1-Alkyl-1,4-dihydro-4-iminoquinoline-3-carboxylic Acids: Synthesis, Structure and Properties

1-Alkyl-1,4-dihydro-4-iminoquinoline-3-carboxylates undergo neutral hydrolysis (in H2O or H2O-EtOH mixtures) to yield water-soluble 4-iminoquinoline-3-carboxylic acids and the corresponding 4-oxo esters. Such 4-imino acids are also accessed by treating an appropriate 1-alkyl-1,4-dihydro-4-oxoquinoline-3-carboxylic acid successively with thionyl chloride and an amine-H2O mixture, or from treatment of a 4-imino ester salt with aqueous amine. In the latter procedures 7-fluoro substituted substrates gave rise to 7-alkylamino derivatives even at room temperature. The title compounds are inferred to have an intramolecularly H-bonded charge transfer structure, and some of their chemical reactions and spectral (HRMS, 1H NMR) properties are described. South African Journal of Chemistry Vol.55 2002: 13-3

The Synthesis of 4-Ethyl-2-propyl-3-substitutedpyrrolo[ 3,4-b]quinoline-1,9-dione Derivatives from 3,3-Dichloro-4-ethyl-thieno[3,4-b]quinoline-1,9-dione and Propylamine

The preparation, spectral properties and structure elucidations of the hitherto undocumented 3-oxo-,  3-thioxo-, 3-propylimino-, 3-imino-, and 3-propylamino- derivatives of 4-ethyl-2-propyl-2,3-dihydro-pyrrolo[3,4-b]quinoline-1,9-dione are described. Mechanistic aspects relating particularly to the formation of the latter two unprecedented products are considered. Magnetic anisotropic effects (deshielding/line broadening of signals) are exhibited by the α-methylene protons of the 4-ethyl moiety in the 1H NMR spectra of the first four of the above, and in several 3,3-dichloro-thieno[3,4-b]quinoline-1,9-diones and intramolecular H-bonded, 1,2-dialkyl-4-oxo-3-quinolinecarboxylic acid precursor substrates.KEYWORDS: 3-Imino-, 3-propylamino-, 3-propylimino-, 3-oxo-, 3-thioxo-substituted 4-ethyl-2-propyl- 2,3-dihydro-pyrrolo[3,4-b]quinoline- 1,9-diones, 4-methyl-, 4-propyl-substituted-3,3-dichloro-thieno[3,4-b]quinoline-1,9-diones, intramolecular H-bonding, magnetic anisotropic effects

Finite-difference schemes for anisotropic diffusion

In fusion plasmas diffusion tensors are extremely anisotropic due to the high temperature and large magnetic field strength. This causes diffusion, heat conduction, and viscous momentum loss, to effectively be aligned with the magnetic field lines. This alignment leads to different values for the respective diffusive coefficients in the magnetic field direction and in the perpendicular direction, to the extent that heat diffusion coefficients can be up to 10 to the 12 th times larger in the parallel direction than in the perpendicular direction. This anisotropy puts stringent requirements on the numerical methods used to approximate the MHD-equations since any misalignment of the grid may cause the perpendicular diffusion to be polluted by the numerical error in approximating the parallel diffusion. Currently the common approach is to apply magnetic field-aligned coordinates, an approach that automatically takes care of the directionality of the diffusive coefficients. This approach runs into problems at x-points and at points where there is magnetic re-connection, since this causes local non-alignment. It is therefore useful to consider numerical schemes that are tolerant to the misalignment of the grid with the magnetic field lines, both to improve existing methods and to help open the possibility of applying regular non-aligned grids. To investigate this, in this paper several discretisation schemes are developed and applied to the anisotropic heat diffusion equation on a non-aligned grid.</p

Discretization methods for extremely anisotropic diffusion

In fusion plasmas there is extreme anisotropy due to the high temperature and large magnetic field strength. This causes diffusive processes, heat diffusion and energy/momentum loss due to viscous friction, to effectively be aligned with the magnetic field lines. This alignment leads to different values for the respective diffusive coefficients in the magnetic field direction and in the perpendicular direction, to the extent that heat diffusion coefficients can be up to $10^{12}$ times larger in the parallel direction than in the perpendicular direction. This anisotropy puts stringent requirements on the numerical methods used to approximate the MHD-equations since any misalignment of the grid may cause the perpendicular diffusion to be polluted by the numerical error in approximating the parallel diffusion. % Currently the common approach is to apply magnetic field aligned grids, an approach that automatically takes care of the directionality of the diffusive coefficients. This approach runs into problems in the case of crossing field lines, e.g., x-points and points where there is magnetic reconnection. This makes local non-alignment unavoidable. It is therefore useful to consider numerical schemes that are more tolerant to the misalignment of the grid with the magnetic field lines, both to improve existing methods and to help open the possibility of applying regular non-aligned grids. To investigate this several discretization schemes are applied to the anisotropic heat diffusion equation on a cartesian grid

