21 research outputs found
Analysis of a diffusive effective mass model for nanowires
We propose in this paper to derive and analyze a self-consistent model
describing the diffusive transport in a nanowire. From a physical point of
view, it describes the electron transport in an ultra-scaled confined
structure, taking in account the interactions of charged particles with
phonons. The transport direction is assumed to be large compared to the wire
section and is described by a drift-diffusion equation including effective
quantities computed from a Bloch problem in the crystal lattice. The
electrostatic potential solves a Poisson equation where the particle density
couples on each energy band a two dimensional confinement density with the
monodimensional transport density given by the Boltzmann statistics. On the one
hand, we study the derivation of this Nanowire Drift-Diffusion Poisson model
from a kinetic level description. On the other hand, we present an existence
result for this model in a bounded domain
Optimal operation of cryogenic calorimeters through deep reinforcement learning
Cryogenic phonon detectors with transition-edge sensors achieve the best
sensitivity to light dark matter-nucleus scattering in current direct detection
dark matter searches. In such devices, the temperature of the thermometer and
the bias current in its readout circuit need careful optimization to achieve
optimal detector performance. This task is not trivial and is typically done
manually by an expert. In our work, we automated the procedure with
reinforcement learning in two settings. First, we trained on a simulation of
the response of three CRESST detectors used as a virtual reinforcement learning
environment. Second, we trained live on the same detectors operated in the
CRESST underground setup. In both cases, we were able to optimize a standard
detector as fast and with comparable results as human experts. Our method
enables the tuning of large-scale cryogenic detector setups with minimal manual
interventions.Comment: 23 pages, 14 figures, 2 table
ANISOTROPIC MESH ADAPTION GOVERNED BY A HESSIAN MATRIX METRIC
ABSTRACT An essential task for any finite element method is to provide appropriate resolution of the mesh to resolve the initial solution. We present a computational method for anisotropic tetrahedral mesh refinement according to an adjustable discretization error. The initial attribute profile is given by an analytical function which is twice continously differentiable. Anisotropy is taken into account to reduce the amount of elements compared to pure isotropic meshes. By the proposed method the spatial resolution in three-dimensional unstructured tetrahedral meshes used for diffusion simulation is locally increased and the accuracy of the discretization improved