Pair Of Bands Research Articles

Enhancing UAV images to improve the observation of submerged whales using a water column correction method

Enhancing <scp>UAV</scp> images to improve the observation of submerged whales using a water column correction method

Seizure onset zone identification using phase-amplitude coupling and multiple machine learning approaches for interictal electrocorticogram

Automatic seizure onset zone (SOZ) localization using interictal electrocorticogram (ECoG) improves the diagnosis and treatment of patients with medically refractory epilepsy. This study aimed to investigate the characteristics of phase-amplitude coupling (PAC) extracted from interictal ECoG and the feasibility of PAC serving as a promising biomarker for SOZ identification. We employed the mean vector length modulation index approach on the 20-s ECoG window to calculate PAC features between low-frequency rhythms (0.5–24 Hz) and high frequency oscillations (HFOs) (80–560 Hz). We used statistical measures to test the significant difference in PAC between the SOZ and non-seizure onset zone (NSOZ). To overcome the drawback of handcraft feature engineering, we established novel machine learning models to learn automatically the characteristics of the obtained PAC features and classify them to identify the SOZ. Besides, to handle imbalanced dataset classification, we introduced novel feature-wise/class-wise re-weighting strategies in conjunction with classifiers. In addition, we proposed a time-series nest cross-validation to provide more accurate and unbiased evaluations for this model. Seven patients with focal cortical dysplasia were included in this study. The experiment results not only showed that a significant coupling at band pairs of slow waves and HFOs exists in the SOZ when compared with the NSOZ, but also indicated the effectiveness of the PAC features and the proposed models in achieving better classification performance .

Comparative performance of theoretical tools in order to quantify the effect of the electric potential on the vibrational wavenumbers and intensities of the SERS of 2‐methylpyrazine adsorbed on a nanostructured silver electrode

AbstractThe effect of the electrode potential in surface‐enhanced Raman scattering (SERS) intensities and wavenumbers of 2‐methylpyrazine (2MP) was analyzed on the basis of a resonant charge transfer (CT) mechanism by using a simple theoretical model in which the metallic surface and its charge density were simulated by atomic silver clusters of different size (n) and charge (q), [Agn]q. Two linear silver atoms (n = 2) with zero charge (q = 0) and three linear silver atoms (n = 3) with positive and negative charges (q = ±1) linked to the two nonequivalent aromatic nitrogen atoms in 2MP were taken into account. The wavenumber shifts of the most intense bands and the SERS‐CT spectra of these two types of metal‐adsorbate supermolecule, [Agn‐N1]q and [Agn‐N4]q, were calculated by using a time‐dependent density functional theory (TD‐DFT) method and the independent mode displaced harmonic oscillator (IMDHO) approximation. A comparison of the effect of different levels of calculation, ab initio/DFT, on the predictions from the two theoretical models (isolated adsorbate/supermolecule) is also performed. Only DFT theoretical results of the metal‐adsorbate supermolecule allow to explain the main role of the pair of bands assigned to totally symmetric ring‐stretching 8a,b modes. The 8a vibration is the strongest band at any electrode potential, whereas the 8b mode reaches a maximum enhancement at −0.50 V and then decreases at −0.75 V. This model of a charged metal‐adsorbate interface allows for detecting the presence of a CT mechanism in a SERS record.

PY-Nodes: An ab-initio python code for searching nodes in a material using Nelder-Mead's simplex approach

