Momentum Space Research Articles

Unveiling diverse coordination-defined electronic structures of reconstructed anatase TiO2(001)-(1 × 4) surface

Transition metal oxides (TMOs) exhibit fascinating physicochemical properties, which originate from the diverse coordination structures between the transition metal and oxygen atoms. Accurate determination of such structure-property relationships of TMOs requires to correlate structural and electronic properties by capturing the global parameters with high resolution in energy, real, and momentum spaces, but it is still challenging. Herein, we report the determination of characteristic electronic structures from diverse coordination environments on the prototypical anatase-TiO2(001) with (1 × 4) reconstruction, using high-resolution angle-resolved photoemission spectroscopy and scanning tunneling microscopy/atomic force microscopy, in combination with density functional theory calculation. We unveil that the shifted positions of O 2s and 2p levels and the gap-state Ti 3p levels can sensitively characterize the O and Ti coordination environments in the (1 × 4) reconstructed surface, which show distinguishable features from those in bulk. Our findings provide a paradigm to interrogate the intricate reconstruction-relevant properties in many other TMO surfaces.

QM, Fukui function, molecular docking, molecular dynamics investigation on Human Estrogen Receptor (HER) with Clioquinol

Clioquinol is an antifungal medication that is used to treat skin diseases such as dermatitis, foot inflammation, sports itch, and ringworm The electron localization and delocalization indices in position space are further quantum chemical instruments that are commonly utilized to understand complex chemical bonding conditions in molecules and solids. LOL is carried out and it's the three-dimensional function of kinetic energy density, and its interpretation is based on the fact that is small in the bonding region. Fukui functions are chemical descriptors that can be used to explain how systems react to electron movement. Molecular docking determines the ligand binding affinity with protein receptors by utilizing the atomic-level coordination processes of molecular interactions that occur between them. A docking study was carried out for Human Estrogen Receptors with the ligand Cloquinol. Through the properties of the molecules, the ligand behavior is analyzed by using Molecular Dynamics. Absorption, Distribution, Metabolism, Excretion, and Toxicity of chemicals a crucial components in the discovery and development of novel medications. A good drug candidate should exhibit the right therapeutic dose, ADMET properties, and adequate efficacy against the therapeutic target.

Observation of accurately designed bound states in the continuum in momentum space

Bound states in the continuum (BICs) in artificial photonic structures have received considerable attention since they offer unique methods for the extreme field localization and enhancement of light-matter interactions. Usually, the symmetry-protected BICs are located at high symmetric points, while the positions of accidental BICs achieved by tuning the parameters will appear at some points in momentum space. Up to now, to accurately design the position of the accidental BIC in momentum space is still a challenge. Here, we theoretically and experimentally demonstrate an accurately designed accidental BIC in a two-coupled-oscillator system consisting of bilayer gratings, where the optical response of each grating can be described by a single resonator model. By changing the interlayer distance between the gratings to tune the propagation phase shift related to wave vectors, the position of the accidental BIC can be arbitrarily controlled in momentum space. Moreover, we present a general method and rigorous numerical analyses for extracting the polarization vector fields to observe the topological properties of BICs from the polarization-resolved transmission spectra. Finally, an application of the highly efficient second harmonic generation assisted by quasi-BIC is demonstrated. Our work provides a straightforward strategy for manipulating BICs and studying their topological properties in momentum space.

Observation of Subdiffusive Dynamic Scaling in a Driven and Disordered Bose Gas.

We explore the dynamics of a tuneable box-trapped Bose gas under strong periodic forcing in the presence of weak disorder. In absence of interparticle interactions, the interplay of the drive and disorder results in an isotropic nonthermal momentum distribution that shows subdiffusive dynamic scaling, with sublinear energy growth and the universal scaling function captured well by a compressed exponential. We explain that this subdiffusion in momentum space can naturally be understood as a random walk in energy space. We also experimentally show that for increasing interaction strength, the gas behavior smoothly crosses over to wave turbulence characterized by a power-law momentum distribution, which opens new possibilities for systematic studies of the interplay of disorder and interactions in driven quantum systems.

