Relative Noise Level Research Articles

Using Pole–Pole Measurements to Calculate Arbitrary 4‐Point Configurations—An Approach to Make Electrical Resistivity Tomography More Flexible and Time‐Efficient

ABSTRACTElectrical resistivity tomography (ERT) is nowadays widely used in archaeological prospection. This study deals with an approach to make ERT more time‐efficient and flexible. It is based on calculating arbitrary 4‐point configurations by superposition of multiple pole–pole measurements. Investigating its applicability for archaeological purposes is the objective of this work. To do so, a synthetic study and a case study are conducted to gain insights into effects of nonideal field conditions, noise susceptibility and other challenges during processing and interpretation. Remains of an early modern manor in Noer served as an exemplary object of investigation. Their high resistivity contrast in relation to the surrounding soil makes them ideal for a functionality test. Beforehand, ground penetrating radar measurements were carried out to constrain the forward model used in the synthetic study. It turns out that the pole–pole conversion is well applicable for archaeological prospection under some conditions. The synthetic study shows that the approach is relatively prone to systematic errors. Therefore, it is recommended to locate the external electrodes at a distance of at least 0.7 times (preferably 1.7 times) the maximum internal electrode spacing from the area of investigation. Other error sources like nonideal electrode coupling must be excluded to keep relative noise levels below 1%. The pole–pole conversion can be considered reliable for absolute noise levels below 0.3 mV. Therefore, an A/D converter resolution of, for example, 16‐bit should be sufficient for a dynamic range of ±10 V. If all conditions are met, the pole–pole conversion has a great potential to make ERT more time‐efficient (up to 50%, depending on configuration sets) and flexible, as it allows to calculate nearly every arbitrary 4‐point configuration in the given setup. Combined with optimization approaches like the ‘Compare R’ method, data sets can also be adapted for specific (archaeological) questions or conditions.

Study of compatibility between a 3T MR system and detector modules for a second-generation RF-penetrable TOF-PET insert for simultaneous PET/MRI.

Simultaneous positron emission tomography/magnetic resonance imaging (PET/MRI) has shown promise in acquiring complementary multiparametric information of disease. However, designing these hybrid imaging systems is challenging due to the propensity for mutual interference between the PET and MRI subsystems. Currently, there are integrated PET/MRI systems for clinical applications. For neurologic imaging, a brain-dedicated PET insert provides superior spatial resolution and sensitivity compared to body PETscanners. Our first-generation prototype brain PET insert ("PETcoil") demonstrated RF-penetrability and MR-compatibility. In the second-generation PETcoil system, all analog silicon photomultiplier (SiPM) signal digitization is moved inside the detectors, which results in substantially better PET detector performance, but presents a greater technical challenge for achieving MR-compatibility. In this paper, we report results from MR-compatibility studies of two fully assembled second-generation PET insert detectormodules. We studied the effect of the presence of the two second-generation TOF-PET insert detectors on parameters that affect MR image quality and evaluated TOF-PET detector performance under different MRI pulse sequenceconditions. With the presence of operating PET detectors, no RF noise peaks were induced in the MR images, but the relative average noise level was increased by 15%, which led to a 3.1 to 4.2-dB degradation in MR image signal-to-noise ratio (SNR). The relative homogeneity of MR images degraded by less than 1.5% with the two operating TOF-PET detectors present. The reported results also indicated that ghosting artifacts (percent signal ghosting (PSG) ⩽ 1%) and MR susceptibility artifacts (0.044 ppm) were insignificant. The PET detector data showed a relative change of less than 5% in detector module performance between running outside and within the MR bore under different MRI pulse sequences except for energy resolution in EPI sequence (13% relative difference). The PET detector operation did not cause any significant artifacts in MR images and the performance and time-of-flight (TOF) capability of the former were preserved under different tested MRconditions.

