Light Intensity Research Papers - Academia.edu (original) (raw)

In the analysis and prediction of real-world systems, two of the key problems are nonstationarity (often in the form of switching between regimes) and overfitting (particularly serious for noisy processes). This article addresses these problems using gated experts, consisting of a (nonlinear) gating network, and several (also nonlinear) competing experts. Each expert learns to predict the conditional mean, and each expert adapts its width to match the noise level in its regime. The gating network learns to predict the probability of each expert, given the input. This article focuses on the case where the gating network bases its decision on information from the inputs. This can be contrasted to hidden Markov models where the decision is based on the previous state(s) (i.e. on the output of the gating network at the previous time step), as well as to averaging over several predictors. In contrast, gated experts soft-partition the input space, only learning to model their region. This...

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- Cognitive Science, Time Series, Nonlinear dynamics, Computers

Recruitment is essential for the maintenance of populations, but far more is typically known about the more easily-observed adult stages than their smaller, often microscopic early life-history counterparts. This discrepancy can be particularly problematic for populations of foundation species that create biogenic habitat for a multitude of other taxa, but are themselves prime candidates for exploitation, fragmentation, and loss, and therefore become the focus of restoration eVorts partly or fully dependent on recruitment. The purpose of this study was to improve ecological understanding for early life-history stages of the habitat-forming marine alga Cystoseira barbata (Stackhouse) C. Agardh (Fucales: Sargassaceae), member of a genus that has experienced considerable fragmentation and population decline on European coasts. Using experimental manipulations of water temperature, light intensity, and sediment accumulation, we observed that sediment virtually precluded recruitment of C. barbata, and greatly impacted the survival of recently settled germlings (up to »83% mortality). Stronger intensities of light facilitated the growth of germlings, including the capacity for »50% of them to outgrow detrimental sediment and survive. Temperature (10 vs. 16°C) had no eVect on early recruitment, survival, or growth. This information helps to identify likely causes and locations of recruitment failure, and by extension, the conditions needed (either naturally or through human intervention) to facilitate recruitment and possible habitat restoration. Ultimately, this knowledge can increase our capacity to predict population persistence and the likely success of restoration eVorts. Communicated by S. D. Connell.

- by Andrew Irving
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- Marine Biology, Life history, Biological Sciences, Environmental Sciences

An hybrid atomic force-scanning near-field optical microscope (AFM-SNOM) has been realized starting from a home-built AFM. The instrument uses a tetrahedral SiN tip for force and near field detection and is designed to provide, besides simple imaging, a full three-dimensional (3-D) mapping of force, friction and light intensity on the sample. High-resolution optical images of dielectric samples are presented together with curves describing the behavior of the collected optical intensity as a function of tip-object distance. AFM images and forcedistance curves are reported as well and are compared with those obtained from the optical channel. Subwavelength features of the samples can be easily appreciated in both kinds of images, and the refractive index of the object can be computed from the attenuation constant of the tunneling light detected by the tip, with the AFM curve providing a convenient way of detecting the contact point. The spatial resolution of this kind of measurement is far better than that obtainable with any other index-measuring device. Homogeneous glass samples as well as monomode channel waveguides were analyzed in our experiments. The refractive index of several different prisms, made either of BK7 (n = 1:519 at = 532 nm) or of SF58 (n = 1:932) glass, could be measured with our near-field technique. As for the channel waveguides, the accuracy of our measurements lets us detect their presence and lateral extension in the substrate but is not yet sufficient to allow the reconstruction of their index profile.

- by franco quercioli
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- Optics, Medical Imaging, Fiber Optics, Telecommunications

Characteristic shape parameters, light intensities and relative water velocities were estimated in thalli of freemoving seaweeds, using three Gracilaria-like species: G. cornea, G. conferta and Gracilariopsis lemaneiformis. Relative velocities over the branches were determined mostly by rotation of the algae in the water as opposed to linear translation. The tree major shape parameters of the thallus, weight, volumetric specific weight and areal specific weight, explain the differences in relative velocity. Relative velocities near the center of the thallus were about 50% to 80% of the external velocity. Light intensities at the vicinity of the center of G. cornea ranged between 60% to 90% of the external light intensity. Light attenuation in the center was proportional to the weight of the thallus. The significance of light and velocity attenuation as a function of shape parameters is discussed.

- by Eitan Kimmel
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- Plant Biology, Environmental Biotechnology, Applied Phycology, Fisheries Sciences

The environment is profoundly important in shaping many aspects of animal phenotype, including courtship and mating behaviours.

The objective of this study was to determine the relationship between light levels in the understory of a broadleaf forest and the content of six ginsenosides (Rg 1 , Re, Rb 1 , Rc, Rb 2, and Rd) in 1-and 2-year-old American ginseng (Panax quinquefolius L.) roots. Our results revealed that ginsenoside contents in 1-and 2 year-old roots collected in September were significantly related to direct and total light levels, and duration of sunflecks. At this time, the effect of light levels accounted for up to 48 and 62% of the variation in ginsenoside contents of 1-and 2-year-old American ginseng roots. Also, red (R) and far red (FR) light, and the R:FR ratio significantly affected Rd, Rc, and Rg 1 contents in 2-year-old roots, accounting for up to 40% of the variation in ginsenoside contents. Crown

- by Shahrokh Khanizadeh
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- Forestry, Horticulture, Phytochemistry, Forest Ecology And Management

