Effect Of Background Light Research Articles

Multi-messenger high-energy signatures of decaying dark matter and the effect of background light

The IceCube Neutrino Observatory at the South Pole has measured astrophysical neutrinos using through-going and starting events in the TeV to PeV energy range. The origin of these astrophysical neutrinos is still largely unresolved, and among their potential sources could be dark matter decay. Measurements of the astrophysical flux using muon neutrinos are in slight tension with starting event measurements. This tension is driven by an excess observed in the energy range of 40–200 TeV with respect to the through-going expectation. Previous works have considered the possibility that this excess may be due to heavy dark matter decay and have placed constraints using gamma-ray and neutrino data. However, these constraints are not without caveats, since they rely on the modeling of the astrophysical neutrino flux and the sources of gamma-ray emission. In this work, we derive background-agnostic galactic and extragalactic constraints on decaying dark matter by considering Tibet-ASγ data, Fermi-LAT diffuse data, and the IceCube high-energy starting event sample. For the gamma-ray limits, we investigate the uncertainties on secondary emission from electromagnetic cascades during propagation arising from the unknown intensity of the extragalactic background light. We find that such uncertainties amount to a variation of up to ∼ 55% in the gamma-ray limits derived with extragalactic data. Our results imply that a significant fraction of the astrophysical neutrino flux could be due to dark matter and that ruling it out depends on the assumptions on the gamma-ray and neutrino background. The latter depends on the yet unidentified sources.

Experimental investigation of chirped amplitude modulation heterodyne ghost imaging.

We have constructed a chirped amplitude modulation heterodyne ghost imaging (CAM-HGI) experimental system that demonstrates a robust ability against background light in experiments. In the experiments, the background light is simulated by irradiating a spatiotemporal random modulated light field onto the target. The effects of background light, modulation depth and modulation duration of the signal light source on CAM-HGI are investigated experimentally. The results show that the quality of CAM-HGI can be improved by increasing the modulation depth and the modulation duration of the signal light source, and more importantly, an image with a good signal-to-noise ratio (SNR) can be achieved even when the irradiation SNR is lower than -30 dB. This technique of CAM-HGI has an important application prospect for laser imaging in strong background light environments.

A study about effects of background light on the gain of Photomultiplier Tubes

Photomultiplier Tubes (PMT) are commonly used in air Cherenkov light detection in extensive air shower of cosmic rays. The Cherenkov telescopes usually work at clear and moonless nights, therefore it is susceptible to the background of stars in the sky; and with the Earth's rotation and revolution, the affection of background is different yet. In this case, we conducted an experiment to evaluate the impacts of night-sky background (NSB) to the gain of PMTs. By optimizing the voltage divider of PMT, the influence brought by NSB on the gain of PMT can be decreased.

Performance analysis of ghost imaging lidar in background light environment

The effect of background light on the imaging quality of three typical ghost imaging (GI) lidar systems (namely narrow pulsed GI lidar, heterodyne GI lidar, and pulse-compression GI lidar via coherent detection) is investigated. By computing the signal-to-noise ratio (SNR) of fluctuation-correlation GI, our analytical results, which are backed up by numerical simulations, demonstrate that pulse-compression GI lidar via coherent detection has the strongest capacity against background light, whereas the reconstruction quality of narrow pulsed GI lidar is the most vulnerable to background light. The relationship between the peak SNR of the reconstruction image and σ (namely, the signal power to background power ratio) for the three GI lidar systems is also presented, and the results accord with the curve of SNR-σ.

Noninvasive monitoring with strongly absorbed light

The transmission of light through tissue is used in noninvasive monitoring, in particular photoplethysmography. Investigations involving the transmission of wavelengths absorbed by bilirubin (short wavelength visible light) have been limited, due to strong absorption by haemoglobin. Achieving transmission of these wavelengths through tissue may advance noninvasive monitoring of substances like bilirubin. This work investigates the use of high power light sources together with improvements in signal-to-noise ratio as a means of enabling the transmission of strongly absorbed light through tissue. A custom device using multiple high-power short-wavelength visible light sources together with low power red and infrared sources, and background light cancellation to improve signal-to-noise ratio, was constructed. Transmission of 454-1200 nm light through tissue was achieved, with pulsations present in measured signals. The transmission through tissue of multiple wavelengths of strongly absorbed light can be achieved by using high power light sources in conjunction with cancelling the effect of background light. Use of these techniques may allow investigations into the noninvasive monitoring of substances such as bilirubin using photoplethysmography.

