Increasing Photon Flux Research Articles

Photosynthetic performance, growth, pigment content, and photoprotective compounds of the mangrove macroalgae Bostrychia calliptera and Bostrychia montagnei (Rhodophyta) under light stress

Increased solar radiation on the Earth’s surface is expected due to global change. Mangrove macroalgae can be negatively affected by increased solar radiation, since some species, such as Bostrychia spp. have been characterized as typical “shade” plants. Thus, we investigated the effects of increasing photon flux densities (PFDs: 170, 267, 443, 638, and 1155 µmol photons m–2 s–1) on the physiological performance of Bostrychia calliptera and Bostrychia montagnei from a tropical mangrove. Several photosynthesis–related parameters indicated that both species decreased their photosynthetic performance under increasing PFDs, with photosynthesis of B. montagnei being more affected than that of B. calliptera. Bostrychia calliptera exhibited highest growth under 638 µmol photons m–2 s–1 while at 1155 µmol photons m–2 s–1 it was inhibited. The highest growth of Bostrychia montagnei was observed under 267 µmol photons m–2 s–1. Higher PFDs led to growth inhibition. The phycobiliprotein and chlorophyll a content of B. montagnei was degraded under increased PFDs. In B. calliptera only chlorophyll a degradation was observed. The mycosporine-like amino acid contents (photoprotective metabolites) of both species were degraded under increasing PFDs, which was more pronounced in B. montagnei. Our results demonstrated that increased solar radiation on estuarine tropical ecosystems will be detrimental to the physiological performance of B. calliptera and B. montagnei. Our results also demonstrated that B. montagnei was more negatively affected by increased light stress than B. calliptera. This can explain its preferential occurrence in more shaded microhabitats compared to B. calliptera. Our data document for the first time light acclimation in the studied macroalgae and the deleterious effects of increased light stress on the genus Bostrychia.

Plant Factories Are Heating Up: Hunting for the Best Combination of Light Intensity, Air Temperature and Root-Zone Temperature in Lettuce Production.

This study analyzed interactions among photon flux density (PPFD), air temperature, root-zone temperature for growth of lettuce with non-limiting water, nutrient, and CO2 concentration. We measured growth parameters in 48 combinations of a PPFD of 200, 400, and 750 μmol m–2 s–1 (16 h daylength), with air and root-zone temperatures of 20, 24, 28, and 32°C. Lettuce (Lactuca sativa cv. Batavia Othilie) was grown for four cycles (29 days after transplanting). Eight combinations with low root-zone (20 and 24°C), high air temperature (28 and 32°C) and high PPFD (400 and 750 μmol m–2 s–1) resulted in an excessive incidence of tip-burn and were not included in further analysis. Dry mass increased with increasing photon flux to a PPFD of 750 μmol m–2 s–1. The photon conversion efficiency (both dry and fresh weight) decreased with increasing photon flux: 29, 27, and 21 g FW shoot and 1.01, 0.87, and 0.76 g DW shoot per mol incident light at 200, 400, and 750 μmol m–2 s–1, respectively, averaged over all temperature combinations, following a concurrent decrease in specific leaf area (SLA). The highest efficiency was achieved at 200 μmol m–2 s–1, 24°C air temperature and 28°C root-zone temperature: 44 g FW and 1.23 g DW per mol incident light. The effect of air temperature on fresh yield was linked to all leaf expansion processes. SLA, shoot mass allocation and water content of leaves showed the same trend for air temperature with a maximum around 24°C. The effect of root temperature was less prominent with an optimum around 28°C in nearly all conditions. With this combination of temperatures, market size (fresh weight shoot = 250 g) was achieved in 26, 20, and 18 days, at 200, 400, and 750 μmol m–2 s–1, respectively, with a corresponding shoot dry matter content of 2.6, 3.8, and 4.2%. In conclusion, three factors determine the “optimal” PPFD: capital and operational costs of light intensity vs the value of reducing cropping time, and the market value of higher dry matter contents.

Understanding and Controlling the Performance-Limiting Steps of Catalyst-Modified Semiconductors.

