Electrochemical Gradient and Mitochondrial DNA in Living Cells

Working under low light conditions is of particular interest in machine vision applications such as night vision, tone-mapping techniques, low-light imaging, photography, and surveillance cameras. This work aims at investigating the perception of color at low light situations imposed by physical principles governing photon emission. The impact of the probabilistic nature of photon emission on our color perception becomes more significant at low light levels. In this regard, physical principles are leveraged to develop a framework to take into account the effects of low light level on color vision. Results of this study shows that the normalized spectral power distribution of light changes with light intensity and becomes more uncertain at low light situation as a result of which the uncertainty of color perception increases. Furthermore, a color patch at low light levels give rise to uncertain color measurements whose chromaticities form an elliptic shape inside the chromaticity diagram around the high intensity chromaticity of the color patch. The size of these ellipses is a function of the light intensity and the chromaticity of color patches however the orientation of the ellipses depends only on the patch chromaticity and not on the light level. Moreover, the results of this work indicate that the spectral composition of light is a determining factor in the size and orientation of the ellipses. The elliptic shape of measured samples is a result of the Poisson distribution governing photon emission together with the form of human cone spectral sensitivity functions and can partly explain the elliptic shape of MacAdam ellipses.

On the base of analyzing the dual-channel systems, a single-channel dual-band false color night imaging principium based on inter-frame compensation is proposed to realize originally dual-channel dual-band on single-channel system with a raster filter setting forward. Single channel double spectrum low light level system can receive stripe image included two spectrum information of low light level in single channel by stripe filter slice. On the aspect of the dual-band low light level images separation and compensation, the technique of spectrum separation and compensation reconstruction were researched, the stripe low light level images were obtained from the scenery actual imaging with the 'long' wave information and the 'short' wave information in turn. The sample block compensation method based on the correlation of the gray space and the inter-frame compensation methods were designed to compensate the split dual-band images. The simulation experimental study of the dual-band low light level image separation and the compensation technique were done, the results indicate that the above methods in the single channel dual-spectrum color low light level system have applied effectively, and have achieved the goal of the dual-band low light level image separation and the compensation.

On the basis of optoelectronic imaging technique, the imaging process of low light level (LLL) night vision system is analyzed. The characteristics of LLL image are discussed in aspects of imaging process and gray level distribution. A imaging modal of ICCD LLL imaging system and a mathematics model to convert daytime image to LLL image are constructed by using spectral integral. The imaging model is composed of scenery reflectance sub-system, atmosphere transmission sub-system and ICCD camera sub-system. Because every scenery has different spectral reflectivity, so do image segmentation first. After abstracting different scenery from daytime image and assigning them their corresponding spectral reflectivity, do integral calculations using the constructed imaging model. Thus the LLL image is generated after gray calculating and the scene simulation of LLL imaging system based on day image is implemented. The experiment results show that the constructed LLL imaging model is effective and the scene simulation is successful. The original daytime image and the generated LLL image are also presented in this paper.

Low light level (LLL) image communication has received more and more attentions in the night vision field along with the advance of the importance of image communication. LLL image compression technique is the key of LLL image wireless transmission. LLL image, which is different from the common visible light image, has its special characteristics. As still image compression, we propose in this paper a wavelet-based image compression algorithm suitable for LLL image. Because the information in the LLL image is significant, near lossless data compression is required. The LLL image is compressed based on improved EZW (Embedded Zerotree Wavelet) algorithm. We encode the lowest frequency subband data using DPCM (Differential Pulse Code Modulation). All the information in the lowest frequency is kept. Considering the HVS (Human Visual System) characteristics and the LLL image characteristics, we detect the edge contour in the high frequency subband image first using templet and then encode the high frequency subband data using EZW algorithm. And two guiding matrix is set to avoid redundant scanning and replicate encoding of significant wavelet coefficients in the above coding. The experiment results show that the decoded image quality is good and the encoding time is shorter than that of the original EZW algorithm.

Taking the LLL CCD TV system as the object of study, on the basis of analysing a LLL image and its noise characteristics in detail, the noise theoretical model of a LLL image is described in a unified fashion by the time and space domain stochastic process. The LLL image processing system is developed. With the direction of this theoretical model, two types of new LLL image noise processing techniques, the interframe comparison denoise method and the adaptive mode filter are put forward and taken to suppress the LLL image time-space domain noise. Finally, test and analysis evaluation on the original and processed images are carried out.

