Signal Integration Time Research Articles

Enrichment-enhanced photoacoustic spectroscopy based on vertical graphene

This manuscript proposes a method to improve the gas detection sensitivity of the photoacoustic spectroscopy (PAS) by the enrichment of the concentration of a gas species based on vertical graphene (VG). This is accomplished by exploiting the characteristics of vertical graphene grown on Ni foam to adsorb gas molecules and subsequently desorb them at high temperatures. After the adsorption by the VG material, the enrichment cell is heated to 150 ℃; then the enriched gas is collected and passed into the PAS cell. A DFB-QCL laser tuned at 5263 nm was used as the excitation light source of the PAS sensor for NO detection. The experimental results showed that at a gas pressure of 760 torr and with a signal integration time of 1 s, the ultimate detection limit of traditional photoacoustic spectroscopy for NO gas is 14 ppb, while that of enrichment-enhanced photoacoustic spectroscopy is 1.3 ppb, proving that this method can increase the sensitivity of one order of magnitude.

Development of trench-shaped microstructure thermal neutron detector using α-Al2O3:C based on optically stimulated luminescence

Optical stimulated luminescence technique is increasingly used in neutron personal dosimetry, due to its capability of fast readout and potential for re-estimation of absorbed dose. The design configuration and performance of the microstructure optically stimulated luminescence neutron detector (MOSLND) using α-Al2O3:C was reported. To improve thermal neutron response, the MOSLND is structured with a matrix of microstructure trenches into the α-Al2O3:C substrate and backfilled with 6LiF. To obtain an optimum trench geometric parameter, several Monte Carlo simulations were performed using Geant4 code. The simulation results show that relatively high energy deposition can be realized for small cell dimensions with deep trenches, and is significantly increased compared with that of simple planar designs. Based on the results of calculation and practical limitation, the device was produced and tested using D2O-modrated 252Cf. The optimized minimal detectable dose (MDD) corresponding to signal integration time of 2 s is 7.2 μSv. The experimental results indicate that MOSLND can be a potential solution for personal neutron dosimetry.

All-fiber-coupled mid-infrared quartz-enhanced photoacoustic sensors

Infrared laser-based gas sensors are mature to take the leap from laboratory prototype to outdoor operation. Considering the demand of high robustness and compactness, the reliability of the optical alignment in a sensor is the top priority. This paper proposes a solution designing an optical system embedded within a sealed metallic cylinder containing an aspheric micro-lens to couple a single-mode interband cascade laser with an indium fluoride glass fiber. The fiber output is plug & play connected to an acoustic detection module of a quartz-enhanced photoacoustic sensor (QEPAS) equipped with a fiber port, avoiding the use of any free-space optics, from the source to the detection module. To demonstrate the operability, three all-fiber-coupled QEPAS sensors were realized for detection of CH4, CO2 and NO reaching sub-ppm ultimate detection limits with a signal integration time of 100 ms.

Study of Angular Resolution Using Imaging Atmospheric Cherenkov Technique

Angular resolution is crucial for the detailed study of gamma-ray sources and current Cherenkov telescopes (e.g., HESS, MAGIC, and VERITAS) that operate below tens of TeV. Several gamma-ray sources with a photon energy larger than 100 TeV have been revealed by the LHAASO in recent years; the angular resolution of the LHAASO is around 0.3∘. A gamma-ray detector with an angular resolution of less than 0.1∘ operating beyond 100 TeV is needed to study the detailed morphology of ultra-high-energy gamma-ray sources further. The cost-effectiveness is crucial for such large-area detectors. In this paper, the impact of telescope aperture, field of view, pixel size, optical point spread function, and signal integration time window on angular resolution is studied. These results can provide essential elements for the design of telescope arrays.

