Spectral Asymmetry Research Articles

Toward a robust physical and chemical characterization of heterogeneous lines of sight: The case of the Horsehead nebula

Dense and cold molecular cores and filaments are surrounded by an envelope of translucent gas. Some of the low- J emission lines of and isotopologues are more sensitive to the conditions either in the translucent environment or in the dense and cold one because their intensities result from a complex interplay of radiative transfer and chemical properties of these heterogeneous lines of sight (LoSs). We extend our previous single-zone modeling with a more realistic approach that introduces multiple layers to take account of possibly varying conditions along the LoS. We used the IRAM-30m data from the ORION-B large program toward the Horsehead nebula in order to demonstrate our method's capability and effectiveness. We propose a cloud model composed of three homogeneous slabs of gas along each LoS, representing an outer envelope and a more shielded inner layer. We used the non-LTE radiative transfer code RADEX to model the line profiles from the kinetic temperature ( the volume density ( kinematics, and chemical properties of the different layers. We then used a fast and robust maximum likelihood estimator to simultaneously fit the observed lines of the and isotopologues. To limit the variance on the estimates, we propose a simple chemical model by constraining the column densities. A single-layer model cannot reproduce the spectral line asymmetries that result from a combination of different radial velocities and absorption effects among layers. A minimal heterogeneous model (three layers only) is sufficient for the Horsehead application, as it provides good fits of the seven fitted lines over a large part of the studied field of view. The decomposition of the intensity into three layers allowed us to discuss the distribution of the estimated physical or chemical properties along the LoS. About 80<!PCT!> of the integrated intensity comes from the outer envelope, while $ of the integrated intensity of the and lines of comes from the inner layer. For the lines of the and the isotopologues, integrated intensities are more equally distributed over the cloud layers. The estimated column density ratio NCeiO in the envelope increases with decreasing visual extinction, and it reaches $25$ in the pillar outskirts. While the inferred of the envelope varies from $25$ to K$ that of the inner layer drops to K$ in the western dense core. The estimated in the inner layer is pccm$ toward the filament, and it increases by a factor of ten toward dense cores. Our proposed method correctly retrieves the physical and chemical properties of the Horsehead nebula. It also offers promising prospects for less supervised model fits of wider-field datasets.

Spectral Index Asymmetries in Double Radio Sources from the VLA Sky Survey

A sample of double radio sources was selected from the Very Large Array Sky Survey to investigate correlations of spectral asymmetries with lobe length ratios and jet-sidedness. The lobe length ratio informs us about the correlation between the lobe pressure and spectral index of FRII lobes from Active Galactic Nuclei. A second analysis was done on the subset with identifiable jets. The correlation of lobe length ratio with spectral index difference was weakly positive, although statistically insignificant. Similarly, there were no statistically significant trends of spectral index difference with jet-sidedness. Further testing with a larger data set may produce a more significant result.

Is It Possible to Detect Coronal Mass Ejections on Solar-type Stars through Extreme-ultraviolet Spectral Observations?

Stellar coronal mass ejections (CMEs) from host stars are an important factor that affects the habitability of exoplanets. Although their solar counterparts have been well observed for decades, it is still very difficult to find solid evidence of stellar CMEs. Using the spectral line profile asymmetry caused by the Doppler shift of erupting plasma, several stellar CME candidates have been identified from spectral lines formed at chromospheric or transition region temperatures of the stars. However, a successful detection of stellar CME signals based on the profile asymmetries of coronal lines is still lacking. It is unclear whether we can detect such signals. Here we construct an analytical model for CMEs on solar-type stars and derive an expression of stellar extreme-ultraviolet (EUV) line profiles during CME eruptions. For different instrumental parameters, exposure times, CME propagation directions, and stellar activity levels, we synthesized the corresponding line profiles of Fe ix λ171.07 and Fe xv λ284.16. Further investigations provide constraints on the instrumental requirements for successful detection and characterization of stellar CMEs. Our results show that it is possible to detect stellar CME signals and infer their velocities based on spectral profile asymmetries using an EUV spectrometer with a moderate spectral resolution and signal-to-noise ratio. Our work provides important references for the design of future EUV spectrometers for stellar CME detection and the development of observation strategies.