Effects of resource availability on the growth, Cd accumulation, and photosynthetic efficiency of three hyperaccumulator plant species

In this paper, on the base of analysis on low light level (LLL) image and infrared (IR) thermal image's characteristics, the researches on the processing and fusion on LLL and IR image has been done. The dual-channel image registration techniques of LLL and IR image are put forward, including digital real-time shift technique and dual-channel fusion stereoscopic color display technique. The color night vision information acquiring and processing system of LLL image (0.4 ~ 0.9nm) and infrared thermal image (8 ~ 14nm) is developed. The systematically experiments have been carried out and some good results have been obtained. This LLL and IR image fusion color night vision system can effectively increase the discovery and recognition probability of object from its background

Patterns of aboveground growth, branching, and leaf display were examined in saplings of Acer saccharum Marsh. (sugar maple) and Fagus grandifola Ehrh. (beech) to determine (1) the responses of aboveground growth rates to variation in forest light regimes and (2) the importance of branching and leaf display patterns to the ability of saplings of these two species to respond to changes in forest light regimes produced by canopy gaps. For both species, rate of height growth, lateral growth, and the production of new shoots in even the low gap light levels created by small canopy gaps (15—75 m2) were as much as an order of magnitude greater than growth rates of saplings beneath closed canopies. However, saplings of both species showed little response to further increases in gap light levels. The strong response of maple saplings to low gap light levels was correlated with an increased in sapling leaf area index and the efficiency of leaf display (measured as leaf area per unit length or surface area of branches). In beech, the more modest response to low light levels in small gaps and the higher growth rates than maple beneath a closed canopy were paralleled by a lack of significant increase in beech leaf area indices in small gaps and a higher efficiency of leaf display beneath a closed canopy than in small gaps. Thus, the magnitude of the response of these two species to small canopy gaps is correlated with their degree of plasticity in patterns of branching and leaf display. Both species can be considered small—gap specialists in the sense that their combinations of shade tolerance, growth responses, and canopy architecture make them particularly successful at exploiting small canopy gaps. However, the two species differ in their placement on a gradient in the degree to which woody plants respond to canopy disturbances.

Low light level surveillance cameras with significantly higher performance and reduced form factor, than present state of the art are critical for many commercial and military applications. Towards this end, a new approach to low light level cameras was successfully demonstrated. In a cooperative research and development effort between Scientific Imaging Technologies, Inc. of Beaverton, Ore., and Intevac EO Sensors of Palo Alto, Calif., back-illuminated, electron-bombarded CCD (EBCCD) sensors were designed and fabricated. Experiments demonstrated the EBCCD's sensitivity and contrast resolution superior to conventional intensified CCD (ICCD) approaches. Low light level signal to noise (STN) and contrast transfer function (CTF) data are presented. A model is derived that describes the performance of the EBCCD and the back-illuminated CCD relative to conventional approaches to nighttime imaging. A design and simulated performance of a video rate 2/3 inch, back-illuminated, electron-bombarded CCD currently under development for low light imaging applications is also described.

The use of low levels of visible or near infrared light for reducing pain, inflammation and edema, promoting healing of wounds, deeper tissues and nerves, and preventing cell death and tissue damage has been known for over forty years since the invention of lasers. Despite many reports of positive findings from experiments conducted in vitro, in animal models and in randomized controlled clinical trials, LLLT remains controversial in mainstream medicine. The biochemical mechanisms underlying the positive effects are incompletely understood, and the complexity of rationally choosing amongst a large number of illumination parameters such as wavelength, fluence, power density, pulse structure and treatment timing has led to the publication of a number of negative studies as well as many positive ones. A biphasic dose response has been frequently observed where low levels of light have a much better effect on stimulating and repairing tissues than higher levels of light. The so-called Arndt-Schulz curve is frequently used to describe this biphasic dose response. This review will cover the molecular and cellular mechanisms in LLLT, and describe some of our recent results in vitro and in vivo that provide scientific explanations for this biphasic dose response.

Low Light Level (LLL) TV cameras, based on the association between image intensifier (II) tubes and solid state image sensors (CCD), add to the extreme performance of electronic tubes, the large system flexibility offered by CCD sensors (video signal). Various combinations of image intensifier tubes and CCDs are investigated. First generation II/CCD appears suitable for many applications where the light level is not too low (> 10-5 lux on the photocathode), but very low light levels require second or third generation devices. Electron bombarded CCDs, not commercially available yet, gives promising results in laboratory experiments. Their very high gain (1,500 at 10 keV) and its very low fluctuations allow both counting and integrating detection modes. Cooled CCDs exhibit rather poor performance in TV mode but their high detectivity them very suitable for still picture imaging. An original application, with detectivity improved, has been carried out in a two-color LLL TV camera. This prototype is based on two 2nd generation II/CCD systems respectively sensitive to the visible and the near IR wavelength range. It takes advantage of the variation of the spectral reflection coefficient of materials to enhance the contrast by image coloration.

