Signatures of moiré-trapped valley excitons in MoSe2/WSe2 heterobilayers.

The formation of moiré patterns in crystalline solids can be used to manipulate their electronic properties, which are fundamentally influenced by periodic potential landscapes. In two-dimensional materials, a moiré pattern with a superlattice potential can be formed by vertically stacking two layered materials with a twist and/or a difference in lattice constant. This approach has led to electronic phenomena including the fractal quantum Hall effect1-3, tunable Mott insulators4,5 and unconventional superconductivity6. In addition, theory predicts that notable effects on optical excitations could result from a moiré potential in two-dimensional valley semiconductors7-9, but these signatures have not been detected experimentally. Here we report experimental evidence of interlayer valley excitons trapped in a moiré potential in molybdenum diselenide (MoSe2)/tungsten diselenide (WSe2) heterobilayers. At low temperatures, we observe photoluminescence close to the free interlayer exciton energy but with linewidths over one hundred times narrower (around 100 microelectronvolts). The emitter g-factors are homogeneous across the same sample and take only two values, -15.9 and 6.7, in samples with approximate twist angles of 60 degrees and 0 degrees, respectively. The g-factors match those of the free interlayer exciton, which is determined by one of two possible valley-pairing configurations. At twist angles of approximately 20 degrees the emitters become two orders of magnitude dimmer; however, they possess the same g-factor as the heterobilayer at a twist angle of approximately 60 degrees. This is consistent with the umklapp recombination of interlayer excitons near the commensurate 21.8-degree twist angle7. The emitters exhibit strong circular polarization of the same helicity for a given twist angle, which suggests that the trapping potential retains three-fold rotational symmetry. Together with a characteristic dependence on power and excitation energy, these results suggest that the origin of the observed effects is interlayer excitons trapped in a smooth moiré potential with inherited valley-contrasting physics. This work presents opportunities to control two-dimensional moiré optics through variation of the twist angle.

Trajectory-BERT: Trajectory Estimation Based on BERT Trajectory Pre-Training Model and Particle Filter Algorithm.

In the realm of aviation, trajectory data play a crucial role in determining the target's flight intentions and guaranteeing flight safety. However, the data collection process can be hindered by noise or signal interruptions, thus diminishing the precision of the data. This paper uses the bidirectional encoder representations from transformers (BERT) model to solve the problem by masking the high-precision automatic dependent survey broadcast (ADS-B) trajectory data and estimating the mask position value based on the front and rear trajectory points during BERT model training. Through this process, the model acquires knowledge of intricate motion patterns within the trajectory data and acquires the BERT pre-training Model. Afterwards, a refined particle filter algorithm is utilized to generate alternative trajectory sets for observation trajectory data that is prone to noise. Ultimately, the BERT trajectory pre-training model is supplied with the alternative trajectory set, and the optimal trajectory is determined by computing the maximum posterior probability. The results of the experiment show that the model has good performance and is stronger than traditional algorithms.

Tuning of the Valley Structures in Monolayer In2Se3/WSe2 Heterostructures via Ferroelectricity.

Recent findings of two-dimensional ferroelectric (FE) materials have enabled the integration of nonvolatile FE functions into device applications based on van der Waals (vdW) heterojunctions (HJs), resulting in versatile technological advances. In this paper, we report the results of direct probing of the electronic structures of In2Se3/WSe2 heterostructures at the single-layer limit, where monolayer (ML)-In2Se3 was found to be either antiferroelectric (AFE, ß') or ferroelectric (ß*) at sufficiently low temperatures. A general type-II band alignment was revealed for this heterostructure. Moreover, we observed significant modulations of the valley structures of WSe2, and in situ transformations between the FE and AFE In2Se3 phases demonstrated the dominant role of the polarizations in the top ML-In2Se3 layer. The observed phenomena can be attributed to the combination of both the linear and quadratic Stark shifts from the out-of-plane electric field, which has only been previously theoretically explored for ML-transition metal dichalcogenides (TMDs).

Strong Moiré Excitons in High-Angle Twisted Transition Metal Dichalcogenide Homobilayers with Robust Commensuration.

The burgeoning field of twistronics, which concerns how changing the relative twist angles between two materials creates new optoelectronic properties, offers a novel platform for studying twist-angle dependent excitonic physics. Herein, by surveying a range of hexagonal phase transition metal dichalcogenides (TMD) twisted homobilayers, we find that 21.8 ± 1.0°-twisted (7a×7a) and 27.8 ± 1.0°-twisted (13a×13a) bilayers account for nearly 20% of the total population of twisted bilayers in solution-phase restacked bilayers and can be found also in chemical vapor deposition (CVD) samples. Examining the optical properties associated with these twisted angles, we found that 21.8 ± 1.0° twisted MoS2 bilayers exhibit an intense moiré exciton peak in the photoluminescence (PL) spectra, originating from the refolded Brillouin zones. Our work suggests that commensurately twisted TMD homobilayers with short commensurate wavelengths can have interesting optoelectronic properties that are different from the small twist angle counterparts.

