Pair Of Bands Research Articles

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.

Alternating twisted multilayer graphene: generic partition rules, double flat bands, and orbital magnetoelectric effect

Recently the alternating twisted trilayer graphene is discovered to exhibit unconventional superconductivity, which motivates us to study the electronic structures and possible correlation effects for this class of alternating twisted multilayer graphene (ATMG) systems. In this work we consider generic ATMG systems with M-L-N stacking configurations, in which the M (L) graphene layers and the L (N) layers are twisted by an angle θ (−θ). Based on analysis from a simplified k⋅p model approach, we derive generic partition rules for the low-energy electronic structures, which exhibit various band dispersions including two pairs of flat bands and flat bands co-existing with various gapless Fermionic excitations. For a mirror-symmetric ATMG system with doubled flat bands, we further find that Coulomb interactions may drive the system into a state with intertwined electric polarization and orbital magnetization orders, which can exhibit an interaction-driven orbital magnetoelectric effect.

Family of Ideal Chern Flatbands with Arbitrary Chern Number in Chiral Twisted Graphene Multilayers.

We consider a family of twisted graphene multilayers consisting of n-untwisted chirally stacked layers, e.g., AB, ABC, etc, with a single twist on top of m-untwisted chirally stacked layers. Upon neglecting both trigonal warping terms for the untwisted layers and the same sublattice hopping between all layers, the resulting models generalize several remarkable features of the chiral model of twisted bilayer graphene (CTBG). In particular, they exhibit a set of magic angles which are identical to those of CTBG at which a pair of bands (i) are perfectly flat, (ii)have Chern numbers in the sublattice basis given by ±(n,-m) or ±(n+m-1,-1) depending on the stacking chirality, and (iii)satisfy the trace condition, saturating an inequality between the quantum metric and the Berry curvature, and thus realizing ideal quantum geometry. These are the first higher Chern bands that satisfy (iii)beyond fine-tuned models or combinations of Landau levels. We show that ideal quantum geometry is directly related to the construction of fractional quantum Hall model wave functions. We provide explicit analytic expressions for the flatband wave functions at the magic angle in terms of the CTBG wave functions. We also show that the Berry curvature distribution in these models can be continuously tuned while maintaining perfect quantum geometry. Similar to the study of fractional Chern insulators in ideal C=1 bands, these models pave the way for investigating exotic topological phases in higher Chern bands for which no Landau level analog is available.

Tunable nonreciprocal transmission based on non-Hermitian optical system with magnetic optical materials in a one-dimensional multilayer structure

In this study, a one-dimensional composite structure composed of a PT-symmetric system and magnetic optical (MO) materials is designed. The nonreciprocal propagation of a one-dimensional multilayer structure is investigated both theoretically and numerically based on the transfer matrix theory. Different from the single nonreciprocal frequency in the parity-time (PT) system, two adjacent band gaps are changed into a pair of nonreciprocal bands under the effect of MO materials and a PT system above the PT exceptional point, and extraordinary transmissions are inspired in some nonreciprocal frequencies. At the same time, the nonreciprocal propagation bands can be tuned based on the different choices of external magnetic field directions. Furthermore, with an increase in the gain/loss factor, the two nonreciprocal band gaps both disappear and form two bands with an extraordinary transmission at certain frequencies. Such peculiar properties in the composite structure may have broad potential applications in communication and integration devices.

Information redundancy across spectral regions for sentence recognition in noise

Two approaches are examined to quantify the synergetic and redundant interactions across spectral regions for sentence recognition in noise. In one approach, the Speech Intelligibility Index is extended such that speech intelligibility is not only influenced by the speech audibility metrics in individual frequency bands but also their pairwise products to capture the synergetic and redundant interactions between pairs of bands. In a second approach, it is assumed that successful keyword recognition is determined by how many independent channels of information is received by the listener. Each channel of information may be uniquely carried by a frequency band, representing the independent contribution of that band, or shared among multiple bands, representing information redundancy. A previously collected dataset was re-analyzed using the two quantification approaches. For each of the 30 listeners in the dataset, correctness in keyword recognition in the IEEE sentences was available for 600 trials. From trial to trial, the sentence-in-noise stimuli varied in terms of signal-to-noise ratio and which frequency bands were removed from the spectrum via filtering. Both approaches provided consistent depictions of how information is shared across spectral regions for the IEEE sentences. Moreover, the information redundancies across frequency regions did not equally impact all listeners.

