Main Spectral Feature Research Articles

A broadband X-ray view of the NLSy1 1E 0754.6+3928

Context. The soft X-ray band of many active galactic nuclei (AGNs) is affected by obscuration due to partially ionised matter crossing our line of sight. In this context, two past XMM-Newton observations that were six months apart and a simultaneous NuSTAR-Swift exposure of the Narrow Line Seyfert 1 galaxy 1E 0754.6+3928, which was approximately eight years later, revealed an intense and variable warm absorber (WA) and hints of additional absorbers in the Fe Kα band. Aims. We aim to provide the first X-ray characterisation of this AGN by discussing its broadband (0.3–79 keV) spectrum and temporal properties. Methods. We conduct a temporal and spectroscopic analysis on two ∼10 ks (net exposure) XMM-Newton snapshots performed in April and October 2006. We also study the high energy behaviour of 1E 0754.6+3928 and model its broadband spectrum by using simultaneous Swift-NuSTAR data. Both phenomenological and physically motivated models are tested. Results. We find the presence of flux variability of ∼150% and 30% for 0.3–2 and 2–10 keV bands, respectively, and spectral changes at months timescales of ΔΓ ∼ 0.4. A reflection component that is consistent with being constant over years and arising from relatively cold material that is far from the central super massive black hole is detected. The main spectral feature shaping the 1E 0754.6+3928 spectrum is a WA. Such a component is persistent over the years and the variability of its ionisation and column density is observed down on months in the ranges 3 × 1022cm−2 ≲ NH ≲ 7.2 × 1022cm−2 and 1.5 ≲ log (ξ/erg s−1 cm) ≲ 2.1. Despite the short exposures, we find possible evidence of two additional high-ionisation and high-velocity outflow components in absorption. Conclusions. Our analysis suggests the existence of a complex system of absorbers in 1E 0754.6+3928. Longer exposures are required in order to characterise, on more solid grounds, the absorbers in this AGN.

Additional complexity in the Raman spectra of U3O8

Uranium oxides are readily amenable to investigation using Raman spectroscopy, and this technique is frequently used as a chemical analysis tool. We show, in triuranium octoxide (U3O8), the presence of previously unreported Raman peaks located below 100 cm−1. By maximum intensity, the strongest peak in U3O8 appears at 54 cm−1 and is resolution limited, making this mode an ideal candidate for chemically identifying U3O8 using Raman spectroscopy. Detailed peak analysis indicates that the main spectral feature between 300 and 500 cm−1 is more accurately described by a septet than a triplet. Two samples of differing oxygen content show only minor differences in bulk crystal structure, but subtle changes in lattice dynamics are suggestive of defect scattering in analogy to UO2+x.

РТ-22 КрАО - патрулирование мазерных H2O источников

Results of systematic observations of a sample of bright H2O maser sources with fluxes, on average, exceeding 200 Jy in their main spectral feature during April- September 2017 (G25.65+1.05, G25.825-0.178, G27.184-0.082, G34.403+0.233, G35.20-0.74, G43.8-0.13, G107.30+5.64) are presented. These observations were carried out in preparation for Very Long Baseline Interferometry observations with an array including the Crimean Astrophysical Observatory 22-m radio telescope. All these sources display fairly strong variability during the time interval considered, encompassing fluxes from ∼40 to ∼2300 Jy. A flare reaching ∼17 000 Jy was detected at a velocity of 42.8 km/s in G25.65+1.05 on September 7, 2017, which subsequently grew to 60 000 Jy at the end of September 2017. This suggests the presence of compactmaser structures.

Observation of cyclotron antiresonance in the topological insulator Bi2Te3

We report on the experimental observation of a cyclotron antiresonance in a canonical 3D topological insulator Bi$_2$Te$_3$. Magneto-reflectance response of single crystal Bi$_2$Te$_3$ was studied in 18 Tesla magnetic field, and compared to other topological insulators studied before, the main spectral feature is inverted. We refer to it as an antiresonance. In order to describe this unconventional behavior we propose the idea of an imaginary cyclotron resonance frequency, which on the other hand indicates that the form of the Lorentz force that magnetic field exerts on charge carriers takes an unconventional form.

