-targeted precursors with bipartite signals, the function of ATP/mt-Hsp70 is not obligatory, as components of the intermembrane-space-sorting pathway may substitute for ATP/mt-Hsp70 function (however, if a tightly folded domain is present in the precursor, ATP/mt-Hsp70 is indispensable); (c) unfolding on the mitochondrial surface of tightly folded segments of preproteins is facilitated by matrix-ATP/mt-Hsp70

Dual character of the electronic structure in YBa2Cu4O8: conduction bands of CuO2 planes and CuO chains

We use microprobe Angle-Resolved Photoemission Spectroscopy (muARPES) to separately investigate the electronic properties of CuO2 planes and CuO chains in the high temperature superconductor, YBa2Cu4O8. In the CuO2 planes, a two dimensional (2D) electronic structure with nearly momentum independent bilayer splitting is observed. The splitting energy is 150 meV at (pi,0), almost 50% larger than in Bi2Sr2CaCu2O(8+d) and the electron scattering at the Fermi level in the bonding band is about 1.5 times stronger than in the antibonding band. The CuO chains have a quasi one dimensional (1D) electronic structure. We observe two 1D bands separated by ~ 550meV: a conducting band and an insulating band with an energy gap of ~ 240meV. We find that the conduction electrons are well confined within the planes and chains with a non-trivial hybridization.Comment: 4 pages, 4 figure

The ρ−ω\rho-\omega splitting in constituent quark models

In this letter we present a solution to describe simultaneously the light isoscalar and isovector vector mesons in constituent quark models. In Ref. [1] the $q\bar q$ spectrum was studied in a generalized constituent quark model constrained by the $NN$ phenomenology and the baryon spectrum. An overall good fit to the available experimental data was obtained. A major problem of this description was the relative position of the vector $\omega$ and $\rho$ mesons. The present results improve the description of the isoscalar meson spectroscopy. They should serve as a step forward in distinguishing conventional quark model mesons from exotic states.Comment: 8 pages, no figures. To be published in Phys. Lett.

Electrostatic Interactions of Asymmetrically Charged Membranes

We predict the nature (attractive or repulsive) and range (exponentially screened or long-range power law) of the electrostatic interactions of oppositely charged and planar plates as a function of the salt concentration and surface charge densities (whose absolute magnitudes are not necessarily equal). An analytical expression for the crossover between attractive and repulsive pressure is obtained as a function of the salt concentration. This condition reduces to the high-salt limit of Parsegian and Gingell where the interaction is exponentially screened and to the zero salt limit of Lau and Pincus in which the important length scales are the inter-plate separation and the Gouy-Chapman length. In the regime of low salt and high surface charges we predict - for any ratio of the charges on the surfaces - that the attractive pressure is long-ranged as a function of the spacing. The attractive pressure is related to the decrease in counter-ion concentration as the inter-plate distance is decreased. Our theory predicts several scaling regimes with different scaling expressions for the pressure as function of salinity and surface charge densities. The pressure predictions can be related to surface force experiments of oppositely charged surfaces that are prepared by coating one of the mica surfaces with an oppositely charged polyelectrolyte

Support of generalized parton distributions in Bethe-Salpeter models of hadrons

The proper support of generalized parton distributions from relativistic constituent quark models with pointlike constituents is studied. The correct support is guaranteed when the vertex function does not depend on the relative minus-momentum. We show that including quark interactions in models with pointlike constituent quarks might lead to a support problem. A computation of the magnitude of the support problem in the Bonn relativistic constituent quark model is presented.Comment: 8 pages, 4 figures. v2: specific calculation included, references and figure added. Submitted to Phys. Lett.