Study of the influence of additive manufacturing applicable surface treatment methods on mechanical part properties for use in aerospace applications

The adequate assessment of the quality of parts produced by additive manufacturing is crucial for their application in the aviation industry. Therefore, parameters of the manufacturing process, which influence the part quality, have to be identified and quantified to reveal existing correlations. Besides, it is essential to gain an overall understanding of the influence of each step in the additive manufacturing chain, including also post-process treatments and inspection methods, on the data, which is used to develop a statement about the additively manufactured parts’ quality. The present study aims on forming such a comprehensive picture. For this purpose, 120 test specimens from AlSi10Mg were manufactured on an EOS M 290. Four different surface treatments (centrifugal blasting, barrel finishing, abrasive flow machining and turning & polishing) were applied to the specimens and compared to the as-built condition regarding the resulting material properties. The relative density, surface roughness, surface hardness, ultimate tensile strength, yield strength, Young’s modulus and the fatigue properties were determined and analysed especially for correlations with the surface treatment and specimen positions in the build space. The surface roughness, fatigue properties and static tensile properties showed to be dependent on the applied surface treatment, while fewer correlations could be found regarding the surface hardness and relative part density. No clear indication was found relating one of the mentioned properties to certain areas in the build space.

Mode‐Interference‐Induced Chiral Exceptional Points in Momentum Space

AbstractNon‐Hermitian metasurfaces with chiral exceptional points (EPs) in their scattering matrices have garnered significant attention due to their potential for optical polarization manipulation and wavefront control. However, existing approaches predominantly operate under normal incidence conditions, limiting their application in the manipulation of chiral EPs in momentum space. Here, the wavelength‐fixed manipulation of the chiral EPs across a wide‐range momentum space using a polyatomic metasurface is realized, which is attributed to the effective modulation of the collective interference of guided‐mode resonances excited by oblique transverse magnetic (TM) and transverse electric (TE) illuminations. Further, both theoretical and experimental analyses are conducted to explore the potential applications of the proposed design in the wavevector‐ and spin‐selective manipulation of reflection intensity and optical encryption. This work provides a straightforward method to realize and manipulate chiral EPs in momentum space at a fixed operational wavelength, paving the way for designing polarization‐selective and wavevector‐selective devices.

Symplectic groupoids and Poisson electrodynamics

We develop a geometric approach to Poisson electrodynamics, that is, the semi-classical limit of noncommutative U(1) gauge theory. Our framework is based on an integrating symplectic groupoid for the underlying Poisson brackets, which we interpret as the classical phase space of a point particle on noncommutative spacetime. In this picture gauge fields arise as bisections of the symplectic groupoid while gauge transformations are parameterized by Lagrangian bisections. We provide a geometric construction of a gauge invariant action functional which minimally couples a dynamical charged particle to a background electromagnetic field. Our constructions are elucidated by several explicit examples, demonstrating the appearances of curved and even compact momentum spaces, the interplay between gauge transformations and spacetime diffeomorphisms, as well as emergent gravity phenomena.

Berry curvature inside a PT -symmetry protected exceptional surface

A three-dimensional non-Hermitian Hamiltonian with parity-time symmetry can exhibit a closed exceptional surface (EP surface) in momentum space, which is a non-Hermitian deformation of the degeneracy line. Since the degeneracy line lacks an internal space, the distributions of Berry curvature inside the EP surface become particularly intriguing. This paper studies the distributions taking a toruslike EP surface as an example. In a meridian cross section, the Berry connection exhibits a vortexlike field with only angular components, while the Berry curvature is perpendicular to this cross section; in a equatorial cross section, the Berry curvature forms a closed curve surrounding the central genus. Both Berry connection and curvature converge along the coplanar axis and diverge at the surface. We find the Berry flux depends on the radius of the integration region and is not quantized inside the EP torus. Approaching the surface, the Berry flux tends to infinity and the dynamical phase oscillates violently. We point out that the streamlines of Berry curvature can be used to estimate the zero or nonzero Berry flux. We generalize the above patterns to the case of EP surfaces with complex shapes and present a proposal of realizing the EP surface in an electrical circuit. Our research outcomes enhance the comprehension of EP surfaces and the topological characteristics of non-Hermitian systems with parity-time (PT) symmetry. Published by the American Physical Society 2024

