Imaging from scattered fields: limited data and degrees of freedom

2012 ◽  
Author(s):  
R. Shane Ritter ◽  
Michael A. Fiddy
Keyword(s):  
Degrees Of Freedom ◽  
Limited Data ◽  
Scattered Fields

scholarly journals Resolution of Born Scattering in Curve Geometries: Aspect-Limited Observations and Excitations

Electronics ◽  
2021 ◽  
Vol 10 (24) ◽  
pp. 3089
Author(s):  
Ehsan Akbari Sekehravani ◽  
Giovanni Leone ◽  
Rocco Pierri
Keyword(s):  
Degrees Of Freedom ◽  
Plane Waves ◽  
Single Frequency ◽  
Limited Data ◽  
Scattering Problems ◽  
Approximation Accuracy ◽  
Imaging Results ◽  
Exact Evaluation ◽  
Spread Function ◽  
Scattered Fields

In inverse scattering problems, the most accurate possible imaging results require plane waves impinging from all directions and scattered fields observed in all observation directions around the object. Since this full information is infrequently available in actual applications, this paper is concerned with the mathematical analysis and numerical simulations to estimate the achievable resolution in object reconstruction from the knowledge of the scattered far-field when limited data are available at a single frequency. The investigation focuses on evaluating the Number of Degrees of Freedom (NDF) and the Point Spread Function (PSF), which accounts for reconstructing a point-like unknown and depends on the NDF. The discussion concerns objects belonging to curve geometries, in this case, circumference and square scatterers. In addition, since the exact evaluation of the PSF can only be accomplished numerically, an approximated closed-form evaluation is introduced and compared with the exact one. The approximation accuracy of the PSF is verified by numerical results, at least within its main lobe region, which is the most critical as far as the resolution discussion is concerned. The main result of the analysis is the space variance of the PSF for the considered geometries, showing that the resolution is different over the investigation domain. Finally, two numerical applications of the PSF concept are shown, and their relevance in the presence of noisy data is outlined.

On the degrees of freedom of scattered fields

1989 ◽  
Vol 37 (7) ◽  
pp. 918-926 ◽  
Author(s):  
O.M. Bucci ◽  
G. Franceschetti
Keyword(s):  
Degrees Of Freedom ◽  
Scattered Fields

scholarly journals NDF of Scattered Fields for Strip Geometries

Electronics ◽  
2021 ◽  
Vol 10 (2) ◽  
pp. 202
Author(s):  
Ehsan Akbari Sekehravani ◽  
Giovanni Leone ◽  
Rocco Pierri
Keyword(s):  
Degrees Of Freedom ◽  
Plane Waves ◽  
Singular Value ◽  
Scattering Operator ◽  
Scattering Problems ◽  
First Order ◽  
Incident Plane ◽  
Minimum Number ◽  
Scattered Fields ◽  
Value Decomposition

Solving inverse scattering problems by numerical methods requires investigating the number of independent pieces of information that can be reconstructed stably. To this end, we address the evaluation of the Number of Degrees of Freedom (NDF) of far-zone scattered fields for some strip geometries under the first-order Born approximation. The analysis is performed by employing the Singular Value Decomposition (SVD) of the scattering operator in the two-dimensional scalar geometry of one or more strips illuminated by a TM polarized plane wave. It is known that investigating the scattering scene at different incident plane waves (multi-view configuration) enhances the NDF. Therefore we mean to examine the minimum number of incident plane waves providing the NDF of the scattered fields both by theoretical estimations and numerical verifications.

Vehicle Ride Quality and Passenger Comfort

1978 ◽  
Vol 22 (1) ◽  
pp. 116-116
Author(s):  
Larry G. Richards ◽  
Ira D. Jacobson
Keyword(s):  
Degrees Of Freedom ◽  
State Of The Art ◽  
Measuring System ◽  
Ride Quality ◽  
Limited Data ◽  
Noise Levels ◽  
Six Degrees Of Freedom ◽  
Marine Vehicles ◽  
Roll Rate ◽  
Temperature And Pressure

The state of the art in ride quality assessment is reviewed. A portable environmental measuring system (PEMS II) has been developed to simultaneously record variation in motion (in all six degrees of freedom), temperature and pressure for various segments of a ride. The results of extensive studies of passenger reactions to diverse vehicles are presented as a set of models relating human comfort ratings to environmental conditions, vehicles studied include aircraft (commuter planes, S-61 helicopter, Boeing 747, Concorde), trains (conventional and special purpose), buses, and cars. Limited data are available on marine vehicles. Models for aircraft involve vertical and lateral accelerations and noise levels; while models for ground based vehicles also involve roll rate.

The motion of a lunar orbiter

1966 ◽  
Vol 25 ◽  
pp. 373
Author(s):  
Y. Kozai
Keyword(s):  
Degrees Of Freedom ◽  
Dimensional Space ◽  
Artificial Satellite ◽  
Equations Of Motion ◽  
Triaxial Ellipsoid ◽  
The Moon ◽  
Secular Motion ◽  
The Earth ◽  
Close Satellite ◽  
The Mean

The motion of an artificial satellite around the Moon is much more complicated than that around the Earth, since the shape of the Moon is a triaxial ellipsoid and the effect of the Earth on the motion is very important even for a very close satellite.The differential equations of motion of the satellite are written in canonical form of three degrees of freedom with time depending Hamiltonian. By eliminating short-periodic terms depending on the mean longitude of the satellite and by assuming that the Earth is moving on the lunar equator, however, the equations are reduced to those of two degrees of freedom with an energy integral.Since the mean motion of the Earth around the Moon is more rapid than the secular motion of the argument of pericentre of the satellite by a factor of one order, the terms depending on the longitude of the Earth can be eliminated, and the degree of freedom is reduced to one.Then the motion can be discussed by drawing equi-energy curves in two-dimensional space. According to these figures satellites with high inclination have large possibilities of falling down to the lunar surface even if the initial eccentricities are very small.The principal properties of the motion are not changed even if plausible values ofJ3andJ4of the Moon are included.This paper has been published in Publ. astr. Soc.Japan15, 301, 1963.

