Minimum Light Intensity Research Articles

基于可调谐半导体激光吸收光谱的开放光路气体传感器方法研究

Tunable diode laser absorption spectroscopy (TDLAS) is a new method to detect trace-gas qualitatively or quantificationally based on the scan characteristic of the diode laser to obtain the absorption spectroscopy in the characteristic absorption region. A time-sharing scanning open-path TDLAS system using two near infrared distributed feedback (DFB) tunable diode lasers is designed to detect CH4 and H2S in leakage of natural gas. A low-cost Fresnel lens is used in this system as receiving optics which receives the laser beam reflected by a solid corner cube reflector with a distance of up to about 60 m. High sensitivity is achieved by means of wavelength-modulation spectroscopy with second-harmonic detection. The minimum detection limits of 1.1 ppm·m for CH4 and 15 ppm·m for H2S are demonstrated with a total optical path of 120 m. The simulation monitoring experiment of nature gas leakage was carried out with this system. According to the receiving light efficiency of optical system and detectable minimum light intensity of detection, the detectable optical path of the system can achieve 1-2 km. The sensor is suitable for natural gas leakage monitoring application.

Elevated CO 2 changes the moderate shade tolerance of yellow birch seedlings

To demonstrate the existence of light thresholds in plant growth and to examine the effects of elevated CO 2 on the shade tolerance of a tree species an experiment consisting of a completely randomized design for a total of 96 yellow birch ( Betula alleghaniensis Britton) seedlings was conducted with 3 light levels (2.9% 7.7% 26.1% of full sunlight) × 2CO 2 levels (350 and 700±10 ppm) with 4 replications in a phytotron. The study proved that thresholds exist and they vary in different plant organs. In ambient CO 2 the thresholds were 13.3% 18.7% 15.0% 15.2% and 15.6% of full sunlight for stem leaf root total plant biomass and the averaged value respectively. In 700 ppm CO 2 the corresponding thresholds were 16.7% 21.3% 18.1% 21.7% and 19.5% for stem leaf root total plant biomass and the averaged value respectively. The lowest threshold in the stem is an indicator of the minimal light intensity for regular growth for seedlings of this species. Below this threshold light-stressful growth occurs. The result of a paired t-test indicated that the thresholds in elevated CO 2 were significantly higher than in ambient CO 2. This suggests that yellow birch will lose its moderate shade tolerance evolutionally becoming a shade-intolerant species and that it may become more difficult to naturally regenerate in the future.

SiO2 single layer for reduction of the standing wave effects in the interference lithography of deep photoresist structures on Si

We demonstrate that the use of a single SiO2 film, with thickness corresponding to one standing wave (SW) period allows the recording of deep photoresist structures on silicon substrates by laser interference, without use of any additional antireflecting coating. This condition corresponds just to the opposite thickness (half SW period) previously proposed for using the SiO2 films for phase-shifting the SW pattern. Theoretical and experimental results demonstrated that for the lithography of deep structures, the contrast of the SW pattern, the minimum light intensity of the SW pattern and the photoresist adhesion are the most important parameters of the process.

Clouds, shadows or twilight? Mayfly nymphs recognise the difference

Summary1. We examined the relative changes in light intensity that initiate night‐time locomotor activity changes in nymphs of the mayfly, Stenonema modestum (Heptageniidae). Tests were carried out in a laboratory stream to examine the hypothesis that nymphs increase their locomotion in response to the large and sustained reductions in relative light intensity that take place during twilight but not to short‐term daytime light fluctuations or a minimum light intensity threshold. Ambient light intensity was reduced over a range of values representative of evening twilight. Light was reduced over the same range of intensities either continuously or in discrete intervals while at the same time nymph activity on unglazed tile substrata was video recorded.2. Nymphs increased their locomotor activity during darkness in response to large, sustained relative light decreases, but not in response to short‐term, interrupted periods of light decrease. Nymphs did not recognise darkness unless an adequate light stimulus, such as large and sustained relative decrease in light intensity, had taken place.3. We show that nymphs perceive light change over time and respond only after a lengthy period of accumulation of light stimulus. The response is much lengthier than reported for other aquatic organisms and is highly adaptive to heterogeneous stream environments.

