Excitation quenching in chlorophyll-carotenoid antenna systems: 'coherent' or 'incoherent'

Plants possess an essential ability to rapidly down-regulate light-harvesting in response to high light. This photoprotective process involves the formation of energy-quenching interactions between the chlorophyll and carotenoid pigments within the antenna of Photosystem II (PSII). The nature of these interactions is currently debated, with, among others, ‘incoherent’ or ‘coherent’ quenching models (or a combination of the two) suggested by a range of time-resolved spectroscopic measurements. In ‘incoherent quenching’, energy is transferred from a chlorophyll to a carotenoid and is dissipated due to the intrinsically short excitation lifetime of the latter. ‘Coherent quenching’ would arise from the quantum mechanical mixing of chlorophyll and carotenoid excited state properties, leading to a reduction in chlorophyll excitation lifetime. The key parameters are the energy gap, Δ=Car−Chl, Δ ε = ε C a r − ε C h l , and the resonance coupling, J, between the two excited states. Coherent quenching will be the dominant process when −<Δ<, − J < Δ ε < J , i.e., when the two molecules are resonant, while the quenching will be largely incoherent when Chl>(Car+). ε C h l > ( ε C a r + J ) . One would expect quenching to be energetically unfavorable for Chl<(Car−). ε C h l < ( ε C a r − J ) . The actual dynamics of quenching lie somewhere between these limiting regimes and have non-trivial dependencies of both J and Δ. Δ ε . Using the Hierarchical Equation of Motion (HEOM) formalism we present a detailed theoretical examination of these excitation dynamics and their dependence on slow variations in J and Δ. Δ ε . We first consider an isolated chlorophyll–carotenoid dimer before embedding it within a PSII antenna sub-unit (LHCII). We show that neither energy transfer, nor the mixing of excited state lifetimes represent unique or necessary pathways for quenching and in fact discussing them as distinct quenching mechanisms is misleading. However, we do show that quenching cannot be switched ‘on’ and ‘off’ by fine tuning of Δ Δ ε around the resonance point, Δ=0. Δ ε = 0. Due to the large reorganization energy of the carotenoid excited state, we find that the presence (or absence) of coherent interactions have almost no impact of the dynamics of quenching. Counter-intuitively significant quenching is present even when the carotenoid excited state lies above that of the chlorophyll. We also show that, above a rather small threshold value of >10cm−1 J > 10 c m − 1 quenching becomes less and less sensitive to J (since in the window −<Δ< − J < Δ ε < J the overall lifetime is independent of it). The requirement for quenching appear to be only that >0. J > 0. Although the coherent/incoherent character of the quenching can vary, the overall kinetics are likely robust with respect to fluctuations in J and Δ. Δ ε . This may be the basis for previous observations of NPQ with both coherent and incoherent features

Dem analysis of effect of the particle size during the material flow in wedge-shaped hopper

"The current analysis was mainly focused to the study of the strained physical effects arising from a decrease of the particles number. The main aspects concerning programming concepts as well as languages having influence on the computer time of simulations is also presented. The limitation in the particles amount was adopted by increasing the particle radii to keep constant the total mass of granular material. In this way, the performed computer simulations of the filling and discharge in three-dimensional hopper using 1980, 10000 and 20400 number of particles were shown that the decrease in particles number with increasing the particle radii produces an artificial friction due to material homogeneity. This is results in the decreased mass fraction and its rate during discharge causing the longest time for the full material discharge; the decreased normal and increased shear pressure of walls

An increase of a down-hole nuclear magnetic resonance tool’s reliability and accuracy by the cancellation of a multi-module DC/AC converter's output’s higher harmonics

Abstract: Described in this paper is a method for improving higher harmonic cancellation in Nuclear Magnetic Resonance (NMR) transmitters, which are used in oil and gas well logging tools operating at 175°C. Multi-module multi-level topology which combines the outputs of several identical power modules operating at 50% duty cycle at the fundamental frequency provide the versatility needed for both low harmonic sine voltage synthesis and amplitude control. Cancellation of the output voltage higher harmonics is achieved by creating fixed relative phase shifts between the individual modules of the multi-module converter. The amplitude control employs the Chireix-Doherty outphasing modulation principle with added feed forward correction circuitry. The possibilities of a 20% increase of the tool signal to noise ratio (SNR), as compared to that of a two-module transmitter has also demonstrated significant increase in the tool life expectancy

Dem analysis of effect of the particle size during the material flow in wedge-shaped hopper