With the discovery of topological semimetals, it has been found that the band touching points near the Fermi level are of great importance. They give rise to many exciting phenomena in these materials. Moreover, these points, commonly known as nodes, are related to several properties of these semimetals. Thus, the proper estimation of their coordinates is extremely needed for better understanding of the properties of these materials. We have designed a Python 3 based code named PY-Nodes for efficiently finding the nodes present in a given material using first-principle approach. The present version of the code is interfaced with the WIEN2k package. For benchmarking the code, it has been tested on some famous materials that possess characteristic nodes. These include – TaAs, a well-known Weyl semimetal, Na3Bi, which is categorized as Dirac semimetal, CaAgAs, classified as a nodal-line semimetal and YAuPb, which is claimed to be non-trivial topological semimetal. In the case of TaAs, 24 nodes are obtained from our calculations. On computing their chiralities, it is found that 12 pairs of nodes having equal and opposite chirality are obtained. Furthermore, for Na3Bi, a pair of nodes are obtained on either side of the Γ-point in the k3 direction. In the case of CaAgAs, several nodes are obtained in the kz=0 plane. These nodes, when plotted in the kx-ky plane, form a closed loop which is generally referred to as a nodal-line. Finally, in the case of YAuPb, large number of nodes are obtained in the vicinity of Γ-point. The results obtained for these materials are in good match with the previous works carried out by different research groups. This assures the reliability and efficiency of the PY-Nodes code for estimating the nodes present in a given material. Program summaryProgram Title: PY-NodesCPC Library link to program files:https://doi.org/10.17632/m97syc9rth.1Licensing provisions: GNU General Public License 3.0Programming language: Python 3External routines/libraries: Math, TimeNature of problem: Searching for the node points corresponding to any given number of bands present in the first Brillouin zone of any material.Solution method: Nelder-Mead's simplex approach is a well-known function-minimization method. This approach is used to minimize the function f(k), which is defined as sum of the absolute energy difference of the adjacent pairs of bands at a given k-point. The local minima will correspond to the node points present in the material.

Three-dimensional reconstruction of flame temperature and H2O concentration using water vapor integrated spectral band emission

Efficient and accurate reconstruction of flame temperature and species concentration is very useful for combustion monitoring. In this work, the integrated spectral band ratio (ISBR) method, which uses the ratio of two integrated spectral radiative intensities to infer temperature, is applied to reconstruct three-dimensional flame temperature and H2O concentration distributions. First, the ratio of two integrated spectral radiative intensities is justified by gas radiation theory to only depend on gas temperature, and the influence of gas concentration and pressure on the ratio is negligible. Then, a spectral band pair is carefully selected for the measurement with an atmospheric path between the detector and the flame. In the selected spectral bands, CO2 and CO emissions are negligible compared to H2O emission, and atmospheric absorption can be ignored. Meanwhile, gas temperature is monotonically related to the ratio of integrated spectral radiative intensities. When the uncertainty of the ratio is 2%, the error of reconstructed temperature is less than 38K with gas temperature close to 3000K, and the error decreases as the gas temperature goes down. Finally, numerical experiments on reconstruction of axisymmetric and non-axisymmetric flames are carried out. Results show that three-dimensional distributions of flame temperature and H2O concentration can be reconstructed with high accuracy.

Tunable interband and intraband plasmons in twisted double bilayer graphene

Flat bands in twisted moir\'e superlattices support a variety of topological and strongly correlated phenomena along with easily tunable electrical and optical properties. Here, we demonstrate the existence of long lived, flat intraband and interband plasmons in twisted double bilayer graphene. We show that the interband plasmons originate from the presence of a Van Hove singularity in the joint density of states and a finite Berry connection between the pair of bands involved. We find that the gapped interband plasmon mode has a universal dispersion, and the plasmon gap is specified by the location of the Van Hove singularity in the joint density of states. Metallic moir\'e systems support an additional intraband plasmon mode which becomes flat in the large momentum limit because of the influence of higher interband transitions. We demonstrate that the undamped and flat plasmon modes in moir\'e systems are highly tunable and can be controlled by varying the vertical electric field and electron doping, and they persist over a wide range of twist angles.

Direct visualization of Rashba-split bands and spin/orbital-charge interconversion at KTaO3 interfaces

Rashba interfaces have emerged as promising platforms for spin-charge interconversion through the direct and inverse Edelstein effects. Notably, oxide-based two-dimensional electron gases display a large and gate-tunable conversion efficiency, as determined by transport measurements. However, a direct visualization of the Rashba-split bands in oxide two-dimensional electron gases is lacking, which hampers an advanced understanding of their rich spin-orbit physics. Here, we investigate KTaO3 two-dimensional electron gases and evidence their Rashba-split bands using angle resolved photoemission spectroscopy. Fitting the bands with a tight-binding Hamiltonian, we extract the effective Rashba coefficient and bring insight into the complex multiorbital nature of the band structure. Our calculations reveal unconventional spin and orbital textures, showing compensation effects from quasi-degenerate band pairs which strongly depend on in-plane anisotropy. We compute the band-resolved spin and orbital Edelstein effects, and predict interconversion efficiencies exceeding those of other oxide two-dimensional electron gases. Finally, we suggest design rules for Rashba systems to optimize spin-charge interconversion performance.