Abnormal phase–amplitude coupling characterizes the interictal state in epilepsy

Objective. Diagnosing epilepsy still requires visual interpretation of electroencephalography (EEG) and magnetoencephalography (MEG) by specialists, which prevents quantification and standardization of diagnosis. Previous studies proposed automated diagnosis by combining various features from EEG and MEG, such as relative power (Power) and functional connectivity (FC). However, the usefulness of interictal phase–amplitude coupling (PAC) in diagnosing epilepsy is still unknown. We hypothesized that resting-state PAC would be different for patients with epilepsy in the interictal state and for healthy participants such that it would improve discrimination between the groups. Approach. We obtained resting-state MEG and magnetic resonance imaging (MRI) in 90 patients with epilepsy during their preoperative evaluation and in 90 healthy participants. We used the cortical currents estimated from MEG and MRI to calculate Power in the δ (1–3 Hz), θ (4–7 Hz), α (8–13 Hz), β (13–30 Hz), low γ (35–55 Hz), and high γ (65–90 Hz) bands and FC in the θ band. PAC was evaluated using the synchronization index (SI) for eight frequency band pairs: the phases of δ, θ, α, and β and the amplitudes of low and high γ. First, we compared the mean SI values for the patients with epilepsy and the healthy participants. Then, using features such as PAC, Power, FC, and features extracted by deep learning (DL) individually or combined, we tested whether PAC improves discrimination accuracy for the two groups. Main results. The mean SI values were significantly different for the patients with epilepsy and the healthy participants. The SI value difference was highest for θ/low γ in the temporal lobe. Discrimination accuracy was the highest, at 90%, using the combination of PAC and DL. Significance. Abnormal PAC characterized the patients with epilepsy in the interictal state compared with the healthy participants, potentially improving the discrimination of epilepsy.

Age and Growth of the Spot-Tail Shark, Carcharhinus sorrah, in the Taiwan Strait

The age and growth of the spot-tail shark, Carcharhinus sorrah, were estimated based on 327 specimens (171 females and 156 males) captured by the coastal/offshore longline or drift net fishery in the waters of the Taiwan Strait from October 2010 to December 2011 and July 2019 to August 2021. Sex-specific whole weight (W)—curved total length (TL) relationships were estimated as follows: W = 7.0 × 10−6 TL2.9313 (n = 171, and p < 0.05) for females, and W = 4.0 × 10−6 TL3.0516 (n = 156, and p < 0.05) for males. The periodicity of growth band pair (including translucent and opaque bands) deposition in precaudal vertebrae was assumed to be 1 year based on centrum edge analysis and verified by a statistical analysis. The band pairs after the birth mark were counted as 0–5 and 0–8 for females and males, respectively. The Gompertz and von Bertalanffy growth function best described the observed length-at-age data for females and males, respectively. The parameters for sex-specific growth equations were estimated as: L∞ = 158.6 ± 9.09 cm TL, kG = 0.2347 ± 0.0245 year−1, and c = −0.3233 ± 0.2043 (n = 171, and p < 0.01) for females, and L∞ = 170.2 ± 9.51 cm TL, k = 0.1461 ± 0.0182 year−1, and t0 = −3.1586 ± 0.2065 (n = 156, and p < 0.01) for males.

Dynamics of rotation in chiral nuclei

The dynamics of chiral nuclei is investigated for the first time with the time-dependent and tilted axis cranking covariant density functional theories on a three-dimensional space lattice in a microscopic and self-consistent way. The experimental energies of the two pairs of the chiral doublet bands in $^{135}$Nd are well reproduced without any adjustable parameters beyond the well-defined density functional. A novel mechanism, i.e., chiral precession, is revealed from the microscopic dynamics of the total angular momentum in the body-fixed frame, whose harmonicity is associated with a transition from the planar into aplanar rotations with the increasing spin. This provides a fully microscopic and dynamical view to understand the chiral excitations in nuclei.