Momentum space separation of quantum path interferences between photons and surface plasmon polaritons in nonlinear photoemission microscopy

Abstract Quantum path interferences occur whenever multiple equivalent and coherent transitions result in a common final state. Such interferences strongly modify the probability of a particle to be found in that final state, a key concept of quantum coherent control. When multiple nonlinear and energy-degenerate transitions occur in a system, the multitude of possible quantum path interferences is hard to disentangle experimentally. Here, we analyze quantum path interferences during the nonlinear emission of electrons from hybrid plasmonic and photonic fields using time-resolved photoemission electron microscopy. We experimentally distinguish quantum path interferences by exploiting the momentum difference between photons and plasmons and through balancing the relative contributions of their respective fields. Our work provides a fundamental understanding of the nonlinear photon–plasmon–electron interaction. Distinguishing emission processes in momentum space, as introduced here, could allow nano-optical quantum-correlations to be studied without destroying the quantum path interferences.

Ukraine-NATO: Problems and Prospects of Partnership

The article contains an overview of the evolution of Ukraine-NATO relations from the beginning of our state’s independence to the present. The author made an attempt to identify and characterize the main periods of the formation of Ukraine-NATO relations, to identify the key problems of partnership development. It is noted that at the beginning of independence, Ukraine chose a neutral and non-aligned status, and then declared multi-vectorism as the basis of foreign security policy, which was a historically determined necessity in the transition period. At that time, Ukraine remained in the field of interests of Russia, which sought to restore its position in the post-Soviet space, and therefore did not have the opportunity to fully integrate into the Euro-Atlantic structures.
 Due to the difficult geopolitical situation, Ukraine was forced to maneuver between the East and the West in order to establish itself in the international field and take its place in the European security architecture. In the 1990s, Ukraine-NATO relations developed quite briskly, but not enough for Ukraine to become a NATO member. However, Ukraine managed to gain the status of a special partner, which subsequently contributed to the deepening of bilateral relations.
 In the 2000s, Ukraine-NATO relations first intensified, and after Yanukovych came to power, Ukraine’s Euro-Atlantic integration was suspended. The situation changed after the Revolution of Dignity, when pro-European democratic forces came to power. Further policy is aimed at deepening Ukraine’s relations with the Alliance. Ukraine has finally decided on its course, but the necessary conditions must be met for successful integration. Also, for its part, NATO should conduct a more targeted policy regardless of Russia, which is not as strong as it has created an image of itself through propaganda. Ukraine receives the undisputed support of the Alliance, but, unfortunately, this is not enough to end the war and restore territorial integrity. Ukraine’s accession to NATO would guarantee Ukraine’s security on the one hand, and strengthen the Alliance’s values on the other. Therefore, NATO needs more determination in Ukraine’s accession to the Alliance.

Speech following Le Fort I Maxillary Advancement in Cleft Maxillary hypoplasia - an objective and subjective outcome analysis.

