Search results for "Polymethyl Methacrylate"
showing 10 items of 26 documents
Observation of Very Narrow Linewidths in the Fluorescence Excitation Spectra of Single Conjugated Polymer Chains at 1.2 K
2007
Fluorescence emission and excitation spectra of single poly[2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene vinylene] polymer molecules embedded in poly(methylmethacrylate) have been recorded at 1.2 K. The ubiquitous spectral diffusion causes large variations in the spectral shape and apparent linewidth in the emission spectra. Nevertheless, we find very narrow (approximately 0.1 cm(-1)) purely electronic zero-phonon lines in the excitation spectra, which are 2 orders of magnitude smaller than previous estimates of the homogeneous linewidth. These results complement the molecular description of the low energy transitions in conjugated polymers.
EMG-guided percutaneous placement of cement-augmented pedicle screws for osteoporotic thoracolumbar burst fractures
2017
Background: Percutaneous techniques have increasingly gained popularity in recent years. The application of technological innovation, including neuromonitoring techniques, has the potential to increase the safety and efficacy of these procedures. Methods: Thirty patients suffering from osteoporotic dorsolumbar burst fracture were prospectively enrolled in this study. The patients underwent percutaneous fenestrated pedicle screw fixation augmented with polymethylmethacrylate (PMMA) injection. A novel surgeon-dedicated neuromonitoring device was used in order to increase the safety and the accuracy of the screw insertion. A second group of 30 patients who did not undergo neuromonitoring durin…
Single Molecule Studies of a Ladder Type Conjugated Polymer: Vibronic Spectra, Line Widths, and Energy Transfer
2014
Confocal fluorescence microscopy and spectroscopy are employed to investigate single poly(ladder-type pentaphenylene) (LPPentP) molecules dispersed in thin poly(methyl methacrylate) (PMMA) films at 1.2 K. Emission spectra of single chains show single as well as multi-chromophore emission indicating variegated communication along the chains. The vibronic structure in the emission spectra resembles the one found for other ladder-type polymers. Purely electronic zero-phonon lines in emission are substantially broadened, most probably due to fast spectral diffusion. By surmounting the limitations of emission spectroscopy, nonemitting donor chromophores, which transfer their excitation energy in…
Refractive micro-optical elements for surface plasmons: from classical to gradient index optics.
2010
Controlling the propagation of surface plasmons along a metal-dielectric interface is a key feature for the development of surface plasmon based circuits. We have designed various two-dimensional refractive dielectric optical elements for surface plasmons (SP) and characterized their capacity to route SP, using near- or far-field techniques. We first present basic devices analogous to usual optical components and the associated challenges for SP optics. We then use a metamaterial approach to locally vary the refractive index and fabricate gradient index structures for SP circuitry.
Closed foldable capsular rings
2004
A new foldable capsular tension and bending ring system with a sharp-edged design is described. The closed foldable capsular rings (CFCR) consist of 8 hydrophobic and 8 hydrophilic ring segments. The CFCRs have a 9.2 mm minimum overall diameter. The CFCRs were inserted using various cartridge systems or a two-folded technique with a forceps. The CFCRs were implanted after phacoemulsification through a small (1.6 to 3.2 mm) incision in 104 human adult eyes without intraoperative complications. No postoperative complications such as capsule folds or inward bending were observed over a 6-month follow-up. Posterior capsule opacification was minimal or absent in all eyes.
Preferential solvation of poly(methyl methacrylate) and a bisphenol A diglycidyl ether by size-exclusion chromatography
2004
The preferential adsorption coefficient, lambda, of poly(methyl methacrylate), PMMA, in solutions formed by an epoxy resin in tetrahydrofuran (THF), was studied by size-exclusion chromatography (SEC). Only PMMA of lowest molar mass was preferentially solvated by epoxy but at low concentrations of epoxy in the mixture. At higher epoxy content PMMA was preferentially solvated by THF. A simultaneous and competitive solvation between the specific interactions PMMA-epoxy and the self association of epoxy at high concentrations would be the responsible of this inversion point. The more compacted coil of PMMA of higher molecular weights in solution could explain the lack of interaction of these po…
Intrastromal corneal ring segment implantation in paracentral keratoconus with coincident topographic and coma axis.
2012
To evaluate the efficacy, predictability, and safety of implantation of Ferrara-type intrastromal corneal ring segments (ICRS) for refractive correction of paracentral keratoconus.Fernández-Vega Ophthalmological Institute, Oviedo, Spain.Cohort study.Snellen uncorrected (UDVA) and corrected (CDVA) distance visual acuities and residual refractive errors were recorded before and 6 months after ICRS implantation for keratoconus. The tunnels for ICRS implantation were created with a femtosecond laser. The power vector and the Alpins method were used to analyze postoperative refractive outcomes.The study evaluated 56 eyes of 49 patients. The mean UDVA was 0.17 ± 0.14 (SD) preoperatively and 0.41 …
Rayleigh-konstanten reiner lösungsmittel und ihre wellenlängenabhängigkeit
1956
Die Rayleigh-Konstanten von Benzol und Toluol bei 366, 405, 436, 546 und 578 mμ und von Schwefelkohlenstoff bei 436, 546 und 578 mμ werden bestimmt. Die Berechnung der absoluten Streuwerte dieser Losungsmittel wird under Anwendung der Rayleighschen Gleichung durchgefuhrt, indem die Streuung des Standard-Losungsmittels mit der einer Polymethylmethacrylat-Fraktion (Mw = 62 500) mit bekannten optischen Konstanten und bekanntem Mw verglichen wird. Dabei werden die Brechungskorrekturen berucksichtigt. Aus den fur die verschiedenen Losungsmittel bei den einzelnen Wellenlangen ermittelten Rayleigh-Konstanten wird nach der Einstein-Smoluchowskischen Schwankungs-theorie der Lichtzerstreuung die Losc…
Spring constants of capsular tension rings.
2004
Purpose To determine the spring constants of several types of capsular tension rings (CTRs). Setting Department of Ophthalmology, Johannes Gutenberg-University, Mainz, Germany. Methods Fourteen models of CTRs provided by 9 companies were tested; all were 11.0 mm in diameter. The CTRs were positioned in a special retainer of a material-testing machine and compressed at a constant speed of 10.0 mm per minute. The distance and force values were recorded, and each CTR model was tested 3 times using a new specimen each time. The resulting measurements were used to calculate a mean spring constant for each CTR model. Results All tested CTRs showed linear proportionality between force and compress…
Physicochemical Surface Properties of Various Intraocular Lenses
2001
<i>Purpose:</i> It is of major interest to understand how intraocular lens (IOL) surfaces interact with aqueous humor or tissues after implantation. Important parameters to describe the physicochemical surface properties are the contact angle and critical surface tension. Therefore, we performed measurements of the contact angle and critical surface tension of several commercially available IOLs. <i>Setting:</i> Department of Ophthalmology, Johannes Gutenberg University, Mainz, University Eye Hospital, Tübingen, and Max Planck Institute for Polymer Research, Mainz, Germany. <i>Methods:</i> A total of 17 commercially available standard quality IOL types (6…