Evolution Of Spectra Research Articles

Evidence of jet-caused 12-year optical periodicity of blazar OJ 287

Blazar OJ 287 is one of the first candidates with the assumed compact system of two supermassive black holes in the center. Orbital interaction in this system has been used to explain the for over a century light curve, in which optical flares are repeated with a quasi-period of 12 years and have almost yearly duration. The absence of the predicted flare in 2022 casts doubt on the dominant model of a close system of binary black holes. The detection of optical flares outside the 12-year period and their interpretation by processes in the jet complicates the construction of a complete picture of the blazar OJ 287 optical variability. Here, we analyze the 50-year evolution of the optical spectrum and prove that the changing coefficient of relativistic boosting of two regions in a helical jet subject to an age-long orientation change forms all flares. Our findings indicate the absence of the compact binary black hole system and the impossibility of drawing reliable conclusions about the central engine of active galactic nuclei based only on the quasi-periodic brightness variability of blazars.

How the blast-wave model describes PID hadron spectra from 5 TeV p-Pb collisions

The blast-wave (BW) spectrum model has been applied extensively to nucleus-nucleus collision data with the intention to demonstrate formation of a quark-gluon plasma (QGP) in more-central A-A collisions. More recently the BW model has been applied to p-p, d-Au and p-Pb collisions. Such results are interpreted to indicate that “collectivity” (flows) and QGP appear in smaller systems. In this talk I review BW analysis of identified-hadron spectra from 5 TeV p-Pb collisions and examine the shape evolution of model spectra with collision centrality. I evaluate data-model fit quality using conventional statistical measures. I conclude that the BW model is not a valid data model.

Quantization of second-order fermions

The quantization of a massive spin-1/2 field that satisfies the Klein-Gordon equation is studied. The framework is consistent, provided it is formulated as a pseudo-Hermitian quantum field theory by the redefinition of the dual field and the identification of an operator that modifies the inner product of states in Hilbert space to preserve a real energy spectrum and unitary evolution. Since the fermion field has mass dimension one, the theory admits renormalizable fermion self-interactions. Published by the American Physical Society 2024

Schottky diodes based on in-plane TaSi2N4–WGe2N4 and TaSi2N4–MoGe2N4 heterojunctions

Ideal metal–semiconductor interfaces in 2D lateral heterojunctions are important to realize high-performance Schottky diodes. Based on the first-principles calculations, we propose in-plane heterojunction diodes composed of the metallic TaSi2N4 and the semiconductive WGe2N4/MoGe2N4 monolayers with extremely low lattice mismatch and nearly free defect states. N-type Schottky contacts are confirmed in both TaSi2N4–WGe2N4 and TaSi2N4–MoGe2N4 heterojunctions by analyzing the energy band alignment, charge transfer, electrostatic differential potential, and effective potential. Then, the volt-ampere characteristics and the rectification effect of heterojunctions are investigated. An ultrahigh rectification ratio of 106/107 is obtained for the TaSi2N4–WGe2N4/MoGe2N4 heterojunction diode via regulating the length of the semiconductor part of the heterojunctions. The regulatory mechanism is elucidated by the asymmetrical evolutions of transmission spectra within positive and negative energy ranges. Finally, the rectification mechanism is revealed by the local density of states and the potential energy drop under bias voltages. These results provide a guideline for designing in-plane heterojunction diodes with ultrahigh rectification.

Electrizaton and cathodoluminescence of single crystal MgO under 2.5 – 15 keV electron beam

Kinetics of single crystal MgO electrization showed a delay in the surface potential establishment. A number of processes taking place in the surface electrization and, in their turn, influenced by it, are discussed: secondary electron emission, accumulated charge distribution and spreading in the sample, modification of defects in the sample by the electron beam. The evolution of cathodoluminescence spectra was recorded during the irradiation process, showing both increases and decreases in intensity. A synergetic effect was suggested to explain the subthreshold generation of defects by the electron beam.

On-the-fly simulation of time-resolved fluorescence spectra and anisotropy.

