bluuebunny/crossref_metadata_2025 huggingface dataset:
A simple and robust machine learning assisted process flow for the layer number identification of TMDs using optical contrast spectroscopy
Authors: Joy Nikhil Joseph , K Ranjuna M , Balakrishnan Jayakumar
Published: November 2022

Layered transition metal dichalcogenides (TMDs) like tungsten disulphide (WS2) possess a large direct electronic band gap (∼2 eV) in the monolayer limit, making them ideal candidates for opto-electronic applications. The size and nature of the bandgap is strongly dependent on the number of layers. However, different TMDs require different experimental tools under specific conditions to accurately determine the number of layers. Here, we identify the number of layers of WS2 exfoliated on top of SiO2/Si wafer from optical images using the variation of optical contrast with thickness. Optical contrast is a universal feature that can be easily extracted from digital images. But fine variations in the optical images due to different capturing conditions often lead to inaccurate layer number determination. In this paper, we have implemented a simple Machine Learning assisted image processing workflow that uses image segmentation to eliminate this difficulty. The workflow developed for WS2 is also demonstrated on MoS2, graphene and h–BN, showing its applicability across various classes of 2D materials. A graphical user interface is provided to enhance the adoption of this technique in the 2D materials research community.
Optimization of high-temperature superconducting bilayer structures using a vortex dynamics simulation
Authors: Rivasto E , Hynninen T , Huhtinen H , Paturi P
Published: November 2022

We argue that the current carrying properties of high-temperature superconducting thin films can be further improved, in particular under the mid-field range (B ≈ 0.1–2 T), via introduction of multilayer structures that compromise between good zero field critical current and vortex pinning performance. In this work we focus on a simple bilayer structure consisting of two adjacent layers of pure YBa2Cu3O

6
+
x

(YBCO) and BaZrO3 (BZO) doped YBCO under magnetic field within the mid-field range oriented parallel to the c-axis of the YBCO unit cell. We have utilized a computational model to simulate the vortex dynamics limited critical current separately from the associated zero field current, which is addressed analytically. The obtained results have allowed us to estimate the optimal layer thicknesses as a function of magnetic field. Our idealized model suggests that the thickness of the doped layer should be substantially smaller than the undoped one, that is around 30% of the total thickness of the film. We have estimated that the current carrying capability of the optimized bilayer structure can be up to 50% higher when compared with corresponding single layer films. Possible deviations from the obtained results associated with the idealized model, most prominently the effect of natural defects, are comprehensively discussed. Our results provide the foundation for the future experimental realization of the proposed bilayer structures. The comparison between the presented results and experimental realization would enable further study of the underlying primitive vortex interactions.
Unpredictable condensate–depletion dynamics in one-dimensional power-law traps
Authors: Sakhel Asaad R , Sakhel Roger R
Published: November 2022

The dynamic depletion of a trapped one-dimensional Bose–Einstein condensate (BEC) that is driven by laser stirring is numerically explored using beyond mean-field methods. For this purpose, the multi-configurational time-dependent Hartree method for bosons (Alon et al 2008 Phys. Rev. A 77 033613) is applied. In order to induce the depletion, the BEC is excited by a negative Gaussian potential (dimple) whose depth is modulated with time. The BEC is examined in various trapping geometries, with different interactions, and the condensate depletion is recorded as a function of time. A general power–law trap is considered that can be experimentally generated and shaped by the holographic methods of Bruce et al (2011 Phys. Rev. A 84 053410). The chief goal is to explore the interplay between trapping geometry and interactions in defining the depletion dynamics. It is chiefly found, that the details of these depletion dynamics are unpredictable and determined by a combination of the principle dimple depth, trap, and interactions. One significant feature of this work is that quite a number of plateaus is reached in the aforementioned dynamics.
First principle studies of TiO2-ZnO alloys under high pressure
Authors: Yang Mengxin , Zhang Yanling , Liang Min , Sun Yuanming , Duan Defang , Tian Fubo
Published: November 2022

The ZnO-TiO2 composite system has been applied as a photocatalyst in the treatment of organic waste and domestic wastewater due to its high separation rate of photogenerated carriers and wide light response range. Using the first-principles approach based on density functional theory, we investigated the crystal structures and the electronic properties of ZnO-TiO2 alloys under high pressure and predicted three stable high-pressure phases (Cmcm ZnTiO3, Imma Zn2TiO4 and Cm ZnTi3O7). Calculations of the phonon spectra and elastic constants showed that the predicted structures are dynamically and mechanically stable. In terms of electronic properties, it was found that the three crystal structures were all semiconductors. With the increase of pressure, the band gap of Cm ZnTi3O7 showed an increasing trend, while the band gap of Cmcm ZnTiO3 and Imma Zn2TiO4 gradually decreased. The calculated band structures showed that the band gap first increases nonlinearly and then decreases as the Zn concentration increases. Pressure can regulate the band gap of the above crystals, making them promising for applications in photocatalysis and microwave devices.
The impact of body mass index on patient radiation dose in general radiography
Authors: Dolenc Laura , Petrinjak Barbara , Mekiš Nejc , Škrk Damijan
Published: November 2022

