Generation of spin-wave dark solitons with phase engineering

We generate experimentally spin-wave envelope dark solitons from rectangular high-frequency dark input pulses with externally introduced phase shifts in yttrium-iron garnet magnetic fims. We observe the generation of both odd and even numbers of magnetic dark solitons when the external phase shift varies. The experimental results are in a good qualitative agreement with the theory of the dark-soliton generation in magnetic films developed earlier [Phys. Rev. Lett. 82, 2583 (1999)].Comment: 6 pages, including 7 figures, submitted to Phys. Rev.

Temperature dependence of nonlinear auto-oscillator linewidths: Application to spin-torque nano-oscillators

The temperature dependence of the generation linewidth for an auto-oscillator with a nonlinear frequency shift is calculated. It is shown that the frequency nonlinearity creates a finite correlation time, tau, for the phase fluctuations. In the low-temperature limit in which the spectral linewidth is smaller than 1/tau, the line shape is approximately Lorentzian and the linewidth is linear in temperature. In the opposite high-temperature limit in which the linewidth is larger than 1/tau, the nonlinearity leads to an apparent "inhomogeneous broadening" of the line, which becomes Gaussian in shape and has a square-root dependence on temperature. The results are illustrated for the spin-torque nano-oscillator.Comment: 4 pages, 1 figur

Generation linewidth of an auto-oscillator with a nonlinear frequency shift: Spin-torque nano-oscillator

It is shown that the generation linewidth of an auto-oscillator with a nonlinear frequency shift (i.e. an auto-oscillator in which frequency depends on the oscillation amplitude) is substantially larger than the linewidth of a conventional quasi-linear auto-oscillator due to the renormalization of the phase noise caused by the nonlinearity of the oscillation frequency. The developed theory, when applied to a spin-torque nano-contact auto-oscillator, predicts a minimum of the generation linewidth when the nano-contact is magnetized at a critical angle to its plane, corresponding to the minimum nonlinear frequency shift, in good agreement with recent experiments.Comment: 4 pages, 2 figure

Critical velocity for the vortex core reversal in perpendicular bias magnetic field

For a circular magnetic nanodot in a vortex ground state we study how the critical velocity $v_c$ of the vortex core reversal depends on the magnitude $H$ of a bias magnetic field applied perpendicularly to the dot plane. We find that, similarly to the case $H$ = 0, the critical velocity does not depend on the size of the dot. The critical velocity is dramatically reduced when the negative (i.e. opposite to the vortex core direction) bias field approaches the value, at which a \emph{static} core reversal takes place. A simple analytical model shows good agreement with our numerical result.Comment: 4 pages, 2 figure

Lineshape distortion in a nonlinear auto-oscillator near generation threshold: Application to spin-torque nano-oscillators

The lineshape in an auto-oscillator with a large nonlinear frequency shift in the presence of thermal noise is calculated. Near the generation threshold, this lineshape becomes strongly non-Lorentzian, broadened, and asymmetric. A Lorentzian lineshape is recovered far below and far above threshold, which suggests that lineshape distortions provide a signature of the generation threshold. The theory developed adequately describes the observed behavior of a strongly nonlinear spin-torque nano-oscillator.Comment: 4 pages, 3 figure

Geo-Spatial Analysis of Reinforced Concrete Building Damage in 2017 Mexico Earthquake

This paper summarizes analyses of structural damage to reinforced concrete buildings seen after the 2017 Mexico City earthquake. With respect to the 2017 earthquake, the authors are part of a multi-institution National Science Foundation (NSF) RAPID effort that involved several in-field data collection missions yielding a dataset with detailed metadata for nearly 120 buildings. This data has been analyzed in conjunction with a high-density data set of around 1400 buildings from the National Autonomous University of Mexico (UNAM). The focus of analyses includes identifying correlations between building attributes (age, height, column ratio, design vulnerabilities, etc.) and site attributes (soil zone and local seismicity) to observed damage severity. The presented analyses rely heavily on geo-spatial mapping of data sets as Mexico City, constructed on a lakebed and having a unique soil profile and variance in seismicity, has geographically variable severity of reinforced concrete building damage. Specifically, the research team has leveraged the capabilities of geo-spatial mapping software ArcGIS Pro to investigate damages with respect to geotechnical zones and the PGA and PSA values from an array of ground motion stations active in the region during the 2017 earthquake. Thus, it has been possible to link metadata for geotechnical zone and ground motion for the closest station to each building. Aside from conclusions about the 2017 Mexico earthquake related to structural damage in reinforced concrete buildings, the authors will share the workflow for data curation and visualization methods for both ArcGIS Pro and MATLAB. These enable raw data from buildings, ground motion stations, and soil zone maps to be rapidly transformed into meaningful data structures, quantitative graphs, and geo-spatial maps. These protocols can be extremely powerful in the aftermath of a subsequent major earthquake to post-process and analyze reconnaissance data in a manner that provides the necessary evidence to support changes in current seismic design codes of practice

Non-resonant wave front reversal of spin waves used for microwave signal processing

It is demonstrated that non-resonant wave front reversal (WFR) of spin-wave pulses caused by pulsed parametric pumping can be effectively used for microwave signal processing. When the frequency band of signal amplification by pumping is narrower than the spectral width of the signal, the non-resonant WFR can be used for the analysis of the signal spectrum. In the opposite case the non-resonant WFR can be used for active (with amplification) filtering of the input signal.Comment: 4 pages, 3 figure