Simultaneous description of wobbling and chiral properties in even–odd triaxial nuclei

A particle-triaxial rigid core Hamiltonian is semi-classically treated. The coupling term corresponds to a particle rigidly coupled to the triaxial core, along a direction that does not belong to any principal plane of the inertia ellipsoid. The equations of motion for the angular momentum components provide a sixth-order algebraic equation for one component and subsequently equations for the other two. Linearizing the equations of motion, a dispersion equation for the wobbling frequency is obtained. The equations of motion are also considered in the reduced space of generalized phase space coordinates. Choosing successively the three axes as quantization axis will lead to analytical solutions for the wobbling frequency, respectively. The same analysis is performed for the chirally transformed Hamiltonian. With an illustrative example one identified wobbling states whose frequencies are mirror image to one another. Changing the total angular momentum I, a pair of twin bands emerged. Note that the present formalism conciliates between the two signatures of triaxial nuclei, i.e., they could coexist for a single nucleus.

Growth Modeling of the Giant Electric Ray Narcine entemedor in the Southern Gulf of California: Analyzing the Uncertainty of Three Data Sets.

Simple SummaryThe study of age and growth patterns in skates and rays can be conducted by analyzing mineral deposition patterns inside the vertebrae as biological features may influence age estimation. For the giant electric ray (Narcine entemedor), age was estimated by analyzing the vertebrae and an annual deposition pattern was found. After considering additional biological features such as birth date and date of capture, a more precise description of growth pattern was made. We concluded that this species is a moderate body size elasmobranch with moderate longevity and fast growth. Our results provide useful information for the future management of this exploited species.The age and growth rate of the giant electric ray, Narcine entemedor, was estimated using growth bands deposited in the vertebral centra of 245 specimens. Differences in size and age distribution were found between the sexes, a pattern that suggests the annual deposition of band pairs, possibly occurring in April. Multimodel inference and back-calculation were performed to three age data sets of females considering their reproductive cycle and time of capture, among which the von Bertalanffy growth function was found to be the most appropriate (L∞ = 81.87 cm TL, k = 0.17 year−1). Our research supports the idea that age can be determined via biological features such as birth date and growth band periodicity. We concluded that N. entemedor is of a moderate body size, moderate longevity and is a fast-growing elasmobranch species.

Water column compensation workflow for hyperspectral imaging data

Our article describes a data processing workflow for hyperspectral imaging data to compensate for the water column in shallow, clear to moderate optical water types. We provide a MATLAB script that can be readily used to implement the described workflow. We break down each code segment of this script so that it is more approachable for use and modification by end users and data providers. The workflow initially implements the method for water column compensation described in Lyzenga (1978) and Lyzenga (1981), generating depth invariant indices from spectral band pairs. Given the high dimensionality of hyperspectral imaging data, an overwhelming number of depth invariant indices are generated in the workflow. As such, a correlation based feature selection methodology is applied to remove redundant depth invariant indices. In a post-processing step, a principal component transformation is applied, extracting features that account for a substantial amount of the variance from the non-redundant depth invariant indices while reducing dimensionality. To fully showcase the developed methodology and its potential for extracting bottom type information, we provide an example output of the water column compensation workflow using hyperspectral imaging data collected over the coast of Philpott's Island in Long Sault Parkway provincial park, Ontario, Canada.•Workflow calculates depth invariant indices for hyperspectral imaging data to compensate for the water column in shallow, clear to moderate optical water types.•The applied principal component transformation generates features that account for a substantial amount of the variance from the depth invariant indices while reducing dimensionality.•The output (both depth invariant index image and principal component image) allows for the analysis of bottom type in shallow, clear to moderate optical water types.