Vehicle-To-Vehicle Data Broadcasting Through Visible Light Communication

Visible Light Communication (VLC) is a fast-growing technology to provide data communication using low-cost through LED-LASER and photodiodes. Which the transmitter and receiver of visible light communication have been designed and realized. In the experiment, the illumination of the receiving surface in different distance between LED-LASER and photodiode receiver has been tested, and the effect of background light has been considered, data transmit bit rate can be achieved at 111.607 kbit/s when the average illumination is 40 lx, with the communication distance of our visible light system at 1.1Cm to 1.5 Km. We first develop a custom V3LC (vehicle-to vehicle visible light communication)research platform using Microcontroller (Arduino interface)on which we experimentally evaluate the feasibility of a V3LC system under working conditions in relation to link resilience to visible light noise and interference. Our experiments show that a receiver's narrow field-of-view angle makes V3LC resilient to visible light noise from sunlight and legacy lighting sources as well as to interference from active VLC transmitters. Our main objective keys findings include: (i) in dense vehicular traffic conditions (e.g., urban highway during peak hours), of packet collisions; (ii) traffic blockage control. In this paper our main motto have to design low cost communication device which have high range and high accuracy so that we outline same basic design of transmission and receiver through microcontroller arduino mega board . Finally, evaluation of our prototype provides evidence that the system can indeed detect potential risks in advance and provide early warnings to the driver in real-world scenarios, lowering the probability of traffic accidents. Keywords: Broadcasting, VVLC, Arduino, Control design, Filter.

Experimental study on visible light communication based on LED

A visible light communication system using white light emitting diode (LED) has been proposed and demonstrated, in which the transmitter and receiver of visible light communication have been designed and realized. In the experiment, the illumination of the receiving surface in different distance between LED and photodiode receiver has been tested, and the effect of background light has been considered. The experiment results show that the data transmit bit rate can be achieved at 111.607 kbit/s when the average indoor illumination is 40 lx, with the communication distance of our visible light system at 1.5 m.

Interactions of dark solitons in photovoltaic photorefractive crystals with diffusion nonlinearity

We investigate the interaction of spatial dark optical soliton pair in open-circuit photovoltaic photorefractive crystals by considering the effect of background light and diffusion nonlinearity. We show that the spatial dark solitons repel each other and travel along different trajectories for the coherent interactions that one undergoes reflection and the other one deflects significantly when they are closely overlapped, and the dark solitons attract and deflect simultaneously along a parabolic trajectory for the case of incoherent interactions. The deflection distance depends on the intensities and the initial separation between the dark solitons.

Self-deflection of partially spatially incoherent beams and solitons in photovoltaic photorefractive crystals

By considering the effect of background light and diffusion, the self-deflection process of partially spatially incoherent (PSIC) beams and photovoltaic (PV) solitons in open-circuit PV photorefractive crystals has been investigated by employing numerical method and the perturbation technique, respectively. The results from the two approaches are in good agreement: the center of PSIC PV solitons moves on a parabolic trajectory, which is similar to those of coherent solitons. In addition, we also discuss that the dependence of self-deflection effect on the coherent parameter θ 0 and find it is slight relative to θ 0 for quasi-soliton but decreases monotonously with θ 0 for PSIC beam.

Effect of intense background radiation on the sensitivity of a laser receiver with an iodine active quantum filter

The effect of background light on the sensitivity of a laser receiver with an iodine active quantum filter (λ=1.315 μm) was theoretically and experimentally investigated. Upon the reception of a 40-ns pulsed signal against the background of 2.5-fold attenuated radiation of a pulsed light source with a brightness temperature of 4 × 104 K, the sensitivity of this receiver for a signal-to-noise ratio of three and a diffraction-limited acceptance angle was experimentally shown to be equal to 20 photons, which exceeds the quantum limit by about a factor of two. This is consistent with the results of theoretical treatment and suggests that upon the detection of optical signals against the background of the solar disk, the sensitivity of this receiver should decrease by only 12%. This receiver was compared with a receiver employing a photomultiplier of the visible range. Upon the reception of optical signals with the same parameters against the background of the solar disk and an interference filter with a transmission band width of 5 nm, the sensitivity of a receiver equipped with an FEU-115 photomultiplier was shown to be equal to about 1400 photons for a signal-to-noise ratio of three.

