Local Properties Research Articles

The Kondo effect in the quantum XX spin chain

We investigate the boundary phenomena that arise in a finite-size XX spin chain interacting through an XX interaction with a spin −12 impurity located at its edge. Upon Jordan–Wigner transformation, the model is described by a quadratic Fermionic Hamiltonian. Our work displays, within this ostensibly simple model, the emergence of the Kondo effect, a quintessential hallmark of strongly correlated physics. We also show how the Kondo cloud shrinks and turns into a single particle bound state as the impurity coupling increases beyond a critical value. In more detail, using both Bethe Ansatz and exact diagonalization techniques, we show that the local moment of the impurity is screened by different mechanisms depending on the ratio of the boundary and bulk coupling JimpJ . When the ratio falls below the critical value 2 , the impurity is screened via the Kondo effect. However, when the ratio between the coupling exceeds the critical value 2 an exponentially localized bound mode is formed at the impurity site which screens the spin of the impurity in the ground state. We show that the boundary phase transition is reflected in local ground state properties by calculating the spinon density of states, the magnetization at the impurity site in the presence of a global magnetic field, and the finite temperature susceptibility of the impurity. We find that the spinon density of states in the Kondo phase has the characteristic Lorentzian peak that moves from the Fermi level to the maximum energy of the spinon as the impurity coupling is increased and becomes a localized bound mode in the bound mode phase. Moreover, the impurity magnetization and the finite temperature impurity susceptibility behave differently in the two phases. When the boundary coupling Jimp exceeds the critical value 2J , the model is no longer boundary conformal invariant as a massive bound mode appears at the impurity site.

Quasi-localization and Wannier obstruction in partially flat bands

The localized nature of a flat band is understood by the existence of a compact localized eigenstate. However, the localization properties of a partially flat band, ubiquitous in surface modes of topological semimetals, have been unknown. We show that the partially flat band is characterized by a non-normalizable quasi-compact localized state (Q-CLS), which is compactly localized along several directions but extended in at least one direction. The partially flat band develops at momenta where normalizable Bloch wave functions can be obtained from a linear combination of the non-normalizable Q-CLSs. Outside this momentum region, a ghost flat band, unseen from the band structure, is introduced based on a counting argument. Then, we demonstrate that the Wannier function corresponding to the partially flat band exhibits an algebraic decay behavior. Namely, one can have the Wannier obstruction in a band with a vanishing Chern number if it is partially flat. Finally, we develop the construction scheme of a tight-binding model for a topological semimetal by designing a Q-CLS.

Revealing molecular insights into surface charge and local viscosity in electroosmotic flows

The limitations of the continuum theory in predicting osmotic response at the nanoscale stem from its lack of molecular-level insight into local fluid properties and the interfacial structure of fluid and electrolyte solutions. To overcome this challenge, our study integrates molecular dynamics (MD) simulation with the continuum framework to explore how surface charge and various hydrodynamic properties impact electroosmotic flow (EOF). The failure of continuum theories to account for molecular interactions and geometric boundaries leads to significant disparities between MD simulations and continuum predictions, influenced by local fluid properties and the electric field. Emphasizing the importance of incorporating appropriate local hydrodynamic properties and atomic interface boundary conditions, our findings bridge the gap between MD simulations and continuum EOF predictions. Our computational results and theoretical model, considering surface charge, atomic interface boundaries, and dynamic structure-based hydrodynamic properties, provide crucial insights and guidance for EOF investigations.

Uhlmann phase of a thermal spin-1 system with zero field splitting

We study the Uhlmann geometric phase of a spin-1 particle subjected to zero-field splitting (ZFS) interaction, modulated by a dimensionless parameter α, under the effect of an external magnetic field with a tilting angle θ. We show that the ZFS term induces a transition in the geometrical phase behavior, characterized by a critical parameter value, α=αc. For α<αc, this phase displays two critical temperatures at θ=π/2, similar to spin-1 systems without ZFS, but with a separation that varies with α. In contrast, for α>αc, the phase exhibits two singularities at a single critical temperature but at different field orientations θ≠π/2. The phase disappears for significantly large |α|, regardless of the values of the Hamiltonian parameters. This behavior clearly departs from the usual thermal Uhlmann phase observed in SU(2) systems. In addition, we analytically calculate the heat capacity, which, for θ=π/2 and nearby values, displays two different regimes according to the sign of α. For α<0, it develops two peaks associated to the multilevel nature of the system, while for α>0 only a single Schottky-anomaly like peak appears as in two level systems. Interestingly, when θ=π/2, the temperature centroids of the Uhlmann phase and the heat capacity coincide in the region between critical temperatures for a given value of α<αc. Furthermore, we demonstrate that when α=0, the Uhlmann phase, a global topological property of the system, can be expressed as a function of the thermal component of the Bures metric, a local geometric property related to the heat capacity.

