bluuebunny/crossref_metadata_2025 huggingface dataset:
Broadband visible light harvesting BODIPY-perylene dyad and triad: Synthesis, photophysical properties, and photooxidation applications
Authors: Gong Yu , Dong Lei , Shen Qiang-Qiang , Li Meng , Gu Yi-Nuo , Zhang Wei-Guang , Xu Xin-Yu , Xue Qing-Jin , Zhu San-E , Zhou Yu-Mei
Published: June 2024

In this study, diiodo boron dipyrromethene (BODIPY) is employed as the energy donor and 3,4,9,10-perylene tetracarboxylic dianhydride (PDA) as the energy acceptor, enabling the synthesis of two new compounds: a BODIPY-perylene dyad named Pl, and a triad named P2. To investigate the impact of the energy donor on the photophysical processes of the system, P1 comprises one diiodo-BODIPY unit and one PDA unit, whereas P2 contains two dhodo-BODIPY moieties and one PDA unit. Due to the good spectral complementarity between diiodo-BODIPY and PDA, these two compounds exhibit excellent light-harvesting capabilities in the 400–620 nm range. Steady-state fluorescence spectra demonstrate that when preferentially exciting the diiodo-BODIPY moiety, it can effectively transfer energy to PDA; when selectively exciting the PDA moiety, quenching of PDA fluorescence is observed in both P1 and P2. Nanosecond transient absorption results show that both compounds can efficiently generate triplet excited states, which are located on the PDA part. The lifetimes of the triplet states for these two compounds are 103 and 89 μs, respectively, significantly longer than that of diiodo-BODIPY. The results from the photooxidation experiments reveal that both P1 and P2 demonstrate good photostability and photooxidation capabilities, with P2 showing superior photooxidative efficiency. The photooxidation rate constant for P2 is 1.3 times that of P1, and its singlet oxygen quantum yield is 1.6 times that of P1. The results obtained here offer valuable insights for designing new photosensitizers.
Control of multi-modal scattering in a microwave frequency comb
Authors: Rivera Hernández J. C. , Lingua Fabio , Jolin Shan W. , Haviland David B.
Published: July 2024

Control over the coupling between multiple modes of a frequency comb is an important step toward measurement-based quantum computation with a continuous-variable system. We demonstrate the creation of square-ladder correlation graphs in a microwave comb with 95 modes. The graphs are engineered through precise control of the relative phase of three pumps applied to a Josephson parametric oscillator. Experimental measurement of the mode scattering matrix is in good agreement with theoretical predictions based on a linearized equation of motion of the parametric oscillator. The digital methods used to create and measure the correlations are easily scaled to more modes and more pumps, with the potential to tailor a specific correlation graph topology.
Investigating the initialization and readout of relative populations of NV− and NV0 defects in diamond
Authors: Kuate Defo Rodrick , Richardson Steven L.
Published: June 2024

The static electric dipole–dipole coupling between donor–acceptor pairs (DAPs) in wide-bandgap semiconductors has recently emerged as a means of realizing a quantum science platform through optically controllable, long-range interactions between defects in the solid state. In this work, we generalize DAPs to consider arbitrary dopant populations and demonstrate that the charge of the NV center in diamond is well suited for quantum science. Explicitly, we leverage experimental results [see Z. Yuan et al., PRR 2, 033263 (2020)] to show that shallow NV centers can be efficiently initialized to a given relative population of the negative and neutral charge states and that modulating the surface termination would allow for control of the timescale over which the initialization and subsequent computations would occur. Furthermore, we argue that the observation of electroluminescence from the neutral charge state of the NV center [see N. Mizuochi et al., Nat. Photon. 6, 299 (2012)], but not from the negative charge state, implies the ability to interface with the NV center’s charge in a manner analogous to the spin interface enabled by the spin-state dependent fluorescence of the NV center.
Solar-blind photonic integrated chips for real-time on-chip communication
Authors: He Rui , Song Yijian , Liu Naixin , Chen Renfeng , Wu Jin , Wang Yufeng , Hu Qiang , Chen Xiongbin , Wang Junxi , Li Jinmin , Wei Tongbo
Published: July 2024

The monolithically integrated self-driven photoelectric detector (PD) with the light-emitting diode (LED) epitaxial structure completely relies on the built-in electric field in the multi-quantum wells region to separate the photogenerated carriers. Here, we propose a novel superlattices–electron barrier layer structure to expand the potential field region and enhance the detection capability of the integrated PD. The PD exhibits a record-breaking photo-to-dark current ratio of 5.14 × 107, responsivity of 110.3 A/W, and specific detectivity of 2.2 × 1013 Jones at 0 V bias, respectively. A clear open-eyed diagram of the monolithically integrated chip, including the PD, LED, and waveguide, is realized under a high-speed communication rate of 150 Mbps. The obtained transient response (rise/decay) time of 2.16/2.28 ns also illustrates the outstanding transient response capability of the integrated chip. The on-chip optical communication system is built to achieve the practical video signals transmission application, which is a formidable contender for the core module of future large-scale photonic integrated circuits.
A size-consistent multi-state mapping approach to surface hopping
Authors: Lawrence Joseph E. , Mannouch Jonathan R. , Richardson Jeremy O.
Published: June 2024

