Spectral Lines Research Articles

Mutual Synchronization of Spintronic Nano-Oscillator Ensembles

Introduction. The use of spintronic components significantly enhances the performance, reduces the size, and lowers the power consumption of modern electronic devices. The spintronic oscillator (SO) is an integral part of spintronic devices. Connecting several SOs (> 100) into ensembles with subsequent synchronization mitigates such SO drawbacks as low output power and high phase noise. These drawbacks appear as a result of an increase in the output power of an SO ensemble compared to a single oscillator under a simultaneous decrease in the spectral linewidth of the ensemble.Aim. To investigate the impact of connection topologies, synchronization mechanisms, and oscillator failures on the synchronization of oscillator ensembles.Materials and methods. The Kuramoto phase model was used to simplify the numerical modeling of synchronization of SOs connected into an ensemble.Results. A Kuramoto equation for phases of SOs connected in an ensemble was derived, and the influence of connection topologies and oscillator failures on the synchronization parameters of an ensemble of N connected oscillators was demonstrated.Conclusion. In order to ensure the shortest transition time of an SO ensemble to the synchronous mode, topologies with a higher number of connections between oscillators (e.g., "all-to-all") are preferable. The results obtained confirm the advantages of local connection of an SO ensemble by a common current, thus forming an "all-to-all" topology. This makes the transition time of the SO ensemble to the synchronous mode less dependent on both oscillator failures and the number of synchronized SOs.

JWST Observations of Young protoStars (JOYS). Overview of gaseous molecular emission and absorption in low-mass protostars

The Mid-InfraRed Instrument (MIRI) on board the James Webb Space Telescope (JWST) allows one to probe the molecular gas composition at mid-infrared (mid-IR) wavelengths with unprecedented resolution and sensitivity. It is important to study these features in low-mass embedded protostellar systems, since the formation of planets is thought to start in this phase. Previous studies were sensitive primarily to high-mass protostars. The aim of this paper is to derive the physical conditions of all gas-phase molecules detected toward a sample of 18 low-mass protostars as part of the JWST Observations of Young protoStars (JOYS) program and to determine the origin of the molecular emission and absorption features. This includes molecules such as CO$_2$, C$_2$H$_2$, and CH$_4$ that cannot be studied at millimeter wavelengths. We present JWST/MIRI data taken with the Medium Resolution Spectrometer (MRS) of 18 low-mass protostellar systems, focusing on gas-phase molecular lines in spectra extracted from the central protostellar positions. The column densities and excitation temperatures were derived for each molecule using local thermodynamic equilibrium (LTE) slab models. Ratios of the column densities (absorption) or total number of molecules (emission) were taken with respect to H$_2$O in order to compare these to ratios derived in interstellar ices. Continuum emission is detected across the full MIRI-MRS wavelength toward 16/18 sources; the other two sources (NGC 1333 IRAS 4B and Ser-S68N-S) are too embedded to be detected. The MIRI-MRS spectra show a remarkable richness in molecular features across the full wavelength range, in particular toward B1-c (absorption) and L1448-mm (emission). Besides H$_2$, which is not considered here, water is the most commonly detected molecule (12/16) toward the central continuum positions followed by CO$_2$ (11/16), CO (8/16), and OH (7/16). Other molecules such as 13CO$_2$, C$_2$H$_2$, 13CCH$_2$, HCN, C$_4$H$_2$, CH$_4$, and SO$_2$ are detected only toward at most three of the sources, particularly toward B1-c and L1448-mm. The JOYS data also yield the surprising detection of SiO gas toward two sources (BHR71-IRS1, L1448-mm) and for the first time CS and NH$_3$ at mid-IR wavelengths toward a low-mass protostar (B1-c). The temperatures derived for the majority of the molecules are 100--300 K, much lower than what is typically derived toward more evolved Class II sources ($ K). Toward three sources (e.g., TMC1-W), hot ($ K) H$_2$O is detected, indicative of the presence of hot molecular gas in the embedded disks, but such warm emission from other molecules is absent. The agreement in abundance ratios with respect to H$_2$O between ice and gas points toward ice sublimation in a hot core for a few sources (e.g., B1-c), whereas their disagreement and velocity offsets hint at high-temperature (shocked) conditions toward other sources (e.g., L1448-mm, BHR71-IRS1). Molecular emission and absorption features trace various warm components in young protostellar systems, from the hot core regions to shocks in the outflows and disk winds. The typical temperatures of the gas-phase molecules of $100-300$ K are consistent with both ice sublimation in hot cores as well as high-temperature gas phase chemistry. Molecular features originating from the inner embedded disks are not commonly detected, likely because they are too extincted even at mid-IR wavelengths by small, unsettled dust grains in upper layers of the disk.