Background adaptation in a rat model of retinopathy of prematurity.

Low dark-adapted, scotopic retinal and visual sensitivity in retinopathy of prematurity (ROP) could be due to disease of the inner retina, or the recently described rod photoreceptor abnormalities. Receptoral disease decreases catch of quanta from both test flashes and steady background lights; increment threshold functions are shifted up and right. In diseases with normal receptors but low retinal sensitivity due to abnormal post receptoral processing, the increment threshold functions are shifted up with no horizontal translation. Herein we test the hypothesis that the rod photoreceptors are the site of ROP disease which causes low dark adapted b-wave sensitivity. The effect of steady background light on the ERG b-wave in a rat model of ROP is studied. ERG stimulus/response functions were obtained using full-field stimuli in the dark-adapted state, and in the presence of a steady background light. In each adaptation condition, log sigma, the test flash intensity that produced a half-maximum b-wave amplitude, was calculated. In pilot experiments, the background light selected had raised log sigma about a log unit in controls. In dark-adapted ROP rats log sigma was significantly higher, 0.35 log unit, than in controls. In the presence of the background light, log sigma in ROP and control rats did not differ significantly indicating a relative shift, up and right, of the increment sensitivity function for the less sensitive ROP rats. The effect of the background light is consistent with receptoral disease causing low dark adapted b-wave sensitivity in ROP rats.

Trichromatic opponent color classification

Stimuli varying in intensity and chromaticity, presented on numerous backgrounds, were classified into red/green, blue/yellow and white/black opponent color categories. These measurements revealed the shapes of the boundaries that separate opponent colors in three-dimensional color space. Opponent color classification boundaries were generally not planar, but their shapes could be summarized by a piecewise linear model in which increment and decrement color signals are combined with different weights at two stages to produce opponent color sensations. The effect of background light on classification was largely explained by separate gain changes in increment and decrement cone signals.

Does rod phototransduction involve the delayed transition of activated rhodopsin to a second, more active catalytic state?

Recovery kinetics of the saturating photocurrent response in amphibian rods suggest regulation of the visual signal by a first-order deactivation reaction with an exponential time constant (tau(c)) of about 2 s. The original hypothesis that tau(c) represents the lifetime of activated rhodopsin (R*) in a single-step deactivation appears at odds with several recent findings, for example, that Ca2+, a known regulator of the enzymatic phosphorylation of R*, does not regulate the value of tau(c). A recently proposed alternative hypothesis, that tau(c) is the lifetime of activated transducin and that the R* lifetime is relatively short (approximately 0.4 s), appears consistent with the Ca2+ data but is difficult to reconcile with a high specific catalytic activity of R*. The present theoretical study proposes a rate-equation model of R* activation and deactivation in amphibian rods that is generally consistent with observed properties of the tau(c)-associated reaction and the action of Ca2+ as well as with the stereotyped nature of the single-photon response. The model is developed by considering the effect of background light on a time-dependent variable, R*eff, defined as the effective total level of R* activity. Central starting assumptions are that Ca2+ reduction mediates the effect of background light on R*eff(t) and that background desensitization of the photocurrent flash response derives from this action of Ca2+. Construction of the model is guided by criteria based on previous experimental findings. Among these are the approximate constancy of background desensitization expressed at near-peak and later times in the flash response, and the large (approximately 10-fold) dynamic range of this desensitization. The proposed model hypothesizes that an event regulated by Ca2+ feedback causes activated rhodopsin to become susceptible to a two-phase, stochastic deactivation process, the second phase of which is characterized by tau(c). A central prediction of the model is the regulated transition of flash-activated R* to "R**", a state exhibiting greatly increased catalytic activity.

All Solid-State Instrument for Absorbance Based Optical Gas Sensor Membranes

The compact instrument is based on a light-emitting diode as radiation source and a photodiode as detector. A fiber optic cable is used for guiding the light to and from the membrane located at the tip. In contrast to earlier designs, the small sensor head is freely accessible to ambient atmospheres. The resulting effect of background light is removed by lock-in amplification using a single integrated circuit synchronous demodulator. Ratioing against a reference signal is carried out in order to eliminate instabilities of light-emitting diodes caused by temperature fluctuations or ageing. The system is demonstrated with membranes for the sensing of ammonia and carbon dioxide in the vapour phase.

