Double-peak Feature Research Articles

Monthly Radial Growth Model of Chinese Fir (Cunninghamia lanceolata (Lamb.) Hook.), and the Relationships between Radial Increment and Climate Factors

Chinese fir (Cunninghamia lanceolata (Lamb.) Hook) is the most commonly grown afforestation species in subtropical China. It is essential that we understand the response of radial tree growth to climate factors, yet most experiments have been conducted based on total annual growth and not on monthly dynamics, which alone can detail the influence of climatic factors. In this study, we aimed to: (i) construct a monthly growth model and compare the growth rate of different social statuses of trees, and (ii) determine the response of radial increments of different social statuses to climate factors. The radial growth was monitored monthly during four years using manual band dendrometers (MBD). The data were fitted using the Gompertz function. Within-stand differences in the social status of Chinese firs resulted in growing period and growth rate length variations. The radial growth began in March, and suppressed trees—especially groups of AS1 and BS1 (suppressed trees of classes I in sites A and B)—stopped in September, whereas dominant and intermediate trees were delayed and stopped in November. The periodic monthly increment curve showed double peaks, and the maximum growth rate occurred in April and August. The peak values were affected by social status, which showed that dominant trees had the greatest radial growth rates. S-shaped Gompertz meant that monthly increment models were successfully fitted to our data, which explained more than 98% of the variation in increment data and passed the uncertainty test. Temperature and precipitation had a significant influence on radial growth, and the correlation between radial growth and air temperature was the highest. Our results also revealed that temperatures explain the double-peak features of Chinese fir. The limiting factors of radial growth changed with the seasons and were mainly affected by temperature and precipitation, which should be considered in predicting the response of tree growth to climate change.

Retrieval of marine inorganic particle concentrations in turbid waters using polarization signals

ABSTRACT The polarization properties of water-leaving radiance (L w) contains rich information about hydrosols, which has great potential to improve the retrieval accuracy of oceanic constituents. However, current ocean colour inversion algorithms are only based on the water-leaving radiation intensity, and the polarization properties have been ignored. Here, based on the radiative transfer simulations, the possibility of retrieving suspended particulate matter in turbid waters based on the polarization properties was investigated. The results showed that the degree of polarization (DOP) of the upward radiation just beneath the water surface has significant angular and spectral variations with respect to the observational geometries, inorganic particle concentrations, solar zenith angles and aerosol optical thicknesses (AOTs). The directional variations in DOP along with viewing zenith angles are typically characterized by a double peak feature with a maximum of 0.5 in the principal plane. In addition, the DOP in the visible bands is highly sensitive to inorganic particle concentrations. The DOP gradually decreases from 412 nm to 555 nm and increases with wavelengths beyond 555 nm, particularly for wavelengths larger than 620 nm. An empirical relationship between the DOP at 670 nm and the inorganic particle concentration was established for different viewing geometries with determination coefficient (R 2) up to 0.9996. Overall, our simulation results indicate that the polarization property of underwater upward radiance has great potential for suspended particulate matter retrieval in coastal waters.

Spectroscopic study of olivine-bearing rocks and its relevance to the ExoMars rover mission

We present the compositional analysis of three terrestrial analogues of Martian olivine-bearing rocks derived from both laboratory and flight-derived analytical instruments. In the first step, state-of-the-art spectroscopic (XRF, NIR and Raman) and diffractometric (XRD) laboratory systems were complementary used. Besides providing a detailed mineralogical and geochemical characterization of the samples, results comparison shed light on the advantages ensured by the combined use of Raman and NIR techniques, being these the spectroscopic instruments that will soon deploy (2021) on Mars as part of the ExoMars/ESA rover payload. In order to extrapolate valuable indicators of the mineralogical data that could derive from the ExoMars/Raman Laser Spectrometer (RLS), laboratory results were then compared with the molecular data gathered through the RLS ExoMars Simulator. Beside correctly identifying all major phases (feldspar, pyroxene and olivine), the RLS ExoMars Simulator confirmed the presence of additional minor compounds (i.e. hematite and apatite) that were not detected by complementary techniques. Furthermore, concerning the in-depth study of olivine grains, the RLS ExoMars simulator was able to effectively detect the shifting of the characteristic double peak around 820 and 850 cm-1, from which the FeMg content of the analyzed crystals can be extrapolated. Considering that olivine is one of the main mineral phases of the ExoMars landing site (Oxia Planum), this study suggests that the ExoMars/RLS system has the potential to provide detailed information about the elemental composition of olivine on Mars.

