bluuebunny/crossref_metadata_2025 huggingface dataset:
Theoretical investigation of distal charge separation in a perylenediimide trimer
Authors: Wang Ke , Xu Yihe , Xie Xiaoyu , Ma Haibo
Published: April 2024

An exciton–phonon (ex–ph) model based on our recently developed block interaction product basis framework is introduced to simulate the distal charge separation (CS) process in aggregated perylenediimide (PDI) trimer incorporating the quantum dynamic method, i.e., the time-dependent density matrix renormalization group. The electronic Hamiltonian in the ex–ph model is represented by nine constructed diabatic states, which include three local excited (LE) states and six charge transfer (CT) states from both the neighboring and distal chromophores. These diabatic states are automatically generated from the direct products of the leading localized neutral or ionic states of each chromophore’s reduced density matrix, which are obtained from ab initio quantum chemical calculation of the subsystem consisting of the targeted chromophore and its nearest neighbors, thus considering the interaction of the adjacent environment. In order to quantum-dynamically simulate the distal CS process with massive coupled vibrational modes in molecular aggregates, we used our recently proposed hierarchical mapping approach to renormalize these modes and truncate those vibrational modes that are not effectively coupled with electronic states accordingly. The simulation result demonstrates that the formation of the distal CS process undergoes an intermediate state of adjacent CT, i.e., starts from the LE states, passes through an adjacent CT state to generate the intermediates (∼200 fs), and then formalizes the targeted distal CS via further charge transference (∼1 ps). This finding agrees well with the results observed in the experiment, indicating that our scheme is capable of quantitatively investigating the CS process in a realistic aggregated PDI trimer and can also be potentially applied to exploring CS and other photoinduced processes in larger systems.
Chemical short-range order enhances fracture toughness of medium entropy alloy CoCrNi
Authors: Jian Wu-Rong , Xu Shuozhi , Chen Dengke , Beyerlein Irene J.
Published: April 2024

Using hybrid molecular dynamics and Monte Carlo simulations, we examine the role of lattice distortion (LD) and chemical short-range ordering (CSRO) on the development of defects ahead of a mode I crack in medium entropy alloy CoCrNi. We show that CSRO noticeably increases fracture toughness. The result can be explained by the effect of CSRO on lowering LD and increasing intrinsic stacking fault energy and the direct impact CSRO has on the energetic barriers for emitting partial dislocations and forming nanotwins from CoCr clusters on the crack tip. CSRO allows the nanotwin domains to further support inelastic deformation, such as dislocation glide and amorphization, leading to stable crack-tip plasticity and postponement of softening. These findings imply that the superior fracture toughness in CoCrNi can be attributed to the non-negligible CSRO that naturally exists.
Influence of guide vane opening on channel vortex and pressure pulsation in Francis turbine runners
Authors: Pang Jiayang , Yao Bing , Liu Xiaobing , Li Jialing , Xiao Ming , Jiang Dengyun , Tang Wen , Zhou Lingjiu , Lai Zhenming
Published: April 2024

In order to investigate the impact of guide vane opening on channel vortex and pressure pulsation within the runner of a Francis turbine, this research examines the cavitation phenomenon, channel vortex phenomenon, and flow field characteristics of a power station's turbine in China. The investigation is conducted using computational fluid dynamics theory. Furthermore, the analysis focuses on the influence of changes in guide vane opening on the flow state within the turbine runner. The findings indicate that the occurrence of rotor cavitation is severe when the opening is small, and increasing the opening reduces the cavitation capacity of the rotor. The presence of a lobe vortex phenomenon is mainly observed within a small range of guide vane openings, and altering the opening modifies both the range of influence and flow characteristics of the lobe vortex. In the middle range of guide vane openings, vortex pressure pulsation dominates within the rotor, with the highest amplitude of pressure pulsation occurring at a 60% opening. In the large opening range, pressure pulsation mainly occurs in the lobe frequency pressure pulsation of the rotor within the lobe-less area. The amplitude of blade frequency is typically small, indicating good hydraulic stability of the unit. These study results elucidate the interval of stable operating conditions for the unit and offer valuable insights for maintaining its stable operation.
HCl trimer: HCl-stretch excited intramolecular and intermolecular vibrational states from 12D fully coupled quantum calculations employing contracted intra- and inter-molecular bases
Authors: Simkó Irén , Felker Peter M. , Bačić Zlatko
Published: April 2024