We combine on-the-fly trajectory surface hopping simulations and the doorway-window representation of nonlinear optical response functions to create an efficient protocol for the evaluation of time- and frequency-resolved fluorescence (TFRF) spectra and anisotropies of the realistic polyatomic systems. This approach gives the effective description of the proper (e.g., experimental) pulse envelopes, laser field polarizations, and the proper orientational averaging of TFRF signals directly from the well-established on-the-fly nonadiabatic dynamic simulations without extra computational cost. To discuss the implementation details of the developed protocol, we chose cis-azobenzene as a prototype to simulate the time evolution of the TFRF spectra governed by its nonadiabatic dynamics. The results show that the TFRF is determined by the interplay of several key factors, i.e., decays of excited-state populations, evolution of the transition dipole moments along with the dynamic propagation, and scaling factor of the TFRF signals associated with the cube of emission frequency. This work not only provides an efficient and effective approach to simulate the TFRF and anisotropies of realistic polyatomic systems but also discusses the important relationship between the TFRF signals and the underlining nonadiabatic dynamics.

Spectralomics – Towards a holistic adaptation of label free spectroscopy

Vibrational spectroscopy, largely based on infrared absorption and Raman scattering techniques, is much vaunted as a label free approach, delivering a high content, holistic characterisation of a sample, with demonstrable applications in a broad range of fields, from process analytical technologies and preclinical drug screening, to disease diagnostics, therapeutics, prognostics and personalised medicine. However, in the analysis of such complex systems, a trend has emerged in which spectral analysis is reduced to the identification of individual peaks, based on reference tables of assignments derived from literature, which are then interpreted as biomarkers. More sophisticated analysis attempts to unmix the spectrum of the complex mixture into constituent components, which are then used to characterise the biochemistry of a sample and changes to it, in terms of its constituent components. Data mining the spectra, and in particular change due to kinetic processes, remains a challenge, and it is proposed that the rate of temporal evolution of the combination spectrum can be used in itself as a label by which to guide the spectral analysis. Ultimately, it is argued that the true potential of label free spectroscopy is best harnessed in a truly “spectralomic” approach, by which the spectral signature of an “event”, such as drug intercalation in the DNA of the nucleus of a cell, or a key stage of a cellular pathway such as oxidative stress, is presented. It is envisioned that, in the future, such Spectralomics pathway analysis will be fully integrated with similar omics approaches, potentially ultimately through deep learning algorithms, and underpinned by systems biology kinetic models, to provide a living human cell atlas, describing the function and dysfunction of organism at a cellular level, as the basis for improved healthcare.

Directional wave spectrum evolution modelling of ship noise

A new underwater acoustic propagation model that is well suited to modelling ship noise is described. The model describes the spatio-temporal evolution of the directional energy spectrum of a sound field. The governing equation can be thought of as an advection-diffusion equation for spectral energy in phase space (position, angle). Numerical simulations of sound fields excited by both isotropic compact sources and by highly anisotropic ship noise provide confidence that the model works well, with caveats that will be discussed. [Work supported by ONR.]

Stochastic diffusion within expanding space–time

The paper examines stochastic diffusion within an expanding space–time framework motivated by cosmological applications. Contrary to other results in the literature, for the considered general stochastic model, the expansion of space–time leads to a class of stochastic equations with non-constant coefficients that evolve with the expansion factor. The Cauchy problem with random initial conditions is posed and investigated. The exact solution to a stochastic diffusion equation on the expanding sphere is derived. Various probabilistic properties of the solution are studied, including its dependence structure, evolution of the angular power spectrum and local properties of the solution and its approximations by finite truncations. The paper also characterizes the extremal behaviour of the random solution by establishing upper bounds on the probabilities of large deviations. Numerical studies are carried out to illustrate the obtained theoretical results.

The generation of noise-like pulses and various solitons with CuO nanorods as a broadband saturable absorber

Copper oxide (CuO) nanorods exhibit unique photoelectric properties due to their high surface area, excellent volume effect, and quantum confinement effect, which have also attracted wide attention in the application of ultrafast photonics. In the present work, CuO nanorods were successfully prepared by a simple synthesis strategy and characterized in detail. The density of electron states (DOS) and the band structure of CuO were predicted by the first principles simulation method. The nonlinear optical response parameters of CuO nanorods were determined by a twin-balanced detector system. Based on the excellent nonlinear optical response, CuO nanorods were exploited as saturable absorbers (SAs) to achieve the noise-like pulse (NLP) mode-locking operation in the erbium (Er)-doped fiber laser (EDFL) at 1552 nm and ytterbium (Yb)-doped fiber laser (YDFL) at 1038.5 nm. Additionally, by shortening the cavity length of EDFL and finely optimizing the intracavity polarization, various solitons, and dual-wavelength solitons were also observed. Moreover, the dynamic evolution of spectra and pulses in YDFL was simulated using scalar nonlinear Ginzburg-Laudau equation (GLE). Our work well demonstrated the broadband and high-efficiency saturable absorption in CuO nanorods, paving the path for investigating multi-soliton dynamics and broadband ultrafast photonics.

