Continuous Spectrum Research Articles

Magnetic field sensor based on multiple Fano resonance in metal-insulator-metal waveguide coupled with cross-shape resonator

Abstract In this paper, an innovative plasmonic magnetic field sensor (MFS) that exploits a Metal-insulator-Metal (MIM) waveguide configuration with an asymmetric cross-shaped resonator is constructed. The design enables the observation of double Fano resonance in the transmission spectrum, resulting from the coupling between continuous spectrum and discrete spectrum. By incorporating magnetic fluid in the asymmetric cross-shape resonator, the Fano line shapes can be tuned by the external magnetic field. Finite-Difference Time-Domain (FDTD) is used to simulate the spectra response to external magnetic fields and geometrical sizes. The proposed structure exhibits remarkable magnetic field sensitivity of 12.1 p m / O e within the detection range of 15 O e to 199 O e . The resolution of MIM magnetic field sensors can reach 0.0826 O e . The optimal figure of merit (FOM) and maximum Q factor of the Fano dip are about 6.9 × 10 − 4 / O e and 66.74, respectively. Meanwhile, The proposed Fano resonance MFS has some advantages, including compact size, high sensitivity, and cost-effectiveness. A strong linear relationship between the magnetic field and resonance wavelength indicates that the proposed structure can find potential applications in diverse fields such as magnetic field sensors, aircraft navigation, and even nuclear energy generation.

A deep learning-based method for assessing tricuspid regurgitation using continuous wave Doppler spectra

Transthoracic echocardiography (TTE) is widely recognized as one of the principal modalities for diagnosing tricuspid regurgitation (TR). The diagnostic procedures associated with conventional methods are intricate and labor-intensive, with human errors leading to measurement variability, with outcomes critically dependent on the operators’ diagnostic expertise. In this study, we present an innovative assessment methodology for evaluating TR severity utilizing an end-to-end deep learning system. This deep learning system comprises a segmentation model of single cardiac cycle TR continuous wave (CW) Doppler spectra and a classification model of the spectra, trained on the TR CW Doppler spectra from a cohort of 11,654 patients. The efficacy of this intelligent assessment methodology was validated on 1500 internal cases and 573 external cases. The receiver operating characteristic (ROC) curves of the internal validation results indicate that the deep learning system achieved the areas under curve (AUCs) of 0.88, 0.84, and 0.89 for mild, moderate, and severe TR, respectively. The ROC curves of the external validation results demonstrate that the system attained the AUCs of 0.86, 0.79, and 0.87 for mild, moderate, and severe TR, respectively. Our study results confirm the feasibility and efficacy of this novel intelligent assessment method for TR severity.

Deep learning-based alpha particles spectroscopy with solid-state nuclear track detector CR-39

A novel approach for alpha particles energy spectroscopy utilizing a sophisticated deep learning machine learning algorithm is introduced. The approach we employ classifies the alpha particles trajectories on a CR-39 detector into six discrete energy levels: 0.5 MeV, 1.5 MeV, 2.5 MeV, 3.5 MeV, 4.5 MeV, and 5.4 MeV. Some 57 different CR-39 detectors were exposed to alpha particles of the stated energy levels using a241Am source. The dosimeters were then subjected to etching and imaging utilizing a Landauer Neutrak© system. A self-developed computer vision method was used to separate the energy-tagged alpha tracks from the CR-39 images. These tracks images were then inputted into an artificial neural network (ANN) algorithm for training. After completing the training, a test dataset was run to assess the algorithm's performance. An average accuracy rate exceeding 98% was attained across the six energy levels.This algorithm has the potential to enhance the precision of alpha particle dosimetry. Furthermore, once generalized to a continuous energy spectrum, as well as for other types of particles such as protons, this algorithm is anticipated to prove highly beneficial for analyzing the outcomes of various laser-driven high-energy particle experiments in general, and specifically for fusion experiments.

Characterisation of IBD heterogeneity using serum proteomics: A multicentre study.

