New findings regarding light intensity and its effects as a zeitgeber in the Sprague-Dawley rat

In most mammals, the suprachiasmatic nucleus of the anterior hypothalamus has been implicated as the central driving mechanism of circadian rhythmicity. The photic input from the retina, via the retino-hypothalamic tract, and modulation from the pineal gland help regulate the clock. In this study, we investigated the effects of low light intensity on the circadian system of the Sprague-Dawley rat. A series of light intensity experiments were conducted to determine if a light level of 0.1 Lux will maintain entrained circadian rhythms of feeding, drinking, and locomotor activity

Algal culture studies for CELSS

Microalgae are well-suited as a component of a Closed Environmental Life Support System (CELSS), since they can couple the closely related functions of food production and atmospheric regeneration. The objective was to provide a basis for predicting the response of CELSS algal cultures, and thus the food supply and air regeneration system, to changes in the culture parameters. Scenedesmus growth was measured as a function of light intensity, and the spectral dependence of light absorption by the algae as well as algal respiration in the light were determined as a function of cell concentration. These results were used to test and confirm a mathematical model that describes the productivity of an algal culture in terms of the competing processes of photosynthesis and respiration. The relationship of algal productivity to cell concentration was determined at different carbon dioxide concentrations, temperatures, and light intensities. The maximum productivity achieved by an air-grown culture was found to be within 10% of the computed maximum productivity, indicating that CO2 was very efficiently removed from the gas stream by the algal culture. Measurements of biomass productivity as a function of cell concentration at different light intensities indicated that both the productivity and efficiency of light utilization were greater at higher light intensities

Suppression of bimolecular recombination by UV-sensitive electron transport layers in organic solar cells

Incorporating UV-sensitive electron transport layers (ETLs) into organic bulk heterojunction (BHJ) photovoltaic devices dramatically impacts short-circuit current (Jsc) and fill factor characteristics. Resistivity changes induced by UV illumination in the ETL of inverted BHJ devices suppress bimolecular recombination producing up to a two orders of magnitude change in Jsc. Electro-optical modeling and light intensity experiments effectively demonstrate that bimolecular recombination, in the form of diode current losses, controls the extracted photocurrent and is directly dependent on the ETL resistivity

Larvae of the Coral Acropora tenuis (Dana 1846) settle under controlled light intensity

Coral restoration using sexual reproduction could have many advantages over the currently more widely used asexual reproduction methods, in particular for maintaining genetic biodiversity. On-going research on controlled sexual reproduction of corals is seeking ways to achieve higher larval settlement and survival rates. Metamorphic settlement is a critical phase for the survival of coral larvae, due to morphological changes as well as threats of predation and competition. This study aimed to identify the effects of light intensity and substrate positioning on the metamorphosis of competent planula stage larvae. Five day old larvae of the Indo-Pacific coral Acropora tenuis (Dana 1846) were obtained from coral spawning under laboratory conditions. The light intensity experiments used 4 treatments: 170, 130, 90 and 45 μmol.m-2.s-1. Substrate positioning experiment treatments were vertical and horizontal orientations of the settlement plates. Coral larval settlement was not significantly correlated with light intensity, despite the higher settlement rates observed under light intensities between 130-170 μmol.m-2.s-1. The highest rate of settlement occurred on the ninth day post fertilisation and was significantly higher (α<0.05, df:2) than the rates on day seven and day eleven. The number of coral larvae settling on horizontal substrate was significantly higher compared to vertical plates, with a ratio of 11:1. This understanding of the factors affecting larval metamorphosis and settlement, in particular the importance of light intensity and substrate orientation, could be applied in the on-going efforts to mass produce juvenile corals for coral reef restoration