We present fully coupled, full-dimensional quantum calculations of the inter- and intra-molecular vibrational states of HCl trimer, a paradigmatic hydrogen-bonded molecular trimer. They are performed utilizing the recently developed methodology for the rigorous 12D quantum treatment of the vibrations of the noncovalently bound trimers of flexible diatomic molecules [Felker and Bačić, J. Chem. Phys. 158, 234109 (2023)], which was previously applied to the HF trimer by us. In this work, the many-body 12D potential energy surface (PES) of (HCl)3 [Mancini and Bowman, J. Phys. Chem. A 118, 7367 (2014)] is employed. The calculations extend to the intramolecular HCl-stretch excited vibrational states of the trimer with one- and two-quanta, together with the low-energy intermolecular vibrational states in the two excited v = 1 intramolecular vibrational manifolds. They reveal significant coupling between the intra- and inter-molecular vibrational modes. The 12D calculations also show that the frequencies of the v = 1 HCl stretching states of the HCl trimer are significantly redshifted relative to those of the isolated HCl monomer. Detailed comparison is made between the results of the 12D calculations on the two-body PES, obtained by removing the three-body term from the original 2 + 3-body PES, and those computed on the 2 + 3-body PES. It demonstrates that the three-body interactions have a strong effect on the trimer binding energy as well as on its intra- and inter-molecular vibrational energy levels. Comparison with the available spectroscopic data shows that good agreement with the experiment is achieved only if the three-body interactions are included. Some low-energy vibrational states localized in a secondary minimum of the PES are characterized as well.
Single-chain fluorescent integrators for mapping G-protein-coupled receptor agonists
Authors: Kroning Kayla , Gannot Noam , Li Xingyu , Putansu Aubrey , Zhou Guanwei , Sescil Jennifer , Shen Jiaqi , Wilson Avery , Fiel Hailey , Li Peng , Wang Wenjing
Published: April 2024

G protein-coupled receptors (GPCRs) transduce the effects of many neuromodulators including dopamine, serotonin, epinephrine, acetylcholine, and opioids. The localization of synthetic or endogenous GPCR agonists impacts their action on specific neuronal pathways. In this paper, we show a series of single-protein chain integrator sensors that are highly modular and could potentially be used to determine GPCR agonist localization across the brain. We previously engineered integrator sensors for the mu- and kappa-opioid receptor agonists called M- and K-Single-chain Protein-based Opioid Transmission Indicator Tool (SPOTIT), respectively. Here, we engineered red versions of the SPOTIT sensors for multiplexed imaging of GPCR agonists. We also modified SPOTIT to create an integrator sensor design platform called SPOTIT for all GPCRs (SPOTall). We used the SPOTall platform to engineer sensors for the beta 2-adrenergic receptor (B2AR), the dopamine receptor D1, and the cholinergic receptor muscarinic 2 agonists. Finally, we demonstrated the application of M-SPOTIT and B2AR-SPOTall in detecting exogenously administered morphine, isoproterenol, and epinephrine in the mouse brain via locally injected viruses. The SPOTIT and SPOTall sensor design platform has the potential for unbiased agonist detection of many synthetic and endogenous neuromodulators across the brain.
Observation of negative surface and interface energies of quantum dots
Authors: Calvin Jason J. , Brewer Amanda S. , Crook Michelle F. , Kaufman Tierni M. , Alivisatos A. Paul
Published: April 2024

Surface energy is a fundamental property of materials and is particularly important in describing nanomaterials where atoms or molecules at the surface constitute a large fraction of the material. Traditionally, surface energy is considered to be a positive quantity, where atoms or molecules at the surface are less thermodynamically stable than their counterparts in the interior of the material because they have fewer bonds or interactions at the surface. Using calorimetric methods, we show that the surface energy is negative in some prototypical colloidal semiconductor nanocrystals, or quantum dots with organic ligand coatings. This implies that the surface atoms are more thermodynamically stable than those on the interior due to the strong bonds between these atoms and surfactant molecules, or ligands, that coat their surface. In addition, we extend this work to core/shell indium phosphide/zinc sulfide nanocrystals and show that the interfacial energy between these materials is highly thermodynamically favorable in spite of their large lattice mismatch. This work challenges many of the assumptions that have guided thinking about colloidal nanomaterial thermodynamics, investigates the fundamental stability of many technologically relevant colloidal nanomaterials, and paves the way for future experimental and theoretical work on nanocrystal thermodynamics.
Individual transcription factors modulate both the micromovement of chromatin and its long-range structure
Authors: Shaban Haitham A. , Friman Elias T. , Deluz Cédric , Tollenaere Armelle , Katanayeva Natalya , Suter David M.
Published: April 2024

The control of eukaryotic gene expression is intimately connected to highly dynamic chromatin structures. Gene regulation relies on activator and repressor transcription factors (TFs) that induce local chromatin opening and closing. However, it is unclear how nucleus-wide chromatin organization responds dynamically to the activity of specific TFs. Here, we examined how two TFs with opposite effects on local chromatin accessibility modulate chromatin dynamics nucleus-wide. We combine high-resolution diffusion mapping and dense flow reconstruction and correlation in living cells to obtain an imaging-based, nanometer-scale analysis of local diffusion processes and long-range coordinated movements of both chromatin and TFs. We show that the expression of either an individual transcriptional activator (CDX2) or repressor (SIX6) with large numbers of binding sites increases chromatin mobility nucleus-wide, yet they induce opposite coherent chromatin motions at the micron scale. Hi-C analysis of higher-order chromatin structures shows that induction of the pioneer factor CDX2 leads both to changes in local chromatin interactions and the distribution of A and B compartments, thus relating the micromovement of chromatin with changes in compartmental structures. Given that inhibition of transcription initiation and elongation by RNA Pol II has a partial impact on the global chromatin dynamics induced by CDX2, we suggest that CDX2 overexpression alters chromatin structure dynamics both dependently and independently of transcription. Our biophysical analysis shows that sequence-specific TFs can influence chromatin structure on multiple architectural levels, arguing that local chromatin changes brought by TFs alter long-range chromatin mobility and its organization.
Shifting fire regimes cause continent-wide transformation of threatened species habitat
Authors: Doherty Tim S. , Macdonald Kristina J. , Nimmo Dale G. , Santos Julianna L. , Geary William L.
Published: April 2024