Recent genetic and transcriptomic data highlight the need for improved molecular characterisation of inflammatory bowel disease (IBD). Proteomics may advance the delineation of IBD phenotypes since it accounts for post-transcriptional modifications. We aimed to assess the IBD spectrum based on inflammatory serum proteins and identify discriminative patterns of underlying biological subtypes across multiple European cohorts. Using proximity extension methodology, we measured 86 inflammation-related serum proteins in 1551 IBD patients and 312 healthy controls (HC). We screened for proteins exhibiting significantly different levels among IBD subtypes and between IBD and HC. Classification models for differentiating between Crohn's disease (CD) and ulcerative colitis (UC) were employed to explore the IBD spectrum based on estimated probability scores. Levels of multiple proteins, such as IL-17A, MMP-10, and FGF-19, differed (fold-change>1.2; FDR<0.05) between ileal vs colonic IBD. Using multivariable models, a protein signature reflecting the IBD spectrum was identified, positioning colonic CD between UC and ileal CD, which were at opposite ends of the spectrum. Based on area under the curve (AUC) estimates, classification models more accurately differentiated UC from ileal CD (median AUCs>0.73) than colonic CD (median AUCs<0.62). Models differentiating colonic CD from ileal CD demonstrated intermediate performance (median AUCs 0.67-0.69). Our findings in serum proteins support the presence of a continuous IBD spectrum rather than a clear separation of CD and UC. Within the spectrum, disease location may reflect a more similar disease than CD vs UC, as colonic CD resembled UC more closely than ileal CD.

Correlation Between Radio Loudness and the Eddington Ratio in Quasars

ABSTRACTQuasars can be categorized into radio‐loud and radio‐quiet populations based on radio properties. The physical mechanisms underlying this dichotomy have long been an active area of investigation. In this work, we analyze multi‐wavelength data from 851 quasars matched between the SDSS DR14 and FIRST catalogs, requiring emission line measurements with signal‐to‐noise ratios &gt; 3, we fit quasar optical continuum spectra and compute the radio loudness, luminosities, and Eddington ratios. We classify quasars as radio‐loud or radio‐quiet using a dividing line of . We find that the distribution of the Eddington ratio and radio luminosity is different between the radio‐loud and radio‐quiet quasars, and the correlation between the Eddington ratio and radio loudness is disparate as well. The Eddington ratio shows a weakly positive correlation with radio loudness in both the whole sample and radio‐loud quasars, which imply that the Eddington ratio contributes to the radio loudness but it is not the dominant factor and that additional factors influence relativistic jet production in radio‐loud quasars. However, the Eddington ratio is anti‐correlated with radio loudness in radio‐quiet quasars, potentially related to the properties of the accretion disk.

Uncovering bound states in the continuum in InSb nanowire networks

Bound states in the continuum (BICs) are exotic, localized states even though their energy lies in the continuum spectra. Since its discovery in 1929, the quest to unveil these exotic states in charge transport experiments remains an active pursuit in condensed matter physics. Here, we study charge transport in InSb nanowire networks in the ballistic regime and subject to a perpendicular magnetic field as ideal candidates to observe and control the appearance of BICs. We find that BICs reveal themselves as distinctive resonances or antiresonances in the conductance by varying the applied magnetic field and the Fermi energy. We systematically consider different lead connections in hashtag-like nanowire networks, finding the optimal configuration that enhances the features associated with the emergence of BICs. Finally, the investigation focuses on the effect of the Rashba spin–orbit interaction of InSb on the occurrence of BICs in nanowire networks. While the interaction generally plays a detrimental role in the signatures of the BICs in the conductance of the nanowire networks, it opens the possibility to operate these nanostructures as spin filters for spintronics. We believe that this work could pave the way for the unambiguous observation of BICs in charge transport experiments and for the development of advanced spintronic devices.

