Pulsed bipolar plasma electrolytic oxidation (PEO) processes carried out under potentiostatic control in electrolytes containing calcium acetate and sodium phosphate with Ca:P ratio of 2 were ...investigated by in situ impedance spectroscopy in order to achieve insights in the coating formation mechanisms and identify suitable means for real-time control of essential coating characteristics and properties. The coating thickness, morphology, chemical and phase compositions have been studied by non-destructive eddy current techniques, scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction analysis. The results demonstrate successful deposition of about 25μm thick porous surface layers composed of amorphous calcium phosphates along with crystalline hydroxyapatite, tricalcium phosphate perovskite and titania phases. It was established that the growth of the PEO is controlled by anodic process of titanium oxidation, whereas precipitation of calcium phosphate containing compounds occurred via chemical mechanisms. Plasma discharge was responsible for partial crystallisation and decomposition of the deposited compounds. Characteristic responses related to anodic oxidation of Ti and processes associated with plasma discharge were identified in the impedance spectra of the PEO process. Kinetic parameters of charge transfer under conditions of high-voltage electrolysis have been evaluated and discussed.
•In situ impedance spectroscopy was used for diagnostics of PEO Ti.•Porous calcium phosphate coatings were obtained in pulsed bipolar mode.•Two characteristic regions were identified in impedance spectra.•Charge transfer resistance and double layer capacitance were evaluated.•Mechanism of hydroxyapatite deposition by PEO was discussed.
Theoretical calculations of the Lamb shift provide the basis required for the determination of the Rydberg constant from spectroscopic measurements in hydrogen. The recent high‐precision ...determination of the proton charge radius drastically reduces the uncertainty in the hydrogen Lamb shift originating from the proton size. As a result, the dominant theoretical uncertainty now comes from the two‐ and three‐loop QED effects, which calls for further advances in their calculations. The present status of theoretical calculations of the Lamb shift in hydrogen and light hydrogen‐like ions with the nuclear charge number up to Z=5 is reviewed. Theoretical errors due to various effects are critically examined and estimated.
Theoretical calculations of the Lamb shift provide the basis required for the determination of the Rydberg constant from spectroscopic measurements in hydrogen. The aim of this paper is to review the present status of theoretical calculations of the Lamb shift in hydrogen and light hydrogen‐like ions. Theoretical errors due to various effects are critically examined and estimated.
Optical atomic clocks are the most accurate measurement devices ever constructed and have found many applications in fundamental science and technology. The use of highly charged ions (HCI) as a new ...class of references for highest-accuracy clocks and precision tests of fundamental physics has long been motivated by their extreme atomic properties and reduced sensitivity to perturbations from external electric and magnetic fields compared with singly charged ions or neutral atoms. Here we present the realization of this new class of clocks, based on an optical magnetic-dipole transition in Ar13+. Its comprehensively evaluated systematic frequency uncertainty of 2.2 × 10-17 is comparable with that of many optical clocks in operation. From clock comparisons, we improve by eight and nine orders of magnitude on the uncertainties for the absolute transition frequency and isotope shift (40Ar versus36Ar) (ref.), respectively. These measurements allow us to investigate the largely unexplored quantum electrodynamic (QED) nuclear recoil, presented as part of improved calculations of the isotope shift, which reduce the uncertainty of previous theory by a factor of three. This work establishes forbidden optical transitions in HCI as references for cutting-edge optical clocks and future high-sensitivity searches for physics beyond the standard model.
Cerium nitrate (Ce(NO3)3) and benzotriazole (BTA) were applied as immersion post-treatments for Plasma Electrolytic Oxidation (PEO) coatings on commercially pure magnesium. The surface morphology of ...the coated samples was characterised by Scanning Electron Microscopy (SEM), and it was found that the micro-pores on the coating surface can be effectively sealed by Ce(NO3)3 immersion post-treatment, whereas BTA did not show any significant effect on the coating microstructure. The corrosion resistance behaviour of the coated samples was examined by electrochemical tests in a 3.5 wt% NaCl solution. According to the results, the Ce(NO3)3 immersion post-treatment showed the better effect in enhancing the corrosion resistance of the PEO coating, compared with BTA immersion post-treatment. The insoluble Ce-containing compounds can provide both a sealing effect and continuous longer-term protection for the PEO-Ce(NO3)3 coating. At the same time, BTA provides only a short-term improvement in the corrosion resistance, due to adsorption on the coating surface.
•Immersion post-treatments of PEO coatings on Mg in Ce(NO3)3 and BTA solutions•BTA is adsorbed in the pores inhibiting anodic reaction in corrosion process.•Ce based compounds are deposited in the pores inhibiting cathodic reaction.•Ce post-treatment combines sealing and inhibition providing longer term effect.
The article is devoted to the smoothing of the tabulated curves describing the aerodynamic profiles. In the course of the iterative process of changing the geometric characteristics of the airfoil ...when designing the wing surface, its smoothness may be disturbed. This necessitates smoothing the profile by deviating from some preset points. The paper deals with the issues of ensuring the convexity of the section of the profile, on which the graph of its curvature has oscillations. A smoothing procedure is described based on smoothness criteria obtained from the necessary and sufficient conditions for the existence of a polynomial of the eighth degree. The results of profile smoothing are presented, which confirm the effectiveness of the developed procedure for ensuring the convexity of the smooth curve.
In this study, a plasma electrolytic oxidation (PEO) process was used to produce oxide coatings on commercially pure aluminium (1100 alloy) at a pulsed dc power mode. The effects of process ...parameters (i.e. current density and treatment time) on the plasma discharge behaviour during the PEO treatment were investigated using optical emission spectroscopy (OES) in the visible and near ultraviolet (NUV) band (285--800 nm). The elements present in the plasma were identified. Stark shifts of spectral lines and line intensity ratios were utilized to determine the plasma electron concentrations and temperatures, respectively. The plasma electron temperature profile, coating surface morphology and coating composition were used to interpret the plasma discharging behaviour. The different coating morphologies and compositions at different coating surface regions are explained in terms of three types of discharge, which originate either at the substrate/coating interface, within the upper layer, or at the coating top layer. The high spike peaks on the plasma intensity and temperature profiles corresponded to discharges originated from the substrate/coating interface, while the base line and small fluctuations were due to discharges at the coating/electrolyte interface.
We report high-precision calculations of the nuclear recoil effect to the Lamb shift of hydrogenlike atoms to the first order in the electron-nucleus mass ratio and to all orders in the nuclear ...binding strength parameter Zα. The results are in excellent agreement with the known terms of the Zα expansion and allow an accurate identification of the nonperturbative higher-order remainder. For hydrogen, the higher-order remainder was found to be much larger than anticipated. This result resolves the long-standing disagreement between the numerical all-order and analytical Zα-expansion approaches to the recoil effect and completely removes the second-largest theoretical uncertainty in the hydrogen Lamb shift of the 1S and 2S states.
A weighted difference of the g factors of the H- and Li-like ions of the same element is theoretically studied and optimized in order to maximize the cancellation of nuclear effects between the two ...charge states. We show that this weighted difference and its combination for two different elements can be used to extract a value for the fine-structure constant from near-future bound-electron g factor experiments with an accuracy competitive with or better than the present literature value.
PDF