"The current analysis was mainly focused to the study of the strained physical effects arising from a decrease of the particles number. The main aspects concerning programming concepts as well as languages having influence on the computer time of simulations is also presented. The limitation in the particles amount was adopted by increasing the particle radii to keep constant the total mass of granular material. In this way, the performed computer simulations of the filling and discharge in three-dimensional hopper using 1980, 10000 and 20400 number of particles were shown that the decrease in particles number with increasing the particle radii produces an artificial friction due to material homogeneity. This is results in the decreased mass fraction and its rate during discharge causing the longest time for the full material discharge; the decreased normal and increased shear pressure of walls

Failure analysis of destructive coils

The failure of the destructive pulsed power coils has been investigated. The destructive coil is the key element of the laboratory system which generates half-period abrupt magnetic field pulses with the amplitudes up to 45 T. The transient coupled non-linear magneto-mechanical model has been applied for finite element simulations. The mechanical behavior and operation threshold of the coil have been examined. It has been found that operation threshold of the coil with relatively thin cylindrical reinforcement could be characterized by the opening of the plastic hinge and estimated numerically. Good agreement with experimental results has been observe

Investigation of lanthanum substitution effects in yttrium aluminium garnet: importance of solid state NMR and EPR methods

Copyright © 2020, Springer Science Business Media, LLC, part of Springer NatureIn this study, yttrium aluminium garnet (YAG) specimens in which yttrium was partially substituted by lanthanum Y3-xLaxAl5O12 (YLaAG) were prepared by an aqueous sol-gel method. YLaAG samples were analyzed by X-ray diffraction (XRD), solid state nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) methods. The presence of Ce3+ ions as an impurity originating from starting material was determined, therefore, luminescence measurements of YLaAG samples were also recorded. It was demonstrated that luminescent properties are strongly dependent on the phase composition of synthesized species. The XRD analysis results showed that only low substitution of yttrium by lanthanum is possible in Y3-xLaxAl5O12 without destroying garnet crystal structure. It was also demonstrated, that solid state NMR and EPR methods are indispensable tools for the explanation of processes and properties observed in the newly synthesized Y3-xLaxAl5O12 compounds. ---- / / / ---- This is the preprint version of the following article: Laurikenas, A., Sakalauskas, D., Marsalka, A. et al. Investigation of lanthanum substitution effects in yttrium aluminium garnet: importance of solid state NMR and EPR methods. J Sol-Gel Sci Technol (2020). https://doi.org/10.1007/s10971-020-05445-2, which has been published in final form at https://link.springer.com/article/10.1007/s10971-020-05445-2. This article may be used for non-commercial purposes in accordance with Springer Terms and Conditions for Sharing and Self-Archiving.This work was supported by a Research grant NEGEMAT (No. S-MIP-19-59) from the Research Council of Lithuania. Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART²

Porous Aluminium Oxide Coating for the Development of Spectroscopic Ellipsometry Based Biosensor: Evaluation of Human Serum Albumin Adsorption

An electrochemically synthesised porous anodic aluminium oxide (pAAO) layer has been analysed by means of spectroscopic ellipsometry. The determined thickness of the formed pAAO layer obtained from spectroscopic ellipsometry measurements and modelling was 322.75 ± 0.12 nm. The radius of the nanopores estimated from SEM images was 39 ± 5 nm and the distance between nanopores was 107 ± 6 nm. The investigation of human serum albumin (HSA) adsorption on the pAAO coating showed that: (i) the protein concentration inside nanopores, depending on exposure time, approximately was from 200 up to 600 times higher than that determined in buffer solution; (ii) the initial phase of the adsorption process is slow (3.23 mg·cm−3·min−1) in comparison with the protein desorption rate (21.2 mg·cm−3·min−1) by means of pAAO layer washing; (iii) conventional washing with PBS solution and deionised water does not completely remove HSA molecules from pAAO pores and, therefore, the HSA concentration inside nanopores after 16 h of washing still remains almost 100 times higher than that present in PBS solution. Thus, due to such binding ability, HSA can be successfully used for the blocking of the remaining free surface, which is applied for the reduction in non-specific binding after the immobilisation of biorecognition molecules on the pAAO surface. It was determined that some desorption of HSA molecules from the pAAO layer occurred during the sensor’s surface washing step; however, HSA concentration inside the nanopores still remained rather high. These results recommend the continued application of pAAO in the development of biosensors.This work is part of a project that has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 778157 CanBioS