scholarly journals Flavodiiron Protein Flv2/Flv4-Related Photoprotective Mechanism Dissipates Excitation Pressure of PSII in Cooperation with Phycobilisomes in Cyanobacteria

2013 ◽  
Vol 164 (2) ◽  
pp. 805-818 ◽  
Author(s):  
Luca Bersanini ◽  
Natalia Battchikova ◽  
Martina Jokel ◽  
Ateeq Rehman ◽  
Imre Vass ◽  
...  
Keyword(s):  
Excitation Pressure

Impingement Cooling Flow and Heat Transfer Under Acoustic Excitations

1997 ◽  
Vol 119 (4) ◽  
pp. 810-817 ◽  
Author(s):  
C. Gau ◽  
W. Y. Sheu ◽  
C. H. Shen
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Shear Layer ◽  
Turbulence Intensity ◽  
Pressure Level ◽  
Unstable Wave ◽  
Impingement Cooling ◽  
Cooling Flow ◽  
Acoustic Excitations ◽  
Excitation Pressure

Experiments are performed to study (a) slot air jet impingement cooling flow and (b) the heat transfer under acoustic excitations. Both flow visualization and spectral energy evolution measurements along the shear layer are made. The acoustic excitation at either inherent or noninherent frequencies can make the upstream shift for both the most unstable waves and the resulting vortex formation and its subsequent pairing processes. At inherent frequencies the most unstable wave can be amplified, which increases the turbulence intensity in both the shear layer and the core and enhances the heat transfer. Both the turbulence intensity and the heat transfer increase with increasing excitation pressure levels Spl until partial breakdown of the vortex occurs. At noninherent frequencies, however, the most unstable wave can be suppressed, which reduces the turbulence intensity and decreases the heat transfer. Both the turbulence intensity and the heat transfer decreases with increasing Spl, but increases with increasing Spl when the excitation frequency becomes dominant. For excitation at high Reynolds number with either inherent or noninherent frequency, a greater excitation pressure level is needed to cause the enhancement or the reduction in heat transfer. During the experiments, the inherent frequencies selected for excitation are Fo/2 and Fo/4, the noninherent frequencies are 0.71 Fo, 0.75 Fo, and 0.8 Fo, the acoustic pressure level varies from 70 dB to 100 dB, and the Reynolds number varies from 5500 to 22,000.

scholarly journals Analysis and Experimental Investigation of Vibration Characteristics of Rotary Platform of Hydraulic Excavator under Complex Working Conditions

2021 ◽  
Vol 2021 ◽  
pp. 1-10
Author(s):  
Tinghao Li ◽  
Fuxiu Liu ◽  
Zhaojun Li ◽  
Mingjin Lu ◽  
Qiulu He
Keyword(s):  
Working Conditions ◽  
Dynamic Characteristics ◽  
Pressure Pulsation ◽  
Vibration Characteristics ◽  
Hydraulic Excavator ◽  
Rotary Platform ◽  
Road Excitation ◽  
Engine Excitation ◽  
Internal Relationships ◽  
Excitation Pressure

The rotary platform is the load-bearing substrate of a hydraulic excavator. The dynamic characteristics of the rotary platform directly affect the reliability and safety of the whole machine of a hydraulic excavator. In this work, the characteristics of the main external excitations acting on the hydraulic excavator such as the engine excitation, pressure pulsation excitation of the piston pump, inertial excitation of the working device, and road excitation are analyzed. The vibration transmission paths under the action of external excitations are ascertained. A vibration test method for the rotary platform of the hydraulic excavator is proposed. The vibration characteristics of the rotary platform under complex working conditions are researched, and the internal relationships between the vibration characteristics of the rotary platform and the engine excitation, pressure pulsation excitation of the piston pump, and road excitation are analyzed experimentally. The results show that the rotary platform is subjected to different excitations when it is under different working conditions. Moreover, the internal relationships between the dynamic characteristics of the rotary platform and the external excitation characteristics can be discovered by analyzing the vibration signals of the rotary platform, and the dynamic characteristics of the whole machine of the hydraulic excavator can be deeply studied based on the vibration characteristics of the rotary platform.