Understanding and controlling factors that restrict the rates of fuel-forming reactions are essential to designing effective catalyst-modified semiconductors for applications in solar-to-fuel technologies. Herein, we describe GaAs semiconductors featuring a polymeric coating that contains cobaloxime-type catalysts for photoelectrochemically powering hydrogen production. The activities of these electrodes (limiting current densities >20 mA cm-2 under 1-sun illumination) enable identification of fundamental performance-limiting bottlenecks encountered at relatively high rates of fuel formation. Experiments conducted under varying bias potential, pH, illumination intensity, and scan rate reveal two distinct mechanisms of photoelectrochemical hydrogen production. At relatively low polarization and pH, the limiting photoactivity is independent of illumination conditions and is attributed to a mechanism involving reduction of substrate protons. At relatively high polarization or pH, the limiting photoactivity shows a linear response to increasing photon flux and is attributed to a mechanism involving reduction of substrate water. This work illustrates the complex interplay between transport of photons, electrons, and chemical substrates in photoelectrosynthetic reactions and highlights diagnostic tools for better understanding these processes.

Well-Designed 3D/2D/2D WO3/Bt/g-C3N4 Z-Scheme Heterojunction for Tailoring Photocatalytic CO2 Methanation with 2D-Layered Bentonite-Clay as the Electron Moderator under Visible Light

Photocatalytic CO2 reduction to renewable hydrocarbon fuels is a promising strategy to address global energy issues; however, producing fuels like CH4 is highly challenging under visible light. In this work, fabrication of a two-dimensional bentonite (2D-Bt) nanosheet mediated WO3/g-C3N4 Z-scheme heterojunction for highly selective photocatalytic CO2 reduction to CH4 under visible light has been investigated. The photocatalytic performance of the newly developed WO3-embedded 2D pillared Bt with 2D g-C3N4 composite for selective photocatalytic CO2 reduction to methane was studied using H2O as the reducing agent under visible light. WO3/Bt/g-C3N4 (WBCN) exhibits the highest photocatalytic activity for CH4 production, which was 6.01, 6.76, and 25.30 times higher than using WO3/g-C3N4, Bt/g-C3N4, and g-C3N4 samples, respectively. Noticeably, WO3-coupled with g-C3N4 was favorable for CO production; however, introducing Bt layered clay was in favor of methane formation during the CO2 reduction process. Additionally, the Z-scheme of the WO3/g-C3N4 composite with Bt as the electron moderator could promote photoinduced charge separation and redox ability of the separated charge carriers, resulting in excellent CO2 reduction to CH4. The rate of reaction was dependent only on the external mass transfer due to surface reactions over the WBCN composite catalyst. With increasing photon flux, methane production was further enhanced due to the thermodynamically favorable process for the activation of CO2 methanation reaction. Besides, good cycling ability was observed due to the presence of a layered clay structure, which was sustained in multiple cycles without obvious deactivation. This study provides a green clay based noble-metal-free approach to construct a structured composite photocatalyst with a Z-scheme charge carrier and would be beneficial for CO2 reduction and other solar energy applications.

Insights into the Light Response of Skeletonema marinoi: Involvement of Ovothiol.

Diatoms are one of the most widespread groups of microalgae on Earth. They possess extraordinary metabolic capabilities, including a great ability to adapt to different light conditions. Recently, we have discovered that the diatom Skeletonema marinoi produces the natural antioxidant ovothiol B, until then identified only in clams. In this study, we investigated the light-dependent modulation of ovothiol biosynthesis in S. marinoi. Diatoms were exposed to different light conditions, ranging from prolonged darkness to low or high light, also differing in the velocity of intensity increase (sinusoidal versus square-wave distribution). The expression of the gene encoding the key ovothiol biosynthetic enzyme, ovoA, was upregulated by high sinusoidal light mimicking natural conditions. Under this situation higher levels of reactive oxygen species and nitric oxide as well as ovothiol and glutathione increase were detected. No ovoA modulation was observed under prolonged darkness nor low sinusoidal light. Unnatural conditions such as continuous square-wave light induced a very high oxidative stress leading to a drop in cell growth, without enhancing ovoA gene expression. Only one of the inducible forms of nitric oxide synthase, nos2, was upregulated by light with consequent production of NO under sinusoidal light and darkness conditions. Our data suggest that ovothiol biosynthesis is triggered by a combined light stress caused by natural distribution and increased photon flux density, with no influence from the daily light dose. These results open new perspectives for the biotechnological production of ovothiols, which are receiving a great interest for their biological activities in human model systems.

Overproduction of PGR5 enhances the electron sink downstream of photosystem I in a C4 plant, Flaveria bidentis.