Discretization methods for extremely anisotropic diffusion

In fusion plasmas there is extreme anisotropy due to the high temperature and large magnetic field strength. This causes diffusive processes, heat diffusion and energy/momentum loss due to viscous friction, to effectively be aligned with the magnetic field lines. This alignment leads to different values for the respective diffusive coefficients in the magnetic field direction and in the perpendicular direction, to the extent that heat diffusion coefficients can be up to $10^{12}$ times larger in the parallel direction than in the perpendicular direction. This anisotropy puts stringent requirements on the numerical methods used to approximate the MHD-equations since any misalignment of the grid may cause the perpendicular diffusion to be polluted by the numerical error in approximating the parallel diffusion. % Currently the common approach is to apply magnetic field aligned grids, an approach that automatically takes care of the directionality of the diffusive coefficients. This approach runs into problems in the case of crossing field lines, e.g., x-points and points where there is magnetic reconnection. This makes local non-alignment unavoidable. It is therefore useful to consider numerical schemes that are more tolerant to the misalignment of the grid with the magnetic field lines, both to improve existing methods and to help open the possibility of applying regular non-aligned grids. To investigate this several discretization schemes are applied to the anisotropic heat diffusion equation on a cartesian grid

Numerical modelling of strongly anisotropic dissipative effects in MHD

In magnetically confined fusion plasmas there is extreme anisotropy due to the high temperature and large magnetic field strength to the extent that thermal conductivity coefficients can be up to $10^{12}$ times larger in the parallel direction than in the perpendicular direction. This anisotropy puts stringent requirements on the numerical methods. A common approach uses field aligned coordinates but in case of magnetic x-points and reconnection local non-alignment is unavoidable. Accuracy in case of high levels of anisotropy for non-field aligned grids is needed for the simulation of instabilities and radial transport processes in the presence of magnetic reconnection, e.g. with edge turbulence. % We therefore consider $2^{nd}$ order numerical schemes which are suitable for non-aligned grids. A novel method for co-located grids, developed to take into account the direction of the magnetic field, has been applied to the unsteady anisotropic heat diffusion equation on a non-field-aligned grid and compared with several other discretisation schemes, including G{\"{u}}nter et al's symmetric scheme. Test cases include variable diffusion coefficients with anisotropy values up to $10^{12}$, and field line bending in divergence and non-divergence free (unit vector) field configurations. % One of the model problems is given by the unsteady heat equation % \begin{equation*} \begin{split} \mbf{q} &= - D_\bot\nabla T - (D_\|-D_\bot)\mbf{b}\mbf{b}\cdot\nabla T, \quad \diff{T}{t} = -\nabla\cdot\mbf{q} + f, \end{split} \label{eq:braginskii} \end{equation*} where $T$ represents the temperature, \mbf{b} represents the unit direction vector of the magnetic field line with respect to the coordinate axes, $f$ is some source term and $D_\|$ and $D_\bot$ represent the parallel and the perpendicular diffusion coefficient respectively. \\ % Preliminary conclusions are that for FDM's the preservation of self-adjointness is crucial for limiting the pollution of perpendicular diffusion to acceptable values. However it is not required for maintaining the order of accuracy in most cases as is demonstrated by our aligned method. Key goal is to improve the co-located method to obtain acceptable levels for the pollution of the pe

Spin transport in graphene nanostructures

Graphene is an interesting material for spintronics, showing long spin relaxation lengths even at room temperature. For future spintronic devices it is important to understand the behavior of the spins and the limitations for spin transport in structures where the dimensions are smaller than the spin relaxation length. However, the study of spin injection and transport in graphene nanostructures is highly unexplored. Here we study the spin injection and relaxation in nanostructured graphene with dimensions smaller than the spin relaxation length. For graphene nanoislands, where the edge length to area ratio is much higher than for standard devices, we show that enhanced spin-flip processes at the edges do not seem to play a major role in the spin relaxation. On the other hand, contact induced spin relaxation has a much more dramatic effect for these low dimensional structures. By studying the nonlocal spin transport through a graphene quantum dot we observe that the obtained values for spin relaxation are dominated by the connecting graphene islands and not by the quantum dot itself. Using a simple model we argue that future nonlocal Hanle precession measurements can obtain a more significant value for the spin relaxation time for the quantum dot by using high spin polarization contacts in combination with low tunneling rates