Human actions are causing widespread increases in fire size, frequency, and severity in diverse ecosystems globally. This alteration of fire regimes is considered a threat to numerous animal species, but empirical evidence of how fire regimes are shifting within both threatened species’ ranges and protected areas is scarce, particularly at large spatial and temporal scales. We used a big data approach to quantify multidecadal changes in fire regimes in southern Australia from 1980 to 2021, spanning 415 reserves (21.5 million ha) and 129 threatened species’ ranges including birds, mammals, reptiles, invertebrates, and frogs. Most reserves and threatened species’ ranges within the region have experienced declines in unburnt vegetation (≥30 y without fire), increases in recently burnt vegetation (≤5 y since fire), and increases in fire frequency. The mean percentage of unburnt vegetation within reserves declined from 61 to 36% (1980 to 2021), whereas the mean percentage of recently burnt vegetation increased from 20 to 35%, and mean fire frequency increased by 32%, with the latter two trends primarily driven by the record-breaking 2019 to 2020 fire season. The strongest changes occurred for high-elevation threatened species, and reserves of high elevation, high productivity, and strong rainfall decline, particularly in the southeast of the continent. Our results provide evidence for the widely held but poorly tested assumption that threatened species are experiencing widespread declines in unburnt habitat and increases in fire frequency. This underscores the imperative for developing management strategies that conserve fire-threatened species in an increasingly fiery future.
Impact of electric vehicle charging demand on power distribution grid congestion
Authors: Li Yanning , Jenn Alan
Published: April 2024

California, a pioneer in EV adoption, has enacted ambitious electric vehicle (EV) policies that will generate a large burden on the state’s electric distribution system. We investigate the statewide impact of uncontrolled EV charging on the electric distribution networks at a large scale and high granularity, by employing an EV charging profile projection that combines travel demand model, EV adoption model, and real-world EV charging data. We find a substantial need for infrastructure upgrades in 50% of feeders by 2035, and 67% of feeders by 2045. The distribution system across California must upgrade its capacity by 25 GW by 2045, corresponding to a cost between $6 and $20 billion. While the additional infrastructure cost drives the electricity price up, it is offset by the downward pressure from the growth of total electricity consumption and leads to a reduction in electricity rate between $0.01 and $0.06/kWh by 2045. We also find that overloading conditions are highly diverse spatially, with feeders in residential areas requiring twice as much upgrade compared to commercial areas. Our study provides a framework for evaluating EVs’ impact on the distribution grid and indicates the potential to reduce infrastructure upgrade costs by shifting home-charging demand. The imminent challenges confronting California serve as a microcosm of the forthcoming obstacles anticipated worldwide due to the prevailing global trend of EV adoption.
Intranasal neomycin evokes broad-spectrum antiviral immunity in the upper respiratory tract
Authors: Mao Tianyang , Kim Jooyoung , Peña-Hernández Mario A. , Valle Gabrielee , Moriyama Miyu , Luyten Sophia , Ott Isabel M. , Gomez-Calvo Maria Luisa , Gehlhausen Jeff R , Baker Emily , Israelow Benjamin , Slade Martin , Sharma Lokesh , Liu Wei , Ryu Changwan , Korde Asawari , Lee Chris J. , Silva Monteiro Valter , Lucas Carolina , Dong Huiping , Yang Yi ,   Yale SARS-CoV-2 Genomic Surveillance Initiative, Gopinath Smita , Wilen Craig B. , Palm Noah , Dela Cruz Charles S. , Iwasaki Akiko , Vogels Chantal B. F. , Hahn Anne M. , Chen Nicholas F. G. , Breban Mallery , Koch Tobias R , Chaguza Chrispin , Tikhonova Irina , Castaldi Christopher , Mane Shrikant , De Kumar Bony , Ferguson David , Kerantzas Nicholas , Peaper David , Landry Marie L , Schulz Wade , Grubaugh Nathan
Published: April 2024

