High Efficient Far-Field Nanofocusing with Tunable Focus Under Radial Polarization Illumination

We design a new nanofocusing lens for far-field practical applications. The constructively interference of cylindrical surface plasmon launched by the subwavelength metallic structure can form a subdiffraction-limited focus, which is modulated by the dielectric grating from the near field to the far field. The principle of designing such a far-field nanofocusing lens is elucidated in details. The numerical simulations demonstrated that nanoscale focal spot (0.12λ ²) can be realized with 3.6λ in depth of focus and 4.5λ in focal length by reasonably designing parameters of the grating. The focusing efficiency can be 7.335, which is much higher than that of plasmonic microzone plate-like lenses. A blocking chip can enhance the focusing efficiency further as the reflected waves at the entrance would be recollected at the focus. By controlling the number of the grooves in the grating, the focal length can be tuned easily. This design method paved the road for utilizing the plasmonic lens in high-density optical storage, nanolithography, superresolution optical microscopic imaging, optical measurement, and sensing.     

Computational Study of Influence of Structuring of Plasmonic Nanolens on Superfocusing

The focusing effect of the plasmonic nanolens is studied systematically. The influence of different construction parameters including the size of the central hole, the ring width of the surrounding concentric grating, the thickness of the metal film, and the distance of the central hole to grating has been simulated by rigorous finite difference time domain method and analyzed. It is found that the intensity of the central nano-spot is linearly proportional to the size of the central hole and inversely linearly proportional to the thickness of the metal film. In addition, the intensity of the lobes can be suppressed effectively by reducing the ring width down to a quarter of plasmon wavelength to achieve a better focusing effect. The influence of the distance of central hole to grating is a little bit complex, but generally, the intensity for the distance of (2n − 1)/2 plasmon wavelength is larger than the case of the distance of nλ_SP. The simulation results can be a general guide for the design of plasmonic nanolenses.     

Detection of sinusoidal gratings by pattern-specific detectors: further evidence for the correlation principle in human vision

 The detection of compound sinusoidal gratings of various spatial frequency separations and four different grating sizes has been studied using the summation-to-threshold paradigm. Contrast interrelation functions have been measured and spatial frequency tuning estimates, based on the slope of the contrast interrelation function at two definite points, were derived using the “negative gradient technique” proposed by Logvinenko [Logvinenko (1995) Biol Cybern 73: 547–552]. It is shown that compound grating detection can be modelled by assuming pattern-specific sensory mechanisms for each of the spatial frequency components, which adapt to the periodicity and the size of the stimulus but not to its envelope function. Further, it is shown that relative sensitivity for a given spatial frequency separation can be predicted with good accuracy by the correlation of the grating components used for superposition. It is suggested that the most plausible implementation of the pattern correlation principle in human grating detection is the “grating cell” model. Received: 10 March 2000 / Accepted in revised form: 4 December 2000     

Enhanced luciferin entry causes rapid wound-induced light emission in plants expressing high levels of luciferase

In-vivo imaging of transgenic tobacco plants (Nicotiana tobacum L.) expressing firefly luciferase under the control of the Arabidopsis phenylalanine ammonia-lyase 1 (PAL1)-promoter showed that luciferase-catalyzed light emission began immediately after the substrate luciferin was sprayed onto the leaves and reached a plateau phase after approximately 60 min. This luminescence could easily be detected for up to 24 h after luciferin application although the light intensity declined continuously during this period. A strong and rapid increase in light emission was observed within the first minutes after wounding of luciferin-sprayed leaves. However, these data did not correlate with luciferase activity analysed by an in-vitro enzyme assay. In addition, Arabidopsis plants expressing luciferase under the control of the constitutive 35S-promoter showed similar wound-induced light emission. In experiments in which only parts of the leaves were sprayed with luciferin solutions, it was shown that increased uptake of luciferin at the wound site and its transport through vascular tissue were the main reasons for the rapid burst of light produced by preformed luciferase activity. These data demonstrate that there are barriers that restrict luciferin entry into adult plants, and that luciferin availability can be a limiting factor in non-invasive luciferase assays. Received: 11 March 2000 / Accepted: 16 May 2000     

