Mark A. Cappelli

Plasma-Activated Water (PAW) promotes plant growth, but whether it should replace conventional nitrogen, supplement it, or prime the crop early in the season is unclear. We compared nine nitrogen strategies differing in source (urea vs. PAW), rate (full, 1/5, 1/10, and zero), and timing on field-grown romaine lettuce in two trials. In Trial 1 (late summer), no treatment effect was significant, although the 80/20 urea/PAW blend and PAW priming co-led in yield and uniformity. Trial 2, grown in cooler autumn–winter conditions with ten times the rainfall and naturally occurring downy mildew on an estimated 62.5% of plants, produced 19–41% lower fresh weights and significant treatment effects. PAW priming (1/5 N as PAW first, then full-rate urea; about 73% of the full seasonal nitrogen) ranked in the top two in both trials, significantly exceeded full-rate urea in Trial 2, and produced 62.5% of heads above a 700 g marketable threshold against 9.4% for urea. The 50/50 blend and PAW priming declined least between trials, while the 80/20 blend and pure urea declined most; reduced-rate treatments from either source were indistinguishable from the control. Yield loss fell disproportionately on the wrapper leaves, consistent with the observed disease. PAW priming maintained yield and improved uniformity across two contrasting seasons and merits further evaluation. “Disease resilience” here denotes yield maintained in a disease-present season, not treatment-driven resistance: disease was not rated plot by plot.

We present experimental observations of counter-propagating interpenetrating hypervelocity plasma jets in the weakly collisional regime (Knudsen numbers, Kn∼0.09–0.27). Two independently operated opposing plasma deflagration accelerators were operated such that the jets they produced collided at a midpoint 68 cm from each device exit plane. Triple Langmuir probe diagnostics of each device's jet at this midpoint prior to collision demonstrated controllable plasma conditions with densities ranging from 1019 to 1020 m−3 and temperatures from 8 to 27 eV across driving capacitor charge voltages of 3–9 kV. Knudsen number analysis confirmed operation in the weakly collisional (Kn∼0.1–10) regime for the parameter space explored. During head-on collisions, we observed significant increases in both density (factors of 1.3–5.3) and temperature (factors of 3.5–19) indicative of stagnation effects, with the magnitude depending strongly on collisionality. High-speed imaging revealed distinct collision dynamics: diffuse interpenetration at lower collisionality transitioning to bright, localized stagnation regions at higher collisionality. At higher voltages (≥5 kV) which corresponded to higher collisionality, measured plasma parameters approached theoretical shock and stagnation predictions from hydrodynamic models, while lower voltage cases showed deviations consistent with kinetic effects. These results provide new experimental benchmarks for validating hybrid plasma simulation codes in the challenging weakly collisional regime relevant to inertial confinement fusion, laser–plasma interactions, and astrophysical jet phenomena.

This Tutorial reviews the mathematical foundations of topological electromagnetics in anisotropic continuum media, using magnetized plasmas as a representative case study. Particular emphasis is placed on the mathematical tools and physical concepts commonly employed in the analysis of topological phenomena in complex electromagnetic materials, and on providing a unified introduction to concepts that are often presented from different perspectives in the literature. We begin by reviewing core concepts in differential geometry and introduce topological invariants in real-space geometry. We then discuss their relevance to topological quantities in electromagnetics, such as Berry curvature and Chern numbers, while emphasizing that these quantities differ in their underlying definitions. The framework is applied to the computation of bulk band topology and surface-wave dispersion relations by constructing decaying field solutions and enforcing boundary conditions. Examples are presented for surface-wave propagation at interfaces between a magnetized plasma and air, dielectric, or metallic media, in both two-dimensional and three-dimensional configurations. This Tutorial offers a foundation for future investigations, including experiments, and supports the development of analytical and numerical methods for other anisotropic, dispersive, and topologically nontrivial media.

Coherent oscillations in the 30–110 MHz range are observed experimentally on a low-temperature, partially magnetized E × B discharge. The oscillations are measured when operating on helium, neon, argon, krypton, and molecular nitrogen. The high frequencies and global fluctuations in current distinguish these modes from the rotating spoke mode common in E × B plasmas. In helium, the frequency scales linearly with the voltage applied across the discharge gap. A characteristic measurement in helium is interpreted with a lower-hybrid drift instability model, which agrees with the experiments by assuming a short axial wavelength.