C4 plants can fix CO2 efficiently using CO2 -concentrating mechanisms (CCMs), but they require additional ATP. To supply the additional ATP, C4 plants operate at higher rates of cyclic electron transport around photosystem I (PSI), in which electrons are transferred from ferredoxin to plastoquinone. Recently, it has been reported that the NAD(P)H dehydrogenase-like complex (NDH) accumulated in the thylakoid membrane in leaves of C4 plants, making it a candidate for the additional synthesis of ATP used in the CCM. In addition, C4 plants have higher levels of PROTON GRADIENT REGULATION 5 (PGR5) expression, but it has been unknown how PGR5 functions in C4 photosynthesis. In this study, PGR5 was overexpressed in a C4 dicot, Flaveria bidentis. In PGR5-overproducing (OP) lines, PGR5 levels were 2.3- to 3.0-fold greater compared with wild-type plants. PGR5-like PHOTOSYNTHETIC PHENOTYPE 1 (PGRL1), which cooperates with PGR5, increased with PGR5. A spectroscopic analysis indicated that in the PGR5-OP lines, the acceptor side limitation of PSI was reduced in response to a rapid increase in photon flux density. Although it did not affect CO2 assimilation, the overproduction of PGR5 contributed to an enhanced electron sink downstream of PSI.

(Invited) Tuning Thermal– and Hot Electron–Driven H2 Generation with Plasmonic TiN/Pt Antenna–Reactor Nanohybrids

Plasmonic nanostructures have recently shown the capability to greatly enhance photocatalytic processes through the generation of highly energetic hot carriers.[1–3] These species, generated upon nonradiative decay of surface plasmons, enable to reach high quantum yield in chemical conversion with increasing photon flux. Photocatalysts composed by plasmonic metals or, more recently, by antenna–reactor systems [4,5] have shown their potential mainly for gas phase reactions (e.g. CO, NH3, and propylene oxidation, CO2 reduction), while detailed investigations of liquid phase reactions have been lacking. [6] Furthermore, the catalytic contribution related to thermoplasmonic heat generation and hot electron creation is still under lively debate.[7] In this invited talk, I will start discussing the challenges that limit the present understanding of hot carrier–driven chemical transformations. Thereafter, I will show our recent efforts to understand thermal and electronic contributions in hydrogen generation with plasmonic TiN/Pt antenna–reactor nanohybrids, correlating catalytic data with Electron Energy Loss Spectroscopy (EELS) spectral images. Uniform and highly dispersed Pt nanocrystals onto the TiN nanocrystals were prepared by reduction of appropriate amount of potassium tetrachloroplatinate (K2PtCl4) in the presence of formaldehyde (HCHO). The obtained plasmonic catalysts include TiN nanocubes with size of 50 nm homogeneously decorated with Pt nanocrystals (Figure 1a). Each plasmonic antenna (TiN nanocubes) is decorated with reactive catalytic center (Pt nanocrystals) to optimize the electromagnetic interactions and boost the photocatalytic efficiency. Once dispersed in water solution, the TiN/Pt nanohybrids show a strong and broad localized plasmonic resonance (LSPR) around 700 nm. In this talk, I will also discuss our Electron Energy Loss Spectroscopy (EELS) results showing the nanometric spatial distribution of different plasmonic modes of TiN/Pt catalysts excited through a highly focused, accelerated electron beam (Figure 1b). The hydrogen evolution experiments from ammonia borane (NH3BH3) hydrolysis were carried out by adding NH3BH3 solution to an aqueous dispersion of TiN/Pt hybrid nanocatalyst in a rounded glass flask under different experimental condition. The maximum temperature achieved by illuminating an aqueous dispersion of TiN/Pt hybrid nanocrystals under a particular light intensity is termed as plasmonic temperature. Different sets of experiments were conducted at plasmonic temperature in the dark with external thermal heating or under that particular light irradiation to distinguish the thermal and electronic contributions, respectively, in our plasmonic catalysis. All photocatalytic reactions were carried out under AM1.5G solar illumination at different light intensity. Figure 1c shows the catalytic hydrogen production rate expressed as turnover frequency (TOF) values for TiN/Pt in the dark and under solar light illumination. The TOF values for TiN/Pt nanocrystals in the dark at RT (22 °C) and under 10 Suns illumination are 32.1 and 346.1 mol(H2) molPt -1 min-1 respectively. Photocatalytic hydrogen evolution rates obtained under solar light show a drastic enhancement, reaching about 11 times TOF value in comparison to dark reaction when using 10 Suns illumination. The plasmonic nature of photocatalytic activity is demonstrated by a set of experiments carried out at different wavelength and revealing a TOF maximum at 700 nm, in well agreement with absorption spectrum of TiN/Pt hybrid nanocatalyst. Interestingly, Figure 1c clearly demonstrates that hot electron contributions in photocatalytic hydrogen production is enhanced under solar illumination, especially at high concentrated power (i.e. 10 Suns), where TOF value reaches 2.3 times the TOF obtained under plasmonic temperature in the dark. To summarize, in this invited talk I will show our effort in plasmonic photocatalysis with TiN/Pt antenna–reactor systems for liquid phase hydrogen generation from ammonium borane. Photocatalytic data will be discussed in terms of thermal and hot electron contribution, electronic vs. multielectronic mechanism, and activation of rate determining step. Finally, these photocatalytic data will be related to nanometer EELS plasmon maps and hot electron generation capability of TiN/Pt hybrids. References P. Christopher, H. Xin and S. Linic, Nat. Chem. 3, 467–472 (2011).P. Christopher, H. Xin, A. Marimuthu and S. Linic, Nat. Mater. 11, 1044–1050 (2012)A. Marimuthu, J. Zhang and S. Linic, Science 339, 1590–1593 (2013).U. Aslam, S. Chavez and S. Linic, Nat. Nanotech. 12, 1000–1005 (2017).D. F. Swearer, H. Zhao, L. Zhou, C. Zhang, H. Robatjazi, J. M. P. Martirez, C. M. Krauter, S. Yazdi, M. J. McClain, E. Ringe, E. A. Carter, P. Nordlander and N. J. Halas, Proc. Natl Acad. Sci. USA 113, 8916–8920 (2016).Y. Kim, J. G. Smith and P. K. Jain, Nat. Chem. 10, 763–769 (2018).L. Zhou, D. F. Swearer, C. Zhang, H. Robatjazi, H. Zhao, L. Henderson, L. Dong, P. Christopher, E. A. Carter, P. Nordlander and N. J. Halas, Science 362, 69–72 (2018). Figure 1