The aim of the present study was to determine the influence of the body mass index (BMI) on the dose area product (DAP) and effective dose (ED) in overweight and obese patients. We also wanted to determine the typical dose values as well as suggest adjustments to clinical practice for overweight and obese patients. In this study we considered 597 patients referred for imaging of the chest in posteroanterior and lateral projection, the lumbar spine in anteroposterior (AP) and lateral projection, the pelvis, the knee in AP and lateral projection, and the shoulder in AP projection. For each examination, the image field size, tube voltage, mAs product, source-to-image receptor distance and values of DAP were collected. Based on their BMI, the patients were divided into three groups (normal weight, overweight and obese). At the end, PCXMC 2.0 software was used to calculate the ED. The study showed a statistically significant DAP and ED increase in overweight and obese patients by 28.9% up to 275.4% in the case of DAP and an increase in ED from 11.0% to 241.9% in all mentioned examinations except knee and shoulder imaging. Typical DAP values ranged from 2.2 to 54.8 µGym2 for normal-weight patients, from 2.2 to 87.6 µGym2 for overweight patients, and from 2.2 to 172.5 µGym2 for obese patients. Spearman’s correlation coefficient revealed very weak to very strong correlations when comparing BMI and DAP, as well as when comparing BMI and ED. A strong and very strong correlation was found in the case of examinations of the torso (except for the comparison of BMI and ED in the case of lateral lumbar spine projection).
Fast-response hot-wire flow sensors for wind and gust estimation on UAVs
Authors: Simon Nathaniel , Piqué Alexander , Snyder David , Ikuma Kyle , Majumdar Anirudha , Hultmark Marcus
Published: November 2022

Due to limitations in available sensor technology, unmanned aerial vehicles (UAVs) lack an active sensing capability to measure turbulence, gusts, or other unsteady aerodynamic phenomena. Conventional in situ anemometry techniques fail to deliver in the harsh and dynamic multirotor environment due to form factor, resolution, or robustness requirements. To address this capability gap, a novel, fast-response sensor system to measure a wind vector in two dimensions is introduced and evaluated. This system, known as ‘MAST’ (for MEMS Anemometry Sensing Tower), leverages advances in microelectromechanical (MEMS) hot-wire devices to produce a solid-state, lightweight, and robust flow sensor suitable for real-time wind estimation onboard an UAV. The MAST uses five pentagonally-arranged microscale hot-wires to determine the wind vector’s direction and magnitude. The MAST’s performance was evaluated in a wind tunnel at speeds up to 5 m s−1 and orientations of 0∘–360∘. A neural network sensor model was trained from the wind tunnel data to estimate the wind vector from sensor signals. The average error of the sensor is 0.14 m s−1 for speed and 1.6∘ for direction. Furthermore, 95% of measurements are within 0.36 m s−1 for speed and 5.0∘ for direction. With a bandwidth of 570 Hz determined from square-wave testing, the MAST stands to greatly enhance UAV wind estimation capabilities and enable capturing relevant high-frequency phenomena in flow conditions.
A new condition-monitoring method based on multi-variable correlation learning network for wind turbine fault detection
Authors: Yao Qingtao , Li Xianze , Xiang Ling , Hu Aijun , Hankun Bing
Published: November 2022

Reasonable and in-depth analysis of the supervisory control and data acquisition (SCADA) dataset can improve the accuracy and reliability of anomaly detection in wind turbines. In this paper, a multi-variable correlation learning network named the attention mechanism temporal convolutional network–gated recurrent unit (AMTCN-GRU) is proposed to extract the multidirectional features of SCADA data for wind turbine condition monitoring. First, the parameters with greater relevance to the prediction target are selected as input parameters of this method. Meanwhile, the cabin vibration signal contains the transient characteristics of the operating system. If the component connected to the cabin fails, the vibration signal will change immediately. Then, the vibration parameter is selected as one of the inputs. In this paper, a novel AMTCN model is proposed to enhance the feature extraction capability, which is constituted by a convolutional block attention mechanism embedded to the TCN’s residual block structure. The extracted features can be weighted again to make the output more relevant to the predicted target. GRU is performed to construct the connections of feature and output for the condition prediction of the wind turbine. Finally, it is proven that the proposed method can accurately and reliably realize anomaly detection in wind turbines by analyzing the SCADA data of the actual wind farm.
Measuring water vapour permeability using remote-reading humidity sensors
Authors: Hall Christopher , Lo Gloria J , Hamilton Andrea
Published: November 2022

The water vapour permeability is a material property used in calculations of the hygrothermal performance of buildings. The standard test method (the ‘cup test’), little changed for decades and based on measuring weight changes, has been shown repeatedly in round-robin comparisons to have poor accuracy and little consistency between laboratories. Here we describe a new approach in which the primary measurement is of the humidity difference across the test sample, which is monitored continuously using sensors that are remotely readable. The box-in-box (BiB) apparatus described is smaller and simpler than that of the standard cup test. The BiB test is of shorter duration and is carried out without disturbance to the sample. New results on calcium silicate sheet, brick ceramic and autoclaved aerated concrete are compared with published vapour permeability values obtained by the standard test (considered to be of lower accuracy).
Thermal equation of states for body-centered cubic tungsten using extended analytic embedded-atom model
Authors: Jong Mi-Ryong , Song Pom , Jon Chung-Guk , Jin Hak-Son , Kim Tae-Song
Published: November 2022