X-ray absorption using the projector augmented-wave method and the Bethe-Salpeter equation

We present an implementation of the Bethe-Salpeter equation (BSE) for core-conduction band pairs within the framework of the projector augmented-wave method. For validation, the method is applied to the $K$ edges of diamond, graphite and hexagonal boron-nitride, as well as four lithium-halides (LiF, LiCl, LiI, LiBr). We compare our results with experiment, previous theoretical BSE results, and the density functional theory-based supercell core-hole method. In all considered cases, the agreement with experiment is excellent, in particular, for the relative position of the peaks as well as the fine structure. Comparing BSE to supercell core-hole spectra, we find that the latter often qualitatively reproduces the experimental spectrum, however, it sometimes lacks important details. This is shown for the $K$ edges of diamond and nitrogen in hexagonal boron nitride, where we can resolve within the BSE experimental features that are lacking in the supercell core-hole method. Additionally, we show that in certain systems the supercell core-hole method performs better if the excited electron is added to the background charge rather than to the lowest conduction band. We attribute this improved performance to a reduced self-interaction.

Whitespotted eagle ray (Aetobatus narinari) age and growth in wild (in situ) versus aquarium-housed (ex situ) individuals: Implications for conservation and management

Elasmobranchs typically display slow growth, late maturity and low fecundity life history characteristics, making them vulnerable to fishing pressures and environmental perturbations. The whitespotted eagle ray (Aetobatus narinari), a large pelagic migratory ray with an endangered status on the IUCN Red List, fits this pattern based on available literature. Historically, age and growth parameters for this ray have been reported through vertebral ageing methods. However, the periodicity of vertebrate band pair formation, which is used for ageing, has not been validated for this species, making ageing accuracy and thus the resulting growth parameters uncertain. In this study, we used both a frequentist and Bayesian method of estimating sex-specific von Bertalanffy growth parameters (DW∞, k) in wild recaptured versus aquarium-housed rays. Additionally, we estimated growth from repeated measurement data collected from aquarium-housed rays, as an alternative approach to obtain growth parameters while allowing for individual variability. Between 2009 and 2020, 589 whitespotted eagle rays were caught, measured, tagged and released along the southwest coast of Florida. Of these rays, 34 were recaptured between 5–1413 days at liberty. Nineteen additional rays were collected during the same period, transported and maintained at Georgia Aquarium, Atlanta, where they were regularly weighted and measured. Data from Association of Zoos and Aquariums accredited facilities provided prior information on maximum size for the Bayesian estimations, and size at birth, size at maturity, and maximum life span. These data were used to plot and interpret von Bertalanffy growth curves. Wild whitespotted eagle rays were found to grow faster and mature earlier than previously thought, with Bayesian estimates of k = 0.28 year-1 in females, and k = 0.30 year-1 in males. Aquarium-housed individuals seemed to grow slower and reach smaller sizes, although data provided by the aquariums showed variable growth patterns depending on the facility. Longevity was estimated at 14-15 years in wild rays while maximum lifespan observed in aquariums was 19-20+ years. Life history parameters and growth trajectories generated from this study offer valuable information to aid with future conservation management strategies of this endangered species.

Isothermal crystallization of polyhydroxyalkanoate (PHA) utilizing Raman spectroscopy to follow chain packing as well as molecular motion

Raman spectra of bioplastic poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHx at 13.8 % Hx) were recorded between −250 cm−1 and 3200 cm−1 during isothermal crystallization at 25⁰C after quenching from the melt in liquid nitrogen. At room temperature the crystallization proceeds slowly, so spectra were recorded over a 14-hour period. While there are spectral changes throughout the spectrum, the focus was on interpretable bands known to be sensitive to crystalline form. These bands included the carbonyl band that sharpens and shifts, a pair of bands on the high energy side of the carbon-hydrogen stretch, and a low frequency band that we assign to the molecular phonon in the crystal unit cell. After appropriate pre-processing of the spectra, they were further analyzed by 2D-COS (two-dimensional correlation spectroscopy) that provides determination of the order in which the polymer functional regions assemble into the crystalline state. According to this analysis one of the methyl CH’s interacts with the carbonyl bond to produce a line at 3000 cm−1. Following that, multiple changes appear in the carbonyl region, the strong CH band at 2930 cm−1 of the crystalline phase grows, then the 80 cm−1 phonon band, and the splitting of the methyl CH only appears after the phonon. From this sequence one can derive a picture of how the polymer unit locks into the crystal form. This can be of interest to commercialization of the materials because mechanical properties are intimately controlled by the crystallinity of the material. By understanding how the crystallization process proceeds, it can be engineered to be “fit for purpose” for a polymer targeted for a specific use.

