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Contrast Ratio (contrast + ratio)
Kinds of Contrast Ratio Selected AbstractsHexyl-Derivatized Poly(3,4-ethylenedioxyselenophene): Novel Highly Stable Organic Electrochromic Material with High Contrast Ratio, High Coloration Efficiency, and Low-Switching VoltageADVANCED MATERIALS, Issue 17 2009Mao Li A novel family of electrochromic materials has been discovered. The electropolymerized poly(hexyl-3,4-ethylenedioxyselenophene) film switches color between a highly absorbing pure blue and a nearly colorless bleached state, achieves both a high contrast ratio of 88,89% and a high CE of up to 773,cm2 C,1 while showing a fast switching time and remarkable stability with the contrast ratio remaining 48% after 10000 cycles. [source] Human Perception of Dental Porcelain Translucency Correlated to Spectrophotometric MeasurementsJOURNAL OF PROSTHODONTICS, Issue 3 2010Min-Chieh Liu DDS Abstract Purpose: This study evaluated the relationship between instrumental measurements and subjective visual assessment of differences in dental porcelain translucency. Materials and Methods: Unshaded feldspathic porcelain was used with controlled amounts of tin oxide to create two groups of 12-mm diameter disks with incremental changes in opacity. Contrast ratio (CR = Yb/Yw) was determined with a spectrophotometer, and used as a measure of porcelain translucency (Group A = 0.20 to 0.40; Group B = 0.6,0.8). Within each group, there were 14 specimens with 11 CRs. Three observer groups (first year dental students, residents, faculty with >10 years of shade matching experience) were recruited to assess the translucency between porcelain disks under two lighting conditions (reflected light, transmitted light). Each subject's ability to distinguish between specimens of differing translucency was determined. Descriptive statistics and three-way ANOVA followed by a post-hoc Tukey-Kramer test were used to evaluate the translucency perception threshold (TPT) of subjects (,= 0.05). Results: The overall mean TPT (,C) was 0.07, while 50% of the subjects could perceive a 0.06 CR difference between porcelain specimens. Three-way ANOVA revealed a significant difference in translucency perception among the observer groups (p < 0.0001), whereas the main effects for porcelain opacity (p= 0.3038) and lighting condition (p= 0.0645) were not significant, and no significant interactions were found. Post-hoc Tukey-Kramer test indicated that the mean TPT observed in the faculty group (,C = 0.04) was significantly lower than those observed in student (,C = 0.09) and resident groups (,C = 0.08), while there was no significant difference between students and residents. Conclusions: The overall mean TPT of all subjects was 0.07, and 50% of the study population perceived a 0.06 CR difference in translucency. Increased shade matching experience (,10 years) significantly improved the ability to perceive differences in translucency; however, neither the viewing condition nor porcelain opacity affected the perceived translucency threshold. [source] Enhanced Electrical Switching and Electrochromic Properties of Poly(p-phenylenebenzobisthiazole) Thin Films Embedded with Nano-WO3ADVANCED FUNCTIONAL MATERIALS, Issue 18 2010Jiahua Zhu Abstract The electrical switching and electrochromic phenomena of a novel nanocomposite comprising poly(p-phenylenebenzobisthiazole) (PBZT) and tungsten oxide (WO3) nanoparticles are investigated as a function of the nanoparticle loading. Both dissolving PBZT and doping PBZT backbone structure with acid are achieved by one simple step. Chlorosulfonic acid (CSA) is used as a solvent and spontaneously transformed to sulfuric acid upon exposure to moisture. The formed sulfuric acid serves as doping agent to improve the electrical conductivity of PBZT. The most significant enhancement of electrical switching is observed in the nanocomposites with low weight fraction (5%). The electrical conductivity of 5% WO3/PBZT nanocomposite thin film is increased by about 200 times and 2 times, respectively, as compared to those of the as-received PBZT and PBZT/CSA thin films. As the nanoparticle loading increases to 20% and 30%, the nanocomposites follow an ohmic conduction mechanism. Stable electrical conductivity switching is observed before and after applying a bias on the pristine PBZT and WO3/PBZT nanocomposite thin films. Electrochromic phenomena of both PBZT and