[Design of Adjustable Liquid Simulated Eye for Spherical Power Detection of Eccentric Photographic Vision Screening Instrument].

A liquid simulated eye was designed to detect different spherical diopter indexes in the type inspection of medical equipment vision screening instrument. This liquid test simulation eye design is composed of three parts: lens, cavity and retina-imitation piston. By using the principle of geometric optics and the optical scattering effect of human retina, the relationship between the accommodation displacement of the designed adjustable liquid simulated eye and the spherical mirror power was calculated and analyzed. The designed liquid test simulated eye can be applied to vision screening instruments, computer refractometers and other optometry equipments based on photography principle in spherical lens measurement and so on.

Chiral Excitonics in Monolayer Semiconductors on Patterned Dielectrics.

Monolayer transition metal dichalcogenides feature tightly bound bright excitons at the degenerate valleys, where electron-hole Coulomb exchange interaction strongly couples the valley pseudospin to the momentum of the exciton. Placed on a periodically structured dielectric substrate, the spatial modulation of the Coulomb interaction leads to the formation of exciton Bloch states with real-space valley pseudospin texture displayed in a mesoscopic supercell. We find this spatial valley texture in the exciton Bloch function is pattern locked to the propagation direction, enabling nano-optical excitation of directional exciton flow through the valley selection rule. The left-right directionality of the injected exciton current is controlled by the circular polarization of excitation, while the angular directionality is controlled by the excitation location, exhibiting a vortex pattern in a supercell. The phenomenon is reminiscent of the chiral light-matter interaction in nanophotonics structures, with the role of the guided electromagnetic wave now replaced by the valley-orbit coupled exciton Bloch wave in a uniform monolayer, which points to new excitonic devices with nonreciprocal functionalities.

Nanoscale Trapping of Interlayer Excitons in a 2D Semiconductor Heterostructure.

For quantum technologies based on single excitons and spins, the deterministic placement and control of a single exciton is a longstanding goal. MoSe2-WSe2 heterostructures host spatially indirect interlayer excitons (IXs) that exhibit highly tunable energies and unique spin-valley physics, making them promising candidates for quantum information processing. Previous IX trapping approaches involving moiré superlattices and nanopillars do not meet the quantum technology requirements of deterministic placement and energy tunability. Here, we use a nanopatterned graphene gate to create a sharply varying electric field in close proximity to a MoSe2-WSe2 heterostructure. The dipole interaction between the IX and the electric field creates an ∼20 nm trap. The trapped IXs show the predicted electric-field-dependent energy, saturation at low excitation power, and increased lifetime, all signatures of strong spatial confinement. The demonstrated architecture is a crucial step toward the deterministic trapping of single IXs, which has broad applications to scalable quantum technologies.

[Analysis of International Standard ISO 80601-2-90:2021 for High-flow Respiratory Therapy Equipment].

The international standard ISO 80601-2-90:2021 specifies basic safety and essential performance requirements, including risks associated with oxygen, flow accuracy, oxygen concentration accuracy, humidification output performance, and corresponding test methods for high-flow respiratory therapy equipment. This study focuses on the key points in ISO 80601-2-90:2021 and the key problems in the test evaluation. This study also briefly introduces the relationship between ISO 80601-2-90:2021 and other standards, and explains the countermeasures that stakeholders should take.

[Biomechanical Study of New Biodegradable Esophageal Stent].

The radial force of the degradable esophageal stent before and after degradation is one of the important indicators for effective treatment of esophageal stricture. Based on a combination of in vitro experiments and finite element analysis, this paper studies and verifies the biomechanical properties of a new type of degradable esophageal stent under different esophageal stricture conditions. Under radial extrusion conditions, the maximum stress at the port of the stent is 65.25 MPa, and the maximum strain is 1.98%; The peak values of stress and strain under local extrusion and plane extrusion conditions both appear in the extrusion area and the compression expansion area at both ends, which are respectively 48.68 MPa, 46.40 MPa, 0.49%, 1.13%. The maximum radial force of the undegraded stent was 11.22 N, and 97% and 51% of the maximum radial force were maintained after 3 months and 6 months of degradation, respectively. The research results verify the safety and effectiveness of the radial force of the new degradable esophageal stent, and provide a theoretical basis for the clinical treatment of esophageal stricture.

Monolayer Semiconductor Auger Detector.

