Continuous Spectrum Research Articles

A functional renormalization group for signal detection and stochastic ergodicity breaking

Signal detection is one of the main challenges in data science. As often happens in data analysis, the signal in the data may be corrupted by noise. There is a wide range of techniques that aim to extract the relevant degrees of freedom from data. However, some problems remain difficult. This is notably the case for signal detection in almost continuous spectra when the signal-to-noise ratio is small enough. This paper follows a recent bibliographic line, which tackles this issue with field-theoretical methods. Previous analysis focused on equilibrium Boltzmann distributions for an effective field representing the degrees of freedom of data. It was possible to establish a relation between signal detection and Z2 -symmetry breaking. In this paper, we consider a stochastic field framework inspired by the so-called ‘model A’, and show that the ability to reach, or not reach, an equilibrium state is correlated with the shape of the dataset. In particular, by studying the renormalization group of the model, we show that the weak ergodicity prescription is always broken for signals that are small enough, when the data distribution is close to the Marchenko–Pastur law. This, in particular, enables the definition of a detection threshold in the regime where the signal-to-noise ratio is small enough.

Multiple-signal-joint-processing-based guard interval shortening method for a CS-NFDM system.

Aiming to further improve the spectral efficiency (SE) of a continuous spectrum modulated nonlinear frequency division multiplexing (CS-NFDM) system, we propose a novel ,to the best of our knowledge, multiple-signal-joint-processing (MSJP)-based guard interval (GI) shortening method. In this method, multiple NFDM time-domain signals are jointly processed as a whole to carry out nonlinear Fourier transform and inverse nonlinear Fourier transform (NFT-INFT) operations. These operations can fuse the multiple NFDM time-domain signals together, which is equivalent to the corresponding inverse process of a fiber transmission. Experimental results show that the normalized SE of the proposed method can reach 0.99 when approaching the limit value of 1 and obtain a 2.33 dB Q2-factor improvement compared with the pre-dispersion compensation (PDC) method under the same GI of 0.03 ns in an 80 km SSMF transmission of a 46 GHz signal bandwidth. Furthermore, in comparison with the PDC method, the proposed method can achieve 32.86% normalized SE improvement in the 1120 km SSMF transmission of 32 GHz signal bandwidth under the SD-FEC of 2.4E-2.

Coherent distributions of the symmetry algebra of spinor regularization generator and hydrogen atom

A new approach is developed for solving spectral problems for operators with continuous spectrum, which consists in the integral transform of the problem by using coherent Schwartz distributions. The constructed family of coherent distributions is a complete analogue of the family of ordinary coherent states. More precisely, it satisfies all Gazeau–Klauder axioms satisfied by the usual coherent states. But in contrast to the coherent states belonging to the point spectrum of the annihilation operator (or operators), the coherent distributions belong to the continuous spectrum of some Hermitian operators. Therefore, the coherent distributions work better than the coherent states as the kernel of the integral representation of generalized eigenfunctions of operators with continuous spectrum. In this work, this approach is demonstrated with an example of solving a basic problem of quantum mechanics, i.e., the problem of the continuous part of the spectrum of the Hamiltonian of the hydrogen atom.

Biomass flame spectroscopy technique to identify wood species through spectral emission during combustion processes