Enhanced disinfestation in grain spawn production through cold plasma and sodium hypochlorite synergy

Heat-resistant fungal conidia are a common source of contamination and can cause significant difficulties in producing spawns. Through the use of PCR method, Aspergillus tubingensis and Aspergillus flavus as common microbial contaminants found in wheat grain spawn were identified that had been sterilized at 120 ºc for 2 h. Since these conidia are highly resistant to standard sterilization techniques, alternative methods were used to treat them with NaOCl and cold plasma and evaluate their effectiveness in reducing contamination. Optical emission spectroscopy (OES) analysis of the plasma showed dominant emissions from the N2 second positive system and N2+ first negative system, while reactive oxygen species (ROS) spectral lines were undetected due to collision-induced quenching effects. Field Emission Scanning Electron Microscopy (FESEM) and Energy Dispersive X-ray Spectroscopy (EDXS) analyses revealed notable alterations in the elemental makeup of conidia surfaces, as evidenced by a marked rise in levels of Na, O, Cl (in the case of NaOCl treatment) and N (in the case of plasma treatment). The conidia size was reduced at lower levels of NaOCl, but with increased concentrations and plasma treatment, the conidia underwent rupture and, in some cases, pulverization. The research suggests that utilizing a combined approach can be highly effective in eliminating heat-resistant fungal conidia and drastically cutting down the sterilization time for producing wheat spawn to only 30 s.

Infrared photoinduced force near-field spectroscopy of silicon carbide

Silicon carbide (SiC) is a promising microelectronic semiconductor with an infrared response that depends on factors such as polytype, growth conditions, and structuring. Recent advances in infrared nano-imaging techniques provide new opportunities to characterize thin films at the nanoscale. We performed tip-enhanced near-field spectral characterization on various 4H-SiC sample surfaces using photoinduced force microscopy (PiFM). The near-field spectra feature a peak associated with a surface phonon polariton (SPhP) resonance, which proves to be highly sensitive to the material’s surface quality. Interestingly, we found that the power absorption at the tip-sample junction, enhanced by the effective tip polarizability, can account for these PiFM spectra, resulting in a blend of both dispersive and dissipative spectral line shapes. As a potential application, a junction-field effect transistor was imaged to evaluate the technique’s ability to map the surface of different p- and n-doped areas, demonstrating high sensitivity and spatial resolution compared to Raman analysis.

Effect of Ar on parameters of nitrogen microwave-induced plasma optical emission spectrometry

The effect of Ar content in the range of 0–100 % was studied separately in the outer, intermediate and nebulizer gas flow on the excitation temperature and electron density, the intensity of element lines and the molecular background in a N2 microwave induced plasma. The addition of Ar to the nebulizer flow leads to an increase in the intensities of both atomic and ionic lines with total excitation energies (Esum) 3–13 eV to 1.7 times, depending on the selected line. Addition to the outer or intermediate flow shifts the atomic-ionic equilibrium towards the formation of ions. As a result, the intensity of ionic lines (Esum = 10–13 eV) increases up to 1.2 times, the decrease in the intensity of atomic lines (Esum = 3–6 eV) reaches up to 20 %. The excitation temperature and electron density in the plasma did not change significantly regardless of which flow the argon was fed into. The intensity of the molecular components of the plasma background (OH, NH, NO) changes significantly when Ar is introduced into the nebulizer flow. The OH intensity increases to 1.8 times, and NH intensity increases to 1.5 times at 100 % Ar relative to pure N2 plasma. Supplying 100 % Ar simultaneously into the intermediate and nebulizer gas flow and N2 into the outer flow allows one to reduce the limits of detection by up to 3.3 times, depending on the selected spectral line of the element.

