Search results for "DIR"
showing 10 items of 10242 documents
Comparison of electron diffraction data from non-linear optically active organic DMABC crystals obtained at 100 and 300 kV
2000
During the recent past, we have synthesized a new class of molecules with intramolecular two-dimensional charge transfer upon excitation. The present report presents such a molecule, 2,6-bis(4-dimethylamino-benzylidene)-cyclohexanone (DMABC), with an unusually high value of the second-order non-linear optical (NLO) coefficients. In order to optimize the macroscopic NLO properties of the compounds, it is necessary to relate their first hyperpolarizability tensors at a molecular level to those at a crystal bulk level. This requires a complete structure determination and refinement. However, the growth of sufficiently large single crystals, which are needed for structural analysis and refineme…
Le qualifiche dei dichiaranti:anomalie del modello italiano e spunti comparatistici.
2011
La chiamata in correità è un istituto processuale che si confronta storicamente con un atteggiamento ambivalente, caratterizzato dallo scettiscismo da un lato e dalla fiducia verso il contributo dei dichiarante, dall'altro. Le premesse storiche vengono utilizzate per mettere in luce i nodi più attuali del dibattito interpretativo.
Child-centered and teacher-directed practices in relation to calculation and word problem solving skills
2019
Abstract This study examined transactional associations between classroom-level math skills and teaching practices. Participants were 523 children from 31 classrooms. Math skills were assessed three times. Teaching practices were observed in Grades 1 and 3. Child-centered practices promoted subsequent calculation skills whereas teacher-directed practices were associated with a lower level of calculation skills. Higher problem-solving skills at Grade 2 predicted more child-centered practices and less teacher-directed practices in third grade. Moreover, calculation skills mediated the effect of child-centered practices on problem-solving skills. The results suggest that teaching practices and…
Nonlinear chiral transport in Dirac semimetals
2018
We study the current of chiral charge density in a Dirac semimetal with two Dirac points in momentum space, subjected to an externally applied time dependent electric field and in the presence of a magnetic field. Based on the kinetic equation approach, we find contributions to the chiral charge current, that are proportional to the second power of the electric field and to the first and second powers of the magnetic field, describing the interplay of the chiral anomaly and the drift motion of electrons moving under the action of electric and magnetic fields.
CHIRAL ANOMALY IN ASHTEKAR'S APPROACH TO CANONICAL GRAVITY
1998
The Dirac equation in Riemann–Cartan spacetimes with torsion is reconsidered. As is well-known, only the axial covector torsion A, a one-form, couples to massive Dirac fields. Using diagrammatic techniques, we show that besides the familiar Riemannian term only the Pontrjagin type four-form dA ∧ dA does arise additionally in the chiral anomaly, but not the Nieh–Yan term d* A, as has been claimed recently. Implications for cosmic strings in Einstein–Cartan theory as well as for Ashtekar's canonical approach to quantum gravity are discussed.
The Chiral Anomaly
1989
The Dirac operator on a manifold M is a first order partial differential operator acting on sections of a spin bundle over M. The Dirac operator is elliptic when the metric of M is positive definite. The main task in this chapter is to study properties of the determinant of the Dirac operator.
The use of zooplankton metrics to determine the trophic status and ecological potential: An approach in a large Mediterranean watershed.
2021
In the European Water Framework Directive, zooplankton was not included as a Biological Quality Element despite its important place in the aquatic trophic web. In the present study on zooplankton abundances and biomasses, we used several metrics to test their ability to detect differences among trophic statuses and ecological potential levels, and collected a large sum of data in more than 60 reservoirs at Ebro watershed, on more than 300 sampling occasions over 10 years. Our results indicate that most zooplankton metrics are correlated to environmental variables that determine reservoirs’ trophic states, especially chlorophyll a and total phosphorus. The metrics with better sensitivity to …
Determination of relative chlorophyll binding affinities in the major light-harvesting chlorophyll a/b complex.
2002
The major light-harvesting complex (LHCIIb) of photosystem II can be reconstituted in vitro from its recombinant apoprotein in the presence of a mixture of carotenoids and chlorophylls a and b. By varying the chlorophyll a/b ratio in the reconstitution mixture, the relative amounts of chlorophyll a and chlorophyll b bound to LHCIIb can be changed. We have analyzed the chlorophyll stoichiometry in recombinant wild type and mutant LHCIIb reconstituted at different chlorophyll a/b ratios in order to assess relative affinities of the chlorophyll-binding sites. This approach reveals five sites that exclusively bind chlorophyll b. Another site exhibits a slight preference of chlorophyll b over ch…
Random mutations directed to transmembrane and loop domains of the light-harvesting chlorophyll a/b protein: impact on pigment binding.
1999
The major light-harvesting complex of photosystem II (LHCII) can be reconstituted in vitro by folding its bacterially expressed apoprotein, Lhcb, in detergent solution in the presence of chlorophylls and carotenoids. To compare the impact of alpha-helical transmembrane domains and hydrophilic loop domains of the apoprotein on complex formation and stability, we introduced random mutations into a segment of the protein comprising the stromal loop, the third (C-proximal) transmembrane helix, and part of the amphipathic helix in the C-terminal domain. The mutant versions of Lhcb were screened for the loss of their ability to form stable LHCII upon reconstitution in vitro. Most steps during the…
Exchange of Pigment-Binding Amino Acids in Light-Harvesting Chlorophyll a/b Protein
1999
Four amino acids in the major light-harvesting chlorophyll (Chl) a/b complex (LHCII) that are thought to coordinate Chl molecules have been exchanged with amino acids that presumably cannot bind Chl. Amino acids H68, Q131, Q197, and H212 are positioned in helixes B, C, A, and D, respectively, and, according to the LHCII crystal structure [Kühlbrandt, W., et al. (1994) Nature 367, 614-621], coordinate the Chl molecules named a(5), b(6), a(3), and b(3). Moreover, a double mutant was analyzed carrying exchanges at positions E65 and H68, presumably affecting Chls a(4) and a(5). All mutant proteins could be reconstituted in vitro with pigments, although the thermal stability of the resulting mut…