We develop a multi-state generalization of the recently proposed mapping approach to surface hopping (MASH) for the simulation of electronically nonadiabatic dynamics. This new approach extends the original MASH method to be able to treat systems with more than two electronic states. It differs from previous approaches in that it is size consistent and rigorously recovers the original two-state MASH in the appropriate limits. We demonstrate the accuracy of the method by applying it to a series of model systems for which exact benchmark results are available, and we find that the method is well suited to the simulation of photochemical relaxation processes.
Continuous Floquet theory in solid-state NMR
Authors: Chávez Matías , Ernst Matthias
Published: June 2024

This article presents the application of continuous Floquet theory in solid-state nuclear magnetic resonance (NMR). Continuous Floquet theory extends the traditional Floquet theory to non-continuous Hamiltonians, enabling the description of observable effects not fully captured by the traditional Floquet theory due to its requirement for a periodic Hamiltonian. We present closed-form expressions for computing first- and second-order effective Hamiltonians, streamlining integration with the traditional Floquet theory and facilitating application in NMR experiments featuring multiple modulation frequencies. Subsequently, we show examples of the practical application of continuous Floquet theory by investigating several solid-state NMR experiments. These examples illustrate the importance of the duration of the pulse scheme regarding the width of the resonance conditions and the near-resonance behavior.
Scaling laws for AC gas breakdown in microscale gaps
Authors: Mahajan Shivani , Wang Haoxuan , Loveless Amanda M. , Semnani Abbas , Venkattraman Ayyaswamy , Garner Allen L.
Published: June 2024

For microscale gaps, DC breakdown voltage is described theoretically and through simulation by accounting for field emission generated electrons and the subsequent ionization of neutral gas and ion-induced secondary electron emission. Here, we extend DC microscale breakdown theory to AC. Particle-in-cell (PIC) simulations show that breakdown voltage V varies linearly with gap distance d independent of frequency and the ion-induced secondary electron coefficient γSE for d≲4μm, where field emission dominates breakdown over ionization and avalanche. For d≳4μm and γSE=0, DC breakdown voltage increases linearly with d; for γSE=0.05, DC breakdown voltage decreases to a minimum before beginning to increase at larger gap distances. For AC fields with γSE=0.05, V behaves similarly to the DC case with the decrease corresponding to secondary emission occurring at higher voltages and larger gap distances with increasing frequency. At 10 GHz and γSE=0.05, V resembles that of the DC case with γSE=0 up to ∼8 μm, suggesting that increasing the frequency effectively changes the number of ions striking the electrodes and the resulting electrons released. Phase space plots showing electron and ion velocities as a function of position across the gap show that electrons and ions are increasingly trapped within the gap with increasing frequency, reducing the number of ions that can strike the cathode and the subsequent secondary emission. Incorporating the resulting effective secondary emission coefficient for AC microscale gaps yields a simple phenomenologically based modification of the DC microscale gas breakdown equation.
Helicity oscillations in Rayleigh–Bénard convection of liquid metal in a cell with aspect ratio of 0.5
Authors: Mitra Rahul , Stefani Frank , Galindo Vladimir , Eckert Sven , Sieger Max , Vogt Tobias , Wondrak Thomas
Published: June 2024

In this paper, we present numerical and experimental results on helicity oscillations in a liquid-metal Rayleigh–Bénard convection cell with an aspect ratio of 0.5. While the numerical simulations use the finite volume library OpenFOAM, the experimental results are obtained by means of contactless inductive flow tomography. We find that helicity oscillations occur during transitions of flow states with different roll numbers that are characterized by significant changes in the Reynolds number. However, helicity oscillations are also observed when the number of rolls is constant and the Reynolds number is changing only very slowly. Notably, the helicity oscillations observed during the transient double-roll state exhibit characteristics remarkably similar to those associated with the Tayler instability, which points to a rather generic and universal character of this phenomenon. Helicity oscillations are also discussed as a possible mechanism for synchronizing the solar dynamo by tidal forces of the orbiting planets.
Vortex–wall interactions in elliptic impinging synthetic jets
Authors: Xu Yang , Fan Di , Wang Lei
Published: June 2024

