Low Signal Research Articles

Detection of Stress Corrosion Cracking in SS304 under Calcium Silicate Thermal Insulation Using Acoustic Emission Technique

Despite its remarkable structural strength, austenitic stainless steels such as SS304 are susceptible to stress corrosion cracking (SCC) under thermal insulation due to the synergism of cyclic loading and chloride-containing environments. This study aims to detect SCC for insulated SS304 samples using the acoustic emission technique (AET) as monitoring tool to characterize the various stages of SCC damage mechanism. As-received (AR) and sensitized (SEN) SS304 samples were prepared as per ASTM G30 and experimented with soluble chloride drip test under calcium silicate thermal insulation following ASTM C692. Both AR and SEN samples revealed SCC behavior correlated with measured acoustic signals. AR samples exhibited a single crack with low energetic signals, whereas SEN showed multiple cracks with higher energetic signal events. The difference can be attributed to microstructure change by heat sensitization and the enhancement of the corrosion environment under calcium silicate insulation when wetted by salt solution. The acoustic emission (AE) parameters were characterized and correlated with different stages of SCC phenomena, showing that AET is useful for predicting SCC to avoid catastrophic failures in industries.

Optimized radiofrequency shimming using low-heating B1+-mapping in the presence of deep brain stimulation implants: Proof of concept.

MRI of patients with Deep Brain Stimulation (DBS) implants is constrained due to radiofrequency (RF) heating of the implant lead. However, "RF-shimming" parallel transmission (PTX) has the potential to reduce DBS heating during MRI. As part of using PTX in such a "safe mode", maps of the RF transmission field (B1+) are typically acquired for calibration purposes, with each transmit coil excited individually. These maps often have large zones of low signal intensity distant from the specific coil that is being excited, raising concerns that low signal-to-noise ratio (SNR) in these zones might negatively impact the ability of the optimized RF shim settings to suppress heating in safe mode. One way to improve SNR would be to increase RF transmission power during B1+ mapping, but this also raises heating concerns especially for coil elements proximal to the implant. Acting with an abundance of caution, it would be useful to investigate methods that permit B1+ mapping with low localized heating while producing high SNR measurements that lead to safe PTX RF shim settings. The present work addresses this issue in proof of concept using electromagnetic simulations and experimental PTX MRI. A two-step optimization algorithm is proposed and examined for a cylindrical phantom with an implanted wire to enable 1) robust B1+ mapping with low localized heating; and 2) robust RF shimming PTX with low localized heating and good B1+ homogeneity over a large imaging volume. Simulation and experimental outcomes were compared with those obtained using an existing simulation-driven workflow for obtaining safe mode RF shim settings, and for quadrature RF transmission using a circularly polarized (CP) birdcage head coil. Experimental results showed that although both existing and proposed safe-mode workflows effectively suppressed localized heating at the wire tip in comparison to the CP coil results, the proposed workflow produced much smaller temperature elevations and much improved signal uniformity. These promising results support continued investigation and refinement of the proposed workflow, involving more realistic scenarios toward ultimate implementations in DBS patients.

Desmoplastic Small Round Cell Tumor: a study of CT, MRI, PET/CT multimodal imaging features and their correlations with pathology