Numerical simulation of high-temperature erosion of heat-resistant steel considering surface scale evolution

A study was conducted on heat-treated, heat-resistant steel S51740 to understand the issues surrounding gas turbine compressors. The study included high-temperature cyclic oxidation and high-temperature erosion tests at 400 °C, 600 °C, and 800 °C. We used the oxidation test data to establish dynamic erosion models using Ansys LS-DYNA software. We focused on the target's surface morphology, stress-strain, transient temperature, and failure characteristics during high-temperature erosion after high-temperature oxidation to reveal the erosion mechanism of oxidized steel. During cyclic oxidation, the specimen's microstructure was refined at 400 °C, with a 10 μm oxidation-affected zone emerging. At 600 °C, austenite appeared, forming a 20 μm oxidation-affected zone. Performance declined at 800 °C due to decarburization and segregation, resulting in a 50 μm oxidation-affected zone. High-temperature erosion on the oxidized specimens featured cutting and a chip-like morphology at 400 °C and 600 °C. At 800 °C, the specimen experienced a notable increase in mass loss and extensive plastic deformation on the surface. Erosion simulations revealed that rising temperatures increase the target's stress distribution, strain, and temperature zones. Reduced material strength leads to lower resistance to impact particles, converting high-speed kinetic energy to internal energy during erosion. Temperature spikes in impacted zones accelerate wear and adversely affect local mechanical properties. Lower ambient temperatures exacerbate the temperature increase from erosion, significantly influencing material erosion and wear resistance.

Development of New Lead Free Ceramic Substrate for Rectangular Patch Antenna Application in X-Band Communication

This work introduces the use of Bi0.5Na0.5TiO3 (BNT) ceramic material as substrates for microstrip patch antennas operating within the frequency range of 8-12GHz. The simulated antenna was constructed using a substrate composed of a synthesized ferroelectric perovskite-based material with a thickness of t=1.02mm. This study investigated the intricate electromagnetic properties including permittivity, permeability, dielectric loss, magnetic loss, and miniaturization factor. Characterization techniques are used to investigate the crystal structure, local vibrational properties, surface morphology, and elemental composition of the synthesized sample. The reflection loss, return loss, and radiation pattern of the split ring microstrip patch antenna with a rectangular base were calculated using CST Microwave Studio version 2019. The parametric adjustment of the synthesized sample's uniqueness was achieved by modifying its thickness for t=0.7mm, t=0.9mm, t=1mm, t=1.02mm, and t=1.04mm.

Adsorption studies of isoxazole derivatives as corrosion inhibitors for mild steel in 1M HCl solution: DFT studies and molecular dynamics simulation.

The corrosion of mild steel is a significant issue in various industries, prompting the need for effective corrosion inhibitors. This study focuses on understanding the corrosion inhibition properties of organic compounds derived from isoxazole, namely series Iso(a), Iso(b), Iso(c), Iso(d), Iso(e), Iso(f), Iso(g), and Iso(h), which could have implications for materials science and industrial applications. By investigating the influence of different substitutions on these compounds, valuable insights can be gained into designing better corrosion inhibitors for practical use. Theoretical studies were conducted using density functional theory (DFT) with the B3LYP functional and the 6-31G (d,p) basis set. These calculations enabled the evaluation of various parameters including frontier orbital energies (EHOMO, ELUMO), energy gap (∆E), electronegativity (χ), absolute hardness (η), softness (σ), fraction of transferred electrons (∆N), as well as local properties such as natural atomic populations and Fukui indices. Additionally, molecular dynamics simulations were performed to study the adsorption behavior of the inhibitors on the surface of Fe (110). The simulations were conducted using Materials Studio version 8.0 software package using COMPASS force field to understand the impact of different functional groups on the inhibitors before and after adsorption on the iron surface.

