scholarly journals Shifting spin on the celestial sphere

2021 ◽  
Vol 104 (8) ◽  
Author(s):  
Sabrina Pasterski ◽  
Andrea Puhm
Keyword(s):  
Celestial Sphere

scholarly journals New Omnidirectional Sensor Based on Open-Source Software and Hardware for Tracking and Backtracking of Dual-Axis Solar Trackers in Photovoltaic Plants

Sensors ◽  
2021 ◽  
Vol 21 (3) ◽  
pp. 726
Author(s):  
Francisco J. Gómez-Uceda ◽  
José Ramirez-Faz ◽  
Marta Varo-Martinez ◽  
Luis Manuel Fernández-Ahumada
Keyword(s):  
Open Source Software ◽  
Energy Production ◽  
Scientific Community ◽  
Radiative Capture ◽  
Low Cost ◽  
Free Software ◽  
Solar Tracking ◽  
Software And Hardware ◽  
Celestial Sphere ◽  
Photovoltaic Plants

In this work, an omnidirectional sensor that enables identification of the direction of the celestial sphere with maximum solar irradiance is presented. The sensor, based on instantaneous measurements, functions as a position server for dual-axis solar trackers in photovoltaic plants. The proposed device has been developed with free software and hardware, which makes it a pioneering solution because it is open and accessible as well as capable of being improved by the scientific community, thereby contributing to the rapid advancement of technology. In addition, the device includes an algorithm developed ex professo that makes it possible to predetermine the regions of the celestial sphere for which, according to the geometric characteristics of the PV plant, there would be shading between the panels. In this way, solar trackers do not have to locate the Sun’s position at all times according to astronomical models, while taking into account factors such as shadows or cloudiness that also affect levels of incident irradiance on solar collectors. Therefore, with this device, it is possible to provide photovoltaic plants with dual-axis solar tracking with a low-cost device that helps to optimise the trajectory of the trackers and, consequently, their radiative capture and energy production.

scholarly journals Asymptotic symmetries and celestial CFT

2020 ◽  
Vol 2020 (9) ◽  
Author(s):  
Laura Donnay ◽  
Sabrina Pasterski ◽  
Andrea Puhm
Keyword(s):  
Principal Series ◽  
Finite Energy ◽  
Continuous Series ◽  
Asymptotic Symmetry ◽  
Null Infinity ◽  
Conformal Dimension ◽  
Contour Integrals ◽  
Celestial Sphere ◽  
Goldstone Modes ◽  
Asymptotic Symmetries

Abstract We provide a unified treatment of conformally soft Goldstone modes which arise when spin-one or spin-two conformal primary wavefunctions become pure gauge for certain integer values of the conformal dimension ∆. This effort lands us at the crossroads of two ongoing debates about what the appropriate conformal basis for celestial CFT is and what the asymptotic symmetry group of Einstein gravity at null infinity should be. Finite energy wavefunctions are captured by the principal continuous series ∆ ∈ 1 + iℝ and form a complete basis. We show that conformal primaries with analytically continued conformal dimension can be understood as certain contour integrals on the principal series. This clarifies how conformally soft Goldstone modes fit in but do not augment this basis. Conformally soft gravitons of dimension two and zero which are related by a shadow transform are shown to generate superrotations and non-meromorphic diffeomorphisms of the celestial sphere which we refer to as shadow superrotations. This dovetails the Virasoro and Diff(S2) asymptotic symmetry proposals and puts on equal footing the discussion of their associated soft charges, which correspond to the stress tensor and its shadow in the two-dimensional celestial CFT.

Unmoved Movers, Celestial Spheres, and Cosmoi: Aristotle’s Diremption of the Divine

Apeiron ◽  
2020 ◽  
Vol 0 (0) ◽  
Author(s):  
Michael J. White
Keyword(s):  
Ultimate Cause ◽  
Celestial Sphere

AbstractIn Meta. Λ 8, Aristotle argues that the heaven (οὐρανός)–and, thus, the cosmos – is numerically unique on the grounds that its first unmoved mover is numerically unique. The latter is numerically unique because it is ‘essence’ (τὸ δὲ τί ἦν εἶναι) and does not have matter. “But whatever is many in number has matter.” I refer to this inference as Aristotle’s metaphysical argument for the uniqueness of the cosmos. A problem arises: (A) If the subsidiary unmoved movers of the planetary spheres are, like the prime unmoved mover, immaterial substances and belong to the same species of unmoved mover (qua “thinkers thinking themselves”), it seems that they could not be numerically distinct from that first unmoved mover – while Aristotle maintains that they are, in fact, numerically distinct. That is, as immaterial substance(s), it/they could not be individuated by matter. However, (B) if they do, as souls or soul-like forms, inform matter (namely, that of the celestial spheres which they move), it seems that there is no reason why the first unmoved mover, which moves the sphere of fixed stars or outermost, celestial sphere, should not similarly inform the matter of that celestial sphere. In the latter case, Aristotle’s argument for the uniqueness of the heaven and cosmos would be vitiated. The first unmoved mover would be the form of the outermost celestial sphere; and there would evidently be no metaphysical reason why that form could not be materially instantiated by other outermost celestial spheres, each enclosing its own cosmos distinct from our own. I argue that neither of the two salient options for resolving this problem with Aristotle’s metaphysical argument for the uniqueness of the cosmos is satisfactory. The result, so I maintain, is Aristotle’s diremption of divinity into two essentially unrelated aspects: divinity as autonomous, ‘hermetic’ cognition and divinity as ultimate cause(s) of cosmic motion and change.

