Enhancing searches for resonances with machine learning and moment decomposition

A key challenge in searches for resonant new physics is that classifiers trained to enhance potential signals must not induce localized structures. Such structures could result in a false signal when the background is estimated from data using sideband methods. A variety of techniques have been developed to construct classifiers which are independent from the resonant feature (often a mass). Such strategies are sufficient to avoid localized structures, but are not necessary. We develop a new set of tools using a novel moment loss function (Moment Decomposition or MoDe) which relax the assumption of independence without creating structures in the background. By allowing classifiers to be more flexible, we enhance the sensitivity to new physics without compromising the fidelity of the background estimation.

Dual Current Loop Control for a Third-Order Passive Damped Filter Based Quasi-Z-Source Inverter

An Impedance Source Inverter (ZSI) offers a solution to low output renewable energy sources, because it provides an unconventional high boost. The interaction of Quasi-Z-Source (qZS) inverter with the load side raises stability concerns. Multiple resonant features need attention when grid is connected. In this paper, the resonant feature of a third order filter based on a qZS inverter is explored, and DC and AC sides dynamic characteristics are analyzed for optimum size selection of passive components. Coupled response of a qZS inverter and the AC side filter is presented. For input variation, a closed loop control is established to take care of stability and the multiple resonant feature. A voltage loop and a dual current loop are used for DC and AC side dynamics respectively. Controllers are designed to mitigate input side disturbance. Results are provided for two design cases (case I, II), the need for damping is highlighted, and measured results validate the design and control methodology.

Experimental and numerical study of the resonant feature of internal gravity waves in the case of ‘dead water’ phenomenon

<p> ‘Dead water’ phenomenon, which is essentially a ship-wave in a stratified fluid is studied experimentally in a laboratory tank. Interfacial waves are excited by a moving ship model in a quasi-two-layer fluid, which leads to the development of a drag force that reaches the maximum at the largest wave amplitude in a critical ‘resonant’ towing speed, whose value depends on the structure of the vertical density profile. We utilize five ships of different lengths but of the same width and wet depth. The experimental analysis focuses on the variability of the interfacial wave amplitudes and wavelengths as a function of towing speed in different stratifications. Data evaluation is based on linear two- and three-layer theories of freely propagating interfacial waves and lee waves. We observe that although the internal waves have considerable amplitude, linear theory still gives a surprisingly adequate description of subcritical to supercritical transition and the associated amplification of internal waves.</p>

Laboratory investigations on the resonant feature of ‘dead water’ phenomenon

Interfacial internal wave excitation in the wake of towed ships is studied experimentally in a quasi-two-layer fluid. At a critical ‘resonant’ towing velocity, whose value depends on the structure of the vertical density profile, the amplitude of the internal wave train following the ship reaches a maximum, in unison with the development of a drag force acting on the vessel, known in the maritime literature as ‘dead water’. The amplitudes and wavelengths of the emerging internal waves are evaluated for various ship speeds, ship lengths and stratification profiles. The results are compared to linear two- and three-layer theories of freely propagating waves and lee waves. We find that despite the fact that the observed internal waves can have considerable amplitudes, linear theories can still provide a surprisingly adequate description of subcritical-to-supercritical transition and the associated amplification of internal waves. We argue that the latter can be interpreted as a coalescence of frequencies of two fundamental stable wave motions, namely lee waves and propagating interfacial wave modes. Graphic abstract

Numerical Study on Controllable Multi-Band Microwave Metamaterial Absorbers

Based on the impedance matching and electromagnetic resonant characteristic of composite materials, we present a single-layer metamaterial absorber consisting of arch copper loop and substrate FR-4, of which the resonant frequency depended on the loop’s geometry perimeter. By combining resonant loops with different dimensions together, we can achieve multi-band absorption. The standard finite difference time domain method was used to calculate the magnitudes of reflectance, and then the induced surface current and power loss distributions were demonstrated to analyze the insight physical picture of the multi-band resonant feature. By optimizing the simulation results, the absorptivities of two absorption peaks are all above 98% when the number of copper loops is two, 95% for three absorption peaks of three loops, and 87% for four absorption peaks of four loops.

Surface Enhanced Magneto-Optics in Noble Metal / Ferromagnetic Metal Multilayers

ABSTRACTWe present an electromagnetic enhancement mechanism for the magneto-optical response of noble metal / ferromagnetic metal multilayer thin films. When such a structure is illuminated in total reflection condition, the resonant coupling of light with the noble metal surface plasmons gives rise to an amplification of the magneto-optically induced component of the light electric field. The experimental results obtained on a 30nm-thick Au / Co / Au model system show that this resonant feature observed in the Kerr rotation and ellipticity corresponds to a strong enhancement of the magneto-optical figure of merit and signal-to-noise ratio.