Detection of a double-peaked H α component from the accretion disc of NGC 4958

Abstract Active Galactic Nuclei are objects associated with the presence of an accretion disc around supermassive black holes found in the very central region of galaxies with a well-defined bulge. In the optical range of the spectrum, a possible signature of the accretion disc is the presence of a broad double-peaked component that is mostly seen in H α. In this paper, we report the detection of a double-peaked feature in the H α line in the nucleus of the galaxy NGC 4958. The narrow-line region of this object has an emission that is typical of a low-ionization nuclear emission-line region galaxy, which is the usual classification for double-peaked emitters. A central broad component, related to the broad-line region of this object, is seen in H α and also in H β. We concluded that the double-peaked emission is emitted by a circular relativistic Keplerian disc with an inner radius ξi = 570 ± 83, an outer radius ξo = 860 ± 170 (both in units of GMSMBH/c2), an inclination to the line of sight i = 27.2 ± 0.7° and a local broadening parameter σ = 1310 ± 70 km s−1.

Point-contact Andreev reflection spectroscopy on the misfit phase superconductors (PbSe)1.12(TaSe2) doped with Cl or Br

We report point-contact Andreev reflection spectroscopy studies on possible topological superconductor candidates Cl- (Br-) doped (${\mathrm{PbSe})}_{1.12}({\mathrm{TaSe}}_{2})$ with superconducting transition temperature ${T}_{c}\ensuremath{\sim}$ 1.2 K. A common double-peak feature is observed for the conductance curves at low temperature in the absence of a zero-bias conductance peak. We analyze conductance curves with the Blonder-Tinkham-Klapwijk model and the extracted superconducting gap follows a typical Bardeen-Cooper-Schrieffer temperature- and field-dependent behavior, with $2{\mathrm{\ensuremath{\Delta}}}_{0}/{k}_{B}{T}_{c}\ensuremath{\approx}3.7$ and 3.8 for Cl and Br doping, respectively. Our results strongly suggest that both Cl- and Br-doped $({\mathrm{PbSe})}_{1.12}({\mathrm{TaSe}}_{2})$ are fully gapped superconductors in an intermediate-coupling regime.

Temperature-switched anomaly in the spin Seebeck effect in Gd3Fe5O12

The magnon-polaron induced anomaly has recently been observed in the magnetic field dependence of the spin seebeck effect in ${\mathrm{Y}}_{3}{\mathrm{Fe}}_{5}{\mathrm{O}}_{12}$ [T. Kikkawa et al., Phys. Rev. Lett. 117, 207203 (2016)]. In the present theoretical work, we show that such an anomaly in ${\mathrm{Gd}}_{3}{\mathrm{Fe}}_{5}{\mathrm{O}}_{12}$ depends strongly on the temperature, and it exists only at high temperature but disappears at low temperature. The finite-temperature magnon-polaron anomaly results from the distortion of the magnon dispersion driven by thermal magnon excitation. In contrast to the scenario in ${\mathrm{Y}}_{3}{\mathrm{Fe}}_{5}{\mathrm{O}}_{12}$, the anomaly in ${\mathrm{Gd}}_{3}{\mathrm{Fe}}_{5}{\mathrm{O}}_{12}$ can present either single-peak or double-peak features at different temperatures.

Microwave magnetoimpedance and ferromagnetic resonance in Pr0.6Sr0.4MnO3.