Do board networks matter for corporate cash holdings? Evidence from Australian firms

Purpose In today’s interconnected world, social capital has emerged as a crucial business competence, drawing significant attention in recent literature. Using social network analysis, this study aims to investigate the impact of network centrality, established by a firm through its board members (i.e. boardroom networks), on corporate cash holdings. Design/methodology/approach This study uses extensive panel data comprising 36,963 firm-year observations of firms listed on the Australian Securities Exchange, spanning a 22-year period (2001–2022). The study uses firm fixed-effect regression along with several alternative specifications and an instrumental variable approach to ensure the robustness of the results. Boardroom network centrality is quantified by five measures that capture different perspectives on networks as viable conduits for resource exchange and information flow: degree, two-step reach, closeness, eigenvector and betweenness. Findings The authors find evidence for the benefits of board networks. Firms with well-connected boards (central firms) are more likely to have smaller cash holdings. The findings also reveal distinct effects stemming from local and global properties of centrality, with local network measures playing a more pronounced role in shaping cash-holding decisions. Overall, the evidence reflects the ability of connected directors to enhance governance by limiting managerial discretion over cash reserves, thus reducing agency conflicts associated with cash holdings. Research limitations/implications This study offers important insights for regulators, investors and practitioners, highlighting the potential for connected directors to effectively curtail managerial autonomy in deploying corporate cash holdings. Originality/value This study contributes to the ongoing discussion about the advantages and drawbacks of board networks, which constitute a vibrant and burgeoning area of research in the finance literature. It also complements scanty network-based studies on firm cash holdings. Importantly, this study extends prior work by providing robust evidence and a comprehensive analysis of the nuanced roles that board networks play in affecting the level of cash reserves.

Local properties of Schrödinger-Virasoro type Lie algebras and a full diamond thin Lie algebra

Let S V ( z ) be a class of Schrödinger-Virasoro type Lie algebras, where z ∈ Z . In this paper, we show that S V ( z ) is 2-local complete (namely, every 2-local derivation is a derivation) for almost all integers z’s. We also introduce the notion of full diamond thin Lie algebras, and construct an example F from S V ( − 1 ) . We completely determine the derivations of F by combinatoric techniques, and show that F is not 2-local complete.

EVALUATE NODE IMPORTANCE BY DECOMPOSING NETWORK WITH A RECURSIVE PERCOLATION PROCESS

Due to structural heterogeneity, the main function and structure of networked systems are significantly influenced by some important nodes rather than each member. In practical, the properties of important nodes could be different from network to network, and thus a variety of algorithms have been specially designed to identify important nodes of different networks and of different dynamics. In this paper we propose a widely applicable algorithm by employing the percolation model in statistical physics, which describes the behavior of connected clusters when nodes are connected randomly. This algorithm appropriately combines the local and global properties of a network, thus it stresses the significance of nodes that neither have a visibly local importance, such as degree and clustering, nor have a visibly global importance, such as betweenness. The effectiveness of our algorithm has been illustrated in a series of networks, including model networks with different degree distributions and different degree correlations, and empirical networks. As a shell decomposition process, the framework of our algorithm has extensive application prospects in analyzing network structure, such as community, core–periphery structure, and shell structures.

Onset of absolute instability on a pitching aerofoil

A global transient linear stability analysis of the three-dimensional time-dependent flow around an aerofoil undergoing small-amplitude pitching motion is performed using the optimally time-dependent (OTD) framework. The most salient linear instabilities associated with the instantaneous basic state are computed and tracked over time. The resulting OTD modes reflect the variations in the basic state and can be used as predictors of its spatial and temporal evolution, including the formation of a laminar separation bubble and its gradual spanwise modulation via primary global instability, leading to secondary instability and finally rapid breakdown to turbulence. The study confirms and expands upon earlier stability analyses of the same case based on the local properties of spanwise averaged velocity profiles in the bubble that predicted the onset of absolute instability soon followed by rapid breakdown of the separation bubble. The three-dimensional structure of the most unstable OTD mode is extracted, which compares well with both the locally absolutely unstable mode and the evolution of the basic state itself.

