Search results for " bonding"
showing 10 items of 934 documents
Computer modeling of metal colloid formation in tracks of swift heavy ions in ionic solids
2001
Abstract We present results of computer modelling of the aggregation of primary radiation defects—F centers—in ionic crystals within tracks of swift heavy ions. We study how F-aggregate properties depend on the initial density of primary Frenkel defects in the track and its radius. The mean number of F centers in aggregates is typically very small, about five defects, which greatly complicates detection of expected metal colloids by ESR.
Radiation-induced point defects in simple oxides
1998
We present a survey of recent theoretical studies of radiation-induced point defects in simple oxides with emphasis on highly ionic MgO, partly-covalent corundum (Al2O3) and ferroelectric KNbO3. The atomic and electronic structure of the electronic (F a and F centers) and hole centers, as well as interstitial atoms therein are discussed in light of the available experimental data. Results for defect diAusion and photo-stimulated F a fi F center conversion are also ana
Studies for low mass, large area monolithic silicon pixel detector modules using the MALTA CMOS pixel chip
2021
Abstract The MALTA monolithic silicon pixel sensors have been used to study dicing and thinning of monolithic silicon pixel detectors for large area and low mass modules. Dicing as close as possible to the active circuitry will allow to build modules with very narrow inactive regions between the sensors. Inactive edge regions of less than 5 μ m to the electronic circuitry could be achieved for 100 μ m thick sensors. The MALTA chip (Cardella et al., 2019) also offers the possibility to transfer data and power directly from chip to chip. Tests have been carried out connecting two MALTA chips directly using ultrasonic wedge wire bonding. Results from lab tests show that the data accumulated in…
Laser spectroscopy with an electrostatic ConeTrap
2017
A compact electrostatic trap has been designed and installed as part of the recent upgrades to the IGISOL IV facility. The ConeTrap provides an in vacuo optical pumping site for low energy (800 eV) ionic ensembles available for interaction periods of 10-100 ms. At present, 6.7(3) % of injected mass A=98 ions can be trapped, stored for 5 ms, extracted and transported to a laser-ion interaction region. This fraction represents those ions for which no perturbation to total energy or energy spread is observed. Proposed enhancements to the trap are designed to improve the trapping efficiency by up to a factor of 5. Differential pumping and reduction in background pressure below the present 10−6 …
A study of a helium-jet ion guide for an on-line isotope separator
1981
Abstract A new method based on helium-jet techniques permits primary recoil ions, produced in radioactive decay or in nuclear reactions to be run directly through a mass separator. Results obtained with a 227 Ac source promise qualities complementary with those obtained with conventional ion sources and indicate an overall efficiency of the order of 10%. Preliminary results with 20 Na recoils from the 20 Ne(p,n)-reaction indicate that most of the ionic species transported out from the target chamber are negatively charged.
Reactions of benzothiete with phosphorus nucleophiles - a novel type of arbuzov rearrangement
1989
The reaction of trialkylphosphites or related P-nucleophiles with benzothiete (1) leads to zwitter ionic species, which show an Arbuzov - like rearrangement to the products 4 and 7, respectively. New heterocyclic ring systems are generated in the case of cyclic esters. The normal SN2 reaction leads to the 1:2 adducts 9, whereas in an SN1 process the 1:1 adduct 13 is formed.
ChemInform Abstract: Reactions of Benzothiete with Phosphorus Nucleophiles. A Novel Type of Arbuzov Rearrangement.
1989
The reaction of trialkylphosphites or related P-nucleophiles with benzothiete (1) leads to zwitter ionic species, which show an Arbuzov - like rearrangement to the products 4 and 7, respectively. New heterocyclic ring systems are generated in the case of cyclic esters. The normal SN2 reaction leads to the 1:2 adducts 9, whereas in an SN1 process the 1:1 adduct 13 is formed.
Capping Parallel β-Sheets of Acetyl(Ala)6NH2 with an Acetyl(Ala)5ProNH2 Can Arrest the Growth of the Sheet, Suggesting a Potential for Curtailing Amy…
2014
We present ONIOM calculations using B3LYP/d95(d,p) as the high level and AM1 as the medium level on parallel β-sheets containing four strands of Ac-AAAAAA-NH2 capped with either Ac-AAPAAA-NH2 or Ac-AAAPAA-NH2. Because Pro can form H-bonds from only one side of the peptide linkage (that containing the C═O H-bond acceptor), only one of the two Pro-containing strands can favorably add to the sheet on each side. Surprisingly, when the sheet is capped with AAPAAA-NH2 at one edge, the interaction between the cap and sheet is slightly more stabilizing than that of another all Ala strand. Breaking down the interaction enthalpies into H-bonding and distortion energies shows the favorable interaction…
Hydrophobicity of ionisable compounds studied by countercurrent chromatography
2011
Countercurrent chromatography (CCC) is a liquid chromatography technique in which the stationary phase is also a liquid. The main chemical process involved in solute separation is partitioning between the two immiscible liquid phases: the mobile phase and the support-free liquid stationary phase. The octanol-water partition coefficients (P(o/w)) is the accepted parameter measuring the hydrophobicity of molecules. It is considered to estimate active principle partitioning over a biomembrane. It was related to the substance biological activity. CCC is able to work with an octanol stationary phase and an aqueous mobile phase. In this configuration, CCC is a useful and easy alternative to measu…
N,N-Di-n-octyl-N,N-dimethyl and N,N-di-n-nonyl-N,N-dimethyl ammonium cholates: 13C and 15N CPMAS NMR, powder X-ray diffraction and thermoanalytical c…
2009
Abstract N,N-Di-n-octyl-N,N-dimethyl cholate (1) and N,N-di-n-nonyl-N,N-dimethyl ammonium cholate (2) have been prepared by crystallization from equimolar mixtures of sodium cholate and quaternary N,N-di-n-alkyl-N,N-dimethyl (n-octyl or n-nonyl) ammonium bromides. The formed crystalline materials have been structurally characterized by 13C and 15N cross polarization magic angle spinning (CPMAS) NMR, powder X-ray diffraction (PXRD) and thermoanalytical (TGA/DTA and DSC) methods and compared with each other. Powder X-ray diffraction patterns of 1 and 2 reveal clear similarities. Combined with the thermoanalytical data of these structures an existence of two hydrated polymorphs (most probably …