Accepted
, , Received Date: 2024-11-13
Abstract +
Anderson localization is a profound phenomenon in condensed matter physics, representing a fundamental transition of eigenstates induced by disorder. The one-dimensional Aubry-André-Harper (AAH) model, an iconic quasiperiodic lattice model, is one of the simplest models that demonstrate the Anderson localization transition. Recently, with the growing interest in quantum lattice models in curved spacetime (CST), the AAH model in CST has been proposed as a way to explore the interplay between Anderson localization and CST physics. While a few CST lattice models have been realized in optical waveguide systems to date, significant challenges remain in the experimental preparation and measurement of states, primarily due to the difficulty of dynamically modulating lattices in such systems. In this study, we propose an experimental scheme using a momentum-state lattice (MSL) in an ultracold atom system to realize the AAH model in CST and study the Anderson localization in this context. Thanks to the individual controllability of the coupling between each pair of adjacent momentum states, the coupling amplitude in the MSL can be encoded as a power-law position-dependent form $J_n \propto n^{\sigma}$, facilitating effective simulation of CST. Numerical calculation results of the MSL Hamiltonian show an emergence of the phase separation in a 34-site AAH chain in CST, where wave packet dynamics exhibit localized behavior on one side of the critical site and extended behavior on the other. The phase separation critical site is observed by extracting turning points of the evolving fractal dimension and the wave packet width derived from evolution dynamic simulations. Furthermore, by modulating the spacetime curvature parameter σ, we propose a method for eigenstates preparation of the AAH chain in CST, and perform numerical simulations in the MSL. Through calculating the fractal dimension of eigenstates prepared following the aforementioned method, we analyze the localization properties of eigenstates under various quasiperiodic modulation phases, confirming the coexistence of localized phase, swing phase, and extended phase in the energy spectrum. Unlike traditional localized and extended phases, eigenstates in the swing phase of the AAH model in CST exhibit different localization properties under different modulation phases, indicating the prescence of a swing mobility edge. Our results provide a feasible experimental approach to study Anderson localization in CST and introduce a new platform for realizing quantum lattice models in curved spacetime.
, , Received Date: 2024-09-05
Abstract +
On-chip erbium-doped/erbium-ytterbium co-doped waveguide amplifiers (EDWAs/EYCDWAs) have received extensive research attention in recent years, As an important component of EDWA, there has been relatively little research on integrated wavelength division multiplexing/demultiplexing devices for 980 nm pump light and 1550 nm signal light. This article aims to propose a compact Ta2O5 980/1550 nm wavelength diplexer based on multimode interference effects. The device employs a structure of symmetric interference and paired interference cascade, which reduces the total length of the segmented multimode interference waveguide to one-third of the ordinary paired multimode interference waveguide without using any complex structures such as subwavelength gratings to regulate the beat length of the pump and signal light. The three-dimensional finite difference time domain (3D-FDTD) tool was used to analyze and optimize the established model. The results demonstrate that the designed MMI diplexer has low insertion loss and high process tolerance, with an insertion loss of 0.4 dB at 980 nm and 0.8 dB at 1550 nm, and the extinction ratios are both better than 16 dB. Moreover, the 1-dB bandwidth is up to 150 nm around the 1550 nm wavelength and up to 70 nm around the 980 nm wavelength. The segmented structure designed in the article greatly reduces the design difficulty of MMI devices and reduces the overall size of 980/1550 nm wavelength division multiplexers/demultiplexers. It is expected to be applied in on-chip integrated erbium-doped waveguide amplifiers and lasers. In addition, the segmented design approach of cascading the hybrid multimode interference mechanism provides a technical reference for separating two optical signals with far apart center wavelengths such as 800/1310 nm and 1550/2000 nm, and has potential application value in communication and mid infrared diplexing devices.
