Localized States Research Articles

Electron-Spin Relaxation in Boron-Doped Graphene Nanoribbons.

Boron-doped graphene nanoribbons are promising platforms for developing organic materials with magnetic properties. Boron dopants can be used to create localized magnetic states in nanoribbons with tunable interactions. Controlling the coherence times of these magnetic states is the very first step in designing materials for quantum computation or information storage. In this work, we address the connection between the relaxation time and the position of the dopants for a series of boron-doped graphene nanofragments. We combine Redfield theory and ab initio calculations of magnetic properties to unveil the mechanism that governs spin relaxation in solution. We demonstrate that relaxation times can be in the order of 1 ms for the selected graphene nanofragments. A detailed analysis of the relaxation mechanism reveals that the spin decoherence is fundamentally driven by fluctuations of the spin-orbit coupling, and the hyperfine interaction facilitated by the thermal motion of the graphene nanofragments. The close connection between relaxation time, hyperfine interaction and the spin-orbit coupling offers the perspective of designing attractive materials with long-lived spin states.

Regulating the Local Spin States in Spinel Oxides to Promote the Activity of Li-CO2 Batteries.

Due to the high energy barrier, slow reaction kinetics, and complex reaction environments of Li-CO2 batteries, the development of durable and efficient catalysts is essential. Transition metal oxides are promising for their availability, stability, and 3d electronic features, with spin states playing an important role in CO2 activation. In this study, the local spin states are regulated by incorporating Ni into Co3O4 and its impact on activity in Li-CO2 batteries is explored. The results show that Ni atoms with high spin states in Ni0.1Co2.9O4 facilitate electron transfer from the catalyst to the unoccupied orbitals of CO2, providing sufficient active sites for the nucleation and growth of small Li2CO3 crystals. These small crystals have a low decomposition barrier, leading to improved battery efficiency. Therefore, Ni0.1Co2.9O4 shows superior catalytic performance with an overpotential of 0.72V and an energy efficiency of ≈70% after 500h. This work provides insights into the relationship between spin states and CO2 reactions, highlighting a promising avenue for developing high-performance metal-CO2 batteries.

A class of stable nonlinear non-Hermitian skin modes

Abstract The non-Hermitian skin effect (NHSE) is a well-known phenomenon in open topological systems that causes a large number of eigenstates to become localized at the boundary. Although many aspects of its theory have been investigated in linear systems, this phenomenon remains novel in nonlinear models. In the first step of this paper, we look at the conditions for the presence of quasi-skin modes in a semi-infinite, one-dimensional, nonlinear, nonreciprocal lattice. In the following phase, we explore the survival time of the quasi-skin mode in a finite nonlinear lattice with open edges. We study the dependency of the survival time on the system's parameters and demonstrate how the nonreciprocity of the system affects the survival time. This study introduces a method for achieving a stable localized state in a nonlinear finite lattice.

Vibrational Relaxation Completes the Excitation Energy Transfer and Localization of Vibronic Excitons in Allophycocyanin α84-β84.

Phycobilisomes are light-harvesting complexes that play a key role in photosynthesis in cyanobacteria, which generate more than 40% of the world's oxygen. The near-unity excitation energy transfer efficiency from phycobilisomes to photosystems highlights its importance in understanding efficient energy transfer processes. Spectroscopic studies have shown that the 280 fs rapid excitonic downhill energy transfer within the α84-β84 chromophore dimer in allophycocyanin (APC), a subunit of phycobilisomes, is crucial to this efficiency. However, the role of strong chromophore-protein interactions and vibrational relaxation requires further exploration to fully explain this efficient downhill energy transfer. A theory is required that adequately describes exciton dynamics in an intermediate region while also incorporating vibrational relaxation mediated by protein bath modes. In this work, we incorporate vibrational relaxation into modified Redfield theory by introducing coupling fluctuation. We holistically simulate the rapid excitation energy transfer process of the α84-β84 chromophore dimer in APC and successfully model the recently observed rapid energy capture. We find that vibrational relaxation dictates capture of excitons by the localized state of the β84 chromophore. The calculated rate shows excellent agreement with previous ultrafast spectroscopic experiments. Our results show that the inclusion of vibrational relaxation is essential for systems that utilize vibronic coupling to enhance energy transfer and capture. Consequently, incorporating vibrational relaxation into Modified Redfield theory shows promise for accurately describing the excitation energy transfer process in other photosynthetic systems.