The Asymmetry Observed between the Effects of Photon-Phonon Coupling and Crystal Field on the Fine Structure of Fluorescence and Spontaneous Four-Wave Mixing in Ion-Doped Microcrystals.

In this paper, we explore the asymmetry observed between the effects of photon-phonon coupling (nested-dressing) and a crystal field (CF) on the fine structure of fluorescence (FL) and spontaneous four-wave mixing (SFWM) in Eu3+: BiPO4 and Eu3+: NaYF4. The competition between the CF and the strong photon-phonon dressing leads to dynamic splitting in two directions. The CF leads to static splitting in one direction under weak phonon dressing. The evolution from strong dressing to weak dressing results in spectral asymmetry. This spectral asymmetry includes out-of-phase FL and in-phase SFWM. Further, the large ratio between the dressing Rabi frequency and the de-phase rate leads to strong FL and SFWM asymmetry due to photon-phonon constructive dressing. Moreover, the experimental results suggest the analogy of a spectra asymmetry router with a channel equalization ratio of 96.6%.

Pallidal multifractal complexity is a new potential physiomarker of dystonia

ObjectiveLow-frequency 4–12 Hz pallidal oscillations are being considered as potential physiomarkers for dystonia. We suggest investigating the multifractal properties of pallidal activity as an additional marker. MethodsWe employed local field potentials (LFP) recordings from 23 patients with dystonia who were undergoing deep brain stimulation (DBS) surgery to explore the connection between disease severity and the multifractal characteristics of pallidal activity. Furthermore, we performed an analysis of LFP recordings from four patients, following the externalization of DBS lead electrodes, to investigate the impact of DBS and neck muscle vibration on multifractal parameters. ResultsGreater dystonia severity exhibited a correlation with a narrower multifractal spectrum width but higher multifractal spectral asymmetry. Both GPi DBS and muscle vibration in dystonia patients expanded the multifractal spectrum width while restoring multifractal spectral symmetry. Notably, the threshold peak intensities for an increase in multifractal spectrum width substantially overlapped with the optimal volume of tissue activated. A broader multifractal spectrum during DBS corresponded to more favorable clinical outcomes. ConclusionsMultifractal properties of pallidal neuronal activity serve as indicators of neural dysfunction in dystonia. SignificanceThese findings suggest the potential of utilizing multifractal characteristics as predictive factors for the DBS outcome in dystonia.

Spectral Asymmetry Induces a Re-Entrant Quantum Hall Effect in a Topological Insulator.

The band inversion of topological materials in three spatial dimensions is intimately connected to the parity anomaly of 2D massless Dirac fermions, known from quantum field theory. At finite magnetic fields, the parity anomaly reveals itself as a non-zero spectral asymmetry, i.e., an imbalance between the number of conduction and valence band Landau levels, due to the unpaired zero Landau level. This work reports the realization of this 2D Dirac physics at a single surface of the 3D topological insulator (Hg,Mn)Te. An unconventional re-entrant sequence of quantized Hall plateaus in the measured Hall resistance can be directly related to the occurrence of spectral asymmetry in a single topological surface state. The effect should be observable in any topological insulator where the transport is dominated by a single Dirac surfacestate.

Gravitational Landau levels and the chiral anomaly

A popular physical picture of the mechanism behind the four-dimensional chiral anomaly is provided by the massless Dirac equation in the presence of constant electric and magnetic background fields. The magnetic field creates highly degenerate Landau levels, the lowest of which is gapless. Any parallel component of the electric field drives a spectral flow in the gapless mode that causes particles to emerge from, or disappear into, the Dirac sea. Seeking a similar picture for the gravitational contribution to the chiral anomaly, we consider the massless Dirac equation in a background spacetime that creates gravitational Landau levels. We find that in this case the resulting spectral flow, with its explicit particle production, accounts for only a small part of the anomalous creation of chiral charge. The balance is provided by the vacuum expectation charge arising from the spectral asymmetry.

