Impedance matching to axion dark matter: considerations of the photon-electron interaction

We introduce the concept of impedance matching to axion dark matter by posing the question of why axion detection is difficult, even though there is enough power in each square meter of incident dark-matter flux to energize a LED light bulb. By quantifying backreaction on the axion field, we show that a small axion-photon coupling does not by itself prevent an order-unity fraction of the dark matter from being absorbed through optimal impedance match. We further show, in contrast, that the electromagnetic charges and the self-impedance of their coupling to photons provide the principal constraint on power absorption integrated across a search band. Using the equations of axion electrodynamics, we demonstrate stringent limitations on absorbed power in linear, time-invariant, passive receivers. Our results yield fundamental constraints, arising from the photon-electron interaction, on improving integrated power absorption beyond the cavity haloscope technique. The analysis also has significant practical implications, showing apparent tension with the sensitivity projections for a number of planned axion searches. We additionally provide a basis for more accurate signal power calculations and calibration models, especially for receivers using multi-wavelength open configurations such as dish antennas and dielectric haloscopes.

The effects of the driving frequencies on micro atmospheric pressure He/N2 plasma jets driven by tailored voltage waveforms

Capacitively coupled micro atmospheric pressure plasma jets (µAPPJs) are important tools for the generation of radicals at room temperature for various applications. Voltage Waveform Tailoring (VWT), which is based on the simultaneous use of a set of excitation frequencies has been demonstrated to provide an efficient control of the Electron Energy Probability Function (EEPF) in such plasmas and, thus, allows optimizing the electron impact-driven excitation and dissociation processes as compared to the classical single-frequency operation mode. In this work, the effects of changing the driving frequencies on the spatio-temporally resolved electron power absorption dynamics, the generation of helium metastables and the dissociation of nitrogen molecules are investigated in He/N2 plasmas based on experiments and simulations. We find that under a single-frequency excitation, the plasma and helium metastable densities are enhanced as a function of the driving frequency at a fixed voltage. When using peaks-type driving voltage waveforms synthesized based on consecutive harmonics of the fundamental driving frequency, the spatial symmetry of the electron power absorption dynamics and of the metastable density profile is broken. Increasing the fundamental frequency at a constant voltage is found to drastically enhance the plasma and metastable densities, which is a consequence of the change of the EEPF. Finally, we compare the energy efficiency of the formation of radicals under single-frequency and VWT operation at different driving frequencies. For a given power dissipated in the plasma, VWT yields a higher helium metastable as well as electron density and a higher dissociation rate of N2.

Clinical and Biomechanical Progression after Ankle Joint Distraction in a Young Adolescent Patient with Haemophilia

Ankle joint distraction (AJD) has been described to be a valuable joint-sparing alternative to arthrodesis or arthroplasty; however, clinical endpoints associated to this surgical intervention are lacking. The current case report describes clinical and biomechanical outcome measures of ankle joint distraction in a 14-year-old patient with severe haemophilia A. Because of persistent and incapacitating pain and the poor response to conservative and invasive treatment options, ankle joint distraction was performed in this 14-year-old patient using an external fixator encompassing two Ilizarov full rings in the tibia and a foot ring fixed to the foot by four K-wires. State-of-the-art medical imaging and non-invasive skin marker-based 3D multi-segment foot modelling were performed in a pre- and post-operative stage. From a structural viewpoint, this AJD was a success since it improved and stabilised the osteo-cartilaginous lesions of the ankle. Biomechanical outcome measures associated with the 18-month follow-up were found to be suboptimal, showing an early plantarflexion pattern at the ankle joint during midstance and a tendency towards increased power absorption at the midfoot with peak power absorption being almost two times higher when compared to boys of the same age. From a functional viewpoint, we observed a clear reduction in the patients’ physical activities until one year after AJD. Despite these functional and structural improvements, recurrent painful phenomena, including the development of a complex regional pain syndrome (CRPS) and a stress fracture of the third metatarsal bone, were observed which are probably related with the development of recurrent subchondral oedema.

Numerical Modeling and Sensitivity Analysis on Microwave Heating of Plastic on a Large Scale

To reduce the carbon emissions during heating in the manufacturing process, microwaves have attracted significant attention. Microwave has a lot of advantages rather than traditional heating method such as rapid heating, lower thermal damage and eco-friendly process. In order to apply microwaves to manufacturing process, uniform and efficient heating is required. We have analyzed the effect of various design parameters such as cavity heights, the application of the reflector, and the number and positions of waveguides for uniform and efficient heating by numerical simulation and verified that by experiment. The results showed that a slight change in the cavity height altered the electromagnetic field distribution and heating parameters, such as the coefficient of variance and power absorption efficiency. With reflectors installed, uniform heating was achieved and power absorption was improved, with the spherical reflector showing the maximum efficiency. The use of double waveguides heated the target material in a uniform manner. An increase in the power supply also led to uniform heating. This large-scale analysis will be helpful in applying microwaves to actual industrial sites.

Total wave power absorption by a multi-float wave energy converter and a semi-submersible wind platform with a fast far field model for arrays

Wave energy converters absorb wave power by mechanical damping for conversion into electricity and multi-float systems may have high capture widths. The kinetic energy of the floats causes waves to be radiated, generating radiation damping. The total wave power absorbed is thus due to mechanical and radiation damping. A floating offshore wind turbine platform also responds dynamically and damping plates are generally employed on semi-submersible configurations to reduce motion, generating substantial drag which absorbs additional wave power. Total wave power absorption is analysed here by linear wave diffraction–radiation–drag models for a multi-float wave energy converter and an idealised wind turbine platform, with response and mechanical power in the wave energy case compared with wave basin experiments, including some directional spread wave cases, and accelerations compared in the wind platform case. The total power absorption defined by capture width is input into a far field array model with directional wave spreading. Wave power transmission due a typical wind turbine array is only reduced slightly (less than 5% for a 10 × 10 platform array) but may be reduced significantly by rows of wave energy converters (by up to about 50%).