scholarly journals Nonlinearity and noise at the rod—rod bipolar cell synapse

2010 ◽  
Vol 28 (1) ◽  
pp. 61-68 ◽  
Author(s):  
E. BRADY TREXLER ◽  
ALEXANDER R.R. CASTI ◽  
YU ZHANG
Keyword(s):  
Quantum Efficiency ◽  
Single Photon ◽  
Signal To Noise Ratio ◽  
Discrete Events ◽  
Amplitude Noise ◽  
Synaptic Noise ◽  
Suction Electrode ◽  
Suppression Mechanism ◽  
Low Amplitude ◽  
Cell Synapse

AbstractIn the retina, rod bipolar (RBP) cells synapse with many rods, and suppression of rod outer segment and synaptic noise is necessary for their detection of rod single-photon responses (SPRs). Depending on the rods’ signal-to-noise ratio (SNR), the suppression mechanism will likely eliminate some SPRs as well, resulting in decreased quantum efficiency. We examined this synapse in rabbit, where 100 rods converge onto each RBP. Suction electrode recordings showed that rabbit rod SPRs were difficult to distinguish from noise (independent SNR estimates were 2.3 and 2.8). Nonlinear transmission from rods to RBPs improved response detection (SNR = 8.7), but a large portion of the rod SPRs was discarded. For the dimmest flashes, the loss approached 90%. Despite the high rejection ratio, noise of two distinct types was apparent in the RBP traces: low-amplitude rumblings and discrete events that resembled the SPR. The SPR-like event frequency suggests that they result from thermal isomerizations of rhodopsin, which occurred at the rate 0.033/s/rod. The presence of low-amplitude noise is explained by a sigmoidal input–output relationship at the rod—RBP synapse and the input of noisy rods. The rabbit rod SNR and RBP quantum efficiency are the lowest yet reported, suggesting that the quantum efficiency of the rod—RBP synapse may depend on the SNR in rods. These results point to the possibility that fewer photoisomerizations are discarded for species such as primate, which has a higher rod SNR.

A New Strategy for Detecting Gear Faults Using Denoising With the Orthogonal Discrete Wavelet Transform (ODWT)

1999 ◽  
Author(s):  
Sidi M. Berri ◽  
J. M. Klosner
Keyword(s):  
Wavelet Transform ◽  
Discrete Wavelet Transform ◽  
Power Transmission ◽  
Discrete Wavelet ◽  
Amplitude Noise ◽  
Transmission Pair ◽  
New Strategy ◽  
Band Pass ◽  
Local Defects ◽  
Low Amplitude

Abstract This paper investigates a new strategy for early detection of defects in a power transmission pair of spur gears. Sensitivity to local defects is enhanced by processing the signal as follows. The orthogonal discrete wavelet transform (ODWT) of the band-pass filtered averaged signal is first obtained. This is followed by thresholding in the wavelet domain, thereby removing the low amplitude noise contribution. The inverse wavelet transform then essentially reconstructs the component of the signal that is due to the defect. Experimental results demonstrate the efficiency of this procedure.

Intensity Calibration and Sensitivity Comparisons for CCD/Raman Spectrometers

1993 ◽  
Vol 47 (12) ◽  
pp. 1965-1974 ◽  
Author(s):  
Mark Fryling ◽  
Christopher J. Frank ◽  
Richard L. McCreery
Keyword(s):  
Quantum Efficiency ◽  
Figure Of Merit ◽  
Instrumental Response ◽  
Fiber Optic ◽  
Collection Efficiency ◽  
Signal To Noise Ratio ◽  
Quantitative Comparison ◽  
Sample Position ◽  
Fiber Output ◽  
Photodiode Arrays

A calibrated tungsten source combined with a fiber optic was used to correct Raman spectra for instrumental response. With the placement of the fiber output at the Raman sample position, the product of throughput, collection efficiency, quantum efficiency, and sampled area could be assessed. This product is related to a spectrometer figure of merit, which provides a quantitative comparison of spectrometer sensitivity and signal-to-noise ratio. Four spectrometer configurations were compared to illustrate the approach. An additional feature of the white light calibration is correction of relative Raman peak intensities. This issue is particularly important due to the substantial differences between CCD quantum efficiency curves and those of photomultipliers or intensified photodiode arrays.

