Propagating wave in a fluid by coherent motion of 2D colloids

Just like in living organisms, if precise coherent operation of tiny movable components is possible, one may generate a macroscopic mechanical motion. Here we report that ~1010 pieces of colloidally dispersed nanosheets in aqueous media can be made to operate coherently to generate a propagating macroscopic wave under a non-equilibrium state. The nanosheets are initially forced to adopt a monodomain cofacial geometry with a large and uniform plane-to-plane distance of ~420 nm, where they are strongly correlated by competitive electrostatic repulsion and van der Waals attraction. When the electrostatic repulsion is progressively attenuated by the addition of ionic species, the nanosheets sequentially undergo coherent motions, generating a propagating wave. This elaborate wave in time and space can transport microparticles over a long distance in uniform direction and velocity. The present discovery may provide a general principle for the design of macroscopically movable devices from huge numbers of tiny components.

Teaching the concept of the uniform plane wave from mathematical modeling

The discovery of electromagnetic waves enabled us to understand electricity, magnetism, and optics under the same field; therefore, it is important for electronic and related engineers to understand the concept of the uniform plane wave, which represents the simplest case of an electromagnetic wave propagating through a medium. However, this concept is taught with a theoretical approach, shows a need for a methodological change towards experimentation to mitigate poor learning in students causing a high failure rate in electromagnetism courses. In this context, this work presents a methodological alternative for teaching the concept of the uniform plane wave, combining the CUVIMA model with the didactics of mathematical modelling, to link experimentation and provide cognitive support to the conceptualization of the physical phenomenon. For it, a single-group design is implemented, with pre-test and post-test, to know about previous ideas and identify the conceptual change achieved for the students. When applying the Student’s t-test at a significance level of 5%, a significant difference is evident between the means of the study groups. It is concluded that there is a favorable and representative conceptual change in the students, with respect to the understanding of the physical phenomenon represented by the concept of the uniform plane wave.

On the integration of reconfigurable intelligent surfaces in real-world environments

<div>The use of reconfigurable intelligent surfaces (RISs) for optimization of propagation channels is one of the most promising and revolutionizing techniques for improving the efficiency of the next generation of communications systems. In this work, we combine the physical optics approximation and the theory of diffraction gratings to study the scattering properties of finite-size metasurfaces mounted on partially reflecting walls and illuminated by directive antennas. We consider both reflective and refractive metasurfaces designed to control both reflection and transmission of waves. We start the analysis under the assumption of uniform, plane-wave illumination, and then discuss non-uniform illuminations by directive antennas.</div>

On the integration of reconfigurable intelligent surfaces in real-world environments

<div>The use of reconfigurable intelligent surfaces (RISs) for optimization of propagation channels is one of the most promising and revolutionizing techniques for improving the efficiency of the next generation of communications systems. In this work, we combine the physical optics approximation and the theory of diffraction gratings to study the scattering properties of finite-size metasurfaces mounted on partially reflecting walls and illuminated by directive antennas. We consider both reflective and refractive metasurfaces designed to control both reflection and transmission of waves. We start the analysis under the assumption of uniform, plane-wave illumination, and then discuss non-uniform illuminations by directive antennas.</div>

The Dubious Authority of Maxwell’s Equations in Free Space

Because of the differential homogeneity of Maxwell's equations in free space, each solution can be additively perturbed in infinitely many ways into a physically unreasonable solution. Thus to be a solution holds no cachet. In particular, the traditional first example --- the uniform plane wave --- must be considered as only a metaphor.

The Dubious Authority of Maxwell’s Equations in Free Space

Because of the differential homogeneity of Maxwell's equations in free space, each solution can be additively perturbed in infinitely many ways into a physically unreasonable solution. Thus to be a solution holds no cachet. In particular, the traditional first example --- the uniform plane wave --- must be considered as only a metaphor.

One Dimensional Heat Transfer through a Uniform Plane Wall by Using Finite Volume Method

In this paper, the finite volume method has been used to investigate one-dimensional conductive heat transfer throw a uniform plane wall. Then the step by step procedures of this numerical solution is described and implemented in a real-world problem where tri-diagonal matrix algorithm and Gaussian elimination matrix method are applied to solve the system of our discretized algebraic system of equations. Finally, to check the accuracy of our method, a comparison between the numerical solution obtained by finite volume techniques and the exact solution is presented which shows a minimum error compared to other existing methods.