PurposeExploring the computed tomography (CT), magnetic resonance imaging (MRI), and fluorodeoxyglucose positron emission tomography (FDG-PET)/CT Multimodal Imaging Characteristics of Desmoplastic Small Round Cell Tumor (DSRCT) to enhance the diagnostic proficiency of this condition.MethodsA retrospective analysis was performed on clinical data and multimodal imaging manifestations (CT, MRI, FDG-PET/CT) of eight cases of DSRCT. These findings were systematically compared with pathological results to succinctly summarize imaging features and elucidate their associations with both clinical and pathological characteristics.ResultsAll eight cases within this cohort exhibited abdominal-pelvic masses, comprising six solitary masses and two instances of multiple nodules, except for one case located in the left kidney, the remaining cases lacked a clear organ source. On plain images, seven cases exhibited patchy areas of low density within the masses, four cases showed calcification within the masses. Post-contrast imaging displayed mild-to-moderate, uneven enhancement. Larger masses displayed patchy areas without significant enhancement at the center. In the four MRI examinations, T1-weighted images exhibited uneven, low signal intensity, while T2-weighted images demonstrated uneven high signal intensity. Imaging unveiled four cases of liver metastasis, four cases of ascites, seven cases of lymph node metastasis, three cases of diffuse peritoneal thickening, and one case involving left ureter invasion with obstruction. In the FDG-PET/CT examinations of seven cases, multiple abnormal FDG accumulations were observed in the abdominal cavity, retroperitoneum, pelvis, and liver. One postoperative case revealed a new metastatic focus near the colonic hepatic region. The range of maximum standardized uptake values (SUVmax) for all lesions are 6.62–11.15.ConclusionsDSRCT is commonly seen in young men, and the imaging results are mostly multiple lesions with no clear organ source. Other common findings include intratumoral calcification, liver metastasis, ascites, peritoneal metastasis, and retroperitoneal lymph node enlargement. The combined use of CT, MRI and FDG-PET/CT can improve the diagnostic accuracy and treatment evaluation of DSRCT. However, it is imperative to underscore that the definitive diagnosis remains contingent upon pathological examination.

Zircon luminescence dating revisited

Abstract. Luminescence dating plays a pivotal role in Quaternary science, yet ongoing methodological challenges persist in refining the temporal range, accuracy, and precision of luminescence methods. Our contribution revisits zircons as potential alternative dosimeters to quartz, feldspar, or calcite for routine dating applications. The essential advantage of zircons over other minerals is the time-invariant and high internal dose rate due to high radionuclide contents, dominating over the external contribution, which is more challenging to assess. Reported drawbacks are low zircon abundance, laborious sample preparation, signal instabilities, unknown optical signal resetting rates, and low signal intensities. Our present study uses modern luminescence detection equipment and analytical methods to investigate mineral separation, mineral characteristics, bleachability, signal spectra and intensities, and the potential to auto-regenerate signals. We present results for two zircon samples that are different in provenance, trace element composition, and luminescence characteristics, each of them containing a couple of hundred grains. Optically stimulated luminescence (OSL) signal resetting rates of zircon in response to simulated sunlight exposure are orders of magnitudes faster than for feldspar and slightly slower than for quartz. The recorded thermoluminescence (TL) spectra confirm previously published results with luminescence emissions in the UV/violet and red wavelength range, supplemented by narrowband emissions associated with rare earth element (REE) dopants. Storage experiments of single zircon grains for auto-regenerated measurements over 1.5 years yielded very low OSL signals. At the same time, after only 3 weeks, we measured acceptable TL signal intensities at the cost of lower bleaching rates. To date, the auto-regeneration approach seems to be a promising and accurate approach to dating zircon light exposure events, especially when combining the natural OSL with auto-regenerated TL. However, further studies are required to optimise signal intensities and establish zircons as viable targets for routine dating applications.

Value construction through sequential sampling explains serial dependencies in decision making.

Deciding between a pair of familiar items is thought to rely on a comparison of their subjective values. When the values are similar, decisions take longer, and the choice may be inconsistent with stated value. These regularities are thought to be explained by the same mechanism of noisy evidence accumulation that leads to perceptual errors under conditions of low signal to noise. However, unlike perceptual decisions, subjective values may vary with internal states (e.g. desires, priorities) that change over time. This raises the possibility that the apparent stochasticity of choice reflects changes in value rather than mere noise. We hypothesized that these changes would manifest in serial dependencies across decision sequences. We analyzed data from a task in which participants chose between snack items. We developed an algorithm, Reval, that revealed significant fluctuations of the subjective values of items within an experimental session. The dynamic values predicted choices and response times more accurately than stated values. The dynamic values also furnished a superior account of the BOLD signal in ventromedial prefrontal cortex. A novel bounded-evidence accumulation model with temporally correlated evidence samples supports the idea that revaluation reflects the dynamic construction of subjective value during deliberation, which in turn influences subsequent decisions.