Vortex structures and flow scenarios of noncircular vortex rings impinging onto walls were studied by conducting a large eddy simulation. Three orifice aspect ratios, ARs = 3, 5, and 7, and six dimensionless orifice-to-wall distances, in the range H = 0.71–1.90, were considered for elliptic impinging synthetic jets. At H = 0.95–1.19, the results exhibit different flow scenarios from those of circular vortex rings, which directly interact with the wall to produce a secondary vortex ring. New scenarios are attributed to mutual interactions between the primary vortex ring, the arc-shaped vortex, the wall, and the arc-shaped vortex is unique to noncircular vortex rings. These scenarios are further divided into two categories depending on whether the primary vortex ring can merge with the arc-shaped vortex, which is strongly affected by their separation distance and circulation ratio at the onset of vortex–wall interactions. For small separation distance and circulation ratio, the primary vortex ring swallows the arc-shaped vortex, leading to a strong crescent-shaped secondary vortex or a secondary vortex ring at different ARs. However, as the separation distance or circulation ratio increases, the interactions between the primary vortex ring and arc-shaped vortex weaken so that the latter escapes from entrainment by the primary vortex ring, leading to a weak crescent-shaped vortex. Finally, an AR-H map is constructed to illustrate the flow scenarios for all the cases. These findings provide new insights into the intricate dynamics of noncircular ring–wall interactions and may help us understand the heat transfer performance of noncircular impinging synthetic jets.
High fidelity dynamic 3D characterization of in-flight exploding foil initiator flyers based on microscope photonic Doppler velocimetry
Authors: Liu Shouxian , Li Jianzhong , Luo Binqiang , Shui Rongjie , Lei Jiangbo , Huang Wenbin , Zhao Xincai , Wang Jing , Ye Yan , Peng Qixian , Zhu Liguo , Zhen Xianxu
Published: June 2024

This paper introduces a novel method for the three-dimensional characterization of flyers based on microscopic photonic Doppler velocimetry (PDV) velocity field measurements. By strategically positioning 56 PDV velocity measurement spots within a circle of 0.50 mm diameter at an interval of approximately 58 μm, we achieve spatially resolved measurements of the velocity history of the flyer during its flight within the barrel and subsequent impact on a transparent window. Crucial data, such as displacement history, impact time, and impact pulse duration, can be extracted at each measurement spot. Furthermore, a correlation analysis of these datasets enables the reconstruction of the flyer's three-dimensional morphology, both during its flight inside the barrel and at the critical moment of impact with the window. This method offers a remarkable temporal resolution in the order of nanoseconds and a spatial resolution in the order of micrometers. With the characteristics of high spatial resolution and high experimental efficiency, the microscope PDV technology is poised to become an essential research tool in the study of action mechanisms, design optimization, and determination of initiation criteria for exploding foil initiators.
Group superatoms: A new concept in cluster science
Authors: Zhao Boyi , Xia Shan , Yu Zhen , Tian Jingwen , Liu Liren
Published: July 2024

A promising research area in nanomaterials is the use of superatomic clusters as building blocks for creating novel molecules or materials with tailored properties. However, assembling these superatoms into functional materials is challenging, and a thorough understanding of this process is still lacking. In this study, we introduce a new concept called the “superatomic family,” which refers to superatoms that share similar valence electron structures but differ in size. We demonstrate this concept with the synthesized [Au6{Ni3(CO)6}4]2− cluster and the designed [Au16{Ni6(CO)10}4]2− and [Au31{Ni10(CO)15}4]5− clusters. These serve as analogs to simple hydrocarbons, such as methane (CH4), silicon hydride (SiH4), and germanium hydride (GeH4). In these supermolecular structures, the central cores of Au6, Au16, and Au31 exhibit the formation of superatomic SP3 hybridized orbitals, which influence the molecular shape and bonding. Moreover, we explored superatomic bonding involving SP3–SP3 hybridized cores, representing a single superatomic bond between members of the superatomic family, analogous to CH3–SiH3 bonds. By integrating the concept of group superatoms into the Lewis structure framework, we present a powerful approach for predicting and engineering cluster properties, thus opening a vast landscape of nanomaterial design possibilities.
Collective Hall current in chiral active fluids: Coupling of phase and mass transport through traveling bands
Authors: Siebers Frank , Bebon Robin , Jayaram Ashreya , Speck Thomas
Published: June 2024

Active fluids composed of constituents that are constantly driven away from thermal equilibrium can support spontaneous currents and can be engineered to have unconventional transport properties. Here, we report the emergence of (meta)stable traveling bands in computer simulations of aligning circle swimmers. These bands are different from polar flocks and, through coupling phase with mass transport, induce a bulk particle current with a component perpendicular to the propagation direction, thus giving rise to a collective Hall (or Magnus) effect. Traveling bands require sufficiently small orbits and undergo a discontinuous transition into a synchronized state with transient polar clusters for large orbital radii. Within a minimal hydrodynamic theory, we show that the bands can be understood as nondispersive soliton solutions fully accounting for the numerically observed properties.
Learning to interact from conversational narratives
Authors: André Virginie , Boulton Alex , Ciekanski Maud , Cousinard Clara
Published: June 2024

This article explores two under-researched types of corpora for use in data-driven learning (DDL): L2 corpora (i.e. in a second or foreign language) and multimodal corpora. It first outlines the development of FLEURON, a dedicated DDL platform designed to support interactional competence in French as a Foreign Language (FFL), based on multimodal corpora of both native and L2 speakers. It then presents an ecological study of how 19 international FFL learners interacted with the platform in a DDL approach at the University of Lorraine. The analysis highlights how L2 corpora in particular can help learners to improve their awareness of complex phenomena related to conversational narratives by engaging their meta-cognitive strategies during their time abroad. The study thus reveals the potential for integrating an L2 component among the range of resources available for teaching and learning spoken interaction.
Comparing theory-based models of grammatical complexity in student writing
Authors: Biber Douglas , Larsson Tove , Hancock Gregory R. , Reppen Randi , Staples Shelley , Gray Bethany
Published: July 2024

