Gradient Asymmetry Research Articles

Altered asymmetry of functional connectome gradients in major depressive disorder.

Major depressive disorder (MDD) is a debilitating disease involving sensory and higher-order cognitive dysfunction. Previous work has shown altered asymmetry in MDD, including abnormal lateralized activation and disrupted hemispheric connectivity. However, it remains unclear whether and how MDD affects functional asymmetries in the context of intrinsic hierarchical organization. Here, we evaluate intra- and inter-hemispheric asymmetries of the first three functional gradients, characterizing unimodal-transmodal, visual-somatosensory, and somatomotor/default mode-multiple demand hierarchies, to study MDD-related alterations in overarching system-level architecture. We find that, relative to the healthy controls, MDD patients exhibit alterations in both primary sensory regions (e.g., visual areas) and transmodal association regions (e.g., default mode areas). We further find these abnormalities are woven in heterogeneous alterations along multiple functional gradients, associated with cognitive terms involving mind, memory, and visual processing. Moreover, through an elastic net model, we observe that both intra- and inter-asymmetric features are predictive of depressive traits measured by BDI-II scores. Altogether, these findings highlight a broad and mixed effect of MDD on functional gradient asymmetry, contributing to a richer understanding of the neurobiological underpinnings in MDD.

Porphyrin-containing conjugated microporous polymers with gradient asymmetric design for efficient oxygen reduction

Gradient asymmetry is employed to design metal-free polymer electrocatalysts. The superior activity of the highly asymmetric PPA-BN is attributed to the abundant active sites and adequate oxygen intermediate adsorption by local charge distribution.

Diverging asymmetry of intrinsic functional organization in autism

Autism is a neurodevelopmental condition involving atypical sensory-perceptual functions together with language and socio-cognitive deficits. Previous work has reported subtle alterations in the asymmetry of brain structure and reduced laterality of functional activation in individuals with autism relative to non-autistic individuals (NAI). However, whether functional asymmetries show altered intrinsic systematic organization in autism remains unclear. Here, we examined inter- and intra-hemispheric asymmetry of intrinsic functional gradients capturing connectome organization along three axes, stretching between sensory-default, somatomotor-visual, and default-multiple demand networks, to study system-level hemispheric imbalances in autism. We observed decreased leftward functional asymmetry of language network organization in individuals with autism, relative to NAI. Whereas language network asymmetry varied across age groups in NAI, this was not the case in autism, suggesting atypical functional laterality in autism may result from altered developmental trajectories. Finally, we observed that intra- but not inter-hemispheric features were predictive of the severity of autistic traits. Our findings illustrate how regional and patterned functional lateralization is altered in autism at the system level. Such differences may be rooted in atypical developmental trajectories of functional organization asymmetry in autism.

Use of fractal curves for reducing spatial thermal gradients and distortion control

In Additive Manufacturing, the desired geometry is achieved by gradual and sequential addition of material. This evolutionary nature of AM, which facilitates the fabrication of complex geometries, also results in distinctive thermal evolution for each unit of material added. An asymmetry in the heat gradients and the resulting thermal imbalance can result in residual stresses and distortions. This thermal imbalance can be mitigated by controlling the spatial spread of the heat inside the system. The aim of the current work is to delve into the fundamental behavior of heat gradients and look at ways to mitigate these gradients in a manner that is applicable to a wider spectrum of setups and scales. Hence, the focus of the current work is on regulating the area-filling paths (scan patterns) to control the spatial distribution of heat. It is hypothesized that fractal area-filling curves, like Hilbert, due to their continuous and recursive nature, can help in better heat distribution and reduce residual stresses and distortions. This concept is actualized for the Wire and Arc Additive Manufacturing (WAAM) process through simulation and experimental validation. Three different geometries and each at three different dimensional scales were taken up for study. For each of these geometries, the area-filling paths were generated in Zigzag, Contour (out-to-in) and Hilbert area-filling methods. Based on the data extracted from the simulation of these cases in Simufact software, the Hilbert pattern was found to have minimal thermal gradients in all cases. This favorable behavior of Hilbert was further corroborated with the help of experiments using weld deposition of the geometries. For the Hilbert area-filling, the distortions are reduced to values 41 % - 53 % for scaled-up, 53 % - 63 % for unscaled and 80 % - 93 % for scaled-down. These results validate the correlation between the differential temperature and distortion and the ability of fractal curves like the Hilbert curve for achieving better thermal distribution, decreasing the differential temperature.