The physical and virtual presence of the local state and citizens’ life satisfaction in urbanising China

China’s rapid and ongoing urbanisation has led to the expansion of the local state. The state, traditionally exhibited as physical institutions of government, has emerged virtually in recent years based on intricate network infrastructure systems, such as social media platforms. Scholars contend that a strong physical state infrastructure enhances government function and can increase citizens’ life satisfaction; in contrast, the state’s virtual presence is unlikely to exert a substantial independent impact because of its reliance on the state’s physical infrastructure. In this research, we calibrated innovative measures of the state’s physical and virtual presence. Combined with data from the 2018 Urbanisation and Quality of Life Survey conducted in 40 sampling sites undergoing rural–urban transition, we further assessed how the local state’s physical and virtual presence is associated with citizens’ self-reported life satisfaction in the context of China’s national new-type urbanisation. Our results, based on three-level mixed-effects regressions, indicate that the local state’s bricks-and-mortar institutions do not correlate with citizens’ life satisfaction; rather, the establishment of a web-based, cost-effective, transparent, and coordinated virtual presence is associated with a higher level of life satisfaction among citizens. At a time when the Chinese central government emphasises its commitment to ‘people-centred’ urbanisation, the findings offer insight into the strategies that local governments could employ to improve governance quality and enhance citizens’ well-being.

Assessment of multiaxially loaded safety components with uniaxial stress state in fatigue critical sites caused by design

AbstractThe focus of this study, using results obtained with hollow specimens of the alloy Al 2024 T3 (AlCuMg2 T3) with a one‐sided bore, was to determine if, under multiaxial loading, the fatigue strength in a notch with a uniaxial stress state can simply be assessed without the application of any multiaxial strength hypothesis. In the fatigue critical location, the bore edge, only a superimposition of normal stress components, resulting from axial loading or/and torsion, occurs. In the case of out‐of‐phase loading, the resulting local uniaxial stress is even lower than the stress under in‐phase loading and leads to an increase of fatigue life to crack initiation under the non‐proportional loading, which is not observed in the case of multiaxial stressing/straining of the material itself. As the local stress state in the crack initiation site is uniaxial, the application of a multiaxial strength hypothesis, for the failure criterion of crack initiation (l=0.2 mm), is not necessary. Furthermore, the benefit of non‐homogenous stress distributions, which allow locally higher stresses than the levels given by the Woehler‐line for unnotched specimens, was underlined by considering highly‐stressed, material‐volume‐related support factors.

Study of the Stress Distribution and a Calculation Model for the Local Bearing Capacity of Concrete Under Headed Bars

In order to obtain the calculation model for the local bearing capacity of concrete Fl under two headed bars, six pull-out concrete specimens were prepared. The effect of the net distance between two headed bars c on Fl was mainly investigated. The test results show that the local bearing capacity of concrete would first decrease and then increase with the increase in c, and the boundary point of the two stages was c = 40 mm. It is determined that the stress transformation from the local compression state to the axial compression state in the stress distribution model is characterized by the variation rate of the vertical stress under individual headed bars, which would infinitely approach a constant value. The constant value under individual headed bars is used as the limit value. The height of the vertical stress under two headed bars is modified, and then the height of the tensile region of the specimen with different c values is determined. Combined with the experimental phenomena and the results, two stages of calculation models are established, respectively: the integral calculation model and the individual calculation model. The integral calculation model focuses on the interaction of the compression region under two headed bars. The individual calculation model mainly focuses on the interaction of the tensile region under two headed bars. The calculation equations considering the influence of the height of the tensile region are established. Two groups of similar test data regarding the local bearing capacity were collected and verified as the integral calculation model and the individual calculation model. The average value of the ratio between the test value and the calculated value is 1.057 and 1.061, the standard deviation is 0.153 and 0.091, and the coefficient of variation is 0.055 and 0.086. It is proved that the calculation model proposed in this paper has a certain accuracy. It can provide a reference for calculating the local bearing capacity of concrete under multiple headed bars.