Evolution of the cosmic ray spectrum during a Forbush decrease

The Antarctic Cosmic Ray Observatory (ORCA) has been in continuous operation since January 2020 and in nominal phase since March 2021 at the Spanish Antarctic Base Juan Carlos I (Livingston Island, Antarctica 62°39′46′′S,60°23′20′′W at 12 m above sea level) at an effective vertical cutoff rigidity of R=2.37 GV. ORCA consists of two neutron monitors, ORC-A with three BF3 counter tubes following the NM64 standard, and ORC-B, with three bare BF3 counter tubes; and a muon telescope, ORC-M consisting of two 1 m2 scintillators with the neutron monitors between them. ORCA provides neutron count rates at two different energy thresholds (provided by ORC-A and ORC-B) and muon count rates and muon incidence directions throughout the ORCA volume. The neutron-producing cosmic rays observed in ORC-A have a lower rigidity threshold than the muon-producing ones observed in ORC-M. The relationship between them gives an idea about the change in the slope of the cosmic ray spectrum at the corresponding thresholds, 2.37 GV for ORC-A and ≈12 GV for ORC-M. This relation allows to investigate the change in the cosmic ray spectrum along the different regions in an Interplanetary Coronal Mass Ejection, i.e. the shock, the sheath and the magnetic cloud. ORCA first observations are presented, focusing on the analysis of the Forbush Decrease (FD) that happened at the beginning of November 2021. We present these observations and show the promising capabilities of the Antarctic Cosmic Ray Observatory, which represents a new concept of cosmic ray and solar energetic particle detector. The cosmic ray spectrum changes during the Forbush decrease detected in early November 2021 as seen in the change in the ratio of ORC-A to ORC-M count rates. This change is clear after the arrival of the shock and during the magnetic cloud being smoother or even flat in the sheath. In addition, the secondary muons show changes in their arrival directions along the ICME, being clear the different behavior in shock, sheath and magnetic cloud.

The relevance of structural variability in the time-domain for computational reflection anisotropy spectroscopy at solid–liquid interfaces

In electrochemistry, reactions and charge-transfer are to a large extent determined by the atomistic structure of the solid–liquid interface. Yet due to the presence of the liquid electrolyte, many surface-science methods cannot be applied here. Hence, the exact microscopic structure that is present under operating conditions often remains unknown. Reflection anisotropy spectroscopy (RAS) is one of the few techniques that allow for an in operando investigation of the structure of solid–liquid interfaces. However, an interpretation of RAS data on the atomistic scale can only be obtained by comparison to computational spectroscopy. While the number of computational RAS studies related to electrochemical systems is currently still limited, those studies so far have not taken into account the dynamic nature of the solid–liquid interface. In this work, we investigate the temporal evolution of the spectroscopic response of the Au(110) missing row reconstruction in contact with water by combining ab initio molecular dynamics with computational spectroscopy. Our results show significant changes in the time evolution of the RA spectra, in particular providing an explanation for the typically observed differences in intensity when comparing theory and experiment. Moreover, these findings point to the importance of structural surface/interface variability while at the same time emphasising the potential of RAS for probing these dynamic interfaces.

Dark matter vorticity and velocity dispersion from truncated Dyson-Schwinger equations

Large-scale structure formation is studied in a kinetic theory approach, extending the standard perfect pressureless fluid description for dark matter by including the velocity dispersion tensor as a dynamical degree of freedom. The evolution of power spectra for density, velocity and velocity dispersion degrees of freedom is investigated in a non-perturbative approximation scheme based on the Dyson-Schwinger equations. In particular, the generation of vorticity and velocity dispersion is studied and predictions for the corresponding power spectra are made, which qualitatively agree well with results obtained from N-body simulations. It is found that velocity dispersion grows strongly due to non-linear effects and at late times its mean value seems to be largely independent of the initial conditions. By taking this into account, a rather realistic picture of non-linear large-scale structure formation can be obtained, albeit the numerical treatment remains challenging, especially for very cold dark matter models.