Timing jitter in photon detection by straight superconducting nanowires: Effect of magnetic field and photon flux

We studied the effect of the external magnetic field and photon flux on timing jitter in photon detection by straight superconducting NbN nanowires. At two wavelengths 800 and 1560 nm, statistical distribution in the appearance time of the photon count exhibits Gaussian shape at small times and exponential tail at large times. The characteristic exponential time is larger for photons with smaller energy and increases with external magnetic field while variations in the Gaussian part of the distribution are less pronounced. Increasing photon flux drives the nanowire from quantum detection mode to the bolometric mode that averages out fluctuations of the total number of nonequilibrium electrons created by the photon and drastically reduces jitter. The difference between Gaussian parts of distributions for these two modes provides the measure for the electron-number fluctuations. Corresponding standard deviation increases with the photon energy. We show that the two-dimensional hot-spot detection model explains qualitatively the effect of magnetic field.

Hot and bright: Thermal and light environments for the culture of Oedogonium intermedium and the geographical limits for large-scale cultivation in Australia

The successful implementation of the intensive cultivation of freshwater macroalgae for bioremediation purposes relies on the consistent year-round uptake of nutrients, which is closely linked to the amount of biomass produced. This study examined how light and temperature influence the biomass productivity and photosynthetic efficiency of a tropical strain of the freshwater macroalga Oedogonium intermedium (Wittrock ex Hirn). We subsequently use this information to identify, at a coarse level, the locations within Australia that can provide a thermal and light environment that is conducive to the intensive year-round, production of this species. The optimal temperature range to cultivate O. intermedium is between 20 and 35 °C, and in general productivity increased with increasing photon flux within this temperature range. At temperatures outside of this optimal range O. intermedium still had positive growth when cultured at a constant temperature of as low as 15 °C and as high as 40 °C, but productivity was impaired, and these temperatures represent the minimum and maximum temperature thresholds for chronic exposure. At low temperatures, higher photon flux rates increased productivity, however, at higher temperatures (>35 °C) a higher photon flux decreased productivity. These experimental insights have enabled us to identify, at a coarse level, locations within Australia that provide a suitable thermal and light environment for the year-round cultivation of O. intermedium. In general, latitudes of ≤25° provide a thermal and light environment that can maintain a high rate of biomass productivity year-round. In contrast, most locations at latitudes higher than 25° provide a suitable environment only during the summer months. During winter the combination of low temperatures and low solar irradiances will prevent the successful cultivation of this tropical strain. In these cooler locations alternative species of locally adapted, freshwater macroalgae should be identified and domesticated to ensure bioremediation outcomes are maintained at these lower latitudes.

