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Topic Review
Fresnel Imager
A Fresnel imager is a proposed ultra-lightweight design for a space telescope that uses a Fresnel array as primary optics instead of a typical lens. It focuses light with a thin opaque foil sheet punched with specially shaped holes, thus focusing light on a certain point by using the phenomenon of diffraction. Such patterned sheets, called Fresnel zone plates, have long been used for focusing laser beams, but have so far not been used for astronomy. No optical material is involved in the focusing process as in traditional telescopes. Rather, the light collected by the Fresnel array is concentrated on smaller classical optics (e.g. 1/20th of the array size), to form a final image. The long focal lengths of the Fresnel imager (a few kilometers) require operation by two-vessel formation flying in space at the L2 Sun-Earth Lagrangian point. In this two spacecraft formation-flying instrument, one spacecraft holds the focussing element: the Fresnel interferometric array; the other spacecraft holds the field optics, focal instrumentation, and detectors.
  • 281
  • 01 Nov 2022
Topic Review
Frequency
Frequency is the number of occurrences of a repeating event per unit of time. It is also referred to as temporal frequency, which emphasizes the contrast to spatial frequency and angular frequency. Frequency is measured in units of hertz (Hz) which is equal to one occurrence of a repeating event per second. The period is the duration of time of one cycle in a repeating event, so the period is the reciprocal of the frequency. For example: if a newborn baby's heart beats at a frequency of 120 times a minute (2 hertz), its period, T, — the time interval between beats—is half a second (60 seconds divided by 120 beats). Frequency is an important parameter used in science and engineering to specify the rate of oscillatory and vibratory phenomena, such as mechanical vibrations, audio signals (sound), radio waves, and light.
  • 4.2K
  • 16 Nov 2022
Topic Review
Free Entropy
A thermodynamic free entropy is an entropic thermodynamic potential analogous to the free energy. Also known as a Massieu, Planck, or Massieu–Planck potentials (or functions), or (rarely) free information. In statistical mechanics, free entropies frequently appear as the logarithm of a partition function. The Onsager reciprocal relations in particular, are developed in terms of entropic potentials. In mathematics, free entropy means something quite different: it is a generalization of entropy defined in the subject of free probability. A free entropy is generated by a Legendre transformation of the entropy. The different potentials correspond to different constraints to which the system may be subjected.
  • 481
  • 04 Nov 2022
Biography
Fred Hoyle
Sir Fred Hoyle FRS (24 June 1915 – 20 August 2001)[1] was an English astronomer who formulated the theory of stellar nucleosynthesis. He also held controversial stances on other scientific matters—in particular his rejection of the "Big Bang" theory, a term coined by him on BBC radio, and his promotion of panspermia as the origin of life on Earth.[2][3][4] He also wrote science fiction nove
  • 863
  • 17 Nov 2022
Biography
Fred Adams
Fred C. Adams (born 1961) is an American astrophysicist who has made contributions to the study of physical cosmology. Fred Adams is professor of physics at the University of Michigan, where his main field of research is astrophysics theory focusing on star formation, background radiation fields, and the early universe. He was educated at Iowa State University, where he earned his B.S. in 19
  • 405
  • 27 Dec 2022
Biography
Franz Josef Giessibl
Franz Josef Gießibl (born 27 May 1962 in Amerang) is a Germany physicist and university professor at the University of Regensburg. Giessibl studied physics from 1982 to 1987 at the Technical University of Munich and at Eidgenössische Technischen Hochschule Zürich. He received a diploma in experimental physics in 1988 with Professor Gerhard Abstreiter and continued with a PhD in physics wit
  • 525
  • 12 Dec 2022
Biography
Frank J. Tipler
Frank Jennings Tipler (born February 1, 1947) is an American mathematical physicist and cosmologist, holding a joint appointment in the Departments of Mathematics and Physics at Tulane University.[1] Tipler has written books and papers on the Omega Point based on Pierre Teilhard de Chardin's religious ideas, which he claims is a mechanism for the resurrection of the dead. He is also known for hi
  • 544
  • 27 Dec 2022
Topic Review
Framework for Building Resilient Water and Infrastructure Systems
Planning and developing resilient socio-technical and natural systems to cope with and respond to unprecedented changes has been one of the top goals of government bodies, researchers, and practitioners worldwide. 
  • 558
  • 24 Apr 2022
Topic Review
Fractional Schrödinger Equation
The fractional Schrödinger equation is a fundamental equation of fractional quantum mechanics. It was discovered by Nick Laskin (1999) as a result of extending the Feynman path integral, from the Brownian-like to Lévy-like quantum mechanical paths. The term fractional Schrödinger equation was coined by Nick Laskin.
  • 1.0K
  • 24 Oct 2022
Topic Review
Fractional Calculus in Electromagnetic Theory
Fractional calculus (FC) was introduced more than 300 years ago as a generalization of classical derivative and integral definitions. It is receiving increasing attention for a growing number of applications in different sciences such as physics, biology, chemistry, engineering, finance, mechanics, optics and, in particular, for modeling physical phenomena related to non-Markovian processes, signal and image processing, dielectric relaxation, viscoelasticity, electromagnetism, control theory, pharmacokinetics, fluids, heat transfer, and so on.
  • 833
  • 27 May 2022
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