Comprehensive assessment of terahertz quantum-cascade lasers performance characteristics

Terahertz (THz) quantum-cascade lasers (QCLs) are attracting an ever-increasing interest for both scientific and industrial applications in key areas, such as high-resolution spectroscopy of atomic and molecular absorption lines. Advancements in the active-region and resonator designs, hence, play a pivotal role in determining the future of this technology, especially regarding the wall-plug efficiency and the operating temperature, which are still the main factors limiting their widespread adoption. A sound characterization approach is, therefore, the foundation of the coming improvements to these semiconductor lasers. To overcome the overreliance on simulation tools for the determination of fundamental device characteristics, we report a comprehensive characterization approach to measure all relevant electrical, optical, and thermal parameters of THz QCLs in a consistent manner. Based on the lattice temperature dependence of the QCL output power, the thermal conductivity of the QCLs is extracted. We then retrieve light–current density–lattice temperature maps to decouple the influence of the bias and lattice temperature on the device performance. Applying this method to two sets of QCLs with different active-region designs allowed us to determine the internal quantum efficiency (∼12%), waveguide losses (8–20 cm−1), and transparency current density. A transparency current density greater than 60% of the threshold current density is observed for the two active regions, which demonstrates leakage currents to be the dominant factor limiting THz QCLs efficiency even at low temperatures and for optimized designs employing tall barriers of nominally pure AlAs.

Design requirements of a spectropolarimeter for solar extreme-ultraviolet observations and characterization of a K-mirror based on Brewster's angle.

Measuring the linear polarization signal in extreme-ultraviolet (EUV) spectral lines, produced by the Hanle effect, offers a promising technique for studying magnetic fields in the solar corona. The required signal-to-noise ratio for detecting the Hanle polarization signals is on the order of 101 (off-limb) to 106 (disk center). Measuring such low signals in the photon starved observations demands highly efficient instruments. In this paper, we present the design of an instrument, SpectroPOLarimeter for Extreme-ultraviolet Observations (SPOLEO), which utilizes reflective components with suitable mirror coatings and thicknesses to minimize the throughput losses. We analyze the system performance within the spectral range from 740 to 800Å. The K-mirror-based polarimeter model provides a polarizing power of 20%-40% in this wavelength range. Based on the system throughput and polarizing power, we discuss various possibilities for achieving the required signal-to-noise ratio, along with their limitations. Due to lack of facilities for fabrication and testing in the EUV, we have calibrated a prototype of the reflection-based polarimeter setup in the laboratory at the visible wavelength of 700nm.

Diagnostic study of atmospheric pressure inductively coupled plasma temperature field based on image and relative spectral line method

Atmospheric pressure inductively coupled plasma (ICP) is widely applied in the production of high-purity coatings and powders. This paper innovatively presents a dual-band imaging ICP temperature diagnostic system that integrates visible light image processing technology and relative spectral line method. The system utilizes a dual-band imaging unit to simultaneously acquire monochromatic grayscale images of ICP at two different wavelengths using a single CCD camera. By establishing the correspondence between the emission intensity received by the emission spectrometer and the grayscale images recorded by the CCD camera, the two-dimensional (2D) electron excitation temperature (EET) field distribution of ICP is obtained by the relative spectral line method. The experimental results demonstrate that the maximum EET is located near to the center line of the RF-driven coil. Additionally, the EET in ICP decreases gradually from the center of the induction coil to the periphery. As the radio frequency (RF) power increases, the maximum EET also increases, and the high-temperature region expands. The accuracy of this method is validated by comparing it with the results obtained from the Boltzmann plot method. Therefore, this method can quickly obtain the transient EET field distribution of ICP, which is significant for optimizing the application of ICP in material processing.

Long-Tune Natural Logarithmic Wavelength Modulation Spectroscopy for Gas Sensing.