A Complementary Metal–Oxide–Semiconductor Image Sensor for On-Chip in Vitro and in Vivo Imaging of the Mouse Hippocampus

This paper describes the development of a complementary metal–oxide–semiconductor (CMOS) image sensor for in vitro and in vivo imaging of the hippocampus. The 176×144 pixel array image sensor is designed based on a modified three-transistor active pixel sensor circuit. Flexibility in readout for real-time imaging and wide dynamic range measurement is implemented using analog and digital output. A minimum light intensity detection level of 50 nW/cm2 has been measured using the image sensor. A novel packaging method is developed to enable both in vitro and in vivo imaging. In this method, a color filter is applied onto the image sensor that selectively blocks excitation light transmittance to below -44 dB. The packaged device thickness measuring 350 µm, limits tissue damage during invasive imaging. Using the device, static images of the mouse brain slice and real time imaging of the hippocampus of a mouse are successfully demonstrated for the first time.

Entrainment of the Human Circadian System by Light

The periodic light-dark cycle is the dominant environmental synchronizer used by humans to entrain to the geophysical 24-h day. Entrainment is a fundamental property of circadian systems by which the period of the internal clock (tau) is synchronized to the period of the entraining stimuli (T cycle). An important aspect of entrainment in humans is the maintenance of an appropriate phase relationship between the circadian system, the timing of sleep and wakefulness, and environmental time (a.k.a. the phase angle of entrainment) to maintain wakefulness throughout the day and consolidated sleep at night. In this article, we review these concepts and the methods for assessing circadian phase and period in humans, as well as discuss findings on the phase angle of entrainment in healthy adults. We review findings from studies that examine how the phase, intensity, duration, and spectral characteristics of light affect the response of the human biological clock and discuss studies on entrainment in humans, including recent studies of the minimum light intensity required for entrainment. We briefly review conditions and disorders in which failure of entrainment occurs. We provide an integrated perspective on circadian entrainment in humans with respect to recent advances in our knowledge of circadian period and of the effects of light on the biological clock in humans.

Flow visualization tools for image analysis of capillary networks.

Video recordings of red blood cell (RBC) flow through capillary networks contain a considerable amount of information pertaining to oxygen transport through the microcirculation. Image analysis of these video recordings has been widely used to determine RBC dynamics (velocity, lineal density and supply rate) and oxygenation (Brunner et al., 2000; Ellis et al., 1990, 1992; Ellsworth et al., 1987; Klyscz et al., 1997; Pries 1988). However, not all capillaries in a given field of view are suitable for image analysis. Typically, capillary segments that are relatively straight and in sharp focus, and exhibit flow of individual RBCs that are well separated by plasma gaps, are good candidates for analysis. We have developed several image processing tools to aid in the selection of such capillaries for analysis and to obtain quick overviews of RBC flow through the microcirculation. Burgess et al. (Microcirc. 2:75, 1995) and Burkell et al. (Annals Biomed. Eng. 24:1, 1996; J. Vasc. Res. 35:2, 1998) have previously introduced mean and variance images to aid in the selection of capillaries for analysis. We have extended their concept and developed similar two dimensional visualization techniques for studies of RBC flow through capillary networks. Five new methods of processing video data were developed. The minimum image highlights all capillaries containing RBCs in a given field of view. The maximum image identifies capillaries that exhibit high lineal density or stopped flow. The range image represents the difference between the maximum and minimum light intensity values that occur at a given pixel over a given time period, and helps to identify capillary segments that are in good focus and are perfused by RBCs and plasma. The difference image represents the cumulative sum of the square of differences in intensity values between consecutive frames and gives an indication of the frequency of passage of RBCs separated by plasma gaps. The transition image represents the number of times the intensity at a given pixel crosses a predefined threshold and indicates the number of RBCs (or trains of RBCs) that passes a given location during the observation period. The above flow visualization techniques are valuable tools to aid in the study of image focus, network geometry, RBC flow paths and dynamics, that can then be used in identifying capillaries for subsequent (separate) detailed analysis to provide quantitative information about RBC flow.

C4 grasses in boreal fens: their occurrence in relation to microsite characteristics.

C(4) plants are rare in cool climates, an ecological pattern attributable to their poor photosynthetic performance at low temperatures relative to C(3) species. However, some C(4) species are able to persist at high latitudes and high elevations, possibly due to the characteristics of the particular microsites they inhabit in these otherwise unfavourable environments. One such species is Muhlenbergia glomerata, which occurs above 60 degrees N in Canada and is found in the atypical C(4) habitat of boreal fens. In this study, we evaluate how microsite features affect the success of M. glomerata in boreal fens. We surveyed 19 populations across northern Ontario during the summers of 1999 and 2000. The ground coverage by woody vegetation was the most important parameter affecting the presence or absence of M. glomerata. Woody plants covered over 50% of the ground area in plots where M. glomerata is absent, but less than 20% where it is present. The minimum light intensity threshold for the presence of the C(4) species was about 32% of full-sunlight at plant height. Surprisingly, in boreal fens M. glomerata was largely restricted to the wetter moss hollows, rather than occurring on the dry hummocks where its greater water use efficiency might have been advantageous. Woody species dominated the hummocks, but were uncommon in the hollows. In these cool northern climates M. glomerata apparently persists because sufficient periods of temperatures favourable to C(4) photosynthesis occur, but this persistence likely requires some factor that suppresses the woody vegetation.