The energy emitted by a flame and its spectra provide critical information about fuels, such as energy type, temperature, and molecular properties. While traditionally used to analyze combustion, we introduce a spectral-time-based index, optical calorific power (OCP), to calculate the total energy released per mass unit (J/Kg), relating to the calorific value of wood-based fuels. Using novel optical variables and machine learning, we identified different wood species during the combustion of the wood samples. Homogeneous samples of four wood species (sapwood and heartwood) were ignited in a temperature-controlled furnace. Spectra were measured using a calibrated spectrophotometer in the 450–900 nm range with a 100ms integration time. Continuous and discontinuous spectral patterns were observed in all samples, used to calculate spectral-time-based optical variables, and separated using the AirPLS algorithm. Discontinuous spectra correlated with Na and K emissions (589.4 nm and 766.5 nm, respectively). Continuous spectra were analyzed to determine optical variables such as flame temperature (K), total continuous radiation (TCR, μW/cm2), and total continuous energy (TCE, μJ). Five supervised classification models, XGBoost, LR, SVM, LDA, and RF, were trained using normalized physical parameters and optical variables with stratified cross-validation. The proposed optical variables yielded an identification accuracy of 93%, precision of 95%, and recall of 93% during combustion using the XGBoost method. These promising results demonstrate the potential of our method for accurately identifying wood species, while offering a cost-effective and novel alternative to NIR-SWIR reflectance spectral identification techniques.

Development of improved higher-order correction for the NIF opacity spectrometer.

X-ray opacity measurements on the National Ignition Facility (NIF) are in the process of reproducing earlier measurements from the Sandia Z Facility, in particular for oxygen and iron plasmas. These measurements have the potential to revise our understanding of the "solar problem" and of the hot degenerate Q class white dwarf structure by probing plasma conditions near the base of their convection zones. Accurate opacity measurements using soft x-ray Bragg crystal spectrometers require correction for higher-order diffraction effects. Extending prior work in this area [Dutra etal., Review of Scientific Instruments 93, 113527 (2022)], we have developed a new method to remove higher-order spectral components from NIF opacity spectrometer data. By modeling absorption and backlighting continuum spectra and subtracting the second- and third-order components from the measured data, we are able to perform this correction while avoiding imprinting first-order model line features onto the data.

Reflectance Spectroscopy of 27 Fine-particulate Mineral Samples from Far-ultraviolet through Mid-infrared (0.12–20 μm)

This paper presents far-ultraviolet through mid-infrared (0.12–20 μm) reflectance spectra of 27 fine-particulate (<10 μm) terrestrial mineral samples, providing continuous spectra that cover an unusually broad spectral range and are of unusually fine particle size relative to most existing spectral libraries. These spectra of common geologic materials are useful for future applications that study the dust on various planetary bodies. Reflectance spectra were acquired of the samples at multiple laboratories at multiple wavelengths. All of the spectra were compared to one another to observe the general, common spectral characteristics (e.g., slope, band shape, and band depth), and the best segments of the spectra representing the mineral reflectance were scaled and spliced together to form a “Frankenspectrum” for each mineral that best represents the full wavelength range of far-ultraviolet, visible, near-infrared, and middle-infrared wavelengths. These scaled and spliced Frankenspectra, as well as the entire set of individual “original” reflectance spectra from each laboratory, are available in the Planetary Data System Geosciences Node.

Minimalist model of the W50/SS433 extended X-ray jet: Anisotropic wind with recollimation shocks

W50 is a radio nebula around the hyperaccreting Galactic microquasar SS433. We focus on one peculiar feature of W50, that is, on a pair of so-called extended X-ray jets (EXJs). These jets have a size of ∼20 pc and a sharp inner boundary, and their spectra are well represented by a featureless X-ray continuum. We argue that EXJs could be an outcome of a powerful anisotropic wind produced by a supercritical accretion disk. In the simplest version of this model, the wind itself consists of two components. The first component is a nearly isotropic outflow that subtends most of the solid angle as seen from the compact source and creates the quasi-spherical part of the W50 nebula. The second component is a more collimated wind that is aligned with the rotation axis of the binary system (polar wind). The isotropic outflow passes through the termination shock, and its increased thermal pressure creates a sequence of recollimation shocks in the polar wind, giving it the appearance of an extended X-ray structure. In this model, the EXJ continuum spectrum is due to synchrotron emission of electrons that are accelerated at the shocks that arise in the polar wind. At variance with many other studies, the EXJ structures in this model are not directly related to the highly collimated and precessing 0.26 c baryonic jets. Instead, the EXJ and the ears of W50 are produced by the part of the wind whose Eddington-level kinetic luminosity is confined to a half-opening angle of 5–10 degrees. This is not necessarily a recollimated version of the 0.26 c jets.