Plasmonic Behaviors of Two-Dimensional Ag/SiO2 Nanocomposite Gratings: Roles of Gap Diffraction and Localized Surface Plasmon Resonance Absorption

Two-dimensional Ag/SiO₂ nanocomposite gratings of 400 and 600 nm in grating constant are fabricated by etching the SiO₂ slabs implanted with Ag ions, and their plasmonic extinction, absorption, and reflection behaviors are investigated. Our results indicate that no scattering light fields can exist near the localized surface plasmon (LSP) resonance wavelength (about 405 nm) of Ag nanoparticles (NPs) due to the intense LSP resonance absorption. Especially, when the gaps between nanocomposite veins have a width close in value to the LSP resonance wavelength of Ag NPs, the local light fields in the grating plane can be slightly enhanced due to an in-phase addition of the incident light fields and the diffractive light fields induced by the gap diffraction, leading to a slight red shift of LSP resonance mode of Ag NPs. Moreover, in the LSP resonance absorption region, although the grating diffraction can still occur, the diffractive light fields are extremely weak, and thus, the local light fields in the grating plane cannot be modified by coherently adding these extremely weak diffractive light fields to the incident light fields. As a result, the LSP resonance mode of Ag NPs will keep its position unchanged even though the grating constant is set to make the first grating order rightly change from evanescent to radiative character.

     

Curling during desiccation protects the foliose lichen Lobaria pulmonaria against photoinhibition

This study aims to assess the photoprotective potential of desiccation-induced curling in the light-susceptible old forest lichen Lobaria pulmonaria by using chlorophyll fluorescence imaging. Naturally curled thalli showed less photoinhibition-induced limitations in primary processes of photosynthesis than artificially flattened specimens during exposures to 450 μmol m⁻² s⁻¹ in the laboratory after both 12- (medium dose treatment) and 62-h duration (high dose treatment). Thallus areas shaded by curled lobes during light exposure showed unchanged values of measured chlorophyll fluorescence parameters (F _V/F _M, Φ_{PS II}), whereas non-shaded parts of curled thalli, as well as the mean for the entire flattened thalli, showed photoinhibitory limitation after light treatments. Furthermore, the chlorophyll fluorescence imaging showed that the typical small-scale reticulated ridges on the upper side of L. pulmonaria caused a spatial, small-scale reduction in damage due to minor shading. Severe dry-state photoinhibition readily occurred in flattened and light-treated L. pulmonaria, although the mechanisms for such damage in a desiccated and inactive stage are not well known. Natural curling is one strategy to reduce the chance for serious photoinhibition in desiccated L. pulmonaria thalli during high light exposures.     

1-D Metal-Dielectric-Metal Grating Structure as an Ultra-Narrowband Perfect Plasmonic Absorber in the Visible and Its Application in Glucose Detection

The need for an easy to fabricate perfect and narrowband light absorber in the visible range of electromagnetic (EM) spectrum has always been in demand for many scientific and device applications. Here, we propose a metal-dielectric-metal (MDM) 1-D grating plasmonic structure as a perfect narrow band light absorber in the visible and its application in glucose detection. The proposed structure consists of a 1- D grating of gold on the top of a dielectric layer on a gold film. Optimization for dielectric grating index (n), grating thickness (t), grating width (W), and grating period (P) has been done to improve the performance of plasmonic structure by calculating its quality factor and figure-of-merit (FOM). The optimized plasmonic structure behaves as a perfect narrowband light absorber. The flexibility to work at a specific wavelength is also offered by the proposed structure through an appropriate selection of the geometrical parameters and refractive index of the dielectric grating. The equivalent RC model is used to understand different components of the proposed structure on the optical response. The absorption response of the structure is invariant to the incident angle. Moreover, the calculated absorbance of the proposed plasmonic structure is ~ 100% with a narrow full-width half maxima (FWHM) of ~ 2.8 nm. We have numerically demonstrated a potential application of the proposed MDM absorber as a plasmonic glucose sensor in the visible range with detection sensitivity in the range of 140 to 195 nm/RIU.