Threshold investigation of shell thickness for enhanced mechanical and tribological performance in 3D-printed curved sandwich structures

Global prominence has been attained by additive manufacturing technology in recent years, driven by its environmental benefits and machining advantages when compared to traditional subtractive methods. Fused deposition modeling (FDM) technology, primarily utilized in polymer and polymer composite 3D printing, allows for precise control of material distribution within components. In this study, mechanical and tribological behaviors of 3D-printed structures are investigated, yielding valuable insights applicable to practical scenarios. The study identifies threshold limits for layer thickness ratios in three-layered curved sandwich structures, which directly impact their specific load capacity. Stress distribution within 3D-printed PLA discs can be accurately predicted by a saturation function dependent on shell thickness, with material-specific constants. Beyond a critical shell thickness, the impact of increased shell thickness on local tribological properties is found to be negligible. These findings generalize effectively to structures characterized by robust outer shells and weaker inner infills. Connections are drawn between tribological behavior and contact mechanical properties, opening avenues for future research involving nonlinear material modeling and advanced simulations. This study contributes to a deeper understanding of 3D printing and polymer tribology while highlighting the transformative potential of additive manufacturing in various industries, offering cost-effective and resource-efficient solutions for optimized mechanical performance.

Efficient calculation of unbiased atomic forces in ab initio variational Monte Carlo

quantum Monte Carlo (QMC) is a state-of-the-art numerical approach for evaluating accurate expectation values of many-body wave functions. However, one of the major drawbacks that still hinders widespread QMC applications is the lack of an affordable scheme to compute unbiased atomic forces. In this study, we propose an efficient method to obtain unbiased atomic forces and pressures in the variational Monte Carlo (VMC) framework with the Jastrow-correlated Slater determinant ansatz or the Jastrow antisymmetrized geminal power ansatz, exploiting the gauge-invariant and locality properties of their geminal representation. We demonstrate the effectiveness of our method for H2 and Cl2 molecules and for the cubic boron nitride crystal. Our framework has a better algorithmic scaling with the system size than the traditional finite-difference method and, in practical applications, is as efficient as single-point VMC calculations. Thus, it paves the way to study dynamical properties of materials, such as phonons, and is beneficial for pursuing more reliable machine-learning interatomic potentials based on unbiased VMC forces. Published by the American Physical Society 2024

Topological alterations in white matter anatomical networks in cervical dystonia

BackgroundAccumulating neuroimaging evidence indicates that patients with cervical dystonia (CD) have changes in the cortico-subcortical white matter (WM) bundle. However, whether these patients’ WM structural networks undergo reorganization remains largely unclear. We aimed to investigate topological changes in large-scale WM structural networks in patients with CD compared to healthy controls (HCs), and explore the network changes associated with clinical manifestations.MethodsDiffusion tensor imaging (DTI) was conducted in 30 patients with CD and 30 HCs, and WM network construction was based on the BNA-246 atlas and deterministic tractography. Based on the graph theoretical analysis, global and local topological properties were calculated and compared between patients with CD and HCs. Then, the AAL-90 atlas was used for the reproducibility analyses. In addition, the relationship between abnormal topological properties and clinical characteristics was analyzed.ResultsCompared with HCs, patients with CD showed changes in network segregation and resilience, characterized by increased local efficiency and assortativity, respectively. In addition, a significant decrease of network strength was also found in patients with CD relative to HCs. Validation analyses using the AAL-90 atlas similarly showed increased assortativity and network strength in patients with CD. No significant correlations were found between altered network properties and clinical characteristics in patients with CD.ConclusionOur findings show that reorganization of the large-scale WM structural network exists in patients with CD. However, this reorganization is attributed to dystonia-specific abnormalities or hyperkinetic movements that need further identification.

Can an isolated middle-series item make a "Dent" in the bow-shaped serial-position curve of comparative judgments?

Studies have shown that local (e.g., midseries) items' specific properties, including being isolated from rest of the items, can generate a local distinctiveness effect, enhancing the memory performance for the local items in serial recall or absolute judgments. However, this has not been the case in relative (comparative) judgments. For the first time, the present study found a local distinctiveness effect in comparative judgments by using an opposite-gender name for the midseries item in an otherwise uniformly one-gender name serial list. The reasons for the previous studies' failure to produce this effect in comparative judgments and the present study's success in obtaining it were discussed. The implication of the finding for the item/order information opponent-process theories was also suggested.