Influence of light intensity, spectrum and orientation on sea bass plasma and ocular melatonin.

Melatonin is involved in the transduction of light information and the photoperiodic control of many important physiological functions in fish. Although artificial photoperiods have been used to improve fish growth and manipulate reproduction, there is little information about the characteristics of light 'quality'. In this paper we describe the effects of a light pulse in the middle of the dark phase on plasma and ocular melatonin in European sea bass. We first determined the light intensity necessary to elicit a melatonin response using white light of varying intensities (0.6-600 mu W/cm(2), experiment 1). Secondly, we tested the effect of the light spectrum on melatonin production using three differently coloured lights (half-peak bandwidth=434-477, 498-575 and 610-687 nm for the blue, green and red lamp, respectively, experiment 2) and, finally, we determined the effect of light orientation (downwards directed versus upwards directed, experiment 3). The results show that the minimum light intensity needed to inhibit or stimulate melatonin levels in both plasma and the eye was 6.0 mu W/cm(2). A linear correlation was found between the logarithm of light intensity and the relative inhibition. In addition, the blue wavelength was more effective in decreasing melatonin levels in the former and increasing the levels in the latter. Nevertheless, red light at sufficient intensity proved effective at significantly suppressing circulating melatonin. Downwards light had a greater effect than upward-directed illumination in suppressing plasma melatonin. In conclusion, the results point to the importance of giving proper consideration to the characteristics of light, to adequately control melatonin production and its related physiological processes.

半導体エレクトロニクス ＳｉＧｅ‐ＢｉＣＭＯＳプロセスによるイメージセンサの試作

We have demonstrated an image sensor using SiGe BiCMOS fabrication process for detecting object illuminated by light in “eye-safe” band. The fabrication process is general 0.8μm 2-poly 2-metal SiGe BiCMOS process for RF application. SiGe-Si photodiodes and Si-SiGe-Si hetero-phototransistors as well as Si homojunction photodiodes and phototransistors have been fabricated and measured. The gain of the hetero-phototransistor was around 100. There was little difference between the sensitivity characteristics of SiGe and Si photodetectors. An image sensor with 32×32 pixels has been fabricated using a phototransistor as a detector, which of the base is made of SiGe layer. The dynamic range was 23dB and the minimum detectable light intensity was 10lux. We have successfully acquired images by using this image sensor. The future issues to use SiGe BiCMOS process for image sensors are discussed.

Light-induced pattern formation in the excitable Belousov–Zhabotinsky medium

Light has been known to suppress wave activity in the vast majority of studies of excitable photosensitive Belousov–Zhabotinsky (BZ) media. In this report, we uncover that light perturbation can induce pattern formation when the dynamics of the BZ system is close to a bifurcation point, though light causes an increase of bromide concentration. The minimal light intensity for initiating pattern formation increases rapidly while the system departs from the bifurcation point. Backfiring behavior was also observed when a global light perturbation was applied to propagating waves. This study was carried out with a three-variable Oregonator model, modified to describe photosensitivity.

Observation and Segmentation of Gray Images of Surface Cells in Open Cellular Ceramic Foams.

The surface cells of cellular ceramic foams are analyzed using an optical microscope. The cell density is so abundant that the cell structure can feature a high cell volume fraction, a high degree of interconnection to neighboring cells, variable cell sizes and a high roughness of cell boundaries. To segment these cell or other strut images, a novel image analysis procedure was designed. This includes an application of an algorithm of detecting local maximum regions of light intensity between cells in images and regarding them as strut regions, while the conventional segment operations can only recognize the global maximum or minimum light intensity regions with a threshold intensity value. Then, an effectiveness of the proposed method was compared with earlier typical methods by quantifying the various properties of the cells in each image. As the results, the proposed method shows a good availability in that this gives more efficient presentation of the tiny cells and their strut regions as well as a programmability and reproducibility. However, the improved boundary construction methods are required to enable the proposed method to become more effective.

