A combination of an electron microscope and a heavy-ion accelerator

Abstract

Some tracks are obtained in several plastics using an organic solvent track etching procedure. The described results are those obtained with ethyl alcohol. The samples (PMMA) are submitted to pure alcohol effect then to water effect. By this way one can get 6 MeV α-tracks but the phenomenon is not reproducible. The most frequent observations are described.     

Observation of anomalous phonon softening in bilayer graphene

The interaction of electron-hole pairs with lattice vibrations exhibits a wealth of intriguing physical phenomena such as the renowned Kohn anomaly. Here we report the observation in bilayer graphene of an unusual phonon softening that provides the first experimental proof for another type of phonon anomaly. Similar to the Kohn anomaly, which is a logarithmic singularity in the phonon group velocity [W. Kohn, Phys. Rev. Lett. 2, 393 (1959)], the observed phonon anomaly exhibits a logarithmic singularity in the optical-phonon energy. Arising from a resonant electron-phonon coupling effect, the anomaly was also expected, albeit not observed, in monolayer graphene. We propose an explanation for why it is easier to observe in bilayer samples.     

Relative importance of basicity in the gas phase and in solution for determining selectivity in electrospray ionization mass spectrometry

Electrospray ionization mass spectrometry is a critically important technique for the determination of small molecules, but its application for this purpose is complicated by its selectivity. For positive ion ESI-MS analysis of basic analytes, several investigators have pointed to the importance of analyte basicity as a source of selectivity. Currently, however, it is not known whether basicity in the gas phase or in solution is ultimately most important in determining responsiveness. The objective of these studies was to investigate the relative importance of basicity in solution and in the gas phase as factors that predict selectivity in positive ion ESI-MS analysis. ESI-MS response was compared for a diverse series of protonatable analytes in two different solvents, neat methanol and methanol with 0.5% acetic acid. A correlation was observed between analyte pK(b) and electrospray response. However, the response for the analytes with very high pK(b) values was significantly higher than would be expected based on concentration of the protonated form or the analyte in solution, and this higher response did not appear to result from gas-phase proton transfer reactions. Although all of the analytes investigated had higher gas-phase basicities than the solvent, their relative responses were not dictated by gas-phase basicity. Higher response was observed for all of the analytes studied in acidified methanol compared with neat methanol, and this higher response was most pronounced for weakly basic analytes. These findings support the use of analyte pK(b) for rational method development in ESI-MS analysis of small molecules.     

Unexpected Hole Doping of Graphene by Osmium Adatoms

The electronic transport of monolayer graphene devices is studied before and after in situ deposition of a sub-monolayer coating of osmium adatoms. Unexpectedly, and unlike all other metallic adatoms studied to date, osmium adatoms shift the charge neutrality point to more positive gate voltages. This indicates that osmium adatoms act as electron acceptors and thus leave the graphene hole-doped. Analysis of transport data suggest that Os adatoms behave as charged impurity scatterers, albeit with a surprisingly low charge-doping efficiency. The charge neutrality point of graphene is found to vary non-monotonically with gate voltage as the sample is warmed to room temperature, suggesting that osmium diffuses on the surface but is not completely removed.     

Unions of minimal prime ideals in rings of continuous functions on compact spaces

As is well-known to those familiar with the Gillman-Jerison text on the ring C(X) of real-valued continuous functions on a topological space (which we may assume is a Tychonoff space), every prime ideal is contained in a unique maximal ideal. In case X is compact, each maximal ideal is of the form M _p for some ${p \in X}$ and consists of all ${f \in C(X)}$ such that f(p) = 0, while the intersection of all minimal prime ideals contained in M _p is the set of all continuous functions which vanish on a neighborhood of p. In this paper, we reverse some inclusions and study the union of all of the minimal prime ideals contained in M _p ; particularly in the case when this set-theoretic union is all of M _p . When this occurs, we call X a UMP-space. By making use of the well-known theorem of Gelfand and Kolmogoroff, we obtain new results without assuming that X is compact. It turns out that all UMP-spaces have the property that each of its nonempty zero-sets has nonempty interior. That is, X is an almost P-space. But this condition is far from sufficient.     

A convenient route to 4-carboxy-4-anilidopiperidine esters and acids

The route selection and development of a convenient synthesis of 4-carboxy-4-anilidopiperidines is described. Previous routes were hampered by the low yield of the target esters as well as the inability to convert the esters to the required free acids. Considerations for large-scale production led to a modified synthesis that utilised a tert-butyl ester of 4-carboxy-4-anilidopiperidines which resulted in a dramatic increase in the overall yield of the target N-propionylated- 4-anilidopiperidine-4-carboxylic acids and their corresponding methyl esters. These compounds are now available for use as precursors and reference standards, of particular value for the production of 11C and 18F-labelled 4-carboxy-4-anilidopiperidine radiotracers.     

In vivo measurements of T1 relaxation times of 31P-metabolites in human skeletal muscle

The T1 relaxation times were estimated for 31P-metabolites in human skeletal muscle. Five healthy volunteers were examined in a 1.5 Tesla wholebody imaging system using an inversion recovery pulse sequence. The calculated T1 relaxation times ranged from 5.517 sec for phosphocreatine to 3.603 sec for -ATP.     

Null charts and naked singularities in spherically symmetric,homothetic spacetimes

We give a unified derivation of a null chart for all spherically symmetric, homothetic spacetimes. These spacetimes contain an interesting class of naked singularities which we are also able to elucidate. Much use is made of graphical representation; in particular a chart of the spacetimes based on their homothetic group motions is introduced. Dust spacetimes, and two homogeneous examples with non-zero pressure (flat Robertson-Walker and a Kantowski-Sachs example) are studied in detail. We show the horizon structure in the null atlas, in comoving coordinates, in terms of the areal radius and comoving time, and in the homothetic diagrams. The critical delay between comoving observers for the onset of nakedness is interpreted in terms of a decreasing mass concentration in the spirit of Thorne's hoop conjecture. We also give a simple criterion for the existence of apparent horizons isolating the various singularities, and study in detail how this criterion is circumvented in the naked examples. We conclude that this type of naked singularity is a consequence of the imposed homothetic symmetry, by showing it to be generally present and timelike in the homothetic group chart even when it is not visible at comoving infinity (before the onset of criticality). It is the delayed final collapse of initially distant observers in inhomogeneous spacetimes that causes the initial singularity to become visible at comoving infinity. We conclude that these examples do not present an obstacle to the Event Horizon Conjecture as summarized by W. Israel (1984). That is, one can formulate criteria for the formation of apparent horizons that do not imply that all singularities are necessarily so enclosed. It is still possible that all singularities stronger than homothetic are isolated by an apparent horizon, in the spirit of Tipler's conjecture.On leave from Department of Physics, Queen's University, Kingston, Ontario, Canada     

Laser control of chemical reactions

Chemical reactions are at the heart of chemistry and the dream of controlling the outcome of these reactions is an old one. Thus, with given reactants, a solvent and perhaps assisted by a catalyst, we would like to 'steer' the reactants into a particular desired product. This review focuses on how to control the dynamics of chemical reactions, beyond traditional temperature control, with the emphasis on unimolecular reactions. The electromagnetic radiation of lasers can induce so-called coherent dynamics. The recent theoretical and experimental results on this coherent control are explained and illustrated with computational and experimental examples.