Residual Background Research Articles

Background Noise Suppression of Optical Sectioning Structured Illumination Microscopy via Fourier Domain Reconstruction

Optical sectioning structured illumination microscopy (OS-SIM) has been attracting considerable interest in fast 3D microscopy. The reconstruction of optical sectioning images in the conventional method employs the root-mean-square (RMS) algorithm in the spatial domain, which is prone to residual background noise. To overcome this problem, we propose a Fourier domain based optical sectioning image reconstruction algorithm (termed Fourier-OS-SIM), which has an improved background noise suppression capability compared to the RMS algorithm. The experimental results verified the feasibility and the effectiveness of the algorithm. The improved performance of the Fourier-OS-SIM may find more applications in biomedical or industrial fields.

Infrared Small Target Detection Using Regional Feature Difference of Patch Image

Aiming at a thorny issue, that conventional small target detection algorithm using local contrast method is not sensitive for residual background clutter, robustness of algorithms is not strong. A Gaussian fusion algorithm using multi-scale regional patch structure difference and Regional Brightness Level Measurement is proposed. Firstly, Regional Energy Cosine (REC) is constructed to measure the structural discrepancy among a small target with neighboring cells. At the same time, Regional Brightness Level Measurement (RBLM) is constructed utilizing the brightness difference characteristics between small target and background areas. Then, a brand new Gaussian fusion algorithm is proposed for the generated saliency map in multi-scale space to characterize the overall heterogeneity in original infrared small target and local neighborhood. Finally, a self-adapting separation algorithm is adopted with the objective to obtain a small target from background interference. This method is able to utmostly restrain background interference and enhance the target. Extensive qualitative and quantitative testing results display that the desired algorithm has remarkable performance in strengthening target region and restraining background interference compared with current algorithms.

Flow of Ethanol into a Medium with Varying Degrees of Rarefaction

Experimental results of observation of ethanol microjets flowing into a highly rarefied medium (vacuum) through a nozzle are presented. The investigation of the outflow process was carried out both horizontally and vertically in the direction of gravity, when the liquid was expelled from the source. The condition of keeping constant the residual background pressure in the vacuum chamber is much lower than the saturated vapour pressure of the working liquid at a given temperature of the blast. The possibility of simulation of complex processes of the flow of micro-liquids in a space with a given rarefied atmosphere on a compact vacuum gas-dynamic test bench is shown. It is found that the continuous efflux from a thin capillary or a hole of small diameter into a vacuum or a strongly rarefied gaseous medium differs significantly from the well-studied modes of efflux into a dense gaseous medium, as well as from the pulse modes of efflux into a vacuum. The paper describes the main features of the flow and the conditions of the instability emergence. It is shown that the long-term flow of a liquid microjet in a vacuum has a high degree of surface instability, with a large number of sudden changes in direction, structure and observed density. An explanation for the causes of microjet failure, caused mainly by a combination of capillary instability and intense evaporation of superheated liquid from the surface of the jet, is proposed. The formation of surface gas caverns causing explosive collapse of the microjet with ejection of vapor-liquid droplets is established.

Data analysis and isotopic ratios measured onboard the Spacecraft Atmosphere Monitor

The Spacecraft Atmosphere Monitor (S.A.M.) is a scientific payload, which includes a Paul quadrupole ion trap (QIT) mass spectrometer and has been continuously operated onboard the International Space Station (ISS) between August 2019 and July 2021. S.A.M. measures the chemical composition of ISS cabin air and reports on major constituents (N2, O2, Ar, CO2, and CH4) once every 2 s. Each second, S.A.M. measures one hundred individual mass spectra stored in 4800 1μs-long channels. This report presents the autonomous onboard data analysis software that calibrates the mass spectrum, removes the residual gas background signal, identifies species of interest, and reports relevant abundances. In addition, we describe a ground-based analysis of downloaded S.A.M.'s data to extract the H, C, N, O, and Ar isotope ratios. We also describe experiments, requested by the ISS Vehicle office, to ascertain if benzene was present in the ISS cabin air (it was not). We demonstrate that S.A.M. instrument measures isotope ratios with precision and accuracy comparable to the state-of-the-art laboratory-size magnetic sector mass spectrometers.

Disproportionation of Nitric Oxide at a Surface-Bound Nickel Porphyrinoid.

