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New insights on ChlD1 function in Photosystem II from site-directed mutants of D1/T179 in Thermosynechococcus elongatus
摘要： The monomeric chlorophyll, ChlD1, which is located between the PD1PD2 chlorophyll pair and the pheophytin, PheoD1, is the longest wavelength chlorophyll in the heart of Photosystem II and is thought to be the primary electron donor. Its central Mg2+ is liganded to a water molecule that is H-bonded to D1/T179. Here, two site-directed mutants, D1/T179H and D1/T179V, were made in the thermophilic cyanobacterium, Thermosynechococcus elongatus, and characterized by a range of biophysical techniques. The Mn4CaO5 cluster in the water-splitting site is fully active in both mutants. Changes in thermoluminescence indicate that i) radiative recombination occurs via the repopulation of *ChlD1 itself; ii) non-radiative charge recombination reactions appeared to be faster in the T179H-PSII; and iii) the properties of PD1PD2 were unaffected by this mutation, and consequently iv) the immediate precursor state of the radiative excited state is the ChlD1+PheoD1? radical pair. Chlorophyll bleaching due to high intensity illumination correlated with the amount of 1O2 generated. Comparison of the bleaching spectra with the electrochromic shifts attributed to ChlD1 upon QA? formation, indicates that in the T179H-PSII and in the WT*3-PSII, the ChlD1 itself is the chlorophyll that is first damaged by 1O2, whereas in the T179V-PSII a more red chlorophyll is damaged, the identity of which is discussed. Thus, ChlD1 appears to be one of the primary damage site in recombination-mediated photoinhibition. Finally, changes in the absorption of ChlD1 very likely contribute to the well-known electrochromic shifts observed at ~430 nm during the S-state cycle.
关键词： ChlD1,Electrochromic shifts,P680,Photosystem II,Reaction center
更新于2025-11-14 15:14:40
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Electronic Structure of Chlorophyll a Solution Investigated by Photoelectron Yield Spectroscopy
摘要： Various bio-related processes are driven by electron transfer reactions. Therefore the electronic structures of bio-molecules in their living environment are keys of their functionalities. One significant example photosynthesis which has attracted much attention due to urgent necessity of clean energy source. In this study, we carried out photoelectron yield spectroscopy (PYS) measurements to demonstrate the electronic structures of oligomerizedChl-a molecules, which is known as an essential reaction center of the photosystem in general green plants, under the atmospheric environment. The ionization energies of the Chl-a aggregates are successfully derived.
关键词： Photoelectron Yield Spectroscopy,Polarization energy,Light harvesting antenna,Photosynthesis,Photosystem,Electronic structure,Ionization energy,Reaction center,Chlorophyll a
更新于2025-09-23 15:23:52
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Sustainable Liquid Luminescent Solar Concentrators
摘要： Luminescent solar concentrators (LSCs) are photovoltaic (PV) complementary devices to overcome the mismatch between the Si-based PV cells, response and the solar spectrum, allowing PV urban integration. Challenges for the luminescent layer include the use of abundant and sustainable natural organic molecules. Here, LSCs composed of a glass container and based on bundles of cylindrical hollow-core plastic optical fibers filled with aqueous solutions of R-phycoerythrin (R-PE), extracted from Gracilaria sp. algae are presented. The R-PE solutions absorb in the UV/visible spectral range (300–550 nm) and convert this radiation into red-emission (550–700 nm) with a maximum absolute quantum yield of ≈0.39. In this work, LSCs with distinct geometries are reported, in which the R-PE emission yields optical conversion efficiency values up to ≈6.88% and ≈4.74% for a planar device and for a bundle of cylindrical LSCs, respectively, which are the largest values known for liquid-based LCSs using sustainable emitting centres. Moreover, the coupling of the LSCs to commercial Si-based PV devices yields power conversion efficiency values of ≈0.27% (planar) and ≈23.03 × 10?3%, (bundle). These values illustrate the potential of this approach for the development of natural-based LSCs meeting the requirements of reliable, sustainable, and competitive energy systems.