, , Received Date: 2024-08-26
Abstract +
, , Received Date: 2024-09-25
Abstract +
The manipulation of particles by acoustic radiation force (ARF) has the advantages of non-invasiveness, high biocompatibility, and wide applicability. The study of acoustic radiation force is an important foundation for improving the accuracy and effectiveness of particle manipulation technology. Based on the acoustic wave theory, a theoretical model for the ARF of a free spherical particle in a bounded viscous fluid is established. The ARF for the case of a normal incident plane wave is derived by applying the translation addition theorem to spherical function. The dynamic equation of a free sphere is required as a correction term for calculating the ARF. The effects of the fluid viscosity, particle material, particle distance from boundary, and the boundary on the ARF are analyzed by numerical simulation. The results show that the resonance peak of the ARF curve is broadened with the increase of the viscosity of the fluid. Compared with the values of the ARFs of a PE sphere in a viscous and an ideal fluid, the fluid viscosity has a small influence and the viscosity effect can be ignored when kR is much less than 1. However, for the cases where kR is greater than or equal to 1, the amplitude of the ARF experienced by a particle in a viscous fluid is much greater than that in an ideal fluid. The influence of fluid viscosity on the ARF is significant and cannot be ignored. Moreover, compared with a liquid material sphere, the oscillation of ARF in an elastic material sphere is more pronounced. This is because the momentum transfer between sound waves and elastic materials is greater than that between sound waves and liquid materials. In addition, the amplitude of the ARF increases with the increase of the reflection coefficient of the impedance boundary, but its resonance frequency is not affected. Finally, the position of the sphere mainly affects the oscillation phenomenon of its ARF. The peaks and dips of the ARF become more densely packed with the growth of distance-to-radius. It is worth noting that the reflection coefficient mainly affects the amplitude of the ARF, while the position of the sphere affects the period of the ARF function. The results indicate that more efficient manipulation of particles can be achieved through appropriate parameter selection. This study provides a theoretical basis for acoustically manipulating a free particle in a bounded viscous fluid and contributes to the better utilization of ARF for particle manipulation in biomedical and other fields.
, , Received Date: 2024-09-14
Abstract +
, , Received Date: 2024-09-18
Abstract +
In the re-entry process of the vehicle into the atmosphere, the high-temperature environment, induced by the compression of the strong shock wave and viscous retardation, is created around the head of a vehicle. These generate a conductive plasma flow field, which provides a direct working environment for the application of magnetohydrodynaimic (MHD) control technology. Numerical simulations based on thermochemical non-equilibrium MHD model are adopted to analyze the surface heat flux of an orbital reentry experiment (OREX) vehicle. The influences of wall catalytic conditions on the aerothermal environment under different flight conditions are discussed. In addition, the control mechanism of an external magnetic field on high-temperature thermochemical non-equilibrium flow field is analyzed. The results show that the distribution of surface heat flux monotonically increases with the catalytic recombination coefficient increasing, and the surface heat flux rises and then drops with the flight altitude decreasing. Moreover, the wall catalytic properties significantly affect the efficiency of MHD control technology, and the total heat flux is closely related to the accumulation of atomic components, diffusion gradient and temperature gradient near the wall region. With an external magnetic field applied, the accumulation of oxygen atoms and nitrogen atoms near the wall can be reduced. Moreover, the Lorentz force can increase the shock standoff distance, and then reduce the component diffusion gradient and wall temperature gradient. Under three different wall catalytic conditions, the ability to control the surface heat flux MHD is ranked from strong to weak as fully catalyzed, partially catalyzed and non-catalyzed.