This article presents a gas sensing method based on long-tune natural logarithmic wavelength modulation spectroscopy (long-tune ln-WMS) and explores means to improve its accuracy. The long-tune spectrum can detect multiple gases with high precision. In ln-WMS, due to the natural logarithm algorithm, the harmonic magnitude which is related to gas concentration would not be affected by the light intensity fluctuations. However, the background signal of the harmonic will become strong and nonlinear in the long-tune spectrum. Three CO2 absorption lines and one H2O line near 2004 nm are applied to verify the proposed theory. The effects of light intensity, modulation depth, gas concentration, and phase shift on the harmonics are tested separately through both simulations and experiments. The results reveal that our proposed method can always keep the harmonics at their maximum which ensures high measurement precision. Moreover, the background signal only varies with the modulation depth, not the concentration and light intensity. Even the mechanical vibrations cannot disturb the harmonics, which enables the proposed method to be suitable for gas detection in harsh environments, especially for heavy dust and severe mechanical vibrations. The CO2 concentration detection results indicate that when the background is eliminated, the accuracy can be achieved with a relative error of below 0.5%, while the error would be greater than 5% with background presence. The proposed long-tune ln-WMS method is effective for trace gas detection (weak absorption) or over-modulation conditions and has potential applications in field inspection.

Triple Spectral Line Imaging of Whole-Body Human Skin: Equipment, Image Processing, and Clinical Data.

Multispectral imaging can provide objective quantitative data on various clinical pathologies, e.g., abnormal content of bio-substances in human skin. Performance of diagnostics increases with decreased spectral bandwidths of imaging; from this point, ultra-narrowband laser spectral line imaging is well suited for diagnostic applications. In this study, 40 volunteers participated in clinical validation tests of a newly developed prototype device for triple laser line whole-body skin imaging. The device comprised a vertically movable high-resolution camera coupled with a specific illumination unit-a side-emitting optical fiber spiral that emits simultaneously three RGB laser spectral lines at the wavelengths 450 nm, 520 nm, and 628 nm. The prototype's design details, skin spectral image processing, and the obtained first clinical data are reported and discussed.

A pixel-level assessment method of the aging status of silicone rubber insulators based on hyperspectral imaging technology and IPCA-SVM model

Acidic environments are a significant factor in the aging and failure of silicone rubber insulators. Addressing the effective assessment of insulators’ aging state to prevent power transmission accidents has been a critical and urgent issue for the power grid. Therefore, hyperspectral imaging (HSI) technology was employed in this paper, capturing spectral line data of silicone rubber in six aging states in both visible and near-infrared regions, respectively. To reduce data redundancy, genetic algorithm (GA) and band weighting were introduced to improve traditional principal component analysis (PCA), with performance compared using overall accuracy (OA) and Kappa, against 12 other feature extraction or dimensionality reduction methods. The improved principal component analysis − support vector machine (IPCA-SVM) model proposed effectively minimizes irrelevant information in hyperspectral original data, exceeding 93% accuracy and improving OA by 8.26% compared to all bands data. Finally, the IPCA-SVM model was used for pixel-level assessment of the surface aging state of silicone rubber insulators, demonstrating its reliability. This method effectively characterizes the aging state of composite insulators, providing a solid foundation for the safe and stable operation of power grids.

Temperature Dependence of Coherent versus Spontaneous Raman Scattering.

Because of their sub picosecond temporal resolution, coherent Raman spectroscopies have been proposed as a viable extension of spontaneous Raman thermometry, to determine dynamics of mode specific vibrational energy content during out of equilibrium molecular processes. Here we show that the presence of multiple laser fields stimulating the vibrational coherences introduces additional quantum pathways, resulting in destructive interference. This ultimately reduces the thermal sensitivity of single spectral lines, nullifying it for harmonic vibrations and temperature independent polarizability. We demonstrate how harnessing anharmonic signatures such as vibrational hot bands enables coherent Raman thermometry.

From Structure to Strength: Analyzing the Impact of Sulfuric Acid on Pig Bone Demineralization Through FTIR, LIBS, and AAS.