Respiratory virus infections in humans cause a broad-spectrum of diseases that result in substantial morbidity and mortality annually worldwide. To reduce the global burden of respiratory viral diseases, preventative and therapeutic interventions that are accessible and effective are urgently needed, especially in countries that are disproportionately affected. Repurposing generic medicine has the potential to bring new treatments for infectious diseases to patients efficiently and equitably. In this study, we found that intranasal delivery of neomycin, a generic aminoglycoside antibiotic, induces the expression of interferon-stimulated genes (ISGs) in the nasal mucosa that is independent of the commensal microbiota. Prophylactic or therapeutic administration of neomycin provided significant protection against upper respiratory infection and lethal disease in a mouse model of COVID-19. Furthermore, neomycin treatment protected Mx1 congenic mice from upper and lower respiratory infections with a highly virulent strain of influenza A virus. In Syrian hamsters, neomycin treatment potently mitigated contact transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). In healthy humans, intranasal application of neomycin-containing Neosporin ointment was well tolerated and effective at inducing ISG expression in the nose in a subset of participants. These findings suggest that neomycin has the potential to be harnessed as a host-directed antiviral strategy for the prevention and treatment of respiratory viral infections.
Sustainable, low-cost, high-contrast electrochromic displays via host–guest interactions
Authors: Wang Yuyang , Lei Chuxin , Guan Weixin , Shi Wen , Shen Ruipeng , Zhang Sean Xiao-An , Yu Guihua
Published: April 2024

Electrochromic (EC) displays with electronically regulating the transmittance of solar radiation offer the opportunity to increase the energy efficiency of the building and electronic products and improve the comfort and lifestyle of people. Despite the unique merit and vast application potential of EC technologies, long-awaited EC windows and related visual content displays have not been fully commercialized due to unsatisfactory production cost, durability, color, and complex fabrication processes. Here we develop a unique EC strategy and system based on the natural host and guest interactions to address the above issues. A completely reusable and sustainable EC device has been fabricated with potential advantages of extremely low cost, ideal user-/environment friendly property, and excellent optical modulation, which is benefited from the extracted biomass EC materials and reusable transparent electrodes involved in the system. The as-prepared EC window and nonemissive transparent display also show comprehensively excellent properties: high transmittance change (>85%), broad spectra modulation covering Ultraviolet (UV), Visible (Vis) to Infrared (IR) ranges, high durability (no attenuation under UV radiation for more than 1.5 mo), low open voltage (0.9 V), excellent reusability (>1,200 cycles) of the device’s key components and reversibility (>4,000 cycles) with a large transmittance change, and pleasant multicolor. It is anticipated that unconventional exploration and design principles of dynamic host–guest interactions can provide unique insight into different energy-saving and sustainable optoelectronic applications.
The Mysteries of Summer Camp, Chronic Illness, and Magic
Authors: Rendlen Chelsea I.
Published: April 2024

Never was the dynamic and complexities of living with chronic mystery illness more apparent than in the summer camp setting. My first year as a counselor brought me face-to-face with the realities of my physical state and how I related to my body in the summer camp context. Now, as an Executive Director of a summer camp, spurred on by the memories of what I endured, and committed to making the space different, I weigh the impact of changing camps, and question what parts of the challenge are necessary to preserve “camp magic”?

Information

© CAB International 2024
Quantum geometrodynamics revived: II. Hilbert space of positive definite metrics
Authors: Lang Thorsten , Schander Susanne
Published: April 2024

This paper represents the second in a series of works aimed at reinvigorating the quantum geometrodynamics program. Our approach introduces a lattice regularization of the hypersurface deformation algebra, such that each lattice site carries a set of canonical variables given by the components of the spatial metric and the corresponding conjugate momenta. In order to quantize this theory, we describe a representation of the canonical commutation relations that enforces the positivity of the operators

q
^

a
b

s
a

s
b

for all choices of s. Moreover, symmetry of

q
^

a
b

and

p
^

a
b

is ensured. This reflects the physical requirement that the spatial metric should be a positive definite, symmetric tensor. To achieve this end, we resort to the Cholesky decomposition of the spatial metric into upper triangular matrices with positive diagonal entries. Moreover, our Hilbert space also carries a representation of the vielbein fields and naturally separates the physical and gauge degrees of freedom. Finally, we introduce a generalization of the Weyl quantization for our representation. We want to emphasize that our proposed methodology is amenable to applications in other fields of physics, particularly in scenarios where the configuration space is restricted by complicated relationships among the degrees of freedom.
Quantum geometrodynamics revived I. Classical constraint algebra
Authors: Lang Thorsten , Schander Susanne
Published: April 2024

In this series of papers, we present a set of methods to revive quantum geometrodynamics which encountered numerous mathematical and conceptual challenges in its original form promoted by Wheeler and De Witt. In this paper, we introduce the regularization scheme on which we base the subsequent quantization and continuum limit of the theory. Specifically, we employ the set of piecewise constant fields as the phase space of classical geometrodynamics, resulting in a theory with finitely many degrees of freedom of the spatial metric field. As this representation effectively corresponds to a lattice theory, we can utilize well-known techniques to depict the constraints and their algebra on the lattice. We are able to compute the lattice corrections to the constraint algebra. This model can now be quantized using the usual methods of finite-dimensional quantum mechanics, as we demonstrate in the following paper. The application of the continuum limit is the subject of a future publication.
External defect immune high quality resonances in microwave topological ring resonator
Authors: Jena Geetanjali , Kulkarni Gopal , Varshney R K , Roy Chowdhury Dibakar
Published: April 2024