, , Received Date: 2024-10-23
Abstract +
, , Received Date: 2024-09-29
Abstract +
,
Abstract +
Quantum nondemolition (QND) measurement aided by high-finesse optical cavities is an important method for generating high-gain spin or momentum squeezed states, which can enhance the sensitivity of atom interferometers to surpass the standard quantum limit. Conventional two-mirror Fabry-Perot cavities have the drawback of a standing wave pattern, leading to inhomogeneous atom-light coupling and subsequent degradation of squeezing enhancement. In this study, we present a novel method for achieving homogeneous quantum nondemolition measurement using an optical ring cavity to generate momentum squeezed states in atom interferometers. We designed and demonstrated a high-finesse (F =2.4(1)×104), high-vacuum compatible (1×10-10 mbar) optical ring cavity that utilizes the properties of traveling wave fields to address the issue of inhomogeneous atom-light interaction. A strontium cold atomic ensemble was prepared and coupled into the cavity mode; the dispersive cavity phase shift caused by the atoms passing through was extracted through differential Pound-Drever-Hall measurement, enabling nondemolition measurement of the atom number. Experimental results indicate that, under a probe laser power of 20 µW, the dispersive phase shift of the ring cavity was measured to be 40 mrad. The effective number of atoms coupled into the cavity mode is around 1×106. Verification of the consistency between the ring cavity dispersive phase shift and QND measurement theory was achieved by adjusting parameters such as matching the atomic position with the cavity mode and tuning the frequency of the probe laser. The optical ring cavity developed in this study provides a significant approach for generating spin or momentum squeezed states in atom interferometers, thus holding promise for enhancing their sensitivity and is expected to find wide applications in cavity-enhanced quantum precision measurements.
,
Abstract +
The direct detection of gravitational waves has opened a new window for understanding the universe and trailblazed multi-messenger astronomy. The frequency band of gravitational waves generated by various astronomical events can cover broadband range, and it is various for detection mechanism and scheme of gravitational waves in different frequency band. For example, The ground-based gravitational wave detection has the frequency band for 10 Hz to 10 kHz to mainly detect which based on Michelson interferometer; The space gravitational wave detection has the frequency band of 0.1 mHz to 1 Hz to mainly detect which based on space interferometer; The pulsar gravitational wave detection has the frequency band for 1×10-9 Hz to 1×10-7Hz to mainly detect which based on pulsar timing array. The next generation ground-based gravitational wave project demands higher sensitivity to detect faint signals, necessitating an assessment system with minimal background noise to accurately measure the laser relative intensity noise. At present, the detection frequency band of ground-based gravitational wave detection devices in operation is mainly concentrated in the range of 10 Hz - 10 kHz. To satisfying the detection sensitivity requirements, the laser relative intensity noise should be accurately evaluated and suppressed to ≤2.0×10-9Hz-1/2@10 Hz and ≤4.0×10-7Hz-1/2@10 kHz by photoelectric feedback. This paper constructed an evaluation and characterization system for ground-based gravitational wave band laser intensity noise which based on low noise and high sensitivity photoelectric detection device and combined with LabVIEW and MATLAB algorithm programming for instrument control and data processing. This low noise evaluation system is used to test the background noise of FFT analyzer SR760, preamplifier SR560, photoelectric detector electronics noise and intensity noise of self-developed optical fiber amplifier, and then the data extraction and image processing are carried out by LabVIEW and MATLAB algorithms, and finally the evaluation of ground-based gravitational wave frequency band system is obtained. The experimental results show that the whole electronic noise for the preamplifier SR560 and FFT analyzer SR760 is lower than 3.8×10-9 Hz-1/2@(10 Hz-10 kHz). The electronic noise for the photodetector is lower than 1.4×10-8V/√Hz@10 Hz&8.1×10-9V/√Hz@10 kHz and the accuracy of the system is calibrated and tested by the standard sinusoidal signal. Finally, the noise of commercial laser is evaluated and compared with the factory data to verify the accuracy of the evaluation system. Related research, device and system development provide hardware, software and theoretical basis for the preparation of high-power low-noise laser light source and gravitational wave detection and provide theoretical basis and evaluation criteria for ground-based gravitational wave detection in China.
