Noise and diffusion of particles obeying asymmetric exclusion processes

The relation between noise and Fick's diffusion coefficient in barrier limited transport associated with hopping or tunneling mechanisms of particles obeying the asymmetric simple exclusion processes (ASEP) is physically assessed by Monte Carlo simulations. For a closed ring consisting of a large number of barriers the diffusion coefficient is related explicitly to the current noise thus revealing the existence of a generalized Nyquist-Einstein relation. Both diffusion and noise are confirmed to decrease as the square root of the number of barriers as a consequence of the correlation induced by ASEP. By contrast, for an open linear chain of barriers the diffusion coefficient is found to be no longer related to current noise. Here diffusion depends on particle concentration but is independent of the number of barriers

Analysis of the muscarinic receptor subtype mediating inhibition of the neurogenic contractions in rabbit isolated vas deferens by a series of polymethylene tetra-amines

1. The pharmacological characteristics of the presynaptic muscarinic receptor subtype, which mediates inhibition of the neurogenic contractions in the prostatic portion of rabbit vas deferens, have been investigated by using a series of polymethylene tetra-amines, which were selected for their ability to differentiate among muscarinic receptor subtypes. 2. It was found that all tetra-amines antagonized McN-A-343-induced inhibition in electrically stimulated rabbit vas deferens in a competitive manner and with affinity values (pA2) ranging between 6.27 ± 0.09 (spirotramine) and 8.51 ± 0.02 (AM170). 3. Competition radioligand binding studies, using native muscarinic receptors from rat tissues (M1, cortex; M2, heart; M3, submaxillary gland) or from NG 108-15 cells (M4) and human cloned muscarinic M1-M4 receptors expressed in CHO-K1 cells, were undertaken with the same tetraamines employed in functional assays. All antagonists indicated a one-site fit. 4. The affinity estimates (pKi) of tetra-amines calculated in binding assays using native receptors were similar to those obtained using cloned receptors. Among these compounds some displayed selectivity between muscarinic receptor subtypes, indicating that they may be valuable tools in receptor characterization. Spirotramine was selective for M1 receptors versus all other subtypes (pKi native: M1, 7.32 ± 0.10; M2, 6.50 ± 0.11; M3, 6.02 ± 0.13; M4, 6.28 ± 0.16; pKi cloned: M1, 7.69 ± 0.08; M2, 6.22 ± 0.14; M3, 6.11 ± 0.16; 6.35 ± 0.11) whereas CC8 is highly selective for M2 receptors versus the other subtypes (pKi native: M1 7.50 ± 0.04; M2, 9.01 ± 0.12; M3, 6.70 ± 0.08; M4, 7.56 ± 0.04; pKi cloned: M1, 7.90 ± 0.20; M2, 9.04 ± 0.08; M3, 6.40 ± 0.07; M4, 7.40 ± 0.04). Furthermore, particularly relevant for this investigation were tetra-amines dipitramine and AM172 for their ability to significantly differentiate M1 and M4 receptors. 5. The apparent affinity values (pA2) obtained for tetra-amines in functional studies using the prostatic portion of rabbit vas deferens correlated most closely with the values (pKi) obtained at either native or human recombinant muscarinic M4 receptors. This supports the view that the muscarinic receptor mediating inhibition of neurogenic contractions of rabbit vas deferens may not belong to the M1 type but rather appears to be of the M4 subtype

Superlattice Growth via MBE and Green’s Function Techniques

A model has been developed to simulate the growth of arrays consisting of a substrate on which alternating layers of quantum dots (QDs) and spacer layers are epitaxially grown. The substrate and spacer layers are modeled as an anisotropic elastic half-space, and the QDs are modeled as point inclusions buried within the half-space. In this model, the strain at the free surface of this half-space due to the buried point QDs is calculated, and a scalar measure of the strain at the surface is subsequently determined. New point QDs are placed on the surface where the previously calculated scalar strain measure is a minimum. Following available DFT results, this scalar strain measure is a weighted average of the in-plane strains. This model is constructed under the assumption that diffusional anisotropy can be neglected, and thus, the results are more in agreement with results from experiments of growth of SiGe QDs than experiments involving QDs of (In,Ga)As