WO3/PBZT nanocomposite thin films with high contrast ratio are observed after applying a bias (3 V). The mechanisms of the nanoparticles in enhancing the electrical switching and electrochromic properties are proposed. [source] Hexyl-Derivatized Poly(3,4-ethylenedioxyselenophene): Novel Highly Stable Organic Electrochromic Material with High Contrast Ratio, High Coloration Efficiency, and Low-Switching VoltageADVANCED MATERIALS, Issue 17 2009Mao Li A novel family of electrochromic materials has been discovered. The electropolymerized poly(hexyl-3,4-ethylenedioxyselenophene) film switches color between a highly absorbing pure blue and a nearly colorless bleached state, achieves both a high contrast ratio of 88,89% and a high CE of up to 773,cm2 C,1 while showing a fast switching time and remarkable stability with the contrast ratio remaining 48% after 10000 cycles. [source] Preparation and characterization of PDLC films formed using a two-step procedureADVANCES IN POLYMER TECHNOLOGY, Issue 1 2007Yu-Che Hsiao Abstract A novel polymer-dispersed liquid crystal composite film was prepared using liquid crystal and dual resins, namely, UV-curable urethane diacrylate and thermo-curable epoxy, with a fixed LC content of 50 wt%. A combination treatment of UV irradiation and heat was performed in sequential steps. At first, the urethane diacrylate resin was cross-linked through UV irradiation and a pre-UV-cured film was formed. Then, the pre-UV-cured film was heat treated for curing the thermo-curable epoxy resin. As the thermal polymerization continued, LC droplets were formed and became embedded within the polymer matrix. PDLC films obtained from the polymer matrix with refractive indices in a range from 1.511 to 1.523 (1.517 ± 0.006) have optimal electro-optical properties. Films with a refractive index higher than 1.523 have high contrast ratio (CR), threshold voltage (Vth), and V90, whereas those with a low refractive index of 1.508 have low CR, Vth, and V90. In this study, we found that PDLC composite films with optimal compositions prepared by dual resins (UV/thermal) have good electro-optical properties. © 2007 Wiley Periodicals, Inc. Adv Polym Techn 26:14,20, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20087 [source] An investigation into the morphology and electro-optical properties of 2-hydroxy ethyl methacrylate polymer dispersed liquid crystalsJOURNAL OF APPLIED POLYMER SCIENCE, Issue 3 2010Huey-Ling Chang Abstract Polymer dispersed liquid crystal (PDLC) films are fabricated using E7 liquid crystals, tetraethylene glycol diacrylate (TeGDA) crosslinking agent, and 0,66.49 mol % 2-hydroxy ethyl methacrylate (HEMA). The effects of different levels of HEMA addition on the microstructure and electro-optical properties of the PDLC samples are examined using scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, and UV-Vis spectroscopy, respectively. The results show that the refractive index of the PDLC films is insensitive to the level of HEMA addition. However, an increasing HEMA content improves the degree of phase separation during the polymerization process and increases the size and uniformity of the liquid crystal domain. As a result, the electro-optical properties of the PDLC films are significantly improved as the level of HEMA addition is increased. Overall, the results show that a PDLC comprising 40 wt % E7 liquid crystals, 33.51 mol % TeGDA and 66.49 mol % HEMA has a high contrast ratio (13 : 1) and a low driving voltage (10 V) and is therefore an ideal candidate for a wide variety of intelligent photoelectric applications. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Diffusion-weighted imaging of the liver: Comparison of navigator triggered and breathhold acquisitionsJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 3 2009Bachir Taouli MD Abstract Purpose To compare a free breathing navigator triggered single shot echoplanar imaging (SS EPI) diffusion-weighted imaging (DWI) sequence with prospective acquisition correction (PACE) with a breathhold (BH) DWI sequence for liver imaging. Materials and Methods Thirty-four patients were evaluated with PACE-DWI and BH DWI of the liver using b-values of 0, 50, and 500 s/mm2. There were 29 focal liver lesions in 18 patients. Qualitative evaluation was performed on a 3-point scale (1,3) by two independent observers (maximum score 9). Quantitative evaluation included estimated SNR (signal to noise