Erosion Profile Research Articles

Magnetic Field Improvement in End Region of Rectangular Planar DC Magnetron Based on Particle Simulation

For a rectangular planar direct current (DC) magnetron, anomalous target erosion may occur in the curve-out region and inner side of the curved region. One key factor is that the magnetic field in the end region is weaker than that in the straight region, and another important factor may be that there is a circumferential component of the magnetic field in the curved region. Through a calculation of three-dimensional magnetic field for the rectangular magnetron, a magnet structure shimmed by permanent magnet bars and ferromagnetic bars is proposed to solve the above problems. Through a three-dimensional non-self-consistent particle simulation and the Yamamura/Tawara formula, the target erosion profile could be predicted. The simulation results show that for an improved uniformity in magnetic field, the entire target utilization could be much enhanced.

Concurrent release of admixed antimicrobials and salicylic acid from salicylate‐based poly(anhydride‐esters)

A polymer blend consisting of antimicrobials (chlorhexidine, clindamycin, and minocycline) physically admixed at 10% by weight into a salicylic acid-based poly (anhydride-ester) (SA-based PAE) was developed as an adjunct treatment for periodontal disease. The SA-based PAE/antimicrobial blends were characterized by multiple methods, including contact angle measurements and differential scanning calorimetry. Static contact angle measurements showed no significant differences in hydrophobicity between the polymer and antimicrobial matrix surfaces. Notable decreases in the polymer glass transition temperature (T(g)) and the antimicrobials' melting points (T(m)) were observed indicating that the antimicrobials act as plasticizers within the polymer matrix. In vitro drug release of salicylic acid from the polymer matrix and for each physically admixed antimicrobial was concurrently monitored by high pressure liquid chromatography during the course of polymer degradation and erosion. Although the polymer/antimicrobial blends were immiscible, the initial 24 h of drug release correlated to the erosion profiles. The SA-based PAE/antimicrobial blends are being investigated as an improvement on current localized drug therapies used to treat periodontal disease.

3차원 입자 모델을 이용한 마그네트론 스퍼터링 음극의 특성 분석

A 3D particle code is developed to analyze electron behavior in a planar magnetron sputtering cathode either in balanced or unbalanced configuration. Three types of collisions are included; electron - neutral elastic, excitation to a metastable state and ionization. Flight path is calculated by a 4-th order Runge-Kutta method with a time step of 10 ps. Effects of electron starting position, magnetic field intensity and configuration were analyzed. For a more efficient and accurate modeling, multithreading technique is considered for multicore CPU computers. Under an assumption of cold ion approach, target erosion profiles are predicted for a flat target surface.

On the carbon and tungsten sputtering rate in a magnetron discharge

Magnetron discharge as sputtering source can serve as an alternative tool for the study of the plasma-wall interaction, with applications for ITER divertor. The present work reports on the influence of the target power density and the nature of the projectile on the erosion of C and W targets. The experimental results concern the sputtering rate of carbon and tungsten targets of a d.c. magnetron discharge in argon and helium atmosphere, at different gas pressures in the range of 10–100mTorr and discharge power densities up to 40Wcm−2 while the discharge current intensity was used as control parameter. In this investigation, carbon and tungsten sputtering rates were measured using two conventional methods based on gravimetric mass loss and profilometry. Target erosion profiles were compared with the profiles of the ion energy flux bombarding the target, calculated from a 2D fluid model.

Simulation to Predict Target Erosion of Planar DC Magnetron

Plasma properties in a planar DC magnetron system are simulated by a non-self-consistent particle method in two dimensions. Through tracing the trajectories of the energetic electrons in the specified electric field and the magnetic field, and treating the collision process by Monte Carlo method, the spatial profile of ionization events can be obtained conveniently. Assuming that the ions speed up from the ionization points and bombard the target with the energy at these points, and according to the Yamamura/Tawara method, the target erosion can be predicted. The magnetic field is calculated by the finite element method, and the electric field is estimated according to the self-consistent simulation and measured results. The influence of the time step size on the target erosion profile is analysed first to find a proper step size. Then the influence of electric field estimated on the erosion profile is discussed. The erosion profile may become narrower if the sheath thickness is increased. Finally, considering the dynamic erosion process, the erosion profile may get wider over time for the magnetron with shunt bar.

