9,483 research outputs found
A time-resolved Electron Nuclear Double Resonance(ENDOR) study of the photoexcited triplet state of free-base tetraphenylporphyrin
No full textA time-resolved Electron Nuclear Double Resonance (ENDOR) study has been made of the photo-excited triplet state of free-base tetraphenylporphyrin in a partially aligned sample with crystalline toluene as the host matrix. This has permitted measurement of the Azz hyperfine tensor elements for each of the different groups of equivalent protons in the
reference frame of the zero-field splitting tensor
Time-resolved EPR and ENDOR study of the photoexcited triplet state of free-base tetraphenylchlorin in a crystalline toluene matrix
No full textA time-resolved EPR and ENDOR study of the photoexcited tripler state of the free-base tetraphenyl-chlorin has been made in a polycrystalline toluene matrix at 120 K. Crystallization of the toluene results in a partially aligned sample. The nature of the orientation of the solute molecules is investigated by time-resolved EPR spectroscopy using the anisotropy of the zero-field splitting tensor of the triplet state as the observable parameter. It is determined that 55% of the tripler molecules are oriented in a single crystal-like domain with the triplet z-axes oriented within 15 degrees of the magnetic field. In the ENDOR study selective excitation, of only those molecules which have their triplet z-axes parallel to the magnetic field, has permitted the measurement of the A(zz) component of the hyperfine coupling tensor of protons, in the reference frame of the zero-field splitting tenser. The sign and magnitude of the matrix couplings are also determined. The use of the partially oriented sample drastically enhanced the signal intensity over that achieved in a randomly oriented sample by increasing the number of molecules with their triplet z-axes parallel to the magnetic field. Additionally, time-resolved ENDOR spectroscopy allowed the hyperfine interactions to be determined at far higher temperatures than usual for the study of tripler states
Time-resolved EPR and ENDOR study of the photoexcited triplet state of free-base tetraphenylbacteriochlorin
No full textProceedings of 1995 Winter Simulation Conference
No full textEvaluation of AGV Routing Strategies Using Hierarchical Simulation / W. Ralf Seifert, M. G. Kay, and J. R. Wilson.TOMpp. 850-856
Magnetic resonance studies and molecular orbital calculations on the doublet and triplet states of bacteriopurpurin: a potential second-generation photosensitizer for photodynamic therapy
No full textBacteriopurpurin is a macrocyclic compound at the saturation level of bacteriochlorins that was specifically
synthesized as a potential photosensitizer in photodynamic therapy. It exhibits a long-wavelength Qy absorption
band at 843 nm, which is a necessary prerequisite for a deep tissue penetration. Magnetic resonance
spectroscopic properties of bacteriopurpurin have been examined by fluorescence-detected magnetic resonance
(FDMR) and electron paramagnetic resonance (EPR) in conjunction with molecular orbital calculations. The
electronic structure of the radical cation state obtained by oxidation of bacteriopurpurin with iodine is mapped
by the determination of isotropic proton hyperfine coupling constants from electron-nuclear double-resonance
spectroscopy at 298 K. A tentative assignment of the couplings to the various proton positions in the molecule
is achieved by comparison of the experimental values with simulated ones based on semiempirical intermediate
neglect of differential overlap calculations and density functional theory. The triplet-state electronic structure
of the ground-state trans-configured bacteriopurpurin is characterized by the determination of the zero-field
splitting parameters which represent sensitive probes for the geometric structure of the molecule. The jDj
and jEj values obtained from time-resolved EPR (24.4 and 5.4 mT) are in favorable agreement with the
respective values obtained from FDMR (24.0 and 5.3 mT). By both techniques, the presence of additional
photoexcited triplet states has been confirmed. It is assumed that they arise from higher-energy tautomers of
bacteriopurpurin. Their occurrence is discussed in terms of a photoinitiated intramolecular one-proton transfer
from either ring II or ring IV of the trans-configured ground state to ring I or ring III to form one of the
cis-configured bacteriopurpurins
A time resolved Electron Nuclear Double Resonance study of the Photoexcited Triplet State of P680 in Isolated Reaction Centers of Photosystem II.