Uncommon metal oxidation states in porphyrinoid cofactors are responsible for the activity of many enzymes. The F430 and P450nor co‐factors, with their reduced NiI‐ and FeIII‐containing tetrapyrrolic cores, are prototypical examples of biological systems involved in methane formation and in the reduction of nitric oxide, respectively. Herein, using a comprehensive range of experimental and theoretical methods, we raise evidence that nickel tetraphenyl porphyrins deposited in vacuo on a copper surface are reactive towards nitric oxide disproportionation at room temperature. The interpretation of the measurements is far from being straightforward due to the high reactivity of the different nitrogen oxides species (eventually present in the residual gas background) and of the possible reaction intermediates. The picture is detailed in order to disentangle the challenging complexity of the system, where even a small fraction of contamination can change the scenario.

Disproportionation of Nitric Oxide at a Surface-Bound Nickel Porphyrinoid.

Uncommon metal oxidation states in porphyrinoid cofactors are responsible for the activity of many enzymes. The F430 and P450nor co-factors, with their reduced NiI- and FeIII-containing tetrapyrrolic cores, are prototypical examples of biological systems involved in methane formation and in the reduction of nitric oxide, respectively. Herein, using a comprehensive range of experimental and theoretical methods, we raise evidence that nickel tetraphenyl porphyrins deposited in vacuo on a copper surface are reactive towards nitric oxide disproportionation at room temperature. The interpretation of the measurements is far from being straightforward due to the high reactivity of the different nitrogen oxides species (eventually present in the residual gas background) and of the possible reaction intermediates. The picture is detailed in order to disentangle the challenging complexity of the system, where even a small fraction of contamination can change the scenario.

Search for the Chiral Magnetic Effect via Charge-Dependent Azimuthal Correlations Relative to Spectator and Participant Planes in Au+Au Collisions at sqrt[s_{NN}]=200 GeV.

The chiral magnetic effect (CME) refers to charge separation along a strong magnetic field due to imbalanced chirality of quarks in local parity and charge-parity violating domains in quantum chromodynamics. The experimental measurement of the charge separation is made difficult by the presence of a major background from elliptic azimuthal anisotropy. This background and the CME signal have different sensitivities to the spectator and participant planes, and could thus be determined by measurements with respect to these planes. We report such measurements in Au+Au collisions at a nucleon-nucleon center-of-mass energy of 200GeV at the Relativistic Heavy-Ion Collider. It is found that the charge separation, with the flow background removed, is consistent with zero in peripheral (large impact parameter) collisions. Some indication of finite CME signals is seen in midcentral (intermediate impact parameter) collisions. Significant residual background effects may, however, still be present.

Measurements of gamma ray, cosmic muon and residual neutron background fluxes for rare event search experiments at an underground laboratory

Ambient radiation background contributed by the penetrating cosmic ray particles and the radionuclides present in the rock materials have been measured at an underground laboratory at Jaduguda, Jharkhand, India, located inside a mine at 555 m depth. The laboratory is being set up to explore rare event search processes, such as direct dark matter search, neutrinoless double beta decay, axion search, supernova neutrino detection, etc., that require specific knowledge of the nature and extent of the radiation environment in order to assess the sensitivity reach and also to plan for its reduction for the targeted experiment. The gamma ray background, which is mostly contributed by the primordial radionuclides and their decay chain products, have been measured inside the laboratory and found to be dominated by rock radioactivity for Eγ≲3MeV. Shielding of these residual gamma rays for the experiment was also evaluated. The cosmic muon flux, measured inside the laboratory using large area plastic scintillator telescope, was found to be: (2.257±0.261±0.042)×10−7cm−2s−1, which agrees reasonably well with simulation results. The neutron background flux has been measured for the radiogenic neutrons and found to be: (1.61±0.03)×10−4cm−2s−1 for no threshold cut. Detailed GEANT4 simulation for the radiogenic neutrons and the cosmogenic neutrons have been carried out. Effects of multiple scattering of both the types of neutrons within the surrounding rock and the cavern walls were studied and the results for the radiogenic neutrons are found to be in reasonable agreement with experimental results. Neutron fluxes contributed by those neutrons of cosmogenic origin have been reported as function of the energy threshold.

