2,122 research outputs found
VLF scattering from red sprites: application of numerical modelling
No full textRed sprites were discovered by chance in 1989 when a low-light TV system was pointed above an active thunderstorm. Red sprites are associated with columns of ionization in the Earth-ionosphere waveguide, from above the thunderstorm into the D region of the ionosphere. The ionized columns have been detected through “VLF sprites,” perturbations of the phase and/or amplitude of subionospheric VLF transmissions, which can be used to study the electrical properties of red sprites. There is extensive experimental evidence that VLF sprites may involve wide scattering angles and can produce back scattered radiation. Here we present a numerical and theoretical study of me scattering of subionospheric VLF transmissions caused by the plasma columns associated with red sprites. Comparison of the VLF scattering from sprites is made between a non-Born rigorous model which assumes the sprites are infinite columns of constant conductivity, and a three dimensional Born scattering code. Both formulations show excellent agreement with one another. The formulations predict VLF sprites similar to those experimentally observed for all scattering angles. This shows that the conclusions of previous studies into VLF sprites making use of the non-Born formulations of Rodger et al. [1997a, b] are valid. The modeling provides strong evidence that red sprite plasma is highly ionized in comparison with the ambient nighttime ionosphere, being nearly 5 orders of magnitude greater than the ambient at some heights
Simulations of DNA coiling around a synthetic supramolecular cylinder that binds in the DNA major groove
No full textIn this work we present the results of a molecular simulation study of the interaction between a tetracationic bis iron((II)) supramolecular cylinder, [Fe-2(C25H20N4)(3)](4+), and DNA. This supramolecular cylinder has been shown to bind in the major groove of DNA and to induce dramatic coiling of the DNA. The simulations have been designed to elucidate the interactions that lead the cylinder to target the major groove and that drive the subsequent DNA conformational changes. Three sets of multi-nanosecond simulations have been performed: one of the uncomplexed d(CCCCCTTTTTCC)d(GGAAAAAGGGGG) dodecamer; one of this DNA complexed with the cylinder molecule; and one of this DNA complexed with a neutralised version of the cylinder. Coiling of the DNA was observed in the DNA-cylinder simulations, giving insight into the molecular level nature of the supramolecular coiling observed experimentally. The cylinder charge was found not to be essential for the DNA coiling, which implies that the DNA response is moderated by the short range interactions that define the molecular shape. Cylinder charge did, however, affect the integrity of the DNA duplex, to the extent that, under some circumstances, the tetracationic cylinder induced defects in the DNA base pairing at locations adjacent to the cylinder binding site
Ruthenium polypyridyl complexes and their modes of interaction with DNA : is there a correlation between these interactions and the antitumor activity of the compounds?
No full textVarious interaction modes between a group of six ruthenium polypyridyl complexes and DNA have been studied using a number of spectroscopic techniques. Five mononuclear species were selected with formula [Ru(tpy) L1L2](2-n)?, and one closely related dinuclear cation of formula [{Ru(apy)(tpy)}2{l-H2N(CH2)6NH2}]4?. The ligand tpy is 2,20:60,200-terpyridine and the ligand L1 is a bidentate ligand, namely, apy (2,20-azobispyridine), 2-phenylazopyridine, or 2-phenylpyridinylmethylene amine. The ligand L2 is a labile monodentate ligand, being Cl-, H2O, or CH3CN. All six species containing a labile L2 were found to be able to coordinate to the DNA model base 9-ethylguanine by 1H NMR and mass spectrometry. The dinuclear cationic species, which has no positions available for coordination to a DNA base, was studied for comparison purposes. The interactions between a selection of four representative complexes and calf-thymus DNA were studied by circular and linear dichroism. To explore a possible relation between DNA-binding ability and toxicity, all compounds were screened for anticancer activity in a variety of cancer cell lines, showing in some cases an activity which is comparable to that of cisplatin. Comparison of the details of the compound structures, their DNA binding, and their toxicity allows the exploration of structure–activity relationships that might be used to guide optimization of the activity of agents of this class of compounds
Shape effects on the activity of synthetic major-groove binding ligands
No full textIn this work we present the results of a molecular simulation study of two different tetracationic bis iron(II) supramolecular cylinders interacting with DNA. One cylinder has been shown to bind in the major groove of DNA and to induce dramatic coiling of the DNA; the second is a derivative of the first, with additional methyl groups attached so as to give a larger cylinder-radius. The simulations show that both cylinders bind strongly to the major groove of the DNA, and induce complex structural changes in A-T rich regions. Whereas the parent cylinder tends to bind along the major groove, the derivatised cylinder tends to twist so that only one end remains within the major groove. Both G-C rich and A-T rich binding sites for the derivatised cylinder are discussed. (c) 2006 Elsevier Inc. All rights reserved
Regional and cellular distribution of ephrin-B1 in adult mouse brain
No full textThe membrane-bound proteins ephrins and their receptors, Eph receptor tyrosine kinases, are
known for their key role during development of the central nervous system (CNS). Ligand/