We report the magnetic field dependence of electrical impedance (magnetoimpedance) of a ferromagnetic Pr0.6Sr0.4MnO3 sample carrying alternating current (ac) of frequency f = 1 MHz to 3 GHz measured using an impedance analyzer and broad band ferromagnetic resonance (f = 2 to 18 GHz) measured using a coplanar wave guide based spectrometer. Ac magnetoresistance is much larger than dc magnetoresistance and its sign at low magnetic fields changes from negative to positive with increasing frequency of the ac current. The field dependence of ac magnetoresistance shows a peak around Hdc = 0 for low frequencies but a double peak feature emerges at Hdc = ±Hp at higher frequencies and it shifts to higher magnetic field as the frequency of ac current increases. The field derivative of microwave power absorption measured by the broad band spectrometer shows features of ferromagnetic resonance and the resonance field increases with increasing frequency of microwave radiation following Kittel's equation for ferromagnetic resonance. A close correlation is found between the ferromagnetic resonance line shape and the positive peak in the ac magnetoresistance, which suggests the possibility of electrical detection of ferromagnetic resonance using high frequency current injected into a conducting magnetic sample.

Circular Dichroism in Nanoparticle Helices as a Template for Assessing Quantum-Informed Models in Plasmonics

As characteristic lengths in plasmonics rapidly approach the sub-nm regime, quantum-informed models that can capture those aspects of the quantum nature of the electron gas that are not accessible by the standard approximations of classical electrodynamics, or even go beyond the free-electron description, become increasingly more important. Here we propose a template for comparing and validating the predictions of such models, through the circular dichroism signal of a metallic nanoparticle helix. For illustration purposes, we compare three widely used models, each dominant at different nanoparticle separations and governed by its own physical mechanism, namely the hydrodynamic Drude model, the generalised nonlocal optical response theory, and the quantum-corrected model for tunnelling. Our calculations show that indeed, each case is characterised by a fundamentally distinctive response, always dissimilar to the predictions of the local optical response approximation of classical electrodynamics, dominated by a model-sensitive absorptive double-peak feature. In circular dichroism spectra, the striking differences between models manifest themselves as easily traceable sign changes rather than neighbouring absorption peaks, thus overcoming experimental resolution limitations and enabling efficient evaluation of the relevance, validity, and range of applicability of quantum-informed theories for extreme-nanoscale plasmonics.

Finite-Larmor-radius equilibrium and currents of the Earth’s flank magnetopause

We consider the one-dimensional equilibrium problem of a shear-flow boundary layer within an ‘extended-fluid model’ of a plasma that includes the Hall and the electron pressure terms in Ohm’s law, as well as dynamic equations for anisotropic pressure for each species and first-order finite-Larmor-radius (FLR) corrections to the ion dynamics. We provide a generalized version of the analytic expressions for the equilibrium configuration given in Cerri et al., (Phys. Plasmas, vol. 20 (11), 2013, 112112), highlighting their intrinsic asymmetry due to the relative orientation of the magnetic field $\boldsymbol{B}$, $\boldsymbol{b}=\boldsymbol{B}/|\boldsymbol{B}|$, and the fluid vorticity $\unicode[STIX]{x1D74E}=\unicode[STIX]{x1D735}\times \boldsymbol{u}$ (‘$\unicode[STIX]{x1D74E}\boldsymbol{b}$ asymmetry’). Finally, we show that FLR effects can modify the Chapman–Ferraro current layer at the flank magnetopause in a way that is consistent with the observed structure reported by Haaland et al., (J. Geophys. Res. (Space Phys.), vol. 119, 2014, pp. 9019–9037). In particular, we are able to qualitatively reproduce the following key features: (i) the dusk–dawn asymmetry of the current layer, (ii) a double-peak feature in the current profiles and (iii) adjacent current sheets having thicknesses of several ion Larmor radii and with different current directions.