Tunneling Currents in the Hyperbolic Phase Space.

We introduce the quantum currents for quantum systems with an SU(1,1) dynamic symmetry group whose evolution is governed by a non-linear Hamiltonian possessing a continuous spectrum and apply them to the analysis of the tunneling dynamics on the hyperbolic phase space.

Absolutely continuous edge spectrum of topological insulators with an odd time-reversal symmetry

We show that non-trivial two-dimensional topological insulators protected by an odd time-reversal symmetry have absolutely continuous edge spectrum. To accomplish this, we establish a time-reversal symmetric version of the Wold decomposition that singles out extended edge modes of the topological insulator.

Magneto-Optical Ceramics with High Transparency for Highly Sensitive Magnetometer via Quantum Weak Measurement.

Sensitive magnetometer technology is desirable for biomagnetic field detection and geomagnetic field measuring. Signal amplification materials such as magneto-optical crystals or ceramics are crucial for enhancing detection sensitivity, but severe optical scattering and low Verdet constant further limit its application. To develop high-sensitivity magnetometers for quantum weak measurement schemes, we have conducted investigations on the powder calcining dynamics and prepared a series of high-optical-quality (Ho/Dy)2Zr2O7 transparent ceramic samples. The Verdet constant of magneto-optical materials was measured across a continuous wavelength spectrum, exhibiting a peak at 283 ± 5 rad/(T·m). We further established an electron transition mechanism to elucidate the exceptional magneto-optical attributes of dysprosium. In addition, samples demonstrated superior performance in weak-value amplification, reaching a low detectable magnetic field threshold of 3.5 × 10-8 T and continuously worked over 6 h with high stability. Our work developed a highly sensitive magnetometer using optimized magneto-optical ceramics and provided guidance on design, fabrication, and application for magneto-optical ceramics in quantum weak measurement.

Robust topological bound states in the continuum in a quantum Hall bar with an anti-dot

Bound states in the continuum (BICs) are quantum states with normalizable wave functions and energies that lie within the continuous spectrum for which extended or dispersive states are also available. These special states, which have shown great applicability in photonic systems for devices such as lasers and sensors, are also predicted to exist in electronic low-dimensional solid-state systems. The non-trivial topology of materials is within the known mechanisms that prevent the bound states to couple with the extended states. In this work we search for topologically protected BICs in a quantum Hall bar with an anti-dot formed by a pore far from the borders of the bar. The bound state energies and wavefunctions are calculated by means of the Recursive S-Matrix method. The resulting bound state energies coexist with extended states and exhibit a pattern complimentary to the Hofstadter butterfly. A symmetry-breaking diagonal disorder was introduced, showing that the BICs with energies far from the Landau levels remain robust. Moreover, the energy difference between consecutive BICs multiplied by the anti-dot perimeter follows the same curve despite disorder. Finally, a BIC-mediated current switching effect was found in a multi-terminal setup for zero and finite temperature, which might permit their experimental detection.

Construction of Topological Bound States in the Continuum Via Subsymmetry.

Topological bound states in the continuum (BICs) are localized topological boundary modes coexisting with a continuous spectrum of extended modes. They have been realized in systems with symmetry-protected topological phases, where their immunity to defects and perturbations depends on the presence of symmetries. Here we propose a method that transforms an in-gap topological boundary state into a BIC by using the concept of subsymmetry. We design the coupling between a system possessing in-gap topological modes and a system possessing a continuum of states that results in topological BICs. We define the criteria for the coupling that yields the desired results. To implement this scheme, we construct representative topological BICs based on one-dimensional Su-Schrieffer-Heeger models and implement them in photonic lattices. Our results not only reveal novel physical phenomena but may also provide methods for designing a new generation of topological devices.