receptor interactions as a result of cell–cell contacts activate intracellular signalling pathways
which mediate specific cellular responses. Activation can occur bidirectionally in both the
receptor and the ligand-bearing cells. Eph receptor and ephrin families have been implicated
in synaptic plasticity in themature brain: effects include long-term potentiation/depression of
excitatory transmission (LTP/LTD) and an action on the structure and number of synaptic
contacts. However, due to the redundancy of binding between receptors and ligands, the role
of individual proteins has not yet been completely elucidated. Ephrin-B1 has been suggested
to play a role in synaptic plasticity in the hippocampus, but its expression and localization at
pre- or post-synaptic sites has been poorly documented, most likely due to the apparent low
activity of the corresponding gene in mature brain. Here we present immunohistochemical
data demonstrating a broad but highly regulated cellular distribution of ephrin-B1 in the
mature mouse brain. We show that ephrin-B1 is expressed post-synaptically on dendritic
spines in the cortex, supporting a role in synaptic plasticity in this region. However, the
prevalent extra-synaptic distribution in regions such as the hippocampus and cerebellum
suggests an additional structural role, perhaps at the neuron/glia interface
Correction to 'Radiation belt electron precipitation into the atmosphere: recovery from a geomagnetic storm'
No full textInternational audienceCorrection to “Radiation belt electron precipitation intothe atmosphere: Recovery from a geomagnetic storm”Craig J. Rodger, Mark A. Clilverd, Neil R. Thomson, Rory J. Gamble, Annika Seppälä,Esa Turunen, Nigel P. Meredith, Michel Parrot, Jean‐André Sauvaud,and Jean‐Jacques BerthelierReceived 17 August 2010; accepted 19 August 2010; published 25 September 2010.Citation: Rodger, C. J., M. A. Clilverd, N. R. Thomson, R. J. Gamble, A. Seppälä, E. Turunen, N. P. Meredith, M. Parrot, J.‐A.Sauvaud, and J.‐J. Berthelier (2010), Correction to “Radiation belt electron precipitation into the atmosphere: Recovery from ageomagnetic storm,” J. Geophys. Res., 115, A09324, doi:10.1029/2010JA016038
Determining the size of lightning-induced electron precipitation patches
No full text[1] We analyze Trimpi signatures during 23 and 24 April 1994 at four sites on or near the Antarctic Peninsula (Palmer, Faraday, Rothera, and Halley) on subionospheric VLF signals received from four U. S. naval transmitters (NAA, NSS, NLK, and NPM). Electron precipitation patches are found to be large, i.e., similar to1500 km x 600 km, with the longer axis orientated east-west. Calculations using a three-dimensional Born scattering model, where patch densities are 1.5 electrons cm(-3) above ambient at the center at similar to84 km altitude, provides results that are consistent with this picture. A high proportion (38%) of the Trimpi events were associated with strong lightning flashes in eastern United States. When lightning discharges had currents >65 kA (positive or negative), there was a >80% chance of seeing an associated Trimpi event. The chance of seeing any Trimpi events fell to near zero for discharges of <45 kA. The largest Trimpi perturbations occur when the center of the precipitation patch is 700-800 km from the receivers. This result is consistent with the modeling calculations for large patches. The equatorward edge of the precipitation patch was estimated to be at &SIM;60&DEG;S, close to the magnetic conjugate of the lightning. The close association of the equatorward edge of the precipitation patch with the conjugate location of the causative lightning is consistent with a quasi-ducted whistler-induced precipitation mechanism. Nonducted whistler-induced precipitation mechanisms would predict a 5&DEG;-10&DEG; latitudinal gap between the lightning and the equatorward edge of the patch. However, the lack of observed whistlers at the time of the Trimpi events is consistent with the nonducted whistler mechanism and is not consistent with the quasi-ducted mechanism, although the distances from duct exit point to receiver may have been too large (&SIM;700-1000 km) for the signals to be detectable. Using the significantly larger patch dimensions determined in this study, it is estimated that lightning may well be 10-100 times more effective at depleting the radiation belts than hiss
Evolutionary comparisons predict that dimerization of human cytochrome P450 aromatase increases its enzymatic activity and efficiency
No full textAvailable online 7 September 2015Abstract not availableLisandra L. Martin, Jessica K. Holien, Dario Mizrachi, C. Jo Corbin, Alan J. Conley, Michael W. Parker, Raymond J. Rodger
Planning, programming, budgeting system and alternative futures contingency budgets: a comparative theoretical analysis
No full textreportI am delighted to express my appreciation for the assistance in the completion of this study provided by many individuals. A very large debt of gratitude is owed to Professor Frank C. Hachman and Mr. Craig Bigler, Associate Utah State Planning Coordinator, in that they are responsible for the original ideas and proposals which developed into the Utah Process and were also intimately involved in the successful carrying out of that project. Other co-workers on the Utah Process project in the State Planning Coordinator\u27s Office to whom special recognition is due include Douglas C. W. Kirk, Bruce L. Heath, and Rhead S. Bowman. In a very real sense, much thanks is due to the entire Utah State Government, but special mention must be made of Governor Calvin L. Rampton and the three State Planning Coordinators under whom the Utah Process was originated and carried out: Kenneth C. Olson, William G. Bruhn, and Burton L. Carlson
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