Isotope Detection in Microwave-Assisted Laser-Induced Plasma

Isotope detection and identification is paramount in many fields of science and industry, such as in the fusion and fission energy sector, in medicine and material science, and in archeology. Isotopic information provides fundamental insight into the research questions related to these fields, as well as insight into product quality and operational safety. However, isotope identification with established mass-spectrometric methods is laborious and requires laboratory conditions. In this work, microwave-assisted laser-induced breakdown spectroscopy (MW-LIBS) is introduced for isotope detection and identification utilizing radical and molecular emission. The approach is demonstrated with stable B and Cl isotopes in solids and H isotopes in liquid using emissions from BO and BO2, CaCl, and OH molecules, respectively. MW-LIBS utilizes the extended emissive plasma lifetime and molecular-emission signal-integration times up to 900 μs to enable the use of low (~4 mJ) ablation energy without compromising signal intensity and, consequently, sensitivity. On the other hand, long plasma lifetime gives time for molecular formation. Increase in signal intensity towards the late microwave-assisted plasma was prominent in BO2 and OH emission intensities. As MW-LIBS is online-capable and requires minimal sample preparation, it is an interesting option for isotope detection in various applications.

Optimizing the computational effort of satellite signal acquisition based on mean recognition convolutional neural network

The ability to synchronize the satellite signals affects the navigation performance. Only after a procedure of acquisition, namely coarse synchronization, the data information needed to position can be extracted from the satellite signals. Conventional acquisition methods rely on extending the signal integration time to improve the correlation quality of the signal. However, extending the coherent integration time results in a large computational burden, which is unrealistic for civilian receivers. In this paper, we try to optimize the computational effort in the satellite navigation signal acquisition phase and propose an algorithm based on the mean value recognition convolutional neural network. The matrix with a high mean value is separated by the convolutional neural network, and then the Doppler shift and code phase from the matrix with a high mean value is introduced, which can effectively change the computation to 1/4338 of the original one. The trained model of the neural network can be embedded into the receiver directly, which has important engineering applications.

Color-scalable flow cytometry with Raman tags.

Flow cytometry is an indispensable tool in biology and medicine for counting and analyzing cells in large heterogeneous populations. It identifies multiple characteristics of every single cell, typically via fluorescent probes that specifically bind to target molecules on the cell surface or within the cell. However, flow cytometry has a critical limitation: the color barrier. The number of chemical traits that can be simultaneously resolved is typically limited to several due to the spectral overlap between fluorescence signals from different fluorescent probes. Here, we present color-scalable flow cytometry based on coherent Raman flow cytometry with Raman tags to break the color barrier. This is made possible by combining a broadband Fourier-transform coherent anti-Stokes Raman scattering (FT-CARS) flow cytometer, resonance-enhanced cyanine-based Raman tags, and Raman-active dots (Rdots). Specifically, we synthesized 20 cyanine-based Raman tags whose Raman spectra are linearly independent in the fingerprint region (400 to 1,600 cm-1). For highly sensitive detection, we produced Rdots composed of 12 different Raman tags in polymer nanoparticles whose detection limit was as low as 12nM for a short FT-CARS signal integration time of 420 µs. We performed multiplex flow cytometry of MCF-7 breast cancer cells stained by 12 different Rdots with a high classification accuracy of 98%. Moreover, we demonstrated a large-scale time-course analysis of endocytosis via the multiplex Raman flow cytometer. Our method can theoretically achieve flow cytometry of live cells with>140 colors based on a single excitation laser and a single detector without increasing instrument size, cost, or complexity.

Quartz-Enhanced Photoacoustic Spectroscopy for One-Health

We report on the development of Quartz-Enhanced Photoacoustic Spectroscopy (QEPAS) technology to detect 8 different air pollutants, namely CH4, NO2, CO2, N2O, CO, NO, SO2 and NH3, with the same acoustic detection module and interchangeable laser sources, to prove the modularity of the technique as well as the adaptability to different lasers. For each gas species, the fine structure of the infrared absorption bands has been simulated by using HITRAN database. Each gas species was detected with an ultimate detection limit well below their typical natural abundance in air even with a signal integration time as low as 0.1 s.