Excitation pressure regulates the activation energy for recombination events in the photosystem II reaction centres of Chlamydomonas reinhardtii

2007 ◽  
Vol 85 (6) ◽  
pp. 721-729 ◽  
Author(s):  
Tessa Pocock ◽  
P. V. Sane ◽  
S. Falk ◽  
N. P.A. Hüner
Keyword(s):  
Activation Energy ◽  
Photosystem Ii ◽  
Redox Potential ◽  
Chlamydomonas Reinhardtii ◽  
Reaction Center ◽  
Growth Conditions ◽  
High Irradiance ◽  
Reaction Centres ◽  
Excitation Pressure

Using in vivo thermoluminescence, we examined the effects of growth irradiance and growth temperature on charge recombination events in photosystem II reaction centres of the model green alga Chlamydomonas reinhardtii. We report that growth at increasing irradiance at either 29 or 15 °C resulted in comparable downward shifts in the temperature peak maxima (TM) for S2QB– charge pair recombination events, with minimal changes in S2QA– recombination events. This indicates that such growth conditions decrease the activation energy required for S2QB– charge pair recombination events with no concomitant change in the activation energy for S2QA– recombination events. This resulted in a decrease in the ΔTM between S2QA– and S2QB– recombination events, which was reversible when shifting cells from low to high irradiance and back to low irradiance at 29 °C. We interpret these results to indicate that the redox potential of QB was modulated independently of QA, which consequently narrowed the redox potential gap between QA and QB in photosystem II reaction centres. Since a decrease in the ΔTM between S2QA– and S2QB– recombination events correlated with growth at increasing excitation pressure, we conclude that acclimation to growth under high excitation pressure narrows the redox potential gap between QA and QB in photosystem II reaction centres, enhancing the probability for reaction center quenching in C. reinhardtii. We discuss the molecular basis for the modulation of the redox state of QB, and suggest that the potential for reaction center quenching complements antenna quenching via the xanthophyll cycle in the photoprotection of C. reinhardtii from excess light.

Daphnetin methylation stabilizes the activity of phosphoribulokinase in wheat during cold acclimation

2012 ◽  
Vol 90 (5) ◽  
pp. 657-666
Author(s):  
Khalil Kane ◽  
Amira Moheb ◽  
Yukihara Fukushi ◽  
René Roy ◽  
Norman P.A Hüner ◽  
...  
Keyword(s):  
Cold Acclimation ◽  
Calvin Cycle ◽  
Biological Significance ◽  
Deae Cellulose ◽  
Triticum Aestivum L ◽  
Spectrometric Analysis ◽  
Dependent Manner ◽  
Aerial Parts ◽  
Dose Dependent ◽  
Excitation Pressure

The methylation of daphnetin (7,8-dihydroxycoumarin) to its 8-methyl derivative is catalyzed by a wheat (Triticum aestivum L.) O-methyltransferase (TaOMT1). This enzyme is regulated by cold and photosystem II excitation pressure (plastid redox state). Here, we investigated the biological significance of this methylation and its potential role in modulating the activity of kinases in wheat. To identify the potential kinases that may interact with daphnetin in wheat, the soluble protein extract from aerial parts of cold-acclimated wheat was purified by DEAE-cellulose separation and affinity chromatography on a daphnetin derivative (7,8-dihydroxy-4-coumarin acetic acid)-EAH sepharose column. Mass spectrometric analysis indicated that wheat phosphoribulokinase (TaPRK) is the major kinase that binds to daphnetin. This TaPRK plays an important role in regulating the flow of carbon through the Calvin cycle, by catalyzing the final step in the regeneration of ribulose 1,5-bisphosphate from ribulose-5-phosphate (Ru5P) and ATP. The activities of TaPRK, endogenous or recombinant, are inhibited by daphnetin in a specific and dose-dependent manner, but not by its monomethyl derivative (7-methyl, 8-hydroxycoumarin). Furthermore, HPLC-MS analysis of wheat extracts reveals that 7,8-dimethoxycoumarin is more abundant than its monomethyl derivative. The results also show that cold acclimation does not alter the level of TaPRK mRNA or its enzyme activity, and thus ensures the stable generation of ribulose 1,5-biphosphate.

Shedding some light on cold acclimation, cold adaptation, and phenotypic plasticity

Botany ◽  
2013 ◽  
Vol 91 (3) ◽  
pp. 127-136 ◽  
Author(s):  
Norman P.A. Hüner ◽  
Rainer Bode ◽  
Keshav Dahal ◽  
Florian A. Busch ◽  
Marc Possmayer ◽  
...  
Keyword(s):  
Phenotypic Plasticity ◽  
Cold Acclimation ◽  
Pinus Banksiana ◽  
Photosynthetic Apparatus ◽  
Nuclear Gene ◽  
Crop Productivity ◽  
Photosynthetic Performance ◽  
Brassica Napus L ◽  
Cellular Energy ◽  
Excitation Pressure

