Modern Physics Letters B

In order to improve the mechanical behavior of the low-temperature ${\mathrm{\text{Sn}}}_{58}\mathrm{\text{Bi}}$ (SnBi) lead-free solder joint, the ${\mathrm{\text{Sn}}}_{0.7}{\mathrm{\text{Ag}}}_{0.5}{\mathrm{\text{Cu}}}_{3.5}{\mathrm{\text{Bi}}}_{0.05}\mathrm{\text{Ni}}$ (SACBN) solder ball with the diameter of 400 $\mu$m was pre-soldered on Cu to obtain the SnBi/SACBN/Cu composite joint. The microstructure and shear behavior of the solder joints were investigated. Experimental results indicate that SnBi solder is well bonded on the SACBN bump due to the elemental diffusion and dissolution between the molten SnBi and solid SACBN bump during the soldering process. The addition of the SACBN bump shows a significant effect on the formation and growth of the $\beta$-Sn grains in the SnBi bulk. Compared with the SnBi/Cu joint, the SnBi bulk in the composite joint shows enlarged $\beta$-Sn dendritic grains. Meanwhile, the interfacial intermetallic compound (IMC) layer transforms from Cu₆Sn₅ into (Cu, Ni)₆Sn₅. Among these three solder joints, the shear strength of the SACBN/Cu joint is the highest, reaching 86.7 MPa. The shear strength of the SnBi/Cu solder joint is enhanced by the SACBN bump from 68.2 MPa to 75.2 MPa. Additionally, the addition of the SACBN bump shows a positive effect on suppressing the brittleness of the SnBi/Cu solder joint.

Research on target recognition in random media by Monte Carlo method has made rapid progress. However, the commonly used probability sampling function of the emitted photons’ directions is not suitable for simulating the radial cross-sectional distribution of a beam. This sampling has little effect on the simulated laser transmission in clouds, but if the laser range profile (LRP) of a target is simulated, it will cause serious distortion because the common sampling method cannot well represent the radial two-dimensional intensity distribution of the beam. In this paper, the traditional sampling method is improved through rigorous derivation, and the superiority of the method is illustrated by simulation data. The simulation results show that the Monte Carlo model of LRP based on the improved sampling method plays well in profile shape of ideal targets identification. This research can bring more reference and significance to target recognition application.

Perfect screening of sub-milligauss magnetic fields (ideal diamagnetism) by a system comprised of a graphene and thin permalloy foil parallel to the graphene layer immersed in $n$-heptane is observed at room temperature. The presence of all three components is necessary for the effect to occur. Ideal diamagnetic response appears at the moment of $n$-heptane injection and disappears when the liquid evaporates. Until then, no change of diamagnetic moment occurs at further variation of the field. The observed ideal diamagnetic feature is either a footprint of a novel type of superconductivity at room temperature or a yet unknown quantum phenomenon in condensed matter physics.

Reference-frame-independent quantum key distribution (RFI-QKD) has been proved to be tolerant against unknown reference frame misalignment, which reserves interesting prospects in implementing global quantum communication. However, few works have been addressed on the performance and feasibility for RFI-QKD in turbulent atmospheric channels. Here, we propose to implement RFI-QKD in practical free-space links with fluctuating transmission efficiency due to beam wandering and broadening. An improved model for estimating the probability distribution of single-photon receiving efficiency has been developed and we also simulated the Gaussian beam spot evolution and secure key rate based on that. Results show that the beam wandering model of probability distribution of transmission efficiency is reasonable to improve the performance of RFI-QKD in free-space channel.

Thermal parameters of the ${\mathrm{\text{Bi}}}_2{\mathrm{\text{Se}}}_3$ compound were investigated by Differential Scanning Calorimetry (DSC) method. Four different phases were identified in the temperature range of $20\le T\le 800^{\circ }$C. Thermodynamical parameters were determined for each phase transition. ${\mathrm{\text{Bi}}}_2{\mathrm{\text{Se}}}_3$ samples were irradiated by 167 MeV energy ${}^{131}$Xe ions at the $5.0\times 10^{12}$, $5.0\times 10^{13}$ and $3.83\times 10^{14}$ ion/cm² intensities. The DSC analyses of the irradiated samples were carried out and determined that the temperature and thermodynamical parameters of the phase transition change in the ${\mathrm{\text{Bi}}}_2{\mathrm{\text{Se}}}_3$ compound under the influence of swift heavy ions. The change mechanism of the thermodynamical parameters has been determined depending on the irradiation doses.