ratio), lesion-to-liver contrast ratio, liver and lesion apparent diffusion coefficients (ADCs), and coefficient of variation (CV) of ADC in liver parenchyma and focal liver lesions (estimate of noise contamination in ADC). Results PACE-DWI showed significantly better image quality, higher SNR and lesion-to-liver contrast ratio when compared with BH DWI. ADCs of liver and focal lesions with both sequences were significantly correlated (r = 0.838 for liver parenchyma, and 0.904 for lesions, P < 0.0001), but lower with the BH sequence (P < 0.02). There was higher noise contamination in ADC measurement obtained with BH DWI (with a significantly higher SD and CV of ADC). Conclusion The use of a navigator echo to trigger SS EPI DWI improves image quality and liver to lesion contrast, and enables a more precise ADC quantification compared with BH DWI acquisition. J. Magn. Reson. Imaging 2009;30:561,568. © 2009 Wiley-Liss, Inc. [source] Translucency of glass-fibre-reinforced composite materialsJOURNAL OF ORAL REHABILITATION, Issue 8 2004T. Nakamura summary, The purpose of this study was to examine the translucency of glass-fibre-reinforced composite framework materials. Vectris and FibreKor, as well as an experimental material, were the glass-fibre-reinforced framework materials used. Targis, Sculpture and Estenia were the types of particulate filler composites veneered onto frameworks. Specimens were fabricated from each material, 0·5 and 1·0 mm thick. In addition, laminate specimens, 1·5 mm thick, were fabricated. The translucency of each specimen was evaluated by determining its contrast ratio. The laminate specimens were examined for colour differences. The experimental framework material was more translucent than the enamel composite when it was not coloured, and was nearly as translucent as the dentine composite when coloured. The commercial tooth-coloured framework materials were nearly as translucent as the dentine composite. It was found that it was possible to reproduce the same colour as the veneering dentine composite, when the framework thickness was 0·5 mm, except in the case of FibreKor. Within the limitations of this study, tooth-coloured, glass-fibre-reinforced framework materials are nearly as translucent as the veneering dentine composite, but these materials affect the colour of the prosthesis if the thickness of the framework material is increased beyond a certain point. [source] Highly stable electrochromic polyamides based on N,N -bis(4-aminophenyl)- N,,N,-bis(4- tert -butylphenyl)-1,4-phenylenediamineJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 9 2009Sheng-Huei Hsiao Abstract A new triphenylamine-containing aromatic diamine monomer, N,N -bis(4-aminophenyl)- N,,N,-bis(4- tert -butylphenyl)-1,4-phenylenediamine, was synthesized by an established synthetic procedure from readily available reagents. A novel family of electroactive polyamides with di- tert -butyl-substituted N,N,N,,N,-tetraphenyl-1,4-phenylenediamine units were prepared via the phosphorylation polyamidation reactions of the newly synthesized diamine monomer with various aromatic or aliphatic dicarboxylic acids. All the polymers were amorphous with good solubility in many organic solvents, such as N -methyl-2-pyrrolidinone (NMP) and N,N -dimethylacetamide, and could be solution-cast into tough and flexible polymer films. The polyamides derived from aromatic dicarboxylic acids had useful levels of thermal stability, with glass-transition temperatures of 269,296 °C, 10% weight-loss temperatures in excess of 544 °C, and char yields at 800 °C in nitrogen higher than 62%. The dilute solutions of these polyamides in NMP exhibited strong absorption bands centered at 316,342 nm and photoluminescence maxima around 362,465 nm in the violet-blue region. The polyamides derived from aliphatic dicarboxylic acids were optically transparent in the visible region and fluoresced with a higher quantum yield compared with those derived from aromatic dicarboxylic acids. The hole-transporting and electrochromic properties were examined by electrochemical and spectro-electrochemical methods. Cyclic voltammograms of the polyamide films cast onto an indium-tin oxide-coated glass substrate exhibited two reversible oxidation redox couples at 0.57,0.60 V and 0.95,0.98 V versus Ag/AgCl in acetonitrile solution. The polyamide films revealed excellent elcterochemical and electrochromic stability, with a color change from a colorless or pale yellowish neutral form to green and blue oxidized forms at applied potentials ranging from 0.0 to 1.2 V. These anodically coloring polymeric materials showed interesting electrochromic properties, such as high coloration efficiency (CE = 216 cm2/C for the green coloring) and high contrast ratio of optical transmittance change (,T%) up to 64% at 424 nm and 59% at 983 nm for the green coloration, and 90% at 778 nm for the blue coloration. The electroactivity of the polymer remains intact even after cycling 500 times between its neutral and fully oxidized states. