Small Deflection Angles Research Articles

Effects of low-frequency voltage on nonlinear standing wave excitation, plasma uniformity, and ion dynamics in dual-frequency asymmetric capacitive discharges

It is known that in very-high-frequency (VHF) capacitively coupled plasmas, the higher harmonics generated by nonlinear sheath motion can enhance the standing wave effect (SWE), which can lead to center-peaked plasma density profiles. In this work, an improved nonlinear electromagnetic model incorporating a transmission line model, an electron momentum balance model, a bulk plasma model, a collisionless nonlinear numerical sheath model, and an ion Monte-Carlo collision (MCC) model is developed to study the effects of low-frequency (LF) voltage VL on the nonlinear standing wave excitation, plasma uniformity, and ion energy and angular distribution functions (IEDFs and IADFs) in dual-frequency (DF) asymmetric capacitive argon discharges at relatively low pressure of 3 Pa. The plasma diffusion in the radial direction and ion dynamics within the LF oscillating sheath are self-consistently considered. The LF voltage VL at 2 MHz varies from 0 to 700 V while the HF voltage VH at 60 MHz is fixed at 100 V. Simulation results indicate that without the addition of an LF source (i.e. VL= 0 V), there are a considerable number of high-order harmonics with short wavelengths, leading to significant SWE and central peak in the radial plasma density profile. Nevertheless, the high-order harmonic excitations tend to be weakened and merely occur around the phase of the full LF sheath collapse due to a shorter characteristic damping time of the surface waves as VL increases. This, combined with increased surface wavelengths of both the driving frequency and the higher harmonics at a higher VL , leads to suppressed standing waves and improved plasma uniformity. Meanwhile, the simulations show that both the low and the high energy peaks of IEDF move towards higher energies, and the energy peak separation width ΔE becomes wider with the increase of VL . The IEDF at the radial center of the powered electrode exhibits a broader ΔE than that at the edge. For the IADF, an increased VL results in more ions incident on the electrode with a smaller deflection angle. Because of a thinner sheath and a higher sheath voltage at the electrode center, the peak value of IADF at the electrode center is greater than that at the edge.

Spacecraft Attitude Measurement and Control Using VSMSCSG and Fractional-Order Zeroing Neural Network Adaptive Steering Law

In order to improve the accuracy and convergence speed of the steering law under the conditions of high dynamics, high bandwidth, and a small deflection angle, and in an effort to improve attitude measurement and control accuracy of the spacecraft, a spacecraft attitude measurement and control method based on variable speed magnetically suspended control sensitive gyroscopes (VSMSCSGs) and the fractional-order zeroing neural network (FO-ZNN) steering law is proposed. First, a VSMSCSG configuration is designed to realize attitude measurement and control integration in which the VSMSCSGs are employed as both actuators and attitude-rate sensors. Second, a novel adaptive steering law using FO-ZNN is designed. The matrix pseudoinverses are replaced by FO-ZNN outputs, which solves the problem of accuracy degradation in the traditional pseudoinverse steering laws due to the complexity of matrix pseudoinverse operations under high dynamics conditions. In addition, the convergence and robustness of the FO-ZNN are proven. The results show that the proposed FO-ZNN converges faster than the traditional zeroing neural network under external disturbances. Finally, a new weighting function containing rotor deflection angles is added to the steering law to ensure that the saturation of the rotor deflection angles can be avoided. Semi-physical simulation results demonstrate the correctness and superiority of the proposed method.

A Fokker–Planck Framework for Studying the Variability of the Magnetic Field Direction in the Alfvénic Streams of the Solar Wind

Turbulent rotations of the magnetic field vector are observed in the Alfvénic streams of the solar wind where the magnetic field strength remains close to a constant. They can lead to reversals of the radial magnetic field component or switchbacks. It is not ruled out from the data that the rotations are divisible into the sum of small random angular deflections. In this work, we develop tools aimed at the analysis of the one-point statistical properties of the directional fluctuations of the magnetic field vector in the solar wind. The angular fluctuations are modeled by a drift-diffusion process which admits the exponential distribution as steady-state solution. Realizations of the stochastic process are obtained by solving the corresponding Langevin equation. It is shown that the cumulative effects of consecutive small-angle deflections can yield frequent reversals of the magnetic field vector even when the concentration parameter of the directional data is large. The majority of the rotations are associated with nearly transverse magnetic field fluctuations in this case.

Optical system design based on DMD and triple-pass TIR prism for asteroid exploration.

