Magnonic Band Structure Established by Chiral Spin-Density Waves in Thin Film Ferromagnets

Recent theoretical studies have demonstrated the possibility to excite and sustain noncollinear magnetization states in ferromagnetic nanowires. The resulting state is referred to as a spin-density wave (SDW). SDWs can be interpreted as hydrodynamic states with a constant fluid density and fluid velocity in systems with easy-plane anisotropy. Here, we consider the effect of the nonlocal dipole field arising from the finite thickness of magnetic thin films on the spatial profile of the SDW and on the associated magnon dispersion. Utilizing a hydrodynamic formulation of the Larmor torque equation, it is found that the nonlocal dipole field modulates the fluid velocity. Such a modulation induces a magnonic band structure unlike the typical dispersion relation for magnons on uniform magnetization. The analytical results are validated by micromagnetic simulations. Band gaps on the order of GHz are numerically observed to depend on the SDW fluid velocity and film thickness for realistic material parameters. The presented results suggest that SDWs can find applications as reconfigurable magnonic crystals.Comment: 5 pages, 5 figure

Whispering gallery mode resonator based ultra-narrow linewidth external cavity semiconductor laser

We demonstrate a miniature self-injection locked DFB laser using resonant optical feedback from a high-Q crystalline whispering gallery mode resonator. The linewidth reduction factor is greater than 10,000, with resultant instantaneous linewidth less than 200 Hz. The minimal value of the Allan deviation for the laser frequency stability is 3x10^(-12) at the integration time of 20 us. The laser possesses excellent spectral purity and good long term stability.Comment: To be published in Optics Letter

Whitham modulation theory and two-phase instabilities for generalized nonlinear Schr\"{o}dinger equations with full dispersion

The generalized nonlinear Schr\"odinger equation with full dispersion (FDNLS) is considered in the semiclassical regime. The Whitham modulation equations are obtained for the FDNLS equation with general linear dispersion and a generalized, local nonlinearity. Assuming the existence of a four-parameter family of two-phase solutions, a multiple-scales approach yields a system of four independent, first order, quasi-linear conservation laws of hydrodynamic type that correspond to the slow evolution of the two wavenumbers, mass, and momentum of modulated periodic traveling waves. The modulation equations are further analyzed in the dispersionless and weakly nonlinear regimes. The ill-posedness of the dispersionless equations corresponds to the classical criterion for modulational instability (MI). For modulations of linear waves, ill-posedness coincides with the generalized MI criterion, recently identified by Amiranashvili and Tobisch (New J. Phys. 21 (2019)). A new instability index is identified by the transition from real to complex characteristics for the weakly nonlinear modulation equations. This instability is associated with long-wavelength modulations of nonlinear two-phase wavetrains and can exist even when the corresponding one-phase wavetrain is stable according to the generalized MI criterion. Another interpretation is that, while infinitesimal perturbations of a periodic wave may not grow, small but finite amplitude perturbations may grow, hence this index identifies a nonlinear instability mechanism for one-phase waves. Classifications of instability indices for multiple FDNLS equations with higher order dispersion, including applications to finite depth water waves and the discrete NLS equation are presented and compared with direct numerical simulations.Comment: 26 pages, 7 figure

Validation of Kalman Filter alignment algorithm with cosmic-ray data using a CMS silicon strip tracker endcap

A Kalman Filter alignment algorithm has been applied to cosmic-ray data. We discuss the alignment algorithm and an experiment-independent implementation including outlier rejection and treatment of weakly determined parameters. Using this implementation, the algorithm has been applied to data recorded with one CMS silicon tracker endcap. Results are compared to both photogrammetry measurements and data obtained from a dedicated hardware alignment system, and good agreement is observed.Comment: 11 pages, 8 figures. CMS NOTE-2010/00

The Ovaherero/Nama Genocide: A Case for an Apology and Reparations

This research examines the consequences of the Ovaherero and Nama massacres occurring in modern Namibia from 1904-08 and perpetuated by Imperial Germany. Recent political advances made by, among other groups, the Association of the Ovaherero Genocide in the United States of America, toward mutual understanding with the Federal Republic of Germany necessitates a comprehensive study about the event itself, its long-term implications, and the more current vocalization toward an apology and reparations for the Ovaherero and Nama peoples. Resulting from the Extermination Orders of 1904 and 1905 as articulated by Kaiser Wilhelm II’s Imperial Germany, over 65,000 Ovaherero and 10,000 Nama peoples perished in what was the first systematic genocide of the twentieth century. This study assesses the historical circumstances surrounding these genocidal policies carried out by Imperial Germany, and seeks to place the devastating loss of life, culture, and property within its proper historical context. The question of restorative justice also receives analysis, as this research evaluates the case made by the Ovaherero and Nama peoples in their petitions for compensation. Beyond the history of the event itself and its long-term effects, the paper adopts a comparative approach by which to integrate the Ovaherero and Nama calls for reparations into an established precedent