Directed flow of charged particles within idealized viscous hydrodynamics at energies available at the BNL Relativistic Heavy Ion Collider and at the CERN Large Hadron Collider

Following the Bo\ifmmode \dot{z}\else \.{z}\fi{}ek-Wyskiel parametrization tilted initial condition, an alternative way to construct a longitudinal tilted fireball based on the Glauber collision geometry is presented. This longitudinal tilted initial condition combined with the Ideal-CLVisc $(3+1)\mathrm{D}$ hydrodynamic model, a nonvanishing directed flow coefficient ${v}_{1}$ in a wide range is observed. After comparing the model's results with experimentally observed data of directed flow coefficient ${v}_{1}(\ensuremath{\eta})$ from $\sqrt{{s}_{NN}}=200\phantom{\rule{4pt}{0ex}}\mathrm{GeV} \text{Cu}+\text{Cu}, \text{Au}+\text{Au}$ collisions at RHIC energy to $\sqrt{{s}_{NN}}=2.76\phantom{\rule{4pt}{0ex}}\mathrm{TeV}$ and $\sqrt{{s}_{NN}}=5.02\phantom{\rule{4pt}{0ex}}\mathrm{TeV} \text{Pb}+\text{Pb}$ collisions at the LHC energy. One finds that directed flow measurements in heavy-ion collisions can set strong constraints on the imbalance of forward and backward incoming nuclei and on the magnitude asymmetry of pressure gradients along the $x$ direction.

Feature engineering for subseasonal-to-seasonal warm-season precipitation forecasts in the Midwestern US: towards a unifying hypothesis of anomalous warm-season hydroclimatic circulation

AbstractThe literature has established dozens of potential predictive indices (PIs) of anomalous warm season precipitation in the Midwestern US that could have utility in subseasonal to seasonal (S2S) forecasts This analysis posits that these predictive indices relate to one of three “modes of action” that work in tandem to drive anomalous hydroclimatic circulation into the continental interior. These include contributions from the (1) geostrophic mass flux, (2) ageostrophic mass flux, and (3) atmospheric moisture supply, and represent semi-independent, interactive forcings on S2S precipitation variability. This study aggregates 24 PIs from the literature that are related to the three modes of action. Using an interpretable machine learning algorithm that accounts for non-linear and interactive responses in a noisy predictive space, we evaluate the relative importance of PIs in predicting S2S precipitation anomalies from March-September. Physical mechanisms driving PI skill are confirmed using composite analysis of atmospheric fields related to the three modes of action. In general, PIs associated with ageostrophic mass flux anomalies are important in early summer, while PIs associated with Atlantic-sourced atmospheric moisture supply are important in late summer. At a two month lead, PIs associated with continental-scale thermodynamic processes are more important relative to PIs associated with local convective phenomena. PIs representing geostrophic mass flux anomalies are also critical throughout the warm season, in real-time and at a 1-2 month lag, but particularly in during transitional months (spring/fall). Several new PIs describing zonal and meridional asymmetry in hemispherical thermal gradients emerge as highly important, with implications for both S2S forecasting and climate change.

Sex-related human brain asymmetry in hemispheric functional gradients

The left and right hemispheres of the human brain are two connected but relatively independent functional modules; they show multidimensional asymmetries ranging from particular local brain unit properties to entire hemispheric connectome topology. To date, however, it remains largely unknown whether and how hemispheric functional hierarchical structures differ between hemispheres. In the present study, we adopted a newly developed resting-state (rs) functional connectivity (FC)-based gradient approach to evaluate hemispheric functional hierarchical structures and their asymmetries in right-handed healthy young adults. Our results showed an overall mirrored principal functional gradient between hemispheres, with the sensory cortex and the default-mode network (DMN) anchored at the two opposite ends of the gradient. Interestingly, the left hemisphere showed a significantly larger full range of the principal gradient in both males and females, with males exhibiting greater leftward asymmetry. Similarly, the principal gradient component scores of two regions around the middle temporal gyrus and posterior orbitofrontal cortex exhibited similar hemisphere × sex interaction effects: a greater degree of leftward asymmetry in males than in females. Moreover, we observed significant main hemisphere and sex effects in distributed regions across the entire hemisphere. All these results are reproducible and robust between test-retest rs-fMRI sessions. Our findings provide evidence of functional gradients that enhance the present understanding of human brain asymmetries in functional organization and highlight the impact of sex on hemispheric functional gradients and their asymmetries.