Recombination efficiency in c-plane (In,Ga)N/GaN quantum wells: saturation of localisation sites versus Auger–Meitner recombination

Abstract Light emitting diodes based on c-plane (In,Ga)N/GaN quantum wells (QWs) can have >90% emission efficiency at modest current densities but this drops significantly at higher excitation, an effect known as efficiency droop that limits device efficacy at high brightness. Several explanations for this have been proposed including the saturation of carrier localisation sites at high excitation densities, resulting in a greater exposure of carriers to defects and hence a significant increase in the associated non-radiative recombination processes. Here, power- and temperature-dependent photoluminescence spectroscopy of c-plane (In,Ga)N/GaN QWs is used to investigate the relationship between the saturation of localised states and emission efficiency. For the samples studied, we find that the saturation of localised sites broadly coincides with the onset of efficiency droop. However, it is also found that as the localised states saturate with increasing excitation, the relative contribution of defect-associated non-radiative processes to overall recombination decreases rather than increases. Based on these observations and on modelling of recombination processes in the QW, it is concluded that the saturation of localised states does not significantly contribute to the reduction in emission efficiency at high excitation. Our studies rather suggest that defect-related non-radiative recombination is out-competed by radiative and Auger–Meitner recombination at the carrier densities required for saturation.

On gravity implication in the wavefunction collapse

Abstract Inspired by an ontic view of the wavefunction in quantum mechanics and motivated
by the universal e¤ect of gravity, we discuss a possible gravity implication in the reduc-
tion scenario of the quantum state. Concretely, we investigate the stability of the spatial
superposition of a massive quantum state under the gravity e¤ect. In this context, we
argue that the stability of the spatially superposed state jYi =
nå
i=1
ai jyii, ai 2 C, depends
on its gravitational self-energy UG
Y originating from the effective mass density distribution
r m (x) through the spatially localized eigenstates jyii. We reveal that the gravitational
self-interaction between the di¤erent spacetime curvatures jGii created by the eigenstate
e¤ective masses m y leads to the reduction of the superposed state to one of the possible
localized states jyki jGki. Among others, we discuss such a gravity-driven state reduc-
tion. Then, we approach the corresponding collapse time t Collapse Y and the induced effective electric current I Y in the case of a charged state, as well as the possible detection aspects.

Mapping the topology-localization phase diagram with quasiperiodic disorder using a programmable superconducting simulator

We explore a topology-localization phase diagram by simulating a one-dimensional Su-Schrieffer-Heeger model with quasiperiodic disorder using a programmable superconducting simulator. We experimentally map out and identify various trivial and topological phases with extended, critical, and localized bulk states. We find that with increasing disorder strength, some extended states can be first replaced by localized states and then by critical states before the system finally becomes fully localized. The critical states exhibit typical features such as multifractality and self-similarity, which lead to surprisingly rich phases with different types of mobility edges and scaling behaviors on the phase boundaries. Our results shed light on the investigation of the topological and localization phenomena in condensed-matter physics. Published by the American Physical Society 2024

INNOVATING URBAN CHINA: The Rise of the Local Venture State and the Making of New Entrepreneurial Spaces

AbstractIn this article we centralize the analytic of the local venture state (LVS) to offer a novel framework for investigating China's new urban entrepreneurialism, which emerged after the 2008 global financial crisis. As a spatiotemporally specific response to the crisis, the LVS goes beyond GDP‐driven developmentalism, seeking to simultaneously promote economic development, indigenous innovation and social equity using a variety of financialized policy instruments. Ethnographic case studies of new entrepreneurial spaces in Beijing's Zhongguancun area situate the LVS at the interface between Zhongguancun's urban space and China's innovation system. They reveal the rationalities behind the rise of the LVS and discrepancies among policy intentions, the implementation thereof and actual local results. Underlying the mixed results of the LVS, we argue, is the complicated power dynamics within the LVS and a fundamental contradiction between the dynamics of technological innovation and those of wealth redistribution. In our examination of China's LVS vis‐à‐vis global struggles to tackle the protracted economic crisis and achieve a more socially inclusive model of urban development, we stress the need to theorize urban entrepreneurialism from the global East with the aim of enriching the literature of urban China and of variegated urban entrepreneurialism.

Quasicrystalline 30° twisted bilayer graphene: fractal patterns and electronic localization properties

The recently synthesized 30° twisted bilayer graphene (30°-TBG) systems are unique quasicrystal systems possessing dodecagonal symmetry with graphene’s relativistic properties. We employ a real-space numerical atomistic framework that respects both the dodecagonal rotational symmetry and the massless Dirac nature of the electrons to describe the local density of states of the system. The approach we employ is very efficiency for systems with very large unit cells and does not rely on periodic boundary conditions. These features allow us to address a broad class of multilayer two-dimensional crystal with incommensurate configurations, particularly TBGs. Our results reveal that the 30°-TBG electronic spectrum consist of extended states together with a set of localized wave functions. The localized states exhibit fractal patterns consistent with the quasicrystal tiling.