Dynamic compressive loading influences degradation behavior of PEG‐PLA hydrogels

Biodegradable hydrogels are attractive 3D environments for cell and tissue growth. In cartilage tissue engineering, mechanical stimulation has been shown to be an important regulator in promoting cartilage development. However, the impact of mechanical loading on the gel degradation kinetics has not been studied. In this study, we examined hydrolytically labile gels synthesized from poly(lactic acid)-b-poly(ethylene glycol)-b-poly-(lactic acid) dimethacrylate macromers, which have been used for cartilage tissue engineering. The gels were subject to physiological loading conditions in order to examine the effects of loading on hydrogel degradation. Initially, hydrogels were formed with two different cross-linking densities and subject to a dynamic compressive strain of 15% at 0.3, 1, or 3 Hz. Degradation behavior was assessed by mass loss, equilibrium swelling and compressive modulus as a function of degradation time. From equilibrium swelling, the pseudo-first-order reaction rate constants were determined as an indication of degradation kinetics. The application of dynamic loading significantly enhanced the degradation time for the low cross-linked gels (P < 0.01) while frequency showed no statistical differences in degradation rates or bulk erosion profiles. In the higher cross-linked gels, a 3 Hz dynamic strain significantly increased the degradation kinetics resulting in an overall faster degradation time by 6 days compared to gels subject to the 0.3 and 1 Hz loads (P < 0.0001). The bioreactor set-up also influenced overall degradation behavior where the use of impermeable versus permeable platens resulted in significantly lower degradation rate constants for both cross-linked gels (P < 0.001). The compressive modulus exponentially decreased with degradation time under dynamic loading. Together, our findings indicate that both loading regime and the bioreactor setup influence degradation and should be considered when designing and tuning a biodegradable hydrogel where mechanical stimulation is employed.

Model for Fast Computation of Blast Furnace Hearth Erosion and Buildup Profiles

A model for estimation of the profiles of erosion and buildup material in the hearth of an ironmaking blast furnace has been developed. The model is based on thermocouple readings in the hearth wall and bottom and solves an inverse heat transfer problem for two-dimensional slices of the hearth geometry to estimate the inner profile. Special attention has been paid to the mathematical formulation of the problem at hand, yielding a general model optimized for fast computation. This includes a flexible formulation of the boundary conditions, a generic setup of the lining materials applied in the hearth refractory, and a sophisticated iterative procedure in the estimation of the location of the internal profile. These steps have led to a model that facilitates process analysis with estimation and reestimation of the furnace hearth conditions over whole campaigns using different parameter settings. The model has been applied to study the evolution of the hearth erosion and buildup formation processes in severa...

Competing Dynamic Solutions in a Parametrically Excited Pendulum: Attractor Robustness and Basin Integrity

The competing solutions of a planar pendulum parametrically excited by the vertical motion of the pivot are investigated in terms of both attractor robustness and basin integrity. Two different measures are considered to highlight how the integrity of the system is modified by changing the amplitude of the excitation. Various attractors, both in-well and out-of-well, are considered, and the integrity profiles of each of them are determined. A detailed discussion of the interaction and mutual erosion of the various attractors is performed by clarifying the role of the two complementary measures, and the most relevant characteristics of the erosion profiles are interpreted in terms of the underlying topological mechanisms involving local or global bifurcations.

Hybrid Particle-in-Cell Erosion Modeling of Two Hall Thrusters

An axisymmetric hybrid particle-in-cell model of the Hall thruster plasma discharge has been upgraded to simulate the erosion of the thruster acceleration channel, the degradation of which is the main life-limiting factor of the propulsion system. Evolution of the thruster geometry as a result of material removal due to sputtering is modeled by calculating wall erosion rates, stepping the grid boundary by a chosen time step and altering the computational mesh between simulation runs. The code is first tuned to predict the nose cone erosion of a 200-W Busek Hall thruster, the BHT-200. Simulated erosion profiles from the first 500 h of operation compare favorably with experimental data. The thruster is then subjected to a virtual life test that predicts a lifetime of 1330 h, well within the empirically determined range of 1287-1519 h. The model is then applied to the BHT-600, a higher-power thruster, to reproduce wear of its exit ring configuration over 932 h of firing. Though some optimized code features remain the same, others need adjustment to achieve comparable erosion results. Better understanding of the physics of anomalous plasma transport and low-energy sputtering are identified as the most pressing needs for improved lifetime models.