,
Abstract +
The five linear primary and secondary alcohols, n-propanol, isopropanol, n-butanol, 2-butanol and 2-pentanol, have similar chain lengths and a little different structures and they are measured by dielectric spectroscopy in this paper to investigate the properties of monohydroxy alcohols. It is found that the dielectric spectra of isopropanol and n-butanol show an abnormal variation. i.e., the relaxation peaks with the highest strength gradually increases with rising temperature in the range of about 145 K-175 K. The analyses state that the abnormal variation originated from that of the Debye dielectric relaxation strength (DDRS) in the monohydroxy alcohols at above temperatures. According to the theoretical model of the DDRS for the monohydroxy alcohols, the abnormal variation is considered as the results of the combined action of decrease and increase of the DDRS due to temperature and the transformation of the structure of the hydrogen bonding molecular chain caused by the alteration of the mobility of molecules, respectively. By comparing the relaxation time of the five monohydroxy alcohols, it is found that the conditions should be harsher to induce the above abnormal variation. In addition, the results also show that strength parameter of Debye processes, intrinsic vibration frequency of the relaxation units and their activation energy in the high-temperature limit in secondary alcohols also raises with the increasing number of carbon atoms, similar to that in the case of primary alcohols. These results could not only provide a new breakthrough point for the investigation of exotic properties in monohydroxy alcohols but also give a reference to explore the effect of molecular chain length on their dynamics.
,
Abstract +
In nanosystems, the metallic nanowires are subjected to significant and cyclic bending deformation upon integration into stretchable and flexible nanoelectronic devices. The reliability and service life of these nanodevices depend fundamentally on the bending mechanical properties of the metallic nanowires that serve as the critical components. A deep understanding of the deformation behavior of the metallic nanowires under bending is not only essential but also imperative for design and manufacture of high-performance nanodevices. To explore the mechanism underlying the bending plasticity of the metallic nanowire, we have conducted a study on the bending deformation of B2-FeAl alloy nanowires with various crystallographic orientations, sizes and cross-sectional shapes by using molecular dynamics simulation. Our results show that the bending behavior of the B2-FeAl alloy nanowires is independent of the size and cross-sectional shape of the nanowire, but it is highly sensitive to its axial orientation. Specifically, both <111>- and <110>-oriented nanowires yield by dislocation nucleation upon bending, in which the <111>-oriented nanowire fails by brittle fracture soon after yielding, while the <110>-oriented nanowire exhibits good ductility due to homogeneous plastic flow raised by continuous nucleation and steady motion of dislocations. In contrast to the aforementioned two nanowires, the bending plasticity of the <001>-oriented nanowire is mediated by stress-induced transformation from B2 to L10 phases, which leads to excellent ductility and higher fracture strain. The orientation dependence of bending deformation can be understood by considering the Schmid factor. Moreover, the plastically bent nanowires with <110> and <001> orientations are able to recover to their original shape upon unloading, particularly, the plastic deformation in the <001>-oriented nanowire is recoverable completely via reverse transformation from L10 to B2 structures, exhibiting superelasticity. This work elucidates the deformation mechanism of the B2-FeAl alloy nanowire subjected to bending load, which provides a crucial insight for the design and optimization of flexible and stretchable nanodevices based on metallic nanowires.
Abstract +
The main goal of this paper is to investigate the properties of the low-energy quadrupole strength in Ni isotopes, especially for the evolution of the pygmy quadrupole states with increasing neutron number. And the effect of shell evolution on the pygmy resonance is also discussed in detail. The Skyrme Hartree-Fock+Bardeen-Cooper-Schrieffer (HF+BCS) theory and the selfconsistent quasiparticle random phase approximation (RPA) method are employed on top of three effective Skyrme interactions named SGII, SLy5 and SKM*. In the calculations, a density-dependent zero-range type force are adopted for the pairing correlations. The properties of the first 2+ state in Ni isotopes are studied firstly. As Fig. (a) shown, a good description on the experimental excited energies of the first 2+ states are achieved, the SGII and SLy5 can give a good description on the reduced electric transition probabilities for 58-68Ni. It is found that the energies of the first 2+ state for 68Ni and 78Ni are obviously high than others, which reflects the obvious shell effect. In addition to the first 2+ states, pygmy quadrupole states between 3 to 5 MeV with relative large electric transition probabilities are evidently found for 70-76Ni in the isoscalar quadruple strength distribution [see Fig. (b)]. With the increasing of neutron number, the pygmy quadrupole states have decreasing energies but hold gradually increasing strengths, and it is more sensitive to the changes in the shell structure. This is due to the fact that the gradually filling of the neutron level 1g9/2 has an very important impact on the pygmy quadrupole states of 70-76Ni, and switch from proton-dominated excitations to neutron-dominated ones. Since the pygmy quadrupole states for 70-76Ni are sensitive to the proton and neutron shell gaps, which can provide information on the shell evolution in neutron-rich nuclei.