Negative intrinsic orbital Hall effect in group XIV materials

Material-dependent signs of the spin Hall conductivity are a useful tool to distinguish the spin Hall effect from other spin phenomenon. Similarly, material-dependent signs of the orbital Hall effect (OHE) can be a useful tool to distinguish the OHE from other effects. But previous theoretical calculations of the orbital Hall conductivity (OHC) found mostly positive sign, making difficult the OHE detection based on the material dependence of the OHC sign. We investigate the intrinsic OHE in elemental group XIV materials Si, Ge, and $\ensuremath{\alpha}$-Sn with diamond cubic structures. We find that the OHC in these materials are gigantic $\ensuremath{\sim}{10}^{3}\phantom{\rule{4pt}{0ex}}(\ensuremath{\hbar}/e){(\mathrm{\ensuremath{\Omega}}\phantom{\rule{0.16em}{0ex}}\mathrm{cm})}^{\ensuremath{-}1}$ and negative. These materials have two pairs of valence bands interacting with each other to generate negative orbital Berry curvature. Further, we suggest the usage of these materials to measure the OHE.

Symmetry-enforced topological band crossings in orthorhombic crystals: Classification and materials discovery

We identify all symmetry-enforced band crossings in nonmagnetic orthorhombic crystals with and without spin-orbit coupling and discuss their topological properties. We find that orthorhombic crystals can host a large number of different band degeneracies, including movable Weyl and Dirac points with hourglass dispersions, fourfold double Weyl points, Weyl and Dirac nodal lines, almost movable nodal lines, nodal chains, and topological nodal planes. Interestingly, spin-orbit coupled materials in the space groups 18, 36, 44, 45, and 46 can have band pairs with only two Weyl points in the entire Brillouin zone. This results in a simpler connectivity of the Fermi arcs and more pronounced topological responses than in materials with four or more Weyl points. In addition, we show that the symmetries of the space groups 56, 61, and 62 enforce nontrivial weak $\mathbb{Z}_2$ topology in materials with strong spin-orbit coupling, leading to helical surface states. With these classification results in hand, we perform extensive database searches for orthorhombic materials crystallizing in the relevant space groups. We find that Sr$_2$Bi$_3$ and Ir$_2$Si have bands crossing the Fermi energy with a symmetry-enforced nontrivial $\mathbb{Z}_2$ invariant, CuIrB possesses nodal chains near the Fermi energy, Pd$_7$Se$_4$ and Ag$_2$Se exhibit fourfold double Weyl points, the latter one even in the absence of spin-orbit coupling, whereas the fourfold degeneracies in AuTlSb are made up from intersecting nodal lines. For each of these examples we compute the ab-initio band structures, discuss their topologies, and for some cases also calculate the surface states.

In-situ observation of nonuniform deformation during tensile test of aluminum alloy sheet by means of screen-printed mechanoluminescence film

Nonuniform deformation in a tensile test of an aluminum alloy sheet was visualized by a coating of ∼ 5 μm thick mechanoluminescence (ML) material film (SrAl2O4:Eu2+) on the specimen. It is reported that ML material emits visible light under mechanical stress, and that the intensity increases with von Mises stress. Fine sized ML particles were used to form thin film on the specimen with a screen-printing technique. During the tensile test of A1050 aluminum sheets, it is observed that the Lüders bands initiated at the shoulders of the specimen, and the bands propagated to the center with tensile deformation. Meanwhile, the yield elongation appeared until a pair of bands initiated at either upper or lower shoulders show collision at the center of the parallel part. In addition, necking and fracture behaviors of the specimens during the tensile test are made clear.

Evolution of the structural polymorphs of poly(l-lactic acid) during the in vitro mineralization of its hydroxyapatite nanocomposites by attenuated total reflection fourier transform infrared mapping coupled with principal component analysis