Spectral sensitivity of larval and juvenile coral reef fishes: implications for feeding in a variable light environment

The spectral sensitivity of larval and juvenile stages of 3 species of coral reef fishes, Apogon compressus (Apogonidae), Pomacentrus amboinensis (Pomacentridae) and Premnas biaculeatus (Pomacentridae) has been investigated using feeding behaviour. Ontogenetic and taxonomic differences in spectral sensitivity were determined by establishing the minimum light intensity at which larvae and juveniles could strike prey at 12 restricted wavelength bands between 355 and 650 nm. Following construction of chromatic action spectra, the wavelength of maximum sensitivity (λmax) and the median wavelength (λP50) of the 3 species were found to be located close to 500 nm. All 3 species increased in sensitivity during growth, with A. compressus becoming the most sensitive prior to settlement. Ontogenetic shifts in spectral sensitivity towards longer wavelengths occurred in P. amboinensis and P. biaculeatus, but not in A. compressus. Spectral efficiency (wavelength-dependent efficiency of photon capture) was modelled for eutrophic and oligotrophic coral reef waters (Jerlov types Oceanic IA, Oceanic III and Coastal 1) at 2 different optical depths. Spectral efficiency was highest in the intermediate coral reef water type (JOIII) in all 3 larval fish taxa throughout early ontogeny, regardless of water depth. The results imply that the larvae would be able to feed across a broad spectrum of coral reef water types and depths.

Laser-Induced Temperature Distribution in Photo-Alignment of Azobenzene Liquid Crystalline Side Chain Polymers

A theoretical model has been worked out to describe a temperature field, which is established within a film of isotropic trans azobenzene liquid crystalline side chain (LCSC) polymers when a linearly polarized laser beam illuminates it, and contributes to the photo-induced alignment behavior of LCSC polymers at an ambient temperature below the glassy transition temperature (Tg). The distribution of the temperature field is analyzed and the mechanism that the mesogens align perpendicular to the electric vector of the light is discussed with this model. The minimum light intensity Ioff required to achieve the photo-induced phase transition of LCSC polymers at a certain temperature below Tg is calculated. A prediction of existence of an offset photo-alignment temperature Toff is made based on this theory model, while below this temperature no photo-induced phase transition can be observed when a light of certain intensity illuminates the sample.

In Vivo Visualization of the Neuromuscular Junction Before and After Autologous Nerve Transfer in the Rat

In vivo visualization of the neuromuscular junction with epifluorescence imaging techniques has become a successful method of observing the ongoing process of re-occupation by regenerating motor axons of former post-synaptic sites after nerve injury. By using a light-integrating video camera for digital documentation, all parts of the neuromuscular junction can be visualized, as detailed as when documented with high-speed film, but with a minimum light intensity to prevent damage of neural or muscular structures. Results from comparisons of pre- and post-synaptic staining indicate a non-reoccupation rate up to 37 percent at a 55-day interval after nerve transfer, and up to 34 percent at a 66-day postoperative interval. Morphologic findings suggest that these high non-reoccupation rates are caused jointly by intramuscular missprouting, an insufficient intramuscular guidance apparatus, and intramuscular microneuroma formation at the insufficient neuromuscular junction.

Interferences of dark coloured waters and wastewater on algae toxicity assessment

Samples of wastewater and natural waters yellow‐brown coloured probably due humic‐like‐substances were studied. Growth rates of the green algae Scenedesmus subspicatus in coloured samples as a function of different lighting were determined. Ranges of maximal algae growth rate, denominated as light saturation, were related with sample colour measured as absorbance at 436 nm. When darker industrial effluents and commercial humic substances solution (0.2 g . L‐1) were assessed, the minimal light intensity to reach the maximal algae growth rate in dark samples was 8000 lux using white universal light. These results are in disagreement with the minimal lighting of 6000 lux proposed for the algae growth inhibition test ‐ ISO 8692. Moreover, the possible interference of dark water samples on parameters used as endpoints, like chlorophyll a in vivo (fluorescence intensity λex = 435 nm, λem = 685 nm) and chlorophyll a in vitro (extraction with ethanol and measurement of absorbency at 665 nm) are discussed. The algae growth test results assaying dark coloured samples were greatly different as compared to the determination of chlorophyll a in vivo and in vitro as endpoints.

