Search

The effect of helium (He)-induced surface microstructure on deuterium (D) plasma-driven permeation through a reduced activation ferritic/martensitic steel CLF-1 has been studied. CLF-1 steel was pre-exposed by He plasma with ion fluence of 1022–1024 He m−2 and an incident energy of 100 eV at 708 K. The following D plasma-driven permeation experiment was performed at 693 K. Steady-state D permeation flux decreases with the increase in He ion fluence. D diffusion coefficient is not significantly affected by He pre-damage, while D reflection coefficient increases with the enhancement of He ion fluence. Scanning electron microscope and transmission electron microscope analyses clearly reveal the evolution of surface roughness and He bubble layer after He plasma exposure. Elastic recoil detection was used to identify He concentration depth profiles in the samples. Both the surface microstructure modification and He bubble layer formation contribute to the reduction of D permeation.

This paper presents an investigation of the performance of a coupled rotational double-beam energy harvester (DBEH) with magnetic nonlinearity. Two spring-connected cantilever beams are fixed on a rotating disc. Repelling magnets are attached to the frame and to the lower beam tip, and an equal-mass block is attached to the tip of the upper beam. To describe the dynamic response, a theoretical model related to the rotational motion of the coupled cantilever beam is derived from the Lagrange equations. In addition, the harmonic balance method, together with the arc-length continuation method, is applied to obtain the frequency response functions (FRFs). Parametric studies are then conducted to analyze the effect of varying the parameters on the energy harvesting performance, and numerical analysis is performed to validate the analytical solutions. Finally, the theoretical model is verified by forward- and reverse-frequency-sweeping experiments. The DBEH in rotational motion can perform effective energy harvesting over a wide range of rotational frequencies (10–35 rad s−1 ). The upper beam is found to exhibit better energy harvesting efficiency than the lower beam around the resonant frequency. This study effectively broadens the energy harvesting bandwidth and provides a theoretical model for the design of nonlinear magnet-coupled double-beam structure in rotational energy harvesting.

The strength of the weak layer not only controls the instability mechanism of the slope, but also the factor of safety to the slope. Studying the stability of the weak layer slope has important theoretical significance and practical engineering value. The instability mechanism and the factor of safety to slope stability with a thin weak layer were studied by finite element strength reduction method and limit equilibrium method. The results show that factor of safety to slope stability decreases with the strength of the weak layer decreases. When the strength of the weak layer is less than 0.6 times the strength of the soil, the instability mechanism of the slope changes from circular arc sliding to polygonal sliding, and its stability is controlled by the strength of the weak layer. The slope stability analysis by limit equilibrium method must be based on the analysis of the instability mechanism to accurately evaluate the slope stability. However, the finite element strength reduction method can be applied to calculate the factor of safety to slope stability and analyze the instability mechanism, and to previous limit equilibrium method.

We design an electromechanical transducer harvesting system with one-to-one internal resonance that can emerge a broader spectrum vibrations. The novel harvester is composed of a Duffing electrical circuit coupled to a mobile rod, and the coupling between both components is realized via the electromagnetic force. Approximate analytical solutions of the electromechanical system are carried out by introducing the multiple scales analysis, also the nonlinear modulation equation for one-to-one internal resonance is obtained. The character of broadband harvesting performance are analyzed, the two peaks and one jump phenomenon bending to the right for variation of control parameters are observed. It is shown that an advanced bandwidth over a corresponding linear model that does not possess a modal energy interchange.

The Internet brings people so much convenience, but also with a variety of viruses, network attacks and other security issues. Vulnerability mining technology is the core technology to solve the security of application software. According to different test objects, it can be divided into source-oriented vulnerability mining technology and binary code vulnerability mining technology. In recent years, software vulnerability mining technology still has many defects, involving dynamic tracking, symbol execution, path constraint collection and solutions. The purpose of this paper is to enable people to safely and safely use the Internet, maintaining the security of network application software has become the core issue of network security. In this paper, by introducing the improved genetic algorithm, the STP solver in KLEE and the improved genetic algorithm and model constraints are implemented to solve the nonlinear constraints in parallel. The solution module of genetic algorithm and model constraint is designed, and the parallel solution module in KLEE and the abstract resolution layer of KQuery are implemented. Finally, the parallel solution module is called by KLEE to generate test cases. The results show that the improved genetic algorithm can solve the nonlinear constraint conditions that cannot be solved in the original model, and generate test cases that can cover the path of the nonlinear constraint conditions, effectively improving the test cover path and test efficiency. Finally, the improved genetic algorithm constraint model is applied to memory leak detection.