Large area hybrid detectors based on Medipix3RX: commissioning and characterization at Sirius beamlines

Hybrid pixel detectors are inherently modular and typically operate at relative low noise levels, while providing high spatial resolution, easing the assembling of large area detectors. This report summarizes the procedures and results regarding the characterization studies performed on the Medipix3RX ASIC based detector, known as PIMEGA, which was developed and is deployed at Sirius synchrotron facility at the Brazilian Synchrotron Light Laboratory. They consist of modular constructions that reach up to 170 × 170 mm2 of active area, with 300 µm thick silicon sensors, and pixel size of 55 × 55 µm2. We investigated the spatial and energy resolutions, structural noise properties, and count-rate linearity up to large fluxes from the synchrotron beamlines. The Modulation Transfer Function presents a considerably slow decay rate as a function of the spatial frequency, reaching 30% at 10.5 lp/mm, for an operation with a threshold setting equivalent to half of the incident energy. We have also found that the energy resolutions of the two highest gain modes are around 15% for 17.5 keV incident photons. In particular, we have found that, for a noise-suppressing set of configurations, the detector presents a dead time of 460 ± 10 ns. Additionally, the pile-up effect leads to a 10% loss of linearity at input fluxes of 2.3 × 105 photons/pixel.s. These results open the possibility for operating these devices with in-depth knowledge of their performance, allowing various scientific experiments, such as X-ray diffraction, computed controlled tomography, and ptychography.

Trailing-Edge Noise Comparability in Open, Closed, and Hybrid Wind Tunnel Test Sections

Open-jet, hard-wall, and hybrid test section configurations are typically used in wind tunnel tests, aiming to represent the ideal free-flight condition. Each test section type requires special adaptations of the experimental hardware and specific correction methodologies that account for systematic measurement errors. Differently from previous research, this paper investigates the comparability of measurements performed in three test section configurations in the same wind tunnel. With this approach, systematic errors related to the facility or boundary-layer tripping methodology are minimized. Basic 2D aerodynamic boundary corrections are evaluated using a DU97W300 airfoil. The corrected lift curve collapsed well while differences in stall behavior and distribution at larger angles of attack are nonnegligible. The trailing-edge noise produced by a NACA-0012, NACA-0018, and NACA-63018 served as reference aeroacoustic sources in this comparability analysis. Moreover, the noise reduction from trailing-edge serrations served as an additional reference for the comparability of relative noise levels. The chord-based Reynolds number of the experiments ranged from 260,000 to 660,000. Unsteady wall pressure measurements performed near the trailing-edge provided a reference for the aeroacoustic noise source terms, demonstrating a negligible change between the different test section types. The applied experimental hardware and acoustic corrections yielded aeroacoustic sources of comparable absolute far-field noise level in the three test section types within . The relative noise levels are comparable within . These results show that aeroacoustic measurements of trailing-edge noise performed in different test section configurations are equivalent, provided that adequate experimental and postprocessing methodologies are systematically implemented.

Theoretical substantiation of the principles of continuous control of grinding equipment modes at the stage of cereal formation

In the article, the object of research is continuous control of the granulometric composition of the grain grinding mass at the exit of the roller mill, by analyzing the spectrum of acoustic noise generated during the grinding of grain products. The development of a vibroacoustic technique for continuous control of distribution according to the criteria of crushed grain products in the operational mode of mill enterprises is presented. Vibroacoustic noises emitted by the crushed fractions of a grain product are decomposed by a spectrum analyzer into additive spectral components according to consumer classification commodity grinding groups. Decomposition into spectra of vibroacoustic signals is carried out by an analogue spectrum analyzer SK4-56 with the establishment of a correspondence between subspectra and group commodity classification consumer units using the theory of pattern recognition by a training method based on the method of potential functions. To simplify the classification identification procedure, unambiguous correspondences are established between the subspectra and the relative noise level in the corresponding frequency range. In contrast to the existing methods of indirect control of the degree of product fineness, by the size of the roll gap or by the amount of power consumed from the network by the drive motor of the roller mill, or by the magnitude of pressure on a slowly rotating roll, or by the magnitude of the electrical resistance of the crushed grain mass coming out of the roll mill and other methods that give a very rough measurement of the particle size distribution, the proposed method of using spectrograms gives a better approximation model, since it relies on the use of Fourier spectra, which give more adequate correspondences between the spectral model and consumer classification groups. Granulometric analysis of the crushed grain mass is carried out in the frequency range from infrasonic frequencies to ultrasonic bandwidths not exceeding 60 kHz.