Rice is a staple food crop around the world, and its demand is likely to rise significantly with growth in population. Increasing rice productivity and production largely depends on the availability of irrigation water. Thus, the efficient application of irrigation water such that the crop doesn’t experience moisture stress is of utmost importance. In the present study, a long short-term memory (LSTM)-based neural network with logistic regression has been used to predict the daily irrigation schedule of drip-irrigated rice. The correlation threshold of 0.75 was used for the selection of features, which helped in limiting the number of input parameters. Also, a dataset based on the recommendation of a domain expert, and another used by the tool Agricultural Production Systems Simulator (APSIM) was used for comparison. Field data comprising of weather station data and past irrigation schedules has been used to train the model. Grid search algorithm has been used to optimize the hyperparameters of the model. Nested cross-validation has been used for validating the results. The results show that the correlation-based selected dataset is as effective as the domain expert-recommended dataset in predicting the water requirement using LSTM as the base model. The models were evaluated on different parameters and a multi-criteria decision evaluation (Technique for Order of Preference by Similarity to Ideal Solution [TOPSIS]) was used to find the best performing.

Based on the Hirota bilinear method and symbolic computation, abundant exact solutions, including lump, lump–soliton, and breather solutions, are computed for the coupled Alice–Bob system of the Hirota–Satsuma–Ito equation in (2 + 1)-dimensions. The three-dimensional figures of these solutions are presented, which illustrate the characteristics of these solutions.

In this paper, nonlinear dynamic model of spur gear pairs with fractional-order damping under the condition of time-varying stiffness, backlash and static transmission error is established. The general formula of fractional-order damping term is derived by using the incremental harmonic balance method (IHBM), and the approximate analytical solution of the system is obtained by use of the iterative formula. The correctness of the results is verified by comparing with the numerical solutions in the existing literature. The effects of mesh stiffness, internal excitation amplitude and fractional order on the dynamic behavior of the system are analyzed. The results show that changing the fractional order can effectively control the resonance position and amplitude in the meshing process. Both the mesh stiffness and internal excitation can control the collision state and the stability.

A digital output Disk Resonator Gyroscope (DRG) on-chip temperature compensation method based on virtual sensor is proposed in this paper. DRG is a combination of solid wave gyroscope and MEMS gyroscope, it has become the research emphasis of high precision gyroscope. In practical application, the ambient temperature changing will cause several problems such as the change of scale factor, zero drift and so on. To increase the environmental adaptability of DRG, the DRG temperature characteristics are analyzed, the temperature compensation models of scale factor and zero output are established in this paper. The concept of virtual temperature sensor is introduced to solve the lead or lag problem caused by integrated temperature sensor. Based on the trend of AC drive amplitude changing with temperature, the temperature measurement is converted into AC voltage amplitude measurement. The virtual temperature sensor is used to complete the on-chip temperature compensation of the DRG angular velocity output, the second-order compensation realizes the scale factor change of 40 ppm/${}^{\circ }$C and zero output change of 27${}^{\circ }$/h over the full temperature range varying from $-40^{\circ }\mathrm{\text{C}}$ to 60${}^{\circ }$C according to the simulation result.

In this paper, we study a non-linear Schrödinger system with the negatively coherent coupling in a weakly birefringent fiber for two orthogonally polarized optical pulses. With respect to the slowly-varying envelopes of two interacting optical modes and based on the existing binary Darboux transformation, we obtain four types of the bound-state solitons: degenerate-I, degenerate-II, degenerate–non-degenerate, and non-degenerate–non-degenerate bound-state solitons. We graphically analyze the interactions between the degenerate or non-degenerate solitons and four types of the bound-state solitons. When the degenerate solitons interact with the bound-state solitons, amplitudes and widths of the degenerate solitons remain unchanged. When the non-degenerate solitons interact with the bound-state solitons, amplitudes and widths of the bound-state solitons remain unchanged.