Conservation of a Spectral Asymmetry Invariant in Optical Fiber Four‐Wave Mixing

AbstractThe conservation of spectral asymmetry is a fundamental feature of the ideal four‐wave mixing process as it exists in a medium combining quadratic chromatic dispersion and third‐order nonlinearity. The robustness of this invariant in an experimental configuration where the excitation conditions of an optical fiber are sequentially updated, mimicking infinite propagation is tested in this paper. This theoretical and experimental study reveals the high sensitivity of the asymmetry to very slight deviations from the ideal case, and the idealized system behaves as an intermediate case between the ideal case of noncascaded four‐wave mixing and propagation in a system governed by the nonlinear Schrödinger equation is shown.

Simple Hurwitz groups and eta invariant

A Hurwitz group is a conformal automorphism group of a compact Riemann surface with precisely $84(g - 1)$ automorphisms, where $g$ is the genus of the surface. Our starting point is a result on the smallest Hurwitz group $\mathrm{PSL}(2,\mathbb{F}_{7})$ which is the automorphism group of the Klein surface. In this paper, we generalize it to various classes of simple Hurwitz groups and discuss a relationship between the surface symmetry and spectral asymmetry for compact Riemann surfaces. To be more precise, we show that the reducibility of an element of a simple Hurwitz group is equivalent to the vanishing of the $\eta$-invariant of the corresponding mapping torus. Several wide classes of simple Hurwitz groups which include the alternating group, the Chevalley group and the Monster, which is the largest sporadic simple group, satisfy our main theorem.

A Bigger Cloud 9? New H i Observations of the RELHIC Candidate M94- Cloud 9

We present new H i observations of the REionization-Limited H i Cloud (RELHIC) candidate, M94-CL9, detected around M94 by Zhou et al. using the Five-hundred-meter Aperture Spherical Telescope (FAST). M94-CL9's H i properties as detected by FAST are consistent with a RELHIC as noted by Benitez-Llambay & Navarro. Our observations with the Robert C. Byrd Green Bank Telescope detect greater H i emission in M94-CL9 and result in H i properties that are larger (corrected velocity width, W 50,c,t = 35.7 ± 0.6 km s−1; and integrated flux, ∫Sdv = 0.28 ± 0.04 Jy km s−1) than those found by Zhou et al. but that match those from the FAST All-Sky H i survey. These larger properties do not preclude M94-CL9 from being a RELHIC, but the wider spectral extent and spectral asymmetry reported here may be in tension with predictions of RELHIC properties.

Spectral Signal Asymmetry Analysis and Encoding of Chromatic Confocal Sensors

Spectral Signal Asymmetry Analysis and Encoding of Chromatic Confocal Sensors

Laser induced fluorescence spectroscopy of aqueous eosin Y solution

Eosin Yellow (EY) is commonly used for staining in medicine, biology, food industry, textiles, painting and cosmetics. The spectroscopic and photochemical properties of this synthetic dye have also attracted attention, making it an excellent tool for chemical identification and biosensor applications. Since EY is prone to photo-degradation upon illumination by photons at wavelengths near to the main absorption bands, special considerations should be taken into account regarding its optical characterization. In the present report, laser induced fluorescence (LIF) features of aqueous EY solution due to excitation at 405 nm and 532 nm wavelengths, under conditions with the least likelihood of photo-degradation, have been assessed by emphasizing the effect of LIF internal filters. The quantum distribution of LIF emission is demonstrated to be dependent on both the excitation wavelength and EY concentration, as well as the detection line of sight. Since the fluorescence spectrum of EY is a convolution of the monomer and dimer emissions, and those contributions change unevenly under the influence of internal filters, the corresponding spectral changeovers were investigated based on the assessment of spectral asymmetry and the use of difference spectra analysis. The inner filter effects, dimerization, and resonance energy transfer between monomers and dimers were the basis for the discussion of the results.