Auger recombination in semiconductors is a many-body phenomenon in which the recombination of electrons and holes is accompanied by excitation of other charge carriers. The excess energy of the excited carriers is normally rapidly converted to heat, making Auger processes difficult to probe directly. Here, we employ a technique in which the Auger-excited carriers are detected by their ability to tunnel out of the semiconductor through a thin barrier, generating a current. We use vertical van der Waals heterostructures with monolayer WSe2 as the semiconductor, with hexagonal boron nitride as the tunnel barrier, and a graphite collector electrode. The Auger processes combined with resonant absorption produce characteristic negative photoconductance. We detect holes Auger-excited by both neutral and charged excitons and find that the Auger scattering is surprisingly strong under weak excitation. Our work expands the range of techniques available for probing relaxation processes in 2D materials.

[Research on Mathematical Distribution of Failure Time and Engineering Evaluation for Medical Electrical Equipment Based on Operation and Maintenance Data].

This study mainly discusses the contents, methods and characteristics of the collection of operation and maintenance data, as well as the establishment and evaluation methods of the distribution model of the failure time of medical electrical equipment. The distribution models of failure time at three levels of medical electrical equipment are established by linear regression method and goodness of fit test:The first is the device level MTBF distribution model, the second is the failure rate distribution model of the failure mode of key components, the third is the calculation model of the influence coefficient of influence factor on the failure mode of key components. This study presents a method of establishing MTBF segment model and implements a calculation model of influence coefficient varying with time.

[Simulation Study on Radiated Immunity Test of Active Implantable Medical Device].

In the electromagnetic compatibility standards of active implantable medical devices such as ISO 14117,radiated immunity test above 450 MHz frequency is recommended to be carried out in the electromagnetic shielding room.However,different test locations and the shape/size of the shielding room may lead to very different electromagnetic field distribution in the radiation exposure area of the sample,thus affecting the consistency of the test.With the model built by COMSOL software,this paper analyzes the impact of different parameters,such as size of the room and position of torso simulator on the distribution of field intensity,and reaches results about the distribution of field intensity on the torso simulator area under tow sizes of shielding rooms and two typical test positions.The results show that the experimental consistency of the electric field intensity on the surface directly below the center of the antenna is not good enough,which may affect the repeatability of the test.

[Exploration of Domestic Medical Electrical Equipment Reliability Promotion Method].

The reliability of domestic medical equipment is one of the main factors that restrict the competitiveness of domestic medical devices. It is also an important factor that endangers the safety of patients and a blind spot in safety risk management. By analyzing the core elements of reliability and the situation of domestic medical device industry, this paper sorts out and analyzes the problems existing in the reliability of medical device industry, and puts forward the key points and problems to be solved to improve the reliability of domestic medical equipment products.

One symbol training receiver for the SPAD-based UVLC system.

For the long distance single photon avalanche diode (SPAD)-based underwater visible light communication (UVLC) system, the multiple-symbol union detection scheme is presented. However, an error floor curve of the bit-to-error ratio (BER) occurs and cannot vanish even though the transmitted power approaches infinity. In this paper, to solve the problems of error floor and channel estimation in the long distance SPAD-based UVLC system, we propose the one training symbol maximum likelihood (ML) detection receiver. First, we add one training symbol in the head of each frame to eliminate the error floor and ensure the reliable blind estimation of the long distance UVLC channel. Meanwhile, the training ML detection (TMLD) receiver is developed. And then, to improve the system performance, a training modified (TM) quasi-ML receiver with Anscombe root transformation is proposed. Compared to the traditional mean detection scheme of the SPAD receiver, the simulation results show that the proposed TM quasi-ML and TMLD schemes significantly improve the error-rate performance.

Direct Position Determination of Unknown Signals in the Presence of Multipath Propagation.

A novel geolocation architecture, termed "Multiple Transponders and Multiple Receivers for Multiple Emitters Positioning System (MTRE)" is proposed in this paper. Existing Direct Position Determination (DPD) methods take advantage of a rather simple channel assumption (line of sight channels with complex path attenuations) and a simplified MUltiple SIgnal Classification (MUSIC) algorithm cost function to avoid the high dimension searching. We point out that the simplified assumption and cost function reduce the positioning accuracy because of the singularity of the array manifold in a multi-path environment. We present a DPD model for unknown signals in the presence of Multi-path Propagation (MP-DPD) in this paper. MP-DPD adds non-negative real path attenuation constraints to avoid the mistake caused by the singularity of the array manifold. The Multi-path Propagation MUSIC (MP-MUSIC) method and the Active Set Algorithm (ASA) are designed to reduce the dimension of searching. A Multi-path Propagation Maximum Likelihood (MP-ML) method is proposed in addition to overcome the limitation of MP-MUSIC in the sense of a time-sensitive application. An iterative algorithm and an approach of initial value setting are given to make the MP-ML time consumption acceptable. Numerical results validate the performances improvement of MP-MUSIC and MP-ML. A closed form of the Cramér-Rao Lower Bound (CRLB) is derived as a benchmark to evaluate the performances of MP-MUSIC and MP-ML.

