Spark Plasma Diffusion Bonding of TiAl/Ti2AlNb with Ti as Interlayer

To solve the problem of poor weldability between TiAl-based and Ti2AlNb-based alloys, spark plasma diffusion bonding was employed to join a TiAl alloy and a Ti2AlNb alloy with a pure Ti foil as interlayer at 950 °C/10 KN/60 min. After welding, slow cooling was carried out at a rate of 5 °C/min, followed by homogenization at 800 °C for 24 h. The microstructural evolution and elemental migration of the joint were analyzed via a scanning electron microscope equipped with an energy dispersive spectrometer, while the mechanical properties of the joint were assessed via microhardness and tensile tests. The results show that the spark plasma diffusion bonding formed a joint of TiAl/Ti/Ti2AlNb without microcracks or microvoids, while also effectively protecting the base metal. Before heat treatment, the maximum hardness value (401 HV) appeared at the Ti2AlNb/Ti interface, while the minimum hardness value (281 HV) occurred in the TiAl base metal. The tensile strength of the heat-treated joint at room temperature was measured to be up to 454 MPa, with a brittle fracture occurring in the interlayer. The tensile strength of the joint at 650 °C was measured to be up to 538 MPa, with intergranular cracks occurring in the TiAl base metal.

Numerical Simulation of Ionospheric Disturbance Generated by Ballistic Missile

To provide theoretical guidance for the detection of ballistic missiles by skywave over-the-horizon radar, this paper first analyses the best way to detect ballistic missiles based on the rocket detection mechanism. Then using the diffusion model, chemical reaction model, and plasma diffusion model of neutral gas in the ionosphere, this paper studies the distribution of electrons and analyses the disturbance effect on the ionosphere caused by the release of ballistic missile exhaust plume in the ionosphere. Moreover, this paper considers the flight speed of the ballistic missile and the flow of the exhaust plume. Then the effects of different seasons, locations, and time zones on the release are compared. The results show that H2O can effectively dissipate background electrons to form spindle-shaped holes after release in the ionosphere. The height of the cavity radius corresponds to the peak of electron density of the background ionosphere, and the daytime dissipation is stronger than the nighttime dissipation, dissipation at low latitude is stronger than that at high latitude, and the seasonal difference is not obvious.

Platelet-Rich Plasma Diffusion in Achilles Tendon: Relationship with Therapeutic Outcomes

Objective: The therapeutic efficacy of platelet-rich plasma in the treatment of Achilles tendinopathy is controversial. Among the variables which can explain the discrepant results, little attention has been paid to the distribution of platelet-rich plasma inside the tendon. The aim of the present study was to evaluate whether this factor is related to the clinical outcome of treatment. Subjects and Methods: Forty patients suffering from mid-portion Achilles tendinopathy were studied. At baseline, pain and function were measured by means of a visual analogue scale and the Victorian Institute of Sport Assessment-Achilles questionnaire. Thereafter, an ultrasound examination was performed, and platelet-rich plasma was injected. Immediately after injection, the plasma distribution was assessed visualizing the material in the tendon. The patients were re-evaluated at 3 and 6 months, computing pain and function values and the percentage of satisfactory outcomes in relation to the distance reached by the plasma from the point of injection. Results: The diffusion inside the tendon was longitudinal in all cases and cross-sectional only in 9. The mean distance from the tip of the needle increased significantly according to the severity of tendon damage. At follow-up, no relationship was found between plasma diffusion and clinical outcomes. Conclusions: Platelet-rich plasma diffusion has no effect on clinical outcome, which mainly depends on the metabolic activation of the whole structure of the tendon.

Drift wave turbulence and anomalous plasma diffusion in lower hybrid cavities observed in the ionosphere

In plasma of the Earth’s upper ionosphere, regions with a depleted plasma density and an increased level of oscillations with a lower hybrid frequency compared to the environment were found. It was established that such plasma density cavities have cylindrical symmetry and are elongated along the geomagnetic field, so that the longitudinal dimensions significantly exceed the transverse ones. Such structures, called lower hybrid cavities, are quite stable, so that during the passage through them spacecraft do not observe significant changes in the parameters of the cavities. Thus, the nature of the change in cavities over time remains unclear. In this paper, we theoretically investigate the temporal evolution of a cavity in plasma of ionosphere. Since depletion of the plasma density is a cylindrically symmetric region, it creates a radial inhomogeneity in the plasma. In turn, the inhomogeneity of plasma leads to the development of low-frequency drift instability and a turbulent state of plasma. The anomalous plasma diffusion across the geomagnetic field resulting from the development of turbulence of drift waves of inhomogeneous plasma is considered as a mechanism for changing the cavity. In this paper the equation of plasma diffusion in cavity is solved, where the initial radial distribution of plasma density is the upside-down Gaussian. Plasma diffusion occurs radially towards the center, since the plasma density increases with increasing radial coordinate. Obtained solution of the diffusion equation gives the rate of decrease in the depth of cavity. In addition to reducing the depth of the cavity, its expansion also occurs, however, the expansion of the cavity is slower than the decrease in depth. The paper gives plots of the plasma density distribution over the radius for several time values, which show the temporal evolution of the cavity. These dependences show that in a time of the order of 1 second the cavity changes significantly, but does not completely disappear.

Application of the Ito theory for Monte Carlo simulation of plasma diffusion

In this paper the full set of stochastic differential equations (SDEs) are presented describing the guiding centre motion of test charged particles in a plasma with an arbitrary inhomogeneous magnetic field, when the drift approximation is applicable. The derivation is based on the Ito formula which is used to determine stochastic differentials of functions of the non-gyro-averaged velocity diffusion in strict correspondence with the general kinetic equations involving Coulomb collision operators. The drift SDEs are obtained by calculating the Ito stochastic integrals within time intervals admitting the gyro-averaging procedure. The proposed SDEs reproduce the well-known Monte Carlo operators for orbital invariants, however additionally accounting for the spatial drift caused by the cross-field diffusion process with a classical diffusion coefficient. All SDE coefficients are explicitly expressed in terms of the Rosenbluth potentials in a gyro-tropic or isotropic background plasma. The SDEs are presented in particular for the case of an axisymmetric toroidal magnetic configuration to describe the spatial two-dimensional poloidal diffusion process providing a detailed description of neoclassical orbital effects.