Search for H2O Maser Flares in Regions of Formation of Massive Stars

Results of systematic observations of a sample of bright H2O maser sources with fluxes, on average, exceeding 200 Jy in their main spectral feature during April–September 2017 (G25.65+1.05, G25.825−0.178, G27.184−0.082, G34.403+0.233, G35.20−0.74, G43.8−0.13, G107.30+5.64) are presented. These observations were carried out in preparation for Very Long Baseline Interferometry observations with an array including the Crimean Astrophysical Observatory 22-m radio telescope. All these sources display fairly strong variability during the time interval considered, encompassing fluxes from ∼40 to ∼2300 Jy. A flare reaching ∼17 000 Jy was detected at a velocity of 42.8 km/s in G25.65+1.05 on September 7, 2017, which subsequently grew to 60 000 Jy at the end of September 2017. This suggests the presence of compact maser structures. The velocities covered by various spectral components range from 5 to 20 km/s. In three sources (G25.65+1.05,G25.825−0.178,G35.20−0.74), a general growth in the fluxes of all the spectral features is observed, which may indicate variations in the conditions for pumping by an external source, for example, variations in the infrared flux from a central source or the passage of a shock. Possible evidence for the presence of bipolar outflows or disk structures in G25.65+1.05 is discussed.

Biological sensing using hybridization phase of plasmonic resonances with photonic lattice modes in arrays of gold nanoantennas

We study biological sensing using the hybridization phase of localized surface plasmon resonances (LSPRs) with diffraction modes (photonic lattice modes) in arrays of gold nanoantennas. We map the degree of the hybridization process using an embedding dielectric material (Si), identifying the critical thicknesses wherein the optical responses of the arrays are mainly governed by pure LSPRs (insignificant hybridization), Fano-type coupling of LSPRs with diffraction orders (hybridization state), and their intermediate state (hybridization phase). The results show that hybridization phase can occur with slight change in the refractive index (RI), leading to sudden reduction of the linewidth of the main spectral feature of the arrays by about one order of magnitude while it is shifted nearly 140 nm. These processes, which offer significant improvement in RI sensitivity and figure of merit, are utilized to detect monolayers of biological molecules and streptavidin-conjugated semiconductor quantum dots with sensitivities far higher than pure LSPRs. We further explore how these sensors can be used based on the uncoupled LSPRs by changing the polarization of the incident light.

Wavy magnetodisk in Saturn's outer magnetosphere

AbstractA simple wavy magnetodisk model can explain periodicities in energetic charged particles observed in Saturn's outer magnetosphere (>20 RS). The model's free parameters are the tilt of magnetodisk in inner magnetosphere (~1.8°), speed of outgoing spiral wave (~8 RS/h), critical radius (~10 RS), and period of rotation (10.64 h). The fidelity of the model is not judged by a least squares fit to the actual data, but rather by the model's accuracy in reproducing the Lomb periodogram of the periodicities. The model accurately simulates the main spectral feature near ~10.7 h plus a secondary (“dual”) period near ~10.95 h. The ability of the wavy magnetodisk with one period to produce the observed dual periodicity in the observations suggests that models having “dual” periods need not be invoked to explain some of the periodicities in Saturn's outer magnetosphere.

Trace detection and differentiation of uranyl(VI) ion cast films utilizing aligned Ag nanorod SERS substrates

Aligned Ag nanorod arrays prepared by oblique angle vapor deposition (OAD) were utilized to observe the SERS response for cast films of adsorbed uranyl ion complexes. These nanorod arrays consisted of preferentially aligned and tilted cylindrically shaped nanorods (average nanorod length = 858 nm). Routine SERS spectra of cast films of uranyl nitrate resulted in 0.87 pg of material analyzed with a detection limit estimated at 0.87 fg of adsorbed uranyl nitrate. The main spectral feature observed was a strong, broad peak centered at 700 cm −1 assigned to the ν 1 symmetric stretch of the uranyl ion, ν s(UO 2). The complex shape of this band is attributed to multiple uranyl complexes adsorbed onto the Ag surface. Uranyl nitrate cast films formed from ethanol solutions were more uniform and had stronger adsorption to the Ag surface compared to films formed from aqueous solutions. Differentiation of uranyl ion cast films formed from four different uranyl systems (i.e., uranyl nitrate hexahydrate, uranyl acetate dihydrate, uranyl formate monohydrate, and uranyl chloride trihydrate) was accomplished using univariate spectral analysis as well as Partial Least Squares Discriminant Analysis (PLSDA). A simple PLSDA calibration was able to correctly classify 27 SERS spectra of unknown uranyl ion cast films based on the type of anionic ligand present.

