Magnetoplasmons in quantum rings

We have studied the structure and dipole charge density response of nanorings as a function of the magnetic field using local-spin density functional theory. Two small rings consisting of 12 and 22 electrons confined by a positively charged background are used to represent the cases of a narrow and a wide ring. The results are qualitatively compared with experimental data existing on microrings and on antidots. A smaller ring containing 5 electrons is also analyzed to allow for a closer comparison with a recent experiment on a two electron quantum ring.Comment: Typeset using Revtex, 13 pages and 11 Postscript figure

Skipping orbits and enhanced resistivity in large-diameter InAs/GaSb antidot lattices

We investigated the magnetotransport properties of high-mobility InAs/GaSb antidot lattices. In addition to the usual commensurability features at low magnetic field we found a broad maximum of classical origin around 2.5 T. The latter can be ascribed to a class of rosetta type orbits encircling a single antidot. This is shown by both a simple transport calculation based on a classical Kubo formula and an analysis of the Poincare surface of section at different magnetic field values. At low temperatures we observe weak 1/B-periodic oscillations superimposed on the classical maximum.Comment: 4 pages, 4 Postscript figures, REVTeX, submitted to Phys Rev

Photocurrent in nanostructures with asymmetric antidots

The steady current induced by electromagnetic field in a 2D system with asymmetric scatterers is studied. The scatterers are assumed to be oriented cuts with one diffusive and another specular sides. Besides, the existence of isotropic impurity scatterers is assumed. This simple model simulates the lattice of half-disk which have been studied numerically recently. The model allows the exact solution in the framework of the kinetic equation. The static current response in the second order of electric field is obtained. The photogalvanic tensor contains both responses to linear and circular polarization of electromagnetic field. The model possesses non-analyticity with regards to the rate of impurity scattering.Comment: 9 pages, 6 figure

Coupling between magnetic field and curvature in Heisenberg spins on surfaces with rotational symmetry

We study the nonlinear $\sigma$-model in an external magnetic field applied on curved surfaces with rotational symmetry. The Euler-Lagrange equations derived from the Hamiltonian yield the double sine-Gordon equation (DSG) provided the magnetic field is tuned with the curvature of the surface. A $2\pi$ skyrmion appears like a solution for this model and surface deformations are predicted at the sector where the spins point in the opposite direction to the magnetic field. We also study some specific examples by applying the model on three rotationally symmetric surfaces: the cylinder, the catenoid and the hyperboloid. The coupling between a magnetic field and the curvature of the substract is an interesting result and we believe that this issue may be relevant to be applied in condensed matter systems, e.g., superconductors, nematic liquid crystals, graphene and topological insulators.Comment: To be published in Physics Letters

Electron-hole bilayer quantum dots: Phase diagram and exciton localization

We studied a vertical ``quantum dot molecule'', where one of the dots is occupied with electrons and the other with holes. We find that different phases occur in the ground state, depending on the carrier density and the interdot distance. When the system is dominated by shell structure, orbital degeneracies can be removed either by Hund's rule, or by Jahn-Teller deformation. Both mechanisms can lead to a maximum of the addition energy at mid-shell. At low densities and large interdot distances, bound electron-hole pairs are formed.Comment: 10 pages, 3 figure

The role of intratidal oscillations in sediment resuspension in a diurnal, partially mixed estuary

Using detailed observations of the mean and turbulent properties of flow, salinity and turbidity that spanned 2001/02, we examined the physical mechanisms underpinning sediment resuspension in the low-energy Swan River estuary, Western Australia. In this diurnal tidally-dominated estuary, the presence of intratidal oscillations, a tidal inequality lasting 2 to 3 hours on the flood tide, generated by interactions of the four main diurnal and semidiurnal astronomical constituents, K₁, O₁, M₂, and S₂, played a major role in modifying vertical stratification and mixing. These intratidal oscillations are controlled by phase differences between the tropic and synodic months rather than being temporally-fixed by bed friction, as occurs in semidiurnal estuaries. Intratidal oscillations are largest, at around 0.1 m, near to the Austral solstice when the lunar and solar declination are in-phase. Despite the seemingly small change in water level, shear-induced interfacial mixing caused destratification of the water column with the top-to-bottom salinity (ΔS) difference of 3.5 present early in the flood tide eroded to less than 0.3 by the end of the intratidal oscillation. High turbidity peaks, of 250 nephelometric turbidity units, coincided with these intratidal oscillations and could not be explained by bed friction since shear stress from mean flow did not exceed threshold criteria. High Reynolds stresses of ∼1 Nm⁻² did, however, exceed τcr and together with negative Reynolds fluxes indicate a net downward transport of material. Destratification of the water column induced by shear instabilities resulted in large overturns capable of moving in situ material towards the bed during intratidal oscillations and these turbidities were ∼10 times greater than those from bed-generated resuspension observed later during the flood tide

Conductance and persistent current of a quantum ring coupled to a quantum wire under external fields

The electronic transport of a noninteracting quantum ring side-coupled to a quantum wire is studied via a single-band tunneling tight-binding Hamiltonian. We found that the system develops an oscillating band with antiresonances and resonances arising from the hybridization of the quasibound levels of the ring and the coupling to the quantum wire. The positions of the antiresonances correspond exactly to the electronic spectrum of the isolated ring. Moreover, for a uniform quantum ring the conductance and the persistent current density were found to exhibit a particular odd-even parity related with the ring-order. The effects of an in-plane electric field was also studied. This field shifts the electronic spectrum and damps the amplitude of the persistent current density. These features may be used to control externally the energy spectra and the amplitude of the persistent current.Comment: Revised version, 7 pages and 9 figures. To appear in Phys. Rev.

