By manipulating the surface-plasmon-polariton (SPP) excitation properties of two nanogrooves, we demonstrate unidirectional launching of SPPs using a groove-doublet structure both numerically and experimentally, with the groove separation being downscaled to 1/4 and even 1/8 of the wavelength. Thus, the total lateral dimension of the SPP launcher is only about 1/3 and 1/6 of the wavelength, which is truly subwavelength. The measured extinction ratio at incident wavelength of 800 nm reaches as high as 130 and 18. Such subwavelength SPP unidirectional launchers may have important applications in highly integrated plasmonic circuits. (C) 2014 AIP Publishing LLC.
Understanding of the atmosphere/forest canopy exchange of volatile organic compounds (VOCs) requires insight into the deposition, emission, and chemical reactions of VOCs below the canopy. Between 18 July and 9 August 2009, VOCs were measured with proton-transfer-reaction mass spectrometry (PTR-MS) at six heights between 1 and 6 m beneath a 23 m high mixed-forest canopy. Measured VOCs included methanol, isoprene, acetone, methacrolein and methyl vinyl ketone (MACR + MVK), monoterpenes, and sesquiterpenes. There are pronounced differences in the behaviour of isoprene and its by-products and that of the terpenes. Non-terpene mixing ratios increase with height, suggesting predominantly downward fluxes. In contrast, the terpene mixing ratios decrease with height, suggesting upward fluxes. A 1-D canopy model was used to compare results to measurements with and without surface deposition of isoprene and MACR + MVK and emissions of monoterpenes and sesquiterpenes. Results suggest deposition velocities of 2.7 mm s(-1) for isoprene and 1.2 mm s(-1) for MACR + MVK and daytime surface emission rates of 63 mu g m(-2) h(-1) for monoterpenes. The modelled isoprene surface deposition is approximately 2% of the canopy-top isoprene emissions and the modelled emissions of monoterpenes comprise approximately 15 to 27% of the canopy-top monoterpene emissions to the atmosphere. These results suggest that surface monoterpene emissions are significant for forest canopy/atmosphere exchange for this mixed-forest location and surface uptake is relatively small for all the species measured in this study.
Perceptual learning, a process in which training improves visual discrimination, is often specific to the trained retinal location, and this location specificity is frequently regarded as an indication of neural plasticity in the retinotopic visual cortex. However, our previous studies have shown that "double training" enables location-specific perceptual learning, such as Vernier learning, to completely transfer to a new location where an irrelevant task is practiced. Here we show that Vernier learning can be actuated by less location-specific orientation or motion-direction learning to transfer to completely untrained retinal locations. This "piggybacking" effect occurs even if both tasks are trained at the same retinal location. However, piggybacking does not occur when the Vernier task is paired with a more location-specific contrast-discrimination task. This previously unknown complexity challenges the current understanding of perceptual learning and its specificity/transfer. Orientation and motion-direction learning, but not contrast and Vernier learning, appears to activate a global process that allows learning transfer to untrained locations. Moreover, when paired with orientation or motion-direction learning, Vernier learning may be "piggybacked" by the activated global process to transfer to other untrained retinal locations. How this task-specific global activation process is achieved is as yet unknown.
Visual saliency is a useful cue to locate the conspicuous image content. To estimate saliency, many approaches have been proposed to detect the unique or rare visual stimuli. However, such bottom-up solutions are often insufficient since the prior knowledge, which often indicates a biased selectivity on the input stimuli, is not taken into account. To solve this problem, this paper presents a novel approach to estimate image saliency by learning the prior knowledge. In our approach, the influences of the visual stimuli and the prior knowledge are jointly incorporated into a Bayesian framework. In this framework, the bottom-up saliency is calculated to pop-out the visual subsets that are probably salient, while the prior knowledge is used to recover the wrongly suppressed targets and inhibit the improperly popped-out distractors. Compared with existing approaches, the prior knowledge used in our approach, including the foreground prior and the correlation prior, is statistically learned from 9.6 million images in an unsupervised manner. Experimental results on two public benchmarks show that such statistical priors are effective to modulate the bottom-up saliency to achieve impressive improvements when compared with 10 state-of-the-art methods.
Two water-soluble triscyclometalated organoiridium complexes, 1 and 2, with polar side chains that form nanoparticles emitting bright-red phosphorescence in water were synthesized. The optimal emitting properties are related to both the triscyclometalated structure and nanoparticle-forming ability in aqueous solution. Nonlinear optical properties are also observed with the nanoparticles. Because of their proper cellular uptake in addition to high emission brightness and effective two-photon absorbing ability, cell imaging can be achieved with nanoparticles of 2 bearing quaternary ammonium side chains at ultra-low effective concentrations using NIR incident light via the multiphoton excitation phosphorescence process.