Quantitative XAFS/EELS analyses of nitrogen species in titanium oxide photocatalysts

With a view to rational designing of a highly functional visible-light TiO2 photocatalyst, nitrogen atoms were doped into TiO2 samples by an ion implantation technique which enables to control the depth and concentration of dopants. Although the absorbance in the visible-light region of the sample increased by the nitrogen doping, photocatalytic activity of the sample was not directly connected with the photo-absorbance. The N K-edge X-ray absorption near edge structure (XANES) spectrum of the photocatalytic active sample (A-cat) showed a characteristic double peak at 398 and 401 eV, and the XANES spectrum of the inactive sample (I-cat) a distinct single peak around 401 eV. These features of the XANES spectra were well reproduced by theoretical simulations based on the model where an O atom in TiO2 was replaced by N ((N)s) for A-cat, and that of quasi NO2 molecule ((NO2)s) for I-cat. Therefore, we have concluded that the nitrogen atom occupying the oxygen site of TiO2 is photocatalytic active species effective for visible light photocatalysis. In addition, the quantitative XANES/ELNES analysis has revealed that the photo-absorbance ratio of I-cat to A-cat corresponds well to the ratio of total doped nitrogen concentration rather than photocatalytic active nitrogen ((N)s) concentration. This result indicates that not only (N)s but also (NO2)s also absorb the visible light. Thus, the absorbance in the visible-light region is not necessarily an indication of the visible-light response of a photocatalyst.

Theoretical calculations of photoelectron spectrum of (Au–CO2)− anion

Photoelectron spectra of the (Au–CO2)− anion complex have been calculated using both quantum path-integral and classical molecular dynamics methods to interpret the experimentally measured spectrum, showing a double-peak feature corresponding to two different anion configurations of Au·CO2− and Au−·CO2. The anionic potential energy surfaces have been developed on the basis of density-functional theory calculation results obtained with several different levels. We found that the calculated photoelectron spectra significantly depend on the relative energies of these two isomers and the isomerization barrier heights. Nuclear quantum effects are playing important roles for obtaining reliable spectra through vibrational quantization. The present calculations also suggest that the photoelectron spectrum intensity around the overlap region of the two anion peaks can provide a fingerprint of the Au·CO2− ↔ Au−·CO2 reaction.

Transferability of a coarse-grained atactic polystyrene model: Thermodynamics and structure

In this paper, we construct a one-bead per monomer coarse grained (CG) model for atactic polystyrene (PS) via a combined structure-based and thermodynamic quantity-based CG method at 1 atm and 463 K by using the hard LJ 12–6 potential as the non-bonded interaction potential and applying iterative Boltzmann inversion method to derive the bonded potentials. Although the CG force field is built at one single thermodynamic state point without any temperature correction or pressure optimization terms, the CG model possesses a rather favorable transferability in a wide temperature of 100–600 K. More importantly, the CG model gives the glass transition temperature of 382 K, which is very close to the atomistic result of 360 K and the experimental value of 363 K. Additionally, the unique double-peak feature and the unusual temperature dependence of the polymerization peak in the experimental scattering spectrum of atactic PS are well captured by the systematic CG model.

Dynamical correlation effects in a weakly correlated material: Inelastic x-ray scattering and photoemission spectra of beryllium

Beryllium is a weakly correlated simple metal. Still we find that dynamical correlation effects, beyond the independent-particle picture, are necessary to successfully interpret the electronic spectra measured by inelastic x-ray scattering (IXS) and photoemission spectroscopies (PES). By combining ab initio time-dependent density-functional theory (TDDFT) and many-body Green's function theory in the $GW$ approximation ($GW\mathrm{A}$), we calculate the dynamic structure factor, the quasiparticle (QP) properties and PES spectra of bulk Be. We show that band-structure effects (i.e., due to interaction with the crystal potential) and QP lifetimes (LT) are both needed in order to explain the origin of the measured double-peak features in the IXS spectra. A quantitative agreement with experiment is obtained only when LT are supplemented to the adiabatic local-density approximation (ALDA) of TDDFT. Besides the valence band, PES spectra display a satellite, a signature of dynamical correlation due to the coupling of QPs and plasmons, which we are able to reproduce thanks to the combination of the $GW\mathrm{A}$ for the self-energy with the cumulant expansion of the Green's function.