After entering the 21st century, asteroid exploration has become one of the key research directions in the field of deep space exploration. In this article, we present a navigation, imaging, and hyperspectral acquisition integrated optical system designed for asteroid exploration. Based on the pixel-level light modulation capability of the digital micromirror device (DMD), this system introduces a triple-pass total internal reflection (TIR) prism to overcome the limitation of small DMD deflection angles, achieving the co-aperture design of the high-resolution imaging branch and the hyperspectral acquisition branch. In view of the actual usage scenarios, we design a new triple-pass TIR prism and optimize it, correcting the on-axis point coma and astigmatism it introduces, and designing it to be lightweight and compact. Compared to existing optical systems for asteroid exploration, this system offers advantages such as compact structure, no moving parts, high spatial resolution, high spectral resolution, and more flexible imaging modes.

Characteristics of temperature-dependent shear flow in an ultrasonicated ferrofluid

The rheological effect of manganese zinc (Mn-Zn) ferrite ferrofluid was studied and the impact of temperature on the magnetoviscosity and viscoelastic system of manganese-zinc ferrite ferrofluid generated by co-precipitation process is investigated. At 25 ◦C, a ferrofluid structure that is both hard and elastic is produced. As the temperature rises, the fluid structure loses its elasticity and becomes semi-rigid. When a low relaxation modulus is applied, the fluid behavior, which is temperature-dependent, exhibits the development of linear stress relaxation and steady state flow. When a greater relaxation modulus is used, non-steady state flow results. At a high temperature of 50 ◦C, steady state flow is quickly obtained, whereas at a low temperature, equilibrium or steady state is attained more slowly. At low temperatures, the fluid exhibits a solid-like structure, whereas at high temperatures, a liquid-like structure forms as the fluid’s viscosity decreases. With the creation of yield stress in the region with high shear rates, shear stress increases with temperature, and yield stress increases with temperature. The viscoelastic system is underdamped, and the amount of fluid deflected at 25 ◦C is small, which prevents the disruption of the fluid’s rheology. This develops as a result of the presence of a small deflection angle, which facilitates the development of high magnetoviscosity at low temperature. High viscous effect forms at low temperatures due to the creation of low shear stress and low deflection angle at temperature 25 ◦C. The sample has a single phase and FCC structure, which X-ray diffraction research has verified.

Research on evolution process of full-layer incision of skin tissue under different laser incidences.

Considering difficulties of achieving vertical incidence of beam in different positions of skin, it is significant to study potential effects of incidence angles of laser on incisions. Surgical platform with a 1064 nm continuous fiber laser was established. Incident angle was adopted and real-time temperature fluctuations in laser operating area could be monitored. The rats were treated with laser at day 0 and day 3 after incision modeling, and H&E, Masson, Sirius Red, and Immuno-histochemical staining and enzyme-linked immunosorbent assay were adopted at day 3, 7, 14 to analyze the performance of healing. Laser with energy density of 67.54 J/mm2 can effectively accelerate wound healing in vivo, in which a laser with incident angle around 60° can effectively avoid scar hyperplasia. Therefore, the use of low energy laser with a small deflection angle has a good clinical application prospect in promoting wound healing.

Representative deflection angle for the single-deflection method of direct simulation Monte Carlo.

The total cross sectionof binary collision is, in general, unbounded due to the long-range interations of molecules. It is conventional to truncate the small angle deflections of collisions. The present work suggests an alternative way of avoiding the difficulty of unboundedness. We employ the mean value theorem of definite integral over the deflection angle for the cross section. A series of numerical experiments were carried out to look for the representative collision cross sectionthrough which the single-angle simulation is amenable to the solution of the Boltzmann equation. Results show that the cross sectionshould be 〈Σ〉=Σ_{D}^{2}/(2Σ_{D}-Σ_{μ}), and the representative deflection for the single-angle simulation be cos〈χ〉=Σ_{μ}/Σ_{D}-1, where Σ_{D} is the diffusion cross sectionand Σ_{μ} is the viscosity cross section. The single-angle computations for the inverse power law and the Lennard-Jones force law perfectly reproduce the conventional scattering algorithms for one-dimensional (1D) simulations of transport coefficients and 1D shock thickness. The computation costs for Lennard-Jones molecules are comparable to the costs for inverse power-law models.

