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Topic Review
Transit
File:Moon transit of sun large.ogv In astronomy, a transit (or astronomical transit) is a phenomenon when a celestial body passes directly between a larger body and the observer. As viewed from a particular vantage point, the transiting body appears to move across the face of the larger body, covering a small portion of it. The word "transit" refers to cases where the nearer object appears smaller than the more distant object. Cases where the nearer object appears larger and completely hides the more distant object are known as occultations. However, the probability of seeing a transiting planet is low because it is dependent on the alignment of the three objects in a nearly perfectly straight line. Many parameters of a planet and its parent star can be determined based on the transit.
  • 1.3K
  • 02 Dec 2022
Topic Review
Fourier Lightfield Microscope
Fourier lightfield microscopy (FLMic) is a technique aimed to capture and process 3D information of microscopic samples. Due to its optical design, FLMic has the inherent capacity of capturing a collection of orthographic perspectives of samples in a single shot. Consequently, FLMic is especially suited for capturing and processing 3D images of dynamic processes, being potentially addressed for real-time applications in both life and material sciences.
  • 1.3K
  • 10 Mar 2022
Topic Review
Self-Assembled III-V Semiconductor Quantum Dots
A fundamental understanding of the growth of semiconductors is essential for the optimization of quantum dot-based optoelectronic devices. Droplet epitaxy has proven to be the successful versatile growth method for instance growing quantum dots with a small fine structure splitting for quantum information technology. Precise control and tuning of the quantum dots for various applications is only possible through a detailed understanding of the growth mechanism at the atomic level, which creates the need for atomic-scale structural and composition characterization. We present an overview of the results of detailed structural and composition analysis by cross-sectional scanning tunneling microscopy and atom probe tomography of quantum dots grown by self-assembled droplet epitaxy where we focus mainly on strain-free GaAs/AlGaAs and strained InAs/InP QDs.
  • 1.3K
  • 19 Jan 2021
Topic Review
Polarization Conversion from Anisotropy Media
Anisotropy of the transmission media exerts a strong influence on the reflection and transmission coefficients. Anomalous refraction yields the consequence of polarization conversion for the refracted wave. We discuss this important physical phenomenon by invoking practical interfaces between strongly anisotropic rocks, e.g., between O-shale and A-shale.  
  • 1.3K
  • 02 Nov 2020
Topic Review
Elementary Charge and Vacuum Energy
Classical electrodynamics was introduced by James Clear Maxwell nearly 150 years ago and it is a subject that had been thoroughly explored over these years. Notwithstanding this long term scrutiny of this subject, there are hidden features in classical electrodynamics that actually heralds the emergence of Quantum electrodynamics in the future. Such examples can be found when analyzing the electromagnetic radiation generated by antennas working in both frequency and time domain and in the case of transition radiation generated by decelerating electrons. Here we discuss one such case. Consider the radiation generated by an antenna working in frequency domain. One can show that the energy dissipated as radiation within half a period of oscillation, say U, satisfies the inequality U ≥ hf →q ≥ e where q  is the magnitude of the oscillating charge in the antenna, e is the elementary charge, f is the frequency of oscillation and h is the Planck constant. This result is derived while adhering strictly to the principles of classical electrodynamics alone. Combining this result with the concept of photons burrowed from quantum mechanics, one can derive an expression for the elementary charge as a function of other natural constants and the energy density of vacuum. The expression predicts the value of elementary charge to an accuracy higher than about 0.1%.
  • 1.3K
  • 01 Nov 2020
Topic Review
Electromagnetically Excited Acoustic Noise and Vibration
Electromagnetically excited acoustic noise is audible sound directly produced by materials vibrating under the excitation of electromagnetic forces. Some examples of electromagnetically excited acoustic noise include the hum of transformers, the whine of some rotating electric machines, or the buzz of fluorescent lamps. The hissing of high voltage transmission lines is due to corona discharge, not magnetism. The phenomenon is also called audible magnetic noise, electromagnetic acoustic noise, or electromagnetically-induced acoustic noise, or more rarely, electrical noise, "coil noise", or "coil whine", depending on the application. The term electromagnetic noise is generally avoided as the term is used in the field of electromagnetic compatibility, dealing with radio frequencies. The term electrical noise describes electrical perturbations occurring in electronic circuits, not sound. For the latter use, the terms electromagnetic vibrations or magnetic vibrations, focusing on the structural phenomenon are less ambiguous. Acoustic noise and vibrations due to electromagnetic forces can be seen as the reciprocal of microphonics, which describes how a mechanical vibration or acoustic noise can induce an undesired electrical perturbation.
  • 1.3K
  • 28 Oct 2022
Topic Review
Equatorial Coordinate System
The equatorial coordinate system is a celestial coordinate system widely used to specify the positions of celestial objects. It may be implemented in spherical or rectangular coordinates, both defined by an origin at the centre of Earth, a fundamental plane consisting of the projection of Earth's equator onto the celestial sphere (forming the celestial equator), a primary direction towards the vernal equinox, and a right-handed convention. The origin at the centre of Earth means the coordinates are geocentric, that is, as seen from the centre of Earth as if it were transparent. The fundamental plane and the primary direction mean that the coordinate system, while aligned with Earth's equator and pole, does not rotate with the Earth, but remains relatively fixed against the background stars. A right-handed convention means that coordinates increase northward from and eastward around the fundamental plane.
  • 1.3K
  • 16 Nov 2022
Topic Review
Reaction
As described by the third of Newton's laws of motion of classical mechanics, all forces occur in pairs such that if one object exerts a force on another object, then the second object exerts an equal and opposite reaction force on the first. The third law is also more generally stated as: "To every action there is always opposed an equal reaction: or the mutual actions of two bodies upon each other are always equal, and directed to contrary parts." The attribution of which of the two forces is the action and which is the reaction is arbitrary. Either of the two can be considered the action, while the other is its associated reaction.
  • 1.2K
  • 30 Oct 2022
Biography
Mani Lal Bhaumik
Mani Lal Bhaumik is an Indian-born American physicist and a bestselling author.[1] Bhaumik was born on March 30, 1931 in a small village in Siuri, Medinipore, West Bengal, India and attended the Krishnagang krishi silpa vidyalaya school.[2][3] As a teenager, Bhaumik spent some time with Mahatma Gandhi in his Mahisadal camp. He received a Bachelor of Science degree from Scottish Church College
  • 1.2K
  • 22 Nov 2022
Topic Review
Mid-Infrared Femtosecond Laser Based on Difference Frequency Generation
The mid-infrared (MIR) spectral region is known as the “molecular fingerprint region”, and almost every kind of gas molecule shows a unique and strong absorption characteristic within that region. The MIR ultrashort pulsed lasers can be widely used in gas detection, cancer diagnosis, pollutant monitoring, food quality control, and other aspects since they own much broader spectral ranges than ultrafast lasers in the visible and near-infrared region. There have been different techniques for the generation of ultrashort pulses in the MIR region of 2-5 µm. However, for the MIR ultrashort pulses generation at wavelengths longer than 5 µm or even 8 µm, difference frequency generation (DFG) is the primary technique.
  • 1.2K
  • 06 Jun 2022
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