scholarly journals Adapting-bump model for eccentric cells of Limulus.

1980 ◽  
Vol 76 (5) ◽  
pp. 539-557 ◽  
Author(s):  
F Wong ◽  
B W Knight
Keyword(s):  
Light Intensity ◽  
Power Spectrum ◽  
Entire Range ◽  
Correlation Factor ◽  
Noise Model ◽  
Average Shape ◽  
Noise Data ◽  
Dim Light ◽  
Data Yield ◽  
Poisson Shot Noise

Light-evoked intracellular voltage noise records have been obtained from Limulus eccentric cells, from threshold light intensity to an intensity .10(5) times threshold. These data are analyzed in terms of a simple "adapting-bump" noise model. It is shown how the model yields a data reduction procedure that slightly generalizes the familiar use of Campbell's theorem for Poisson shot noise: the correlative effect of adaptation amends Campbell's theorem by a single multiplicative factor, which may be estimated directly from the power spectrum of the noise data. The model also permits direct estimation of the bump shape from the power spectrum. The bump shape estimated from noise at dim light is in excellent agreement with the average shape of bumps observed directly in the dark. The data yield a bump rate that is linear with light up through about 50 times threshold intensity but that falls short of linearity by a factor of 35 at the brightest light. The bump height decreases as the -0.4 power of light intensity across the entire range. Bump duration decreases by a factor of 2 across the entire range, and the adaptation correlation factor descends from unity to about one-third. The modest change of the adaptation correlation shows that naive application of Campbell's theorem to such data is adequate for rough estimation of the model's physiological parameters. This simple accounting for all the data gives support to the adapting-bump model.

scholarly journals Adapting bump model for ventral photoreceptors of Limulus.

1982 ◽  
Vol 79 (6) ◽  
pp. 1089-1113 ◽  
Author(s):  
F Wong ◽  
B W Knight ◽  
F A Dodge
Keyword(s):  
Light Intensity ◽  
Calcium Ions ◽  
Light Adaptation ◽  
Noise Model ◽  
Current Fluctuations ◽  
Major Mechanism ◽  
Bump Height ◽  
Noise Characteristics ◽  
Dim Light ◽  
Average Size

Light-evoked current fluctuations have been recorded from ventral photoreceptors of Limulus for light intensity from threshold up to 10(5) times threshold. These data are analyzed in terms of the adapting bump noise model, which postulates that (a) the response to light is a summation of bumps; and (b) the average size of bump decreases with light intensity, and this is the major mechanism of light adaptation. It is shown here that this model can account for the data well. Furthermore, the model provides a convenient framework to characterize, in terms of bump parameters, the effects of calcium ions, which are known to affect photoreceptor functions. From responses to very dim light, it is found that the average impulse response (average of a large number of responses to dim flashes) can be predicted from knowledge of both the noise characteristics under steady light and the dispersion of latencies of individual bumps. Over the range of light intensities studied, it is shown that (a) the bump rate increases in strict proportionality to light intensity, up to approximately 10(5) bumps per second; and (b) the bump height decreases approximately as the -0.7 power of light intensity; at rates greater than 10(5) bumps per second, the conductance change associated with the single bump seems to reach a minimum value of approximately 10(-11) reciprocal ohms; (c) from the lowest to the highest light intensity, the bump duration decreases approximately by a factor of 2, and the time scale of the dispersion of latencies of individual bumps decreases approximately by a factor of 3; (d) removal of calcium ions from the bath lengthens the latency process and causes an increase in bump height but appears to have no effect on either the bump rate or the bump duration.

Dim light vision of Squilla mantis L

1963 ◽  
Vol 205 (5) ◽  
pp. 927-940 ◽  
Author(s):  
H. Schiff
Keyword(s):  
Light Intensity ◽  
Mediterranean Sea ◽  
Environmental Conditions ◽  
Green Fluorescence ◽  
Fiber Analysis ◽  
Near Ultraviolet ◽  
Intensity Changes ◽  
Dim Light ◽  
Dim Light Vision ◽  
Shape And Size

The anatomy of the eye of Squilla mantis and the geometrical optics derived from it are briefly described. The shape and size of the electroretinogram (ERG) are dependent on a) position where it is picked up, b) the light intensity, and c) the change of intensity. Single-fiber analysis confirms the results obtained by the anatomy and the ERG of the eye. Frequency of response of a single secondary fiber to intensity changes of light is proportional to the derivate dI/dt ( I = intensity; t = time). The Squilla sees a moving object as the sum of the intensity changes caused by that object, varied in time and space. The eyes have a maximum of sensitivity for light of 535–555 mµ wavelength, and a second maximum in the near ultraviolet light, the latter partly seen as green fluorescence due to an eye pigment. Anatomy, physiology, and the environmental conditions have been combined to explain the vision of this animal, adapted to his life in the blue-violet twilight of the deeper Mediterranean sea.