In the past, the role of light as an energy source was largely ignored in research focused on cold acclimation and freezing tolerance in plants. However, cold acclimation is an energy-requiring process. We summarize research illustrating that photoautrophs as diverse as cyanobacteria (Plectonema boryanum), green algae (Chlorella vulgaris, Dunaliella salina, Chlamydomonas raudensis), crop plants (Triticum aestivum L., Secale cereale L., Brassica napus L.), and conifers (Pinus banksiana) L.) tailor the structure and function of the photosynthetic apparatus to changes in temperature and irradiance to maintain cellular energy balance called photostasis. Modulation of either temperature or irradiance results in a similar imbalance in cellular energy that is sensed through changes in chloroplastic excitation pressure. Thus, concepts of photostasis and excitation pressure provide the context through which one can explain the congruence of phenotypic plasticity and photosynthetic performance associated with cold acclimation and photoacclimation. Photosynthetic organisms can sense changes in temperature and irradiance through modulation of the redox state of the photosynthetic electron transport chain, which, in turn, governs phenotype through the regulation of nuclear gene expression and chloroplast biogenesis. We suggest that elucidation of the molecular mechanism(s) by which excitation pressure regulates phenotypic plasticity and photosynthetic performance will be essential in addressing the challenge of maintaining or perhaps enhancing crop productivity under the suboptimal growth conditions predicted to occur as a consequence of climate change.

Numerical Simulation and Analysis of Hydraulic Excitation System Based on Water Hammer by the Method of Characteristics

2011 ◽  
Vol 295-297 ◽  
pp. 2210-2215 ◽  
Author(s):  
Hui Xian Zhang ◽  
Zi Ming Kou ◽  
Juan Wu ◽  
Chun Yue Lu
Keyword(s):  
Numerical Simulation ◽  
Method Of Characteristics ◽  
Experimental System ◽  
Water Hammer ◽  
Vibration Exciter ◽  
Transient Pressure ◽  
Excitation System ◽  
The Method Of Characteristics ◽  
System Pressure ◽  
Excitation Pressure

To study artificially produced and actively controlled water hammer wave caused by hydraulic vibration exciter, a mathematical model was established and an experimental system was designed to verify it. Through the given partial differential equations, a computer code based on the method of characteristics was developed to calculate transient pressure distributed along the pipe under different rotational frequency of vibration exciter. The numerical simulation indicates that there is a simple harmonic vibration rising at the cross sections along the pipe, corresponding to different excitation pressure at every cross section. In addition, the excitation pressure can also be adjusted by system pressure via overflow valve. So, this work is expected to serve for the optimum design of the hydraulic excitation system and play a theoretical guiding role to experimental research in future.

scholarly journals Salt adaptability in a halophytic soybean (Glycine soja) involves photosystems coordination

2019 ◽  
Author(s):  
Wenjun He ◽  
Kun Yan ◽  
Lanxing Bian ◽  
Xiaoli Tang ◽  
Mengxin An ◽  
...  
Keyword(s):  
Salt Stress ◽  
Glycine Max ◽  
Reaction Center ◽  
Yellow River ◽  
Feedback Inhibition ◽  
Glycine Soja ◽  
Electron Flow ◽  
Great Decrease ◽  
Acceptor Side ◽  
Excitation Pressure

Abstract Background: Glycine soja is a halophytic soybean native to saline soil in Yellow River Delta, China. Photosystem I (PSI) performance and the interaction between photosystem II (PSII) and PSI remain unclear in Glycine soja under salt stress. This study aimed to explore salt adaptability in Glycine soja in terms of photosystems coordination. Results: Potted Glycine soja was exposed to 300 mM NaCl for 9 days with a cultivated soybean, Glycine max, as control. Under salt stress, the maximal photochemical efficiency of PSII (Fv/Fm) and PSI (△MR/MR0) were significantly decreased with the loss of PSI and PSII reaction center proteins in Glycine max, and greater PSI vulnerability was suggested by earlier decrease in △MR/MR0 than Fv/Fm and depressed PSI oxidation in modulated 820 nm reflection transients. Inversely, PSI stability was defined in Glycine soja, as △MR/MR0 and PSI reaction center protein abundance were not affected by salt stress. Consistently, chloroplast ultrastructure and leaf lipid peroxidation were not affected in Glycine soja under salt stress. Inhibition on electron flow at PSII acceptor side helped protect PSI by restricting electron flow to PSI and seemed as a positive response in Glycine soja due to its rapid recovery. Reciprocally, PSI stability aided in preventing PSII photoinhibition, as the simulated feedback inhibition by PSI inactivation induced great decrease in Fv/Fm under salt stress. In contrast, PSI inactivation elevated PSII excitation pressure through inhibition on PSII acceptor side and accelerated PSII photoinhibition in Glycine max, according to the positive and negative correlation of △MR/MR0 with efficiency that an electron moves beyond primary quinone and PSII excitation pressure respectively. Conclusion: Therefore, photosystems coordination depending on PSI stability and rapid response of PSII acceptor side contributed to defending salt-induced oxidative stress on photosynthetic apparatus in Glycine soja. Photosystems interaction should be considered as one of the salt adaptable mechanisms in this halophytic soybean.

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