The present study tests the empirical adequacy of competing models of grammatical complexity in university student
writing, based on analysis of disciplinary texts from L1-English and L2-English students. The results show that grammatical
complexity in student writing must be treated as a multi-dimensional linguistic construct, distinguishing among both structural
types and syntactic functions. We compare the results here to previous research (Biber et al., 2024a, b), showing a similar patterning of complexity features in student writing and the broader domain of general
writing. Two of these groupings – dependent phrases functioning as noun modifiers, and finite dependent clauses functioning as
clause-level constituents – are especially interesting. These two groupings represent the strongest co-occurrence patterns in
general writing, but only the dependent clause grouping is represented in student writing. This discrepancy is interpreted
relative to the development of advanced proficiency in the use of complexity features by university students.
A new approach to combined proton-photon therapy for metastatic cancer patients
Authors: Torelli Nathan , Bicker Yves , Marc Louise , Fabiano Silvia , Unkelbach Jan
Published: June 2024

Objective. Proton therapy is a limited resource and is typically not available to metastatic cancer patients. Combined proton-photon therapy (CPPT), where most fractions are delivered with photons and only few with protons, represents an approach to distribute proton resources over a larger patient population. In this study, we consider stereotactic radiotherapy of multiple brain or liver metastases, and develop an approach to optimally take advantage of a single proton fraction by optimizing the proton and photon dose contributions to each individual metastasis. Approach. CPPT treatments must balance two competing goals: (1) deliver a larger dose in the proton fractions to reduce integral dose, and (2) fractionate the dose in the normal tissue between metastases, which requires using the photon fractions. Such CPPT treatments are generated by simultaneously optimizing intensity modulated proton therapy (IMPT) and intensity modulated radiotherapy (IMRT) plans based on their cumulative biologically effective dose (BED
α

/β
). The dose contributions of the proton and photon fractions to each individual metastasis are handled as additional optimization variables in the optimization problem. The method is demonstrated for two patients with 29 and 30 brain metastases, and two patients with 4 and 3 liver metastases. Main results. Optimized CPPT plans increase the proton dose contribution to most of the metastases, while using photons to fractionate the dose around metastases which are large or located close to critical structures. On average, the optimized CPPT plans reduce the mean brain BED2 by 29% and the mean liver BED4 by 42% compared to IMRT-only plans. Thereby, the CPPT plans approach the dosimetric quality of IMPT-only plans, for which the mean brain BED2 and mean liver BED4 are reduced by 28% and 58%, respectively, compared to IMRT-only plans. Significance. CPPT with optimized proton and photon dose contributions to individual metastases may benefit selected metastatic cancer patients without tying up major proton resources.
Multivariate signal-to-noise ratio as a metric for characterizing spectral computed tomography
Authors: Rajagopal Jayasai R , Farhadi Faraz , Saboury Babak , Sahbaee Pooyan , Negussie Ayele H , Pritchard William F , Jones Elizabeth C , Samei Ehsan
Published: June 2024

Objective. With the introduction of spectral CT techniques into the clinic, the imaging capacities of CT were expanded to multiple energy levels. Due to a variety of factors, the acquired signal in spectral CT datasets is shared between these images. Conventional image quality metrics assume independence between images which is not preserved within spectral CT datasets, limiting their utility for characterizing energy selective images. The purpose of this work was to develop a metrology to characterize energy selective images by incorporating the shared information between images within a spectral CT dataset. Approach. The signal-to-noise ratio (SNR) was extended into a multivariate space where each image within a spectral CT dataset was treated as a separate information channel. The general definition was applied to the specific case of contrast to define a multivariate contrast-to-noise ratio (CNR). The matrix contained two types of terms: a conventional CNR term which characterized image quality within each image in the spectral CT dataset and covariance weighted CNR (Covar-CNR) which characterized the contrast in each image relative to the covariance between images. Experimental data from an investigational photon-counting CT scanner was used to demonstrate the insight of this metrology. A cylindrical water phantom containing vials of iodine and gadolinium (2, 4, and 8 mg ml−1) was imaged under conditions of variable tube current, tube voltage, and energy threshold. Two image series (threshold and bin images) containing two images each were defined based upon the contribution of photons to reconstructed images. Analysis of variance (ANOVA) was calculated between CNR terms and image acquisition variables. A multivariate regression was then fitted to experimental data. Main Results. Image type had a major difference on how Covar-CNR values were distributed. Bin images had a slightly higher mean and wider standard deviation (Covar-CNRlo: 3.38 ±17.25, Covar-CNRhi: 5.77 ± 30.64) compared to threshold images (Covar-CNRlo: 2.08 ±1.89, Covar-CNRhi: 3.45 ± 2.49) across all conditions. ANOVA found that each acquisition variable had a significant relationship with both Covar-CNR terms. The multivariate regression model suggested that material concentration had the largest impact on all CNR terms. Signficance. In this work, we described a theoretical framework to extend the SNR to a multivariate form that is able to characterize images independently and also provide insight regarding the relationship between images. Experimental data was used to demonstrate the insight that this metrology provides about image formation factors in spectral CT.
Increased performance of A-DA’D-A type acceptor based organic solar cell using a thermally coevaporated cathode-modifying blend layer
Authors: Li Longdi , Li Jiatong , Qiu Mengyu , Jia Boyu , Qin Dashan , Zhan Xiaowei
Published: June 2024