The present research aimed to investigate the demineralizing effects of sulfuric acid on pig bone. Alterations in collagen and phosphate contents and changes in the elemental composition of the bone during the 14-day-long immersion in sulfuric acid solutions of different concentrations were estimated using ATR-FTIR, LIBS, and AAS. FTIR spectra at amide I (1800-1600 cm-1) and phosphate ν1/ν3 (PO43-) (1300-900 cm-1) domains were scrutinized using the deconvolution method for monitoring changes in the protein secondary structure and mineral content. The results implicated sulfuric acid as a powerful demineralization agent and effective in targeting mineral components, such as hydroxyapatite, while leaving the collagen matrix relatively preserved with a complex secondary structure. Collagen maturity marker values gave valuable insights into the structural integrity of the bone. LIBS and AAS indicated changes in bone hardness; phosphorous-to-carbon ratio; and calcium, phosphorous, and magnesium content in the solutions left after the immersion period. The changes in the ratio of ionic-to-atomic calcium lines in the LIBS spectra indicated hardening of the bone, with increasing acid concentration and prolonged action, due to the deposition of calcium sulfate on the surface. The calcium concentration in the solutions decreased with increased acid concentration, while the change in phosphorus and magnesium concentrations was reversed.

414.9 W in-band pumped Er/Yb co-doped fiber amplifier seeded by a random fiber laser.

We demonstrated a 414.9 W large-mode-area Er/Yb co-doped fiber amplifier with a good time-domain stability, seeded by a 1568 nm random fiber laser (RFL) seed with a half-open cavity. We believe this to be the highest output power of the RFL in a 1.5 µm band to date. At the maximum output power, the optical efficiency was 36.9% and the 3 dB linewidth was 0.69 nm. The 1535 nm fiber lasers were used as the pumping source of the main amplifier to avoid the parasitic lasing of Yb ions. The spectral linewidth broadening was suppressed during the amplification process due to the stable temporal output of the RFL seed. The M2 factor increased from 2.28 at 145.7 W to 2.83 at 280.8 W. Our research provides a robust approach for achieving high-power and high-spectral-purity RFLs in the 1.5 µm band.

Finite-field Cholesky decomposed coupled-cluster techniques (ff-CD-CC): theory and application to pressure broadening of Mg by a He atmosphere and a strong magnetic field.

For the interpretation of spectra of magnetic stellar objects such as magnetic white dwarfs (WDs), highly accurate quantum chemical predictions for atoms and molecules in finite magnetic field are required. Especially the accurate description of electronically excited states and their properties requires established methods such as those from coupled-cluster (CC) theory. However, respective calculations are computationally challenging even for medium-sized systems. Cholesky decomposition (CD) techniques may be used to alleviate memory bottlenecks. In finite magnetic field computations, the latter are increased due to the reduction of permutational symmetry within the electron-repulsion-integrals (ERIs) as well as the need for complex-valued data types. CD enables a memory-efficient, approximate description of the ERIs with rigorous error control and thus the treatment of larger systems at the CC level becomes feasible. In order to treat molecules in a finite magnetic field, we present in this work the working equations of the left and right-hand side equations for finite field (ff)-EOM-CD-CCSD for various EOM flavours as well as for the approximate ff-EOM-CD-CC2 method. The methods are applied to the study of the modification of the spectral lines of a magnesium transition by a helium atmosphere that can be found on magnetic WD stars.

The Value-added Catalog of OB Stars in LAMOST DR7

In this work, we update the catalog of OB stars based on the Large Sky Area Multi-Object Fiber Spectroscopic Telescope data release 7 and modify the OB stars’ selection criteria in spectral line indices’ space. The new catalog includes 37,778 spectra of 27,643 OB stars, of which 3827 OB stars are newly identified. The spectral subclasses of 27,643 OB stars are obtained using the automatic classification code MKCLASS. We find that the modified OB star selection criteria can better improve the completeness of late B-type stars by analyzing their spectral classification results given by MKCLASS. We also identify 3006 Be-type stars or candidates by examining the Balmer lines in their spectra and find that the frequency of our Be-type stars (10.9%) is consistent with previous results. The spatial distribution of OB stars indicates that they are mainly located in the Galactic disk. This new catalog of OB stars will provide valuable data for studying the structure and evolution of the Milky Way.

