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Modulation Depth (modulation + depth)
Selected AbstractsUltrafast Photonics: Graphene,Polymer Nanofiber Membrane for Ultrafast Photonics (Adv. Funct.ADVANCED FUNCTIONAL MATERIALS, Issue 5 2010Mater. Loh and co-workers demonstrate on page 782 an electrospun graphene,polymer nanocomposite that exhibits wideband saturable absorbance for laser pulse shaping. A freestanding, mechanically robust membrane which is composed of nanofiber network of graphene-polymer nanocomposite is fabricated by electrospinning and applied as a mode locker in fiber lasers. The performance of these graphene-polymer nanocomposites is better than single-wall carbon nanotubes in terms of modulation depth and nonsaturable loss. [source] Graphene,Polymer Nanofiber Membrane for Ultrafast PhotonicsADVANCED FUNCTIONAL MATERIALS, Issue 5 2010Qiaoliang Bao Abstract A freestanding membrane composed of a nanofiber network of a graphene,polymer nanocomposite is fabricated by electrospinning and applied as an optical element in fiber lasers. The functionalization of graphene with conjugated organic molecules provides a handle for improving mechanical and thermal properties as well as tuning the optical properties. A small loading (0.07,wt%) of functionalized graphene enhances the total optical absorption of poly(vinyl acetate) (PVAc) by 10 times. The electrospun graphene,polymer nanocomposites exhibit wideband saturable absorbance for laser pulse shaping, and attain a larger modulation depth and smaller nonsaturable loss than single-walled carbon nanotubes. The results show that electrospun graphene nanocomposites are promising candidates as practical and efficient photonic materials for the generation of ultrashort pulses in fiber lasers. [source] Atomic-Layer Graphene as a Saturable Absorber for Ultrafast Pulsed LasersADVANCED FUNCTIONAL MATERIALS, Issue 19 2009Qiaoliang Bao Abstract The optical conductance of monolayer graphene is defined solely by the fine structure constant, ,,=, (where e is the electron charge, is Dirac's constant and c is the speed of light). The absorbance has been predicted to be independent of frequency. In principle, the interband optical absorption in zero-gap graphene could be saturated readily under strong excitation due to Pauli blocking. Here, use of atomic layer graphene as saturable absorber in a mode-locked fiber laser for the generation of ultrashort soliton pulses (756 fs) at the telecommunication band is demonstrated. The modulation depth can be tuned in a wide range from 66.5% to 6.2% by varying the graphene thickness. These results suggest that ultrathin graphene films are potentially useful as optical elements in fiber lasers. Graphene as a laser mode locker can have many merits such as lower saturation intensity, ultrafast recovery time, tunable modulation depth, and wideband tunability. [source] The influence of polymer concentration, applied voltage, modulation depth and pulse frequency on DNA separation by pulsed field CEJOURNAL OF SEPARATION SCIENCE, JSS, Issue 17-18 2010Zhenqing Li Abstract DNA fragments (0.1,10,kbp (kbp, kilo base pair)) separation by square-wave pulsed field CE in hydroxyethylcellulose (HEC, 1300,K) polymer was performed in this work. The effects of polymer concentration, pulse field strength, pulse frequency and modulation depth were investigated. We found that low HEC (about 0.1%) concentration is suitable for the separation of small DNA fragments (<1,kbp), whereas higher HEC concentration (>0.5%) is appropriated for high-mass DNA molecular (>1,kbp) separation. The mobility of DNA fragments is nearly linearly related to average separation voltage under pulsed field conditions. Higher modulation depth is suited to separate the longer DNA fragments and lower modulation depth favors the resolution of short DNA fragments. Thus, the intermediate modulation depth (100%) and pulse frequency (about 31.3,Hz) are prerequisite for high-resolution DNA separation. [source] Optical mm-wave generation based on phase modulation along with optical filteringMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 8 2007Jianxin Ma Abstract We have investigated the generation and transmission of optical millimeter (mm)-wave signal based on optical phase modulator (PM) and fiber Bragg grating (FBG) filter. With an optimized modulation depth of PM and a higher carrier suppression ratio via a notch filter, the generated optical mm-wave can be transmitted over a long-distance without fading. We have also theoretically analyzed the impact of time shift on the eye closure of optical and electrical signal due to the fiber dispersion, which is well in accord with the experimental results. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1787,1793, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22622 [source] Refractive index-modulated grating in two-mode planar polymeric waveguide produced by two-photon polymerizationPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 7 2007Yi Dong Abstract A polymeric waveguide film was manufactured by spinning the materials on quartz substrate. Two-photon-initiated photopolymerization was carried out by tight-focusing femtosecond laser pulses in the two-mode planar waveguide. A typical index-modulated grating of 2.5,×,2,mm areas without morphology was fabricated. The results show that peak-to-peak modulation depth of the surface profile of grating region was only about 7,nm. The diffraction efficiency (DE) of the grating with a spacing period 2,µm was 0.17% and the corresponding index modulation reached 5.7,×,10,3. Copyright © 2007 John Wiley & Sons, Ltd. [source] 3251: From elementary concept in animal models to new frontiers in humans: neurovascular coupling in the ocular circulationACTA OPHTHALMOLOGICA, Issue 2010C RIVA Purpose The retina and optic nerve, both optically accessible components of the central nervous system, are ideally suited for the investigation of the intrinsic physiological process by which blood ,ow, metabolism and neural activity are tightly coupled (Roy and Sherrington. 1890). Methods Using various techniques in the cat and human eye, the changes in blood flow in the retina and optic nerve in response to increased neural activity by flicker stimulation have been determined. The effect of varying the stimulus parameters, such as flicker modulation depth, frequency, luminance and red-green color ratio, on the blood flow response was investigated. Putative mediators of the activity-induced flow changes and the relationship between activity, blood flow and metabolic changes were assessed. Results Visual stimulation with flicker increases rapidly and markedly both retinal and optic nerve blood ,ows (functional hyperemia). Moreover, the data reveal unequivocally the presence, under specific conditions of flicker, of a neurovascular/neurometabolic coupling in these tissues, partly mediated by local potassium ions and nitric oxide production. Furthermore, the activity-induced hyperemia is altered during a number of physiological and pharmacological interventions and in some pathologic conditions. Conclusion Flicker stimulation of the retina offers a new and powerful means to modulate blood flow and investigate the neurovascular coupling in the neural eye tissues. Exploration of this activity-induced hyperemia and the mechanism(s) underlying the neurovascular coupling will lead to an increased understanding of the pathophysiology of various ocular diseases. [source] Maximum-Likelihood Approach to Single-Molecule Polarization Modulation AnalysisCHEMPHYSCHEM, Issue 9 2003Kenneth D. Osborn Mobile or not mobile? Polarization modulation has been used to probe single-molecule dynamic heterogeneity of dye molecules that are either surface-bound or incorporated in the biological system calmodulin,plasma membrane calcium ATPase. A maximum-likelihood approach was applied to determine modulation depth and phase shift of the fluorescence trajectories (see picture), which give a measure of the orientational mobility of the molecules. [source] Prolonged maturation of auditory perception and learning in gerbilsDEVELOPMENTAL NEUROBIOLOGY, Issue 9 2010Emma C. Sarro Abstract In humans, auditory perception reaches maturity over a broad age range, extending through adolescence. Despite this slow maturation, children are considered to be outstanding learners, suggesting that immature perceptual skills might actually be advantageous to improvement on an acoustic task as a result of training (perceptual learning). Previous non-human studies have not employed an identical task when comparing perceptual performance of young and mature subjects, making it difficult to assess learning. Here, we used an identical procedure on juvenile and adult gerbils to examine the perception of amplitude modulation (AM), a stimulus feature that is an important component of most natural sounds. On average, Adult animals could detect smaller fluctuations in amplitude (i.e., smaller modulation depths) than Juveniles, indicating immature perceptual skills in Juveniles. However, the population variance was much greater for Juveniles, a few animals displaying adult-like AM detection. To determine whether immature perceptual skills facilitated learning, we compared naïve performance on the AM detection task with the amount of improvement following additional training. The amount of improvement in Adults correlated with naïve performance: those with the poorest naïve performance improved the most. In contrast, the naïve performance of Juveniles did not predict the amount of learning. Those Juveniles with immature AM detection thresholds did not display greater learning than Adults. Furthermore, for several of the Juveniles with adult-like thresholds, AM detection deteriorated with repeated testing. Thus, immature perceptual skills in young animals were not associated with greater learning. © 2010 Wiley Periodicals, Inc. Develop Neurobiol 70: 636,648, 2010 [source] | |||||||||||||