Wear Mechanisms in Electron Sources for Ion Propulsion, II: Discharge Hollow Cathode

The wear of the keeper electrode in discharge hollow cathodes is a major impediment to the implementation of ion propulsion onboard long-duration space science missions. The development of a predictive theoretical model for hollow cathode keeper life has long been sought, but its realization has been hindered by the complexities associated with the physics of the partially ionized gas and the associated erosion mechanisms in these devices. Thus, although several wear mechanisms have been hypothesized, a quantitative explanation of life test erosion profiles has remained incomplete. A two-dimensional model of the partially ionized gas in a discharge cathode has been developed and applied to understand the mechanisms that drove the erosion of the keeper in two long-duration life tests of a 30-cm ion thruster. An extensive set of comparisons between predictions by the numerical simulations and measurements of the plasma properties and of the erosion patterns is presented. It is found that the near-plume plasma oscillations, predicted by theory and observed by experiment, effectively enhance the resistivity of the plasma as well as the energy of ions striking the keeper.

High-energy events and short-term changes in superficial beach sediments

Laboratorio de Oceanografia Geologica, Fundacao Universidade Federal do Rio Grande (Av. Italia, km 8, Campus Carreiros, 96201-900 Rio Grande, RS, Brasil) lcalliari@log.furg.br The sediment distribution along modern beaches is the result of the complex interaction between the sediment source, the wave energy level and the general offshore slope upon which the beach is constructed (KOMAR, 1998). Sediments tend to be sorted according to the energy levels that the beach is exposed, so that beaches exposed to higher wave energy levels are expected to be composed by coarser sediments. In the composition of beach sediments, quantities of heavy minerals might be present. Since they are denser than quartz grains, they present a different hydraulic behaviour when compared to lighter grains. The behaviour of heavy minerals has been studied mainly related to erosional and/or accretional beach processes (e.g. SLINGERLAND, 1977; KOMAR et al., 1989; KOMAR, 1998). The straight wave-dominated southernmost coastline of Brazil is characterised by an extensive sandy coastal plain. The study area comprehends 220 km of sandy beaches located between the Patos Lagoon inlet and the Uruguayan border (Fig. 1). Beaches in this region are classified as dissipative and intermediate, associated to one or two longshore sandbars (CALLIARI; KLEIN, 1993). Seasonal variations are present, with accretion profiles during spring and summer and erosion profiles during autumn and winter. The climate of this coastal region is under the control of the high-pressure centre of the Atlantic anticyclone, whose latitudinal migration and the passage of polar front systems in 6-10 days intervals have a seasonally modifying influence on the climate. During cold fronts events, more common during winter months, SW winds become stronger (8 m.s

Particle-in-Cell/Monte Carlo Collision simulation of planar DC magnetron sputtering

In this paper a numerical simulation of a planar DC magnetron discharge is performed with the Particle-in-Cell/Monte Carlo Collision (PIC/MCC) method. The magnetic field used in the simulation is calculated with finite element method according to experimental configuration. The simulation is carried out under the condition of gas pressure of 0.665 Pa and voltage magnitude of 400V. Typical results such as the potential distribution, charged particle densities, the discharge current density and ion flux onto the target are calculated. The erosion profile from the simulation is compared with the experimental data. The maximum erosion position corresponds to the place where the magnetic field lines are parallel to the target surface.

Dynamical Integrity and Control of Nonlinear Mechanical Oscillators

The dynamical integrity of nonlinear mechanical oscillators is analyzed in a systematic way extending a previous authors' work. The definition of the safe basin, which is a crucial point that entails choosing what is dynamically acceptable, is critically reviewed. Two different integrity measures are used to quantify the magnitude of the safe basin. When drawn as functions of a varying parameter, they give the so-called erosion profiles, which are the key tool for studying the variation of dynamical integrity. The main focus is on the practically most interesting cases in which the parameter is the excitation amplitude and the integrity reduces as it increases. With the aim of reducing erosion, namely of shifting the erosion profiles toward larger excitation amplitudes, a control method is then applied. It is based on eliminating the homo/heteroclinic bifurcation of the hilltop saddle, which is the triggering event for the considered erosions, by optimally choosing the shape of the periodic excitation. The erosion curves of four different mechanical oscillators, chosen with the aim of covering some main mechanical, dynamical and control features, are numerically constructed and systematically compared with each other. It is found that the control is always able to shift the erosion profiles, although to different extents. Furthermore, its effectiveness may extend above, sometimes well above, the theoretical predictions. Several supplementary specific issues of dynamics and control interest are discussed in detail.