Photoluminescence spectrum of divacancy in porous and nanocrystalline cubic silicon carbide

The divacancy in silicon carbide (SiC) is a prominent solid state defect quantum bit that bears a relatively strong fluorescence and optically detected magnetic resonance contrast (ODMR) at room temperature. These properties exemplify it for quantum sensing of biological molecules. To this end, we previously developed a top-down method to create divacancies in cubic SiC nanoparticles (NPs) as non-perturbative ODMR biomarkers. In this process, large SiC particles are synthesized and then stain etched to form porous SiC and then ultrasonication and filtering are applied to the solution to extract few nanometer diameter SiC NPs. We called this process no-photon exciton generation chemistry (NPEGEC). We showed that by adding aluminum to carbon and silicon in the synthesis process of cubic SiC, one can engineer divacancy defects in SiC NPs by NPEGEC. An alternative traditional way to introduce vacancies to the SiC lattice is irradiation. Here, we compare the fluorescence spectra of divacancies as created by neutron irradiation in porous cubic SiC and NPEGEC technique in SiC NPs, and the results are analyzed in detail by means of first principles calculations. We find that the irradiation technique produces a larger shift in the fluorescence spectrum with residual background fluorescence than that for divacancies in SiC NPs, which is most likely caused by the parasitic defects left after irradiation and annealing in the former sample. These results imply that the chemistry technique applied to prepare divacancies in few nanometer SiC NPs may preserve the bulk-like quality of divacancy quantum bits near the surface.

Features of the Flow of a Model Liquid Into a Medium With a Variable Degree of Rarefaction

Abstract Experimental results of observing ethanol microjets expiring into a highly rarefied medium (vacuum) through a nozzle are presented. The study of the process was carried out both at the horizontal and vertical liquid stream from the source compared to the direction of gravity The residual background gas pressure in the vacuum chamber was maintained at a level much lower than the saturated vapor pressure of the working fluid at a given outlet temperature. The possibility of modeling complex processes of microfluids expiring into a medium with a given rarefied atmosphere on a compact vacuum gas-dynamic stand is shown. It is established that the long-term flow from a thin capillary or a small-diameter hole into a vacuum or a highly rarefied gas medium differs significantly from the well-studied flow modes into a dense gas medium, as well as from the pulsed flow modes into a vacuum. The paper describes the main features of the flow and the conditions for the occurrence of instability. It is shown that the long-term flow of a liquid microjet in a vacuum has a high degree of surface instability, with a large number of sudden changes in the direction, structure, and observed density. An explanation of the reasons for the destruction of the microjet (due to the combination of capillary instability and intense evaporation of superheated liquid from the surface of the jet) is proposed. The formation of surface gas caverns causing explosive destruction of the microjet with the release of vapor–liquid droplets is established.

Progress in Fast and Red Plastic Scintillators

Radiological detection where Cherenkov residual background can be prominent requires scintillators with increased emission wavelength. Cherenkov residual background precludes the use of UV-emitting sensors such as plastic scintillators. However, the literature is scarce in red-emitting plastic scintillators and only one commercial scintillator is currently available (BC-430, from Saint-Gobain Crystals and Detectors). In addition, X-ray imaging or time-of-flight positron emission tomography (ToF-PET) applications are also demanding on this type (color) of scintillators, but such applications also require that the material displays a fast response, which is not particularly the case for BC-430. We present herein our latest developments in the preparation and characterization of fast and red plastic scintillators for this application. Here, ‘fast’ means nanosecond range decay time and ‘red’ is an emission wavelength shifted towards more than 550 nm. At first, the strategy to the preparation of such material is explained by decomposing the scintillator to fundamental elements. Each stage is then optimized in terms of decay time response, then the elemental bricks are arranged to give plastic scintillator formulations that are compatible with the abovementioned characteristics. The results are compared with the red-emissive BC-430 commercial plastic, and the ultra-fast, violet-emitting BC-422Q 1% plastic. In particular, the first-time use of trans-4-dimethylamino-4′-nitrostilbene in the scintillation field as a red wavelength shifter allowed preparing plastic scintillators with the following properties: λemmax 554 nm, photoluminescence decay time 4.2 ns, and light output ≈ 6100 ph/MeV. This means a scintillator almost as bright as BC-430 but at least three times faster. This new sensor might provide useful properties for nuclear instrumentation.