Systemic Study of Orbital and Spin Nematicity in NaFe1−x Co x As by NMR

Nematic order, a self-organized state with rotational symmetry broken, has been observed in both copper-oxide and iron-pnictide high temperature superconductors. However, its origin is still a mystery in the iron pnictides although it is considered as a key to understand the mechanism of superconductivity. Here, we report a systemic nuclear magnetic resonance (NMR) study on NaFe1−xCoxAs (0 ≤x ≤ 0.042) that an orbital order, accompanied by an instant spin nematicity, occurs at at a temperature T∗ far above structural transition temperature Ts in the tetragonal phase. We show that the observed NMR spectra splitting and its evolution is due to an incommensurate orbital order that sets in below T∗ and becomes commensurate below Ts. We show that the electric field gradient asymmetry parameter is a good measure for the orbital order parameter which undergoes a Landau-like 2nd-order phase transition. We further show that the spin nematicity is well accounted for by the observed orbital order.

Impact of fuelling and impurity on pedestal dynamics and instabilities in the HL-2A tokamak

In recent experiments of the HL-2A tokamak, the effect on the pedestal dynamics by the plasma fuelling with supersonic molecular beam injection (SMBI) has been intensively investigated. Experimental results in several tokamaks suggested that SMBI is a promising technique for ELM mitigation. In addition to the fuelling, the impact of impurities on the pedestal dynamics and instabilities has been investigated in HL-2A. Experimental results have shown that during the H-mode phase, a broadband electromagnetic (EM) turbulence was driven by peaked impurity density profile at the edge plasma region, and governed by double critical gradients of the impurity density. The absolute value of the threshold in positive gradient region is much lower than that in the negative region. This strong asymmetry in the critical gradients has been predicted by theoretical simulation. The results reveal that pedestal dynamics and heat loads can be actively controlled by exciting or changing pedestal instabilities.

Dependence of nuclear quadrupole resonance transitions on the electric field gradient asymmetry parameter for nuclides with half-integer spins

Allowed transition energies and eigenstate expansions have been calculated and tabulated in numerical form as functions of the electric field gradient asymmetry parameter for the zero field Hamiltonian of quadrupolar nuclides with I=3/2,5/2,7/2, and 9/2. These results are essential to interpret nuclear quadrupole resonance (NQR) spectra and extract accurate values of the electric field gradient tensors. Applications of NQR methods to studies of electronic structure in heavy element systems are proposed.

Geostationary Operational Environmental Satellite Imager infrared channel-to-channel co-registration characterization algorithm and its implementation in the ground system

Channel-to-channel co-registration is an important performance metric for the Geo- stationary Operational Environmental Satellite (GOES) Imager, and large co-registration errors can have a significant impact on the reliability of derived products that rely on combinations of multiple infrared (IR) channels. Affected products include the cloud mask, fog and fire detection. This is especially the case for GOES-13, in which the co-registration error between channels 2 (3.9 μm) and 4 (10.7 μm) can be as large as 1 pixel (or ∼ 4k m) in the east-west direction. The GOES Imager IR channel-to-channel co-registration characterization (GII4C) algorithm is pre- sented, which allows a systematic calculation of the co-registration error between GOES IR channel image pairs. The procedure for determining the co-registration error as a function of time is presented. The algorithm characterizes the co-registration error between corresponding images from two channels by spatially transforming one image using the fast Fourier transfor- mation resampling algorithm and determining the distance of the transformation that yields the maximum correlation in brightness temperature. The GII4C algorithm is an area-based approach which does not depend on a fixed set of control points that may be impacted by the presence of clouds. In fact, clouds are a feature that enhances the correlations. The results presented show very large correlations over the majority of Earth-viewing pixels, with stable algorithm results. Verification of the algorithm output is discussed, and a global spatial-spectral gradient asym- metry parameter is defined. The results show that the spatial-spectral gradient asymmetry is strongly correlated to the co-registration error and can be an effective global metric for the qual- ity of the channel-to-channel co-registration characterization algorithm. Implementation of the algorithm in the GOES ground system is presented. This includes an offline component to deter- mine the time dependence of the co-registration errors and a real-time component to correct the co-registration errors based on the inputs from the offline component. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI. (DOI: 10

Universal steganalysis for RGB images based on color gradient matrix

A steganalysis algorithm for RGB images based on color gradient matrix was proposed in this paper.The algorithm was constructed with color gradient matrix of the RGB image,and 16-dimensional statistical features,including gradient asymmetry,gradient energy,gradient mean,gradient variance,gradient entropy and so on.Support Vector Machine(SVM) took the 16-dimensional statistical features to detect hidden message in RGB images.The experimental results indicate that the proposed algorithm realizes the reliable steganalysis of JSteg,F5,OutGuess,Steghide and MB1,which is suitable for universal steganalysis for RGB images.