Signal coding in cockroach photoreceptors is tuned to dim environments

2012 ◽  
Vol 108 (10) ◽  
pp. 2641-2652 ◽  
Author(s):  
K. Heimonen ◽  
E.-V. Immonen ◽  
R. V. Frolov ◽  
I. Salmela ◽  
M. Juusola ◽  
...  
Keyword(s):  
Information Transfer ◽  
Periplaneta Americana ◽  
Single Photon ◽  
Signal To Noise Ratio ◽  
Temporal Integration ◽  
High Sensitivity ◽  
Single Photons ◽  
Low Frequencies ◽  
Whole Cell Patch Clamp ◽  
High Level

In dim light, scarcity of photons typically leads to poor vision. Nonetheless, many animals show visually guided behavior with dim environments. We investigated the signaling properties of photoreceptors of the dark active cockroach ( Periplaneta americana) using intracellular and whole-cell patch-clamp recordings to determine whether they show selective functional adaptations to dark. Expectedly, dark-adapted photoreceptors generated large and slow responses to single photons. However, when light adapted, responses of both phototransduction and the nontransductive membrane to white noise (WN)-modulated stimuli remained slow with corner frequencies ∼20 Hz. This promotes temporal integration of light inputs and maintains high sensitivity of vision. Adaptive changes in dynamics were limited to dim conditions. Characteristically, both step and frequency responses stayed effectively unchanged for intensities >1,000 photons/s/photoreceptor. A signal-to-noise ratio (SNR) of the light responses was transiently higher at frequencies <5 Hz for ∼5 s after light onset but deteriorated to a lower value upon longer stimulation. Naturalistic light stimuli, as opposed to WN, evoked markedly larger responses with higher SNRs at low frequencies. This allowed realistic estimates of information transfer rates, which saturated at ∼100 bits/s at low-light intensities. We found, therefore, selective adaptations beneficial for vision in dim environments in cockroach photoreceptors: large amplitude of single-photon responses, constant high level of temporal integration of light inputs, saturation of response properties at low intensities, and only transiently efficient encoding of light contrasts. The results also suggest that the sources of the large functional variability among different photoreceptors reside mostly in phototransduction processes and not in the properties of the nontransductive membrane.

Dark count probability and quantum efficiency of avalanche photodiodes for single-photon detection

2003 ◽  
Vol 83 (14) ◽  
pp. 2955-2957 ◽  
Author(s):  
Y. Kang ◽  
H. X. Lu ◽  
Y.-H. Lo ◽  
D. S. Bethune ◽  
W. P. Risk
Keyword(s):  
Quantum Efficiency ◽  
Single Photon ◽  
Avalanche Photodiodes ◽  
Single Photon Detection ◽  
Dark Count ◽  
Photon Detection

scholarly journals Three-Dimensional Imaging via Time-Correlated Single-Photon Counting

2020 ◽  
Vol 10 (6) ◽  
pp. 1930
Author(s):  
Chengkun Fu ◽  
Huaibin Zheng ◽  
Gao Wang ◽  
Yu Zhou ◽  
Hui Chen ◽  
...  
Keyword(s):  
3D Imaging ◽  
Single Photon ◽  
Signal To Noise Ratio ◽  
Photon Counting ◽  
Three Dimensional ◽  
Similarity Index ◽  
Signal To Noise ◽  
Single Photon Counting ◽  
Imaging Results ◽  
Noise Ratio

Three-dimensional (3D) imaging under the condition of weak light and low signal-to-noise ratio is a challenging task. In this paper, a 3D imaging scheme based on time-correlated single-photon counting technology is proposed and demonstrated. The 3D imaging scheme, which is composed of a pulsed laser, a scanning mirror, single-photon detectors, and a time-correlated single-photon counting module, employs time-correlated single-photon counting technology for 3D LiDAR (Light Detection and Ranging). Aided by the range-gated technology, experiments show that the proposed scheme can image the object when the signal-to-noise ratio is decreased to −13 dB and improve the structural similarity index of imaging results by 10 times. Then we prove the proposed scheme can image the object in three dimensions with a lateral imaging resolution of 512 × 512 and an axial resolution of 4.2 mm in 6.7 s. At last, a high-resolution 3D reconstruction of an object is also achieved by using the photometric stereo algorithm.