Recently, topological ring resonators (TRRs) have emerged as a burgeoning platform for exploring the topological aspects of photonic systems and resonator dynamics. Integrating topology into cavity dynamics offers a new paradigm to unveil various fascinating phenomena, including backscattering immune wave propagation, unidirectional transmission, and reflection-free energy transport. With this background, we provide a scheme to achieve robust high Q resonances in a metal-based topological photonic crystal (TPC) exhibiting defect-immune spectral characteristics in the microwave frequency regime. Coupled with a ring resonator, our proposed topological platform demonstrates the excitation of high Q resonances in the range 230–540. Except for the resonances, a robust microwave transmission (

∼

0

dB

) is observed in the investigated frequency regime 7.1–7.6 GHz depicting a minimal scattering loss even around the sharp corners of the ring resonator. Further, the topological robustness of the propagating microwave and the excited resonances are examined by introducing an external Si obstacle at the domain interface. Our study reveals a minimal transmission loss (

<

7

dB

) and negligible perturbation (

<

8
%

) in the Q factors when the Si barrier placed towards the input end of the straight topological waveguide. In addition, we have also demonstrated a novel way of exciting new resonances in the ring resonator that holds considerable promise for designing a TRR-based all-pass notch filter in the microwave regime.
Capillary-based, multifunctional manipulation of particles and fluids via focused surface acoustic waves
Authors: Pei Zhichao , Tian Zhenhua , Yang Shujie , Shen Liang , Hao Nanjing , Naquin Ty D , Li Teng , Sun Lining , Rong Weibin , Huang Tony Jun
Published: April 2024

Surface acoustic wave (SAW)-enabled acoustofluidic technologies have recently attracted increasing attention for applications in biology, chemistry, biophysics, and medicine. Most SAW acoustofluidic devices generate acoustic energy which is then transmitted into custom microfabricated polymer-based channels. There are limited studies on delivering this acoustic energy into convenient commercially-available glass tubes for manipulating particles and fluids. Herein, we have constructed a capillary-based SAW acoustofluidic device for multifunctional fluidic and particle manipulation. This device integrates a converging interdigitated transducer to generate focused SAWs on a piezoelectric chip, as well as a glass capillary that transports particles and fluids. To understand the actuation mechanisms underlying this device, we performed finite element simulations by considering piezoelectric, solid mechanic, and pressure acoustic physics. This experimental study shows that the capillary-based SAW acoustofluidic device can perform multiple functions including enriching particles, patterning particles, transporting particles and fluids, as well as generating droplets with controlled sizes. Given the usefulness of these functions, we expect that this acoustofluidic device can be useful in applications such as pharmaceutical manufacturing, biofabrication, and bioanalysis.
Electronic properties of polyethylene naphthalate as derived from photo-stimulated discharge, luminescence experiments and quantum chemical calculation
Authors: Mendoza Lopez Duvan , Teyssedre Gilbert , Boudou Laurent , Berquez Laurent , Laurent Christian , Iwata Shinya , Takada Tatsuo
Published: April 2024

The electronic properties of thin films of poly(ethylene 2,6-naphthalate)—PEN, are investigated based on their photo-physical (optical absorption, photoluminescence) and electrical (space charge distribution, photo-stimulated discharge) behavior. Photo-stimulated currents are associated with optical absorption of the material leading to space charge dissipation as demonstrated by space charge distribution measurement. Based on this set of experimental results and quantum chemical calculation performed on PEN macromolecular system, we propose a new scheme for the electronic levels of PEN. This scheme allows understanding the mechanisms at play in photo-stimulated discharge. One of the main conclusions of our work is that photo-stimulated current measurements do not probe the energy level of traps. Detrapping of charges results from a two-step process where the photon energy is absorbed by chromophores that restitute a part of this energy to trapped charges through various mechanisms. Moreover, the new scheme allows discussing the components of the luminescence excited under different stresses, being electric field, electronic and UV irradiation, charge recombination and thermal activation.
A versatile method for exploring the magnetooptical properties of polar saturated and unsaturated ferromagnetic metallic thin films
Authors: Patra Rajkumar , Sharma Apoorva , Stöcker Hartmut , Monecke Manuel , Salvan Georgeta , Mattheis Roland , Schmidt Heidemarie
Published: April 2024

Polar unsaturated ferromagnetic thin films are promising for low-power and high-speed nonvolatile resistive and optical memories. Here we measure the magnetooptical (MO) response of polar unsaturated Co90Fe10 and Co40Fe40B20 thin films in the spectral range from 400 nm to 1000 nm using vector MO generalized ellipsometry (VMOGE) in an out-of-plane applied magnetic field of ±0.4 T where magnetization of the ferromagnetic (FM) thin film is not saturated. Using magnetooptical simulation software (MagOpS®), we extract the complex MO coupling constant (
Q
) of the polar unsaturated FM thin films from difference spectra of VMOGE data recorded in a polar configuration at Hz
= +0.4 T and Hz
= −0.4 T. The presented approach opens a path to determine
Q
of both polar saturated and polar unsaturated FM thin films for simulating the MO properties of application-relevant optical memory multilayer structures.
Simulation comparison of the positive and negative surface discharges induced by metal particles in a plate–surface–plate structure under DC excitation in atmospheric air
Authors: Jiang Hui , Lai Yundong , Gong Ziyi , Han Yufei , Shao Tao
Published: April 2024