Preferences of Growing Fowls for Different Light Intensities in Relation to Age, Strain and Behaviour

AbstractThe preferences of broiler and layer strains of fowl for four different intensities of incandescent luminaire (6, 20, 60 and 200 lux; Osram, 60W, pearl) were tested at 2 and 6 weeks of age. With each strain, four replicates of 12 birds were each allowed to move freely between four compartments illuminated continuously at the different intensities for 6 days. The distribution of light intensities among the compartments was changed daily. After 2 days of conditioning, the birds’ location and behaviour were recorded once every 15min over 23h on each of the remaining 4 days. The other hour was devoted to changing light intensities and refilling the feeders and drinkers. Six, mutually exclusive behaviours were defined: resting, perching, feeding, drinking, litter-directed activity and locomotion.With both strains, most time was spent in the brightest (200 lux) environment at 2 weeks of age. but in the dimmest (6 lux) at 6 weeks. This apparent change in preference was associated only with the two behaviours which took up most time, resting and perching, whereas the highest intensity was consistently preferred for all other behaviours. Older birds thus preferred to be in dim light when they were relatively inactive.The finding that older birds prefer to spend much of their time in a light environment of < 10 lux intensity, depending on behaviour, is contrary to current recommendations that minimum light intensities for broilers and laying hens should be increased to as much as 20 lux. Some variation in the spatial or temporal distribution of ambient light intensity, to provide both dimly (< 10 lux) and brightly (eg > 50 lux) lit environments, might benefit the welfare of older poultry, although further work is needed to establish their optimal light environment.

Influence of Light, Relative Humidity, and Maturity of Populations on Discharge of Ascospores of Venturia inaequalis

ABSTRACT Ascospore release in 20 populations of Venturia inaequalis was generally suppressed in wind tunnel tests during darkness and simulated rain, but the following relieved this suppression: (i) exposure to low relative humidity during simulated rain and (ii) protracted incubation of leaf samples and the consequent senescence of the pathogen population. No counterpart to (i) was observed under orchard conditions. Although V. inaequalis also released a high percentage of ascospores during darkness in field studies under simulated rain late in the season of ascospore release, this phenomenon has not been reported for natural rain events. A threshold value of 0.5 muW/cm(2) at 725 nm was identified as the minimum stimulatory light intensity. Ascospore release increased with increasing light intensity from 0.5 to 5.2 muW/cm(2) at 725 nm. There was also an intrinsic increase in ascospore release as duration of rain increased. In orchards, the combined impact of both processes is probably responsible for a delay in reaching peak ascospore release at several hours after sunrise. Ascospore release during darkness will generally constitute a small proportion of the total available supply of primary inoculum. Significant ascospore release, and therefore infection periods, can be assumed to begin shortly after sunrise, when rain begins at night in orchards with low potential ascospore dose (PAD). A PAD level of 1,000 ascospores per m(2) of orchard floor per season is suggested as a threshold, above which the night-released ascospores should not be ignored.

Minimum light intensity required to suppress nocturnal melatonin concentration in human saliva

We set out to determine the minimum intensity of light able to suppress nocturnal melatonin levels as measured in normal human saliva. Five healthy male volunteers were exposed to light at different intensities (<10, 500, 1000, 2500, and 5000 lux) in a repeated measure design. Suppression of melatonin was dependent on both light intensity and duration of light exposure. Minimum intensities of light suppressing nocturnal melatonin levels were calculated as 393, 366, 339, and 285 lux for exposure durations of 30, 60, 90, and 120 min, respectively. Minimum effective intensity and duration of light exposure showed a linear inverse relationship. These results suggest that less intensity of light than previously reported suffices to suppress melatonin in humans, and that caution is required in interpreting studies using long exposure to dim light as a background condition.

Phototactic Behavior of Bemisia argentifolii (Homoptera: Aleyrodidae) Crawlers

First instars (crawlers) of Bemisia argentifolii Bellows & Perring were observed in the field and laboratory to move upward on plants, presumably in search of acceptable feeding sites. Laboratory experiments were conducted on a host plant and an artificial surface to determine if this movement was random, or a response to light (phototaxis) or gravity (geotaxis). Greenhouse-reared B. argentifolii crawlers were positively phototactic in experiments conducted on a host plant and on an artificial surface of black construction paper. Crawlers moved up or down the petiole of cheeseweed, Malva parviflora L., with equal facility, toward a light source placed either above or below the leaf blade. Response was always toward the light (positive phototaxis) and there was no response to gravity, either positive or negative. Crawlers placed on an artificial surface in a dark arena and presented with a point light source had a significant mean angular dispersion toward the light. Crawlers illuminated with uniform overhead lighting or kept in darkness moved about the arena at random. Crawlers maintained in darkness on cheeseweed and the artificial surface moved a significantly shorter distance from their origin than did those exposed to light. Such behavior suggests that some minimal light intensity may be necessary to stimulate crawler activity. The positive phototactic response may contribute to survival of B. argentifolii by enabling individuals eclosing from fall laid eggs, on leaves that become senescent during the winter, to find suitable leaves for development higher on the plant.