Proper mixing of reagents is of paramount importance for an efficient chemical reaction. While on a large scale there are many good solutions for quantitative mixing of reagents, as of today, efficient and inexpensive fluid mixing in the nanoliter and microliter volume range is still a challenge. Complete, i.e., quantitative mixing is of special importance in any small-scale analytical application because the scarcity of analytes and the low volume of the reagents demand efficient utilization of all available reaction components. In this paper we demonstrate the design and fabrication of a novel centrifugal force-based unit for fast mixing of fluids in the nanoliter to microliter volume range. The device consists of a number of chambers ͑including two loading chambers, one pressure chamber, and one mixing chamber͒ that are connected through a network of microchannels, and is made by bonding a slab of polydimethylsiloxane ͑PDMS͒ to a glass slide. The PDMS slab was cast using a SU-8 master mold fabricated by a two-level photolithography process. This microfluidic mixer exploits centrifugal force and pneumatic pressure to reciprocate the flow of fluid samples in order to minimize the amount of sample and the time of mixing. The process of mixing was monitored by utilizing the planar laser induced fluorescence ͑PLIF͒ technique. A time series of high resolution images of the mixing chamber were analyzed for the spatial distribution of light intensities as the two fluids ͑suspension of red fluorescent particles and water͒ mixed. Histograms of the fluorescent emissions within the mixing chamber during different stages of the mixing process were created to quantify the level of mixing of the mixing fluids. The results suggest that quantitative mixing was achieved in less than 3 min. This device can be employed as a stand alone mixing unit or may be integrated into a disk-based microfluidic system where, in addition to mixing, several other sample preparation steps may be included. Physics 80, 075102-1 075102-2 Noroozi et al. Rev. Sci. Instrum. 80, 075102 ͑2009͒ 075102-3 Noroozi et al. Rev. Sci. Instrum. 80, 075102 ͑2009͒ 075102-5 Noroozi et al. Rev. Sci. Instrum. 80, 075102 ͑2009͒ 075102-6 Noroozi et al. Rev. Sci. Instrum. 80, 075102 ͑2009͒ 075102-7 Noroozi et al. Rev. Sci. Instrum. 80, 075102 ͑2009͒

- by zahra noroozi
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- Engineering, Water, Time Series, Fluorescence

Introduction The change in light intensity that takes place when an ambient air sample is drawn into the detection chamber of a chemiluminescence monitor generates changes in the concentrations of several species, such as NO 2 , NO and O 3 . Although this phenomenon has been known for several decades, there is still no commonly accepted approach on when or how to correct for it in NO 2 and O 3 readings. Discussion In this work, we have assessed the expanded uncertainty of two chemiluminescence NO x analysers commercially available according to EN 14211:2005, with the aim of establishing the maximum allowable standard uncertainty due to the reaction between NO and O 3 in the sampling system.

- by Fernando Alonso
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- Air Quality, Environmental Monitoring, Air pollution, Biological Sciences

Touch (or tactile) sensors are gaining renewed interest as the level of sophistication in the application of minimum invasive surgery and humanoid robots increases. The spatial resolution of current large-area (greater than 1 cm 2 ) tactile sensor lags by more than an order of magnitude compared with the human finger. By using metal and semiconducting nanoparticles, a ∼100-nm-thick, large-area thin-film device is self-assembled such that the change in current density through the film and the electroluminescent light intensity are linearly proportional to the local stress. A stress image is obtained by pressing a copper grid and a United States 1-cent coin on the device and focusing the resulting electroluminescent light directly on the charge-coupled device. Both the lateral and height resolution of texture are comparable to the human finger at similar stress levels of ∼10 kilopascals.

- by Ravi Saraf
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- Robotics, Science, Transmission Electron Microscopy, Multidisciplinary

The relationship between liquid equivalent snowfall rate and visibility is investigated using data collected at the National Center for Atmospheric Research Marshall Snowfall Test Site during two winter field seasons and using theoretical relationships. The observational data include simultaneous liquid equivalent snowfall rate, crystal types, and both automated and manual visibility measurements. Theoretical relationships between liquid equivalent snowfall rate and visibility are derived for 27 crystal types, and for ''dry'' and ''wet'' aggregated snowflakes. Both the observations and theory show that the relationship between liquid equivalent snowfall rate and visibility depends on the crystal type, the degree of riming, the degree of aggregation, and the degree of wetness of the crystals, leading to a large variation in the relationship between visibility and snowfall rate. Typical variations in visibility for a given liquid equivalent snowfall rate ranged from a factor of 3 to a factor of 10, depending on the storm. This relationship is shown to have a wide degree of scatter from storm to storm and also during a given storm. The main cause for this scatter is the large variation in cross-sectional area to mass ratio and terminal velocity for natural snow particles. It also is shown that the visibility at night can be over a factor of 2 greater than the visibility during the day for the same atmospheric extinction coefficient. Since snowfall intensity is defined by the U.S. National Weather Service using visibility, this day/night difference in visibility results in a change in snowfall intensity category caused by only whether it is day or night. For instance, a moderate snowfall intensity during the day will change to a light snowfall intensity at night, and a heavy snowfall intensity during the day will change to a moderate snowfall intensity at night, for the same atmospheric extinction coefficient. Thus, the standard relationship between snowfall intensity and visibility used by many national weather services (1/4 mile or less visibility corresponds to heavy snowfall intensity, between 5/16 and 5/8 mile corresponds to moderate intensity, and greater than 5/8 mile corresponds to light intensity) does not always provide the correct indication of actual liquid equivalent snowfall rate because of the variations in snow type and the differences in the nature of visibility targets during day and night. This false indication may have been a factor in previous ground-deicing accidents in which light snow intensity was reported based on visibility, when in fact the actual measured liquid equivalent snowfall rate was moderate to heavy.

- by Roy Rasmussen
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- Seasonality, Atmospheric sciences, Applied, Data Collection

Indoor hydroxyl radical concentrations were estimated using a new indoor air quality model which employs the SAPRC-99 atmospheric chemistry model to simulate indoor homogenous reactions. Model results indicate that typical indoor hydroxyl radical concentrations are lower than typical outdoor summertime urban hydroxyl radical levels of 5-10 Â 10 6 molecules cm À3 ; however, indoor levels can be similar to or greater than typical nighttime outdoor hydroxyl radical levels of approximately 5 Â 10 4 molecules cm À3 . Effects of selected parameters on indoor hydroxyl radical concentrations are presented herein. Indoor hydroxyl radical concentrations are predicted to increase non-linearly with increasing outdoor ozone concentrations, indoor alkene emission rates, and air exchange rates. Indoor hydroxyl radical concentrations decrease with increasing outdoor nitric oxide concentrations. Indoor temperature and indoor light intensity have moderate impacts on indoor hydroxyl radical concentrations. Outdoor hydroxyl radical concentrations, outdoor nitrate (NO 3 d ) radical concentrations, outdoor hydroperoxy radical concentrations, and hydroxyl radical removal by indoor surfaces are predicted to have no appreciable impact on indoor hydroxyl radical concentrations. Production of hydroxyl radicals in indoor environments appears to be controlled primarily by reactions of alkenes with ozone, and nitric oxide with hydroperoxy radical. Estimated indoor hydroxyl radical levels may potentially affect indoor air quality. Two examples are presented in which reactions of d-limonene and a-pinene with indoor hydroxyl radicals produce aldehydes, which may be of greater concern than the original compounds. r