Metastability and avalanche dynamics in strongly correlated gases with long-range interactions

We experimentally study the stability of a bosonic Mott insulator against the formation of a density wave induced by long-range interactions and characterize the intrinsic dynamics between these two states. The Mott insulator is created in a quantum degenerate gas of 87-Rubidium atoms, trapped in a 3D optical lattice. The gas is located inside and globally coupled to an optical cavity. This causes interactions of global range, mediated by photons dispersively scattered between a transverse lattice and the cavity. The scattering comes with an atomic density modulation, which is measured by the photon flux leaking from the cavity. We initialize the system in a Mott-insulating state and then rapidly increase the global coupling strength. We observe that the system falls into either of two distinct final states. One is characterized by a low photon flux, signaling a Mott insulator, and the other is characterized by a high photon flux, which we associate with a density wave. Ramping the global coupling slowly, we observe a hysteresis loop between the two states-a further signature of metastability. A comparison with a theoretical model confirms that the metastability originates in the competition between short- and global-range interactions. From the increasing photon flux monitored during the switching process, we find that several thousand atoms tunnel to a neighboring site on the timescale of the single-particle dynamics. We argue that a density modulation, initially forming in the compressible surface of the trapped gas, triggers an avalanche tunneling process in the Mott-insulating region.

Differences in the photoacclimation and photoprotection exhibited by two species of the ciguatera causing dinoflagellate genus, Gambierdiscus

In culture, Gambierdiscus spp. have been shown to prefer irradiances that are relatively low (≤250μmol photonsm−2s−1) versus those to which they are frequently exposed to in their natural environment (>500μmol photonsm−2s−1). Although several behavioral strategies for coping with such irradiances have been suggested, it is unclear as to how these dinoflagellates do so on a physiological level. More specifically, how do long term exposures (30days) affect cell size and cellular chlorophyll content, and what is the photosynthetic response to short term, high irradiance exposures (up to 1464μmol photonsm−2s−1)? The results of this study reveal that cell size and chlorophyll content exhibited by G. carolinianus increased with acclimation to increasing photon flux density. Additionally, both G. carolinianus and G. silvae exhibited reduced photosynthetic efficiency when acclimated to increased photon flux density. Photosynthetic yield exhibited by G. silvae was greater than that for G. carolinianus across all acclimation irradiances. Although such differences were evident, both G. carolinianus and G. silvae appear to have adequate biochemical mechanisms to withstand exposure to irradiances exceeding 250μmol photonsm−2s−1 for at least short periods of time following acclimation to irradiances of up to 150μmol photonsm−2s−1.

Enabling Overall Water Splitting on Photocatalysts by CO-Covered Noble Metal Co-catalysts.

Photocatalytic overall water splitting requires co-catalysts that efficiently promote the generation of H2 but do not catalyze its reverse oxidation. We demonstrate that CO chemisorbed on metal co-catalysts (Rh, Pt, Pd) suppresses the back reaction while maintaining the rate of H2 evolution. On Rh/GaN:ZnO, the highest H2 production rates were obtained with 4-40 mbar of CO, the back reaction remaining suppressed below 7 mbar of O2. The O2 and H2 evolution rates compete with CO oxidation and the back reaction. The rates of all reactions increased with increasing photon absorption. However, due to different dependencies on the rate of charge carrier generation, the selectivities for O2 and H2 formation increased in comparison to CO oxidation and the back reaction with increasing photon flux and/or quantum efficiency. Under optimum conditions, the impact of CO to prevent the back reaction is identical to that of a Cr2O3 layer covering the active metal particle.

Photosynthetic capacity of the capsule wall and its contribution to carbon fixation and seed yield in castor (Ricinus communis L.)