Peaked dielectric responses in Ti3C2 MXene nanosheets enabled composites with efficient microwave absorption

The microwave dielectric behavior of sandwich-like Ti3C2 MXene nanosheets with efficient microwave absorption was investigated by a combination of experiments and simulations. The obvious frequency dispersion effect and the double-peaked feature of dielectric spectra in Ti3C2 MXene nanosheets could be observed over the frequency range of 2–18 GHz, giving rise to superior microwave attenuation capability. Furthermore, a revised Drude-Lorentz model was proposed to explain the peaked feature of permittivity, and simulated results were demonstrated to agree well with the experimental measurements. It was concluded that the hopping migration between Ti3C2 MXene nanosheets with longer relaxation time than “micro-dipole” relaxation within nanosheets makes a superior contribution to overall absorbing performance.

Two-stage Energy Release Process of a Confined Flare with Double HXR Peaks

Abstract A complete understanding of the onset and subsequent evolution of confined flares has not been achieved. Earlier studies mainly analyzed disk events so as to reveal their magnetic topology and the cause of confinement. In this study, taking advantage of a tandem of instruments working at different wavelengths of X-rays, EUVs, and microwaves, we present dynamic details about a confined flare observed on the northwestern limb of the solar disk on 2016 July 24. The entire dynamic evolutionary process starting from its onset is consistent with a loop–loop interaction scenario. The X-ray profiles manifest an intriguing double-peak feature. From the spectral fitting, it has been found that the first peak is nonthermally dominated, while the second peak is mostly multithermal with a hot (∼10 MK) and a super-hot (∼30 MK) component. This double-peak feature is unique in that the two peaks are clearly separated by 4 minutes, and the second peak reaches up to 25–50 keV; in addition, at energy bands above 3 keV, the X-ray fluxes decline significantly between the two peaks. This, together with other available imaging and spectral data, manifest a two-stage energy release process. A comprehensive analysis is carried out to investigate the nature of this two-stage process. We conclude that the second stage with the hot and super-hot sources mainly involves direct heating through a loop–loop reconnection at a relatively high altitude in the corona. The uniqueness of the event characteristics and the complete dataset make the study a nice addition to present literature on solar flares.

Tuning mechanical response in granular layers by adding rigid particle channel

The inhomogeneity of spatial packing by particles with different physical properties can significantly affect mechanical properties of granular packings. In this paper, a new approach by adding rigid particle channel is put forward to tune the mechanical response of granular layers induced by external loading. Based on the single-layer channel model, a phase diagram is firstly proposed to describe the crossover of mechanical response between a single-peaked and double-peaked feature, in which the tunable range of external loading and effective region of channel position are two key factors that reflect the tuning effect of this approach. Its tuning mechanism is further explored based on the variations of propagating feature of contact forces, and a linear function is proposed to predict the optimal position of the channel in systems with different sizes. Furthermore, the dependence of tuning effect on the spatial configuration and the number of rigid particle layers is also discussed in a double-layer and multi-layer rigid particle channel models, which can obviously improve the tunable effect but also undergo different tuning processes. By adding different rigid particle channels to actively change propagation paths of contact forces and weaken the anisotropy in vertical stress field within granular system, it has been verified that this approach is feasible to enhance the elasticity of whole system and tune its mechanical response.

Experimental study on pore structure and performance of sintered porous wick

Porous wicks were prepared via powder metallurgy using NH4HCO3 powders as pore-forming agent. The pore-forming agent particle size was varied to control the pore structure and equivalent pore size distribution feature of porous wick. The effect of pore-forming agent particle size on the porosity, pore structures, equivalent pore size distribution and capillary pumping performance were investigated. Results show that with the particle size of pore-forming agent decrease, the green density and the volume shrinkage of the porous wicks gradually increase and the porosity reduces slightly. There are two types of pores inside the porous wick, large-sized prefabricated pores and small-sized gap pores. With the particle size of pore-forming agent decrease, the size of the prefabricated pores becomes smaller and the distribution tends to be uniform. Gap pores and prefabricated pores inside the wick can make up different types of pore channels. The equivalent pore size of wick is closely related to the structure of pore channels. Furthermore, the equivalent pore size distribution of wick shows an obvious double-peak feature when the pore-forming agent particle size is large. With the particle size of pore-forming agent decrease, the two peaks of equivalent pore size distribution approach gradually to each other, resulting in a single-peak feature. Porous wick with single-peak feature equivalent pore size distribution possesses the better capillary pumping performances.

