Electromagnetic momentum carried by light is observable through the mechanical effects radiation pressure exerts on illuminated objects. Momentum conversion from electromagnetic fields to elastic ...waves within a solid object proceeds through a string of electrodynamic and elastodynamic phenomena, collectively bound by momentum and energy continuity. The details of this conversion predicted by theory have yet to be validated by experiments, as it is difficult to distinguish displacements driven by momentum from those driven by heating due to light absorption. Here, we have measured temporal variations of the surface displacements induced by laser pulses reflected from a solid dielectric mirror. Ab initio modelling of momentum flow describes the transfer of momentum from the electromagnetic field to the dielectric mirror, with subsequent creation/propagation of multicomponent elastic waves. Complete consistency between predictions and absolute measurements of surface displacements offers compelling evidence of elastic transients driven predominantly by the momentum of light.
The prospects for photoconductive (PC) terahertz (THz) generation are studied for wide-bandgap semiconductors exhibiting transient mobility. Such semiconductors offer practical benefits (by resisting ...dielectric breakdown and minimizing Joule heating) as well as improved frequency responses (by accentuating high-frequency PC THz emission). It is shown that GaP can offer these wide-bandgap and transient mobility characteristics. The ultrafast photoexcitation and subsequent transient mobility are investigated for a GaP PC THz emitter with photoexcitation fluences of 18, 36, and 72 μJ/cm 2 . The 100 fs rise and 700 fs fall in the transient photocurrent, due to the respective photoexcitation and transient mobility responses, yields far-field THz emission that improves upon that of the well-established GaAs PC THz emitter. It is ultimately found that semiconductors with both wide-bandgap and transient mobility characteristics can offer strategic improvements for emerging high-power PC THz technologies.
As computational power and relevant literature increases, more researchers are using multiphysics simulation for their work. Numerically combining physics simulations of electromagnetic and fluid ...dynamics is assisted by the fact their finite difference methods both use a staggered mesh and an initialized geometry of materials. Major differences occur when trying to include introductory heat transfer methods such as the Energy Balance method into electromagnetic and fluid dynamic simulators. For the Energy Balance method, a node equation is made for each unknown temperature and the equation coefficients are found by consulting a look up table from literature. In this work we present a simple approach to expand upon the Energy Balance method in a way that enables easy integration with other finite difference solvers. This approach automates the creation of node equations for general material geometries and combinations of heat transfer modes.
In 1968, Veselago postulated the existence of left-handed electromagnetic media bearing the unique ability to sustain electromagnetic plane waves with contradirectional power and phase flow (V. ...Veselago, Sov. Phys. Usp., 10, 509). Counter-intuitive optical properties predicted to be associated with left-handed media include negative refraction, a reversed Doppler effect, a reversed Cherenkov effect, and negative radiation pressure. While the phenomenon of negative refraction has been well-studied and realized across the electromagnetic spectrum using engineered structures known as metamaterials, the other traits predicted for left-handed media have received comparatively little attention.
There are several different expressions for the electromagnetic force density inside a material. In addition to the canonical Lorentz force density, there exist at least four other expressions based ...on the Abraham, Minkowski, Einstein-Laub, and Chu formulations of electrodynamics. Experiments to distinguish the various expressions are sparse because differences are apparent only under exotic conditions such as inside deformable media or media moving at relativistic speeds. In this work, we carefully examine the seminal 1973 experiment by Ashkin and Dziedzic to look for clues to isolate a single true force density expression. The experiment consisted of high-powered laser pulses directed onto an air-water interface, which caused the interface to bulge upwards (opposing gravity) regardless of the illumination direction. The results have been interpreted using both the Minkowski and Abraham formulations of electrodynamics. What remains is to analyze the results using the other formulations.
MirDIP is a well-established database that aggregates microRNA-gene human interactions from multiple databases to increase coverage, reduce bias, and improve usability by providing an integrated ...score proportional to the probability of the interaction occurring. In version 5.2, we removed eight outdated resources, added a new resource (miRNATIP), and ran five prediction algorithms for miRBase and mirGeneDB. In total, mirDIP 5.2 includes 46 364 047 predictions for 27 936 genes and 2734 microRNAs, making it the first database to provide interactions using data from mirGeneDB. Moreover, we curated and integrated 32 497 novel microRNAs from 14 publications to accelerate the use of these novel data. In this release, we also extend the content and functionality of mirDIP by associating contexts with microRNAs, genes, and microRNA-gene interactions. We collected and processed microRNA and gene expression data from 20 resources and acquired information on 330 tissue and disease contexts for 2657 microRNAs, 27 576 genes and 123 651 910 gene-microRNA-tissue interactions. Finally, we improved the usability of mirDIP by enabling the user to search the database using precursor IDs, and we integrated miRAnno, a network-based tool for identifying pathways linked to specific microRNAs. We also provide a mirDIP API to facilitate access to its integrated predictions. Updated mirDIP is available at https://ophid.utoronto.ca/mirDIP.
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