THE SENSORY PHOTORECEPTORS OF Halobacterium halobium REVISITED: ACTION SPECTRA and INFLUENCE OF BACKGROUND LIGHT*

Abstract– Action spectra of the light‐dependent behavior of Halobacterium and the effect of background light have been measured with regard to the current hypothesis of Spudich and Bogomolni [Nature312,509–513 (1984)], which proposes sensory rhodopsin I (sRI587) to be the receptor for long‐wavelength light, and its photoproduct S373 to be the receptor for UV light. The action spectrum shows three maxima for attractant responses (prolonged swimming intervals) at 565, 590, and 610 nm, and two maxima for repellent responses (shortened intervals) at 370 and 480 nm. The latter is assigned to sensory rhodopsin II (P‐480). All peaks are red‐shifted after substitution of the endogeneous retinal by 3, 4‐dehydroretinal. The peaks at 590 and 610 nm are suppressed by long‐wavelength background light. Ultraviolet background light converts all attractant peaks into repellent peaks. The response at 370 nm is strongly activated by visible background light, the maximal effect occurring with 510 nm. The activated state declines with a half‐life of about 1.2 s. In a growing culture, full sensitivity to UV and blue light is restored about 10 h earlier than sensitivity to long‐wavelength light. Some of the results cannot easily be explained by the sRI587/S373 hypothesis. Explanations for the three maxima in the long‐wavelength range and for the maximal activation of the UV response by 510 nm light are discussed.

An experimental study of a metal-oxide-semiconductor photomultiplier

An investigation of the solid-state metal-oxide-semiconductor photomultiplier (MOSPM) has been performed. A semiquantitative description is given of the MOSPM and associated device physics. Experimental results are presented and interpreted, including the electrical response in the dark, the optical response, the dependence on applied voltage ramp rate, the dependence on light-pulse rise-time, and the effects of background light and optical intensity. An experimental comparison of the MOSPM with a GaAs photomultiplier tube (PMT) is also made. In terms of responsivity, the present MOSPM is equivalent to that for the PMT operated at 1300 V. However, the noise for the MOSPM under the present operating conditions is three orders of magnitude larger than that for the PMT. Methods for significantly reducing the noise are discussed. The MOSPM appears to have potential for utilization in the detection of low-intensity, fast-rise time light pulses.

Effects of calcium channel blockers and DCMU on motility and the photophobic response of Gyrodinium dorsum

The effects of the calcium channel blockers, verapamil, diltiazem and lanthanum ions and the Ca2+ dependency on motility as well as the photophobic response (stop-response) of Gyrodinium dorsum were studied. At Ca2+ concentrations below 10-3 M, motility was inhibited. La3+ inhibits the stop-response, in contrast to verapamil and diltiazem. The only calcium channel blocker that increased the amount of non-motile cells was verapamil. The results indicate that motility are Ca2+ dependent and that the stop-responses of G. dorsum could be affected by extracellular Ca2+. Effects of the photosythesis inhibitor (DCMU) on the stop-response was also determined. With background light of different wavelength (614, 658 and 686 nm) the stop-response increased. DCMU inhibited this effect of background light. Negative results with the monoclonal antibody Pea-25 directed to phytochrome and the results with DCMU, indicate that the stop-response of G. dorsum is coupled to photosynthesis rather than to a phytochrome-like pigment. Oxygen evolution, but not cell movement, was completely inhibited by 10-6 M DCMU.

Adapting lights and lowered extracellular free calcium desensitize toad photoreceptors by differing mechanisms.