Study of the EFG tensor at 75As nuclei in Ge‐As‐Se chalcogenide glasses

Asymmetry parameters of the electric field gradient tensor at (75) As nuclei were determined for chalcogenide glassy semiconductors (CGS) of the Ge-As-Se system by comparing the experimental and simulated (75) As nuclear quadrupole resonance nutation interferograms. The electric field gradient asymmetry in CGS was analyzed, and it is believed that a structural change in these glassy semiconductors takes place at r¯ = 2.425. Electron paramagnetic resonance spectra of the Ge-As-Se system were obtained for the first time. A comparison was made between the results of analysis of the Ge-As-Se system by nuclear quadrupole resonance and electron paramagnetic resonance methods, and this allowed us to make the supposition that a structural phase transition occurs at r¯ = 2.4 from two-dimensional to three-dimensional CGS structure.

Nuclear magnetic relaxation induced by exchange-mediated orientational randomization: Longitudinal relaxation dispersion for spin I = 1

The frequency dependence of the longitudinal relaxation rate, known as the magnetic relaxation dispersion (MRD), can provide a frequency-resolved characterization of molecular motions in complex biological and colloidal systems on time scales ranging from 1 ns to 100 μs. The conformational dynamics of immobilized proteins and other biopolymers can thus be probed in vitro or in vivo by exploiting internal water molecules or labile hydrogens that exchange with a dominant bulk water pool. Numerous water (1)H and (2)H MRD studies of such systems have been reported, but the widely different theoretical models currently used to analyze the MRD data have resulted in divergent views of the underlying molecular motions. We have argued that the essential mechanism responsible for the main dispersion is the exchange-mediated orientational randomization (EMOR) of anisotropic nuclear (electric quadrupole or magnetic dipole) couplings when internal water molecules or labile hydrogens escape from orientationally confining macromolecular sites. In the EMOR model, the exchange process is thus not just a means of mixing spin populations but it is also the direct cause of spin relaxation. Although the EMOR theory has been used in several studies to analyze water (2)H MRD data from immobilized biopolymers, the fully developed theory has not been described. Here, we present a comprehensive account of a generalized version of the EMOR theory for spin I = 1 nuclides like (2)H. As compared to a previously described version of the EMOR theory, the present version incorporates three generalizations that are all essential in applications to experimental data: (i) a biaxial (residual) electric field gradient tensor, (ii) direct and indirect effects of internal motions, and (iii) multiple sites with different exchange rates. In addition, we describe and assess different approximations to the exact EMOR theory that are useful in various regimes. In particular, we consider the experimentally important dilute regime, for which approximate analytical results are derived. As shown by the analytical expressions, and confirmed by exact numerical calculations, the dispersion is governed by the pure nuclear quadrupole resonance frequencies in the ultraslow-motion regime, where the relaxation rate also exhibits a much stronger dependence on the electric field gradient asymmetry than in the motional-narrowing regime.

The effect of concomitant gradient fields on diffusion tensor imaging

Concomitant gradient fields are transverse magnetic field components that are necessarily present to satisfy Maxwell's equations when magnetic field gradients are utilized in magnetic resonance imaging. They can have deleterious effects that are more prominent at lower static fields and/or higher gradient strengths. In diffusion tensor imaging schemes that employ large gradients that are not symmetric about a refocusing radiofrequency pulse (unlike Stejskal-Tanner, which is symmetric), concomitant fields may cause phase accrual that could corrupt the diffusion measurement. Theory predicting the error from this dephasing is described and experimentally validated for both Reese twice-refocused and split gradient single spin-echo diffusion gradient schemes. Bias in apparent diffusion coefficient values was experimentally found to worsen with distance from isocenter and with increasing duration of gradient asymmetry in both a phantom and in the brain. The amount of error from concomitant gradient fields depends on many variables, including the diffusion gradient pattern, pulse sequence timing, maximum effective gradient amplitude, static magnetic field strength, voxel size, slice distance from isocenter, and partial Fourier fraction. A prospective correction scheme that can reduce concomitant gradient errors is proposed and verified for diffusion imaging.

Giant spin-orbit-induced spin splitting in two-dimensional transition-metal dichalcogenide semiconductors

Fully relativistic first-principles calculations based on density functional theory are performed to study the spin-orbit-induced spin splitting in monolayer systems of the transition-metal dichalcogenides MoS${}_{2}$, MoSe${}_{2}$, WS${}_{2}$, and WSe${}_{2}$. All these systems are identified as direct-band-gap semiconductors. Giant spin splittings of 148--456 meV result from missing inversion symmetry. Full out-of-plane spin polarization is due to the two-dimensional nature of the electron motion and the potential gradient asymmetry. By suppression of the Dyakonov-Perel spin relaxation, spin lifetimes are expected to be very long. Because of the giant spin splittings, the studied materials have great potential in spintronics applications.