- by Charles Weschler
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- Environmental Engineering, Chemistry, Atmospheric Chemistry, Atmospheric Science

Four strains of aerobic heterotrophic bacteria were isolated on crude oil with the aim to test whether their presence and activity might support the growth of cyanobacteria in oil-polluted microbial mats and whether the cyanobacterial exudates might play a role in stimulating their degradative activities. The strains were phylogenetically related to known oil-degrading species from the genera Marinobacter, Pseudomonas and Sphingomonas. Three strains (GM41, GM61 and GM63) grew well on C 5 eC 18 alkanes but not on 7 tested aromatics, whereas one strain (i.e. GM42) grew best on phenanthrene and pentane. All strains showed ability to metabolize a range of cyanobacterial photosynthetic and fermentative exudates. In coculture experiments, the addition of the Pseudomonas-related GM41 strain to the cyanobacterium Synechocystis PCC6803, found in the same mat, resulted in 8-fold increase in the cyanobacterial biomass. This growth was more pronounced when hexadecane was added to the culture medium. The addition of representative substrates of cyanobacterial exudates to the phenanthrene-degrading strain GM42 resulted in variable effects. While acetate, pyruvate and glucose enhanced phenanthrene degradation, alanine and butanol showed no effect. We conclude that aerobic heterotrophic bacteriaecyanobacteria consortia can be very useful for bioremediating oil-polluted sites, circumventing the costly use of organic and inorganic fertilizers.

- by Stjepko Golubic
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- Carbon Dioxide, Carbon Cycle, Microbial mats, Organic production
- by Anders Kiessling
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- Water quality, Aquaculture, FISH, Temperature

Morphogenesis of the reproductive structure of buckwheat and the impact of light conditions on flowering time and duration have been investigated using the variety 'La Harpe'. Inflorescences were initiated acropetally, in leaf axils, by the shoot apical meristem until its arrest of functioning which was accompanied by the abortion of the last inflorescence produced. The buckwheat inflorescence is a compound raceme that produces laterally flowered cymose clusters, the number of which was affected by the position of the inflorescence along the main stem. Similarly, the number of flowers in a lateral cluster was dependent on the inflorescence's position on the stem. The development of each inflorescence was stopped as its meristem stopped functioning and, in a situation reminiscent of the shoot apical meristem, the latest initiated cyme aborted. The development of each cyme was also terminated with the abortion of a few young flowers. The variety 'La Harpe' is a facultative short-day plant: the number of nodes generated before the initiation of the first inflorescence and the number of days from sowing to macroscopic appearance of this inflorescence were reduced in 8 h days as compared with 16 h days. The number of inflorescences, and thus flowering duration, was also strongly reduced by short days. It was unaffected by light irradiance in 8 h days while, in 16 h days, it was prolonged when light intensity was increased, suggesting the interaction of two different mechanisms for its regulation. Buckwheat is a distylous species, but inflorescence structure and flowering behaviour were not affected by floral morph. irradiance (75 lmol m ÿ2 s ÿ1 ); HI, high irradiance (150 lmol m ÿ2 s ÿ1 ); SDP, short-day plants; LDP, long-day plants; Sn, sterile nodes; Dne, day neutral; Ppd, photoperiod response.

- by Muriel Quinet
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- Geography, Plant Biology, France, Experimental Botany

The performance of fluorescence detectors in capillary electrophoresis is maximized when the excitation light intensity is modulated in time with optimal frequencies. This is especially true when photomultiplier tubes are used to detect the fluorescent light. The photomultiplier tube amplified raw output signal can in principle be captured directly by a personal computer sound card (PCSC) and processed by a lock-in emulated by software. This possibility is demonstrated in the present work and the performance of this new setup is compared with a traditional data acquisition system. The results obtained with this &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot;PCSC and lock-in emulated by software&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot; were of the same quality or even better compared to that obtained by conventional time integrators (Boxcars) and data acquisition boards. With PCSC the limits of detection (LOD) found for both naphthalene-2,3-dicarboxaldehyde-derivatized tyrosine and alanine were 3.3 and 3.5fmol (injection of 5nL of samples at 0.66 and 0.70micromol/L), respectively. This is at least three times better compared to conventional systems when light emitting diodes (LEDs) are used as the excitation source in fluorescence detectors. The PCSC linear response range was also larger compared to conventional data acquisition boards. This scheme showed to be a practical and convenient alternative of data acquisition and signal processing for detection systems used in capillary electrophoresis.

- by Tarso Kist and +1
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- Analytical Chemistry, Signal Processing, Capillary electrophoresis, Data acquisition

Highly reducing sediments are prevalent in seagrass environments. Under anoxic conditions, hydrogen sulfide can accumulate as an end product of anaerobic respiration at levels which may be toxic to halophytes. The photosynthetic response of Zostera marina L. (eelgrass) to manipulations in sediment sulfide concentration and light regimes was examined in Chincoteague Bay in June 1991. Neutral density screens were used in a mesocosm experiment to decrease downwelling irradiance to 50 and 15% of insolation. Sediment sulfide levels were enriched using Na2S and lowered using FeSO4. Photosynthesis vs. irradiance (PI) relationships were determined experimentally at ten light levels throughout the 21 day experiment. Photoadaptation was detected in response to the previous 4 day light history of the plants, as maximum photosynthesis (Pmax) decreased in response to lower daily light levels. Negative impacts of sulfide on eelgrass in this study were observed through reductions in Pmax, increases in the light intensity at which gross photosynthesis equals respiration, and decreases in the initial slope of the PI curve. The effects of eutrophication through reduced light and increased sediment sulfide on Pmax were additive. Elevated sediment sulfide levels may contribute to seagrass loss in stressed areas as the potential for utilization of available light is reduced.