Erosion Processes of the Discharge Cathode Assembly of Ring-Cusp Gridded Ion Thrusters

An ion thruster discharge cathode assembly (DCA) erosion theory is presented based on near-DCA NSTAR plasma measurements and experimental results for propellant flow rate effects on ion number density. The plasma potential structures are utilized in an ion trajectory algorithm to determine the location and angle at the DCA of bombarding ions. These results suggest that the plasma potential structure causes a chamfering of the DCA orifice. Results from tests with an instrumented DCA show that increasing DC propellant flow rate causes a decrease in keeper orifice ion number density, most likely due to charge-exchange and elastic collisions. Combining these two results, the known wear-test and extended life test (ELT) DCA erosion profiles can be qualitatively explained. Specifically, the change in the wear profile from the DCA downstream face to the orifice for the ELT may be a result of the reduction in DCA propellant flow rate when the thruster operating point is changed from the TH 15 to TH 8.

Simulation to improve the magnetic field in the straight section of the rectangular planar DC magnetron

For the rectangular planar DC magnetron, Gaussian type erosion profile may occur in the straight section of target and lead to lower target utilization. Considering the influence of magnetic field on the trajectories of energetic electrons, the target erosion profile and deepest eroded position are analyzed, and then the approaches of magnetic field improvement are proposed. Based on this, two magnet structures with AlNiCo and SmCo are discussed, which could be improved by fitting a shunt bar. According to 2D non-self-consistent particle simulation and Yamamura/Tawara formula, the target erosion profile could be predicted. Via the simulation, the approaches of magnetic field improvement are verified. In the same order of magnetic field intensity, the horizontal component of the magnetic field with wider distribution and larger concavity is proved to make the target utilization much increased.

Apparent Dewetting of Ultrathin Multilayered Polyelectrolyte Films Incubated in Aqueous Environments

We have investigated and characterized changes in film morphology and surface structure that occur when ultrathin multilayered polyelectrolyte films fabricated from linear poly(ethylene imine) (LPEI), sodium poly(styrene sulfonate) (SPS), and two hydrolytically degradable polyamines (polymers 1 and 2) are incubated in physiologically relevant environments. Characterization of the physical erosion profiles of films having the structure (LPEI/SPS)10(1/SPS)4(2/SPS)4 (approximately 80 nm thick) by atomic force microscopy (AFM), reflective optical microscopy, and scanning electron microscopy (SEM) demonstrated that these materials undergo large-scale changes in surface structure and morphology upon incubation in phosphate-buffered saline (PBS) at 37 degrees C. The patterns and structures generated during this transformation (e.g., nucleation and growth of holes, coalescence of holes, formation of cell-type structures, and the subsequent breakup of these features into droplets) are similar in many ways to those observed for the dewetting of thin films of conventional polymers, such as polystyrene, on nonwetting surfaces. The processes reported here are sufficiently slow (they occur over approximately 100 h) and occur under sufficiently mild conditions (e.g., incubation in PBS at 37 degrees C) to permit characterization and quantification of the structures and features that arise during the course of these transformations. The apparent dewetting of these ultrathin films upon exposure to aqueous environments creates future opportunities to investigate and characterize processes of mass transport in this class of ionically cross-linked assemblies.

