Reduction in ionic permeability of a silicone hydrogel contact lenses after one month of daily wear

[EN] Purpose. To compare the ionic permeability using the ionoflux method of new and worn samples of a silicone hydrogel contact lens material. Methods. An ionoflux experimental setup was established to measure the ionic permeability (NaCl) of soft contact lenses. Samples of a silicone hydrogel lens (Comfilcon A, Coopervision, Pleasanton, CA) with optical powers of -1.00, -1.50 and -4.75 diopters (D) were used in this study. Three samples of each power were measured after being worn for one month on a daily wear basis. Lenses were cleaned and disinfected every night using multipurpose disinfecting solutions. Three samples of new lenses from the same batch and the same optical power were also measured to evaluate the effect of lens wear on the ionic permeability of the lens material. Before measurement, the lenses were equilibrated with a 1 M NaCl solution during one week before of each measurement. Results. Lens power had minimal effect on the ionic permeability of a modern silicone hydrogel contact lens with the -1.00 lens having a 15% lower permeability compared to the other two lenses. After one month of lens wear the apparent ionic permeability for lenses with -1.50 D decreased by 15%. In the case of -1.00 and -4.75 D lenses there was a decrease of 26%. Conclusions. The ionic permeability of silicone hydrogel lenses of different optical powers was not significantly different. Worn lenses present a significant reduction of the ionic permeability after a month of wear. The potential effect this reduction on lens movement and discomfort associated to lens wear should be further evaluated.The authors have no proprietary interest in any of the materials mentioned in this article. This work was funded in part by FEDER through the COMPTETE Program and by the Portuguese Foundation for Science and Technology (FCT) in the framework of projects PTDC/SAU-BEB/098391/2008, PTDC/SAU-BEB/098392/2008 and the Strategic Project PEST-C/FIS/UI607/2011.Ferreira Da Silva, AR.; Compañ Moreno, V.; Gonzalez-Meijome, JM. (2015). Reduction in ionic permeability of a silicone hydrogel contact lenses after one month of daily wear. Materials Research Express. 2(6). https://doi.org/10.1088/2053-1591/2/6/065007S26Yoon, S. C., & Jhon, M. S. (1982). The transport phenomena of some model solutes through postcrosslinked poly(2-hydroxyethyl methacrylate) membranes with different tactic precursors. Journal of Applied Polymer Science, 27(8), 3133-3149. doi:10.1002/app.1982.070270834Yasuda, H., Lamaze, C. E., & Ikenberry, L. D. (1968). Die Makromolekulare Chemie, 118(1), 19-35. doi:10.1002/macp.1968.021180102MURPHY, S., HAMILTON, C., & TIGHE, B. (1988). Synthetic hydrogels: 5. Transport processes in 2-hydroxyethyl methacrylate copolymers. Polymer, 29(10), 1887-1893. doi:10.1016/0032-3861(88)90407-7Nicolson, P. C., & Vogt, J. (2001). Soft contact lens polymers: an evolution. Biomaterials, 22(24), 3273-3283. doi:10.1016/s0142-9612(01)00165-xMonticelli, M. V., Chauhan, A., & Radke, C. J. (2005). The Effect of Water Hydraulic Permeability on the Settling of a Soft Contact Lens on the Eye. Current Eye Research, 30(5), 329-336. doi:10.1080/02713680590934085Guan, L., Jiménez, M. E. G., Walowski, C., Boushehri, A., Prausnitz, J. M., & Radke, C. J. (2011). Permeability and partition coefficient of aqueous sodium chloride in soft contact lenses. Journal of Applied Polymer Science, 122(3), 1457-1471. doi:10.1002/app.33336Cheng, M.-L., & Sun, Y.-M. (2005). Observation of the solute transport in the permeation through hydrogel membranes by using FTIR-microscopy. Journal of Membrane Science, 253(1-2), 191-198. doi:10.1016/j.memsci.2005.01.017CHHABRA, M., PRAUSNITZ, J., & RADKE, C. (2007). A single-lens polarographic measurement of oxygen permeability (Dk) for hypertransmissible soft contact lenses. Biomaterials, 28(30), 4331-4342. doi:10.1016/j.biomaterials.2007.06.024González-Méijome, J. M., López-Alemany, A., Almeida, J. B., & Parafita, M. A. (2009). Surface AFM microscopy of unworn and worn samples of silicone hydrogel contact lenses. Journal of Biomedical Materials Research Part B: Applied Biomaterials, 88B(1), 75-82. doi:10.1002/jbm.b.31153González-Méijome, J. M., López-Alemany, A., Almeida, J. B., & Parafita, M. A. (2008). Dynamic in vitro dehydration patterns of unworn and worn silicone hydrogel contact lenses. Journal of Biomedical Materials Research Part B: Applied Biomaterials, 90B(1), 250-258. doi:10.1002/jbm.b.31279Pozuelo, J., Compañ, V., González-Méijome, J. M., González, M., & Mollá, S. (2014). Oxygen and ionic transport in hydrogel and silicone-hydrogel contact lens materials: An experimental and theoretical study. Journal of Membrane Science, 452, 62-72. doi:10.1016/j.memsci.2013.10.010Wolffsohn, J. S., Hunt, O. A., & Basra, A. K. (2009). Simplified recording of soft contact lens fit. Contact Lens and Anterior Eye, 32(1), 37-42. doi:10.1016/j.clae.2008.12.00

e-VLBI observations of Circinus X-1: monitoring of the quiescent and flaring radio emission on AU scales