Experimental and Theoretical Characterization of Rh Single Atoms Supported on γ-Al2O3 with Varying Hydroxyl Contents during NO Reduction by CO

Oxide-supported Rh catalysts are important components of commercial three-way catalysts for pollution abatement. Despite their universal application, many mysteries remain about the active structure of Rh on oxide supports as these materials often contain a mixture of nanoparticles and single-atom Rh species on the same support, even after aging. Probe molecule Fourier transform infrared (FTIR) spectroscopy in this work shows that atomically dispersed Rh on γ-Al2O3 prefer to strongly bind CO when exposed to NO and CO mixtures and that light-off of NO reduction occurs at temperatures similar to CO desorption, suggesting that the first and rate-determining step in NO–CO reactions may be the desorption of CO from single-atom Rh dicarbonyl complexes, Rh(CO)2. Two sets of symmetric and asymmetric stretching frequencies associated with distinct Rh(CO)2 species are observed in FTIR spectra at 2084/2010 and 2094/2020 cm–1. During temperature ramps, the latter pair of bands at 2094/2020 cm–1 converts to the 2084/2010 cm–1 bands at 463 K before all symmetric and asymmetric bands disappear at 573 K. Bands then appear in the range of 1975–1985 cm–1 associated with Rh monocarbonyl, Rh(CO), species upon the disappearance of the 2084/2010 cm–1 bands, suggesting that CO desorbs sequentially from Rh(CO)2 by forming Rh(CO) intermediates. Combined DFT and FTIR experiments suggest that local OH coverage on the γ-Al2O3 surface distinguishes the two Rh(CO)2 species: the higher frequency species resides on a less hydroxylated region and migrates to a more hydroxylated region at higher temperatures, causing the CO vibrational frequency to decrease by ∼10 cm–1. CO desorption occurs from this Rh(CO)2 structure with high local OH coverage, consistent with the DFT predicted trend of CO binding energies. Because of the coincidence of CO desorption with the light-off of NO reduction, local support hydroxylation of atomically dispersed Rh1/γ-Al2O3 catalysts likely affects both the Rh structure after CO desorption and the kinetics of NO reduction, studies of which are enabled by the Rh(CO)2 model developed here.

Effects of pairing gap and band gap on superfluid density in the inner crust of neutron stars

Calculations of the superfluid density in the inner crust of neutron stars using different approaches are in strong disagreement, which causes a debate on the accountability of pulsar glitches based on superfluidity. Using a simple unified model, we study the dependence on approximation of the superfluid density in a periodic potential. In comparison with the Hartree-Fock-Bogoliubov theory, which treats the effects of the band gap and the pairing gap on equal footing, we examine a Hartree-Fock-BCS-type (HF-BCS-type) approximation in which the former is preferentially incorporated and another approximation in which the latter is preferentially incorporated. We find that, when the pairing gap and the band gap are comparable as in the inner crust of neutron stars, they need to be treated on equal footing, and the HF-BCS approximation can considerably underestimate the superfluid density even if the pairing gap is much smaller than the Fermi energy. Our result suggests that the validity of the HF-BCS approximation for evaluating the superfluid density in neutron star crusts is questionable.