Here the thermal equation of states (EOS) for body-centered cubic (bcc) tungsten (W) is evaluated using embedded atom method (EAM). To reproduce the materials properties under high pressure and high temperature reasonably well, we extend EAM by improving the analytic expressions of the functions of electron density and embedding energy based on the quantum-mechanical results of the electron density distribution and the energy variation with respect to the electron density. Then we determine the parameters of the extended analytic model for bcc W. We evaluate volume dependence of structure energy, elastic properties as function of volume, monovacancy and divacancy properties, lattice vibration at various volumes, and variation of the Gibbs free energy with respect to temperature, pressure and volume within the framework of the quasiharmonic approximation. By minimizing the Gibbs free energy, we determine the thermal EOS, variation of volume or lattice parameter with respect to pressure and temperature. The linear thermal expansion coefficient as function of temperature under different pressures is also evaluated. All calculation results fit well to the experimental and other reliable theoretical calculation results, showing the reliability of the extended analytic EAM in the extended domains of electron density, atomic volume, temperature and pressure.
Precursor engineering for efficient and stable perovskite solar cells
Authors: Luan Fuyuan , Li Haiyan , Gong Shuiping , Chen Xinyu , Shou Chunhui , Wu Zihua , Xie Huaqing , Yang Songwang
Published: November 2022

The perovskite film prepared by the two-step spin coating method is widely used in photovoltaic devices due to its good film morphology and great reproducibility. However, there usually exists excessive lead iodide (PbI2) in the perovskite film for this method, which is believed to passivate the grain boundaries (GBs) to increase the efficiency of the perovskite solar cells. Nevertheless, the excessive PbI2 at the GBs of perovskite is believed to induce the decomposition of the perovskite film and undermine the long-term stability of devices. In this study, we utilize precursor engineering to realize the preparation of perovskite solar cells with high efficiency and stability. The concentration of organic salts (AX: A = MA+, FA+; X = I−, Cl−) in the precursor solution for the second step of the two-step spin coating method is adjusted to optimize the perovskite light-absorbing layer so that the excessive PbI2 is converted into perovskite to obtain a smooth and pinhole-free perovskite film with high performance. Our results indicate that by adjusting the concentration of AX in the precursor solution, PbI2 in the film could be completely converted into perovskite without excessive AX residue. Both the efficiency and stability of the perovskite solar cells without excessive PbI2 have been significantly improved. A planar perovskite solar cell with the highest power conversion efficiency (PCE) of 21.26% was achieved, maintaining about 90% of the initial PCE after 300 h of storage in a dry air environment and in the dark, about 76% of the initial PCE after 300 h of continuous illumination of 1 Sun.
Vacancy clustering effect on the electronic and transport properties of bilayer graphene nanoribbons
Authors: Miranda L P , da Costa D R , Peeters F M , Costa Filho R N
Published: November 2022

Experimental realizations of two-dimensional materials are hardly free of structural defects such as e.g. vacancies, which, in turn, modify drastically its pristine physical defect-free properties. In this work, we explore effects due to point defect clustering on the electronic and transport properties of bilayer graphene nanoribbons, for AA and AB stacking and zigzag and armchair boundaries, by means of the tight-binding approach and scattering matrix formalism. Evident vacancy concentration signatures exhibiting a maximum amplitude and an universality regardless of the system size, stacking and boundary types, in the density of states around the zero-energy level are observed. Our results are explained via the coalescence analysis of the strong sizeable vacancy clustering effect in the system and the breaking of the inversion symmetry at high vacancy densities, demonstrating a similar density of states for two equivalent degrees of concentration disorder, below and above the maximum value.
CoT-XNet: contextual transformer with Xception network for diabetic retinopathy grading
Authors: Zhao Shuiqing , Wu Yanan , Tong Mengmeng , Yao Yudong , Qian Wei , Qi Shouliang
Published: November 2022

Objective. Diabetic retinopathy (DR) grading is primarily performed by assessing fundus images. Many types of lesions, such as microaneurysms, hemorrhages, and soft exudates, are available simultaneously in a single image. However, their sizes may be small, making it difficult to differentiate adjacent DR grades even using deep convolutional neural networks (CNNs). Recently, a vision transformer has shown comparable or even superior performance to CNNs, and it also learns different visual representations from CNNs. Inspired by this finding, we propose a two-path contextual transformer with Xception network (CoT-XNet) to improve the accuracy of DR grading. Approach. The representations learned by CoT through one path and those by the Xception network through another path are concatenated before the fully connected layer. Meanwhile, the dedicated pre-processing, data resampling, and test time augmentation strategies are implemented. The performance of CoT-XNet is evaluated in the publicly available datasets of DDR, APTOS2019, and EyePACS, which include over 50 000 images. Ablation experiments and comprehensive comparisons with various state-of-the-art (SOTA) models have also been performed. Main results. Our proposed CoT-XNet shows better performance than available SOTA models, and the accuracy and Kappa are 83.10% and 0.8496, 84.18% and 0.9000 and 84.10% and 0.7684 respectively, in the three datasets (listed above). Class activation maps of CoT and Xception networks are different and complementary in most images. Significance. By concatenating the different visual representations learned by CoT and Xception networks, CoT-XNet can accurately grade DR from fundus images and present good generalizability. CoT-XNet will promote the application of artificial intelligence-based systems in the DR screening of large-scale populations.
Ensemble Kalman inversion for magnetic resonance elastography
Authors: Iglesias Marco , McGrath Deirdre M , Tretyakov M V , Francis Susan T
Published: November 2022