Value construction through sequential sampling explains serial dependencies in decision making

Deciding between a pair of familiar items is thought to rely on a comparison of their subjective values. When the values are similar, decisions take longer, and the choice may be inconsistent with stated value. These regularities are thought to be explained by the same mechanism of noisy evidence accumulation that leads to perceptual errors under conditions of low signal to noise. However, unlike perceptual decisions, subjective values may vary with internal states (e.g. desires, priorities) that change over time. This raises the possibility that the apparent stochasticity of choice reflects changes in value rather than mere noise. We hypothesized that these changes would manifest in serial dependencies across decision sequences. We analyzed data from a task in which participants chose between snack items. We developed an algorithm, Reval, that revealed significant fluctuations of the subjective values of items within an experimental session. The dynamic values predicted choices and response times more accurately than stated values. The dynamic values also furnished a superior account of the BOLD signal in ventromedial prefrontal cortex. A novel bounded-evidence accumulation model with temporally correlated evidence samples supports the idea that revaluation reflects the dynamic construction of subjective value during deliberation, which in turn influences subsequent decisions.

Accidental renal cell carcinoma detected on 68Ga-Pentixafor PET/MR.

The value of gallium-68 (68Ga)-Pentixafor positron emission tomography/magnetic resonance (PET/MR) image in renal carcinoma is unknown. Herein, we reported 68Ga-Pentixafor PET/MR findings in a 47-year-old man with accidental renal carcinoma. Gallium-68-Pentixafor PET/MR showed a small nodule in the left kidney with iso-signal on T1WI and low signal on T2WI. This lesion had intense 68Ga-Pentixafor uptake with a maximum standardized uptake value (SUVmax) of 7.05. This case suggested the potential of 68Ga-Pentixafor PET/MR in the image evaluation of renal carcinoma.

Method to improve the classification accuracy by in situ laser cleaning of painted metal scraps during laser-induced breakdown spectroscopy based sorting

Abstract Scrap metals are typically covered with surface contaminants, such as paint, dust, and rust, which can significantly affect the emission spectrum during laser-induced breakdown spectroscopy (LIBS) based sorting. In this study, the effects of paint layers on metal surfaces during LIBS classification were investigated. LIBS spectra were collected from metal surfaces painted with black and white paints by ablation with a nanosecond pulsed laser (wavelength = 1064 nm, pulse width = 7 ns). For the black-painted samples, the LIBS spectra showed a broad background emission, emission lines unrelated to the target metals, large shot-to-shot variation, and a relatively low signal intensity of the target metal, causing poor classification accuracy even at high shot numbers. Cleaning the black paint layer by ablating over a wide area prior to LIBS analysis resulted in high classification accuracy with fewer shot numbers. A method to determine the number of cleaning shots necessary to obtain high classification accuracy and high throughput is proposed on the basis of the change in LIBS signal intensity during cleaning shots. For the white-painted samples, the paint peeled off the metal surface after the first shot, and strong LIBS signals were measured after the following shot, which were attributed to the nanoparticles generated by the ablation of the paint, allowing an accurate classification after only two shots. The results demonstrate that different approaches must be employed depending on the paint color to achieve high classification accuracy with fewer shot numbers.

Effects of Biological and Enzymatic Ageing on the Surface Properties of Mg-modified Biochar

The excellent surface properties of Mg-modified biochar have highlighted a broad application prospect for soil heavy metal mitigation. However, the soil biotic aging process can have an impact on the physical and chemical properties of biochar as well as the heavy metal removal performance. Therefore, MgCl2-modified biochar was subjected to a six-month microbial and enzymatically aged test to explore the effects of different biotic aging processes on the physical and chemical properties. The Pb2+ adsorption performance of Mg-modified biochar that experienced different aging processes was compared using isothermal adsorption experiments. The results showed that after microbial aging, the Mg-modified biochar pyrolyzed at 700 ℃ displayed a low persistent free radical signal, with the biofilm secreted by microorganisms wrapped on the surface of the biochar, leading to the increase in the oxygen-containing functional groups on the biochar surface and the increase in the maximum adsorption capacity of Pb2+ from 55.31 mg·g-1 to 86.27 mg·g-1. In contrast, a higher free radical signal of 500 ℃ pyrolyzed biochar suggested that the free radical inhibited the growth and reproduction of microorganisms on the biochar surface, resulting in an insignificant enhancement in maximum adsorption capacity to Pb2+ compared to that with unmodified biochar. The pores of the Mg-modified biochar were severely damaged during the enzymatically aged process, resulting in a decrease in the adsorption capacity of Pb2+ to 22.18 mg·g-1, which was significantly lower than that of the unmodified biochar. Therefore, the adsorption capacity of microbially aged Mg-modified biochar is superior to that of enzymatically aged Mg-modified biochar, mainly because the oxygen-containing functional groups exhibited on the surface of the biochar covered by microorganisms come from the extracellular secretions of microorganisms, which promote the removal of Pb2+.