Defoliation occurs in castor due to several reasons, but the crop has propensity to compensate for the seed yield. Photosynthetic efficiency in terms of functional (gas exchange and chlorophyll fluorescence) and structural characteristics (photosynthetic pigment profiles and anatomical properties) of castor capsule walls under light- and dark-adapted conditions was compared with that of leaves. Capsule wall showed high intrinsic efficiency of photosystem II (F v/F m, 0.82) which was comparable to leaves (F v/F m, 0.80). With increasing photon flux densities (PFD), actual quantum yields and photochemical quenching coefficients of the capsule walls were similar to that in leaves, while electron transport rates reached a maximum corresponding to about 118 % of the leaves. However, maximum net photosynthetic rate of the capsule walls (2.60 µmol CO2 m−2 s−1) was less than one-fourth of the leaves (15.67 µmol CO2 m−2 s−1) at the CO2 concentration of 400 µmol mol−1, and the difference was attributed to about 80 % lower stomatal density and the 75 % lower total chlorophyll content of capsule walls than the leaves. Furthermore, seed weight in dark-adapted capsules was 2.70–12.42 % less as compared to the capsules developed under light. The results indicate that castor capsule walls are photosynthetically active (about 15–30 % of the leaves) and contribute significantly to carbon fixation and seed yield accounting for 10 % photoassimilates towards seed weight.

Attenuator design method for dedicated whole-core CT.

In whole-core CT imaging, scanned data corresponding to the central portion of a cylindrical core often suffer from photon starvation, because increasing photon flux will cause overflow on some detector units under the restriction of detector dynamic range. Either photon starvation or data overflow will lead to increased noise or severe artifacts in the reconstructed CT image. In addition, cupping shaped beam hardening artifacts also appear in the whole-core CT image. In this paper, we present a method to design an attenuator for cone beam whole-core CT, which not only reduces the dynamic range requirement for high SNR data scanning, but also corrects beam hardening artifacts. Both simulation and real data are employed to verify our design method.

Comparison of four outdoor pilot-scale photobioreactors.

BackgroundMicroalgae are a potential source of sustainable commodities of fuels, chemicals and food and feed additives. The current high production costs, as a result of the low areal productivities, limit the application of microalgae in industry. A first step is determining how the different production system designs relate to each other under identical climate conditions. The productivity and photosynthetic efficiency of Nannochloropsis sp. CCAP 211/78 cultivated in four different outdoor continuously operated pilot-scale photobioreactors under the same climatological conditions were compared. The optimal dilution rate was determined for each photobioreactor by operation of the different photobioreactors at different dilution rates.ResultsIn vertical photobioreactors, higher areal productivities and photosynthetic efficiencies, 19–24 g m−2 day−1 and 2.4–4.2 %, respectively, were found in comparison to the horizontal systems; 12–15 g m−2 day−1 and 1.5–1.8 %. The higher ground areal productivity in the vertical systems could be explained by light dilution in combination with a higher light capture. In the raceway pond low productivities were obtained, due to the long optical path in this system. Areal productivities in all systems increased with increasing photon flux densities up to a photon flux density of 30 mol m−2 day−1. Photosynthetic efficiencies remained constant in all systems with increasing photon flux densities. The highest photosynthetic efficiencies obtained were; 4.2 % for the vertical tubular photobioreactor, 3.8 % for the flat panel reactor, 1.8 % for the horizontal tubular reactor, and 1.5 % for the open raceway pond.ConclusionsVertical photobioreactors resulted in higher areal productivities than horizontal photobioreactors because of the lower incident photon flux densities on the reactor surface. The flat panel photobioreactor resulted, among the vertical photobioreactors studied, in the highest average photosynthetic efficiency, areal and volumetric productivities due to the short optical path. Photobioreactor light interception should be further optimized to maximize ground areal productivity and photosynthetic efficiency.

A novel crystal-analyzer phase retrieval algorithm and its noise property.

A description of the rocking curve in diffraction enhanced imaging (DEI) is presented in terms of the angular signal response function and a simple multi-information retrieval algorithm based on the cosine function fitting. A comprehensive analysis of noise properties of DEI is also given considering the noise transfer characteristic of the X-ray source. The validation has been performed with synchrotron radiation experimental data and Monte Carlo simulations based on the Geant4 toolkit combined with the refractive process of X-rays, which show good agreement with each other. Moreover, results indicate that the signal-to-noise ratios of the refraction and scattering images are about one order of magnitude better than that of the absorption image at the edges of low-Z samples. The noise penalty is drastically reduced with the increasing photon flux and visibility. Finally, this work demonstrates that the analytical method can build an interesting connection between DEI and GDPCI (grating-based differential phase contrast imaging) and is widely suitable for a variety of measurement noise in the angular signal response imaging prototype. The analysis significantly contributes to the understanding of noise characteristics of DEI images and may allow improvements to the signal-to-noise ratio in biomedical and material science imaging.