Magnetic resonance elastography (MRE) is an MRI-based diagnostic method for measuring mechanical properties of biological tissues. MRE measurements are processed by an inversion algorithm to produce a map of the biomechanical properties. In this paper a new and powerful method (ensemble Kalman inversion with level sets (EKI)) of MRE inversion is proposed and tested. The method has critical advantages: material property variation at disease boundaries can be accurately identified, and uncertainty of the reconstructed material properties can be evaluated by consequence of the probabilistic nature of the method. EKI is tested in 2D and 3D experiments with synthetic MRE data of the human kidney. It is demonstrated that the proposed inversion method is accurate and fast.
Dose perturbations in proton pencil beam delivery investigated by dynamically deforming silicone-based radiochromic dosimeters
Authors: Jensen Simon V , Muren Ludvig P , Balling Peter , Petersen Jørgen BB , Valdetaro Lia B , Poulsen Per R
Published: November 2022

Objective. Proton therapy with pencil beam delivery enables dose distributions that conform tightly to the shape of a target. However, proton therapy dose delivery is sensitive to motion and deformation, which especially occur in the abdominal and thoracic regions. In this study, the dose perturbation caused by dynamic motion with and without gating during proton pencil beam deliveries were investigated using deformable three-dimensional (3D) silicone-based radiochromic dosimeters. Approach. A spread-out Bragg peak formed by four proton spots with different energies was delivered to two dosimeter batches. All dosimeters were cylindrical with a 50 mm diameter and length. The dosimeters were irradiated stationary while uncompressed and during dynamic compression by sinusoidal motion with peak-to-peak amplitudes of 20 mm in one end of the dosimeter and 10 mm in the other end. Motion experiments were made without gating and with gating near the uncompressed position. The entire experiment was video recorded and simulated in a Monte Carlo (MC) program. Main results. The 2%/2 mm gamma index analysis between the dose measurements and the MC dose simulations had pass rates of 86%–94% (first batch) and 98%–99% (second batch). Compared to the static delivery, the dose delivered during motion had gamma pass rates of 99%–100% when employing gating and 68%–87% without gating in the experiments whereas for the MC simulations it was 100% with gating and 66%–82% without gating. Significance. This study demonstrated the ability of using deformable 3D dosimeters to measure dose perturbations in proton pencil beam deliveries caused by dynamic motion and deformation.
Agreement between standard and continuous wireless vital sign measurements after major abdominal surgery: a clinical comparison study
Authors: Haahr-Raunkjaer Camilla , Skovbye Magnus , Rasmussen Søren M , Elvekjaer Mikkel , Sørensen Helge B D , Meyhoff Christian S , Aasvang Eske K
Published: November 2022

Objective. Continuous wireless monitoring outside the post-anesthesia or intensive care units may enable early detection of patient deterioration, but good accuracy of measurements is required. We aimed to assess the agreement between vital signs recorded by standard and novel wireless devices in postoperative patients. Approach. In 20 patients admitted to the post-anesthesia care unit, we compared heart rate (HR), respiratory rate (RR), peripheral oxygen saturation (SpO2), and systolic and diastolic blood pressure (SBP and DBP) as paired data. The primary outcome measure was the agreement between standard wired and wireless monitoring, assessed by mean bias and 95% limits of agreement (LoA). LoA was considered acceptable for HR and PR, if within ±5 beats min−1 (bpm), while RR, SpO2, and BP were deemed acceptable if within ±3 breaths min−1 (brpm), ±3%-points, and ±10 mmHg, respectively. Main results. The mean bias between standard versus wireless monitoring was −0.85 bpm (LoA −6.2 to 4.5 bpm) for HR, −1.3 mmHg (LoA −19 to 17 mmHg) for standard versus wireless SBP, 2.9 mmHg (LoA −17 to 22) for standard versus wireless DBP, and 1.7% (LoA −1.4 mmHg to 4.8 mmHg) for SpO2, comparing standard versus wireless monitoring. The mean bias of arterial blood gas analysis versus wireless SpO2 measurements was 0.02% (LoA −0.02% to 0.06%), while the mean bias of direct observation of RR compared to wireless measurements was 0.0 brpm (LoA −2.6 brpm to 2.6 brpm). 80% of all values compared were within predefined clinical limits. Significance. The agreement between wired and wireless HR, RR, and PR recordings in postoperative patients was acceptable, whereas the agreement for SpO2 recordings (standard versus wireless) was borderline. Standard wired and wireless BP measurements may be used interchangeably in the clinical setting.
Review: III–V infrared emitters on Si: fabrication concepts, device architectures and down-scaling with a focus on template-assisted selective epitaxy
Authors: Tiwari Preksha , Triviño Noelia Vico , Schmid Heinz , Moselund Kirsten E
Published: November 2022