Observation of electron–phonon coupling and linear dichroism in PL spectra of ultra-small CsPbBr3 nanoparticle solution

Blue-emission (∼480 ​nm) CsPbBr3 nanoparticles with ultra-small size (∼2.1 ​nm) are synthesized using the liquid nitrogen freezing with the ligand of dodecylbenzene sulfonic acid (DBSA). Asymmetric narrow emissions at the low energy side, with the full width at half-maximum of ∼20 ​nm, are observed in solution and film at room temperature. The spectral asymmetry is mainly ascribed to phonon vibronic replica with averaged phonon energy of ∼40 ​meV. Moreover, exciting this CsPbBr3 nanoparticles solution using linearly polarized 6 ns pulsed laser at 355 ​nm, we observe polarized emission with polarization degree (PPL) of ∼7%, and PPL decreases more than 20% in the vibronic progression. However, the PPL goes to zero in frozen solutions as well as in films. Thus we speculate the polarized emission is due to the photoinduced re-alignment of nanoparticles, and the diminished PPL at the phonon side band may be due to the non-adiabatic electronic-to-vibronic transitions. The novel phenomena from the ultra-small CsPbBr3 nanoparticle demonstrated in this work may provide fundamental insights into its photophysics with direct implications for optoelectronics.

Recognizing emotions induced by wearable haptic vibration using noninvasive electroencephalogram.

The integration of haptic technology into affective computing has led to a new field known as affective haptics. Nonetheless, the mechanism underlying the interaction between haptics and emotions remains unclear. In this paper, we proposed a novel haptic pattern with adaptive vibration intensity and rhythm according to the volume, and applied it into the emotional experiment paradigm. To verify its superiority, the proposed haptic pattern was compared with an existing haptic pattern by combining them with conventional visual-auditory stimuli to induce emotions (joy, sadness, fear, and neutral), and the subjects' EEG signals were collected simultaneously. The features of power spectral density (PSD), differential entropy (DE), differential asymmetry (DASM), and differential caudality (DCAU) were extracted, and the support vector machine (SVM) was utilized to recognize four target emotions. The results demonstrated that haptic stimuli enhanced the activity of the lateral temporal and prefrontal areas of the emotion-related brain regions. Moreover, the classification accuracy of the existing constant haptic pattern and the proposed adaptive haptic pattern increased by 7.71 and 8.60%, respectively. These findings indicate that flexible and varied haptic patterns can enhance immersion and fully stimulate target emotions, which are of great importance for wearable haptic interfaces and emotion communication through haptics.

Spectral Asymmetry and Index Theory on Manifolds with Generalised Hyperbolic Cusps

We consider a complete Riemannian manifold, which consists of a compact interior and one or more $\varphi$-cusps: infinitely long ends of a type that includes cylindrical ends and hyperbolic cusps. Here $\varphi$ is a function of the radial coordinate that describes the shape of such an end. Given an action by a compact Lie group on such a manifold, we obtain an equivariant index theorem for Dirac operators, under conditions on $\varphi$. These conditions hold in the cases of cylindrical ends and hyperbolic cusps. In the case of cylindrical ends, the cusp contribution equals the delocalised $\eta$-invariant, and the index theorem reduces to Donnelly's equivariant index theory on compact manifolds with boundary. In general, we find that the cusp contribution is zero if the spectrum of the relevant Dirac operator on a hypersurface is symmetric around zero.

Observations and modeling of spectral line asymmetries in stellar flares

Context. Stellar flares are energetic events occurring in stellar atmospheres. They have been observed on various stars using photometric light curves and spectra. On some cool stars, flares tend to release substantially more energy than solar flares. Spectroscopic observations have revealed that some spectral lines exhibit asymmetry in their profile in addition to an enhancement and broadening. Asymmetries with enhanced blue wings are often associated with coronal mass ejections, while the origin of red asymmetries is currently not well understood. A few mechanisms have been suggested, but no modeling has been performed so far. Aims. We observed the dMe star AD Leo using the 2-meter Perek telescope at Ondřejov observatory, with simultaneous photometric light curves. In analogy with solar flares, we modeled the Hα line emergent from an extensive arcade of cool flare loops and explain the observed asymmetries using the concept of coronal rain. Methods. We solved the non-LTE (departures from local thermal equilibrium) radiative transfer in Hα within cool flare loops taking the velocity distribution of individual rain clouds into account. For a flare occurring at the center of the stellar disk, we then integrated radiation emergent from the whole arcade to obtain the flux from the loop area. Results. We observed two flares in the Hα line that exhibit a red wing asymmetry corresponding to velocities up to 50 km s−1 during the gradual phase of the flare. Synthetic profiles generated from the model of coronal rain have enhanced red wings that are quite compatible with observations.