The spectrum of anti-GQ1B antibody syndrome: beyond Miller Fisher syndrome and Bickerstaff brainstem encephalitis.

Since the initial identification of Miller Fisher syndrome (MFS) and Bickerstaff brainstem encephalitis (BBE),significant milestones have been achieved in understanding these diseases.Discoveries of common serum antibodies (IgG anti-GQ1b), antecedent infections, neurophysiological data, andneuroimaging suggested a shared autoimmune pathogenetic mechanism rather than distinct pathogenesis, leadingto the hypothesis that both diseases are part of a unified syndrome, termed "Fisher-Bickerstaff syndrome". The subsequent identification of atypical anti-GQ1b-positive forms expanded the classification to a broader condition known as "Anti-GQ1b-Antibody syndrome". An exhaustive literature review was conducted, analyzing a substantial body of research spanning from the initialdescriptions of the syndrome's components to recent developments in diagnostic classification and researchperspectives. Anti-GQ1b syndrome encompasses a continuous spectrum of conditions defined by a common serological profilewith varying degrees of peripheral (PNS) and central nervous system (CNS) involvement. MFS and BBE represent theopposite ends of this spectrum, with MFS primarily affecting the PNS and BBE predominantly involving the CNS.Recently identified atypical forms, such as acute ophthalmoparesis, acute ataxic neuropathy withoutophthalmoparesis, Guillain-Barré syndrome (GBS) with ophthalmoparesis, MFS-GBS and BBE-GBS overlap syndromes,have broadened this spectrum. This work aims to provide an extensive, detailed, and updated overview of all aspects of the anti-GQ1b syndromewith the intention of serving as a stepping stone for further shaping thereof. Special attention was given to therecently identified atypical forms, underscoring their significance in redefining the boundaries of the syndrome.

Dark matter from evaporating primordial black holes in the early universe

Primordial Black Holes (PBHs) could dominate in the early universe and, evaporating before Big bang Nucleosynthesis, provide new freeze in mechanism of dark matter (DM) production. The proposed scenario is considered for two possible mechanisms of PBH formation and the corresponding continuous PBH mass spectra so that the effect of non-single PBH mass spectrum is taken into account in the results of PBH evaporation, by which PBH dominance in the early universe ends. We specify the conditions under which the proposed scenario can explain production of dark matter in very early universe.

Quantum spin supersolid as a precursory Dirac spin liquid in a triangular lattice antiferromagnet

Based on the recent experiments on the triangular lattice antiferromagnet Na2BaCo(PO4)2, we propose the easy-axis XXZ spin-1/2 model on the triangular lattice, that exhibits a quantum spin supersolid, to be a precursory Dirac spin liquid. Despite the presence of a three-sublattice magnetic order as a spin supersolid, we suggest that this system is close to a Dirac spin liquid by exploring its spectroscopic response. The physical consequence is examined from the spectroscopic response, and we establish the continuous spectra near the M point in addition to the K point excitation from the spinon continuum on top of the three-sublattice order. Moreover, the satellite peaks were predicted at the mid-points connecting the Γ and K points. This proposal offers a plausible understanding of the recent inelastic neutron scattering measurement in Na2BaCo(PO4)2 and could inspire further research in relevant models and materials, such as K2Co(SeO3)2 and Rb2Co(SeO3)2, and even more anisotropic magnets like PrMgAl11O19. Published by the American Physical Society 2024