     

Maximum Photosynthetic Yield of Green Microalgae in Photobioreactors

The biomass yield on light energy of Dunaliella tertiolecta and Chlorella sorokiniana was investigated in a 1.25- and 2.15-cm light path panel photobioreactor at constant ingoing photon flux density (930 μmol photons m⁻² s⁻¹). At the optimal combination of biomass density and dilution rate, equal biomass yields on light energy were observed for both light paths for both microalgae. The observed biomass yield on light energy appeared to be based on a constant intrinsic biomass yield and a constant maintenance energy requirement per gram biomass. Using the model of Pirt (New Phytol 102:3–37, 1986), a biomass yield on light energy of 0.78 and 0.75 g mol photons⁻¹ and a maintenance requirement of 0.0133 and 0.0068 mol photons g⁻¹ h⁻¹ were found for D. tertiolecta and C. sorokiniana, respectively. The observed yield decreases steeply at low light supply rates, and according to this model, this is related to the increase of the amount of useable light energy diverted to biomass maintenance. With this study, we demonstrated that the observed biomass yield on light in short light path bioreactors at high biomass densities decreases because maintenance requirements are relatively high at these conditions. All our experimental data for the two strains tested could be described by the physiological models of Pirt (New Phytol 102:3–37, 1986). Consequently, for the design of a photobioreactor, we should maintain a relatively high specific light supply rate. A process with high biomass densities and high yields at high light intensities can only be obtained in short light path photobioreactors.     

Kinetic models for phycocyanin production by high cell density mixotrophic culture of the microalga Spirulina platensis

Phycocyanin production by high cell density cultivation of Spirulina platensis in batch and fed-batch modes in 3.7-L bioreactors with a programmed stepwise increase in light intensity program was investigated. The results showed that the cell density in fed-batch culture (10.2 g L⁻¹) was 4.29-fold that in batch culture (2.38 g L⁻¹), and the total phycocyanin production in the fed-batch culture (0.795 g L⁻¹) was 3.05-fold that in the batch culture (0.261 g L⁻¹). An unstructured kinetic model to describe the microalga culture system including cell growth, phycocyanin formation, as well as glucose consumption was proposed. The data fitted the models well (r ² > 0.99). Furthermore, based on the kinetic models, the potential effects of light limitation and photoinhibition on cell growth and phycocyanin formation can be examined in depth. The models demonstrated that the optimal light intensity for mixotrophic growth of Spirulina platensis in batch or fed-batch cultures using a 3.7-L bioreactor was 80160 μE m⁻² s⁻¹, and the stepwise increase in light intensity can be replaced by a constant light intensity mode. Received 28 July 1998/ Accepted in revised form 8 October 1998     

Retinal and cortical nonlinearities combine to produce masking in V1 responses to plaids

The visual response of a cell in the primary visual cortex (V1) to a drifting grating stimulus at the cell’s preferred orientation decreases when a second, perpendicular, grating is superimposed. This effect is called masking. To understand the nonlinear masking effect, we model the response of Macaque V1 simple cells in layer 4Cα to input from magnocellular Lateral Geniculate Nucleus (LGN) cells. The cortical model network is a coarse-grained reduction of an integrate-and-fire network with excitation from LGN input and inhibition from other cortical neurons. The input is modeled as a sum of LGN cell responses. Each LGN cell is modeled as the convolution of a spatio-temporal filter with the visual stimulus, normalized by a retinal contrast gain control, and followed by rectification representing the LGN spike threshold. In our model, the experimentally observed masking arises at the level of LGN input to the cortex. The cortical network effectively induces a dynamic threshold that forces the test grating to have high contrast before it can overcome the masking provided by the perpendicular grating. The subcortical nonlinearities and the cortical network together account for the masking effect. Melinda Koelling is formerly from Center for Neural Science and Courant Institute, New York University.     