Nuclear burning in an accretion flow around a stellar-mass black hole embedded within an AGN disc

ABSTRACT A stellar-mass black hole, embedded within the accretion disc of an active galactic nuclei (AGN), has the potential to accrete gas at a rate that can reach approximately ${\sim}10^9$ times the Eddington limit. This study explores the potential for nuclear burning in the rapidly accreting flow towards this black hole and studies how nucleosynthesis affects metal production. Using numerical methods, we have obtained the disc structure while considering nuclear burning and assessed the stability of the disc. In contrast to gas accretion onto the surface of a neutron star or white dwarf, the disc remains stable against the thermal and secular instabilities because advection cooling offsets the nuclear heating effects. The absence of a solid surface for a black hole prevents excessive mass accumulation in the inner disc region. Notably, nuclear fusion predominantly takes place in the inner disc region, resulting in substantial burning of $\rm ^{12}C$ and $\rm ^{3}He$, particularly for black holes around $M = 10\,{\rm M}_\odot$ with accretion rates exceeding approximately ${\sim}10^7$ times the Eddington rate. The ejection of carbon-depleted gas through outflows can lead to an increase in the mass ratio of oxygen or nitrogen to carbon, which may be reflected in observed line ratios such as N v/C iv and O iv/C iv. Consequently, these elevated spectral line ratios could be interpreted as indications of supersolar metallicity in the broad-line region.

Unveiling the rebrightening mechanism of GRS 1915+105: Insights from a change in the quasi-periodic oscillations and from a wind analysis

We report a significant rebrightening event in the microquasar GRS 1915+105 that was observed in July 2021 with NICER and NuSTAR. This event was characterized by quasi-periodic oscillations (QPOs) in the soft state, but is typically free of these oscillations. It was also marked by an increase in the disk wind ionization degree. By employing the Hilbert-Huang transform (HHT), we decomposed the stable low-frequency QPO from the light curves using data from NICER and NuSTAR. Our spectral analysis shows a weak change in the Fe XXV absorption lines and a strong change in the Fe XXV absorption edge with QPO phase. Other spectral parameters, including the photon index and the seed photon temperature, correlate positively with the QPO phase, but the electron temperature is inversely correlated. Based on our findings we propose that the observed QPOs were caused by magnetic activity and not by precession. The magnetic field drove a failed disk wind of high-ionization low-velocity material. These results support the accretion ejection instability model and provide deeper insights into the dynamics of accretion-ejection processes that are magnetized by a black hole.

A Novel Neural Network Architecture Dedicated for LIBS Spectrum Analysis With Its Application to Steel Pipe Classification

Abstract As a non-destructive rapid composition analysis method, Laser-induced breakdown spectroscopy (LIBS) has received widespread attention in recent years. However, its application in the steel industry has not achieved an effective breakthrough in its detection accuracy due to the existence of matrix effect. This paper introduces a neural network model for LIBS spectral line analysis, which can automatically construct the features and analyze the correlation between them, and this model has been applied in the steel sample classification of seamless steel pipe with good results.

Ultrabright and Efficient Green Perovskite Light-Emitting Diodes Enabled by Well-Crystallized Dense CsPbBr3 Nanocubes.

Perovskite light-emitting diodes (PeLEDs) are promising for next-generation high-definition displays. One of the keys to achieving high performance PeLEDs lies in how to fabricate crystalline and dense perovskite films. However, there exist challenges to directly grow well-crystallized CsPbBr3 nanocrystal thin films on transport layers due to low solubility in solvents and fast precipitation of all-inorganic CsPbBr3, and the corresponding bright, efficient, and stable green PeLEDs have rarely been reported. Herein, we report an efficient strategy to prepare well-crystallized and dense CsPbBr3 nanocubes for ultrabright and efficient green PeLEDs. We introduce sulfobetaine zwitterion as crystallization control agent and strontium fluoride nanocrystals as nucleation seeds to grow high-quality CsPbBr3 nanocube films. Eventually, the CsPbBr3 films enable green PeLEDs with a maximum luminance of 162 767 cd m-2 and a champion external quantum efficiency of 21.3% along with a narrow spectral line width of ∼14.7 nm, representing state-of-the-art performances in green PeLEDs.