Analysis of the Low-Energy Theorem for \gamma p \to p \pi^0

The derivation of the `classical' low-energy theorem (LET) for \gamma p \rightarrow p\pi^0 is re-examined and compared to chiral perturbation theory. Both results are correct and are not contradictory; they differ because different expansions of the same quantity are involved. Possible modifications of the extended partially conserved axial-vector current relation, one of the starting points in the derivation of the LET, are discussed. An alternate, more transparent form of the LET is presented.Comment: 5 pages, Revtex, no figures, no table

A Predictive Model for Convective Flows Induced by Surface Reactivity Contrast

Concentration gradients in a fluid along a reactive surface due to contrast in surface reactivity generate convective flows. These flows result from contributions by electro and diffusio osmotic phenomena. In this study we have analyzed reactive patterns that release and consume protons, analogous to bimetallic catalytic conversion of peroxide. Here, we present a simple analytical model that accurately predicts the induced potentials and consequent velocities in such systems over a wide range of input parameters. Our model is tested against direct numerical solutions to the coupled Poisson, Nernst-Planck, and Navier-Stokes equations. Our analysis can be used to predict enhancement of mass transport and the resulting impact on overall catalytic conversion, and is also applicable to predicting the speed of catalytic nanomotors

Heteroduplex analysis of the RNA of clone 3 Moloney murine sarcoma virus

Heteroduplex analysis of the RNA isolated from purified virions of clone 3 Moloney murine sarcoma virus (M-MSV) hybridized to cDNA's from Moloney murine leukemia virus (M-MLV) and clone 124 M-MSV shows that the main physical component of clone 3 RNA is missing all or most of the 1.5-kilobase (kb) clone 124 M-MSV specific sequence denoted beta s (S. Hu et al. Cell 10:469-477, 1977). This sequence is either deleted in clone 3 RNA or substituted by a very short (0.3-kilobase) sequence. In other respects, clone 3 and clone 124 RNAs show the same heteroduplex structure relative to M-MLV. Since beta s is believed to contain the src gene(s) of clone 124 RNA, this result leaves as an unresolved question the nature of the src gene(s) of the clone 3 M-MSV RNA complex

Unitary ambiguity in the extraction of the E2/M1 ratio for the γN↔Δ\gamma N\leftrightarrow\Delta transition

The resonant electric quadrupole amplitude in the transition $\gamma N\leftrightarrow\Delta(1232)$ is of great interest for the understanding of baryon structure. Various dynamical models have been developed to extract it from the corresponding photoproduction multipole of pions on nucleons. It is shown that once such a model is specified, a whole class of unitarily equivalent models can be constructed, all of them providing exactly the same fit to the experimental data. However, they may predict quite different resonant amplitudes. Therefore, the extraction of the E2/M1($\gamma N\leftrightarrow\Delta$) ratio (bare or dressed) which is based on a dynamical model using a largely phenomenological $\pi N$ interaction is not unique.Comment: 10 pages revtex including 4 postscript figure

Efficient computation of matched solutions of the Kapchinskij-Vladimirskij envelope equations for periodic focusing lattices

A new iterative method is developed to numerically calculate the periodic, matched beam envelope solution of the coupled Kapchinskij-Vladimirskij (KV) equations describing the transverse evolution of a beam in a periodic, linear focusing lattice of arbitrary complexity. Implementation of the method is straightforward. It is highly convergent and can be applied to all usual parameterizations of the matched envelope solutions. The method is applicable to all classes of linear focusing lattices without skew couplings, and also applies to all physically achievable system parameters -- including where the matched beam envelope is strongly unstable. Example applications are presented for periodic solenoidal and quadrupole focusing lattices. Convergence properties are summarized over a wide range of system parameters.Comment: 20 pages, 5 figures, Mathematica source code provide

Electron microscopic visualization of tRNA genes with ferritin-avidin: biotin labels

A method is described for indirect electron microscopic visualization and mapping of tRNA and other short transcripts hybridized to DNA. This method depends upon the attachment of the electron-dense protein ferritin to the RNA, the binding being mediated by the remarkably strong association of the egg white protein avidin with biotin. Biotin is covalently attached to the 3' end of tRNA using an NH2 (CH2) 5NH2 bridge. The tRNA-biotin adduct is hybridized to complementcrry DNA sequences present in a single stranded nonhomology loop of a DNA:DNA heteroduplex. Avidin, covalently crosslinked to ferritin is mixed with the heteroduplex and becomes bound to the hybridized tRNA-biotin. Observation of the DNA:RNA-biotin:avidin-ferritin complex by electron microsdopy specifically and accurately reveals the position of the tRNA gene, with a frequency of labeling of approximately 50%

Were Presolar Grains Destroyed by the Nebular Process Responsible for the Volatile Element Fractionation?

We present SiC abundances from a number of CM and CR chondrites using NanoSIMS raster ion imaging of acid residues. We find higher SiC abundances for CRs than previously estimated based on noble gases

Regions of beta 2 and beta 4 responsible for differences between the steady state dose-response relationships of the alpha 3 beta 2 and alpha 3 beta 4 neuronal nicotinic receptors

We constructed chimeras of the rat beta 2 and beta 4 neuronal nicotinic subunits to locate the regions that contribute to differences between the acetylcholine (ACh) dose-response relationships of the alpha 3 beta 2 and alpha 3 beta 4 receptors. Expressed in Xenopus oocytes, the alpha 3 beta 2 receptor displays an EC50 for ACh approximately 20-fold less than the EC50 of the alpha 3 beta 4 receptor. The apparent Hill slope (n(app)) of alpha 3 beta 2 is near one whereas the alpha 3 beta 4 receptor displays an n(app) near two. Substitutions within the first 120 residues convert the EC50 for ACh from one wild-type value to the other. Exchanging just beta 2:104-120 for the corresponding region of beta 4 shifts the EC50 of ACh dose-response relationship in the expected direction but does not completely convert the EC50 of the dose- response relationship from one wild-type value to the other. However, substitutions in the beta 2:104-120 region do account for the relative sensitivity of the alpha 3 beta 2 receptor to cytisine, tetramethylammonium, and ACh. The expression of beta 4-like (strong) cooperativity requires an extensive region of beta 4 (beta 4:1-301). Relatively short beta 2 substitutions (beta 2:104-120) can reduce cooperativity to beta 2-like values. The results suggest that amino acids within the first 120 residues of beta 2 and the corresponding region of beta 4 contribute to an agonist binding site that bridges the alpha and beta subunits in neuronal nicotinic receptors