A recent detection of the peculiar neutron star X-ray binary Circinus X-1 with electronic very long baseline interferometry (e-VLBI) prompted the suggestion that compact, non-variable radio emission persists through the entire 16.6-day orbit of the binary system. We present the results of a high angular resolution monitoring campaign conducted with the Australian Long Baseline Array in real-time e-VLBI mode. e-VLBI observations of Circinus X-1 were made on alternate days over a period of 20 days covering the full binary orbit. A compact radio source associated with Circinus X-1 was clearly detected at orbital phases following periastron passage but no compact radio emission was detected at any other orbital phase, ruling out the presence of a persistent, compact emitting region at our sensitivity levels. The jet was not resolved at any epoch of our 1.4-GHz monitoring campaign, suggesting that the ultrarelativistic flow previously inferred to exist in this source is likely to be dark. We discuss these findings within the context of previous radio monitoring of Circinus X-1.Comment: Accepted for publication in MNRAS. 7 pages, 5 figure

A relativistic helical jet in the gamma-ray AGN 1156+295

We present the results of a number of high resolution radio observations of the AGN 1156+295. These include multi-epoch and multi-frequency VLBI, VSOP, MERLIN and VLA observations made over a period of 50 months. The 5 GHz MERLIN images trace a straight jet extending to 2 arcsec at P.A. -18 degrees. Extended low brightness emission was detected in the MERLIN observation at 1.6 GHz and the VLA observation at 8.5 GHz with a bend of about 90 degrees at the end of the 2 arcsecond jet. A region of similar diffuse emission is also seen about 2 arcseconds south of the radio core. The VLBI images of the blazar reveal a core-jet structure with an oscillating jet on a milli-arcsecond (mas) scale which aligns with the arcsecond jet at a distance of several tens of milli-arcseconds from the core. This probably indicates that the orientation of the jet structure is close to the line of sight, with the northern jet being relativistically beamed toward us. In this scenario the diffuse emission to the north and south is not beamed and appears symmetrical. For the northern jet at the mas scale, proper motions of 13.7 +/-3.5, 10.6 +/- 2.8, and 11.8 +/- 2.8 c are measured in three distinct components of the jet (q_0=0.5, H_0=65 km /s /Mpc are used through out this paper). Highly polarised emission is detected on VLBI scales in the region in which the jet bends sharply to the north-west. The spectral index distribution of the source shows that the strongest compact component has a flat spectrum, and the extended jet has a steep spectrum. A helical trajectory along the surface of a cone was proposed based on the conservation laws for kinetic energy and momentum to explain the observed phenomena, which is in a good agreement with the observed results on scales of 1 mas to 1 arcsec.Comment: 19 pages with 18 figures. Accepted for publication in the A&

Book Reviews

Book Review 1Book Title: Atlas of Microscopic Structures of Fur Skins Vol. 1Book Authors: Anton Blažej et al.Elsevier Amsterdam and SNTl, Prague, 1989. 378 pages.Book Review 2Book Title: Ornithology for AfricaBook Author: Gordon L. MacleanUniversity of Natal Press, 1990. 270 pages.Book Review 3Book Title: Biology of the Vespine WaspsBook Authors: Makoto Matsuura & Seiki YamaneSpringer-Verlag, Berlin, 1990. 323 pages, numerous figures, tables and photographs. ISBN 3-540-51900-9Book Review 4Book Title: Horns, Pronghorns, and AntlersBook Authors: Edited by G.A. Bubenik & A.B. BubenikSpringer-Verlag, New York. ISBN 0-387-97176-9. 562 pp.Book Review 5Book Title: Ecophysiology of Desert Arthropods and ReptilesBook Author: J.L. Cloudsley-ThompsonSpringer-Verlag, 1991. 203 pagesBook Review 6Book Title: Practical Taxonomic ComputingBook Author: Richard J. PankhurstCambridge University Press. 202 page

A return to strong radio flaring by Circinus X-1 observed with the Karoo Array Telescope test array KAT-7

Circinus X-1 is a bright and highly variable X-ray binary which displays strong and rapid evolution in all wavebands. Radio flaring, associated with the production of a relativistic jet, occurs periodically on a ~17-day timescale. A longer-term envelope modulates the peak radio fluxes in flares, ranging from peaks in excess of a Jansky in the 1970s to an historic low of milliJanskys during the years 1994 to 2007. Here we report first observations of this source with the MeerKAT test array, KAT-7, part of the pathfinder development for the African dish component of the Square Kilometre Array (SKA), demonstrating successful scientific operation for variable and transient sources with the test array. The KAT-7 observations at 1.9 GHz during the period 13 December 2011 to 16 January 2012 reveal in temporal detail the return to the Jansky-level events observed in the 1970s. We compare these data to contemporaneous single-dish measurements at 4.8 and 8.5 GHz with the HartRAO 26-m telescope and X-ray monitoring from MAXI. We discuss whether the overall modulation and recent dramatic brightening is likely to be due to an increase in the power of the jet due to changes in accretion rate or changing Doppler boosting associated with a varying angle to the line of sight.Comment: 7 pages, 5 figures, accepted for publication in MNRAS 14 May 201