To objectively evaluate the effect of maxillary advancement on speech and VPI using video-fluoroscopy (VFS), direct nasoendoscopy, and speech evaluation and subjectively assess patients and their peer's perception regarding their speech outcome. 27 cleft patients who underwent Lefort 1 maxillary advancement were divided into 2 groups- Group A with 4-7mm of advancement and Group B with 8-13mm advancement. VFS in lateral view, nasoendoscopy, and speech recordings were performed pre and 6 months postoperatively. VFS assessed the relative position of velum in relation to the pharyngeal wall, speech was evaluated for changes in nasal emission, resonance, and articulation along with nasal endoscopy to assess the overall function of the velopharyngeal valve. Subjective speech evaluation was done with a Patient-Reported Outcome Measure [PROM] questionnaire. As per VFS, for every 1mm maxillary advancement, the velopharyngeal gap at rest increased by 1.75mm in group A and 1.58mm in group B. The compensatory changes in group B were more pronounced. Post-operative VFS showed velar closure remained the same as preoperative closure in 86.7%, and worsened in 13.3% in group A whereas it remained unchanged in 66.7%, improved in 25%, and worsened in 8.3% in group B. In nasoendoscopy, the closure pattern showed no change in 86.6%, improved in 6.7%, and deteriorated in 8.3% in group A while there was no change in 83.4%, improved in 8.3%, and deteriorated in 8.3% in group B. Dental and labiodental articulation statistically improved [p < 0.05] after surgery. PROM reported 85.7% of patients with improved speech, 82.1% improved sound quality along with 89.3% improvement in articulation. The primary cause for functional impairment and poor aesthetics in cleft deformity is the maxillary hypoplasia and therefore, should be the focus during correction. The pre-operative VP status or the amount of maxillary advancement could not predict the postoperative VP status. Maxillary advancement over 10mm did not seem to significantly affect the final VP status. Articulation improves due to increased tongue space and favorable dental segment positioning. Mild to moderate immediate post op changes in nasality improves or even reverts to their preoperative status in the majority of the cases in about six months.

Reconstructing the baryonic acoustic oscillations in the presence of photo-z uncertainties

ABSTRACT The reconstruction method has been widely employed to improve the baryon acoustic oscillations (BAO) measurement in spectroscopic survey data analysis. In this study, we explore the reconstruction of the BAO signals in the realm of photometric data. By adapting the Zel’dovich reconstruction technique, we develop a formalism to reconstruct the transverse BAO in the presence of photo-z uncertainties under the plane-parallel approximation. We access the performance of the BAO reconstruction through comoving N-body simulations. The transverse reconstruction potential can be derived by solving a 2D potential equation, with the surface density and the radial potential contribution acting as the source terms. The solution is predominantly determined by the surface density. As is evident in dense samples, such as the matter field, the transverse BAO reconstruction can enhance both the strength of the BAO signals and their cross correlation with the initial conditions. At z = 0, the cross-correlation is increased by a factor of 1.2 at $k_\perp = 0.2 \, \mathrm{Mpc}^{-1}h$ and 1.4 at $k_\perp = 0.3 \, \mathrm{Mpc}^{-1}h$, respectively. We contrast the 2D potential results with the 3D Poisson equation solution, wherein we directly solve the potential equation using the position in photo-z space, and find good agreement. Additionally, we examine the impact of various conditions, such as the smoothing scales and the level of photo-z uncertainties, on the reconstruction results. We envision the straightforward application of this method to survey data.

How boundaries work in higher education: an ethnographic account of Ph.D. students’ identity formation

ABSTRACT In this article, I argue that Ph.D. students’ construction of academic identity depends on the boundary-making process in academia. The presented ethnographic account of Ph.D. students at one of the research-intensive universities in Turkey is based on 15 months of fieldwork, including observations and 21 in-depth interviews with PhD students. This ethnographic study employs a two-headed approach: institution-based boundary-formation and Ph.D. students’ socialisation into academic habitus. The findings reveal that, first, the identity building process in doctoral education is constituted by the practices of institution-based boundaries, which enable Ph.D. students to accumulate symbolic and social capital; second, the practices of distinction through socialisation into academic life are developed, embodied, habituated, and integrated to academic identity and academic life as part of a habitus of doctoral education; third, identity formation is a social space of relational positions characterised by the supervisor-enforced social order, rooted in both authority and domination.

