scholarly journals A New Type of Shape-Invariant Beams with Structured Coherence: Laguerre-Christoffel-Darboux Beams

Photonics ◽  
2021 ◽  
Vol 8 (4) ◽  
pp. 134
Author(s):  
Rosario Martínez-Herrero ◽  
Massimo Santarsiero ◽  
Gemma Piquero ◽  
Juan Carlos González de Sande
Keyword(s):  
Spectral Density ◽  
Spatial Coherence ◽  
Intensity Profile ◽  
Paraxial Approximation ◽  
Simple Analytical Expression ◽  
Analytical Expression ◽  
New Class ◽  
Shape Invariant ◽  
Cross Spectral Density ◽  
New Type

A new class of sources presenting structured coherence properties is introduced and analyzed. They are obtained as the incoherent superposition of coherent Laguerre-Gaussian modes with suitable coefficients. This ensures that the shape of the intensity profile and the spatial coherence features of the propagated beams are invariant during paraxial approximation. A simple analytical expression is obtained for the cross-spectral density of the sources of this class, regardless of the number of superposed modes. Properties of these sources are analyzed and described by several examples.

scholarly journals Variant-Coherence Gaussian Sources

Photonics ◽  
2021 ◽  
Vol 8 (9) ◽  
pp. 403
Author(s):  
Franco Gori ◽  
Massimo Santarsiero
Keyword(s):  
Spectral Density ◽  
Source Area ◽  
Spectral Densities ◽  
Differential Constraint ◽  
Modal Expansion ◽  
Shape Invariant ◽  
Degree Of Coherence ◽  
Cross Spectral Density ◽  
The Laplace Transform ◽  
Space Variant

The celebrated Gaussian Schell model source with its shift-invariant degree of coherence may be the basis for devising sources with space-variant properties in the spirit of structured coherence. Starting from superpositions of Gaussian Schell model sources, we present two classes of genuine cross-spectral densities whose degree of coherence varies across the source area. The first class is based on the use of the Laplace transform while the second deals with cross-spectral densities that are shape-invariant upon paraxial propagation. For the latter, we present a set of shape-invariant cross-spectral densities for which the modal expansion can be explicitly found. We finally solve the problem of ascertain whether an assigned cross-spectral density is shape-invariant by checking if it satisfies a simple differential constraint.

MICROEARTHQUAKE LOCATION USING A MAXIMUM LIKELIHOOD PROCESSOR

Geophysics ◽  
1976 ◽  
Vol 41 (5) ◽  
pp. 960-969 ◽  
Author(s):  
H. D. Leslie ◽  
R. P. Porter ◽  
R. C. Spindel
Keyword(s):  
Maximum Likelihood ◽  
High Resolution ◽  
Spectral Density ◽  
Short Range ◽  
Sound Pressure ◽  
Spatial Coherence ◽  
Resolving Power ◽  
Array Processor ◽  
Cross Spectral Density ◽  
Mid Atlantic Ridge

Sonobuoy arrays located over the Mid‐Atlantic Ridge, during the French‐American Mid‐Ocean Undersea Study (FAMOUS), have been used to measure the spatial coherence of sound pressure radiated from sea quakes and provide refined estimates of epicenter locations. These measurements were made with array elements separated by two km and tracked to an accuracy of 30 m relative to a bottom‐moored transponder. Spatial coherence, the normalized cross‐spectral density, has been found to be as high as 0.7 at 13 Hz and to be typically about 0.5 between 16 and 60 Hz. Short‐range events are significantly more coherent than long‐range events whose onset is smeared in time. A maximum‐likelihood array processor has been used to obtain accurate estimates of horizontal epicenter locations. The high‐resolution processor yields about three times the resolving power of the conventional delay and sum processor. The resolving power obtained with these arrays is consistent with measured spatial coherence.

A New Random Data Description and Its Use in Transferring Road Roughness to Vehicle Response

1974 ◽  
Vol 96 (2) ◽  
pp. 676-679 ◽  
Author(s):  
J. C. Wambold ◽  
W. H. Park ◽  
R. G. Vashlishan
Keyword(s):  
Spectral Density ◽  
Frequency Distribution ◽  
Descriptive Analysis ◽  
Joint Probability ◽  
Amplitude Distribution ◽  
Matrix Functions ◽  
Initial Portion ◽  
Power Spectral ◽  
Road Roughness ◽  
Cross Spectral Density

The initial portion of the paper discusses the more conventional method of obtaining a vehicle transfer function where phase and magnitude are determined by dividing the cross spectral density of the input/output by the power spectral density (PSD) of the input. The authors needed a more descriptive analysis (over PSD) and developed a new signal description called Amplitude Frequency Distribution (AFD); a discrete joint probability of amplitude and frequency with the advantage of retaining amplitude distribution as well as frequency distribution. A better understanding was obtained, and transfer matrix functions were developed using AFD.