关键词： sustainability,organic–inorganic hybrids,luminescent solar concentrators,R-phycoerythrin,natural optically active center,bundles
更新于2025-09-23 15:23:52
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Assignment of NMR resonances of protons covalently bound to photochemically active cofactors in photosynthetic reaction centers by 13C–1H photo-CIDNP MAS-J-HMQC experiment
摘要： Modified versions of through-bond heteronuclear correlation (HETCOR) experiments are presented to take advantage of the light-induced hyperpolarization that occurs on 13C nuclei due to the solid-state photochemically induced dynamic nuclear polarization (photo-CIDNP) effect. Such 13C–1H photo-CIDNP MAS-J-HMQC and photo-CIDNP MAS-J-HSQC experiments are applied to acquire the 2D 13C–1H correlation spectra of selectively 13C-labeled photochemically active cofactors in the frozen quinone-blocked photosynthetic reaction center (RC) of the purple bacterium Rhodobacter (R.) sphaeroides wild-type (WT). Resulting spectra contain no correlation peaks arising from the protein backbone, which greatly simplifies the assignment of aliphatic region. Based on the photo-CIDNP MAS-J-HMQC NMR experiment, we obtained assignment of selective 1H NMR resonances of the cofactors involved in the electron transfer process in the RC and compared them with values theoretically predicted by density functional theory (DFT) calculation as well as with the chemical shifts obtained from monomeric cofactors in the solution. We also compared proton chemical shifts obtained by photo-CIDNP MAS-J-HMQC experiment under continuous illumination with the ones obtained in dark by classical cross-polarization (CP) HETCOR. We expect that the proposed approach will become a method of choice for obtaining 1H chemical shift maps of the active cofactors in photosynthetic RCs and will aid the interpretation of heteronuclear spin-torch experiments.
关键词： MAS-J-HSQC,Solid-state photo-CIDNP,HETCOR,MAS-J-HMQC,Bacterial reaction center
更新于2025-09-23 15:23:52
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Novel Phased Array-Fed Dual-Reflector Antenna with Different Orthogonal Cross-Section by Imaging Reflector Antenna and Ring-Focus Cassegrain Antenna
摘要： We propose a novel phased array-fed dual-re?ector antenna that reduces performance degradation caused by multiple re?ection. The marked feature of the proposed con?guration is that di?erent re?ector pro?les are employed for the two orthogonal directions. The re?ector pro?le in the beam-scanning section (vertical section) is set to an imaging re?ector con?guration, while the pro?le in the orthogonal non-beam-scanning section (horizontal section) is set to a ring-focus Cassegrain antenna con?guration. In order to compare the proposed antenna with the conventional antenna in which multiple re?ection was problematic, we designed a prototype antenna of the same size, and veri?ed the validity of the proposed antenna. The results of the veri?cation were that the gain in the designed central frequency increased by 0.4 dB, and the ripple of the gain frequency properties that was produced by multiple re?ection was decreased by 1.1 dB. These results demonstrated the validity of the proposed antenna.
关键词： Beam-Scanning Function,Imaging Re?ector Antenna,Ring-focus Cassegrain Antenna,Center-Fed Re?ector Antenna,Phased Array-fed Re?ector Antenna,Doubly Curved Re?ector
更新于2025-09-23 15:23:52
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Dynamical distortions of structural signatures in molecular high-order harmonic spectroscopy
摘要： We study the signature of two-center interferences in molecular high-order harmonic spectra, with an emphasis on the spectral phase. With the help of both ab initio computations based on the time-dependent Schr?dinger equation and the molecular strong-field approximation (SFA) as developed by Chiril? et al. [Phys. Rev. A 73, 023410 (2006)] and Faria [Phys. Rev. A 76, 043407 (2007)], we observe that the phase behavior is radically different for the short and the long trajectory contributions. By means of Taylor expansions of the molecular SFA, we link this effect to the dynamics of the electron in the continuum. More precisely, we find that the value of the electric field at recombination time plays a crucial role in the shape of the destructive interference phase jump.
关键词： molecular spectroscopy,spectral phase,strong-field approximation,two-center interferences,time-dependent Schr?dinger equation,high-order harmonic generation
更新于2025-09-23 15:23:52
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Strongly anisotropic spin relaxation in the neutral silicon vacancy center in diamond
摘要： Color centers in diamond are a promising platform for quantum technologies, and understanding their interactions with the environment is crucial for these applications. We report a study of spin-lattice relaxation (T1) of the neutral charge state of the silicon vacancy center in diamond. Above 20 K, T1 decreases rapidly with a temperature-dependence characteristic of an Orbach process and is strongly anisotropic with respect to magnetic-field orientation. As the angle of the magnetic field is rotated relative to the symmetry axis of the defect, T1 is reduced by over three orders of magnitude. The electron spin coherence time (T2) follows the same temperature dependence but is drastically shorter than T1. We propose that these observations result from phonon-mediated transitions to a low-lying excited state that are spin conserving when the magnetic field is aligned with the defect axis, and we discuss likely candidates for this excited state.