Measurement of methane, nitrous oxide and ammonia in atmosphere with a compact quartz-enhanced photoacoustic sensor

We demonstrated a 19-inches 6U-rack sensing system based on quartz-enhanced photoacoustic spectroscopy for simultaneous detection of methane, nitrous oxide, and ammonia in atmosphere. The system embeds two detection modules, each one equipped with a quantum cascade laser as light source and a spectrophone composed of a T-shaped quartz tuning fork coupled with acoustic resonator tubes. The sensing system results compact, lightweight, and portable, with a computer interface for an easy end-user operation. The calibration was performed in laboratory environment with certified concentrations. Because of the NH3 large and permanent dipole moment, ammonia QEPAS signal was used to model and characterize adsorption/desorption processes, for an accurate and reliable sensor calibration. At 0.1 s signal integration time, detection limits of 28 ppb, 9 ppb, and 6 ppb were obtained for CH4, N2O, and NH3, respectively. Since these detection limits were well below the natural abundance of the three analytes in atmosphere, the sensor was employed to monitor CH4, N2O, and NH3 concentrations in laboratory air.

Low-energy X-ray spectroscopy with RGB-HD SiPMs coupled to CsI(Tl) scintillator

The continuous improvement of Silicon Photomultiplier (SiPM) characteristics opens new perspectives for the application of these detectors in middle to low energy X-ray scintillation light readout. Compared to traditional PET detectors this application poses an additional challenge because of the much lower number of photons generated in the scintillator. Many SiPM characteristics influence the energy resolution of the detected radiation, including Photon Detection Efficiency (PDE), primary noise and Excess Noise Factor (ENF). The most recent development of the RGB-HD SiPM technology at Fondazione Bruno Kessler (FBK, Italy) provides a PDE up to 40% at 550 nm while keeping the Dark Count Rate (DCR) below 500 kc.p.s./mm2. A low DCR value is fundamental in improving the energy resolution for soft X-rays. In this work we coupled a 1×1 mm2 RGB-HD SiPM to a 0.9×0.9×2 mm3 CsI(Tl) crystal allowing the detection of 55Fe 5.9 keV photons with an energy resolution of 39% FWHM. A 4×4 mm2 RGB-HD SiPM with a 3×3×5 mm3 CsI(Tl) was used for the readout of a 57Co source (6.4 keV, 14.4 keV and 122 keV) in order to prove the dynamic range of the system. The energy resolution of these three peaks shows different trends with respect to the SiPM bias and to the signal integration time. This is related to the fact that SiPM parameters such as PDE, DCR and ENF, and readout parameters such as integration time, become more or less relevant depending on the energy of the primary photon.

Intracellular Heat Transfer and Thermal Property Revealed by Kilohertz Temperature Imaging with a Genetically Encoded Nanothermometer.

Despite improved sensitivity of nanothermometers, direct observation of heat transport inside single cells has remained challenging for the lack of high-speed temperature imaging techniques. Here, we identified insufficient temperature resolution under short signal integration time and slow sensor kinetics as two major bottlenecks. To overcome the limitations, we developed B-gTEMP, a nanothermometer based on the tandem fusion of mNeonGreen and tdTomato fluorescent proteins. We visualized the propagation of heat inside intracellular space by tracking the temporal variation of local temperature at a time resolution of 155 μs and a temperature resolution 0.042 °C. By comparing the fast in situ temperature dynamics with computer-simulated heat diffusion, we estimated the thermal diffusivity of live HeLa cells. The present thermal diffusivity in cells was about 1/5.3 of that of water and much smaller than the values reported for bulk tissues, which may account for observations of heterogeneous intracellular temperature distributions.

