243,302 research outputs found
Destabilized carbenium ions: [alpha]-carbamoyl-[alpha],[alpha]-dimethylmethyl cations
No full textWolf R, Grützmacher H-F. Destabilized carbenium ions: [alpha]-carbamoyl-[alpha],[alpha]-dimethylmethyl cations. Journal of physical organic chemistry. 1990;3(5):301-308
Clustering of ions at atomic dimensions in quantum plasmas
No full textBy means of particle simulations of the equations of motion for ions interacting among themselves under the influence of newly discovered Shukla–Eliasson attractive force (SEAF) in a dense quantum plasma, we demonstrate that the SEAF can bring ions closer at atomic dimensions. We present simulation results of the dynamics of an ensemble of ions in the presence of the SEAF without and with confining external potentials and collisions between ions and degenerate electrons. Our particle simulations reveal that under the SEAF, ions attract each other, come closer, and form ionic clusters in the bath of degenerate electrons that shield ions. Furthermore, an external confining potential produces robust ion clusters that can have cigar- and ball-like shapes, which remain stable when the confining potential is removed. The stability of ion clusters is discussed. Our results may have applications to solid density plasmas (density exceeding 1023 per cm3), where the electrons will be degenerate and quantum forces due to the electron recoil effect caused by the overlapping of electron wave functions and electron tunneling through the Bohm potential, electron-exchange and electron-exchange and electron correlations associated with electron-1/2 spin effect, and the quantum statistical pressure of the degenerate electrons play a decisive role
"Closing the R&D Gap, Evaluating the Sources of R&D Spending"
No full textBoth spending and tax policies have been implemented in the United States with the goal of stimulating private sector research and development (R&D). Karier questions whether current R&D policy, especially the research and experimentation tax credit, can contribute to closing the gap between nondefense expenditures on R&D in the United States and such expenditures in other countries, such as Japan and Germany. He also explores possible changes to our current R&D policy to make it more effective.
Gaseous [M - H]+ ions of alpha,omega-diphenylalkanes: cyclization to [M + H]+ type ions of benzocycloalkanes as recognized by chain-length dependent proton exchange
No full textKuck D. Gaseous [M - H]+ ions of alpha,omega-diphenylalkanes: cyclization to [M + H]+ type ions of benzocycloalkanes as recognized by chain-length dependent proton exchange. International Journal of Mass Spectrometry and Ion Processes. 1992;117(1-3):441-455.Metastable [M - H]+ ions of alpha,omega-diphenylalkanes C6H5(CH2)xC6H5 where x = 3-6 (structures 3-6 respectively), generated by hydride abstraction in the chemical ionization (i-butane) source, eliminate benzene after proton exchange between the aromatic rings. The proton exchange is slow for ions [3 - H]+ and [4 - H]+, but fast and apparently complete for ions [5 - H]+ and [6 - H]+. These observations, combined with collision activation experiments, suggest the cyclization of the [M - H]+ ions to isomeric protonated 1-phenylbenzocycloalkane and 1-benzylbenzocycloalkane derivatives, i.e. to [M1 + H]+ type ions, with a preference for protonated tetralin structures. Hydrogen exchange between the aliphatic chain and the rings is absent or negligible for [M - H]+ ions of 3-5 but is significant for ions [6 - H]+
Bactericidal action of positive and negative ions in air
No full textYesIn recent years there has been renewed interest in the use of air ionisers to control of the spread of airborne infection. One characteristic of air ions which has been widely reported is their apparent biocidal action. However, whilst the body of evidence suggests a biocidal effect in the presence of air ions the physical and biological mechanisms involved remain unclear. In particular, it is not clear which of several possible mechanisms of electrical origin (i.e. the action of the ions, the production of ozone, or the action of the electric field) are responsible for cell death. A study was therefore undertaken to clarify this issue and to determine the physical mechanisms associated with microbial cell death.
In the study seven bacterial species (Staphylococcus aureus, Mycobacterium parafortuitum, Pseudomonas aeruginosa, Acinetobacter baumanii, Burkholderia cenocepacia, Bacillus subtilis and Serratia marcescens) were exposed to both positive and negative ions in the presence of air. In order to distinguish between effects arising from: (i) the action of the air ions; (ii) the action of the electric field, and (iii) the action of ozone, two interventions were made. The first intervention involved placing a thin mica sheet between the ionisation source and the bacteria, directly over the agar plates. This intervention, while leaving the electric field unaltered, prevented the air ions from reaching the microbial samples. In addition, the mica plate prevented ozone produced from reaching the bacteria. The second intervention involved placing an earthed wire mesh directly above the agar plates. This prevented both the electric field and the air ions from impacting on the bacteria, while allowing any ozone present to reach the agar plate. With the exception of Mycobacterium parafortuitum, the principal cause of cell death amongst the bacteria studied was exposure to ozone, with electroporation playing a secondary role. However in the case of Mycobacterium parafortuitum, electroporation resulting from exposure to the electric field appears to have been the principal cause of cell inactivation.