The Andreev conductance in $\mathrm{\Delta }$-shaped quantum dots (QDs) system coupled with Majorana bound states (MBSs) is studied and resulting conductance spectrum displays resonant and non-resonant processes. These fluctuated resonances render features like insulating band, bonding (antibonding) in the low-bias region due to non-trivial role of interdot coupling $t_c$ and dots-MBSs coupling $\lambda$. On comparing QD levels $({𝜀}_1,{𝜀}_2,{𝜀}_3)$, and the coupling between the MBSs, coherent oscillating dynamics of an electron between the nanowire and the QDs can be portrayed. The insulating band is robust against $\lambda$, but highly sensitive to $t_c$, which causes to increase (decrease) the conductance. We can claim that under finite bias voltage, transport can facilitate the researchers to expose the essential features of the Majorana fermion in such closed systems composed of MBSs.

Temperature as an environmental parameter influences the evolution of an open quantum system. In detail, temperature lies in Lindblad operator of quantum master equation that the evolution of an open quantum system follows. Hence, one can implement a temperature estimation of thermal baths through a measurement of quantum Fisher information about temperature brought from quantum states. Such a method by calculating quantum Fisher information about a parameter to estimate its value avoids measuring the parameter directly and it does not change the value of the parameter due to making measurements. In this paper, we consider a model consisting of a XXZ spin-$\frac{1}{2}$ chain coupled locally to independent thermal baths with different temperature. Based on the model, we investigate optimal temperature estimation for thermal baths with respect to an open quantum system subjected to non-steady states. We first study optimal probe time for temperature estimation in the case of non-steady states and find that the optimal time shows different features for different types of system variables. It proves that in a certain duration there exists a tradeoff between the trial times and the attaining amount of Fisher information in each trial. In addition, we pay attention to an issue on optimal probe states. We demonstrate that in many cases the optimal states are not always the maximally entangled states and even maybe the separable states, which is related with the measuring time, system couplings.

In this paper, to characterize the effect of topological defects on the entanglement of topological states, we introduce the concept of local entanglement entropy. By using the spinless $p_x+i{p}_y$ superconductor with quantized vortices, we numerically calculated the local entanglement entropy. In the topological superconducting (weak-pairing) phase, we found that the local entanglement entropy turns to 0.5 for a Majorana zero mode. For the system with two/four Majorana zero modes, by calculating local entanglement entropy, we found the non-locality effect of Majorana zero modes. In the future, we will use local entanglement entropy to characterize the defect effect on other many-body systems with long entanglement, for example, topological order and quantum spin liquid.

A theoretical investigation has been made of the magnetoplasmon excitations in a quasi-one-dimensional electron system composed of vertically stacked, self-assembled InAs/GaAs quantum dots. The smaller length scales involved in the experiments impel us to consider a perfectly periodic system of two-dimensionally confined InAs quantum dot layers separated by GaAs spacers. Subsequent system is subjected to a two-dimensional confining (harmonic) potential in the $x$–$y$ plane and an applied magnetic field (B) in the symmetric gauge. This scheme defines virtually a system of quantum wire comprised of vertically stacked quantum dots (VSQD). We derive and discuss the Dyson equation, the generalized (nonlocal and dynamic) dielectric function, and the inverse dielectric function for investigating the single-particle and collective (magnetoplasmon) excitations within the framework of (full) random-phase approximation (RPA). As an application, we study the influence of the confinement potential and the magnetic field on the component eigenfunctions, the density of states (DOS), the Fermi energy, the collective excitations, and the inverse dielectric functions. How the B-dependence of DOS validate the VSQD mimicking the realistic quantum wires, the Fermi energy oscillates as a function of the Bloch vector, the intersubband single-particle continuum bifurcates at the origin, a collective excitation emerges and propagates within the gap of the split single-particle continuum, and the alteration in the well- and barrier-widths allows to customize the excitation spectrum in the desired energy range are some of the remarkable features of this investigation. These findings demonstrate, for the very first time, the significance of investigating the system of VSQD subjected to a quantizing magnetic field. Given the edge over the planar quantum dots and the foreseen applications in the single-electron devices and quantum computation, investigating the system of VSQD is deemed vital. The results suggest exploiting magnetoplasmon qubits to be a potential option for implementing the solemn idea of quantum state transfer in devising quantum gates for the quantum computation and quantum communication networks.