- by William Dennison
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- Plant Biology, Aquatic botany, Barrier Island, Light Intensity

We designed 4x4 matrix TFTs arrays using current mirror amplifiers. Advantages of current mirror amplifiers are they need less requiring switches and the conversion time is short. The TFTs arrays 4x4 matrix using current mirror circuits have been fabricated and tested with success. The TFTs array directly can process signals coming from 16 pixels in the same node. This enables us to make the summation of the light intensities of close pixels during a reading.

- by nur huda
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- Thin Film Transistor, Light Intensity

Photosynthesis is the process by which Nature coordinates a tandem of protein complexes of impressive complexity that function to harness staggering amounts of solar energy on a global scale. Advances in biochemistry and nanotechnology have provided tools to isolate and manipulate the individual components of this process, thus opening a door to a new class of highly functional and vastly abundant biological resources. Here we show how one of these components, Photosystem I (PSI), is incorporated into an electrochemical system to yield a stand-alone biohybrid photoelectrochemical cell that converts light energy into electrical energy. The cells make use of a dense multilayer of PSI complexes assembled on the surface of the cathode to produce a photocatalytic effect that generates photocurrent densities of 2lA/cm2atmoderatelightintensities.WedescribetherelationshipbetweenthecurrentandvoltageproductionofthecellsandthephotoinducedinteractionsofPSIcomplexeswithelectrochemicalmediators,andshowthattheperformanceofthepresentdeviceislimitedbydiffusionaltransportoftheelectrochemicalmediatorsthroughtheelectrolyte.Thesebiohybriddevicesdisplayremarkablestability,astheyremainactiveinambientconditionsforatleast280days.Evenatbench−scaleproduction,thematerialsrequiredtofabricatethecellsdescribedinthismanuscriptcost2 lA/cm 2 at moderate light intensities. We describe the relationship between the current and voltage production of the cells and the photoinduced interactions of PSI complexes with electrochemical mediators, and show that the performance of the present device is limited by diffusional transport of the electrochemical mediators through the electrolyte. These biohybrid devices display remarkable stability, as they remain active in ambient conditions for at least 280 days. Even at bench-scale production, the materials required to fabricate the cells described in this manuscript cost 2lA/cm2atmoderatelightintensities.WedescribetherelationshipbetweenthecurrentandvoltageproductionofthecellsandthephotoinducedinteractionsofPSIcomplexeswithelectrochemicalmediators,andshowthattheperformanceofthepresentdeviceislimitedbydiffusionaltransportoftheelectrochemicalmediatorsthroughtheelectrolyte.Thesebiohybriddevicesdisplayremarkablestability,astheyremainactiveinambientconditionsforatleast280days.Evenatbench−scaleproduction,thematerialsrequiredtofabricatethecellsdescribedinthismanuscriptcost10 cents per cm 2 of active electrode area.

- by Kevin Emmett
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- Photochemistry, Multidisciplinary, Biocatalysis, Electricity

The electrostriction contribution to the nonlinear refractive index in optical fiber was theoretically calculated and measured. Nonlinearity was induced directly by insertion of the optical fiber into an intense external electric field. With this technique both the Kerr and the electrostrictive contributions to the intensity dependence of the nonlinear refractive index in a step-index fiber were measured. Good agreement between

- by Andrea Melloni
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- Quantum Physics, Feedback Control, Refractive Index, Weak Dependence

In this paper, we present the implementation of a new class of optical pressure sensors in a robotic tactile-sensing system based on polydimethylsiloxane (PDMS). The sensor consists of a tapered optical fiber, where an optical signal goes across, embedded into a PDMS-gold nanocomposite material (GNM). By applying different pressure forces onto the PDMS-based nanocomposite, changes in the optical transmittivity of the fiber can be detected in real time due to the coupling between the GNM and the tapered fiber region. The intensity reduction of a transmitted light is correlated to the pressure force magnitude. Light intensity is converted into an electric signal by a system suitable for robotic implementation. High sensitivity using forces by applying weights of a few grams is proved. Sensitivity on the order of 5 g is checked. A detailed algorithm for the detection of roughness and shapes by means of a robotic finger is proposed.

- by Svetlana Pavlova
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- Instrumentation, Optical Sensor, Magnetic Random Access Memory, Tactile Sensor

According to recent competition theory, the population dynamics of phytoplankton species in monoculture can be used to make a priori predictions of the dynamics and outcome of competition for light. The species with lowest ''critical light intensity'' should be the superior light competitor. To test this theory, we ran monoculture experiments and competition experiments with two green algae (Chlorella vulgaris and Scenedesmus protuberans) and two cyanobacteria (Aphanizomenon flos-aquae and a Microcystis strain) in light-limited continuous cultures. We used the monoculture experiments to estimate the critical light intensities of the species. Scenedesmus had by far the highest critical light intensity. The critical light intensities of Chlorella, Aphanizomenon, and Microcystis were rather similar. According to observation, Aphanizomenon had a slightly lower critical light intensity than Chlorella and Microcystis. However, according to a model fit to the monoculture experiments, Chlorella had a slightly lower critical light intensity than Microcystis, which in turn had a slightly lower critical light intensity than Aphanizomenon. These subtle differences between observed and fitted critical light intensities could be attributed to differences in the light absorption spectra of the species. The competition experiments were all consistent with the competitive ordering of the species according to the fitted critical light intensities: Chlorella displaced all three other species, Microcystis displaced both Aphanizomenon and Scenedesmus, and Aphanizomenon only displaced Scenedesmus. Not only the final outcomes, but also the time courses of competition predicted by the theory, were in excellent agreement with the experimental results for nearly all species combinations.