The results of the study suggest that the bactericidal action attributed to negative air ions by previous researchers may have been overestimated
Gas phase reactions of protonated 1,3-diphenylpropyne and some isomeric [C15H13]+ ions
No full textBäther W, Kuck D, Grützmacher H-F. Gas phase reactions of protonated 1,3-diphenylpropyne and some isomeric [C15H13]+ ions. Organic Mass Spectrometry. 1985;20(9):572-577.Metastable (3-phenyl-2-propynyl)benzenium ions, generated by electron impact induced fragmentation from the appropriately substituted 1,4-dihydrobenzoic acid, react by loss of ·CH3 and C6H6. The study of deuterated derivatives reveals that hydrogen/deuterium exchanges involving all hydrogen and deuterium atoms precede the fragmentations. The results suggest a skeletal rearrangement by electrophilic ring-closure reactions giving rise to protonated phenylindene and protonated 9,10-methano-9,10-dihydroanthracene prior to the elimination of C6H6 and ·CH3, respectively. A study of isomeric [C15H13]+ ions by collision-induced decomposition and by deuterium labelling shows that these ions interconvert by hydrogen migrations and skeletal rearrangements
The hydrolysis of hydroxamic acid complexants in the presence of non-oxidizing metal ions 2: Neptunium (IV) ions.
No full textHydroxamic acids are salt free, organic compounds with affinities for cations such as Fe3+, Np4+ and Pu4+, and have been identified as suitable reagents for the control of Pu and Np in advanced nuclear fuel reprocessing. The results of a UV-visible, near-IR spectrophotometric study of the 1:1 and 2:1 complexes formed between formo- and aceto-hydroxamic acids (FHA, AHA) and Np(IV) ions are interpreted using speciation diagrams for the identification of the species present at different pH and ligand to metal ratios. A kinetic model that describes the instability of the complex due to hydrolysis of the hydroxamate moiety, previously developed for the Fe(III)-AHA complexes (Andrieux et al. in J. Solution Chem. 36:1201-1217, [2007]), is tested here against experimental Np(IV)-FHA data. Consequently, the complexation constant for formation of the 1:1 Np(IV)-FHA complex in nitric acid is estimated at K-1=2715 and indications are that complexation protects the ligand against hydrolysis at 0.1 > pH >-0.1
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EISCAT/CRRES observations: Nightside ionospheric ion outflow and oxygen-rich substorm injections
No full textWe present combined observations made near midnight by the EISCAT radar, all-sky cameras and the combined released and radiation efects satellite (CRRES) shortly before and during a substorm. In particular, we study a discrete, equatorward-drifting auroral arc, seen several degrees poleward of the onset region. The arc passes through the field-aligned beam of the EISCAT radar and is seen to be associated with a considerable upflow of ionospheric plasma. During the substorm, the CRRES satellite observed two major injections, 17 min apart, the second of which was dominated by O+ ions. We show that the observed are was in a suitable location in both latitude and MLT to have fed O+ ions into the second injection and that the upward flux of ions associated with it was sufficient to explain the observed injection. We interpret these data as showing that arcs in the nightside plasma-sheet boundary layer could be the source of O+ ions energised by a dipolarisation of the mid- and near-Earth tail, as opposed to ions ejected from the dayside ionosphere in the cleft ion fountain
Mass spectrometry of alkylbenzenes and related compounds. Part II. Gas phase ion chemistry of protonated alkylbenzenes (alkylbenzenium ions)
No full textKuck D. Mass spectrometry of alkylbenzenes and related compounds. Part II. Gas phase ion chemistry of protonated alkylbenzenes (alkylbenzenium ions). Mass Spectrometry Reviews. 1990;9(6):583-630
Sorption Mechanism of Lead Ions From Aqueous Solution By Imperata Cylindrica Dried Leaf Particle: Effect of Temperatures
No full textThis study was conducted to investigate the sorption mechanism of Pb2+ ions from aqueous solution onto
Imperata cylindrica (IC) dried leaf particles. The effect of temperatures (30, 35 and 40oC) was scrutinised
from a batch adsorption system using a synthetic liquid waste containing Pb2+ ions. Adsorption of lead ions
mechanism was investigated by intraparticle diffusion model. The results showed that higher adsorption rate
occurred at higher temperature, and obeyed the pseudo second order adsorption model. The overall rate of
lead uptake was found to be controlled by external mass transfer at the beginning of adsorption, then
gradually changes to intraparticle diffusion controlled at a later stage. The intraparticle diffusion constant
increased with increasing temperature. The values of effective diffusion coefficient (Di) increased at higher
temperatures, which were 5.5466 × 10−9, 6.8215 × 10−9, and 7.3726 × 10−9 m2/s at 30, 35, and 40 ◦C,
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