The blend thin films of bathocuproine and fullerene (BCP:C60) have been thermally coevaporated to modify the active layer/cathode interfaces in organic solar cells. The BCP forms a much smaller-barrier contact with cathode than the C60. Because the surface zone of active layer is polymer donor-rich and small-molecular acceptor-deficient, C60 molecules make insufficiently large contact area with electron acceptor, leading to inefficient electron extraction. However, BCP molecules penetrate the surface of active layer, due to the smaller molecular size of BCP than that of C60, and likely form sufficiently large contact area with electron acceptor thereby to enable efficient electron extraction. Compared to conventional 10 nm BCP, 10 nm BCP:C60 (1:1 in mass ratio) enables higher efficiency based on the active layer using A-DA’D-A type acceptor, mostly because C60 constituent dissociates some excitons photogenerated in the polymer donor of surface zone and thereby increases short-circuit current density. The current research provides novel insights into the development of cathode-modifying layers for organic solar cells.
Optoelectronic, thermoelectric and 3D-Elastic properties of lead-free inorganic perovskites CsInZrX6 (I, Cl and Br) for optoelectronic and thermoelectric applications
Authors: Harbi A , Pingak Redi Kristian , Moutaabbid M
Published: June 2024

Halide perovskite materials have recently gained worldwide attention since they offer a new cost-effective way to generate renewable and green energy. In the current work, the structural, electrical, elastic, optical and thermoelectric properties of new perovskites CsInZrX6 (I, Cl and Br) were explored by density-functional theory (DFT). The results indicated that the computed lattice parameters agree really well with the current experimental and theoretical results. Moreover, the band structure profile strongly suggests that the compounds exhibit a semiconducting nature with a direct band gap. The analysis of their optical properties reveals that the perovskites possess a low reflectivity (below 23%) and a high optical absorption coefficient (106 cm−1). This is also supported by the evaluation of their calculated elastic constants and their related parameters in cubic structure which show that these compounds are brittle, mechanically stable and possess covalent bonds. On the other hand, in addition to exhibiting outstanding optoelectronic and mechanical characteristics, CsInZrCl6 also possesses dynamical stability, making it a promising candidate for application in various optoelectronic devices except for solar cells due to its relatively large bandgap. Furthermore, the BoltzTraP software was used to compute the materials’ thermoelectric properties, with the computed values of the figure of merit (ZT) for CsInZrBr6, CsInZrCl6 and CsInZrI6 being 0.76, 0.73 and 0.725, respectively. This is also a strong indication that these materials are potential for thermoelectric applications.
Electronic and optical characteristics of CaLiX3 (X = Cl, Br, I) perovskite compounds using the Tran–Blaha modified Becke–Johnson potential
Authors: Allaf Hatem , Allali Djamel , Radjai Missoum , Bouhemadou Abdelmadjid , Saad Essaoud Saber , Bedjaoui Abdelhak , Bin-Omran Saad , Khenata Rabah , Al-Douri Yarub , Chaba Mouna Sarah
Published: June 2024

We present the results of a comprehensive investigation using the full-potential linearized augmented plane wave approach to analyze the structural characteristics, electronic structures, and optical spectra of the perovskite compounds CaLiX3 (X = Cl, Br, or I). Various functionals were employed to simulate the exchange–correlation interactions. The calculated equilibrium structural parameters, obtained using the generalized gradient approximation, are consistent with the existing findings in the literature. The computed electronic structures reveal that the Tran–Blaha modified Becke–Johnson potential significantly enhances the bandgap. For all CaLiX3 compounds studied, we predicted an indirect bandgap. Additionally, we observed a gradual decrease in the bandgap as the atomic size of the X element increases. The electronic states constituting the various energy bands were evaluated by computing the partial and total densities of states. In addition, we computed a variety of optical spectra, including the complex dielectric function, absorption coefficient, refractive index, extinction coefficient, reflectivity, and electron energy loss function. The results demonstrate that a decrease in the bandgap leads to an increase in the zero-frequency limit of the dielectric function

ε

(
0
)

.