关键词： anisotropy,spin relaxation,quantum technologies,diamond,silicon vacancy center,Orbach process
更新于2025-09-23 15:23:52
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[IEEE 2018 20th International Conference on Transparent Optical Networks (ICTON) - Bucharest (2018.7.1-2018.7.5)] 2018 20th International Conference on Transparent Optical Networks (ICTON) - Wavelength and Space Division Packet Super-Channel Switching System for Future Data Center Optical Networks with a Switching Capacity of 53.3 Tb/s/port
摘要： Data center (DC) traffic is expected to grow at a staggering annual rate over the next years. However, current DC networks, making use of point-to-point optical links and electronical switching systems, may be unable to meet this traffic demand with a reasonable energy consumption. Moreover, DC network traffic, characterized by dense matrices and bursty hot-spots, constitutes an additional challenge for DC networks designers. To address the capacity and energy bottlenecks and meet the traffic demands in future DC networks, this paper proposes a novel high-capacity optical switching system that employs time division multiplexing (TDM), wavelength division multiplexing (WDM), and space division multiplexing (SDM) to realize coherently modulated packet spatial super-channels (pSSCs). This optical switching system is based on three newly developed core-joint switching subsystems: an electro-absorption (EA)-based joint switch with ns switching speed, an acousto optical modulator (AOM)-based joint switch with μs switching speed, and a free-space mirror-based joint switch with ms switching speed. These switching subsystems are used in a network testbed to experimentally demonstrate a 2×2 switching node with 64 wavelength channels, 7-core pSSCs modulated at 32 GBd. The results confirm a record switching capacity of 53.3 Tb/s/port and network protection in case of a multi-core fiber (MFC) failure in less than 10 ms.
关键词： spatial division multiplexing,spatial switching,data center networking,coherent optical switching
更新于2025-09-23 15:22:29
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Design of A Two-Dimensional “T” Shaped Metamaterial with Wideband, Low Loss
摘要： A novel two-dimensional (2D) metamaterial structure with center symmetric "T" shaped unit is designed, fabricated, and measured in this paper. The proposed metamaterial comprises of a 2 × 2 array of area 4.3 mm × 4.3 mm, etched on single side of FR4 substrate. The simulation and measurement show that the novel metamaterial has a double negative range frequency of 20.16–37.47 GHz with an absolute width of 17.31 GHz, relative width of 60.07%, small unit loss of 0.16 dB, and small size of 0.07 λ0 in 2D. Furthermore, the double negative region of the proposed metamaterial operates through K band and Ka band, it can be widely used in satellite communication and broadband digital transmission.
关键词： center symmetric "T" shaped,Two dimensions,low loss,wide band
更新于2025-09-23 15:22:29
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Performance-Aware Energy Saving for Data Center Networks
摘要： Today’s data center networks (DCNs) tend to have tens to hundreds of thousands of servers to provide massive and sophisticated services. The architectural design of DCNs usually over-provisioned for peaks workloads and fault-tolerance. Statistically, DCNs remain highly under-utilized with typical utilization of around 30%. Network over-provisioning and under-utilization can be exploited for energy-saving. Most research efforts on data center network energy saving focus on how to save maximum energy with little or no consideration to the performance of the residual network. Thus, the DCN performance degraded and the network left vulnerable to sudden traffic surges. In this paper, we have studied energy-saving problem in DCNs while preserving network performance. The problem was formulated as MILP that is solvable by CPLEX to minimize the energy consumed by DCN, meanwhile, safety threshold constraints for links utilization are met. To overcome CPLEX high computational time, a heuristic algorithm to provide practical and efficient solution for the MILP is introduced. The heuristic algorithm uses switches grouping and links consolidation to switch the traffic to a small number of network devices and turn-off unused switches and links. Valiant load-balancing is used to distribute the loads over active links. Simulation experiments using synthetic and real packet traces were conducted to validate the heuristic in terms of energy consumption and network performance. The results show that the heuristic can save up to 45% of the network energy and improves the average imbalance-scores for links and switches by more than 50% with minimal effect on network performance.
关键词： Load Balancing,Energy Saving,Data Center Networks
更新于2025-09-23 15:22:29