Acetylcholinesterase-capped Mesoporous Silica Nanoparticles Controlled by the Presence of Inhibitors

[EN] Two different acetylcholinesterase (AChE)-capped mesoporous silica nanoparticles (MSNs), S1-AChE and S2-AChE, were prepared and characterized. MSNs were loaded with rhodamine B and the external surface was functionalized with either pyridostigmine derivative P1 (to yield solid S1) or neostigmine derivative P2 (to obtain S2). The final capped materials were obtained by coordinating grafted P1 or P2 with AChE ' s active sites (to give S1-AChE and S2-AChE, respectively). Both materials were able to release rho-damine B in the presence of diisopropylfluorophosphate (DFP) or neostigmine in a concentration-dependent manner via the competitive displacement of AChE through DFP and neostigmine coordination with the AChE ' s active sites. The responses of S1-AChE and S2-AChE were also tested with other enzyme inhibitors and substrates. These studies suggest that S1-AChE nanoparticles can be used for the selective detection of nerve agent simulant DFP and paraoxon.Financial support from the Spanish Government and FEDER funds (Project MAT2015‐64139‐C4‐1‐R, AGL2015‐70235‐C2‐2‐R) and the Generalitat Valencia (Project PROMETEOII/2014/047) is gratefully acknowledged. Ll. P. is grateful to the Universitat Politécnica de Valencia for his grant.Pascual, L.; El Sayed Shehata Nasr, S.; Marcos Martínez, MD.; Martínez-Máñez, R.; Sancenón Galarza, F. (2017). Acetylcholinesterase-capped Mesoporous Silica Nanoparticles Controlled by the Presence of Inhibitors. Chemistry - An Asian Journal. 12(7):775-784. https://doi.org/10.1002/asia.201700031S775784127Alberti, S., Soler-Illia, G. J. A. A., & Azzaroni, O. (2015). Gated supramolecular chemistry in hybrid mesoporous silica nanoarchitectures: controlled delivery and molecular transport in response to chemical, physical and biological stimuli. 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Cytosine-phosphodiester-guanine oligodeoxynucleotide (CpG ODN)-capped hollow mesoporous silica particles for enzyme-triggered drug delivery. Dalton Transactions, 40(39), 10203. doi:10.1039/c1dt11114kAgostini, A., Mondragón, L., Bernardos, A., Martínez-Máñez, R., Marcos, M. D., Sancenón, F., … Murguía, J. R. (2012). Targeted Cargo Delivery in Senescent Cells Using Capped Mesoporous Silica Nanoparticles. Angewandte Chemie International Edition, 51(42), 10556-10560. doi:10.1002/anie.201204663Agostini, A., Mondragón, L., Bernardos, A., Martínez-Máñez, R., Marcos, M. D., Sancenón, F., … Murguía, J. R. (2012). Targeted Cargo Delivery in Senescent Cells Using Capped Mesoporous Silica Nanoparticles. Angewandte Chemie, 124(42), 10708-10712. doi:10.1002/ange.201204663Aznar, E., Villalonga, R., Giménez, C., Sancenón, F., Marcos, M. D., Martínez-Máñez, R., … Amorós, P. (2013). Glucose-triggered release using enzyme-gated mesoporous silica nanoparticles. Chemical Communications, 49(57), 6391. doi:10.1039/c3cc42210kChen, M., Huang, C., He, C., Zhu, W., Xu, Y., & Lu, Y. (2012). A glucose-responsive controlled release system using glucose oxidase-gated mesoporous silica nanocontainers. Chemical Communications, 48(76), 9522. doi:10.1039/c2cc34290aDíez, P., Sánchez, A., Gamella, M., Martínez-Ruíz, P., Aznar, E., de la Torre, C., … Pingarrón, J. M. (2014). Toward the Design of Smart Delivery Systems Controlled by Integrated Enzyme-Based Biocomputing Ensembles. Journal of the American Chemical Society, 136(25), 9116-9123. doi:10.1021/ja503578bDíez, P., Sánchez, A., Torre, C. de la, Gamella, M., Martínez-Ruíz, P., Aznar, E., … Villalonga, R. (2016). Neoglycoenzyme-Gated Mesoporous Silica Nanoparticles: Toward the Design of Nanodevices for Pulsatile Programmed Sequential Delivery. ACS Applied Materials & Interfaces, 8(12), 7657-7665. doi:10.1021/acsami.5b12645Yang, X., Pu, F., Chen, C., Ren, J., & Qu, X. (2012). An enzyme-responsive nanocontainer as an intelligent signal-amplification platform for a multiple proteases assay. Chemical Communications, 48(90), 11133. doi:10.1039/c2cc36340bDatz, S., Argyo, C., Gattner, M., Weiss, V., Brunner, K., Bretzler, J., … Bein, T. (2016). Genetically designed biomolecular capping system for mesoporous silica nanoparticles enables receptor-mediated cell uptake and controlled drug release. Nanoscale, 8(15), 8101-8110. doi:10.1039/c5nr08163gSun, X., Zhao, Y., Lin, V. S.-Y., Slowing, I. I., & Trewyn, B. G. (2011). Luciferase and Luciferin Co-immobilized Mesoporous Silica Nanoparticle Materials for Intracellular Biocatalysis. Journal of the American Chemical Society, 133(46), 18554-18557. doi:10.1021/ja2080168Liu, P., Wang, X., Hiltunen, K., & Chen, Z. (2015). Controllable Drug Release System in Living Cells Triggered by Enzyme–Substrate Recognition. 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Chemical Communications, 47(33), 9459. doi:10.1039/c1cc12740cEl Sayed, S., Milani, M., Milanese, C., Licchelli, M., Martínez-Máñez, R., & Sancenón, F. (2016). Anions as Triggers in Controlled Release Protocols from Mesoporous Silica Nanoparticles Functionalized with Macrocyclic Copper(II) Complexes. Chemistry - A European Journal, 22(39), 13935-13945. doi:10.1002/chem.201601024Tukappa, A., Ultimo, A., de la Torre, C., Pardo, T., Sancenón, F., & Martínez-Máñez, R. (2016). Polyglutamic Acid-Gated Mesoporous Silica Nanoparticles for Enzyme-Controlled Drug Delivery. Langmuir, 32(33), 8507-8515. doi:10.1021/acs.langmuir.6b01715Giménez, C., Climent, E., Aznar, E., Martínez-Máñez, R., Sancenón, F., Marcos, M. D., … Rurack, K. (2014). Über den chemischen Informationsaustausch zwischen gesteuerten Nanopartikeln. Angewandte Chemie, 126(46), 12838-12843. doi:10.1002/ange.201405580De la Torre, C., Agostini, A., Mondragón, L., Orzáez, M., Sancenón, F., Martínez-Máñez, R., … Pérez-Payá, E. (2014). Temperature-controlled release by changes in the secondary structure of peptides anchored onto mesoporous silica supports. Chem. Commun., 50(24), 3184-3186. doi:10.1039/c3cc49421gOroval, M., Climent, E., Coll, C., Eritja, R., Aviñó, A., Marcos, M. D., … Amorós, P. (2013). An aptamer-gated silica mesoporous material for thrombin detection. Chemical Communications, 49(48), 5480. doi:10.1039/c3cc42157kPascual, L., Sayed, S. E., Martínez-Máñez, R., Costero, A. M., Gil, S., Gaviña, P., & Sancenón, F. (2016). Acetylcholinesterase-Capped Mesoporous Silica Nanoparticles That Open in the Presence of Diisopropylfluorophosphate (a Sarin or Soman Simulant). Organic Letters, 18(21), 5548-5551. doi:10.1021/acs.orglett.6b02793Comes, M., Rodríguez-López, G., Marcos, M. D., Martínez-Máñez, R., Sancenón, F., Soto, J., … Beltrán, D. (2005). Host Solids Containing Nanoscale Anion-Binding Pockets and Their Use in Selective Sensing Displacement Assays. 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Aqueous Methanol Extracts of Cochlospermum tinctorium (A. Rich) Possess Analgesic and Anti-inflammatory Activities