Stereoelectronic srtructure of γ-chloropropyltrichlorostannane. Ab initio calculation

The quantum-chemical calculations by the RHF/3-21G* and MR2/3-21G* methods of the Cl(CH2)3SnCl3 and ClCH2SnCl3 molecules with full optimization of their geometry was performed. The Cl(CH2)3SnCl3 molecule was also calculated by the RHF/3-21G* method at different distances between the Sn atom and the Cl atom in the C-Cl fragment. From the results of the calculations 35Cl NQR frequencies were estimated and the electric field gradient asymmetry parameters at the 35Cl nuclei of these molecules. The abnormally high electron density on the Cl atom of the C-Cl fragment in the Cl(CH2)3SnCl3 molecule is due mainly to the polarization of this compound under the influence of significant positive charge on the Sn atom directly through the field. The polarization of the C-Cl bond in the molecule is of the opposite direction to the polarization of the related bond in the ClCH2SnCl3 molecule because of the peculiarities of their geometries. The transfer of the electron density from the Cl atom of the C-Cl fragment to the Sn atom in the Cl(CH2)3SnCl3 molecule is not observed.

Biomechanical design and long-term stability of trees: Morphological and wood traits involved in the balance between weight increase and the gravitropic reaction

Studies on tree biomechanical design usually focus on stem stiffness, resistance to breakage or uprooting, and elastic stability. Here we consider another biomechanical constraint related to the interaction between growth and gravity. Because stems are slender structures and are never perfectly symmetric, the increase in tree mass always causes bending movements. Given the current mechanical design of trees, integration of these movements over time would ultimately lead to a weeping habit unless some gravitropic correction occurs. This correction is achieved by asymmetric internal forces induced during the maturation of new wood. The long-term stability of a growing stem therefore depends on how the gravitropic correction that is generated by diameter growth balances the disturbance due to increasing self weight. General mechanical formulations based on beam theory are proposed to model these phenomena. The rates of disturbance and correction associated with a growth increment are deduced and expressed as a function of elementary traits of stem morphology, cross-section anatomy and wood properties. Evaluation of these traits using previously published data shows that the balance between the correction and the disturbance strongly depends on the efficiency of the gravitropic correction, which depends on the asymmetry of wood maturation strain, eccentric growth, and gradients in wood stiffness. By combining disturbance and correction rates, the gravitropic performance indicates the dynamics of stem bending during growth. It depends on stem biomechanical traits and dimensions. By analyzing dimensional effects, we show that the necessity for gravitropic correction might constrain stem allometric growth in the long-term. This constraint is compared to the requirement for elastic stability, showing that gravitropic performance limits the increase in height of tilted stem and branches. The performance of this function may thus limit the slenderness and lean of stems, and therefore the ability of the tree to capture light in a heterogeneous environment.

Asymmetry and Gradient Asymmetry Functions: Density‐Based Skewness and Kurtosis

Abstract. Functional measures of skewness and kurtosis, called asymmetry and gradient asymmetry functions, are described for continuous univariate unimodal distributions. They are defined and interpreted directly in terms of the density function and its derivative. Asymmetry is defined by comparing distances from points of equal density to the mode. Gradient asymmetry is defined, in novel fashion, as asymmetry of an appropriate function of the density derivative. Properties and illustrations of asymmetry and gradient asymmetry functions are presented. Estimation of them is considered and illustrated with an example. Scalar summary skewness and kurtosis measures associated with asymmetry and gradient asymmetry functions are discussed.

Manifestation of Berry’s Phase in Nuclear Quadrupole Resonance Spectra of Rotating Powder Samples

The effect of Berry’s phase on the nuclear quadrupole resonance (NQR) spectra of rotating powder samples is studied experimentally, and its application for the determination of the electric field gradient asymmetry η is demonstrated. The NQR frequency splittings, which are observed for the spin 3/2 nucleus of 35Cl in powder samples of p-dichlorobenzene (C6H4Cl2) and cyanuric chloride (C3N3Cl3), are interpreted as a manifestation of Berry’s phase, associated with the adiabatically changing Hamiltonian due to sample rotation. The accumulation of Berry’s phase during the rotation process is responsible for the observed dependence of the NQR line shape on the rotation frequency and the asymmetry parameter. The proposed method for the determination of η involves the analysis of the NQR powder patterns of the rotating samples.