Metabolic modeling of Chlamydomonas reinhardtii: energy requirements for photoautotrophic growth and maintenance

In this study, a metabolic network describing the primary metabolism of Chlamydomonas reinhardtii was constructed. By performing chemostat experiments at different growth rates, energy parameters for maintenance and biomass formation were determined. The chemostats were run at low irradiances resulting in a high biomass yield on light of 1.25 g  mol⁻¹. The ATP requirement for biomass formation from biopolymers (K _x ) was determined to be 109 mmol g⁻¹ (18.9 mol mol⁻¹) and the maintenance requirement (m _ATP) was determined to be 2.85 mmol g⁻¹ h⁻¹. With these energy requirements included in the metabolic network, the network accurately describes the primary metabolism of C. reinhardtii and can be used for modeling of C. reinhardtii growth and metabolism. Simulations confirmed that cultivating microalgae at low growth rates is unfavorable because of the high maintenance requirements which result in low biomass yields. At high light supply rates, biomass yields will decrease due to light saturation effects. Thus, to optimize biomass yield on light energy in photobioreactors, an optimum between low and high light supply rates should be found. These simulations show that metabolic flux analysis can be used as a tool to gain insight into the metabolism of algae and ultimately can be used for the maximization of algal biomass and product yield.     

Excitation and Optimization Modeling of Surface Plasmon Polaritons in a Concentric Circular Metallic Grating Film

Interaction behavior between surface plasmon polaritons (SPPs) and Hankel-distributed diffracted waves (DWs) on a silver concentric circular grating film is studied using a rigorous coupled-wave technique for circular structure. It is shown that the numerical technique reveals the excitation characteristics of SPPs in the circular metal grating as well as provides an accurate calculation of SPP intensities for further optimization designs. Results show that the SPPs can be excited by various DWs through the control of wavelength and angle of the incident light. The most efficient excitation of SPPs from this circular metal grating structure can be obtained from the +1^st-order DW under a normal incidence with wavelength close to the grating period, and the optimal thickness and duty cycle of the grating are found to be 370 and 0.5 nm, respectively. It is shown that the optimized intensity of SPPs excited from circular metal grating can be higher than that from strip metal grating by over one order of magnitude.     

Migratory Responses of Benthic Diatoms to Light and Temperature Monitored by Chlorophyll Fluorescence

As an important adaptation for survival in the sediments of intertidal flats, benthic diatoms move up and down in response to a wide range of environmental stimuli. We investigated the vertical migration of two diatoms—Cylindrotheca closterium (Agradh) Kützing (B-25) and Nitzschia sp. (B-3)—under different combinations of light intensity and temperature conditions. An imaging pulse amplitude modulated (PAM) fluorometer was used to measure the minimum fluorescence (F ₀) in order to monitor variations in diatom biomass in surface sediments. Rapid light curves (RLCs) were applied to assess their photosynthetic activities. Both species had increased motility under higher temperatures, with the longer valved C. closterium being twice as fast as the shorter valved Nitzschia sp. The former was also influenced by exposure to light intensities of 100 or 250 μmol m⁻² s⁻¹, whereas the latter was not. Consequently, no light/temperature interaction effect was associated with the vertical migration of Nitzschia sp., perhaps because of its lower photosynthetic capacity and smaller cell size. Therefore, we conclude that motile benthic diatoms exhibit species-specific responses to light and temperature due to differences in their photosynthetic capability and morphological characteristics.     

Speed of signal transfer in the chloroplast accumulation response

Chloroplast photorelocation movement is important for plants to perform efficient photosynthesis. Phototropins were identified as blue-light receptors for chloroplast movement in Arabidopsis thaliana and in the fern Adiantum capillus-veneris, whereas neochrome functions as a dual red/blue light receptor in the latter. However, the signal transduction pathways involved in chloroplast movement remain to be clarified. To investigate the kinetic properties of signalling from these photoreceptors to the chloroplasts, we deduced the speed of signal transfer using Adiantum capillus-veneris gametophytes. When a region of dark-adapted gametophyte cells was subjected to microbeam irradiation, chloroplasts moved towards the irradiated area even in subsequent darkness. We therefore recorded the movement and calculated the speeds of signal transfer by time-lapse imaging. Movement speeds under red or blue light were similar, e.g., about 1.0 μm min⁻¹ in prothallial cells. However, speeds varied according to cell polarity in protonemal cells. The speed of signal transfer from the protonemal apex to the base was approximately 0.7 μm min⁻¹, but roughly 2.3 μm min⁻¹ in the opposite direction. The speed of signal transfer in Arabidopsis thaliana mesophyll cells was approximately 0.8 μm min⁻¹ by comparison. Surprisingly, chloroplasts located farthest away from the microbeam were found to move faster than those in close proximity to the site of irradiation both in Adiantum capillus-veneris and A. thaliana.     