,
Abstract +
During overcharging of lithium-ion batteries, lithium plating can occur on the anode surface when the maximum lithium intercalation concentration is exceeded, while the cathode is in a lithium-poor state. This situation can lead to significant issues related to battery lifespan and safety. In this paper, the geometric structure of the positive electrode particles is generated based on tomography data, while the negative electrode particles are represented by spheres of different sizes. Using the homogenization method, the carbon filler, binder and electrolyte are regarded as a single porous conductive adhesive domain. Based on the main mechanism of lithium-ion battery overcharge, a coupled three-dimensional electrochemical - mechanical - thermal overcharge model at the particle scale is developed for NCM cathode and graphite anode. The coupled mathematical model consists of four parts, namely the electrochemical model, the lithium plating model, the thermal model and the stress-strain model. In terms of lithium precipitation, the particle radius parameter and charging rates are investigated. The results show that the lithium plating concentration of the particles near the separator is higher, following the "principle of proximity" - the sequence of lithium deintercalation is related to the migration path. The surface of anode particles with small particle size is more prone to lithium precipitation due to the high maximum lithium ion concentration on the surface of the particles, the low surface lithium precipitation overpotential, and the high average Von Mises stress. At high charging rate, fast charge transfer and ion diffusion rates result in a low voltage at the anode triggering lithium precipitation. At a low rate, polarization and low temperature result in more lithium precipitation on the surface of the anode particles. In terms of stress, the spatial distribution between particles and thermal effects are investigated. The ratio of the distance from the contact surface to the center of the particle to the particle radius is calculated and defined as the contact depth (Jr), in order to better describe the law of particle contact stress. It is shown that the contact depth between particles is inversely proportional to the stress at the contact area. When the heat generation effect is considered, the temperature of the battery rises faster with the increase of the charging rate. The electrochemical parameters related to temperature and the lithium concentration diffusion gradient increase significantly, and the influence of temperature on the particle stress is also more significant. The relevant results can provide theoretical basis and guidance for designing battery and optimizing charge strategies.
, , Received Date: 2024-09-14
Abstract +
During the study of resistive switching devices, researchers have found that the influence of the insertion layer cannot be ignored. Many reports have confirmed that the appropriate insertion layer can significantly improve the performance of the resistive switching devices. Therefore, in this work, we use magnetron sputtering to fabricate three devices: Cu/MgO/Cu, Cu/MgO/MoS2/Cu and Cu/MoS2/MgO/Cu. Through the characterization test of each device and the measurement of the I-V curve, it is found that the resistive switching characteristics of the Cu/MgO/Cu device will change greatly after adding an MoS2 insertion layer. The analysis results show that the inserted MoS2 layer does not change the main transmission mechanism (space charge limited conduction) of the device, but affects the regulating function of interfacial potential barrier, the effect also is relatedto the location of MoS2 inserted into the layer. Among the Cu/MgO/Cu, Cu/MgO/MoS2/Cu and Cu/MoS2/MgO/Cu devices, the Cu/MgO/MoS2/Cu device exhibits a larger switching ratio (about 103) and a lower reset voltage (about 0.21 V), which can be attributed to the regulation of the interface barrier between MgO and MoS2. In addition, when the MoS2 layer is inserted between the bottom electrodes Cu and MgO, the leakage current of the device is significantly reduced. Therefore, Cu/MoS2/MgO/Cu device has the highest commercial value from the point of view of practical applications. Finally, according to the XPS results and XRD results, we establish the conductive filament models for the three devices, and analyze the reasons for the different resistive switching characteristics of the three devices.
- 1
- 2
- 3
- 4
- 5
- ...
- 17
- 18
