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Topic Review
Double-Blind FROG
Double-Blind FROG is a method for simultaneously measuring two unknown ultrashort laser pulses. Well established ultrafast measurement techniques like Frequency-Resolved Optical Gating (FROG) and its simplified version GRENOUILLE can only measure one unknown ultrashort laser pulse at a time. Another version of FROG, called cross-correlation FROG (XFROG), also measures only one pulse, but it involves two pulses: a known reference pulse and the unknown pulse to be measured. In modern optics experiments, ultrashort laser pulses have been used in a great variety of engineering application and scientific research, for example, biomedical engineering, material science, nonlinear spectroscopy, ultrafast chemistry, etc. Often, these experiments involve using two potentially different input laser pulses, for example, Raman spectroscopy, two-color pump-probe experiments, and non-degenerate four-wave mixing. In many situations, an output pulse is generated by a nonlinear optical process, such as harmonic generation, continuum generation, or optical parametric oscillation. In all such cases, measuring more than one pulse simultaneously is required to completely characterize the experiment and understand its results in order to eventually understand the underlying science of the process under study. Thus a measurement device capable of measuring two pulses simultaneously is highly desired.
  • 557
  • 20 Oct 2022
Topic Review
Draco
Draco, Latin for "the dragon," is a large and distinctive constellation in the northern celestial hemisphere. It is renowned for its winding shape, resembling a serpentine dragon winding around the celestial pole, and is home to several notable deep-sky objects, including the Cat's Eye Nebula and the Draco Dwarf Galaxy.
  • 337
  • 08 Mar 2024
Topic Review
Drag
In fluid dynamics, drag (sometimes called air resistance, a type of friction, or fluid resistance, another type of friction or fluid friction) is a force acting opposite to the relative motion of any object moving with respect to a surrounding fluid. This can exist between two fluid layers (or surfaces) or between a fluid and a solid surface. Unlike other resistive forces, such as dry friction, which are nearly independent of velocity, the drag force depends on velocity. Drag force is proportional to the velocity for low-speed flow and the squared velocity for high speed flow, where the distinction between low and high speed is measured by the Reynolds number. Even though the ultimate cause of drag is viscous friction, turbulent drag is independent of viscosity. Drag forces always tend to decrease fluid velocity relative to the solid object in the fluid's path.
  • 1.3K
  • 22 Nov 2022
Topic Review
Drag Polar
The drag polar or drag curve is the relationship between the lift on an aircraft and its drag, expressed in terms of the dependence of the drag coefficient on the lift coefficient. It may be described by an equation or displayed in a diagram called a polar plot.
  • 9.7K
  • 24 Oct 2022
Topic Review
Dref Friction Spinning
Friction Spinning or Dref Spinning is a textile technology that suitable for spinning coarse counts of yarns and technical core-wrapped yarns. Dref yarns are bulky, with low tensile strength making them suitable for blankets and mop yarns, they can be spun from asbestos, carbon fibres and make filters was water systems.[clarification needed] Yarns such as Rayon and Kevlar can be spun using this method. The technology was developed around 1975 by Dr. Ernst Fehrer.
  • 282
  • 14 Oct 2022
Topic Review
Drinking Bird
Drinking birds, also known as insatiable birdies, dunking birds, drinky birds, water birds, dipping birds, and “Sippy Chickens” are toy heat engines that mimic the motions of a bird drinking from a water source. They are sometimes incorrectly considered examples of a perpetual motion device.
  • 2.1K
  • 25 Nov 2022
Topic Review
DUNE Experiment
The Deep Underground Neutrino Experiment (DUNE) is a neutrino experiment under construction, with a near detector at Fermilab and a far detector at the Sanford Underground Research Facility that will observe neutrinos produced at Fermilab. An intense beam of trillions of neutrinos from the production facility at Fermilab (in Illinois) will be sent over a distance of 1,300 kilometers (810 mi) with the goal of understanding the role of neutrinos in the universe. More than 1,000 collaborators work on the project. The experiment is designed for a 20-year period of data collection. The primary science objectives of DUNE are The science goals are so compelling that the 2014 Particle Physics Project Prioritization Panel (P5) ranked this as "the highest priority project in its timeframe" (recommendation 13). The importance of these goals has led to proposals for competing projects in other countries, particularly the Hyper-Kamiokande experiment in Japan, scheduled to begin data-taking in 2027. The DUNE project, overseen by Fermilab, has suffered delays to its schedule and growth of cost from less than $2B to $3B, leading to articles in the journals Science and Scientific American described the project as "troubled." As of 2022, the DUNE experiment has a neutrino-beam start-date in the early-2030's, and the project is now phased.
  • 547
  • 24 Oct 2022
Topic Review
Dye-Sensitized Solar Cells
Dye-sensitized solar cells (DSSCs) have emerged as promising alternatives to traditional silicon-based solar cells due to their relatively high conversion efficiency, low cost, flexibility, and environmentally benign fabrication processes.
  • 1.7K
  • 25 Oct 2020
Topic Review
Earth Hour
Earth Hour is a worldwide movement organized by the World Wildlife Fund (WWF). The event is held annually, encouraging individuals, communities, and businesses to turn off non-essential electric lights, for one hour, from 8:00 to 9:00 p.m. on the last Saturday of March, as a symbol of commitment to the planet. It was started as a lights-off event in Sydney, Australia, in 2007. Occasionally, in years when Holy Saturday falls on the last Saturday of March, Earth Hour is moved a week early rather than its usual date.
  • 298
  • 14 Oct 2022
Topic Review
Ecliptic Coordinate System
The ecliptic coordinate system is a celestial coordinate system commonly used for representing the apparent positions, orbits, and pole orientations of Solar System objects. Because most planets (except Mercury) and many small Solar System bodies have orbits with only slight inclinations to the ecliptic, using it as the fundamental plane is convenient. The system's origin can be the center of either the Sun or Earth, its primary direction is towards the vernal (March) equinox, and it has a right-hand convention. It may be implemented in spherical or rectangular coordinates.
  • 4.0K
  • 19 Oct 2022
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