The local integration of III–Vs on Si is relevant for a wide range of applications in electronics and photonics, since it combines a mature and established materials platform with desired physical properties such as a direct and tuneable bandgap and high mobility. The large thermal expansion coefficient and lattice mismatch, however, pose a challenge for the direct growth of III–Vs on Si. In this paper we will review fabrication concepts to overcome this mismatch for the local integration of III–Vs on Si. In particular, we will briefly discuss processing methods based on aspect ratio trapping, nanowire growth, and template-assisted selective epitaxy (TASE). The focus of this review will be on the latter, where we will provide an overview of the different possibilities and embodiments of TASE and their promise for locally integrated active photonic devices.
CMOS compatible manufacturing of a hybrid SET-FET circuit
Authors: del Moral A , Amat E , Engelmann H-J , Pourteau M-L , Rademaker G , Quirion D , Torres-Herrero N , Rommel M , Heinig K-H , von Borany J , Tiron R , Bausells J , Perez-Murano F
Published: November 2022

This study analyzes feasibility of complementary metal–oxide–semiconductor (CMOS)-compatible manufacturing of a hybrid single electron transistor–field effect transistor (SET-FET) circuit. The fundamental element towards an operating SET at room temperature is a vertical nanopillar (NP) with embedded Si nanodot generated by ion-beam irradiation. The integration process from NPs to contacted SETs is validated by structural characterization. Then, the monolithic fabrication of planar FETs integrated with vertical SETs is presented, and its compatibility with standard CMOS technology is demonstrated. The work includes process optimization, pillar integrity validation, electrical characterization and simulations taking into account parasitic effects. The FET fabrication process is adapted to meet the requirements of the pre-fabricated NPs. Overall, this work establishes the groundwork for the realization of a hybrid SET-FET circuit operating at room temperature.
Effects of nitrogen flux and RF sputtering power on the preparation of crystalline a-plane AlN films on r-plane sapphire substrates
Authors: Cai Tingsong , Guo Yanan , Liu Zhibin , Zhang Ruijie , Xue Bin , Wang Chong , Liu Naixin , Yi Xiaoyan , Li Jinmin , Wang Junxi , Yan Jianchang
Published: November 2022

A-plane aluminum nitride (AlN) with high quality is crucial to fabricate high-performance non-polar deep-ultraviolet optoelectronic devices. In this work, we prepared crystalline a-plane AlN films on r-plane sapphire substrates by combining reactive magnetron sputtering and high temperature annealing (HTA). The effects of N2 flux and radio frequency (RF) sputtering power on the crystal quality, the surface morphology and the in-plane stress state of a-plane AlN films were comprehensively investigated. The results suggest that the properties of high temperature annealed a-plane AlN (HTA-AlN) films positively depend on the initial states of the sputtered AlN (SP-AlN) films. Increasing the N2 flux or the RF sputtering power can improve the crystalline quality of SP-AlN films by reducing the kinetic energy of deposited particles, which facilitates a-plane AlN deposition. A higher N2 flux smoothens the surface morphology due to the relieved bombardment effect, which is confirmed by the enlarged in-plane tensile stress state. However, a higher sputtering power leads to a rougher surface because of the accelerated deposition rate. With optimized sputtering parameters, a high-quality a-plane HTA-AlN template was obtained with full width at half maximum values of (11–20) plane x-ray rocking curves as low as 1188 and 1224 arcsec along [0001] and [1–100] directions, respectively. The surface presents an ordered stripe-like morphology with a root-mean-square value of 0.79 nm. Our work provides a convenient and effective strategy to prepare high quality a-plane AlN templates and accelerate the versatile application of non-polar deep-ultraviolet light-emitting diode devices.
Design and testing of a capacitive interface for underwater stretch sensors
Authors: Walker Christopher , Rosset Samuel , Anderson Iain
Published: November 2022

The growing popularity of wearable electronics has seen substantial research in soft and flexible strain sensors. From athletic performance analysis to human augmentation, there is a wide range of applications being developed. An area often overlooked is the connections between a network of wearable sensors and their measurement electronics. In dry applications this is as simple as cabling between the two. In underwater environments however this becomes more complicated. Capacitive strain sensors have been used to demonstrate underwater sensor-based motion capture in both a robotic fish and smart glove for divers. Wired connections introduced failure points and eliminated the modularity of the system for potted electronics. In this paper we have demonstrated the use of a capacitive interface as a wireless method to connect wearable strain sensors across an encapsulation to electronics. This removes the need to have wires permanently protruding through the encapsulation. The interfaces’ impact on strain sensor sensitivity and measurement method has been investigated for both resistive and capacitive-based strain sensing.
A frequency-dependent variable-damping control based variable-orifice damper for smart base-isolation system
Authors: Li Zhong-Xian , Wen Dongbin , Shi Yundong , Wei Xin
Published: November 2022