Photostimulation of Japanese Quail by Dim Light Depends upon Photophase Contrast, not Light Intensity

1988 ◽  
Vol 38 (3) ◽  
pp. 536-543 ◽  
Author(s):  
W. E. Meyer ◽  
J. R. Millam ◽  
F. A. Bradley
Keyword(s):  
Light Intensity ◽  
Japanese Quail ◽  
Dim Light

Comparison of Measured Low-Frequency Engine Noise With Combustion and Jet Noise Predictions for a Turbofan Engine With an Internal Lobed Mixer Nozzle

2007 ◽  
Author(s):  
Lysbeth S. Lieber ◽  
Donald S. Weir
Keyword(s):  
Low Frequency ◽  
Jet Noise ◽  
Combustion Noise ◽  
Noise Model ◽  
Engine Noise ◽  
Turbofan Engine ◽  
Technology Program ◽  
Modeling Techniques ◽  
Noise Data ◽  
Static Conditions

This paper presents an examination of the low-frequency engine noise of a turbofan engine with an internal lobed mixer nozzle, and identifies the contributions of the combustion and exhaust jet component noise sources within the low frequency portion of the spectrum by applying recently developed modeling techniques. This investigation was performed as part of the NASA Quiet Aircraft Technology Program. Because the mixer reduces the total jet noise, the combustion noise source becomes a significant contributor. In addition, the character of the jet noise for the mixer nozzle is different from that for a single-stream or coannular nozzle. Although the internal mixer reduces the low-frequency shear-induced jet noise, it also produces an additional higher frequency contribution to the jet noise due to enhanced turbulence levels produced by the mixing process. Therefore, the modeling techniques that predict the low-frequency component source noise must capture sufficient physics of the noise generation process for the combustor and mixer nozzle to accurately represent the component spectral distributions. The improved modeling of component source noise for both combustor and jet sources was addressed as part of the NASA Quiet Aircraft Technology Program. This activity included development of a new narrowband combustion noise model, as well as the application of a recent jet noise model for nozzles with internal forced mixers. The noise data used in this study was taken during the NASA Engine Validation of Noise Reduction Concepts (EVNRC) Program. Both static and flight noise measurements were made at a range of power settings using the Honeywell TFE731-60 turbofan engine. The engine configuration of interest for this study employed a nozzle with an internal lobed mixer. Comparison of static and flight data with predictions from the combustion and jet noise models indicates that combustor noise has a significant contribution to lower-frequency engine noise (in the 400–1000 Hz range), particularly for flight conditions, where the jet noise is reduced due to flight effects, and also for lower power settings at static conditions. However, further calibration of the combustion and jet noise prediction techniques will be required, with isolated component noise data, before these models may be applied with certainty to model total engine noise in the low-frequency range.

scholarly journals A Directionally Sensitive Motion Detecting Neurone in the Brain of a Moth

1983 ◽  
Vol 102 (1) ◽  
pp. 253-271 ◽  
Author(s):  
F. Claire Rind
Keyword(s):  
Visual Field ◽  
Light Intensity ◽  
Bright Light ◽  
Firing Frequency ◽  
Large Area ◽  
Directional Response ◽  
Stimulus Movement ◽  
Two Factors ◽  
Dim Light ◽  
The Brain

1. In the moth, Manduca sexta, a pair of neurones, one on each side of the brain, were characterized morphologically and physiologically as descending interneurones, selective for horizontal motion over a large area of the moth's visual field. 2. Their cell bodies and dendritic processes are located in the protocerebrum of the brain. Their axons, 12–15 [μm diameter, project down the ipsilateral connective, branching profusely on the ipsilateral side of the suboesophageal, prothoracic and pterothoracic ganglia. 3. Each neurone responds to movement over either retina. Their preferred directions are from front to back across the ipsilateral eye and back to front over the contralateral one. Movement in the opposite direction supresses their usual ‘resting’ discharge. The neurones are particularly sensitive to movements within the frontal, ventral visual field. 4. Each neurone responds repeatedly, for up to 5 h, to a stimulus oscillating back and forth across the retinae. The response is not diminished during concurrent wing flapping. 5. An increase in the velocity of stimulus movement produces a proportional increase in firing frequency. For stripes of 2.5 cm wavelength and subtending 32° at the eye, the maximum response occurs at a velocity of 3cm/s which gives a contrast frequency of 1.2 Hz. 6. The latency of the neurone's response, measured from its axon as it enters the pterothoracic ganglion, depends on at least two factors: light intensity and the speed of stimulus movement. 7. The neurone gives a directional response to stripes of period 6–4° in bright light. The response falls to 16° in dim light. 8. At night, in dim light, the latency of response is much reduced and the threshold light intensity, necessary for a directional response, decreases by two orders of magnitude.

scholarly journals Light intensity regulates flower visitation in Neotropical nocturnal bees