Atmospheric Pressure Chemical Ionization Source. 2. Desorption−Ionization for the Direct Analysis of Solid Compounds

The flowing afterglow-atmospheric pressure glow discharge (APGD) ionization source described in part 1 of this study (in this issue) is applied to the direct analysis of condensed-phase samples. When either liquids or solids are exposed to the ionizing beam of the APGD, strong signals for the molecular ions of substances present on their surfaces can be detected without compromising the integrity of the solid sample structure or sample substrate. As was observed for gas-phase compounds in part 1 of this study, both polar and nonpolar substances can be ionized and detected by mass spectrometry. The parent molecular ion (or its protonated counterpart) is usually the main spectral feature, with little or no fragmentation in evidence. Preliminary quantitative results show that this approach offers very good sensitivity (detection limits in the picogram regime are reported for several test compounds in part 1 of this study) and linear response to the analyte concentration. Examples of the application of this strategy to the analysis of real-world samples, such as the direct analysis of pharmaceutical compounds or foods is provided. The ability of this source to perform spatially resolved analysis is also demonstrated. Preliminary studies of the mechanisms of the reactions involved are described.

Time-resolved step scan FTIR spectroscopy and DFT investigation on triplet formation in Peridinin-Chlorophyll-a-Protein from Amphidinium carterae at low temperature

We have used time-resolved step-scan FTIR spectroscopy to investigate the process of triplet formation in the peridinin–chlorophyll-a–protein (PCP) at 100 K. Results have led to the identification of possible marker bands for peridinin (Per) and 3Per. Band assignment has been carried out performing a DFT investigation on Per, 3Per and on model molecules. The main spectral feature is a couple of bands at 1746 (negative) and 1719 (positive) cm–1. The assignment of these two bands to the lactonic C═O of Per in (respectively) its fundamental S0 and triplet T1 state is based on: (1) comparison with FTIR spectra of isolated Per in literature; (2) good agreement with DFT calculations for Per and 3Per; (3) the downshift of the band upon triplet formation as predicted by DFT calculations in Per and similar lactonic systems; (4) the kinetic of band disappearance, in agreement with literature data. Another possible band for Per in its fundamental state has been identified at 1523 cm–1.

Time-resolved step scan FTIR spectroscopy and DFT investigation on triplet formation in peridinin–chlorophyll-a–protein from Amphidinium carterae at low temperature

We have used time-resolved step-scan FTIR spectroscopy to investigate the process of triplet formation in the peridinin–chlorophyll-a–protein (PCP) at 100 K. Results have led to the identification of possible marker bands for peridinin (Per) and3Per. Band assignment has been carried out performing a DFT investigation on Per,3Per and on model molecules. The main spectral feature is a couple of bands at 1746 (negative) and 1719 (positive) cm–1. The assignment of these two bands to the lactonic C═O of Per in (respectively) its fundamental S0 and tripletT1state is based on: (1) comparison with FTIR spectra of isolated Per in literature; (2) good agreement with DFT calculations for Per and3Per; (3) the downshift of the band upon triplet formation as predicted by DFT calculations in Per and similar lactonic systems; (4) the kinetic of band disappearance, in agreement with literature data. Another possible band for Per in its fundamental state has been identified at 1523 cm–1.The results are in overall agreement with a recent step-scan FTIR study on PCP at 298 K (Alexandre et al.,Biophys. J. 93 (2007), 2118–2128) even though some small discrepancies emerge, probably related to the different temperature at which experiments were carried out. Further DFT calculations have been performed to rationalise these spectral discrepancies. From a methodological point of view, the work demonstrates the potential of a combined step-scan FTIR/DFT approach in the study of photophysical processes in proteins. Furthermore, it has been shown that, when small differential IR signals are concerned, nagging photothermal effects can interfere and can possibly lead to misleading interpretations.