The origins of the peaks and structures in the optical spectra were identified.
Paraxial propagation characteristics of a controllable anomalous hollow vortex beam in free space
Authors: Qiu Yuzhong , Liu Zhirong
Published: June 2024

Propagation of a recently proposed controllable anomalous hollow vortex (CAHV) beam is investigated. Based on the integral formula of generalized Huygens–Fresnel diffraction, analytical expression for the CAHV beam through a paraxial ABCD optical system is derived. The factors that affect the intensity pattern are determined by the beam’s controllable parameters a, c
x, c
y, and the topological charge m. Results show that the Gaussian distribution features are controlled by parameter a, and the horizontal and vertical stretching deformations of the beam are adjusted by parameters c
x and c
y, respectively. For a controllable anomalous hollow (CAH) beam, when propagating in free space, it could initially maintain anomalous hollow property and the size of the spot increases with the increase of the propagation distance. Due to the CAHV beam carries the optical vortex, a dark hollow channel appears in the center of the beam during propagation, and the channel structure changes with the increase of topological charge. Additionally, the Poynting vector of CAHV beam proves the direction of energy flow corresponding to the intensity distribution. Results obtained in this paper could have potential applications in particle trapping and optical control.
Upper bound on thermal gravitational wave backgrounds from hidden sectors
Authors: Drewes Marco , Georis Yannis , Klaric Juraj , Klose Philipp
Published: June 2024

Hot viscous plasmas unavoidably emit a gravitational wave background, similar to electromagnetic black body radiation.
We study the contribution from hidden particles to the diffuse background emitted by the primordial plasma in the early universe.
While this contribution can easily dominate over that from Standard Model particles, we find that both are capped by a generic upper bound that makes them difficult to detect with interferometers in the foreseeable future.
We illustrate our results for axion-like particles and heavy neutral leptons.
Finally, our results suggest that previous works overestimated the gravitational wave background from particle decays out of thermal equilibrium.
Gamma-rays and neutrinos from giant molecular cloud populations in the galactic plane
Authors: Roy Abhijit , Joshi Jagdish C. , Cardillo Martina , Sarmah Prantik , Sarkar Ritabrata , Chakraborty Sovan
Published: June 2024

The recent IceCube detection of significant neutrino flux from the inner Galactic plane has provided us valuable insights on the spectrum of cosmic rays in our Galaxy. This flux can be produced either by a population of Galactic point sources or by diffused emission from cosmic ray interactions with the interstellar medium or by a mixture of both. In this work, we compute diffused gamma-ray and neutrino fluxes produced by a population of giant molecular clouds (GMCs) in our Galaxy, assuming different parametrizations of the Galactic diffused cosmic ray distribution. In particular, we take into account two main cases: (I) constant cosmic ray luminosity in our Galaxy, and (II) space-dependent cosmic ray luminosity, based on the supernovae distribution in our Galaxy. For Case-I, we found that the neutrino flux from GMCs is a factor of ∼ 10 below compared to π
0 and KRA
γ
best-fitted models of IceCube observations at 105 GeV. Instead, for Case-II the model can explain up to ∼ 90 % of the neutrino flux at that energy. Moreover, for this last scenario IceCube detector could be able to detect neutrino events from the Galactic centre regions. We then calculated gamma-ray and neutrino fluxes from individual GMCs and noticed that several current and future Cherenkov telescopes and neutrino observatories have the right sensitivities to study these objects. In particular, very neutrino-bright region such as Aquila Rift is favourable for detection by the IceCube-Gen2 observatory.
From lab to life: assessing the impact of real-world interactions on the operation of rapid serial visual presentation-based brain-computer interfaces
Authors: Ahsan Awais Muhammad , Ward Tomas , Redmond Peter , Healy Graham
Published: June 2024

Objective. Brain-computer interfaces (BCI) have been extensively researched in controlled lab settings where the P300 event-related potential (ERP), elicited in the rapid serial visual presentation (RSVP) paradigm, has shown promising potential. However, deploying BCIs outside of laboratory settings is challenging due to the presence of contaminating artifacts that often occur as a result of activities such as talking, head movements, and body movements. These artifacts can severely contaminate the measured EEG signals and consequently impede detection of the P300 ERP. Our goal is to assess the impact of these real-world noise factors on the performance of a RSVP-BCI, specifically focusing on single-trial P300 detection. Approach. In this study, we examine the impact of movement activity on the performance of a P300-based RSVP-BCI application designed to allow users to search images at high speed. Using machine learning, we assessed P300 detection performance using both EEG data captured in optimal recording conditions (e.g. where participants were instructed to refrain from moving) and a variety of conditions where the participant intentionally produced movements to contaminate the EEG recording. Main results. The results, presented as area under the receiver operating characteristic curve (ROC-AUC) scores, provide insight into the significant impact of noise on single-trial P300 detection. Notably, there is a reduction in classifier detection accuracy when intentionally contaminated RSVP trials are used for training and testing, when compared to using non-intentionally contaminated RSVP trials. Significance. Our findings underscore the necessity of addressing and mitigating noise in EEG recordings to facilitate the use of BCIs in real-world settings, thus extending the reach of EEG technology beyond the confines of the laboratory.
Damage Identification of Railway Bridge trough temporal Autoregressive modelling under Train Loads
Authors: Anastasia S. , García-Macías E. , Ubertini F. , Gattulli V. , Poveda P. , Torres B. , Ivorra S.
Published: June 2024