Study on the aerodynamic performance of nacelle inlet under crosswind

Flow separation will occur in the nacelle inlet under crosswind operation, which will result in engine intake distortion and even engine surge. To study the reference characteristics of the flow field of the short tank inlet separation under the influence of crosswind, this paper observed the cloud map of the total price loss coefficient by changing the flow deflection Angle and flow velocity, made a qualitative analysis of the total pressure distortion degree, then calculated the average total pressure loss coefficient and distortion index, and conducted a quantitative analysis to explore the improvement of the total pressure distortion under different flow field factors. The results show that the degree of total pressure distortion is improved with the increase of incoming flow velocity at a small inlet deflection Angle, but with the increase of incoming flow deflection Angle, the ability of incoming flow velocity to improve the total pressure distortion gradually weakens until it disappears. The inlet deflection Angle plays a decisive role in the improvement effect of incoming flow velocity on the total pressure distortion.

Improving the Electro-Optical Deflection Performance of KTN Crystals Based on the Temperature Compensation Effect

The laser deflector is a crucial device used to change the direction of light beam propagation in various fields, including lithography, lidar, and scanning. In this paper, we conduct a systematic study of two KTa(1–x)NbxO3 (KTN) crystals that use different physical deflection mechanisms. We analyze their dielectric properties, entropy, domain structure, and deflection performance. We also address the drawback of the small deflection angle of the compositional gradient KTN deflector crystal by proposing a new temperature-compensated temperature control strategy to improve its deflection performance. The gradient temperature control mechanism maximizes the dielectric constant in different regions of the KTN crystals, leading to a threefold (10.67 mrad) increase in deflection angle compared to conventional uniform temperature control equipment. This optimized temperature control mechanism can significantly enhance the practical application of KTN crystals, providing a new avenue for achieving a large deflection angle beam deflector.

Parameter design of solar optical reflection lighting system array for shadowless lighting in threshold zone of short freeway tunnel

A solar optical reflection (SOR) lighting system has been developed to illuminate the threshold zone of short freeway tunnel in the premise of zero energy consumption. To improve the limited illumination performance of SOR lighting system due to the obstruction of moving vehicles on reflected sunlight rays, this study develops a fast and simple parameter design method for shadowless lighting based on an array of multiple SOR lighting systems that makes reflected sunlight emit to the threshold zone from different angles. The effectiveness of shadowless lighting is verified by the application on a two-lane freeway of Shaanxi Province, China. Results show that the shadowless lighting can significantly improve the illuminance in threshold zone, and the improvement rate is higher for the area farther from the tunnel entrance inside the tunnel. In order to achieve shadowless lighting avoid both the vehicle and inter-system blocking on reflected sunlight, the systems should be installed roadside in a staggered array that: 1) their heights descend and lateral distances from the curb shrink in turn from near to far from the tunnel entrance, with as small vertical and horizontal deflection angles of the reflectors as possible, or 2) their heights remain identical with a reduction in the vertical deflection angles of the reflectors from near to far from the tunnel entrance.

Thermo-Hydrodynamic Effect of Gas Split Floating Ring Seal with Rayleigh Step Grooves

The force equilibrium and moment equilibrium play a significant role on the sealing performance of gas split floating ring seals. A small deflection angle may generate seriously wear on sealing surface and cause seal failure. Therefore, the thermo-hydrodynamic lubrication analysis of gas split floating ring seal with Rayleigh grooves is investigated considering the deflection angle and frictional heat of surface contact, which is beneficial to grasp the hydrodynamic characteristics and rules under high-temperature and high-speed conditions. Pressure and temperature distributions of sealing rings are numerically calculated for the cases with different deflection angle, rational speed, seal pressure and ambient temperature. Then, the hydrodynamic effect and sealing performance are analyzed. The obtained results show that, the surface Rayleigh step grooves do not present obvious hydrodynamic effect when split seal ring has no deflection. While, a significant hydrodynamic effect can be obtained when the split seal ring presents a deflection angle about dozens of micro radians. Here, a 10% increase of opening force is achieved when the deflection angle reaches 80 μrad in the case of speed 30,000 r/min and seal pressure 0.2 MPa. Moreover, the hydrodynamic effect becomes obvious with increasing deflection angle as well as rotational speed. Meanwhile, the growth of rotational speed results in an obvious increase of film temperature. The increase of ambient temperature has a significant influence on the decrease of leakage rate. When the ambient temperature increases from 340 K to 540 K, the leakage rate reduces exceeding 50%, however, it does not present obvious effect on the opening force. The proposed model has the potential to provide the theoretical basis and design guidance for surface grooves of gas split floating ring seal in the future.

