Perspectives from above and beyond the proton drip-line

This paper will review the dramatic increase in our knowledge of one and two proton unbound nuclei [1] such as recoil decay tagging [2] are revealing unique insights into the structure of nuclei beyond the proton drip-line. These studies of excited states provide complementary information to proton radioactivity studies, particularly regarding the role of deformation [3]. Radioactive beams are being used to study two-proton unbound resonances and to study explosive nuclear astrophysical reactions in the region of the proton drip-line.     

Atom probe tomography of size‐controlled phosphorus doped silicon nanocrystals

Doping of silicon nanocrystals is essential to control their electronic and optical properties. The incorporation of an impurity into a silicon nanovolume is a nontrivial task due to the self‐purification effect. Here, a systematic atom probe tomography study of the phosphorus distribution and incorporation in size‐controlled silicon nanocrystals embedded in silicon dioxide is presented. Qualitatively, it turns out that the phosphorus distribution in the system follows a universal, nanocrystal‐size independent trend: phosphorus‐enrichment at the interface with a substantial phosphorus‐incorporation in the silicon nanocrystal as small as 2 nm in diameter. This clearly contradicts strict self‐purification. These observations are explained by the bulk‐solubility and ‐segregation behaviour, kinetic effects related to the diffusion lengths, and nanoscale interface strain. The quantitative determination of the amount of phosphorus atoms per quantum dot enables a systematic understanding of phosphorus‐induced effects on optical and electronic properties of silicon nanovolumes.     

Isolation and Characterization of a ssDNA Aptamer against Major Soluble Antigen of Renibacterium salmoninarum

Bacterial kidney disease (BKD) is a major health problem of salmonids, affecting both wild and cultured salmon. The disease is caused by Renibacterium salmoninarum (Rs), a fastidious, slow-growing and strongly Gram-positive diplobacillus that produces chronic, systemic infection characterized by granulomatous lesions in the kidney and other organs, often resulting in death. Fast detection of the pathogen is important to limit the spread of the disease, particularly in hatcheries or aquaculture facilities. Aptamers are increasingly replacing conventional antibodies as platforms for the development of rapid diagnostic tools. In this work, we describe the first instance of isolating and characterizing a ssDNA aptamer that binds with high affinity to p57 or major soluble antigen (MSA), the principal antigen found on the cell wall surface of Rs. Specifically, in this study a construct of the full-length protein containing a DNA binding domain (MSA-R2c) was utilized as target. Aptamers were isolated from a pool of random sequences using GO-SELEX (graphene oxide-systematic evolution of ligands by exponential enrichment) protocol. The selection generated multiple aptamers with conserved motifs in the random region. One aptamer with high frequency of occurrence in different clones was characterized and found to display a strong binding affinity to MSA-R2c with a K_d of 3.0 ± 0.6 nM. The aptamer could be potentially utilized for the future development of a sensor for rapid and onsite detection of Rs in water or in infected salmonids, replacing time-consuming and costly lab analyses.     

A characterization theorem for tilings having countably many singular points

LetT be a tiling of the plane. At most countably many points of U{bdry T T inT} fail to lie in a nondegenerate edge ofT if and only ifT has at most countably many singular points. The result fails without the requirement that the edges be nondegenerate. Moreover, countably many cannot be replaced by finitely many in the theorem.     

Bottom-up view of water network-mediated CO2 reduction using cryogenic cluster ion spectroscopy and direct dynamics simulations

The transition states of a chemical reaction in solution are generally accessed through exchange of thermal energy between the solvent and the reactants. As such, an ensemble of reacting systems approaches the transition state configuration of reactant and surrounding solvent in an incoherent manner that does not lend itself to direct experimental observation. Here we describe how gas-phase cluster chemistry can provide a detailed picture of the microscopic mechanics at play when a network of six water molecules mediates the trapping of a highly reactive "hydrated electron" onto a neutral CO(2) molecule to form a radical anion. The exothermic reaction is triggered from a metastable intermediate by selective excitation of either the reactant CO(2) or the water network, which is evidenced by the evaporative decomposition of the product cluster. Ab initio molecular dynamics simulations of energized CO(2)·(H(2)O)(6)(-) clusters are used to elucidate the nature of the network deformations that mediate intracluster electron capture, thus revealing the detailed solvent fluctuations implicit in the Marcus theory for electron-transfer kinetics in solution.     

Variable time lag and backward ejection in full-dimensional analysis of strong-field double ionization

Ensembles of 400,000 two-electron trajectories in three space dimensions are used with Newtonian equations of motion to track atomic double ionization under very strong laser fields. We report a variable time lag between e-e collision and double ionization, and find that the time lag plays a key role in the emergence directions of the electrons. These are precursors to production of electron momentum distributions showing substantial new agreement with experimental data.