Directional dependence of the plasmonic gain and nonreciprocity in drift-current biased graphene

Abstract Here, we investigate the nonreciprocal propagation and amplification of surface plasmons in drift-current biased graphene, using both Galilean and relativistic-type Doppler shift transformations of the graphene’s conductivity. Consistent with previous studies, both conductivity models predict strongly nonreciprocal propagation of surface plasmons due to the drag effect caused by the drifting electrons. In particular, the Galilean Doppler shift model leads to stronger spectral asymmetries in the plasmon dispersion with regimes of unidirectional propagation. Remarkably, it is shown that both conductivity models predict regimes of nonreciprocal plasmon amplification in a wide angular sector of in-plane directions when the drift-current biased graphene sheet is coupled to a plasmonic substrate (namely, SiC), with the plasmon amplification rate being substantially higher for the relativistic Doppler shift model.

Modification of conventional peak shapes to accurately represent spectral asymmetry: High-Resolution X-ray photoelectron spectra of [C4C1Pyrr][NTf2] and [C8C1Im][NTf2] ionic liquids

X-ray photoelectron spectroscopy (XPS) is one of the most widely used techniques for surface characterization. Analysis of XPS data is challenging and requires the analyst to fit the data with synthetic line shapes to reach physically meaningful interpretations. Experimental spectral envelopes, however, are complex and display asymmetric features that are often ignored or attributed to additional chemical components. The high-resolution XPS spectra of [C4C1Pyrr][NTf2] and [C8C1Im][NTf2] all exhibit a degree of asymmetry which is systematically observed at the higher binding energy side of photoemission envelopes. We present the development of a refined fitting procedure for XPS spectra of these ionic liquid-based systems which include (a) Shirley background offset necessary to account for the insulator-like region and (b) spectral asymmetry in C 1s and N 1s regions. Further, Shirley and trapezoid components are applied to compensate for inelastic scattering taking place during electron transitions as high as 7.8 eV above the start of the fitting region in C 1s high-resolution spectrum. To demonstrate the fitness of this model, we present an analysis of a 2:1 mixture of [C4C1Pyrr][NTf2]: [C8C1Im][NTf2].

Changes in EEG Measures of a Recipient of the mRNA COVID-19 Vaccine - A Case Study.

The current study is aimed to evaluate the effect of COVID-19 vaccine on human EEG and the persistence of the effect. Within a one-year-long resting EEG study period, the healthy male subject was administered two Comirnaty doses three weeks apart to prevent COVID-19. Fourteen recordings were acquired from the subject in one year: twelve reference and two post-vaccination recordings after administrating the second dose of Comirnaty. The changes in absolute powers of EEG frequency bands, EEG spectral asymmetry index (SASI), and Higuchi's fractal dimension (HFD) were analyzed. The results indicated a statistically significant increase in absolute gamma power, SASI and HFD values on the fifth day after the vaccination, while the EEG had restored its normal character on the twelfth day after vaccination. These measures seem to have higher sensitivity for the detection of the effects of the vaccine Clinical Relevance- This is the first study evaluating COVID-19 vaccine effect on healthy human EEG. The study indicated that the vaccine disturbs EEG but the impact is not long-lasting.

The spectral line asymmetry of the Doppler effect in relativistic plasmas

In this work, we present a comparative study between the relativistic and non-relativistic Doppler effects on spectral line profiles in ultra-hot plasmas in a laboratory system. We have established an exact formula of the relativistic Doppler profile in ultra-high-temperature plasma that is not a Gaussian one (unlike the non-relativistic Doppler profile that is Gaussian). We have also derived a new FWHM (Full Width at Half Maximum) formula of the corresponding profile that is different from the non-relativistic FWHM (). We have also shown that, in the relativistic case, Doppler broadening exhibits an asymmetry of spectral line profile (non-Gaussian profile). To ensure the validity of our investigation, we have compared our theoretical calculation with the experimental results and found a good agreement.