Time-multiplexed vector light field display with intertwined views via metagrating matrix

Three-dimensional (3D) display is the future technology of display. The insufficient refreshable information provided by the screen is one of the major bottlenecks that hinders the development of light field 3D display. In this paper, a time-multiplexed vector light field display is proposed to increase the amount of information by exploiting the time redundancy. A view modulator with fully coverage of metagrating matrix is adopted to generate two groups of time-sequentially lit-up intertwined views. With a small deflection angle of incidence, the intertwined-view based time-multiplexing strategy is beneficial because of the less stray light and crosstalk, compared with the successively arranged views. Therefore, the system volume and complexity of directional backlight are reduced. In the experimental demonstration, a time-multiplexed vector light field 3D display is constructed with 18 views. The horizontal field of view reaches 51°. The potential applications include human-computer interaction, commercial exhibition, and medical hygiene.

Modelling the near-wellbore rock fracture tortuosity: Role of casing-cement-rock well system, perforation and in-situ stress

Near-wellbore rock fracture is a key subject in subsurface energy extraction. Casing perforation completion is perhaps the most used type of well design mainly in comparison to the open hole completion. However, the effects of the combined casing-cementing-rock structure on pressure transmission in fracturing the rock have not been sufficiently addressed, but is key to understanding some important phenomena in hydraulic fracturing, such as fracture tortuosity. Here we develop a combined analytical-numerical model to investigate the rock fracture mechanism near the wellbore with realistic consideration of the boundary condition imposed by the complete well system. Different well configurations can lead to variation in the pressure applied on the rock formation and hence affect the fracture propagation near the wellbore. Our results show, as the pressure transmission through the well structure is enhanced, the fracture propagates more closely to the perforation orientation with a smaller deflection angle and the breakdown pressure is increased. The near-well tortuosity of the crack can be reduced by decreasing the thickness of casing and cement sheath, reducing Young's modulus of casing and increasing Young's modulus of cement up to around 15 GPa, based on the realistic range of values of the well parameters. The effects of in-situ stress condition and perforation angle and length on the near-well cracking are also investigated. The developed model can be used to aid decision making in terms of improved understanding of hydraulic fracturing technology and well design optimization.

Study of the Relationship between Metal–Support Interactions and the Electrocatalytic Performance of Pt/Ti4O7 with Different Loadings

The application potential of Pt/Ti4O7 has been reported, but the lack of research on the relationship between Pt loading, MSI, and catalytic activity hinders further development. Micron-sized Ti4O7 powders synthesized by a thermal reduction method under an H2 atmosphere were used as a support material for Pt-based catalysts. Using a modified polyol method, Pt/Ti4O7-5, Pt/Ti4O7-10, and Pt/Ti4O7-20 with different mass ratios (Pt to Pt/Ti4O7 is 0.05, 0.1, 0.2) were successfully synthesized. Uniformly dispersed platinum nanoparticles exhibit disparate morphologies, rod-like for Pt/Ti4O7-5 and approximately spherical for Pt/Ti4O7-10 and Pt/Ti4O7-20. Small-angle deflections and lattice reconstruction induced by strong metal–support interactions were observed in Pt/Ti4O7-5, which indicated the formation of a new phase at the interface. However, lattice distortions and dislocations for higher loading samples imply the existence of weak metal–support interactions. A possible mechanism is proposed to explain the different morphologies and varying metal–support interactions (MSI). With X-ray photoelectron spectroscopy, spectrums of Pt and Ti display apparent shifts in binding energy compared with commercial Pt-C and non-platinized Ti4O7, which can properly explain the changes in absorption ability and oxygen reduction reaction activity, as described in the electrochemical results. The synthetic method, Pt loading, and surface coverage of the support play an important role in the adjustment of MSI, which gives significant guidance for better utilizing MSI to prepare the target catalyst.

ECCPA: Calculation of classical and quantum cross sections for elastic collisions of charged particles with atoms

ECCPA: Calculation of classical and quantum cross sections for elastic collisions of charged particles with atoms

High Efficiency Flexible Control of Wave Beams Based on Addition and Subtraction Operations on All Dielectric Reflection Metasurfaces

In order to reduce the ohmic loss, we propose all dielectric reflection metasurface in terahertz band. The unit structure can be encoded to construct all dielectric reflection encoding metasurfaces. The all dielectric coded metasurfaces consist of the physical coded particles with the coded digits. Since it is impossible for us to design and prepare coded particles of infinitely small size, the traditional coded metasurfaces only control the limited scattering beam directions especially for small deflection angles, and cannot achieve continuous control of scattering angles. This severely limits the wide application of coded metasurfaces. In order to achieve multi-directions and large angle scattering, we introduce the Fourier convolution principle from digital signal processing on all dielectric reflection encoding metasurfaces. Through the addition and subtraction operations of all dielectric encoding metasurface sequences, the freely manipulation of scattering beams can be achieved, especially for larger deflection angles. More importantly, compared with the traditional gradient phase coded metasurfaces, the mixed coded metasurfaces by addition and subtraction operations of encoding sequences can greatly improve the scattering cross section.