Time-varying media enable electromagnetic nonreciprocity, frequency conversion, and the production of momentum space bandgaps in time crystals. However, most theoretical descriptions contain fundamental omissions in their treatment of how the medium properties are modulated, notably in the creation and removal of polarizable constituents. Neglecting the consequences of the momentum that these particles contribute to the medium plays a significant role in the outcome, and in some cases gives rise to nonphysical amplification of the waves. This is a problem traceable to the methods by which the medium's properties are modulated, and in this article, we give a specific example for the case in which the polarizable constituents are free-electron carriers injected and removed by ionization and recombination. We show that when momentum conservation is accounted for consistently in the modulation process, one avoids spurious postcollapse field growth commonly interpreted as amplification, or gain. This analysis applies broadly to other polarizable constituents and points to the importance of addressing how these constituents of the medium are introduced or altered; otherwise one encounters questions about how the surroundings perform work on the medium to account for this predicted gain.

Traditional monetary policy’s effectiveness in controlling inflation through interest rate changes has weakened, as empirical data show easing no longer reliably drives consumer price inflation. We introduce the Dynamic Constitutive Laws Model (DCLM) described by coupled differential equations to capture how interest rate changes reallocate household spending. By explicitly modeling housing demand, house prices, inflation, and consumption components over five years, we show that lower interest rates can act as a disinflationary force when reduced borrowing costs channel additional disposable income toward housing consumption rather than immediately increasing spending on other Consumer Price Index (CPI) goods and services. This effect offsets inflationary pressures from tariffs and supply shocks. Calibrated on U.S. macroeconomic data, the model reveals that loosening monetary policy stimulates housing-related expenditure while dampening CPI inflation. Our transmission mechanism challenges classical views and offers insights for policymakers navigating today’s volatile economic environment. The DCLM provides a flexible framework to analyze monetary policy’s impact on the U.S. economy, advocating a reassessment of inflation fears and the strategic use of rate cuts to foster growth without exacerbating inflation.

The rotating spoke oscillation is observed in experiments on a planar direct-current magnetron discharge. Previous studies on the same device found that the spoke rotation direction can reverse when the current increases. At low currents, the spoke disturbances propagate opposite the E×B drift direction. At higher currents, the spokes reverse to propagate in the E×B direction. In between, a chaotic state appears without coherent spokes. In this paper, we use higher-order spectral analyses to study the evolution of the oscillation spectrum in this intermediate state. The bispectrum shows a phase coherence between modes that points to nonlinear three-wave coupling processes. We solve for the quadratic power transfer functions using two-point measurements along the plasma circumference. The results show a period doubling process that takes place in the transition from a coherent spoke to a chaotic spectrum. Nonlinear wave interactions spread energy over a broad range of frequencies to form sidebands. Recovery of coherent +E×B spoke modes coincides with a reversal of the direction of quadratic power transfer back into the main frequency mode.

The increasing demand for sustainable energy has spurred the exploration of advanced technologies for biodiesel production. This paper investigates the use of Dielectric Barrier Discharge (DBD)-generated low-temperature plasmas to enhance the conversion of fatty acid methyl esters (FAMEs) into hydrogenated fatty acid methyl esters (H-FAMEs) and other high-value hydrocarbons. A key mechanistic advance is achieved via in situ distillation: at the reactor temperature, unsaturated C18 and C20 FAMEs remain liquid due to their low melting points, while the corresponding saturated C18:0 and C20:0 FAMEs (with melting points of approximately 37–39 °C and 46–47 °C, respectively) solidify and deposit on a glass substrate. This phase separation continuously exposes fresh unsaturated FAME to the plasma, driving further hydrogenation and thereby delivering high overall conversion efficiency. The non-thermal, energy-efficient nature of DBD plasmas offers a promising alternative to conventional high-pressure, high-temperature methods; here, we evaluate the process efficiency, product selectivity, and scalability of this room-temperature, atmospheric-pressure approach and discuss its potential for sustainable fuel-reforming applications.