Study on the quantum confinement effect on ultraviolet photoluminescence of crystalline ZnO nanoparticles with nearly uniform size

Crystalline ZnO nanoparticles with nearly uniform size were studied using photoluminescence and Raman spectroscopy. The main spectral feature of ultraviolet photoluminescence is attributed to the recombination of free exciton (FX) and the first surface phonon replica of FX emission. The energy of FX emission shows a clear blueshift as the size of nanoparticles decreases, indicating that the quantum confinement effect exists in the electronic structure of nano-ZnO, although no confinement effect on the vibrational modes has been found in the same series of samples.

Magneto-optical spectra of closely spaced magnetite nanoparticles

The Faraday rotation spectrum of composites containing magnetite nanoparticles is found to be dependent on the interparticle spacing of the constituent nanoparticles. The composite materials are prepared by combining chemically synthesized Fe3O4 (magnetite) nanoparticles (8-nm diameter) and poly(methylmethacrylate). Composites are made containing a range of nanoparticle concentrations. The peak of the main spectral feature depends on nanoparticle concentration; this peak is observed to shift from approximately 470 nm for (dilute composites) to 540 nm (concentrated). We present a theory based on the discrete-dipole approximation which accounts for optical coupling between magnetite particles. Qualitative correlations between theoretical calculations and experimental data suggest that the shifts in spectral peak position depend on both interparticle distance and geometrical configuration.

Mapping variations in weight percent silica measured from multispectral thermal infrared imagery—Examples from the Hiller Mountains, Nevada, USA and Tres Virgenes-La Reforma, Baja California Sur, Mexico

Remotely sensed multispectral thermal infrared (8–13 μm) images are increasingly being used to map variations in surface silicate mineralogy. These studies utilize the shift to longer wavelengths in the main spectral feature in minerals in this wavelength region (reststrahlen band) as the mineralogy changes from felsic to mafic. An approach is described for determining the amount of this shift and then using the shift with a reference curve, derived from laboratory data, to remotely determine the weight percent SiO 2 of the surface. The approach has broad applicability to many study areas and can also be fine-tuned to give greater accuracy in a particular study area if field samples are available. The approach was assessed using airborne multispectral thermal infrared images from the Hiller Mountains, Nevada, USA and the Tres Virgenes-La Reforma, Baja California Sur, Mexico. Results indicate the general approach slightly overestimates the weight percent SiO 2 of low silica rocks (e.g. basalt) and underestimates the weight percent SiO 2 of high silica rocks (e.g. granite). Fine tuning the general approach with measurements from field samples provided good results for both areas with errors in the recovered weight percent SiO 2 of a few percent. The map units identified by these techniques and traditional mapping at the Hiller Mountains demonstrate the continuity of the crystalline rocks from the Hiller Mountains southward to the White Hills supporting the idea that these ranges represent an essentially continuous footwall block below a regional detachment. Results from the Baja California data verify the most recent volcanism to be basaltic–andesite.

Infrared absorption spectrum of matrix-isolated noble-gas hydride molecules: Fingerprints of specific interactions and hindered rotation

Noble-gas hydride molecules with the general formula HNgY (Ng denotes noble-gas atom and Y denotes electronegative fragment) are usually prepared in solid noble gases. In many cases, the matrix-isolated HNgY molecules show a characteristic structure of the H-Ng stretching absorption: A close doublet as the main spectral feature and a weaker satellite at higher energy. This characteristic band structure is studied here for matrix-isolated HXeBr and HKrCl molecules. Based on the experimental and theoretical results, we suggest a model explaining the common features of the band structure of the HNgY molecules in noble-gas matrices. In this model, the main doublet bands are attributed to matrix sites where the splitting is caused by specific interactions of the embedded molecule with noble-gas matrix atoms in certain local morphology. The weaker blueshifted band is probably a fingerprint of hindered rotation (libration) of the embedded molecule in the lattice. This librational band has a mirror counterpart at lower energies appearing at higher matrix temperatures. Our present ab initio calculations for the one-to-one Xe...HXeBr complexes and the simulation of hindered rotation in a matrix support this image.

Axial excitation of tightly interlaced chiral sculptured thin films: “averaged” circular Bragg phenomenon

Abstract Interlaced chiral sculptured thin films (STFs) are proposed. The main spectral feature – the circular Bragg phenomenon – of the axial excitation response of a tightly interlaced chiral STF is shown to be an “average” of the same features individually displayed by the constituent chiral STFs.

