21,622 research outputs found
Segmented coronagraph design and analysis (SCDA): an initial design study of apodized vortex coronagraphs
The segmented coronagraph design and analysis (SCDA) study is a coordinated
effort, led by Stuart Shaklan (JPL) and supported by NASA's Exoplanet
Exploration Program (ExEP), to provide efficient coronagraph design concepts
for exoplanet imaging with future segmented aperture space telescopes. This
document serves as an update on the apodized vortex coronagraph designs devised
by the Caltech/JPL SCDA team. Apodized vortex coronagraphs come in two flavors,
where the apodization is achieved either by use of 1) a gray-scale
semi-transparent pupil mask or 2) a pair of deformable mirrors in series. Each
approach has attractive benefits. This document presents a comprehensive review
of the former type. Future theoretical investigations will further explore the
use of deformable mirrors for apodization.Comment: White Paper (2016-2017
Colloquium: Physics of optical lattice clocks
Recently invented and demonstrated, optical lattice clocks hold great promise
for improving the precision of modern timekeeping. These clocks aim at the
10^-18 fractional accuracy, which translates into a clock that would neither
lose or gain a fraction of a second over an estimated age of the Universe. In
these clocks, millions of atoms are trapped and interrogated simultaneously,
dramatically improving clock stability. Here we discuss the principles of
operation of these clocks and, in particular, a novel concept of "magic"
trapping of atoms in optical lattices. We also highlight recently proposed
microwave lattice clocks and several applications that employ the optical
lattice clocks as a platform for precision measurements and quantum information
processing.Comment: 18 pages, 15 figure
Embedding approach to modeling electromagnetic fields in a complex two-dimensional environment
An approach is presented to combine the response of a two-dimensionally inhomogeneous dielectric object in a homogeneous environment with that of an empty inhomogeneous environment. This allows an efficient computation of the scattering behavior of the dielectric cylinder with the aid of the CGFFT method and a dedicated extrapolation procedure. Since a circular observation contour is adopted, an angular spectral representation can be employed for the embedding. Implementation details are discussed for the case of a closed 434 MHz microwave scanner, and the accuracy and efficiency of all steps in the numerical procedure are investigated. Guidelines are proposed for choosing computational parameters such as truncation limits and tolerances. We show that the embedding approach does not increase the CPU time with respect to the forward problem solution in a homogeneous environment, if only the fields on the observation contour are computed, and that it leads to a relatively small increase when the fields on the mesh are computed as well
Earth orbital teleoperator system man-machine interface evaluation
The teleoperator system man-machine interface evaluation develops and implements a program to determine human performance requirements in teleoperator systems
Orbital Angular Momentum Waves: Generation, Detection and Emerging Applications
Orbital angular momentum (OAM) has aroused a widespread interest in many
fields, especially in telecommunications due to its potential for unleashing
new capacity in the severely congested spectrum of commercial communication
systems. Beams carrying OAM have a helical phase front and a field strength
with a singularity along the axial center, which can be used for information
transmission, imaging and particle manipulation. The number of orthogonal OAM
modes in a single beam is theoretically infinite and each mode is an element of
a complete orthogonal basis that can be employed for multiplexing different
signals, thus greatly improving the spectrum efficiency. In this paper, we
comprehensively summarize and compare the methods for generation and detection
of optical OAM, radio OAM and acoustic OAM. Then, we represent the applications
and technical challenges of OAM in communications, including free-space optical
communications, optical fiber communications, radio communications and acoustic
communications. To complete our survey, we also discuss the state of art of
particle manipulation and target imaging with OAM beams
Improved Formalism for Precision Higgs Coupling Fits
Future e+e- colliders give the promise of model-independent determinations of
the couplings of the Higgs boson. In this paper, we present an improved
formalism for extracting Higgs boson couplings from e+e- data, based on the
Effective Field Theory description of corrections to the Standard Model. We
apply this formalism to give projections of Higgs coupling accuracies for
stages of the International Linear Collider and for other proposed e+e-
colliders.Comment: 34 pages, 4 figures; v4: clarifications and new references added; v5,
additional references adde
Image inversion analysis of the HST OTA (Hubble Space Telescope Optical Telescope Assembly), phase A
Technical work during September-December 1990 consisted of: (1) analyzing HST point source images obtained from JPL; (2) retrieving phase information from the images by a direct (noniterative) technique; and (3) characterizing the wavefront aberration due to the errors in the Hubble Space Telescope (HST) mirrors, in a preliminary manner. This work was in support of JPL design of compensating optics for the next generation wide-field planetary camera on HST. This digital technique for phase retrieval from pairs of defocused images, is based on the energy transport equation between these image planes. In addition, an end-to-end wave optics routine, based on the JPL Code 5 prescription of the unaberrated HST and WFPC, was derived for output of the reference phase front when mirror error is absent. Also, the Roddier routine unwrapped the retrieved phase by inserting the required jumps of +/- 2(pi) radians for the sake of smoothness. A least-squares fitting routine, insensitive to phase unwrapping, but nonlinear, was used to obtain estimates of the Zernike polynomial coefficients that describe the aberration. The phase results were close to, but higher than, the expected error in conic constant of the primary mirror suggested by the fossil evidence. The analysis of aberration contributed by the camera itself could be responsible for the small discrepancy, but was not verified by analysis
Planning natural repointing manoeuvres for nano-spacecraft
In this paper the natural dynamics of a rigid body are exploited to plan attitude manoeuvres for a small spacecraft. By utilising the analytical solutions of the angular velocities and making use of Lax pair integration, the time evolution of the attitude of the spacecraft in a convenient quaternion form is derived. This enables repointing manoeuvres to be generated by optimising the free parameters of the analytical expressions, the initial angular velocities of the spacecraft, to match prescribed boundary conditions on the final attitude of the spacecraft. This produces reference motions which can be tracked using a simple proportional-derivative controller. The natural motions are compared in simulation to a conventional quaternion feedback controller and found to require lower accumulated torque. A simple obstacle avoidance algorithm, exploiting the analytic form of natural motions, is also described and implemented in simulation. The computational efficiency of the motion planning method is discussed
Characteristic extraction tool for gravitational waveforms
We develop and calibrate a characteristic waveform extraction tool whose major improvements and corrections of prior versions allow satisfaction of the accuracy standards required for advanced LIGO data analysis. The extraction tool uses a characteristic evolution code to propagate numerical data on an inner worldtube supplied by a 3+1 Cauchy evolution to obtain the gravitational waveform at null infinity. With the new extraction tool, high accuracy and convergence of the numerical error can be demonstrated for an inspiral and merger of mass M binary black holes even for an extraction worldtube radius as small as R=20M. The tool provides a means for unambiguous comparison between waveforms generated by evolution codes based upon different formulations of the Einstein equations and based upon different numerical approximations
Planning natural repointing manoeuvres for nano-spacecraft
In this paper the natural dynamics of a rigid body are exploited to plan attitude manoeuvres for a small spacecraft. By utilising the analytical solutions of the angular velocities and making use of Lax pair integration, the time evolution of the attitude of the spacecraft in a convenient quaternion form is derived. This enables repointing manoeuvres to be generated by optimising the free parameters of the analytical expressions, the initial angular velocities of the spacecraft, to match prescribed boundary conditions on the final attitude of the spacecraft. This produces reference motions which can be tracked using a simple proportional-derivative controller. The natural motions are compared in simulation to a conventional quaternion feedback controller and found to require lower accumulated torque. A simple obstacle avoidance algorithm, exploiting the analytic form of natural motions, is also described and implemented in simulation. The computational efficiency of the motion planning method is discussed
- âŠ