Continuum spectrum of atomic lithium in a magnetic field of white dwarfs

ABSTRACT This paper reports on computational results of continuum spectra of atomic lithium in white-dwarf-strength magnetic fields. The adiabatic-basis-expansion method with R-matrix propagation has been used to study photoionization of magnetized alkali metal atoms. The R-matrix propagation technique and the two-dimensional matching scheme were utilized to obtain wavefunctions of the continuum states. Cross-sections of photoionization are calculated for lithium atoms in magnetic fields. Continuum spectra for its various bound-free transitions in magnetic white dwarf stars are presented as a function of field strengths ranging from 11.75 to 117.50 MG. Comparison is made between continuum spectra of diamagnetic hydrogen and lithium atoms. The comparison shows good agreement or remarkable difference for final continuum states with different symmetries in the photoionization processes concerned. A detailed analysis has been performed to understand the obtained results. The good agreement displayed manifests the reliability of the extended adiabatic-basis-expansion method. This method is suited to produce a large number of photoionization cross-section data for alkali metal atoms in a strong magnetic field, and therefore can serve as a tool to simulate continuum spectra observed in the atmospheres of magnetic white dwarfs with alkali metal atoms.

Regularity of the integrated density of states in the continuous spectrum

Regularity of the integrated density of states in the continuous spectrum

The prevalence of misophonia in a representative population-based survey in Germany.

Misophonia is a new disorder, currently defined as significant emotional and physiological distress when exposed to certain sounds. Although there is a growing body of literature on the characteristics of the disorder, the prevalence in the general population is still relatively unknown. This study therefore aims at determining the prevalence and symptom severity of misophonia in a large and representative general population sample in Germany. To examine the prevalence of misophonic sounds, misophonic reactions and misophonia severity, a cross-sectional population representative survey in Germany has been conducted. Participants (N = 2.522) were questioned retrospectively about misophonic symptoms using the Amsterdam Misophonie Scale - Revised (AMISOS-R). Overall 33.3% reported to be sensitive to at least one specific misophonic sound. Within the total sample, subthreshold symptoms were reported by 21.3%, mild symptoms were reported by 9.9%, moderate to severe symptoms were reported by 2.1%, and severe to extreme symptoms were reported in 0.1% of participants. Based on the diverging presentations and prevalence rates of misophonic sounds, reactions and symptoms according to the severity, it seems worthwhile to conceptualize misophonia as a rather continuous spectrum disorder (subthreshold, mild, moderate to severe), still taking into account that an additional categorical diagnostic approach might be necessary to derive a diagnosis in clinical practice.

Discrete trapping levels of localized states in amorphous silicon nitride

The spectrum of localized hole states (traps) in amorphous silicon nitride, a-Si3N4, is experimentally studied using the method of thermally stimulated depolarization. The experiment is compared with theoretical calculations using three models of the energy spectrum of traps: discrete spectrum (monoenergetic trap), continuous spectrum, and Gaussian trap distribution. The experiment is quantitatively described by a model of a discrete spectrum of traps with an energy of 1.15 eV and a width of no more than 0.01 eV. In the case of a continuous and Gaussian spectrum of traps, the contribution to depolarization is made by the deepest traps. The blurring of the trap energy level in a-Si3N4 due to the absence of long-range order (fluctuations in the Si–N bond length and fluctuations in the N–Si–N and Si–N–Si angles) does not exceed 0.01 eV.

Recent Development and Advancement in Quantum Dots in Pharmaceutical and Biomedical Fields for the Delivery of Drugs

Abstract: Nanoscale semiconductors known as quantum dots (QDs) are essential for drug testing because they bridge the gap between nanotechnology and the testing of drugs. QDs are a valuable tool in theranostics and treatment because of their unique physicochemical features. Due to their photoluminescence and electronic properties, including broad and continuous absorption spectra, narrow emission spectra from visible to near-infrared wavelengths, and long-lasting and high brightness, they are suitable probe materials for use in (bio)sensing (immunological) platforms. Several studies use QDs due to their optical, magnetic, electrical, photochemical, and biological features that allow them to be employed in various scientific domains. When utilized in drug delivery systems, fluorescent markers, such as QDs, can track the metabolism of drugs in the human body. Many medicinal applications, such as disease diagnosis and medication research, can benefit from these fluorescent tests. In this review article, the application of QD in drug delivery and immunoassay sensing has been described in detail.