Theoretical Studies of the Physical Properties of Rodlike and Related Polymers

1988 ◽  
Vol 134 ◽  
Author(s):  
W. J. Welsh ◽  
J. E. Mark ◽  
Y. Yang ◽  
G. P. Das
Keyword(s):  
High Performance ◽  
Liquid Crystalline ◽  
Theoretical Work ◽  
Environmental Resistance ◽  
New Class ◽  
Protonated Forms ◽  
New Type ◽  
Electrooptical Properties ◽  
Cis And Trans ◽  
Strong Acids

ABSTRACTThis review focuses on a new type of para-catenated aromatic polymer being used in the preparation of high-performance films and fibers of exceptional strength, thermal stability, and environmental resistance, including inertness to essentially all common solvents. Polymers of this type include the cis- and trans-poly(p-phenylene benzobisoxazole) (PBO), the cis- and trans-forms of the corresponding poly(pphenylene benzobisthiazole) (PBT), and the structurally similar poly(5,5ʹ-bibenzoxazole-2.2ʹ-diyl-l,3-phenylene) (AAPBO) and poly(2,5-benzoxazole) (ABPBO) and their sulfurcontaining analogues. Because of their rigidity, these polymers become highly oriented in solution and some display liquid crystalline behavior. The purpose of this paper is to summarize the authorsʹ theoretical work on the structures, conformational energies, intermolecular interactions, electronic properties, electrical conductivity, and electrooptical properties of these chains, including, in some cases, the so-called articulated forms and the protonated forms known to exist in strong acids. The emphasis is on how such studies provide a molecular understanding of the unusual properties and processing characteristics of this new class of materials.

A New Class of Oxide Superconductor (Nd, Ce, Sr)2CuO4

1989 ◽  
Vol 156 ◽  
Author(s):  
E. Takayama-Muromachi
Keyword(s):  
Crystal Structure ◽  
Crystal Chemistry ◽  
Superconducting Phase ◽  
Type Structure ◽  
Oxide Superconductor ◽  
New Class ◽  
System 2 ◽  
New Type ◽  
System 1 ◽  
Tetragonal Cell

ABSTRACTSince the discovery of the high-Tc superconductor in the La-Ba-Cu-O system [1], a great deal of experimental and theoretical effort have been made to clarify the nature of the Cu-based oxides. In order to elucidate mechanism of the high-Tc superconductivity, discovery of a new type of superconductor is no doubt of great importance. Recently, Akimitsu et al. found a new oxide superconductor in the Nd-Ce-Sr-Cu-O system [2]. Soon after their discovery, the superconducting phase was isolated and identified [3]. It has a tetragonal cell with space group P4/nmm and has a structure closely related to but different from the K2NiF4− or T'-Nd2CuO4− -type structure. Although, Tc of the Nd-Ce-Sr-Cu oxide is not so high (ca. 20 K) compared with the 1–2–3 or Bi(Tl)-based superconductors, it has aroused interest widely due to a very simple crystal structure. In this article, I will discuss superconductivity and crystal chemistry of the Nd-Ce-Sr-Cu oxide. Also, various compounds isostructural to it will be presented.

Allee’s Effect Bifurcation in Generalized Logistic Maps

2019 ◽  
Vol 29 (03) ◽  
pp. 1950039
Author(s):  
J. Leonel Rocha ◽  
Abdel-Kaddous Taha
Keyword(s):  
Allee Effect ◽  
Dynamical Behavior ◽  
Complete Classification ◽  
Unimodal Maps ◽  
New Class ◽  
New Type ◽  
Local And Global Bifurcations ◽  
One Dimensional Maps ◽  
Necessary And Sufficient

This paper concerns the study of the Allee effect on the dynamical behavior of a new class of generalized logistic maps. The fundamentals of the dynamics of this 4-parameter family of one-dimensional maps are presented. A complete classification of the nature and stability of its fixed points is provided. The main results relate to the Allee effect bifurcation: a new type of bifurcation introduced for this class of unimodal maps. A necessary and sufficient condition so that the Allee fixed point is a snap-back repeller is established. In addition, in the parameters space is defined an Allee’s effect region, which determines the existence of an essential extinction for the generalized logistic maps. Local and global bifurcations of generalized logistic maps are investigated.

A Novel, Low-Cost C-C Composite Heat Sink Material

1996 ◽  
Vol 445 ◽  
Author(s):  
W. Kowbel ◽  
V. Chellappa ◽  
J.C. Withers
Keyword(s):  
Thermal Conductivity ◽  
Heat Sink ◽  
Low Cost ◽  
Mechanical And Thermal Properties ◽  
New Class ◽  
Dielectric Coatings ◽  
Potential Applications ◽  
New Material ◽  
New Type ◽  
Composite Heat

AbstractRapid advances in high power electronics packaging require the development of new heat sink materials. Advanced composites designed to provide thermal expansion control as well as improved thermal conductivity have the potential to provide benefits in the removal of excess heat from electronic devices. Carbon-carbon (C-C) composits are under consideration for several military and space electronic applications including SEM-E electronic boxes. The high cost of C-C composits has greatly hindered their wide spread commercialization. A new manufacturing process has been developed to produce high thermal conductivity (over 400 W/mK) C-C composites at greatly reduced cost (less than $50/lb). This new material has potential applications as both a heat sink and a substrate. Dielectric coatings such as A1N and diamond were applied to this new type of heat sink material. Processing, as well as mechanical and thermal properties of this new class of heat sink material will be presented.

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