RPCA-DRNN technique for monaural singing voice separation

In this study, we propose a methodology for separating a singing voice from musical accompaniment in a monaural musical mixture. The proposed method uses robust principal component analysis (RPCA), followed by postprocessing, including median filter, morphology, and high-pass filter, to decompose the mixture. Subsequently, a deep recurrent neural network comprising two jointly optimized parallel-stacked recurrent neural networks (sRNNs) with mask layers and trained on limited data and computation is applied to the decomposed components to optimize the final estimated separated singing voice and background music to further correct misclassified or residual singing and background music in the initial separation. The experimental results of MIR-1K, ccMixter, and MUSDB18 datasets and the comparison with ten existing techniques indicate that the proposed method achieves competitive performance in monaural singing voice separation. On MUSDB18, the proposed method reaches the comparable separation quality in less training data and lower computational cost compared to the other state-of-the-art technique.

KATRIN background due to surface radioimpurities

The goal of the KArlsruhe TRItrium Neutrino (KATRIN) experiment is the determination of the effective electron antineutrino mass with a sensitivity of 0.2eV/c2 at 90% C.L.11C.L. - confidence level.. This goal can only be achieved with a very low background level in the order of 10mcps22mcps - milli count per second. in the detector region of interest. A possible background source are α-decays on the inner surface of the KATRIN Main Spectrometer. Rydberg atoms, produced in sputtering processes accompanying the α-decays, are not influenced by electric or magnetic fields and freely propagate inside the vacuum of the Main Spectrometer. Here, they can be ionized by thermal radiation and the released electrons directly contribute to the KATRIN background. Two α-sources, 223Ra and 228Th, were installed at the Main Spectrometer with the purpose of temporarily increasing the background in order to study α-decay induced background processes. In this paper, we present a possible background generation mechanism and measurements performed with these two radioactive sources. Our results show a clear correlation between α-activity on the inner spectrometer surface and background from the volume of the spectrometer. Two key characteristics of the Main Spectrometer background – the dependency on the inner electrode offset potential, and the radial distribution – could be reproduced with this artificially induced background. These findings indicate a high contribution of α-decay induced events to the residual KATRIN background.

Comments on “A new method to subtract dayglow for auroral observation of SSUSI in LBH ranges based on the improved AURIC” by Wang et al. (2021)

A paper A new method to subtract dayglow for auroral observation of SSUSI in LBH ranges based on the improved AURIC reports a new method to estimate the dayglow intensities in DMSP/SSUSI LBH bands using an improved AURIC model. It is claimed that the new method offers a better alternative than the SSUSI operational algorithm which uses a data based table. The paper showed a few examples and compared them with SSSUI operational results. The comparison indicated that the new method didn't offer any improvement and provided net auroral images with strong residual dayglow. On the other hand, the auroral oval can be easily recognized in the SSUSI data using the operational algorithm, despite some weak residual background which is expected due to count errors in the data. There are likely a few reasons why the method led to poor results: (1) dayglow contribution in SSUSI data covers solar zenith angles (SZA) beyond 90° and the AURIC model is limited to SZA ≤90°, (2) In addition to SZA, SSUSI radiances also depend on look angle (along and cross track pixels). Such a look-angle effect was apparently not reported in the paper. (3) The localized peaks in the plots (radiance versus SZA) were likely due to changes in solar EUV flux, SZA as well as noises caused Southern Atlantic Anomaly, MeV particles at sub-auroral latitude and glint in the Ap dependent data bins. The examples in the paper indicate that the new algorithm is not appropriate to estimate net SSUSI dayglow intensity.

Laser-induced thermal source for cold atoms

We demonstrate a simple and compact approach to laser cool and trap atoms based on laser-induced thermal ablation (LITA) of a pure solid granule. A rapid thermalisation of the granule leads to a fast recovery of the ultra-high vacuum condition required for a long trapping lifetime of the cold gas. We give a proof-of-concept of the technique, performing a magneto-optical trap on the 461 nm ^1S_0rightarrow ,^1P_1 transition of strontium. We get up to 3.5 million of cold strontium-88 atoms with a trapping lifetime of more than 4 s. The lifetime is limited by the pressure of the strontium-free residual background vapour. We also implement an original configuration of permanent magnets to create the quadruple magnetic field of the magneto-optical trap. The LITA technique can be generalized to other atomic elements such as transition metals and lanthanide atoms, and shows a strong potential for applications in quantum technologies ranging from quantum computing to precision measurements such as outdoor inertial sensing.