Influence of Pump Properties on the Tunability of 1.5 μm Low-Noise Single Frequency Fiber Amplifier

In this work, we investigate the impact of the pump configuration (wavelength and pump scheme i.e., backward forward) on the tuning range in a watt level low intensity noise single-frequency Erbium/Ytterbium doped fiber amplifier. Two different pump wavelengths, 976 nm and 940 nm, and three different pumping schemes were numerically and experimentally investigated. Tunability over 47 nm (1533 nm-1580 nm) with relative intensity noise level as low as −155 dB/Hz is achieved using an unconventional pumping scheme where the active fiber is pumped in both directions with two different pump wavelengths.

Suppressing Shot Noise Using Quadratic Variable Step-Size Quantization for the Initial Acquisition of Camera-Raw Image Data.

Digital images from today's premium digital cameras have a higher dynamic range than what humans can perceive. Maximumly keeping the image information captured by sensors while reducing the file size of the output raw image data is highly desirable. In this paper, we show that the extractable image information contained in high-quality HDR images taken by premium cameras can be preserved using a bit-depth of only 8 to 9 bits/pixel when the shot-noise-introduced extra entropy is suppressed. The quadratic variable step-size quantization is used to suppress the shot-noise-introduced entropy. The ratio of the quantization step-size of the quadratic quantizer over the shot noise amplitude is introduced as a parameter to measure the relative quantization noise level, and is used to design the quadratic quantizers that maximally suppress the shot noise. Finally, quadratically quantized real CFA camera-raw image data are losslessly compressed. Compared with the lossless compression on linearly quantized data, at least more than 50% bitrate savings are achieved. Such high bitrate savings without loss of extractable image information are very attractive. Thus, it is highly worthwhile to explore, in the future, hardware implementations of quadratic quantization in image sensors.

Characterization of exoplanetary atmospheres through a model-unbiased spectral survey methodology

Context. Collecting a large variety of exoplanetary atmosphere measurements is crucial to improve our understanding of exoplanets. In this context, it is likely that the field would benefit from broad species surveys, particularly using transit spectroscopy, which is the most successful technique of exoplanetary atmosphere characterization so far. Aims. Our goal is to develop a model-unbiased technique using transit spectroscopy to analyze every qualified atomic spectral line in exoplanetary transit data, and search for relative absorption, that is, a decrease in the flux of the line when the planet is transiting. Methods. We analyzed archive data from HDS at Subaru, HIRES at Keck, UVES at VLT, and HARPS at LaSilla to test our spectral survey methodology. It first filtered individual lines by relative noise levels. It also corrected for spectral offsets and telluric contamination. Our methodology performed an analysis along time and wavelength. The latter employed a bootstrap corroboration. Results. We highlight the possible detections of Mn I and V II in HD 209459b data taken by HDS at Subaru (5.9σ at 5916.4 Å, 5.1σ at 6021.8 Å). The previous detection of Ca I in the same planet is classified as inconclusive by our algorithm, but we support the previous detection of Sc II (3.5σ at 6604.6 Å). We also highlight the possible detection of Ca I, Sc II, and Ti II in HD 189733 data taken by UVES at VLT (4.4σ at 6572.8 Å, 6.8σ at 6604.6 Å, and 3.5σ at 5910.1 Å), in addition to the possible detection of Al I in WASP-74b data taken by UVES at VLT (5.6σ at 6696.0 Å).

Genome-wide gene expression noise in Escherichia coli is condition-dependent and determined by propagation of noise through the regulatory network.