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2330,2343, 2009 [source] Effect of AlGaAs cladding layer on GaInNAs/GaAs MQW p-i-n photodetectorPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2008Y. F. Chen Abstract The electronic properties of GaInNAs/GaAs multiple-quantum-well (MQW) p-i-n photodetector with AlGaAs cladding layer have been studied. By applying a higher band gap Al0.3Ga0.7As to the photodetector, a substantial reduction in dark current was observed owing to an inherent difficulty for holes to surmount the high potential barrier between MQW and the cladding layer heterojunction under a reverse bias. The dark current obtained was as low as 4.1 pA at -3.5 V for a device with Al0.3Ga0.7As cladding layer as compared to 22 ,A also at -3.5 V for a similar device without the Al0.3Ga0.7As cladding layer. The photo/dark current contrast ratios obtained were 4.2×104 and 11, respectively, for devices with and without an Al0.3Ga0.7As cladding layer at -3.5 V. In addition, peak responsivity of 1 mA/W was measured at around 1150 nm. Two orders of magnitude increase in the rejection ratio were realized between 1150 and 1250 nm at -2.0 V. The GaInNAs/GaAs MQW p-i-n photodetector was demonstrated with the AlGaAs cladding layer potentially providing a higher photo/dark current contrast ratio and higher responsivity rejection ratio. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Effects of surfactant and molecular weight of polyol on grating formation and switching of holographic PDLCPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 11 2008S. S. Shim Abstract The interposition of surfactants between polymer and liquid crystal (LC) droplets was theoretically predicted by the positive spreading coefficient (0,<,,31) and utilized to interpret the morphology, grating formation kinetics, diffraction efficiency, and switching of the holographic polymer dispersed liquid crystal (HPDLC), prepared from various types (octanoic acid, poly oxyethylene octyl phenyl ether, and perfluoro-1-butanesulfonyl fluoride) and amounts (0,9 wt%) of surfactant and molecular weights of polyol (PPG). Regardless of the surfactant type, diffraction efficiency increased with the addition and increasing amount of surfactant, a tendency consistent with increasing value of spreading coefficient, which is determined by the formulations of grating formation. In contrast, diffraction efficiency showed a maximum with the polypropylene glycol (PPG) molecular weight. Surfactant effectively reduced the anchoring energy and electrically drove the film which otherwise was not driven. Overall, surfactant with greater ,31 gave smaller droplet, greater diffraction efficiency, driving voltage, contrast ratio, and smaller response time. Copyright © 2008 John Wiley & Sons, Ltd. [source] Surfactant Effects on Morphology and Switching of Holographic PDLCs Based on Polyurethane Acrylates,CHEMPHYSCHEM, Issue 1 2007Ju Yeon Woo Abstract Effects of octanoic acid (OA) on the morphology, diffraction efficiency, and electro-optic properties of the transmission mode of holographic polymer,dispersed liquid crystals (HPDLC) are studied. Droplet size decreases with increasing OA content (0,9,%), and this leads to a monotonic increase in off-state diffraction with increasing OA content. However, on-state diffraction decreases with increasing applied voltage and shows a minimum at 6,% OA, for which minimum switching voltage (5 V,,m,1) and maximum contrast ratio (10) are obtained. Rise time and decay time decrease with increasing OA content. Interposition of OA between polymer and LC droplet is theoretically predicted by the spreading coefficient (,>0) calculated on the basis of the solubility parameter, while the coalescence behavior of droplets is described by a dimensionless group () called coalescence number. [source] | ||||||||||||||||||||||||||||