- by Franjo Weissing
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- Ecology, Green Algae, Light Intensity, Experimental Tests

The transmission light intensity method is carried out on a classical platform to study the reciprocity of Faraday effect in water-based Fe 3 O 4 ferrofluid and its diluents. Setting the polarization direction of the analyzer at an angle of 45 • to that of the polarizer, the switchable DC magnetic field and the alternating magnetic field are imposed to ferrofluid. The ferrofluid film is replaced by magneto-optical glass for contrastive experiments. The results indicate that ferrofluid is different with magneto-optical glass. Even though the direction of magnetic field is reversed, the rotation direction of the polarized light does not change for ferrofluid. The theoretical model of magneto-optical rotation was used to describe the origin of the reciprocity of Faraday effect in ferrofluid and the non-reciprocity in magneto-optical glass. These findings suggest that the magnetic moments of nanoparticles in ferrofluid tend to the same orientation with the magnetic field because of the rotation of particles.

- by shibin wang
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- Magnetic field, Ferrofluid, Optical physics, Reciprocity

The behavior of S. platensis was investigated in this study through fed-batch pulse-feeding cultures performed at different carbon dioxide feeding rates (F = 0.44-1.03 g L −1 d −1 ) and photosynthetic photon flux density (PPFD = 80-250 mol photons m −2 s −1 ) in a bench-scale helical photobioreactor. To achieve this purpose, an inorganic medium lacking the carbon source was enriched by gaseous carbon dioxide from a cylinder. The maximum cell concentration achieved was 12.8 g L −1 at PPFD = 166 mol photons m −2 s −1 and F = 0.44 g L −1 d −1 of CO 2 . At PPFD = 80 and 125 mol photons m −2 s −1 , the carbon utilization efficiency (CUE) reached maximum values of 50 and 69%, respectively, after about 20 days, and then it decreased, thus highlighting a photolimitation effect. At PPFD = 166 mol photons m −2 s −1 , CUE was ≥90% between 20 and 50 days. The photosynthetic efficiency reached its maximum value (9.4%) at PPFD = 125 mol photons m −2 s −1 . The photoinhibition threshold appeared to strongly depend on the feeding rate: at high PPFD, an increase in the amount of fed CO 2 delayed the inhibitory effect on biomass growth, whereas at low PPFD, excess CO 2 addition caused the microalga to stop growing.

A Monte Carlo calculation for light intensities scattered from a random Gaussiancorrelated surface is presented for the first time. It is shown that small randomness on a grating surface can considerably change the intensities and, in particular, -the surface polariton resonances. These results should be used to check perturbation-theory calculations.

- by Nicolás García
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- Light Scattering, Monte Carlo, Surface Roughness, Electromagnetic Waves

An alternative approach to quantification of the contribution of non-Q B -reducing centers to Chl a fluorescence induction curve is proposed. The experimental protocol consists of a far-red pre-illumination followed by a strong red pulse to determine the fluorescence rise kinetics. The far-red pre-illumination induces an increase in the initial fluorescence level (F 25 ls ) that saturates at low light intensities indicating that no light intensity-dependent accumulation of Q À A occurs. Far-red light-dose response curves for the F 25 ls -increase give no indication of superimposed period-4 oscillations. F 25 ls -dark-adaptation kinetics following a far-red pre-pulse, reveal two components: a faster one with a half-time of a few seconds and a slower component with a half-time of around 100 s. The faster phase is due to the non-Q B -reducing centers that re-open by recombination between Q À A and the S-states on the donor side. The slower phase is due to the recombination between Q À B and the donor side in active PS II reaction centers. The pre-illuminationinduced increase of the F 25 ls -level represents about 4-5% of the variable fluorescence for pea leaves ($2.5% equilibrium effect and 1.8-3.0% non-Q B -reducing centers). For the other plant species tested these values were very similar. The implications of these values will be discussed.

- by Gert Schansker
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- Kinetics, Photochemistry, Photosynthesis, Plant Biology

Light is one of the most important abiotic factors influencing the (skeletal) growth of scleractinian corals. Light stimulates coral growth by the process of light-enhanced calcification, which is mediated by zooxanthellar photosynthesis. However, the quantity of light that is available for daily coral growth is not only determined by light intensity (i.e. irradiance), but also by photoperiod (i.e. the light duration time). Understanding and optimizing conditions for coral growth is essential for sustainable coral aquaculture. Therefore, in this study, the question was explored whether more light (i.e. more photons), presented either as irradiance or as light duration, would result in more growth. A series of nine genetically identical coral colonies of Galaxea fascicularis L. were cultured for a period of 18 weeks at different light duration times 8 hours 150 mE m 22 s 21 :16 hours dark, 12 hours 150 mE m 22 s 21 :12 hours dark, 16 hours 150 mE m 22 s 21 :8 hours dark, 24 hours 150 mE m 22 s 21 :0 hours dark) and different irradiance levels (8 hours 150 mE m 22 s 21 :16 hours dark, 8 hours 225 mE m 22 s 21 :16 hours dark and 8 hours 300 mE m 22 s 21 :16 hours dark). Growth was determined every two weeks by measuring buoyant weight. Temperature, salinity and feeding levels were kept constant during the experiment. To detect possible acclimation of the corals to an increased light duration, rates of net photosynthesis and dark respiration were measured, hereby comparing coral colonies grown under an 8:16 hours light (150 mE m 22 s 21 ):dark cycle with corals grown under a 16:8 hours light (150 mE m 22 s 21 ):dark cycle. No increase in growth was detected with either increasing photoperiod or irradiance. Continuous lighting (24 hours 150 mE m 22 s 21 :0 hours dark) resulted in immediate bleaching and the corals died after 14

- by Miriam Schutter and +3
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- Genetics, Zoology, Photosynthesis, Plant Biology

The photosynthetic characteristics of four transgenic rice lines over-expressing rice NADP-malic enzyme (ME), and maize phosphoenolpyruvate carboxylase (PC), pyruvate,orthophosphate dikinase (PK), and PC+PK (CK) were investigated using outdoor-grown plants. Relative to untransformed wild-type (WT) rice, PC transgenic rice exhibited high PC activity (25-fold increase) and enhanced activity of carbonic anhydrase (more than two-fold increase), while the activity of ribulose-bisphosphate carboxylase/oxygenase (Rubisco) and its kinetic property were not significantly altered. The PC transgenic plants also showed a higher light intensity for saturation of photosynthesis, higher photosynthetic CO(2) uptake rate and carboxylation efficiency, and slightly reduced CO(2) compensation point. In addition, chlorophyll a fluorescence analysis indicates that PC transgenic plants are more tolerant to photo-oxidative stress, due to a higher capacity to quench excess light energy via photochemical and...

