995 research outputs found
How to tune the absorption spectrum of chlorophylls to enable better use of the available solar spectrum
Photon capture by chlorophylls and other chromophores in light-harvesting complexes and photosystems is the driving force behind the light reactions of photosynthesis. Excitation of photosystem II allows it to receive electrons from the water-oxidizing oxygen-evolution complex and to transfer them to an electron-transport chain that generates a transmembrane electrochemical gradient and ultimately reduces plastocyanin, which donates its electron to photosystem I. Subsequently, excitation of photosystem I leads to electron transfer to a ferredoxin which can either reduce plastocyanin again (in so-called “cyclical electron-flow”) and release energy for the maintenance of the electrochemical gradient, or reduce NADP+ to NADPH. Although photons in the far-red (700–750 nm) portion of the solar spectrum carry enough energy to enable the functioning of the photosynthetic electron-transfer chain, most extant photosystems cannot usually take advantage of them due to only absorbing light with shorter wavelengths. In this work, we used computational methods to characterize the spectral and redox properties of 49 chlorophyll derivatives, with the aim of finding suitable candidates for incorporation into synthetic organisms with increased ability to use far-red photons. The data offer a simple and elegant explanation for the evolutionary selection of chlorophylls a, b, c, and d among all easily-synthesized singly-substituted chlorophylls, and identified one novel candidate (2,12-diformyl chlorophyll a) with an absorption peak shifted 79 nm into the far-red (relative to chlorophyll a) with redox characteristics fully suitable to its possible incorporation into photosystem I (though not photosystem II). chlorophyll d is shown by our data to be the most suitable candidate for incorporation into far-red utilizing photosystem II, and several candidates were found with red-shifted Soret bands that allow the capture of larger amounts of blue and green light by light harvesting complexes.info:eu-repo/semantics/publishedVersio
Transverse emittance measurement in 2D and 4D performed on a Low Energy Beam Transport line: benchmarking and data analysis
2D and 4D transverse phase-space of a low-energy ion-beam is measured with
two of the most common emittance scanners. The article covers the description
of the installation, the setup, the settings, the experiment and the benchmark
of the two emittance meters. We compare the results from three series of
measurements and present the advantages and drawbacks of the two systems.
Coupling between phase-space planes, correlations and mitigation of deleterious
effects are discussed. The influence of background noise and aberrations of
trace-space figures on emittance measurements and RMS calculations is
highlighted, especially for low density beams and halos. A new data analysis
method using noise reduction, filtering, and reconstruction of the emittance
figure is described. Finally, some basic concepts of phase-space theory and
application to beam transport are recalled
Nitrogen Doped Graphene Generated by Microwave Plasma and Reduction Expansion Synthesis
The article of record as published may be found at http://dx.doi.org/10.1166/nnl.2016.2055This work aimed to produce nitrogen doped graphene from Graphite Oxide (GO) by combining the
Expansion Reduction Synthesis (RES) approach, which utilizes urea as doping/reducing agent, with
the use of an Atmospheric Plasma torch (Plasma), which provides the high temperature reactor
environment known to thermally exfoliate it. The use of this combined strategy (Plasma-RES) was
tried in an attempt to increase the surface area of the products. The amount of nitrogen doping
was controlled by varying the urea/GO mass ratios in the precursor powders. X-ray diffraction
analysis, SEM, TEM, BET surface areas and conductivity measurements of the diverse products
are presented. Nitrogen inclusion in the graphene samples was corroborated by the mass spectral
signal of the evolved gases generated during thermal programmed oxidation experiments of the
products and by EDX analysis. We found that the Plasma-RES method can successfully generate
doped graphene in situ as the urea and GO precursors simultaneously decompose and reduce
in the discharge zone. When using the same amount of urea in the precursor mixture, samples obtained by Plasma-RES have higher surface area than those generated by RES, however, they contain a smaller nitrogen content
Palladium-Gallium Intermetallic Compounds for the Selective Hydrogenation of Acetylene: Part II: Surface Characterization and Catalytic Performance
Structural and Catalytic Investigation of Active-Site Isolation in Pd-Ga Intermetallic Compounds
Ultrafast Raman laser mode-locked by nanotubes
We demonstrate passive mode-locking of a Raman fiber laser using a nanotube-based saturable absorber coupled to a net normal dispersion cavity. This generates highly chirped 500 ps pulses. These are then compressed down to 2 ps , with 1.4 kW peak power, making it a simple wavelength-versatile source for various applications
- …