The interaction of visible and UV-B light during photodamage and repair of Photosystem II

In order to understand the mechanism of photodamage induced by solar radiation under natural conditions, we studied the interaction of visible and ultraviolet-B light in the inactivation and repair of the Photosystem II complex by using oxygen evolution and flash-induced chlorophyll fluorescence measurements. In isolated spinach thylakoids and Synechocystis 6803 cells, in which de novo protein synthesis is blocked by lincomycin, photodamage of Photosystem II by visible and UV-B light is characterized by linear semilogarithmic inactivation curves for both separate and combined illumination protocols. The extent of PS II inactivation obtained after combined illumination can be well simulated by assuming independent damaging events induced by visible and UV-B photons. In intact Synechocystis cells capable of protein repair, simultaneous illumination by visible and UV-B light impairs Photosystem II activity to a smaller extent than expected from the independent damaging events. This protective effect is pronounced at low visible light (130 μE m⁻² s⁻¹), but becomes negligible at high intensities (1300 μE m⁻² s⁻¹). Exposure of intact Synechocystis 6803 cells to direct sunlight leads to a rapid inactivation of PS II, accompanied by the accumulation of donor side inhibited centers. This phenomenon, which shows the impairment of the manganese cluster of water oxidation was not observed when the ultraviolet components of sunlight were filtered out. We conclude that visible and UV-B photons inactivate PS II via non-interacting mechanisms, which affect different target sites. In intact cells, the two spectral regions do interact, and results in synergistically enhanced protein repair capacity when UV-B radiation is accompanied by low intensity visible light, which provides protection against photodamage. However, this ameliorating effect becomes insignificant at high light intensities characteristic of direct sunlight. This revised version was published online in June 2006 with corrections to the Cover Date.     

Enhancement of marennine production by blue light in the diatom <Emphasis Type="Italic">Haslea ostrearia</Emphasis>

The marine diatom Haslea ostrearia Simonsen produces a blue pigment, marennine, which is used for greening oysters. This microalga is cultured industrially indoors with artificial light. The influence of light quality on marennine production by cultures of H. ostrearia was investigated in the laboratory and at a semi-pilot scale (300 L tanks). In the first series of experiments in the laboratory, a clone of H. ostrearia was cultured under light of different colors (white, blue, green, yellow, and red) and at two irradiances (‘low’ and ‘high’, 20 and 100 μmol photons m⁻² s⁻¹, respectively). Compared to the white light controls, growth was increased in blue light at the ‘low’, but not at the ‘high’ irradiance, and marennine production at the end of the exponential phase was the highest in cells grown under blue light, regardless of the light quality or intensity during growth. Increased marennine production during growth was also observed, whichever color of light (blue or white) was used during the acclimation phase. In a second series of experiments, intraclonal differences were studied by comparing marennine production in seven clones differing with regard to their mean cell size. The total marennine expressed either per cell or per culture volume, was higher in blue light for all the clones. Complementary experiments carried out under semi-industrial conditions confirmed this effect of blue light, which could be relevant for the industrial, indoor production of marennine.     

How does light and phosphorus fertilisation affect the growth and ectomycorrhizal community of two contrasting dipterocarp species?