The evolution from BCS to Bose pairing in two-band superfluids: Quantum phase transitions and crossovers by tuning band offset and interactions

We show that in two-band s-wave superfluids it is possible to induce quantum phase transitions (QPTs) by tuning intraband and interband s-wave interactions, in sharp contrast to single-band s-wave superfluids, where only a crossover between Bardeen-Cooper-Schrieffer (BCS) and Bose-Einstein condensation (BEC) superfluidity occurs. For non-zero interband and attractive intraband interactions, we demonstrate that the ground state has always two interpenetrating superfluids possessing three spectroscopically distinct regions where pairing is qualitatively different: I) BCS pairing in both bands (BCS-BCS), II) BCS pairing in one band and BEC pairing in the other (BCS-BEC), and III) Bose pairing in both bands (BEC-BEC). Furthermore, we show that by fine tuning the interband interactions to zero one can induce QPTs in the ground state between three distinct superfluid phases. There are two phases where only one band is superfluid (S 1 or S 2), and one phase where both bands are superfluid , a situation which is absent in one-band s-wave systems. Lastly, we suggest that these crossovers and QPTs may be observed in multi-component systems such as 6Li, 40K, 87Sr, and 173Yb.

Floquet Engineering Topological Dirac Bands.

We experimentally realized a time-periodically modulated 1D lattice for ultracold atoms featuring a pair of linear bands, each with a Floquet winding number. These bands are spin-momentum locked and almost perfectly linear everywhere in the Brillouin zone: a near-ideal realization of the 1D Dirac Hamiltonian. We characterized the Floquet winding number using a form of quantum state tomography, covering the Brillouin zone and following the micromotion through one Floquet period. Last, we altered the modulation timing to lift the topological protection, opening a gap at the Dirac point that grew in proportion to the deviation from the topological configuration.

Two pairs of topological Shockley surface bands in the ternary compound SnSb2Te4

The electronic states in ternary compound ${\mathrm{SnSb}}_{2}{\mathrm{Te}}_{4}$ wwere studied by first-principles and tight-binding calculations, and two pairs of topological Shockley surface bands below its Fermi energy were revealed theoretically. One shows the Rashba-type structure and the other shows a more complicated $\ensuremath{\omega}$-shaped bending structure. Combined with spin- and angle-resolved photoemission spectroscopy measurements, the existence of the predicted topological surface states was confirmed. Our theoretical and experimental investigations reveal the complex topological structures in ternary topological insulators, providing a new platform for studying novel topological properties in materials.

Dirac-cone-like electronic states on nematic antiferromagnetic FeSe and FeTe

We investigate the Dirac-cone-like (DCL) topological electronic properties of nematic-like antiferromagnetic (AFM) states of monolayer FeSe and FeTe designed artificially through first-principles calculations and Wannier-function-based tight-binding (WFTB) method. Our calculations reveal most of them have a pair of DCL bands on the Γ–X line in the Brillouin zone (BZ) near the Fermi level and open a gap of about 20 meV in the absence and presence of spin–orbit coupling (SOC), respectively, similar to the lowest-energy pair-checkerboard AFM FeSe. We further confirm that they are weak topological insulators based on nonzero Z 2 and fragile surface states, which are calculated by the WFTB method. For FeSe and FeTe in pair-checkerboard AFM states, we find that the in-plane compression strain in a certain range can give rise to another pair of DCL bands located on the Γ–X′ line in the BZ. In addition, the magnetic moments, energies, and Fe–Se/Te distances for various nematic-like AFM configurations are presented. These calculations the combining effect of magnetism and topology in a single material and the understanding of the superconducting phenomena in iron-based FeSe and FeTe.

Magic angles and flat Chern bands in alternating-twist multilayer graphene system

Based on the effective continuum model, we study alternating-twist multilayer graphene system and emergence of magic angles and flat band topology. All the alternating-twist multilayer graphene system (from triple layers to few layers) are found to have flat bands at magic angles where the area of AA stacking equals n-fold (n is an integer) electron cyclotron area. From the pseudo-Landau-level representation, there is always an isolated Dirac band in the alternating-twist graphene system constructed by odd number of layers. Since each pair of flat bands can be perceived as the zeroth pseudo-Landau-levels in two dimensional Dirac fermions, electron in the flat band pair can feel a pseudo-magnetic field with the same magnitude but the opposite sign. Calculated Chern number for each flat band is +1 (or -1) which can be tuned by twisting in the vicinity of magic angles or by gating. The concurrent appearance of strong correlation and band topology of flat bands in the alternating-twist multilayer graphene may pave an avenue for the new understanding of superconductivity observed in triple-layered graphene, and supply a new playground for realizing (quantum) anomalous Hall effect.