Surface discharge induced by metal particles is a common insulation failure in many high-voltage equipment. In order to further understand the mechanisms of this surface discharge, a 2D simulation model of a plate–surface–plate structure with a pin is established and verified by experiments in this paper to simulate the actual discharge configurations, and the evolution characteristics of the positive and negative surface discharges are compared. The evolutions of both positive and negative discharges could be divided into two phases: the bridging phase and the expansion phase. As the electric field in the gap between the streamer and the dielectric surface is strengthened by the effect of the space charge, the ionization sources and the secondary electrons excited on the dielectric surface, the dielectric surface presents attraction to the streamer, and subsequently the two streamer routes first touch the dielectric surface and then arrive at the grounding electrode. However, the channel branching is the most distinctive characteristic of the positive and negative discharges. In the positive discharge, the channel first branches, then merges, and finally expands, and the gaps of pin to dielectric surface and pin to grounding electrode are broken down by two slender positive branches, respectively. The negative discharge presents a stout channel without branching, which develops and expands simultaneously. This is ascribed to the thinner space charge layer, the weaker shielding effect of the internal electric field and the more active movement of the internal charges in the positive discharge. Another important factor for the discharge branching is the appropriate matching of the sheath thickness and the curvature radius of the channel’s head.
Analysis of the impact of edge diffraction on the manipulation of photonic nanojets and photonic hooks using an energy-based model in diffraction-based structures
Authors: Xu Ji , Li Sheng , Wang Jun , Zhang Baifu , Yao Han , Chi Tiantian , Cheng Huichao , Pang Ting , Lu Yunqing , Liu Ning
Published: April 2024

Photonic nanojets (PNJs) and photonic hooks (PHs) are two significant effects in Mesotronics. However, it is difficult to analyze and control the two phenomena generated by diffraction-based structures, such as rectangles and right-angled trapezoids, using diffraction theory. This work focuses on the modulation of incident fields by edge diffraction and the reconstruction of energy distribution, and proposes a model based on energy flows and energy reconstruction, called the ‘energy-based model’, to analyze the formation of PNJs and PHs through such structures. This model reveals that the morphology of PNJ and PH originates from the contributions of different regions of the incident energy, especially the crucial influence of edge diffraction, and successfully clarifies the modulation mechanism of the near-field and far-field regions of PNJ, as well as the tailoring mechanism of the two arms of PH. On the one hand, the model provides reasonable and intuitive explanations for the control of energy flow paths resulting from edge diffraction in rectangles and their variants with different parameters on the generation of PNJs and PHs. On the other hand, it also serves as a basis for reverse design. By adjusting energy flow and energy reconstruction through alterations in incident conditions or structural shapes, PHJs and PHs can be tailored easily and flexibly. The model is also been validated to be applicable in explaining many reported works. The results indicate that the ‘energy-based model’, which describes the energy flow paths resulting from edge diffraction, offers intuitive, convenient, and predictive advantages in analyzing the morphological variations of PNJs and PHs generated by diffraction-based structures, such as rectangles, trapezoids, and their variants. This provides a valuable reference for relevant research on Mesotronics.
Atomistic simulations of the interaction of edge dislocations with β-Nb precipitates in Zr-Nb alloys
Authors: Lin Junru , Chen Shuaijie , Bai Yiding , Zhang Shuo , Wang Tieshan , Zhao Jiangtao
Published: April 2024

Experiments have shown that precipitation can affect the mechanical properties of zirconium alloy, but the interaction mechanism between dislocations and Nb precipitates in zirconium alloys is still unclear. Thus, a systematic molecular dynamics study was performed to investigate the interaction between edge dislocations and Nb precipitates. It was found that the dislocation passed through Nb precipitate by shear mechanism or bypass mechanism of forming jogs, and the critical resolved shear stress increased with the diameter of the precipitate. After completion of the interaction, dislocations formed jogs due to climb when the precipitates were larger than 2 or 3 nm. Some atoms in the precipitate were more disordered after dislocation shearing, and dislocation fragments were generated around the precipitate, both of which lead to the precipitate hardening. The calculation of obstacle strength further confirmed that unsheared Nb precipitates until hundreds of nanometers were the weak obstacle for dislocations.
Role of gas composition in weakened nonlinear standing wave excitation and improved plasma radial uniformity in very-high-frequency asymmetric capacitive Ar/CF4 discharges
Authors: Zhou Fang-Jie , Zhang Yu-Ru , Zhao Kai , Wen De-Qi , Wang You-Nian
Published: April 2024

The higher harmonics generated by nonlinear sheath motion would enhance the standing wave effect, and thus lead to center-peaked plasma density profile in very-high-frequency (VHF) capacitive discharges. In this work, a nonlinear transmission line (NTL) model introduced in Zhou et al (2021 Plasma Sources Sci. Technol.
30 125017) has been extended, with radial transport of various particles and nonlinear sheath motion into account, to investigate the effects of CF4 fraction

α

on the nonlinear standing wave excitation and plasma radial uniformity in VHF (60 MHz) capacitively coupled Ar/CF4 plasmas at 3 Pa. The results indicate that for pure Ar discharges (i.e.