A global map of gullied hillslopes on Mars

The distribution of gullies on Mars has been used to support different modes of formation involving CO2, H2O or entirely dry processes. We mapped the extent of gullied hillslope using a global mosaic of ConTeXt camera (CTX) at 6 m/pixel and High Resolution Imaging Science Experiment (HiRISE) browse products at ∼3 m/pixel. Our new global catalog of gullied hillslopes allows for quantitative, area-based analysis of gullies both at global and regional scale, which was not possible with point-based or more localized previous datasets. We analyzed aspect and gradient information derived from MOLA topography for every mapped gullied hillslope. We have confirmed the trends identified in previous works, which are that the mean gradient of gullied hillslopes is lower than 30°, the angle of repose of dry material on Mars, and that the preferred aspect of gullied hillslopes is latitude-dependent, with a shift between pole-facing to equator-facing happening around 40° in both hemispheres. We established a hierarchy of factors that can explain the global distribution of gullied hillslopes: Latitude is the strictest control because gullies are constrained between 26°-83°S and 28°-76°N. The availability of steep slopes is a strong control over gully distribution, and we observed that gullied hillslopes aspect reflects the orientation of large regional reliefs, which implies that hillslope aspect is less of a factor than the hillslope gradient in explaining gully distribution. We analyzed the correlation of gully distribution with a subsurface water ice consistency map, and we found that gullies are preferentially distributed on areas with some ground ice rather than no ice at all. We identified for the first time a bias toward an east-facing trend for southern hemisphere gullies poleward of ∼40° of latitude. We also linked our gullied hillslopes dataset with a global crater morphometry dataset: 63% of the gullied area on Mars is found in craters, and we find that the area covered by gullies in a given crater is positively correlated with the depth and diameter ratio of this crater.Our observations point toward a complex interplay between local slope, insolation, and thermal properties of the substrate to explain the spatial distribution of the current population of gullies. Finally, we have assessed the very high resolution (sub-meter) imagery coverage of gullies to be 36% and that the repeated coverage reaches 21% of gullies, hence this would need expanding to better understand the spatial trends in active gullies.

Interaction of MRI Contrast Agent [Gd(DOTA)]- with Lipid Membranes: A Molecular Dynamics Study.

Contrast agents are important imaging probes in clinical MRI, allowing the identification of anatomic changes that otherwise would not be possible. Intensive research on the development of new contrast agents is being made to image specific pathological markers or sense local biochemical changes. The most widely used MRI contrast agents are based on gadolinium(III) complexes. Due to their very high charge density, they have low permeability through tight biological barriers such as the blood-brain barrier, hampering their application in the diagnosis of neurological disorders. In this study, we explore the interaction between the widely used contrast agent [Gd(DOTA)]- (Dotarem) and POPC lipid bilayers by means of molecular dynamics simulations. This metal complex is a standard reference where several chemical modifications have been introduced to improve key properties such as bioavailability and targeting. The simulations unveil detailed insights into the agent's interaction with the lipid bilayer, offering perspectives beyond experimental methods. Various properties, including the impact on global and local bilayer properties, were analyzed. As expected, the results indicate a low partition coefficient (KP) and high permeation barrier for this reference compound. Nevertheless, favorable interactions are established with the membrane leading to moderately long residence times. While coordination of one inner-sphere water molecule is maintained for the membrane-associated chelate, the physical-chemical attributes of [Gd(DOTA)]- as a MRI contrast agent are affected. Namely, increases in the rotational correlation times and in the residence time of the inner-sphere water are observed, with the former expected to significantly increase the water proton relaxivity. This work establishes a reference framework for the use of simulations to guide the rational design of new contrast agents with improved relaxivity and bioavailability and for the development of liposome-based formulations for use as imaging probes or theranostic agents.

