Modern Physics Letters B

A 4 mm thick heat-treated aluminum alloy AA 6061-T6 has been butt welded in 1 G position using a 12-kW disk laser. A novel high magnesium content filler rod ER 4943 belonging to the 4xxx series of aluminum alloys has been used to investigate its effects on microstructure, mechanical properties and alloying elements segregation in the fusion zone. The results have also been compared with an autogenous laser butt welded joint case. A solidified microstructure has been analyzed by EBSD. It was found that additional solute content brought by filler rod into the molten pool caused a higher proportion of equiaxed grain zone after solidification due to an enhanced constitutional supercooling ahead of solid/liquid interface. For an autogenous butt welded joint, the columnar morphology sustained for a longer period and a narrower equiaxed grain zone were observed. Point analysis by an EDS revealed a higher retention of magnesium and silicon inside the solid solution with filler rod welding. In addition, the area map of magnesium also observed a denser distribution of magnesium inside the fusion zone. Both hardness and tensile strength of filler rod welded joint were higher than without filler rod welding. It is believed that a higher proportion of equiaxed grains and additional solute content within the solid solution are the primary causes of higher mechanical properties owing to hampered dislocation motion. The much desirable results obtained in terms of microstructure and mechanical properties could be of great significance to the welding industry.

Circular laser beam oscillations have been applied at 0.5 mm and 1 mm amplitude with four different frequencies of 30, 60, 100 and 200 Hz during dissimilar laser beam welding of 2-mm-thick heat-treated AA2060-T8 with AA6061-T6. The results have been compared with a rectilinear welding case. The width of solidified weld beads produced by laser beam oscillations is wider than that of rectilinear welding due to an increase in the area of the processed zone. Welding defects inside the fusion zone were evaluated by subjecting the joints to 100% of X-ray examination, and it was found that there was absolutely no crack and negligible level of porosity in the fusion zone. Laser beam oscillations have been applied the first time to investigate the evolution of the dendritic equiaxed zone in the central region as well as the nondendritic equiaxed zone besides the fusion line in case of 2060-T8. Optical microscopy was employed to observe the microstructure. It was found that laser beam oscillations have a significant positive impact on the microstructure both in the central region and in the vicinity of the fusion line. The inhibited ability of the formation of equiaxed dendrites due to lesser solute content has been compensated by altering the thermal conditions inside the fusion zone, and a wider equiaxed dendritic region has been achieved. In addition, the nondendritic equiaxed zone, which is undesirable during welding of aluminum–lithium alloys, has been significantly reduced in width by employing laser beam oscillations. In case of rectilinear welding, the average width of the nondendritic equiaxed zone was found to be 43 $\mu$m, while the oscillatory welding reported an average width of the nondendritic equiaxed zone as low as 6 $\mu$m. Enhanced fluid flow inside the melt pool and repeated interaction of the beam with the molten pool are the most probable causes of the observed results. This investigation suggests that laser beam oscillations can be successfully used to alter the microstructure and produce high-quality welds using AA 2060-T8/6061-T6 and can be replaced with conventional rectilinear laser welding for industrial applications.

As a basic industry in the country’s development, the transportation industry has a significant relationship to its normal operation for developing and constructing the national economy. The increase in carbon emissions from transport is an increasingly growing problem, and countries worldwide are also taking measures to reduce emissions. Using time series data over the period from 1990 to 2016, this paper applies the visibility graph approach to transform it into a complex network and excavate some information about the data, then evaluates all countries based on the TOPSIS method. We find that the development of transportation is an important symbol to measure the degree of modernization of a country’s transportation, and low-income countries have lower carbon emissions due to slower transportation development. The results of transportation carbon emissions are especially encouraging for the Chinese government given its long-term and sustained efforts to expand railway and waterway infrastructure, and provide a new perspective for further research on the development trend of global transportation carbon emissions. Meanwhile, it is urgent to speed up the development and use of clean energy for economically developed countries.