With the development of computer technology and communication technology, computer network will increasingly become an important means of information exchange, and permeate into every field of social life. However, the network has the potential threat and the reality existence each kind of security question, therefore we must take the strong security policy to ensure the network security. The purpose of this paper is to study the network computer security hidden trouble and vulnerability mining technology. In this paper, the types of security hidden dangers are analyzed, and the vulnerability detection technology Fuzzing technology is deeply studied. Then, the inspection and test time is analyzed for the existing vulnerability detection tools. The experimental results prove that vulnerability detection technology can protect network security with high efficiency of vulnerability detection. In this paper, three vulnerability detection tools WS Fuzzer, Web Fuzz and Webvul Scan were used to analyze the detection time of open source system, personal blog, shopping mall and forum. The average detection time was 1.9s, 8.7s, 20.5s and 59.7s, respectively. It can be seen that the vulnerability mining technology has a certain practical role.

We propose a scheme of a sensitive biosensor based on optical bistability (OB) in a biological semiconductor quantum dot (SQD)-DNA coupled nanohybrid. By plotting bistability phase diagrams within the system's parameter space, we show that the bistable effect can be switched on or off by only tuning the pumping intensity or the detuning of the pump field from the exciton resonance. Simultaneously, we reveal that the bistability only exists in the strong SQD-DNA coupling regime. Specifically, we derive the matching relation between the excitation conditions and the coupling strength when the bistability just appears. Moreover, we demonstrate that the OB is highly sensitive to the SQD-DNA coupling strength which is strongly correlated to the length of DNA molecules and DNA concentration. This investigation may be useful for opening a new way to build optical switches and providing a novel and convenient platform to detect DNA molecules.

Noether symmetry of Nielsen equation and Noether conserved quantity deduced directly from Noether symmetry for dynamical systems of the relative motion are studied. The definition and criteria of Noether symmetry of a Nielsen equation under the infinitesimal transformations of groups are given. Expression of Noether conserved quantity deduced directly from Noether symmetry of Nielsen equation for the system are obtained. Finally, an example is given to illustrate the application of the results.

We present a study for the impact of exciton-phonon and exciton-plasmon interactions on bistable four-wave mixing (FWM) signals in a metal nanoparticle (MNP)-monolayer MoS2 nanoresonator hybrid system. Via tracing the FWM response we predict that, depending on the excitation conditions and the system parameters, such a system exhibits 'U-shaped' bistable FWM signals. We also map out bistability phase diagrams within the system's parameter space. Especially, we show that compared with the exciton-phonon interaction, a strong exciton-plasmon interaction plays a dominant role in the generation of optical bistability, and the bistable region will be greatly broadened by shortening the distance between the MNP and the monolayer MoS2 nanoresonator. In the weak exciton-plasmon coupling regime, the impact of exciton-phonon interaction on optical bistability will become obvious. The scheme proposed may be used for building optical switches and logic-gate devices for optical computing and quantum information processing.

Using density-functional calculations within the generalized gradient approximation (GGA)+U framework, we investigate the structural, electronic, and magnetic properties of the ground states of SrFeOn (n = 2 and 2.5). The magnetism calculations show that the ground states of both SrFeO2 and SrFeO2.5 have G type antiferromagnetic ordering, with indirect band gaps of 0.89 and 0.79 eV, respectively. The electronic structure calculations demonstrate that Fe cations are in the high-spin state of (dz2)2 (dxz, dyz)2 (dxy)1(dx2–y2)1 (S = 2), unlike the previous prediction of (dxz, dyz)3 (dxy)1 (dz2)1 (dx2–y2)1 (S = 2) for SrFeO2, and in the high-spin state of (dxy, dxz, dyz, dx2–y2, z2)5 (S = 5/2) for SrFeO2.5.

Structural equation and Mei conserved quantity of Mei symmetry for Appell equations in holonomic systems with unilateral constraints are investigated. Appell equations and differential equations of motion for holonomic mechanic systems with unilateral constraints are established. The definition and the criterion of Mei symmetry for Appell equations in holonomic systems with unilateral constraints under the infinitesimal transformations of groups are also given. The expressions of the structural equation and Mei conserved quantity of Mei symmetry for Appell equations in holonomic systems with unilateral constraints expressed by Appell functions are obtained. An example is given to illustrate the application of the results.