- by Maurice Ku
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- Kinetics, Photosynthesis, Plant Biology, Maize

Two calculation paths for estimating the particle size distribution (PSD) of a polymer latex from single-angle dynamic light scattering (DLS) measurements are evaluated on the basis of a numerical example. In the more common "double-step method," two calculation steps are applied, with the intermediate estimation of the particle light intensity distribution (PLID). In the "single-step method," the calculation is performed in one operation. From the specification of several PSDs, a mathematical model is used to produce the synthetic measurements. An iterative procedure was applied for determining the diameter range and the number of PSD points. The inversion operations were carried out using a regularization technique. For narrow distributions with diameters in the range 100-1000 nm, the PSD and the PLID are similar in shape, and both calculation paths produce similar results. For broad PSDs in the range 100-1000 nm, and for arbitrary PSDs in the range 10-100 nm (i.e., in the Rayleigh region), the single-step method proved preferable. C 2000 Academic Press

- by Jorge Vega
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- Engineering, Light Scattering, Sensitivity Analysis, Physical sciences
- by Russell Babcock
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- Biological Sciences, Environmental Sciences, Deep water, Light Intensity

The in uence of light intensity reduction on Spirulina platensis cultivation was investigated, using urea and KNO3 as nitrogen sources. The reduction of light intensity from 5 to 2 klux was studied both on the 9th and the 13th day of cultivation. Increases of up to 29% in the total chlorophyll production were observed for the cultivations with light intensity reduction, in comparison with the cultivations carried out at ÿxed light intensities. ?

- by Eliane Danesi
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- Engineering, Technology, Biomass, Spirulina platensis

The Voltage flicker, a phenomenon of annoying light intensity fluctuation, caused by rapid change in industrial and domestic load such as Electric Arc Furnaces (EAF), rolling mills, welding equipments and pumps operating periodically has been a major concern for supply utilities, electricity regulatory agencies and customers. Static Voltage Compensators (SVC's) and Static Synchronous Compensators (STATCOM) have been able to solve the voltage flicker problem by rapidly controlling the reactive power. But, the control of active power along with reactive power control helps to mitigate the voltage flicker problem more effectively. In this paper, voltage flicker mitigation of EAF with STATCOM along with Battery Energy Storage System (BESS) is presented and performance results of the system using PSCAD/EMTDC software are analyzed.

- by Vasudeo Virulkar
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- Power Quality, Reactive Power, Electric arc furnace, Energy Storage

Suspension cultures derived from Agrobacterium tumefaciens-transformed calli were established in Nerium oleander L. The presence of the bacterial T-DNA in the transformed calli was detected by the polymerase chain reaction as well as plant hormone autotrophy. The ability of the cultures to accumulate oleandrin was confirmed using high performance liquid chromatography. The effect of fungal elicitors prepared from Aspergillus niger and Rhizopus stolonifer, on oleandrin production was studied during the suspension cultures of N. oleander. A rapid induction and highest oleandrin production were obtained with 2 ml dry cell powder solution of A. niger-prepared elicitor (with the concentration of 10 g l−1). The oleandrin yield reached a maximum of 3.164 mg l−1 in 25-days upon employing A. niger elicitors. It was 8.8-fold higher than that of control cultures which reached a maximum of 0.35 mg l−1. When R. stolonifer elicitor was used for the same culture period, the maximum oleandrin concentration was 0.34 mg l−1. All the transformed cultures were grown in hormone-autotrophic MS medium supplemented with 30 g l−1 sucrose at 25 °C under diffuse fluorescent light providing 37.5 mmol−2 s−1 light intensity in 12 h photoperiods.

- by Amy Kamal
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- Production, Environmental Biotechnology, Cell Culture, Bacteria

Humans rarely confuse variations in light intensity, such as shadows, shading, light sources and specular reflections, from variations in material properties, such as albedo or pigment. This review explores the cues, or regularities in the visual world that evidence suggests vision exploits to discriminate light from material. These cues include luminance relations, figural relations, 3D-shape, depth, colour, texture, and motion. On the basis of an examination of the cues together with the behavioural evidence that they are used by vision, I propose a set of heuristics that may guide vision in the task of distinguishing between light and material. I argue that while there is evidence for the use of these heuristics, little is known about their relative importance and the manner in which they are combined in naturalistic situations where there are multiple cues as to what is light and what is material. Finally, I discuss two theoretical frameworks, the generic view principle and Bayesian estimation, that are beginning to help us understand the visual processes involved in distinguishing between light and material.

- by Frederick Kingdom
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- Psychophysics, Motion perception, Color Perception, Visual Processing

The simultaneous use of Fenton reagent and irradiation for the treatment of textile wastewaters generated during a hydrogen peroxide bleaching process is investigated. The experimental conditions tested during this study provide the simultaneous occurrence of Fenton, Fenton-like and photo-Fenton reactions. The batch experimental results are assessed in terms of total organic carbon reduction. Identification of some of the chemical constituents of the effluent was performed by means of GC-MS. Other pollution related features of the initial effluent-like COD and color were also measured. The main parameters that govern the complex reactive system, i.e., light intensity, temperature, pH, Fe(II) and H2O2 initial concentrations have been studied. Concentrations of Fe(II) between 0 and 400 ppm, and H2O2 between 0 and 10,000 ppm were used. Temperatures above 25 degrees C and up to 70 degrees C show a beneficial effect on organic load reduction. A set of experiments was conducted under diff...