Cochlopermum tinctorium A. Rich. (Cochlospermaceae) is a commonly used medicinal plant in the West Africa sub-region for the management of various conditions including pain and inflammatory conditions. In the present study, we report the analgesic and anti-inflammatory activities of the aqueous methanol leaf (20–80 mg/kg), root (7.5–30 mg/kg), and root bark (20–80 mg/kg) extracts of the plant. The analgesic potentials of the extracts were studied using acetic acid induced writhing and hot plate tests in mice while the anti-inflammatory activity was investigated using carrageenan-induced paw edema in rats.The extracts significantly and dose dependently inhibited the acetic acid-induced writhing in mice. However, the highest protection against writhing was produced by aqueous methanol leaf extract at the dose of 80 mg/kg (96.65%) which even was greater than that of the standard agent, ketoprofen (82.30%). The extracts did not significantly increase mean latency of response in the hot plate test. However, aqueous methanol root bark extract at the dose of 20 mg/kg significantly (P < 0.05) increased the mean latency of pain response. While the extracts of the root and root bark extracts of the plant afforded non dose-dependent protection against carrageenan-induced edema, the aqueous methanol leaf extract significantly and dose-dependently inhibited carrageenan-induced hind paw edema at the end of the third hour.The present study suggests that the aqueous methanol leaf, root, and root bark extracts of Cochlopermum tinctorium possess analgesic and anti-inflammatory activities which lend some credence to the ethnomedical claim of the use of the plant in the management of pain and inflammatory conditions