Niche overlap with an exotic competitor mediates the abundant niche‐centre relationship for a native lady beetle

AbstractAimThe abundant niche‐centre hypothesis has been used to describe patterns of species abundance relative to position in ecological niche space. Such relationships, however, are inconsistently recovered and may be obscured due to non‐equilibrium distributions, such as those caused novel interactions with exotic species. Here, we explore patterns of fitness for the nine‐spotted lady (Coccinella novemnotata) following the introduction of an exotic competitor, the seven‐spotted lady beetle (C. septempunctata). We examine how niche overlap between species may be causing a range reduction for C. novemnotata through a modified abundant niche‐centre relationship.LocationNorth America.MethodsWe applied a time‐oriented view of the abundant niche‐centre relationship for C. novemnotata, both before and after the introduction of C. septempunctata. We tested for both niche overlap and correlation between C. novemnotata body size (i.e. fitness) and the distance from its niche centroid relative to the invasion status of C. septempunctata.ResultsThe current niche space currently occupied by C. novemnotata is equivalent to its historic niche but has shifted to avoid overlap with C. septempunctata. A historic abundant niche‐centre relationship with larger individuals closer to the niche centroid was observed for C. novemnotata. However, this pattern changed to have smaller beetles near the niche centroid when the current distribution was considered.Main ConclusionsFitness patterns displayed by C. novemnotata are effectively described by the abundant niche‐centre hypothesis. However, this relationship was modified with the introduction of C. septempunctata. Coccinella novemnotata is not excluded from previously suitable areas that correspond to niche space nearest to its niche centroid. Abundant niche‐centre relationships may provide strong predictions of species' fitness across a species geographic range; however, these relationships may be obscured by novel pressures resulting in non‐equilibrium states.

A precise localization algorithm for unmanned aerial vehicles integrating visual-internal odometry and cartographer

Accurate positioning in space is an important foundation for ensuring the stability of autonomous flight and successful mapping and navigation of unmanned aerial vehicles (UAVs). At present, the SLAM algorithm based on the Cartographer algorithm for real-time positioning and mapping is widely used in fields such as robot navigation and autonomous driving. However, in the context of UAV applications, this algorithm has a high dependence on the amount of point cloud information in the surrounding environment, and cannot achieve precise positioning in open spaces with insufficient lighting and fewer feature points, resulting in significant mapping errors. In order to solve the problem of low positioning estimation accuracy in the Cartographer algorithm in above environment, this paper proposes a precise positioning algorithm for UAVs that integrates VIO and Cartographer. This algorithm can continuously output more accurate position estimation information during UAV flight, compensating for the problem of inaccurate position estimation caused by partial feature loss or coordinate system drift in point clouds. In addition, this algorithm ensures navigation obstacle avoidance in narrow spaces by improving positioning accuracy and mapping accuracy, making it more applicable in the field of UAVs. Finally, the effectiveness of the proposed positioning algorithm was verified through experimental analysis of the Cartographer dataset and practical testing of UAVs in real scenarios.

Dark radiation from the primordial thermal bath in momentum space

Motivated by the stunning projections for future CMB surveys, we evaluate the amount of dark radiation produced in the early Universe by two-body decays or binary scatterings with thermal bath particles via a rigorous analysis in momentum space. We track the evolution of the dark radiation phase space distribution, and we use the asymptotic solution to evaluate the amount of additional relativistic energy density parameterized in terms of an effective number of additional neutrino species ΔN eff. Our approach allows for studying light particles that never reach equilibrium across cosmic history, and to scrutinize the physics of the decoupling when they thermalize instead. We incorporate quantum statistical effects for all the particles involved in the production processes, and we account for the energy exchanged between the visible and invisible sectors. Non-instantaneous decoupling is responsible for spectral distortions in the final distributions, and we quantify how they translate into the corresponding value for ΔN eff. Finally, we undertake a comprehensive comparison between our exact results and approximated methods commonly employed in the existing literature. Remarkably, we find that the difference can be larger than the experimental sensitivity of future observations, justifying the need for a rigorous analysis in momentum space.