Improving the iGNSS-R Ocean Altimetric Precision Based on the Coherent Integration Time Optimization Model

Improving the altimetric precision under the requirement of ensuring the along-track resolution is of great significance to the application of iGNSS-R satellite ocean altimetry. The results obtained by using the empirical integration time need to be improved. Optimizing the integration time can suppress the noise interference from different sources to the greatest extent, thereby improving the altimetric precision. The inverse relationship between along-track resolution and signal integration time leads to the latter not being infinite. To obtain the optimal combination of integral parameters, this study first constructs an analytical model whose precision varies with coherent integration time. Second, the model is verified using airborne experimental data. The result shows that the average deviation between the model and the measured precision is about 0.16 m. The two are consistent. Third, we apply the model to obtain the optimal coherent integration time of the airborne experimental scenario. Compared with the empirical coherent integration parameters, the measured precision is improved by about 0.1 m. Fourth, the verified model is extrapolated to different spaceborne scenarios. Then, the optimal coherent integration time and the improvement of measured precision under various conditions are estimated. It was found that the optimal coherent integration time of the spaceborne scene is shorter than that of the airborne scene. Depending on the orbital altitude and the roughness of the sea surface, its value may also vary. Moreover, the model can significantly improve the precision for low signal-to-noise ratios. The coherent integration time optimization model proposed in this paper can enhance the altimetric precision. It would provide theoretical support for the signal optimization processing and sea surface height retrieval of iGNSS-R altimetry satellites with high precision and high along-track resolution in the future.

Cloud-Based Single-Frequency Snapshot RTK Positioning.

With great potential for being applied to Internet of Things (IoT) applications, the concept of cloud-based Snapshot Real Time Kinematics (SRTK) was proposed and its feasibility under zero-baseline configuration was confirmed recently by the authors. This article first introduces the general workflow of the SRTK engine, as well as a discussion on the challenges of achieving an SRTK fix using actual snapshot data. This work also describes a novel solution to ensure a nanosecond level absolute timing accuracy in order to compute highly precise satellite coordinates, which is required for SRTK. Parameters such as signal bandwidth, integration time and baseline distances have an impact on the SRTK performance. To characterize this impact, different combinations of these settings are analyzed through experimental tests. The results show that the use of higher signal bandwidths and longer integration times result in higher SRTK fix rates, while the more significant impact on the performance comes from the baseline distance. The results also show that the SRTK fix rate can reach more than 93% by using snapshots with a data size as small as 255 kB. The positioning accuracy is at centimeter level when phase ambiguities are resolved at a baseline distance less or equal to 15 km.

Register of the human brain acoustic area spectrum

Abstract. Last years, there were developed methods based on the human brain and body acoustic signals application. We consider human brain micro vibrations as an ancient, highly reliable, relatively rapid channel of the central nervous system with all the organism cells and structures. There is offered a method of the human brain acoustic area spectrum analysis and registration. Experimental sample “Register of the human brain micro vibrations spectrum is developed. The model of the human brain acoustic area generation is offered – neurovascular reflex and related with human brain blood vessels smooth muscularity nerve cells metabolism. In comparison with classical EEG, it is demonstrated that acoustic encephalogram also reflects human brain neuroreflex activity. Piezoelectric sensors, which feature in silicone membrane existence, are investigated. Such type of construction allowed to register human brain mechanical vibrations in the gamut from 0.1 up to 27 Hz. Spectral analysis is specific in that signal integration time is 160 seconds. Meanwhile, 12600 spectral harmonics of the human brain reticular activating system were reliably extracted. For convenience, all the acoustic area spectrum of the human brain was shrunk into segmental frame of reference which is frequency structured matrix of functional conditions multiplicity “multiple arousal” of 24х625 frequency cells size. All the developed technologies and device might be used for the organism adaptation estimations, psycho-emotional conditions estimations and functional-topical diagnosis of the internal parts of the human body.