α
=

0%), the nonlinearly excited harmonics with short wavelength significantly enhance the electron power absorption at the radial center, resulting in a pronounced central-high plasma density profile. As

α

increases, the high-order harmonics are gradually damped due to the increase of resistance, as well as the longer wavelength caused by thicker sheath thickness. Thus, the radial profile of the electron absorbed power density shifts from center-peak to edge-high. Besides, at the radial center, the electron density and Ar+ ion density decrease with

α

, CF3
+ ion density shows an increasing trend, while F− ion density initially rises and then decreases. Moreover, the density profiles of all the species become more uniform at higher CF4 fraction, due to the suppressed nonlinear standing wave excitation and the longer wavelength of the nonlinear harmonics.
Spatially fractionated radiation therapy: a critical review on current status of clinical and preclinical studies and knowledge gaps
Authors: Prezado Yolanda , Grams Michael , Jouglar Emmanuel , Martínez-Rovira Immaculada , Ortiz Ramon , Seco Joao , Chang Sha
Published: April 2024

Spatially fractionated radiation therapy (SFRT) is a therapeutic approach with the potential to disrupt the classical paradigms of conventional radiation therapy. The high spatial dose modulation in SFRT activates distinct radiobiological mechanisms which lead to a remarkable increase in normal tissue tolerances. Several decades of clinical use and numerous preclinical experiments suggest that SFRT has the potential to increase the therapeutic index, especially in bulky and radioresistant tumors. To unleash the full potential of SFRT a deeper understanding of the underlying biology and its relationship with the complex dosimetry of SFRT is needed. This review provides a critical analysis of the field, discussing not only the main clinical and preclinical findings but also analyzing the main knowledge gaps in a holistic way.
Patient-specific temperature distribution prediction in laser interstitial thermal therapy: single-irradiation data-driven method
Authors: Gao Tingting , Liang Libin , Ding Hui , Wang Guangzhi
Published: April 2024

Laser interstitial thermal therapy (LITT) is popular for treating brain tumours and epilepsy. The strict control of tissue thermal damage extent is crucial for LITT. Temperature prediction is useful for predicting thermal damage extent. Accurately predicting in vivo brain tissue temperature is challenging due to the temperature dependence and the individual variations in tissue properties. Considering these factors is essential for improving the temperature prediction accuracy. Objective. To present a method for predicting patient-specific tissue temperature distribution within a target lesion area in the brain during LITT. Approach. A magnetic resonance temperature imaging (MRTI) data-driven estimation model was constructed and combined with a modified Pennes bioheat transfer equation (PBHE) to predict patient-specific temperature distribution. In the PBHE for temperature prediction, the individual specificity and temperature dependence of thermal tissue properties and blood perfusion, as well as the individual specificity of optical tissue properties were considered. Only MRTI data during one laser irradiation were required in the method. This enables the prediction of patient-specific temperature distribution and the resulting thermal damage region for subsequent ablations. Main results. Patient-specific temperature prediction was evaluated based on clinical data acquired during LITT in the brain, using intraoperative MRTI data as the reference standard. Our method significantly improved the prediction performance of temperature distribution and thermal damage region. The average root mean square error was decreased by 69.54%, the average intraclass correlation coefficient was increased by 37.5%, the average Dice similarity coefficient was increased by 43.14% for thermal damage region prediction. Significance. The proposed method can predict temperature distribution and thermal damage region at an individual patient level during LITT, providing a promising approach to assist in patient-specific treatment planning for LITT in the brain.
A scan-specific quality control acquisition for clinical whole-body (WB) MRI protocols
Authors: Keaveney Sam , Hopkinson Georgina , Markus Julia E , Priest Andrew N , Scurr Erica , Hughes Julie , Robertson Scott , Doran Simon J , Collins David J , Messiou Christina , Koh Dow-Mu , Winfield Jessica M
Published: April 2024

Objective. Image quality in whole-body MRI (WB-MRI) may be degraded by faulty radiofrequency (RF) coil elements or mispositioning of the coil arrays. Phantom-based quality control (QC) is used to identify broken RF coil elements but the frequency of these acquisitions is limited by scanner and staff availability. This work aimed to develop a scan-specific QC acquisition and processing pipeline to detect broken RF coil elements, which is sufficiently rapid to be added to the clinical WB-MRI protocol. The purpose of this is to improve the quality of WB-MRI by reducing the number of patient examinations conducted with suboptimal equipment. Approach. A rapid acquisition (14 s additional acquisition time per imaging station) was developed that identifies broken RF coil elements by acquiring images from each individual coil element and using the integral body coil. This acquisition was added to one centre’s clinical WB-MRI protocol for one year (892 examinations) to evaluate the effect of this scan-specific QC. To demonstrate applicability in multi-centre imaging trials, the technique was also implemented on scanners from three manufacturers. Main results. Over the course of the study RF coil elements were flagged as potentially broken on five occasions, with the faults confirmed in four of those cases. The method had a precision of 80% and a recall of 100% for detecting faulty RF coil elements. The coil array positioning measurements were consistent across scanners and have been used to define the expected variation in signal. Significance. The technique demonstrated here can identify faulty RF coil elements and positioning errors and is a practical addition to the clinical WB-MRI protocol. This approach was fully implemented on systems from two manufacturers and partially implemented on a third. It has potential to reduce the number of clinical examinations conducted with suboptimal hardware and improve image quality across multi-centre studies.
Pulse-echo ultrasound attenuation tomography
Authors: Korta Martiartu Naiara , Salemi Yolgunlu Parisa , Frenz Martin , Jaeger Michael
Published: April 2024