- by MONTSERRAT GARRABOU PEREZ
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- Water, Photochemistry, Water Purification, Environmental Monitoring

Rhodobacter sphaeroides O.U. 001 is a purple non-sulfur bacterium which evolves hydrogen from the breakdown of organic acids under illumination and anaerobic conditions. In this study, the effect of light intensity, light wavelength and illumination protocol on the growth and hydrogen production of R. sphaeroides O.U. 001 was investigated in gas-tight glass photobioreactors with defined medium. The results showed that the rate of hydrogen production increased with increasing light intensity and reached saturation at around 270 W/m 2 . Also it was found that lack of infrared light (750-950 nm wavelength) decreased photoproduction of hydrogen by 39%. Another factor evaluated was the effect of different illumination protocols on the growth and hydrogen production. It was observed that illumination after inoculation stimulates hydrogen production, increases substrate conversion efficiency and hydrogen production rate; no hydrogen was produced during the dark periods. ᭧

- by Meral Yucel and +1
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- Engineering, Chemical Engineering, Rhodobacter sphaeroides, Hydrogen Energy

The theoretical framework of intensity-modulated photocurrent spectroscopy (IMPS) is extended to photoelectrode processes involving surface-bound intermediates, and the effects of charged intermediates on the steady state and periodic components of the potential drop across the semiconductor[electrolyte interface are analysed. The steady state concentration of charged intermediates alters the band bending and introduces a light intensity dependence into the normalised IMPS response. At the same time, fight-induced modulation of the concentration of the intermediate generates a periodic perturbation of the band bending and consequently of the surface recombination rate. The analysis also takes into aexount the charging current associated with the periodic component of the photoinduced band bending. It is shown that the experimental IMPS response can still be analysed using the phenomenological approach developed for one-step charge transfer reactions, and the relationships between the phenomenological and real rate constants are derived. Diagnostic criteria for different mechanisms are outlined. © 1997 Elsevier Science S.A.

- by David Fermín
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- Analytical Chemistry, Electroanalytical Chemistry, Electron Transfer, Steady state

Root exudates influence significantly physical, chemical and biological characteristics of rhizosphere soil. Their qualitative and quantitative composition is affected by environmental factors such as pH, soil type, oxygen status, light intensity, soil temperature, plant growth, nutrient availability and microorganisms. The aim of the present study was to assess the influence of growth substrate and plant age on the release of carboxylates from Lupinus albus L. and Brassica napus L.

- by Markus Puschenreiter
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- Soil, Plant Biology, Time-of-flight mass spectrometry, Plant Physiology

Blue light and red light can be used to improve the efficiency of photosynthesis and increase the production of extracellular polysaccharide. Growth and extracellular polysaccharide production by Porphyridium cruentum were measured as a function of light wavelength and intensity. Light quality was a key factor for controlling the growth and polysaccharide production. The growth rate of P. cruentum increased with enhanced of light intensity, however a light level beyond the saturation point inhibited the growth of microalgae. A chromatic spectrum of blue and red light was used to enhance the growth and extracellular polysaccharide production due to the characteristics of the photosynthetic process. Efficient light transfer was the most important parameters in optimizing the mass culture of the photosynthetic organism.

- by Stanley Barnett
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- Chemical Engineering, Production, Biochemical Engineering, Kinetics

The cultivation of photosynthetic microorganisms such as the microalga Spirulina platensis can provide an alternative source of food. The water in Mangueira Lagoon (Rio Grande do Sul state, southern Brazil) has several required nutrients for the growth of Spirulina and could be added to culture medium to reduce the cost of producing S. platensis. Although little studied, repeated batch cultivation is a very useful technique because it has a better cost-benefit ratio than other cultivation methods. In a series of runs, we studied the influence of cell concentration, renewal rate and strain on the specific growth rate and biomass productivity of S. platensis during repeated batch cultivation, the runs taking place in 2-l Erlenmeyer flasks for 2160 h at 30°C and a light intensity of 2500 lux under a 12 h photoperiod. The three factors studied had a significant (P < 0.05) effect on the results (specific growth rate and productivity). Using Zarrouk's medium, the highest specific growth rate (l X ) was 0.111 day )1 while the biomass productivity (P X ) was 0.0423 g l )1 day )1 , while Mangueira Lagoon water supplemented with 10% Zarrouk's medium gave l X = 0.113 day )1 and a productivity P X = 0.0467 g l )1 day )1 . These values were two to three times higher than the results obtained in batch cultivation, indicating that the repeated batch cultivation of S. platensis is attractive and convenient. for the study of photosynthetic organisms growing

- by chris yakymyshyn
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- Mechanical Engineering, Biofilms, Biosensors, Light Scattering

Synergism between k-carrageenan and locust bean gum (LBG) was studied using the photon transmission technique. Synergistic effects in these polymeric mixtures strongly affected the physical properties of the gel structure. The transmitted light intensities, I tr , versus temperature variations were investigated during the gelation and liquefaction processes. Slight synergistic peaks were detected in gel-sol and sol-gel transition temperatures for high k-carrageenan/LBG ratios (approx. 80/2). Moreover, apparent synergistic peaks were observed in gel-sol and sol-gel transition activation energies for the mixtures approximately with the ratios of 80/10.

- by Önder Pekcan
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- Activation Energy, Phase transition, Light Intensity, Food Sciences
- by Francesca Bosellini
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- Geology, Environmental Control, Facies, Light Intensity

The objective of this study was to create a predictive model to classify stars, galaxies, and quasars, along with comparing different classification models to find the superior one. I hypothesized that it was possible to successfully train a machine learning model to classify stars, galaxies, and quasars using astronomical data provided by the Sloan Digital Sky Survey (SDSS). A multinomial logistic regression model has been trained and tested. It had an accuracy of 0.87, a weighted average precision, recall, and an f-1 score of 0.87, and a cross-validation accuracy score of 0.8664. The next model, a decision tree, had an accuracy of 0.99, weighted average precision, recall, and an f-1 score of 0.99, a cross-validation accuracy score of 0.99, and a cross-validation accuracy score of 0.9858. The decision tree model had significantly superior performance compared to the logistic regression model and was a good fit and accurate classifier for stars, galaxies, and quasars, proving my hypothesis to be correct. The model from this study could be used as a reliable classification tool for a wide variety of astronomical purposes to accelerate the expansion of the sample sizes of stars, galaxies, and especially quasars.