The damage identification of railway bridges poses a formidable challenge given the large variability in the environmental/operational conditions that such structures are subjected to along their lifespan. Within a research project devoted to the continuous monitoring of a real in-operation bridge, the Mascarat Viaduct in Alicante (Spain), this paper investigates the potential use of strain sensors and autoregressive (AR) modelling to extract highly sensitive damage features. The viaduct, built in the beginning of the 20th century, belongs to the TRAM line 9 in the province of Alicante (Spain). The viaduct is instrumented with a dense network of strain sensors and accelerometers for monitoring the structural response under train passages. As an initial exploratory investigation, and with the aim of developing a physics-based digital twin of the viaduct, this work presents an introductory numerical assessment of the potential use of strain measurements and AR models for fast damage identification. To this aim, a finite element model (FEM) of the viaduct has been developed to simulate the dynamic response of the viaduct under moving train loads. On this basis, a two-class damage classifier (damaged or non-damaged) is developed by exploiting time series of continuously identified AR parameters. The presented results and discussion evidence the usefulness of the proposed methodology, offering an unsupervised damage detection approach with minimum computational efforts.
Vibration serviceability of footbridges in crowded conditions: crowd dynamics simulations vs guidelines’ predictions
Authors: Tubino F , Venuti F
Published: June 2024

Vibration serviceability assessment in crowded conditions requires a reliable human-induced loading model taking into account pedestrian interaction. Current guidelines provide simplified procedures to determine the maximum dynamic response based on very simplified loading models. The main objective of this paper is to assess the reliability of current guidelines for vibration serviceability assessment of footbridges. With this aim, an extensive campaign of numerical simulations of bidirectional pedestrian traffic is carried out through an agent-based model, considering variable pedestrian densities and deck widths. The results of numerical simulations are first compared against the experiments available in the literature in terms of fundamental diagram of the mean walking speed as a function of pedestrian density. Then, starting from numerical simulations, the dynamic response of a class of footbridges is estimated numerically and compared with guidelines’ predictions in order to assess their reliability.
Crowd-induced loading on footbridges: reliability of an Equivalent Spectral Model
Authors: Tubino F , Van Nimmen K
Published: June 2024

Vibration serviceability assessment of footbridges requires a reliable probabilistic model for multi-pedestrian loading and a suitable approach to take into account human-structure interaction. In the present paper, the human-induced dynamic response of footbridges is analysed using a mode superimposition approach. The power spectral density functions of the modal loads are defined according to an equivalent spectral model, and suitable equivalent dynamic properties of each mode are estimated for the human-structure coupled system. The validation against the Eeklo Footbridge benchmark dataset confirms the reliability of the proposed approach.
Experimental study of active human-structure interaction during running on footbridges
Authors: Lottefier Jasper , Broeck Peter Van den , Vanwanseele Benedicte , Nimmen Katrien Van
Published: June 2024

Slender footbridges are predominantly sensitive to human-induced vibrations. While the previous two decades have focussed on pedestrian-induced vibrations, topical research questions are investigating the impact of running actions. The currently available load model for vibration serviceability assessments only applies to a single runner on a rigid surface. The present work investigates whether low-frequency vertical vibrations of the supporting surface affect the running motion, known as active human-structure interaction. To facilitate characterisation, an extensive measurement campaign was organised. First, a treadmill was placed on a rigid surface as reference and secondly on a vibrating footbridge, excited by a mechanical shaker. The measurement setup enables the simultaneous registration of the contact forces, body motion, running motion metrics on a step-by-step basis and the structural response. The results indicate that human-structure interaction phenomena do occur while running on a vertical vibrating surface. The main effects include changes of the peak contact force, determined by the relative phase between the body motion and the footbridge’s motion. Moreover, when running (near) resonance, two stable running regimes can occur. The first resembles a non-resonant runner (constantly alternating between in- and out-of-phase) while the second resembles resonant running by keeping a fairly constant phase with the structure.
Lightweight footbridges subjected to streams of pedestrians: tests and discussion of a crowd-structure interaction model
Authors: Gallegos-Calderón Christian , Naranjo-Pérez Javier , Jiménez-Alonso Javier F. , Díaz Iván M.
Published: June 2024

Human-induced vibrations in slender lightweight footbridges have been extensively investigated in the last 30 years. In existing guidelines, the dynamic response of a footbridge can be assessed considering the pedestrians as external non-interacting loads acting on the structure. For a more realistic load model, individuals defined as single Degree of Freedom (DOF) dynamic systems moving along the structure have been employed by researchers and practitioners. Hence, Human-Structure Interaction (HSI) is considered in the dynamic analysis. Adopting this approach to calculate the vibration levels on a footbridge may lead to a costly computational problem when dealing with a crowd due to the large number of DOFs associated to the pedestrians. Recently, a frequency-domain procedure based on a coupled crowd-structure system has been proposed by the authors to overcome the aforementioned issue. To further validate the proposal, the analytical results should be contrasted with experimental measurements. In this sense, this paper presents the dynamic response of two footbridges under the action of streams of walking pedestrians. A laboratory fibre reinforced polymer structure is firstly analysed, and an in-service cable-stayed steel footbridge is secondly studied. The vibration serviceability of both pedestrian structures is assessed considering 0.20 and 0.50 pedestrians/m2. For each bridge, the experimental results are compared with predictions computed through the application of load models from existing guidelines. In addition, the frequency-domain proposal is employed to calculate the steady-state structural response while accounting for HSI. Since dynamic parameters of the human body must be defined for the second approach, different values available in literature are employed. Results demonstrate the overestimation of the response when provisions stated in current design documents are used. Also, the benefits of the novel procedure to consider Crowd-Structure Interaction on lightweight footbridges are highlighted.
Modal analysis of a footbridge under pedestrian traffic and additional shaker loading
Authors: Purpura Laura , Güner Hüseyin , Hoffait Sébastien , Dënoel Vincent
Published: June 2024