Infrared Small Target Detection Based on Weighted Three-Layer Window Local Contrast

The performance of small target detection restricts the development of the infrared search and track (IRST) system. Against the complicated background clutter of the infrared (IR) image, the small targets are difficult to separate from a noisy background. Aiming at solving the problem of residual background clutter in the local contrast method, a weighted three-layer window local contrast method (WTLLCM) is proposed in this letter. First, the images are filtered by a layered gradient kernel to enhance the contrast between targets and background. Then, a three-layer window is utilized to calculate the local contrast of the filtered images. Next, it is worth mentioning that a simple target aggregation strategy is considered to preserve the integrity of the target. Especially, a new region intensity level (NRIL) algorithm is proposed to weigh the local contrast map to further suppress the background. Finally, the targets are detected by adaptive threshold segmentation. Compared with state-of-the-art small targets detection baseline algorithms based on local contrast, extensive experimental results demonstrate the superiority of the proposed method, especially in complex backgrounds. And instead of utilizing multi-scale windows, multi-scale targets detection is accomplished by using a single-scale window to reduce the calculation of the method.

Decoupling of Spin Decoherence Paths near Zero Magnetic Field.

We demonstrate a method to quantify and manipulate nuclear spin decoherence mechanisms that are active in zero to ultralow magnetic fields. These include (i) nonadiabatic switching of spin quantization axis due to residual background fields and (ii) scalar pathways due to through-bond couplings between 1H and heteronuclear spin species, such as 2H used partially as an isotopic substitute for 1H. Under conditions of free evolution, scalar relaxation due to 2H can significantly limit nuclear spin polarization lifetimes and thus the scope of magnetic resonance procedures near zero field. It is shown that robust trains of pulsed dc magnetic fields that apply π flip angles to one or multiple spin species may switch the effective symmetry of the nuclear spin Hamiltonian, imposing decoupled or coupled dynamic regimes on demand. The method should broaden the spectrum of hyperpolarized biomedical contrast-agent compounds and hyperpolarization procedures that are used near zero field.

Increase of the barium ion-trap lifetime via photodissociation

The lifetime of ${\mathrm{Ba}}^{+}$ ions confined in a Paul trap is found, under typical conditions, to be limited by chemical reactions with residual background gas. An integrated ion-trap and time-of-flight mass spectrometer are used to analyze the reactions of the trapped ${\mathrm{Ba}}^{+}$ ions with three common gases in an ultrahigh vacuum system (${\mathrm{H}}_{2}$, ${\mathrm{CO}}_{2}$, and ${\mathrm{H}}_{2}\mathrm{O}$). It is found that the products of these reactions can all be photodissociated by a single ultraviolet laser at 225 nm, thereby allowing the recovery of the ${\mathrm{Ba}}^{+}$ ions and leading to an increase of the effective trap lifetime. For a Coulomb crystal, the lifetime increased from roughly 6 h to 2 days at room temperature. It is suggested that higher enhancement factors are possible in systems with stronger traps. In addition, photodissociation wavelengths for other common trapped-ion systems are provided.

CNNs for enhanced background discrimination in DSNB searches in large-scale water-Gd detectors

Gadolinium-loading of large water Cherenkov detectors is a prime method for the detection of the Diffuse Supernova Neutrino Background (DSNB). While the enhanced neutron tagging capability greatly reduces single-event backgrounds, correlated events mimicking the IBD coincidence signature remain a potentially harmful background. Neutral-Current (NC) interactions of atmospheric neutrinos potentially dominate the DSNB signal especially in the low-energy range of the observation window that reaches from about 12 to 30 MeV.The present paper investigates a novel method for the discrimination of this background. Convolutional Neural Networks (CNNs) offer the possibility for a direct analysis and classification of the PMT hit patterns of the prompt events. Based on the events generated in a simplified SuperKamiokande-like detector setup, we find that a trained CNN can maintain a signal efficiency of 96% while reducing the residual NC background to 2% of the original rate. Comparing to recent predictions of the DSNB signal and measurements of the NC background levels in Super-Kamiokande, the corresponding signal-to-background ratio is about 4:1, providing excellent conditions for a DSNB discovery.

Fitting ultracold resonances without a fit

We present a numerical procedure allowing one to extract Feshbach resonance parameters from numerical calculations without relying on approximate fitting procedures. Our approach is based on a simple decomposition of the reactance matrix in terms of poles and residual background contribution, and can be applied to the general situation of inelastic overlapping resonances. A simple lineshape for overlapping inelastic resonances, equivalent to known results in the particular cases of isolated and overlapping elastic features, is also rigorously derived.