Weakening wave impact on submarine-launched vehicles by imitating humpback whale belly grooves

Inspired by humpback whale belly grooves which may impart stability, we hypothesized that adding grooves to the head of submarine-launched vehicle (SLV) would weaken the effect of wave force. An experimental instrument was built to test a prototype submarine-launched vehicle (SLVP; no grooves) and 9 bionic submarine-launched vehicles (SLVBs) with different grooves on the head. The deflection angles of the SLVP and SLVBs were measured as they crossed the water-air interface in wavy conditions. The experimental results showed that the SLVBs had smaller deflection angles than the SLVP, which supported the initial hypothesis. The angular deflection of the SLVP and SLVBs in wavy conditions was then analyzed using a simulation. The simulated and experimental results agreed, confirming the validity of the simulated models. By measuring the torque experienced at the center of gravity of the SLVs and the flow field distributions near the heads of the SLVs in the simulation, the mechanism behind the differences in angular deflection of the SLVs with and without grooves was revealed.

Photon polarization effects in polarized electron–positron pair production in a strong laser field

Deep understanding of the impact of photon polarization on pair production is essential for the efficient generation of laser-driven polarized positron beams and demands a complete description of polarization effects in strong-field QED processes. Employing fully polarization-resolved Monte Carlo simulations, we investigate correlated photon and electron (positron) polarization effects in the multiphoton Breit–Wheeler pair production process during the interaction of an ultrarelativistic electron beam with a counterpropagating elliptically polarized laser pulse. We show that the polarization of e−e+ pairs is degraded by 35% when the polarization of the intermediate photon is resolved, accompanied by an ∼13% decrease in the pair yield. Moreover, in this case, the polarization direction of energetic positrons at small deflection angles can even be reversed when high-energy photons with polarization parallel to the laser electric field are involved.

Full treatment of the proton radiography technique for laser-driven capacitor-coil targets

Ultrafast proton radiography has been frequently used for direct measurement of the electromagnetic fields around laser-driven capacitor-coil targets. The goal is to accurately infer the coil currents and their magnetic field generation for a robust magnetic field source that can lead to many applications. The technique often involves numerical calculations for synthetic proton images to reproduce experimental measurements. While electromagnetic fields are the primary source for proton deflections around the capacitor coils, stopping power and small angle deflection can also contribute to the observed experimental features. Here we present a comprehensive study of the proton radiography technique including all sources of proton deflections as a function of coil shapes, current magnitudes, and proton energies. Good agreements were achieved between experimental data and numerical calculations that include both the stopping power and small angle deflections, particularly when the induced coil currents were small.

Effects of pin morphology on the interface defects of the FSWed lap joints of 2A12 aluminum alloy

The current work aims to study the effects of stirring pin morphology on the FSWed lap joints defects and mechanical properties. The 2A12 aluminum alloy friction stir welding lap joints were obtained using two shapes and three thread lengths of stirring pins by experiments. Besides the interface defects forming mechanism were studied by joints plastic metal flow numerical simulation. The results show that the conical pin can lead to uniform and continuous plastic metal velocity field which forms a Hook defect with sharp end, smaller deflection angle (minimum 8°) and larger size (maximum 0.18mm). It also will lead to a larger failure load (maximum is 9.5kN), and the fracture position easily occurs at the Advancing side (AS) of lower plate. The three section pin has a periodic shearing effect causing velocity difference between the arc edge and cutting section of the pin which forms a Hook defect with thicker end, larger deflection angle (maximum 42°) and smaller size (minimum 0.06mm). It also causes discontinuous wavy debris forms in the AS. The three section pin leads to a lower failure load (maximum is just 7.6kN), and the fracture position turns to occur at the lap interface. The increase of the thread length can promote the exchange of plastic metal in the thickness direction and interface materials flow velocity. So the angle (from 20°to 150°) and size (from 0.1mm to 0.6mm) of Hook increases but the height of Cold Lap reduces (increasing the effective sheet thickness of retreating side from 0.69mm to 0.95mm). In addition, the increase of the thread length can make the periodic shear effect of three section pin gradually weak. It is also found that the fracture position is closely related to the shape and the thread length of pins. When using conical pin, the fracture occurs at AS of lower plate or Retreating Side of Nugget Zone (NZ-RS) of upper plate; When using three section pin, the fracture occurs at the bonding interface. And with the increase of the thread length, the fracture position changes from the bonding interface to the NZ-RS of upper plate, and finally to the AS of lower plate.