- by Yulun Wu
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- Machine Learning, Classification (Machine Learning), Data Analysis, Astrophysics

Light-emitting diodes (LEDs) with various light wavelengths (red, yellow, green, blue and white) and various levels of light intensity (750, 1500 and 3000 mol m −2 s −1 ) are applied to study the effects of light sources on chlorophyll a (Chl) and phycocyanin (Phy) production of Spirulina platensis. Logistic rate equations are used to depict the kinetic behavior of algal growth and pigments formation under various light sources and intensities. According to the regression results, a red LED is the best for algae growth. On the other hand, yellow light gives the best specific Chl production rate with a light intensity of 750 or 1500 mol m −2 s −1 , and blue light yields the best specific pigments (for Chl and Phy) production rates at 3000 mol m −2 s −1 . From the model fitting results, it is found that, at a higher light intensity, a higher specific Chl production rate accompanied by a higher S. platensis biomass is obtained. However, as for Phy production, a higher biomass results in a lower specific Phy production rate. The only exception is the use of blue light, which shows a positive effect on both Chl and Phy production rates under a higher light intensity.

- by Yung-Chuan Liu
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- Chemical Engineering, Biochemical Engineering, Kinetics, Modeling

Photooxidation of triethylamine (TEA) in the presence of O2, N2, and H2O over titanium oxide (TiO2) was investigated using a flat plate reactor. TEA was photocatalytically oxidized to CO2 and some by-products on TiO2 thin film catalysts. The intrinsic oxidation rate of the reaction was determined and was dependent on TEA concentration, humidity level, and light intensity. Photocatalytic deactivation was observed in these reactions. Fourier transform infrared (FTIR) and temperature-programmed desorption with a mass spectrometer as a detector (TPD-MS) were used to characterize the surface of the catalyst and study the deactivation mechanism. FTIR and TPD-MS results suggest that accumulation of carboxylic acid species, –N–N=O, and some other carbonaceous species occurred during the reaction. These by-product species or intermediates were chemisorbed on the catalyst surface. They were stable under reaction conditions and might be responsible for deactivation of TiO2 by either poisoning the active sites directly or blocking the adsorption of TEA on the catalyst surface.

- by James D Freihaut
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- Chemical Engineering, Catalysis, Thin Film, Indoor air pollution

Key words: Red algae, ['orphyridium, photosynthesis, phycoerythrin, phycocyanin, sulfated Light utilization (tficiency was studied in two polysaccharides. species (~f the unicelhdar red algae, Porphyridium sp., a marine species, and R aerugineum, a fresh water species, having as their main accessory pigments phycoerythrin and phycocvanin, respectively. When ctdtivated under three photon flux densities o175 (hmg, 150 (mediztm) and 300 (high)/umole qlmnm m : ~-i, the growth rate for the two algae was one doubling per day under medium and high Fhototz ttllX but on,!v one doubling per ever)'. 2 days zmder tlze low photon flux. Under all photon fluxes the maximum cell concentration was higher for Porphyridium sp. than for P. aerugineum, and the total cell polysaccJlaride was higher for P. aerugineum than Jbr Porphyridium sp. In P. aerugineum cell polysaccharides increased with iHereasmg photon flux, but cell number remained a/mosl ('onsmnt. hz contrast, Porphyridium ,sp. responded to varying photon flux by changing cell ~oncemration, and the differences in cell poly-,saccharMes were much smaller at the different light bltensities. [he chlorophyll a content of P. aerugineum was much higher than that of Porphyridium ,Sl~. The ratio of phycobiliproteins to chlorophyll a was higJzer in Porphyridium sp., and the changes in this ratl,~ with increasing light intensifies were more marked in P. aerugineum. The photosynthetic rates tn general arid the differences in the rates between the hi,oh aJtd low photon flux were higher in Porphyridium sp. than in P. aerugineum. The dif-,fi'.renee.s in growth characteristics between the two algae seem to result from differences in light absorb,nee of the cultures resulting front the diffi, mnce, itz cellular pigment ratio attd concentration.

- by Zvy Dubinsky
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- Multidisciplinary, Light Intensity

This article deals with the synthesis of polydimethylsiloxanes (PDMSs) substituted with chain or end benzyl acrylate groups by the hydrosilation of appropriate hydro-siloxanes, followed by phase transfer catalysed reaction of chloromethylated aromatic groups with the sodium salt of acrylic acid. Dierential scanning photocalorimetry (DPC) was used to study the crosslinking behaviour of the mentioned functional PDMSs in the presence of dierent photoinitiators. The reaction rate, the ®nal conversion and the inhibition period characterizing the crosslinking were found to be dependent on reaction atmosphere, light intensity, nature and concentration of photoinitiator and on polymer functional groups content. Ó

We propose a novel and simplified method to fabricate complex 3-dimensional structures in SU-8 photoresist using maskless grayscale lithography. The proposed method uses a Digital Micro-mirror Device (DMD ® ) to modulate the light intensity across a single SU-8 photoresist layer. Top and back-side exposure are implemented in the fabrication of original structures such as cantilevers, covered channels with embedded features and arrays of microneedles. The fabrication of similar structures in SU-8 with other techniques often requires complex physical masks or the patterning of several stacked layers. The effects of critical process parameters such as software mask design, exposure and developing conditions on the quality of 3-D structures are discussed. A number of applications using bridges, cantilevers and micromixers fabricated using this methodology are explored.

- by Amritha Rammohan
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- Materials Engineering, Analytical Chemistry, Cantilevers, Dimensional

Samples from two coastal experimental ecosystems were incubated in vitro and sampled over 24 h. Production rates were measured by the 14C method, the O2 and CO, light-dark bottle methods, and the I80 method. 0, production in the... more

- by Gary Hitchcock
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- Earth Sciences, Limnology, Biological Sciences, Environmental Sciences