Deuterium retention and ammonia production from D-implanted 316 L stainless steel: insights for future fusion reactors

We present a systematic study that quantifies deuterium (D) retention and ammonia (ND3) production from 316 L stainless steel (SS316L) following the implantation of D ions in conditions similar to the ones expected in the ITER tokamak, i.e. with kinetic energy below 300 eV. Using Temperature Programmed Desorption (TPD) after deuterium ion implantation at 250 eV/D, we show that deuterium retention increases linearly with the D fluence up to 1021 D+m−2, with a retention probability of 18%. For higher D fluence, deuterium retention increases sub-linearly. Analysis of the TPD spectra evolution with varying storage time in vacuum after D implantation, shows that D retention is influenced by D diffusion into the bulk of SS316L. Subsequent to D ion implantation, we evidence the efficient production of ND3 molecules during TPD, between 400 K and 750 K, from the nitrogen present naturally in SS316L. Up to 21% of the D release during TPD can be found in ND3 molecules, indeed. The fraction of ND3 in the total D release depends both on the D ion fluence and the nitrogen concentration profile in the bulk. At least 7% of the D release is found in the form of ND3 molecules, even at a fluence of 2 × 1021 D+m−2 and for a natural N concentration bulk profile. Both N diffusion and D diffusion into the bulk appear to dictate the kinetics of ND3 production. Our findings of efficient production of ND3 in D-implanted austenitic 316 L stainless steel underline the need for similar studies on reduced-activation ferritic/martensitic (RAFM) steels that contain similar content of nitrogen and will be used in fusion reactor prototypes.

Revisiting the Quasiparticle Band Structure and Optical Properties of Few‐Layer InSe

The many‐body GW combined with the Bethe–Salpeter equation (BSE) method including the spin‐orbit coupling (SOC) effect has been adopted to revisit the band structure and optical absorption spectra evolution of single‐layer, double‐layer, three‐layer, and bulk InSe. The many‐body effect is found to play an important role in both the band structure and the optical properties of InSe structures. Not only the band gap but also the energy dispersion is influenced by the electron–electron many‐body interaction. Electron–hole interaction strongly affects the optical properties of InSe structures, especially the single‐layer InSe. Compared with previous reports, the calculations show that, including SOC, two bound excitonic peaks have emerged for monolayer InSe, with the strong bound exciton being s‐state‐like, while the other p‐state‐like. BSE also predicts abundance of bounded “dark” excitons exists for monolayer InSe, indicating that monolayer InSe is a proper platform for studying excitons. Although the spin‐orbit interaction influence on the highest valence band and the lowest conducted band seems trivial, its effect on the optical properties of InSe is remarkable.

Two-dimensional heavy fermions in the van der Waals metal CeSiI.

Heavy-fermion metals are prototype systems for observing emergent quantum phases driven by electronic interactions1-6. A long-standing aspiration is the dimensional reduction of these materials to exert control over their quantum phases7-11, which remains a significant challenge because traditional intermetallic heavy-fermion compounds have three-dimensional atomic and electronic structures. Here we report comprehensive thermodynamic and spectroscopic evidence of an antiferromagnetically ordered heavy-fermion ground state in CeSiI, an intermetallic comprising two-dimensional (2D) metallic sheets held together by weak interlayer van der Waals (vdW) interactions. Owing to its vdW nature, CeSiI has a quasi-2D electronic structure, and we can control its physical dimension through exfoliation. The emergence of coherenthybridization of f and conduction electrons at low temperature is supported by the temperature evolution of angle-resolved photoemission and scanning tunnelling spectra near the Fermi level andby heat capacity measurements. Electrical transport measurements on few-layer flakes reveal heavy-fermion behaviour and magnetic order down to the ultra-thin regime. Our work establishes CeSiI and related materials as a unique platform for studying dimensionally confined heavy fermions in bulk crystals and employing 2D device fabrication techniques and vdW heterostructures12 to manipulate the interplay between Kondo screening, magnetic order and proximity effects.

The Spectrum of Global Electron Content: A New Potential Indicator of Space Weather Activity.