In this paper, the double-chain model for deoxyribonucleic acid (DNA) is studied analytically by taking advantage of two reliable methodologies: the new auxiliary equation method (NAEM) and the expa function method. The deoxyribonucleic acid (DNA) contains the genetic information that creatures require for their survival and reproduction. The used approaches produce exact explicit solutions to the double chain model of DNA in mathematical biology, which are presented in this paper. Many novel solutions such as trigonometric, exponential, singular, and hyperbolic solutions, are obtained by using the aforementioned techniques. Numerical simulations are employed to supplement the obtained solutions, making this research biologically relevant. Eventually, kink wave, nonlinear wave, plane wave-front and doubly soliton profiles of solutions are presented in analysis and discussion section. It is indeed important to note that the solutions produced using these techniques are more generalized and can be more useful to demonstrate the internal interactions of the double chain DNA model.

In this paper, the gradient anechoic coating whose density changes exponentially along direction of thickness is investigated. A numerical model is established by finite element method (FEM) to analyze the underwater sound absorption performance under different density distribution. The calculation results show that the exponential anechoic coating has better sound absorption performance compared with the homogeneous medium and linear anechoic coating. In addition, a discrete layered method is proposed to achieve gradient characteristics. In order to change the equivalent density of each layer, periodically distributed semi-cylindrical steel scatterers with different diameters are embedded in each layer. Therefore, the density function of the whole coating changes in exponential gradient with stepped function. Based on the sound absorption mechanism of multiple scattering and waveform conversion, the sound absorption is improved in low-frequency band from 0 Hz to 1000 Hz. The exponential gradient anechoic coating has potential applications in underwater sound absorption and vibration control.

In this paper, a digital closed-loop measurement and control system of MEMS vibrating silicon gyro is proposed, which includes the sensitive structure model of gyro and the design of interface circuit. Because of the high sensitivity and precision of the MEMS gyroscope under the condition of modal matching, the measurement and control circuit is established under the condition of modal matching. The system uses automatic gain control (AGC) to control the amplitude of self-excited oscillation of the driving loop, which has the characteristics of simple and quick start. First, the working principle of gyro sensitive structure is introduced and an interface circuit with digital drive and detection mode is designed. Second, a high precision one-bit sigma-Delta ($\mathrm{\Sigma }\mathrm{\Delta })$ analog-to-digital converter (ADC) is designed, and the signal-to-noise ratio (SNR) of the modulator is 102.5 dB at 10 kHz bandwidth. Third, a nonlinear multiplier is used in the driving loop to realize fast self-excited start-up of gyro, and a proportional integral (PI) controller is used in the self-excited loop to realize stable oscillation. Finally, Simulink is used to simulate and verify the sensitive structure model and the measurement and control system. The nonlinearity of the gyroscope is tested by experiment, and the well measurement and control precision of the gyro interface circuit is verified.

An elastic topological insulator with pseudo-spin characteristics is designed based on honeycomb lattice phononic crystals with positive hexagonal carriers, which can realize path defect immunity and backscattering suppression transmission characteristics. By introducing a positive hexagon carrier with a certain size at the narrow diameter junction of the two-dimensional honeycomb structure to achieve symmetry breaking, a four-fold accidental degeneracy point can be obtained by adjusting the cell parameters. The main variable of the primitive cell is the hexagonal carrier side length $S$. It is found that the four-fold Dirac point can be opened and a band gap can be formed by contracting the positive hexagonal carrier. Inversion of the energy band occurred in the separated two-fold degenerate state, for which the transformation of mediocre state and nonmediocre state had been realized so that the structure with acoustic pseudo-spin and topological edge state could be obtained. Based on the principle of body-edge state correspondence, the topologically protected edge acoustic transmission is simulated by the construction of the edge states combined with the connection of different structural systems. Further, different elastic phonon crystal structures are constructed, and the characteristics of path defect immunity and back-scattering suppression of elastic wave propagation by topological edge states are verified. The designed elastic topological insulators have great application prospects in the regulation of elastic waves.

Quantum direct communication (QDC) uses the basic principle of quantum mechanics to realize the secure communication between legal parties. Deterministic secure quantum communication (DSQC), as a branch of QDC, is a way to transmit secret message with the aid of classical bits. In this paper, a multi-party DSQC based on $d$-dimension $k$-particles GHZ states is proposed, in which unitary operation is not required. On the basis of $d$-dimension single-photon measurement results, the communication parties encode and decode the message through performing modulo addition and subtraction. In addition, the scheme uses the added $d$-dimension single photon for eavesdropping detection. The scheme has expansibility and universality. It can scale to as many parties in any dimension as required. Based on the star-shaped communication structure, it can be extended to a network to achieve the rapid communication of secret message across regions.