First-in-human Evaluation of Safety and Dosimetry of [64Cu]FBP8: A fibrin-binding PET Probe.

This study presents for the first time in humans the biodistribution, clearance and dosimetry estimates of [64Cu]Fibrin Binding Probe #8 ([64Cu]FBP8) in healthy subjects. [64Cu]FBP8-PET previously demonstrated its potential in two recent applications: thrombus imaging and pulmonary fibrosis. This prospective study included 8 healthy subjects to evaluate biodistribution, safety and dosimetry estimates of [64Cu]FBP8, a fibrin-binding positron emission tomography (PET) probe. All subjects underwent up to 3 sessions of PET/Magnetic Resonance Imaging (PET/MRI) 0-2h, 4h and 24h post injection. Dosimetry estimates were obtained using OLINDA 2.2 software. Subjects were injected with 400 MBq of [64Cu]FBP8. Subjects did not experience adverse effects due to the injection of the probe. [64Cu]FBP8 PET images demonstrated fast blood clearance (half-life = 67min) and renal excretion of the probe, showing low background signal across the body. The organs with the higher doses were: the urinary bladder (0.075 vs. 0.091 mGy/MBq for males and females, respectively); the kidneys (0.050 vs. 0.056 mGy/MBq respectively); and the liver (0.027 vs. 0.035 mGy/MBq respectively). The combined mean effective dose for males and females was 0.016 ± 0.0029 mSv/MBq, lower than the widely used [18F]fluorodeoxyglucose ([18F]FDG, 0.020mSv/MBq). This study demonstrates the following properties of the [64Cu]FBP8 probe: low dosimetry estimates; fast blood clearance and renal excretion; low background signal; and whole-body acquisition within 20min in a single session. These properties provide the basis for [64Cu]FBP8 to be an excellent candidate for whole-body non-invasive imaging of fibrin, an important driver/feature in many cardiovascular, oncological and neurological conditions.

Parametric optomechanics

We investigate two-phonon parametric opto-mechanical generation in a solid state optical cavity pumped with two resonant counter-propagating coherent optical fields. We show that the optical frequencies of the fields must differ by more than the characteristic frequency of the stimulated Brillouin scattering in the material to support the parametric process. The optical harmonics associated with the subsequent optical scattering over the sound waves can be utilized for the excitation of low noise microwave signals.

Bearing fault diagnosis based on sparsity structure pruning graph attention network

Abstract Graph neural networks have been widely used in the field of bearing fault diagnosis, which can deal with non-Euclidean space data and dig deep the relationship between signals. However, most graph neural networks do not distinguish the importance of nodes in information aggregation, and do not take edge noise and data redundancy into account when constructing the graph structure, which affects the diagnostic accuracy. To solve these problems, a fault diagnosis method of graph attention network based on sparsity structure pruning is proposed. Firstly, a sparsity coefficient is introduced to construct the graph structure, and pruning operations are carried out according to the coefficient and the weight of the edges to avoid invalid fusion of information. Then, a graph attention network model based on sparsity structure pruning is constructed, and features of different scales are aggregated into new node representations through multi-head attention mechanism. Finally, the fault diagnosis of bearing is carried out according to the extracted signal discrimination characteristics. To verify the effectiveness of the proposed method, experiments are performed on two different fault diagnosis datasets and compared with other graph neural network methods. The results show that the accuracy and stability of the proposed method are superior to other methods even under the condition of low signal to noise ratio (SNR).

De novo functional discovery of peptide-MHC restricted CARs from recombinase-constructed large-diversity monoclonal T cell libraries.