Numerical Modeling of RF Magnetron Sputtering with Metallic or Dielectric Target

A self-consistent modeling of two-dimensional and temporal (2D-t) structures of RF magnetron plasma with a metallic (copper) and a dielectric (SiO2) target is performed at 5 mTorr in argon by using plasma hybrid model consisting of a particle-in-cell/Monte Carlo (PIC/MC) simulation for electrons and the relaxation continuum (RCT) model for ions. The erosion profiles of both targets are numerically predicted through the flux velocity distribution of ions incident on the surface. The mechanism of plasma maintenance in a dielectric target is quite different from that in a metallic one. Two major differences exist in an erosion profile between both targets. One is the presence of dual peaks in the erosion profile of the dielectric target. The other is the discrepancy in the position of the maxima between incident ion flux and erosion depth on the dielectric target. These are direct influences of the radially localized structure in an interfacial sheath based on the charge accumulation on a dielectric surface.

Theoretical Approaches to Erosion and Wetting Phenomena during Laser Brazing Process

The theoretical approaches to the erosion and wetting/flowing phenomena during the laser brazing process were made by the computer simulation. The erosion kinetics of the Inconel 600 base metal was investigated using Au-18%Ni filler metal. The erosion profile during the laser brazing was estimated by applying the additivity rule to the Nernst-Brunner theory based on the measured thermal cycle of the filler metal droplet. The computed erosion profiles in the laser brazed joints were fairly consistent with the experimental ones. The wetting and flowing of the melted Au-18%Ni filler metal on the Inconel 600 butt joint during the laser brazing were analyzed by the metal flow model. The filler metal droplet wetted and spread on the base metal and simultaneously infiltrated into the joint gap with the lapse of time. In the single beam brazing, the filler metal did not infiltrate into the 0.1mm wide joint gap at the completion of brazing, however, the filler metal could be filled up in it in the tandem beam brazing.

An experimental study on geometric characteristics of beach erosion profiles

The beach profile and sediment transport are very important factors in the design of coastal structures, and the beach profile is mainly affected by a number of parameters, such as wave height and period, beach slope, and the material properties of the bed. In this study, considering wave height ( H 0=6.5, 11.5, 16, 20, 23, 26 and 30 cm), wave period ( T=1.46 and 2.03 s), beach slope ( m=1/10 and 1/15) and mean sediment diameter ( d 50=0.18, 0.26, 0.33 and 0.40 mm), an experimental investigation of coastal erosion profile (storm profile) was carried out in a wave flume using regular waves, and geometric characteristics of erosion profile were determined by the resultant erosion profile. Dimensional and non-dimensional equations were obtained by using linear and non-linear regression methods through the experimental data and were compared with previously developed equations in the literature. The results have shown that the experimental data fitted well to the proposed equations with respect to the previously developed equations.

Critical erosion profiles in macro-tidal estuary sediments: Implications for the stability of intertidal mud and the slope of mud banks

Vertical profiles of the critical erosion threshold ( τ crit) in sediment have been measured at 11 stations along the axis of the Tamar Estuary and at a single station in a tributary of the Tamar at St. John's Ford. The τ crit of surface sediment increased from 0.04 Pa in the upper, brackish estuary to 0.09 Pa in the lower estuary. In the upper estuary τ crit only increased slightly with depth whereas in the marine estuary τ crit increased rapidly from 0.09 Pa at the surface to 0.25 Pa at 15 cm below the sediment surface. The results showed that the relationship between τ crit and bulk density ( ρ b) obtained previously for surface sediment was also applicable to sediments from depths of 10–15 cm and probably deeper. Profiles of ρ b were measured to depths of 70 cm using a corer. In the lower (marine) estuary ρ b increased with depth in the sediment from 1580 kg m −3 at the surface to 1720 kg m −3 at 70 cm. In the upper estuary ρ b values were lower at 1170–1200 kg m −3 and profiles were almost homogeneous indicating that consolidation was not occurring. The mid-estuary was transitional between these two situations. These results are consistent with the seasonal accumulation and loss of ‘mobile’ sediment observed previously in the upper estuary with changes in river flow, and with the apparent stability of intertidal mud in the lower marine estuary deduced from historical bathymetric survey records. The slopes of the intertidal mud banks ranged from 1–2% in the lower estuary to 20–25% in mid-estuary but, instead of continuing to increase in steepness towards the head as the estuary became narrower, the measured slopes actually decreased. It is speculated that the lack of consolidation through continual mobilisation and settlement cycles combined with an increase in silt content in the upper estuary resulted in sediment that lacked the mechanical strength to maintain steep slopes.