Damping devices are commonly used in the isolation layer of base-isolated structures to provide additional damping to control the structural responses. Normally, large damping for the isolation layer is useful to minimize the resonance effect under low-frequency ground motions, and small damping is preferred to reduce the structural responses under high-frequency ground motions. Traditional passive dampers are widely adopted in engineering practice. Due to the fixed damping characteristic, however, the performance of base-isolated structures with passive dampers cannot stay optimal under ground motions with different frequency characteristics. To realize an optimal control of base-isolated structures, semi-active control has been increasingly valued for its efficiency and intelligence to adjust the damping characteristics based on feedback information from the structure and ground motion. However, a large number of sensors and hardware components are required for semi-active control, which makes the system complex and costly. In this paper, a variable-orifice damper (VOD) for smart base-isolation system is proposed. The VOD can adaptably adjust its damping according to the frequency of the ground motion without additional power or sensors. Theoretical analysis and sinusoidal excitation tests were carried out to investigate the behavior of VOD. A series of numerical simulations of a base‐isolated structure equipped with the proposed VOD and subjected to ground motions are also conducted. A semi-active control with ON-OFF strategy, and two passive controls (passive-on and passive-off) are conducted for comparison. The simulation results show that the VOD can result in an optimal control under ground motions with different frequency characteristics.
An initial magnet experiment using high-temperature superconducting STAR® wires
Authors: Wang Xiaorong , Bogdanof Timothy J , Ferracin Paolo , Ghiorso William B , Gourlay Stephen A , Higley Hugh C , Kadiyala Janakiram Kaushal , Kar Soumen , Lee Reginald , Luo Linqing , Maruszewski Maxwell A , Memmo Robert , Myers Cory S , Prestemon Soren O , Sandra Jithin Sai , Selvamanickam Venkat , Teyber Reed , Turqueti Marcos , Wu Yuxin
Published: November 2022

A dipole magnet generating 20 T and beyond will require high-temperature superconductors such as Bi2Sr2CaCu2O

8
−
x

and REBa2Cu3O

7
−
x

(RE = rare earth, rebco). Symmetric tape round (star®) wires based on rebco tapes are emerging as a potential conductor for such a magnet, demonstrating a whole-conductor current density of 580 A mm−2 at 20 T, 4.2 K, and at a bend radius of 15 mm. There are, however, few magnet developments using star® wires. Here we report a subscale canted

cos
θ

dipole magnet as an initial experiment for two purposes: to evaluate the conductor performance in a magnet configuration and to start developing the magnet technology, leveraging the small bend radius afforded by star® wires. The magnet was wound with two star® wires, electrically in parallel and without transposition. We tested the magnet at 77 and 4.2 K. The magnet reached a peak current of 8.9 kA, 78% of the short-sample prediction at 4.2 K, and a whole-conductor current density of 1500 A mm−2. The experiment demonstrated a minimum viable concept for dipole magnet applications using star® wires. The results also allowed us to identify further development needs for star® conductors and associated magnet technology to enable high-field rebco magnets.
Fabrication and characterization of NbN/(TaN/NbN)
N
stacked Josephson junctions
Authors: Zhang Lu , Tao Yuanhe , Zhong Yulong , Yan Kaixin , Zeng Junwen , Shi Weifeng , Wu Ling , Wang Huiwu , Chen Lei , Peng Wei , Wang Zhen
Published: November 2022

In this work, we present a detailed study of the electrical properties of stacked NbN/(TaN/NbN)
N
Josephson junctions. Cross-sectional scanning transmission electron microscopy analysis of the 5-stacked junction shows that the multilayer interface is very flat, each barrier has the same thickness, and the sidewalls of the junctions are nearly perpendicular to the substrate. Stacked junctions of different sizes and stacking numbers all have only one transition in their current–voltage curves. This indicates that the critical currents of the junctions in the stacked junctions are almost the same, showing the stability and repeatability of the multilayer fabrication and etching process. At 4.2 K, the 4-stacked junction shows excellent Josephson properties with characteristic voltage V
c of 3.54 mV, which is about four times the 0.88 mV of the single junction. The temperature dependence of critical current density J
c and V
c of the stacked junction with N = 1, 2, 4 were measured, all of which can be fitted with dirty-limit theory. Stacked junctions with larger V
c or more stacked layers can be achieved by optimizing electrode and barrier thickness, barrier resistivity, and thermal relaxation rate, etc.
Isolated ultra-bright attosecond pulses via non-collinear gating
Authors: Kennedy J P , Dromey B , Yeung M
Published: November 2022

When light with relativistic intensity is incident on a solid target, bright attosecond pulses of extreme ultraviolet and x-ray radiation can be generated in the reflected beam. Unfortunately, the use of multi-cycle laser pulses results in trains of these attosecond pulses. Here we investigate a non-collinear gating scheme applied to surface high-harmonic generation to allow for the extraction of a single intense attosecond pulse from this train. Using 3D and 2D particle in cell (PIC) simulations we demonstrate that it is possible to angularly isolate a single attosecond pulse from the main driving laser pulse using this interaction geometry with intensities I > 1020 W cm−2. This result opens the door to generating bright attosecond pulses from relativistic plasmas without the need to spectrally filter the driving laser pulse.
Observation of collectivity enhanced magnetoassociation of 6Li in the quantum degenerate regime
Authors: Naniyil Vineetha , Zhou Yijia , Simmonds Guy , Cooper Nathan , Li Weibin , Hackermüller Lucia
Published: November 2022