Phosphorus concentrations in many south-east Asian tropical rain forest soils are very low. To determine the growth responses of seedlings of a light-demanding (Shorea leprosula) and a more shade-tolerant (Hopea nervosa) dipterocarp species to increasing P, we carried out a nursery fertilisation experiment. Responses of symbiotic ectomycorrhizal (EcM) fungi to the treatments were also determined. Seedlings were grown under high light (13 mol m⁻² d⁻¹) or moderate light (4 mol m⁻² d⁻¹) in shade-chambers and were fertilised with a solution containing 0, 1, 10 or 100 mg L⁻¹ P. The growth of Hopea and Shorea showed different responses to the light and P fertilisation treatments with Hopea having greater growth under moderate light conditions and Shorea having greater growth under high light conditions. Shorea responded to P fertilisation by increasing its foliar P concentrations and growth rates, whereas Hopea did not take up additional P and did not improve its growth rates. There was no effect of either light or P fertilisation on total EcM colonisation or EcM diversity, but around half of the EcM morphotypes observed were affected by one of these two abiotic perturbations, most notably for Riessiella sp. which increased with P fertilisation suggesting it may not be a mutualistic fungus. These results show how niche partitioning in both dipterocarp seedlings and EcM fungi can be divided along contrasting axes.     

Dynamic studies of phloem and xylein flow in fully differentiated plants by fast nuclear-magnetic-resonance microimaging

Summary A fast nuclear-magnetic-resonance imaging method was developed in order to measure simultaneously and quantitatively the water flow velocities in the xylem and the phloem of intact and transpiring plants. Due to technical improvements a temporal resolution of 7 min could be reached and flow measurements could be performed over a time course of 12–30 h. The novel method was applied to the hypocotyl of 35– to 40-day-old, leafy plants ofRicinus communis which were subjected to different light-dark regimes. The results showed that the xylem flow velocities and the xylem volume flow responded immediately to light on-off changes. Upon illumination the flow velocity and the volume flow increased as expected in respect to literature. In contrast, the phloem flow velocity did not change in response to the light-dark regimes. Interestingly, though, the volume flow in the phloem increased during darkness. These findings can be explained by assuming that the conducting area of the phloem becomes enlarged during the dark period due to opening of sieve pores.     

Effect of snow depth on under-ice irradiance and growth of <Emphasis Type="Italic">Aulacoseira baicalensis</Emphasis> in Lake Baikal

Lake Baikal freezes for 4–5 months each year; yet the planktonic diatoms that grow under the ice include some of the largest species found in freshwater. An important factor influencing their growth is the depth of snow. In this study, a population of Aulacoseira baicalensis developed where there was little or no snow on the ice but declined where there was 10 cm of snow, because 99% of the available light was attenuated. Culture studies of light response showed that A. baicalensis was adapted to relatively low light intensities (<40 μmol m⁻² s⁻¹) that were close to the average that a cell experiences in L. Baikal when mixed vertically by convection to depths that can exceed 100 m. On sunny days, cell division could be inhibited down to >10 m depth but narrow (<15 μm) diameter cells trapped in high light intensities in sub-ice layers switched to auxosporulation and size regeneration.     

Nuclear factors GT-1 and 3AF1 interact with multiple sequences within the promoter of the Tdc gene from Madagascar periwinkle: GT-1 is involved in UV light-induced expression.

Plant secondary metabolites of the terpenoid indole alkaloid (TIA) class comprise several compounds with pharmaceutical applications. A key step in the TIA biosynthetic pathway is catalysed by the enzyme tryptophan decarboxylase (TDC), which channels the primary metabolite tryptophan into TIA metabolism. In Catharanthus roseus (Madagascar periwinkle), the Tdc gene is expressed throughout plant development. Moreover, Tdc gene expression is induced by external stress signals, such as fungal elicitor and UV light. In a previous study of Tdc promoter architecture in transgenic tobacco it was shown that the −538 to −112 region is a quantitative determinant for the expression level in different plant organs. Within this sequence one particular region (−160 to −99) was identified as the major contributor to basal expression and another region (−99 to −37) was shown to be required for induction by fungal elicitor. Here, the in vitro binding of nuclear factors to the −572 to −37 region is described. In extracts from tobacco and C. roseus, two binding activities were detected that could be identified as the previously described nuclear factors GT-1 and 3AF1, based on their mobility and binding characteristics. Both factors appeared to interact with multiple regions in the Tdc promoter. Mutagenesis of GT-1 binding sites in the Tdc promoter did not affect the basal or elicitor-induced expression levels. However, induction of the Tdc promoter constructs by UV light was significantly lower, thereby demonstrating a functional role for GT-1 in the induction of Tdc expression by UV light. Received: 2 February 1998 / Accepted: 5 March 1999