PUNCH-THROUGH CHARACTERISTICS OF AVALANCHE PHOTODIODES UNDER THE GEIGER MODE

2010 ◽  
Vol 24 (03) ◽  
pp. 357-362
Author(s):  
JIANPING GUO ◽  
CHANGJUN LIAO ◽  
ZHENGJUN WEI ◽  
JINDONG WANG
Keyword(s):  
Single Photon ◽  
Collection Efficiency ◽  
Signal To Noise Ratio ◽  
Avalanche Photodiodes ◽  
Single Photon Detector ◽  
Voltage Curve ◽  
Current Voltage ◽  
Geiger Mode ◽  
Current Voltage Curve ◽  
Selection Of

A passive quench circuit is used to study the punch-through characters of avalanche photodiodes under the Geiger mode. The photocurrent–voltage curve indicated clearly the punch-through voltage while the dark current–voltage curve is insensitive to the punch-through. The experiments demonstrate different distributions of the carries. The dark carriers counts increase much faster than the photo-carriers counts due to the different collection efficiency. A proper selection of the bias can increase the signal-to-noise ratio (SNR) of the single photon detector.

scholarly journals RESEARCH OF RELATION OF SAMPLERS FREQUENCY CHARACTERISTICS

2021 ◽  
Vol 13 (0) ◽  
pp. 1-5
Author(s):  
Tomaš Tankeliun
Keyword(s):  
High Frequency ◽  
Signal To Noise Ratio ◽  
Low Frequency ◽  
Vertical Channel ◽  
Discrete Elements ◽  
Sampling Device ◽  
High Frequency Signal ◽  
Analog To Digital ◽  
Amplitude Noise ◽  
Sampling Oscilloscope

The approach to reduce the amplitude noise of a vertical channel of the sampling oscilloscope is presented in this paper. In general, the vertical channel of the sampling oscilloscope consists of a high-frequency sampling circuit and a relatively low-frequency sample transmission path along with a high bit resolution analogto-digital converter. The paper presents a method to improve the sensitivity of the vertical channel of a stroboscopic oscilloscope by extending the conventional channel architecture. The main vertical channel unit of the oscilloscope is a sampling device (sampler), which made of discrete elements and usually implemented using high frequency diodes. The sampler performs a transformation of the sample of the high-frequency signal under test into a low-frequency equivalent signal (otherwise called a balance impulse). In a conventional sampling device, this pulse is quantized once the amplitude is at its highest, thus achieving the best signal-to-noise ratio. The paper analyzes the operating parameters of the sampling device circuit and their influence on the output signal of the sampler. In this approach uses the fastest (15 MHz) high-resolution (18-bit) analog-to-digital converters currently on the market to reduce the amplitude noise of vertical channel based on conventional architecture. Our research has shown that it is possible to obtain an increase in the signal-tonoise ratio of almost 1.3 times.

scholarly journals Hyperpolarized 129Xe Time-of-Flight MR Imaging of Perfusion and Brain Function

Diagnostics ◽  
2020 ◽  
Vol 10 (9) ◽  
pp. 630
Author(s):  
Yurii Shepelytskyi ◽  
Francis T. Hane ◽  
Vira Grynko ◽  
Tao Li ◽  
Ayman Hassan ◽  
...  
Keyword(s):  
Computed Tomography ◽  
Single Photon ◽  
Signal To Noise Ratio ◽  
Neurological Diseases ◽  
Photon Emission ◽  
Time Of Flight ◽  
Hemodynamic Response ◽  
Dynamic Imaging ◽  
Blood Oxygenation ◽  
Emission Computed Tomography

Perfusion measurements can provide vital information about the homeostasis of an organ and can therefore be used as biomarkers to diagnose a variety of cardiovascular, renal, and neurological diseases. Currently, the most common techniques to measure perfusion are 15O positron emission tomography (PET), xenon-enhanced computed tomography (CT), single photon emission computed tomography (SPECT), dynamic contrast enhanced (DCE) MRI, and arterial spin labeling (ASL) MRI. Here, we show how regional perfusion can be quantitively measured with magnetic resonance imaging (MRI) using time-resolved depolarization of hyperpolarized (HP) xenon-129 (129Xe), and the application of this approach to detect changes in cerebral blood flow (CBF) due to a hemodynamic response in response to brain stimuli. The investigated HP 129Xe Time-of-Flight (TOF) technique produced perfusion images with an average signal-to-noise ratio (SNR) of 10.35. Furthermore, to our knowledge, the first hemodynamic response (HDR) map was acquired in healthy volunteers using the HP 129Xe TOF imaging. Responses to visual and motor stimuli were observed. The acquired HP TOF HDR maps correlated well with traditional proton blood oxygenation level-dependent functional MRI. Overall, this study expands the field of HP MRI with a novel dynamic imaging technique suitable for rapid and quantitative perfusion imaging.

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