Reply: We are pleased to receive insightful comments on our work by Brown and coauthors. They raise several important methodology issues with respect to studies of pupil measurement that deserve further discussion and wider consideration. Brown and coauthors suggest that our study was intended to measure the pupil under dark-adapted conditions. This, however, was not our intent. We make a strict distinction between the dark-room conditions described in our study and true dark adaptation, which we reserve for the unique physiological state of rod-driven retinal sensitivity occurring after approximately 35 minutes of complete darkness in the normal eye.1 Brown and coauthors are rightly concerned that the time interval between the first flash exposure and subsequent measurements by the second examiner could have been insufficient for full pupil recovery. If the order of examiner was not randomized, this would lead to a sequence effect whereby the second examiner would measure a consistently smaller pupil size. They provide a plot of pupil size as a function of time in 2 eyes photographed using their recently published technique2 to illustrate this point. In our original publication, we reported that examiner order was arbitrary. In fact, 1 examiner was first in all but 2 cases. This provided an opportunity to test Brown and coauthors' hypothesis. Using a 2-way repeated measures analysis of variance (ANOVA) model, we compared the mean pupil size measured at each light level across examiners and also tested for an interaction between examiner and light level for the digital photographic method of measurement. If the concerns expressed by Brown and coauthors were a factor in our experiments, we would expect to find a significant interaction between these 2 variables. We found no interaction between light level and examiner (Figure 1; P=.09) and no difference between the 2 examiners in pupil size measurements (P=.20).Figure 1.: Mean measured pupil diameter by examiner as a function of light level for the photographic measurement method.Because any observed differences in pupil size could be due to examiner effects or sequence effects, we further explored their concern by testing for differences between examiners in mean pupil diameter with a 2-way ANOVA comparing light level across methods of measurement for each examiner sequence (examiner 1 then examiner 2; examiner 2 then examiner 1). We did not find a significant sequence effect on pupil size when we compared light levels by method interactions or method of measurement for either test sequence and show the comparison of pupil size by light level for each examiner (Figure 1). These findings should satisfy the concerns expressed by Brown and coauthors. Although the concern about an examiner sequence effect is valid and they identify a methodological weakness of our design, it did not influence our reported results. Brown and coauthors suggest that the time between photographs was not controlled or measured. Although we elected not to report these data, they were recorded and provide further evidence to allay their concerns. We show the difference between examiners for pupil diameter measurements as a function of time (Figure 2). The slope of this function was not significantly different than zero by linear regression (−0.018 mm/min; 95% confidence interval −0.050 to +0.014). The time between pupil measurements was 3.5 minutes at the medium light level (5 lux) and 4.3 minutes at the low light level (<0.63 lux).Figure 2.: Difference in measured pupil diameter between examiner 1 and examiner 2 as a function of the time difference between the 2 measurements. Number = 45 (×3 light levels); r 2 = 0.00, P = .98, Y = (0.130)X. The slope of this function was not statistically different than zero.A second hypothesis proposed by Brown and coauthors is that the variations observed in pupil size measurements with the Colvard pupillometer were possibly due to a prolonged tonic proximal accommodative response, and they suggest that we repeat our study with a randomized examiner order to address this issue. This raises another important concern of any pupil measurement study; namely, control of accommodation. The normal time course of pupil recovery from a convergent accommodative stimulus is seconds.3 Given that more than 2 minutes had passed between each examiner's measurements, the pupil should have had sufficient time to completely recover from an accommodative stimulus. We are grateful for the comments of Brown and coauthors and appreciate the opportunity to respond to their concerns. Michael Twa OD Melissa Bailey OD, PhD Mark Bullimore MCOptom, PhD John Hayes PhD

Effective sensory processing requires matching the gain of neural responses to the range of signals encountered. For rod vision, gain controls operate at light levels at which photons arrive rarely at individual rods, light levels too low to cause adaptation in rod phototransduction. Under these conditions, adaptation within a conserved pathway in mammalian retina maintains sensitivity as light levels change. To relate retinal signals to behavioral work on detection at low light levels, we measured how background light affects the gain and noise of primate ganglion cells. To determine where and how gain is controlled, we tracked rod-mediated signals across the mouse retina. These experiments led to three main conclusions: (1) the primary site of adaptation at low light levels is the synapse between rod bipolar and AII amacrine cells; (2) cellular noise after the gain control is nearly independent of background intensity; and (3) at low backgrounds, noise in the circuitry, rather than rod noise or fluctuations in arriving photons, limits ganglion cell sensitivity. This work provides physiological insights into the rich history of experiments characterizing how rod vision avoids saturation as light levels increase.

Guest Editorial: Shedding new light on the twilight zone

While many aspects of human vision at low light levels have been studied in great detail, motion perception has rarely been investigated so far. Here we address differential effects of light level on the perception of coherent motion, heading from radial flow, and biological motion. We determined detection thresholds under photopic, mesopic, and scotopic conditions. Results indicate that the perception of specific motion types differs in vulnerability to changes in light level. Thresholds for coherent motion and heading from radial flow increased monotonically from photopic to mesopic and scotopic light levels. We suppose that observed deficits are due to temporal pooling under rod-dominated vision. In contrast, detection thresholds for biological motion, which is distinguished by temporal dynamics and a specific spatial distribution of nearby signals, were exclusively elevated under mesopic conditions. Thresholds under scotopic conditions matched those under photopic conditions. Selective constraints under mesopic conditions might be explained by a detrimental interaction of rod and cone vision as well as by activity of different rod pathways. Findings suggest that very early retinal signal processing can have complex effects on the perception of different motion types, which is generally considered to rely on cortical areas.