Tales of the sea: Seafarers’ sense of place in the management of socialities and safety culture at sea

Workplaces can be tricky for migrant workers like seafarers to navigate, especially on board cargo ships which in recent times have become multi-ethnic in composition. Diverse cultures and individual differences can pose challenges to working relationships on board, which in turn can have negative implications on operational safety. In this context, the article highlights the role of seafarers’ sense of place in enacting harmonious socialities and safety culture on board. Sense of place refers to marked positioning in space where seafarers conduct themselves in relation to others in terms of hierarchy. In turn, this helps fashion the collective mind among seafarers as a way of dealing with the challenges of life at sea, including operational safety on board. This article draws from data gathered from fieldwork on board four ocean-going cargo ships and informal conversations with seafarers in seafarer centers in the United Kingdom between 2010 and 2020.

Anomalous far-field polarization around bound states in the continuum in non-Bravais lattices.

It is generally believed that at-Γ bound states in the continuum (BICs) are enclosed by a linearly polarized vortex in momentum space when the structures have mirror (σz) symmetry, in-plane inversion (I) symmetry, and time reversal symmetry (T). Here, we reveal an anomalous situation in which at-Γ BICs can be enclosed by linearly and elliptically polarized far-field even when the σz, I, and T symmetries are all maintained in non-Bravais lattices, which is radically different from previous cognition. Asymmetric, diatomic structures are designed to elaborate this intriguing phenomenon. By controlling the geometric parameters or refractive indexes of the two meta-atoms, the far-field polarization around the at-Γ BICs gradually deviates from linear polarization and approaches circular polarization. Our findings reveal that non-Bravais lattices can provide a novel platform to manipulate the far-field polarization, showing important applications in quantum entanglement, structured light, and radiation modulation.

Plant spectral diversity from high‐resolution multispectral imagery detects functional diversity patterns in coastal dune communities

AbstractQuestionRemote sensing is a fundamental tool to monitor biodiversity and spectral diversity may represent a proxy for different biodiversity facets such as taxonomic (TD) and functional diversity (FD). We used fine‐resolution multispectral imagery to explore spectral diversity (SD) patterns across spatial scales (i.e., plot, transect, area), and assess SD relationships with TD and FD along an environmental gradient.LocationCoastal sand dune, Viareggio, Italy (“Migliarino–San Rossore–Massaciuccoli” Regional Park, 43°83′ N, 10°25′ E).MethodsWe measured TD as species richness, while SD and FD were computed using probability density functions based on pixel and species position in multivariate spaces. We compared SD and FD patterns in space occupation, and we tested whether these patterns are coordinated along the sea–inland gradient. We also assessed univariate relationships between SD and biodiversity facets, and we tested how these facets were partitioned across scales.ResultsWe found a strong correspondence between functional and spectral patterns in space occupation and along the environmental gradient, with a lack of significance when considering TD. However, TD and SD showed higher variation at broader scale while most FD variation occurred at plot level.ConclusionBy measuring FD and SD with a common methodological framework, we demonstrate that SD approximates functional patterns in plant communities. Moreover, we show that SD retrieved using high‐resolution images can capture different aspects of FD, and that the occupation of the spectral space is analogous to the occupation of the functional space.

Role of spatial positioning strategy for speech recognition in a simulated environment: Effects of age and hearing loss

In realistic listening environments, the physical position of the listener and target talker, relative to competing talkers, affects the signal-to-noise ratio and availability of spatial cues for release from masking. While the importance of signal-to-noise ratio and spatial cues for speech recognition has been demonstrated in the laboratory, a listener’s ability to leverage these acoustic cues by manipulating their position in an environment has received less attention. This study evaluated how changes in listener position within a simulated environment effect speech recognition for four listener groups that differed in age (younger or older) and hearing status (normal or impaired hearing). The simulated environment consisted of 8–10 speech maskers, individually rendered under headphones for specific locations within the space, with target and listener positions that varied across conditions. The intensity of the target varied throughout testing to estimate the psychometric function for keyword recognition of each listener in each position. Subjective reports of preferred listening position were collected before and after testing to determine the extent to which these listener groups strategically position themselves to maximize their speech recognition in noise. Results will be discussed in terms of the potential gains in speech recognition associated with optimal positioning strategies.