Study of a gel dosimeter based on Ag nanoparticles for applications in radiation therapy with synchrotron X-rays at ultrahigh dose rate compared to 60Co γ-rays

A silver nitrate (AgNO3) gel was developed and evaluated as a dosimeter for synchrotron X-ray-based studies in microbeam radiation therapy (MRT) and FLASH radiation therapy. The gel was irradiated at the European Synchrotron Radiation Facility (ID17 Biomedical beamline) with a continuous X-ray spectrum in the 50-600 keV range and a dose rate of 11.6kGy/s. The spectrophotometric response after irradiation at this beamline was compared with the response at a conventional 60Co γ-ray source providing a dose rate of 0.27 Gy/s. Ag+ ions in the gel dosimeter undergo reduction to Ago nanoparticles, as detected at 450 nm, which is a surface plasmon resonance band. The intensity of this band increased linearly with increasing absorbed dose up to 100 Gy, and improved with the addition of glycerol. The gel dosimeter exhibited the lowest detectable dose (LDD) of 75.9% lower and a dose deposition of 76% higher for ID17 beamline irradiation than for 60Co irradiation. The theoretical relative response HQ,Qo for the gel irradiated at the synchrotron was 1.70, which is in close agreement with the experimental relative response FQ,Qo = 1.76. These results confirm the dose enhancement in the gel irradiated with orthovoltage X-rays. The good properties of the silver nitrate gel, together with its increased sensitivity to orthovoltage X-ray irradiation and modest overall uncertainty of 5.8% (2σ), confirm that the gel is a valid dosimeter for measurements at ultrahigh dose rates for synchrotron radiotherapy. The dosimeter is also a promising candidate for dose enhancement factor measurements in nanoparticle-based radiotherapy techniques.

All-dielectric transmissive narrow-band filters adjustable within wide spectral range

The challenge of obtaining transmission spectra with both a wider tunable spectral range and high resolution persists. In this paper, a novel all- dielectric transmissive grating structure based on Mie resonance is proposed. The structure excites the Mie resonance by embedding a high refractive index contrast grating in a KF-Si film system band-stop filter. The dipole resonance energy is confined within the high refractive index silicon grating material, expanding the cutoff bandwidth of the KF-Si film system to over 400 nm and achieving single-peak transmission in the visible range. And the continuous transmission spectrum has an adjustable range of 300 nm with the highest spectral resolution (FWHM) (∼20 nm) can be achieved by adjusting the grating period. To suppress the coupling energy excitation between the higher-order magnetic dipole and the substrate, a silicon-rich nitride (SRN) matching layer is introduced between the KF-Si film system and the substrate. This layer enhances the intensity of the resonance peaks while simultaneously suppressing the short-wavelength sidebands, thereby improving the saturation and purity of the spectrum. In addition, we obtained a large angular tolerance of up to 15° by stacking the silicon film system. This work is of great significance for the advancement of hyperspectral imaging and display technology.

No eigenvectors embedded in the singular continuous spectrum of Schrödinger operators

No eigenvectors embedded in the singular continuous spectrum of Schrödinger operators

A progress in the inverse matrix method in QCD sum rules

In traditional QCD sum rules, the simple hadron spectral density model of the “delta-function-type ground state + theta-function-type continuous spectrum” determines that there is no perfect parameter selection. In recent years, inverse problem methods, particularly the inverse matrix method, have shown better handling of QCD sum rules. This work continues to develop the inverse matrix method. Considering that the narrow-width approximation may still be a good approximation, we separate the ground state from the spectral density. We then follow the general steps of the inverse matrix method to extract physical quantities such as decay constants that we may be more interested in.