The Mei symmetry and Mei conserved quantity of the Nielsen equation for a non-Chetaev-type non-holonomic non-conservative system are studied. The differential equations of motion of the Nielsen equation for the system, the definition and the criterion of Mei symmetry and the condition and the form of Mei conserved quantities deduced directly from the Mei symmetry for the system are obtained. Finally, an example is given to illustrate the application of the results.

Based on the definition of higher-order adiabatic invariants of a mechanical system, a new type of adiabatic invariants, i.e. generalized Lutzky adiabatic invariants, of a disturbed holonomic nonconservative mechanical system are obtained by investigating the perturbation of Lie symmetries for a holonomic nonconservative mechanical system with the action of small disturbance. The adiabatic invariants and the exact invariants of the Lutzky type of some special cases, for example, the Lie point symmetrical transformations, the special Lie symmetrical transformations, and the Lagrange system, are given. And an example is given to illustrate the application of the method and results.

A temperature-insensitive acceleration sensor using two fibre Bragg gratings (FBGs), based on reflection spectrum intensity modulation and optical power detection, is proposed and demonstrated. A cantilever beam is used to generate acceleration-induced axial strain along two sensing gratings, which are glued on the two opposite surfaces of the beam. Because the two gratings operate within the linear spectral range of a light source, formed by a thermally-tunable extrinsic Fabry-Perot optical filter, the intensity difference of the two reflections from the gratings is proportional to the acceleration applied. This eliminates the need for sophisticated wavelength interrogation of the gratings, and it also endows the sensor with immunity to temperature variation. Compared with a commercial micromachined accelerometer, the sensor is proven to be capable of accurately detecting acceleration.

The Mei symmetry and conserved quantity of general discrete holonomic system are investigated in this paper. The requirement for an invariant formalism of discrete motion equations is defined to be Mei symmetry. The criterion when a conserved quantity may be obtained from Mei symmetry is also deduced. An example is discussed for applications of the results.

This paper studies the Mei symmetry and Mei conserved quantity for nonholonomic systems of unilateral Chetaev type in Nielsen style. The differential equations of motion of the system above are established. The definition and the criteria of Mei symmetry, loosely Mei symmetry, strictly Mei symmetry for the system are given in this paper. The existence condition and the expression of Mei conserved quantity are deduced directly by using Mei symmetry. An example is given to illustrate the application of the results.

This paper studies the Lie symmetries and Noether conserved quantities of discrete mechanical systems with variable mass. The discrete Euler–Lagrange equation and energy evolution equation are derived by using a total variational principle. The invariance of discrete equations under infinitesimal transformation groups is defined to be Lie symmetry. The condition of obtaining the Noether conserved quantities from the Lie symmetries is also presented. An example is discussed for applications of the results.

This paper investigates the Lie symmetries and Noether conserved quantities of discrete non-conservative mechanical systems. The variational principle of discrete mechanics, from which discrete motion equations of systems are deduced, is generalized to the case of including the time variational. The requirement for an invariant group transformation is defined to be the Lie symmetry and the criterion when the Noether conserved quantities may be obtained from Lie symmetries is also presented. An example is discussed for applications of the results.

Based on the general theory of dislocation and kink, we have constructed the three kink models corresponding to the 1/2 〈111〉{011} and 1/2 〈111〉{112} edge dislocations (EDs) in bcc Fe using the molecular dynamics method. We found that the geometric structure of a kink depends on the type of ED and the structural energies of the atom sites in the dislocation core region, as well as the geometric symmetry of the dislocation core and the characteristic of the stacking sequence of atomic plane along the dislocation line. The formation energies and widths of the kinks on the 1/2 〈111〉{011} and 1/2 〈111〉{112} EDs are calculated, the formation energies are 0.05eV and 0.04eV, and widths are 6.02b and 6.51b, respectively (b is the magnitude of the Burgers vector). The small formation energies indicate that the formation of kink in the edge dislocation is very easy in bcc Fe.

This paper investigates structure equation and Mei conserved quantity of Mei symmetry of Appell equations for non-Chetaev nonholonomic systems. Appell equations and differential equations of motion for non-Chetaev nonholonomic mechanical systems are established. A new expression of the total derivative of the function with respect to time t along the trajectory of a curve of the system is obtained, the definition and the criterion of Mei symmetry of Appell equations under the infinitesimal transformations of groups are also given. The expressions of the structure equation and the Mei conserved quantity of Mei symmetry in the Appell function are obtained. An example is given to illustrate the application of the results.