Although it is well appreciated that gene expression is inherently noisy and that transcriptional noise is encoded in a promoter's sequence, little is known about the extent to which noise levels of individual promoters vary across growth conditions. Using flow cytometry, we here quantify transcriptional noise in Escherichia coli genome-wide across 8 growth conditions and find that noise levels systematically decrease with growth rate, with a condition-dependent lower bound on noise. Whereas constitutive promoters consistently exhibit low noise in all conditions, regulated promoters are both more noisy on average and more variable in noise across conditions. Moreover, individual promoters show highly distinct variation in noise across conditions. We show that a simple model of noise propagation from regulators to their targets can explain a significant fraction of the variation in relative noise levels and identifies TFs that most contribute to both condition-specific and condition-independent noise propagation. In addition, analysis of the genome-wide correlation structure of various gene properties shows that gene regulation, expression noise, and noise plasticity are all positively correlated genome-wide and vary independently of variations in absolute expression, codon bias, and evolutionary rate. Together, our results show that while absolute expression noise tends to decrease with growth rate, relative noise levels of genes are highly condition-dependent and determined by the propagation of noise through the gene regulatory network.

The relative intensity noise of a vertical-cavity surface-emitting laser with a fiber Bragg grating external cavity

The research deals with the topical problem of stabilizing the optical parameters of a single-mode vertical-cavity surface-emitting laser. A solution to the problem is proposed by forming an external cavity based on a Bragg grating induced into an optical polarization-maintaining fiber. In this experimental research, the authors estimated the contribution of an external cavity to the relative intensity noise of a vertical-cavity surface-emitting laser. The stability of the laser generation with a varying phase of back reflections at various pump currents is investigated. The relative intensity noise of laser radiation in the pump current range of 1.1–6.3 mA is estimated using a photodetector with a bandwidth of 8.5 MHz. The phase change of the back reflections was carried out by shifting the optical fiber end with a 100 nm step. As a result of the research, it was obtained that the vertical-cavity surface-emitting laser with such an external cavity shows a stable emission in the current range of 1.8–3.2 mA. However, one can observe instability with constant switching between adjacent longitudinal modes outside this range. The most stable laser operation mode with an external cavity against a change in the phase of back reflections is registered at a pump current of 2.78 mA. Utilizing an external cavity with the fiber Bragg grating made it possible to reduce the relative intensity noise from 7.2∙10–10 1/Hz to 1.5∙10–11 1/Hz in the currents range 1.86–3.2 mA. The study can be useful in applications that require an optical radiation coherent source with a low relative intensity noise level (such as coherent optical communication or fiber-optic sensors).

Multi-color stimulated Raman scattering with a frame-to-frame wavelength-tunable fiber-based light source.

We present multi-color imaging by stimulated Raman scattering (SRS) enabled by an ultrafast fiber-based light source with integrated amplitude modulation and frame-to-frame wavelength tuning. With a relative intensity noise level of -153.7 dBc/Hz at 20.25 MHz the light source is well suited for SRS imaging and outperforms other fiber-based light source concepts for SRS imaging. The light source is tunable in under 5 ms per arbitrary wavelength step between 700 cm−1 and 3200 cm−1, which allows for addressing Raman resonances from the fingerprint to the CH-stretch region. Moreover, the compact and environmentally stable system is predestined for fast multi-color assessments of medical or rapidly evolving samples with high chemical specificity, paving the way for diagnostics and sensing outside of specialized laser laboratories.

Noise Tailoring in Memristive Filaments.

In this study, the possibilities of noise tailoring in filamentary resistive switching memory devices are investigated. To this end, the resistance and frequency scaling of the low-frequency 1/f-type noise properties are studied in representative mainstream material systems. It is shown that the overall noise floor is tailorable by the proper material choice, as demonstrated by the order-of-magnitude smaller noise levels in Ta2O5 and Nb2O5 transition-metal oxide memristors compared to Ag-based devices. Furthermore, the variation of the resistance states allows orders-of-magnitude tuning of the relative noise level in all of these material systems. This behavior is analyzed in the framework of a point-contact noise model highlighting the possibility for the disorder-induced suppression of the noise contribution arising from remote fluctuators. These findings promote the design of multipurpose resistive switching units, which can simultaneously serve as analog-tunable memory elements and tunable noise sources in probabilistic computing machines.