The putative center in NGC 1052

Context: Many active galaxies harbor powerful relativistic jets, however, the detailed mechanisms of their formation and acceleration remain poorly understood. Aims: To investigate the area of jet acceleration and collimation with the highest available angular resolution, we study the innermost region of the bipolar jet in the nearby low-ionization nuclear emission-line region (LINER) galaxy NGC\,1052. Methods: We combined observations of NGC\,1052 taken with VLBA, GMVA, and EHT over one week in the spring of 2017. Our study is focused on the size and continuum spectrum of the innermost region containing the central engine and the footpoints of both jets. We employed a synchrotron-self absorption model to fit the continuum radio spectrum and we combined the size measurements from close to the central engine out to $ to study the jet collimation. Results: For the first time, NGC\,1052 was detected with the EHT, providing a size of the central region in-between both jet bases of $43\ perpendicular to the jet axes, corresponding to just around $250\,R_ S $ (Schwarzschild radii). This size estimate supports previous studies of the jets expansion profile which suggest two breaks of the profile at around $3 10^3\,R_ S $ and $1 10^4\,R_ S $ distances to the core. Furthermore, we estimated the magnetic field to be 1.25\,Gauss at a distance of $22\ from the central engine by fitting a synchrotron-self absorption spectrum to the innermost emission feature, which shows a spectral turn-over at $ 130\,$GHz. Assuming a purely poloidal magnetic field, this implies an upper limit on the magnetic field strength at the event horizon of $2.6 10^4\,$Gauss, which is consistent with previous measurements. Conclusions: The complex, low-brightness, double-sided jet structure in NGC\,1052 makes it a challenge to detect the source at millimeter (mm) wavelengths. However, our first EHT observations have demonstrated that detection is possible up to at least 230\,GHz. This study offers a glimpse through the dense surrounding torus and into the innermost central region, where the jets are formed. This has enabled us to finally resolve this region and provide improved constraints on its expansion and magnetic field strength.

Determination of rare earth elements in synthetic calcium phosphates by high-resolution continuum source electrothermal atomic absorption spectrometry

Ceramic, cement and composite biomaterials have been developed based on hydroxyapatites (HA) and tricalcium phosphates (TCP), which are analogous in phase and chemical composition to the mineral component of bone tissue. The crystal structures of HA and TCP are arranged in isomorphic substitutions. Recently, research has focused on the modification of HA and TCP structures with ions of various metals, including rare earth ions (REEs), with the aim of creating materials with a range of beneficial properties for medical applications. REEs are known to have a number of useful properties, including antibacterial, antitumour, catalytic, magnetic and luminescent properties. The replacement of some of the Ca ions in the structures of HA and TCP with REE ions therefore makes it possible to obtain a material with biocompatibility and biological activity, giving it the required properties depending on the REE used and its concentration. In order to achieve the specified properties, it is necessary to control not only the structure (phase composition, lattice parameters of the powders) and the presence of characteristic functional groups, but also the chemical elemental composition. Modifications of hydroxyapatites and tricalcium phosphates containing from one to several different alloying elements are currently being developed. Various analytical methods are used for this purpose, including X-ray, atomic emission and a number of others. This article is devoted to the study of the analytical capabilities of the method of atomic absorption spectrometry with electrothermal atomization and a continuous spectrum source in relation to the determination of Eu and Yb in hydroxyapatites and tricalcium phosphates. The article considers the optimal conditions and modes of analysis, including temperature-time programs, the use of modifiers, the construction of calibration curves, and other factors that can be adjusted for more precise results. The results demonstrated the possibility of simultaneous determination of both Eu and Yb in the concentration range of 0.09 to 2 wt.%, with a relative standard deviation of less than 6 rel.%.

Fano resonances in gated phosphorene junctions

Fano resonances appear in plenty of physical phenomena due to the interference phenomena of a continuum spectrum and discrete states. In gated bilayer graphene junctions, the chiral matching at oblique incidence between the spectrum of electron states outside the electrostatic barrier and hole bound states inside it gives rise to an asymmetric line shape in the transmission as a function of the energy or Fano resonance. Here, we show that Fano resonances are also possible in gated phosphorene junctions along the zigzag direction. The special pseudospin texture of the charge carriers in the zigzag direction allows at oblique incidence the interference phenomena of the spectrum of electron states outside the electrostatic barrier with hole bound states inside it, giving rise to an asymmetric Fano line shape in the transmission. Due to the energy scale of the electrostatic barriers in phosphorene ultra thin barriers are required to observe the Fano resonance phenomenon. The preservation of the pseudospin texture with the closing of the phosphorene band gap opens the possibility to observe Fano resonances in smaller and wider electrostatic barriers. The asymmetric Fano line shape is susceptible to the transverse wave vector, the strength and width of the electrostatic barrier. Additionally, the conductance shows a characteristic mark in the position where the Fano resonances take place. The similarities and differences with respect to Fano resonances in bilayer graphene are also addressed.