A tale of three taxes: photo-gyro-gravitactic bioconvection

The term bioconvection encapsulates the intricate patterns in concentration, due to hydrodynamic instabilities, that may arise in suspensions of non-neutrally buoyant, biased swimming microorganisms. The directional bias may be due to light (phototaxis), gravity (gravitaxis), a combination of viscous and gravitational torques (gyrotaxis) or other taxes. The aim of this study is to quantify experimentally the wavelength of the initial pattern to form from an initially well-mixed suspension of unicellular, swimming green algae as a function of concentration and illumination. As this is the first such study, it is necessary to develop a robust and meticulous methodology to achieve this end. The phototactic, gyrotactic and gravitactic alga Chlamydomonas augustae was employed, with various red or white light intensities from above or below, as the three not altogether separable taxes were probed. Whilst bioconvection was found to be unresponsive to changes in red light, intriguing trends were found for pattern wavelength as a function of white light intensity, depending critically on the orientation of the illumination. These trends are explored to help unravel the mechanisms. Furthermore, comparisons are made with theoretical predictions of initial wavelengths from a recent model of photo-gyrotaxis, encouragingly revealing good qualitative agreement

Effects of zooplankton size and concentration and light intensity on the feeding behavior of Atlantic mackerel \u3cem\u3eScomber scombrus\u3c/em\u3e

Atlantic mackerel Scomber scombrus had low clearance rates when fed older stage copepodites of the copepod Calanus finmarchicus at high concentrations and high clearance rates at low concentrations. These rates were consistent with filter feeding at high concentrations and particulate feeding at low concentrations. Intermediate and small copepods presented together at high concentrations were cleared at lower rates than the large C. finmarchicus, suggesting lower filtration efficiencies. Intermediate and small copepods were presented over a range of light intensities (8.2 x 10-8 to 1.6 x 100 µE m-2 s-1). Feeding rate did not change significantly between 1.6 x 100 and 2.0 x 10-6 µE m-2 s-1, but decreased to nearly zero at 8.2 x 10-8 µE m-2 s-1, indicating a light intensity threshold for feeding of about 10-7 µE m-2 s-1. This threshold enables mackerel to feed throughout the night near the ocean surface. Swimming speed decreased to a lesser degree than feeding rate at the lowest light intensity, indicating that the change in filter-feeding rate is only partially due to the change in speed. The school dispersed in both low and high light levels, but spacing between fish did not appear to be related to feeding rate

Quantifying Losses and Assessing the Photovoltage Limits in Metal–Insulator–Semiconductor Water Splitting Systems

Metal–insulator–semiconductor (MIS) photo‐electrocatalysts offer a pathway to stable and efficient solar water splitting. Initially motivated as a strategy to protect the underlying semiconductor photoabsorber from harsh operating conditions, the thickness of the insulator layer in MIS systems has recently been shown to be a critical design parameter which can be tuned to optimize the photovoltage. This study analyzes the underlying mechanism by which the thickness of the insulator layer impacts the performance of MIS photo‐electrocatalysts. A concrete example of an Ir/HfO2/n‐Si MIS system is investigated for the oxygen evolution reaction. The results of combined experiments and modeling suggest that the insulator thickness affects the photovoltage i) favorably by controlling the flux of charge carriers from the semiconductor to the metal electrocatalyst and ii) adversely by introducing nonidealities such as surface defect states which limit the generated photovoltage. It is important to quantify these different mechanisms and suggest avenues for addressing these nonidealities to enable the rational design of MIS systems that can approach the fundamental photovoltage limits. The analysis described in this contribution as well as the strategy toward optimizing the photovoltage are generalizable to other MIS systems.The competing roles of the insulator layer in metal–insulator–semiconductor water splitting systems are quantitatively explored. Nonidealities such as defects at interfaces significantly limit the photovoltage generated by these systems. Removing these nonidealities and engineering insulators with better selectivity for charge carriers are suggested as critical strategies toward approaching the fundamental photovoltage limits for efficient and stable solar water splitting.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/154631/1/aenm201903354_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/154631/2/aenm201903354-sup-0001-SuppMat.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/154631/3/aenm201903354.pd

Effects of the light regime on nutrient assimilation by phytoplankton in the Baja California and northwest Africa upwelling systems

The ability of natural phytoplankton assemblages in the Baja California and northwest Africa upwelling regions to assimilate nitrate, ammonium and silicic acid at simulated in situ light intensity and in the dark, was determined in 6 hr tracer experiments using the stable isotopes 15N and 30Si. Nitrate was almost never taken up in the dark, but dark uptake rates of ammonium and silicic acid ranged from zero to values equal to those measured at saturating light intensity...

Production of carbohydrates, lipids and polyunsaturated fatty acids (PUFA) by the polar marine microalga Chlamydomonas malina RCC2488

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