Wave Function Localization Reduces the Bandgap of Disordered Double Perovskite Cs2AgBiBr6.

Double perovskite Cs2AgBiBr6 is a promising alternative to lead-based perovskites with excellent stability and attractive optoelectronic properties. However, a relatively large bandgap severely limits its performance in many applications such as solar cells and photodetectors. It has been reported that a random distribution of Ag and Bi atoms in Cs2AgBiBr6 effectively reduces its bandgap without introducing dopants or impurities, while the mechanism remains unclear. Here, using density functional theory calculations, we demonstrate that the Ag-Bi disorder in Cs2AgBiBr6 generates localized electronic states as band edges to regulate the bandgap. The disordered structures segregate Ag and Bi atoms in the lattice, and the formed homoatomic clusters lead to wave function localization. Moreover, the bandgap decrease exhibits a non-monotonic dependence on the degree of disorder. Our results are comparable with experimental observations and provide crucial insights into understanding the order-disorder transition in double perovskites.

THE PERCEIVED EFFECT OF RURAL TRANSPORTATION ON AGRICULTURAL PRODUCE IN IGBARA-OKE, NIGERIA

This study examines the perceived effects of rural transportation on agriculture produce in Igbara-Oke, Ifedore Local Government area Ondo State Nigeria. Case study research design was adopted while both primary and secondary data were utilized. Using a purposive multi-stage sampling technique, the total populations of farmers (2,139) at Igbara-oke, was determined and a 15% sample size was taken. Questionnaire was administered to 337 respondents. Focus Group Discussion (FGD) were held across the study area. Both descriptive and inferential statistics were used to analyzed the data at p value ≤ 0.05, while the qualitative data were content analyzed. Based on the ranking of the effect of transportation on agriculture, spoilage of farm produce was the highest (25.4%). Chi-square revealed a significant difference between the scale of agricultural engagement and transportation accessibility to farm locations (0.258). Transportation had a significant negative effect on agricultural produce, therefore, there should be rehabilitation of more rural feeder roads from farmlands to the markets is recommended.

Variable‐Range Hopping Conduction in Amorphous, Non‐Stoichiometric Gallium Oxide

AbstractAmorphous, non‐stoichiometric gallium oxide (a‐GaOx, x < 1.5) is a promising material for many electronic devices, such as resistive switching memories, neuromorphic circuits and photodetectors. So far, all respective measurements are interpreted with the explicit or implicit assumption of n‐type band transport above the conduction band mobility edge. In this study, the experimental and theoretical results consistently show for the first time that for an O/Ga ratio x of 0.8 to 1.0 the dominating electron transport mechanism is, however, variable‐range hopping (VRH) between localized states, even at room temperature and above. The measured conductivity exhibits the characteristic exponential temperature dependence on T−1/4, in remarkable agreement with Mott's iconic law for VRH. Localized states near the Fermi level are confirmed by photoelectron spectroscopy and density of states (DOS) calculations. The experimental conductivity data is reproduced quantitatively by kinetic Monte Carlo (KMC) simulations of the VRH mechanism, based on the ab‐initio DOS. High electric field strengths F cause elevated electron temperatures and an exponential increase of the conductivity with F1/2. Novel results concerning surface oxidation, magnetoresistance, Hall effect, thermopower and electron diffusion are also reported. The findings lead to a new understanding of a‐GaOx devices, also with regard to metal|a‐GaOx Schottky barriers.

Ant logic and necrolocutors

As environmental research increasingly values and foregrounds traditional knowledge in a reinvigorated participatory turn, many of the original problematics and harms re-emerge through ostensible collaborations with knowledge-holders. These issues are not just instances of ethical oversight; they are the result of ant logic: narrow, spatialized conceptualizations of power, knowledge, and death as contained and fixed within bodies and space and preoccupations with visibility that produces ontological conceptions of local communities, traditional knowledge-holders, state actors, and neoliberal forces. This article unwinds the tight Foucauldian grip with which environmental social sciences are held to reveal power, knowledge, and death as vibrant, immaterial actors and explores the role of ant logic as an actor itself. In doing so, another key environmental actor is uncovered, one who leverages the death-centric form of articulation to define power and knowledge: the necrolocutor.