scholarly journals Celestial superamplitude in $$ \mathcal{N} $$ = 4 SYM theory

2021 ◽  
Vol 2021 (8) ◽  
Author(s):  
Hongliang Jiang
Keyword(s):  
Field Theory ◽  
Conformal Field Theory ◽  
Scattering Amplitudes ◽  
Momentum Space ◽  
Ward Identity ◽  
Yang Mills ◽  
Conformal Field ◽  
New Perspective ◽  
Celestial Sphere

Abstract Celestial amplitude is a new reformulation of momentum space scattering amplitudes and offers a promising way for flat holography. In this paper, we study the celestial amplitudes in $$ \mathcal{N} $$ N = 4 Super-Yang-Mills (SYM) theory aiming at understanding the role of superconformal symmetry in celestial holography. We first construct the superconformal generators acting on the celestial superfield which assembles all the on-shell fields in the multiplet together in terms of celestial variables and Grassmann parameters. These generators satisfy the superconformal algebra of $$ \mathcal{N} $$ N = 4 SYM theory. We also compute the three-point and four-point celestial super-amplitudes explicitly. They can be identified as the conformal correlation functions of the celestial superfields living at the celestial sphere. We further study the soft and collinear limits which give rise to the super-Ward identity and super-OPE on the celestial sphere, respectively. Our results initiate a new perspective of understanding the well-studied $$ \mathcal{N} $$ N = 4 SYM amplitudes via 2D celestial conformal field theory.

scholarly journals The JPL 1986–3 Extragalactic Reference Frame

1988 ◽  
Vol 133 ◽  
pp. 461-464
Author(s):  
O.J. Sovers ◽  
C.D. Edwards ◽  
C.S. Jacobs ◽  
G.E. Lanyi ◽  
R.N. Treuhaft
Keyword(s):  
Rotation Axis ◽  
Time Variability ◽  
Radio Sources ◽  
Dual Frequency ◽  
Deep Space Network ◽  
Space Network ◽  
Celestial Sphere ◽  
Almost All ◽  
Comparable Quality

Intercontinental dual-frequency radio interferometric measurements were carried out during 1978 to 1985 between NASA's Deep Space Network stations in California, Spain, and Australia. Analysis of 6800 pairs of delay and delay rate observations made during 51 sessions produced a catalog of positions of 106 extragalactic radio sources, fairly uniformly distributed over the celestial sphere between −45° and +85° declination. Almost all of the resulting source positions have formal uncertainties between 0.5 and 3 milliarcseconds, with their distributions peaking somewhat below 1 mas. Root-mean-square uncertainties are 2.1 and 2.0 mas for RA and declination, respectively. Evidence is found for a long-term drift of the Earth's rotation axis in inertial space, relative to the 1984 IAU precession and nutation models. Tests for time variability of positions of 32 frequently observed sources place limits at the 1 mas/yr level. Comparisons with independently determined source catalogs of comparable quality show differences of positions of common sources that amount to a few mas, and may indicate the level of systematic errors in VLBI source position measurements.

scholarly journals The Celestial Reference System in Relativistic Framework

1990 ◽  
Vol 141 ◽  
pp. 99-110
Author(s):  
Han Chun-Hao ◽  
Huang Tian-Yi ◽  
Xu Bang-Xin
Keyword(s):  
Coordinate System ◽  
Reference Frame ◽  
Reference System ◽  
Light Deflection ◽  
Coordinate Systems ◽  
Definition Of ◽  
Celestial Sphere ◽  
Celestial Reference System ◽  
Relativistic Framework

The concept of reference system, reference frame, coordinate system and celestial sphere in a relativistic framework are given. The problems on the choice of celestial coordinate systems and the definition of the light deflection are discussed. Our suggestions are listed in Sec. 5.

scholarly journals 35. The variation of sporadic meteor radiant density and the mass law exponent over the celestial sphere

1968 ◽  
Vol 33 ◽  
pp. 373-381
Author(s):  
O.I. Belkovič ◽  
J. A. Pupyšev
Keyword(s):  
State University ◽  
Yagi Antenna ◽  
Celestial Sphere ◽  
Observational Program

At the Engelgardt Observatory of the V.I. Uljanov-Lenin Kazan State University systematic azimuthal radio echo observations are carried out at a wavelength of 8 m. Simple radio echo equipment is used with a five-element Yagi antenna. The observational program provides for a 30° turn of the antenna in azimuth every 5 min.

Algorithm Design and Implementation of Dynamic Star Simulator

2013 ◽  
Vol 722 ◽  
pp. 187-193
Author(s):  
Xiao Fang Zhao ◽  
Guang Bin Liu ◽  
Chao Shan Liu
Keyword(s):  
Traditional Method ◽  
Algorithm Design ◽  
Star Tracker ◽  
Simulation Algorithm ◽  
Arc Length ◽  
Visual Axis ◽  
Star Image ◽  
Design And Implementation ◽  
Simulation Testing ◽  
Celestial Sphere

In order to realize the simulation testing and calibration of star tracker in the lab, a simulation algorithm for dynamic and celestial sphere star image was proposed. This algorithm could complete simulation of star image at any time and any visual axis point, also could realize in-orbit simulation according to a given track. A new method of space district dividing was also presented in order to improve the traditional method of space district dividing by ascension and declination, fully considered declination arc length gradually shortened with latitude increasing. It can remarkably enhance the updating frequency simulation star image.

Sign in / Sign up

Export Citation Format

Share Document