Representing utility and deploying the body

2020 ◽  
Vol 43 ◽  
Author(s):  
David Spurrett
Keyword(s):  
Functional Activity ◽  
Degrees Of Freedom ◽  
The Body ◽  
Target Article ◽  
Processing Demands ◽  
The Many

Abstract Comprehensive accounts of resource-rational attempts to maximise utility shouldn't ignore the demands of constructing utility representations. This can be onerous when, as in humans, there are many rewarding modalities. Another thing best not ignored is the processing demands of making functional activity out of the many degrees of freedom of a body. The target article is almost silent on both.

Analysis of power law assumptions for short-period comets and Kuiper bodies

1999 ◽  
Vol 173 ◽  
pp. 289-293 ◽  
Author(s):  
J.R. Donnison ◽  
L.I. Pettit
Keyword(s):  
Power Law ◽  
Pareto Distribution ◽  
Limited Data ◽  
Short Period ◽  
Probability Plots ◽  
Exponential Probability

AbstractA Pareto distribution was used to model the magnitude data for short-period comets up to 1988. It was found using exponential probability plots that the brightness did not vary with period and that the cut-off point previously adopted can be supported statistically. Examination of the diameters of Trans-Neptunian bodies showed that a power law does not adequately fit the limited data available.

Predictive value of the ankle brachial index in patients with acute ischemic stroke

VASA ◽  
2014 ◽  
Vol 43 (1) ◽  
pp. 55-61 ◽  
Author(s):  
Konstantinos Tziomalos ◽  
Vasilios Giampatzis ◽  
Stella Bouziana ◽  
Athinodoros Pavlidis ◽  
Marianna Spanou ◽  
...  
Keyword(s):  
Ischemic Stroke ◽  
Hospital Mortality ◽  
Acute Ischemic Stroke ◽  
Ankle Brachial Index ◽  
Arterial Disease ◽  
National Institutes Of Health ◽  
Limited Data ◽  
Severe Stroke ◽  
Hospital Outcome ◽  
Peripheral Arterial

Background: Peripheral arterial disease (PAD) is frequently present in patients with acute ischemic stroke. However, there are limited data regarding the association between ankle brachial index (ABI) ≤ 0.90 (which is diagnostic of PAD) or > 1.40 (suggesting calcified arteries) and the severity of stroke and in-hospital outcome in this population. We aimed to evaluate these associations in patients with acute ischemic stroke. Patients and methods: We prospectively studied 342 consecutive patients admitted for acute ischemic stroke (37.4 % males, mean age 78.8 ± 6.4 years). The severity of stroke was assessed with the National Institutes of Health Stroke Scale (NIHSS)and the modified Rankin scale (mRS) at admission. The outcome was assessed with the mRS and dependency (mRS 2 - 5) at discharge and in-hospital mortality. Results: An ABI ≤ 0.90 was present in 24.6 % of the patients whereas 68.1 % had ABI 0.91 - 1.40 and 7.3 % had ABI > 1.40. At admission, the NIHSS score did not differ between the 3 groups (10.4 ± 10.6, 8.3 ± 9.3 and 9.3 ± 9.4, respectively). The mRS score was also comparable in the 3 groups (3.6 ± 1.7, 3.1 ± 1.8 and 3.5 ± 2.3, respectively). At discharge, the mRS score did not differ between the 3 groups (2.9 ± 2.2, 2.3 ± 2.1 and 2.7 ± 2.5, respectively) and dependency rates were also comparable (59.5, 47.6 and 53.3 %, respectively). In-hospital mortality was almost two-times higher in patients with ABI ≤ 0.90 than in patients with ABI 0.91 - 1.40 or > 1.40 but this difference was not significant (10.9, 6.6 and 6.3 %, respectively). Conclusions: An ABI ≤ 0.90 or > 1.40 does not appear to be associated with more severe stroke or worse in-hospital outcome in patients with acute ischemic stroke.

Das Experten-Novizen-Paradigma und die Vertrauenskrise in der Psychologie

2016 ◽  
Vol 23 (4) ◽  
pp. 131-140 ◽  
Author(s):  
Philip Furley ◽  
Karsten Schul ◽  
Daniel Memmert
Keyword(s):  
Degrees Of Freedom

Zusammenfassung. Das Ziel des vorliegenden Beitrages ist es anhand eines vielverwendeten Paradigmas in der Sportwissenschaft – dem Experten-Novizen-Vergleich – zu prüfen, ob die momentane Vertrauenskrise in der Psychologie ebenfalls die Sportpsychologie betreffen könnte. Anhand einer exemplarischen Studie zeigen wir, dass es innerhalb dieses Paradigmas zu kontroversen Befunden kommt, welche durch die vermuteten Ursachen der Vertrauenskrise (Researcher Degrees of Freedom, kleine Stichprobengrößen) erklärt sein könnten. Zusätzlich argumentieren wir, dass weitere Faktoren (Konfundierung, Stichprobengrößen, Rosenthal Effekt, Expertise-Definition) innerhalb dieses Paradigmas die Reproduzierbarkeit von Erkenntnissen in Frage stellen. Wir diskutieren mögliche Maßnahmen, wie die dargestellten Probleme des Experten-Novizen-Paradigmas in zukünftigen Forschungsarbeiten gelöst werden können.

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