Extracellular recordings were made across the outer segment layer of isolated, superfused toad retinas. Under these recording conditions, the photovoltage reflects primarily the current flowing through the outer-segment membrane of red rods. In normal toad Ringer solution, a dim conditioning flash desensitized a test flash response. The desensitization reached a peak 1.8-2.0 s after the conditioning flash and then declined approximately as an exponential with time constant 6 s. Lowered extracellular calcium, [Ca2+]o, desensitized the photoresponse. It required approximately ten times more light to reach a half-maximal response for each ten-fold change in [Ca2+]o from 10(-6) to 10(-9) M. When [Ca2+]o was less than 10(-7) M, substitution of Li+ for Na+ as the predominant monovalent cation in the superfusate permitted responses to continue and a resensitization of up to approximately 1 log unit was observed. The effects of lowered [Ca2+]o on response kinetics were markedly different from the effects of background lights producing a comparable desensitization. Low [Ca2+]o increased absolute latency and time-to-peak of the flash response. Background lights decreased time-to-peak, leaving latency unchanged. The effects of background lights and lowered [Ca2+]o are not additive. Moderate backgrounds had little effect on the intensity/response function in low [Ca2+]o. Conditioning flashes facilitated the test flash response in 10(-7) M-[Ca2+]o superfusate. These results can be understood in terms of the Ca2+ hypothesis of transduction (Hagins & Yoshikami, 1974) if it is assumed that lowered [Ca2+]o exposes an endogenous Ca2+ buffer. The data also provide evidence for a role of Na+/Ca2+ exchange in regulating intracellular Ca2+ concentration in the toad photoreceptor. A quantitative model based on these assumptions is derived and compared with the experimental data.

The effects of low calcium and background light on the sensitivity of toad rods.

1. We have examined the effects of decreases in extracellular Ca(2+) concentration on the intracellularly recorded light responses of rods from the toad, Bufo marinus. In agreement with previous results (Brown & Pinto, 1974; Lipton, Ostroy & Dowling, 1977), Ca(2+) concentrations below 10(-6) M produced a depolarization of rod resting membrane potential of approximately 30-40 mV and a corresponding increase in the maximum amplitude of the rod's light responses, so that saturating flashes in normal and low Ca(2+) Ringer produced hyperpolarizations to approximately the same membrane potential.2. The rod's sensitivity was reduced in low Ca(2+) Ringer by an amount dependent upon the extracellular Ca(2+) concentration. At 10(-6) M-Ca(2+), sensitivity was approximately 0.6 log units below normal. Thereafter, it dropped nearly linearly with [Ca(2+)](o) to a value approximately 4.0 log units below normal at 10(-9) M-Ca(2+). Most of the decline occurred within 1-2 min after the solution change as the membrane potential depolarized, but sensitivity continued to fall slowly with time at the lowest Ca(2+) concentrations. Exposure to low Ca(2+) solutions altered the kinetics of the receptor response to brief flashes, delaying response onset and time-to-peak but affecting the time course of decay very little.3. The sensitivity of the rod to maintained steps of light was also reduced in low Ca(2+). Furthermore, the changes in sensitivity produced by background illumination were very much smaller in low Ca(2+) than in normal Ringer. In some cases backgrounds actually increased sensitivity.4. In 10(-8) M-Ca(2+), backgrounds which themselves produced no response in the rod and no changes in rod sensitivity produced large decreases in response latency for responses of all amplitudes, and pronounced changes in time-to-peak and time-to-decay for moderate and large amplitude responses.5. Since the effects of background light and low Ca(2+) on the wave form of the rod are distinct and in some cases antagonistic, and since the changes in receptor sensitivity produced by backgrounds and low Ca(2+) are not additive, the decreases in sensitivity produced by exposure to low Ca(2+) appear to be caused by a mechanism distinct from normal light adaptation. We suggest that they are caused by an increase in the buffering capacity of the receptor cytosol for Ca(2+) and that Ca(2+) is the excitatory messenger or ;internal transmitter', as originally suggested by Yoshikami & Hagins (1971).

Cathode-ray-tube actuator in a noncontact analogue tachometer

The paper describes an electro-optical method for noncontact measurement of instantaneous angular velocity of a shaft. The tachometer employs a standard cathode-ray tube as a voltage to light-spot position actuator, a black-white contrast edge on a diameter of the shaft end, and a photomultiplier light detector. The light spot is projected onto the shaft end and switched rapidly along the contrast edge about the shaft centre. Any detector output (at the switching frequency) is amplified, and by using a sampling function circle generator, the system is able to position the light-spot so as to minimise the detector output. Thus, this closed-loop system operates to maintain the light-spot on the contrast edge and the input to the circle generator is the tachometer output. The instrument must be focused on the shaft end; no special calibration is required and the light spot readily locks onto a rotating contrast edge. An experimental instrument has been used on shafts down to 3 mm in diameter, which has a range of at least 20000 rev/min in either direction, a bandwidth of about 1 kHz with a resolution of about 400rev/min limited by noise, owing to the effect of background light on the photomultiplier. Greater resolution may be obtained at the expense of bandwidth.