The evolution of the structural polymorphs of poly(l-lactic acid) (PLLA) during the in vitro mineralization of its hydroxyapatite (HA) nanocomposites is crucial for understanding the degradation mechanism of PLLA under physiological conditions. It was studied by attenuated total reflection Fourier transform infrared (ATR FTIR) mapping coupled with principal component analysis (PCA). The intensity ratios of the band pairs 1211/1186 cm−1 and 1384/1361 cm−1 (i.e., I1211/I1186 and I1384/I1361) of the first principal component (PC1) were used to trace the variations of the conformations and the states of order of PLLA, respectively. Two alternate transitions between amorphous and crystalline PLLA, as well as between α- and α′-PLLA were found for both porous and compact PLLA/HA nanocomposites during the mineralization. However, for PLLA states of order, more and more amorphous forms were observed with degradation, while for PLLA conformations, the alternate transition between α- and α′-PLLA was gradually hindered as mineralization proceeds. Our results demonstrate that the change of PLLA states of order is greater than the one of PLLA conformations, indicating that the hydrolyzation of amorphous PLLA is the major way of the mineralization of PLLA/HA nanocomposites. This developed method is sensitive to the changes of the structural polymorphs of PLLA and can be used to trace their evolution during the degradation.

A broadband metal coaxial resonator antenna loaded with dielectric lens

A design method of metal coaxial resonator antenna (MCRA) is proposed in this article. According to this method, a broadband MCRA working in high-order modes is designed. The proposed antenna fuses two frequency bands of different high-order mode pairs, thus achieving 30% fractional bandwidth. The measured operating frequency band of the antenna is 2.95–4.1 GHz, in which the gain is more than 8.5 dBi. In addition, in order to improve the gain, a low-profile dielectric lens (DL) is designed. With the DL loaded, the −10 dB S11 band shifts to 3.1–4.1 GHz, and the gain of is more than 11 dBi. A close agreement has been achieved between the measured and simulated results.

Assessing Suitability of Sentinel-2 Bands for Monitoring of Nutrient Concentration of Pastures with a Range of Species Compositions

The accurate and timely assessment of pasture quantity and quality (i.e., nutritive characteristics) is vital for effective pasture management. Remotely sensed data can be used to predict pasture quantity and quality. This study investigated the ability of Sentinel-2 multispectral bands, convolved from proximal hyperspectral data, in predicting various pasture quality and quantity parameters. Field data (quantitative and spectral) were gathered for experimental plots representing four pasture types—perennial ryegrass monoculture and three mixtures of swards representing increasing species diversity. Spectral reflectance data at the canopy level were used to generate Sentinel-2 bands and calculate normalised difference indices with each possible band pair. The suitability of these indices for prediction of pasture parameters was assessed. Pasture quantity parameters (biomass and Leaf Area Index) had a stronger influence on overall reflectance than the quality parameters. Indices involving the 1610 nm band were optimal for acid detergent fibre, crude protein, organic matter and water-soluble carbohydrate concentration, while being less affected by biomass or LAI. The study emphasises the importance of accounting for the quantity parameters in the spectral data-based models for pasture quality predictions. These explorative findings inform the development of future pasture quantity and quality models, particularly focusing on diverse swards.

Spectral properties of Andreev crystals

We present an exhaustive study of Andreev crystals (ACs) -- quasi-one-dimensional superconducting wires with a periodic distribution of magnetic regions. The exchange field in these regions is assumed to be much smaller than the Fermi energy. Hence, the transport through the magnetic region can be described within the quasiclassical approximation. In the first part of the paper, by assuming that the separation between the magnetic regions is larger than the coherence length, we derive the effective nearest-neighbour tight-binding equations for ACs with a helical magnetic configuration. The spectrum within the gap of the host superconductor shows a pair of energy-symmetric bands. By increasing the strength of the magnetic impurities in ferromagnetic ACs, these bands cross without interacting. However, in any other helical configuration, there is a value of the magnetic strength at which the bands touch each other, forming a Dirac point. Further increase of the magnetic strength leads to a system with an inverted gap. We study junctions between ACs with inverted spectrum and show that junctions between (anti)ferromagnetic ACs (always) never exhibit bound states at the interface. In the second part, we extend our analysis beyond the nearest-neighbour approximation by solving the Eilenberger equation for infinite and junctions between semi-infinite ACs with collinear magnetization. From the obtained quasiclassical Green functions, we compute the local density of states and the local spin polarization in anti- and ferromagnetic ACs. We show that these junctions may exhibit bound states at the interface and fractionalization of the surface spin polarization.