Chimeric antigen receptors (CAR) that mimic T cell receptors (TCR) on eliciting peptide-major histocompatibility complex (pMHC) specific T cell responses hold great promise in the development of immunotherapies against solid tumors, infections, and autoimmune diseases. However, broad applications of TCR-mimic (TCRm) CARs are hindered to date largely due to lack of a facile approach for the effective isolation of TCRm CARs. Here, we establish a highly efficient process for de novo discovery of TCRm CARs from human naïve antibody repertories by combining recombinase-mediated large-diversity monoclonal library construction with T cell activation-based positive and negative screenings. Panels of highly functional TCRm CARs with peptide-specific recognition, minimal cross-reactivity, and low tonic signaling were rapidly identified towards MHC-restricted intracellular tumor-associated antigens MAGE-A3, NY-ESO-1, and MART-1. Transduced TCRm CAR-T cells exhibited pMHC-specific functional avidity, potent cytokine release, and efficacious and persistent cytotoxicity. The developed approach could be used to generate safe and potent immunotherapies targeting MHC-restricted antigens.

Gallium-67 SPECT/CT and diffusion-weighted MRI in the palatal tumor: report of a rare case with adenocarcinoma not otherwise specified

BackgroundAdenocarcinoma not otherwise specified (NOS) is an uncommon malignant minor salivary gland tumor. We report gallium-67 SPECT/CT and diffusion-weighted MRI (DWI) in the palatal tumor, especially a rare case with adenocarcinoma NOS.Case presentationAn 85-year-old female patient presented with swelling on the palate within 3 months. DWI and apparent diffusion coefficient (ADC) maps indicated high and low signal intensities on the lesion, respectively. ADC value of the lesion was 0.58 × 10–3 mm2s−1. Gallium-67 SPECT/CT showed increased uptake on the lesion and no metastasis. The maximum SUV for the palatal lesion was 7.36. Histopathological diagnosis by a biopsy was adenocarcinoma NOS.ConclusionThe gallium-67 SPECT/CT and DWI should be effective for assessment of the palatal tumor.

Time-efficient, high-resolution 3T whole-brain relaxometry using Cartesian 3D MR Spin TomogrAphy in Time-Domain (MR-STAT) with cerebrospinal fluid suppression.

Current three-dimensional (3D) MR Spin TomogrAphy in Time-Domain (MR-STAT) protocols use transient-state, gradient-spoiled gradient-echo sequences that are prone to cerebrospinal fluid (CSF) pulsation artifacts when applied to the brain. This study aims to develop a 3D MR-STAT protocol for whole-brain relaxometry that overcomes the challenges posed by CSF-induced ghosting artifacts. We optimized the flip-angle train within the Cartesian 3D MR-STAT framework to achieve two objectives: (1) minimization of the noise level in the reconstructed quantitative maps, and (2) reduction of the CSF-to-white-matter signal ratio to suppress CSF-associated pulsation artifacts. The optimized new sequence was tested on a gel/water phantom for accuracy evaluation of the quantitative maps, and on healthy volunteers to explore the effectiveness of the CSF artifact suppression and robustness of the new protocol. An optimized sequence with high parameter-encoding capability and low CSF signal response was proposed and validated in the gel/water phantom experiment. From in vivo experiments with 5 volunteers, the proposed CSF-suppressed sequence produced quantitative maps with no CSF artifacts and showed overall greatly improved image quality compared with the baseline sequence. Statistical analysis indicated low intersubject and interscan variability for quantitative parameters in gray matter and white matter (1.6%-2.4% for T1 and 2.0%-4.6% for T2), demonstrating the robustness of the new sequence. We present a new 3D MR-STAT sequence with CSF suppression that effectively eliminates CSF pulsation artifacts. The new sequence ensures consistently high-quality, 1-mm3 whole-brain relaxometry within a rapid 5.5-min scan time.