The energy-frequency diagram of the (1+1)-dimensional Φ4 oscillon

Two different methods are used to study the existence and stability of the (1+1)-dimensional Φ4 oscillon. The variational technique approximates it by a periodic function with a set of adiabatically changing parameters. An alternative approach treats oscillons as standing waves in a finite-size box; these are sought as solutions of a boundary-value problem on a two-dimensional domain. The numerical analysis reveals that the standing wave’s energy-frequency diagram is fragmented into disjoint segments with ωn+1< ω < ωn, where ωn = ω0/(n + 1), n = 0, 1, 2, ., and ω0 is the endpoint of the continuous spectrum (mass threshold of the model). The variational approximation involving the first, zeroth and second harmonic components provides an accurate description of the oscillon with the frequency in (ω1, ω0), but breaks down as ω falls out of that interval.

Dirac points and inverse problems of quantum graphs associated with Archimedean tilings

Abstract One interesting phenomenon of graphene is the presence of the conical singularity&amp;#xD;or Dirac points. Using the quantum graph model, we show that there exist three&amp;#xD;classes of possible Dirac points for all of the periodic quantum graphs associated with&amp;#xD;Archimedean tilings, when the potentials are identical and even. They occur at the&amp;#xD;periodic eigenvalues, anti-periodic eigenvalues and other double eigenvalues of the dispersion&amp;#xD;relations respectively. We also characterize their associated potentials. Moreover,&amp;#xD;we show that there are no other possible Dirac points. Finally, we solve an&amp;#xD;inverse spectral problem for the potential, given the knowledge of the pure point and&amp;#xD;absolutely continuous spectra.

Relaxation of weakly collisional plasma: Continuous spectra, discrete eigenmodes, and the decay of echoes

Relaxation of weakly collisional plasma: Continuous spectra, discrete eigenmodes, and the decay of echoes

The high-energy cyclotron line in 2S 1417-624 discovered with Insight-HXMT during the 2018 outburst

We report a detailed timing and spectral analysis of the X-ray pulsar 2S 1417-624 using the data from Insight-HXMT during the 2018 outburst. The pulse profiles are highly variable with respect to both unabsorbed flux and energy. A double-peaked pulse profile from the low flux evolved to a multi-peaked shape in the high-flux state. The pulse fraction is negatively correlated to the source flux in the range of sim (1--6)$\ $ erg cm$^ $ s$^ $, consistent with Rossi X-ray Timing Explorer (RXTE) studies during the 2009 giant outburst. The energy-resolved pulse profiles around the peak outburst showed a four-peak shape in the low-energy bands and gradually evolved to triple peaks at higher energies. The continuum spectrum is well described by typical phenomenological models, such as the cut-off power law and the power law with high-energy cut-off models. Notably, we discovered high-energy cyclotron resonant scattering features (CRSFs) for the first time, which are around 100 keV with a statistical significance of sim 7sigma near the peak luminosity of the outburst. This CRSF line is significantly detected with different continuum models and provides very robust evidence for its presence. Furthermore, pulse-phase-resolved spectroscopy confirmed the presence of the line, whose energy varied from 97 to 107 keV over the pulse phase and appeared to have a maximum value at the narrow peak phase of the profiles.

On absolutely continuous spectrum for one-channel unitary operators

On absolutely continuous spectrum for one-channel unitary operators

Absence of bound states for quantum walks and CMV matrices via reflections

We give a criterion based on reflection symmetries in the spirit of Jitomirskaya–Simon to show absence of point spectrum for (split-step) quantum walks and Cantero–Moral–Velázquez (CMV) matrices. To accomplish this, we use some ideas from a recent paper by the authors and collaborators to implement suitable reflection symmetries for such operators. We give several applications. For instance, we deduce arithmetic delocalization in the phase for the unitary almost-Mathieu operator and singular continuous spectrum for generic CMV matrices generated by the Thue–Morse subshift.

Perturbation Theory of the Continuous Spectrum in the Theory of Nuclear Reactions

Perturbation Theory of the Continuous Spectrum in the Theory of Nuclear Reactions