The time evolution of the total number of free electrons in the Earth's ionosphere, i.e., the Global Electron Content (GEC), during more than two solar cycles is analyzed in this work. The GEC time series has been extracted from the Global Ionospheric Maps (GIMs) of Vertical Total Electron Content (VTEC) estimated by UPC-IonSAT with TOMION-v1 software from global GPS measurements since the end of 1996. A dual-layer voxel-based tomographic model solved with a forward Kalman scalar filter, from dual-frequency carrier GPS data only, provides the so-called UQRG GIM after VTEC kriging interpolation, with a resolution of 15 min in time, 5° in longitude and 2.5° in latitude. UQRG is one of the best behaving GIMs in the International GNSS Service (IGS).In this context, the potential application of the GEC spectrum evolution as a potential space weather index is discussed and demonstrated.

Effects of anisotropy on the electronic structure and nonlinear optical rectification in a quantum dot with hydrogen molecular ion

In this study, the effects of anisotropy and quantum dot size on energy levels and nonlinear optical rectification of a D_{2}^{ + } molecular complex confined to a two-dimensional quantum dot are investigated. The energy eigenvalues and corresponding eigenfunctions of the resulting eigenvalue equation are obtained using the adiabatic approach and the two-dimensional diagonalization method. We conclude that the evolution of the energy spectrum depends predominantly on the anisotropy-induced change of geometric confinement size. In addition, it has been determined that the peak position of the nonlinear optical rectification shifts to lower or higher energies as the asymmetry of the system increases, depending on whether the QD is in the oblate or prolate case. This feature can be considered an advantage in tuning the nonlinear optical properties of systems based on two-dimensional semiconductor heterostructures.

Compensating isotope effect on molecular emission of hydroxyl and imidogen isotopologues in laser-induced plasma

BackgroundThe molecular isotopologues in laser-induced plasma exhibit riddling emission behaviors in terms of wavelength, intensity, and temporal evolution of spectra due to the isotope effect. Although this phenomenon introduces uncertainty to isotope analyses based on molecular spectra, its underlying mechanism remains undisclosed. ResultsIn this study, laser-induced breakdown spectroscopy (LIBS) is employed to identify the emission behavior of hydrogen, oxygen, and nitrogen isotopologues in a plasma plume. The goal is to discern the details of the isotope effect and mitigate resulting uncertainty. The molecular emissions of hydroxyl (OH) and imidogen (NH) were measured from plasma ablated on isotopically enriched water samples. Time-resolved detection clearly reveals distinct isotopic disparities in intensity variation and optimum gate delay, which were attributed to plasma thermo-hydrodynamics. Lighter isotopologues exhibit earlier and faster associations than their heavier counterparts due to their fast reaction rates and expansion velocities. The extent of the isotope effect hinged on plasma characteristics governed by measurement conditions. Consequently, comparing spectral intensity between molecular isotopologues cannot directly indicate the nominal isotope abundance of the sample. To address it, a compensation strategy has been devised, quantifying isotope effects through parameters like the slope and optimum delay of time-resolved detection. The approach successfully predicts nominal isotope abundance using compensated intensity ratios, with an absolute bias of less than 3 %. SignificanceThis study not only offered fundamental insights into the isotope effect in laser-induced plasma but also proposed an alternative method for isotope quantification that circumvents complicated calibration processes.

A rapid Surface-Enhanced Raman scattering method for the determination of trace Hg2+ with tapered optical fiber probe

Surface-enhanced Raman scattering (SERS) offers a route for trace detection of mercury ions (Hg2+) owing to its great enhancement near the surface of the substrate. However, most of the methods are inconvenient due to the long reaction time and the strict measurement conditions. Based on a reaction between silver nanoparticles (AgNPs) and mercury ions, a simple but effective method is proposed in this paper. In the experimental research, a tapered optical fiber (TOF) modified with AgNPs is employed as a sensing probe and Rhodamine 6G (R6G) is taken as the Raman reporter. The SERS substrate is consumed by the Hg2+, causing a spectrum decrease. In the Hg2+ concentration range of 10−12 M to 10−4 M, the spectra evolution is detected using a mobile Raman spectrometer. By analyzing the decrease of the Raman peak after a 5-minutes interval, the concentration of Hg2+ can be quantified. A limit of detection of 5.15 × 10−13 M is achieved, which is much below the maximum Hg2+ content of drinkable water specified by USEPA (10−8 M). Verification tests were performed with the inductively coupled plasma-mass spectrometry (ICP-MS), the results showed that the proposed SERS method is effective for real samples detection. In addition, the reproductivity and the selectivity are experimentally confirmed. With this reliable, rapid, ultrasensitive and accurate method, trace Hg2+ could be detected in many applications.