Planned stitching, practical suturing: assembling community voices and mobilisation across difference in Johannesburg’s corridors of freedom

The City of Johannesburg’s Corridors of Freedom (CoF), launched in 2013, were intended to cut across the economically and racially divided city using infrastructure and interventions in the built environment around new transport nodes. Undertaken in haste for political reasons and projected to be delivered as swiftly as possible, those driving this mega project oversaw substantial consultation exercises, but provided relatively few spaces for direct engagement to shape the project. This paper presents the experiences of a team of engaged-researchers, a long-standing NGO in partnership with University-based scholars jointly investigating the CoF development process. Interested in the ways in which the CoF initiative sought to ‘stitch’ the city together, our contribution to the project was to engage with different communities, clarify their different experiences with participation in the Corridors development and explore the possibility of collaboration across these different communities. Using the conceptual framework of stitching and suturing, the paper, in two parts, interrogates the roles that engaged partners can have in complex and diverse communities and our ability to support engagement. We reveal the limitations of engaged research when faced with political and institutional cycles that do not synchronise with the research projects, and point to the cleavages and disruptions that result when the local state does not systematically incorporate the needs and lived realities of its residents.

Uncovering bound states in the continuum in InSb nanowire networks

Bound states in the continuum (BICs) are exotic, localized states even though their energy lies in the continuum spectra. Since its discovery in 1929, the quest to unveil these exotic states in charge transport experiments remains an active pursuit in condensed matter physics. Here, we study charge transport in InSb nanowire networks in the ballistic regime and subject to a perpendicular magnetic field as ideal candidates to observe and control the appearance of BICs. We find that BICs reveal themselves as distinctive resonances or antiresonances in the conductance by varying the applied magnetic field and the Fermi energy. We systematically consider different lead connections in hashtag-like nanowire networks, finding the optimal configuration that enhances the features associated with the emergence of BICs. Finally, the investigation focuses on the effect of the Rashba spin–orbit interaction of InSb on the occurrence of BICs in nanowire networks. While the interaction generally plays a detrimental role in the signatures of the BICs in the conductance of the nanowire networks, it opens the possibility to operate these nanostructures as spin filters for spintronics. We believe that this work could pave the way for the unambiguous observation of BICs in charge transport experiments and for the development of advanced spintronic devices.

Disordered Heisenberg XYZ magnetic chains with exponential correlations: Localization and quantum state transfer

Our study investigates the Quantum State Transfer Protocol within a one-dimensional quantum Heisenberg spin chain model that features exponentially correlated disorder in the spin coupling distribution. We conducted extensive numerical simulations to explore how varying degrees of correlation impact the transfer of quantum states through this model of a quantum channel. Our results demonstrate that the extent of correlation significantly influences quantum communication along the channel. Specifically, we observed that in the strongly correlated regime, quantum communication remains largely unaffected even in large systems. These findings are interpreted in the context of the localization properties inherent to the disordered channel.

Robust and energy-efficient RPL optimization algorithm with scalable deep reinforcement learning for IIoT

The increasing complexity and quantity of the Industrial Internet of Things (IIoT) pose new challenges to the traditional routing protocol for low-power and lossy networks (RPL) in terms of dynamic management, data transmission reliability, and energy efficiency optimization. This paper proposes a scalable deep reinforcement learning (DRL) algorithm with a multi-attention actor double critic model for routing optimization (MADC) to meet the requirements of IIoT for efficient and intelligent routing decisions while improving data transmission reliability and energy efficiency. Specifically, MADC employs the centralized training and decentralized execution (CTDE) learning paradigm to decouple the model’s training and inference tasks, which reduces the difficulty and computational cost of model learning and improves the training efficiency. In addition, a lightweight actor network based on multi-scale convolutional attention mechanism is designed in MADC, which can provide intelligent and real-time decision-making capabilities for resource-constrained nodes with low computational and storage complexities. Moreover, a scalable critic network utilizing multiple attention mechanisms is proposed. It is not only suitable for dynamic and changing network environments but also can more comprehensively and accurately evaluate local observation states, providing more accurate and efficient guidance for model optimization. Furthermore, MADC incorporates a double critic network architecture to mitigate potential overestimation issues during training, thereby ensuring the model’s robustness and reliability. Simulation results demonstrate that MADC outperforms existing RPL optimization algorithms in terms of energy efficiency, data transmission reliability, and adaptability.