Local Structure, Structural, Vibrational, and Optical Properties of Natural Zircon

Structural properties of Indian metamict single zircon crystals are studied by comparing their properties with those of synthetic zircon synthesized via solid‐state reaction method, which serves as the standard. X‐Ray diffraction (XRD) data reveal changes in lattice parameters and the presence of strain, metamictization, etc. It is found that the degree of crystallinity is ≈63.8% indicating the simultaneous presence of crystalline and disordered regions. These changes are likely due to the presence of several radioactive/nonradioactive elements. The presence of such elements is observed and the sample composition is analyzed through total reflection X‐Ray fluorescence. XRD crystallographic data are further utilized as input for analyzing X‐Ray absorption spectroscopy data recorded around Zr central absorbing atom. X‐Ray absorption near‐edge structure shows slight modification in the white line feature and some disorder compared to the synthetic one. Reduced coordination number observed from extended X‐Ray absorption fine structure suggests the presence of disorder in local structure. Micro‐Raman spectroscopy indicates that crystalline behavior varies across different locations, suggesting that the sample has undergone varying degrees of metamictization, confirming a nonuniform distribution of elements. The work documents and analyses structural evolution within isolated silica tetrahedron network in association of Zr4+ cation as a function of self‐irradiation and recovery over millions of years and correlating the same with optical properties.

Sex differences in cholinergic signaling affect functional outcomes for theta-gamma coordination in hippocampal subcircuits following experimental febrile status epilepticus.

Sex determines cognitive outcome in animal models of early life seizure, where males exhibit impaired hippocampal-dependent learning and memory compared with females. The physiological underpinnings of this sex effect are unclear. Cholinergic signaling is essential for the generation of hippocampal oscillations, and supplementation of cholinergic precursors prior to status epilepticus in immature male rats prevents subsequent memory deficits. We hypothesized that there are sex differences in acetylcholine circuits and their response to experimental febrile status epilepticus (eFSE). eFSE was induced in male and female rat pups. We transversed the hippocampus of postnatal day >60 control (CTL) and eFSE rats with a 64-channel laminar silicon probe to assay cholinergic-dependent theta oscillations under urethane anesthesia. Local field potential properties were compared during (1) baseline sensory stimulation, (2) pharmacological stimulation via acetylcholine reuptake blockade, and (3) sensory stimulation after muscarinic acetylcholine receptor block (atropine). In all groups, a baseline tail pinch could elicit theta oscillations via corticohippocampal synaptic input. Following atropine, a tail pinch response could no longer be elicited in CTL male, CTL female, or eFSE female rats. In contrast, induced slow theta power in eFSE males after atropine was not decreased to spontaneous levels. Analysis of oscillation bandwidths revealed sex differences in acetylcholine modulation of theta frequency and slow gamma frequency and power. This study also identified significant effects of both sex and eFSE on baseline theta-gamma comodulation, indicating a loss of coupling in eFSE males and a potential gain of function in eFSE females. There are differences in cholinergic modulation of theta and gamma signal coordination between male and female rats. These differences may underlie worse cognitive outcomes in males following eFSE. Promoting the efficacy of muscarinic acetylcholine signaling prior to or following early life seizures could elucidate a mechanism for the temporal discoordination of neural signals within and between hippocampus and neocortex and provide a novel therapeutic approach for improving cognitive outcomes.

Strong Raman enhancement in structured colloids: localization of light

Raman spectroscopy is a powerful technique for studying the interaction between light and matter. Here we show a significant enhancement of Raman emission over a broad range of pumping wavelengths from strongly scattering media comprising spatially correlated photonic structures of core–shell TiO2@Silica scatterers mixed with silica nanoparticles and suspended in ethanol. Long-range Coulomb interactions between nanoparticles inside these photonic colloidal structures induce a correlation in the scatterers’ positions (TiO2@Silica), affecting local and global photonic properties. The anomalous enhancement in Raman signal increases as the scattering strength is increased (through either scatterer concentration or pumping wavelength); however, the signal strength continues to behave linearly with excitation power, ruling out classical nonlinear and interferential phenomena. These observations may indicate strong photon correlation in strongly localized electromagnetic modes, inducing successive photon interactions with the atoms or molecules. Aside from the fundamental relevance to understanding measurable properties in this regime of strongly localized electromagnetic modes, our demonstration of strongly enhanced Raman emission over a broad range of pumping wavelengths provides new opportunities for the development of advanced photonic materials and devices.