Small-scale infrared surround scan system with image motion blur compensation based on multisegment optical wedges

We study an infrared surround scan system based on a photodetector array with an entrance pupil of a small diameter with no specific requirements for achieving versatility and a high dynamic performance. A cooled midinfrared photodetector with an objective and a compensator for the tangential motion blur of an image are housed within a rotating unit. Command and data exchange are ensured using a rotating communication device mounted on a rotation axis of the moving unit. Multisegment assemblies of optical wedges are used instead of single wedges in the compensator for the tangential motion blur of the image. We demonstrate that this engineering design makes it possible to increase the signal integration time by several times compared with a basic design with single-segment wedges.

Effect of an electric field on liquid helium scintillation produced by fast electrons

The dependence on applied electric field ($0 - 40$ kV/cm) of the scintillation light produced by fast electrons and $\alpha$ particles stopped in liquid helium in the temperature range of 0.44 K to 3.12 K is reported. For both types of particles, the reduction in the intensity of the scintillation signal due to the applied field exhibits an apparent temperature dependence. Using an approximate solution of the Debye-Smoluchowski equation, we show that the apparent temperature dependence for electrons can be explained by the time required for geminate pairs to recombine relative to the detector signal integration time. This finding indicates that the spatial distribution of secondary electrons with respect to their geminate partners possesses a heavy, non-Gaussian tail at larger separations, and has a dependence on the energy of the primary ionization electron. We discuss the potential application of this result to pulse shape analysis for particle detection and discrimination.

Measurement of tropospheric HO2 radical using fluorescence assay by gas expansion with low interferences

An instrument to detect atmospheric HO2 radicals using fluorescence assay by gas expansion (FAGE) technique has been developed. HO2 is measured by reaction with NO to form OH and subsequent detection of OH by laser-induced fluorescence at low pressure. The system performance has been improved by optimizing the expansion distance and pressure, the influence factors of HO2 conversion efficiency are also studied. The interferences of RO2 radicals were investigated by determining the conversion efficiency of RO2 to OH during the measurement of HO2. The dependence of the conversion of HO2 on NO concentration was investigated, and low HO2 conversion efficiency was selected to realize the ambient HO2 measurement, where the conversion efficiency of RO2 derived by propane, ethene, isoprene and methanol to OH has been reduced to less than 6% in the atmosphere. Furthermore, no significant interferences from PM2.5 and NO were found in the ambient HO2 measurement. The detection limits for HO2 (S/N = 2) are estimated to 4.8 × 105 cm−3 and 1.1 × 106 cm−3 (ρHO2= 20%) under night and noon conditions, with 60 sec signal integration time. The instrument was successfully deployed during STORM-2018 field campaign at Shenzhen graduate school of Peking University. The concentration of atmospheric HOx radical and the good correlation of OH with j(O1D) was obtained here. The diurnal variation of HOx concentration shows that the OH maximum concentration of those days is about 5.3 × 106 cm−3 appearing around 12:00, while the HO2 maximum concentration is about 4.2 × 108 cm−3 appearing around 13:30.

Near-Infrared Quartz-Enhanced Photoacoustic Sensor for H2S Detection in Biogas

A quartz-enhanced photoacoustic spectroscopy (QEPAS) sensor for H2S detection operating in near-infrared spectral range is reported. The optical source is an erbium-doped fiber amplified laser with watt-level optical power. The QEPAS spectrophone is composed of a quartz tuning fork with a resonance frequency of 7.2 kHz, a quality factor of 8500, and a distance between prongs of 800 µm, and two tubes with a radius of 1.3 mm and a length of 23 mm acting as an organ pipe resonator. With this spectrophone geometry, the photothermal noise contribution of the spectrophone was removed and the theoretical thermal noise level was achieved. The position of both tubes with respect to custom quartz tuning fork has been investigated as a function of signal amplitude, Q-factor, and noise of the QEPAS sensor when a high-power laser was used. Benefit from the linearity of the QEPAS signal to the excitation laser power, a detection sensitivity of 330 ppb for H2S detection was achieved at atmospheric pressure and room temperature, when the laser power was 1.6 W and the signal integration time was set to 300 ms, corresponding to a normalized noise equivalent absorption of 3.15 × 10−9 W cm−1/(Hz)1/2. The QEPAS sensor was then validated by measuring H2S in a biogas sample.

