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New Journal of Physics - latest papers
Latest articles for New Journal of Physics
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Structure and dynamics of a Rouse polymer in a fluctuating correlated medium
We study the static and dynamical properties of a harmonically confined Rouse polymer coupled to a fluctuating correlated medium, which affect each other reciprocally during their stochastic evolution. The medium is modeled by a scalar Gaussian field which can feature modes with slow relaxation and long-range spatial correlations. We show that these modes affect the long-time behavior of the average position of the center of mass of the polymer, which, after a displacement, turns out to relax algebraically towards its equilibrium value. This is a manifestation of the non-Markovian nature of the effective evolution of the position of the center of mass, once the degrees of freedom of the medium have been integrated out. In contrast, we show that the coupling to the medium speeds up the relaxation of higher Rouse modes. We further characterize the typical size of the polymer as a function of its polymerization degree and of the correlation length of the medium, particularly when the system is driven out of equilibrium via the application of a constant external driving force. Finally, we study the response of a linear polymer to a tensile force acting on its terminal monomers.
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A general model for linearly polarized optical vector beams
We propose an approach for deriving a broad class of propagation models for inhomogeneously, linearly polarized ‘vector’ beams. Our formulation leverages a complex scalar potential along with an appropriately constructed Lagrangian energy density. Importantly, we show that polarization inhomogeneities can be included by simple addition of a spatially dependent polarization angle to the complex potential phase. Thus, phase and polarization are seen to be equivalent from an energy perspective. As part of our development, we also show how the complex scalar potential arises naturally when considering polarization angle as a field symmetry during construction of the Lagrangian. We further show that the definition of linear momentum density in terms of the complex potential holds a distinct advantage over the conventional definition for inhomo-geneously polarized beams.
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Mean first passage time of active Brownian particles in two dimensions
The mean first passage time (MFPT) is a key metric for understanding transport, search, and escape processes in stochastic systems. While well characterized for passive Brownian particles, its behavior in active systems—such as active Brownian particles (ABPs)—remains less understood due to their self-propelled, nonequilibrium dynamics. In this paper, we formulate and analyze an elliptic partial differential equation (PDE) to characterize the MFPT of ABPs in two-dimensional domains, including circular, annular, and elliptical regions. For annular regions, we analyze the MFPT of ABPs under various boundary conditions. Our results reveal rich behaviors in the MFPT of ABPs that differ fundamentally from those of passive particles. Notably, the MFPT exhibits non-monotonic dependence on the initial position and orientation of the particle, with maxima often occurring away from the domain center. We also find that increasing swimming speed can either increase or decrease the MFPT depending on the geometry and initial orientation. Asymptotic analysis of the PDE in the weak-activity regime provides insight into how activity modifies escape statistics of the particles in different geometries. Finally, our numerical solutions of the PDE are validated against Monte Carlo simulations.
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QSHS: an axion dark matter resonant search apparatus
We describe a resonant cavity search apparatus for axion dark matter constructed by the quantum sensors for the hidden sector collaboration. The apparatus is configured to search for QCD axion dark matter, though also has the capability to detect axion-like particles, dark photons, and some other forms of wave-like dark matter. Initially, a tuneable cylindrical oxygen-free copper cavity is read out using a low noise microwave amplifier feeding a heterodyne receiver. The cavity is housed in a dilution refrigerator (DF) and threaded by a solenoidal magnetic field, nominally 8 T. The apparatus also houses a magnetic field shield for housing superconducting electronics, and several other fixed-frequency resonators for use in testing and commissioning various prototype quantum electronic devices sensitive at a range of axion masses in the range 2.0– . The apparatus as currently configured is intended as a test stand for electronics over the relatively wide frequency band attainable with the cavity mode used for axion searches. We present performance data for the resonator, DF, and magnet, and plans for the first science run.
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Degree-based connected graph construction with assortativity constraint
Degree-based graph construction is a fundamental problem in network science. A graph is simple if there are no self-loops and no multiple links between any pair of nodes in the graph. A degree sequence is graphical if d can be represented as the degree sequence of at least one simple graph, where the graph is called a realization of the sequence d. In this work, we introduce a novel method (LSFGR) for generating simple graphs from graphical degree sequences, focusing additionally on connectedness and on assortativity. LSFGR guarantees connected graphs for all potentially connected degree sequences. In the case where a degree sequence has no simple realization, LSFGR produces graphs with at most one node with self-loops. In addition, the graphs generated from LSFGR characterize real-world networks with medium assortativity.