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Rodolfo Liporoni ◽  
Guaraci Duran Cordeiro ◽  
Paulo Inácio Prado ◽  
Clemens Schlindwein ◽  
Eric James Warrant ◽  
...  
Keyword(s):  
Light Intensity ◽  
Strong Dependence ◽  
Foraging Activity ◽  
Know How ◽  
Minimum Light ◽  
Light Levels ◽  
Flower Visitation ◽  
Five Factors ◽  
Main Variable ◽  
Dim Light

Abstract The foraging activity of diurnal bees often relies on flower availability, light intensity and temperature. We do not know how nocturnal bees, which fly at night and twilight, cope with these factors, especially as light levels vary considerably from night to day and from night to night due to moon phase and cloud cover. Given that bee apposition compound eyes function at their limits in dim light, we expect a strong dependence of foraging activity on light intensity in nocturnal bees. Besides being limited by minimum light levels to forage, nocturnal bees should also avoid foraging at brighter intensities, which bring increased competition with other bees. We investigated how five factors (light intensity, flower availability, temperature, humidity, and wind) affect flower visitation by Neotropical nocturnal bees in cambuci (Campomanesia phaea, Myrtaceae). We counted visits per minute over 30 nights in 33 cambuci trees. Light intensity was the main variable explaining flower visitation of nocturnal bees, which peaked at intermediate light levels occurring 25 min before sunrise. The minimum light intensity threshold to visit flowers was 0.00024 cd/m2. Our results highlight the dependence of these nocturnal insects on adequate light levels to explore resources.

The klinokinetic behaviour of infective Trichonema larvae in light

Parasitology ◽  
1965 ◽  
Vol 55 (3) ◽  
pp. 579-582 ◽  
Author(s):  
N. A. Croll
Keyword(s):  
Light Intensity ◽  
Vertical Migration ◽  
Industrial Research ◽  
Imperial College ◽  
Field Station ◽  
Dim Light ◽  
Visible Wavelengths

Trichonema larvae are affected by light of visible wavelengths and there is a klinokinetic response to light intensity, the smallest rates of turning occurring in light of about 300 ft-c, and the rate of turning increasing with increased intensity (900 ft-c). In dim light the vertical migration of larval nematodes would be greatest, which explains in part the large recoveries from grass at dawn and dusk.I thank Professor O. W. Richards, F.R.S., for permission to work at the Imperial College Field Station, and Professor B. G. Peters for help and advice. The work was financed by the Department of Scientific and Industrial Research.

Cryopreservation of Sweetpotato Shoot Tips by Vitrification

HortScience ◽  
1997 ◽  
Vol 32 (3) ◽  
pp. 472B-472
Author(s):  
Joyce C. Pennycooke ◽  
Leigh E. Towill
Keyword(s):  
Light Intensity ◽  
Solid Medium ◽  
Dark Period ◽  
Aluminum Foil ◽  
Shoot Tips ◽  
Nodal Segments ◽  
Ms Medium ◽  
Endogenous Compounds ◽  
Dim Light

Cryopreservation offers the simplest and most economical way for the long-term conservation of germplasm and vitrification is the preferred method to accomplish this. Undefined endogenous compounds are produced during plant growth and shoot tip preculture conditions. These may influence “cryopreservability” and interact with cryoprotectants that are artificially added during the cryogenic protocol. We are beginning to examine these aspects to improve cryopreservation. Nodal segments of PI 296057 were propagated on a hormone-free modified Murashige and Skoog (MS) solid medium and were grown with 16 hr/8 hr photoperiod. Shoot tips were excised at 0, 3 or 10 hr in light after the dark period. Excised shoot tips were precultured in 0.06 M sucrose in MS for 24 hr and 0.3 M sucrose in MS for 24 hr and then treated with 0.4 M sucrose plus 2 M glycerol for 20 min or 1 hr before being dehydrated in PVS2 [30% (w/v) glycerol, 15% (w/v) ethylene glycol and 15% (w/v) dimethylsulfoxide in MS and 0.4 M sucrose[for 10, 16 or 26 min at 22°C. Shoot tips were placed on thin strips of aluminum foil, which were folded to enclose the shoot tips and then immersed in a liquid nitrogen (LN) slush. Rapid warming and dilution were achieved by transferring the foil strips from LN into 3 ml of 1.2 M sucrose at 22°C for 20 min. All cultures were incubated in darkness for 2 days then dim light for 3 days before transfer to the usual light intensity. Elimination of iron and nitrogen from MS medium in post thaw culture for 5 days increased the viability of LN-treated samples. Maximum survival after LN exposure was achieved with excision immediately after the dark photoperiod, cultured for 1 hr in 0.4 M sucrose plus 2 M glycerol and exposed for 16 min in 100% PVS2 at 22°C. Previously, Towill and Jarret (1992, Plant Cell Reports 11: 175–178) reported that surviving shoot tips developed callus and a variable percentage subsequently formed shoots. In this line all surviving shoot tips eventually formed shoots.

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