Reduced acquisition time for L-shell x-ray fluorescence computed tomography using polycapillary x-ray optics.

X-ray fluorescence computed tomography (XFCT) is an emerging molecular imaging modality for preclinical and clinical applications with high atomic number contrast agents. XFCT allows detection of molecular biomarkers at tissue depths of 4-9mm at L-shell energies and several centimeters for K-shell energies, while maintaining high spatial resolution. This is typically not possible for other molecular imaging modalities. The purpose of this study is to demonstrate XFCT imaging with reduced acquisition times. To accomplish this, x-ray focusing polycapillary optics are utilized to simultaneously increase x-ray fluence rate and spatial resolution in L-shell XFCT imaging. A prototype imaging system using a polycapillary focusing optic was demonstrated. The optic, which was custom-designed for this prototype, provided a high fluence rate with a focal spot size of 2.6mm at a source to isocenter distance of 3cm with a ten times higher fluence rate compared to standard collimation. The study evaluates three different phantoms to explore different trade-offs and limitations of L-shell XFCT imaging. A low-contrast gold phantom and a high-contrast gold phantom, each with three target regions with gold concentrations of 60, 80, and 100 μgml for low contrast and 200, 600, and 1000μgml for high contrast, and a mouse-sized water phantom with gold concentrations between 300 and 500μgml were imaged. X-ray fluorescence photons were measured using a silicon drift detector (SDD) with an energy resolution of 180eV FWHM at an x-ray energy of 11keV. Images were reconstructed with an iterative image reconstruction algorithm and analyzed for contrast to noise ratio (CNR) and signal to noise ratio (SNR). The XFCT data acquisition could be reduced from 17h to under 1h. The polycapillary x-ray optic increases the x-ray fluence rate and lowers the amount of background scatter which leads to reduced imaging time and improved sensitivity. The quantitative analysis of the reconstructed images validates that concentrations of 60μgml of gold can be visualized with L-shell XFCT imaging. For a mouse-sized phantom, a concentration of 300μgml gold was detected within a 66min measurement. With a high fluence rate pencil beam from a polycapillary x-ray source, a reduction in signal integration time is achieved. It is presented that subtle amounts of contrast agents can be detected with L-shell XFCT within biologically relevant time frames. Our basic measurements show that the polycapillary x-ray source technology is appropriate to realize preclinical L-shell XFCT imaging. The integration of more SDDs into the system will lower the dose and increase the sensitivity.

A posteriori synchronization of scanning transmission electron microscopy signals with kilopixel per second acquisition rates

The stability and sensitivity of scanning transmission electron microscopes as well as detectors collecting e.g. electrons which suffered different scattering processes, or secondary radiation, have increased tremendously during the last decade. In order to fully exploit capabilities of simultaneously recording various signals with up to 1000 px/s acquisition rates the central issue is their synchronization. The latter is frequently a non-trivial problem without commercially available solution especially if detectors of different manufacturers are involved. In this paper, we present a simple scanning pattern enabling a posteriori synchronization of arbitrarily many signals being recorded entirely independently. We apply the approach to the simultaneous atomic-scale acquisition of signals from an annular dark-field detector and electron energy loss as well as energy-dispersive x-ray spectrometers. Errors emerging in scanning direction due to the independence of the respective processes are quantified and found to have a standard deviation of roughly half the pixel spacing. Since there are no intermediate waiting periods to maintain synchronicity, the proposed acquisition process is, in fact, demonstrated to be 12% faster than a commercial hardware-synchronized solution for identical sub-millisecond signal integration times and hence follows the trend in electron microscopy to extract more information per irradiating electron.