9,027 research outputs found
Approaches to new fluoride ion sources
Fluoride ion sources have been surveyed and perfluoroalkyl anions and hindered amine/HF adducts prepared and investigated as reagents. The perfluoroalkyl anions (I) and (II) have been used in an attempt to fluorinate various organic compounds such as alkyl halides, alkyl tosylates, aryl halides and acetyl chloride. The following new compounds have been synthesised and identified by glc-mass spec and, where possible, (^19)F nmr. These arose from reaction of the substrate with the perfluoroalkyl anion rather than with F(^-). Preliminary work on hindered amine bases, particularly proton sponge and tri-n-octylamine, with HF was undertaken, these being studied as possible soluble fluoride ion sources. Solid adducts were obtained in most cases from ether solutions and they were shown to behave as fluoride ion sources under various conditions
Accurate measurement of ^{13}C - ^{15}N distances with solid-state NMR
Solid-state NMR technique for measureing distances between hetero-nuclei in
static powder samples is described. It is based on a two-dimensional
single-echo scheme enhanced with adiabatic cross-polarization. As an example,
the results for intra-molecular distances in -crystalline form of
glycine are presented. The measured NMR distances ^13 C(2) - ^15 N and ^13 C(1)
- ^15 N are 1.496 0.002 \AA and 2.50 0.02 \AA, respectively.Comment: 12 page
Self-induced water intoxication : a case report
CITATION: Emsley, R. A. & Taljaard, J. J. F. 1988. Self-induced water intoxication : a case report. South African Medical Journal, 74:80-81.The original publication is available at http://www.samj.org.zaA 19-year-old female schizophrenic with self-induced water intoxication is described. Factors of pathogenic significance included primary polydipsia and non-maximal urinary diluting capacity.Publisher’s versio
Fidelity enhancement by logical qubit encoding
We demonstrate coherent control of two logical qubits encoded in a
decoherence free subspace (DFS) of four dipolar-coupled protons in an NMR
quantum information processor. A pseudo-pure fiducial state is created in the
DFS, and a unitary logical qubit entangling operator evolves the system to a
logical Bell state. The four-spin molecule is partially aligned by a liquid
crystal solvent, which introduces strong dipolar couplings among the spins.
Although the system Hamiltonian is never fully specified, we demonstrate high
fidelity control over the logical degrees of freedom. In fact, the DFS encoding
leads to higher fidelity control than is available in the full four-spin
Hilbert space.Comment: 10 pages, 2 figure
Harnessing the potential of neural networks for effective decision making in the decision to bid process
Quantum information processing using strongly-dipolar coupled nuclear spins
Dipolar coupled homonuclear spins present challenging, yet useful systems for
quantum information processing. In such systems, eigenbasis of the system
Hamiltonian is the appropriate computational basis and coherent control can be
achieved by specially designed strongly modulating pulses. In this letter we
describe the first experimental implementation of the quantum algorithm for
numerical gradient estimation on the eigenbasis of a four spin system.Comment: 5 pages, 5 figures, Accepted in PR
The new-generation antipsychotics -integrating the neuropathology and pharmacology of schizophrenia
No Abstract
New determination of structure parameters in strong field tunneling ionization theory of molecules
In the strong field molecular tunneling ionization theory of Tong et al.
[Phys. Rev. A 66, 033402 (2002)], the ionization rate depends on the asymptotic
wavefunction of the molecular orbital from which the electron is removed. The
orbital wavefunctions obtained from standard quantum chemistry packages in
general are not good enough in the asymptotic region. Here we construct a
one-electron model potential for several linear molecules using density
functional theory (DFT). We show that the asymptotic wavefunction can be
improved with an iteration method and after one iteration accurate asymptotic
wavefunctions and structure parameters are determined. With the new parameters
we examine the alignment-dependent tunneling ionization probabilities for
several molecules and compare with other calculations and with recent
measurements, including ionization from inner molecular orbitals
Publisher's Note: ^13C NMR study of the director distribution adopted by the modulated nematic phases formed by liquid-crystal dimers with odd numbers of atoms in their spacers [Phys. Rev. E 96, 062702 (2017)]
Weighing of trapped ion crystals and its applications
We have developed a novel scheme to measure the secular motion of trapped
ions. Employing pulsed excitation and analysis of the fluorescence of laser
cooled ions, we have measured the centre-of-mass mode frequency of single as
well as entire ion crystals with a frequency precision better than 5e-4 within
an interrogation time on the order of seconds, limited only by the fluorescence
collection efficiency and the background noise. We have used this method to
measure the mass of ions and observed charge exchange collisions between
trapped calcium isotopes.Comment: 24 pages, 15 figure
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