Optical properties and nondestructive estimation of anthocyanin content in plant leaves.

Absorption and reflectance spectra of maple (Acer platanoides), cotoneaster (Cotoneaster alaunica), dogwood (Cornus alba) and pelargonium (Pelargonium zonale) leaves with a wide range of pigment content and composition were studied in visible and near-infrared spectra in order to reveal specific anthocyanin (Anth) spectral features in leaves. Comparing absorption spectra of Anth-containing and Anth-free leaves with the same chlorophyll (Chl) content, absorption spectra of Anth in leaves were derived. The main spectral feature of Anth absorption in vivo was a peak around 550 nm; the peak magnitude was closely related to Anth content. A quantitative nondestructive technique was developed to subtract Chl contribution to reflectance in this spectral region and retrieve Anth content from reflectance over a wide range of pigment content and composition. Anth reflectance index in the form ARI = (R550)-1 - (R700)-1, where (R550)-1 and (R700)-1 are inverse reflectances at 550 and 700 nm, respectively, allowed an accurate estimation of Anth accumulation, even in minute amounts, in intact senescing and stressed leaves.

Break-junction experiments on the Kondo semiconductor CeNiSn: tunnelling versus direct conductance

The rare-earth Kondo semiconductor CeNiSn is investigated by point-contact and tunneling spectroscopy using mechanically controllable break junctions. I(V) characteristics and their derivatives are recorded for contacts from the metallic to the tunneling regime at temperatures between 0.1–8 K and in magnetic fields up to 8 T. It is found that CeNiSn behaves like a compound with typical metallic properties instead of exhibiting the expected semiconducting behavior. The main spectral feature is a pronounced zero-bias conductance minimum of about 10 meV width, which appears to be of magnetic nature. These break-junction experiments provide no clear-cut evidence for an energy (pseudo) gap in CeNiSn.

Photoluminescence of CdSe nanocrystals embedded in a SiO x thin film matrix

Room- and low-temperature photoluminescence studies are reported on CdSe nanocrystals embedded in an SiO x thin film matrix. The main spectral feature for all samples and both temperatures is a broad band whose position does not change considerably with nanocrystallite size. The band is assigned to recombination through defect states, whose energy depends on the nanocrystallite size in such a way that they counter-balance the similar dependence of the optical band gap on the nanocrystallite size. A noticeable asymmetry on the low-energy side of this band at low temperatures is attributed to the existence of a variety of surface defect states and/or a large number of volume defect states in these nanocrystals. There is evidence to suggest that the energy band diagram of CdSe nanocrystals in SiO x matrix is considerably different from that of SiO x /CdSe multi-quantum wells.

Optical anisotropy and spontaneous ordering in Ga0.5In0.5P: An investigation using reflectance-difference spectroscopy.

We have applied reflectance-difference spectroscopy (RDS) to the study of optical anisotropy in spontaneously ordered Ga[sub 0.5]In[sub 0.5]P grown by metal-organic chemical-vapor deposition. The degree of order in Ga[sub 0.5]In[sub 0.5]P has been associated previously with a shift of the band-gap energy [Delta][ital E][sub 0] and a crystal-field valence-band splitting [Delta][sub [ital C]]. Theoretically, both quantities are, to first order, quadratic functions of the long-range order parameter [eta], which varies from 0 to 1 for disordered and perfectly ordered Ga[sub 0.5]In[sub 0.5]P, respectively. The main RD spectral feature in partially ordered Ga[sub 0.5]In[sub 0.5]P is a bulk-induced, asymmetric peak at [ital E][sub 0] with a long tail that extends well below [ital E][sub 0] and a sharp high-energy cutoff at [ital E][sub 0]+[Delta][sub [ital C]]. We find experimentally and theoretically that the intensity of this RD spectral feature is proportional to [radical]([Delta][ital E][sub 0]) and, therefore, is linear with the order parameter. This makes RDS particularly useful for measuring the optical anisotropy of high-band-gap Ga[sub 0.5]In[sub 0.5]P. We also compare heterostructures of GaAs and Al[sub 0.5]In[sub 0.5]P on Ga[sub 0.5]In[sub 0.5]P with uncoated Ga[sub 0.5]In[sub 0.5]P in an effort to separate bulk-, surface-, and interface-induced RD spectral features.