Objective. We present the first fully two-dimensional attenuation imaging technique developed for pulse-echo ultrasound systems. Unlike state-of-the-art techniques, which use line-by-line acquisitions, our method uses steered emissions to constrain attenuation values at each location with multiple crossing wave paths, essential to resolve the spatial variations of this tissue property. Approach. At every location, we compute normalized cross-correlations between the beamformed images that are obtained from emissions at different steering angles. We demonstrate that their log-amplitudes provide the changes between attenuation-induced amplitude losses undergone by the different incident waves. This allows us to formulate a linear tomographic problem, which we efficiently solve via a Tikhonov-regularized least-squares approach. Main results. The performance of our tomography technique is first validated in numerical examples and then experimentally demonstrated in custom-made tissue-mimicking phantoms with inclusions of varying size, echogenicity, and attenuation. We show that this technique is particularly good at resolving lateral variations in tissue attenuation and remains accurate in media with varying echogenicity. Significance. Based on a similar principle, this method can be easily combined with computed ultrasound tomography in echo mode for speed-of-sound imaging, paving the way towards a multi-modal ultrasound tomography framework characterizing multiple acoustic tissue properties simultaneously.
Task-based automatic keV selection: leveraging routine virtual monoenergetic imaging for dose reduction on clinical photon-counting detector CT
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Authors: Rajendran Kishore , Bruesewitz Michael , Swicklik Joseph , Ferrero Andrea , Thorne Jamison , Yu Lifeng , McCollough Cynthia , Leng Shuai
Published: April 2024

Objective. Photon-counting detector (PCD) CT enables routine virtual-monoenergetic image (VMI) reconstruction. We evaluated the performance of an automatic VMI energy level (keV) selection tool on a clinical PCD-CT system in comparison to an automatic tube potential (kV) selection tool from an energy-integrating-detector (EID) CT system from the same manufacturer. Approach. Four torso-shaped phantoms (20–50 cm width) containing iodine (2, 5, and 10 mg cc−1) and calcium (100 mg cc−1) were scanned on PCD-CT and EID-CT. Dose optimization techniques, task-based VMI energy level and tube-potential selection on PCD-CT (CARE keV) and task-based tube potential selection on EID-CT (CARE kV), were enabled. CT numbers, image noise, and dose-normalized contrast-to-noise ratio (CNRd) were compared. Main results. PCD-CT produced task-specific VMIs at 70, 65, 60, and 55 keV for non-contrast, bone, soft tissue with contrast, and vascular settings, respectively. A 120 kV tube potential was automatically selected on PCD-CT for all scans. In comparison, EID-CT used x-ray tube potentials from 80 to 150 kV based on imaging task and phantom size. PCD-CT achieved consistent dose reduction at 9%, 21% and 39% for bone, soft tissue with contrast, and vascular tasks relative to the non-contrast task, independent of phantom size. On EID-CT, dose reduction factor for contrast tasks relative to the non-contrast task ranged from a 65% decrease (vascular task, 70 kV, 20 cm phantom) to a 21% increase (soft tissue with contrast task, 150 kV, 50 cm phantom) due to size-specific tube potential adaptation. PCD-CT CNRd was equivalent to or higher than those of EID-CT for all tasks and phantom sizes, except for the vascular task with 20 cm phantom, where 70 kV EID-CT CNRd outperformed 55 keV PCD-CT images. Significance. PCD-CT produced more consistent CT numbers compared to EID-CT due to standardized VMI output, which greatly benefits standardization efforts and facilitates radiation dose reduction.
Axisymmetric hybrid Vlasov equilibria with applications to tokamak plasmas
Authors: Kaltsas D A , Kuiroukidis A , Morrison P J , Throumoulopoulos G N
Published: April 2024

We derive axisymmetric equilibrium equations in the context of the hybrid Vlasov model with kinetic ions and massless fluid electrons, assuming isothermal electrons and deformed Maxwellian distribution functions for the kinetic ions. The equilibrium system comprises a Grad–Shafranov partial differential equation and an integral equation. These equations can be utilized to calculate the equilibrium magnetic field and ion distribution function, respectively, for given particle density or given ion and electron toroidal current density profiles. The resulting solutions describe states characterized by toroidal plasma rotation and toroidal electric current density. Additionally, due to the presence of fluid electrons, these equilibria also exhibit a poloidal current density component. This is in contrast to the fully kinetic Vlasov model, where axisymmetric Jeans equilibria can only accommodate toroidal currents and flows, given the absence of a third integral of the microscopic motion.