Search results for "Light intensity"
showing 10 items of 146 documents
Picosecond Time Resolved Analysis of the Fast and Slow Reversible Non-Photochemical Chlorophyll Fluorescence Quenching
1998
Photosystem II, which is a potential target of adverse effects of supersaturating light, is strongly dependent on a mechanism, which allows to switch over between efficient photochemical energy conversion at limiting light intensity and efficient photothermal energy conversion under strong light. The mechanisms for the thermal dissipation of light absorbed in excess are reflected by the socalled non-photochemical quenching of chlorophyll fluorescence (NPQ). Under excessive illumination two major components contribute to the overall NPQ which can be distinguished by their different kinetics of dark relaxation. The fast reversible component is supposed to be linked to the light-induced format…
New trends in photobiology
1993
Abstract At the beginning of our century few scientists paid attention to the phenomenon of inactivation of photosynthesis by high light intensities which was later called photoinhibition. In the period 1925–1950, the idea was established that photoinhibition is a reversible inactivation, determined by light intensity and exposure time, followed by irreversible damage of the photosynthetic apparatus. However, the absence of a uniform terminology demonstrates that photoinhibition was not completely perceived and understood. In 1956, B. Kok gave the first definition of photoinhibition as a photochemical inactivation of pigment complexes.
Light and Primary Production Shape Bacterial Activity and Community Composition of Aerobic Anoxygenic Phototrophic Bacteria in a Microcosm Experiment
2020
ABSTRACT Phytoplankton is a key component of aquatic microbial communities, and metabolic coupling between phytoplankton and bacteria determines the fate of dissolved organic carbon (DOC). Yet, the impact of primary production on bacterial activity and community composition remains largely unknown, as, for example, in the case of aerobic anoxygenic phototrophic (AAP) bacteria that utilize both phytoplankton-derived DOC and light as energy sources. Here, we studied how reduction of primary production in a natural freshwater community affects the bacterial community composition and its activity, focusing primarily on AAP bacteria. The bacterial respiration rate was the lowest when photosynthe…
Stimuli-Responsive Polymeric Nanocarriers for Drug Delivery, Imaging, and Theragnosis.
2020
In the past few decades, polymeric nanocarriers have been recognized as promising tools and have gained attention from researchers for their potential to efficiently deliver bioactive compounds, including drugs, proteins, genes, nucleic acids, etc., in pharmaceutical and biomedical applications. Remarkably, these polymeric nanocarriers could be further modified as stimuli-responsive systems based on the mechanism of triggered release, i.e., response to a specific stimulus, either endogenous (pH, enzymes, temperature, redox values, hypoxia, glucose levels) or exogenous (light, magnetism, ultrasound, electrical pulses) for the effective biodistribution and controlled release of drugs or genes…
Mediator-Induced Changes in Macromolecular Permeability in the Rat Mesenteric Microcirculation
1995
An intravital fluorescence microscopic method for measurement of changes in macromolecular permeability has been established in the mesenterial microcirculation of the rat. After exteriorization of the fat-free distal part of the ileal mesentery, a 1-hr period of stabilization was followed by the injection of FITC-labeled macromolecules. Five minutes later, histamine, leukotriene B4, or leukotriene C4 was topically applied to the tissue by means of a micromanipulator. Areas of 1 mm2 were videotaped with a SIT camera. The fluorescence intensity of these areas was measured by an analogous video image processing system and displayed as gray value histograms. The shift of the frequency of gray …
Accelerometer-assessed sedentary work, leisure time and cardio-metabolic biomarkers during one year : Effectiveness of a cluster randomized controlle…
2017
BackgroundIt is unknown whether reducing sedentary time at work and during leisure time is possible and effective during one year.MethodsOffice workers with young children were recruited for this one-year cluster-randomized controlled trial through kindergartens and primary schools from 7 clusters in the city of Jyväskylä, Finland. After a lecture, face-to-face tailored counseling was used to set contractually binding goals regarding reducing and breaking up sitting periods and increasing light intensity physical activity during work and leisure time. Primary outcomes of total, work and leisure sedentary time (ResultsParticipants from intervention (N = 71) and control (N = 62) regions were …
Transcriptional analysis of rat photoreceptor cells reveals daily regulation of genes important for visual signaling and light damage susceptibility.
2013
Photoreceptor cells face the challenge of adjusting their function and, possibly, their susceptibility to light damage to the marked daily changes in ambient light intensity. To achieve a better understanding of photoreceptor adaptation at the transcriptional level, this study aimed to identify genes which are under daily regulation in photoreceptor cells using microarray analysis and quantitative PCR. Included in the gene set obtained were a number of genes which up until now have not been shown to be expressed in photoreceptor cells, such as Atf3 (activating transcription factor 3) and Pde8a (phosphodiesterase 8A), and others with a known impact on phototransduction and/or photoreceptor s…
Inflammation, muscle damage and post-race physical activity following a mountain ultramarathon
2021
BACKGROUND: The study aimed at exploring whether muscle membrane disruption, as a surrogate for muscle damage, and inflammation recovery following a mountain ultramarathon (MUM) was related with race performance and post-race physical activity. METHODS: Blood samples were obtained from thirty-four athletes (29 men and 5 women) before a 118-km MUM, immediately after and three and seven days post-race. Creatine kinase (CK), lactate dehydrogenase (LDH) and C-reactive protein (CRP) were compared between faster (FR) and slower (SR) runners. Physical activity performed during the week following the MUM was objectively analyzed using accelerometers and compared between FR and SR. RESULTS: CK was s…
Accelerometer-Measured Physical Activity Levels and Patterns Vary in an Age- and Sex-Dependent Fashion among Finnish Children and Adolescents
2022
Background: The purpose of this study was to measure physical activity (PA), sedentary behavior (SB), and hour-by-hour PA patterns with an accelerometer in a population-based sample of Finnish children and adolescents. Methods: A total of 3274 participants (3rd, 5th, 7th, 9th graders) from 176 schools wore a hip-worn triaxial accelerometer for seven days during waking hours. Mean amplitude deviation of the acceleration data was used to assess PA intensity that was converted to metabolic equivalents and categorized into light, moderate, and vigorous PA. Angle for posture estimation was used to measure SB and standing. Results: The majority of participants’ PA consisted of light PA, and they …
On thermal influence of laser beam irradiation on optical absorption of amorphous as-evaporated As2S3 films
1998
Abstract Photoinduced changes of the optical absorption in amorphous as-evaporated As 2 S 3 thin films are studied. Before the measurements films were kept at dark for more than two years. The long storage time ensured that the relaxational structural changes caused by the deposition process were absent. As a light source a CW unfocused 488.0 nm Ar laser line was used. The intensity of the laser beam was varied from rather low intensity values up to intensities which raised the temperature of the films above the glass transition temperature. Based on the behavior of the saturation values of the absorption we were able to state that the exposed As 2 S 3 films started to polymerize at 63–69°C…