Optoelectronic convolutional neural networks based on time-stretch method

In this paper, a new architecture of optoelectronic convolutional neural networks (CNNs) based on time-stretch method is proposed. In this loop-shaped structure mainly composed of fiber optical and electronic devices, computations of data from each layer of CNN which are carried by light pulses with high repetition rate can be accomplished in a serial way. Therefore, a 5-layer CNN with two convolution layers, two mean pooling layers and one fully-connected layer are implemented. Under the test of handwriting digit recognition, its accuracy can reach up to 95% under ideal circumstances. Tests under different relative noise levels have been conducted and analyzed as well.

Stability Design of Resonance Frequency Tracking System for Sensing Resonator

We propose a novel cascade control system to suppress the relative frequency noise between laser frequency and resonance frequency for improving the stability of resonance frequency tracking of sensing resonator. The phase locking loop (PLL) of the cascade control with optical single sideband (OSSB) modulator is designed to provide a standard reference of the laser frequency for reducing the relative frequency noise in tracking system. And, we precisely extract the closed-loop error signal of the resonance frequency tracking with Pound-Drever-Hall (PDH) modulation technology. Then, we theoretically analyze the dynamic model of cascade control system considering relative frequency noise and optical nonlinearity. The algorithm of cascade control system is designed to further improve the stability of resonance frequency tracking for sensing resonator with a prescribed ${H}_{\boldsymbol {\infty }}$ performance. The experimental result shows that the relative frequency noise level is suppressed 30dB. Moreover, the Allan deviation analysis shows that the stability of resonance frequency tracking of sensing resonator compared with the free spectral range (FSR) is improved to ${1.493}\times {10} ^{ -{9}}$ . The experimental results validate the effectiveness of our proposed cascade control system to improve the tracking precision of resonance frequency for sensing resonator.

A 5 GHz and 7.5 V multi-amplitude modulator driving circuit for practical high-speed quantum key distribution.

Quantum key distribution (QKD) offers the ability of information theoretic security key exchange. The secure key rate is an important indicator for the practical QKD systems, which determines what kinds of applications can be supported. One most effective way to enhance the secure key rate is to increase the system repetition frequency. Here, we report an implementation of a high-speed DC-coupled modulator driving circuit with a repetition rate of up to 5 GHz. The circuit outputs a multi-amplitude return-to-zero pattern pulse with a maximum amplitude of 7.5 V. The design adapts to the various electro-optic modulators widely employed in QKD systems. The minimum pulse width is measured as 75 ps, with the relative noise level less than 1.5% for all the output amplitudes under random modulation.

The EUROFORGEN NAME Ampliseq™ custom panel: A second tier panel developed for differentiation of individuals from the Middle East/North Africa

The interest in ancestry informative markers as an investigative tool to identify the biogeographical ancestry of potential suspects is increasing. For this purpose, many different panels have been designed to distinguish individuals from major geographical regions. The EUROFORGEN North Africa and Middle East ancestry panel is a second-tier panel designed for differentiating Middle Eastern/North African populations from other population groups. An Ion AmpliSeq™ custom panel (Thermo Fisher Scientific) was designed to sequence populations of interest using the Ion S5™ (Thermo Fisher Scientific). Of the 111 SNPs selected in the first version of the panel, 107 SNPs were successfully incorporated in the AmpliSeq™ multiplex PCR. More than 600 individuals from 13 different countries in the Middle East, North Africa, and Europe were typed. The performance of the sequencing assay was assessed by calculating relative locus balances, heterozygote balances, and noise levels. Lastly, likelihood ratios were calculated using the GenoGeographer software.