The association process of Feshbach molecules is well described by a Landau–Zener (LZ) transition above the Fermi temperature, such that two-body physics dominates the dynamics. However, using 6Li atoms and the associated Feshbach resonance at B
r = 834.1 G, we observe an enhancement of the atom–molecule coupling as the fermionic atoms reach degeneracy, demonstrating the importance of many-body coherence not captured by the conventional LZ model. In the experiment, we apply a linear association ramp ranging from adiabatic to non-equilibrium molecule association for various temperatures. We develop a theoretical model that explains the temperature dependence of the atom–molecule coupling. Furthermore, we characterize this dependence experimentally and extract the atom–molecule coupling coefficient as a function of temperature, finding qualitative agreement between our model and experimental results. In addition, we simulate the dynamics of molecular association during a nonlinear field ramp. We find that, in the non-equilibrium regime, molecular association efficiency can be enhanced by sweeping the magnetic field cubically with time. Accurate measurement of the atom–molecule coupling coefficient is important for both theoretical and experimental studies of molecular association and many-body collective dynamics.
Magneto-optical double zero-index media and their electromagnetic properties in the bulk
Authors: Feng Fanghu , Wang Neng , Wang Guo Ping
Published: November 2022

Double-zero-index media (DZIM) with zero permittivity and permeability are one important class in zero-refractive index photonics. Here, we extended the concept of DZIM and proposed a more general type, i.e., the magneto-optical DZIM (MODZIM), of which the permittivity and the determinant of the Hermitian permeability tensor are simultaneously zero. By formulating the Maxwell’s equations in the basis of complex-valued axes and using some mathematical principles, we studied the electromagnetic (EM) properties in the bulk of the MODZIM with different boundaries and impurities. Inside the MODZIM which is infinite along in the out-of-plane direction, it is shown that the scalar (out-of-plane) field is not uniform in general, in contrast to traditional DZIM where the scalar field is always uniform in the bulk. Nevertheless, for a normal incidence, the uniform scalar field inside the MODZIM can be achieved by optimizing the boundary conditions and doping some types of impurities, such as resonant round cylinders and arbitrary shaped media with a zero permeability. As long as the scalar field is uniform, the propagation of the EM wave inside the MODZIM can be analyzed with closed-form expressions. Our work will extend the study of zero-refractive-index photonics and provide deeper understanding of wave dynamics in the bulk of MODZIM.
Theoretical and experimental investigation of the metal–insulator transition in disordered anti-dot graphene
Authors: Zhang Ting , Zhang Haijing , Pan Jie , Sheng Ping
Published: November 2022

We study the transport behavior of anti-dot graphene both theoretically and experimentally, where the term ‘anti-dot’ denotes the graphene layer to be nanostructured with a periodic array of holes. It has been shown that the electronic band structure of the anti-dot graphene can be described by a 4 by 4 effective Hamiltonian (Pan J et al 2017 Phys. Rev. X. 7 031043) with a gap around the Dirac point, attendant with a 0 to π variation of the Berry phase as a function of energy, measured from the band edge. Based on the diagrammatic method analysis and experiments, we identify an energy-dependent metal-to-insulator transition (MIT) in this two-dimensional (2D) system at a critical Fermi energy ɛ
c, characterized by the divergence of the localization length in the Anderson localization phase to a de-localized metallic phase with diffusive transport. By measuring the conductance of square samples with varying dimension and at different Fermi energies, experiments were carried out to verify the theory predictions. While both theory and experiment indicate the existence of a 2D MIT with similar localization length divergence exponent, the values of the critical energy ɛ
c and that of the localization length do not show quantitative agreement. Given the robust agreement in the appearance of a 2D MIT, we attribute the lack of quantitative agreement to the shortcomings in the theoretical model. The difficulties in addressing such shortcomings are discussed.
Low-frequency underwater sound absorption metamaterial
Authors: Wang Tian , Wang Gui-Bo , Zhang Ruo-Jun , Ke Man-Zhu
Published: November 2022

Air bubbles in liquid are known for exhibiting low-frequency resonance and can be considered as passive scatterers. In this paper, we design an acoustic metamaterial consisting of an air bubble in a water-filled metal shell with an opening to develop low frequency underwater sound absorber. Numerical simulation is carried out by using finite element method, and the results show that the metamaterial sound absorber achieves quasi-prefect sound absorption coefficient (up to 0.96) at the frequency of 900 Hz based on the coupling resonance between the elastic bubble and the metal shell matrix. By replacing the single unit with a 3-unit composite structure, the acoustic metamaterial absorber can extend the working frequency from 830 Hz to1330 Hz, with still high absorption coefficient above 0.8. Our design acoustic metamaterial has potential applications in underwater noise control.
Coexistence of multiscroll chaotic attractors in two coupled inertial Hopfield neurons: numerical simulations and experiment
Authors: Sriram Sridevi , Danao Adile Adoum , Fonzin Theophile Fozin , Rajagopal Karthikeyan , Kengne Jacques
Published: November 2022

