Search results for "Periodic table"
showing 10 items of 262 documents
Synthesis of Sesquiterpenes via silicon-guided rearrangement of epoxydecalins
2008
A survey of the rearrangement of methyldecalins via C-5 carbocation intermediates, with special attention to the silicon-guided rearrangement of epoxydecalins is provided. A TMS group properly positioned on either C-1 or C-9 promotes the acidic rearrangement of 10-methyl-4,5-epoxydecalins and 10-methyl-5,6-epoxydecalins with exclusive migration toward C-5 of the methyl or methylene groups linked directly to C-10. The application of this biomimetic approach to the synthesis of a number of spirocyclic and eremophilane sesquiterpenes is reported.
Alkaline cavities and tetrahedra in and solid solutions
1997
Seven different crystals were grown with 0 < x < 2 while seven different crystals were grown with , the limit value x = 1 corresponding to the clearly defined compound. A crystallographic study of these solid solutions was performed by comparison with the pure crystal. Structures were solved in the Pnma space group for the rubidium solid solutions and in the space group for the potassium ones. It was shown that the distribution of Cs and Rb, or Cs and K, among the two cationic sites called and was not random: Rb and K exhibit a higher affinity for the smallest cavity, the site. While the phase transition of and can be interpreted as rotations of the rigid tetrahedra mainly around the a dire…
Summary of Working Group 3 at NuFact’00: interface between machine and physics
2001
Abstract The main conclusions from the Working Group 3 presentations and deliberations at NuFact’00 are summarized.
Evidence for three microscopically different kinds ofE1 transition in lead-region nuclei
1988
A survey of electric dipole transition rates, or B(E1) values, is done for lead-region nuclei with 82≦Z≦90 and 112≦N≦134. It is found that the major part of the E1 transitions are hindered by a factor of about 106–107 and these transitions are interpreted to proceed via admixtures of the collective 1− state. A second group, which is generally 10–100 times less hindered and is involving the πi13/2 orbital in the initial states, is suggested to proceed via the allowed πi11/2→πh9/2 admixtures in the wave functions. These two groups are compared to a third newly established category, the α-cluster or IBAp-boson mode, of the so-called vibron model.
Improved instrument for the determination of the neutron electric charge
2015
Abstract We present an improved instrument for the determination of the neutron electric charge with ultracold neutrons. Several technical upgrades with respect to a former experiment will be discussed in detail. As a first test, we applied the apparatus to investigate the influence of gravitational attraction by means of a massive block of lead. The calculated sensitivity for a charge measurement is δ q n ≈ 2.14 × 10 − 20 e / day . Planned modifications increasing the sensitivity up to δ q n ≈ 1.34 × 10 − 21 e / day are demonstrated.
Excitation and ionization of Rydberg atoms by short half-cycle pulses
1999
Simple semiclassical formulas are derived for the probability of excitation and ionization of Rydberg atoms irradiated by a half-cycle pulse whose duration is shorter than the Kepler period. The calculated ionization probabilities are in good agreement with the experimental data of Jones, You, and Bucksbaum [Phys. Rev. Lett. 70, 1236 (1993)] and with previous calculations.
Complex chemistry with complex compounds
2016
In recent years gas-phase chemical studies assisted by physical pre-separation allowed for the investigation of fragile single molecular species by gas-phase chromatography. The latest success with the heaviest group 6 transactinide seaborgium is highlighted. The formation of a very volatile hexacarbonyl compound Sg(CO)6 was observed similarly to its lighter homologues molybdenum and tungsten. The interactions of these gaseous carbonyl complex compounds with quartz surfaces were investigated by thermochromatography. Second-generation experiments are under way to investigate the intramolecular bond between the central metal atom of the complexes and the ligands addressing the influence of re…
Diffraction of neutral helium clusters: evidence for "magic numbers".
2004
The size distributions of neutral 4He clusters in cryogenic jet beams, analyzed by diffraction from a 100 nm period transmission grating, reveal magic numbers at N=10-11, 14, 22, 26-27, and 44 atoms. Whereas magic numbers in nuclei and clusters are attributed to enhanced stabilities, this is not expected for quantum fluid He clusters on the basis of numerous calculations. These magic numbers occur at threshold sizes for which the quantized excitations calculated with the diffusion Monte Carlo method are stabilized, thereby providing the first experimental confirmation for the energy levels of 4He clusters.
Periodic Table of the Elements, History, Education and Evaluation
2021
The periodic tables of transition metal thiophosphates MPS3, transition metal dichalcogenides MX2 and other materials, the origin of chemical elements and toxic trace elements in dried mushrooms are provided. The effective nucleus-electron attraction is proportional to the effective nuclear charge (Zeff) and inversely proportional to the effective principal quantum number (n*). The periodic arch is one of many modern visual displays that have been developed to augment the traditional periodic table of the chemical elements. The table is related to the multiparameter optimisation of N atom, nuclear magnetic resonance and everyday life. Educational activities were developed and evaluated. Se …
<i>Amblyseius fennicus</i> sp. n. (Acarina, Gamasina: Phytoseiidae) from Finland, with a key to the <i>A. americanus</i> group
2012
A new species is described belonging to the Amblyseius (s. str.) americanus group (Denmark & Muma, 1989). It was collected regularly from trunks of old trees in Finland. A key is given including the known species of the A. americanus group.