Photo-transport properties of Pb2CrO5 single crystals

We report photo-thermoelectric transport phenomena in Pb2CrO5 single crystals. Without illumination, this material exhibits an insulating behavior characterized by an activation-type temperature variation of the electrical conductivity. The Seebeck coefficient contrastingly shows a crossover from high-temperature insulating to low-temperature metallic behavior, which is attributed to degenerate carriers in a donor level. We have found that under illumination, both the conductivity and the Seebeck coefficient increase in magnitude with increasing photon flux density in the degenerate-conduction regime. This result is difficult to understand within a simple photo-doping effect, which usually leads to a decrease in the Seebeck coefficient under illumination. The observed phenomenon is discussed in terms of a two-carrier contribution to the transport properties.

Time- and angle-resolved photoemission spectroscopy with optimized high-harmonic pulses using frequency-doubled Ti:Sapphire lasers

Time- and angle-resolved photoemission spectroscopy (trARPES) using femtosecond extreme ultraviolet high harmonics has recently emerged as a powerful tool for investigating ultrafast quasiparticle dynamics in correlated-electron materials. However, the full potential of this approach has not yet been achieved because, to date, high harmonics generated by 800nm wavelength Ti:Sapphire lasers required a trade-off between photon flux, energy and time resolution. Photoemission spectroscopy requires a quasi-monochromatic output, but dispersive optical elements that select a single harmonic can significantly reduce the photon flux and time resolution. Here we show that 400nm driven high harmonic extreme-ultraviolet trARPES is superior to using 800nm laser drivers since it eliminates the need for any spectral selection, thereby increasing photon flux and energy resolution to <150meV while preserving excellent time resolution of about 30fs.

Photo-Seebeck effect in tetragonal PbO single crystals

We report the observation of photo-Seebeck effect in tetragonal PbO crystals. The photo-induced carriers contribute to the transport phenomena, and consequently the electrical conductivity increases and the Seebeck coefficient decreases with increasing photon flux density. A parallel-circuit model is used to evaluate the actual contributions of photo-excited carriers from the measured transport data. The photo-induced carrier concentration estimated from the Seebeck coefficient increases almost linearly with increasing photon flux density, indicating a successful photo-doping effect on the thermoelectric property. The mobility decreases by illumination but the reduction rate strongly depends on the illuminated photon energy. Possible mechanisms of such photon-energy-dependent mobility are discussed.

Photosynthetic Electron Transport System Promotes Synthesis of Au-Nanoparticles

In this communication, a novel, green, efficient and economically viable light mediated protocol for generation of Au-nanoparticles using most vital organelle, chloroplasts, of the plant system is portrayed. Thylakoids/chloroplasts isolated from Potamogeton nodosus (an aquatic plant) and Spinacia oleracea (a terrestrial plant) turned Au3+ solutions purple in presence of light of 600 µmol m−2 s−1 photon flux density (PFD) and the purple coloration intensified with time. UV-Vis spectra of these purple colored solutions showed absorption peak at ∼545 nm which is known to arise due to surface plasmon oscillations specific to Au-nanoparticles. However, thylakoids/chloroplasts did not alter color of Au3+ solutions in dark. These results clearly demonstrated that photosynthetic electron transport can reduce Au3+ to Au0 which nucleate to form Au-nanoparticles in presence of light. Transmission electron microscopic studies revealed that Au-nanoparticles generated by light driven photosynthetic electron transport system of thylakoids/chloroplasts were in range of 5–20 nm. Selected area electron diffraction and powder X-ray diffraction indicated crystalline nature of these nanoparticles. Energy dispersive X-ray confirmed that these nanoparticles were composed of Au. To confirm the potential of light driven photosynthetic electron transport in generation of Au-nanoparticles, thylakoids/chloroplasts were tested for their efficacy to generate Au-nanoparticles in presence of light of PFD ranging from 60 to 600 µmol m−2 s−1. The capacity of thylakoids/chloroplasts to generate Au-nanoparticles increased remarkably with increase in PFD, which further clearly demonstrated potential of light driven photosynthetic electron transport in reduction of Au3+ to Au0 to form nanoparticles. The light driven donation of electrons to metal ions by thylakoids/chloroplasts can be exploited for large scale production of nanoparticles.