Unusual Exciton-Phonon Interactions at van der Waals Engineered Interfaces.

Raman scattering is a ubiquitous phenomenon in light-matter interactions, which reveals a material's electronic, structural, and thermal properties. Controlling this process would enable new ways of studying and manipulating fundamental material properties. Here, we report a novel Raman scattering process at the interface between different van der Waals (vdW) materials as well as between a monolayer semiconductor and 3D crystalline substrates. We find that interfacing a WSe2 monolayer with materials such as SiO2, sapphire, and hexagonal boron nitride (hBN) enables Raman transitions with phonons that are either traditionally inactive or weak. This Raman scattering can be amplified by nearly 2 orders of magnitude when a foreign phonon mode is resonantly coupled to the A exciton in WSe2 directly or via an A1' optical phonon from WSe2. We further showed that the interfacial Raman scattering is distinct between hBN-encapsulated and hBN-sandwiched WSe2 sample geometries. This cross-platform electron-phonon coupling, as well as the sensitivity of 2D excitons to their phononic environments, will prove important in the understanding and engineering of optoelectronic devices based on vdW heterostructures.

Interlayer Exciton Optoelectronics in a 2D Heterostructure p-n Junction.

Semiconductor heterostructures are backbones for solid-state-based optoelectronic devices. Recent advances in assembly techniques for van der Waals heterostructures have enabled the band engineering of semiconductor heterojunctions for atomically thin optoelectronic devices. In two-dimensional heterostructures with type II band alignment, interlayer excitons, where Coulomb bound electrons and holes are confined to opposite layers, have shown promising properties for novel excitonic devices, including a large binding energy, micron-scale in-plane drift-diffusion, and a long population and valley polarization lifetime. Here, we demonstrate interlayer exciton optoelectronics based on electrostatically defined lateral p-n junctions in a MoSe2-WSe2 heterobilayer. Applying a forward bias enables the first observation of electroluminescence from interlayer excitons. At zero bias, the p-n junction functions as a highly sensitive photodetector, where the wavelength-dependent photocurrent measurement allows the direct observation of resonant optical excitation of the interlayer exciton. The resulting photocurrent amplitude from the interlayer exciton is about 200 times smaller than the resonant excitation of intralayer exciton. This implies that the interlayer exciton oscillator strength is 2 orders of magnitude smaller than that of the intralayer exciton due to the spatial separation of electron and hole to the opposite layers. These results lay the foundation for exploiting the interlayer exciton in future 2D heterostructure optoelectronic devices.

[Research on Field Strength of Radiated Immunity Test for Active Implantable Medical Devices].

In order to compare the radiation immunity test level of ISO 14708 series standards and the domestic and international environmental radiation standards and then to ascertain whether the radiated immunity test level has reached the limit of the radiation strength in the relevant radiation environmental standards, this paper calculated the radiation field intensity and power density according to the radiated immunity test of ISO 14708 standards, and compared with the limit of ICNIRP 1998 and GB 8702-2014.

[A Torso Simulator Design for Implantable Nerve Stimulator Test].

This paper introduces ISO 14708-3:2017, the new edition of the international standard for implantable neurostimulator, and emphasizes the new requirements in the clause of protection from RF electromagnetic interference. To meet this new requirements, this paper presents a design of torso simulator for the testing of implantable neurostimulator. The design includes volume conductor, electrodes and grids, which can simulate the actual operating environment of implantable neurostimulator in RF electromagnetic interference testing. The torso simulator is verified by performance in the last part of the paper.

Realization of Valley and Spin Pumps by Scattering at Nonmagnetic Disorders.

The recent success in optical pumping of valley polarization in two-dimensional transition metal dichalcogenides (TMDs) has greatly promoted the concept of valley-based informatics and electronics. However, between the demonstrated valley polarization of transient electron-hole pair excitations and practical valleytronic operations, there exist obvious gaps to fill, among which is the valley pump of long-lived charge carriers. Here we discover that the quested valley pump of electrons or holes can be realized simply by scattering at the ubiquitous nonmagnetic disorders, not relying on any specific material property. The mechanism is rooted in the nature of the valley as a momentum space index: the intervalley backscattering in general has a valley contrasted rate due to the distinct momentum transfers, causing a net transfer of population from one valley to another. As examples, we numerically demonstrate the sizable valley pump effects driven by charge current in nanoribbons of monolayer TMDs, where the spin-orbit scattering by nonmagnetic disorders also realizes a spin pump for the spin-valley locked holes. Our finding points to a new opportunity towards valley spintronics, turning disorders from a deleterious factor to a resource of valley and spin polarization.