This paper investigates the possibility of identifying the modal properties of footbridges while they are subjected to pedestrian traffic using the CSI algorithm. The analysis is based on vibration data collected from a footbridge under different pedestrian densities. The results show that the CSI algorithm provides consistent modal properties, but the identified damping ratio seems to be significantly influenced by pedestrians. This is likely due to the human-structure interaction. Identified apparent damping ratios appear plausible, but of course not representative of the bare structure. Overall, while the CSI algorithm helps alleviate the limitations of the authors’ previous approache to modal identification with a custom shaker, the practical usefulness of identifying modal properties of footbridges under pedestrian traffic is therefore limited.
On the Dynamic Assessment of a Cable-Stayed Footbridge: The Iron Bridge
Authors: Colmenares Daniel , Ruhani Shaho , Karoumi Raid
Published: June 2024

Human-induced loads may produce resonance when the forcing frequency coincides with the natural frequency of the system. In this work, the dynamic assessment of a pedestrian cable-stayed bridge in Uppsala, Sweden is presented. The dynamic properties of the system have been identified and a loading scenario is evaluated. A comparison between the theoretical and measured acceleration of the bridge is made using a detailed finite element model. Different modelling aspects are considered and evaluated by studying their influence on the natural frequencies of the system such as the tie rods system, railings, and boundary conditions. Moreover, a parametric analysis of the elastic modulus of the cast iron material with respect to the boundary conditions of the system is presented to quantify the uncertainties of the system. Special focus is given to the resonant response of the first natural frequency of the bridge potentially compromising the serviceability limit state of the structure. Furthermore, the scenario of a single pedestrian jogging on the spot is evaluated and a hypothetical standing crowd is considered to illustrate the benefits of taking into account the human-structure interaction effect. A considerable reduction of the dynamic response of the system is found, highlighting the importance of the human-structure-interaction effect.
Dynamic response of floors induced by a single walking pedestrian: deterministic and probabilistic approaches
Authors: Bayat Elyas , Tubino Federica
Published: June 2024

Current design standards evaluate floor vibration performance by analyzing a single walking individual as a multi-harmonic fixed load applied to the anti-nodes of the floor mode shapes. These guidelines do not consider the impact of varying walking paths on the dynamic response of floors. Moreover, because pedestrian walking forces are inherently stochastic, the deterministic methods employed by current standards can yield unreliable estimations of vibration response. The present paper aims to investigate the dynamic response of simply supported rectangular floors under a single walking pedestrian. At first, a deterministic loading model is assumed; then a probabilistic approach is adopted taking into account the stochastic nature of pedestrian walking force. From the deterministic standpoint, the present study reports an exact closed-form solution to calculate the dynamic response of floors subjected to a pedestrian walking load moving along a generic walking path. Then, an approximated closed-form solution is proposed to calculate the vibration response of floors for the critical walking path which provides the maximum dynamic response. Finally, a probabilistic approach is incorporated to address the variability in both walking load and walking path.
Vibration serviceability assessment of complex-shaped CLT floor
Authors: Milojević M , Racic V , Marjanović M , Nefovska-Danilović M
Published: June 2024

Cross-laminated timber (CLT) floors are typically an assembly of prefabricated panels connected together on the site. CLT offers a wide range of configuration possibilities, as it can be easily pre-cut into various shapes and sizes, making it suitable for use in different architectural design requirements. However, available CLT design guidelines do not apply to complex-shaped CLT floors, i.e. unconventional geometry of floor plans including concave polygons, arches and openings. This paper presents a numerical vibration analysis of such a floor with openings, which represents a standard floor structure for residential and commercial buildings. Influence of panel orientation and inter-panel connections on modal properties and vibration response induced by a single pedestrian walking is analysed and discussed.
Experimental analysis of cross-laminated timber floors
Authors: Nefovska-Danilović M , Racic V , Milojević M , Mišković Z , Savatović S
Published: June 2024

Cross-laminated timber (CLT) floors have gained in popularity due to their outstanding strength, aesthetic appeal, good fire resistance, and high level of prefabrication. However, due to their high stiffness-to-weight ratio, CLT floors are highly susceptible to pedestrian-induced vibrations. In design practice, vibration serviceability is usually assessed by assuming a floor as a set of CLT panels with no inter-panel connections, which leads to overestimation of the vibration response. In this paper, an experimental dynamic testing was carried out to identify modal properties and pedestrian-induced response of two CLT floors with different number of panels in a floor assembly. Influence of the inter-panel connections on the floor modal properties and pedestrian-induced vibration response is particularly studied and discussed.