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In recent years, there has been increasing interest in the understanding and application of nanoparticle assemblies driven by external fields. Although these systems can exhibit marked transitions in behavior compared to non-interacting counterparts, it has often proven challenging to connect their dynamics with underlying physical mechanisms or even to verifiably establish their structure under realistic experimental conditions. We have studied colloidal iron oxide nanoparticles that assemble into ordered, few-particle linear chains under the influence of oscillating and pulsed magnetic fields. In this work, our goal has been to answer the following question: by what physical mechanisms does the magnetic switching of a linear chain evolve from the switching of its constituent particles? Cryo-TEM has been used to flash freeze and image the structures formed by oscillatory drive fields, and magnetic relaxometry has been used to extract the multiple time constants associated with magnetic switching of the short chains. Armed with the physical structure from microscopy and the field-dependent switching times from magnetic measurements, we have conducted extensive micromagnetic simulations, revealing probable physical mechanisms for each time constant regime spanning$$10^{6}$$($$\approx$$1 μs to 1 s) in time. These types of magnetic nanomaterials have great potential for biomedical technologies, particularly magnetic particle imaging and hyperthermia, and rigorous elucidation of their physics will hasten their optimization. 

We describe a new method for solving the linearized 1D Vlasov–Poisson system by using properties of Cauchy-type integrals. Our method remedies critical flaws of the two standard methods, reveals a previously unrecognized Gaussian-in-time-like decay, and can also account for an externally applied electric field. The Landau approximation involves deforming the Bromwich contour around the poles closest to the real axis due to the analytically continued dielectric function, finding the long-time behavior for a stable system: Landau damping. Jackson's generalization encircles all poles while sending the contour to infinity, assuming its contribution vanishes, which is not true in general. This gives incorrect solutions for physically reasonable configurations and can exhibit pathological behavior, of which we show examples. The van Kampen method expresses the solution for a stable equilibrium as a continuous superposition of waves, resulting in an opaque integral. Case's generalization includes unstable systems and predicts a decaying discrete mode for each growing discrete mode, an apparent contradiction to both the Jackson solution and ours. We show, without imposing additional constraints, that the decaying modes are never present in the time evolution due to an exact cancellation with part of the continuum. Our solution is free of integral expressions, is obtained using algebra and Laurent series expansions, does not rely on analytic continuations, and results in a correct asymptotically convergent form in the case of infinite sums. The analysis used can be readily applied in higher-dimensional, electromagnetic systems and also provides a new technique for evaluating certain inverse Laplace transforms. 

We present a method for solving the linearized Vlasov-Poisson equation, based on analyticity properties of the equilibrium and initial condition through Cauchy-type integrals, that produces algebraic expressions for the distribution and field, i.e., the solution is expressed without integrals. Standard extant approaches involve deformations of the Bromwich contour that give erroneous results for certain physically reasonable configurations or eigenfunction expansions that are misleading as to the temporal structure of the solution. Our method is more transparent, lacks these defects, and predicts previously unrecognized behavior. 

We present the results of a survey fielded in June of 2022 as a lens to examine recent data reliability issues on Amazon Mechanical Turk. We contrast bad data from this survey with bad data from the same survey fielded among US workers in October 2013, April 2018, and February 2019. Application of an established data cleaning scheme reveals that unusable data has risen from a little over 2% in 2013 to almost 90% in 2022. Through symptomatic diagnosis, we attribute the data reliability drop not to an increase in bad faith work, but rather to a continuum of English proficiency levels. A qualitative analysis of workers’ responses to open-ended questions allows us to distinguish between low fluency workers, ultra-low fluency workers, satisficers, and bad faith workers. We go on to show the effects of the new low fluency work on Likert scale data and on the study’s qualitative results. Attention checks are shown to be much less effective than they once were at identifying survey responses that should be discarded. 

This search for magnetic monopoles (MMs) and high electric charge objects (HECOs) with spins 0, $1/2$, and 1, uses for the first time the full MoEDAL detector, exposed to $6.46{\mathrm{fb}}^{-1}$proton-proton collisions at 13 TeV. The results are interpreted in terms of Drell-Yan and photon-fusion pair production. Mass limits on direct production of MMs of up to 10 Dirac magnetic charges and HECOs with electric charge in the range $10e$to $400e$, were achieved. The charge limits placed on MM and HECO production are currently the strongest in the world. MoEDAL is the only LHC experiment capable of being directly calibrated for highly ionizing particles using heavy ions and with a detector system dedicated to definitively measuring magnetic charge. Published by the American Physical Society2025