No full textA time-resolved ENDOR spectrum of the triplet state of the primary donor of photosystem II in isolated reaction centers
has been obtained at cryogenic temperatures. Selective excitation of donor molecules, which have their z triplet axes parallel to the magnetic field, has permitted the measurement of the Azz component of the hyperfine coupling tensor of protons, in
the reference frame of the zero field splitting tensor. For comparison, measurements have also been made on the photoexcited triplet state of monomeric chlorophyll a in vitro. The results indicate that in the temperature range 10-20 K the triplet state of the primary donor of photosystem II is largely located on a monomeric chlorophyll a molecule
The syntax of Moroccan Arabic/French and Moroccan Arabic/Standard Arabic code switching.
No full textContact between different speech communities represents one breeding ground for change and accommodation which can affect the forms as well as the functions of language. Code switching (CS), as one result of this contact situation, is an important site to display the dominance of one language over another, or to witness the resolve of a speech community to incorporate another language so as to satisfy their needs, be them syntactic, lexical or pragmatic. The aim of this thesis is to trace down the formal manifestations of this type of language negotiation whereby switching occurs between two or more languages. It will be shown that, in a CS situation, collision of languages is highly regularised by specific syntactic features. A number of different models to CS structural constraints are considered, and one particular approach based on the analysis of selectional properties of the functional heads is advocated; this I will call the Functional Parameter Constraint (FPC). The underlying assumption of the FPC, which owes it theoretical motivation to recent syntactic research (e. g. Abney 1986, Ouhalla 1991, Chomsky 1995), is that interlanguage parameters, as opposed to language universals, constrain CS. Parameters are restricted to the features of functional categories given that their lexical counterparts are conceptually selected entries which are drawn from an invariant universal vocabulary, and therefore, are not to be parameterised (Chomsky 1995). Following Ouhalla (1991), three selectional properties for which functional categories can be parameterised cross-linguistically are identified, namely c-selection, m-selection and grammatical features. A corpus consisting of naturally occurring data was gathered to test the empirical validity of the hypothesis set for the study. The results of the examination of Moroccan Arabic/French and Moroccan/Standard Arabic bilingual conversations provide the sought empirical support
The electronic structure of the lutein triplet state in plant light-harvesting complex II
No full textCarotenoid molecules are essential for the life of photosynthetic organisms in that they protect the cell from the photo-oxidative damage induced by light-stress conditions. One of the photo-protective mechanisms involves triplet-triplet energy transfer from the chlorophyll molecules to the carotenoids: a process that is strongly dependent on the electronic properties of the triplet states involved. Here, we obtain a clear description of the triplet state of lutein in LHCII from higher plants for the first time by density functional theory (DFT) calculations. DFT predictions have been validated by comparison with hyperfine couplings obtained with pulsed-ENDOR spectroscopy. Knowledge of the spin density distribution, the frontier orbitals and orbital excitations forms a basis for discussing the requirements for an efficient triplet-triplet energy transfer. The results obtained for the lutein in LHCII are compared with those of the highly-substituted carotenoid peridinin in PCP from Amphidinium carterae [Di Valentin et al., Biochim. Biophys. Acta, 2008, 1777, 295-307]. The presence of substituents in the peridinin molecule does not alter significantly the triplet state electronic structure compared to lutein. Despite the unusual spectroscopic behaviour of the peridinin excited singlet state, lutein and peridinin have similar triplet state properties. In both molecules the unpaired spins are delocalized uniformly over the whole pi-conjugated system in an alternating even-odd pattern
Measurements of W + W - production in decay topologies inspired by searches for electroweak supersymmetry
No full textAbstract This paper presents a measurement of fiducial and differential cross-sections for W + W - production in proton–proton collisions at s = 13 TeV with the ATLAS experiment at the Large Hadron Collider using a dataset corresponding to an integrated luminosity of 139 fb - 1 . Events with exactly one electron, one muon and no hadronic jets are studied. The fiducial region in which the measurements are performed is inspired by searches for the electroweak production of supersymmetric charginos decaying to two-lepton final states. The selected events have moderate values of missing transverse momentum and the ‘stransverse mass’ variable m T2 , which is widely used in searches for supersymmetry at the LHC. The ranges of these variables are chosen so that the acceptance is enhanced for direct W + W - production and suppressed for production via top quarks, which is treated as a background. The fiducial cross-section and particle-level differential cross-sections for six variables are measured and compared with two theoretical SM predictions from perturbative QCD calculations
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