Detection of low-power RF signals using active mode-locking based coupled optoelectronic oscillator

A novel method to detect and amplify broadband low power radio frequency (RF) signal with high gain based on coupled optoelectronic oscillator (COEO) is proposed and experimentally demonstrated. When the frequency of the weak signal matches the COEO oscillation mode, it can obtain the high gain of active mode-locking in the COEO optical loop. The system can selectively detect and amplify RF signals from 1 to 10 GHz by observing the optical pulse repetition rate state. The experimental results show that sensitivity of detection as low as −89 dBm with a maximum gain of 34.32 dB at 1.002 GHz, and an average gain of 30.52 dB for low power RF signals. The real application of the method for detecting low power Quadrature Phase Shift Keying (QPSK) modulation is investigated and the spectral waveforms is discussed.

Design and Analysis of FBG-Based Vibration Sensor for Low Frequency Applications

Design and Analysis of FBG-Based Vibration Sensor for Low Frequency Applications

Multi-Channel Lightweight Contrast Prediction Coding for Features Extraction of Radar Emitter Signals

This letter presents a novel multi-channel improved contrastive predictive coding (CPC) method to extract signals features. Specifically, to extract low pulse width radar signals features and meet the real-time requirements of signals identification, we design a lightweight encoder to realize the CPC features encoding function. Then, we construct a multi-channel CPC features decoder to mine and extract subtle individual signals features from the perspective of multi-domain and multi-channel information input. Simulation results verify the effectiveness of our proposed method, which can achieve state-of-the-art results in both accuracy and running time compared to the existing optimal methods. All our models and code are available at https://github.com/jn-z/MC-CPC.

External Cavity Quantum Cascade Laser Vibrational Circular Dichroism Spectroscopy for Fast and Sensitive Analysis of Proteins at Low Concentrations.

Proteins are characterized by their complex levels of structures, which in turn define their function. Understanding and evaluating these structures is therefore crucial to illuminating biological processes. One of the possible analytical methods is vibrational circular dichroism (VCD), which expands the structural sensitivity of classical infrared (IR) absorbance spectroscopy by the chiral sensitivity of circular dichroism. While this technique is powerful, it is plagued by low signal intensities and long measurement times. Here we present an optical setup leveraging the high brilliance of a quantum cascade laser to measure proteins in D2O at a path length of 204 μm. It was compared to classical Fourier-transform infrared spectroscopy (FT-IR) in terms of noise levels and in its applicability to secondary structure elucidation of proteins. Protein concentrations as low as 2 mg/mL were accessible by the laser-based system at a measurement time of 1 h. Further increase of the time resolution was possible by adapting the emission to cover only the amide I' band. This allowed for the collection of spectral data at a measurement time of 5 min without a loss of performance. With this high time resolution, we are confident that dynamic processes of protein can now be monitored by VCD, increasing our understanding of these reactions.

Exploring the impact mechanism of ambient gas properties on laser-induced breakdown spectroscopy to guide the raw signal improvement

BackgroundLaser-induced breakdown spectroscopy (LIBS) has long been regarded as the future superstar for chemical analysis. However, hindered by the fact that the signal source of LIBS is a spatially and temporally unstable plasma that interacts dramatically with ambient gases, LIBS has always suffered from poor signal quality, especially low signal repeatability. Although ambient gases act as one of the most direct and critical factors affecting LIBS signals, a clear understanding on how ambient gas properties impact LIBS signals is still lacking to act as guideline for the signal quality improvement. ResultsIn this work, the impact mechanism of three main ambient gas properties, including specific heat ratio (γ), molar mass (M), and ionization energy (E) was investigated by ignoring secondary properties, accurately proportioning gas mixtures, and experimental comparative study by applying various plasma diagnosis methods. The results indicate that these three properties impact signal repeatability by impacting the intensity of the back-pressing process within the plasma, where the sound speed determined by γ and M plays an important role. The properties impact the signal intensity by impacting three energy transfer processes in the plasma, including the laser energy absorption, the energy allocation between gas and sample species, and the heat dissipation. Based on the impact mechanism, guidelines of regulating the ambient gas properties to improvement LIBS signal were further provided. SignificanceFor the first time, the impact mechanism of main ambient gas properties on LIBS signals was clearly and intuitively revealed. The impact mechanism not only provided a deeper understanding of the plasma evolution process but also provided practical guidelines for improving LIBS signal quality, facilitating accurate quantification of the LIBS technique.