Absorbed driven diffusion can provide positive heat and work output

We investigate overdamped Brownian motion in a fluctuating potential on a one-dimensional interval bordered by absorbing boundaries. The potential switches randomly between the ∨-shaped and the ∧-shaped form and is symmetric with respect to the origin. We derive exact expressions describing the absorption process, dynamics and stochastic energetics of the particle. The mean absorption time can exhibit a pronounced minimum as the function of the potential switching rate. Moreover, there exists a parameter region where both the output work and the released heat are positive. We give a plausible explanation for this phenomenon based on typical statistical features of absorbed trajectories. The presented analytical method can be generalized to other models based on dichotomous switching between two potential shapes.

Coherent Image Source Modeling of Sound Fields in Long Spaces with a Sound-Absorbing Ceiling

Sound-absorbing boundaries can attenuate noise propagation in practical long spaces, but fast and accurate sound field modeling in this situation is still difficult. This paper presents a coherent image source model for simple yet accurate prediction of the sound field in long enclosures with a sound absorbing ceiling. In the proposed model, the reflections on the absorbent boundary are separated from those on reflective ones during evaluating reflection coefficients. The model is compared with the classic wave theory, an existing coherent image source model and a scale-model experiment. The results show that the proposed model provides remarkable accuracy advantage over the existing models yet is fast for sound prediction in long spaces.

Finite-Difference Time-Domain Simulations

This work discusses the Finite-Difference Time-Domain (FDTD) technique to simulate an electromagnetic wave assuming one, two and three dimensions. The propagation medium is assumed to be a free space bounded by two absorbing boundaries, perfect matched layer (PML) and perfect electric conductor (PEC). The FDTD-1D is considered in free space while FDTD-2D and 3D are considered both in free space and in a free space-medium consisting of dielectric sphere and cylinder in the center. In this case, we model the incident and the scattered electromagnetic fields reflected back from hitting the dielectric cylinder and sphere. Moreover, the simulation starts by generating an electromagnetic pulse either in the middle or at one end of the medium and this pulse can be either Gaussian or sinusoidal. For the FDTD-3D, an antenna dipole is assumed to be the source generator of the electromagnetic pulse. We also provide the analytic solutions to confirm the accuracy of the FDTD technique.

An HHL-based algorithm for computing hitting probabilities of quantum walks

We present a novel application of the HHL (Harrow-Hassidim-Lloyd) algorithm --- a quantum algorithm solving systems of linear equations --- in solving an open problem about quantum walks, namely computing hitting (or absorption) probabilities of a general (not only Hadamard) one-dimensional quantum walks with two absorbing boundaries. This is achieved by a simple observation that the problem of computing hitting probabilities of quantum walks can be reduced to inverting a matrix. Then a quantum algorithm with the HHL algorithm as a subroutine is developed for solving the problem, which is faster than the known classical algorithms by numerical experiments.

Broadband signal reconstruction for SHM: An experimental and numerical time reversal methodology

Structural Health Monitoring (SHM) aims to shift aircraft maintenance from a time-based to a condition-based approach. Within all the SHM techniques, Acoustic Emission (AE) allows for the monitoring of large areas by analyzing Lamb waves propagating in plate like structures. In this study, the authors proposed a Time Reversal (TR) methodology with the aim of reconstructing an original and unaltered signal from an AE event. Although the TR method has been applied in Narrow-Band (NwB) signal reconstruction, it fails when a Broad-Band (BdB) signal, such as a real AE event, is present. Therefore, a novel methodology based on the use of a Frequencies Compensation Transfer Function (FCTF), which is capable of reconstructing both NwB and real BdB signals, is presented. The study was carried out experimentally using several sensor layouts and materials with two different AE sources: (i) a Numerically Built Broadband (NBB) signal, (ii) a Pencil Lead Break (PLB). The results were validated numerically using Abaqus/CAETM with the implementation of absorbing boundaries to minimize edge reflections.

3D high order seismic imaging in Gulf of Mexico in the context of RTM algorithm using adjoint-based methods.

<p>The present work consists in imaging salt bodies from earth subsoil in the context of Reverse Time Migration (RTM) algorithm. The study of salt domes is economically important because they form a natural trap for hydrocarbons. For instance, more than a half of the hydrocarbon reserves that still exist today are related to salt bodies.</p><p>However, seismic images coming from strong salt tectonics area, are contaminated with spurious signal, like multiple events. Therefore, it is important to know how to treat and filter multiples in order to have seismic images that are geologically interpretable.</p><p>For this purpose, we solved the forward 3D elastic seismic wave equations using high order finite differences. The earth parameters come from 3D velocity and density models in a salt tectonic region in the North Gulf of Mexico. To obtain the imaging condition we compute the sensitivity kernels by using the adjoint solution of wave equation and by applying checkpointing. We tested this algorithm with simultaneous and separated sources. Fluid - solid interfaces at the ocean bottom is introduced, interfaces are well retrieved at large offsets.</p><p>Furthermore, we applied CPML absorbing boundaries, and replace also free surface conditions for absorbing boundaries to attenuate free surface multiples. The images we obtained from sensitivity kernels are easily interpretable. The calculations were performed on CALMIP supercomputing platforms in Toulouse France. </p>