Double magnetocaloric peak feature observed in quaternary Ni-Mn-In based Heusler alloys

We present the results of the studies of magnetic and magnetocaloric (MCE) properties of quaternary Heusler alloys Ni48.5Mn35In15Co1.5 and Ni50Mn35In13.5Al1.5 in temperature range between 80 K and 400 K. While doping initial ternary Ni-Mn-In alloy with 1.5 at.% Al does not change TCA as well as MS, doping with 1.5 at.% Co significantly increases both TCA and MS. The direct magnetocaloric measurements around martensitic transition and austenite Curie temperature reveal the competition between the contributions of different signs. The latter is related to the vicinity of transition temperatures of austenite and martensite, resulting in mixed state, where both phases undergo magnetic order-disorder transformation in the same temperature region. Additionally temperature dependencies of adiabatic temperature change ΔTad and magnetic entropy ΔSM of the system exhibit additional peak feature which we attribute to intermartensitic transition occurring in these alloys.

The profile of the bending mode band in solid CO2

Context. Solid carbon dioxide (CO2 ) is one of the most abundant species detected in icy grain mantles in dense molecular clouds. Its identification is based on the comparison between astronomical and laboratory spectra. In the past 30 yr the profile of solid CO2 infrared absorption bands has been extensively studied experimentally, however, the debate on the structure (amorphous versus crystalline) of CO2 samples obtained in laboratory by the thin-film technique is still open.Aims. The aim of this work is to investigate if the presence of the double peak feature in the profile of the CO2 bending mode band is related to the crystalline or amorphous structure of the sample.Methods. We performed new laboratory experiments depositing CO2 under ultra high vacuum (UHV) conditions at 17 K. We investigated, using infrared transmission spectroscopy, the influence of various experimental parameters on the profile of the CO2 bands, namely deposition rate, sample thickness, annealing, and presence of H2 O, CH3 OH or CO co-deposited with CO2 . Results. We found that, within experimental uncertainties, under UHV conditions the profile of the CO2 bands in pure solid samples does not depend on the deposition rate or the sample thickness in the ranges investigated. In all cases the bending mode band profile shows a double peak (at 660 and 655 cm-1 ). The spectra also show the Fermi resonance features that cannot be active in crystalline samples. On the other hand, when a small fraction of H2 O or CH3 OH is co-deposited with CO2 the double peak is not observed while it is observed when a CO2 :CO mixture is considered. Furthermore, we measured the density of solid CO2 and the refractive index (at 543.5 nm) at 17 K and at 70 K: ρ (17 K)= 1.17 g cm-3 , ρ (70K)= 1.49 g cm-3 , n (17K)= 1.285, and n (70K)= 1.372. Conclusions. Our experimental results indicate that the presence of the double peak in the profile of the bending mode band is not an indication of a crystalline structure of the sample and they do not exclude the presence of amorphous solid CO2 in space.

Effects of Different Additives on the Ignition and Combustion Characteristics of Micrometer-Sized Aluminum Powder in Steam

To improve the ignition and combustion characteristics of micrometer-sized aluminum powder in steam at 900 °C, the present study focuses on the effects of adding different contents of Mg, NaF, and NaBH4. Experiments were conducted in two high-temperature tubular resistance furnaces to measure ignition temperatures, maximum combustion temperatures, and ignition delay times and to understand the combustion features of all samples. The experimental results show that Mg addition results in a reduced ignition temperature and ignition delay time of the micrometer-sized aluminum powder and causes two burning stages (a double-peak feature) because the Mg powder preferentially ignites before the micrometer-sized aluminum powder. The maximum combustion temperature increases with increasing Mg content. The ignition temperature and the ignition delay time are also significantly decreased with increased NaF or NaBH4 addition. However, the addition of NaF or NaBH4 lowers the maximum combustion temperature. The morpholo...