Scatterometer Backscatter Imaging Using Backus–Gilbert Inversion

Wind scatterometer measurements are collected over an irregular grid, and processing is required to generate backscatter images on an Earth-centered grid. The most common algorithms used for this are “drop in the bucket” (DIB) and variations of the scatterometer image reconstruction (SIR) algorithm. These algorithms are also used for radiometer brightness temperature imaging. The Backus–Gilbert (BG) algorithm has been used for radiometer imaging but has not been applied to scatterometer backscatter imaging. In this paper, the application of BG to scatterometer backscatter imaging is explored and its performance is compared to DIB and SIR. Like SIR, optimally tuned BG is capable of producing higher resolution images than DIB, though its noise performance is slightly inferior to SIR’s. While BG and SIR produce similar results for radiometer data, the higher relative noise level of scatterometer data increases the differences between the SIR and BG algorithm performance, and limits the performance of BG relative to SIR in scatterometer imaging. Comparison of the SIR and BG algorithms in scatterometer imaging offers important insights into the inversion/reconstruction problem.

Измерение шумов волоконно-оптических источников излучения

Noise measurement technique of fiber-optical radiation sources was developed. The experimental device for carrying out the specified measurements was done. The analysis of noise sources in spontaneous emission amplifiers showed that the main source is phase noise of spontaneous radiation. When optical radiation is detected in the photodetector, additional noise appears in the output electrical signal. In it, additional noise of the photodetector is added to the noise of radiation source: shot noise arising from the conversion of optical signal into electrical and thermal noise of the converter elements. Spectrum analyzer is used to separate phase noise of spontaneous emission and noise of photodetector. The measurements record two noise spectra, one – the total noise of spontaneous emission amplifier and photodetector, the other – the noise spectrum of one photodetector. As a result of mathematical processing phase noise of radiation source is allocated. The spontaneous emission amplifier works as a part of fiber-optical gyroscope. The integrated optical phase modulator circuit and synchronous detector operating at frequency of 100 kHz are used to reduce noise. Therefore in these researches noise analysis is performed in the narrow spectral range near the specified frequency. Thus, the relative optical noise levels in of 1 Hz bandwidth for several spontaneous emission amplifiers were measured. They were on the order −130 dB in compared to the intensity of effective signal. Then relative levels of optical noise from sources with different emission bands were investigated. It has been established that with increase in emission bandwidth, the relative magnitude of optical noise decreases. The results obtained qualitatively coincide with results of theoretical calculations. This conforms the correctness of developed methodology for measuring the relative optical noise level of quantum generators.

Laser Power Stabilization beyond the Shot Noise Limit Using Squeezed Light

High levels of laser power stability are necessary for high precision metrology applications. The classical limit for the achievable power stability is determined by the shot noise of the light used to generate a power control signal. Increasing the power of the detected light reduces the relative shot noise level and allows higher stabilities. However, sufficiently high power is not always available and the detection of high laser powers is challenging. Here, we demonstrate a nonclassical way to improve the achievable power stability without increasing the detected power. By the injection of a squeezed vacuum field of light we improve the classical laser power stability beyond its shot noise limit by 9.4_{-0.6}^{+0.6} dB at Fourier frequencies between 5 and 80kHz. For only 90.6 μA of detected photocurrent we achieve a relative laser power noise of 2.0_{-0.1}^{+0.1}×10^{-8}/sqrt[Hz]. This is the first demonstration of a squeezed light-enhanced laser power stabilization and its performance is equivalent to an almost tenfold increase of detected laser power in a classical scheme. The analysis reveals that the technique presented here has the potential to achieve stability levels of 4.2×10^{-10}/sqrt[Hz] with 58mA photocurrent measured on a single photodetector.

High-energy dissipative soliton-driven fiber optical parametric oscillator emitting at 1.7 µm

We report a fiber optical parametric oscillator (FOPO) synchronously pumped in a C-band, delivering high-energy picosecond pulses exceeding the nanojoule level of around 1700 nm. The gain medium is a dispersion-shifted fiber, pumped by highly-chirped pulses from a mode-locked dissipative soliton fiber laser. Optimizing the pump wavelength along with time-dispersion-tuning of the FOPO enabled a broad tunability from 1617–1876 nm for the idler wave. In addition, relative intensity noise levels below −140 dBc Hz−1 have been achieved, paving the way for using such a source in biophotonics and instrumentation.