MULTI-CAMERA GEOMETRIC CALIBRATION: PRE-CALIBRATION AND ON-THE-JOB CALIBRATION OF THE MAIA MULTISPECTRAL SYSTEM

Abstract. Though with a less dramatic growth compared to photogrammetry, remote sensing from multispectral imagery taken by UAV (Unmanned Aerial Vehicles) platforms is applied to vegetation health monitoring, crop management, water quality assessments, geological inspections and much more, with a sizeable number of multispectral cameras now available on the market. As for satellite images, a key point in remote sensing is calibration, both geometric and radiometric, and the modelling of disturbances, to get well co-registered reflectance data. Leaving aside radiometric calibration, this paper focuses on how to best georeference the different bands one with respect to the other. This is normally achieved by the so-called band-to-band registration (BBR). Here, a straightforward approach is proposed, that exploits the multi-camera geometry and, unlike BBR, all the information contents of the bands, as inter-band matches are searched (and possibly found) for every pair of bands and not only between a reference and a slave band. Tests on images taken with the 9-band MAIA S2 camera are presented, discussing the pro and cons of pre-calibration and on-the-job calibration of the camera parameters of each sensor. The results found show that the proposed method is at least as good as the BBR ones.

104 Acute mononeuritis multiplex in a patient with plasma cell leukaemia

A 74 year old male with a history of plasma cell leukaemia, treated with VMP (bortezomib, melphalan, prednisolone) presented with a 2 week history of lumbar back pain and weakness of the hands and ankles.Clinical examination confirmed asymmetric weakness in the hands and ankles. Sensory examination was initially normal, reflexes preserved and plantars mute. Other than the known IgG paraproteinaemia and longstanding hyponatraemia, bloods, including a vasculitis screen, were unremarkable. MRI brain and spine were non-contributary. CSF examination revealed paired bands consistent with the presence of an IgG paraprotein, but was otherwise bland. Nerve conduction studies showed a severe sensorimotor axonal neuropathy.The patient was treated with plasma exchange followed by IV methylprednisolone but continued to progress developing more proximal weakness and sensory loss to the knees and elbows, with loss of deep tendon reflexes within 2 weeks. Sural nerve biopsy showed axonal degeneration but no vasculitis or malignant infiltration. The patient became increasingly fatigued and cachectic and the decision was made jointly with the haematologists to palliate.Plasma cell leukaemia is a rare and aggressive subtype of multiple myeloma with a poor prognosis which has been associated with malignant nerve infiltration. Bortezomib may also cause a peripheral neuropathy.o.poole@nhs.net

Moiré band structures of the double twisted few-layer graphene

Very recently, unconventional superconductivity has been observed in the double twisted trilayer graphene (TLG), where three monolayer graphene (MLG) are stacked on top of each other with two twist angles [J. M. Park, et al., Nature 590, 249 (2021); Z. Hao, et al., Science 371, 1133 (2021); X. Zhang, et al., Phys. Rev. Lett.127, 166802 (2021)]. When some of MLGs in the double twisted TLG are replaced by bilayer graphene (BLG), we get a new family of double twisted moire heterostructure, namely double twisted few layer graphene (DTFLG). In this work, we theoretically investigate the moire band structures of the DTFLGs with diverse arrangements of MLG and BLG. We find that, depending on the relative rotation direction of the two twist angles (alternate or chiral twist) and the middle van der Waals (vdW) layer (MLG or BLG), a general (X+Y+Z)-DTFLG can be classified into four categories, i.e. (X+1+Z)-ATFLG, (X+2+Z)-ATFLG, (X+1+Z)-CTFLG and (X+2+Z)-CTFLG, each of which has its own unique band structure. Here, X, Y, Z denote the three vdW layers, i.e. MLG or BLG. Interestingly, the (X+1+Z)-ATFLGs have a pair of perfect flat bands at the magic angle about $1.54^\circ$ coexisting with a pair of linear or parabolic bands, which is quite like the double twisted TLG. Meanwhile, when the twist angle is smaller than a "magic angle" $1.70^\circ$, the (X+2+Z)-CTFLGs can have two isolated narrow bands at $E_f$ with band width less than 5 meV. The influence of electric field and the topological features of the moire bands have been studied as well. Our work indicates that the DTFLGs, especially the (X+1+Z)-ATFLG and (X+2+Z)-CTFLG, are promising platforms to study the moire flat band induced novel correlation and topological effects.