In this contribution, we consider the dynamics of a pair of coupled inertial neurons with hyperbolic tangent activation function. The two inertial neurons are coupled by adding to each one’s amplitude a perturbation proportional to the other one. The model is governed by a fourth-order autonomous system with hyperbolic tangent nonlinearities. The analysis of the coupled system yields nine equilibrium points some of which experience Hopf type bifurcation. When adjusting the coupling coefficients, striking nonlinear patterns are disclosed such as the coexistence of numerous bifurcation branches, merging crisis, multiple Hopf bifurcations, coexisting self-excited motions (e.g. two coexisting double-scroll chaos, four coexisting period-n cycles, four coexisting single-scroll chaos), and four-scroll chaotic attractors. These latter features are diagnosed with the help of classic numerical tools (e.g. 1D and 2D maximum Lyapunov exponent diagrams, 1D bifurcation diagrams of local peaks of variables, frequency spectrum plots, phase space trajectory plots, and attraction basins). The analogue electronic circuit design of the coupled inertial neurons system is carried out and simulated in PSpice to verify diverse types of features reported during the theoretical study. One of main achievements of the present article is that the coupling of inertial neurons can be regarded as an alternative scheme to obtain multiscroll chaotic signals.
Solitons, single- and synchronous dual-wavelength noise-like pulses and hybrid regimes from a thulium-doped fiber laser
Authors: Ibarra-Garrido A , Durán-Sánchez M , Pottiez O , Bello-Jiménez M , Alaniz-Baylón J , Rodríguez-Morales L A , Armas-Rivera I , Ibarra-Escamilla B
Published: November 2022

In a passively mode-locked thulium-doped fiber laser within the anomalous dispersion regime, we experimentally demonstrate conventional soliton (CS), hybrid (noise-like pulse (NLP) and solitons), as well as switchable single-wavelength and synchronous dual-wavelength NLP regimes. By properly adjusting the PCs, we can switch between CS to hybrid and single- or dual-wavelength NLP regimes. With sufficient pumping power and through manual polarization adjustments, self-starting mode locking at 1996 nm can be observed. At the pump power of 2.5 W, stable mode locking with an output power of 86 mW is obtained. When generating the CS state, Kelly sidebands due to the spectral interference of dispersive waves are observed. Keeping the pump power at 2.5 W but with a modification of the polarization adjustment we can switch to five different regimes involving NLPs with squared envelope. The noise-like nature of the squared pulses was confirmed in each case through an autocorrelation measurement. By additional adjusting of the PCs, single- and synchronous dual-wavelength squared NLPs can be generated, at either one of two wavelengths in the former case, and at both simultaneously in the latter. The pulse trains from the single-wavelength operations display a small difference in their repetition frequencies inherently determined by intracavity dispersion, whereas in dual-wavelength operation the pulse train displays a single repetition rate whose value is intermediate between the single-wavelength frequencies. The obtained results are valuable to deepen our understanding on the formation of CS and dual-wavelength pulses with noise-like squared profiles in fiber lasers.
Stable high-efficiency continuous-wave diamond Raman laser at 1178 nm
Authors: Sun Yuxiang , Li Muye , Kitzler Ondrej , Mildren Richard Paul , Bai Zhenxu , Zhang Hongchao , Lu Jian , Feng Yan , Yang Xuezong
Published: November 2022

We demonstrate a high-efficiency continuous-wave (CW) diamond Raman laser operating at 1178 nm with enhanced stability by using a V-cavity design. A maximum Stokes power of 39 W with a conversion efficiency of 45% was achieved using a linearly-polarized 1018 nm Yb-doped fiber pump laser. The Stokes CW power stability showed superior stability over a linear cavity when characterized over periods up to 15 min. The Stokes output was found to switch between linear, elliptical, and random polarization with varying pump polarization. The results represent a major step towards stable, efficient and high-power CW lasers at 1178 nm and at wavelengths outside the main Yb, and Nd emission bands.
Magnon-mediated multi-channel high-order sideband generation in cavity magnonics
Authors: Fu Yan , Yang Lin , Cao Man , Kong Cui
Published: November 2022

We propose a scheme to describe magnon-mediated multi-channel high-order sideband generation in a cross cavity magnonic system. The high-order sideband generation is composed of equally spaced discrete output frequency components, which is essential tools for light communication, precision metrology, timing and spectroscopy. Beyond the generally linearized description by using the perturbative method, we deal with the Heisenberg–Langevin equations in the non-perturbative regime to obtain the output spectrum of high-order sidebands. Unlike conventional methods of using power that requires externally adjustable incident beams, here we demonstrate magnon-mediated high-order sideband generation in a cavity magnonic device by utilizing its intrinsically good tunability. Furthermore, until now most of the work in cavity magnonics is mainly restricted to the frequency/time domain, while we realize the modulation of sideband effects by the manipulation of cavity-magnon polaritons in real space, that is the external magnetic field with a tunable angle. By tuning the angle, we can obtain multi-channel high-order sideband generation, which may offer the potential for selectively transferring coherent information processing technologies.
Spectral radiance standard transfer for an integrating sphere as a radiation source in the ultraviolet band
Authors: Li Jia-wei , Chen Hong-yao , Zhang Li-ming , Huang Wen-xin , Yang Bao-yun
Published: November 2022

We developed a new source, having uniform spectral radiance, for a large-aperture UV integrating sphere with pressed polytetrafluoroethylene coating. Since lamp panel systems have high uncertainty due to a low signal-to-noise ratio at 250 nm, to transfer the spectral radiance scale from 250 nm to 350 nm to the source, we developed and calibrated a filter radiometer based on a solar blind phototube. The spectral radiance was obtained via a model of the source and a recursive estimation of the model parameters. A standard FEL lamp validated the usage of the filter radiometer. Finally, the filter radiometer to calibrate the new source. The results show that the radiance of the source at 250 nm is five times the top-of-the-atmosphere spectral irradiance, and the expanded uncertainty is 4.7%.